Raman spectra of two ternary glasses of composition Ge₅As₃₇S₅₈ and

As₄Ge₃₀S₆₆ have been investigated. An influence of addition of third element on the

spectra of binary glasses has been studied by comparison with spectra of two binary

glasses of composition Ge₃₃S₆₇ and As₄₀S₆₀. Glass structure and phase separation effects

are discussed

Pribylova, H.

Stronski, A.V.

Tolmachov, I.D.

Vlček, M.

Semiconductor Physics Quantum Electronics & Optoelectronics

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

 Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 432-435.  PACS 63.50.Lm, 77.84.Bw, 78.30.Ly Raman scattering in sulphide glasses  I.D. Tolmachov1,*, A.V. Stronski1, H. Pribylova2, M. Vlček21V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,  41, prospect Nauky, 03028 Kyiv, Ukraine 2Faculty of Chemical Technology, University of Pardubice,  Studentská 573, 532 10 Pardubice, Czech Republic, *E-mail: tolmach_igor@mail.ru  Abstract. Raman spectra of two ternary glasses of composition Ge5As37S58 and As4Ge30S66 have been investigated. An influence of addition of third element on the spectra of binary glasses has been studied by comparison with spectra of two binary glasses of composition Ge33S67 and As40S60. Glass structure and phase separation effects are discussed.   Keywords: Raman scattering, chalcogenide glasses.  Manuscript received 24.09.10; accepted for publication 02.12.10; published online 30.12.10.    1. Introduction  Investigations of non-crystalline solids occupy one of the leading places in modern solid state physics. High research interest paid to these materials is caused by a number of their inherent properties (an opportunity to tailor continuously the composition and physical properties, effective production and treatment, stability in various media, etc.) which provide many opportunities for their practical applications. Studying of non-crystalline solid state is also of great importance from the viewpoint of the fundamental science. Chalcogenide vitreous semiconductors are very interesting materials of this class. Beside the mentioned physical properties inherent to glassy state, they have also many specific properties such as transparency in the infrared region of spectrum, a variety of photoinduced phenomena and high nonlinear optical properties, which made them very perspective in such practical applications as telecommunications, sensors, optical data storage, etc. Investigation of structure of these materials and it’s relation to the composition and physical properties is a key for effective application. Raman scattering is one of the commonly used ways to investigate the structure of the glassy state. In this paper, we present the results of Raman spectroscopic studies concerning two ternary chalcogenide glasses of composition Ge5As37S58 and As4Ge30S66 and comparison with binary glasses As40S60 and Ge33S67. 2. Experimental Glasses of compositions As40S60, Ge5As37S58, Ge33S67 and As4Ge30S66 were synthesized by direct melting of initial high purity elements in evacuated silica ampoules. Ge33S67 and As4Ge30S66 glasses were held at 750 °C for 5 h and then melted at 800 – 970 °C for 10 – 12 h. As40S60 and Ge5As37S58, glasses were melted at 650 – 800 °C for 8 – 24 h. After synthesis, the ampoules with melts were quenched in cold water. Raman spectra were investigated using IR Fourier spectrophotometer Bruker IFS55 Equinox with FRA-106 attachment. Nd-YAG laser light with the wavelength 1.064 μm was used for excitation. 3. Results and discussion Raman spectra of binary glasses As40S60 and Ge33S67 are presented in Figs 1a and 1b, respectively. The spectrum of As40S60 glass consists of the main band centered at 344 cm-1 and a broad band in the lower frequency region (50 – 250 cm-1). There is also a weak band at 497 cm-1. The spectrum of Ge33S67 glass contains the main peak at 344 cm-1 with the shoulder at 372 cm-1, which is usually referred to as A1c “companion” mode. Also, there is the distinguished peak at 436 cm-1 and weak band at 488 cm-1. In the lower frequency region (50 – 250 cm-1), there is a broad band with features at 85, 117, 154, 208 cm-1. The Raman spectrum of As4Ge30S66 glass is presented in Fig. 2a. The higher frequency region (300 – 600 cm-1) contains the broad band with two maxima near 346 and 435 cm-1. This band can be deconvoluted into four Gaussian bands centered at 346, 375, 403 and 435 cm-1, as shown in Fig. 1. There is also a weak band at 495 cm-1 in this region. The lower frequency part of the spectrum (50 – 300 cm-1) also can be deconvoluted into Gaussian bands centered at 88, 114, 152, 186, 210 and 246 cm-1 (see Fig. 2).   © 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine  432  Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 432-435.  0 100 200 300 400 5000,00,10,20,30,40,50,60,7Intensity, a.u.Wavenumber, cm-1322 35934440238418916823680150118215497 a 0 100 200 300 400 500 6000,000,020,040,060,080,10Intensity, a.u.Wavenumber, cm-134437243648820815411785 b  Fig. 1. Raman spectra of binary glasses As40S60 (a) and Ge33S67 (b).   In Fig. 2b, the Raman spectrum of Ge5As37S58 glass is presented. There is a broad band centered near 343 cm-1 in the higher frequency region (260 – 500 cm-1). Deconvolution of this band leads to five Gaussian-shaped lines (see Fig. 2) with the maxima at 320, 167, 189, 214 and 237 cm-1. There is also a weak band at 496 cm-1. In the lower frequency region (60 – 260 cm-1) there is a broad band which has local peculiarities at 150, 167, 189, 214 and 237 cm-1. The most intensive band in the spectrum of Ge33S67 glass is located at 344 cm-1. In the case of As4Ge30S66 glass, it is shifted towards 346 cm-1. This band has been previously observed in binary glasses of Ge–S system either of stoichiometric or non-stoichiometric composition [1-5]. The peak at 346 cm-1, as usually accepted, corresponds to the A1 symmetric stretching vibrations in the main structural units of the glass – Ge(S1/2)4 tetrahedra, and in the case of ternary As4Ge30S66 system, it also contains a contribution from symmetrical vibrations of As(S1/2)3 pyramidal units [6]. Two other bands – A1c companion mode at 375 cm-1, and the band near 435 cm-1 have been also observed in GexS1-x glasses of different compositions, but their origin still remains controversial. Authors of the paper [7] associated the band 375 cm-1 with the presence of medium range order structures in these glasses. A model was assumed, according to which, glassy Ge(S, Se)2, as opposed to SiO2, are formed not by a three-dimensional random network, but have rather layer-like structure consisted of medium-range order regions. The typical scale of these structures is about 10 to 20 Å.  100 200 300 400 500 6000,000,050,100,150,20Intensity, a.u.Wavenumber, cm-140311424634643537521049515288186 a 200 4000,000,050,100,15Intensity, a.u.Wavenumber, cm-121418923715034249611581320140391364402167 b  Fig. 2. Raman spectra of ternary glasses Ge30As4S66 (а) and Ge5As37S58 (b).   Authors of [3] investigated evolution of Raman spectra with temperature. They observed two stage crystallization of glassy GeS2. It was found that the A1c mode is present in spectra during the rise of temperature  © 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine  433  Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 432-435.  and remains after the transition to 3D-crystalline state (at ~750 ºC), and also it is present at temperatures higher than 850 ºC as a shoulder (when the transition to the 2D-crystalline state occurs). After slow cooling down to room temperature, material retains 2D-crystalline structure that also has the А1с mode in its spectrum. Therefore, by analogy with the 2D-crystalline state, the А1с mode in glassy GeS2 was ascribed to symmetrical vibrations of sulphur bridge atoms in edge-shared tetrahedra. Authors of [5] provided comparison of Raman spectra of glassy GeS2 obtained under different quenching temperatures and cooling rates. A conclusion has been drawn that А1с mode together with 433 cm-1 band can be ascribed to vibrations in edge-shared tetrahedra. In paper [3], 433 cm-1 band was ascribed to the stretching vibrations of S–S bonds that were either present separately in glass matrix or bond together with tetrahedral elements. This opinion is supported by the authors of [8]. They stated that the 434 cm-1 band that was observed by them in germanium sulphide films, corresponds to the vibrations of S–S bonds interconnecting Ge(S1/2)4 tetrahedra. Authors of [3] claims that the presence of such bonds in stoichiometric glass indicates the presence of homopolar Ge–Ge bonds. The band at 260 cm-1, the intensity of which was growing up with the increase of Ge concentration was ascribed to the presence of these bonds. The authors, however, didn’t explain why the intensity of 433 cm-1 band (along with A1c band) decreases with increasing of the sulphur content. Authors of [5] don’t support the assumption about the presence of homopolar bonds in glassy GeS2. The bands at 200, 237 and 256 cm-1 which were observed in samples of glassy GeS2 obtained at different synthesis conditions, were ascribed to the vibrations in three-fold coordinated structures consisted of Ge and S atoms, for instance, to the vibrations in crystalline nanophase c-GeS. As mentioned in [5], c-GeS nanoparticles with sizes about 7–12 Å may exist in the glass structure, or, depending on the synthesis conditions, may form larger c-GeS particles within the matrix of glassy GeS2. In the paper [4], the band near 440 cm-1 that was observed in glasses of nearly stoichiometric compositions GexS1-x, was ascribed to the F2 mode of tetrahedra Ge(S1/2)4. In paper [9], the structure of As4Ge30S66 glass was investigated by means of X-ray diffraction. By comparison of experimental results with those of numerical simulation, a conclusion was drawn that the structure of glass is given by inhomogeneous network with regions expressing a quasi-layer type stacking interlinked with regions of random network where the amount of homopolar bonds is kept minimum. The 495 cm-1 band observed in the spectrum of As4Ge30S66 is characteristic for the presence of S–S bonds. Presence of these bonds implies the existence of edge-shared Ge(S1/2)4 tetrahedra in the structural backbone of the glass, which must lead to the appearance of redundant S atoms.  The 246 cm-1 band was observed earlier in the GexA40-xS60 glass spectra [10]. When x = 0, a weak band near 231 cm-1 was observed, which was growing and shifting towards the higher frequencies with increasing x until 245 cm-1 when x = 36. This feature was related by authors with increasing amount of homopolar Ge–Ge bonds compared to As–As. As claimed in [10], homopolar Ge–Ge bonds are located in Ge–S4-nGen tetrahedra and/or in Ge2S6/2 ethane-like clusters. Similar peculiarity was observed in [11] during the investigation of series of compounds (Ge2S3)x(As2S3)1-x where 0<x<1. When x>0.5, the broad band centered at 250 cm-1 appeared and began to increase. As stated in [11], this band corresponds to the vibrations in ethane-like Ge2S6 nanophase that segregates from GeS2. According to the results of calculations provided in [5], ethane-like nanophase possesses the intensive peak at 250 cm-1 and also several bands near 400 cm-1. In the decomposition of the main peak in the As4Ge30S66 spectrum (see Fig. 2), there is a broad band centered at 403 cm-1. Therefore, bands at 246 and 403 cm-1 can be ascribed to the vibrations in ethane-like nanophase Ge2S6. In Fig. 3, the difference between spectra of As4Ge30S66 and Ge33S67 glasses normalized to the intensity of the main peak is shown. The difference spectra clearly reveal the changes made by addition of arsenic to the Ge33S67 glass. The abrupt transition from minimum to maximum near 346 cm-1 is due to the red shift of the main band. The difference spectrum has maximum near 250 cm-1 corresponding to the appearance of this band in the spectrum of As4Ge30S66 glass, and minima at 374 and 438 cm-1 due to the softening of corresponding bonds. The former peculiarity can be ascribed to the precipitation of ethane-like nanophase, while the latter to the decrease of the Ge(S1/2)4 tetrahedra concentration.  The Raman spectrum of Ge5As37S58 glass (see Fig. 2b) is almost similar to the spectrum of binary As40S60 glass. The main broad band in the spectra of As40S60 and Ge5As37S58 glasses at 342 cm-1 corresponds to the band characteristic for AsxS100-x glasses of different compositions. The bands at 321, 343 and 361 cm-1 that are present in the decomposition of main band are typical to the As42S58 glass enriched by arsenic as compared to the stoichiometric As40S60 glass. The 342 cm-1 band, as generally accepted [6, 10, 11], corresponds to the symmetric ν1 vibrations of pyramidal As(S1/2)3 units. The band at 361 cm-1 corresponds to the intensive mode of crystalline As4S4 [6]. The increase in this band intensity is characteristic of AsxS1-x compositions when x>40, that is arsenic enriched as compared to the stoichiometric glass [6, 12]. Numerical calculations provided in [12] allow to ascribe the band at 361 cm-1 to the presence of As4S4 clusters in material. In the lower frequency region of the Ge5As37S58 spectrum, we can also see the bands observed earlier by the authors of [6] in the As42S58 glass, in particular: the bands at 150 (corresponds to the 147 cm-1 band), 167, 189, 214 and 237 cm-1 (corresponds to the  © 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine  434  Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 432-435.  234 cm-1 band). Bands at 150, 167, 189 and 214 cm-1 can also be ascribed to the vibrations in As4S4 clusters [6, 11]. The band near 496 сm-1 that is characteristic of S-S bonds appears in spectra of glass of either stoichiometric As40S60 or non-stoichiometric Ge5As37S58 glass with Ge additive. Thus, presence in the spectrum of As40S60 glass bands at 361, 150, 167, 189 and 214 cm-1 that are characteristic of As4S4 clusters, and the band at 496 cm-1, suggests the non-homogeneity and nanophase separation in stoichiometric glass. In Fig. 4, the difference between spectra of Ge5As37S58 and As40S60 glasses normalized to the intensity of the main peak is shown. As can be seen from Fig. 4, introduction of Ge additives leads to appearance of the minima at 310 and 330 cm-1, which corresponds to the anti-symmetrical and symmetrical vibrations of AsS3 pyramids [6]. The positive peaks near 241, 383 and 408 cm-1 can be ascribed to the vibrations in ethane-like clusters that can be formed in glass with addition of Ge.    0 100 200 300 400 500 Intensity difference, a.u.GeS2Wavenumber, cm-1Intensity, a.u.As4Ge30S66 -0,04-0,03-0,02-0,010,000,010,02 112141250 374438346 Fig. 3. Difference between spectra of As4Ge30S66 and Ge33S67 glasses normalized to the intensity of the main peak.    100 200 300 400 500Intensity difference, a.u.241331310383408Wavenumber, cm-1Intensity, a.u.As40S60Ge5As37S58-0,006-0,004-0,0020,0000,0020,0040,006   Fig. 4. Difference between spectra of Ge5As37S58 and As40S60 glasses normalized to the intensity of the main peak.     4. Conclusions Raman spectra of two ternary glasses with compositions Ge5As37S58 and As4Ge30S66 have been investigated. An influence of third element addition on the spectra of binary glasses has been studied by comparison with two binary glasses of composition Ge33S67 and As40S60. The observed peaks in Raman spectra are characteristic either to the main elements forming structural backbone of the glasses (tetrahedral Ge(S1/2)4 units and pyramidal As(S1/2)3 units) or various inclusions (molecular As4S4 clusters and ethane-like nanophase Ge2S6/2). Inhomogeneity and nanophase separation can be observed in glasses of either non-stoichiometric or stoichiometric composition.  References 1. X. Feng, W.J. Bresser, P. Boolchand, Direct evi-dence for stiffness threshold in chalcogenide glasses // Phys. Rev. Lett. 78 (23), p. 4422-4425 (1997). 2. Z. Cernosek, J. Holubova, E. Cernoskova, M. Frumar, Homogeneity threshold in sulphur rich Ge–S glasses // JOAM, 3(2), p. 459-462 (2001). 3. 3. I.P. Kotsalas, C. Raptis, Structural Raman studies of GexS1-x chalcogenide glasses // JOAM, 3(3), p. 675-684 (2001). 4. L. Cai, P. Boolchand, Nanoscale phase separation of GeS2 glass // Phil. Mag., 82(15), p. 1649-1657 (2002). 5. R. Holomb, P. Johansson, V. Mitsa, I. Rosola, Local structure of technologically modified g-GeS2: resonant Raman and absorption edge spectroscopy combined with ab initio calculations // Phil. Mag., 85 (25), p. 2947-2960 (2005).  © 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine  435  Semiconductor Physics, Quantum Electronics & Optoelectronics, 2010. V. 13, N 4. P. 432-435.  6. E.F. Venger, A.V. Melnichuk, A.V. Stronski, Photoinduced Phenomena in Chalcogenide Glassy Semiconductors and Their Practical Application. Akademperiodika, Kyiv, 2007 (in Russian). 7. P.M. Bridenbaugh, G.P. Espinosa, J.E. Grifiths, et al. // Phys. Rev. B, 20(10), p. 4140 (1979). 8. C.C. Huang, D.W. Hewak, Deposition and characterization of germanium sulphide glass planar waveguides // Optics Express, 12 (11), p. 2501-2506 (2004). 9. F. Sava, A. Anghel, I. Kaban, W. Hoyer, M. Popescu, Atomic scale structure of Ge30As4S66 // JOAM, 7(4), p. 1971-1975 (2005). 10. E. Vateva, E. Skordeva, Nanoscale arrangement in the GexAs(Sb)40-xS60 systems // JOAM, 4(1), p. 3-12 (2002). 11. S. Mamedov, D.G. Georgiev, Tao Qu, P. Boolchand, Evidence for nanoscale phase separation of stressed–rigid glasses // J. Phys.: Condens. Matter. 15, p. S2397-S2411 (2003). 12. R.M. Holomb, V.M. Mitsa, Simulation of Raman spectra of AsxS100-x glasses by the results of ab initio calculations of AsnSm clusters vibrations // JOAM, 6(4), p. 1177-1184 (2004).  © 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine  436 

Raman scattering in sulphide glasses

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Raman scattering in sulphide glasses

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Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)