TcSUH
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Bi-Weekly Seminar
Interface Magic in Nanostructural Metamaterials
Date: Friday September 03, 2010
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Interface engineered metamaterial is not the materials engineering, it is the engineered materials with designed innovative properties. In the nanoscale materials, interface plays a key role in governing their physical properties and resulting in the discovery of various anomalous physical phenomena with excellent opportunity for new active device and engineered nanosystem developments. Recently, we have systematically focused on the studies of multilayered layered structures and nanoscale ordered structures such as multilayered ferroelectric BaTiO3/SrTiO3 heterostructures and ferromagnetic LaBaCo2O5.5 nanostructures and found many interesting physical phenomena, such as domain clamped ferroelectric phenomena, unusual magnetic properties, and ultrafast oxygen exchange chemical dynamic behavior. Also, a series of models were developed to understand these interface phenomena. Details will be presented in the talk.
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Bi-Weekly Seminar
Electrochemical Nanofabrication and Material Synthesis
Date: Friday July 23, 2010
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
In the last several decades, the electrochemical processes were proven to be enabling fabrication routes behind the train of high-tech enterprise. Today, the devices with sub-100 nm dimensions are produced routinely using the electrodeposi-tion and electropolishing as the standard processing operations in magnetic recording, microprocessors and MEMS/NEMS technologies. There are many other examples where the electrochemical processes are used as convenient if not "the only" approach to deliver desired structures, materials or catalytic surfaces. The traditional felds of electrochemical research like corrosion, anodization, or electrodeposition are rapidly being involved in different contemporary scientifc disciplines where the word "nano" is frequently used prefx. In this talk, several examples of the electrochemical nanofabrication and material synthesis are presented. In the first part, the optimum design and fabrication of Pt catalyst monolayer (ML) on Au(111) is demonstrated using surface limited red-ox reaction (SLRR). The morphology of the most active catalyst ML is identifed and compared with predictions of DFT calculations. The new synthesis route for catalyst ML fabrication using SLRR guided by molecular templates is discussed as well. Continuing the talk farther, the nanoporous Au electrodes produced by dealloying process are demonstrated as the generic ultrasound sensor devices. The sensitivity of these electrodes towards the incoming ultrasound excitation is compared against the state of the art piezoelectric ultrasound sensors. The transducer equation is presented highlighting the fundamental advantage of the electrochemical ultrasound sensors in terms of their design-determined sensitivity and reduced cost. The fnal part of the talk focuses on revealing the role of additives in electrodeposition process of magnetic flms. The functional relation between concentration of organic additives in the electrodeposition solution and their incorporation into magnetic alloys is described. The dependence of magnetic flms properties on additive concentration in the solution is quantifed shining a new light to the understanding and appreciation of the organic adsorption phenomenon at the electrode surface during electrodeposition of magnetic alloys.
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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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