Surface Defects and Self-Diffusion on Pyrite {100}: an Ultra-High Vacuum Scanning Tunneling Microscopy and Theoretical Modeling Study
A variety of defects on {100} cleavage surfaces of pyrite (FeS2) are observed directly using ultra high vacuum scanning tunneling microscopy. Step edges are aligned along <10> and <11> surface directions. Atomic scale images indicate that the atomic structure, with a respect to the Fe lattice, and local density of occupied states is unchanged at a step edge, including kink and corner sites. The inferred presence of monosulfides at step edges, based on X-ray photoelectron spectra on similar surfaces elsewhere, does not lead to occupied states higher in energy that dz2 dangling bond states at Fe sites. A sequence of consecutive images at the atomic scale captured evidence of dynamic structural changes at defects on this surface at room temperature. Step edges are seen to be generally stable over the course of the STM observations, whereas vacancies, their surrounding sites, and corner step edge sites are not. Theoretical maps of the attachment energy for an Fe adatom over a {100} surface cell indicate the presence of low energy diffusion channels along the topology of the closest S atoms in the uppermost atomic S monolayer. Calculation of the activation energy barriers for the self-diffusion of an Fe adatom over a {100} terrace predict low 0.1 eV diffusion barriers along channels and 0.24 eV across channels. Subsequently, calculated Fe adatom mobilities over the time scale of the STM observations are very high, ranging from 105-106 ? over the course of one minute, calculated for room temperature and depending on the diffusion direction. The structural changes documented in the STM images are explained as resulting from the natural process of surface self-diffusion.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1012325
- Report Number(s):
- PNNL-SA-32460; AMMIAY; KC0303020
- Journal Information:
- American Mineralogist, 85:1428-1436, Vol. 85, Issue 10; ISSN 0003-004X
- Country of Publication:
- United States
- Language:
- English
Similar Records
In Situ Studies of Surface Mobility on Noble Metal Model Catalysts Using STM and XPS at Ambient Pressure
Atomic-scale dynamics of atoms and dimers on the Si(001) surface