Indium

Indium • Other Metal

Primary XPS region: In3d
Overlapping regions: N/A
Binding energies of common chemical states:

Chemical state	Binding energy In3d_5/2
In metal	443.8 eV
In₂O₃	444.0 eV

Experimental information

Smaller binding energy shifts of some indium compounds compared to indium metal.
- Chemical state differentiation can be difficult with XPS only.
- Collect principal In MNN peak as well as In3d.
- Bigger chemical shifts observed for In MNN compared to In3d.
See trace In if used as powder mounting foil.

Interpretation of XPS spectra

In3d region has well-separated spin-orbit components (Δ_metal=7.6eV).
- Peaks have asymmetric peak shape for metal.
- Loss features are observed to higher binding energy side of 3d_3/2 spin-orbit component for In metal.
In3d peaks may also show asymmetry for indium oxide, if other compounds are present (e.g. hydroxide) or there are vacancies/defects in the oxide lattice.
Small or negligible binding energy shifts for compounds, such as oxides.
- In3d peaks broaden with respect to metal peaks for compounds.
- Subtle shifts in CIGS samples.
- Use X-ray induced In MNN Auger peaks to aid chemical state assignment.

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About this element

Symbol: In
Date of discovery: 1863
Name origin: Indigo spectrum
Appearance: silverish
Discoverer: Ferdinand Reich
Obtained from: zinc refining

Melting point: 430 K
Boiling point: 2345 K
Density[kg/m³]: 7310
Molar volume: 15.76 × 10^-6 m³/mol
Protons/Electrons: 49
Neutrons: 66
Shell structure: 2,8,18,18,3
Electron configuration: [Kr]4d105s25p1
Oxidation state: 3
Crystal structure: tetragonal

Most elements were discovered while scientists searched for other materials, and indium is no exception. This very soft, silvery-white metal has a bright luster and emits a high-pitched “cry” when bent. One of the first major applications for indium was as a coating for bearings on high-performance aircraft during World War II. Later, tin-doped indium oxide, transparent and colorless in thin films, became a main component in liquid crystal, flat panel and plasma displays. Not surprisingly the demand for indium has risen dramatically, and lower-cost alternatives, such as carbon nanotubes and conducting polymers, are being studied.

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