This article presents a concept and the first results for the setup of an 8keV laboratory transmission x-ray microscope with a polycapillary optic as condenser at the BliX in Berlin. The incentive of building such a microscope is that the penetration depth for hard x-rays is much higher than in the soft x-ray range, e.g. The water window. Therefore, it is possible to investigate even dense materials such as metal compounds, bones or geological samples. The future aim is to achieve a spatial resolution better than 200 nm

Baumbach, S.

Bjeoumikhova, S.

Kanngießer, B.

Malzer, W.

Stiel, H.

Wilhein, T.

English

Repositorium für Naturwissenschaften und Technik  (TIB Hannover)

Journal of Physics: Conference SeriesOPEN ACCESSSetup of an 8 keV laboratory transmission x-raymicroscopeTo cite this article: S Baumbach et al 2014 J. Phys.: Conf. Ser. 499 012005 View the article online for updates and enhancements.Related contentPolycapillary optics for medicalapplications-High-resolution X-ray imaging bypolycapillary optics and lithium fluoridedetectors combination-Smart X-ray optics-This content was downloaded from IP address 194.95.157.36 on 26/10/2020 at 11:09Setup of an 8 keV laboratory transmission x-raymicroscopeS. Baumbach1, B. Kanngießer2, W. Malzer2, H. Stiel3,S. Bjeoumikhova4 and T. Wilhein 11Institute for X-Optics, RheinAhrCampus Remagen, University of Applied Sciences Koblenz,Joseph-Rovan-Allee 2, 53424 Remagen, Germany2Berlin Laboratory for innovative X-ray Technologies (BliX), Institute for Optics and AtomicPhysics, Technical University of Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany3Berlin Laboratory for innovative X-ray Technologies (BliX), Max-Born-Institut,Max-Born-Strasse 2A, 12489 Berlin, Germany4IFG, Institute for Scientific Instruments GmbH, Rudower Chausse 29/31, 12489 Berlin,GermanyE-mail: baumbach@rheinahrcampus.deAbstract. This article presents a concept and the first results for the setup of an 8 keVlaboratory transmission x-ray microscope with a polycapillary optic as condenser at the BliX inBerlin. The incentive of building such a microscope is that the penetration depth for hard x-raysis much higher than in the soft x-ray range, e.g. the water window. Therefore, it is possible toinvestigate even dense materials such as metal compounds, bones or geological samples. Thefuture aim is to achieve a spatial resolution better than 200 nm.1. IntroductionFull field laboratory hard x-ray microscopes have been developed in the last decade and theachieved resolution is below 40 nm [1, 2]. One of the challenges of setting up a hard x-raytransmission microscope in the lab is the long focal length of several millimeters of the objectivelens, which leads to very long image distances to get a high detector resolution. Additionally,in order to get a high photon flux in the image plane, the numerical apertures of the condenserand the objective lens should match. This leads to further implications for the design of thecondenser lens as well as for a suitable detector system with proper spatial resolution to avoidlong image distances. In this article we are showing the first results obtained with a polycapillaryoptic as condender in our laboratory hard x-ray transmission microscope.2. Experimental SetupThe experiment setup, see figure 1, consists of a copper x-ray tube (A), a polycapillary optic(B), the object within a pinhole (C), a zone plate as objective lens and central stop (D) and ax-ray CCD (E). In the following the different components are described.2.1. X-ray sourceThe x-ray source of the laboratory x-ray microscope is a micro focus tube. The tube has acopper target to get the characteristic line emission at 8.05 keV and a source size of about 50 µm22nd International Congress on X-Ray Optics and Microanalysis IOP PublishingJournal of Physics: Conference Series 499 (2014) 012005 doi:10.1088/1742-6596/499/1/012005Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd 1Figure 1. Schematic setup of the transmission microscope.(FWHM)[3]. Reducing radiation damages to the CCD the maximum acceleration voltage of thetube has been set to 30 kV.2.2. CondenserA polycapillary is used as condenser. This optic consists of very thin and bowed hollow glascapillaries acting as wave guide based on total external reflection [4]. All capillaries are pointingto the focal spot resulting in 50 µm spot size (FWHM). A proper condenser should have a highacceptance angle at the entry, a divergence angle at the exit of the capillary matched to thenumerical aperture of the zone plate and a high efficiency. In practice, not all conditions canbe realized in one device and one has to make a compromise. In our setup the aperture of thecondenser optic does not match to the zone plate aperture, i.e. light collected by the condenserdoes not completely contribute to image formation. But due to the focusing properties ofthe polycapillary, an increase of the intensity in the object plane is reached and the object isilluminated under different angles. In figure 3 one can see the illumination cone of the capillaryoptic in a distance of 405 mm to the focal spot.Figure 2. Schematic drawing ofa polycapillary optic. Image takenfrom [4].Table 1. Parameters of thepolycapillary optic. Values aredenoted in mm.f1 Din L f2 Dout62.3 2.2 45.4 18 1.22.3. Objective lens and central stopA tungsten zone plate with a focal length of about 32.5 mm at 8.05 keV and an outermost zonewidth of 50 nm is used as objective lens. The zone plate produces a magnified image of theilluminated object on a CCD with 20 µm · 20 µm pixel size. The central stop (CS) is mountedin front of the zone plate and the illumination cone of the polycapillary forms a shadow of theCS on the CCD preventing background illumination. In this shadow the magnified image of theobject is formed by the objective. Ideally, the position of the CS is at the exit of the condenseroptic. But due to the beam divergency of each capillary a CS on a polycapillary would not forma sharp shadow on the CCD.22nd International Congress on X-Ray Optics and Microanalysis IOP PublishingJournal of Physics: Conference Series 499 (2014) 012005 doi:10.1088/1742-6596/499/1/01200523. First resultsIn the first steps a 30 µm in diameter Pt/Ir-pinhole was used as an object. The resulting imagewith 108-fold magnification is shown in figure 4. An aluminium aperture with 4 mm in diameterin front of the detector blocks all the light around the image area.To get a first valuation of the achievable spatial resolution a gold mesh with 5.5 µm bar widthand 10.5 µm spaces was used. The resulting 143-fold image is shown in figure 5. For a 143-foldmagnification and a pixel size of 20 µm the resulting effecitve pixel size is 140 nm and thereforethe Shannon-Nyquist-theorem gives a maximum spatial resolution of 4 · 140 nm = 560 nm. Thecorresponding line plot through the edge of a mesh bar is shown in figure 6 and the measurementfrom 10% to 90% edge profile gives an estimated spatial resolution of about 580 nm, i.e. theresolution of the system is mainly detector limited.Figure 3. Image of the polycapillaryillumination cone. Focal spot to CCDdistance is 405 mm.Figure 4. Image of a 30 µm in diameterPt/Ir-pinhole. 108-fold magnification.Figure 5. Image of a gold mesh with 1500line pairs per inch. 143-fold magnification.Figure 6. Line plot through the egde of amesh bar, (black box in figure 5).4. Summary and OutlookWe have shown that a polycapillary optic can be used as an x-ray condenser in a laboratory8 keV x-ray transmission microscope. The resolution of the current system is in the sub micro22nd International Congress on X-Ray Optics and Microanalysis IOP PublishingJournal of Physics: Conference Series 499 (2014) 012005 doi:10.1088/1742-6596/499/1/0120053meter region and is still detector limited. A better detector resolution would be achieved with ahigher magnification, respectively a longer image distance. But a detector system with smallerpixel sizes, e.g. an image intensifier and a phosphor screen with grain sizes about 2 µm wouldbe the proper choice. In future it is planned to optimize the condenser optic in order to increasethe photon flux in the object plane and to get a more adapted output angle to the zone plate.With the described improvements a resolution below 200 nm would be feasible.AcknowledgementsA special thanks to Mr. Pambos Charalambous (www.ZonePlates.com) for the fabrication ofthe zone plates.References[1] A Tkachuk, M Feser, et al 2006 Proc. of SPIE Vol. 6318 Developments in X-Ray Tomography V[2] Y S Chu,J M Yi,et al 2008 Applied Physics Letters 92, 103119[3] IFG 2012 X-ray source and power supply manual IFG Institue for Scientific Instuments GmbH RudowerChaussee 29/31, 12489 Berlin, Germany[4] A Bjeoumikhov, S Bjeoumikhova, R Wedell 2006 Part. Part. Syst. Charact., Vol. 22 p. 384-390[5] R Goergl, P Wobrauschek, Ch Streli, H Aiginger, M Benedikt 1995 X-Ray Spectrometry, Vol. 24, 157-16222nd International Congress on X-Ray Optics and Microanalysis IOP PublishingJournal of Physics: Conference Series 499 (2014) 012005 doi:10.1088/1742-6596/499/1/0120054

Setup of an 8 keV laboratory transmission x-ray microscope

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Setup of an 8 keV laboratory transmission x-ray microscope

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