INVESTIGATION OF ALUMINUM BLOW-OFF BEAM COMPOSITION BY LASER IONIZATION MASS-SPECTROMETRY

The neutral particle composition of Al blow-off beams was studied usin g a time-of-flight mass spectrometer (TOFMS) with UV laser photoioniza tion. The neutral components of the Al beam were injected into the MS and the particles were ionized by the UV laser pulse. The ions were ma ss separated by a reflectron type TOFMS so as to find out if there wer e multi-atomic components in the beam besides the atoms. Two kinds of neutral particles were found in the blow-off beam by this method, name ly Al atoms and Al-2 dimers. Clusters consisting of more than two atom s have not been found. The delay time between the ruby and excimer las er pulses (i.e. the generation of the beam and the ionization of the n eutral particles) was varied in order to determine the velocity distri bution of the particles. The velocity distributions of both constituen ts showed a double peaked structure indicating the presence of particl e packets originating from different sources. The first and second pea ks of the velocity distributions could be fairly well fitted by Maxwel lian distribution functions.