Experiments with a low-resolution scanning transmission ion microscope, using hydrogen ions from a field ionization source, indicate that it will be feasible by this approach to aim at high-resolution ion microscopy. Micrographs of unstained biological specimens have been obtained by critical range absorption of a 55 keV hydrogen ion beam at a resolution of 2000 A.As a first step toward the development of a high-resolution scanning transmission ion microscope, we have constructed and operated a 65 kV prototype ion-gun scanning transmission ion microscope which accelerates and focuses hydrogen ions from a field ionization (1) source. Our aim is to emulate and complement the achievements of scanning transmission electron microscopy (2), ultimately at comparable resolution, by taking advantage of the interaction properties of fast ions with matter (3). The latter include processes such as charge exchange and molecular ion dissociation which should result in contrast mechanisms unavailable to the electron microscope.We present here experimental data that are relevant to the feasibility of a high-resolution scanning transmission ion microscope and show the first low-resolution images of biological specimens obtained with the prototype instrument.Previous attempts at using ions, and in particular protons, to make images of small objects with conventional electron microscope optics have been reviewed by Grivet (4) and more recently by Levi-Setti (3). The aim was to obtain higher resolution than with electrons. This was believed to be possible because of the ion's shorter De Broglie wavelength. The potential of proton charge exchange as a possible new source of contrast was recognized by Chanson and Magnan (5).Several factors, however, conspired to abort this development of the proton microscope as a high-resolution and viable instrument. In our view, the principal limitations originated in the approach of conventional microscopy itself, where the large rate of proton energy loss (10-30 eV/A in traversing organic materials at 100 keV) causes irreparable chromatic aberration. For this reason, we have chosen the approach of scanning transmission microscopy, where no optics is affected by the beam-specimen interaction so that the latter can be used to advantage in producing contrast.The considerations leading to the optimum parameters and the resulting performance in the scanning transmission electron microscope have been recently reviewed by A. V. Crewe (6) and E. Zeitler (7). We have extended the analysis of these authors to the case of a proton probe (8). The basic problem consists of optimizing the design parameters to obtain the maximum probe current in the smallest beam spot. How closely the theoretical microscope resolution can be approached in practice depends essentially on the specific brightness of the ion (or electron) source, since the probe current must exceed that required to obtain an intelligible picture in a practicable scan time. We consider a microscope consisting of a source of radius 6 and an ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.