| AVS 57th International Symposium & Exhibition | |
| Vacuum Technology | Monday Sessions |
| Session VT+MS-MoA |
| Session: | Gas Analysis in Vacuum and Process Applications |
| Presenter: | H.C. Peebles, Sandia National Laboratories |
| Authors: | H.C. Peebles, Sandia National Laboratories M.S. Benner, Sandia National Laboratories T.K. Mehrhoff, Independent Contractor to Sandia National Laboratories |
| Correspondent: | Click to Email |
Mass spectroscopy is routinely used to quantify gases in analytical measurements and process diagnostics. In many of these applications, gases enter the ion source of the mass spectrometer through a molecular leak. Sections of the gas manifold on the high pressure side of the leak may contain extreme temperature gradients such as a gas source operating at a very high temperature or a cryogenic trap at low temperature with the remaining manifold components near room temperature. Calibration of the mass spectrometer response to the molar quantity of gas present in the manifold must take into account the thermal gradient over pressures that can span the range from viscous flow to the molecular flow regime where thermal transpiration dominates. This paper will present a method for calibrating the molar quantity of gas present in a manifold with a large but constant temperature gradient using a pressure gauge and molar calibration source (MCS) attached to a room temperature section of the manifold. The MCS is a calibrated gas volume and integrated pressure gauge maintained at constant temperature. Molar quantities of gas released from the MCS into the manifold are related to the response of the pressure gauge using empirical n/P functions. These functions accurately relate the manifold pressure to the molar quantity of gas in the manifold as long as the temperature distribution across the manifold remains stable. An example will be presented showing the application and stability of n/P functions used in thermal desorption measurements of hydrogen isotope concentrations in thin metal films. The construction and critical performance characteristics of the MCS will also be described.
Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin company, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.