Ultraviolet Photoelectron Spectroscopy (UPS)

Ultraviolet photoelectron spectroscopy (UPS) is often performed with X-ray Photoelectron Spectroscopy (XPS), a powerful surface chemical characterization technique. Unique to UPS, its selective low-energy signal photoelectrons enable specific measurement of valence-band properties, as well as the electronic work function of the surface.

Strengths

• Very high surface specificity: information depth 2-4 nm
• Highly accurate spectral fingerprinting
• Selective valence-band signal: bonding orbital properties
• Reliable work function measurements possible

Limitations

• UPS peaks are not used for elemental quantification: degree of hybridization and extent of BE-shift is too substantial
• Robust density of electronic states / orbital occupancy typically requires Advanced Modeling
• Work function measurement requires careful setup to isolate sample low-KE cutoff from detector behavior

Learn More

Example Outputs Instruments Used How UPS Works

• Solid phase
• Must be stable under ultra-high vacuum conditions
• Maximum Sample Dimensions: 60mm (L) x 60mm (W) x 20mm (T)

In UPS measurements, a high-energy laser beam is applied to the sample surface, and characteristic photoelectrons are emitted via the photoelectric effect. The emitted photoelectrons are then analyzed by energy to produce a spectrum of peaks associated with the quantitative concentration of specific elemental species.

Unlike XPS, UPS uses an ultraviolet-laser source, which limits the amount of energy imparted to the surface atoms.

As a result, UV photoelectrons are selectively emitted from outer (valence-band) orbitals, and the information depth is more surface specific. These features enable more detailed analysis of the valence-band properties and bonding states and provide a direct measurement of work function.

The ability to clean the surface using Argon ion clusters ensures that work function measurements can be done with clean rather than environmentally contaminated surfaces.