21. Recent Results from the ~tony Brook Scanning Microscope

We have recently completed our first run [21.1] with the Stony Brook scan­ ning microscope at the National Synchrotron Light Source (NSLS), using a Fresnel zone plate fabricated at IBM as the principal focusing element. The brightness of this synchrotron radiation source coupled with our high- reso­ lution optics have made a substantial improvement in resolution and through­ put compared with our earlier 'work [21.2,3] which lacked these features. The microscope images biological specimens by forming a submicron spot of monochromatic soft x rays which it scans in a raster fashion across the spe­ cimen, located in a one-atmosphere environment. The resolution is presently determined by the size of this spot. The transmitted radiation is detected by a flow proportional counter, the output of which is used to control a computer-generated real-time image. Since the specimen is in air, the ineffi­ cient optics are all located upstream of the specimen, and the detector is over 50% efficient, the radiation dose to unstained wet natural specimens is minimized. We believe [21.4] that the resolution limit for scanning micro­ scopy of unfixed specimens will be set more by damage considerations than by optics; our scheme aims to minimize this damage. This paper considers the components of the microscope in turn, starting from the monochromator and the optics. How we test our optics is considered in some detail as it illustrates the microscope's capabilities as well as the optical performance achieved to date. Some of our first images of biolo­ gical specimens are then presented. We conclude with some remarks about the future of the microscope.