Synthesis of SnS Nanoparticles by a Green Hydrothermal Route

Mechanics, Materials Science & Engineering, May 2017

ISSN 2412-5954

Synthesis of SnS Nanoparticles by a Green Hydrothermal Route 8 L. Ansel Mely1, P. Annie Vinosha1, M. Mary Jaculine2, Rudhra Nivedita Nathan3, S. Jerome Das1, a 1

Department of Physics, Loyola College, Chennai, India

2

Department of Physics, Velammal Engineering College, Chennai, India

3

PG Department of Physics, Women's Christian College, Chennai, India

a

melyansel@gmail.com, jerome@loyolacollege.edu DOI 10.2412/mmse.48.4.664 provided by Seo4U.link

Keywords: tin sulphide, semiconductor nanoparticles, hydrothermal, photoluminescence.

ABSTRACT. The IV VI semiconductor nanoparticle tin sulphide (SnS), has sparked rigorous interest in the scientific commune because of the array of promising applications it offers such as in photovoltaics, near-infrared detectors and biomedical applications. In the present work, phase pure SnS nanoparticles were effectively synthesized by a green hydrothermal technique using the precursors tin chloride pentahydrate and thiourea. The as-prepared nanoparticles were subjected to various characterizations in order to analyze their optical, structural and transport properties. The Powder Xray Diffraction (XRD) measurements revealed the purity and crystalline nature of the SnS nanoparticles. The average crystallite size of 10.65 nm, calculated by the Scherrer's formula was in good agreement with the observations from the Transmission Electron Microscope (TEM) micrographs. The transport properties of the synthesized nanoparticles were studied using dielectric analysis. Further, the UV-visible spectroscopy (Uv-vis) and Photoluminescence spectroscopy (PL) results advocate that the primed SnS nanoparticles will be an appropriate applicant for photovoltaic and other light emitting applications.

Introduction. In recent years there is considerable interest in semiconductor nanoparticles due to their optical and electrical properties being different from those of their bulk counterparts, due to the quantum confinement effect [1]. Synthesis and application of IV- VI semicondctor nanoparticles have become the research hotspot of research among which nanoparticles tin sulphide (SnS) has gained substantial attention in the recent years owing to its multitude of merits such as exhibiting p and n type behaviour, narrow band gap; bulk direct band gap of 1.3 eV and indirect bandgap of 1.1 eV; high optical absorption coefficient for photons and high photoelectric conversion efficiency of up to 25%, ampleness of raw material and meagre toxicity. Tin sulphide and can be extensively used in areas of electronics non-linear optics, luminescence, energy storage and conversion and many more [2], [3].

Due to the versatile coordinating characteristic of SnS, it shows a variety of phases such as SnS, SnS2, Sn2S3, Sn3S4 and Sn4S5 [4]. Further it adopts a strongly distorted NaCl structure with double layers of tightly bound Sn-S atoms with the bonding between layers of Vanderwaal type [5]. In the present effort, the structural and optical properties of hydrothermally prepared SnS nanoparticles were investigated for potential optical applications.

Materials and methods Materials used. In the present work, tin chloride pentahydrate (SnCl2.5H2O) and thiourea (NH2CSNH2) were purchased from Merck and used without further purification. The tin slphide (SnS) nanoparticles were synthesized by a scrupulous hydrothermal method using a cylindrical Teflon-lined stainless steel autoclave of 200 ml capacity. Double distilled water was served as solvent for the experiment.

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-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Mechanics, Materials Science & Engineering, May 2017

ISSN 2412-5954

Experimental. SnS nanoparticles were synthesized by an impeccable hydrothermal method using the tin and sulphur precursors in the molar ratio 1:3. The precursor solutions for tin and sulphur respectively were prepared by separately dissolving appropriate measured amount of tin chloride pentahydrate and thiourea in 80 ml of double distilled water. Clear solutions were obtained with the aid of magnetic stirring. Subsequently, the thiourea solution was added drop-wise to the tin solution under constant magnetic stirring inorder to get a homogenous mixture. The solution thus obtained was filled upto 80% volume o cooling down of the autoclave at ambient temperature, the obtained yellow precipitate was collected and centrifuged with distilled water and ethanol. The obtained products were dried using a hot air oven and then ground well to gain SnS nanoparticles.

Results and Discussion Structural and morphological analysis

Fig. 1. XRD pattern of the synthesized SnS nanoparticles.

Fig. 1 exhibits the powder X-ray diffraction (XRD) spectrum of the prepared SnS nanoparticles as angular range 20(021), (101), (040), (131), (210), (141), (211), (112), (231), (042) and (080) planes unveil the formation of phase pure SnS nanoparticles as the indexed peaks match incredibly well with the standard JCPDS card number 39-0354 with no characteristic peaks of SnS2 and SnO2. The pattern shows the formation of orthorhombic phase herzenbergite SnS nanoparticles with Pbnm space group.

Using Scherrer's formula the crystallite size (D) of the synthesised nanoparticles was estimated to be 10.65 nm corresponding to the major diffraction peak at (040) plane.

Subsequently, the dislocation density ( ) and strain ( ) were estimated to be and 0.1632 lin-2 m-4 from the formulae:

(1) (2)

where

is the full width at half maximum and

is the diffraction angle.

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Mechanics, Materials Science & Engineering, May 2017

ISSN 2412-5954

Fig. 2. TEM micrographs of the synthesized SnS nanoparticles.

The morphology and particle size of the synthesized SnS nanoparticles were studied using TEM analysis by Joel/JEM 2100 Transmission Electron Microscope. The images (Fig. 2 a - b) disclose that most of the SnS nanoparticles have nearly spherical morphology with little agglomeration and the particle size varies from 6 to 10 nm.

Dielectric Analysis. The variation of dielectric constant and dielectric loss with frequency for the SnS nanoparticles are shown in Fig. 3.a and b. The powder sample was pelletized and coated with silver paint on the surface and placed between two copper electrodes. It can be observed from the Fig.s that the dielectric constant and loss decrease respectively with corresponding increase in frequency which can be attributed to the space-charge polarization.

a)

b) Fig. 3. a) The variation of dielectric constant Vs log frequency, b) The variation of dielectric loss Vs log frequency.

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Optical Analysis

a)

b)

c) 2

Fig. 4. a) Uv-

versus

1/2

band gap of SnS nanoparticles.

The UV-visible absorption (UV) spectra were determined using VARIAN in the wavelength span of 250 800 nm. The absorbance spectra shown in Fig. 4,a indicates that the synthesized SnS nanoparticles can be used for solar cell applications since it has a strong absorption in the visible light region. The absorption edge of the as-synthesized SnS nanoparticles show a blue shift in comparison to its bulk counterpart, which has an absorption onset at 953 nm [4].

The bandgap being a vital characteristics of a semiconductor, was studied by UV and estimated using Tauc's law

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(3)

where, and are the absorption coefficient, photon energy, proportionality constant and direct band gap respectively.

Based on the type of electronic transition the value of can be assmed to be 2 or 1/2, i.e. for direct and indirect transitions respectively. By extrapolating the linear part of the plots in Fig.s 4.b and 4.c, the direct and indirect optical band gaps were estimated to be 1.54 and 1.13 eV. It is known that in semiconductor nanoparticles, the band gap increase with decrease in particle size which can be attributed to quantum confinement of particles. The obtained band gap values project that the synthesized nanoparticles can be used for photovoltaic applications.

The Photoluminescence (PL) spectrum of the synthesized nanoparticles, shown in Fig. 5, shows two emission peaks wherein the 484.02 nm peak signifies blue emission which is dissimilar from that of SnS2 (570 nm) and bulk SnO2 (360 nm). The sturdy peak at 543.97 nm can be credited to a high level transition in SnS semiconductor nanocrystallites. From literature, it is clear that, this kind of band edge arises from the recombination of excitons and/or shallowly trapped electron hole pairs. The PL spectrum suggests that the synthesised SnS nanoparticles can be used as blue and UV light emitters [5-8].

Fig. 5. PL spectrum of the synthesized SnS nanoparticles.

Summary. Summing up, tin sulphide nanoparticles were effectively prepared by an impeccable hydrothermal method. The structural and optical properties of the synthesized material were studied wherein the structure and phase purity were confirmed by the powder X-Ray diffraction pattern. The crystallite size was estimated to be 10.65 nm using Scherrer's formula. The direct and indirect band gaps of the synthesized nanoparticles were found to be 1.54 and 1.13 eV from the Uv-visible absorption spectroscopy, which propose the synthesised SnS nanoparticles as a prospective material for photovoltaic applications.

Acknowledgements. The authors are grateful to the management of Loyola College, Chennai - 34 for awarding the project (3LCTOI14PHY002) under Loyola College TOI-Scheme.

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