Temperature desorption spectroscopy
Temperature desorption spectroscopy (TDS) is a method for observing desorped molecules from a surface when the surface temperature is increased. When molecules contact a surface, they adsorb onto it, releasing energies as binding energy. The binding energy varies with the combination of the adsorbate and surface, which changes the desorption temperature. Thus TDS shows information on the binding energy. Since TDS observes the mass of desorped molecules, it shows what molecules are adsorbed on the surface. Moreover, TDS recognizes the different adsorption conditions of the same molecule from the differences between the desorption temperatures of different molecules. TDS also obtains the amount of adsorbed molecules on the surface from the intensity of the peak of the TDS spectrum. To measure TDS, one needs a mass spectrometer, such as a quadrupole mass spectrometer or a time-of-flight (TOF) mass spectrometer, under ultrahigh vacuum (UHV) conditions. The amount of adsorbed molecules is counted by increasing the temperature at a heating rate of 10 K/sec. Several masses are simultaneously counted by the mass spectrometer, and the intensity of each mass as a function of temperature is obtained as a TDS spectrum. If the heating procedure is controlled by a computer, TDS is called temperature programmed desorption (TPD). TPD is a more accurate method than TDS, although the obtained features are the same as TDS.
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