TcSUH
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Special Seminar
Analysis of Surface Nano-structures by XPS
by: Prof. Sven M. Tougaard
Date: Thursday November 11, 2004
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
The accuracy and capability of NPS for analysis of surface nano-structures has improved significantly in the past decade. This was achieved by modeling the change in energy distribution with the path the XPS electrons travel to reach the surface. When this is compared to measured energy spectra, the depth distribution of atoms can readily be determined. The method, which is now widely used, provides analysis with sub nano-meter depth resolution in the 0 - ~10 nm depth range. We discuss the underlying physics as well as the prospects of a newly proposed model for automatic data analysis intended for XPS imaging. We will also discuss several practical applications of the technique as for example to thin metal-oxide films, SiO-nitrides, low energy ion implants in SiO2, surface segregation phenomena in PS-PDMS diblock copolymers, etc.
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Special Seminar
A Global Odyssey: From Science to Administration; From the U.S. to the Orient
by: Dr. Ching Wu Chu
Date: Thursday October 14, 2004
Time: 4:00 pm – 5:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
Life is a strange encounter. Three years ago, a difficult-to-refuse opportunity dogged me repeatedly and finally has helped expand my horizon from that of a scientist in the trenches at the University of Houston to that of the President of Hong Kong University of Science and Technology (HKUST) in the Orient, a young and rising premier university in the most dynamic region of our 21st century world. The vision, generosity, and hard work of colleagues on both sides of the Pacific these past three years have demonstrated once again that exceptions do exist to the expression "one cannot have his cake and eat it too." Science in our Houston lab has continued to flourish in the past three years, while new heights have been scaled by HKUST on her way to becoming a world-class university. Synergistic collaboration is being developed between UH and HKUST in the area of the almighty nanoscience and technology. In this talk, I will share with you my experience on this unusual odyssey and point out the opportunities and challenges ahead for us all as citizens of the global village.
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Special Seminar
Collective Modes in Unconventional Superconductors
by: Prof. Peter Brusov
Date: Friday September 24, 2004
Time: 12:00 pm – 1:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
After the recent discovery of collective modes in unconventional superconductors (USC), their study becomes very important. Collective modes (CM) in HTSC exhibit themselves in many experiments: ultrasound attenuation (UA) and microwave absorption (MWA), neutron scattering, photoemission and Raman scattering, etc. The large peak in the dynamical spin susceptibility in HTSC arises from a weakly damped spindensity- wave CM. This gives rise to a dip between the sharp low energy peak and the higher binding energy hump in the ARPES spectrum. Also, the CM of amplitude fluctuation of the d-wave gap yields a broad peak above the pairbreaking threshold in the B1g Raman spectrum. The contribution of collective modes to UA and MWA may be substantial. We consider two-dimensional and three-dimensional models of p- and d-pairing for superconductors built by the path integration technique. Within these models we calculate the collective excitations in different unconventional superconductors [high temperature superconductors (HTSC), heavy fermion superconductors (HFSC), etc.] under p- and d-pairing. We consider both bulk and 2D systems. Some recent ideas concerning realization in HTSC of the mixtures of different states are investigated. In particular, we consider the mixture of two d-wave states in HTSC (of dx2-y2 and dXY states). Obtained results could be used for interpretation of the sound attenuation and microwave absorption data as well as for identi?cation of the type of pairing and order parameter in unconventional superconductors. They allow us to distinguish pure d-wave state from the mixture of two d-wave states in HTSC.
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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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