Particle-surface interactions are very important processes making physics practically impossible to apply without putting those interactions into the equation. For particle detection applications, the detection event is triggered by total or partial particle energy deposition upon impact on the detector. Mass spectrometry common ion detectors are Channeltr ons and MCPs, which inherently destroy the particle upon measurement. The IonCCD, a product from the rapidly emerging technology will be characterized against keV ion impact when used in a dispersive mass analyzer.

The IonCCD is used as focal plane array in a sector field instrument of Mattauch-Herzog geometry (MH-MS ). When miniaturized, MH-MS is best suited for low mass range applications (< 100 u). Differently from the two first detector families that most often operate in particle counting mode (time resolved detection) the IonCCD operates in an integration mode (charge integrator). In this case, dispersed ions neutralize on the electrode pixels for a well-defined time known as the integration time. While the potential energy of the detected ions is used for detection, the ion kinetic energy leads to ion-surface interaction, an artifact amplified at extreme low mass detection. This latter can be eliminated by floating the IonCCD or operating it in higher magnetic fields.

 

The artifact manifesting in the mass spectra as distortion (negative peak) due to keV ion impact induced secondary electron emission was modeled and investigated experimentally using electronic stopping power fingerprints. We demonstrate that the artifact increases linearly with ion impact velocity and is dependent in an oscillatory fashion on ion nuclear charge. Both findings are in agreement with the electronic stopping of keV ions with the TiN surface of the IonCCD. 3D simion modeling suggests efficient peak artifact suppression by operating the IonCCD in higher B-field (> 4000 G) and less elegantly by IonCCD-magnet face retarding field. Same model was used to enhance the performance of the instrument, confirming the dynamic mass range (Mmax/Mmin) increase from 16 to 70.

 

The potential IonCCD damage upon keV ion impact through the nuclear stopping effect was investigated by means of atomic Force Microscopy and X-ray Photoelectron Spectroscopy. While AFM confirmed the expected increase in surface roughness, XPS showed no stoichiometry change due to implantation or preferential ion sputtering. The discoloration observed after extensive use was related to carbon layer formation in the roughened irradiated pixel area. Nuclear stopping effects do not seem to affect the detector performance at practical doses.