As part of NIST's response to the Materials Genome Initiative (MGI), this project seeks to unite contact-resonance atomic force microscopy and molecular dynamics simulation, which are capable of overlapping length scales. This union will improve model validity and fundamental understanding of material phenomena.
Close collaboration between those performing experiments and simulations will yield better understanding of material phenomena by using the strengths of each technique. In response to the MGI, researchers in the Nanomechanical Properties Group are launching new efforts to unite experimental measurements and computer simulations using the diameter-dependence of elastic moduli of zinc oxide (ZnO) as a case study. We chose to initially investigate molecular dynamics simulations because they are capable of accessing similar length scales as experimental techniques such as contact-resonance atomic force microscopy.
ZnO nanostructures hold tremendous promise for novel and versatile devices due to their demonstrated intrinsic semiconducting and piezoelectric properties, as well as the amazing structural diversity that can be achieved by current synthesis techniques. ZnO nanostructures can take the form of nanowires, nanobelts, nanorings, and nanohelices. The ability to create such structures with predictable and reproducible measures of performance depends on having knowledge of the mechanical properties of ZnO nanostructures.
Physical experiments and computer simulations aimed at understanding the diameter dependence of elastic moduli of ZnO nanowires each have inherent strengths and weaknesses. An experimental measurement, such as contact-resonance atomic force microscopy, will encompass all physical phenomena capable of producing diameter dependence. However, it is very difficult to conduct experiments that evaluate the magnitude of different physical phenomena that each can contribute to the observed diameter-dependence. Simulation techniques, such as molecular dynamics, can directly evaluate independent sources of diameter-dependence, but are only as realistic as the models used to define the underlying physics. The experimental results, and results from other modeling techniques such as density functional theory, will be used to improve underlying physical models used in molecular dynamics. This feedback loop will ultimately improve model validity and fundamental understanding of material phenomena, which are both critical aspects of the MGI.