The transport of bromine out of a graphite source at 300 to 1350K was studied with molecular-beam mass spectrometry. The mass-spectrometer signals from both Br and Br2 varied approximately linearly with the total pressure in the source. A theoretical comparison with the gas-phase density of Br in the source gave good fits. A pressure-dependent grain-boundary diffusion part and a pressure-independent, probably bulk diffusion related part of the signals could be separated in the analysis of the results. Apparent desorption energies for Br and Br2 from the graphite surface were found to be 0.7 and 0.3eV, respectively, from the temperature dependence of the bulk diffusion signal.

Diffusion and Desorption Steps in the Transport of Br and Br2 from a Graphite Effusion Source at High Temperatures, Observed by Molecular-Beam Mass Spectrometry. Sigurdsson, A., Holmlid, L.: Journal of Applied Physics, 1987, 61[8], 2849-55