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New capabilities and applications of compact source-optic ...

  1. 1. 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 ABSTRACT Polycapillary and doubly curved crystal x-ray optics have gained broad acceptance and are now being used in a wide variety of applications. Beginning as optics integrated into research setups, they were then used to enhance the performance of existing x-ray analytical instruments and are now widely used as essential components in x-ray spectrometers and diffractometers designed to utilize their capabilities. Development of compact x-ray sources, matched to the optic input requirements have allowed 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. INTRODUCTION Having undergone rapid development over the past ten years, polycapillary and doubly curved crystal optics have gained broad acceptance. Indeed, this field is undergoing an important transition in which the focus of papers and presentations are primarily or exclusively on applications and not on the design and characteristics of the optics. For example, in summer 2001 conferences there were over thirty papers that utilized polycapillary or doubly curved crystal optics. In many cases, these optics enhance the sensitivity or improve the convenience of standard x-ray analysis equipment. An example is the use of a collimating optic in an x-ray diffractometer to increase the diffracted beam intensity and at the same time, produce a parallel beam 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 allow traditional laboratory or even synchrotron based measurements to migrate to in situ or in-line use in sample preparation or manufacturing 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 other organizations and individuals. 1.1. History and overview of polycapillary optics The basic physics that underlies polycapillary x-ray optics was described in 19231 and the possibility to guide x rays in hollow capillary tubes was discussed in 19312 . The principles of operation of polycapillary optics are shown in Figure 1. Optics using multiple channels each involving multiple reflections were first reported in 19893 . These were comprised of single thin- walled glass capillary tubes guided through thin metal screens. The next major advance was the use of polycapillary fibers in which many hollow capillary channels were contained in a single glass fiber of about the same size as the original single glass capillaries4 . These polycapillary fibers were also threaded through thin metal grids. Such multifiber polycapillary optics allowed significant reduction in size and increase of the useable x-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 original capillary 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. R ~ 5 0 0 m m Θ c = 3 .8 m r a d d < 5 µ m 2 2 cR d Θ ≤ d Θ c g la s s n 2 n 1θ c a ir mrad keVEnergy c ][ 32 ≈Θ Figure 1. Schematic representation of the principles of capillary 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.
  2. 2. 1.2. History and overview of Doubly Curved Crystal (DCC)TM optics Three-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 referred to as monochromatic x-ray optics. Focusing geometries for producing a point image from a point x-ray source were described and investigated in early work during the 1950s6,7 . Only in the 1980s and 1990s, were the x-ray optical properties of DCC optics systematically studied by Wittry et al using a ray tracing method8-13 . Fabrication and applications of DCC were also reported in several publications by Wittry and his coworkers14-16 . However, the widespread use of DCC optics for primary monochromatic 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 Johann type double curved mica crystal for monochromatic micro XRF applications. The high intensity gain of the mica DCC was based on a novel crystal-bending technology. This proprietary technology can provide elastic bending of crystals into various complex shapes with precise figure control. (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.
  3. 3. Point-to-point focusing geometry of a DCC optic is shown in Figure 5. In this geometry, the diffracting planes of the crystal remain parallel to the curved crystal surface. The crystal surface, which is a toroidal shape, has the Johann geometry in the focal circle plane and axial symmetry in the perpendicular direction8 . A large solid angle is collected from an x-ray source which is then focused to a small spot. Due to point-to-point focusing of x-rays, the achievable spot size is related to the spot size of the x-ray source. Photographs of doubly curved crystal optics are shown in Figure 6. 1.3. Optics Capabilities 1.3.1. Polycapillary (polychromatic) optics. One of the distinguishing features of polycapillary optics is their broad energy (wavelength) bandwidth. They are therefore sometimes referred to as polychromatic optics. Other optics in this class include other reflective optics such as monocapillary optics, 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 and Table II. Only monolithic optics are shown in Table II since they can give focal spot sizes much smaller than multifiber focusing optics for which the spot size is limited by the polycapillary fiber width. In special cases, such as for neutron focusing, multifiber focusing optics may be used because of their larger collecting area. Also multifiber collimating optics are often selected for applications requiring a large cross section parallel beam as for large area thin film texture studies18 or x-ray lithography19 . Bending Radius in Vertical Plane = 2Rsin2 θB Bending Radius in Horizontal Plane = 2R Axial symmetry along SI Figure 5. Geometry of doubly curved crystal optic (DCC)TM Figure 6. Photographs of doubly curved crystal optics
  4. 4. 1.3.2. Doubly curved crystal (DCC)TM optics A principle benefit of doubly curved crystal optics is the ability to provide an intense monochromatic focused beam. Various crystal materials can be used for DCC optics, including Si, Ge, quartz and mica. The collection solid angle of DCC optics is determined by the capture angle in the dispersive plane and the included rotational angle φ. The capture angle in the dispersive plane is typically 1-5 degrees and the rotational angle can be 5-90 degrees. The focal spot size of the reflected beam is mainly determined 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 Kα1 Reflection efficiency 10% to 20% Collection solid angle 0.005 to 0.1 steradians. Convergent angles 1-5 degree x 5-90 degrees Focused beam size 10-100u depending on the source size Table III. Characteristics of DCC optics 2. X-RAY BEAMS 2.1. Polycapillary optics A principle benefit of polycapillary optics is the ability to capture x rays from a divergent source over a large angle and to redirect them into a quasiparallel or focused x-ray beam, thus avoiding the inverse square dependence of x-ray intensity on the distance from the source that has limited many applications of x rays since their discovery over 100 years ago. A comparison between 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 or free-electron-laser (FEL) x-ray sources. Such sources are large, expensive and complex. For many applications, polycapillary optics 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 be maximized for a given source-optic distance by increasing the optic input area. This means for many standard x-ray sources which often have source-spot to window distance of several cm, a multifiber lens is often used (the largest area high quality monolithic optics at present is ~ 100 mm2 ). However, with reduction of the source- optic distance to a few mm, even monolithic 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 pinhole aperture. Collimating Optics • Multifiber – Output beam size: 10 x 10, 20 x 20, 30 x 30 mm2 – Output divergence: ~ 4mrad CuKα – Capture angle: 4.2°, 7°, 8.8 ° – Axial and planar divergence are identical – Up to 30 % transmission efficiency • Monolithic – Output beam size diameter: 0.5mm, 1.5mm, 4mm, 6mm – Output divergence: ~1 mrad MoKα, ~2 mrad CuKα – Capture angle: up to 20 ° – Transmission efficiency: up to 30 % (geometry and energy dependent) Table I. Characteristics of collimating polycapillary optics. Focusing Monolithic Optics –Point to point focusing –Small focal spots •< 25 µm @ Cu Kα •< 15 µm @ Mo Kα –Capture angle: up to 20° –Transmission efficiency: up to 30 % (geometry and energy dependent) Table II. Characteristics of focusing polycapillary optics.
  5. 5. Recently, several close-access, microfocus x-ray sources have been developed. When coupled with monolithic optics, x-ray flux and flux density values have been obtained with compact low-power sources that are comparable to or greater than those obtained with conventional high-power rotating anode sources equipped with conventional optics. An integrated source-optic system is shown in Figure 8. By choice of optic, this can produce a quasiparallel beam or a focused beam. Table IV shows the beam characteristics with focusing X-Ray Beams and Table V and Table VI with collimating X-Ray Beams. 2.2. Doubly curved crystal optics. Because of the large collection solid angle of DCC optics21 , intense monochromatic beams can be obtained even with low power compact x-ray sources. Characteristics of monochromatic focused DCC based X-Ray Beams are shown in Table VII. Multiple doubly curved crystal optics can be integrated with the source and focused on the same spot to provide higher intensity as shown schematically in Figure 9. 0 5 10 15 20 25 30 10 0 10 1 10 2 10 3 10 4 10 5 10 6 Scatter x-ray spectra (W-anode, 30kV, 0.1mA) Fe and Cr from the aperture material Ar in air W Lγ W Lβ W Lα Polycapillary focusing optic 0.1 mm aperture 100 mm from the source Counts Energy (keV) Figure 7. X-ray energy spectrum from 3 W tungsten x-ray source with a polycapillary focusing optic and with a conventional pinhole aperture (ref. 30). Figure 8. X-ray BeamTM , with integrated optic alignment and shutter assembly. B eam F lux • W ith C u-anode source (50 kV , 50W , source spot: 0.15 m m ): C u K α intensity: 1.0 × 109 photon/second Flux density: 1.2 × 106 photon/s/µ m 2 • W ith M o-anode source (50 kV , 50W , source spot: 0.15 m m ): M o K α : 5.6 × 107 photon/secon d Flux density: 1.8 × 105 photon/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 Beam flux 1.9 x 109 p/s 40kV, 80W (Bede Microsource) 1.0 x 109 p/s 40 kV, 50W (Oxford 5011 source) Beam divergence (FWHM) 2.0 mrad. (0.12°) 2.0 mrad. Beam diameter 1.5 mm 6.0 mm Beam flux 1.9 x 109 p/s 40kV, 80W (Bede Microsource) 1.0 x 109 p/s 40 kV, 50W (Oxford 5011 source) Beam divergence (FWHM) 2.0 mrad. (0.12°) 2.0 mrad. Beam diameterBeam diameter 1.5 mm1.5 mm 6.0 mm6.0 mm Beam fluxBeam flux 1.9 x 109 p/s 40kV, 80W (Bede Microsource) 1.9 x 109 p/s 40kV, 80W (Bede Microsource) 1.0 x 109 p/s 40 kV, 50W (Oxford 5011 source) 1.0 x 109 p/s 40 kV, 50W (Oxford 5011 source) Beam divergence (FWHM) Beam divergence (FWHM) 2.0 mrad. (0.12°) 2.0 mrad. (0.12°) 2.0 mrad.2.0 mrad. Table V. Collimating X-Ray BeamTM with Cu Kα source (ref. 20). Beam diameter 1.0 mm 4.0 mm Beam flux at 50kV, 40W (Oxford UltraBright source) 7.1 x 107 p/s 3.5 x 108 p/s Beam divergence (FWHM) 1.0 mrad. 0.06° 1.0 mrad. Beam diameter 1.0 mm 4.0 mm Beam flux at 50kV, 40W (Oxford UltraBright source) 7.1 x 107 p/s 3.5 x 108 p/s Beam divergence (FWHM) 1.0 mrad. 0.06° 1.0 mrad. Beam diameterBeam diameter 1.0 mm1.0 mm 4.0 mm4.0 mm Beam flux at 50kV, 40W (Oxford UltraBright source) Beam flux at 50kV, 40W (Oxford UltraBright source) 7.1 x 107 p/s7.1 x 107 p/s 3.5 x 108 p/s3.5 x 108 p/s Beam divergence (FWHM)Beam divergence (FWHM) 1.0 mrad. 0.06° 1.0 mrad. 0.06° 1.0 mrad.1.0 mrad. Table VI. Collimating X-Ray BeamTM with Mo Kα source (ref. 20).
  6. 6. 3. APPLICATIONS 3.1. Focused beam applications 3.1.1. Micro x-ray fluorescence (MXRF) MXRF is currently the most widely used application of polycapillary optics, being an integral part of several commercial MXRF instruments. The small size and low power enables development of in-line MXRF systems for semiconductor and other materials based industries and development of remote or portable environmental and mineralogical (for example, planetary rover) instruments. MXRF systems can take many different forms, some of which are illustrated in Figs. 10-17. Currently attainable focal spot sizes are listed in Table II. Optics Beam energy (keV) Solid angle (Sr.) Source Beam size (FWHM) Flux (No. photons/s) Ge (220) -Cr 5.4 0.03 Trufocus 8050Cr 14w 70µ 3 x 109 Si (111) -Cu 8.0 0.015 two optics Trufocus 8050Cu 14w 40µ 1 x 109 Si(111)-Cu 8.0 0.005 Oxford 5011Cu 50w 100µ 1 x 109 Si(220)-WLa 8.4 0.01 Hamamatsu W 10W 13µ 1 x 108 Si (220) -Mo 17.5 0.01 Trufocus 8050Cu 14w 40µ 1 x 108 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. Figure 10. Standard MXRF configuration. The sample can be scanned to measure the distribution with ~ 10 µm resolution
  7. 7. 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 outside the area of interest get into the detector and reduce the image contrast. A polycapillary optic collects x-rays from an area defined by the optic spot size and focuses them on the detector, reducing the background and enhancing the 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 11. Dual optic MXRF system. Particularly useful for measurement of spatial distributions in radioactive samples (ref 22). Figure 12. MXRF X-ray Beam incorporated into an SEM. Figure 13. Monolithic focusing optic as a spatial filter in an ESEM (ref. 23).
  8. 8. 3.1.2. Monochromatic micro x-ray fluorescence (MMXRF) Monochromatic x-ray micro beams provide several advantages over MXRF techniques using polychromatic excitation for some applications, including larger working distance and simpler quantitative analysis. More importantly, monochromatic excitation 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 (10-15 g) levels for surface concentration of medium or high Z elements can be achieved with 500s measurement times using low power sources27 . A typical configuration for MMXRF is shown in Figure 18, and a comparison of measured MXRF and MMXRF spectra from an environmental particulate sample is shown in Figure 19. Figure 14. Electron Probe Wavelength Dispersive Spectroscopy (EPWDS) Source Polycapillary Optic Flat crystal Counter Figure 15. Micro Wavelength Dispersive X-Ray Fluorescence (MWDXRF)( ref. 24) Figure 16. Monolithic focusing optic to increase the efficiency (>300 x) of super conductor microcalorimeter detector (ref. 29). Figure 17. XRF spectrum from 0.5 µm WSiO2 particle on SiO2 substrate (ref. 26)
  9. 9. 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 smooth surfaces and is an important analytical tool for wafer surface contamination control in semiconductor chip manufacture. However, 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 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 to meet the total reflection requirement. The flux density on the reflection surface is several orders of magnitude higher than that of conventional systems with higher power sources27 . This yields very high sensitivity for localized contaminant detection. 3.1.4. Rapid x-ray reflectometry, XRR D etector S am ple D C C S ou rce D etector S am ple D C C S ou rce Figure 18. Setup for MMXRF focused X-Ray Beam measurement 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 1 1 0 1 0 0 1 0 0 0 1 0 0 0 0 S rB r B r P b A s P b (A s ) Z n S K C a C r N i T i M n C u Z n F e Coutns(600seconds) E n e rg y (k e V ) M o tube w ith capillary optic, 40kV 0.5m A, 7mm 2 PIN detector, 12m m from the sample M o tube w ith Si(220) D CC, 40kV 0.2m A, 25mm 2 PIN detector, 15m m from the sample Figure 19. MXRF and MMXRF spectra from concentrated environmental particulate sample with MoK excitation. Point Source Doubly Curved Crystal Slit Detector X Y Z Point Source Doubly Curved Crystal Slit Detector X Y Z 2 4 6 8 10 12 14 16 18 20 0 100 200 300 Si Ar Ni Fe Zn Br (3pg) Co un ts/ 50 0s E(keV) Figure 20. Setup and spectrum for monochromatic focused X-Ray Beam TXRF measurement (ref. 27).
  10. 10. X-ray reflectometry (XRR) is an important technique for characterizing thin film thickness, roughness, and density. In this application, 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 sequentially scanning the incidence angle. A DCC optic can provide s small focal spot and a range of incidence angles as shown in Figure 21. The entire reflectivity-angle curve can then be recorded with a position sensitive detector27 . 3.1.5. Other focused beam applications Other 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 in Figure 22. XAFS measures the local microstructure with atomic resolution and XANES can be used to determine the chemical state of selected constituents. These applications as well as most of the applications discussed in Section,3.1.1., make use of the broad energy (or wavelength) band-width transmitted by polycapillary optics. This distinguishes polycapillary optics from diffractive optics such as flat or curved crystal optics and multilayer thin film optics. Additional applications of focusing optics (not discussed in this review) include; focusing of low energy (cold) neutrons for prompt gamma activation analysis (PGAA) and neutron depth profiling30 , which give measured neutron intensity gains as high as 80 and focal spot sizes as small as 90 µm, making neutron microanalysis possible for the first time, and concentration of high- energy (20-50 keV) x rays for astrophysical spectroscopic measurements31 . 3.2. Collimated beam applications Doubly Curved Crystal Point Source Sam ple PSD Doubly Curved Crystal Point Source Sam ple PSD 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1E-5 1E-4 1E-3 0.01 0.1 1 Reflectivity Angle(degree) XRR data for 800Å TiN film on Si w afer using Tungsten Lα line 100s @ 3.5W (35kV, 0.1m A) source setting 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1E-5 1E-4 1E-3 0.01 0.1 1 Reflectivity Angle(degree) XRR data for 800Å TiN film on Si w afer using Tungsten Lα line 100s @ 3.5W (35kV, 0.1m A) source setting Figure 21. Setup and reflectivity spectrum for a rapid x-ray reflectivity measurement (ref. 27). Detector 1 Detector 2 SamplePolycapillary Figure 22. Setup for x-ray absorption fine structure (XAFS)(ref. 28) and for x-ray absorption near edge spectroscopy (µ XANES) (ref. 29).
  11. 11. 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 because they convert a highly divergent beam (up to 20o depending on the capture angle) into a quasiparallel beam with divergence of 1-4 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 . The quasiparallel beam from the polycapillary collimator relaxes constraints on sample position, shape, roughness, and transparency 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 for in-line diffraction instruments for quality control and feedback in manufacturing and process environments. Such systems are under 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 Figure 23. General arrangement for x-ray diffraction (XRD) measurement (after ref. 18). 1 0 2 0 3 0 4 0 5 0 6 0 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 2 K W P a r a l l e l - B e a m D i f f r a c t o m e t e r 2 0 W X O S P r o t o t y p e S y s t e m Intensity cts/s2KWDiffractometer cts/10sXOSPrototypeSystem 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 and a 20 W polycapillary based Collimated Beam System (ref. 32).
  12. 12. sample position on the diffracted peak. Figure 26 shows a pole figure measurement of the texture of a 100 Å silver thin film on a silicon crystal34 . An example of the flexibility provided by a parallel beam Collimated Beam System is illustrated in Figure 27 where a setup is shown for powder diffraction measurements which eliminates preferred orientation errors35 and in Figure 28 which shows an arrangement for in plane scattering measurements. 4 6 4 7 4 8 4 9 0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 0 m m 2 m m 4 m m - 2 m m - 4 m m D e g r e e s 2 T h e t a Countsperseco 4 6 4 7 4 8 4 9 0 1 0 0 0 2 0 0 0 0 m m 1 m m 2 m m - 1 m m - 2 m m 4 6 4 7 4 8 4 9 0 1 0 0 0 2 0 0 0 1 m m 2 m m D e g r e e s 2 T h e t a Countspersec Figure 25. Diffracted beam shape and position for Si(100) with polycapillary Collimated Beam System and conventional Bragg- Brentano geometry (ref. 33).Figure 26. Pole figure-100 Å Ag on Si(111) texture map (ref. 34). Air Flow Figure 27. Powder XRD with Collimated X-Ray Beam to eliminate preferred orientation errors (ref. 35). Sample Detector Source Sample Detector Side View Top View Optic Source Optic Figure 28. Setup for in-plane scattering
  13. 13. 3.2.2. Single crystal diffraction. The benefits noted above for powder diffraction also apply to single crystal diffraction applications. Perhaps the most important and most studied single-crystal application to date has been the use of a Collimated Beam System for protein crystallography36 . Figure 29 is a schematic representation of such a measurement and a diffraction pattern for Lysozyme is shown in Figure 30. The diffracted beam intensity obtained with a polycapillary monolithic optic with a slightly convergent (<0.5o ) beam and a 50 W microfocus source is equal to or greater than that from a 5 kW rotating anode source equipped with the most advanced confocal optics, with resolution < 2 Å and Rmerge < 6 % for Lysozyme37 . At the present time the local divergence (divergence of x rays from each capillary channel) of ~0.12o , limits the unit cell size of molecules that can be analyzed to <~200 Å. A similar X-ray Beam based system which also includes a graphite monochromator 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 beam spots. Together with special software40 for analysis of convergent beam diffraction patterns, these can be used for screening of very small protein crystals41 , microdiffraction measurements with very low source power (<10W) for example for planetary rovers, and for portable, remote, or in-line microdiffraction measurements. Similarly, slightly or highly focusing polycapillary optics can be used for neutron diffraction from small crystals for macromolecular structure, high pressure, or low temperature studies42 . 3.2.3. X-ray lithography Figure 29. Schematic representation of protein crystallography measurement. Figure 30. Diffraction pattern for Lysozyme (ref. 23).
  14. 14. Polycapillary collimating optics can also be used to produce a quasiparallel beam for x-ray lithography19 . A setup for this is shown in Figure 31. 4. MEDICAL A potential major area of applications for polycapillary optics is in medicine43 . Used as magnifying angular filters, they have been demonstrated to give significant and important increase in contrast and resolution for mammography44 and are under active investigation for other soft tissue imaging and for cancer therapy. These applications of polycapillary optics are not reviewed in this paper because of limited space and because they are at an earlier stage of general acceptance and application that the examples given. Also, they have recently been reviewed in two papers in the Denver 2001 Conference proceedings45, 46 . 5. CONCLUSIONS Polycapillary and doubly curved crystal optics have gained broad acceptance and are now being used in a broad variety of applications. Beginning as optics integrated by users into research setups, they were then used to enhance the performance of existing x-ray analytical instruments and are now widely used as essential components in x-ray spectrometers and diffractometers designed to utilize their capabilities. Development of compact x-ray sources, matched to the optic input requirements have allowed large reduction of 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 systems for new applications in industry, science, or medicine. REFERENCES * Corresponding author to whom questions or comments should be directed ( 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). • Applications – Large volum e – Sm all features – Large dies – M em ory chips – G aAs sem iconductors – D eep Lithography • M ichrom echanical system s • Benefits – M ass production – Sm all resolution – Parallel Beam Figure 31. X-ray lithography (XRL), with potential applications and benefits.
  15. 15. 3. V.A. Arkd’ev, A.I. Kolomitsev, M.A. Kumakhov, I.Yu. Ponomarev, I.A. Khodeev, Yu. P. Chertov, and M. Shakparonov, “Wide-Band X-ray Optics with a Large Angular Aperture,” Sov. Phys. Usp. 32(3), 271 (1989). 4. M.A. Kumakhov and F.F. Komarov, “Multiple Reflection from Surface X-ray Optics,” Phys. Rep., 191(5), 289 (1990). 5. W.M. Gibson and M.A. Kumakhov, “Application of X-ray and Neutron Optics,” Proc. SPIE, vol. 1736, 172-189 (1992). M.A. Kumakhov, U.S. Patent No. 5,192,869, “Device for Controlling Beams of Particles, X-Rays, and Gamma Quanta”, Appl. 5/91, Issue 6/93. 6. G. Hagg and N. Karlsson, “Aluminum Monochromator with Double Curvature for High-Intensity X-Ray Powder Photographs” Acta Cryst., 5, 728-730 (1952). 7. D.W. Berreman, J.W.M. Dumond, and P.E. Marmier, “New Point-Focusing Monochromator,” Rev. Sci. Instr,. 25, 1219-1220 (1954). 8. D. B. Wittry and D. M. 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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 their Applications 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 and Environmental 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-ray Absorption 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 and Micro-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 Activation Analysis 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-ray Astronomy,” 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. private communication. 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 for Macromolecular 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 a Polycapillary 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. 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