2D topological insulator bismuth selenide analyzed by in situ XPS

Wang, Xinglu; Smyth, Christopher M.; Khosravi, Ava; Cormier, Christopher R.; Shallenberger, Jeffrey R.; Addou, Rafik; Wallace, Robert M.

doi:10.1116/1.5130891

Bismuth selenide (Bi₂Se₃), a two-dimensional topological insulator material purchased from Alfa Aesar, was analyzed using in situ x-ray photoelectron spectroscopy (XPS). The XPS spectra obtained from a fresh surface exfoliated in ultrahigh vacuum include a survey scan, high resolution spectra of O 1s, Bi 5d, Se 3d, Bi 4f, Se 3p, Se LMM, C 1s, and the valence band. Quantitative analysis indicates a Se deficient surface composition of Bi₂Se_2.8, which is consistent with the Fermi level position in the conduction band detected in this work.

Accession #: 01613
Technique: XPS, XAES
Host Material: Bi₂Se₃ single crystal
Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Major Elements in Spectra: Bi, Se
Minor Elements in Spectra: C
Published Spectra: 7
Spectra in Electronic Record: 7
Spectral Category: Comparison

INTRODUCTION

Topological insulators (TIs), such as Bi₂Se₃, exhibit topologically protected surface/edge states, making TIs attractive, defect-tolerant materials for applications in spintronics and quantum computing (Ref. 1). Bi₂Se₃ is characterized by a layered structure, in which each layer includes five layers of Se and Bi atoms that are stacked alternately with Se atoms on the top and bottom (Ref. 2). Neighboring Bi₂Se₃ layers are bound by the weak van der Waals force. In this study, a bulk Bi₂Se₃ single crystal purchased from Alfa Aesar was exfoliated under ultrahigh vacuum (UHV) conditions and subsequently characterized in situ in a UHV cluster tool using x-ray photoelectron spectroscopy (XPS) (Ref. 3).

SPECIMEN DESCRIPTION (ACCESSION #01613)

Host Material: Bi₂Se₃ single crystal

CAS Registry #: 12068-69-8

Host Material Characteristics: Homogeneous; solid; single crystal; semiconductor; inorganic compound; other

Chemical Name: Bismuth selenide; dibismuth triselenide

Source: Alfa Aesar

Host Composition: Bi₂Se₃

Form: Single crystal

Structure: Rhombohedral

History and Significance: Bi₂Se₃ crystal is fixed to a sample holder by carbon tape. UltraTape® polyethylene low adhesion cleanroom tape is used for in situ exfoliation under UHV conditions.

As Received Condition: Lateral size of ∼0.1–0.8 cm, metallic in appearance

Analyzed Region: In situ exfoliated host material

Ex Situ Preparation/Mounting: The host was mounted on carbon tape affixed to a clean molybdenum holder.

In Situ Preparation: In situ exfoliation under UHV conditions

Charge Control: None

Temp. During Analysis: 300 K

Pressure During Analysis: 1 × 10⁻⁷Pa

Preanalysis Beam Exposure: ∼200 s

INSTRUMENT DESCRIPTION

Manufacturer and Model: Scienta Omicron Custom Design 035008 Wafer Analysis Module

Analyzer Type: Spherical sector

Detector: Channeltron

Number of Detector Elements: 7

INSTRUMENT PARAMETERS COMMON TO ALL SPECTRA

Spectrometer

Analyzer Mode: Constant pass energy

Throughput (T = E^N): N = −1

Excitation Source Window: Not specified

Excitation Source: Al K_α monochromatic

Source Energy: 1486.7 eV

Source Strength: 500 W

Source Beam Size: 1400 × 1400 μm²

Signal Mode: Multichannel direct

Geometry

Incident Angle: 45°

Source-to-Analyzer Angle: 90°

Emission Angle: 45°

Specimen Azimuthal Angle: 0°

Acceptance Angle from Analyzer Axis: 0°

Analyzer Angular Acceptance Width: 8° × 8°

Ion Gun

Manufacturer and Model: ULVAC-PHI FIG-5CE

Energy: 1000 eV

Current: 0.001 mA

Current Measurement Method: Biased stage

Sputtering Species: Ar⁺

Spot Size (unrastered): 150 μm

Raster Size: 10 000 × 10 000 μm²

Incident Angle: 50°

Polar Angle: 37°

Azimuthal Angle: 135°

Comment: Sputtering was performed using a differentially pumped ion gun to obtain the energy calibration spectra only.

DATA ANALYSIS METHOD

Energy Scale Correction: The energy scale was calibrated using sputter-cleaned Au, Ag, and Cu foils, as is described in ASTM E2108 (Ref. 4).

Recommended Energy Scale Shift: 0

Peak Shape and Background Method: Peak shape: All the peaks are fitted using a Gaussian-Lorentzian product formula. Background: A hybrid Shirley-Sherwood/Slope/Shirley-Vegh-Salvi-Castle background embedded in AAnalyzer® was used on the Bi 5d and Se 3d regions. A hybrid Shirley-Sherwood/Shirley-Vegh-Salvi-Castle background was used on the Bi 4f and Se 3p regions (Ref. 5). Peak fit residuals are shown in Spectra 3b, 4b, and 5b.

Quantitation Method: The sensitivity factors employed to calculate relevant atomic ratios are supplied by Physical Electronics.

SPECTRAL FEATURES TABLE

Spectrum ID #	Element/Transition	Peak Energy (eV)	Peak Width FWHM (eV)	Peak Area (eV × counts/s)	Sensitivity Factor	Concentration (at. %)	Peak Assignment
01613-02	O 1s	…	…	…	…	…	…
01613-03	Bi 5d	…	…	1377.1	1.259	38.5	…
01613-03	Bi 5d_5/2	25.0	0.68	…	…	…	Bi₂Se₃
01613-03	Bi 5d_3/2	28.1	0.71	…	…	…	Bi₂Se₃
01613-04	Se 3d	…	…	1117.7	0.722	54.4	…
01613-04	Se 3d_5/2	53.5	0.65	…	…	…	Bi₂Se₃
01613-04	Se 3d_3/2	54.4	0.67	…	…	…	Bi₂Se₃
01613-05	Bi 4f_7/2	158.0	0.63	6497.6	…	…	Bi₂Se₃
01613-05	Bi 4f_5/2	163.3	0.64	4873.2	…	…	Bi₂Se₃
01613-05	Se 3p_3/2	159.8	1.74	759.2	…	…	Bi₂Se₃
01613-05	Se 3p_1/2	165.5	1.74	379.6	…	…	Bi₂Se₃
01613-06	Se LMM	282.4	4.83	911.9	…	…	Bi₂Se₃
01613-06	C 1s	…	…	60.0	0.296	7.1	…
01613-06	C 1s	283.8	0.91	…	…	…	C species
01613-06	Se LMM	295.2	3.54	948.2	…	…	Bi₂Se₃
01613-07	VB1	1.3	…	…	…	…	Bi₂Se₃
01613-07	VB2	3.1	…	…	…	…	Bi₂Se₃
01613-07	VBM	0.62	…	…	…	…	Bi₂Se₃

Spectrum ID #	Element/Transition	Peak Energy (eV)	Peak Width FWHM (eV)	Peak Area (eV × counts/s)	Sensitivity Factor	Concentration (at. %)	Peak Assignment
01613-02	O 1s	…	…	…	…	…	…
01613-03	Bi 5d	…	…	1377.1	1.259	38.5	…
01613-03	Bi 5d_5/2	25.0	0.68	…	…	…	Bi₂Se₃
01613-03	Bi 5d_3/2	28.1	0.71	…	…	…	Bi₂Se₃
01613-04	Se 3d	…	…	1117.7	0.722	54.4	…
01613-04	Se 3d_5/2	53.5	0.65	…	…	…	Bi₂Se₃
01613-04	Se 3d_3/2	54.4	0.67	…	…	…	Bi₂Se₃
01613-05	Bi 4f_7/2	158.0	0.63	6497.6	…	…	Bi₂Se₃
01613-05	Bi 4f_5/2	163.3	0.64	4873.2	…	…	Bi₂Se₃
01613-05	Se 3p_3/2	159.8	1.74	759.2	…	…	Bi₂Se₃
01613-05	Se 3p_1/2	165.5	1.74	379.6	…	…	Bi₂Se₃
01613-06	Se LMM	282.4	4.83	911.9	…	…	Bi₂Se₃
01613-06	C 1s	…	…	60.0	0.296	7.1	…
01613-06	C 1s	283.8	0.91	…	…	…	C species
01613-06	Se LMM	295.2	3.54	948.2	…	…	Bi₂Se₃
01613-07	VB1	1.3	…	…	…	…	Bi₂Se₃
01613-07	VB2	3.1	…	…	…	…	Bi₂Se₃
01613-07	VBM	0.62	…	…	…	…	Bi₂Se₃

ANALYZER CALIBRATION TABLE

Spectrum ID #	Element/Transition	Peak Energy (eV)	Peak Width FWHM (eV)	Peak Area (eV × counts/s)	Sensitivity Factor	Concentration (at. %)	Peak Assignment
…	Au 4f	83.9	0.73	26 358.3	…	…	…
…	Ag 3d	368.1	0.57	32 184.6	…	…	…
…	Cu 2p_1/2	932.2	0.88	29 998.7	…	…	…

Spectrum ID #	Element/Transition	Peak Energy (eV)	Peak Width FWHM (eV)	Peak Area (eV × counts/s)	Sensitivity Factor	Concentration (at. %)	Peak Assignment
…	Au 4f	83.9	0.73	26 358.3	…	…	…
…	Ag 3d	368.1	0.57	32 184.6	…	…	…
…	Cu 2p_1/2	932.2	0.88	29 998.7	…	…	…

GUIDE TO FIGURES

Spectrum (Accession) #	Spectral Region	Multiplier	Comment #^b
01613-01	Survey	1	1
01613-02	O 1s	1	1
01613-03	Bi 5d	1	1
01613-04	Se 3d	1	1
01613-05	Bi 4f, Se 3p	1	1
01613-06	Se LMM, C 1s	1	1
01613-07	Valence band	1	1

Spectrum (Accession) #	Spectral Region	Multiplier	Comment #^b
01613-01	Survey	1	1
01613-02	O 1s	1	1
01613-03	Bi 5d	1	1
01613-04	Se 3d	1	1
01613-05	Bi 4f, Se 3p	1	1
01613-06	Se LMM, C 1s	1	1
01613-07	Valence band	1	1

^a

No voltage shift applied.

^b

Bi₂Se₃ single crystal.

. Accession #:01613-01Host Material:Bi2Se3Technique:XPSSpectral Region:SurveyInstrument:Scienta Omicron Custom Design 035008 Wafer Analysis ModuleExcitation Source:Al Kα monochromaticSource Energy:1486.7 eVSource Strength:500 WSource Size:1.4 × 1.4 mm2Analyzer Type:Spherical sector analyzerIncident Angle:45°Emission Angle:45°Analyzer Pass Energy:50 eVAnalyzer Resolution:2.1 eVTotal Signal Accumulation Time:837 sTotal Elapsed Time:861 sNumber of Scans:3Effective Detector Width:5.9 eV

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Accession #:	01613-01
Host Material:	Bi₂Se₃
Technique:	XPS
Spectral Region:	Survey
Instrument:	Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source:	Al K_α monochromatic
Source Energy:	1486.7 eV
Source Strength:	500 W
Source Size:	1.4 × 1.4 mm²
Analyzer Type:	Spherical sector analyzer
Incident Angle:	45°
Emission Angle:	45°
Analyzer Pass Energy:	50 eV
Analyzer Resolution:	2.1 eV
Total Signal Accumulation Time:	837 s
Total Elapsed Time:	861 s
Number of Scans:	3
Effective Detector Width:	5.9 eV

Accession #:	01613-01
Host Material:	Bi₂Se₃
Technique:	XPS
Spectral Region:	Survey
Instrument:	Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source:	Al K_α monochromatic
Source Energy:	1486.7 eV
Source Strength:	500 W
Source Size:	1.4 × 1.4 mm²
Analyzer Type:	Spherical sector analyzer
Incident Angle:	45°
Emission Angle:	45°
Analyzer Pass Energy:	50 eV
Analyzer Resolution:	2.1 eV
Total Signal Accumulation Time:	837 s
Total Elapsed Time:	861 s
Number of Scans:	3
Effective Detector Width:	5.9 eV

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Accession #:	01613-01
Host Material:	Bi₂Se₃
Technique:	XPS
Spectral Region:	Survey
Instrument:	Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source:	Al K_α monochromatic
Source Energy:	1486.7 eV
Source Strength:	500 W
Source Size:	1.4 × 1.4 mm²
Analyzer Type:	Spherical sector analyzer
Incident Angle:	45°
Emission Angle:	45°
Analyzer Pass Energy:	50 eV
Analyzer Resolution:	2.1 eV
Total Signal Accumulation Time:	837 s
Total Elapsed Time:	861 s
Number of Scans:	3
Effective Detector Width:	5.9 eV

Accession #:	01613-01
Host Material:	Bi₂Se₃
Technique:	XPS
Spectral Region:	Survey
Instrument:	Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source:	Al K_α monochromatic
Source Energy:	1486.7 eV
Source Strength:	500 W
Source Size:	1.4 × 1.4 mm²
Analyzer Type:	Spherical sector analyzer
Incident Angle:	45°
Emission Angle:	45°
Analyzer Pass Energy:	50 eV
Analyzer Resolution:	2.1 eV
Total Signal Accumulation Time:	837 s
Total Elapsed Time:	861 s
Number of Scans:	3
Effective Detector Width:	5.9 eV

. . Accession #: 01613-02. Host Material: Bi2Se3. Technique: XPS. Spectral Region: O 1s. Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module. Excitation Source: Al Kα monochromatic. Source Energy: 1486.7 eV. Source Strength: 500 W. Source Size: 1.4 × 1.4 mm2. Analyzer Type: Spherical sector. Incident Angle: 45°. Emission Angle: 45°. Analyzer Pass Energy 15 eV. Analyzer Resolution: 0.6 eV. Total Signal Accumulation Time: 661 s. Total Elapsed Time: 741 s. Number of Scans: 10. Effective Detector Width: 1.77 eV

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Accession #: 01613-02
Host Material: Bi₂Se₃
Technique: XPS
Spectral Region: O 1s

Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source: Al K_α monochromatic
Source Energy: 1486.7 eV
Source Strength: 500 W
Source Size: 1.4 × 1.4 mm²
Analyzer Type: Spherical sector
Incident Angle: 45°
Emission Angle: 45°
Analyzer Pass Energy 15 eV
Analyzer Resolution: 0.6 eV
Total Signal Accumulation Time: 661 s
Total Elapsed Time: 741 s
Number of Scans: 10
Effective Detector Width: 1.77 eV

. . Accession #: 01613-03. Host Material: Bi2Se3. Technique: XPS. Spectral Region: Bi 5d. Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module. Excitation Source: Al Kα monochromatic. Source Energy: 1486.7 eV. Source Strength: 500 W. Source Size: 1.4 × 1.4 mm2. Analyzer Type: Spherical sector. Incident Angle: 45°. Emission Angle: 45°. Analyzer Pass Energy 15 eV. Analyzer Resolution: 0.6 eV. Total Signal Accumulation Time: 1723 s. Total Elapsed Time: 1883 s. Number of Scans: 20. Effective Detector Width: 1.77 eV

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Accession #: 01613-03
Host Material: Bi₂Se₃
Technique: XPS
Spectral Region: Bi 5d

Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source: Al K_α monochromatic
Source Energy: 1486.7 eV
Source Strength: 500 W
Source Size: 1.4 × 1.4 mm²
Analyzer Type: Spherical sector
Incident Angle: 45°
Emission Angle: 45°
Analyzer Pass Energy 15 eV
Analyzer Resolution: 0.6 eV
Total Signal Accumulation Time: 1723 s
Total Elapsed Time: 1883 s
Number of Scans: 20
Effective Detector Width: 1.77 eV

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Accession #: 01613-03
Host Material: Bi₂Se₃
Technique: XPS
Spectral Region: Bi 5d

Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source: Al K_α monochromatic
Source Energy: 1486.7 eV
Source Strength: 500 W
Source Size: 1.4 × 1.4 mm²
Analyzer Type: Spherical sector
Incident Angle: 45°
Emission Angle: 45°
Analyzer Pass Energy 15 eV
Analyzer Resolution: 0.6 eV
Total Signal Accumulation Time: 1723 s
Total Elapsed Time: 1883 s
Number of Scans: 20
Effective Detector Width: 1.77 eV

. . Accession #: 01613-04. Host Material: Bi2Se3. Technique: XPS. Spectral Region: Se 3d. Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module. Excitation Source: Al Kα monochromatic. Source Energy: 1486.7 eV. Source Strength: 500 W. Source Size: 1.4 × 1.4 mm2. Analyzer Type: Spherical sector. Incident Angle: 45°. Emission Angle: 45°. Analyzer Pass Energy 15 eV. Analyzer Resolution: 0.6 eV. Total Signal Accumulation Time: 1402 s. Total Elapsed Time: 1562 s. Number of Scans: 20. Effective Detector Width: 1.77 eV

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Accession #: 01613-04
Host Material: Bi₂Se₃
Technique: XPS
Spectral Region: Se 3d

Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source: Al K_α monochromatic
Source Energy: 1486.7 eV
Source Strength: 500 W
Source Size: 1.4 × 1.4 mm²
Analyzer Type: Spherical sector
Incident Angle: 45°
Emission Angle: 45°
Analyzer Pass Energy 15 eV
Analyzer Resolution: 0.6 eV
Total Signal Accumulation Time: 1402 s
Total Elapsed Time: 1562 s
Number of Scans: 20
Effective Detector Width: 1.77 eV

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Accession #: 01613-04
Host Material: Bi₂Se₃
Technique: XPS
Spectral Region: Se 3d

Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source: Al K_α monochromatic
Source Energy: 1486.7 eV
Source Strength: 500 W
Source Size: 1.4 × 1.4 mm²
Analyzer Type: Spherical sector
Incident Angle: 45°
Emission Angle: 45°
Analyzer Pass Energy 15 eV
Analyzer Resolution: 0.6 eV
Total Signal Accumulation Time: 1402 s
Total Elapsed Time: 1562 s
Number of Scans: 20
Effective Detector Width: 1.77 eV

. . Accession #: 01613-05. Host Material: Bi2Se3. Technique: XPS. Spectral Region: Bi 4f, Se 3p. Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module. Excitation Source: Al Kα monochromatic. Source Energy: 1486.7 eV. Source Strength: 500 W. Source Size: 1.4 × 1.4 mm2. Analyzer Type: Spherical sector. Incident Angle: 45°. Emission Angle: 45°. Analyzer Pass Energy 15 eV. Analyzer Resolution: 0.6 eV. Total Signal Accumulation Time: 3060 s. Total Elapsed Time: 3220 s. Number of Scans: 20. Effective Detector Width: 1.77 eV

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Accession #: 01613-05
Host Material: Bi₂Se₃
Technique: XPS
Spectral Region: Bi 4f, Se 3p

Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source: Al K_α monochromatic
Source Energy: 1486.7 eV
Source Strength: 500 W
Source Size: 1.4 × 1.4 mm²
Analyzer Type: Spherical sector
Incident Angle: 45°
Emission Angle: 45°
Analyzer Pass Energy 15 eV
Analyzer Resolution: 0.6 eV
Total Signal Accumulation Time: 3060 s
Total Elapsed Time: 3220 s
Number of Scans: 20
Effective Detector Width: 1.77 eV

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Accession #: 01613-05
Host Material: Bi₂Se₃
Technique: XPS
Spectral Region: Bi 4f, Se 3p

Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source: Al K_α monochromatic
Source Energy: 1486.7 eV
Source Strength: 500 W
Source Size: 1.4 × 1.4 mm²
Analyzer Type: Spherical sector
Incident Angle: 45°
Emission Angle: 45°
Analyzer Pass Energy 15 eV
Analyzer Resolution: 0.6 eV
Total Signal Accumulation Time: 3060 s
Total Elapsed Time: 3220 s
Number of Scans: 20
Effective Detector Width: 1.77 eV

. . Accession #: 01613-06. Host Material: Bi2Se3. Technique: XAES. Spectral Region: Se LMM, C 1s. Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module. Excitation Source: Al Kα monochromatic. Source Energy: 1486.7 eV. Source Strength: 500 W. Source Size: 1.4 × 1.4 mm2. Analyzer Type: Spherical sector. Incident Angle: 45°. Emission Angle: 45°. Analyzer Pass Energy 15 eV. Analyzer Resolution: 0.6 eV. Total Signal Accumulation Time: 2820 s. Total Elapsed Time: 2980 s. Number of Scans: 20. Effective Detector Width: 1.77 eV

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Accession #: 01613-06
Host Material: Bi₂Se₃
Technique: XAES
Spectral Region: Se LMM, C 1s

Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source: Al K_α monochromatic
Source Energy: 1486.7 eV
Source Strength: 500 W
Source Size: 1.4 × 1.4 mm²
Analyzer Type: Spherical sector
Incident Angle: 45°
Emission Angle: 45°
Analyzer Pass Energy 15 eV
Analyzer Resolution: 0.6 eV
Total Signal Accumulation Time: 2820 s
Total Elapsed Time: 2980 s
Number of Scans: 20
Effective Detector Width: 1.77 eV

. . Accession #: 01613-07. Host Material: Bi2Se3. Technique: XPS. Spectral Region: Valence band. Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module. Excitation Source: Al Kα monochromatic. Source Energy: 1486.7 eV. Source Strength: 500 W. Source Size: 1.4 × 1.4 mm2. Analyzer Type: Spherical sector. Incident Angle: 45°. Emission Angle: 45°. Analyzer Pass Energy 15 eV. Analyzer Resolution: 0.6 eV. Total Signal Accumulation Time: 1863 s. Total Elapsed Time: 2103 s. Number of Scans: 30. Effective Detector Width: 1.77 eV

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Accession #: 01613-07
Host Material: Bi₂Se₃
Technique: XPS
Spectral Region: Valence band

Instrument: Scienta Omicron Custom Design 035008 Wafer Analysis Module
Excitation Source: Al K_α monochromatic
Source Energy: 1486.7 eV
Source Strength: 500 W
Source Size: 1.4 × 1.4 mm²
Analyzer Type: Spherical sector
Incident Angle: 45°
Emission Angle: 45°
Analyzer Pass Energy 15 eV
Analyzer Resolution: 0.6 eV
Total Signal Accumulation Time: 1863 s
Total Elapsed Time: 2103 s
Number of Scans: 30
Effective Detector Width: 1.77 eV

ACKNOWLEDGMENTS

This work was supported in part by NEWLIMITS, a center in nCORE, a Semiconductor Research Corporation (SRC) program sponsored by the National Institute of Standards and Technology (NIST) through Award Number 70NANB17H041. This work was also supported by PSU Two-Dimensional Crystal Consortium for the materials under National Science Foundation (NSF) Cooperative Agreement No. DMR-1539916.

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2020

Author(s)

2D topological insulator bismuth selenide analyzed by in situ XPS

INTRODUCTION

SPECIMEN DESCRIPTION (ACCESSION #01613)

INSTRUMENT DESCRIPTION