Research Overview

Our research focuses on determining the electronic properties of surfaces, interfaces, ultrathin films and nanoscale structures using a number of experimental approaches. Our work spans a wide range of materials systems from simple metals to complex oxides. Current projects include studying fundamental aspects of organic molecule adsorption on crystalline oxide and metal surfaces for photovoltaics and organic electronics; probing the electronic structure and morphology of transition metal oxyfluorides for energy storage applications; investigating structure-reactivity relationships of gas-phase reactions catalized at nanofaceted surfaces; exploring the role of radiation-induced reactions in materials that are candidates for resists in extreme ultraviolet lithography; and exploring energy and momentum correlations between coincident pairs of photoemitted electrons. 

We use a variety of techniques to perform these studies including high-resolution and angle resolved photoemission spectroscopy, inverse photoemission spectroscopy using a newly developed grating spectrograph, the novel technique of Auger-photoelectron coincidence spectroscopy (APECS) with synchrotron radiation (which was developed in our labs), and a variety of scanning probe techniques including variable temperature STM and AFM.

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       Recent Highlight

Lithiation of Epitaxial CoO(111) Thin Films
In lithium-ion conversion batteries, CoO reacts with Li to produce two electrons:

2Li+ + 2e- + CoO ↔ Li2O + Co0

To simulate the discharge of a conversion battery in a well-controlled environment CoO(111) thin films have been grown and exposed to atomic lithium in UHV. STM revealed triangular features originating at step edges and defects on the CoO surface upon lithiation, as seen in the figure on the left. These features are attributed to the epitaxial growth of a monolayer of Li2O(111) on the oxygen-terminated CoO(111) surface. The lateral size of these features increased as a function of Li exposure until they covered the CoO surface.

Upon subsequent Li exposures, angle-resolved XPS measurements of the Co:CoO ratio suggested that the Li-CoO reaction continued in a layer-by-layer fashion, consuming each layer of O. The plot on the left shows ARXPS data (black dots) corresponding to three different lithium coverages and the associated fits (red lines) which assume a uniformly thick overlayer of Li2O + CoO or an overlayer in which 10% of the CoO is unreacted.

       Recent Publications