Papers by Author: Lih Juann Chen

Abstract: In situ ultrahigh vacuum transmission electron microscope (TEM) is a powerful tool to investigate the dynamic changes of nanostructures on silicon. By observing growth and phase transitions in situ, understanding of their mechanisms can be used to model relevant processes. With the precise knowledge of the changes occurred on an atomic level, accurate control of the growth process can be achieved. The dynamical changes occurred on the nano scale are often unexpected, which also underscores the importance of the approach. In this presentation, we highlight two examples to demonstrate the unique capability of in situ TEM to study the dynamical changes. The examples include collective movement of Au nanoparticles and directed movement of Au-Si droplets on Si bi-crystal.

Abstract: Quasi-vertical ZnS nanostructures with different Ga doping level ( ZnS:Ga nanowalls ) have been synthesized in high yield from the mixed powders in the vacuum furnace at 1150 oC. ZnS:Ga nanowalls were grown vertically on the substrate with the size in the range of several microns and the thickness down to 15 nm and have very rough edges. The possible growth mechanism of nanowalls is likely governed by a vapor-solid (VS) growth mechanism. Room-temperature cathodoluminescence spectra of ZnS : Ga nanowalls show two emission peaks at approximately 443 nm and 578 nm. The emission mechanisms are discussed.

Abstract: Vertically aligned ZnO nanorods have been synthesized on a-plane sapphire via a metal catalyzed vapor phase transport and condensation process in a two-zone vacuum furnace. Planar-tip ZnO nanorods were synthesized using commercial ZnO and graphite powder as the source of Zn vapor controlled by a simple vapor-liquid-solid (VLS) process. On the other hand, tapered-tip ZnO nanorods were synthesized from pure ZnO powder governed by both VLS and vapor-solid processes. From room temperature cathodoluminescence measurements, planar-tip ZnO nanorods are applicable for room temperature UV nanolasers.

Abstract: Self-assembled low-resistivity NiSi nanowire arrays have been grown on relaxed epitaxial Si0.7Ge0.3 on (001)Si. The formation of the one-dimensional ordered structure is attributed to the nucleation of NiSi nanodots on the surface undulations induced by step bunching on the surface of SiGe film owing to the miscut of the wafers from normal to the (001)Si direction. Furthermore, the nanodots were connected along individual arrays and turned into nanowires with increasing amount of Ni and a-Si. Since the periodicity of surface bunching can be tuned with appropriate vicinality and misfit, the undulated templates promise to facilitate the growth of ordered, catalyst-free NiSi nanowires with selected periodicity and size for utilization in high-speed Si-Ge nanodevices.

Abstract: Dynamic study of the growth of TiSi2 nanorods on Si bicrystal was conducted in an ultrahigh vacuum transmission electron microscope. The growth of the nanorods was affected by the underlying dislocation grids significantly. The dislocation grids confined the shape of the nanoclusters and nanorods. Compared to the time of the nanorod remaining at the same length, the elongating time is relatively short. The dislocation network confined the nanorod to match the dislocation interspacing and the step-wise growth of the nanorod was found. The growth mechanism is attributed to the compliant effect. The observation was constructive to the basic understanding of the stress effect on the initial stage of the reaction of metals on Si.