are obtained by a new kind of fluorescence microscope where individual fluorophores are turned on one by one and their positions accurately measured.

Improved Sensing

More than knowing where all the atoms are, researchers also want to know their charge, local magnetic properties, chemical identity, and so forth. While scanning probe techniques have provided revolutionary images of the properties of nanostructures, this has only scratched the surface, so to speak. What is needed is the continued development of tools that can probe the local properties in new ways. A recent success, over 10 years in the making, was the first detection of a single electron spin using an atomic force microscope. It took years of concentrated effort by world-class scientists to bring this to fruition. It illustrates the importance of long-term commitments to research, as well as the potential problems with the changing landscape of the industrial research laboratories.

A Greater Understanding

The final pressing need is for an increased understanding of the fundamental properties of nanostructures, as well as knowledge of the most appropriate design rules for creating nanoscale systems. First, a set of simple paradigms to describe nanoscale phenomena is needed. Many of these models are now well developed— single-electron charging, conductance quantization, and so forth—but more remain to be discovered and sorted out. For example, how does one understand systems in which the nuclei in a structure no longer move much more slowly than the electrons, as in a usual solid? How does one cope with nanostructures in which the motions of the electrons are strongly correlated and the independent particle picture breaks down (see Chapter 2)?

Another pressing need is for a set of new analytic and computational tools to allow researchers to address ever-more-complex nanoscale systems (see Chapter 11). This is important in order to continue the evolution of the field from a descriptive to a predictive discipline. A huge part of the challenge of dealing with a complex system is in integrating the separate computational and calculational techniques used to describe different aspects of the problem—the combination of approaches that address the electronic, structural, and optical properties in a unified way, for example.

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