Orbitals and Energies #
Note – these are listed in BINDING ENERGY
In 3s ≈ 830 eV
In 3p ≈ 665 eV
In 3d ≈ 444 eV
In 4s ≈ 123 eV
In 4p ≈ 78 eV
In 4d ≈ 17 eV
In 5p ≈ 1 eV
Common Overlaps for In 3d #
Ti 2p – Er 4s – Re 4p – Bi 4d
Theory and Background #
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Plasmon-loss structure is prominent for metallic In. Expect distinct loss peaks on the high-BE side of the main line; an oft-cited separation for a strong plasmon loss in metallic In is ~11–12 eV from the main 3d₅/₂ (exact values vary with sample/geometry). These appear as satellite “replicas” and are not separate chemical states.[1]
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Final-state screening & many-body tails: Metallic final states cause asymmetric main peaks with a high-BE tail; the asymmetry magnitude depends on conduction-electron density. Expect clear asymmetry for In⁰, weak/none for fully ionic In³⁺.
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Intrinsic vs extrinsic losses: Besides intrinsic shake/plasmon satellites, extrinsic inelastic scattering adds a long high-BE background; a Tougaard-type background (rather than simple Shirley) often models this better, especially when metallic In is present.
Experimental Advice #
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Preferential sputtering & chemical reduction: Ar⁺ sputtering preferentially removes oxygen from In oxides → oxygen-deficient InₓOᵧ or even metallic In⁰ at the surface, along with the growth of plasmon-loss structure and metallic asymmetry. If you must depth-profile oxides/ITO, lower energy, grazing incidence, or cluster sputtering can mitigate—but still monitor chemistry continuously.[2]
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“Small-shift” problem: In 3d chemical shifts between In⁰, In₂O₃, and In(OH)₃ are sub-eV and frequently overlap across labs. Always acquire In MNN and compute α′ (or use a Wagner plot) to speciate robustly.
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Thermal/handling quirks: Indium is soft and smears; ensure clean, firm mounting. Beware trace In foil contamination if you use it as a backing—its metallic 3d + plasmons can appear unexpectedly.
Data Analysis Guidance #
Use Tougaard (or mixed) backgrounds for metallic spectra to capture plasmon-loss tail; Shirley can underfit the high-BE side and falsely inflate “oxide” components.
References #
1
Detweiler, Zachary M., et al. “The oxidation and surface speciation of indium and indium oxides exposed to atmospheric oxidants.” Surface Science 648 (2016): 188-195.
2
Shard, Alexander G., and Mark A. Baker. “Practical guides for x-ray photoelectron spectroscopy: Use of argon ion beams for sputter depth profiling and cleaning.” Journal of Vacuum Science & Technology A 42.5 (2024).
