Characterization of Mechanical Deformation of Nanoscale Volumes
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Characterization of Mechanical Deformation of Nanoscale Volumes Christopher R. Perrey, William M. Mook, C. Barry Carter*, William W. Gerberich Department of Chemical Engineering and Materials Science University of Minnesota, 421 Washington Ave. S.E., Minneapolis, MN 55455 * corresponding author: [email protected] ABSTRACT The mechanical properties of nanoscale volumes and their associated defect structure are key to many future applications in nanoengineered products. In this study, techniques of mechanical testing and microscopy have been applied to better understand the mechanical behavior of nanoscale volumes. Nanoindentation has been used to investigate important mechanical material parameters such as the elastic modulus and hardness for single nanoparticles. New sample preparation methods must be developed to allow the necessary TEM characterization of the inherent and induced defect structure of these nanoparticles. Issues of chemical homogeneity, crystallinity, and defect characteristics at the nanoscale are being addressed in this study. This integration of investigative methods will lead to a greater understanding of the mechanical behavior of nanostructured materials and insights into the nature of defects in materials at the nanoscale. INTRODUCTION Testing and characterization of small volumes has become increasingly important for numerous applications. For instance, the mechanical properties of silicon components in micro-electromechanical systems (MEMS) can depend on the specific small-scale geometries being used [1]. This dependence needs to be understood to predict failure modes and to improve both device reliability and design [2]. Both molecular dynamic simulations [3] and indentation experiments of small volumes [4-6] indicate that nanostructured materials can support larger stresses than their bulk counterparts. This phenomena is known as the indentation size effect [7-9]. An explanation of this effect is the dislocations that develop at high pressures are confined by the small volume or nanostructure being probed and are forced close together; thus resulting in extremely high stresses. The consequences of these very high internal stresses have potential for the design of nanostructured materials with enhanced mechanical properties. However, to evaluate properties via nanoindentation, it is necessary to accurately determine contact area, crystal orientation, and the inherent and induced defect structure within the small volume. Ideally, it should be possible to nondestructively image an individual nanoparticle before and after indentation using transmission electron microscopy (TEM). The results can then be compared to molecular dynamic simulations of equal volume with identical composition, structure and boundary conditions. This study is the first step in that process and details the direct mechanical response of single nanospheres of silicon with radii between 20 to 50 nm, as well as the characterization of similar nanospheres using TEM.
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EXPERIMENTAL The particles studied
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