Kazuhide Nagashima

High precision isotope micro-imaging of materials

Abstract Secondary ion mass spectrometry (SIMS) is widely used to identify the isotope ratio of the micro-area of materials. We demonstrate that the precision and spatial resolution of an ion microscope using SIMS coupled with a newly developed solid-state ion imager can be extended to two-dimensional isotope ratio imaging with permil-precision. An isotopic map for oxygen clearly reveals the distribution of 4% enrichment of 16 O in spinel particles embedded in melilite from a Ca–Al-rich inclusion of a carbonaceous chondrite. This characterization technique called isotopography thus provides the eyes to see small heterogeneity of isotope abundance in micro-scale. It is likely to find broad application in earth, material, and life science research.

Noise characteristics of stacked CMOS active pixel sensor for charged particles

Abstract The noise characteristics of a stacked CMOS active pixel sensor (SCAPS) for incident charged particles have been analyzed under 4.5xa0keV Si + ion irradiation. The source of SCAPS dark current was found to change from thermal to electron leakage with decreasing device temperature. Leakage current at charge integration part in a pixel has been reduced to 0.1xa0electronsxa0s −1 at 77xa0K. The incident ion signals are computed by subtracting reset frame values from each frame using a non-destructive readout operation. With increase of irradiated ions, the dominant noise source changed from read noise, and shot noise from the incident ions, to signal frame fixed-pattern noise from variations in sensitivity between pixels. Pixel read noise is equivalent to ten incident ions. The charge of an incident ion is converted to 1.5xa0electrons in the pixel capacitor. Shot noise corresponds to the statistical fluctuation of incident ions. Signal frame fixed-pattern noise is 0.7% of the signal. By comparing full well conditions to noise floor, a dynamic range of 80xa0dB is achieved. SCPAS is useful as a two-dimensional detector for microanalyses such as stigmatic secondary ion mass spectrometry.