The present work deals with the study of the structural properties of nanosized SnS2 films deposited by the close-spaced vacuum sublimation (CSVS) method. Surface morphology of the obtained films was determined by the scanning electron microscope (SEM-102Е). Structural investigations of the films were performed with the Raman spectroscopy. The analysis of chemical composition of the layers was carried out by
the scanning electron microscope by energy dispersive X-ray (ЕDS) spectroscopy. The structure features of SnxSy films were investigated by the modulation-polarization spectroscopy (MPS) technique of surface plasmon resonance

Kosiak, Volodymyr Volodymyrovych

Maksimenko, L.S.

Opanasiuk, Anatolii Serhiiovych

Rudenko, S.P.

Serdega, B.K.

Stetsenko, Μ.Ο.

Vozny, A.A.

Косяк, Владимир Владимирович

Косяк, Володимир Володимирович

Опанасюк, Анатолий Сергеевич

Опанасюк, Анатолій Сергійович

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 4 No 2, 02NAESP06(4pp) (2015)   2304-1862/2015/4(2)02NAESP06(4) 02NAESP06-1  2015 Sumy State University  Detection of Structural Characteristics of Nanosized SnxSy Film by  the Modulation-polarization Spectroscopy of Plasmon Resonance  A.A. Vozny1, Μ.Ο. Stetsenko2,*, S.P. Rudenko2, V.V. Kosyak1, L.S. Maksimenko2, A.S. Opanasyuk1, B.K. Serdega2  1 Sumy State University, 2, Rymsky Korsakov Str., 40007 Sumy, Ukraine 2 V. Lashkaryov Institute of Semiconductor Phisics, NAS of Ukraine, pr. Nauky 45, 03028 Kiev, Ukraine   (Received 28 July 2015; published online 29 August 2015)  The present work deals with the study of the structural properties of nanosized SnS2 films deposited by the close-spaced vacuum sublimation (CSVS) method. Surface morphology of the obtained films was de-termined by the scanning electron microscope (SEM-102Е). Structural investigations of the films were per-formed with the Raman spectroscopy. The analysis of chemical composition of the layers was carried out by the scanning electron microscope by energy dispersive X-ray (ЕDS) spectroscopy. The structure features of SnxSy films were investigated by the modulation-polarization spectroscopy (MPS) technique of surface plasmon resonance.  Keywords: Thin films, SnxSy, Co-evaporation, Surface morphology, X-ray diffraction, Surface plasmon resonances, Modulation-polarization spectroscopy.   PACS numbers: 61.05.C –, 73.20.Mf, 61.72. – y                                                             *StetsenkoMax@gmail.com 1. INTRODUCTION  The tin-sulfur system can form a variety of crystal-line phases such as SnS, Sn2S3, SnS2 with a different band gaps. A number of these compounds can be ob-tained by both p- and n-type conductivity. This allows creating solar cells (SC) with a heterojunction based on different phases of the same compound (e.g. n-SnS2/p-SnS), which significantly simplifies their production and reduces cost [1]. Increasing of efficiency of SC needs optimization of structural characteristics of sur-face layers of SnxSy as a component. Application of modulation-polarization spectroscopy (MPS) of surface plasmon resonance technique allows characterizing the structure of nanosized films by studying their polariza-tion characteristics [2]. The interaction between electromagnetic radiation and metal, metal-dielectric and semiconductor films can manifest itself in a resonant excitation of surface plasmon polaritons (SPP) on infinite flat metal-dielectric surface or localized surface plasmons (LSP) on separated metal nanoparticles and between nano-particles due to their dipole-dipole interactions [3]. Manifestation of surface plasmon resonance (SPR) in nanocomposite films takes place in presence of optical density in them or in a metal nanoparticles, such as gold nanoparticles in tin matrices of oxide or sulfide  (SnO2 and SnS2) [4, 5]. The LSP excitations in Ag-SnS nanocomposite were studied in [6]. The materialisation of SPR in nanosized SnO2 films without metal nanopar-ticles was shown in [7]. LSPR of anisotropic semicon-ductor nanocrystals was investigated in works [8, 9]. Therefore the questions about research of SPR phe-nomenon in nanosized SnxSy films are important.   2. EXPERIMENTAL DETAILS  SnxSy thin films were obtained on ultrasonically cleaned glass substrates in vacuum chamber under interstitial gas pressure not higher than 5∙10 – 3 Pа. Temperature of substrates was Ts  175 C. Film thickness was to 50 nm. The CSVS was used as growth method. This method allows to obtain films with small deviation from stoichiometry in conditions close to thermodynamic equilibrium. For this purpose a system for co-evaporation of sulfur and tin was created and approbated [10]. Surface morphology of the films was investigated by a scanning electron microscope (SEM-102Е).  Thickness of the samples was studied using AFM (Digital Instrument’s multimode scanning probe micro-scope (SPM) with‘‘Nanoscope IIIa’’ controller). The chemical composition of the films was estimat-ed by X-ray radiation energy-dispersive analysis (ЕDS).  Structural analysis of the SnxSy films was per-formed by Raman spectroscopy. The samples were studied by the Renishaw's Raman spectrometer at room temperature. The laser with a wavelength of 514 nm was used as excitation source.  The SPR is the most informative polarization effect in terms of properties of nanostructured films. Diag-nostic of different SPR types with parameters of these resonances and information about optical parameters, morphological and structural features of nanomaterials was performed by measuring of polarization parameter as the polarization difference  (θ, ). Research setup [11] consisting of a goniometer con-nected to a monochromator allows to measure both the angular polarization characteristics of internal reflec-tion parameters at various wavelengths  and spectral characteristics at appropriate incident angles  of radi-ation. The angular and spectral characteristics of the polarization difference (, )  Rs2 – Rp2 of the internal reflection coefficients at which polarization azimuths of radiation alternated between perpendicular and paral- A.A. VOZNY, M.O. STESTENKO, S.P. RUDENKO, ET AL. PROC. NAP 4, 02NAESP06 (2015)   02NAESP06-2 lel positions relative to the incident plane (s- and  р-polarization, respectively) were investigated. If nec-essary, the angular and spectral dependences of Rs2(, ) and Rp2(, ) reflection coefficients separately were measured. Technical parameters of the measure-ment setup were as follows. A diffraction monochroma-tor MDR-4 (with a halogen tube KGM-150 at the input and Franck-Ritter polarizer at the output) served as a source of spectral radiation in the wavelength range   0.4-1 m. A photoelastic polarization modulator [12] acted as dynamic phase plate with a modulation fre-quency of f  60 kHz. The output radiation was directed at a photodetector PD (silicon photodiode). Detected signal was registered by a selective amplifier equipped with a phase-lock detector (lock-in-voltmeter) tuned to the modulation frequency. The variable component value was a magnitude of the difference of internal reflection coefficients of s- and p-polarizations. The resulting value is the polarization difference ((, )  Rs2-Rp2).  3. RESULTS AND DISCUSSION  Figure 1 shows SEM image of SnxSy films. It was determined that the films obtained at substrate tem-perature (Ts) 175 C and thicknesses of 50 nm are poly-crystalline and consist of platelet-shaped grains. The average grain size is 150 nm.    Fig. 1 – Plane-view SEM image of SnxSy film obtained at Ts  175 C  The Raman scattering spectrum for the sample is shown in Fig. 2. As could be seen, the spectrum include strong peak at 315 cm – 1 that corresponding to the A1g mode of SnS2 phase [13-15]. Weak Raman peak at 155 cm – 1 is assigned to the Sn2S3 [16, 17]. The modes at 97, 224 and 288 cm – 1 related to SnS phase were also detected [16, 18-20]. Figure 3 shows angular characteristics of polariza-tion difference (), reflection coefficients of p-polarized Rp2() and s-polarized Rs2() radiation. The sign of am-plitude of () at various wavelength of radiation is changing due to different resonant contributions of  s- and p-polarizations at surface plasmons excitations. These are confirmed by appropriate characteristics of Rs2() and Rp2() (Fig. 3b, c). Figure 4 shows spectral characteristics of polarization difference () at incident angles greater than the critical angle of total internal reflection (  cr  43). Asymmetrical contour in characteristics of () can be caused by presence of two partially overlapping resonances in the films. On the one hand extremum in   Fig. 2 – Raman scattering spectra of the sample        Fig. 3 – Angular dependencies: a) polarization difference;  b) reflection coefficient of p-polarized; c) s-polarized light  a short-wavelength range is caused by resonant excita-tion of localized surface plasmons (LSP) on rough sur-face of SnxSy films. On the other hand extremum in a  DETECTION OF STRUCTURAL CHARACTERISTICS OF. … PROC. NAP 4, 02NAESP06 (2015)   02NAESP06-3 long-wavelength range is caused by excitations of sur-face plasmon-polaritons (SPP) on continuous and ho-mogeneous surface [21]. Phase-synchronous condition consists in coincidence of frequencies () and wave vectors (k) of exciting radiation and surface plasmons and exists in the angle range of   cr. One can see that extrema of () has a blue-shifts in the angle range of 43    60, which corresponding to LSP and SPP resonances: LSP  527-477 nm and SPP  800-575 nm, respectively. The minima in Fig-ure 4(a) and 4(b) are caused by excitation of LSP in non-radiative and radiative modes, respectively. In Figure 4(b) minimum of () at the angles less than the critical one   cr also has a slight blue-shift of   570-530 nm.      Fig. 4 – Spectral dependencies of the polarization difference in the angle range: a) 43.5-60, b) 20-35  The resonant excitations of LSP are determined by the extrema with negative values of () due to greater interaction between films and s-polarization light and by the extrema with positive values of () due to greater interaction between film and p-polarization light. Such curve features of () are typical for na-nosized films with a cluster structure.    Fig. 5 – Angular dependencies of amplitude and FWHM of LSP and SPP resonances  Figure 5 shows dependencies of amplitude and FWHM (full width at half maximum) on the incident angle for LSP and SPP resonances. These results are obtained using procedure of decomposition of spectral dependencies into elementary components that are described by Gaussian function [22]. The FWHM parameter is responsible for the damp-ing of resonance. It is shown that FWHM has a mini-mum at maximum amplitude both of LSP and SPP resonances. Moreover the minimum value of LSP corre-sponds to a maximum value of SPP in the angular am-plitude dependencies of LPP and SPP resonances.  4. CONCLUSION  The surface morphology and phase composition of nanosized SnxSy films with thickness of 50 nm obtained by CSVS method with a Ts  175 C were studied. For the first time two mechanisms of resonant interaction between radiation and electron subsystem of SnxSy films with excitations of localized surface plasmons and surface plasmon-polaritons were shown in the angular and spectral characteristics of the polarization differ-ence (, ) of internal reflection coefficients of  s- and p-polarized radiation in the wide wavelength range of   400-1000 nm. With the help of diagnostic technique of modula-tion-polarization spectroscopy of surface plasmon reso-nance it was obtained that morphology surface of SnxSy films has a inhomogeneous and continuous structure.   REFERENCES  1. A. Sanchez-Juareza, A. Ortiz, J. Electrochem. Soc. 147, 3708 (2000). 2. L.J. Berezhinsky, L.S. Maksimenko, I.E. Matyash, S.P. Rudenko, B.K. Serdega, Opt. Spectrosc. 105, 257 (2008). 3. S.A. Maier, Plasmonics: fundamentals and applications (Springer: 2007). 4. S. Singh, B.D. Gupta, Meas. Sci. Technol. 21, 115202 (2010). 5. J. Li, Z. Yang, Y. Zhang, S. Yu, Q. Xu, Q. 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Detection of Structural Characteristics of Nanosized SnxSy Film by the Modulation-polarization Spectroscopy of Plasmon Resonance

Detection of Structural Characteristics of Nanosized SnxSy Film by the Modulation-polarization Spectroscopy of Plasmon Resonance

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