  The outgassing rates of three nominally identical 304L stainless steel vacuum
chambers were measured to determine the effect of chamber coatings and heat
treatments. One chamber was coated with titanium nitride (TiN) and one with
amorphous silicon (a-Si) immediately following fabrication. The last chamber
was first tested without any coating, and then coated with a-Si following a
series of heat treatments. The outgassing rate of each chamber was measured at
room temperatures between 15 and 30 {\deg}C following bakes at temperatures
between 90 and 400 {\deg}C. Measurements for bare steel showed a significant
reduction in the outgassing rate by nearly a factor of 20 after a 400 {\deg}C
heat treatment (3.5x10-12 Torr L s-1 cm-2 prior to heat treatment, reduced to
1.7x10-13 Torr L s-1 cm-2 following heat treatment). The chambers that were
coated with a-Si showed minimal change in outgassing rates with heat treatment,
though an outgassing rate reduced by heat treatments prior to a-Si coating was
successfully preserved throughout a series of bakes. The TiN coated chamber
exhibited remarkably low outgassing rates, up to four orders of magnitude lower
than the uncoated stainless steel, but the uncertainty in these rates is large
due to the sensitivity limitations of the spinning rotor gauge accumulation
measurement and the possibility of a small pump speed due to inhomogeneity in
the TiN coating. The outgassing results are discussed in terms of
diffusion-limited versus recombination-limited processes.
