SSL Seminar Series 2005 No.5

Combined talks (two speakers)

Date: May 16 (Monday), 2005
Time: 4:00pm-5:00pm
Venue: Physics Resource Room (Blk S13 # 02-16)

Speaker I: Speaker I: Mr. Tan Sian Khong
Title: In-situ XPS and SIMS analysis of O 2 + beam-induced silicon oxidation

Abstract:
In this study, the chemical composition variation of silicon under 4 keV O 2 + ion beam bombardment at 0° , 15° , 30° , 45° , 55° and 70° incidence angle was studied by in-situ small area XPS. The changes in secondary ion profile ( 30 Si + , 44 SiO + , 56 Si 2 + , 60 SiO 2 + ) during oxygen ion beam bombardment was simultaneously monitored. The objective of this work is to directly correlate the secondary ion profile during oxygen ion beam bombardment to the crater bottom composition as a function of ion beam incidence angle, especially in the SIMS surface transient region. The evolution of the secondary ion profile obtained from SIMS shows similar trends with the variation of oxygen concentration in the crater surface measured by XPS. It is shown that when the oxygen ion beam incidence angle is below 40° , silicon dioxide is the dominant species on the crater surface and the matrix ion species ratio (MISR) value of 44 SiO + / 56 Si 2 + is higher than that of 30 Si + / 56 Si 2 + . For incidence angles greater than 40° , the formation of sub-oxide is favored and thus the MISR value of 44 SiO + / 56 Si 2 + is lower than that of 30 Si + / 56 Si 2 . At 40° bombardment, there are similar amounts of SiO 2 and sub-oxides present on the crater surface and the MISR values of 44 SiO + / 56 Si 2 + and 30 Si + / 56 Si 2 + are also similar.

Speaker II: Mr. Sunil Singh Kushvaha
Title: In situ STM investigation of Sb, Ge and Al nanostructures on graphite

Abstract:
We have used in-situ scanning tunneling microscopy ( STM ) to investigate the growth of Sb, Ge and Al nanostructures on highly oriented pyrolytic graphite (HOPG) in ultra-high vacuum. Three-dimension (3D) spherical, 2D thin film and 1D nanorods with average diameter of several nanometers have been synthesized by thermal evaporation of Sb at different flux on HOPG at room temperature (RT). At higher flux and substrate temperature ~ 100°C, only crystalline 2D and 1D structures of Sb were obtained. At atomic scale, the 3D and 2D structures of Sb have same bulk crystalline structure but the 1D nanorods shows different crystalline structure. At initial stages, nucleation of Ge clusters occurred at step edges and defect sites of graphite. We found various types of Ge structures on HOPG at different deposition conditions and stages, including nanowires, clusters, cluster chains, and double layer ramified islands. Initially Al was found to nucleate at step edges and defect sites of HOPG and form 3D islands with narrow size distributions at RT. With further deposition, c raters were observed on the top facet of the flattened Al islands on terraces and steps. This system offers the possibility to obtain different shapes and dimensionality of nanostructures by selecting proper growth conditions like flux, exposure time, and substrate temperature.