The structure of hematite [001] surfaces by scanning tunneling microscopy: Image interpretation, surface relaxation, and step structure
- Stanford Univ., CA (United States)
Scanning tunneling microscopy (STM) is used to study the structure of [001] hematite single-crystal surfaces. STM images taken at negative sample bias consistently show a hexagonal array of atomic sites with 3-[angstrom] periodicity, as expected for the surface O array and in agreement with photoelectron spectroscopy studies of hematite surfaces after O[sub 2] and H[sub 2]O exposure which show that states at the top of the valence band have O character. Molecular orbital calculations suggest that these states are localized on O sites. In contrast, STM images taken at positive sample bias were variable, sometimes showing hexagonal arrays with O periodicity and sometimes showing arrays with equivalent Fe periodicity. With the above findings in mind, the authors used negative bias images to study relaxation of O positions on the hematite [001] surface. Surface O positions are apparently relaxed to a regularized hexagonal array with a single-mode distribution of O-O interatomic distances; in the equivalent bulk plane, O-O distances form a bimodal distribution because of distortion by octahedral face sharing across the (001) plane. STM images also show that step densities on hematite [001] fracture surfaces are high, often one step every 20-30 [angstrom]. The atomic structure near step edges appears to be reconstructed relative to terraces, but convolution of atomic and electronic structure information in STM images makes precise interpretation of step structure difficult.
- OSTI ID:
- 6893443
- Journal Information:
- American Mineralogist; (United States), Vol. 77:9-10; ISSN 0003-004X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
HEMATITE
CRYSTAL FACES
MOLECULAR STRUCTURE
CRYSTAL STRUCTURE
INTERATOMIC DISTANCES
OPTICAL MICROSCOPY
SURFACE PROPERTIES
VARIATIONS
DISTANCE
IRON ORES
MICROSCOPY
MINERALS
ORES
OXIDE MINERALS
580000* - Geosciences
360602 - Other Materials- Structure & Phase Studies