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The goal of this project is to increase our understanding of the interaction of hydrocarbons with aluminum-based alloys, including the complex metallic alloys that are very close in structure to quasicrystals. The motivation for these studies comes from the earlier observations for quasicrystalline surfaces that they have a low coefficient of friction, and might demonstrate superlubricity. Since quasicrystalline or quasicrystalline materials are being used as low-friction coatings in machines, it is important to understand how the interaction of typical lubricants (hydorcarbons) affects the frictional properties of the alloy surfaces. The methods to be employed are low-energy electron diffraction (LEED) and temperature-programmed desorption.

Our approach to this project has several parallel components. First, one set of experiments will be carried out on the complex Al13Co4(100) surface, which approximates the structure and compositions of the 10-fold surface of the AlNiCo quasicrystal. Earlier computer simulation studies have suggested that there is no ordering for the short alkanes on this quasicrystal surface, an indication that the superlubricity may be preserved in the presence of at least some hydrocarbons.

We have obtained a crystal of this complex metallic alloy from the University of Munich. This surface has never been characterized, and therefore our first studies are to characterize this surface using low-energy electron diffraction. We have taken the experimental data for this, and have extracted the necessary intensities for the analysis, and we have sent the data to our collaborator, Katariina Pussi at Lappeenranta University of Technology for analysis. The reason for not doing the analysis in-house is that when this structure is solved, it will be the most complex clean surface structure ever determined using LEED. The computational requirements exceed our own resources. It is expected that the analysis will be complete in a few months.

In the meantime, as a prelude to studying the interactions of hydrocarbons with this surface, we have begun by setting a benchmark using Xe adsorption. We have carried out adsorption isobars using LEED, and have also observed the diffraction from one monolayer of Xe on this surface. The Xe appears to form a higher-order commensurate structure, and we are in the process of analyzing that structure. We would like to extend these studies to a smaller gas, probably Ar or Kr, in order to test the effect of size on the ordering. Following these studies, we will begin our structural studies of the hydrocarbons on this surface.

When we have the structure analysis complete for the Al13Co4(100) surface, we will be able to construct model potentials for the rare gases and alkanes on this surface and to carry out adsorption simulations using the same methods employed earlier by Curtarolo's group at Duke University.

In parallel with these studies, we are studying the thermal desorption spectra of hydrocarbons from Al(111) and AlNi(100) surfaces, as a prelude to carrying out the same studies on the complex alloy. These studies have required building a new sample holder and electronics, and are in progress.