High-purity niningerite (MgS) was synthesized by BenchChem under vacuum conditions for use in laboratory simulations of solar-ion space weathering of sulfide minerals that are expected to be present on the surface of Mercury. MgS was initially characterized via x-ray photoelectron spectroscopy prior to investigations into the preferential loss of near-surface sulfur in niningerite with 2 keV H2+ irradiation. Survey and high-resolution (Mg 1s, Mg 2p, S 2p) x-ray photoelectron spectra of as-received magnesium sulfide powder (99.9%) are presented, including surface contaminants that originate from exposure to atmosphere (C 1s, O 1s). Minor impurities derived from sample synthesis (Al 2s, Al 2p) and packaging or processing (F 1s) are noted in the survey spectrum.
Accession #: 01995
Technique: XPS
Specimen: MgS
Instrument: PHI Versaprobe III
Major Elements in Spectra: Mg, S, O
Minor Elements in Spectra: C, Al, F
Published Spectra: 6
Spectral Category: Comparison
INTRODUCTION
On Earth, magnesium sulfide does not form independently as a terrestrial mineral due to the availability of oxygen on Earth, but rather as a byproduct of the steelmaking process (Ref. 1) and finds applications in its synthesized form as a blue-green phosphor in the semiconductor industry (Refs. 2 and 3). Recently, there has been strong interest in this material related to advances in magnesium-sulfide energy storage as a cheaper, safer alternative to lithium-ion batteries (Refs. 4 and 5).
On planetary surfaces, sulfides are ubiquitous, found on rocky bodies like the Moon, asteroids, meteorites, Earth, and Mars, primarily as iron-bearing minerals like: troilite (FeS), pyrrhotite, pyrite (FeS2), and pentlandite [(Fe,Ni)9S8] (Refs. 6 and 7). However, an interest in iron-free sulfides with a special focus on magnesium and calcium sulfides was initiated based on MESSENGER data of Mercury's surface, where X-ray fluorescence spectra showed a strong correlation between locations high in sulfur with regions of enhanced signatures for magnesium and calcium (Refs. 8 and 9).
The interaction of space weathering with the surfaces of sulfides relevant to Mercury was investigated using X-ray photoelectron spectroscopy (XPS). The work presented here is related to a larger study where CaS and MgS samples were irradiated with solar-wind-type ion species at characteristic solar wind speeds to investigate the formation of metallic capping layers (Ref. 10), observed in iron metal sulfides, that do not predominate on Mercury.
Sample handling of sulfide materials is critical for surface analytical investigations, as MgS is highly reactive in air, rapidly forming magnesium sulfates with oxidation and hydroxides with humidity; while carbonates are produced with exposure to CO2 and adventitious carbon. Fluorine contamination can occur during sample synthesis and processing in systems that utilize fluorocarbon O-rings or Teflon seals, adhesives, HF-etched surfaces, or are enclosed in heat-sealed Teflon bags (Ref. 11). Thus, MgS is necessarily synthesized in vacuum, then ground and packed in a glovebox with O2 and H2O concentrations below 20 ppm. Upon receival, the MgS container was opened in an inert (N2) environment and pellets were prepared by pressing powder material in 8-mm diameter Al sample cups within a N2-purged glove-bag prior to XPS analysis.
SPECIMEN DESCRIPTION (ACCESSION # 01995)
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
CAS Registry #: 12032-36-9
Specimen Characteristics: Homogeneous; powder; polycrystalline; semiconductor; inorganic compound; powder
Chemical Name: Magnesium Sulfide
Source: BenchChem, 5999 Trade Center Dr, Austin, TX 78744
Composition: MgS
Form: 99.9% purity powder MgS
Structure: Halite (cubic), Fm-3m
History and Significance: The specimen was received in a vacuum-packed plastic container and cold stored, unopened at ∼10 °C in a sample refrigerator. The sample was opened and prepared in a N2-purged glove tent (∼15 min).
As Received Condition: Eggshell white powder. Bulk chemical analysis shows Mg and S, with Al, C, and O.
Analyzed Region: Approximate center of pressed pellet.
Ex Situ Preparation/Mounting: ∼0.1 g of material was pressed at 1500 PSI into an 8-mm diameter aluminum cup between two, clean, stainless-steel plates; the filled cup was subsequently mounted to a 304 stainless steel sample platen and held in place by double-sided permanent scotch tape.
In Situ Preparation: None
Charge Control: Dual-beam charge compensation is delivered by both an electron flood source (1 eV, 20 μA) and a floating-column ion source (H2+ 10 eV, 7 mA) during XPS analysis.
Temp. During Analysis: 298 K
Pressure During Analysis: 3.0 × 10−6 Pa
Pre-analysis Beam Exposure: 0 s
INSTRUMENT DESCRIPTION
Manufacturer and Model: PHI Versaprobe III
Analyzer Type: Spherical sector
Detector: Multichannel plate resistive
Number of Detector Elements: 128
INSTRUMENT PARAMETERS COMMON TO ALL SPECTRA
Spectrometer
Analyzer Mode: Constant pass energy
Throughput (T = EN): N = 0
Excitation Source Window: 2.4 μm Al window
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.13 W
Source Beam Size: 200 μm diameter
Signal Mode: Multichannel direct
Geometry
Incident Angle: 0°
Source-to-Analyzer Angle: 45°
Emission Angle: 45°
Specimen Azimuthal Angle: −°
Acceptance Angle from Analyzer Axis: 0°
Analyzer Angular Acceptance Width: 5° × 5°
Ion Gun
Manufacturer and Model: PHI floating-column electron-bombardment differentially pumped ion source.
Energy: 10 eV
Current: N/A
Current Measurement Method: Faraday cup
Sputtering Species and Charge: H2+
Spot Size (unrastered): ∼1000 μm
Raster Size: 0 × 0 μm2
Incident Angle: 60°
Polar Angle: 69.3°
Azimuthal Angle: 270°
Comment: No sputter cleaning was done prior to sample analysis. Ion gun is used exclusively for sample neutralization and parameters reflect settings for neutralization. For Au, Ag, and Cu calibration spectra, samples were irradiated for 30 min with 3 keV Ar+ with 3 × 3 mm2 raster and Zalar rotation.
DATA ANALYSIS METHOD
Energy Scale Correction: The binding energy scale was referenced to C 1s = 284.8 eV.
Recommended Energy Scale Shift: +1.9 eV
Peak Shape and Background Method: Symmetric Gaussian–Lorentzian functions were fit to data after Shirley background subtraction.
Quantitation Method: Elemental relative abundance is calculated in atomic percentage (at. %) using PHI multipak 9.8.0.19. Photoelectron peak areas were integrated between two user-selected endpoints, one located at a binding energy above and one below the peak; total peak area includes all counts between endpoints above the Shirley background, where the background function is defined by the identical endpoints. Relative sensitivity factors were calculated internally by PHI multipak, which utilizes a database of transition-specific Scofield photoelectron production cross sections convolved with source-analyzer geometric details and electron transmission efficiency, a function of pass energy. Relative concentration [C(i)] for each element is calculated as C(i) = [I(i)/SF(i)]/[I(1)/SF(1) + … + I(i)/SF(i) + … + I(n)/SF(n)], where I(i) is the peak intensity above background and SF(i) is the sensitivity factor for the transition.
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 . |
---|---|---|---|---|---|---|---|
01995-01a | Al 2s, Al 2p | … | … | … | 0.256 | 2.32 | … |
01995-01b | F 1s | … | … | … | 1.000 | 1.81 | F |
01995-02 | S 2p | 160.4 | 1.48 | 941 | 0.717 | 11.56 | MgS doublet |
01995-02 | S 2p | 162.7 | 1.70 | 180 | 0.717 | … | S doublet |
01995-02 | S 2p | 166.9 | 1.44 | 35 | 0.717 | … | MgSO3 doublet |
01995-02 | S 2p | 167.8 | 1.70 | 54 | 0.717 | … | MgSO4 doublet |
01995-03 | Mg 2p | 49.9 | 1.66 | 800 | 0.167 | 18.29 | MgS, MgO, MgCO3, MgSO3, MgSO4 |
01995-04 | Mg 1s | 1303.8 | 2.06 | 4828 | 1.035 | … | MgS, MgO, MgCO3, MgSO3, MgSO4 |
01995-05 | O 1s | 531.4 | 2.01 | 6648 | 0.733 | 50.70 | MgO, MgCO3, MgSO3, MgSO4 |
01995-06 | C 1s | 284.8 | 1.82 | 638 | 0.314 | 15.33 | C-C |
01995-06 | C 1s | 288.9 | 3.02 | 143 | 0.314 | … | MgCO3 |
Spectrum ID # . | Element/Transition . | Peak Energy (eV) . | Peak Width FWHM (eV) . | Peak Area (eV counts/s) . | Sensitivity Factor . | Concentration (at. %) . | Peak Assignment . |
---|---|---|---|---|---|---|---|
01995-01a | Al 2s, Al 2p | … | … | … | 0.256 | 2.32 | … |
01995-01b | F 1s | … | … | … | 1.000 | 1.81 | F |
01995-02 | S 2p | 160.4 | 1.48 | 941 | 0.717 | 11.56 | MgS doublet |
01995-02 | S 2p | 162.7 | 1.70 | 180 | 0.717 | … | S doublet |
01995-02 | S 2p | 166.9 | 1.44 | 35 | 0.717 | … | MgSO3 doublet |
01995-02 | S 2p | 167.8 | 1.70 | 54 | 0.717 | … | MgSO4 doublet |
01995-03 | Mg 2p | 49.9 | 1.66 | 800 | 0.167 | 18.29 | MgS, MgO, MgCO3, MgSO3, MgSO4 |
01995-04 | Mg 1s | 1303.8 | 2.06 | 4828 | 1.035 | … | MgS, MgO, MgCO3, MgSO3, MgSO4 |
01995-05 | O 1s | 531.4 | 2.01 | 6648 | 0.733 | 50.70 | MgO, MgCO3, MgSO3, MgSO4 |
01995-06 | C 1s | 284.8 | 1.82 | 638 | 0.314 | 15.33 | C-C |
01995-06 | C 1s | 288.9 | 3.02 | 143 | 0.314 | … | MgCO3 |
Al was found in the chemical analysis of the sample.
F is expected to originate from the vacuum sealing process (Ref. 11).
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 4f7/2 | 83.99 | 0.78 | 26 680 | 6.805 | … | Gold metal |
… | Ag 3d5/2 | 368.16 | 0.68 | 41 886 | 6.277 | … | Silver metal |
… | Cu 2p | 932.54 | 1.04 | 49 413 | 2.626 | … | Copper metal |
Spectrum ID # . | Element/Transition . | Peak Energy (eV) . | Peak Width FWHM (eV) . | Peak Area (eV counts/s) . | Sensitivity Factor . | Concentration (at. %) . | Peak Assignment . |
---|---|---|---|---|---|---|---|
… | Au 4f7/2 | 83.99 | 0.78 | 26 680 | 6.805 | … | Gold metal |
… | Ag 3d5/2 | 368.16 | 0.68 | 41 886 | 6.277 | … | Silver metal |
… | Cu 2p | 932.54 | 1.04 | 49 413 | 2.626 | … | Copper metal |
GUIDE TO FIGURES
Spectrum ID # . | Element/Transition . | Voltage Shifta . | Multiplier . | Baseline . | Comment # . |
---|---|---|---|---|---|
01995-01 | Survey | −1.9 | 1 | 0 | – |
01995-02 | S 2p | −1.9 | 1 | 0 | – |
01995-03 | Mg 2p | −1.9 | 1 | 0 | – |
01995-04 | Mg 1s | −1.9 | 1 | 0 | – |
01995-05 | O 1s | −1.9 | 1 | 0 | – |
01995-06 | C 1s | −1.9 | 1 | 0 | – |
Spectrum ID # . | Element/Transition . | Voltage Shifta . | Multiplier . | Baseline . | Comment # . |
---|---|---|---|---|---|
01995-01 | Survey | −1.9 | 1 | 0 | – |
01995-02 | S 2p | −1.9 | 1 | 0 | – |
01995-03 | Mg 2p | −1.9 | 1 | 0 | – |
01995-04 | Mg 1s | −1.9 | 1 | 0 | – |
01995-05 | O 1s | −1.9 | 1 | 0 | – |
01995-06 | C 1s | −1.9 | 1 | 0 | – |
Voltage shift of the archived (as-measured) spectrum relative to the printed figure. The figure reflects the recommended energy scale correction due to a calibration correction, sample charging, flood gun, or other phenomenon.
Accession #: . | 01995-01 . |
---|---|
■ Specimen: | Magnesium Sulfide (MgS) bulk Niningerite powder |
■ Technique: | XPS |
■ Spectral Region: | Survey |
Instrument: | PHI Versaprobe III |
Excitation Source: | Al Kα monochromatic |
Source Energy: | 1486.6 eV |
Source Strength: | 42.1 W |
Source Size: | 200 × 200 μm2 |
Analyzer Type: | Spherical sector analyzer |
Incident Angle: | 0° |
Emission Angle: | 45° |
Analyzer Pass Energy: | 224 eV |
Instrument Resolution: | 2.2 eV |
Total Signal Accumulation Time: | 3375 s |
Total Elapsed Time: | 3375 s |
Number of Scans: | 10 |
Comments: | Data acquisition step size: 0.4 eV |
Accession #: . | 01995-01 . |
---|---|
■ Specimen: | Magnesium Sulfide (MgS) bulk Niningerite powder |
■ Technique: | XPS |
■ Spectral Region: | Survey |
Instrument: | PHI Versaprobe III |
Excitation Source: | Al Kα monochromatic |
Source Energy: | 1486.6 eV |
Source Strength: | 42.1 W |
Source Size: | 200 × 200 μm2 |
Analyzer Type: | Spherical sector analyzer |
Incident Angle: | 0° |
Emission Angle: | 45° |
Analyzer Pass Energy: | 224 eV |
Instrument Resolution: | 2.2 eV |
Total Signal Accumulation Time: | 3375 s |
Total Elapsed Time: | 3375 s |
Number of Scans: | 10 |
Comments: | Data acquisition step size: 0.4 eV |
Accession #: . | 01995-01 . |
---|---|
■ Specimen: | Magnesium Sulfide (MgS) bulk Niningerite powder |
■ Technique: | XPS |
■ Spectral Region: | Survey |
Instrument: | PHI Versaprobe III |
Excitation Source: | Al Kα monochromatic |
Source Energy: | 1486.6 eV |
Source Strength: | 42.1 W |
Source Size: | 200 × 200 μm2 |
Analyzer Type: | Spherical sector analyzer |
Incident Angle: | 0° |
Emission Angle: | 45° |
Analyzer Pass Energy: | 224 eV |
Instrument Resolution: | 2.2 eV |
Total Signal Accumulation Time: | 3375 s |
Total Elapsed Time: | 3375 s |
Number of Scans: | 10 |
Comments: | Data acquisition step size: 0.4 eV |
Accession #: . | 01995-01 . |
---|---|
■ Specimen: | Magnesium Sulfide (MgS) bulk Niningerite powder |
■ Technique: | XPS |
■ Spectral Region: | Survey |
Instrument: | PHI Versaprobe III |
Excitation Source: | Al Kα monochromatic |
Source Energy: | 1486.6 eV |
Source Strength: | 42.1 W |
Source Size: | 200 × 200 μm2 |
Analyzer Type: | Spherical sector analyzer |
Incident Angle: | 0° |
Emission Angle: | 45° |
Analyzer Pass Energy: | 224 eV |
Instrument Resolution: | 2.2 eV |
Total Signal Accumulation Time: | 3375 s |
Total Elapsed Time: | 3375 s |
Number of Scans: | 10 |
Comments: | Data acquisition step size: 0.4 eV |
Accession #: 01995-02
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: S 2p
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 2400 s
Total Elapsed Time: 6390 s
Number of Scans: 30
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
Accession #: 01995-02
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: S 2p
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 2400 s
Total Elapsed Time: 6390 s
Number of Scans: 30
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
Accession #: 01995-03
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: Mg 2p
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 1800 s
Total Elapsed Time: 9999 s
Number of Scans: 30
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
Accession #: 01995-03
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: Mg 2p
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 1800 s
Total Elapsed Time: 9999 s
Number of Scans: 30
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
Accession #: 01995-04
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: Mg 1s
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 450 s
Total Elapsed Time: 10 452 s
Number of Scans: 10
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
Accession #: 01995-04
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: Mg 1s
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 450 s
Total Elapsed Time: 10 452 s
Number of Scans: 10
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
Accession #: 01995-05
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: O 1s
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 600 s
Total Elapsed Time: 3978 s
Number of Scans: 10
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
Accession #: 01995-05
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: O 1s
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 600 s
Total Elapsed Time: 3978 s
Number of Scans: 10
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
Accession #: 01995-06
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: C 1s
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 1800 s
Total Elapsed Time: 8190 s
Number of Scans: 40
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
Accession #: 01995-06
Specimen: Magnesium Sulfide (MgS) bulk Niningerite powder
Technique: XPS
Spectral Region: C 1s
Instrument: PHI Versaprobe III
Excitation Source: Al Kα monochromatic
Source Energy: 1486.6 eV
Source Strength: 42.1 W
Source Size: 200 × 200 μm2
Analyzer Type: Spherical sector
Incident Angle: 0°
Emission Angle: 45°
Analyzer Pass Energy: 26 eV
Instrument Resolution: 0.25 eV
Total Signal Accumulation Time: 1800 s
Total Elapsed Time: 8190 s
Number of Scans: 40
Comments: Total elapsed time includes previous scans in acquisition order. Data acquisition step size: 0.1 eV
ACKNOWLEDGMENTS
We thank the Swiss National Science Foundation Fund (No. P500PT_217998), the National Science Foundation Astronomy Program (No. 2009365), and the NASA Solar System Workings Program (No. 12000470-028) for financial support. XPS spectra were acquired at the University of Virginia Nanoscale Materials Characterization Facility (NMCF), supported in part by the School of Engineering and Applied Science.
AUTHOR DECLARATIONS
Conflict of Interest
The authors have no conflicts to disclose.
Author Contributions
Noah Jäggi: Conceptualization (equal); Data curation (lead); Formal analysis (lead); Investigation (lead); Methodology (equal); Project administration (equal); Resources (supporting); Software (equal); Validation (equal); Visualization (lead); Writing – original draft (lead); Writing – review & editing (equal). Catherine A. Dukes: Conceptualization (equal); Data curation (supporting); Formal analysis (supporting); Investigation (supporting); Methodology (equal); Project administration (equal); Resources (lead); Software (equal); Supervision (lead); Validation (equal); Writing – review & editing (equal).
DATA AVAILABILITY
The data that support the findings of this study are available within the article and its supplementary material.