Determination of the amount of gas adsorption on SiO2/Si(100) surfaces to realize precise mass measurement

The adsorption isotherms on SiO2/Si(100) surfaces were measured using a vacuum mass comparator. Samples with a surface area difference of 816.6 cm(2) were used for the measurement, and a substitution weighing method was adopted to reduce the uncertainty due to the drift and non-linearity of the indication of the mass comparator. We measured adsorption isotherms of water vapour on the SiO2/Si(100) surfaces outgassed at a temperature of 500degreesC and found that dissociative adsorption caused an irreversible increase of 0.028 mug cm(-2) with an uncertainty of 0.004 mug cm(-2) (k = 1). We also found that the physical adsorption of water molecules on hydroxylated surfaces had a monolayer capacity of 0.004 mug cm(-2) with an uncertainty of 0.002 mug cm(-2) (k = 1). In addition, the adsorption isotherms for ethanol vapour and n-octane vapour, which were different from water vapour in adsorption properties, were measured and analysed.