Differences between surface preparation by vacuum, flowing gas, and heat. Initial cleaning of samples is faster using a combination of heat and flowing gas such as done with the FlowPrep. When time is not an important factor, vacuum can yield an ultimately more complete degassing. With most samples, the difference between the two methods is not detectable. Therefore, flowing gas is typically used to gain the benefit of speed.
Elevated temperature is the most important factor in gaining an effective degas of sample surfaces.
When temperature can be raised to a level that causes adsorbed molecules to be released from their adsorbed sites, the sweeping action of flowing gas is very effective in flushing out the desorbed gases before they can be readsorbed. C. Otherwise, damage to the sample structure could result for some types of sensitive materials. There are two choices. First, one can transfer samples with the sample tube filled with a non-adsorbing gas at atmospheric pressure. Some samples do not take up contaminants very rapidly and simply sealing the sample tube with a stopper protects the sample sufficiently during transfer.