Ph.D. Candidate (2008)

Department of Chemical Engineering
Doherty Hall Room B202
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-5662 (lab)
412-268-4531 (office)
412-268-7139 (fax)

I am studying the atomic and electronic structure of chiral metal surfaces using temperature programmed desorption of adsorbed xenon and ultraviolet photoemission spectroscopy of both the clean surface and with xenon adsorbed. Xenon has a van der Waals diameter of approximately 4 Angstroms, interacts weakly with substrate atoms and other co-adsorbed species, and has only one possible adsorption conformation (roughly that of a sphere). These properties make xenon a good probe of individual adsorption sites on a heterogeneous crystal surface.

The energy required for a xenon atom to desorb from a specific adsorption site on a surface is determined by the local atomic and electronic structure of the adsorption site. As such, temperature programmed desorption (TPD) of xenon can be used to determine the distribution of adsorption sites, in terms of adsorption energy, on a crystal surface.

Ultraviolet photoemission spectroscopy of adsorbed xenon (PAX for short) can be used to probe the local work function distribution of crystal surfaces. The binding energies of electrons in xenon atoms, adsorbed on a crystal surface, are sensitive to the work function of the local adsorption site. Thus, the photoemission spectra of adsorbed xenon can yield some insight as to the local work function distribution of a crystal surface. PAX was developed by Dr. Klaus Wandelt and others in the late 1970's and early 1980's.

All of my research is performed in ultra-high vacuum chamber, much of which I built or modified, with a base pressure in the high 1e-11 Torr range (I use stacked turbopumps to achieve this base pressure). Crystal samples are spot welded between two Ta wires which are attached to copper blocks on the main sample manipulator body. The copper blocks are electrically insulated from the manipulator using sapphire wafers. Sample cooling is provided by a Gifford-McMahon compressed He refrigerator to which the manipulator body is attached. Sample temperature is measured by means of a type-K thermocouple spot welded directly to the rim of the crystal samples. In all, crystal samples can be cooled to less than 50 Kelvin and resistively heated to 1300+ Kelvin. Temperature programmed desorption measurements are performed using an Extrel MAX mass spectrometer which can detect the desorption of less than 0.005 ML of xenon from a sample surface. UV photoemission experiments are performed using a Specs Phobios 150 hemispherical energy analyzer; in all studies, HeI radiation from a Specs UV 10/35 source is used as the excitation source. A picture of the chamber is provided below.

J. Horvath, L. Baker, A.J. Gellman, "Enantiospecific Orientation of R-3-Methylcyclohexanone on the Chiral Cu(643)R&S Surfaces", submitted for publication

L. Baker, A.J. Gellman, "Vicinal Cu(111) surfaces studied by ultraviolet photoemission spectroscopy and temperature programmed desorption of adsorbed xenon (working title)", in preparation

I am actually going to get this updated soon with a document or two that actually provide most of my data to date and a useful discussion of what is going on but for now I have a single page pdf that presents a summary of some of my data on copper surfaces.

Summary of TPD and PAX on copper surfaces