Design considerations for simple gas dosers in surface science applications Available to Purchase

The flux distributions and enhancement factors for various gas doser designs typically used in surface science applications and chemisorption studies have been calculated and compared. The following conclusions, which will aid the experimentalist in the choice of doser design, can be made. (1) The enhancement factor expected for a given doser can easily be derived from Fig. 2. (2) The optimum doser design is a multichannel array with a radius slightly larger than that of the sample, and a distance from the sample < 10% of the sample diameter. (Complications of this design are discussed.) (3) Because of space requirements, the sample–doser distance must sometime be ≥40% of the sample diameter, in which cases it is better to use a cosine emitter. A good, very simple doser design is described that consists of a small cosine emitter with a sample–doser distance of 1/2 the sample diameter. This provides an enhancement factor >50% of the optimum theoretical enhancement, with only slight (±15%) flux gradients. (4) For a given doser distance, a needle doser provides the largest enhancement factor, but always has a very strong gradient in flux across the sample.