Adjustments being made to a high-vacuum scanning tunnelling microscope (STM). High-vacuum STMs are used in atomic-scale studies of metal deposition on semiconductor substrates. The STM operates by bringing a very fine point electrode (a few atoms thick at the tip) to within a few Angstroms of the sample's surface. As the electron clouds around atoms of the sample and tip meet, a small 'tunnelling' current passes. The electrode scans across the surface, the tunnelling current being kept constant by vertical movements of the electrode. Processing these motion data produces a 3-dimensional map of the surface.