Crystal face specificity of nitrogen adsorption on a platium field emission tip

The adsorption of nitrogen on platinum is studied with a field emission microscope equipped with a probe-hole assembly to enable quantitative emission measurements on individual crystal faces. The results are implemented by photoelectric measurements on platinum films. Adsorption at 80 K is found to result in a large and face-specific decrease in the work function. On crystal planes containing B₅ and B₆ sites this decrease is larger than on those exposing B₃ and B₄ sites only. No significant crystal face specificity is found, however, for the rate of temperature programmed desorption of nitrogen. It follows that the heat of nitrogen adsorption is essentially equal for faces with B₃, B₄, B₅ and B₆ sites. This result is at variance with certain postulates in the literature.