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Method of fabricating ribbed crystals for focusing synchrotron X-radiation
308
Nuclear Instruments and Methods in Physics Research 224 (1984) 308-309 North-ttolland, Amsterdam
M E T H O D OF FABRICATING RIBBED CRYSTALS FOR F O C U S I N G S Y N C H R O T R O N X-RADIATION Joe W O N G and Edward G. S T E L L A General Electric Corporate Research and Development, 1 River Road, PO Box 8, Schenectady, N Y 12301, USA
Received 14 October 1983 and in revised form 20 January 1984
A method of fabricating single-crystalsof silicon having a ribbed structure for focusing intense synchrotron X-radiation above 5 keV is described. The critical step in the fabrication process is the rib-cutting procedure which is given in some detail.
1. Introduction Because of the natural divergence of synchrotron radiation and the large distance between the sample and the source, it is desirable to focus the radiation to increase the useful intensity; e.g. in EXAFS study of dilute species and in X-ray microprobe analysis. It is most advantageous to focus the horizontal divergence which can contribute 100 times more to the intensity than focusing the vertical divergence. The focusing of synchrotron X-radiation can be achieved either by the use of mirrors [1] or curved crystals [2]. The concept of sagittal focusing of synchrotron X-radiation with curved crystals having a ribbed structure (Fig. 1) has been experimentally demonstrated by Sparks et al. [3]. The present note describes a procedure for fabricating such crystals.
2. Fabrication method The method consists of a series of carefully worked out processing steps used in fabricating single-crystal materials with a ribbed structure shown schematically in fig. 1. The procedure is described for the case of a S i ( l l l ) crystal having the following finished dimensions: a = 76 mm, b = 35 mm, h = 15 mm, t = 0.5 mm~ w = 0.5 mm and s = 2 mm (80 mil), which is the width of the saw blade used. The (111) surface of a commercially available 4 inch diameter boule of S i ( l l l ) crystal is first oriented and rough ground to within 0.5 o. A slightly oversize 15 mm thick disk is cut out. The top face of the disk is X-ray oriented again, now to within 0.25 ° or better and ground flat in situ with a 180 grit diamond wheel, 0.5 inches wide and 7 inches in diameter. The bottom side of the disk is then ground parallel to the top surface to yield a 15 mm thick disk. From this parallel disk, a 0167-5087/84/$03.00 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
rectangular block 76 mm × 35 m m x 15 mm is cut. One of the (111) faces of the above block is optically polished. The final finish is carried out with 0.03 t~m A1203. To remove the polish strains, the polished surface is gently etched in a 95% HNO3-5% HF solution (by volume) at 0 ° C for 14 min. The etch rate is approximately 2.5 # m / m i n and about 1.5 mil of surface material is removed. The surface is given a final 1/2 h chemical polish with a Syton solution [4]. To prepare the block for rib-cutting, the polished S i ( l l l ) surface is first glued down with glycol phthalate on a parallel steel plate lined with a lintfree cloth to protect the polished Si surface from mechanical damage. The faces of the steel plate are parallel to within 0.1 mil. The edges along the 76 cm length of the Si block are rounded off with a SiC stone to obviate chipping upon contact with the cutting wheel during the rib-cutting. Thin glass plates about 30 mil thick are then cemented with glycol phthalate onto the top surface of the Si block and on the steel plate along the perimeter of the Si block. These glass plates serve as support and are found to be essential, to avoid chipping during cutting. The mounted Si block is now aligned in a micromatic wafer slicing machine installed with a 6 inch diamond blade, 80 mil thick. The diamond grit size is 150 and the concentration is 100 M. The corner edges of the diamond wheel are rounded off to a 10 mil radius, to obviate the chipping of cut material at the moment of impact with the wheel and to reduce the strain gradient at the foot of the rib in the final structure. The cutting parameters are: spindle speed = 3600 revolutions/min, rate of feed = 1/3 inch/min. The ribs are first cut, 80 rail space and 20 mil rib width. Each cut is made in one single pass. It takes about 3 h to cut 16 ribs. The end materials are then ground off with the same diamond blade, to ensure the same thickness of the crystal inside and outside the region of the ribs. Seventy mils of material are removed per cut. The 10 mil overlap
J. Wong, E.G. Stella / Fabrication of ribbed crystals
309
Fig. 1. Schematic of a ribbed crystal showing the essential dimensional features for fabrication.
Fig. 2. Photograph of a Si(lll) crystal fabricated with 16 ribs, 0.5 mm thick and 2 mm apart.
is to ensure no residual uncut rib. If the end materials were removed before the ribs were cut, the last rib to be cut would have little support during cutting and could easily be chipped off, as experienced in a trial run. After the end materials are totally removed, the ribbed crystal is carefully dismounted from the steel plate, by dissolving the glycol phthalate in acetone. The crystal is then dried and gently etched in a 95% HNO3-5% H F solution in an ice bath for 15 min, to remove the saw damage. The final structure is shown in fig. 2 and is ready to be tested in a synchrotron radiation facility.
3. Results and concluding remarks The procedure described above is an outcome of a number of systematic trial runs of fabricating such a ribbed crystal. Three good Si(111) ribbed crystals such
as that shown in fig. 2 have been fabricated and tested successfully [3] at the Cornell High Energy Synchrotron Source (CHESS). We appreciate technical discussions and suggestions from M. Rich, C.J. Sparks, Jr., G.C. Ice, and B.W. Batterman in the course of this work.
References [1] V. Rehn, in: Workshop on X-ray instrumentation for synchrotron radiation research, April 1978, SSRL Report 78/04, pp. VII-13. [2] C.J. Sparks, Jr., B.S. Bovie and J.B. Hastings, Nucl. Instr. and Meth. 172 (1980) 237. [3] C.J. Sparks, Jr., G.E. Ice, J. Wong and B.W. Batterman, Nucl. Instr. and Meth. 194 (1982) 73. [4] Product of REMET chemical corporation.
Nuclear Instruments and Methods in Physics Research 224 (1984) 308-309 North-ttolland, Amsterdam
M E T H O D OF FABRICATING RIBBED CRYSTALS FOR F O C U S I N G S Y N C H R O T R O N X-RADIATION Joe W O N G and Edward G. S T E L L A General Electric Corporate Research and Development, 1 River Road, PO Box 8, Schenectady, N Y 12301, USA
Received 14 October 1983 and in revised form 20 January 1984
A method of fabricating single-crystalsof silicon having a ribbed structure for focusing intense synchrotron X-radiation above 5 keV is described. The critical step in the fabrication process is the rib-cutting procedure which is given in some detail.
1. Introduction Because of the natural divergence of synchrotron radiation and the large distance between the sample and the source, it is desirable to focus the radiation to increase the useful intensity; e.g. in EXAFS study of dilute species and in X-ray microprobe analysis. It is most advantageous to focus the horizontal divergence which can contribute 100 times more to the intensity than focusing the vertical divergence. The focusing of synchrotron X-radiation can be achieved either by the use of mirrors [1] or curved crystals [2]. The concept of sagittal focusing of synchrotron X-radiation with curved crystals having a ribbed structure (Fig. 1) has been experimentally demonstrated by Sparks et al. [3]. The present note describes a procedure for fabricating such crystals.
2. Fabrication method The method consists of a series of carefully worked out processing steps used in fabricating single-crystal materials with a ribbed structure shown schematically in fig. 1. The procedure is described for the case of a S i ( l l l ) crystal having the following finished dimensions: a = 76 mm, b = 35 mm, h = 15 mm, t = 0.5 mm~ w = 0.5 mm and s = 2 mm (80 mil), which is the width of the saw blade used. The (111) surface of a commercially available 4 inch diameter boule of S i ( l l l ) crystal is first oriented and rough ground to within 0.5 o. A slightly oversize 15 mm thick disk is cut out. The top face of the disk is X-ray oriented again, now to within 0.25 ° or better and ground flat in situ with a 180 grit diamond wheel, 0.5 inches wide and 7 inches in diameter. The bottom side of the disk is then ground parallel to the top surface to yield a 15 mm thick disk. From this parallel disk, a 0167-5087/84/$03.00 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
rectangular block 76 mm × 35 m m x 15 mm is cut. One of the (111) faces of the above block is optically polished. The final finish is carried out with 0.03 t~m A1203. To remove the polish strains, the polished surface is gently etched in a 95% HNO3-5% HF solution (by volume) at 0 ° C for 14 min. The etch rate is approximately 2.5 # m / m i n and about 1.5 mil of surface material is removed. The surface is given a final 1/2 h chemical polish with a Syton solution [4]. To prepare the block for rib-cutting, the polished S i ( l l l ) surface is first glued down with glycol phthalate on a parallel steel plate lined with a lintfree cloth to protect the polished Si surface from mechanical damage. The faces of the steel plate are parallel to within 0.1 mil. The edges along the 76 cm length of the Si block are rounded off with a SiC stone to obviate chipping upon contact with the cutting wheel during the rib-cutting. Thin glass plates about 30 mil thick are then cemented with glycol phthalate onto the top surface of the Si block and on the steel plate along the perimeter of the Si block. These glass plates serve as support and are found to be essential, to avoid chipping during cutting. The mounted Si block is now aligned in a micromatic wafer slicing machine installed with a 6 inch diamond blade, 80 mil thick. The diamond grit size is 150 and the concentration is 100 M. The corner edges of the diamond wheel are rounded off to a 10 mil radius, to obviate the chipping of cut material at the moment of impact with the wheel and to reduce the strain gradient at the foot of the rib in the final structure. The cutting parameters are: spindle speed = 3600 revolutions/min, rate of feed = 1/3 inch/min. The ribs are first cut, 80 rail space and 20 mil rib width. Each cut is made in one single pass. It takes about 3 h to cut 16 ribs. The end materials are then ground off with the same diamond blade, to ensure the same thickness of the crystal inside and outside the region of the ribs. Seventy mils of material are removed per cut. The 10 mil overlap
J. Wong, E.G. Stella / Fabrication of ribbed crystals
309
Fig. 1. Schematic of a ribbed crystal showing the essential dimensional features for fabrication.
Fig. 2. Photograph of a Si(lll) crystal fabricated with 16 ribs, 0.5 mm thick and 2 mm apart.
is to ensure no residual uncut rib. If the end materials were removed before the ribs were cut, the last rib to be cut would have little support during cutting and could easily be chipped off, as experienced in a trial run. After the end materials are totally removed, the ribbed crystal is carefully dismounted from the steel plate, by dissolving the glycol phthalate in acetone. The crystal is then dried and gently etched in a 95% HNO3-5% H F solution in an ice bath for 15 min, to remove the saw damage. The final structure is shown in fig. 2 and is ready to be tested in a synchrotron radiation facility.
3. Results and concluding remarks The procedure described above is an outcome of a number of systematic trial runs of fabricating such a ribbed crystal. Three good Si(111) ribbed crystals such
as that shown in fig. 2 have been fabricated and tested successfully [3] at the Cornell High Energy Synchrotron Source (CHESS). We appreciate technical discussions and suggestions from M. Rich, C.J. Sparks, Jr., G.C. Ice, and B.W. Batterman in the course of this work.
References [1] V. Rehn, in: Workshop on X-ray instrumentation for synchrotron radiation research, April 1978, SSRL Report 78/04, pp. VII-13. [2] C.J. Sparks, Jr., B.S. Bovie and J.B. Hastings, Nucl. Instr. and Meth. 172 (1980) 237. [3] C.J. Sparks, Jr., G.E. Ice, J. Wong and B.W. Batterman, Nucl. Instr. and Meth. 194 (1982) 73. [4] Product of REMET chemical corporation.