Electric field penetration effects in time-of-flight measurements

The field imperfections in the mass spectrometers were studied by means of two Plasma desorption time-of-flight mass spectrometers. The experiment was performed by investigating the influence of the field leakage due to the post acceleration on the measured values of the initial axial energy of secondary ions, in the presence of the grounded grids, which are usually employed to separate the fields inside the mass spectrometers. It has been found that the changes of 0.4% in the effective lengths of the acceleration gap and the field free region respectively are possible due to the field penetration into those regions from the post acceleration gap of the mass spectrometer. The analyses also show clearly the significance of the influence of the field penetration of the post acceleration on the measured values of the initial axial energy. The initial axial energies of H⁺, H2 ⁺, ⁶Li⁺, ⁷Li⁺, Na⁺ and Cs⁺ measured under the minimum field penetration condition were found to be 4.7 eV, 4.7 eV, 0.6 eV, 0.7 eV, 0.7 eV and 1.3 eV respectively, and they had been reduced to 4.4 eV, 4.4 eV, 0.3 eV, 0.4 eV, 0.4 eV and 1.0 eV once the values were corrected separately for field penetration. These results indicate that the field penetration through a grid is a secondary effect and it is hardly unavoidable in the mass spectrometers.  

doi:10.4038/sljp.v4i0.191  

Sri Lankan Journal of Physics, Vol.4 (2003) 35-45