Ph.D. Thesis Defense---Dunwei Wang

Dunwei Wang wangdw at stanford.edu
Thu Jul 14 19:12:17 PDT 2005


Dear Lab members,

I'll defend next Wednesday. Hope you can attend. Thanks!

Dunwei

________________________________________________________
Title: Synthesis and properties of germanium nanowires
Adviser: Hongjie Dai
July 20th, Wednesday, 10am
CIS-X Auditorium

Abstract:

As the scaling of electronic devices is approaching its theoretical limit,
germanium (Ge) has gained renewed interest as a choice of materials for
future electronics due to its low bandgap and high carrier mobilities.
Chemically derived low dimensional nanostructures such as nanowires have
attracted intense research interest owing to the facile synthesis and high
structure perfection. Ge nanowires (GeNWs) have combined advantages and
are particularly appealing. I present that single crystalline GeNWs can be
readily synthesized by a simple chemical vapor deposition (CVD) method at
a low temperature of 275°C from gold (Au) nanocluster seeds. Excellent
control over the synthesis is gained to achieve 100% yield of GeNWs
relative to the Au seeds by understanding and optimizing the growth
chemistry. The potential of GeNWs as building blocks for electronic
devices is demonstrated by successful fabrication of complementary field
effect transistors (FETs) based on p- and n-type GeNWs. Electrical
transport and x-ray photoelectron spectroscopy (XPS) data are correlated
to glean the effects of Ge surface chemistry to the electrical
characteristics of GeNWs. Various chemical functionalization schemes are
investigated to passivate GeNWs surface using alkanethiols and alkyl
Grignard reactions. The stability of functionalization against oxidation
of germanium for various alkyl chain lengths is elucidated by XPS. Long
chain alkanethiols (>=C12) are found to impart the most stable GeNW
passivation against oxidation upon extended exposure to ambient air.







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