Physica E 115 (2020) 113708 Available online 9 September 2019 1386-9477/© 2019 Elsevier B.V. All rights reserved. Surface optical phonon (SOP) mode in ZnS/Poly (methylmethacrylate) nanocomposites Milica Curcic a , Branka Hadzic a , Martina Gilic a, * , V. Radojevic b , Andjelika Bjelajac c , Ivana Radovic d , Dejan Timotijevic a , Maja Romcevic a , Jelena Trajic a , Nebojsa Romcevic a a Institute of Physics Belgrade, University of Belgrade, 11080, Belgrade, Serbia b Faculty of Technology and Metallurgy, University of Belgrade, 11000, Belgrade, Serbia c Inovation Center of Faculty of Technology and Metallurgy, 11000, Belgrade, Serbia d Vin� ca Institute of Nuclear Sciences, University of Belgrade, 11000, Belgrade, Serbia A R T I C L E INFO Keywords: Nanostructured materials Optical properties Phonons Light absorption and refection ABSTRACT The polymer nanocomposite ZnS/Poly (methylmethacrylate) was prepared by the solution casting method and its structural and optical properties were investigated using XRD, SEM, TEM, HRTEM, and Raman spectroscopy. The basic material, ZnS, has the cubic structure and its crystallite size was estimated to be 2.3 nm, which implies that a strong confnement regime is in effect. Analysis of Raman spectra was performed using the ftting pro- cedure based on effective medium theory. As a result, the surface optical phonon (SOP) mode was detected. It was found that the shape and position of the SOP mode depend on the type of the composite. 1. Introduction As a semiconductor, the zinc sulfde (ZnS) has gained considerable attention and is found to be applicable in optoelectronic, electrolumi- nescent, and blue light emitting diode devices [1–8]. ZnS has two available allotropic forms – the wurtzite and zinc blende. The crystal- lographic form of wurtzite is hexagonal, whereas the zinc blende has the cubic crystallographic structure, is more stable and as such, is more common of the two. The ZnS in the form of the bulk material has a direct band gap positioned primarily in the UV region [9,10]. The wurtzite and the zinc blende forms have the band gaps of 3.77 and 3.72 eV, respec- tively. The band gap increases with a decrease in size from the bulk to the nanoscale [11,12]. Since ZnS easily absorbs moisture and oxidizes in air [13], it is not very stable as a pure compound in the atmosphere. Therefore, surfactants or capping agents are added to the ZnS nano- particles to prevent structural transformation and surface reactions. A nanocomposite consists of two or more different materials in which at least one of the components has a dimension smaller than 100 nm [14]. In polymer nanocomposites, the composing elements are an organic polymermatrix and inorganic components (semiconductors). Nanocomposites can include three dimensional metal matrix compos- ites, lamellar composites, colloids, porous materials, gels, as well as copolymers in which nanosized material is dispersed within the bulk matrix. The properties of the nanocomposites depend on their compo- nents, morphology, and interface characteristic. In order to extend the area of their potential applications, mechanical, thermal, and electronic properties of conventional polymer materials had to be improved [15, 16]. As a thermoplastic polymer, Poly (methylmethacrylate) i.e. PMMA has many excellent properties. Its favorable properties include excellent transparency and ultraviolet resistance, as well as good abrasion resis- tance, hardness, and stiffness. Consequently, it is widely used in many applications, for example in lenses, light pipes, bathroom fttings, sky- lights, toys, etc. In addition, PMMA is non-degradable and biocompat- ible, which qualifes it for use in tissue engineering where typical applications are fracture fxations, intraocular lenses, and dentures [17]. For nanocrystals of relatively small dimensions, surface modes and the effects of dimension are expected to appear, along with the normal modes of an infnite lattice. Namely, in the frequency range between longitudinal optical phonon frequency (ω LO ) and transversal optical phonon frequency (ω TO ), a new mode known as a surface optical phonon (SOP) mode appears. In our previous papers [18–22] we worked on investigating surface optical phonons (SOP) in semiconducting nanoparticles or thin flms. In all those cases, SOP appeared because the nano-objects of investigated materials were well separated in the air. In this paper we report the synthesis and structural and optical * Corresponding author. E-mail address: martina@ipb.ac.rs (M. Gilic). Contents lists available at ScienceDirect Physica E: Low-dimensional Systems and Nanostructures journal homepage: http://www.elsevier.com/locate/physe https://doi.org/10.1016/j.physe.2019.113708 Received 10 May 2019; Received in revised form 20 August 2019; Accepted 6 September 2019