surface contamination

in surface analysis
Material in the experimental surface which is either not characteristic of the sample or which would not be present if the sample had been prepared in an absolute vacuum by methods not contacting other substances to the sample.
PAC, 1979, 51, 2243. (General aspects of trace analytical methods—IV. Recommendations for nomenclature, standard procedures and reporting of experimental data for surface analysis techniques) on page 2247 [Terms] [Paper]