The University of Hawai'i Cameca Ims 1280 Has a New Solid State Imaging Detector Called

The University of Hawai'i Cameca ims 1280 has a new solid state imaging detector called SCAPS. A stacked CMOS-type active pixel sensor for charged particles, SCAPS was developed at the Tokyo Institute of Technology (Nagashima et al., 2001, Yurimoto et al., 2003). The SCAPS detector will permit direct ion imaging of fine-grained samples and will permit identification of isotopically or chemically anomalous grains at a spatial resolution of a few tenths of a micron (Nagashima et al., 2004; Kobayashi et al., 2005).

SCAPS is composed of a rectangular array of 608x576 independent micro-detectors or "pixels." When placed in the position where the channel plate normally sits, SCAPS can collect two-dimensional ion images. The SCAPS detector has sufficiently well understood and reproducible characteristics to permit quantitative isotope analysis in two dimensions using a stigmatic SIMS such as the Cameca ims 1280. SCAPS has several advantages over conventional systems, including two-dimensional detection, wide dynamic range, no insensitive period, direct detection of charged particles, constant ion sensitivities among nuclides, and a high degree of robustness. The SCAPS can measure high ion flux with an accuracy of within twice the statistical error and with a detection limit corresponding to 3 ions.

The SCAPS vacuum housing equipped to the UH ims-1280 ion microprobe is shown in the left image. The top-right image shows inside of the SCAPS vacuum housing. The SCAPS device (bottom-right image) is attached to a cold finger and liquid nitrogen dewar, in order to cool the SCAPS down to ~80K. The central gold part of the SCAPS is imaging area composed of 608×576 pixels.

27Al+ ion image obtained with SCAPS. Sample was a Cu-grid with 25 µm pitch on an Al-substrate. SCAPS can detect ions directly and avoid degrading spatial resolution associated with signal conversions in a conventional imaging system composed of micro-channel plate, fluorescent screen, and CCD camera. (right): An intensity profile across a boundary between Al-substrate and Cu-grid shows lateral resolution of SCAPS+ims-1280 is high as ~0.5 µm.

Comparison of scanning electron image (BSE) and SCAPS isotope images (Si-/O- and d18O) of an area within a Ca-Al rich inclusion in Efremovka meteorite. The BSE and SCAPS Si-/O- images show that the area is composed of anorthite, melilite, fassaite, and spinel. Variation in oxygen isotopic compositions is clearly visible. d18O gives the shift in isotope ratio in parts per thousand relative to standard mean ocean water (SMOW), i.e., bright gray regions have oxygen-isotope composition similar to SMOW, while dark gray regions have anomalous oxygen-isotope composition. The image demonstrates that our imaging technique has a capability of quantitative O-isotope mapping with permil-level precision and ~1 µm spatial resolution.