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Bulk samples of Ge-Sb-S-I chalcoiodide glasses of different compositions were prepared by plasma enhanced chemical vapor deposition (PECVD). GeI4, SbI3 and elemental sulfur were the initial substances. Impurities content, optical, and structural properties of the samples were studied. The data obtained were analyzed and compared with the properties of the bulk samples prepared by interaction of the same initial substances into reactive-distillation column at 650°C. The dependence of optical properties of the glasses on preparation technique was discussed.
© 2016 Optical Society of America
1. Introduction
Chalcogenide glasses cause an increasing interest of researchers as a promising material for prospective optical applications in the IR range, such as fiber lasers and amplifiers, nonlinear fiber all-optical switching devices, and others [1]. In comparison with the oxide and fluoride glasses, chalcogenide glasses have a wider IR transparency window and a higher index of refraction [2]. However, large values of two-photon absorption coefficient greatly restrict application of many chalcogenide systems [3] in nonlinear optics. One of the ways of increasing the quality factor F = n2/2λβ of nonlinear optical devices may be using materials with a wider optical band gap, for instance, chalcogenide glasses based on Ge and S [4–7]. The challenges of glass fusion in the Ge-S system are yet narrow glass-forming regions and a high explosion hazard. This stimulated studies of chalcogenide glasses in ternary systems, such as Ge-Sb-Se [8, 25], Ge-Sb-S [9, 10], Ge-Ga-S [10] and Ge-As-Se [8]. The addition of iodine increases the stability of the Ge-Sb-S glass against crystallization and germanium sulfide iodides have a higher glass-forming ability compared to sulfides due to a larger number of possible spatial configurations forming a glass network [11]. Besides, the presence of iodine in the glass composition increases solubility of rare earth elements [12].
“Traditional” method of preparation of the glasses is melting of the elements into evacuated and sealed quartz glass ampoule at 800-1000 оС during 10-40 hours into a rocking furnace [13]. Purity is the most important parameter of the glasses. High temperature and long duration of the process lead to the substantial contamination of the final glasses from the materials of setup because of interaction of the melt with the walls of ampoule [14].
During the last few years’ novel methods of preparation of high-pure Ge-Sb-S-I glasses have been developed in order to overcome the disadvantages of the “traditional” method and thereby extended the area of applications of the glasses [15, 16]. The suggested techniques differ substantially from the “traditional” method due to they comprise two independent stages – preparation of a glassy batch in the open system at a lower temperature and the following homogenization of the batch into a rocking furnace. How it has been recently shown on the example of other chalcogenide systems [19] synthesizing in the open reactor system especially under the dynamic vacuum conditions guarantees increasing of purity of the final glasses in comparison with synthesizing in the sealed ampoule. At the same time, the contemporary approaches distinguish greatly from each other by the way of initiation of chemical reactions. The high-pure batch may be formed by thermal interaction of volatile precursors at 650 оС into reactive-rectification column [15] or by electron impacts excitation of the chemical bonds of the initial substances vapors in plasma discharge [16].
The aim of this work is a comparative analysis and estimation of possibilities of different methods of preparation in terms of optical properties and impurities content of Ge-Sb-S-I bulk samples, prepared from the same precursors.
2. Experimental
The plasma-chemical synthesis of Ge-Sb-S-I bulk samples was carried out at the facility, the scheme of which is shown in [16]. The loading of the initial substances (sulfur - 99,99 at.% purity, GeI4 - 99.9 at % purity and SbI3 - 99.99 at.% purity) into the quartz glass reservoirs, supplied by external heaters was done in the atmosphere of high pure helium. Helium has been chosen as a career gas as plasma feed gas due to it is available purer state in terms of carbon-containing impurities (CO2, CH4) and water traces. The bulk samples for comparison were obtained by interaction of GeI4, SbI3 and elemental sulfur into evacuated reaction-rectification column in the atmosphere of high-pure argon at 650 °C [15]. Before loading of the initial substances the column was heated at 600-700 °C during 5-6 hours and evacuated under dynamic vacuum conditions up to 1·10−5 Torr to delete the traces of water. Loading of the initial substances was implemented by vacuum evaporation. During the process of preparation the total pressure in the system was in the range of 1·10−1 - 1·10−2 Torr; it depended on the vapor pressure of iodine. In both cases the bulk samples were the cylinders with 5 mm diameter, 20 mm length and the same chemical content. The bulk sample of different chemical content have been prepared (Table 1).
Table 1. Chemical content of Ge-Sb-S-I glasses, at.%.
It was previously shown that the chemical composition of the germanium based chalcoiodine glasses is stable when the content of iodine is less than 10 at % [20]. The Ge25Sb8S60I7 and Ge20Sb10S65I5 glasses prepared by different methods have been investigated and compared.
The content of impurities in the bulk glass samples was determined by atomic emission spectroscopy with a dc arc discharge as a light source (spectrograph with crossed dispersion STE-1). The transmission spectra of the samples were taken with FTIR spectrometer Tensor - 27 (Bruker). X-ray microanalysis was carried out on the scanning electron microscope SEM-515, equipped with the energy dispersive analyzer EDAX-9900. The Raman scattering spectra of glasses were investigated on the NTEGRA Spectra complex produced by NT-MDT company (Zelenograd) using a HeNe laser with the wavelength of 632.8 nm and power of 0.6 mW. The Raman scattering spectra of the samples obtained at room temperature were studied in reflection mode.
3. Results and discussion
3.1 Comparison of metal impurity content of the Ge-Sb-S-I bulk samples prepared by different methods
The content of impurities was determined by atomic emission spectroscopy with a dc arc discharge as a light source (spectrograph with crossed dispersion STE-1). Comparison of metal impurity content of the samples prepared by different methods is shown in Table 2. The data presented prove that in both cases the contamination from materials of the setup is insignificant. The excessive content of Ca, K and Fe in the thermal method in comparison with the PECVD method may be explained due to higher temperature, longer duration and constant contact of the melted batch with materials of setup. The same reasons lead to the fact that in case of the thermal method the silicon content in the final glasses rarely drops below several ppm.
Table 2. Comparison of metal impurity content into bulk samples, prepared by different methods.
The usage of plasma discharge as the initiator of chemical interactions instead of thermal heating significantly reduces the concentration of silicon. The rest of the content of impurities in the bulk samples obtained by different methods is comparable.
3.2 Structural comparison of the Ge-Sb-S-I bulk samples prepared by different methods
3.2.1. Raman investigation of Sb-S-I bulk samples
The results of correlation between the glass structure and optical properties of Ge-Sb-S glasses have been previously published [21, 22, 26]. It was established that the increase of Sb2S3 content causes decrease of the GeS4 units and increase of SbS3 entities. With addition of iodine the glass net undergoes substantial changes due to the altering of the structural fragments forming the novel net. Possible structural units which may be formed by germanium, antimony, sulfur and iodine due to thermal interaction were established previously [23, 24].
In order to pinpoint the structural fragments of antimony, which are able to present in Ge-Sb-S-I glass net the investigation of the mechanism of interaction of SbI3 with elemental sulfur into non-equilibrium plasma discharge was carried out. For that purpose the Sb-S-I bulk samples of different compositions - oversaturated and depleted by sulfur - were prepared. The molar ratios of the components SbI3:S into vapor phase were 1:2 and 2:1. The data are presented on Fig. 1 (a) and 1(b).
The Raman spectra obtained are significantly different from each other. The Raman spectrum of the bulk sample abundant with sulfur Fig. 1(a) contains 150, 220, 439, 457 and 475 cm−1 vibration bands, that are responsible for bending and stretching of S8 rings [23, 24]. Besides, it comprises the line near 185 cm−1 referred to vibration of Sb-Sb bonds in the structural unit S2Sb-S2Sb [23] and 249 cm−1 addressed to SbSI [23].
The Raman spectrum of the bulk sample depleted of sulfur Fig. 1(b) includes 107, 139, and 320 cm−1 bands addressing to vibration of SbSI structural units [23]; 216 and 235 cm−1 lines are referred to linear S-S-S bending mode. Thus, structural unit S2Sb-S2Sb is absent in the bulk sample with the lack of sulfur.
3.2.2. Raman investigation of Ge-Sb-S-I bulk samples
Raman spectra of Ge-Sb-S-I bulk glasses prepared by different methods are represented in Fig. 2(a) and 2(b).
Fig. 2 Raman spectra of Ge-Sb-S-I bulk samples, prepared by thermal method (a) and PECVD method (b).
The spectra in Fig. 2(a) characterize the samples of Ge-Sb-S-I bulk glasses of different content prepared by the thermal method. They consist of broad lines with pick on 345 cm−1, associated with the contributions of the different vibrations of GeS1+6/2, GeS2+6/2 and Ge2S6/2 clusters [25], lines on 185 and 432 cm−1 which are referred to vibration of Sb-Sb bonds in the structural unit S2Sb-S2Sb, and the lines near 240 cm−1 characterize stretching of mixed tetrahedra GeS4-xIx (where x = 1, 2, 3) [24]. With increasing of germanium content the concentration of S2Sb-S2Sb structural units in glass net decreases the same way like in case of Ge-Sb-S system without iodide [22], but despite the usage of antimony iodide as the source of antimony the bands of antimony iodides derivatives do not appear on the Fig. 2(a). As well with the increasing of germanium content the line of mixed tetrahedra GeS4-xIx (where x = 1, 2, 3) become more apparent. The peak in the region of 485 cm−1 belongs to vibrations of the S-S-S linear chain.
The spectra in Fig. 2(b) characterize the samples of Ge-Sb-S-I bulk glasses of different content prepared by PECVD method. They include the same bands on 345, 185, 432 and 240, 255 cm−1, referring to GeS2, S2Sb-S2Sb and GeS4-xIx structural units respectively. But there is an additional line, referring to the structural unit S2Sb-S2Sb on 235 cm−1, and 150, 215 and 475 cm−1 vibration bands that are responsible for stretching of S8 rings. The intensive band on 150 cm−1 interferes to identify presence or absence of the band on 149 cm−1 of SbSI structure.
Thus, the only significant difference between the Ge-Sb-S-I bulk glasses prepared by different methods is a form of sulfur presence in the glass network. In spite of the similar conditions of homogenization the samples prepared by plasma include sulfur in the form of rings S8, in the samples obtained by thermal method sulfur is in a linear modification. Also it should be noted, iodine is held in the glass net only in the form of germanium sulfoiodides GeS4-xIx (where x = 1, 2, 3) of different content.
3.3. IR absorption spectra Ge-Sb-S-I glasses
The IR absorption spectra Ge-Sb-S-I bulk samples are presented in the Figs. 3(a) and 3(b). The spectra include the adsorption bands of different functional groups. The bands located near 4.0 μm refer to S-H groups, 4.3 μm line is absorption of CO2 molecular, the absorption bands in the region of 10.1 and 12.2 microns are the intrinsic absorption of S-S bonds, near 8-10 μm are the the bands of GeS4 and S-S structural fragments, also in the range of 8-10 the bands of Si-O and Ge-O are located [26].
The absorption bands of CO2 and CS2 are absent in the bulk sample, prepared by plasma.CO2 is formed due to interaction of carbon-containing impurities with the traces of oxygen. It is possible to suggest that in case of plasma discharge the impurities react more intensively with oxygen, which leads to their complete selective burning out. Thus, the plasma process acts like an additional stage of purification.
3.4. Chromato-mass-spectroscopy analysis of exhausted gas mixtures
In order to clarify the data of IR-spectroscopy, the exhausted gas mixtures were analyzed by chromate-mass-spectrometry (Fig. 4). The concentration of CO2 in the gas mixture after plasma discharge is more than three times higher than without plasma. The partial conversion of carbon-containing impurities into carbon dioxide may be one of the reasons of excessive formation of CO2. Another reason may be cracking of S8 rings in plasma discharge, releasing of carbon nanoparticles and their following selective burning out by oxygen traces:
Fig. 4 Chromato-mass-spectroscopic date of the concentration of CO2 in the exhausted gas mixtures (1 – PECVD preparation; 2 – thermal preparation).
4. Summary
Bulk samples of Ge-Sb-S-I chalcoiodide glasses of different compositions were prepared by plasma enhanced chemical vapor deposition and into reactive-distillation column at 650°C from GeI4, SbI3 and elemental sulfur. The optical properties of the bulk samples were studied and compared. It was proven that the samples synthesized via plasma are purer in terms of carbon impurities content. The data of the analysis of exhausted gas mixtures confirm the intensive conversion of carbon-containing impurities into CO2 due to their interaction with oxygen traces during the plasma process.
Funding
Russian Science Foundation (15-19-00147).
References and links
1. G. I. Stegeman and A. Miller, “Physics of all-optical switching devices,” in: J. E. Midwinter (Ed.), Photonics in Switching (Academic Press, 1993), pp. 81–145.
2. J. S. Sanghera, L. B. Shaw, L. E. Busse, V. Q. Nguyen, P. C. Pureza, B. C. Cole, B. B. Harrison, I. D. Aggarwal, R. Mossadegh, F. Kung, D. Talley, D. Roselle, and R. Miklos, “Development and infrared applications of chalcogenide glass optical fibers,” Fiber Integr. Opt. 19(3), 251–274 (2000). [CrossRef]
3. K. Ogusu, J. Yamasaki, S. Maeda, M. Kitao, and M. Minakata, “Linear and nonlinear optical properties of Ag-As-Se chalcogenide glasses for all-optical switching,” Opt. Lett. 29(3), 265–267 (2004). [CrossRef] [PubMed]
4. J. M. Harbold, F. O. Ilday, F. W. Wise, and B. G. Aitken, “Highly nonlinear Ge-As-Se and Ge-As-S-Se glasses for all-optical switching,” IEEE Photonics Technol. Lett. 14(6), 822–824 (2002). [CrossRef]
5. L. Petit, N. Carlie, R. Villeneuve, J. Massera, M. Couzi, A. Humeau, G. Boudebs, and K. Richardson, “Effect of the substitution of S for Se on the structure and non-linear optical properties of the glasses in the system Ge0.18Ga0.05Sb0.07S0.70−xSex,” J. Non-Cryst. Solids 352(50-51), 5413–5420 (2006). [CrossRef]
6. S.-S. Chu, S.-F. Wang, H.-Z. Tao, Z.-W. Wang, H. Yang, C.-G. Lin, Q.-H. Gong, and X.-J. Zhao, “Large and ultrafast third-order nonlinear optical properties of Ge-S based chalcogenide glasses,” Chin. Phys. Lett. 24(3), 727–729 (2007). [CrossRef]
7. D. A. Yashunin, A. P. Velmuzhov, A. V. Nezhdanov, A. A. Murzanev, Yu. A. Malkov, M. A. Kudryashov, A. I. Mashin, L. A. Mochalov, A. S. Lobanov, A. I. Korytin, A. V. Vorotyntsev, V. M. Vorotyntsev, and A. N. Stepanov, “Comparative study of nonlinear optical properties of Ge-S-I glasses with different macrocompositions,” J. Non-Cryst. Solids 453, 84–87 (2016). [CrossRef]
8. S. Dai, F. Chen, Y. Xu, Z. Xu, X. Shen, T. Xu, R. Wang, and W. Ji, “Mid-infrared optical nonlinearities of chalcogenide glasses in Ge-Sb-Se ternary system,” Opt. Express 23(2), 1300–1307 (2015). [CrossRef] [PubMed]
9. T. Wang, X. Gai, W. Wei, R. Wang, Z. Yang, X. Shen, S. Madden, and B. Luther-Davies, “Systematic z-scan measurements of the third order nonlinearity of chalcogenide glasses,” Opt. Mater. Express 4(5), 1011–1022 (2014). [CrossRef]
10. B. Qiao, S. Dai, Y. Xu, P. Zhang, X. Shen, T. Xu, Q. Nie, W. Ji, and F. Chen, “Third-order optical nonlinearities of chalcogenide glasses within Ge-Sn-Se ternary system at a mid-infrared window,” Opt. Mater. Express 5(10), 2359–2365 (2015). [CrossRef]
11. S. A. Dembovsky and V. V. Kirilenko, “Glass formation and chemical compounds in the systems AIV–BVI–CVII (AIV=Si, Ge; BVI=S, Se; CVII=Br, I),” Glass Phys. Chem. 3, 225–230 (1975).
12. V. Krasteva, D. Hensley, and G. Sigel Jr., “The effect of compositional variations on the properties of rare-earth doped Ge-S-I chalcohalide glasses,” J. Non-Cryst. Solids 222, 235–242 (1997). [CrossRef]
13. J.-L. Adam and X. Zhang, “Chalcogenide Glasses: Preparation, Properties and Applications,” in Handbook (Woodhead Publishing. 2014).
14. G. G. Devyatykh, M. F. Churbanov, I. V. Scripachev, V. A. Shipunov, E. M. Dianov, and V. G. Plotnichenko, ““Heterophase impurity inclusions in chalcogenide glass optical fibers”, Proc. SPIE. 1228 Infrared Fibers II, 116–126 (1990). [CrossRef]
15. A. P. Velmuzhov, A. A. Sibirkin, V. S. Shiryaev, M. F. Churbanov, A. I. Suchkov, A. M. Potapov, R. M. Shaposhnikov, V. G. Plotnichenko, and V. V. Koltashev, “Preparation of Ge-Sb-S-I glass system via volatile Iodides,” Optoelectron. Adv. Mater. Rapid Commun. 13(8), 936–939 (2011).
16. L. A. Mochalov, A. S. Lobanov, A. V. Nezhdanov, A. V. Kostrov, and V. M. Vorotyntsev, “Preparation of Ge-S-I and Ge-Sb-S-I glasses by Plasma-enhanced Chemical Vapor Deposition,” J. Non-Cryst. Solids 423–424, 76–80 (2015). [CrossRef]
17. X. Hang, X.-F. Peng, S.-X. Dai, X. Dong, P.-Q. Zhang, Y.-S. Xu, L. Xing, and Q.-H. Nie, “Raman gain of Ge-Sb-Se chalcogenide glass,” Wuli Xuebao 65(15), 154 (2016).
18. L. Petit, N. Carlie, H. Chen, S. Gaylord, J. Massera, G. Boudebs, J. Hu, A. Agarwal, L. Kimerling, and K. Richardson, “Compositional dependence of the nonlinear refractive index of new germanium-based chalcogenide glasses,” J. Solid State Chem. 182(10), 2756–2761 (2009). [CrossRef]
19. A. V. Vorotyntsev, L. A. Mochalov, A. S. Lobanov, A. V. Nezhdanov, A. I. Mashin, and V. M. Vorotyntsev, “PECVD synthesis of As-S glasses,” Russ. J. Appl. Chem. 89(2), 179–184 (2016). [CrossRef]
20. A. P. Velmuzhov, M. V. Sukhanov, A. D. Plekhovich, A. I. Suchkov, and V. S. Shiryaev, “Thermal decomposition study of GeSI2 and Ge2S3I2 glassy alloys,” J. Non-Cryst. Solids 411, 40–44 (2015). [CrossRef]
21. M. Olivier, P. Němec, G. Boudebs, R. Boidin, C. Focsa, and V. Nazabal, “Photosensitivity of pulsed laser deposited Ge-Sb-Se thin films,” Opt. Mater. Express 5(4), 781–793 (2015). [CrossRef]
22. L. Petit, N. Carlie, F. Adamietz, M. Couzi, V. Rodriguez, and K. C. Richardson, “Correlation between physical, optical and structural properties of sulfide glasses in the system Ge–Sb–S,” Mater. Chem. Phys. 97(1), 64–70 (2006). [CrossRef]
23. C. H. Perry and D. K. Agrawal, “The Raman spectrum of ferroelectric SbSI,” Solid State Commun. 8(4), 225–230 (1970). [CrossRef]
24. J. S. Sanghera, J. Heo, and J. D. Mackenzie, “Chalcohalide glasses,” J. Non-Cryst. Solids 103(2-3), 155–178 (1988). [CrossRef]
25. K. Tanaka and M. Yamaguchi, “Resonant Raman scattering in GeS2,” J. Non-Cryst. Solids 227–230, 757–760 (1998). [CrossRef]
26. V. S. Shiryaev, J. Troles, P. Houizot, L. A. Ketkova, M. F. Churbanov, J.-L. Adam, and A. A. Sibirkin, “Preparation of optical fibers based on Ge–Sb–S glass system,” Opt. Mater. 32(2), 362–367 (2009). [CrossRef]
