Photoelectron Spectrometer XPS and UPS

What is the Problem? OLEDs and OPVs consist of thin films of organic materials, sandwiched between contacting electrodes. We need analytical tools which tell us:

• Elemental composition of metal, metal oxide and organic surfaces (top 1-10 nm)
• The molecular state of those elements in that same region
• The frontier orbital energies which control rates of charge transfer, photopotentials, onset voltages, etc.

What is our approach? We use high-vacuum surface electron spectroscopies: X-ray photoelectron spectroscopy and UV-photoelectron spectroscopy to provide the elemental, molecular and energetic information we require about these materials.

XPS uses high energy X-ray photons to excite “core” electrons in the near-surface region UPS uses lower energy photons in the deep UV region to excite valence electrons.

The small sampling depth of XPS and UPS arises because most of the photoelectrons generated do NOT make it out of the solid – they are scattered below the surface and not detected. Only those within 1-10 nm of the surface get out and can be analyzed.