Abstract: In a scanning tunneling microscope, the tunnel tip comprises an optically transparent body coated with a semiconductor layer, such as a GaAs layer. A sample being investigated comprises a magnetic material. Tunnel microscope operation permits investigation of the magnetic properties at or near the surface of the sample where a spin-polarized beam of light impinges upon the sample surface, through the transparent body of the tunnel tip, or after traveling through the sample, or when made to impinge upon the surface at an angle of incidence from an axis normal to the sample surface. In addition to conventional scanning tunneling microscope electronics, an oscillator-controlled phase-sensitive detector or gating means and a display unit are provided for direct viewing of the magnetic properties and the topography of the sample.

Abstract: The transistor comprises two electrodes, (source (22) and drain (23), with a semiconductor tunnel channel (21A, 21B) arranged therebetween. A gate (24) for applying control signals is coupled to the channel. The semiconductor channel consists of a plurality of regions differing in their current transfer characteristics: contact regions (21c), connected to the source and drain electrodes, and a tunneling region (21t) arranged between the contact regions. The energy of free carriers in the contact regions differs from the energy of the conduction band or the valence band of the tunneling region which forms a low energy tunnel barrier the height (.DELTA.E) of which can be modified by control signals applied to the gate. The operating temperature of the device is kept sufficiently low to have the tunnel current through the barrier outweigh currents of thermionically excited carriers.