Micro X-ray fluorescence using a pinhole aperture in quasi-contact mode

Abstract

A cone shaped pinhole aperture (inner diameter, 0.3 mm and outer cone slope, 60 degrees) was developed to reduce the primary X-ray beam size of a conventional XRF setup. This aperture was used in combination with a single capillary. The pinhole was placed very close to the sample surface, that is, in quasi-contact mode. The gap size between the aperture and the sample was adjusted to be less than 0.5 mm. The X-ray fluorescence produced by the sample was measured from this gap at a small takeoff angle. The lateral resolution was evaluated using a tungsten wire placed at different gap sizes. The best resolution, which is almost equal to the pinhole size, was obtained in quasi-contact mode. The X-ray fluorescence signals of Au Lα and Co Kα from a Au-Co grating were analyzed while scanning the sample in front of the conical aperture. From this line scan, it was evident that the best resolution and the highest intensities of X-ray fluorescence were obtained in quasi-contact mode.