Nanoindentation studies of materials

have recognized that surface contacts between materials are highly dependent on their mechanical properties1,2. Many different indentation and impression tests have been developed in an effort to measure such mechanical properties from a contact of known geometry. In the past two decades, however, a veritable revolution has occurred in indentation testing, owing to the development of new sensors and actuators that allow instrumented indentations to be routinely performed on submicron scales. The resulting technique, termed nanoindentation, has now become ubiquitous for mechanical property measurements at surfaces. The most common use of nanoindentation is for the measurement of hardness and elastic modulus3-5, and there has been considerable progress in the measurement of other mechanical parameters as well, including hardening exponents6-10, creep parameters11-15, and residual stresses16-19. Such measurements have broad application across the physical sciences, and there are several recent reviews on the use of nanoindentation for property extraction20-22. However, nanoindentation also lends itself to more fundamental inquiries in materials science. New capabilities in in situ and ex situ imaging, acoustic emission detection, and high-temperature testing are now being used to probe nanoscale phenomena such as defect nucleation and dynamics, mechanical instabilities or strain localization, and phase transformations. This article presents an overview of nanoindentation’s current role and future promise in the study of some of these physical phenomena, with special emphasis on experimental approaches.