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SSL Seminar Series 2003 No.3
Combined talks (Two speakers)
Date: November 13 (Thursday), 2003
Time: 4:00-5:00pm
Venue: Physics Resource Room (Blk S13 # 02-16)
Speaker I: Mr. Chen Wei (PhD
Candidate)
Title: Co nanocluster deposition on 6H-SiC(0001)- templates
Abstract:
We demonstrate that the carbon-rich 6H-SiC(0001)- honeycomb-like
reconstructed surface can be used as an effective template for the
growth of high density, monodispersed and uniform-sized nanoclusters.
In-situ UHV (ultrahigh vacumm) STM (scanning tunneling microscopy)
is used to systematically study the nucleation of cobalt (Co) nanoclusters
on this SiC honeycomb template. During the initial stages of Co
cluster growth, the boundaries between neighboring honeycomb structures
serve as active sites for Co cluster adsorption. After 2? thick
Co deposition at room temperature, high density, monodispersed and
regular-sized (3-4 nm) Co nanoclusters are formed on this reconstructed
6H-SiC(0001) surface without the nucleation of Co single crystal
3D islands due to restricted adatom surface diffusion on the underlying
honeycomb template. The regeneration of the honeycomb template is
achieved by annealing the as-deposited 2?Co/SiC sample to higher
than 800K. It is found that this carbon-rich SiC honeycomb template
is chemically inert to Co and thermally stable, and acts as a diffusion
barrier preventing Co from reacting with underlying Si atoms to
form cobalt silicide during annealing. A narrow size distribution
of Co nanoclusters (~6.8nm in diameter) is achieved by annealing
the as-deposited 2?Co/SiC sample at 800K for 20 minutes. Deposition
of Co on the SiC honeycomb template at different temperatures is
also presented and discussed.
Speaker II: Dr. Xu Hai (Research
Fellow)
Title: 6H-SiC(0001) Surface Reconstruction and Oxidation
Abstract:
Silicon carbide (SiC) has many potential applications in high
temperature, high power and high frequency devices compared to traditional
silicon (Si) materials because of its large breakdown field and
high electron mobility. For not only the heteroepitaxial growth
but also the nanostructure formation at compound semiconductor surface
it is essential to control the surface chemical composition and
the surface atomic structure. In this present study using scanning
tunneling microscopy(STM) and low -energy electron diffraction (LEED),
we investigated Si terminated 6H-SiC(0001) surface reconstruction
and transition after heat treatment at increasing temperature. Especially,
we reported on our STM and LEED study of the 6 ¡Á 6
superstructure of 6H-SiC(0001) surface and propose a evolution model
which explained very well the formation of the 6 ¡Á
6 superstructure and previous STM results .
Secondly, obtaining high quality oxides on SiC is an important step
in the fabrication of metal-oxide-semiconductor devices. For this
reason, studies of the oxidation mechanism and chemical composition
of thermally grown oxides on SiC have attracted a lot of attention
recently. In this work, we also systematically study the energetic,
equilibrium geometry and possible reaction pathways of O2 chemisorption
using STM and XPS. In order to study the stability of oxide products
grown by different oxidation paths on SiC, a comparative experiment
on the interaction of molecular and atomic oxygen with Si-terminated
6H-SiC(0001)3x3 surface was carried out. It was found that different
non-stoichiometric silicon oxycarbide species were formed via different
oxidation paths. In molecular thermal oxidation, in addition to
SiO2, the oxidation product is mainly SiOC3. However, silicon oxycarbides
are presented as SiO3C when the sample was prepared by atomic oxygen
oxidation. Furthermore, this SiO3C phase shows a good thermal stability
under 1000 C annealing.
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