AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS-WeP

Paper SS-WeP26
A Calibrated Adsorption and Thermal Desorption System using Glass Capillary Arrays and a Capillary Valve Flow Source

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: R.H. Jackson, University of Maine
Authors: R.H. Jackson, University of Maine
B.G. Frederick, University of Maine
D.J. Dwyer, University of Maine
Correspondent: Click to Email
We demonstrate a calibrated thermal desorption system utilizing a glass capillary array doser as a calibrated beam source. Absolute calibration of the mass spectrometer signal in molecules per second is achieved using both calculated and measured flux distributions from the doser to calibrate the doser flux to the inlet appeture of a differentially pumped thermal desorption mass spectrometer. By a re-parameterization of the formalism of Winkler and Yates,@footnote 1@ we have reduced the order of the necessary integrations from 3 to 2, which simplifies treatment of arbitrarily shaped planar targets. Fourier convolution methods are used to calculate of the flux to a target at any position in a plane parallel to the doser face. These calculations are compared to direct measurements of the doser flux in 3 dimensions. The pressure versus time, measured by a spinning rotor gauge in a gas cell of known volume, determines the flow rate to the doser. The flow closely obeys the simple effusion model after accounting for finite base pressure. A transient molecular flow model is applied to the establishment of the flow from the capillary valve, providing good estimates of the time to steady state for the flow. This Calibrated Thermal Desorption Spectrometer is applied to a study of oxygen on Pd(110) and the coverage results are compared to values from nuclear reaction analysis. @FootnoteText@ @footnote 1@A. Winkler and J. T. Yates Jr. "Capillary array dosing and angular desorption distribution measurements: A general formalism", J. Vac. Sci. Technol. A 6(5), Sep/Oct 1988.