Stoichiometric and Oxygen-Terminated
␣-Cr2O3„101̄2… Surfaces
Accession # 00557
Technique: XPS
Host Material: Cr2O3 (101̄2) single
crystal
Mark W. Abee and David F. Cox
Instrument: Leybold-Heraeus
LHS-11
Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
X-ray photoelectron spectroscopy 共XPS兲 spectra are presented for two different preparations of a
Cr2O3共101̄2兲 single crystal surface. A nearly stoichiometric surface is prepared by Ar-ion
bombardment and annealing to 900 K in vacuum. An oxygen-terminated surface is prepared by
dissociative adsorption of O2 . Both surfaces exhibit 共1 ⫻ 1兲 LEED periodicities. XPS shows a slight
broadening 共0.2 eV兲 and an increase in intensity of the O 1s feature following O2 adsorption. The
increase in oxygen signal is representative of a coverage of nearly one oxygen atom per surface Cr
cation. © 2000 American Vacuum Society.
Major Elements in Spectrum: Cr, O
Minor Elements in Spectrum: Ta
Printed Spectra: 8
Spectra in Electronic Record: 9
Spectral Category: comparison
Original Submission: 2/15/2000
Keywords: x-ray photoelectron spectroscopy; single crystal; chromium oxide; Cr2O3
Accepted for Publication:
8/29/2000
PACS: 79.60.Bm, 81.65.Mq, 81.05.Mh
SPECIMEN DESCRIPTION
Host Material: Cr2O3 共101̄2兲 single crystal
CAS Registry #: 1308-38-9
Host Material Characteristics: homogeneous; solid; single crystal; dielectric; inorganic compound; ceramic
Chemical Name: chromium 共III兲 oxide
Source: Earth Jewelry Co., Ltd.
Host Composition: Cr2O3
Form: single crystal
Structure: ␣-Cr2O3 is an electrical insulator with the corundum
structure 共Refs. 1 and 2兲. The bulk chromium coordination
geometry is a distorted octahedron, and oxygen anions are coordinated by a distorted tetrahedral arrangement of cations. In
the corundum structure, one-third of the possible cations sites
are vacant, with the vacancies located along the 共101̄2兲 and
other crystallographically equivalent planes 共Ref. 3兲. The
共101̄2兲 surface is slightly corrugated due to the alternating tilt
of incomplete octahedra relative to the macroscopic 共101̄2兲
plane 共Ref. 3兲.
900 K in ultrahigh vacuum 共Ref. 4兲. An O-terminated surface
was prepared by repeated treatments involving O2 exposures at
163 K and heating in vacuum to 673 K.
Pre-Analysis Beam Exposure: No pre-analysis beam exposure
was used.
Charge Control: It was found that XPS spectra could be collected
from the insulating Cr2O3 共101̄2兲 surface at room temperature
because of uniform steady state charging. To reference the
binding energy scale, short XPS runs were made at a sample
temperature of 900 K where the conductivity of the material is
sufficient to prevent charging. At 900 K, the Cr 2p3/2 binding
energies fall at 576.9⫾0.2 eV for an ion bombarded and 900 K
annealed 共ordered兲 surface. This value is within the range typically attributed to Cr3⫹ in Cr2O3 共Refs. 5, 6, and 7兲.
Temp. During Analysis: 298 K
Pressure During Analysis: ⬍3⫻10⫺8 Pa
INSTRUMENT DESCRIPTION
Manufacturer and Model: Leybold-Heraeus LHS-11
Analyzer Type: spherical sector
Detector: Standard Venetian blind type electron multiplier
History & Significance: Previous characterization work 共Ref. 4兲
has shown that a nearly stoichometric Cr2O3共101̄2兲 surface can
be prepared by ion bombardment and annealing in ultrahigh
vacuum. The results are consistent with a simple nonpolar surface termination giving predominantly five-coordinate Cr3⫹
surface cations. O2 exposures where dissociative adsorption
dominates give an O-terminated surface with a saturation coverage of nearly one oxygen atom per surface Cr3⫹ cation.
INSTRUMENT PARAMETERS COMMON TO ALL
SPECTRA
As Received Condition: As-grown single crystal boule grown by
a flame fusion method.
Excitation Source Window: 1.5 ␮m aluminum window
Number of Detector Elements: 1
䊏 Spectrometer
Analyzer Mode: constant pass energy
Throughput „ T Ä E N …: N⫽⫺1
Analyzed Region: The 共101̄2兲 face of the host material was analyzed.
Excitation Source: Mg K ␣
Ex Situ PreparationÕMounting: A 1 mm thick specimen was cut
from the boule then oriented by Laue backreflection and mechanically polished to within 1° of the 共101̄2兲 surface with a
final grit of 0.25 ␮m diamond. The polished crystal was
mounted on a tantalum holder supported by two 1 mm tantalum
wires connected to copper electrical feedthroughs in a sample
rod manipulator.
Source Strength: 300 W
In Situ Preparation: The nearly stoichiometric 共1 ⫻ 1兲 surface
was prepared by Ar-ion sputtering followed by annealing to
Emission Angle: 0°
Source Energy: 1253.6 eV
Signal Mode: pulse single channel
䊏 Geometry
Incident Angle: 42°
Source to Analyzer Angle: 42°
Specimen Azimuthal Angle: 0°
134 Surface Science Spectra, Vol. 7, No. 2, 2000 1055-5269/2000/7(2)/134/9/$17.00
© 2000 American Vacuum Society
Acceptance Angle from Analyzer Axis: 0°
used for the peak area determinations.
Comments: The ion gun is located in a preparation chamber
adjacent to the anaylsis chamber where the XPS experiments
are performed.
Quantitation Method: Leybold sensitivity factors were used to
determine the approximate compositions for the two different
preparations.
䊏 Ion Gun
ACKNOWLEDGMENTS
Manufacturer and Model: Leybold-Heraeus IQE 10/35
Energy: 2000 eV
We gratefully acknowledge financial support from the DOE Office
of Basic Energy Sciences 共DE-FG02-97ER14751兲.
Current: 8 ␮A
REFERENCES
Current Measurement Method: unbiased stage
Sputtering Species: Ar
Comment: The specimen was Ar-ion bombarded for initial cleaning before producing the ordered surfaces.
DATA ANALYSIS METHOD
Energy Scale Correction: The binding energy scales have been
shifted to align the Cr 2p3/2 peak to 576.9 eV to compensate for
steady state charging. The binding energy scale was referenced
by taking short XPS runs at 900 K where the conductivity of
the material is sufficient to prevent charging 共Ref. 4兲.
Recommended Energy-Scale Shift: A value of ⫺6.25 eV was
added to the binding energy to correct for charging for the
nearly stoichiometric surface 共Accession #s 557-1, 2, 3, 4兲, and
a value of ⫺7.75 eV was added to the O-terminated surface
共Accession #s 557-5, 6, 7, 8兲 to correct for charging.
Peak Shape and Background Method: A linear background was
1. D. Adler, Solid State Phys. 21, 83 共1968兲.
2. R. E. Newnham and Y. M. de Haan, Z. Kristall. 117, 235
共1962兲.
3. V. E. Hendrich and P. A. Cox, in The Surface Science of Metal
Oxides 共Cambridge University, Cambridge, 1994兲, pp. 49–51.
4. Steven C. York, Mark W. Abee, and David F. Cox, Surf. Sci.
437, 386 共1999兲.
5. C. D. Wagner, W. M. Riggs, L. E. Davis, J. F. Moulder, and G.
E. Muilenberg, Handbook of X-Ray Photoelectron Spectroscopy 共Perkin-Elmer, Eden Prairie, MN, 1979兲.
6. J. F. Moulder, W. F. Stickle, P. E. Sobol, K. D. Bomben, and J.
Chastain, Handbook of X-Ray Photoelectron Spectroscopy
共Perkin–Elmer, Eden Prairie, MN, 1992兲.
7. J. S. Foord and R. M. Lambert, Surf. Sci. 169, 327 共1986兲.
8. Anne-Claire Christiaen, Mark W. Abee, and David F. Cox,
Surf. Sci. Spectra 4, 220 共1998兲.
9. Anne-Claire Christiaen, Mark W. Abee, and David F. Cox,
Surf. Sci. Spectra 4, 279 共1998兲.
SPECTRAL FEATURES TABLE
Spectrum
ID #
00557-02a
b
ElementÕ
Transition
Peak
Energy
„eV…
Peak Width
FWHM
„eV…
Peak Area
„ctsÕs…
Sensitivity
Factor
Concentration
„at. %…
Peak
Assignment
Cr 2p 3/2
576.9
3.2
3221
3.0
38.9
¯
00557-03
O 1s
530.8
1.7
2968
0.61
61.1
00557-04
O KLL
742.5
¯
¯
¯
00557-04
Cr LM M
726.4
00557-06a
¯
¯
Cr 2p 3/2
576.9
3.2
3790
3.0
36.8
b
¯
¯
¯
00557-07
O 1s
530.8
1.9
3304
0.61
63.2
00557-08
O KLL
742.7
¯
¯
¯
¯
00557-08
Cr LM M
726.6
¯
¯
¯
¯
¯
¯
¯
¯
¯
¯
¯
a
The Cr sensitivity factor is for the integrated area under the Cr 2p1/2 and 2p3/2 transitions.
Steady state charging of Cr2O3 shifts the O 1s line more than 6 eV from tantalum oxide or adsorbed oxygen from the conductive holder. Hence,
the oxygen concentration originates from Cr2O3 alone.
b
Footnote to Spectrum 00557-01: Survey spectrum for the nearly stoichiometric surface prepared by ion bombardment and annealing to 900
K in ultrahigh vacuum. A small Ta signal from the sample holder can also be observed.
Footnote to Spectrum 00557-04: O KLL and Cr LMM regions for the nearly stoichiometric surface prepared by ion bombardment and
annealing to 900 K in ultrahigh vacuum.
Footnote to Spectrum 00557-05: Survey spectrum for the O-terminated surface prepared by repeated exposures to O2 in ultrahigh vacuum.
A small Ta signal from the holder can also be observed.
Surface Science Spectra, Vol. 7, No. 2, 2000
␣-Cr2O3(101̄2) by XPS
135
ANALYZER CALIBRATION TABLE
Spectrum
ID #
¯
ElementÕ
Transition
Peak
Energy
„eV…
Peak Width
FWHM
„eV…
Peak Area
„ctsÕs…
Sensitivity
Factor
Concentration
„at. %…
Peak
Assignment
Ag 3d 5/2
368.1
1.06
¯
¯
¯
¯
Comment to Analyzer Calibration Table: 60 eV pass energy.
GUIDE TO FIGURES
Spectrum
„Accession… #
Spectral
Region
Sample
Voltage*
Multiplier
Baseline
Comment #
557-1
Survey
⫹6.25
1
0
1
557-2
Cr 2p
⫹6.25
1
0
1
557-3
O 1s
⫹6.25
1
0
1
557-4
O KLL/Cr LMM
⫹6.25
1
0
1
557-5
Survey
⫹7.75
1
0
2
557-6
Cr 2p
⫹7.75
1
0
2
557-7
O 1s
⫹7.75
1
0
2
557-8
O KLL/Cr LMM
⫹7.75
1
0
2
Ag 3d 5/2
0
1
0
3
557-9 †NP‡**
*Inferred sample potential relative to spectrometer ground due to charging, flood gun, or other phenomena.
**[NP] signifies not published; digital spectra are archived in SSS database but not reproduced in the printed journal.
1. Stoichiometric surface.
2. O-terminated surface.
3. Calibration spectrum.
136
Surface Science Spectra, Vol. 7, No. 2, 2000
␣-Cr2O3(101̄2) by XPS
Accession #
00557-01
Host Material
Cr2O3 共101̄2兲 single crystal
Technique
Spectral Region
Instrument
Excitation Source
Source Energy
Source Strength
Source Size
XPS
survey
Leybold-Heraeus LHS-11
Mg K ␣
1253.6 eV
300 W
not specified
Analyzer Type
spherical sector
Incident Angle
42°
Emission Angle
0°
Analyzer Pass Energy
200 eV
Analyzer Resolution
2.10 eV
Total Signal Accumulation Time
6880 s
Total Elapsed Time
Number of Scans
Comment
Surface Science Spectra, Vol. 7, No. 2, 2000
not specified
40
See footnote below the Spectral Features Table.
␣-Cr2O3(101̄2) by XPS
137
䊏 Accession #: 00557-02
䊏 Host Material: Cr2O3 (101̄2)
single crystal
䊏 Technique: XPS
䊏 Spectral Region: Cr 2 p
Instrument: Leybold-Heraeus
LHS-11
Excitation Source: Mg K ␣
Source Energy: 1253.6 eV
Source Strength: 300 W
Source Size: not specified
Incident Angle: 42°
Analyzer Type: spherical sector
Analyzer Pass Energy: 60 eV
Analyzer Resolution: 1.06 eV
Emission Angle: 0°
Total Signal Accumulation Time:
7200 s
Total Elapsed Time: not specified
Number of Scans: 40
Comment: Cr 2p region for the
nearly stoichiometric surface
prepared by ion bombardment and
annealing to 900 K in ultrahigh
vacuum.
䊏 Accession #: 00557-03
䊏 Host Material: Cr2O3 (101̄2)
single crystal
䊏 Technique: XPS
䊏 Spectral Region: O 1 s
Instrument: Leybold-Heraeus
LHS-11
Excitation Source: Mg K ␣
Source Energy: 1253.6 eV
Source Strength: 300 W
Source Size: not specified
Incident Angle: 42°
Analyzer Type: spherical sector
Analyzer Pass Energy: 60 eV
Analyzer Resolution: 1.06 eV
Emission Angle: 0°
Total Signal Accumulation Time:
7200 s
Total Elapsed Time: not specified
Number of Scans: 40
Comment: O 1s region for the
nearly stoichiometric surface
prepared by ion bombardment and
annealing to 900 K in ultrahigh
vacuum.
138
Surface Science Spectra, Vol. 7, No. 2, 2000
␣-Cr2O3(101̄2) by XPS
䊏 Accession #: 00557-04
䊏 Host Material: Cr2O3 (101̄2)
single crystal
䊏 Technique: XPS
䊏 Spectral Region: O KLL ;
Cr LMM
Instrument: Leybold-Heraeus
LHS-11
Excitation Source: Mg K ␣
Source Energy: 1253.6 eV
Source Strength: 300 W
Source Size: not specified
Incident Angle: 42°
Analyzer Type: spherical sector
Analyzer Pass Energy: 60 eV
Analyzer Resolution: 1.06 eV
Emission Angle: 0°
Total Signal Accumulation Time:
9600 s
Total Elapsed Time: not specified
Number of Scans: 40
Comment: See footnote below the
Spectral Features Table.
Surface Science Spectra, Vol. 7, No. 2, 2000
␣-Cr2O3(101̄2) by XPS
139
Accession #
00557-05
Host Material
Cr2O3 共101̄2兲 single crystal
Technique
Spectral Region
Instrument
Excitation Source
Source Energy
Source Strength
Source Size
XPS
survey
Leybold-Heraeus LHS-11
Mg K ␣
1253.6 eV
300 W
not specified
Analyzer Type
spherical sector
Incident Angle
42°
Emission Angle
0°
Analyzer Pass Energy
200 eV
Analyzer Resolution
2.10 eV
Total Signal Accumulation Time
6880 s
Total Elapsed Time
Number of Scans
Comment
140
Surface Science Spectra, Vol. 7, No. 2, 2000
not specified
40
See footnote below the Spectral Features Table.
␣-Cr2O3(101̄2) by XPS
䊏 Accession #: 00557-06
䊏 Host Material: Cr2O3 (101̄2)
single crystal
䊏 Technique: XPS
䊏 Spectral Region: Cr 2 p
Instrument: Leybold-Heraeus
LHS-11
Excitation Source: Mg K ␣
Source Energy: 1253.6 eV
Source Strength: 300 W
Source Size: not specified
Incident Angle: 42°
Analyzer Type: spherical sector
Analyzer Pass Energy: 60 eV
Analyzer Resolution: 1.06 eV
Emission Angle: 0°
Total Signal Accumulation Time:
7200 s
Total Elapsed Time: not specified
Number of Scans: 40
Comment: Cr 2p region for the
O-terminated surface prepared by
exposure to O2 in ultrahigh
vacuum.
Surface Science Spectra, Vol. 7, No. 2, 2000
␣-Cr2O3(101̄2) by XPS
141
䊏 Accession #: 00557-07
䊏 Host Material: Cr2O3 (101̄2)
single crystal
䊏 Technique: XPS
䊏 Spectral Region: O 1 s
Instrument: Leybold-Heraeus
LHS-11
Excitation Source: Mg K ␣
Source Energy: 1253.6 eV
Source Strength: 300 W
Source Size: not specified
Incident Angle: 42°
Analyzer Type: spherical sector
Analyzer Pass Energy: 60 eV
Analyzer Resolution: 1.06 eV
Emission Angle: 0°
Total Signal Accumulation Time:
7200 s
Total Elapsed Time: not specified
Number of Scans: 40
Comment: O 1s region for the
O-terminated surface prepared by
repeated exposure to O2 in
ultrahigh vacuum.
䊏 Accession #: 00557-08
䊏 Host Material: Cr2O3 (101̄2)
single crystal
䊏 Technique: XPS
䊏 Spectral Region: O KLL ;
Cr LMM
Instrument: Leybold-Heraeus
LHS-11
Excitation Source: Mg K ␣
Source Energy: 1253.6 eV
Source Strength: 300 W
Source Size: not specified
Incident Angle: 42°
Analyzer Type: spherical sector
Analyzer Pass Energy: 60 eV
Analyzer Resolution: 1.06 eV
Emission Angle: 0°
Total Signal Accumulation Time:
6240 s
Total Elapsed Time: not specified
Number of Scans: 26
Comment: O KLL and Cr LMM
regions for the O-terminated
surface prepared by repeated
exposures to O2 in ultrahigh
vacuum.
142
Surface Science Spectra, Vol. 7, No. 2, 2000
␣-Cr2O3(101̄2) by XPS