Hard X-ray nanoprobe scanner

Abstract

X-ray scientists are continually striving to improve the quality of X-ray microscopy, due to the fact that the information obtained from X-ray microscopy of materials can be complementary to that obtained from optical and electron microscopes. In contrast to the ease with which one can deflect electron beams, the relative difficulty to deflect X-ray has constrained the development of scanning X-ray microscopes (SXMs) based on a scan of an X-ray small probe. This restriction has caused severe complications that hinder progress toward achieving ultimate resolution. Here, a simple and innovative method for constructing an SXM equipped with a nanoprobe scanner is proposed. The nanoprobe scanner combines X-ray prisms and advanced Kirkpatrick-Baez focusing mirrors. By rotating the prisms on the order of degrees, X-ray probe scanning with single-nanometre accuracy can be easily achieved. The validity of the concept was verified by acquiring an SXM image of a test pattern at a photon energy of 10 keV, where 50 nm line-and-space structures were resolved. This method is readily applicable to an SXM with a single-nanometre resolution and will assist effective utilization of increasing brightness of fourth-generation synchrotron radiation sources.

Keywords: X-ray mirrors; X-ray nanoprobes; X-ray optics; X-ray prisms; hard X-rays; scanning X-ray microscopy.

Figure 1

A conceptual schematic of the hard X-ray nanoprobe scanner. (a) A schematic of the hard X-ray nanoprobe scanner. (b) A cross section of the scheme.

Figure 2

Schematic and performance of an X-ray prism. (a) A schematic of an X-ray prism and the trajectory of a deflected X-ray beam. (b) Incident-angle dependence of the deflection angle and transmission of the prism. The solid blue (red) line indicates the calculated deflection angle at a photon energy of 10 keV (12 keV). The dashed blue (red) line indicates the calculated transmission at 10 keV (12 keV), when the incident-beam width is 0.6 mm (see the supporting information). The black dots indicate the deflection angles examined by the experiment. (c) Images of the deflected X-ray beams while the incident angle to the prism was varied from 5.4 to 27.9°. The bottom image shows the result without the prism. The scale bar denotes 30 µm.

Figure 3

Demonstration results of the nanoprobe scanner. (a) Far-field images of the focused X-ray without (top) and with (bottom) the prisms. The scale bar denotes 1 mm. (b) The two-dimensional wavefront error of the nanoprobe scanner at the grating plane. The scale bar denotes 50 µm. (c) Focusing profiles in the horizontal (left) and vertical (right) directions. The red dots indicate the experimental data. The black solid lines represent the fitting results with the sum of three Gaussian functions. The focus size was 53.2 nm (H) × 52.5 nm (V) in FWHM. (d) An SXM image obtained using the nanoprobe scanner. A transmission image of the radial test pattern made of 500 nm thick tantalum. The scale bar denotes 0.5 µm.