Papers by Author: Sung Sik Chang

Abstract: The spark processing of metallic Sn yields a powder, which is a mixture of nanosize Sn and crystalline SnO2. This paper reports the characteristics of nanosize Sn powders. Scanning tunneling microscopy (STM) and transmission electron microscopy (TEM) studies reveal an existence of spherical shaped nanocrystals ranging from 2 to 5 nm in size. In contrast the measured surface area of spark processed Sn (sp-Sn) powders by BET is 27.7 m2/g and calculated average size of sp- Sn is about 31 nm, which is close to one order of magnitude larger than the observed size. Further, the characteristics of sp-Sn powders are studied by Raman, and differential thermal analysis (DTA).

Abstract: This paper reports the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) studies of porous Zn (p- Zn) prepared by electrochemical etching. Further, the post annealing of the p- Zn is carried out and STM/STS investigations are also performed. STM studies of these samples reveal the porous structure and display small, pseudo-spherical shaped crystals in the range of 2 and 100 nm, 2 and 50 nm, and similar average corrugation of 9 nm for p- Zn and oxidized p-Zn. STS analysis of freshly prepared p- Zn shows a band gap of 2.4 eV along with metallic conductance behavior. However, oxidized p- Zn reveals a distinct wide band gap (3 eV) and shows shallow donor states near the conduction band.