7 counts/s flux can be expected. Note that increasing the acquisition time should lead to significant signal level enhancement with our EDX-SDD device. These results show that it is possible to collect the fluorescence signal using a RG-7388 thinner
capillary without any loss on the signal level if it is close enough to the surface. Of course, using a brighter primary source such as a rotating anode or a liquid-metal jet anode electron-impact X-ray source [20], a significantly higher signal (up to 100 times) can be expected Moreover, replacing the cylindrical capillary at the entry of the detector by an elliptical one would lead to an extra gain of 20 [21, 22]. Thus sub-micro-resolution XRF would be possible with an in-lab excitation source. Of course, working with a synchrotron source would lead to higher signal magnitude
which could allow to further shrink the capillary radius, and a sub-100-nm lateral resolution could probably be reached. The short capillary-sample working distance suggests that the cylindrical capillary could act as a scanning probe microscope Pifithrin-�� manufacturer tip to acquire simultaneously sample topography and chemical mapping by XRF analysis [23], as already demonstrated for simultaneous SNOM-XAS XEOL [17] apparatus. Moreover, within this perspective, the spatial resolution of the detection would not be limited by the critical angle θ c because the extremity of the glass tube would be approached in mechanical near-field interaction with the sample. Conclusions In this work, we have developed a test-bed consisting in a low power Rh-source focused with a polycapillary lens on a cobalt sample and in a cylindrical capillary to collect the fluorescence signal
at the vicinity of the surface. Both capillaries are positioned in a confocal-like configuration. The primary beam has been first characterized, and the lateral profile of the X-ray spot was found to be a Gaussian which radius and magnitude depend on the X-ray energy range. The average radius measured at 1/e is 22 μm. Then, a cobalt sample was placed in the focal plane of the lens, and the generated fluorescence was collected through a cylindrical capillary fixed on a SDD EDX dectector. The thin detection capillary was then scanned across the sample fluorescence emitting zone. Significant Clomifene signal was collected over a total capillary travel in very good agreement with what can be deduced from simple geometrical considerations. The fluorescence signal magnitude increases as r cap 1.8 where r cap is the capillary radius. The extrapolated value for a 0.5-μm radius capillary suggests that sub-1-μm resolution XRF should be possible with a laboratory source. Of course, increasing the source brightness, i.e. working with liquid-metal or synchrotron sources could probably lead to reach 100-nm resolution. Operating at short working distances will allow the increase of the signal level detection.
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