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Seminar

Transition Metal Oxides with Unsaturated Coordination Spheres and Low Dimensional Spin Systems

Dr. Angela  Moller

by: Dr. Angela Moller

Date: Monday November 05, 2007

Time: 11:00 am – 12:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Transition metal oxides belong to an exceptional class of materials for studying correlated systems. In particular various degrees of freedom (structure, spin, orbital, charge and order/disorder) play an important role and are in the focus of our recent research activities. Apart from common transition metal oxides exhibiting high oxidation states and spherical coordination spheres, e.g. octahedron or tetrahedron, I will present selected compounds with unsaturated coordination spheres (e.g. dumb-bell) and low oxidation states (e.g. monovalent nickel, d9, S = 1-2 ). Starting from solid state synthesis techniques and analytics I will proceed to the physical properties (VIS-NIR-MIR-FIR and Raman spectroscopy, (T), M(H), cp) and approach the field of low dimensional spin systems.

Seminar

Merging Form and Function: Insights into Electronically and Magnetically Active Ceramics

by: Dr. Peter Kahlifah

Date: Thursday February 22, 2007

Time: 11:00 am – 12:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

The power of periodic solids is their hybridization of vast arrays of atomic orbitals. This enables strong magnetism, excellent electronic conduction, and a host of intriguing collective phenomena which are generally absent in molecular compounds. The oxides of ruthenium are some of the most interesting transition metal oxides, as they can be very conductive (due to their extended 4d orbitals) while retaining strong magnetic interactions (which are rare outside of the 3d oxides). I will talk about the wide variety of properties observed for the ruthenates I have synthesized and studied, including geometric frustration, orbital ordering, and quantum (T=0) phase transitions. Some properties can be simply explained by a close look at crystal structures, while others need a detailed calculation of their electronic structures, and a few are pushing the envelope of the modern understanding of crystalline solids. I will discuss how a detailed understanding of and control over the energy levels of solids can offer promising solutions to the global need for clean energy.

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Seminar

Structural Studies of Functional Framework Materials

by: Dr. Karena W. Chapman

Date: Monday February 19, 2007

Time: 11:00 am – 12:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

The evolving demands of our modern society fuel a perpetual drive to develop innovative materials for advanced technological and industrial applications. Pivotal to the rational design of next generation materials optimized for real world applications, is the fundamental understanding of the key structural features underlying functional behavior. Here we present recent applications of advanced scattering methods to the development of two novel material functionalities in cyanide-bridged molecular frameworks: negative thermal expansion behavior and reversible hydrogen storage.

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Seminar

Scientific and Technological Opportunities of Ultra-High Density Nanowire Arrays

by: Dr. Dunwei Wang

Date: Wednesday February 14, 2007

Time: 11:00 am – 12:00 pm

Location: Science & Research Building 1 – Building 550 — Room 634

Overview

With their dimensions exceeding conventional lithographic methods limit, semiconductor nanowires have attracted intensive research efforts as building blocks for future electronics. While various individual nanowire-based devices are demonstrated to outperform existing MOSEFT, successful integration into complex functional units is still missing. The fundamental distinction between current semiconductor technology and nanowire-based electronics is that the latter requires regular device structures for optimum performance, whereas the former relies on fabricating arbitrary ones based on functionalities. This imposes great challenge of nanowire research in terms of arrangement and integrations. I will present our recent advancements in this area using ultra-high density nanowire arrays with excellent arrangement for electronic applications. A wide range of topics will be covered and they include controlled placement of p- and n-type nanowires in a single array; understandings of the surface effects on nanowire electrical properties; statistically significant high performance field effect transistors and monolithic Si-only nanowire networks. Integrated nanowire circuitries with complementary symmetry are therefore enabled for energy efficient applications and they are amenable to high degree of integrations. Furthermore, our studies shed light on nanoscale sciences and technologies in general and will pave ways toward many applications in relevant scales such biological sensing and energy conversions.

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