The electronic structure of hematite (001) surfaces: Applications to the interpretation of STM images and heterogeneous surface reactions
- Virginia Polytechnic Institute and State Univ., Blacksburg, VA (United States)
- Pacific Northwest National Lab., Richland, WA (United States)
Scanning tunneling microscope (STM) images and scanning tunneling spectroscopy (STS) spectra of hematite ({alpha}-Fe{sub 2}O{sub 3}) surfaces were calculated using ab-initio methods, not only to interpret experimentally collected STM data, but also to gain insight into atomic level changes in electronic structure that are associated with heterogeneous surface reactions. The electronic structure and wave functions inside the studied crystal were obtained as a periodic solution of the Schroedinger equation by using the program Crystal92. STM images and STS spectra were calculated by applying a technique similar to the Tersoff and Hamann (1985) method. Experimental STM images of the upper valence band of hematite (001) surfaces, cleaved in air, show a periodic array of bright spots that differs slightly from the O-O separation in the bulk. However, our calculations show that these spots are located at the Fe positions of the surface Fe atoms and above the Fe atoms between the first and second hexagonally close-packed O layers. The calculated STS spectra for tip positions above the three non-equivalent Fe positions show significant differences, in particular because the contribution of O 2p-like and Fe 3d-like states changes with the distance between the tip and the respective Fe atom underneath. Hematite crystals that were used to obtain STM images experimentally in previous studies were cleaved in air, and the presence of adsorbed H{sub 2}O and O{sub 2} was considered in this study. Calculations that optimize the surface atomic arrangement with respect to total energy of the slab indicate that H{sub 2}O and O{sub 2} adsorbed to the surface have binding energies too low to withstand the dragging force and the electric potential applied during the scanning process. In addition, only calculations of STM images of fresh hematite surfaces exactly mimic the periodicity of high electronic density spots, as observed in experiments.
- DOE Contract Number:
- FG06-89ER75522
- OSTI ID:
- 569831
- Journal Information:
- American Mineralogist, Vol. 81, Issue 11-12; Other Information: PBD: Nov-Dec 1996
- Country of Publication:
- United States
- Language:
- English
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