Work function of bulk and e-beam evaporated Au thin films measured by UPS and Kelvin probe methods

The electron work function (WF) of gold is a key parameter for interpreting charge transfer and contact formation in electronic and sensing structures, yet reported values vary strongly with surface condition and measurement methodology. Here, we present a comparative study of the WF of (i) bulk Au sheets and (ii) 100 nm Au thin films deposited by electron-beam evaporation. Surface composition and cleanliness were verified by X-ray photoelectron spectroscopy (XPS), while WF was determined by ultraviolet photoelectron spectroscopy (UPS) from the secondary-electron cutoff using a small negative sample bias. Complementary relative measurements were performed by Kelvin probe force microscopy (KPFM) and macroscopic Kelvin probe/scanning Kelvin probe (KP/SKP), calibrated against highly oriented pyrolytic graphite (HOPG). XPS survey spectra revealed only Au features and weak residual carbon contamination. Low-energy Ar + sputter cleaning significantly reduced the C1s signal on bulk Au. UPS yielded an average WF of 4.59 eV for bulk Au prior to sputtering and 4.63 eV after sputter cleaning, whereas the Au thin film exhibited a lower WF of 4.49 eV. In contrast, KPFM and KP/SKP provided area-averaged WFs close to 4.7–4.75 eV for both bulk and thin-film Au. The results highlight the sensitivity of WF to surface state, measurement environment, and data-analysis procedure, and demonstrate that combining UPS with calibrated CPD-based techniques enables a consistent interpretation of effective WF values across local and macroscopic length scales.