Molecular-Beam Sources Fabricated from Multichannel Arrays. I. Angular Distributions and Peaking Factors

Abstract

An apparatus for measuring the leak rates and angular distributions of the molecular flux from multichannel sources was constructed. Four types of beam sources were tested: A single capillary, a crinkly foil stack, an electron-beam milled quartz membrane, and two sources constructed by fiber optics techniques. The leak rates of the sources were compared to the predictions of Knudsen flow. The angular distributions were characterized by a ``peaking factor,'' defined as the ratio of the center-line beam intensity from the source to that from a cosine emitter of the same total flow rate. The measured peaking factors agreed with the theoretical predictions of free molecule flow at low source pressures and approached the limit for isentropic flow at high source pressures.