A three-axis goniometer in an UHV molecular beam experiment

A sample manipulator with six degrees of freedom, which is part of a molecular beam scattering apparatus used to study gas-surface interactions, is described. Incidence parameters such as the angle of incidence and the azimuthal angle can be set and particles leaving the surface both in and out the plane of incidence can be measured (to within 0.1° accuracy). The latter is achieved, under computer control, by a combination of the movement of the manipulator and the movement of the detector. Cooling of the sample to liquid N₂ temperatures and heating to at least 1600 K is possible. A mathematical relation among the positions of the manipulator and of the detector, the required incidence angle of the particles and the final angle of the scattered particles to be measured is derived.