Metal-insulator-metal sensors monitoring charge flow during thermal desorption

Abstract

Metal-insulator-metal sensors with a new design have been developed which allow us to perform thermal desorption spectroscopy of weakly bound adsorbates. The sensor can be temperature ramped utilising an ITO layer which is electrically isolated from the two metal layers such that a sensitive measurement of the device current is not hampered. An accurate reading of the temperature of the metal surface is derived from the I-V curve of the sensor which is found to be temperature sensitive. Concurrently with the thermal desorption spectrum the device current is recorded allowing us to correlate the latter with distinct desorption processes. For the molecules, H2O, small alcohols, NH3 and HCOOH we obtain thermal desorption spectra. Concurrently with recoding the spectra we detect characteristic device currents. These are found to solely result from interactions between the substrate and the first monolayer of molecules. We suggest that these are due to shifts of the Fermi level of the top metal film in the MIM device induced by the charge transfer processes connected with molecular adsorption and desorption.