Current Research

    Professor Langell's research focuses on the surface properties of transition metal oxides (TMO) and other metal compounds. Single crystal substrates are studied to elucidate their surface structure and gas adsorption properties. Recently, mixed metal oxides and oxide solid solutions have been investigated both in thin film epitaxy and polycrystalline form. Work is also underway to model several types of TMO surface defects in a quantitative and characterizable manner.
TMOs are ubiquitous in nature and their gas adsorption properties are relevant to a range of heterogeneous properties. These include catalysis, environmental chemistry and chemical remediation, materials science and a number of device applications. The surface properties are studied by a variety of surface sensitive techniques, including high resolution electron energy loss spectroscopy (HREELS), photoemission (XPS, UPS), low energy electron diffraction (LEED), thermal desorption mass spectrometry (TDS), electron stimulated desorption (ESD), secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES).
The rocksalt (MO, M = MnO, FeO, NiO and CoO), spinel (M₃O₄, M = Mn, Fe, Ni, Co) and corundum (M₂O₃, M = Mn, Fe) 3d TMOs are emphasized in the single crystal work. Solid solution surface chemistry involves two or more of these materials in both single crystal and polycrystalline form. With the exception of nickel, the cations in these materials have been shown to readily inter-convert oxidation states, an important atomic-level mechanism for solid-state partial oxidation reactions. Use of HREELS in TMO adsorbate analysis requires the application of deconvolution procedures, several of which are presently under development in this laboratory. Surface hydroxylation, a ubiquitous phenomenon for TMOs at ambient conditions, is being probed for its influence on TMO redox properties and as a controlling feature in a wide range of gas adsorption phenomena. Finally, vicinally-cut "stepped" TMO surfaces are being used to model low-coordination defects, and by correlation of adsorption characteristics with step width, the information is used for quantitative determination of the relative importance of terrace and edge adsorbate sites in TMO gas adsorption properties.

Recent Key Publications

E. M. Malone, S. C.Pettito and M. A. Langell, “Fuchs-Kliewer Phonon Spectrum of Co₃O₄(110) Single Crystal Surfaces by High Resolution Electron Energy Loss Spectroscopy”, Solid State Comm. 130 9, 571-575 (2004).

D. L. Pugmire, C. M. Woodbridge, N. M. Boag and M. A. Langell, “Adsorption and Decomposition of Nickelocene on Ag(100): A HREELS and TPD Study”, Surface Sci. 472, 155-171 (2001).

M. A. Langell, J. G. Kim, D. L. Pugmire and W. McCarroll, “The Nature of Oxygen at Rocksalt and Spinel Oxide Surfaces”, J. Vac. Sci. Technol. 19(4), 1977-1982 (2001).

M. A. Langell, F. Gevrey and M.W. Nydegger, “Surface Composition of Mn_xCo_1-xO Solid Solutions by X -ray Photoelectron and Auger Spectroscopies”, Appl. Surface Sci. 153, 114-127 (2000).

Recent Graduates and Current Affiliations

· Cynthia M. Woodbridge, Ph.D. 2002, Assistant Professor of Chemistry, Hillsdale College, Hillsday, MI.
· David L. Pugmire, Ph.D. 2000, Staff Scientist, Los Alamos National Laboratory, Los Alamos, NM.
· Michael W. Nydegger, MS. 1999, Lecturer, Butler Community College, Butler, KS.