| Research Abstract |
We have developed and manufactured a trial device of 2-dimensional CCD ion-detector system for the CAMECA 3f Secondary Ion Mass Spectrometer (SIMS) for observing high-resolution 2-dimensional isotope distribution on a polishd specimen surface. The system is composed of following units. (1) CCD detector unit, (2) CCD cooling dewar, (3) CCD drive unit, (4) CCD control unit, (5) CCD monitor unit, (6) control computer unit and (7) color monitor. The CCD detector unit is constructed by a Micro Channel Plate, a fluorescence film and a CCD (Japan TI Co. Ltd, type VID-272 : 6 x 9 mm : 789 x 242 pixels) , and the secondary ion is transformed and amplified to electron. It was found that the most important point for obtaining high S/N ratio is the reduction of dark current. For this purpose, the CCD is refrigerated to-60 ﾟC using liquid Ni, and this treatment makes possible weak ion image measurement and long term exposure. After the elimination of noise from the observed data, several steps of image correction (brightness correction, contrast correction, accumulation time correction, MCP sensitivity fluctuation correction, image distortion correction) were made.
This system have been applied on the observation of 2-dimensional distribution of ^<16>O and ^<18>O oxygen isotope on a Allende chondrite meteorite, and succeeded to obtain ^<18>O distribution mapping which has never been reported previously. As the results, it becomes possible to obtain the 2-dimensional information of 250 x 250 mum area specimen surface from one irradiation of primary ion beam and measuring very weak ion image (200 count/sec in the case of ^<18>O). Although there are several problems to solve for improving this system in future, this result proves the high sensitivity of the CCD detector system.
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