Position-sensitive detectors and monolayer structural studies

One of the scientific domains where the recent introduction of position sensitive detectors (PSDs) has been a decisive factor, is the structural study of physisorbed monolayers and the different phase transitions which occur in these two-dimensional systems. The difficulties of the experiments and the decisive contribution of the PSD are described. The reproducibility needed in the position of a moving detector in order to reach the performance required for this kind of study is estimated. The study of small changes in spectra found in submonolayer phase transitions studies can however be achieved. The example used is of a graphite sample compared with graphite with one full tetrafluoromethane monolayer. (U.K.)