New capabilities and applications of compact source-optic ...Document Transcript
New capabilities and applications of compact source-optic combinations T. Bievenue, J. Burdett, Z.W. Chen, N. Gao, D.M. Gibson, W.M. Gibson*, H. Huang, and I.Yu. Ponomarev X-Ray Optical Systems, Inc., 30 Corporate Circle, Albany, NY 12203 ABSTRACTPolycapillary and doubly curved crystal x-ray optics have gained broad acceptance and are now being used in a wide variety ofapplications. Beginning as optics integrated into research setups, they were then used to enhance the performance of existingx-ray analytical instruments and are now widely used as essential components in x-ray spectrometers and diffractometersdesigned to utilize their capabilities. Development of compact x-ray sources, matched to the optic input requirements haveallowed large reduction in the size, power, and weight of x-ray systems which are now resulting in development of compact x-ray instruments for portable, remote, or in-line analytical tools for new applications in industry, science, or medicine.Key words: x-ray optics, polycapillary, doubly curved crystal, x-ray sensors, MXRF, XRD, 1. INTRODUCTIONHaving undergone rapid development over the past ten years, polycapillary and doubly curved crystal optics have gained broadacceptance. Indeed, this field is undergoing an important transition in which the focus of papers and presentations areprimarily or exclusively on applications and not on the design and characteristics of the optics. For example, in summer 2001conferences there were over thirty papers that utilized polycapillary or doubly curved crystal optics. In many cases, theseoptics enhance the sensitivity or improve the convenience of standard x-ray analysis equipment. An example is the use of acollimating optic in an x-ray diffractometer to increase the diffracted beam intensity and at the same time, produce a parallelbeam which simplifies alignment and alleviates sample position, smoothness, shape, and transparency constraints.Furthermore, in an impressive number of cases, the effect of the optics is dramatic enough to enable entirely new applications,either by making new kinds of measurements possible or, more often, by reducing the size, power, and cost enough to allowtraditional laboratory or even synchrotron based measurements to migrate to in situ or in-line use in sample preparation ormanufacturing environments. This paper will summarize such enabling studies and measurements by X-Ray Optical Systems(XOS) in collaboration with the Center for X-Ray Optics (CXO) at the University at Albany and a large number of otherorganizations and individuals. 1.1. History and overview of polycapillary optics a ir θc n1The basic physics that underlies polycapillary x-ray optics was g la s s 32 Θc ≈ n2 mrad 1described in 1923 and the possibility to guide x rays in hollow Energy [ keV ]capillary tubes was discussed in 19312. The principles ofoperation of polycapillary optics are shown in Figure 1. Opticsusing multiple channels each involving multiple reflections werefirst reported in 19893. These were comprised of single thin- d Θ c R~500 m mwalled glass capillary tubes guided through thin metal screens. RΘ c2 Θ = 3 .8 m r a d c d ≤ d< 5 µmThe next major advance was the use of polycapillary fibers in 2which many hollow capillary channels were contained in asingle glass fiber of about the same size as the original singleglass capillaries4. These polycapillary fibers were also threaded Figure 1. Schematic representation of the principles of capillary optics.through thin metal grids. Such multifiber polycapillary optics Θc is the critical angle for total external reflection, R is the radius of curvature of the capillary and d is the capillary diameter.allowed significant reduction in size and increase of the useablex-ray energy. A photograph of such a multifiber optic and a cross section of a single fiber are shown in Figure 2.A very important advance, development of monolithic polycapillary optics, was announced in 19925. For both the originalcapillary optics and the multifiber polycapillary optics, the cross section of individual hollow capillary channels is constant,For monolithic optics, however, the cross section of the channels change along the length of the optic, as shown in Figure 3.Photographs of monolithic optics are shown in Figure 4.
(a) (b) Figure 2. a) Multifiber polycapillary collimating optic. The length is ~10 cm and the width is 2 cm. b) Polycapillary fiber. This example has ~400, 50 µm channels and is ~600 µm flat-to=flat. More typical polycapillary fibers have ~2000, 5-10 µm channels and are ~500 µm wide. Figure 3. Collimating and focusing monolithic polycapillary optics. Figure 4. Photographs of bare and packaged monolithic optics.1.2. History and overview of Doubly Curved Crystal (DCC)TM opticsThree-dimensional focusing of x rays can also be achieved by using doubly curved crystal optics. Unlike polycapillary optics,DCC optics are based on Bragg diffraction and provide a monochromatic beam. For this reason, they are sometimes referredto as monochromatic x-ray optics. Focusing geometries for producing a point image from a point x-ray source were describedand investigated in early work during the 1950s6,7. Only in the 1980s and 1990s, were the x-ray optical properties of DCCoptics systematically studied by Wittry et al using a ray tracing method8-13. Fabrication and applications of DCC were alsoreported in several publications by Wittry and his coworkers14-16. However, the widespread use of DCC optics for primarymonochromatic beam applications was impeded by the difficulty in fabricating DCC optics.An important development was reported in 199817. In that paper, an intense micro Cu Kα1 beam was obtained using a Johanntype double curved mica crystal for monochromatic micro XRF applications. The high intensity gain of the mica DCC wasbased on a novel crystal-bending technology. This proprietary technology can provide elastic bending of crystals into variouscomplex shapes with precise figure control.
Bending Radius in Vertical Plane = 2Rsin2θB Bending Radius in Horizontal Plane = 2R Axial symmetry along SI Figure 5. Geometry of doubly curved crystal optic (DCC)TMPoint-to-point focusing geometry of a DCC optic is shown in Figure 5. In this geometry, the diffracting planes of the crystalremain parallel to the curved crystal surface. The crystal surface, which is a toroidal shape, has the Johann geometry in thefocal circle plane and axial symmetry in the perpendicular direction8. A large solid angle is collected from an x-ray sourcewhich is then focused to a small spot. Due to point-to-point focusing of x-rays, the achievable spot size is related to the spotsize of the x-ray source. Photographs of doubly curved crystal optics are shown in Figure 6. Figure 6. Photographs of doubly curved crystal optics1.3. Optics Capabilities1.3.1. Polycapillary (polychromatic) optics.One of the distinguishing features of polycapillary optics is their broad energy (wavelength) bandwidth. They are thereforesometimes referred to as polychromatic optics. Other optics in this class include other reflective optics such as monocapillaryoptics, single or nested cones, flat or curved arrays (multichannel plate or “lobster eye” optics, and Kirkpatrick-Beaz optics).Current capabilities of commercially available collimating and focusing polycapillary optics are summarized in Table I andTable II. Only monolithic optics are shown in Table II since they can give focal spot sizes much smaller than multifiberfocusing optics for which the spot size is limited by the polycapillary fiber width. In special cases, such as for neutronfocusing, multifiber focusing optics may be used because of their larger collecting area. Also multifiber collimating optics areoften selected for applications requiring a large cross section parallel beam as for large area thin film texture studies18 or x-raylithography19.
Collimating Optics Focusing Monolithic Optics • Multifiber –Point to point focusing – Output beam size: 10 x 10, 20 x 20, 30 x 30 mm2 – Output divergence: ~ 4mrad CuKα –Small focal spots – Capture angle: 4.2°, 7°, 8.8 ° – Axial and planar divergence are identical • < 25 µm @ Cu Kα – Up to 30 % transmission efficiency • < 15 µm @ Mo Kα • Monolithic – Output beam size diameter: 0.5mm, 1.5mm, 4mm, 6mm –Capture angle: up to 20° – Output divergence: ~1 mrad MoKα, ~2 mrad CuKα – Capture angle: up to 20 ° –Transmission efficiency: up to 30 % – Transmission efficiency: up to 30 % (geometry and (geometry and energy dependent) energy dependent) Table I. Characteristics of collimating polycapillary optics. Table II. Characteristics of focusing polycapillary optics.1.3.2. Doubly curved crystal (DCC)TM opticsA principle benefit of doubly curved crystal optics is the ability to provide an intense monochromatic focused beam. Variouscrystal materials can be used for DCC optics, including Si, Ge, quartz and mica. The collection solid angle of DCC optics isdetermined by the capture angle in the dispersive plane and the included rotational angle φ. The capture angle in the dispersiveplane is typically 1-5 degrees and the rotational angle can be 5-90 degrees. The focal spot size of the reflected beam is mainlydetermined by the x-ray source size. The capabilities of commercially available DCC optics are summarized in Table III.Output beam energies Mo Lα1, Cr Kα1, Cu Kα1, W Lα1, W Lβ1, Mo Kα1, or Ag Kα1Reflection efficiency 10% to 20%Collection solid angle 0.005 to 0.1 steradians.Convergent angles 1-5 degree x 5-90 degreesFocused beam size 10-100u depending on the source size Table III. Characteristics of DCC optics 2. X-RAY BEAMS2.1. Polycapillary opticsA principle benefit of polycapillary optics is the ability to capture x rays from a divergent source over a large angle and toredirect them into a quasiparallel or focused x-ray beam, thus avoiding the inverse square dependence of x-ray intensity on thedistance from the source that has limited many applications of x rays since their discovery over 100 years ago. A comparisonbetween a polycapillary focusing optic and a conventional 0.1 mm pinhole aperture is shown in Figure 720.To overcome the traditional 1/D2 limitation, high power laboratory x-ray sources such as rotating anode sources (up to 18 kW),or laser plasma sources have been developed. Desire for increased intensity has also motivated development of synchrotron orfree-electron-laser (FEL) x-ray sources. Such sources are large, expensive and complex. For many applications, polycapillaryoptics make it possible to migrate techniques demonstrated on such sources to systems using low power sources.For polycapillary optics, the capture angle is limited by the angle subtended by the source at the input of the optic. This can bemaximized for a given source-optic distance by increasing the optic input area. This means for many standard x-ray sourceswhich often have source-spot to window distance of several cm, a multifiber lens is often used (the largest area high qualitymonolithic optics at present is ~ 100 mm2). However, with reduction of the source- optic distance to a few mm, evenmonolithic optics can have a large capture angle. In this case, it is important that the source spot size be small (<0.1 mm). Fig.7 shows the x-ray intensity increase obtained with a focusing monolithic polycapillary optic relative to a conventional pinholeaperture.
Recently, several close-access, microfocus x-ray sources have been developed. When coupled with monolithic optics, x-ray Scatter x-ray spectra (W -anode, 30kV, 0.1mA) flux and flux density values have been obtained with compact Polycapillary focusing optic low-power sources that are comparable to or greater than 10 6 W Lα W Lβ 0.1 m m aperture 100 m m from the source those obtained with conventional high-power rotating anode 5 W Lγ sources equipped with conventional optics. An integrated 10 Ar in air source-optic system is shown in Figure 8. By choice of optic, this can produce a quasiparallel beam or a focused beam. 4 10 Counts 10 3 Table IV shows the beam characteristics with focusing X-Ray 10 2 Beams and Table V and Table VI with collimating X-Ray 1 Beams. 10 Fe and Cr from the aperture m aterial 0 10 0 5 10 15 Energy (keV) 20 25 30 B e a m F lu xFigure 7. X-ray energy spectrum from 3 W tungsten x-ray sourcewith a polycapillary focusing optic and with a conventional pinhole • W ith C u -a n o d e s o u r c e (5 0 k V , 5 0 W , s o u r c e s p o t: 0 .1 5 m m ):aperture (ref. 30). C u K α in te n s ity : 1 .0 × 1 0 9 p h o to n /se c o n d F lu x d e n sity: 1 .2 × 1 0 6 p h o to n /s /µ m 2 • W ith M o -a n o d e s o u r c e (5 0 k V , 5 0 W , s o u r c e s p o t: 0 .1 5 m m ): M o K α : 5 .6 × 1 0 7 p h o to n /se c o n d F lu x d e n sity: 1 .8 × 1 0 5 p h o to n /s /µ m 2 Table IV. Characteristics of X-ray BeamTM with focusing monolithic optics (ref. 20). Beam diameter 1.5 mm 6.0 mm Figure 8. X-ray BeamTM, with integrated optic alignment and shutter assembly. Beam flux 1.9 x 109 p/s 1.0 x 109 p/s 40kV, 80W (Bede 40 kV, 50W (Oxford 5011 Microsource) source) Beam divergence 2.0 mrad. 2.0 mrad. (FWHM) (0.12°) Table V. Collimating X-Ray BeamTM with Cu Kα source (ref. 20).2.2. Doubly curved crystal optics. Beam diameter 1.0 mm 4.0 mmBecause of the large collection solid angle of DCC optics21,intense monochromatic beams can be obtained even with low Beam flux at 50kV, 40W 7.1 x 107 p/s 3.5 x 108 p/s (Oxford UltraBright source)power compact x-ray sources. Characteristics ofmonochromatic focused DCC based X-Ray Beams are shown Beam divergence (FWHM) 1.0 mrad. 1.0 mrad.in Table VII. Multiple doubly curved crystal optics can be 0.06°integrated with the source and focused on the same spot toprovide higher intensity as shown schematically in Figure 9. Table VI. Collimating X-Ray BeamTM with Mo Kα source (ref. 20).
Optics Beam energy Solid angle Source Beam size Flux (keV) (Sr.) (FWHM) (No. photons/s) Ge (220) -Cr 5.4 0.03 Trufocus 8050Cr 70µ 3 x 109 14w Si (111) -Cu 8.0 0.015 Trufocus 8050Cu 40µ 1 x 109 two optics 14w Si(111)-Cu 8.0 0.005 Oxford 5011Cu 100µ 1 x 109 50w Si(220)-WLa 8.4 0.01 Hamamatsu W 13µ 1 x 108 10W Si (220) -Mo 17.5 0.01 Trufocus 8050Cu 40µ 1 x 108 14w Table VII. Examples of focusing, monochromatic X-Ray Beams. (a) (b) Figure 9. Schematic (a) and photograph (b) of focusing, monochromatic X-Ray Beam with multiple DCC optics. 3. APPLICATIONS3.1. Focused beam applications3.1.1. Micro x-ray fluorescence (MXRF)MXRF is currently the most widely used application ofpolycapillary optics, being an integral part of severalcommercial MXRF instruments. The small size and lowpower enables development of in-line MXRF systems forsemiconductor and other materials based industries anddevelopment of remote or portable environmental andmineralogical (for example, planetary rover) instruments.MXRF systems can take many different forms, some ofwhich are illustrated in Figs. 10-17. Currently attainablefocal spot sizes are listed in Table II. Figure 10. Standard MXRF configuration. The sample can be scanned to measure the distribution with ~ 10 µm resolution
The compact size and flexibility of focused X-ray Beam systems facilitates their incorporation into existing processing or diagnostic instruments. An example is shown in Figure 12. An interesting application in a low-voltage scanning electron microscope (LV-SEM) or environmental SEM (ESEM) is shown in Figure 1323. In this case the electron beam spreads in the high pressure environmental chamber and fluorescent x rays generated Figure 11. Dual optic MXRF system. Particularly useful for measurement of spatial distributions in radioactive samples (ref 22).outside the area of interest get into the detector and reducethe image contrast. A polycapillary optic collects x-raysfrom an area defined by the optic spot size and focuses themon the detector, reducing the background and enhancing the Figure 12. MXRF X-ray Beam incorporated into an SEM.image contrast. High-resolution x-ray fluorescence measurements, not only greatly increase the elemental discrimination and measurement sensitivity but in some important cases can give chemical as well as compositional information. This can be done by wavelength dispersive detection with a collimating optic to increase the diffracted beam intensity as shown in Figure 1424 and Figure 15 or by use of a ultra high resolution microcalorimeter detector as shown in Figure 1625. An example of the XRF spectrum from such a measurement is shown in Figure 1726.Figure 13. Monolithic focusing optic as a spatial filter in an ESEM(ref. 23).
Source Flat crystal Polycapillary Optic Counter Figure 16. Monolithic focusing optic to increase the efficiency (>300 x) of super conductor microcalorimeter detector (ref. 29). Figure XRF spectrum from 0.5 µm WSiO2 particle on SiO2 Figure 17.15. Micro Wavelength Dispersive X-Ray Fluorescence substrate (ref. 26) 24) (MWDXRF)( ref.Figure 14. Electron Probe Wavelength Dispersive Spectroscopy(EPWDS)3.1.2. Monochromatic micro x-ray fluorescence (MMXRF)Monochromatic x-ray micro beams provide several advantages over MXRF techniques using polychromatic excitation forsome applications, including larger working distance and simpler quantitative analysis. More importantly, monochromaticexcitation eliminates the x-ray scattering background under the fluorescent peaks and therefore gives very high sensitivity.Detection limits at ppb levels for bulk contaminants or femto gram (10-15g) levels for surface concentration of medium or highZ elements can be achieved with 500s measurement times using low power sources27. A typical configuration for MMXRF isshown in Figure 18, and a comparison of measured MXRF and MMXRF spectra from an environmental particulate sample isshown in Figure 19.
C o u tn s (6 0 0 s e c o n d s ) 10000 K S Ca Fe Mn 1000 Zn 100 Cu P b (A s ) Pb Br Ni Zn As Br Sr Ti Cr 10 1 2 4 6 8 10 12 14 16 18 20 E n e rg y (k e V ) M o tub e w ith cap illar y op tic, 40 kV 0.5 m A , 7 m m 2 P IN d etector, 12m m from the sam p le M o tub e w ith S i(220) D C C , 4 0 kV 0.2 m A , 25m m 2 P IN d etector, 15m m from the sam p le Figure 19. MXRF and MMXRF spectra from concentrated environmental particulate sample with MoK excitation. S ou rce 3.1.3. Focused beam total x-ray fluorescence, TXRF Total reflection x-ray fluorescence (TXRF) is a surface analytical technique for ultra-trace analysis of particles, residues, and impurities on DCC smooth surfaces and is an important analytical tool for wafer surface contamination control in semiconductor chip manufacture. However, D e te c to r because conventional TXRF systems provide large beam size, localized information is difficult to obtain. Using DCC optics, x-ray photons can be focused to perform localized area TXRF. A schematic diagram for S a m p le such a measurement is shown in Figure 20. A slit is used to restrict divergence in the scattering plane to less than the critical angle in order toFigure 18. Setup for MMXRF focused X-Ray Beam meet the total reflection requirement. The flux density on the reflectionmeasurement surface is several orders of magnitude higher than that of conventional systems with higher power sources27. This yields very high sensitivityfor localized contaminant detection. Detector Slit 300 Br (3pg) Doubly Curved Crystal Co un 200 ts/ 50 0s Si 100 Ar Ni Zn X Fe Z 0 2 4 6 8 10 12 14 16 18 20 Point Source Y E(keV) Figure 20. Setup and spectrum for monochromatic focused X-Ray Beam TXRF measurement (ref. 27).3.1.4. Rapid x-ray reflectometry, XRR
X-ray reflectometry (XRR) is an important technique for characterizing thin film thickness, roughness, and density. In thisapplication, the reflectivity of monoenergetic x-ray photons is measured as a function of incident angle near the critical angle.In a conventional XRR measurement, a highly collimated beam is used and the reflectivity curve is obtained by sequentiallyscanning the incidence angle. A DCC optic can provide s small focal spot and a range of incidence angles as shown in Figure21. The entire reflectivity-angle curve can then be recorded with a position sensitive detector27. PSD 1 0 .1 D o u b ly C u rve d R e fle c tivity 0 .0 1 C rys ta l S a m p le 1 E -3 1 E -4 1 E -5 P o in t S o u rc e 0 .0 0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 1 .6 A n g le (d e g re e ) X R R d a ta fo r 8 0 0 Å T iN film o n S i w a fe r u s in g T u n g s te n L α lin e 1 0 0 s @ 3 .5W (3 5 kV , 0 .1 m A ) so u rce s e ttin gFigure 21. Setup and reflectivity spectrum for a rapid x-ray reflectivity measurement (ref. 27).3.1.5. Other focused beam applicationsOther applications of polycapillary monolithic focusing optics, sometimes together with a collimating optic are; x-ray absorption fine structure (EXAFS or XAFS)28 and x-ray absorption near edge spectroscopy (XANES)29 as shown inFigure 22. XAFS measures the local microstructure with atomic resolution and XANES can be used to determine the chemicalstate of selected constituents. These applications as well as most of the applications discussed in Section,3.1.1., make use ofthe broad energy (or wavelength) band-width transmitted by polycapillary optics. This distinguishes polycapillary optics fromdiffractive optics such as flat or curved crystal optics and multilayer thin film optics. D etecto r 2 D etecto r 1 Poly capilla ry Sam ple Figure 22. Setup for x-ray absorption fine structure (XAFS)(ref. 28) and for x-ray absorption near edge spectroscopy (µ XANES) (ref. 29).Additional applications of focusing optics (not discussed in this review) include; focusing of low energy (cold) neutrons forprompt gamma activation analysis (PGAA) and neutron depth profiling30, which give measured neutron intensity gains as highas 80 and focal spot sizes as small as 90 µm, making neutron microanalysis possible for the first time, and concentration ofhigh- energy (20-50 keV) x rays for astrophysical spectroscopic measurements31.3.2. Collimated beam applications
3.2.1. Powder x-ray diffraction (Powder XRD) (phase analysis, stress-strain, texture).Collimating polycapillary optics increase the diffracted intensity (10-1000 X depending on the application). This is becausethey convert a highly divergent beam (up to 20o depending on the capture angle) into a quasiparallel beam with divergence of1-4 milliradians as shown in Table I. The number (fraction) of x-rays diffracted from a crystal therefore greatly increases,depending on the intrinsic (Darwin) width of the diffracting crystal. Figure 23 shows the general arrangement for phase, stress,or texture measurements and Figure 24 shows the increase in diffracted beam intensity with a polycapillary collimator32. Figure 23. General arrangement for x-ray diffraction (XRD) measurement (after ref. 18).The quasiparallel beam from the polycapillary collimator relaxes constraints on sample position, shape, roughness, andtransparency and therefore eliminates the sample preparation required for conventional Bragg-Brentano (parafocusing)geometry. This, together with the reduced power, size, weight and cost make collimating x-ray systems natural candidates forin-line diffraction instruments for quality control and feedback in manufacturing and process environments. Such systems areunder development and implementation for the semiconductor, steel, pharmaceutical, and cement industries among others.Figure 25 shows measurements involving diffraction from a silicon single crystal33 that illustrates the effect of changing the P ro to ty p e S y s te m 4 0 0 0 D if fr a c to m e te r 3 5 0 0 2 K W P a r a lle l- B e a m D iffr a c to m e te r 3 0 0 0 2 0 W X O S P ro to ty p e S y s te m 2 5 0 0 In te n s ity 2 0 0 0 c ts /1 0 s X O S c ts /s 2 K W 1 5 0 0 1 0 0 0 5 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 2 θ [d e g ]Figure 24. Comparison of the diffracted beam intensity from a SRM 688 basalt standard between a 2 kW parallel beam diffractometer anda 20 W polycapillary based Collimated Beam System (ref. 32).
sample position on the diffracted peak. Figure 26 shows a pole figure measurement of the texture of a 100 Å silver thin film ona silicon crystal34.An example of the flexibility provided by a parallel beam Collimated Beam System is illustrated in Figure 27 where a setup isshown for powder diffraction measurements which eliminates preferred orientation errors35 and in Figure 28 which shows anarrangement for in plane scattering measurements. Side View Detector Optic Source Sample Top View Air Flow Source Optic Sample DetectorFigure 27. Powder XRD with Collimated X-Ray Beam to eliminate preferredorientation errors (ref. 35). Figure 28. Setup for in-plane scattering 4000 C o u n ts p e r s e c C o u n ts p e r se co 3000 2000 2000 1000 1000 0 46 47 48 49 0 46 47 48 49 D e g re e s 2 T h e ta D e g re e s 2 T h e ta 0m m 2m m 0m m 4m m 1m m -2 m m 2m m -4 m m -1 m m -2 m m Figure 25. Diffracted beam shape and position for Si(100) with polycapillary Collimated Beam System and conventional Bragg- Brentano 26. Pole figure-100 Å Ag on Si(111) texture map (ref. 34). Figure geometry (ref. 33).
3.2.2. Single crystal diffraction.The benefits noted above for powder diffraction also apply to single crystal diffraction applications. Perhaps the mostimportant and most studied single-crystal application to date has been the use of a Collimated Beam System for proteincrystallography36. Figure 29 is a schematic representation of such a measurement and a diffraction pattern for Lysozyme isshown in Figure 30.Figure 29. Schematic representation of protein crystallography measurement. Figure 30. Diffraction pattern for Lysozyme (ref. 23).The diffracted beam intensity obtained with a polycapillary monolithic optic witha slightly convergent (<0.5o) beam and a 50 W microfocus source is equal to or greater than that from a 5 kW rotating anodesource equipped with the most advanced confocal optics, with resolution < 2 Å and Rmerge < 6 % for Lysozyme37. At thepresent time the local divergence (divergence of x rays from each capillary channel) of ~0.12o, limits the unit cell size ofmolecules that can be analyzed to <~200 Å. A similar X-ray Beam based system which also includes a graphitemonochromator and which is available commercially has recently been announced38.By using more strongly convergent beams39 (up to ~ 2o), it is possible to obtain even higher x-ray density on smaller beamspots. Together with special software40 for analysis of convergent beam diffraction patterns, these can be used for screening ofvery small protein crystals41, microdiffraction measurements with very low source power (<10W) for example for planetaryrovers, and for portable, remote, or in-line microdiffraction measurements. Similarly, slightly or highly focusing polycapillaryoptics can be used for neutron diffraction from small crystals for macromolecular structure, high pressure, or low temperaturestudies126.96.36.199. X-ray lithography
Polycapillary collimating optics can also be used to produce a quasiparallel beam for x-ray lithography19. A setup for this isshown in Figure 31. • A p p lica tio n s – L a rg e v o lu m e – S m a ll fe a tu re s – L a rg e d ie s – M e m o ry c h ip s – G a A s se m ic o n d u cto rs – D e e p L ith o g ra p h y • M ic h ro m e c h a n ic al s y s te m s • B e n e fits – M a s s p ro d u c tio n – S m a ll re s o lu tio n – P a ra lle l B e a mFigure 31. X-ray lithography (XRL), with potential applications and benefits. 4. MEDICALA potential major area of applications for polycapillary optics is in medicine43. Used as magnifying angular filters, they havebeen demonstrated to give significant and important increase in contrast and resolution for mammography44 and are underactive investigation for other soft tissue imaging and for cancer therapy. These applications of polycapillary optics are notreviewed in this paper because of limited space and because they are at an earlier stage of general acceptance and applicationthat the examples given. Also, they have recently been reviewed in two papers in the Denver 2001 Conference proceedings45,46 . 5. CONCLUSIONSPolycapillary and doubly curved crystal optics have gained broad acceptance and are now being used in a broad variety ofapplications. Beginning as optics integrated by users into research setups, they were then used to enhance the performance ofexisting x-ray analytical instruments and are now widely used as essential components in x-ray spectrometers anddiffractometers designed to utilize their capabilities. Development of compact x-ray sources, matched to the optic inputrequirements have allowed large reduction of the size, power, and weight of x-ray systems which are now resulting indevelopment of compact x-ray instruments for portable, remote, or in-line systems for new applications in industry, science, ormedicine. REFERENCES* Corresponding author to whom questions or comments should be directed (email@example.com)1. A.H. Compton, Phil. Mag. 45, 1121 (1923).2. F. Jentzch and E. Näring, “Die Forteitung von Licht—und Rötgenstrahlen durch Rören,” Zeitschr. F. Techn. Phys., 12, 185 (1931).
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W. Bailey, J. Bentley, and J. A. Small Eds. San Francisco Press, Part II pp.1730-1731.16. Z. W. Chen and D. B. Wittry, “Microprobe X-Ray Fluorescence with the use of Point-Focusing Diffractors,” Appl. Phys. Lett., 71, 1884-1886 (1997).17. Z. W. Chen and D. B. Wittry, “Microanalysis by Monochromatic Microprobe X-Ray Fluorescence- Physical Basis, Properties, andFuture Prospects,” J. Appl. Phys., 84, 1064-1073 (1998).18. Kardiawarman, B.R. York, X.-W. Qian, Q.-F. Xiao, C.A. MacDonald, and W.M. Gibson, “Application of a Multifiber Collimating Lensto Thin Film Structure Analysis,” Proc. SPIE, vol. 2519, 197-206, (1995).19. Z.W. Chen, R. Youngman, T. Bievenue, Q.-F. Xiao, C.E.Turcu, R.K. Grygier, and S. Mrowka, “Polycapillary Collimator for Laser-Generated Plasma Source X-Ray Lithography,” SPIE Proc., vol. 3767, 52-58 (1999)20. Internal XOS data.21. N. Gao, I.Yu. Ponomarev, Q.F. Xiao, W.M. Gibson, and D.A. Carpenter, “Monolithic Polycapillary Focusing Optics and theirApplications in Microbeam X-Ray Fluorescense,” Appl. Phys. Lett., 69, 1529 (1996).22. G.J. Havrilla and N. Gao, “Dual-Capillary Optic MXRF”, Proc. of Denver 2001 X-Ray Conf. (2001).23. N. Gao and D. Rohde,” Using a Polycapillary Optic as a Spatial Filter to Improve Micro X-Ray Analysis in Low-Vacuum andEnvironmental SEM Systems,” Proc. Microsc. Microanl., 7, 700 (2001).24. H. Soejima and T. Narusawa, “A Compact X-Ray Spectrometer with Multi-Capillary X-Ray Lens and Flat Crystals,” Proc. 49th Ann.Denver X-Ray Conf., July (2000).25. D.A. Wollman, C. Jezewski, G.C. Hilton, Q.-F. Xiao, K.D. Irwin, L.L. Dulcie, and J.M. Martinis, Proc Microscopy and Microanalysis,3, 1075-76 (1997).26. D. A. Wollman, K.D. Irwin, G.C. Hilton, L.L. Dullcie, D.E. Newbury, and J.M. Martinis, J. Microscopy, 188, 196-223 (1997).27. Z.W. Chen, XOS, private communication.28. T. Taguchi, Q.-F. Xiao, and J. Harada, “A New Approach for In-Laboratory XAFS Equipment,” Proc. 10th Int. Conf. On X-rayAbsorption Fine Structure, (1998).29. K. Janssens, K. Proost, L. Vincze, G. Vittiglio, G. Falkenberg, F. Wei, W. He, and Y, Yan, “Polycapillary-Based Micro-XRF andMicro-Xanes by means of Conventional and Synchrotron Radiation”, Proc. of Denver 2001 X-Ray Conf. (2001).30. H.H. Chen-Mayer, G.P. Lamaze, D.F.Rmildner, R. Zeisler, and W.M. Gibson, “Neutron Imaging and Prompt Gamma ActivationAnalysis using a Monolithic Capillary Neutron Lens,” Proc. Japanese Conf., J. Phys. Soc. Japan, to be published (2001)31. C.H. Russell, M. Gubarev, J. Kolodziejczak, M.K. Joy, C.A. MacDonald, and W.M. Gibson, “Polycapillary X-ray Optics for X-rayAstronomy,” Advances in X-Ray Analysis (Proc. of 48th Ann. Denver X-ray Conf.), vol. 43, (1999).32. XOS internal data, M. Haller, private communication.33. S. Bates, 6th European Powder Diffraction Conf., Budapest, 1998 (oral presentation). Data from S. Bates, KRATOS Corp. privatecommunication.34. K.M. Matney, M. Wormington, and D.K. Bowen, Bede Scientific Corp., private communication.35. T. Yamanoi and H. Nakazawa, “Parallel-Beam X-ray Diffractometry using X-ray Guide Tubes”, J. Appl. Cryst., 33, 389-391 (2000).36. S.M. Owens, J.B. Ullrich, I.Yu. Ponomarev, D.C. Carter, R.C. Sisk, J.X. Ho, and W.M. Gibson, “Polycapillary X-Ray Optics forMacromolecular Crystallography”, SPIE Proc., vol. 2859, 200-9 (1996).37. M. Gubarev, E. Ciszak, I. Ponomarev, W. Gibson, and M. Joy, “First Results from a Macromolecular Crystallography System with aPolycapillary Collimating Optic and a Microfocus X-ray Generator”, Jour. Appl. Cryst., 33 (3), 882-887 (2000); M. Gubarev, E. Ciszak, I.Ponomarev, W. Gibson, and M. Joy, “A Compact X-ray System for Macromolecular Crystallography”, Rev. Sci. Instr., 71, 3900 - 05 (2000).
38. S.I. Foundling, M. Li, B. Michell, S.M. Edved, and R. Durst, “Proteum M: The compact laboratory solution,” presented at Am. Cryst.Assoc. Conf., July, 2001.39. S.M. Owens, F.A. Hofmann, C.A. MacDonald, and W.M. Gibson, “Microdiffraction using Collimating and Convergent BeamPolycapillary Optics,” in Advances in X-Ray Analysis, Proc. of the 46th Ann. Denver X-Ray Conf., vol. 41, 314-318 (1997).40. J.X. Ho, E.H. Snell, C.R. Sisk, J.R. Ruble, D.C. Carter, S.M. Owens, and W.M. Gibson, “Stationary Crystal Diffraction with aMonochromatic Convergent X-Ray Source and Application for Macromolecular Crystal Data Collection,” Acta Cryst., D54, 200-214 (1998).41. H. Huang, C..A. MacDonald, W.M. Gibson, J.X. Ho, J.R. Ruble, J. Chik, A. Parsegian, and I. Ponomarev, “Focusing PolycapillaryOptics for Diffraction,” Proc. of Denver 2001 X-Ray Conf. (2001).42. W.M. Gibson, H.H. Chen-Mayer, D.F.R. Mildner, H.J. Prask, A.J. Schultz, R. Youngman, T. Gnäupel-Herold, M.E. Miller, and R. Vitt,“Polycapillary Optics Based Neutron Focusing for Small Sample Neutron Crystallography,” Proc. of Denver 2001 X-Ray Conf., (2001).43. W.M. Gibson, C.A. MacDonald, and M.A. Kumakhov, in Technology Requirements for Biomedical Imaging,” S.K. Mun, ed., I.E.E.E.Press, vol. 2580, 164-169 (1991); C.A. MacDonald and W.M. Gibson, “Medical Applications of Polycapillary X-Ray Optics,” Proc. SPIE,vol. 2519, 186-196 (1995).44. D.G. Kruger, C.C. Abreu, E.G. Hendee, A. Kocharian, W.W. Peppler, C.A. Mistretta, C.A. MacDonald, “Imaging Characteristics of X-Ray Capillary Optics in Mammography,” Medical Physics, 23 (2), 187-196, (1996).45. F. A. Sugiro, C.A. MacDonald and W.M. Gibson, “High Contrast Imaging with Polycapillary Optics”, Proc. of Denver 2001 X-RayConf. (2001).46. W.M. Gibson, H. Huang, J. Nicolich, P. Klein, and C.A. MacDonald, “Optics for Angular Filtering of X-Rays in Two Dimensions,”Proc. of Denver 2001 X-Ray Conf. (2001)