G. Lang Farmer
My research centers on applications of trace element abundances and radiogenic isotopic data from natural materials to study the origin and evolution of Earth's lithosphere. Currently, my research group has used hafnium and neodymium isotope data from silicic sediments to investigate the paleogeography of ancient continents, used sediment isotopic data to study past instabilities in the East Antarctic Ice Sheet, investigated the origin of Mo-bearing granitic rocks in North America, and used space-time-compositions patterns in volcanic activity in western North America to assess the evolution the deep continental lithosphere beneath this region over the past 70 million years.
"Development of MicroInterdigitated Electrode Arrays as Ion Sources for TIMS", Funding from National Science Foundation
Thermal ionization mass spectrometry is the technique of choice for high precision determinations of the isotopic abundances of elements found in both natural and manufactured materials. However, the precision of isotopic measurements performed in this fashion depends on the efficiency of the techniques used in the mass spectrometer to generate ions from elements extracted from sample materials. This project involves an effort to improve the ionization efficiency of high temperature (<1,300oC) liquid glass ion emitters, a type of metal ion source that is routinely used in thermal ionization mass spectrometry but that typically only ionizes one in every ten of the metal atoms loaded into the instrument for analysis. The approach will be to increase the proportion of metal ions generated in the liquid glass using electrolysis techniques, in which the liquid glass will serve as an electrolyte when placed in contact with two metal electrodes of opposite electrical polarity (an “electrochemical cell”). The electrochemical cell will consist of a micro-interdigitated electrode array (IDA) produced by sputtering tungsten onto a silicon or sapphire wafer. The final cell design of the device will be developed through a series of prototypes for the IDA, itself, and for a high melting temperature ceramic holder and electrical connector. The various prototype configurations will be designed to optimize heating and electrical continuity of the IDA and to maximize the ion currents created within the liquid glass. The main goal will be to improve the ionization efficiency of lead by at least a factor of five which in order to improve the precision U-Pb age determinations for very small samples (picogram size). A secondary goal will be to develop and commercialize a new class of ion source for use in private sector thermal ionization mass spectrometers.