LSU Surface Science Research

Materials Science Research Topics

In this section you will find links to more details of our research effort. Although we are primarily experimentalists, we also do modelling and a bit of theory to help explain our data. This is particularly important in helping to explain the photoelectron angular distributions that we find with our display analyzer.

Our underlying motivation is to understand the connections between the electronic and geometric structures of surfaces and films with magnetic and other properties.

Much of our work is conducted at the LSU CAMD synchrotron light source where we use several different beamlines for just about any photon-induced experiment that you can imagine. This includes the typical alphabet-soup of surface techniques such as UPS, XPS, ARPES, EXAFS, MCD, MLD(AD) etc.

Half-Metallic Oxide Thin-Films

We are interested in thin-films which are useful for computer disk head sensors and MRAM. Half-metallic materials such as Fe3O4 have one spin type at the Fermi level and hold great promise in devices based on spin-dependent transport. In principle, a spin-dependent conductor can provide enhanced sensitivity to magnetic field. We have focused on thin-films of this oxide grown on Cu substrates, for obvious device-related reasons. Remarkably, our STM studies show that one can grow large oriented crystallites of this material.

We are currently using photoemission at CAMD to further characterize properties of this material.

Magnetic Multilayers
The nature of magnetic coupling between layers of magnetic and non-magnetic materials depends on quantum-well states which couple via the Fermi surfaces of the two materials. We questioned whether bulk Fermi surfaces were relevant in these thin-film systems, and we were surprised at what Ni/Cu(001) revealed! The results of an angle-resolved photoemission study of nickel on copper are available here.

Electronic Structure

Experiment We conduct angle-resolved photoelectron spectroscopy (ARPES) using a display analyzer. This instrument allows us to measure the electronic structure in cross-sectional slices through the Brillouin zone by collecting photoelectron angular distributions. We can compare these directly with theoretical predictions extracted from band structure which we show in our study of the 3d bands of Cu(001). One of our interests is to use the polarization-dependence and dichroism (such as that we see in Co/Cu(001) and Co/Cu(111)) in photoemission to extract more information on the spin variable in the electronic band structure.

Theory We are currently working with Randall Hall (LSU Chem.) using Peter Blaha's WIEN97 LAPW code to calculate electronic band structures using the generalized gradient approximation to the LSDA. This allows us to predict the initial state Fermi Surface coutours that we probe in photoemission. We find that the visualization of these complex 3D beasts is not a trivial matter as in this d-band FS of Ni (this is one of several). We are also using this to help us predict angle-resolved dichroism and the strong polarization dependences that exist in photoemission.

Initial Stages of Oxidation

The initial stages of oxidation of Mg(0001) has alsi been observed with STM. The work, conducted by A. Goonewardene shows that O initially adsorbs and subsequently goes subsurface giving remarkable lumps and bumps. Raju Karunamuni is here with the STM.

Microtomography

Microtomography is one of our latest interests. Although it probes the structure of materials on a larger size scale than the surface work described above, (voxel ~ 2 microns) it has great potential for visualizing the interior of materials. Recently, we have been funded with Les Butler and Frank Cartledge (LSU Chemistry) to construct this instrument at CAMD. Les has done some marvelous work with the instrument design and movies that visualize the interiors of a broad array of materials.