INVESTIGATIONS ON THE ION ENERGY-DISTRIBUTION IN AN ANALYTICAL RADIOFREQUENCY GLOW-DISCHARGE AND ITS MASS-SPECTROMETRIC APPLICATION

For studies of fundamental processes, the energy distributions of diff erent ion species formed in an analytical radiofrequency glow discharg e (RF GD) were determined by two different methods. On the one hand, t he energy spectra were recorded by scanning the accelerating voltage a t narrow energy slit between the electrostatic and magnetic analyzer o f a double-focusing mass spectrometer (SMI, Varian MAT, Bremen, German y). On the other hand, a grid, to which a variable retarding potential could be applied, was placed between the ion source and the mass spec trometric analyzer. It was found that the kinetic energy of the ions o f 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 molec ular ions like MO+ (M = matrix). The absolute values of the average ki netic energies of the sample ions as determined by the retarding poten tial 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 (Arf) ions relative to the intensi ty of the ions of the sample material by more than one order of magnit ude, which helps to improve the analytical capabilities of RF GDMS. (C ) 1997 Elsevier Science B.V.