TcSUH
Bi-Weekly Seminar
X-ray Scattering Studies of Semiconductor Nanoclusters in Zeolites
by: Milinda Abeykoon
Date: Friday February 29, 2008
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
When electrons and holes in a semiconductor are confined to ultra-small regions of space (typically 1-25 nm), the optical and electronic properties of the semiconductor become strongly size-dependent. Such structures are called quantum dots, nanowires or nanoclusters, depending upon their shape and dimensionality. These nanostructures are of great interest for a variety of potential electronic, photochemical and nonlinear optical applications and are necessary for an analysis of the transition from molecular to bulk semiconductor properties.
This talk will discuss the structure of HgSe and Se semiconductor nanoclusters synthesized in both Nd-Y (spherical pore) and LTL (tubular pore) zeolites. The molecular structures of these systems were modeled by performing the Rietveld refinement on X-ray Bragg data. A remarkable feature in our X-ray diffraction patterns, continuous diffuse scattering under the Bragg peaks, will also be discussed along with our PDF (Pair Distribution Function) data. We use the results of optical studies to complement our X-ray structural work.
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Bi-Weekly Seminar
The Ultrasensitive SQUID-Based Sensing Applications for Biomedical Imaging and Diagnostics
Date: Friday February 15, 2008
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Superconducting QUantum Interference Device (SQUID) is the most sensitive and stable detector of magnetic flux available. The SQUID sensing provides the unmatched sensitivity and temporal resolution used for detection of the electromagnetic field perturbation associated with the neuronal currents in the brain, fetal cardiac activity, and the nuclear spin magnetization in ultra-low field NMR/MRI. In this presentation, I will summarize the current status of SQUID biomedical applications relevant to their present scientific and technological challenges, focusing on those applications that convey fundamental technological breakthroughs in corresponding biomedical fields. I will then describe our activities in the area of fetal cardiac monitoring, vulnerable plaque detection, cancer diagnostics and ultra-low field MR imaging. I will also present new research highlights from our recent clinical study in London aimed at developing a new ultrasensitive magnetic probe for detecting the spread of breast cancer.
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Bi-Weekly Seminar
The Unified Electronic Phase Diagram of High Tc
by: Prof. Pei Hor
Date: Friday February 01, 2008
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
I will discuss the construction of a unified electronic phase diagram (UEPD) by analyzing various characteristic temperatures and energies of high-Tc cuprates using a dimensionless universal hole-doping concentration (pu). There are three converging characteristic temperatures (T*'s) and their corresponding energies (E*'s) as pu increases in the underdoped regime. T*'s and E*'s merge together with the Tc (pu) and 3.5kB Tc (pu) curves at pu ~ 1.1 in the overdoped regime, respectively. They finally go to zero at pu ~ 1.3. The UEPD follows an asymmetric half-bell-shaped Tc-curve in which Tc appears at pu ~ 0.4, reaches a maximum at pu~ 1, and rapidly goes to zero at pu ~1.3. The asymmetric UEPD curve is at odds with the well-known symmetric superconducting dome for La2-xSrxCuO4 in which two characteristic temperatures and energies that converge as pu increases and merge together when Tc goes to zero at pu ~ 1.6,. The unified phase diagram clearly shows that pseudogap is necessary for high temperature superconductivity. I will discuss some universal intrinsic properties of high- Tc that can be easily understood in terms of the UEPD.
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Bi-Weekly Seminar
Progress Report on Two Nano-Material Studies
Date: Friday November 09, 2007
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Ion-Beam Assisted Fabrication of GaN nanorod and Applications Abstract: GaN is a direct Band Gap Semiconductor. Its ternary compound with In or with Al could cover a very broad band region with potential applications in Laser source, Light Emitting Diode, high efficiency solar cell and optoelectronics. We have studied GaN nanorod formation during MBE growth of GaN film on Si[111] substrate, and its fabrication assisted by ion implantation on Si before the the MBE growth. In this talk, I will give a progress report on our nanorod growth studies, Ion Beam Assisted growth, Nanorod characterization, and its potential applications. (Collaboration with Q. Y. Chen, L. W. Tu, and H.W. Seo). Field Ionization of Carbon Nano Tubes and Applications Abstract: The removal of electrons from any species by interaction with a high electrical field is called Field Ionization. The most notable work on field ionization conducted by Mueller?s team at Penn State [Phys. Rev 102, 624 (1956)] is a perfect example, which later developed into the famous Field Ion Microscope (FIM). Focus Ion Beam (FIB) is another example, where a sharp tip can emit focused liquid metal ions such as Ga ions when positively biased. We have studied field ionization of Carbon Nano Tubes under residual hydrogen gas, and produced huge proton current. In this talk, I will discuss the implication of our experiment and its potential applications. (Collaboration with Jiarui Liu).
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Bi-Weekly Seminar
Nanostructured Pt alloy Core-Shell Fuel Cell Electrocatalysts - Synthesis, Structure, and Performance
by: Dr. Peter Strasser
Date: Thursday October 25, 2007
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
The identification of more active, more cost-effective and more stable electrocatalysts for the oxygen reduction reaction (ORR) continues to bea scientific priority in low-temperature Fuel Cell catalysis research.Among all currently known electrocatalyst materials, Pt alloys have remained one of the most attractive catalyst concepts, in particularfrom a power density perspective.
We have recently discovered a new class of Pt core shell nanoparticle electrocatalysts which exhibit ORR activities exceeding those of conventional uniformly alloyed Pt-rich catalysts. We also have put forward a hypothesis for the enhancement mechanism which focused on lattice strain in the Pt rich Shell of the nanoparticles resulting from the electrochemical de alloying synthesis. Our experiments have been corroborated by DFT computational modeling.
We also report on recent strategies to experimentally realize the high electrocatalytic RDE activities of our new catalysts in realistic single PEM fuel cell devices.
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