University of Wisconsin-Madison Physical Sciences Lab

WiscSIMS

Image of WiscSIMS

WiscSIMS, the Wisconsin Secondary Ion Mass Spectrometer, is a Cameca SIMS1280 instrument operated by the UW Madison Geology Dept. It is capable of analyzing sample spots of 10 microns to as small as 0.25 microns diameter, for isotopic composition, to precision of up to 100 parts per million. However, its targeting of samples is limited by its built-in optical microscope and color camera to a few microns resolution.

Noriko Kita, senior scientist, contacted PSL seeking ultraviolet illumination, to improve visible resolution. Available design data for the complex optical system (much of which is contained inside the vacuum system) was quite limited.

As an initial step the light source was quickly and inexpensively converted by PSL electronics engineer Dan Wahl to a blue LED, improving resolvable widths by about 1.4:1. With these results the Geology Dept. sought and was granted NSF funding for PSL to carry development further.

Ken Kriesel, PSL mechanical engineer, performed a design study to estimate cost versus three candidate wavelengths and resolutions. A target wavelength was selected and a process of reverse engineering and gradual improvement followed. The instrument can now resolve spots of less than 2 microns diameter (several times the number of features per unit area of the original system). Further development is feasible.

The manufacturer’s engineer had said it couldn’t be done. At PSL we’ve done it.

Original full-visible resolution image Blue 455nm resolution image
402nm UV resolution image 375nm UV image
365nm UV resolution monochrome image 365nm UV resolution color image