RESEARCH

Overview

Our research program focuses on understanding the large-scale physical and chemical behavior of the Earth and other planets through experimental study of geological materials under extreme conditions of pressure and temperature. More generally, we use the laser-heated diamond anvil cell together with optical spectroscopy and x-ray techniques to explore crystal structures, phase relations, elasticity, and deformation behavior in a wide range of materials at ultra-high pressure and temperature conditions.

Elasticity and sound velocity at high-pressures: Geophysics and materials science

Brillouin spectroscopy in the diamond anvil cell

We use Brillouin spectroscopy in the diamond anvil cell to measure elastic wave velocities at high pressures and temperatures and use the results to construct compositional models for Earth’s interior. We also study sound velocities in a range of single crystal materials to examine anisotropic elasticity, interatomic interactions, mechanical properties, compressibility, and phase transition mechanisms.

Using lasers to generate ultrahigh P-T states of matter

Ramp compression

Ramp compression using high-powered lasers provides a means to generate extreme pressures in the solid state. In collaboration with colleagues at LLNL, we have initiated a program to study materials such as Fe and SiO2 to 10s of Mbar pressures using laser-based ramp compression platforms at the Omega facility at the University of Rochester and, in the future, the National Ignition Facility at LLNL.

Optical spectroscopy for materials science and mineralogy

Carbon soot deposit.

Micro-Raman spectroscopy has many applications including non-destructive phase identification, study of phase transitions, and constraining thermodynamic properties. Our micro-Raman system is adapted for high-pressure studies in the diamond anvil cell. In recent years, our system has also been used for many ambient pressure projects, often in collaboration with scientists from other disciplines including studies of amorphous carbon phases, Si/Ge thin films, art objects, various geological samples, and gems.

Strength and rheology under compression

Diamond anvil cell

New diamond anvil cell techniques have been developed to measure lattice strains under intentionally non-hydrostatic conditions using synchrotron x-ray diffraction. These studies constrain yield strength and provide insights into other properties including elastic moduli, equation of state, and texture development to very high pressures. We are using this method to study different types of materials including metals, silicates, oxides, nitrides, superhard solids, nanomaterials, etc.

Ramping Up The Pressure

Download Ramping up the Pressure

Stewardship Science, The SSGF Magazine, 2011-2012, pp. 8-11

By Thomas R. O'Donnell

"We want to understand how the high pressures and temperatures in these planets affect the crystal structure - the arrangement of atoms and whether they are solid or liquid," says Thomas Duffy, a professor in the Princeton University Department of Geosciences. Researchers also want to know how those conditions affect "a host of physical properties: how dense these materials are, whether they are insulators or metals" and others.