Atomic Observation of the Sublimation Process of the Pb (111) Surface

The dynamic behavior of the sublimation process using ultrafine Pb particles produced by the gas evaporation technique was examined at the level of atomic resolution using a transmission electron microscope equipped with a real-time video-recording system. The ultrafine Pb particles coated with a carbon layer with a thickness of the order of 5 nm were prepared in the electron microscope by heating particles on carbon film at 300°C. Sublimation of the Pb particle covered with the carbon layer took place above 470°C, which is slightly higher than the melting point of Pb. Sublimation occurred at the surface with a higher surface energy. The sublimation process of the (111) surface was clearly observed at an atomic level. It was found that two- or four-atomic-layer step flow was observed at the (111) surface. At the (111) surface between the stacking faults, two-layer and successive one-layer sublimation occurred.

Capacitance-Voltage (C-V) Hysteresis in the Metal-Oxide-Semiconductor Capacitor with Si Nanocrystals Deposited by the Gas Evaporation Technique

Capacitance-Voltage (C-V) hysteresis was observed in the Metal-Oxide-Semiconductor (MOS) capacitor with silicon nanocrystals. The MOS capacitor was fabricated by thermal oxidation of Si nanocrystals, which were deposited on an ultra-thin thermal oxide grown previously on a p-type Si substrate. The Si nanocrystals were deposited by the gas evaporation technique with a supersonic jet nozzle. The size uniformity and the crystallinity of the Si nanocrystals are found to be better than those fabricated by the conventional gas evaporation technique. The C-V hysteresis in the MOS capacitor is attributed to electron charging and discharging of the nanocrystals by direct tunneling though the ultra-thin oxide between the nanocrystals and the substrate. The flat-band voltage shift observed during the C-V measurement depends on the size and density of the nanocrystals and also on the magnitude of the positive gate bias for charging. The retention characteristic is also discussed.

Formation of Ge Nanocrystals Passivated with Si by Gas Evaporation of Si and Ge

Two methods are employed in the gas evaporation technique to form Ge nanocrystals with the Si-passivated surface. One uses one boat with a SiGe alloy as a source, and the other uses two boats each with Si and Ge. As a result of characterization by the x-ray diffraction (XRD) measurement, Raman scattering and x-ray photoelectron spectroscopy (XPS), it is found that Ge nanocrystals with the Si-passivated surface were formed by coevaporation of Si and Ge from two boats, while SiGe alloy nanocrystals were formed by evaporation of the Si-Ge alloy source from one boat.