Imaging of 30nm gold spheres by dark-field scanning transmission x-ray microscopy

Abstract

In a scanning transmission x-ray microscope (STXM), such as that operated at the beamline X-lA at the National Synchrotron Light Source, it is possible to obtain dark-field images by blocking the undeviated transmitted photons so that only x rays scattered by the specimen are detected. Although the signal that is detected in dark-field is much weaker than the conventional bright-field signal the method offers much higher contrast of small features and the possibility of detecting small features with higher signal to noise for the same incident x-ray flux. Also, the signal depends on both the amplitude and phase of the specimen, rather than just the amplitude. One important application of dark-field x-ray microscopy is the imaging of gold-labelled biological specimens. This unites the advantages of x-ray microscopy (the ability of imaging thick biological objects, low radiation dose) with those of gold labelling (specific-site or specific-protien labelling, well documented protocols).The x-ray microscope consists of the scanning transmission x-ray microscope, in which a zone-plate is used to focus monochromatic x rays to a probe, through which the sample is scanned.