Sigma Pi Sigma Hosts First Poster Session & Reception at the
APS March Meeting
On
Tuesday, March, 14, 2006, the physics honor society Sigma Pi Sigma
hosted its first ever poster session and reception at an APS March
Meeting in Baltimore, MD. The event was a lot of fun, with people
bubbling out into the hallway from the reception room, talking
about the posters and absorbing information from a demonstration
about the physics of Spandex for several hours. Those in attendance
included Sigma Pi Sigma donors and members of all ages, as well
as a cadre of invited students and APS members, among whom were
many faculty members.
The posters were the center of attention at the reception, and
the primary topic was condensed matter physics, as one would expect
at the APS March meeting. Meredith Hyldahl displayed her work
on luminescent solar concentrators to improve the efficiency of
solar energy, and David Hung exhibited his research on nano-porous
gold, with very snazzy images of sponge-like gold samples. Deng
Cao and Jerrod Schiffbauer from West Virginia University, working
with their faculty mentor Martina Bachlechner, presented their
posters on molecular dynamical simulations. See
more details about these students, their home institutions,
and their research below.
Ruth Davis, noted scientist and Sigma Pi Sigma member, spoke
briefly about her role as Chair of the Sigma Pi Sigma Development
Committee, emphasizing that donations to Sigma Pi Sigma are one
of the chief reasons that SPS is able to fund student travel to
research meetings and other programs. Ruth and fellow committee
member, Ken Ford, were especially welcome additions to the evening’s
events. Director Gary White then took full advantage of his position,
telling the group a brief tale about his own efforts to be the
first to document the physics of Spandex, missteps and all.
A final poster, put together by national office staff showed
how the society has begun to implement the ethics recommendations
put forth by attendees at the 2004 Sigma Pi Sigma Congress. Two
featured items were a new ethics
website developed by members of the SPS Council and a new
effort to develop Sigma Pi Sigma chapters at schools that graduate
physicists from under-represented groups.
Following are the titles & abstracts of the poster presentations:
Author: Meredith Hyldahl, Penn State Behrend
School Of Science
Title: A Study Of CdSe/ZnS Core-Shell Quantum
Dots For Use In Luminescent Solar
Concentrators
Abstract: A Luminescent Solar Concentrator (LSC)
is a translucent plate that uses embedded fluorescent materials
to absorb sunlight. The fluorescence that is produced is then
transferred to the edges of the plate via total internal reflection
where it is absorbed by photovoltaic cells. We compare a LSC made
of CdSe/ZnS
core-shell quantum dots (QD) (Evident Technologies) embedded in
a transparent
epoxy to a LSC made with the fluorescent organic dye Lumogen Red
(BASF) cast in
a thin polymer film. Fluorescence and absorption spectra and edge
light output
measurements are reported in this study. The Lumogen Red LSC outperforms
the
QD LSC suggesting a lower fluorescence quantum yield for the QDs.
QDs are also
easily oxidized, whereas the Lumogen Red dye is relatively more
stable in the
presence of oxygen. The merits of QDs as a fluorescent material
for a LSC are discussed in terms of light output, photostability,
and cost.
Author: David Hung, Johns Hopkins University
Title: Fabrication of 3D-Ordered Nanoporous
Gold for Chemical Sensors
Abstract: 3D ordered nanoporous materials provide
high surface-to-volume ratio and controlled nano-scale periodic
architecture, making them attractive for applications such as
energy storage, catalysis, separations, chemical sensing, and
tissue engineering. 3D-ordered nanoporous gold structures were
fabricated by electrodeposition of gold into colloidal crystal
templates formed by self-assembly. The structures are replicas
of the colloidal crystal and have pore sizes and feature sizes
that are dependent on the particle size. When the dimensions of
a conductor are sufficiently small the resistance is dominated
by surface scattering. A prototype chemical sensor was created
exploiting this architecture. Molecules with sulfhydryl groups
adsorb strongly to gold surfaces and can be monitored by the change
in resistance. A resistance change of approximately 2 percent
was achieved and a chemical sensor based on surface scattering
has been demonstrated.
Authors: Deng Cao & Martina E. BachlechnerWest
Virginia University
Title: Pair distribution functions of silicon/silicon
nitride interfaces
Abstract: Using molecular dynamics simulations,
we investigate different mechanical and structural properties
of the silicon/silicon nitride interface. One way to characterize
the structure as tensile strain is applied parallel to the interface
is to calculate pair distribution functions for specific atom
types. The pair distribution function gives the probability of
finding a pair of atoms a distance $r $apart, relative to the
probability expected for a completely random distribution at the
same density. The pair distribution functions for bulk silicon
nitride reflect the fracture of the silicon nitride film at about
8 {\%} and the fact that the centerpiece of the silicon nitride
film returns to its original structure after fracture. The pair
distribution functions for interface silicon atoms reveal the
formation of bonds for originally unbound atom pairs, which is
indicative of the interstitial-vacancy defect that causes failure
in silicon.
Authors: Jarrod E. Schiffbauer & Martina
E. Bachlechner, West Virginia University
Title: A molecular-dynamics study of defects
and failure mechanisms in strained heteroepitaxial interfaces
Abstract: The formation and growth of pits and
pit-like structures through a delamination-driven mechanism have
been observed in the analysis of comprehensive molecular dynamics
simulations of a laterally strained Si(111)/Si$_{3}$N$_{4}$(0001)
interfacial system. These phenomena contribute to the ultimate
mechanical failure of the simulated samples. Several factors play
a key role the nucleation and growth of the pits including temperature
and strain rate. Here we present an overview of the dependence
of pit nucleation and morphology on both global and local conditions
for a representative range of temperatures and applied strain
rates.
