Scanning transmission ion microscope with a field ion source.

Abstract

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 ...

Helium ion microscopy

“…GFIS have been investigated for a long time 1,[8][9][10] for their use in microscopes. [11][12][13][14] The idea is based on the initial design of a field ion microscope by M€ uller. 15,16 However, only recently, a stable ion source with a high brightness and small virtual source size has been realized by Ward, Notte, and Economou for use in a microscope.…”

The history and development of the helium ion microscope

“…The Levi‐Seti group achieved some level of success using a hydrogen beam (Fig. ) to produce transmission images of a variety of samples (Escovitz et al ., . )…”

“…Applications such as these included high‐resolution imaging, semiconductor mask repair, lithography, and nanofabrication. In the 1970–1990 time frame, GFIS‐based systems were pursued by the Levi‐Seti group at the University of Chicago (Escovitz et al ., ), Seliger's group at the Hughes Research in Malibu (Rensch et al ., ), Aihara's group at JEOL (Aihara, ), and Siegel's group at Cornell (Hanson and Siegel, ). Each of these groups attempted to collect sufficient current by using multiple emission sites on the emitter and consolidating them into a single beam.…”

Observation of High Resolution Microstructures in Thermal Sprayed Coatings and Single Deposited Splats Using Ion Beam Milling

“…Since the first FIB system based on the field ionization of liquid gallium for microprobe applications was developed in 1970s, 5,6) it has been continuously evolved. [7][8][9] As a FIB milling technique facilitates delicate control of beam sizes under 10 nm with current densities of under 1$10 A/cm 2 at desired locations, 10) many researchers in thermal spray field have successfully used the FIB to investigate the cross sectional microstructures of isolated single splats, which are difficult by conventional metallographic preparations due to the splat size with micrometer scales, on substrate by SEM such as air plasma sprayed Ni-5% Al single splats, 11) high velocity oxy-fuel (HVOF) WC-Co splats, 12) high-powder hybrid plasma sprayed yittria-stabilized zirconia splats, 13) and cold sprayed aluminum splats.…”