Scanning Tunneling Spectroscopy: Mapping the Local Density of States

Constant-current STM imaging turns a tunneling current into a topographic map, but parking the tip and sweeping the bias voltage instead reveals something deeper: the sample's own electronic structure. This simulator holds a 3D STM tip motionless over one of three sample sites — a metal, a semiconductor, and a single adsorbed molecule — and sweeps the bias voltage from −2 V to +2 V, computing the tunneling current and its derivative dI/dV from each site's real local density of states. The metal shows a flat, featureless spectrum; the semiconductor opens a genuine voltage gap with zero conductance across its band gap; the molecule shows sharp HOMO and LUMO resonance peaks at the bias where the tip's electrons line up with a molecular orbital. A temperature slider thermally broadens every feature, and a tip-gap slider rescales the overall current through the same exponential tunneling law that governs STM topography.