A gas ionisation Direct-STIM detector for MeV ion microscopy

Direct-Scanning Transmission Ion Microscopy (Direct-STIM) is a powerful technique that yields structural information in sub-cellular whole cell imaging. Usually, a Si p-i-n diode is used in Direct-STIM measurements as a detector. In order to overcome the detrimental effects of radiation damage which appears as a broadening in the energy resolution, we have developed a gas ionisation detector for use with a focused ion beam. The design is based on the ETH Frisch grid-less off-axis Geiger–Müller geometry. It is developed for use in a MeV ion microscope with a standard Oxford Microbeams triplet lens and scanning system. The design has a large available solid angle for other detectors (e.g. proton induced fluorescence). Here we report the performance for imaging ReNcells VM with μm resolution where energy resolutions of <24 keV fwhm could be achieved for 1 MeV protons using isobutane gas