Investigations on the ion energy distribution in an analytical radiofrequency glow discharge and its mass spectrometrical application

Abstract

For studies of fundamental processes, the energy distributions of different ion species formed in an analytical radiofrequency glow discharge (RF GD) were determined by two different methods. On the one hand, the energy spectra were recorded by scanning the accelerating voltage at narrow energy slit between the electrostatic and magnetic analyzer of a double-focusing mass spectrometer (SM1, Varian MAT, Bremen, Germany). On the other hand, a grid, to which a variable retarding potential could be applied, was placed between the ion source and the mass spectrometric analyzer. It was found that the kinetic energy of the ions of the discharge gas (Ar +) and of CO + ions (residual gas) lies about 10 eV lower than the kinetic energy of the sample material ions or molecular ions like MO + (M = matrix). The absolute values of the average kinetic energies of the sample ions as determined by the retarding potential technique were found to be about in the range of 15 eV. With the aid of the obtained results it was possible to reduce the intensity of the detected CO + and discharge gas (Ar +) ions relative to the intensity of the ions of the sample material by more than one order of magnitude, which helps to improve the analytical capabilities of RF GDMS.