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Solid
State and Surface Physics
Research Groups
Professor
Gary Collins studies the local atomic and electronic structure of
solids using three nuclear probe techniques: perturbed gamma-gamma
angular correlation (PAC), Massbauer effect (ME), and positron lifetime
spectroscopies. Belonging to a sub-field known as Nuclear Solid-State
Physics, these techniques are used to discriminate between different
lattice locations of probes in solids with atomic-scale resolution.
PAC and ME measure hyperfine interactions of moments of excited
nuclear states with electronic fields in solids. The fields depend
on the types and arrangement of atoms within one or two atomic shells
of the probes, so that the interactions "fingerprint"
the various local environments. The evolution of solids under thermal,
mechanical or irradiation treatment can be monitored through changes
in site fractions of the signals. Point defects, for example, are
detected when they come next to the probe atoms by diffusion. At
WSU, these have included lattice vacancies, self-interstitial and
hydrogen atoms, and small defect clusters. Formation, migration,
and binding energies have been measured, and structures of vacancy-solute
complexes have been identified through details of the interactions.
Most research at WSU is on metallic systems, for which optical and
resonance techniques are not possible. Local phenomena that have
been observed include trapping and detrapping of hydrogen atoms
at vacancies, vacancy-interstitial annihilation reactions, and restructuring
of vacancy complexes that depend sensitively on local forces between
atoms in metals. More information is available on Collins's
research group home page, including downloadable reprints and
tutorial descriptions of nuclear probe techniques.
Professor
Dexheimer uses state-of-the-art femtosecond laser spectroscopic
techniques to study ultrafast processes in condensed matter systems,
including electronic materials for optoelectronic applications.
Current research activities in her group include studies of the
ultrafast dynamics of photoexcited carriers in semiconductors and
in molecular-based electronic materials, as well as the development
of techniques for ultrafast time-resolved measurements in the far-infrared,
or terahertz frequency range.
Professor
Thomas Dickinson's research activities center on applications of
physics to materials science. The areas of interest include fracture
of materials and the interaction of laser light with material surfaces.
The fracture studies involve detection and characterization of particles
(e.g., electrons, ± ions, photons, and neutral species) accompanying
crack propagation (fractoemission). The goals of this research are
to utilize these emissions to further our understanding of the atomic
processes responsible for material failure. One new aspect of this
work is relating the observed emission properties to (a) chaotic
processes associated with dynamic crack growth and (b) the resulting
fractal dimension of the fracture surfaces. Along these lines, Professor
Dickinson is using a Scanning Tunneling Microscope and Atomic Force
Microscope to characterize fracture surfaces of materials at the
1 level of resolution.. His group is particularly interested
in the energetics of the formation of "rough surfaces"
that are created during crack propagation. Such issues relate to
the physics and engineering of arresting cracks. Another area of
study involves the process known as "photoablation," which
is the removal or etching of surface material by intense excimer
laser bombardment. Of particular interest is detailed understanding
of the emission mechanisms and characterization of the species and
energies of the ejected atoms and molecules. This work is of considerable
importance to the microelectronics processing industry and the detection
of trace elements in soil undergoing environmental remediation.
All research is carried out under ultrahigh vacuum conditions and
employs a wide range of probes including optical, mass, and electron
spectroscopies.
Additional Information
Professor
Kelvin Lynn has broad experience in using fundamental particles
and techniques in understanding physics, materials science and industrial
questions. He has developed positron beams for studying problems
in physics, both fundamental and applied in nature. This beam technique
is used to measure the electronic structure of metals and alloys
and to carry out defect profiling in thin films of semiconductors
(i.e. epilayers), polymers and metals and their respective interfaces.
Point defects as low as 1 in 10 million have been detected and in
some cases the chemical environment around these defects has been
identified. Other work involves the study of defects in wide band
gap semiconductors with an emphasis on room temperature radiation
detectors. A newly developed method to study the fundamental source
of 1/f noise in metal films is also being pursued. Other collaborative
work is being carried out with Lawrence Livermore and Brookhaven
National Laboratories.
Professor
McCluskey utilizes optical and electrical techniques to investigate
impurities, phase separation, and diffusion in semiconductors. Fourier
transform infrared (FTIR) spectroscopy is used to study hydrogen
vibrational modes in semiconductors, an important subject from both
scientific and technological viewpoints. In order to probe the vibrational
properties of impurities in semiconductors, large hydrostatic pressures
are applied with diamond anvil cells (DACs). This technique is applied
to the study of phase transitions and impurity-host interactions.
Professor
McCluskey is investigating the properties of GaN and the alloys
InGaN and AlGaN. These materials are used to make blue lasers and
light-emitting diodes (LEDs), as well as high-power/high-frequency
transistors. One topic of interest is phase separation in annealed
InGaN quantum wells. The formation of In-rich InGaN nanostructures
in the light-emitting region is analyzed using both optical and
structual characterization techniques. In addition, InGaN quantum-well
intermixing is studied as a method of tuning the emission wavelength
of blue lasers. In AlGaN, electrical measurements under pressure
may unravel the mystery of whether Si forms a deep level called
a "DX center."
Professor
Lai-Sheng Wang's research (Tri-Cities Campus) focuses on the study
of metal and semiconductor clusters with photoelectron spectroscopy
and laser spectroscopy. These clusters, containing two to thousands
of atoms, are intermediates between elemental atoms and bulk condensed
matter and often exhibit unique and interesting properties. Metal
clusters are ideal models for solid surfaces and catalysts; and
because of their finite sizes, can be studied in greater detail
and are more theoretically amenable. They are generated by focusing
an intense laser pulse on a target material in a He carrier gas
with supersonic expansion, and then mass analyzed and subjected
to various laser interrogations. Our goal is to understand how the
physical and chemical properties of a cluster change as atoms assemble
one by one to a bulk condensed phase. In particular, we study the
nonmetal-metal transitions in metal clusters of the closed shell
elements, the emergence and evolution of band gaps in semiconductor
clusters, and the cluster-molecule interactions, and search for
special and stable clusters that may become bases for new materials.
http://hano.tricity.wsu.edu/~physics
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