Investigating ion-surface collisions with a niobium superconducting tunneljunction detector in a time-of-flight mass spectrometer

The performance of an energy sensitive, niobium superconducting tunnel junc tion (STJ) detector is investigated by measuring the pulse height produced by impacting molecular and atomic ions at different kinetic energies. Ions are produced by laser desorption and matrix-assisted laser desorption in a time-of-flight mass spectrometer. Our results show that the STJ detector pu lse height decreases for increasing molecular ion mass, passes through a mi nimum at around 2000 Da, and then increases with increasing mass of molecul ar ions above 2000 Da. The detector does not show a decline in sensitivity for high mass ions as Is observed with microchannel plate ion detectors. Th ese detector plus height measurements are discussed in terms of several phy sical mechanisms involved in an ion-surface collision. Copyright (C) 2000 J ohn Whey & Sons, Ltd.