This study was to determine whether high-pressure phases exist in certain coatings of nanocrystalline silicon structures through the use of high-resolution transmission electron microscopy. Understanding the phase evolution of nano-scale materials such as silicon will lead to novel applications of this useful material. At the Advanced Materials Characterization Laboratory high-resolution images of silicon coatings and their associated electron diffraction patterns were taken with the transmission electron microscope and analyzed. The spacings between the rows of atoms in the structures were measured and compared to the Pearson's Handbook of Crystallographic Data and the JCPDS (Joint Committee on Powder Diffraction Standards) database, which contain known values for different phases of materials. The electron diffraction patterns of the samples were compared to computer simulations of various phases of silicon created using the Desktop Microscopist software. The analysis of the micrographs has shown the possibility of the existence of meta-stable tetragonal phases of silicon in the coatings examined. This study is still ongoing and further analysis of the phase evolution of nanomaterials is needed to help fulfill the necessity for better materials for the future. This study may help lead to better applications of silicon nanomaterials in many devices such as biological sensors to detect the presence of various chemicals.

This research was funded by Simons Grant 265210 and through the MRSEC for Thermal Spray Research, NSF DMR0080021.