American University of Beirut
Physics Department
Invites you to a talk entitled
Growth and characterization of silicon and germanium
nanostructures
By
Dr. Mahmoud Israel
Institute of Physics of Rennes (IPR), Nano-sciences Materials Department & Institute of Electronics and
Telecommunications of Rennes (IETR), Microelectronics and Microsensors Department
France
Abstract
Silicon (Si) and Germanium (Ge) nanowires
were synthesized by Low Pressure Chemical
Vapor Deposition (LPCVD) reactor using Vapor
Liquid Solid (VLS) process. Gold (Au) was used
as catalyst and silane (SiH4) and the germane
(GeH4) as precursor gas. The gold catalyst
droplets are formed by continuous dewetting of
gold layers on the substrate. The properties of
the grown samples were investigated scanning
electron microscopy (SEM) combined with
Raman spectroscopy; the investigations were
made as function of the type of substrate,
temperature, pressure, thickness of gold layer
and growth duration. The structural
characterization of nanowires by transmission
electron microscopy shows growth of crystalline
structure along <111> for Si and along <110>
for Ge nanowires. The micro-Raman analyses
showed an optical resonance phenomenon inside
the nanowires which strongly depends on their
local diameters. These effects were explained by
the optical modes appearing according to the
local diameter of the nanowire, the excitation
wavelength and the nature of the substrate used.
In addition, the Raman lines recorded along the
same profiles did not show spectral shift; this
behavior was related to resonances associated
with the development of local optical modes. We
discuss these effects upon the type of substrate
on which the isolated nanowires were transferred
(dielectric versus metallic substrates).
Figure 1: Tapered GeNWs or ‘nanocones’. The
average GeNW length is 7.5 ± 1 μm and average
diameter of the base is 480 ± 20 nm
Date: Thursday, December 10, 2015
Time: 4:00 p.m.
Place: Emile Bustani for Physics, Rm. 333