Schematic diagram of the TPD apparatus

Partial pressures were measured using a Dycor M200M quadru-pole mass spectrometer. In its PRESSURE-TIME mode the mass spectrometer displayed and recorded the partial pressures of 

TPD data acquisition for both temperature and pressure was accomplished using an IBM-XT PC. The acquisition software was written in ASYST by W. Clark and modified by G. Chottiner in the Physics Department of Case Western Reserve University. Pressure data was digitized by the mass spectrometer, but the continuous voltage signal from the thermocouple was converted into discrete numbers and fed to the computer by a Keithley 570 A/D converter. The pressure data could be plotted as a function of time or 

To minimize confusion between the desorption features from the sample surface and those from the sample holder and/or mounting materials, a collimator for the mass spectrometer was used. The circular opening of the collimator was about the size of the sample (1.1 cm diameter). During TPD experiments, the sample surface faced the opening of the collimator and was 3-5 mm away from it. 

For a linear heating model, equation 2.4 is differentiated to find the peak temperature Tp at which the desorption rate is a maximum (d S/dt - 0), 

Redhead s first and second order formulas can be easily obtained by substituting n - 1 and 2 into ( 2.5 ) as  

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