The structure of hematite [001] surfaces by scanning tunneling microscopy: Image interpretation, surface relaxation, and step structure

Journal Article · · American Mineralogist; (United States)

OSTI ID:6893443

Eggleston, C M; Hochella, Jr, M F ^[1]

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1. 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), Journal Name: American Mineralogist; (United States) Vol. 77:9-10; ISSN AMMIAY; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602 -- Other Materials-- Structure & Phase Studies
58 GEOSCIENCES
580000* -- Geosciences
CRYSTAL FACES
CRYSTAL STRUCTURE
DISTANCE
HEMATITE
INTERATOMIC DISTANCES
IRON ORES
MICROSCOPY
MINERALS
MOLECULAR STRUCTURE
OPTICAL MICROSCOPY
ORES
OXIDE MINERALS
SURFACE PROPERTIES
VARIATIONS