Theoretical Exploration of Silicon Nanowires under External Stress

Silicon nanowires (SiNWs) have attracted increasing scientific interest because of their promising application as the building blocks of silicon-based nanodevices. Although the novel properties (including electronic, electrical, and optical properties) of SiNWs have been intensively investigated, SiNWs under external stress are much less studied, due mainly to the difficulty of carrying out in-situ tensile or bending measurements on individual SiNWs. However, understanding the mechanical properties of SiNWs is extremely important for nanodevices' design and fabrication, as the small size SiNW components in devices could be naturally under tension, compression, or shearing due to the connection and interaction with other components of the device, causing mechanical stability problems and subsequent alteration of device performance. Consequently, theoretical exploration of the elastic and plastic deformations and of the micromechanics of the yielding process of SiNWs under external stress is needed to guide experiments, which is the motivation behind the research.In this project, the researchers propose to carry out a systematic study to elucidate the intrinsic mechanical, electronic, and optical properties of SiNWs under external stress, based on density functional theoretical calculations. The models of SiNWs that are along,,, anddirections and that are saturated with hydrogen atoms will be geometrically optimized first. Then, the researchers will study the dependence of the mechanical properties, such as Young's modulus and Poisson's ratio, on the crystallographic directions and diameters of SiNWs. The transition from elastic deformation to plastic deformation, due to large axial stretching or compression strains, and non-axial bending and torsional strains, will be investigated for each type of the SiNWs. The electronic and optical property changes induced by the external stress will be explored. The effects of surface saturation using small species such as O, OH, N, CO, and small chemical and biological molecules will also be examined, which will provide useful knowledge for the design of nanosensors. The preliminary calculations revealed that the external stress could tune the electronic band structures ofSiNWs from an indirect to a direct feature, thus indicating the possibility of using strained SiNWs for light emitting applications. The computational experience in SiNWs and promising preliminary results form the solid foundation for this project. The findings will provide important information and guidance for use of silicon nanostructures in nanoelectronics, optoelectronics, and nanosensors.