Nanoscale Structures: Lability, Length Scales, and Fluctuations
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Nanoscale
Structures: Lability, Length Scales, and Fluctuations Ellen D. Williams
Abstract This article is an edited transcript based on the David Turnbull Lecture given by Ellen D. Williams of the University of Maryland on December 2, 2003, at the Materials Research Society Fall Meeting in Boston. Williams received the award for “groundbreaking research on the atomic-scale science of surfaces and for leadership, writing, teaching, and outreach that convey her deep understanding of and enthusiasm for materials research.” This article focuses on the special properties of small structures that provide much of the exciting potential of nanotechnology. One aspect of small structures—their susceptibility to thermal fluctuations—may create or necessitate new ways of exploiting nanostructures. The advent of scanned probe imaging techniques created new opportunities for observing and understanding such structural fluctuations and the related evolution of nanostructure. Direct observations show that it is relatively easy for large numbers of atoms—the kinds of numbers that are present in nanoscale structures— to pick up and move about on the surface cooperatively with substantial impact on nanoto micron-scale structures. Such labile evolution of structure can be predicted quantitatively by using length-scale bridging techniques of statistical mechanics coupled with scanned probe observations of structural and temporal distributions. The same measurements also provide direct information about the stochastic paths of structural fluctuations that can be used outside of the traditional thermodynamic framework. Future work involves moving beyond the classical thermodynamic picture to assess the impact that the stochastic behavior has on the physical properties of individual nanostructures. Keywords: fluctuations, lability, mass transport, morphology, scanned probe microscopy, stability, nanocrystals, nanostructure.
Introduction It is a great honor for me to receive the David Turnbull Lectureship, and a special pleasure that Professor Turnbull himself was able to be present for this talk. In beginning this presentation, I would like to emphasize how old problems in materials science are revisited when new tools become available to address them or when new applications require a different perspective on previous understanding. In the work I will be discussing here, the old problem is surface mass transport, the new tool has been scanned probe microscopy, and the new application is nanoscale materials properties.
MRS BULLETIN/SEPTEMBER 2004
We can begin by asking what makes materials science special at the nanoscale? We do not expect nanoscale materials or systems to act like small-scale models of the macroscopic and effectively continuum world we live in. When we get down to the nanoscale, very different types of properties arise. One origin of novel properties for materials with size scales on the order of a nanometer is the large surfaceto-volume ratio. When this is large, the special properties of surfaces such as quantum
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