MICRO X-RAY BEAM PRODUCED WITH A SINGLE GLASS CAPILLARY FOR XRF ANALYSIS

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1 Copyright JCPDS-International Centre for Diffraction Data 2013 ISSN MICRO X-RAY BEAM PRODUCED WITH A SINGLE GLASS CAPILLARY FOR XRF ANALYSIS Shintaro Komatani 1),2), Shintaro Hirano 1), Tomoki Aoyama 2), Yoshihiro Yokota 2), Hideo Ueda 2), Kouichi Tsuji 1) 1) Applied Chemistry & Bioengineering, Graduate School of Engineering, Osaka City University, Sugimoto , Sumiyoshi-ku Osaka Japan TEL/FAX: +81-(0) ; tsuji@a-chem,eng.osaka-cu.ac.jp 2) HORIBA, Ltd. 2 Kisshoin-Miyanohigashi-cho, Minami-ku, Kyoto, Kyoto , Japan ABSTRACT XRF analysis is available for the quantification of elements and provides a great advantage in material science. Although XRF analysis has the advantage of nondestructive analysis, SEM-EDS gives elemental maps with a spatial resolution of a fewer micrometers. Thus, the developments and applications of micro-xrf analysis are important research trends of XRF analysis. A single glass capillary lens is the effective X-ray optics for micro-xrf in the laboratory. Actually, a beam diameter of 10 micrometers is available with commercial instruments such as X-ray analytical microscope. In the author's research group, a combination of a single glass capillary and a conical pinhole was studied for improving a spatial resolution in a micro XRF analysis. In this study, another approach is discussed. We used a micro-focused X-ray tube (focal spot size: 50 x 50 micrometers, Mo anode, 50 kv, 0.5 ma) and a single glass straight capillary evaporated with Au and a small metal ball (400 m). The center part of X-rays emitted from the X-ray tube was stopped by the metal ball, while the outer part of X-rays was totally reflected on the inner wall of the single capillary. A focused X-ray beam had m in diameter, and was observed at a distance of 43 mm from the output of the glass capillary. Moreover, the divergence angle of the beam was 6 mrad. This long working distance with low divergence angle will be a practically useful advantage of this X-ray optic. INTRODUCTION With the development of nanotechnology, there has been a strong demand for high resolution and high speed X-ray analytical microscope. Thus, for the development of the micro-xrf analysis, it is important to research the trends of XRF and apply XRF to wide areas (Tsuji, et al., 2012). In the case of conventional X-ray analytical microscopes in Figure 1, the focused primary X-ray with conventional X-ray tube and single glass capillary lens (Ohzawa, et al., 2004) or poly capillary lens (Kumakhov, 2000; Wegrzynek, et al., 2008) were used for the X-ray micro analysis.

2 This document was presented at the Denver X-ray Conference (DXC) on Applications of X-ray Analysis. Sponsored by the International Centre for Diffraction Data (ICDD). This document is provided by ICDD in cooperation with the authors and presenters of the DXC for the express purpose of educating the scientific community. All copyrights for the document are retained by ICDD. Usage is restricted for the purposes of education and scientific research. DXC Website ICDD Website -

3 Copyright JCPDS-International Centre for Diffraction Data 2013 ISSN The most important performances of the X-ray analytical microscope are spatial resolution and sensitivity. To achieve high spatial resolution of X-ray microscope, it is not enough to reduce the focus spot size of incident X-ray beam. As shown in Figure 2, low divergence angle is required to keep fine X-ray beam inside the sample, because the analysis depth of X-ray microscope is deep. Further, a high intensity beam is required for the fine measurement and the long working distance for uneven surface analysis. But, reducing the spot size and divergence angle will simply reduce the intensity of X-ray beam. Therefore it is necessary to develop a focusing capillary lens with long working distance (WD), small spot size, high intensity, and low divergence angle at the same time. The X-ray beam with such performance is required not only for an X-ray analysis microscope but the confocal 3D-XRF spectrometer used for analysis below the surface (Janssens, K., et al., 2004; Patterson, et al., 2006; Nakano and Tsuji, 2010; Tsuji and Nakano, 2011; Nakano, et al., 2011). Actually, a beam diameter of 10 m is available with commercial instruments such as X-ray analytical microscope (Ohzawa, et al., 2004). In the author's research group, a combination of a single glass capillary lens and a conical pinhole was studied for improving a spatial resolution in a micro XRF analysis (Matsuda, et al., 2009). X-ray source X-ray beam CCD camera Y Sample Capillary lens Fluorescent X-ray (a) Highly divergent beam (b) Low divergent beam Short Long Fluorescent Fluorescent WD X-ray WD X-ray Measuring object X Sample stage XY Scanning Transmitted X-ray Base material Sample with uneven surface Fig.1 Schematic diagram of the X-ray analytical microscope. A focused X-ray beam is irradiated onto the sample, and fluorescence X-ray is acquired for elemental analysis. By scanning the sample stage in X-axis and Y-axis direction, it can get the elemental map images. At the same time, by measuring the intensity of transmitted X-ray, a transmitted X-ray image is obtained. This image has the information of thickness, density and internal structure of the sample. Here a glass capillary to achieve small spot size and high intensity of incident X-ray beam is used. Fig.2 The relation of two kinds of X-ray beams, (a) highly divergent beam and short WD and (b) low divergent beam and long WD In this paper, another approach is discussed. We have developed a new method that successfully satisfies the above requirements. Our method uses Au coated capillary lens (Nakazawa, et al., 2011a; Nakazawa, et al., 2011b) and a small metal ball placed between an X-ray source and the capillary lens. The ball blocks unwanted X-rays which spread the spot

4 Copyright JCPDS-International Centre for Diffraction Data 2013 ISSN shape. A focused X-ray beam had m in diameter, and was observed at a distance of 43 mm from the output of the glass capillary lens. Moreover, the divergence angle of the beam was 6 mrad. This long working distance with low divergence angle will be a practical useful advantage of this X-ray optic. Here, we report that the expansion of X-ray micro analyzer using this technique. X-RAY TRACING SIMULATION We developed an Au coated glass capillary lens, which can achieve a long working distance, small spot area, high intensity and low divergence angle for the new X-ray analytical microscope whit a unique arrangement of the X-ray source, a capillary lens evaporated with Au and a small metal ball. Figure 3 shows the schematic image of the Au coated glass capillary lens: inside diameter is 700 m and the length is 39 mm. Gold is electroplated inside the capillary lens with 100 nm thickness. The ball (400 m diameter) made by Solder (tin 60%, lead 40% contain it) which was generally used in an electric printed circuit board was used. The X-ray source is Mo anode; the focal spot size is 50 m. The X-rays are totally reflected on the inner wall of the capillary lens. The critical angle depends on the density of the glass capillary lens and energy of the X-ray as shown in the following equation: where c (degree) is the critical angle of the total internal reflection of X-ray, E(keV) is energy of X-ray, and (g/cm 3 )is the density of reflective material. (1) In the case of Mo K (17.44 kev), the critical angle is 0.26 o as the capillary uses Au (density = g/cm 3 ). Therefore the X-ray beam is focused at 145 mm from the focal spot of the X-ray tube. 50 m focus of an X-ray tube [mm] Small metal ball 400 m diameter 41 mm 63 mm 145 mm 39 mm Glass capillary with Au coating 700 m diameter 0.26 [mm] 43 mm Focal spot (100 m) of X-ray beam Fig.3 Simulation result of Au coated glass capillary

5 Copyright JCPDS-International Centre for Diffraction Data 2013 ISSN The metal ball is utilized to block of the low angle X-rays and non-absorbed X-rays. Figure 3 shows the diagram of the simulation results of the focal spot size of the X-ray beam at the focus position with 50 m focus of the X-ray tube. As a result, the spot size is 100 m. EXPERIMENTAL SETUP Figure 4 shows our experimental setup for micro-xrf analysis using the Au Coated glass capillary lens with the small metal ball. The X-ray tube was equipped with a Mo target (MCBM B, rtw, Germany; the focal spot size: m in accordance to EN standards: EN /1999). The X-ray tube was operated at voltage of 50 kv and tube current of 0.5 ma. The Si-PIN detector, (XR-100CR, Amptek Inc., USA, sensitive area: 7 mm 2, energy resolution: 194 ev at 5.9 kev) was used. The X-ray signal outputted from the detector was processed by the analog shaping amplifier (PX2CR, Amptek Inc., USA), the analog to digital converter (ADC500, Laboratory Equipment Corporation, Japan) and the multichannel analyzer (NT-2400H, Laboratory Equipment Corporation, Japan). The original glass capillary was made from soda glass and Au coated capillary lens. It was set according to geometry of Figure 3. The designed length, input focal distance, and output focal distance (OFD) were 39, 63, and 43 mm, respectively, for Mo K. The center of the metal ball was from the target of an X-ray tube at 41mm distance. Au coated glass capillary lens was controlled by a manual X Y Z stage 2 (GYM03S-C1 X Y stage and GZM035-X1 Z stage; Kohzu Precision Co., Ltd., Japan). The metal ball was placed on an automatic X Y Z stage 1 (YM05A-R1 X Y stage and ZA05A-V1 Z stage; Kohzu Precision Co., Ltd., Japan). Furthermore, the wire used as a sample for this evaluation was also controlled on X-Y-Z stage 3 (YA05A-R1 X Y stage and ZA07-11 Z stage; Kohzu Precision Co., Ltd., Japan). Each automatic positioning stage was controlled at 0.25 m steps by stepping motors driven by a computer. The set of motor drivers and a motor controller (NT2400, Laboratory Equipment Co., Japan) tweaked the X-Y-Z stages to adjust the optical system and the evaluation. X-ray tube Mo Small metal ball (a) X-Y-Z stage 1 (b) Glass capillary with Au coating X-Y-Z stage 2 Glass capillary X-Y-Z stage 3 Cu wire Detector Cu wire stage Detector Fig.4 Schematic view (a) and the photograph (b) of the experimental system for Au coated glass capillary.

6 Copyright JCPDS-International Centre for Diffraction Data 2013 ISSN EVALUATION Positioning of the Au Coated glass capillary lens with small metal ball First, we set up the capillary lens and the X-ray CCD camera (XC-502; X-ray Precision, Inc., Japan) to the geometry shown in Figure 5. These positions were calculated by the simulation. The CCD camera can monitor the X-ray beam collected by the capillary lens. We moved the small metal ball in the level direction, observing the image of a CCD camera. The captured image is shown in the Figure 6. When there were no metal ball on a capillary (position (i) in Fugue 5), it can be seen to be irradiated with X-rays about 1 mm in the shape of a circle from the result of a CCD camera image. Furthermore, X-rays with high intensity could be seen in the center. Probably, there were the X-rays condensed by total internal reflection. When the metal ball moved by 2.5 m step, the position to which the X-ray beam was focused the most will appear (position (ii) in Figure 5). When it is moved further, it will return to about 1 mm X-ray image (position (iii) in Figure 5). We defined the optimal position which the X-ray beam was focused most, and fixed the metal ball to the position (position (ii) in figure 5). X-ray source (i) (ii) (iii) 41 mm Small metal ball 145 mm Glass capillary with Au coating CCD camera 43 mm : Primary X-ray : Total reflected X-ray 2.5 mm (i) (ii) (iii) 2.5 mm Fig.5 Theoretical schematic representation of the trace of Mo K with small metal ball. (i)(ii)(iii) are positions of small metal ball. (i) is a metal ball on the left of a capillary top, (ii) is on the center, and (iii) is on the right. Fig.6 X-ray CCD image with when this small metal ball moves from a position (i) to (ii) and (iii). (i)(ii)(iii) in this figure correspond to (i)(iii)(iii) in figure 5. Evaluation of the beam diameter and the divergence angle of the X-ray micro beam The X-ray beam size was estimated by the wire scanning method (Yonehara, et al., 2010). A Cu wire (30 m diameter) was used. The Cu wire was placed perpendicular to the X-ray beam at 43 mm from the capillary output. The wire was scanned perpendicular to the X-ray beam using the X-axis of the sample stage 3 in Figure 4. The intensity of the X-ray fluorescence was recorded for every wire position. The minimum step size was 25 m, and the measuring time was 20 seconds per step.

7 Copyright JCPDS-International Centre for Diffraction Data 2013 ISSN The X-ray beam of the capillary lens (position (ii) in Figure 5) which adjusted the position of the metal ball was evaluated. The plot of the ball on position (ii) in Figure 7 shows the intensity profiles of Cu Ká for the scanned distance. The measured beam size (full width at half-maximum, FWHM) was m. On the other hand, the plot of the ball position (i) in Figure 7 shows the profile of a capillary without a metal ball. This X-ray beam size is 1,025 m following the scanning distance of the position of a wire where X-ray was observed. As a result, the ball blocked unwanted X-rays which spread spot shape. Also, when we measured the copper wire by this system with and without the ball, we were not able to observe the X-rays fluorescence of the Au on the spectrum from gold coating of the capillary inside. Furthermore, when this system is with the metal ball, fluorescence X-rays (Sn, Pb) of lead on a spectrum did not occur. These system peaks were extremely lower than collected primary X-rays. We also investigated the divergence angle of the X-ray micro beam. The beam diameters were estimated as the wire was shifted in parallel to the X-ray beam in mm steps using the Z-axis in Figure 4.A linear relationship between the evaluated beam sizes and distance between the capillary end and the wire are shown in Figure 8. Considering the gradient of the line, the estimated divergence angle of the X-ray micro beam was 6 mrad. Intensity / counts 4,000 3,500 3,000 2,500 2,000 1,500 1, Ball on position (i) Ball on position (ii) Beam size FWHM 1,025 m m ,000 1,200 Scanned distance /ìm FWHM / m Divergence angle 6 mrad Distance between capillary end and sample / mm Fig.7 X-ray Intensity profile of Cu Ka of two types capillaries which have metal ball on position (i) and (ii) in figure 6 obtained by the wire scanning method. Fig.8 Valuation of the beam size as a function distance to Au coated glass capillary Estimation of the gain Table 1 shows the intensities of X-rays when the small metal ball was set at the positions of (i) and (ii) in Figure 5. The X-ray intensities of Cu K from a Cu plate were measured at both positions. The Cu plate was placed at a position 43 mm away from the capillary end, and the intensity of the fluorescence X-ray was measured with a measuring time of 100 s.

8 Copyright JCPDS-International Centre for Diffraction Data 2013 ISSN When the small metal ball was placed at (i) in figure 4, the sample was irradiated with both total reflection X-rays and direct x-rays. When the metal ball was placed at (ii) in Figure 4, the sample was irradiated with only total reflection X-rays. We evaluated the direct X-ray intensity profile by subtracting the profile (ii) from the profile (i) in figure 7. The obtained Cu K intensities at metal ball position (i) and (ii) in figure 4 were 189,391 counts and 34,211 counts, respectively. Moreover, the difference of both counts was 155,020 counts, which indicates the direct X-ray intensity. The X-ray flux densities, which mean the X-ray intensities per unit area, were calculated. The flux density of the Au coated glass capillary with small metal ball was 16.4 times greater than that of the collimator without total reflection, as shown in Table 1. The results indicate that the Au Coated glass capillary with small metal ball could efficiently focus to a small area. In this method, the low-energy X-rays were high efficiency, because of the total reflection same as general single glass capillary lens (Ohzawa, et al., 2004). This system was designed under the optics design of Figure 3 with the metal ball so that Mo-Ká (17.44keV) is collected in the focus. As the sample (Cu-Ka (8.04keV)) of this experiment was detected, this is effective for the analysis of the transition metal. Table 1. Spatial resolution, X-ray intensities of Cu K, and X-ray flux densities for the micro-xrf. X-ray profile of Metal ball position (i) X-ray profile of Metal ball position (ii) Evaluated the direct X-ray profile with collimation Intensity of Cu K (counts) 189,391 34,211 (i)-(ii) :155,180 Spatial resolution ( m) 1,025 m 118 m (i) :1,025 m X-ray flux density (a.u.) CONCLUSIONS A micro X-ray beam was obtained with the combination of a small metal ball and a gold coated glass capillary which provides total reflection. Long working distance of 43 mm, m focal spot size, 6 mrad divergence angle and 16.4 times X-ray intensity were achieved. Long working distance is especially useful for the development of the advanced X-ray analytical microscope and also confocal 3D-XRF instrument. With the improvement of the optical system, this method has a potential for producing an X-ray beam with realization of microscopic area, fast measurement, and uneven surface analysis.

9 Copyright JCPDS-International Centre for Diffraction Data 2013 ISSN ACKNOWLEDGEMENTS This work was financially supported by JSPS KAKENHI (Grant-in-Aid for Science Research (B) ) and JSPS-FWF Bilateral Joint Research Project. REFERENCES Tsuji, K., Nakano, K., Takahashi, Y., Hayashi, K., Ro, C.-U. (2012). X-ray Spectrometry, Anal. Chem. 84, Kumakhov, M.A (2000). Capillary optics and their use in x-ray analysis, X-Ray Spectrom. 29, Ohzawa, S., Komatani, S., Obori, K. (2004). High intensity monocapillary X-ray guide tube with 10 micrometer spatial resolution for analytical X-ray microscope, Spectrochim, Acta, Part B. 59, Matsuda, A., Nakano, K., Komatani, S., Ohzawa, S., Uchihara, H., Tsuji, K. (2009). Fundamental characteristics of polycapillary X-ray optics combined with glass conical pinhole for micro X-ray fluorescence spectrometry, X-Ray Spectrom. 38, Nakazawa, T., Nakano, K., Yoshida, M., Tsuji, K. (2011a). Enhancement of XRF intensity by using Au coated glass-capillary, Advances in X-ray Analysis. 54, Nakazawa, T., Nakano, K., Yoshida, M., Tsuji, K. (2011b). Enhancement of XRF intensity by using Au-coated glass monocapillary, Powder Diffraction. 26, Yonehara, T., Orita, D., Nakano, K., Komatani, S., Ohzawa, S., Bando, A., Uchihara, H., Tsuji, K. (2010). Development of a transportable ì-xrf spectrometer with polycapillary half lens, X-Ray Spectrom. 39, Janssens, K., Proost, K., Falkenberg, G. (2004) Confocal microscopic X-ray fluorescence at the HASYLAB microfocus beamline: characteristics and possibilities, Spectrochim. Acta B, 59, Patterson, B.M., Campbell, J., Havrilla, G.J. (2006). Three Dimension Elemental Imaging Using a Confocal X-ray Fluorescence Microscope, American Laboratory, 38,

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