TcSUH
Special Seminar
Prospects of Dilute Nitrides III-V Heterostructures for IR Photovoltaics and Recent Developments at TCSAM
by: Alex Freundlich
Date: Friday August 06, 2004
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
The unusual bandgap shrinkage that accompanies the incorporation of small amounts of nitrogen (< few percent) in III-V semiconductors has sparked both theoretical and experimental research in the arena of dilute nitrogen containing III-V alloys. While considerable progress has been made, the encountered low solubility of N in these alloys and their poor optical properties have thus far hindered the expected rapid proliferation of the technology for IR and optoelectronic applications. The presentation highlights results of recent investigations at University of Houston on development of Ga(In)AsN based alloys and heterostructures (by RF- chemical beam epitaxy). Some key conditions favoring incorporation of large amounts of N (up to 7%) in epilayers are deciphered. In particular, the criticality of N-RF-plasma conditions (real time plasma spectroscopy) upon the incorporation of nitrogen in the solid and in controlling the optical properties of grown epilayers will be addressed. Based on experimental data presented here, a new dilute nitride-superlattice material design (lattice matched to InP) is devised and its potential for mid-IR applications (0.4-0.6 eV) will be discussed.
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Special Seminar
The Promise of MgB2 Superconductors in Electric Power Energy
by: Prof. Kamel Salama
Date: Friday May 07, 2004
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Since the discovery of its superconductivity in early 2001, Magnesium Diboride (MgB 2) has drawn a great deal of worldwide research interest. This new high temperature superconductor has a critical temperature of 39.4 K, an upper critical ?eld of 29 Tesla, and a relatively long coherence length of about 5 nm. In addition, MgB 2 exhibits no intrinsic current blockage by grain boundaries and comparatively weak anisotropy and thermal ?uctuations. Research on MgB2 at TCSAM demonstrates promising results of high current carrying capability sustained to applied magnetic ?eld in the temperature range of liquid hydrogen and liquid neon. Thirty-meter long Fe-sheathed MgB 2 wires and tapes have been fabricated using the powder-in-tube method with ultra-?ne starting precursors. High critical current density of 3 x 105 A/cm2 at 20 K and self-?eld has been obtained. Coils wound from MgB 2 wires also possess superior superconducting properties. These results reveal the promise of MgB for electric power applications at 20-5 K.
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Special Seminar
Theory of High-Temperature Superconductivity - A New Perspective
by: Prof. W. P. Su
Date: Friday January 16, 2004
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Theoretical analysis of an effective model of d-wave superconductivity in two dimensions reveals a subtle interplay between phase separation, superconductivity and antiferromagnetism. The main theoretical result can be described in terms of elementary phase separation concepts in a binary alloy. This provides a deep understanding of the phase diagram of a hole-doped cuprate superconductor. A microscopic model of d-wave superconductivity will also be discussed.
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Special Seminar
Nanoscale Magnetic Recording
by: Dr. Dimitri Litvinov
Date: Friday September 05, 2003
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Magnetic recording is rapidly shifting into the realm of nanoscale technologies. At 1 Terabit/in2, the size of a recording bit is 50x13nm2 (assuming 4:1 bit aspect ratio.) To store such small magnetic features, the characteristic dimensions of all supporting recording system components have to be shrunk correspondingly. The read/write transducers are being scaled down into 40nm range. The characteristic size of the smallest magnetic feature in a recording medium is being refined to hit the 5nm mark. The flying height of the recording heads is targeted to be a few nanometers at the most. The servoing capabilities of the tracking system are being optimized for the capability to position a recording transducer on a 3.5†diameter media disk with a precision of 10nm in a fraction of a millisecond. This presentation will review the major critical issues related to the recording physics, device fabrication, and system integration at nanoscale. The prospects of extending magnetic recording technologies above Terabit/in2 range as well as alternative approaches to data storage and retrieval will be discussed. Among the open issues critical to the development of nanoscale probe recording is the ability to fabricate magnetic transducers with the dimensions in the nanometer range as well as the detailed understanding of the recording physics of such nanomagnetic devices. Magnetic probe heads with a cross-section of 60x60nm2 were successfully fabricated using focused ion-beam (FIB) processing. The ability of such probe heads to controllably conduct magnetic flux is critical to the performance of a recording system. The results of both experimental and theoretical study of micro/nano-magnetic behavior of fabricated nanoscale probe heads will be reported. The recording demonstration using 60nm wide magnetic nanowriters will be presented. The key advantages of FIB technology with respect to magnetic materials processing will be reviewed. The resolution limits and Ga+ ions interaction with magnetic materials will be discussed.
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Special Seminar
High Energy Atomic Beam Nanolithography
Date: Friday December 06, 2002
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Ion beam proximity (IBP) lithography is “stencil printing†where helium ions are the “paint†and the stencils are thin silicon membranes with etched open windows. Diffraction, penumbral blur, and ion scattering in the resist are all consistent with 1 nm printing. However, the scattering of the lithography ions by electrostatic charge in the mask and substrate limit the practical resolution to the 50-100 nm regime. This seminar describes the discovery of a remarkable source of energetic helium atoms that eliminates this last obstacle to sub-10 nm printing. Applications to nanomagnetics and nanoelectronics will be discussed.
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