Applied Physics

The Department has just created a Ph.D. in Applied Physics, to provide curriculum and research opportunities for students who wish to use physics in the development of new technology. A number of the faculty conduct projects in applied physics that are related to their basic research interests, including those listed below.

High-Field Superconducting Magnets: Prof. P. McIntyre leads a group (see image) who are developing a new generation of superconducting magnets for future hadron colliders. As Europe builds its Large Hadron Collider (LHC), Dr. McIntyre's group is developing magnets that can double the field strength that will be used in its magnets. The new 15 Tesla technology uses a new superconductor, Nb3Sn, and a new magnetic design -- stress management and conductor optimization.

Tevatron Tripler, LHC Doubler, Ultimate Energy Hadron Collider: The new dipole technology will be key to the future of hadron colliding beams, making it possible to triple the energy of Fermilab's Tevatron (to 6 TeV), double the energy of CERN's LHC (to 28 TeV), and someday to build an ultimate-energy collider (~100 TeV).

High-Temperature Superconductors: Prof. P. McIntyre also leads a small group who are developing a new structured cable using the high-temperature superconductor Bi-2212. Six strands of multifilament Bi-2212 wire are cabled around a hollow spring core, then jacketed in an Inconel sheath. The 3 mm diameter cable carries ~ 1,000 A of current at very high magnetic field. The structured cable provides structural support for the brittle strands, and makes it possible to react it into the superconducting state in large coils. The group plans to use the cable to extend the high-field frontier for magnetic resonance spectroscopy -- a key tool used in structural biology to measure the 3-D structure of proteins and other oligomolecules of life. It also has potential for applications in electric power transmission, energy storage, and transportation.

Silicon Microdevices for Biotechnology: Prof. P. McIntyre is aditionally developing a family of silicon microdevices for use in solid-phase DNA sequencing. Graduate students Mark Volpi and Sabas Abuabara (see image) worked on the development of a process in which dense patterns of columnar pores are etched completely through a silicon wafer. Each pore is only 2 mm in diameter, and 10,000 pores are etched in each 1 mm² patch on the wafer. The group has succeeded in attaching single-strand DNA probes to the side walls of the pores; the attached population and the speed of attachment are much greater than has been possible with planar arrays. For use in sequencing by hybridization, a library of ~ 100 different sequences of interest are loaded in the patches of a 1 cm² device (see image). A solution of denatured sample DNA is then washed over the surface. The sample DNA hybridizes wherever there is a complementary sequence, enabling rapid, accurate detection of gene expression and mutations.

Pulse Techniques in NMR Spectroscopy: Prof. N. Duller is developing novel techniques for CW and pulsed nuclear magnetic resonance. He is working with his graduate student on a method for displaying and recording the dispersion component of RF susceptibility of nuclei in liquids and solids. The project involves a number of interesting signal processing methods, including frequency-to-voltage conversion, rf and audio mixers, and synchronous demodulators.

Ocean Remote Sensing: Prof. E. Fry (experimental) and Prof. G. Kattawar (theoretical) are developing a major new advance for remote sensing of the oceans (see image). The concept provides the first highly accurate remote sensed profiles of sound speed and temperature in the ocean. In a simplified version, mines and other submerged objects can be located with dramatically improved visibility; it is completely independent of their structure or composition.The technique is based on a lidar in which the transmitted laser beam has a very narrow bandwidth (50 MHz). Essentially all backscatteredlight is Brillouin shifted by approximately 17.5 GHz, and is thus well separated from the laser frequency. Sound speed is proportional to this optical (Brillouin) frequency shift; the high spectral resolution required to determine it is achieved using the edges of absorption lines of molecular iodine.

Materials Physics of Quantum Semiconductor Structures: Prof M. Weimer's group is working together with colleagues around the country to push the frontiers of materials science and perfect new semiconductor structures that are important for a broad range of civilian and military applications. The improved materials are key to a new laser technology that is in widespread demand because it operates at wavelengths in the mid-infrared (the 3-5 micron range) where the earth s atmosphere is essentially transparent. Absorption of light by molecules in the atmosphere has previously limited free-space optical communication and remote chemical sensing, but at these wavelengths illumination of objects for night vision as well as the optical monitoring of greenhouse gases and other industrial pollutants becomes practical. The laser materials are fabricated at a variety of government (MIT Lincoln Labs, Air Force Research Laboratory), academic (University of Iowa), and commercial (HRL Labs) laboratories using molecular beam epitaxy (MBE), and their atomic arrangements are analyzed at Texas A&M with scanning tunneling microscopy (STM). These joint efforts are sponsored by grants from the National Science Foundation and the Air Force Research Laboratory.

MBE permits the creation of new classes of materials not ordinarily found in nature. These materials are designed through an appropriate choice and sequence of atoms that is controlled on a layer-by-layer basis. This new degree of freedom allows one to tailor the electronic and optical properties of the resulting composite to suit specific purposes. Artificially structured semiconductors, for example, display many useful characteristics, including the tuned emission and absorption of light at selected frequencies throughout the electromagnetic spectrum, a phenomenon commonly referred to as 'bandgap engineering'.

STM (see image) is an extremely powerful technique for surveying the relationship between atomic geometry and electronic properties in both naturally occurring and artificially structured semiconductors. It has revolutionized our approach to materials science and, in the words of Nobelist Gerd Binnig, changed our emotional relationship with atoms. The scanning tunneling microscope provides a two-dimensional map of the arrangement of atoms at a conducting surface that, for the particular compound semiconductors employed in the growth of mid-infrared lasers, allows one to visualize where individual atoms are, as well as their chemical identity. STM is therefore an ideal tool for correlating MBE growth parameters such as composition, temperature, and growth rate, with the atomic-scale characteristics of the semiconductor interfaces that are crucial to device performance.