Reflection Electron Energy Loss Spectroscopy (REELS)
Reflection electron energy loss spectroscopy (REELS) is used to determine surface electronic structure information such as the bandgap (Eg). REELS operates by irradiating the sample with a beam of electrons and measuring the energies of the reflected electrons (both elastically and inelastically scattered). Bandgaps of >3eV are accessible with REELS. The REELS information depth is up to ~15nm (material-dependent), similar to that of XPS.
In some cases, REELS can detect the π→π* transition in sp2 carbon. As such, REELS can be used as a complementary technique to XPS to detect sp2 carbon-containing species such as graphite and aromatic polymers.
Ideal Uses of REELS
- Measuring the bandgap of “medium” bandgap materials (>3eV), specifically at the surface of the material
Strengths
- Fast acquisition (<10min)
- Surface-sensitive (≤15nm)
- Nondestructive
- Suitable for most XPS samples
Limitations
- Limited to bandgaps >3eV
- Not suitable for narrow bandgap materials such as Si, Ge, and GaAs
REELS Technical Specifications
- Spot Size: 1mm x 1.5mm
- Information Depth: ≤15nm
- Electron Energy: 1keV
- Maximum Sample Dimensions: 6cm x 6cm x 2cm (W x L x H)
- REELS is performed under ultra-high vacuum; samples must be vacuum-compatible
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