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 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. INTRODUCTION

Having 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

The basic physics that underlies polycapillary x-ray optics wasdescribed in 19231 and the possibility to guide x rays in hollowcapillary 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-walled glass capillary tubes guided through thin metal screens.The next major advance was the use of polycapillary fibers inwhich 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 threadedthrough thin metal grids. Such multifiber polycapillary opticsallowed 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.

R ~ 5 0 0 m mΘ c = 3 .8 m r a d

d < 5 µm 2

2cR

dΘ

≤

d Θ c

g la s s n 2

n 1θ c

a ir

mradkeVEnergyc ][

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 ofcurvature of the capillary and d is the capillary diameter.

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 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.

(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.

Point-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.

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 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.

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)TM

Figure 6. Photographs of doubly curved crystal optics

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. 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 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 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.

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.

Recently, several close-access, microfocus x-ray sources havebeen developed. When coupled with monolithic optics, x-rayflux and flux density values have been obtained with compactlow-power sources that are comparable to or greater thanthose obtained with conventional high-power rotating anodesources equipped with conventional optics. An integratedsource-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-RayBeams and Table V and Table VI with collimating X-RayBeams.

2.2. Doubly curved crystal optics.

Because of the large collection solid angle of DCC optics21,intense monochromatic beams can be obtained even with lowpower compact x-ray sources. Characteristics ofmonochromatic focused DCC based X-Ray Beams are shownin Table VII. Multiple doubly curved crystal optics can beintegrated with the source and focused on the same spot toprovide higher intensity as shown schematically in Figure 9.

0 5 10 15 20 25 3010

0

101

102

103

104

105

106

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

Co

un

ts

Energy (keV)

Figure 7. X-ray energy spectrum from 3 W tungsten x-ray sourcewith a polycapillary focusing optic and with a conventional pinholeaperture (ref. 30).

Figure 8. X-ray BeamTM, with integrated opticalignment and shutter assembly.

B ea m F lu x

• W ith C u -a n o d e so u rce (5 0 k V , 5 0 W , so u rce sp o t: 0 .1 5 m m ):

C u K α in ten s ity : 1 .0 × 1 0 9 p h oton /sec on d

F lu x d e n sity: 1 .2 × 1 0 6 p h oton /s /µm 2

• W ith M o -a n o d e so u rce (5 0 k V , 5 0 W , so u rc e sp o t: 0 .1 5 m m ):

M o K α : 5 .6 × 1 0 7 p h oton /sec on d

F lu x d e n sity: 1 .8 × 1 0 5 p h oton /s /µm 2

Table IV. Characteristics of X-ray BeamTM with focusing monolithicoptics (ref. 20).

Beam diameter 1.5 mm 6.0 mm

Beam flux 1.9 x 109 p/s40kV, 80W (Bede

Microsource)

1.0 x 109 p/s40 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/s40kV, 80W (Bede

Microsource)

1.0 x 109 p/s40 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 flux Beam flux 1.9 x 109 p/s40kV, 80W (Bede

Microsource)

1.9 x 109 p/s40kV, 80W (Bede

Microsource)

1.0 x 109 p/s40 kV, 50W (Oxford 5011

source)

1.0 x 109 p/s40 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).

3. APPLICATIONS

3.1. Focused beam applications

3.1.1. 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.

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 0.015two 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 bescanned to measure the distribution with ~ 10 µm resolution

The compact size and flexibility of focused X-ray Beam systemsfacilitates their incorporation into existing processing ordiagnostic instruments. An example is shown in Figure 12. Aninteresting application in a low-voltage scanning electronmicroscope (LV-SEM) or environmental SEM (ESEM) is shownin Figure 1323. In this case the electron beam spreads in the highpressure environmental chamber and fluorescent x rays generated

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 theimage contrast.

High-resolution x-ray fluorescence measurements, not onlygreatly increase the elemental discrimination andmeasurement sensitivity but in some important cases cangive chemical as well as compositional information. Thiscan be done by wavelength dispersive detection with acollimating optic to increase the diffracted beam intensity asshown in Figure 1424 and Figure 15 or by use of a ultra highresolution microcalorimeter detector as shown in Figure1625. An example of the XRF spectrum from such ameasurement is shown in Figure 1726.

Figure 11. Dual optic MXRF system. Particularly useful formeasurement 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).

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.

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)

3.1.3. Focused beam total x-ray fluorescence, TXRF

Total reflection x-ray fluorescence (TXRF) is a surface analyticaltechnique for ultra-trace analysis of particles, residues, and impurities onsmooth surfaces and is an important analytical tool for wafer surfacecontamination control in semiconductor chip manufacture. However,because conventional TXRF systems provide large beam size, localizedinformation is difficult to obtain. Using DCC optics, x-ray photons canbe focused to perform localized area TXRF. A schematic diagram forsuch a measurement is shown in Figure 20. A slit is used to restrictdivergence in the scattering plane to less than the critical angle in order tomeet the total reflection requirement. The flux density on the reflectionsurface is several orders of magnitude higher than that of conventionalsystems with higher power sources27. This yields very high sensitivity

for localized contaminant detection.

3.1.4. Rapid x-ray reflectometry, XRR

Detector

Sam ple

D CC

Source

Detector

Sam ple

D CC

Source

Figure 18. Setup for MMXRF focused X-Ray Beammeasurement

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 rB r

P bA s

P b (A s )Z n

S KC a

C rN i

T i

M n

C u

Z n

F e

Co

utn

s (

60

0 s

ec

on

ds

)

E n e r g y ( k e V )

M o tube w ith cap illary op tic, 40kV 0.5m A, 7m m 2 P IN detector, 12m m from the sam ple

M o tube w ith S i(220) D CC, 40kV 0.2m A, 25m m 2 P IN detector, 15m m from the sam ple

Figure 19. MXRF and MMXRF spectra from concentrated environmental particulatesample 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)

Counts/500s

E(keV)

Figure 20. Setup and spectrum for monochromatic focused X-Ray Beam TXRF measurement (ref. 27).

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.

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 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.

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

D oubly C urved C rystal

Po int Source

Sam ple

PSD

D oubly C urved C rystal

Po int Source

Sam ple

PSD

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.61E-5

1E-4

1E-3

0.01

0.1

1

Re

fle

cti

vit

y

A ng le(degree)

XR R data for 800Å TiN film on Si w afer using Tungsten Lαline

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 1.61E-5

1E-4

1E-3

0.01

0.1

1

Re

fle

cti

vit

y

A ng le(degree)

XR R data for 800Å TiN film on Si w afer using Tungsten Lαline

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 (µXANES) (ref. 29).

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.

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

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

Int

en

sit

y

cts

/s 2

KW

Dif

fra

cto

me

ter

cts

/10

s X

OS

Pr

oto

typ

e S

ys

tem

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 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 anarrangement 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

Co

un

ts p

er s

ec

o

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

Co

un

ts p

er s

ec

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 preferredorientation errors (ref. 35).

Sample

Detector

Source

Sample

Detector

Side View

Top View

Optic

Source Optic

Figure 28. Setup for in-plane scattering

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.

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 temperaturestudies42.

3.2.3. X-ray lithography

Figure 29. Schematic representation of protein crystallography measurement. Figure 30. Diffraction pattern forLysozyme (ref. 23).

Polycapillary collimating optics can also be used to produce a quasiparallel beam for x-ray lithography19. A setup for this isshown in Figure 31.

4. MEDICAL

A 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. CONCLUSIONS

Polycapillary 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 (wgibson@xos.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).

• Applications– Large vo lum e – Sm all features– Large d ies– Mem ory ch ips– GaAs sem iconductors– Deep L ithography

• M ichrom echanical system s

• Benefits– Mass production– Sm all reso lution– Paralle l Beam

Figure 31. X-ray lithography (XRL), with potential applications and benefits.

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Annual Meeting, and MSC/SMC 19th Annual Metting 1992, G. 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)