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2 The Research Program The research program of the Center for Nanoscale Science and Technology is carried out by three groups: Electron Physics, Nanofabrication Research, and Energy Research. The Electron Physics Group has been in existence for more than 50 years (and led by the CNST director for over half that time); it was transferred intact to the CNST when the center was established. The Nanofabrication Research Group is a new effort that has been in existence only since the CNST was founded. While significant staffing has already taken place, hiring for this group continues at a brisk pace. The Energy Research Group is very new, currently populated only by the acting group leader, supported by a small number of postdoctoral researchers. Searches for group members are underway. The panel’s observations and recommendations for each group are discussed separately below. ELECTRON PHYSICS GROUP With its history of more than 50 years, the Electron Physics Group is well established at NIST, having an impressive track record of accomplishments in electron optics, spin-polarized magnetic imaging (scanning electron microscope with polarization analysis, or SEMPA), laser manipulation of atoms, and nanoscale characterization. This group was incorporated as a whole into the CNST at the inception of the center. The science done in this group is of very high quality, currently focusing on nanomagnetics, theory and modeling of nanostructures, nanotechnology with laser-controlled atoms, and atomic-scale characterization and fabrication. Twenty-three technical staff members (project leaders, postdocs, visitors, and support staff) constitute the group. The work on laser control of atoms is among the best in its field. In particular, the Magneto-Optical Trap Ion Source (MOTIS) is very exciting and unique, potentially moving forward focused ion beam (FIB) technology, which has stagnated for more than a decade. Such leading-edge, high-risk research is exactly the type of work that an organization like NIST should be doing. The current Cooperative Research and Development Agreement with FEI Company will provide a mechanism for coupling with the manufacturing of a tool at the appropriate time. In this role, it would be appropriate for the CNST to bring the best talent to work together on this and, if successful, to use the tool to study high-impact questions to which it is ideally suited. The ultrahigh vacuum (UHV) cryogenic scanning tunneling microscopy (STM) work is of high quality. The instrument itself is a magnificent tour de force that exhibits seldom-matched expertise in instrument design. In particular, the application of the cryogenic STM to understand the electronic states of graphene is a good example of the use of such an instrument to address the science behind these possibly technologically important materials. A spin-off from this work, well aligned with the NIST mission, is the realization that graphene, because of its large Landau level spacing at room 8
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temperature, might be used as a resistance standard, providing an excellent tie to the NIST mission. The nanomagnetics effort, including imaging SEMPA and ferromagnetic resonance (FMR) imaging of domain motion, is being applied to studies in magnetic storage such as Magnetoresistive Random Access Memory. This group should collaborate more closely with a storage technology company in order to couple with technologically relevant problems in magnetic storage. The group is adequately staffed and of very high quality, and it appears to be well leveraged through collaborations with other NIST groups. The theoretical component of the effort is among the best in its field. The interplay between experiment and theory is extremely powerful, enabling the group to attack complex, important problems successfully. Efforts on interference lithography for magnetic-dynamics studies and on spin-transfer torques for magnetoelectronic devices are also impressive. The facilities of the Electron Physics Group are extremely impressive. The Atomic Scale Quantum Nanoelectronics Laboratory is in the final stage of construction. It centers on a new ultralow-temperature scanning probe microscope (SPM) that has been designed to address the challenge of measuring and understanding electronic structure– property relationships as device sizes continue to decrease. Measurements with very high spatial and energy resolution are required in order to understand such systems for future electronics. The scanning tunneling microscope that is being built is very impressive and, to the knowledge of the panel, one of a kind. Maximizing the impact of such a unique capability will demand judicious choice of the science problems to be addressed, as the CNST leadership is well aware. The current evaluation yields the following conclusions. The technical merit relative to the state of the art is at the level of the best in the field. The laboratory facilities are state of the art and in many cases unique. Outstanding accomplishments indicate achievement of stated objectives and impact. NANOFABRICATION RESEARCH GROUP The Nanofabrication Research Group was formed in 2007 and has grown to include expertise in nanofabrication, directed self-assembly, nanoplasmonics and metamaterials, nanophotonics, nanoelectromechanical systems and microelectromechanical systems (MEMS), and nanoscale electronic measurements. Recruiting efforts are underway for staff with expertise in theory and in situ/dynamic electromagnetics, with further planned hires in novel lithographic processing and/or molecularly controlled assembly. The new group leader brings a broad perspective and a set of new ideas to the CNST that, coupled with the talents of the impressive recent hires, promise great opportunity for this group. Projects reviewed by the panel covered several of the focus areas of the group. The effort on nanoplasmonics, which has demonstrated a MEMS structure formed with nano-processing capable of measuring photon pressure in a “left-handed” metamaterial system, is particularly clever. This MEMS structure was an exemplary demonstration of the processing capability of the NIST Nanofab facility. Even more impressive output 9
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from this group is anticipated as the new staff ramp up their research programs at the CNST. The facilities of the Nanofabrication Research Group are excellent, and the results are stunning. For example, in-house sputter disposition, FIB, and reactive-ion etching (RIE) were used to make left-handed metamaterials (multilayered Ag/a-Si) cantilever structures, which were combined with the predicted radiation response in a left-handed metamaterial to perform the first-ever measurement of the negative radiation pressure response by observing the cantilever deflection (microns) in a scanning electron microscope (SEM). The panel’s evaluation yields the following conclusions: Some of the efforts are producing outstanding results. This rather new group has articulated an outstanding vision and direction. Many staff members are very new, so the quantity of results is expected to increase dramatically over the next few years. The laboratories are excellent. The combination of creative personnel with excellent facilities that enable them to push in new, unexpected directions makes for an exceptional infrastructure. Excellent success in achieving stated objectives has been shown to date. ENERGY RESEARCH GROUP The Energy Research Group is the newest organization within the CNST. The group leader is serving in an acting capacity, supported by a small number of postdoctoral researchers. Four hires are planned in 2009. The Energy Research Group aims to combine measurement research in areas that overlap energy and nanometer science. The stated goals of the group are these: energy storage, transport, and conversion, including light–matter interaction, charge transfer, and energy transfer; catalytic activity; and interfacial structure in energy-related devices. The description of the group’s dual role in improving measurements in the energy area and particularly in nanometer-dimensional problems in energy is insufficiently focused. The plan to focus on nanometer aspects of energy research does not suggest disciplinary activities characteristic of a well-considered program driven by the investigation of physical principles through good measurements. The talents desired in each of the four prospective hires are, as described to the panel, almost impossible to imagine being embodied in single individuals. Anyone who might appear to bring such a wide distribution of talents as are desired will probably not be deeply trained in any. For example, it is difficult to imagine someone who would have advanced understanding of industrial energy, thermoelectrics, and field emission. The main accomplishments in this new group to date center on the behavior of organic photovoltaic devices. Activities such as the use of a conductive atomic force microscope (AFM) to measure the spatial distribution of electron emission from a working organic photovoltaic device are interesting, but they do not probe the physical reasons for the observed nonuniform spatial distribution of photocurrent or of surface potential under illumination conditions. 10
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The proposed plans for coupling electrode characterization techniques to actual working electrodes in order to learn what factors affect electrochemical-cell behavior are crude compared to successful UHV research in this area completed more than 20 years ago in laboratories at Case Western Reserve University; the University of California, Santa Barbara; and the University of California, Berkeley. Most of the measurement techniques proposed for the study will not probe the essential key issues at work in electrochemistry. Although not specifically mentioned, it would appear that planned work in catalysis has not been considered with sufficient care―with understanding of the scientific status of the field and with knowledge of key problems remaining to be solved. Much is well understood in this field after more than 20 years of atomic-level experimental research on single-crystal model catalysts coupled with modern theory involving, for example, density functional methods that have reached chemical accuracy. Work of the following should be considered: Gerhard Ertl, recipient of the 2007 Nobel Prize in chemistry, at the Fritz Haber Institut, Berlin, Germany; Jens Norskov, of the Danish Technical University-Lyngby, Denmark; D.W. Goodman, of Texas A&M University, College Station, Texas; and H.J. Freund, of the Fritz Haber Institut, Berlin, Germany. The work presented in the laboratory visited by the panel is embryonic, including nanoscale photoresponse in photovoltaic (PV) materials using the electrostatic force mode of AFM and the development of functional tips suitable for photoresponse measurement in liquid environments. Future plans include measurement of the time- resolved transient photoresponse of energy materials using ultrafast optical physics by a scientist to be hired. In summary, the CNST should undertake a careful reexamination of the goals and approaches of the Energy Research Group before continued investment. To date, the technical merit relative to the state of the art appears low. The CNST should undertake a serious reexamination of the focus and direction of the group before significant hiring takes place. The laboratory facilities are excellent. There has been no discernible impact of the work to date, however, owing at least partially to lack of staff. 11