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11 Tools, Instrumentation, and Facilities for Condensed-Matter and Materials Physics Research The quest to observe, predict, and control the arrangements and motions of the particles that constitute condensed-matter systems is central to the condensed- matter and materials physics (CMMP) enterprise. The constituent particles span an enormous range of sizesâfrom electrons and atoms to macromoleculesâand their motions span a correspondingly immense range of timescales. As a result, the experimental, computational, and theoretical tools required to study them are extremely diverse. Many of these tools are developed by individual research groups; other tools, such as synchrotron x-ray and neutron scattering, are developed at large-scale national laboratory facilities. Technical innovations that extend the limits of measurement and prediction lie at the forefront of CMMP research. For example, scanning probe microscopes were developed to image surfaces at scales too small to be resolved by ordinary optical microscopy, and they immediately transformed the fundamental understanding of surface science. Moreover, the benefits of new techniques often stretch far beyond condensed-matter physics; scanning probe microscopes have now evolved into universal tools at the nanoscale for the physical and life sciences. Experimental condensed-matter tools underlie many noninvasive medical diagnostics, while theoretical and computational tools from CMMP, such as local electron density approximations and numerical simu- lation methods, are now used by pharmaceutical companies. The past decade has seen the advent of promising techniques, such as coherent and pulsed x-rays, novel optics based on exotic materials, multiscale modeling, and topological approaches to the study of magnetic and superconducting materials. As CMMP researchers seek to answer fundamental questions about materials, they will continue to design 193
194 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s tools, or adapt tools for new applications, that will benefit CMMP, other scientific disciplines, and society at large. Tools and Instrumentation for CMMP Research Measurement techniques designed to probe the properties of matter at smaller length, time, or energy scales or with greater quantitative resolution and sensitivity advance the forefront of condensed-matter and materials physics research. Likewise, techniques designed to synthesize high-quality materials with precisely controlled structures underpin many great CMMP discoveries. By pushing the boundaries of materials fabrication and measurement forward, experimental CMMP researchers have uncovered new phenomena that were often unanticipated. These discoveries have not only transformed CMMP, but they themselves have led in turn to new ways to manipulate and image matter, crucial to many new technological advances with a broad range of applications. New computational and theoretical techniques that push forward the boundar- ies of prediction also play a prominent role in advancing CMMP. To some extent, theory and computation are interlinkedâtheory nearly always forms the basis for new approximations or algorithms that substantially increase the efficiency of computations. Conversely, numerical computation is often indispensable in theory. Theoretical innovations, such as the application of field theories to condensed- matter systems and linear response theory have not only allowed researchers to tackle previously intractable problems, but, like many of the greatest experimental and computational techniques, have also changed the landscape of CMMP by revealing unexpected phenomena or deep, previously hidden connections among phenomena. As discussed later, computation can dramatically amplify the power of analytical tools. Indeed, the first electronic digital computer itself was built in order to carry out theoretical CMMP calculations. The research community is at the brink of an era in which powerful computer simulations will be integrated into measurement tools, enabling the extraction of information in unprecedented detail from measured quantities. Simulations will extend the reach of analytical theoretical techniques, connecting conceptual devel- opments to experimental measurements. The results will guide researchers through the realms of materials possibilities so vastly expanded by the ability to control the structure of the material at the nanoscale. Closing the loop, new detectors and de- vices will be made possible by new, purposefully designed, functional materials to further increase the power of measurements. Some of these breakthroughs will be made in single-investigator laboratories and, following the example of the scanning tunneling microscope, will turn into commodity instruments. Other advances will rely on the unique powers of staggeringly expensive large-scale instruments and teams of experts supported by large national facilities; these tools will need to be
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 195 broadly available and âuser friendlyâ for a wide cross section of researchers. Thus, all agencies supporting CMMP research should provide strong instrumentation programs to enable the research work in the CMMP field to be carried out effi- ciently and well. There is a need for keeping the infrastructure supporting CMMP research at universities up to date and for providing modern instruments for the training of the next generation of researchers. Instrumentation in CMMP Research CMMP researchers have a track record of developing new measurement tools that have enabled advances not only within CMMP, but also in other areas that encompass the physical, chemical, biological, and medical sciences. Indeed, the continued development of techniques with sufficient spatial resolution and sen- sitivity to measure structure, composition, and properties of condensed-matter over various length scales (from nano to macro), dimensionalities, and timescales is essential. During the past decade there have been significant advances in the use of tools in imaging, scattering, and spectroscopy. In this section, the Committee on CMMP 2010 briefly highlights advances in some of these areas. Imaging Techniques Imaging techniques provide structural images, direct and indirect, and prop- erty maps. Microscopy alone and microscopy combined with tomographic tech- niques are the most commonly used techniques to create images in two and three dimensions, respectively. Recent developments in x-ray microscopy, based largely on improvements of the fabrication of the optics, have enabled the observation of molecular length-scale height variations on a surface. Image measurements are now accomplished over an area of many microns, with a resolution of 200 nanometers (nm) and a step height of 0.6 nm with this technique. X-ray imaging has also enabled imaging at greater depths within a sample than is possible with electrons. With third-generation synchrotron sources, it is possible to study opaque objects using hard x-rays, while soft x-rays are used for soft materials and to probe near the surface of materials. X-ray beams can be focused to dimensions on the order of 100 nm to enable better resolution; the limiting resolution with x-rays is yet to be reached. A new development involves imaging by neutrons. Imaging is based on the notion that neutrons are characterized by a de Broglie wave packet with a spatial distribution that is sufficiently large to permit interference, very much in the same way as light. With the development of appropriate âoptics,â including transmission gratings based on differences in neutron-capture cross sections and incoherent scattering cross sections, two-dimensional images of various materials can be
196 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s c Â reated. In fact, a three-dimensional image, based on the scattering length density distribution, can be reconstructed. While scanning probe techniques have become ubiquitous in CMMP and have had an enormous impact on the understanding of materials, particularly at the nanoscale, many challenges remain. The inability to scan large areas of samples rapidly and issues related to thermal drift remain to be solved. Other issues await- ing resolution relate to the interpreting of data that are influenced by interactions between the cantilever tip and the sample. In the future, further progress in in- strumentation and data analysis, smaller cantilevers together with better deflection sensors, and improved sample-preparation techniques will lead to greater sensitiv- ity and resolution. Multifunctional cantilevers, wherein a local âfieldâ is applied while simultaneously probing the local response of the system, are part of a future strategy to ensure the increased impact of these techniques in the understanding of nanoscale properties. More sophisticated detection systems to enhance sensitivity further and improved computer algorithms for data interpretation and analysis will increase the utility and wide accessibility of these techniques that are so essential to modern CMMP materials characterization. Scattering Techniques Scattering is also used to provide information about the structure and dy- namics of condensed matter. For example, diffraction techniques, the best known of the scattering processes, provide information about the long-range order of a sample, with tenths-of-a-nanometer resolution, and the use of x-rays, combined with information gleaned from neutron measurements, has led to a better under- standing of the crystallography of complex macromolecules. Neutron scattering has grown in recent years as a regular tool for the characterization of samples. Neutron scattering techniques provide information about dynamics from 10â12 seconds to seconds and structure at length scales from 0.1 nm to 103 nm. Neutrons convey information about interatomic forces on the basis of measurement of the energy of the scattered neutrons. The incident intensity (flux) of neutrons and the efficiency with which the scattered neutrons are detected are key factors that determine the performance of a neutron source. The third-generation neutron sources (for example, the Spallation Neutron Source [SNS] at Oak Ridge National Laboratory) provide large increases in sensitivity that will result in better speed in data acquisition (seconds or minutes versus hours or a day, depending on the system and the information collected) and will enable measurements of lower concentrations of a given species. The latter is important because it will enable the analysis of multicomponent systems. Other types of scattering techniques provide direct spatial depth profiling in- formation of materials, including Rutherford backscattering spectrometry, forward
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 197 recoil spectrometry, nuclear reaction analysis, and secondary ion mass spectrom- etry. These techniques involve the use of incident energetic ion beams; analysis of species emanating from the sample provides information about the concentration of a given species as a function of depth. The effective use of combinations of neutron and x-ray scattering with ion-beam techniques can provide more detailed information about the structure and dynamics of nanocomposites, heterostruc- tures, and complex liquids at smaller length scales. Spectroscopy Techniques The use of spectroscopy techniques for imaging has grown rapidly in re- cent years. These techniques, which have been very successful in the imaging of soft materials, including biological materials and polymers, have been invaluable. New developments that involve the use of scanning force probes, scanning force magnetic resonance (a sample is placed on a cantilever in the presence of a small ferroelectric tip which creates an inhomogeneous field that has the effect of polar- izing the spins in the sample) have enabled the three-dimensional imaging of an individual atom as well as single spins. Infrared and Raman techniques have been used to image samples based on a vibrational signature associated with a molecule. Researchers have been suc- cessful in using the Raman effect, inelastically scattered light that is shifted in wavelength relative to the incident wavelength, to improve the sensitivity of the identity of certain molecules within a sample. Surface-enhanced Raman scatter- ing has laid the foundation for the development of surface-enhanced spectros- copies that include surface-enhanced fluorescence and surface-enhanced infrared spectroscopy. The latest developments include single-molecule surface-enhanced Raman spectroscopy and tip-enhanced scanning near-field optical microprobe Raman spectroscopy. Simultaneous Measurement Capabilities New strategies that involve in situ characterization of materials using x-rays or neutrons are becoming routine. Specifically, some research groups use x-rays or neutrons to measure the properties of materials (dynamics structure, phase transi- tions, and so on) that are simultaneously subjected to external perturbations (stress, temperature, and various kinds of fields). With the use of tomographic techniques, information about the interior of samples can now be learned without the need to section them destructively for analysis with transmission electron microscopy (TEM) or scanning probe techniques. The availability of these combined techniques enables increased spatial and temporal resolution and rapid data acquisition. In some cases the duration of measurements could be reduced from tens of hours to minutes.
198 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s Another significant advance is the use of scanning force techniques in con- junction with other techniques for learning about properties, such as electrical conductivity and magnetism, in unprecedented detail at the nanoscale. Instruments are approaching the stage at which the resolution of joint probes is comparable to atomic force microscope measurements of topography. In situ TEM capabilities are also being developed to enable the direct observation of changes in atomic ar- rangement (structure) of a material while it simultaneously experiences external perturbations owing to changes in temperature, mechanical stresses, or electric fields. This is a powerful technique that is currently exploited by a number of elec- tron microscopists. The development of more sophisticated theory and multiscale algorithms that enable better use of experimental data to characterize samples will be a continuing challenge. Computation in CMMP Research As the materials and phenomena of interest have become increasingly com- plex, computation has emerged as an essential tool in the process of interpreting experimental data and analyzing theoretical models. Over the past decade or two, computational CMMP has developed fully into a branch of study in its own right, on a par with experimental and theoretical CMMP. From the beginning, computational CMMP has not only allowed researchers to confront previously insoluble problems but has also provided a means to discover new phenomena. There are two paradigms in computational CMMP. One extends the power of theoretical modeling by numerical solution of âsimpleâ models, both classical and quantum, which capture the essential physics of the system of interest. These results are used either directly in interpreting and predicting experimentally observed phenomena or as an aid to âpencil and paperâ analysis by developing and validating approximations to study models that cannot be solved exactly. The sec- ond paradigm is the direct solution of the quantum mechanical equations to make quantitative predictions about the behavior of particular materials at the atomic scale. In both, breakthroughs in the development of theory and algorithms, aided by enormous increases in computer speed and memory, have enabled dramatic progress in the past decade. Techniques developed for the numerical investigation of simple models have had widespread applicability beyond CMMP. Monte Carlo methods are now stan- dard tools in all fields of science and engineering and are even used in industrial contexts. Some recent approaches that have promise for significant impact in CMMP are phase retrieval methods and new forms of Monte Carlo algorithms, including ones that can evolve dynamically. New field theoretical algorithms are having increasing impact. With the density matrix renormalization group (DMRG) method, significant progress has been made toward eliminating the âsign problemâ
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 199 bottleneck, ubiquitous in numerical studies of systems of interacting electrons; this method has also had a significant impact in quantum chemistry, quantum information theory, and nuclear and high-energy physics. With these methods, it is now possible quantitatively to study models that cap- ture aspects of the essential physics of materials with strongly correlated electrons, such as complex oxides, including the high-temperature superconducting cuprates and magnetoresistive manganites, and two-dimensional electron gases. Figure 11.1 shows an example of the rich variety of ground-state orderings that have been observed in models of the cuprates with the DMRG method. Methods for the direct solution of the underlying quantum mechanical equa- tions allow quantitative, material-specific, first-principles prediction of structure and properties. The ongoing development of efficient algorithms allows the study of ever-more-complex structures, including crystals with very large unit cells, and nanostructured systems. New classes of algorithms and the incorporation of many-body physics allow the extension of these methods to a broader range of materialsânotably, correlated electron systems with magnetic, orbital, and FIGURE 11.1â Plots showing the stripe ordering of the charge and spin on a two-dimensional CuO 2 plane in the high-temperature superconductor (La,Nd,Sr)CuO4. (Left) As suggested by neutron- s Â cattering experiments. (Right) As calculated for the t-J model using the density matrix renormaliza- tion group method. SOURCE: Reprinted with permission from S.R. White and D.J. Scalapino, âDensity Matrix Renormalization Group Study of the Striped Phase in the 2D t-J Model,â Phys. Rev. Lett. 80, 1272 (1998). Copyright 1998 by the American Physical Society.
200 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s charge ordering, and systems under ultrahigh pressure relevant to geophysics. New capabilities are being developed to study systems in applied electric and magnetic fields and to extend computations for excited states. Such computational capability is necessary for predicting optical and transport properties. An example is shown in Figure 11.2. The direct solution of the underlying quantum mechanical equations also plays a key enabling role in the design of new materials. In this work, the target is particular structures and properties, requiring the solution of the âinverse problemâ to find a corresponding material. In an experimental framework, combinatorial solid-state methods survey the structure and properties for entire compositional ranges for complex solids containing three or more different elements. Similarly, computational methods for the prediction of structure and properties of solids now are accurate and fast enough to allow first-principles materials design, in which the FIGURE 11.2â The current induced by varying voltages across carbon chains of varying lengths sandwiched between gold and aluminum leads can be computed using first-principles methods. The carbon nanowires differ from conventional wires in that the current is not proportional to the voltage. SOURCE: J.B. Neaton, K.H. Khoo, C.D. Spataru, and S.G. Louie, âElectron Transport and Optical Prop- erties of Carbon Nanostructures from First Principles,â Comput. Phys. Commun. 169, 1-8 (2005).
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 201 FIGURE 11.3â The structure of lithium nickel manganese oxide, a promising new battery material designed using computational methods, consists of layers of transition metal (nickel and manganese, blue layer) separated from lithium layers (green) by oxygen (red). SOURCE: K. Kang, Y.S. Meng, J. BrÃ©ger, C.P. Grey, and G. Ceder, âElectrodes with High Power and High Capacity for Rechargeable Lithium Batteries,â Science 311, 977 (2006). Reprinted with permission from the American Associa- tion for the Advancement of Science. structural parameters and selected properties for large sets of real and hypothetical structures can be surveyed to identify interesting materials for new physics and applications, including room-temperature ferromagnetic semiconductors for spin- tronics and new battery materials (see Figure 11.3). By using the first-principles calculations as input into parameterizations of the composition space, searches can be extended to even larger spaces of materials. Similar principles can be applied to the design of heterogeneous materials and devices. Much of the important physics in materials systems takes place at length scales well beyond which fully first-principles methods are practical. This range is extended by molecular dynamics simulations with parameterized interatomic potentials. The associated loss in accuracy at the atomic level is compensated by the ability to use tremendously larger numbers of atoms (100 million or more) and the ability to study the time evolution of phenomena. One area in which such computations have proved particularly valuable is in the study of mechanical prop- erties, such as strength of materials, plastic deformation, fracture, and friction, in âS.C. Erwin and I. Zutic, âTailoring Ferromagnetic Chalcopyrites,â Nat. Mater. 3, 410 (2004). âC.C. Fischer, K.J. Tibbetts, D. Morgan, and G. Ceder, âPredicting Crystal Structure by Merging Data Mining with Quantum Mechanics,â Nat. Mater. 5, 641 (2006).
202 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s which the behavior is determined by line and planar defects that are created and propagated through the system. An example of such calculational results is given in Figure 11.4. As impressive as such simulations are, they are still far short of macroscopic scales: a solid cube 1 micron on a side contains over a thousand times more atoms. Within the past decade, priority has been given to developing truly multiscale methods for modeling materials properties, with seamless integration of atomic scale, intermediate length scale, and continuum methods. Similar multiscale ap- proaches are needed to treat materials physics involving time evolution (dynam- ics) on a wide range of timescales. While great progress has been made, additional breakthroughs are needed. As new measurement tools are developed, computational approaches will be essential to interpreting larger amounts of data and extracting subtle signals and correlations. Simulations can be invaluable in separating artifacts from intrinsic behavior. Both in the numerical study of simple models and in first-principles FIGURE 11.4â Snapshot from a molecular-dynamics simulation showing the behavior of nanocrystal- line aluminum during deformation. The crystal grain at the center is 70 nm in diameter and is defined by clear grain boundaries (blue atoms). Deformation is seen to drive the formation of planar defects (red atoms) that start at the grain boundary and grow into the grainâs interior. SOURCE: V. Yamakov, D. Wolf, S.R. Phillpot, A.K. Mukherjee, H. Gleiter, âDislocation Processes in the Deformation of Nano- crystalline Aluminium by Molecular-Dynamics Simulation,â Nat. Mater. 1, 45 (2002).
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 203 simulations, novel unanticipated physical behavior can arise, giving new insights and guiding experimental investigation. Fundamental issues need to be addressed in the next decade to build on this progress. More efficient, accurate, and broadly applicable methods must be de- veloped to study dynamics, effects of thermal fluctuations, and excited states of materials. There are many promising avenues for further progress in techniques for studying systems with strong correlations. Particular attention should be paid to improving the conceptual and algorithmic framework for studying energy trans- formation in solids, such as in electromagnetic radiation, energetic particles, and heat generation. Efforts should continue to be made to increase the efficiency of algorithms by drawing on forefront research in numerical methods and computer science. New approaches to multiscale methods for spatial and temporal variations should be pursued. A concerted effort should be made to integrate simulations into experimental data analysis and help with the proper interpretation of the experimental measurements to increase the power of the developing experimental probes described in this chapter. Lastly, the push to integrate simulations into new materials design should intensify, with work continuing in parallel both on realiza- tions for particular systems and on the development of broadly applicable tools based on knowledge gained from these collaborations. Centers and Facilities in CMMP Research Both the complexity of scientific challenges and the resources required to con- duct a successful CMMP research program have increased in recent years. A major scientific challenge to the field is how to synthesize or fabricate materials in which the electronic, atomic, and molecular organization varies spatially, and in some systems, temporally. A related challenge is how to understand principles, or rules, that govern the behavior of materials over different length scales and timescales. To address these challenges, sophisticated tools (experimental, computational, and theoretical) are needed to probe the structure and properties of materials over a wide range of length scales and timescales. For synthesis, fabrication tools such as focused ion beams, molecular beam epitaxy, and lithography have become prohibi- tively expensive for operation by a single principal investigator (PI). Measurement tools to probe structure and properties are also very expensive, with centers and facilities addressing many of these needs. The associated requirements to educate students on how to perform experiments using new techniques and facilities are a pressing and constantly evolving need. In this section, the committee describes the current status of the research infrastructure and its ability to address, for example, the six CMMP challenges introduced in Chapter 1 and explicitly discussed in this report. The status and role of centers and mid- and large-scale facilities in rela- tion to single and small-group principal investigators are discussed. This chapter
204 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s also contains recommendations and proposed prioritization of resources for the construction of future facilities. Various facilities and centers involving interdisciplinary, multi-Âinvestigator r Â esearch groups, with top-down, well-directed missions, now play an increas- ingly important role in CMMP research. National Science Foundation (NSF) and Department of Energy (DOE) expenditures for building and supporting large, multiuser facilities have thus increased considerably. However, there is a concern that the balance between support for the individual investigator and facility con- struction and operation is leaning too heavily toward the latter. This scenario presents a natural dilemma, since individual investigators are the users of these facilities and are the source of important scientific breakthroughs. Yet advanced instrumentation and facilities are needed to conduct the research programs of individual investigators. The committee emphasizes here that strong individual research programs, state-of-the-art equipment, and world-class facilities are all important for advancing the field of CMMP, and a proper balance in the funding of each is essential. In addition, midsize facilities are an important part of the CMMP research enterprise and require careful management to ensure that they have a continued impact. Starting in the 1970s, NSF provided resources for central user facilities through the Materials Research Laboratories (MRL) program. Current multi- investigator research centers, such as Materials Research Science and Engineering Centers, which replaced the MRLs in the mid-1990s, and the Science and Technol- ogy Centers, are highly utilized by CMMP researchers. These centers are focused on collaborative, interdisciplinary projects as well as on education and public outreach. The centers have had a large impact on fostering the interdisciplinary aspects of CMMP. Beyond the MRL-type mechanism for providing central facilities, âgenericâ multiuser facilities have existed at many institutions, available to local users for a fee. Such facilities, which generally cost in the range of $1 million to $3 million per year of operation, would provide materials characterization facilities such as nuclear magnetic resonance (NMR) spectroscopy, x-ray diffraction, or transmis- sion electron microscopy, and are operated by their host institution. To supplement the present basic central-facility instrumentation now available at the top CMMP research universities in the United States, basic nanofacilities for the synthesis of nanomaterials and their characterization are needed. For more sophisticated and specialized nanofacilities needs, access to the DOE Nanoscale Science Research Centers (NSRCs) is available. The rising costs of sophisticated instruments, often well beyond the rate of inflation, place an increasing burden on institutions. For example, the new aberration-corrected transmission electron microscope costs approximately $4 million and requires support staff for operation and upkeep. Institutions around the world are beginning to acquire such instruments, and this
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 205 certainly introduces a new metric to the cost of doing cutting-edge research in CMMP. One crisis associated with the utility of mid-scale facilities is that some institu- tions have difficulty finding resources to maintain and to support such instruments appropriately once they are acquired. First, maintenance service contracts can be very expensive. Second, state-of-the-art instruments often require support staff with Ph.D.-level expertise, who are needed to train students and to help with the interpretation of data. The problem is compounded by the fact that often there is no viable career path in many institutions for Ph.D. scientists doing these jobs. Two recent National Research Council (NRC) reports highlight the problems and challenges associated with the operation of these facilities., In addition to funding centers and mid-scale facilities, the NSF Division of Materials Research (NSF DMR) now invests a significant portion of its resources toward funding large-scale facilities: the synchrotron facilities at Cornell University and at the University of Wisconsin-Madison, a beam line at the neutron-scattering facility at the National Institute of Standards and Technology, and the National High Magnetic Field Laboratory at Florida State University. NSF DMR should set budget priorities between single PIs and small groups, centers, and facilities. The major concern, as discussed in Chapter 10, is that federal funding for basic research in CMMP has remained essentially flat while the average success rate for propos- als from single investigators has decreased dramatically in the past decade. The problem is compounded by costs associated with research at universities outpacing inflation rates. The committee believes that to fully leverage the investment in these centers and facilities, the current balance of funding between single PIs and small groups of PIs relative to centers and facilities should not decline in the future. During FY 2004, NSF initiated a new program that expands the types of fa- cilities available to institutions: the National Facilities (NAF) program. The NAF program supports unique experimental capabilities for materials research and a wide range of other disciplines. Resources from NSF DMR are leveraged with resources from other directorates within NSF to support the NAF program, which should accomplish the goal of extending the utility of mid-scale facilities. Another program at NSF, the Instrumentation for Materials Research-Major Instrumenta- tion Projects, provides about $2 million to $20 million for instrumentation such as high-field magnets and beam-line instrumentation. âNational Research Council, Midsize Facilities: The Infrastructure for Materials Research, ÂWashington, D.C.: The National Academies Press, 2006. âNational Academy of Sciences, National Academy of Engineering, and Institute of Medicine, Advanced Research Instrumentation and Facilities, Washington D.C.: The National Academies Press, 2006.
206 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s DOE funds large-scale scientific user facilities such as light sources, Âneutron sources, electron microscopy facilities, and nanoscience centers. The light sources and neutron facilities provide beam lines for a wide range of materials analysis. The need for increased sensitivity and resolution (spatial and temporal) to study properties at the nanoscale or atomic scale makes the use of large-scale facilities an increasingly necessary component of CMMP research, as documented by user demand. The interdisciplinarity of CMMP research is reflected in part by the demo- graphics of investigators supported by NSF DMR and by DOE Basic Energy Sci- ences. Figure 11.5 shows the demographics of materials researchers supported by NSF DMR; besides physicists, this enterprise involves engineers, chemists, bi- ologists, mathematicians, and researchers in other disciplines. It should be noted that the establishment of the new biomaterials program within NSF DMR is ex- pected to further change the demographics of researchers who compete for these r Â esources. It is clear from the foregoing that the culture of CMMP research is being transformed in such a manner that the role of the individual principal investigator continues to evolve. In addition to the increasing role of large facilities and sophis- ticated instrumentation, the research problems that are now taking center stage FIGURE 11.5â Faculty supported by the Division of Materials Research at the National Science Founda- tion in 2004 by departmental affiliation. The actual number of faculty is indicated in the parentheses in the inset. NOTE: MS&E, Materials Science and Engineering. SOURCE: National Science Foundation.
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 207 have become increasingly interdisciplinary. Centers now play an important role in meeting CMMP challenges. Nevertheless, single PIs hold the potential for mak- ing the most significant breakthroughs in science, as they have in the past. Grant sizes and success rates are beginning to impact the ability of CMMP researchers to conduct cutting-edge and high-risk scientific exploration and to train the next generation of CMMP researchers and technology developers properly. Nowadays, CMMP researchers report that they are diversifying their research portfolios for the survival of their research groups. CMMP researchers comment that diversification often means that in practice they work on certain problems only because funding is available and not because that work is where they can make the most significant difference toward advancing the field. Strong support of the individual investiga- tor coupled with access to world-class instrumentation and facilities is needed for cutting-edge CMMP research, to train students to do such research, and to com- pete and collaborate with Europe and Asia to advance science and exploit societal applications of CMMP discoveries. Scientific User Facilities for CMMP Research The Committee on CMMP 2010 was charged to âidentify, discuss, and sug- gest priorities for construction, purchase, and operation of tools and facilities ranging from instrumentation for the individual investigator to the national user facilities.â To address this charge, the committee convened a workshop with gov- ernment, university, and industry stakeholders to discuss the future needs for facilities in CMMP (see Appendix C). This section focuses on the present status of user facilities for CMMP research and identifies needs for the future based on the community input received at the workshop. In turn, the committee consid- ers here light sources, neutron sources, electron microscopy, high-magnetic-field facilities, nanocenters and materials synthesis, and high-performance computing facilities. Prioritized recommendations are provided for each class of facility (see the respective âRecommendationsâ subsections below), but the committee did not rank order the classes. DOE, NSF, and the National Institute of Standards and Technology (NIST) support scientific user facilities for CMMP research. DOE is by far the largest sup- porter, accounting for approximately 85 percent of the investment. These agencies construct and operate light, neutron, and electron-beam sources; high-magnetic- field laboratories; and nanocenters. The facilities are available to users around the country and elsewhere, based on an equitable review process of the merits of a research proposal. The facilities are reviewed every few years with the goal of pro- viding new techniques to users and of optimizing the use of the facilities. The types of scientific problems examined at these laboratories are diverse and include areas such as geology, magnetism, structural biology, catalysis, and many others.
208 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s Light Sources Many of the developments in CMMP of the past decade have depended heav- ily on electron-accelerator-based sources of radiation, popularly referred to as light sources. These sources vary from free-electron lasers to generate far-infrared radiation, with capitalizations on the order of $5 million, through to large-scale facilities such as the Advanced Photon Source (APS) at Argonne National Labora- tory, with a replacement value on the order of $1 billion. Light sources allow the extension of the power of the optical microscope to obtain images of condensed matter at smaller and smaller distances in real space as well as in the space spanned by momentum and energy and, in what is becoming increasingly important, a mixture of the two. Examples of results from the past decade include ultraviolet photoemission work elucidating the exotic normal and superconducting states of the copper oxides, high-resolution phase contrast images of insects, pictures of nanoscale antiferromagnetic domains, and thousands of new entries in protein structure databases. Light sources can be used as nanoprobes, for imaging, dif- fraction, molecular crystallography, in situ high-pressure experiments, and x-ray microscopy for a wide range of novel materials. The importance of light sources will increase over the next decade, and indeed they are indispensable to meeting all of the CMMP grand challenges simply because of the power of images obtained at the length scales ultimately responsible for macroscopic physical phenomena and underpinning the functionality of materials, devices, and organisms. In the coming decade, the committee therefore looks for- ward to the continuation, among other things, of diffraction studies to locate atoms in new materials and novel nanostructures with, for example, impact on the energy problem and future information technology; high-resolution photoemission to probe emergent quantum phenomena in transition metal oxides; and time-resolved studies of dynamical processes in biology. Third-generation light sources offer the possibility of single-molecule spectroscopy to determine electronic structure, oxi- dation states, symmetry of chemical bonds, and local atomic structure. In addition, and what will lead to a qualitatively new science, new methods are being devel- oped to exploit higher brilliance (by many orders of magnitude) and coherence in the light sources. There is expected to be great progress in x-ray scanning probe microscopy where there are plans to reach nanometer resolution, phase contrast imaging, and, most exciting, the wholesale importation of techniques from modern pulsed (visible) optics to the accelerator-based sources. The latter will mean that researchers will be able to exploit transform-limited x-ray pulses to look at linear excitations and non-equilibrium phenomena essential for the functionality of systems ranging from biological membranes to quantum computers.
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 209 Current Status of Light Sources The world has a large variety of accelerator-based light sources. The United States has a presence in each of the major current categories of light sources, including large third-generation synchrotrons devoted to soft and hard x-rays, several free-electron lasers to produce infrared radiation, a recently refurbished second-generation x-ray synchrotron, several ultraviolet synchrotrons, several free- electron lasers to produce infrared radiation, and an x-ray free-electron laser whose construction was endorsed in the last decadal survey of CMMP and is now under construction. Therefore, the current position of the United States in this general area appears healthy and world leading. DOE currently operates light sources to meet the needs of a large number of users, projected to be more than 10,000 investigators in the near future (see Fig- ure 11.6). At the APS, for example, the number has increased at a relatively constant rate of about 500 users per year since 1997. It is noteworthy that the fraction of users from the life sciences has increased rapidly, from less than 10 percent in 1990 to approximately 45 percent in 2003. Physics and materials science account for just over 25 percent of the use, with materials science having twice as many users (see Figure 11.6). Most users are academics; government and industry account for a combined use of approximately 25 percent. Light sources are primarily used for hard x-rays for scattering experiments. Spectroscopy is the second more popular use, with most of the use occurring at the National Synchrotron Light Source and the Advanced Light Source (ALS). Imag- ing experiments are becoming increasingly popular, particularly for soft Âmaterials ( Â using soft x rays), with most of the work done at ALS (see Figure 11.7). The En USERS FIGURE 11.6â (Left) The number of users at U.S. synchrotron facilities, 1982-2005. (Right) The demographics of users of the Advanced Photon Source. SOURCE: Department of Energy. 11-6 a,b
210 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s FIGURE 11.7â The types of experiments conducted at U.S. light sources. NOTE: NSLS, National Synchrotron Light Source; SSRL, Stanford Synchrotron Radiation Laboratory; ALS, Advanced Light Source; APS, Advanced Photon Source. SOURCE: Department of Energy. p Â rimary advantage of using a beam line at a light source for these types of experi- ments is the improved sensitivity over other techniques. Medium-Term Developments for Light Sources In the medium term, the U.S. position looks less secure. No synchrotron facili- ties currently under construction worldwide are located in the United States except oneâthe Linac Coherent Light Source (LCLS). Indeed, the LCLS represents the only new start in the past decade. The LCLS will be the first x-ray free-electron laser in the world, giving the United States a unique window on the first experiments in single-molecule imaging. The LCLS will therefore be a tremendous tool for meeting the challenges discussed in Chapter 4 (âWhat Is the Physics of Life?â) and Chapter 6 (âWhat New Discoveries Await Us in the Nanoworld?â), and for developing the capabilities of both the CMMP and accelerator communities for a next step in the development of light sources: namely, the seeded free-electron laser. In addition, the LCLS has the potential to make large contributions to many other disciplines,
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 211 including biology, atomic and molecular science, and even plasma physics. The LCLS will also, from both a technical and a community-building point of view, provide opportunities for further cross-fertilization between CMMP and its lively neighboring disciplines. As shown in Figure 11.8, there are currently three times as many beam ports outside as inside the United States; there are about 123 beam ports in the United States now. This difference is estimated to grow to approximately seven times as many beam ports outside the United States by 2009 with the construction of new synchrotrons abroad. FIGURE 11.8â The total number and location of third-generation synchrotron beam ports around the world. SOURCE: Department of Energy.
212 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s It is clear that unless new initiatives are undertaken, the United States will be faced with aging and less-than-world-class infrastructure over the next decade. The impact of accelerator-driven light sources over the past decade suggests a goal of full utilization of existing third-generation sources as well as the construction of a major new source. The third-generation light sources are key tools for meeting all of the grand scientific challenges whose descriptions are at the core of this report. They provide vital information on the micro- and nanostructures emerging from simple ingredients (Chapter 2); on the materials and increasingly on the processes for energy extraction and utilization (Chapter 3); on biomolecules, membranes, and larger systems pertaining to the physics of life (Chapter 4); on nanomaterials and nanosystems (Chapter 6); and on the materials and device structures that will underpin the continuation of the information technology revolution (Chapter 7). The committee points out that slower non-equilibrium phenomena (Chapter 5) are well studied using third-generation synchrotrons, but faster, dynamic effects, especially in small structures, and also effects where coherence is important, will demand more-advanced types of light sources. What is most exciting, though, is that the need for new infrastructure coincides with several extraordinary developments in the generation and exploitation of light at accelerators: â¢ Demonstration experiments on coherent beams providing holograms of nanocrystals, dynamics of magnets, polymers, and even of flames; â¢ The beginning of picosecond and even subpicosecond time-resolved x-ray science, with applications both in molecular and solid-state science; â¢ New optics, fabricated using nano- and microtechnology originally devel- oped for the semiconductor industry, allowing phase contrast as well as more traditional scanning probe imaging; â¢ Worldwide growth of interest in coherent terahertz radiation for imaging, with applications ranging from security (including luggage screening) to medicine, but also for spectroscopy, especially in conjunction with high magnetic fields; â¢ New special-purpose sample environments, ranging from sample stages that incorporate scanning probe microscope drivers to pressure cells and series-connected hybrid magnets. Application areas opened by these sample environments range from the engineering of micro- and nanomechanical systems to Earth and planetary sciences, where high-pressure environments occur naturally but cannot be accessed directly; â¢ Concepts for low-cost ($5 million to $10 million) compact x-ray sources providing time-averaged fluxes and brilliance comparable to second-gen- eration synchrotrons and short-pulse performance superior to any capa- bilities offered at large facilities today. The underlying operating principle is the inverse Compton effect, where a relatively low energy electron beam,
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 213 prepared in a superconducting linear accelerator, passes through a laser cavity in which the optical fields act as an undulator. If the promise of these concepts is realized, CMMP (as well as many other areas of science) will be transformed as a result of the possibilities afforded by immediate and intimate contact between the fabrication, x-ray characterization, and other characterization in the discovery and study of a new material. This will bring x-ray analysis much closer to the mainstream of CMMP charac- terization, in the same way that routine electrical, magnetic, and electron microscopy are used; â¢ Concepts for seeding x-ray lasers to produce single, transform-limited, co- herent pulses rather than random sequences of closely spaced pulses as with the present self-stimulation paradigm. This will greatly enhance our abil- ity to do high-resolution x-ray spectroscopy, but more importantly, it will allow x-rays to image non-equilibrium dynamics of condensed matter in both classical and quantum regimes. Experiments that might become pos- sible are numerous, and range from investigations of the time-dependent changes in thin gate oxide transistors as they are switched, to measurements of time-dependent structural changes in active nanoscale biological systems such as ion channels; and â¢ Blossoming of interest in the energy-recovery linear accelerator concept as a method for delivering more spatial coherence and higher brilliance beams than are possible with third-generation synchrotrons. If they performed as predicted, energy-recovery linear accelerators would allow the promise of the current generation of demonstration experiments exploiting spatially coherent beams (described in the first bullet point, above) to be fulfilled for a much larger class of scientific problems. Obvious from the list above and from Figure 11.9 are the tremendous oppor- tunities as well as large potential costs of future light sources. Conservatively, the implementation of one exemplar of the two large concepts, namely, the seeded free- electron laser and the energy-recovery linear accelerator, as well as construction of another more conventional third-generation synchrotron light source, would cost on the order of $3 billion, and the corresponding annual operating expenses would eventually run to approximately $500 million. This means that prioritization for these facilities is especially important. Recommendations for Light Sources in CMMP Research Informed by presentations and discussion at the CMMP 2010 Facilities Work- shop (see Appendix C) and subsequent discussion by the Committee on CMMP 2010, the committee identifies the recommendations in this subsection as priorities (in the order in which they appear below) for future investment in light sources.
214 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s FIGURE 11.9â Increased x-ray brilliance, which measures the flux of photons per unit of phase space volume, can be achieved by combinations of increases in raw beam power and improvements in beam coherence. NOTE: VUV, vacuum-ultraviolet. SOURCE: D.E. Moncton, Massachusetts Institute of Technology.
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 215 The first recommendation is for systematic long-term planning for future U.S. light sources. The second and third recommendations are aimed at benefiting optimally from investments already made. The fourth recommendation is for planning, design, and construction of the next synchrotron facility in the next decade, and the final recommendation is to enable entry into the next phase of light sources, providing small brilliant light sources for the laboratory. A past NRC committee reached remarkably similar conclusions in 1994. A key feature of the development of light sources over the past decade has been their transformation from facilities primarily of interest to the core CMMP programs of DOE and NSF to resources pertinent to the agendas of a much broader range of government agencies and private groups, including especially those con- cerned with the biomedical sciences, such as the National Institutes of Health (NIH) and pharmaceutical companies. This means that even while DOE and NSF should continue in their roles as key stewards of large- and medium-scale facilities, respectively, it is essential to engage strongly with the other interested organizations for planning and funding purposes if the full potential of light sources is to be realized in the United States. It is for this reason that the committee recommends a research and development (R&D) consortium, which has the highest priority in the list below, with expertise in cutting-edge light source technology but without legacy investments and decisions to protect. Another interesting aspect derives from the growing cost of new facilities, and the committee expects that for the very largest machines, such as a seeded x-ray free-electron laser, there will be a growing trend toward international coopera- tion. Nonetheless, it will be important for the United States to bring technology as well as money to the table when strategic international decisions (for example, site selection) are made; this is another reason why the committee considers the implementation of the first recommendation to be very important. Recommendation:â DOE and NSF, partnering with NIH and NIST, should create a consortium focused on research and development needs required for next-generation light sources. The consortium, with an independent chairper- son, should include stakeholders from universities, industry, and government (both laboratories and agencies). The consortium should formulate a light source technology roadmap and make recommendations on the R&D needed to reach milestones on the roadmap for a new generation of light sources, such as seeded x-ray free-electron lasers, energy-recovery linear-accelerator-driven âNational Research Council, Free Electron Lasers and Other Advanced Sources of Light: Scientific Research Opportunities, Washington, D.C., National Academy Press, 1994. âThe committee used the term âconsortiumâ in the sense of a partnership among the stakeholders described in the recommendation for developing a light source technology roadmap. The committee expects that the âconsortiumâ will follow federal rules for providing advice to federal agencies.
216 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s devices, and other promising concepts. The consortium should also take into account cost containment and the internationalization of research facilities. The sponsoring agencies of the consortium should fund the R&D needed to reach the milestones on the roadmap. Recommendation:â DOE should exploit fully the existing third-generation synchrotrons; this means utilizing the remaining straight sections at the N Â ational Synchrotron Light Source, Stanford Positron Electron Accelerating Ring, Advanced Light Source, and Advanced Photon Source, and recapitaliz- ing obsolete beam lines at all four facilities. This also means proceeding with the high-magnetic-field sample environment for APS. In addition, it means providing personnel and consumables for beam lines in accord with best international practice. New beam lines and instrumentation should be added according to need. Recommendation:â DOE should complete and fully fund the operations of the Linac Coherent Light Source. Recommendation:â DOE should prepare an engineering design for and then begin construction of a major new light source in the United States such as the National Synchrotron Light Source II (NSLS-II). The NSLS-II design should follow a trend in regional synchrotron light sources of employing more mod- erate beam energies but, through use of more sophisticated insertion devices, achieving good spectral coverage, including the x-ray region. Because the ac- celerator and instrumentation design goals for NSLS-II are very challenging and a significant extrapolation of the current state of the art, it would be desir- able to have an open, transparent, and independent review of the engineering design. Recommendation:â DOE and NSF should create opportunities for $5 million to $10 million facilities with suitable operating funds to take advantage of com- pact x-ray sources and infrared free-electron lasers. The associated scientific possibilities are enormous, in the first case making medium-intensity x-ray beams as accessible as high-end electron microscopes, and in the second case, providing tunable, high-intensity radiation in a part of the electromagnetic spectrum with rapidly growing technological and scientific relevance. Neutron Sources New materials will play a pivotal role in solving some of the societal issues that face the world in the 21st century. These issues include the development of clean
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 217 and abundant sources of renewable energy, the availability of sufficient potable water, and the protection of the environment from anthropogenic activity. The newest generation of materials is only just beginning to creep into our daily lives, but it is already clear that some will have a major impact. For example, wide band gap semiconductors based on gallium nitride will clearly provide the basis for solid- state lighting devices that consume far less electricity than conventional lighting such as incandescent and fluorescent lamps do. Conducting polymers may well play a major role in the search for affordable and efficient solar energy. Against this backdrop of materials discovery and deployment, it is important to understand the central role that major facilities have played in underpinning the knowledge of new materials and accelerating their progress toward real applica- tions. Neutrons are important in the world of both organic and inorganic materials. For example, following the discovery of high-temperature cuprate superconductors in 1986, neutrons were immediately deployed in order to understand the structures of these exciting materials and to explore the relationship between magnetism and superconductivity. Several of the early papers from major facilities became citation classics, such as work on the structure of YBa2Cu3O7âx, that on magnetic fluctuations in La2âxSrxCuO4, and the study of stripe correlations in copper oxide superconductors. Small-angle neutron scattering played a central role in under- standing polymer chain structure and conformation. The same pattern repeated itself when bulk samples of buckminsterfullerene, C60, were synthesized in the early 1990s. The power of neutron scattering was immediately harnessed to characterize the structure of the buckminsterfullerene and to study the properties of the new superconducting fulleride derivatives that were discovered immediately afterward. Recent achievements include in situ imaging work at NIST on water movement in hydrogen fuel cells (Figure 11.10), studies of electronic phase segregation and short-range order in transition metal oxides, and polarized neutron reflectometry applied to spintronic materials. Other recent achievements involved the use of neu- tron reflectivity to study block copolymer thin films. Neutron spin echo techniques provided new insights into polymer chain dynamics and transitions. There can be no doubt that neutron sources and related major facilities will make major contributions to all of the grand challenge areas identified in this report. History shows that with each new generation of advanced materials, the power of the nationâs major facilities is used to address some of the key scientific and technological issues. The neutron is a unique probe for studying condensed matter. Its penetrating power enables it to probe large objects up to 1,500 kilograms in weight, making it suitable for characterizing defects in macroscopic engineering structures. At the atomic level, the magnetic moment of the neutron makes it sensitive to the spin and orbital properties of transition metal ions in important materials such as highly magnetoresistive oxides. And the unique sensitivity of neutrons to the location and
218 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s a b FIGURE 11.10â (Left) Image of water motion in the channels of a hydrogen fuel cell. (Right) The cor- responding fuel cell. SOURCES: J.P. Owejan, General Motors Corporation, and the National Institute of Standards and Technology. 11-10 a, b motion of hydrogen atoms will continue to be unmatched for studies of hydrogen storage materials, catalysts, polymers, and biomaterials. Current Status of Neutron Sources The neutron community in the United States is entering an exciting period. The commissioning of the Spallation Neutron Source and the refit of the High Flux Isotope Reactor (HFIR), both located at Oak Ridge National Laboratory (ORNL), will bring leadership-class source capability back to the United States for the first time in more than 30 years. SNS will be a factor of 8 times more intense than the ISIS spallation facility in the United Kingdom, which is currently the most intense spallation source in the world. Furthermore, the new generation of instruments, with their improved optics and detectors, will give a further advantage, leading to an overall gain in signal of 20 to 100 times. In terms of reactor sources, the HFIR facility is comparable in power to the high-flux beam reactor at the Institut Laue- Langevin in Grenoble, France, albeit with fewer beam lines and instruments, so the combined source capability at ORNL will be best-in-class. Scientific leadership, of course, is not simply dependent on source intensity but also on the development of innovative instruments, versatile sample environ- ments, powerful data-analysis infrastructure, and the recruitment of talented and energetic instrument scientists. Even more, of course, it depends on the creativity of the science community in employing these instruments.
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 219 However, even with the advent of SNS, the United States remains beam-line and instrument poor compared with Europe. In 2010, for example, there will be about 170 neutron instruments in Europe, compared with only 70 in the United States. In addition, the rate of growth of neutron sources in the Asia-Pacific region will likely surpass the capabilities in the United States within the next decade. For example, China is building three new neutron sources, the Japan Proton Ac- celerator Research Complex is being completed in Japan, there is a major reactor upgrade in Korea, and a new Australian research reactor has recently started up. In the light of the 1997 closure of Brookhaven National Laboratoryâs High Flux Beam Reactor (HFBR) and the possible closure of Argonne National Laboratoryâs Intense Pulsed Neutron Source (IPNS) in 2009, it is essential that the remaining facilities at NIST and the Los Alamos Neutron Scattering Center (LANSCE) at Los Alamos National Laboratory be sustained at internationally competitive levels and that the remaining expertise at Brookhaven and Argonne National Laboratories be retained and harnessed. One very positive development in the U.S. neutron community over the past 15 years has been the growth of the user base (Figure 11.11). In particular, the overall number of users has increased from approximately 650 in 1990 to more than 1,500 LANSCE FIGURE 11.11â Growth of the U.S. neutron user community between 1990 and 2005. NOTE: NCNR, National Institute of Standards and Technology (NIST) Center for Neutron Research; HFBR, High Flux Beam Reactor; HFIR, High Flux IsotopeFIG 11.11 Intense Pulsed Neutron Source. SOURCE: Reactor; IPNS, Patrick Gallagher, National Institute of Standards and Technology. Revised. no longer a jpeg. It is now an Illustrator file
220 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s in 2005. The data in Figure 11.11 also show the negative impact of the closure of HFBR in 1997, from which it took the community 6 years to recover. The graph also shows the impressive growth since 2000 of the user base at LANSCE and the huge impact of the NIST Center for Neutron Research. The other significant development over the past decade has been the changing pattern of industrial use of neutrons. The data are partly anecdotal, but the num- bers of primary industrial users have diminished as the amount of basic research at some of the major industrial laboratories, such as at IBM research laboratories and at Bell Laboratories, has been reduced. In addition, there is some evidence that more work is being done in industry through university collaborators. Looking to the future, if the funding agencies pursue full utilization of the available U.S. sources, which will require increased operating funds as well as capital investments (see the following subsection), the size of the U.S. neutron user base is expected to approach that of Europe today over the next 15 years. These pro- jections assume that the second target station will be built at SNS, that IPNS will remain open, and that all the facilities will have a full complement of instruments (see two subsections below). Medium-Term Developments A number of important upgrades to the existing facilities have already been approved but not yet funded: the SNS Power Upgrade ($160 million), a Âsecond cold source/guide hall at NIST ($100 million), and the LANSCE accelerator refurbishÂ ment ($170 million, funded by the National Nuclear Security Administration). In addition, a number of other major projects are in the advanced stages of p Â lanningâspecifically, the second target station at SNS (the Long Wavelength Target Station [LWTS], $500 million)âand a second guide hall at HFIR ($150Â mil- lion) has also been under discussion. SNS is designed to accommodate a second target station fed from the same accelerator complex, while operating at a lower repetition rate than that at the existing High Power Target Station (HPTS). This would double the number of beam lines that can be supported, enabling a much broader scientific program and providing the optimal route to a significant number of additional high-flux beam lines (about 25) without the expense of building an entirely new source. More importantly, a lower repetition rate would lend itself to optimizing the target station environment and its instruments for long-wavelength (cold) neutrons. In the long term, the LWTS would more than double the scientific capability of SNS for about 25 percent of the capital cost while providing space for enough additional instruments to double the user community at SNS. The proposed LWTS will be a nanoscience neutron source with an order-of- magnitude better performance in many applications compared with the HPTS. The use and sophistication of neutron diffraction and crystallography are growing
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 221 strongly in the study of complex materials having both atomic scale and nanoscale features. These include hybrid organic-inorganic materials for sensors, mesoporous solids for chemical separations and catalysis, and supramolecular complexes of biomolecules. The LWTS will be ideal for neutron reflectometry, which strongly impacts the study of polymer thin films and interfaces, magnetic films and multi- layers, liquid surfaces, biological membranes, bilayers, and in situ corrosion studies. In addition, neutron spectroscopy using long-wavelength neutrons is increasingly being applied to the study of the low-energy dynamics of complex systems, such as polymer (reptation), proteins, and molecules in confined geometries or adsorbed on surfaces. The cold source for the second guide hall at HFIR would be placed in a region of very high flux leading to the highest steady-state cold neutron source in the world (by a factor of about two to three). The science opportunities for the second guide hall would eventually fall into the same realm as the SNS second target but would be tailored to the complementary strengths of a continuous versus pulsed source. In addition to these major capital projects, a number of other developments will be required in order to achieve the full potential of the source capabilities. These developments, which are interdependent and therefore not prioritized in the list below, are as follows: â¢ Robust funding of research programs; neutron science is single-investigator driven. In order for projects that involve the use of neutrons to be carried out, faculty must have their own grants to support graduate students and postdoctoral assistants; â¢ Full staffing of beam lines; the current level of three to four staff scientists per instrument needs to increase to at least five to better utilize the invest- ment in the instrumentation; â¢ Continued funding to permit full operating time of facilities in order to accommodate all very highly rated proposals; â¢ Significant investment in ancillary equipment or sample environments, for example, samples in extreme environments of temperature, pressure, and magnetic field; and â¢ Substantial investment in software development, including data analysis, vi- sualization, modeling, and so on. The project on Distributed Data Analysis for Neutron Scattering Experiments (DANSE) is an excellent start and may provide the basis for a future coordinated national effort in this area. It is also important to recognize that the quality of the science emerging from the facilities will be severely compromised if the instruments are not state of the art. This will require an investment of approximately $100 million per year, compared with about $25 million that is being spent at present.
222 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s Beyond the full-utilization scenario described above, the United States will need a new national facility, driven by the age of some of the existing facilities and the intriguing new concepts that are developing, such as very cold neutron sources for ultralong neutron wavelengths, long pulsed sources, and novel continuous sources. The committee emphasizes that the long-term strategy must be planned during the coming decade, based on experience with the current facilities, bearing in mind the needs of individual investigators working in CMMP and the instru- mentation and facilities they need to carry out state-of-the-art research. Recommendations for Neutron Sources in CMMP Research Recommendation:â DOE should complete the instrument suite for the SNS at Oak Ridge National Laboratory, together with provision of state-of-the-art ancillary equipment for these instruments, in order to gain the maximum benefit from the recent investment in the SNS. Recommendation:â DOE should construct the second target station at SNS as the top priority for major capital investment for neutron sources, since it will facilitate a wide range of new science and will provide qualitatively different capabilities for cold neutron studies. Recommendation:â DOE, NSF, and the Department of Commerce should sustain commitments to the existing neutron facilities at Los Alamos National Laboratory and the National Institute of Standards and Technology as needed to meet the growing demand for neutron studies and to train new users in neutron-scattering techniques. Recommendation:â With support from the funding agencies and in the next 5 years, the research community should begin to make longer-term plans for a future neutron source. Electron Microscopy Electron microscopy is an integral part of the discovery and development of new materials. Of all CMMP papers produced each year, a significant fraction contains data relying on some type of electron microscopy. The two major types of electron microscopy are scanning electron microscopy (SEM), which images the reflected beam, and transmission electron microscopy, which detects the transmit- ted beam. While the fundamental principles underlying electron microscopy have been known for at least half a century, the recent rate of instrumental advance is
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 223 the highest since the invention of the electron microscope, with enormous poten- tial to solve key questions of CMMP. Traditional areas of success include studies of crystalline solids as well as solid interfaces. More recently, new technology has enabled new directions in nanomaterials, soft matter such as (bio-) polymers, organic/inorganic composites, and dynamic processes at the atomic scale. New techniques include tomography as well as holography for magnetic materials and dopant profiles. Electron microscopy is well positioned to address a wide range of important, upcoming characterization challenges in CMMP. These include tomography and the three-dimensional mapping of electronic structure at the atomic level; local structure-property determination for individual, embedded nanophases and their interaction with the surrounding matrix; and the three-dimensional imaging of magnetic fields at the nanoscale (Figure 11.12). FIGURE 11.12â After the electron beam penetrates a sufficiently thin sample, the three principal mo- dalities of a transmission electron microscope provide complementary information. SOURCE: Ulrich Dahmen, Lawrence Berkeley National Laboratory.
224 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s Current Status of Electron Microscopy Facilities DOE supports three electron beam sources: one each at Argonne, Lawrence Berkeley, and Oak Ridge National Laboratories (ANL, LBNL, and ORNL). The number of users of these sources has grown somewhat over the past two decades to approximately 500 in 2006 from 350 in 1985. The smaller base of Â users of e Â lectron-beam sources reflects the fact that electron microscopes are comparatively widespread, and the national facilities offer significant opportunities to the more sophisticated users: atomic resolution imaging at LBNL, in situ studies such as radiation effects at ANL, and microanalysis and spectroscopy at ORNL. Yet the largest usage, perhaps as high as 80 to 90 percent of the aggregate workload, of electron microscopy takes place at smaller, local facilities or in the laboratories of individual PIs, because of the ubiquitous use of electron microscopy for CMMP materials characterization. Nevertheless, there is an increasing gap, in terms of both the initial cost of systems and the continued upkeep and support for techni- cal staff, between the more standard yet highly used characterization facilities on the one hand and the highest-end facilities that advance the forefront of the field on the other hand. Currently, electron microscopy happens at three levels of sophistication. âWorkÂ horseâ microscopes typically are commercial instruments for routine microscopy, sample preparation, and user training. High-end machines are leading-edge com- mercial instruments that typically are found at local or regional facilities, operat- ing in support of area universities, national laboratories, and industry. High-end machines play an important educational role for the use and design of microscopes, techniques, and associated instrumentation, and they provide for training of the next generation of microscopists in CMMP. Finally, at the cutting edge there are one-of-a-kind, next-generation instruments, optimized for specific electron- optical beam line applications. Support at all three levels will be a key for the continued success of this type of experimental facility within the general CMMP f Â ramework. The main hurdle for reaching the highest spatial resolution has not been the electronâs wavelength but limitations, such as aberration, associated with the de- sign of the focusing lens. As a consequence, with traditional approaches it has not been possible to go below the 1 angstrom (0.1 nanometer) level and reach true subatomic resolution. The recent advent of aberration-corrected instruments has been a breakthrough for electron microscopy (in fact, providing a leap for TEM as well as for SEM performance; see Figure 11.13). These new instruments hold promise of enabling entirely new insights into areas such as the subsurface map- ping of electron distributions, quantum confinement, spintronics, real-time flux bundle imaging, nanomagnetism, catalysis, and electrochemistry.
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 225 FIGURE 11.13â The evolution of microscopy resolution over time. The Department of Energy Transmis- sion Electron Aberration-corrected Microscope (TEAM) array could break through the 0.1 nanometer resolution barrier. NOTE: OÃ M, One-Angstrom Microscope; ORNL, Oak Ridge National Laboratory; STEM, Scanning Transmission Electron Microscope; BNL, Brookhaven National Laboratory; TEM, Transmission Electron Microscope; ARM, Atomic Resolution Microscope. SOURCE: Ulrich Dahmen, Lawrence Berkeley National Laboratory. Adapted from H. Rose, âCorrection of Aberrations, A Promis- ing Means for Improving the Spatial and Energy Resolution of Energy-Filtering Electron Microscopes,â Ultramicroscopy 56, 11-25 (1994).
226 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s Medium-Term Developments Two research directions were identified as being particularly promising for advancing electron microscopy during the next 10 years: the imaging of phenom- ena far from equilibrium and the imaging of a materialâs response to direct, in situ manipulation. Currently, almost all work is done on static samples at or near equilibrium. With the development of faster detectors and emitters, a goal is to achieve high temporal resolution (down to picoseconds). Coupled with millivolt spectral resolution, this will make it possible to track atomic-scale dynamics in real time, including phase-transformation kinetics and chemical reactions. The further development of in situ manipulation systems for TEM will open up a host of opportunities for studies of nanomechanics, in situ deposition and growth of samples, and the interaction of materials with applied electric, magnetic, strain, and photon fields. For high-end instruments, further developments will likely combine highly focused electron beams with other types of probes, turning electron microscopes into more complex probe stations. At the forefront level, a completely different ap- proach to overcoming aberration issues may be to do away with lenses altogether. Lensless, aberration-free imaging might be achieved if the full information (that is, both amplitude and phase) contained in the scattered wave function can be recovered. The DOE Transmission Electron Aberration-corrected Microscope (TEAM) Project The current leading effort that capitalizes on aberration-correcting electron optics is the Transmission Electron Aberration-corrected Microscope (TEAM) project, bringing together five leading microscopy groups supported by DOE to jointly design and construct a new-generation microscope with extraordinary ca- pabilities. The project is part of DOEâs 20-year roadmap of Facilities for the Future of Science, and after its completion in 2009, the instrument will be made available to the scientific user community at the National Center for Electron Microscopy. The vision for the TEAM project is the idea of providing a sample space for electron-scattering experiments in a tunable electron optical environment by re- moving some of the constraints that have limited electron microscopy until now. The resulting improvements in spatial, spectral, and temporal resolution, the increased space around the sample, and the possibility of exotic electron-optical settings will enable new types of experiments. The TEAM microscope will feature unique corrector elements for spherical and chromatic aberrations, a novel atomic force microscopy-inspired specimen stage, a high-brightness gun, and numerous other innovations that will extend resolution down to the half-angstrom level. The improvement in sensitivity, brightness, signal to noise, and stability will make it
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 227 possible to address major challenges such as single-atom spectroscopy and atomic- resolution tomography. The machine is being designed as a platform for a sequence of instruments, each optimized for different performance goals that were identified in a series of workshops. The most important scientific driving force that emerged from these workshops is the need for in situ experiments to observe directly the relationship between structure and properties of individual nanoscale objects. Successive instru- ments built on the TEAM platform would provide unique experimental capabilities to probe the dynamics and mechanisms of reactions, such as catalysis in a gaseous environment, or the effects of gradients in temperature, composition, stress, and magnetic or electric fields on the structure of materials at the atomic level. The ability to probe nanoscale volumes of materials with atomic resolution meets one of the important scientific challenges in CMMP. The United States has not been a leader in the field of electron microscopy for considerable time, with much Âof the cutting-edge development taking place in Asia and Europe. If fully funded, the TEAM array will be an opportunity for the United States to reclaim a forefront position and will provide best-in-class instrumentation at the international level. Recommendations for Electron Microscopy in CMMP Research Recommendation:â DOE and NSF should support the CMMP communityâs needs for electron microscopy instrumentation at universities on a competi- tive basis. Cutting-edge electron microscopy technique development (such as the DOE TEAM project) should be continued in order to fully reestablish U.S. competitiveness in developing the next generation of electron microscopes. Recommendation:â Revitalize U.S. electron microscopy. Integrated support across all three facility levels (standard, high end, forefront) is urgently re- quired to realize the full benefit to the CMMP community of recent technical achievements in the field of electron optics. This support includes not only capital investment in new instruments on a competitive basis, but also the sup- port of career instrument scientists and operating costs at electron microscopy facilities. Recommendation:â Fund technique development. At present, technique de- velopment typically is a by-product of other research projects. To stimulate technical innovation in the field, programs dedicated to electron microscopy technique development will make a significant difference. âFor more information on the TEAM workshops, see the reports at http://ncem.lbl.gov/team3.htm; last accessed September 17, 2007.
228 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s Recommendation:â Hold crosscutting workshops. There are major opportunities to reach out and connect with communities that use other, yet related techniques to image nanoscale phenomena, such as atom-probe and ion microscopes for three-dimensional imaging at the atomic scale, and x-ray nanoprobes. All of these communities, from electron microscopy to x-ray nanoprobe, are now gearing up to study similar materials problems and will face many similar scientific as well as technique-related challenges; yet the communities operate in parallel. Interdisciplinary, broadly based, and forward-looking workshops to address such common issues should be encouraged. High-Magnetic-Field Facilities Magnetic fields interact with moving charges. Because the typical length scales associated with this interaction scale decrease with increasing magnetic-field strength, high magnetic fields can probe small spatial features and the associated fast processes. In order to achieve magnetic lengths comparable to the size of a quantum dot of 6-nanometer diameter, fields of about 20 tesla (T) are required; 80 T are necessary to shrink this length by another factor of two. As a consequence, the study of magnetic phenomena on the scale of a few nanometers, and from there on down to atomic dimensions, necessitates pushing the limits of what is possible with current magnet technology. Traditional areas of success for high-field research have been the study of fun- damental mechanisms in correlated quantum systems such as low-dimensional magnetism, the quantum Hall effect, and superconductivity, as well as the investiga- tion of the properties of interacting magnetic flux bundles (âvortex matterâ) inside superconductors. Separately, high-field research has enabled magnetic resonance studies in organic materials, providing important insights into membrane protein structures, hemoglobin, and the underpinnings of photosynthesis. Furthermore, CMMP research provides advanced materials, including superconductors with better performance, special conductors, and high-strength alloys. These materials form the critical components for magnets used in applications ranging from atomic particle accelerators to medical magnetic resonance imaging (MRI). Two recent studies have looked into the current status and the potential for future developments of high-field magnet research. For more detailed informa- tion and discussions of the various technical issues, the committee refers to these reports., âNational Research Council, Opportunities in High Magnetic Field Science, Washington, D.C.: The National Academies Press, 2005. âReport of the International Union of Pure and Applied Physics working group on Facilities for Condensed Matter Physics: High Magnetic Fields, 2004. Available at http://www.iupap.org/wg/fcmp/ hmff/highmagneticreport.pdf; last accessed September 17, 2007.
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 229 Current Status of High-Magnetic-Field Facilities Magnet facilities fall into two categories, delineated by magnet technology and, thus, by the maximum achievable magnet field strength. Smaller high-field mag- nets (<20 T) are currently based on technology using superconducting niobium compounds and are available commercially. These magnets are found in single PI laboratories as well as in local multiuser facilities. Costs rise steeply with increas- ing field. Niobium-titanium magnets deliver up to 11 T, while Nb3Sn goes up to 20 T in driven magnets (at a cost of $1 million to $2 million) and up to ~22 T in persistent-mode NMR magnets (at a cost of $5 million to $15 million per system). For these smaller magnet systems there have been no major technological advances in recent years. Large magnets (>30 T) comprise both continuous-field (direct current [dc]) and pulsed systems, are typically unique in design, and, because of their complexity and costs, are mostly located at dedicated high-field facilities, such as the National High Magnetic Field Laboratory (NHMFL) in the United States. At U.S. national facilities, large magnets are currently available that can reach up to 45 T in con- tinuous mode (hybrid superconducting/resistive magnets), and up to 60 T for 100 microseconds in pulsed mode. As pointed out in the reports mentioned above, the value of the maximum achievable field is not the only important parameter for high-field research. Depending on the application, the quality and usefulness of a facility are determined also by factors such as the homogeneity of the field, the diameter of the magnet bore, or the availability of an environment amenable to low-noise measurements. Furthermore, for much of CMMP research, another important factor is the simultaneous access to low sample temperatures, that is, a large ratio of magnetic-field strength to temperature. In this area, the NHMFL has been a leader with its High B/T Facility. With high-field magnet user facilities come challenges of energy costs in the face of increasing magnet hours driven by user demand. This challenge motivates higher-efficiency magnets, but they involve larger capital investment. As each magnet technology becomes more broadly used (for example, resistive magnets for nuclear and electron resonance), the issues shift toward addressing and integrating different magnet specifications (for example, peak field, time at fixed field, and field homogeneity) desired by the CMMP, chemistry, and biology user communities. Medium-Term Developments High-magnetic-field research in CMMP is driven by the prospect of using the field as an exquisitely sensitive tuning parameter to explore emergent Â quantum phases of matter and by being able to perform precision spectroscopy using tech- niques such as NMR. In the area of complex fluids, the same spectroscopic methods can be used to track trace elements, while quadrupolar NMR opens up almost the
230 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s entire periodic table as candidate nuclei. This capability will allow for a new level of structure-function correlation in glasses, ceramics, catalysts, and porous materials (for example, zeolites and batteries). Technological challenges for the coming decade center on the development of new magnet technology beyond niobium. The recent report Opportunities in High Magnetic Field Science10 identified a 30-T high-resolution NMR magnet, a 60-T dc hybrid magnet, and a 100-T long-pulse magnet as grand challenges. All of these require conductor materials in forms that are not yet commercially available, which in itself poses a materials research and development challenge. The NHMFL has been taking the lead in meeting these challenges and, furthermore, has embarked on developing additional magnet systems for low power consumption, complex fluids research, and ultrahigh fields (200 T/1 microsecond pulsed magnet). New superconducting materials, such as MgB2 or high-Tc materials such as yttrium barium copper oxide (YBCO) or bismuth strontium calcium copper oxide (BSCCO), offer several advantages in terms of larger upper critical field strength and higher operating temperatures (eliminating the need to cool with cryogens such as liquid helium). Mulifilament MgB2-based technology currently can go as high as 10 T, but 30 T or more appear eventually achievable. Commercial magnets based on this new technology are around the corner, with MRI applications as a major driver. Bi-2212 magnet wires promise greater than 50-T fields, among other advantages, while YBCO offers the highest fields. However, there are still many research and development challenges in terms of fabricating sufficiently long wires or tapes out of these materials and in improving their tensile strength, as required to withstand the forces generated in high-field magnets. Successful development of these materials could lead to relatively low cost and easy-to-operate magnets and would broaden the accessibility of high fields to small groups. Special pulsed and hybrid magnets also will benefit from the integration of high-Tc components. Resistive plus high-Tc technology should get well beyond 50 T. For pulsed magnets, multishot 100-T fields are within reach. An important direction besides magnet development will be the integration of high fields with beam lines. This would allow the investigation of the neutron and x-ray scattering properties of materials in high magnetic fields. Currently, there are interesting design proposals to add hybrid magnets of fields of about 30 T to beam lines at the SNS at ORNL, and at the APS at ANL. Another plan, involving a collaboration of NHMFL, Jefferson Laboratory, and the University of California at Santa Barbara, envisions combining advanced magnet technology with an infrared free-electron laser. This would allow access to the terahertz regime that is resonant with magnetic-field energy scales. 10âNational Research Council, Opportunities in High Magnetic Field Science, Washington, D.C.: The National Academies Press, 2005.
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 231 Recommendations for High-Magnetic-Field Facilities in CMMP Research Recommendation:â NSF should continue the support of the National High Magnetic Field Laboratory and high-magnetic-field instrumentation develop- ment following the priorities recommended by the recent National Research Council report Opportunities in High Magnetic Field Science.11 Recommendation:â The research community, with support from the federal agencies, should exploit the opportunities for superconducting magnets pro- vided by the recent and imminent high-Tc conductor forms. This will benefit small-scale users and high-field NMR users, and will allow for more powerful hybrid magnets. Nanocenters and Materials Synthesis The past decade has given rise to significant investment in the establishment of a diverse portfolio of nanoscience research centers. This development was made possible by the stewardship of the multiagency National Nanotechnology Initiative (NNI). The centers complement traditional major neutron and photon sources for CMMP research and include strong user support in their mission statements. The centers differ in character from one another according to the directives of their sponsoring agencies. But, more significantly, they are in many ways distinct in character from large-scale facilities such as neutron and photon sources. The primary focus of the nanocenters is on the creation of new materials as well as on the advanced characterization of materials, while the other major facilities deal pri- marily with advanced characterizations. This focus represents a turning point, an acknowledgment of the central importance of the need for new materials in order to invigorate CMMP. This is a theme that needs to be extended and broadened in the next decade in order for the United States to recapture its leadership in the area of the discovery of new materials. In this subsection, nanocenters are discussed and the model is considered for the design and discovery of new materials of interest to CMMP researchers, such as bulk crystals, novel thin films, and superlattices. Current Status of Nanocenters and Materials Synthesis Researchers at many institutions face challenges associated with the avail- ability of materials. They may lack the expertise or the appropriate equipment 11âNational Research Council, Opportunities in High Magnetic Field Science, Washington, D.C.: The National Academies Press, 2005.
232 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s for the synthesis or growth of new or high-quality materials. The NSF National Nanotechnology Infrastructure Network (NNIN) program is intended to address these issues. The NNIN program is largely directed at providing capabilities for the synthesis and fabrication of materials and for providing computational and theoretical tools and expertise. A network of 13 universities around the country (see Figure 11.14) participates in this program to provide and share facilities for nanoscience and engineering research. In addition to the NSF NNIN program, DOE has established Nanoscale Science Research Centers at five national laboratories: the Center for Nanophase Materials Sciences at ORNL, the Molecular Foundry at LBNL, the Center for Integrated Nan- otechnologies jointly operated by Sandia National Laboratories and Los Alamos National Laboratory, the Center for Nanoscale Materials at ANL, and the Center for Functional Nanomaterials at Brookhaven National Laboratory. These centers are largely dedicated to materials synthesis, fabrication, and characterization. They provide access to electron-beam nanowriters, lithography and stamping for nano- fabrication; x-ray nanoprobes and facilities for complex materials formation and soft hybrid materials; and infrastructure for theory simulations. The nanocenters are distributed facilities that embrace interdisciplinary ap- proaches to solving nanoscience and nanotechnology problems using a full suite of modern instrumentation. At many of the nanocenters, theory and simulation FIGURE 11.14â Institutions participating in the National Nanotechnology Infrastructure Network pro- gram. NOTE: UCSB, University of California at Santa Barbara; PSU, Pennsylvania State University; TNLC (NCSU), Triangle National Lithography Center (North Carolina State University). SOURCE: See http://www.nnin.org.
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 233 are on a similar footing with experimental science. Also, the pursuit of world-class, in-house scientific research programs is on a similar footing with user support services. The nanocenters provide a pathway from fundamental science to applica- tions with the possibility of commercialization and the creation of new start-up companies. The balance between science and user-service programs at the nanocenters is approached differently, depending on the sponsoring agency. For example, the DOE NSRCs encourage a model whereby each Ph.D. staff member pursues basic science research and user-support services. The NIST Center for Nanoscale Science and Technology has separate divisions that emphasize scientific programs and user sup- port. The NIST scientific programs focus on solving major measurement-related obstacles in the path from discovery to production. The Department of Defense (DOD) supports an in-house, mission-oriented Institute for Nanoscience at the Naval Research Laboratory. Medium-Term Developments The challenge ahead is to learn how to sustain the progress of the nanoscience era and to optimize accessibility to a diverse range of instruments and facilities. In cases where nanocenters are co-located with other major facilities, the planning of one-stop shopping needs to be perfected so that newly created nanosystems can be interrogated with electrons, neutrons, and x-rays in a single visit. Metrics need to be refined for monitoring the success of the new nanocenters. The funding for operations needs to support the diverse suite of equipment at the nanocenters. Models need to be evaluated for a balance of in-house science and user sup- port. Barriers will need to be lowered to facilitate the transition from science to commercialization. The nanocenters have addressed a gap in research culture by acknowledging the importance of synthesis, processing, and fabrication of new materials and systems. Recognizing this, it is imperative to accelerate the momentum and to energize other areas of new-materials exploration and discovery of vital interest to CMMP. The design and synthesis of novel systems are the foundation to address all of the CMMP grand challenges. The energy challenge needs new materials for storing hydrogen, thermoelectrics, organic light-emitting diode (LED) crystals, and high-performance superconductors and ferromagnetics. Information technology needs new materials for spintronic, organic, and molecular electronics that ex- hibit quantum coherence properties suitable for quantum computation prototyp- ing. Multiferroics, magnetic semiconductors, and half-metallic ferromagnets are specific systems also of great interest to spintronics. As the art of crystal growth matures into a science, the resulting insights might apply to the understanding of the physics of soft-matter crystallization. Protein crystallography data collection at
234 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s photon sources would benefit immensely from such a development. This example highlights the multidisciplinary nature of the quest that brings together chemists, biologists, engineers, and physicists. The new crystal discovery centers of the future can be distributed, as are the nanocenters. The models for creating and operating them might also benefit from examining the NSF NNIN and DOE NSRC models. Presumably viable hybrid organizational structures will evolve that best serve the particular materials missions of these future efforts. A target budgetary level per year might be similar to that for NSF of its NNIN program, and for DOE a level of the equivalent of one or two of its five NSRC facilities (for further discussion, see Chapter 9). Why is it imperative to move forward on a new-materials discovery agenda now? The United States is not in a lead role in the creation of new materials. It needs to recapture its lost status, because the consequences of delay and neglect are long- term erosion of the U.S. competitive edge and a loss of intellectual property. New materials invigorate all of the CMMP grand challenges. While new-materials dis- covery is cross-disciplinary, at present there is no obvious academic home for new- materials initiatives. This problem needs to be remedied. New-materials discovery embraces theory and simulation in the sense of virtual fabrication. New materials created via computer models, including electronic band structure codes, provide insights and guidelines to direct the design of new materials in the laboratory. The new-materials discovery centers of the future will also provide fertile training grounds for future generations of graduate students. The nanocenters started the culture change by emphasizing the creation of new materials. The transformation needs to be extended to embrace the larger landscape of new-materials discovery beyond the nano-realm. The time is ripe to focus on this strategic scientific goal, to plan multidisciplinary team approaches, and to identify visionary management, scientific advisers, and stakeholders, as stated above. Balance must be sought be- tween support of the individual investigators and small groups of investigators relative to centers, instrumentation, and major facilities investments. Recommendations for Materials Synthesis and Nanocenters in CMMP Research Nanoscience is a core discipline whose advances will affect all of the other challenges, from emergent phenomena (Chapter 2) to information technology (Chapter 7). The past decade has already seen significant federal investment in nanotechnology infrastructure. Notable are the NSF-funded Nanoscale Science and Engineering Centers and the National Nanotechnology Infrastructure Net- work, as well as the new DOE-funded Nanoscale Science Research Centers at the national laboratories. These facilities serve a critical need and deserve continued support. Nanoscience by its very nature spans an enormously wide variety of disciplines, from condensed-matter physics to engineering to chemistry and biol-
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 235 ogy. This makes it all the more critical to develop an intellectual resource network that allows scientists from one discipline to have access to the knowledge of all of the others. There is need for training opportunities for students, postdoctoral researchers, and faculty that allow them to reach beyond the standard disciplinary boxes. There is also need to develop knowledge repositories like those that exist in biology, where genomes and so on are stored and made widely available. The NSF and DOE-funded nanoscience centers should take the lead in meeting these needs, teaching short courses on particular techniques and subfields, as well as providing repositories of information. Recommendation:â DOE and NSF should develop distributed national facili- ties in support of the design, discovery, and growth of new materials for both fundamental and applied CMMP research.12 Recommendation:â DOE should evaluate the new NSRCs by metrics described in Chapter 9. The National Nanotechnology Coordination Office (NNCO), in its arrangement of the triennial review of the NNI, should evaluate all NNI- funded centers and networks of centers by similar metrics. Large-Scale High-Performance Computing Facilities High-performance computing is well recognized as a prerequisite for scientific and technological preeminence. High-priority, significant resources at the federal level are therefore directed toward the ongoing development and maintenance of state-of-the-art computational facilities for general scientific research, includ- ing CMMP. In understanding how such resources address the needs of CMMP researchers, it is important to note that large-scale computation is an important component of many scientific fields that share these resources. Below, the com- mittee describes the major U.S. high-performance computing facilities and shows data as to how the available resources are shared among disciplines. Current Status of Computing Facilities The largest and most powerful systems define the limits of the types of compu- tational studies that can be carried out at present. For the U.S. CMMP community, these computational facilities are supported by NSF, DOE, and DOD. Building on the system of NSF supercomputing centers of the 1990s, the devel- 12âThe National Research Council study Assessment of and Outlook for New Materials Synthesis and Crystal Growth will make detailed recommendations on how best to support this need. The report is expected to be released in the summer of 2008.
236 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s opment of the TeraGrid began in 2000 as the worldâs largest, most comprehensive distributed cyberinfrastructure for open scientific research. Partners in this dis- tributed framework include the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign, the San Diego Super- computer Center (SDSC) at the University of California at San Diego, Argonne National Laboratory, the Center for Advanced Computing Research (CACR) at the California Institute of Technology, Pittsburgh Supercomputing Center, Indiana and Purdue Universities, Oak Ridge National Laboratory, and the Texas Advanced Computing Center at the University of Texas at Austin. As of 2005, the TeraGrid had about 1600 users. A relatively small fraction is used for materials and (all of) physics research (see Figure 11.15). DOE supports scientific computing primarily through the National Energy Re- search Scientific Computing Center (NERSC) and through Leadership Computing Facilities (LCF) at the national laboratories. NERSC is described by DOE as âone of the largest facilities in the world devoted to providing computational resources and expertise for basic scientific research,â with 2677 users in 2005. Reflecting the broad DOE mission, a relatively small fraction of resources (about 9 percent) is devoted to computation for materials research (see Figure 11.15). At national laboratories, such as ORNL where materials are a larger compo- nent of research, the fraction of resources at the LCF is correspondingly higher. a b FIGURE 11.15â (Left) National Science Foundation TeraGrid usage, by discipline, in FY 2005. NOTE: âComputer & Info,â computer science and information technology. (Right) Department of Energy Na- tional Energy Research Scientific Computing Center usage, by discipline, in 2005. NOTE: âLattice QCD,â lattice quantum chromodynamics. SOURCES: (Left) National Science Foundation TeraGrid. (Right) National Energy Research Scientific Computing Center, Lawrence Berkeley National Laboratory. 11.15 a,b
T o o l s , I n s t ru m e n tat i o n , and Facilities for CMM P R e s e a r c h 237 At ORNLâs National Center for Computational Sciences, about 25 percent of the centerâs resources are used for materials computations. A number of the LCFs are also partners in the NSF TeraGrid. DOD has a large network of supercomputer centers (the High Performance Computing Modernization Program) to support the computing needs of DOD researchers, with 4550 users in 2005. Materials research falls in the category âCCMâ (Computational Chemistry, Biology, and Materials Science). The share for this category can be seen in Figure 11.16. While the focus of this discussion has been on high-performance computing, there is much interesting and innovative work done in computational materials that does not demand computational resources at the highest available level, but where accessibility and throughput are key considerations. Much valuable work is done at computing facilities at the state level, at individual universities, in depart- ments, and by research groups. Support for computational facilities from sources such as the NSF Major Research Instrumentation program should be encouraged, and budgeting for computer equipment in theoretical and computational CMMP FIGURE 11.16â FY 2006 Department of Defense high-performance computing requirements, alloca- tions, and utilization breakdown for individual âcomputational technology areas.â Computational Chemistry, Biology, and Materials Science (CCM) is third from the left; other areas are Computational Structural Mechanics (CSM), Computational Fluid Dynamics (CFD), Computational Electromagnetics and Acoustics (CEA), Climate/Weather/Ocean Modeling and Simulation (CWO), Signal/Image Process- ing (SIP), Forces Modeling and Simulation (FMS), Environmental Quality Modeling and Simulation (EQM), Electronics, Networking and Systems (ENS), and Integrated Modeling and Test Environments (IMT). SOURCE: C.J. Henry, Department of Defense High Performance Computing Modernization Program.
238 C o n d e n s e d - M at t e r and M at e r i a l s P h ys i c s individual and small-group proposals should be considered the norm. However, this hierarchical structure, while it evolved largely to meet the needs of researchers, does come with problems of its own. As computational power increases, issues of professional systems administration and user support personnel for computing clusters become increasingly important. The diversity of facilities can make the system hard to navigate for researchers seeking resources. This latter challenge is particularly common for computational junior faculty members starting careers in computational CMMP. Conclusions The need for sophisticated tools (experimental, computational, and theoreti- cal) to probe the structure and properties of materials over a wide range of length scales is essential for continued progress in CMMP research. The new-generation facilities (light and neutron sources, magnetic-field facilities, and electron micro- scopes), which offer higher fluxes and energies, provide significant advantages with regard to resolution, sensitivity, and data acquisition. Two additional challenges will continue to be important in the future: the simultaneous measurement of structure and dynamics over various time and length scales and dimensions, and the simul- taneous measurement of structure and dynamics while the system is perturbed independently by an external field (magnetic, stress, electric, and so on). The synthesis, structure, and properties of materials are all intimately con- nected, so researchers will increasingly need to be intimately familiar with this entire spectrum of activities. Lessons learned from one class of materials will increasingly be used to understand the behavior of seemingly different classes of materials. For the first time in history, the complexity of CMMP is such that new advances in the field will depend on strong support for large-scale facilities, mid- scale facilities, interdisciplinary research centers, and individual investigators who actually carry out the research. Students will have to understand computational methods, together with the full spectrum of experimental endeavors (synthesis, fabrication, and measurement) to become successful researchers.