Mass Spectrometer

A UTI Model 100C quadrupole mass spectrometer, capable of detecting molecules with mass to charge ratios from 1 to 300, is used to collect TPRS and ESD data.

When performing TPRS experiments, the mass spectrometer is used to detect products desorbing from the crystal surface during heating. The spectrometer is enclosed by a shield with a 1/8" diameter aperture, to optimize detection of the molecules desorbing directly from the center of the crystal. The mass spectrometer signal of the gaseous desorption products is monitored as a function of both time and temperature using the TPRS98 program interfaced to the mass spectrometer and thermocouple.

Isothermal ESD of the multilayers and monolayer of reactants on the Mo(110) surface is carried out to determine the products of electron irradiation. The electron beam used in our experiments is generated using the same UTI Model 100C quadrupole mass spectrometer used for detection. Electrons emitted from the mass spectrometer filament are accelerated to an energy of 55 eV. The electron energy can be modified by biasing the crystal.