Albert A. Michelson Professor of Physics
The properties of matter such as specific heat, thermal expansion, and bulk modulus depend on the microscopic nature of the interatomic interactions. Measurements of these properties are macroscopic in nature, i.e., carried out on large scale samples relative to atomic or molecular sizes. This research characterizes the physical, thermal, and electrical properties of materials with the goal to relate the microscopic interactions with the macroscopic measurements.
A variety of techniques are employed to measure these properties. Ultrasonic and surface acoustic waves are used to determine the elastic properties of both bulk and thin film materials as a function of external parameters such as temperature and pressure. Dielectric spectroscopy is used to measure the electrical properties and to relate them to molcular dynamics. These measurements range over a frequency span of eleven orders of magnitude. A precision capacitance bridge allows for displacement measurement to the sub angstrom range, and is used in the thermal expansion measurements. Heat capacity and phase transitions are determined using a differential scanning calorimeter. An optical system is used in conjunction with a the dielectric spectrometer to correlate the optical properties with the electrical properties. In many of the measurements, external parameters such as pressure (to 150,000 atmospheres) and temperature (4.2K to 500K) are imposed.
Recent projects span a variety of materials and properties. The thermal expansion of the two isotopes of lithium have been measured and related to the mass dependence of the anharmonicity of the lattice vibrations. To get a better understanding of shape memory alloys, ultrasonic and electrical conductivity measurements have been carried out as a function of temperature and pressure. The dielectric properties of many exotic liquid crystal polymers and polymer dispersed liquid crystals have been measured in order to understand their molecular dynamics and optical transmission properties. These materials have potential use in flat panel displays and in windows as sun-roofs for automobiles.