The thinnest possible uniform and stable oxide layer grown thermally on Si (111) is 0.8 nm thick. This oxide is grown at around 500ºC, in a self-limiting process, which has earlier been fully characterized with surface sensitive, high-resolution core level photoemission at the ASTRID storage ring facility at Aarhus, Denmark. Such oxides are too thin for use in current generations of CMOS-devices, yet they have potential applications in devices, where controlled tunneling could be of importance, or as diffusion barriers. To study the tunneling properties of this oxide covering the Si (111) surface isolated nanometer-sized Sn islands in different diameters and concentrations were deposited at 500ºC and became negatively charged, with different charges depending on their size. The deposition was done from a Knudsen source in a way programmed to produce a systematic variation of the Sn coverage across about 2 cm of the surface. This is done to allow locally resolved photoemission characterization of the system, at a resolution (with a photon beam width) of around 150 micron. The resulting shifts of Si 2p and Sn 4d core levels at, and across the surface, with varying amounts of Sn, and charge on the Sn islands, are used to determine the local changes in band bending and fields in the oxide. This method thus offers a unique possibility to evaluate MOS properties of nano-systems in-situ without direct electrical contacts.