Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED)

Details Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED)

Jun 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991gecoa..55.1723s&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 55, Issue 6, pp.1723-1736

Physics

35

Scientific paper

The pure calcite surface was examined using techniques sensitive to the near-surface (XPS and LEED) immediately after fracture in ultra-high vacuum (10 -10 mbar) and then following exposure to various atmospheres and aqueous solutions that were free of trace metals. These spectroscopic techniques allow molecular-level observations that offer the possibility of gaining more insight into geochemical processes elucidated from macroscopic solution studies. Several absolute electron binding energies for the atoms in calcite were redetermined with XPS using the gold dot method. The results are 290.1 ± 0.1 eV for C 1 s , 347.7 and 351.2 ± 0.15 eV for and , respectively, and 531.9 ± 0.15 eV for O 1 s . Photoelectron energy shifts from main peak positions suggest that immediately after fracture in ultra-high vacuum, bond reconfiguration leads to the formation of carbide-like bonds between Ca and C at the surface. Calcite that has been exposed to water, even as vapour from the atmosphere, shows binding energy shifts that indicate the presence of S · CO 3 H and S · CaOH where S · represents the calcite surface. Surface hydration is also supported, independently, by the XPS peak intensity ratios and is consistent with adsorption theory derived from macroscopic solution studies. The modified oxygen Auger parameter, ', (using O 1 s and O(KVV)), was found to be 1043.9 eV for all samples of calcite tested, whether powder or cleaved from Iceland Spar, clean or contaminated by adventitious carbon, freshly fractured, or exposed briefly to water, or in the process of dissolution or precipitation. LEED patterns of the {101} cleavage surface of samples that were freshly fractured in air and that were exposed to dissolving or precipitating solutions showed that the top few atomic layers exhibit long range order. Lattice spacings at the surface are statistically identical to those of bulk calcite, though some surface CO 3 groups may be rotated relative to the bulk structure. This work provides direct, molecular-level evidence for the processes of reconfiguration and hydration at the calcite surface. These results provide a basis for future spectroscopic studies of trace metal adsorption on calcite and subsequent solid-solution formation.

Affiliated with

Also associated with

No associations

Rating

Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED), we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1283257