High Resolution Transmission Electron Microscopy Study on the Structure of Ge Nanoparticles by Using an Ultrahigh Vacuum-Molecular Beam Epitaxy-Transmission Electron Microscope System

Ge nanoparticles were deposited on thinned Si substrates in an ultrahigh vacuum molecular beam epitaxy instrument (UHV-MBE) and transferred into an UHV-field emission transmission electron microscope (UHV-FE-TEM) through an UHV-transferring system. TEM observation indicated that the Ge nanoparticles had a round shape and were 2 to 5 nm in diameter. The crystalline Ge nanoparticles exhibited single crystals, single-twinned crystals, and decahedral multi-twinned particles (MTPs). It was found that the crystal structure of some nanoparticles changes from a diamond structure to a novel structure, which is proposed to be a β-Sn structure, with a =0.38 nm and c =0.71 nm. The particles with the new structure are not formed when the substrate temperature is above 370°C. The structure of MTPs has been discussed. Some Ge nanocrystals even became amorphous and then fluctuated continually during HRTEM observation.