Paper EW-WeL6
Novel Dual Mode Air Photoemission and Kelvin Probe System for Work Function Analysis of Nanometer Films

Wednesday, October 31, 2012, 1:40 pm, Room West Hall

KP Technology have developed a novel surface characterization instrument – the Air Photoemission System (APS) – which yields information on both the absolute work function and the Density Of States (DOS) near the Fermi level of metals and semiconductors deposited as bulk, thin films, layers, devices etc. The new system uses low photon excitation energies (3.5 – 7.0eV )

and has been used to characterize thin films such as Cobalt-Phylocyanine (CoPc) on Transparent Conducting Oxides (TCOs) used in electroluminescent displays. We have combined this technique with our ultra-high relative work function resolution (1 – 3meV ) macroscopic scanning Kelvin Probe Systems and can build up 2D work function maps of surfaces with lateral resolution of 100 – 2000mm.

The work function is an extremely surface-sensitive property of a material, modified by thin or monomolecular adsorbed layers, surface charging and for semiconductors, illumination. Indeed, work function changes of 500 - 1000meV magnitude can be observed with nanometer thick films deposited on glass, TCOs, metals and semiconductors. Our Kelvin Probe systems are also extremely versatile, capable of automatic work function/Fermi-level monitoring operating in ambient, controlled atmosphere (nitrogen, humidity) and using a custom head unit, UHV over a wide temperature range (4 – 1000K ). Using a 1.24 – 3.1eV monochromatic light source, SKP can be extended to provide Surface Photovoltage Spectroscopy (SPS) which is an ideal tool for surface characterization of organic semiconductors and solar cells, allowing clarification of the energy band diagram and adsorption phenomena. This presentation will provide illustrative data on materials such as wide bandgap semiconductors (ITO), TCOs (TiN, TiO₂), nanometer thickness films and OLEDs.