Top-Seeded Solution Growth and Optical Properties of Deep-UV

Dec 27, 2016 - A prototype Glan−Taylor polarizer made from a new deep ultraviolet birefringent Ba2Ca(B3O6)2 (BCBO) crystal shows promising polarizin...
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Top-Seeded Solution Growth and Optical Properties of Deep-UV Birefringent Crystal Ba2Ca(B3O6)2 Zhen Jia,†,‡ Ningning Zhang,† Yingying Ma,† Liwei Zhao,† Mingjun Xia,† and Rukang Li*,†,‡ †

Beijing Center for Crystal Research and Development, Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China ‡ University of Chinese Academy of Sciences, Beijing, 100049, P. R. China S Supporting Information *

ABSTRACT: Single crystals of the birefringent material Ba2Ca(B3O6)2 (BCBO) with dimensions up to 40 × 28 × 10 mm3 were successfully grown by top-seeded solution growth (TSSG) method from B2O3−NaF flux. It exhibits high transmittance in the range of 190−3000 nm with UV cutoff of 178 nm, which is much shorter than that (189 nm) of the commercial UV birefringent crystal, the high-temperature phase of BaB2O4 (α-BBO). Meanwhile, BCBO crystal has large birefringence (Δn = no − ne = 0.2524−0.0862) in the wavelength range from 178 to 3000 nm and without phase transition from room temperature to the melting point. A prototype of Glan−Taylor polarizer made from BCBO crystal showed an optical extinction ratio of 104:1, which is comparable to those of commercial birefringence crystals. The experimental results demonstrate that the BCBO crystal can be a new promising birefringent crystal for UV, especially the sub-200 nm deep-UV range.

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due to a phase transition at 925 °C.22 Commercially available αBBO is doped with Sr2+ to get rid of the phase transition, which leads to the inhomogeneity of crystals from batch to batch.23 This stresses the importance of searching for new birefringent crystals which can replace CaCO3, YVO4, α-BBO, and other crystals applied in UV, especially the deep-UV range. Recently, several new developed birefringence crystals such as Ca3(BO3)2,24 Ba3Y(B3O6)2,25 Ba2Mg(B3O6)2,26,27 and Ba2Na3(B3O6)2F28,29 were reported. Among them, Ba2Mg(B3O6)2 seems to be a compromising choice of birefringence crystal with a short cutoff at 177 nm and large birefringence.26,27 Guided by the idea that the borates containing cations with smaller ionic radii exhibit shorter wavelength UV absorption edges,30 BCBO crystals could possess a shorter transmittance cutoff wavelength in comparison to α-BBO. In 2011, on the basis of the calculation of the anisotropic refractive indices of borates, Qin and Li pointed out that BCBO crystal should have a large birefringence.19 Consequently, in this work we systematically investigated the growth and optical characterizations of BCBO crystal, and the results indicate that it has a conspicuous application prospect in the UV, especially in the sub-200 nm deep UV range, for it has a large birefringence and short cutoff.

INTRODUCTION Birefringent crystals are of great importance as they can be fabricated as various polarization devices such as optical circulator,1 beam splitters,2 and electro-optics Q switch,3 which have wide applications in scientific instrumentation, optical communications, and laser industry.4 Availability of UV and deep UV polarization light has greatly facilitated experimental and theoretical studies. The driver for such interests has involved the prospects of tantalizing applications such as 193 nm immersion lithography,5,6 laser-induced photochemical reaction,7 photodissociation,8,9 and mass spectrometry.10 To date, several commercial birefringence crystals have been developed, such as CaCO3,11 YVO4,12 MgF2,13 α-BBO,14 etc. Among them, CaCO3 and YVO4 crystals possess large birefringence, but they can be only applicable in the visible or near-infrared range due to their low transmittance in the UV wavelength. Although MgF2 crystal has a short UV transmittance cutoff of 110 nm, its birefringence is extremely small (0.0128 at 253.7 nm).15 By virtue of the two important parameters transparent to the deep-UV region,16−18 large anisotropic polarizabilities of the planar BO3 or B3O6 groups,19 borates are promising candidates of the deep-UV birefringent crystals. The most notable of them is α-BBO, a commercial birefringent optical crystal with a wide transmission range from 189 to 3500 nm.14,20,21 However, some drawbacks prevent its practical applications in the wavelength below 200 nm (close to its UV cutoff). For example, the transmittance of α-BBO crystal at 193 nm, the important wavelength in immersion lithography is below 40%.20 Meanwhile, the perfect pure α-BBO crystal is obtained with difficulty since it tends to crack during growth © 2016 American Chemical Society

Received: September 27, 2016 Revised: December 6, 2016 Published: December 27, 2016 558

DOI: 10.1021/acs.cgd.6b01428 Cryst. Growth Des. 2017, 17, 558−562

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Article

EXPERIMENTAL SECTION

Crystal Growth. Bulk single crystals of BCBO were grown by the top-seeded solution growth (TSSG) method with a composition of BCBO/H3BO3/NaF = 1:1.2:1.0 in molar ratio. The starting materials of BaCO3 (99.99%, 646.49 g), CaCO3 (99.99%, 163.95 g), H3BO3 (99.99%, 729.23 g), and NaF (99.99%, 68.78 g) powders were purchased from Tianjin FengFan Chemical Reagent Co., Ltd. and used without further purification. The temperature of the furnace was heated up to 1150 °C to melt the mixture in a Pt crucible with a diameter and height of 85 mm. Then the cooled Pt crucible was transferred to a resistive furnace equipped with a Pt−Rh/Pt thermocouple and a programmable temperature controller. After the mixture was melted once again, the solution was mechanically stirred for 24 h to a homogeneous solution. The exact saturation temperature was determined (about 910 °C) by observing the growth or dissolution of the crystal seeds on the surface of the solution. Then the seed was slightly dipped into the solution with a rotating rate of 30 r/min, and the melt was cooled at a rate of 0.2 °C/day. After growing for over 20 days, the grown crystal was raised above the melt surface and cooled at a rate of 200 °C/day to room temperature. An attempt using the Czochralski growth method was also performed with a seed oriented along the [001] direction, the cooling rate of 1−2 °C/day, and rotation and pulling rates of 30 r/min and 0.1−1 mm/day, respectively. Viscosity Measurement. The viscosity of the growth solution was investigated with a Brookfield DV-II+ Pro viscosity meter at the temperature range of 870−960 °C. Conoscopic Interference Pattern. The conoscopic interference pattern of the BCBO crystal was observed by a Nikon ECLIPSE E400POL polarizing microscope on the c-cut plate crystal (with a thickness of 3.0 mm oriented along the [001] direction). X-ray Diffraction Rocking Curve. The X-ray diffraction (XRD) rocking curve was performed on a PANalytical X’Pert PRO MPD diffractometer. The [001] oriented wafer of BCBO was mechanically polished on both sides. Hardness Measurement. The hardness of BCBO crystal was measured on a MHVD-1000IS image analysis multifunction digital micro hardness tester. Thermal Analysis. The thermal analysis of the BCBO crystal was investigated on a Labsys TG-DTA16 (SETARAM) thermal analyzer. About 10 mg polycrystalline samples were put in a small platinum crucible and heated from room temperature to 1200 °C at a rate of 10 °C/min. Thermal-Expansion Coefficients. The thermal-expansion coefficients of the BCBO crystal were obtained from refinements of the powder X-ray diffraction data with the GSAS package. The XRD data with about 1.0 g of powdered single crystal were collected with a Bruker D8 diffractometer with a Cu Kα radiation from 295 to 993 K with an interval of 100 K. The scanning range was from 10° to 70°, with a rate of 0.5 s/step and a scanning step of 0.03°. Transmission Spectrum. The room temperature optical transmission spectrum of a polished BCBO crystal (the thickness is 1.0 mm oriented along the [001] direction) was recorded with a Lambda 900 UV/vis/NIR (PerkinElmer) spectrophotometer in the range of 185− 3000 nm in air and with a McPherson Vuvas2000 spectrophotometer in the range of 120−220 nm in a vacuum. Refractive Index Measurement. The refractive indices dispersion were measured using HR SpectroMaster UV−vis-IR apparatus (Trioptics, Germany) by the minimum deviation method.31 Extinction Ratio Measurement. A He−Ne laser (Melles Griot 25-LHP-151−230) was used as a light source to generate the 633 nm laser beam. Both the calcite and BCBO polarizer were Glan−Taylor type prisms. The intensity of transmitted beam was recorded using a Newport 918UV power detector.

Figure 1. As-grown (a) and morphology (b) of BCBO crystal, the ccut plate (c) for conoscopic interference view (d) of BCBO crystal.

method with NaF and B2O3 as flux. At the growth temperature (910 °C), the viscosity was measured as 160 cP (Figure S1). The viscosity value is close to that (180 cP) of β-BaB2O4 melt with NaF flux at 927 °C.32 Structure solution from a crystallite broken from the grown crystal showed that BCBO crystallizes into the rhombohedral space group R3̅ with lattice parameters of a = 7.1387 (16) Å, and c = 17.682 (7) Å (Table S1), in accordance with the data reported by Liebertz and Fröhlich.33 The conoscopic interference pattern (Figure 1d) of the symmetrical fringe pattern and black cross-striped extinctions unambiguously show that the as-grown BCBO crystal is optical homogeneous and there is an absence of strain inside. The XRD rocking curve indicates that the fwhm of (001) crystal wafer is 0.0190 (Figure S2). Further tests reveal that the Mohs hardness of (001) plane is 4.5, about the same as that of commercial α-BBO. Thermal Analysis of the BCBO Crystals. The thermal analysis of powdered BCBO was carried out. The differential scanning calorimetry (DSC) signal (Figure 2a) shows a sharp endothermic peak at an onset temperature of 1116 °C. Furthermore, the powder X-ray diffraction data of the residue after DSC measurements is identical to that of the initial compound powders (Figure 2a, inset), which means that BCBO is a congruently melting compound. Therefore, in principle, BCBO single crystal could be grown using the Czochralski method. Subsequently, we tested this method and successfully got a bulk BCBO crystal with the size about 22 × 32 × 6 mm3 (Figure S3). The thermal-expansion coefficients of a crystal have great influences on crystal growth and its practical applications. The mean thermal expansion coefficient α can be obtained from the expression: α=

ΔL L × ΔT

(1)

where L is the unit cell parameters of the BCBO crystal at 295 K, ΔT is the increment of the experimental temperature versus 295 K, ΔL is the increment of the unit cell parameters versus that of 295 K. Because of uniaxial characteristics of BCBO, there are only two independent principal components of the thermal expansion coefficient tensor, that is, αa = αb and αc. As shown in Table S2 and Figure 2b, the linear thermal expansion

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RESULTS AND DISCUSSION Growth and Crystal Structure of the BCBO Crystals. A colorless, transparent, bulk BCBO single crystal with sizes up to 40 × 28 × 10 mm3 (Figure 1a) was obtained via the TSSG 559

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Figure 2. (a) The DSC curve and XRD patterns (inset) before and after the DSC analysis of BCBO, (b) the thermal-expansion coefficients of BCBO crystal in different directions.

Figure 3. (a) The transmission spectrum of Ba2Ca(B3O6)2, (b) the measured refractive indices and the fitted curves by the Sellmeier equations (inset: BCBO prism used for the measurement).

coefficients in the [001] and [100] orientations are αc = 2.99 (5) × 10−5/K and αa = 6.4 (3) × 10−6/K with an αa/αc ratio of 4.67, which is significantly smaller than that of α-BBO (αc/αa = 9). With a weaker anisotropic thermal expansion, the BCBO crystal should be less inclined to crack than α-BBO during growth, processing, and application. Optical Properties. Figure 3a indicates that the BCBO crystal is transparent from 178 to 3000 nm, and the UV absorption cutoff edge (178 nm, Figure 3a, inset) is 11 nm shorter in comparison to that of α-BBO (189 nm), which is well in accordance with previous theoretical understanding.30 The BCBO crystal, belonging to the space group R3̅, has two principal refractive indices, no and ne. To measure the refractive indices, the sample was cut as a right-angle prism with an apex angle of 30.06°, and the two right angle surfaces are (100) and (001), respectively (Figure 3b, inset). The experimental values with a high accuracy of 1.0 × 10−7 at 13 different wavelengths over the full transmission range of BCBO are listed in Table S3. Figure 3b shows the fitted dispersion curves of the BCBO prism, and the Sellmeier’s equations fitted by the least-squares fitting method are given as follows: no2 = 2.78830 +

0.01864 − 0.01583λ 2 λ 2 − 0.01656

(2)

ne2 = 2.39994 +

0.01254 − 0.00285λ 2 λ − 0.01314

(3)

2

shows the highest birefringence and relatively shorter deep-UV transmittance cutoff. Table 1. Comparison of Selected Properties of Several Important UV and Deep-UV Birefringent Crystals

a

crystal

space group

Δn (at 253.7 nm)

cut-off

reference

Ba2Ca(B3O6)2 α-BBO Ba2Mg(B3O6)2 Ba2Na3(B3O6)2F Ba2Na3(B3O6)2F Ca3(BO3)2 MgF2

R3̅ R3̅ R3̅ P63/m P63/m R3̅c P42/mnm

0.1563 0.1529 0.145 0.1306 0.1422 0.1163a 0.0128a

178 189 177 186 175 180 110

this work 23 26 28 29 24 15

Calculated from the Sellmeier’s equations.

Design and Characterization of Glan-Taylor Type Polarizer. A Glan−Taylor type polarizer of the BCBO crystal was fabricated with two identical prisms. In view of the transmission, refractive index, and symmetric field-of-view of the polarizer, the prisms were cut at apex angles of 37.15° toward the c axis (Figure 4b).27 The two prisms with a small air space between them were glued to two parallel pieces of glass and then placed in an aluminum alloy holder. For the extinction ratio measurement, a 633 nm He−Ne laser light beam passed through a Glan−Taylor polarizer made of calcite, and then the light was sent into a second Glan− Taylor polarizer made of the BCBO crystal (Figure 4a). The output light power was recorded while rotating the BCBO polarizer with respect to the perfectly crossed direction. Figure 4c shows that the maximum output power was obtained when the polarizer was 0° or 180° positioned. The ratio of maximum output and minimum powers when the polarization direction of the BCBO polarizer was positioned parallel or perpendicular to the calcite polarizer was 3.1 × 104:1 for the BCBO polarizer,

where λ is the wavelength expressed in unit of μm. The values of refractive indices for no and ne at specific wavelengths are no > ne, which indicates that BCBO is a negative uniaxial optical crystal. The results show that the BCBO crystal has large birefringence (Δn = no − ne = 0.1001−0.1563) in the measured wavelength range (2.3254−0.2537 μm). The calculated birefringence (Δn = 0.1241) at 589.3 nm from the Sellmeier equations is in good accordance with the theoretical predictions (Δn = 0.1175).19 In comparison with other potential birefringent crystals in the deep-UV range (Table 1), BCBO 560

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Figure 4. (a) Apparatus set up for laser extinction experiment, (b) the Glan−Taylor polarizer of BCBO crystal. (c) Measured transmitted beam intensity versus rotating angle of the Glan−Taylor polarizer constructed from BCBO crystal.

which is at the same level of that with a commercial α-BBO polarizer.28

ORCID

Zhen Jia: 0000-0002-5897-4575 Mingjun Xia: 0000-0001-8092-6150

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CONCLUSION In summary, on the basis of the theoretical understanding of the borates containing cations with smaller ionic radii exhibiting shorter wavelength UV absorption edges, a new UV and deepUV birefringent material Ba2Ca(B3O 6) 2 was proposed. Refractive index measurements demonstrate that BCBO is a uniaxial optical crystal with large birefringence (Δn = no − ne = 0.0862−0.2524) from the infrared (3.0 μm) to deep-UV (178 nm) range. Furthermore, the BCBO compound melts congruently with no phase transitions and is suitable to be grown by the Czochralski method. The optical tests indicate that the Glan−Taylor type polarizer of BCBO has a similar performance and same level of extinction ratio (∼104) as that made of α-BBO. Therefore, the BCBO crystal can be a potential substitute for commercial birefringent crystal in the UV or deep-UV range.

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Funding

National Natural Science Foundation of China (Nos. 90922036, 51032004/E0201), National Instrumentation Program of China (No. 2012YQ120048). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS One of the authors (Z.J.) would like to thank Mr. S. Guo from this center for his help in measuring the refractive indices.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b01428. The viscosity for the melts of BCBO with NaF and B2O3flux, the X-ray diffraction rocking curve for the [001] BCBO wafer, the as-grown (a) and the morphology (b) of the BCBO crystal obtained by the Czochralski method, the crystallographic data, the unit cell parameters at different temperatures, the refractive indices in 13 different wavelengths (PDF) Accession Codes

CCDC 1507533 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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REFERENCES

(1) Koga, M.; Matsumoto, T. J. Lightwave Technol. 1992, 10, 1210− 1217. (2) Xu, F. C.; Chen, W. L.; Zhang, M. Q.; Wang, L. Y.; Wei, R. Y.; Wang, Q. P. Proc. SPIE 1995, 2540, 182−189. (3) Brenier, A.; Tu, C.; Zhu, Z.; Li, J. Appl. Phys. B: Lasers Opt. 2010, 98, 401−406. (4) Hassler, R. A.; Gregory, G. G.; Freniere, E. R. Proc. SPIE 2002, 4769, 43−54. (5) Sirat, G. Y.; Goldstein, M. Optical Microlithography Xxi. Pts 1−3 2008, 6924. (6) Nomura, H.; Furutono, Y. Microelectron. Eng. 2008, 85, 1671− 1675. (7) Shimizu, Y.; Sugimoto, S.; Kawanishi, S.; Suzuki, N. Laser Chem. 1997, 17, 97−108. (8) McCunn, L. R.; Bennett, D. I. G.; Butler, L. J.; Fan, H. Y.; Aguirre, F.; Pratt, S. T. J. Phys. Chem. A 2006, 110, 843−850. (9) Goncher, S. J.; Sveum, N. E.; Moore, D. T.; Bartlett, N. D.; Neumark, D. M. J. Chem. Phys. 2006, 125, 224304. (10) Zawadowicz, M. A.; Abdelmonem, A.; Mohr, C.; Saathoff, H.; Froyd, K. D.; Murphy, D. M.; Leisner, T.; Cziczo, D. J. Anal. Chem. 2015, 87, 12221−12229. (11) Chang, J. Y.; Chang, Y. C.; Tien, H. T.; Sun, C. C. 2002 IEEE/ LEOS International Conference on Optical Mems, Conference Digest, 2002, pp 127−128. (12) DeShazer, L. G. Proc. SPIE 2002, 4481, 10−16. (13) Sedlmeir, F.; Zeltner, R.; Leuchs, G.; Schwefel, H. G. L. Opt. Express 2014, 22, 30934−30942. (14) Solntsev, V. P.; Tsvetkov, E. G.; Gets, V. A.; Antsygin, V. D. J. Cryst. Growth 2002, 236, 290−296. (15) Dodge, M. J. Appl. Opt. 1984, 23, 1980−1985.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. 561

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(16) Chen, C. T.; Wu, Y. C.; Jiang, A. D.; Wu, B. C.; You, G. M.; Li, R. K.; Lin, S. J. J. Opt. Soc. Am. B 1989, 6, 616−621. (17) Wu, B. C.; Tang, D. Y.; Ye, N.; Chen, C. T. Opt. Mater. 1996, 5, 105−109. (18) Petrov, V.; Noack, F.; Shen, D. Z.; Pan, F.; Shen, G. Q.; Wang, X. Q.; Komatsu, R.; Alex, V. Opt. Lett. 2004, 29, 373−375. (19) Qin, F.; Li, R. K. J. Cryst. Growth 2011, 318, 642−644. (20) Zhou, G. Q.; Xu, J.; Chen, X. D.; Zhong, H. Y.; Wang, S. T.; Xu, K.; Deng, P. Z.; Gan, F. X. J. Cryst. Growth 1998, 191, 517−519. (21) Wu, S. F.; Wang, G. F.; Xie, J. L.; Wu, X. Q.; Zhang, Y. F.; Lin, X. J. Cryst. Growth 2002, 245, 84−86. (22) Hubner, K. H. Neues Jahrb. Mineral. Monatsh. 1969, 335. (23) Liu, J. F.; He, X. M.; Xu, J.; Zhou, G. Q.; Zhou, S. M.; Zhao, G. J.; Li, S. Z. J. Cryst. Growth 2004, 260, 486−489. (24) Zhang, S. Y.; Wu, X.; Song, Y. T.; Ni, D. Q.; Hu, B. Q.; Zhou, T. J. Cryst. Growth 2003, 252, 246−250. (25) He, M.; Chen, X. L.; Sun, Y. P.; Liu, J.; Zhao, J. T.; Duan, C. J. Cryst. Growth Des. 2007, 7, 199−201. (26) Li, R. K.; Ma, Y. CrystEngComm 2012, 14, 5421−5424. (27) Zhao, J.; Ma, Y. Y.; Li, R. K. Appl. Opt. 2015, 54, 9949−9953. (28) Wang, X.; Xia, M.; Li, R. K. Opt. Mater. 2014, 38, 6−9. (29) Zhang, H.; Zhang, M.; Pan, S. L.; Yang, Z. H.; Wang, Z.; Bian, Q.; Hou, X. L.; Yu, H. W.; Zhang, F. F.; Wu, K.; Yang, F.; Peng, Q. J.; Xu, Z. Y.; Chang, K. B.; Poeppelmeier, K. R. Cryst. Growth Des. 2015, 15, 523−529. (30) Li, R. K. J. Non-cryst. Solids 1989, 111, 199−204. (31) Jenkins, F. A.; White, H. E. Fundamentals of Optics; MacGrawHill: New York, 4th ed., 1976. (32) Hong, X. G.; Lu, K. Q.; Li, L.; Tang, D. Y. J. Cryst. Growth 1998, 193, 610−614. (33) Liebertz, J.; Fröhlich, R. Z. Kristallogr. 1984, 168, 293−297.

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