The central theme of my research has been to use vibrational spectroscopy on solid state materials (much at high pressure) to gain a better understanding of their bulk thermoelastic properties as well as to examine changes in structure while under pressure. This work began in 1977 on MgO, and after a brief hiatus, continued in 1986 to the present. Materials studied include forsterite, enstatite, and all of their high pressure polymorphs. Several perovskites (both minerals as well as non-minerals; garnets, including 6 rock-forming garnets as well as YAG and binary solid solutions; the orthosilicates monticellite and fayalite; and the clinopyroxenes diopside and hedenburgite. New work includes amphiboles and feldspars. While work has centered on geophysically (geologically) relevant materials, the methods and analysis techniques are broadly applicable to a wide variety of materials.
The central purpose of the spectroscopy in my lab has been to obtain vibrational information useful for determining thermodynamic properties. This is a subset of possibilities. Laser spectroscopy can be performed on samples on the order of μ-meters. As a example, in situ detection of phases synthesized in a laser heated diamond anvil cell has proven very effective.
Experiemental work in the past has included both laser Raman and laser fluorescence spectroscopy. Many of the materials studied have been studied at high pressure in the diamond anvil cell while MgO has been studied at high temperature (1 atm so far) and high pressure and subambient temperatures (down to 90 K).
These techniques can be applied to a huge variety of scientific problems from biological applications to material science to semiconductors to ceramics to superconductors as well as any geophysical or planetary science issue. Vibrational spectroscopy not only allows unambiguous identification of the phase in question, it also allows the measurement of a large range of thermoelastic properties at high pressures inaccessible by any other means. In my publications, you will find the development of techniques to measure sound velocities via acoustic mode measurements via an optical method at high pressures and thermal expansition measurements at high pressures via an optical measurement at room temperature. My latest publications (in preparation) will deal with various properties of perovskites, including phase changes, thermal pressure, and heat capacities over a range of conditions.
The beauty of thermodynamics is that once two parameters have been measured, all other of the thermodynamic parameters can be obtained from them. In my case, measuring the vibrations in a system means the internal vibrational energy is measured. Couple this with known volumes and the Grueneisen parameter, thermal pressures are known. The temperature derivative of the energy is the heat capacity and heat capacity over temperature integrated over temperature yields the entropy. From entropy versus pressure, we can ascertain the thermal expansion. Thus, measurement of frequency versus pressure and the volumes versus pressure will yield all the above information. This yields an internally consistent picture for each material. See page on thermo properties.
Summary
Measurement of the structure, dynamics, and thermophysical properties of phases vs.pressure and/ or temperature. Experimental techniques: laser Raman and laser fluorescence spectroscopy in the diamond anvil cell (laser and/or externally heated/cooled), x-ray diffraction. Geophysicists use the values obtained in my laboratories for modeling planetary interiors, particularly for mineral composition, convection and temperatures.
Recent projects include Raman study of the solid solution series of tremolite to ferro-actinolite; spectroscopic and thermodynamic characterization of perovskites,thermal pressures of deep earth/planetary materials and high pressure-high temperature behavior of pyroxenes.
Current experimental apparatus: Confocal Raman system and externally heated membrane diamond anvil cell
Teaching Interests and Philosophy
My broad educational background has allowed me to teach a wide range of topics and subjects over the 30+ years of my scientific career. This versatility has lent itself well to interdisciplinary teaching, in topics ranging from advanced solid state physics and geophysics down to teaching art students the science of light and color from their perspective. I have been passionate about the universe, minerals, light and color since I can remember and like to impart my enthusiasm to students at all levels. I have created courses as well as taken over standardized courses for premeds and engineering majors. Topics in my courses include electricity and magnetism, thermodynamics, quantum mechanics, electrochemistry, optics, Newtonian mechanics, relativity, light and color, astronomy, solid state physics, mineralogy, and mineral physics.
Most of my teaching experience is in the area of physics and as such, it is my experience that the more engaged and the more practice a student gets in analytical thinking, the better they learn. My teaching methods include engaging the student in as much as hands on experience and live demonstrations as possible. I have extensively used the web for graded homework, which allows for self-evaluation and allows more time for the teaching assistants, if any, for more one on one with the students. Communication via web allows students access to course materials and communication with me and other students via classroom forum and extensive websites with additional reading and links, solutions to problems, and classroom information. I try to impart the wonder and fascination I feel about the world around us into my teaching.
