TcSUH
Bi-Weekly Seminar
Cyclotron Phonon Scattering and Linear Magneto-Resistance in Suspended Multilayer Graphene
Date: Friday May 07, 2010
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Magneto-transport in graphitic structures has been a fascinating subject for decades, and the discovery of anomalous integer quantum Hall effect has attracted enormous research interest in graphene since 2005. I will discuss recent efforts in my group to address the high-bias electron transport in suspended multilayer graphene devices created by a new experimental approach. We study the hot electron effect and magneto-resistance (MR) in suspended multilayer graphene under magnetic fields up to 15 T. A suppression of the hot electron effect is observed under high magnetic fields, indicating strong cyclotron-phonon scattering. In addition, we find a positive linear MR background on top of Shubnikov-de Hass (SdH) oscillations at drain-source bias Vd = 0. At finite Vd, the SdH oscillations are suppressed and a linear MR is clearly demonstrated. Potential origin of the linear MR is discussed.
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Bi-Weekly Seminar
An Overview on Ion Beam Channeling in Single Crystal: Discovery, Understanding, Applications, Current Status and Future
Date: Friday April 23, 2010
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
When an energetic Ion projectile enters a single crystal along a major crystalline axial or planar direction, the collective Coulomb potential from a crystal steers the ion away from the lattice. Ion channeling in a crystalline solid can be observed as great reduction of close encounter process such as elastic Rutherford scattering, ion induced x-ray emission, and nuclear reactions, due to the steering of ions away from the nuclei array. Channeling phenomenon was first discovered at Oak Ridge National Lab from a Monte Carlo simulation back in the earlier 1960's. It was quickly verified by several experiments, and Lindhard provided a theoretical treatment on channeling. The phenomenon is well adopted as a powerful real-space analytical tool which can be used for studies on lattice dynamics, depth resolved crystalline defect analysis, strain analysis and ion-beam crystallography.Potential applications include the use of channeling in particle beam guiding and beam splitting in high energy accelerators. Resonant Coherent Excitation (RCE) which is the radiation produced by channeling ions are considered in applications in tunable polarized X-Ray sources. This talk will give an overview on channeling, historical remarks, present status of channeling, our present efforts, contribution and future plan on channeling.
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Bi-Weekly Seminar
Effect of Additive Incorporation on Magnetic, Corrosion and Mechanical Properties of 2.4 T CoFe Alloys
Date: Friday October 02, 2009
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
The recent trends in magnetic recording technology demonstrate that electrodeposited high moment alloys will be the material of choice for fabrication of future magnetic recording heads. The current research in electrode- position of soft magnetic alloys is driven by the need for ultimately soft magnetic alloys with 2.4 T magnetic moment, good corrosion resistance and low stress levels. In order to achieve these properties it is essential that our understanding of additive incorporation into magnetic deposit is improved and its benefts and draw- backs quantifed. In this talk, results demonstrating two separate mechanisms, (1) molecular incorporation and (2) electroreduction, for saccharine (additive) incorporation into CoFe alloys are presented. These results are supported with analytical model describing the sulfur incorporation into magnetic deposit. The effect and importance of each incorporation mechanism on magnetic softness and corrosion potential of CoFe alloys is discussed with intention to identify the dominant one. The analytical model describing the effect of saccharine concentration on corrosion potential of CoFe alloys is discussed as well. In the last part of the talk, results from in-situ stress measurements during electrodeposition of CoFe alloys are presented. The effect of saccha- rine concentration on stress evolution/level in CoFe deposit is discussed through the scope of the saccharine incorporation mechanisms and overall sulfur incorporation rate in magnetic deposit.
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Bi-Weekly Seminar
Development of Nanostructured Systems for Energy, Environmental and Biomedical Applications
Date: Friday September 18, 2009
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
The main topic of this presentation will focus on development of nanostructured particulate systems and fabrication of advanced devices for power systems, energy storage, environmental protection, national security and health care. I will present novel nanoenergetic systems that have the potential to enable a more concentrated energy release and potentially can be used for various military applications such as an actuation parts, igniter, propulsion unit, gas-generators as well as an active part for high power electromagnetic pulse generators. I will describe a novel cost-effective and energy efficient production of nanostructured complex oxides that we referred to as Carbon Combustion Synthesis of Oxides (CCSO). In this process, the reactive oxidation of carbon/graphite nanoparticles generates a steep thermal wave (temperature gradient of up to 500 °C/cm) that propagates through the solid reactant mixture (oxides, carbonates or nitrates) converting it to the desired products. The high rate of gas release enables synthesis of highly porous complex oxides having a particle size in the range of 50-800 nm. The experimental results of fabrication of various systems such as hard and soft magnetic materials, superconductors, multiferroics, bulk ceramic resistors, capacitors, photocatalysts with p-n junction, MRI contrast agents and cancer hyperthermia will be presented. Key factors that affected to the device characteristics (magnetization, conductivity, magnetic resonance relaxivity and other) will be discussed. Finally, I will describe a novel medical device that we referred to as Encapsulated Contrast Agent Marker (ECAM) for MRI cancer prostate brachytherapy (PB). While MRI is the modern superior imaging modality, for cancer treatment it is currently not used in PB because the implanted radioactive titanium seeds appear artifacts (negative contrast) and cannot be accurately localized within the prostate and periprostatic tissue. The innovative development of an MRI visible ECAMs technology will provide a precise targeted magnetic resonance imaging for PB and can impact over 200,000 in US (12,000 in Texas) men diagnosed annually with localized prostate cancer. Development of this emerging technologies warrant a multifaceted approach, which includes interdisciplinary collaboration, partnerships with industry and academia, and integration of modern problems into our curriculum.
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Bi-Weekly Seminar
Ion Implantation, Past, Present, and Future: The Future is in the Area of Material Modification for Biology Research
Date: Friday September 04, 2009
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Ion Implantation is the injection of energetic ions into a solid, thereby changing the physical properties of the solid by impurity doping, and/or by radiation damage. It is mostly used in semiconductor device fabrication and in metal finishing as well as in various applications in materials science research and technology. In this talk, I will briefly review the process of ion implantation, its characteristics, and its applications in material modification. I will give a few examples of our current activities using ion implantation. More importantly, I will be proposing applications related to ion beam modification of soft materials for biological applications. Although ion implantation has been around for more than forty years, biological applications of ion implantation have come of age gradually in the last decade or so. I will be discussing some recent developments in ion implantation modification of polymers and ion beam modification of surface hydrophilicity for applications in protein pattern printing and subsequent living cell adhesion. The intention of this talk is to seek feedback, interaction, and collaboration from the biology, biochemistry, biophysics, and biomedical communities.
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