Cryotrapping assisted mass spectrometry for the analysis of complex gas mixtures

A simple method is described for the unambiguous identification of the individual components in a gas mixture showing strong overlapping of their mass spectrometric cracking patterns. The method, herein referred to as cryotrapping assisted mass spectrometry, takes advantage of the different vapor pressure values of the individual components at low temperature (78 K for liquid nitrogen traps), and thus of the different depletion efficiencies and outgassing patterns during the fast cooling and slow warming up of the trap, respectively. Examples of the use of this technique for gas mixtures with application to plasma enhanced chemical vapor deposition of carbon and carbon-nitrogen hard films are shown. Detection of traces of specific C-3 hydrocarbons (< 50 ppm of initial methane) in methane/hydrogen plasmas and the possible trapping of thermally unstable C-N compounds in N-2 containing deposition plasmas are addressed as representative examples of specific applications of the technique. (c) 2007 American Vacuum Society.