Mark T. Bernius

Cryogenic Sample Stage for the CAMECA IMS-3f Ion Microscope.

A simple and inexpensive cold stage developed for use with the Cameca IMS‐3f ion microscope is described. It is easy to use, and temperatures near to that of liquid nitrogen are obtained. Data are presented showing the first analysis of frozen hydrated biological samples with the ion microscope.

Mass analyzed secondary ion microscopy

This paper reviews and critically assesses progress in the field of surface and near‐surface imaging microscopies based on secondary ion mass spectrometry. The ion microscope performs a variety of analytical functions, including complete mass spectra and isotope ratios from areas on the submicron scale, and lateral distribution analysis using ion imaging, with high sensitivity for all elements of the periodic table. Recent developments have improved the ion microscope’s ability to image a specimen’s elemental morphology with spatial resolutions below 100 nm. Criteria for the quantitative evaluation of ion images and the instruments that produce them are reviewed within the framework of information‐transmission theory. A complete and general description of the physical principles guiding the types of instrumentation available is thus presented, with emphasis on the accuracy and precision of an analytical measurement. Several directions for future developments are proposed.

Simps: Secondary ion mass image processing system

A secondary ion mass image processing system (SIMIPS) is presented as a quantitative image analysis tool, with emphasis on an efficient man-machine interface. The combined applications of digital image processing and pattern recognition ensure an intelligent problem-resolving scheme and optimal extraction of information. The system performance is evaluated, and typical applications are presented to illustrate the versatility and usefulness of SIMIPS in analyzing digital images.

Development and characterization of a charge‐coupled device detection system for ion microscopy

The construction of a prototype system capable of directly detecting and digitizing secondary‐ion images using a charge‐coupled device (CCD) is described. The CCD, alone, replaces the microchannel plate, fluorescent screen, and optical recording medium currently in use as the detection system on a CAMECA IMS‐3f ion microanalyzer. Using the CCD as the image detector ensures that the secondary‐ion signal is digitized in the most direct manner possible. A description of the hardware and image‐acquisition process is given. Some of the first secondary‐ion images to be detected using a CCD are presented, and the performance of the CCD as a detector of keV ions is evaluated. While preliminary trials appear promising, results indicate that the optimum efficiency is limited by the design of CCDs commercially available.

High-resolution imaging with the stigmatic ion microscope

An exposition of the lateral image resolution specific to the ion optics in the stigmatic ion microscope (based on ion sputtering mass spectrometry) is presented, with emphasis on investigations leading to the current level of understanding of high‐resolution operation. Modifications are presented for the CAMECA IMS‐3f ion microscope which extends instrumental magnifications to over 2000 diameters and smallest resolvable distances in undistorted images to 0.1 μm. This is necessary to keep pace with the increasingly stringent requirements for the analysis of the shrinking features in fabricated very‐large‐scale integration devices. Conditions for ensuring the formation of undistorted images are given, and the performance of the instrument under these conditions is evaluated. The current concerns of ion microscopic image analysis are then presented and discussed.

Dark‐field stigmatic ion microscopy for structural contrast enhancement

Dark‐field images are observed with a stigmatic (immersion objective lens) secondary ion mass spectroscopic ion microscope by means of an eccentric objective aperture, and are a useful extension of shadow contrast imaging. The spatial resolution in these images is comparable with conventional bright‐field imaging, provided that a narrow energy bandpass is selected to minimize chromatic aberrations. It is demonstrated that the dark‐field method is useful for correlating surface relief with chemical contrast in the compositional secondary ion mass spectroscopic mapping of conventional ion microscopy. Further, based on the information acquired in the dark‐field imaging mode, digital techniques to compensate for asperity artifacts in conventional ion microscopy are proposed.

Ion Microanalysis of Frozen-Hydrated Cultured Cells

Inorganic cations (Na+, K+, Ca+ +, etc.) play important roles in cell function, and cultured cells provide an excellent system to understand the role of ions in the state of health and disease. Ion microscopy, based on secondary ion mass spectrometry (SIMS), provides a powerful technique for such studies (1). The unique ion optics of the instrument are capable of producing visual ion images showing cell morphology with a lateral resolution of ~0.5 µm. However, reliable means of sample preparation and an understanding of SIMS effects is necessary before such studies can be undertaken.

Elimination of residual image distortion in the stigmatic ion microscope

A combination electrostatic octupole stigmator and cosine deflector has been incorporated into the secondary ion‐optical lattice of the stigmatic ion microscope. Distortion‐free images are obtained with a ∼15% improved image resolution and a ∼10% increased secondary ion signal measured at the detector, the latter improvement being beneficial also for depth‐profile (ion microprobe) work. The details outlined in this paper, which are easy to implement, are offered to users of the CAMECA IMS‐3f secondary ion mass spectrometer for a significant improvement in its imaging capability.

Response to ‘‘Comment on ’Mass analyzed secondary ion spectroscopy’’’ [Rev. Sci. Instrum. 59, 2508 (1988)]

Two references in our review article were in error; we regret the oversight. The technical points of disagreement are discussed, and a table comparing the University of Chicago scanning ion microprobe and the Cornell stigmatic ion microscope is provided to clarify one by R. Levi‐Setti [Rev. Sci. Instrum. 59, xxx (1988)].

Temperature stage for ultralow‐temperature oxygen plasma ashing (L2TA)

This paper describes an apparatus that allows the decomposition of organic materials by a radio frequency excited oxygen plasma afterglow at temperatures as low as −70 °C prior to analytical study. The usefulness of this technique is demonstrated by the freeze drying and ashing of frozen‐hydrated biological samples. Subsequent analysis indicates that the cell morphology seen in two dimensions remains intact after such treatment.