The electronic structure of hematite {001} surfaces; applications to the interpretation of STM images and heterogeneous surface reactions

Abstract

Other| December 01, 1996 The electronic structure of hematite {001} surfaces; applications to the interpretation of STM images and heterogeneous surface reactions Udo Becker; Udo Becker Virginia Polytechnic Institute and State University, Department of Geological Sciences, Blacksburg, VA, United States Search for other works by this author on: GSW Google Scholar Michael F. Hochella; Michael F. Hochella Search for other works by this author on: GSW Google Scholar Edoardo Apra Edoardo Apra Search for other works by this author on: GSW Google Scholar Author and Article Information Udo Becker Virginia Polytechnic Institute and State University, Department of Geological Sciences, Blacksburg, VA, United States Michael F. Hochella Edoardo Apra Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online Issn: 1945-3027 Print Issn: 0003-004X Copyright © 1996 by the Mineralogical Society of America American Mineralogist (1996) 81 (11-12): 1301–1314. https://doi.org/10.2138/am-1996-11-1201 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Udo Becker, Michael F. Hochella, Edoardo Apra; The electronic structure of hematite {001} surfaces; applications to the interpretation of STM images and heterogeneous surface reactions. American Mineralogist 1996;; 81 (11-12): 1301–1314. doi: https://doi.org/10.2138/am-1996-11-1201 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Scanning tunneling microscope (STM) images and scanning tunneling spectroscopy (STS) spectra of hematite (α-Fe2O3) 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 Schrödinger 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 nonequivalent 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 H2O and O2 was considered in this study. Calculations that optimize the surface atomic arrangement with respect to total energy of the slab indicate that H2O and O2 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.STS spectra calculated for equivalent Fe positions on terraces and near steps show the increased electron density of the top of the valence band for step sites, which is experimentally observed as higher intensities of bright spots at steps.These calculations show that the local electronic structure of surfaces can be very different from bulk electronic properties and that conclusions drawn from cluster calculations representing the bulk can be misleading. In addition, this theoretical approach helps to explain the increased reactivity at specific sites on hematite, such as steps and kinks, in terms of the electronic surface structure of this mineral. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.