Determination of thermal diffusivity and optical gap of an amorphous P 20 Se 80 alloy through photoacoustic measurements R.N.A. Maia a , M.C. Siqueira a , R.M.T. Araujo a , K.D. Machado a, ⁎, S.F. Stolf b a Departamento de Física, Centro Politécnico, Universidade Federal do Paraná, 81531–990, Curitiba, Paraná, Brazil b Centro de Engenharia e Ciências Exatas, UNIOESTE, 85903–000, Toledo, PR, Brazil abstract article info Article history: Received 25 March 2015 Received in revised form 18 June 2015 Accepted 22 June 2015 Available online 30 June 2015 Keywords: Amorphous materials; Semiconductors; Thermal properties; Optical properties We investigated the thermal diffusivity and optical properties at room temperature of an amorphous P 20 Se 80 alloy produced by mechanical alloying considering two apparatuses based on the photoacoustic technique. The room temperature thermal diffusivity α s of P 20 Se 80 was determined using the open photoacoustic cell configuration considering the thermal diffusion and thermoelastic bending effects, and we found that P 20 Se 80 has the highest reported value of α s among amorphous alloys produced by mechanical alloying. The optical absorption and the optical gap were obtained through a photoacoustic spectroscopy apparatus, and the optical gap was determined to be in the near infrared region. The alloy presents strong absorption in the UV and visible regions, which suggests possible applications in heat transfer or cooling devices, and photodetectors. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Nonoxide chalcogenide alloys formed by elements of the V–VI families (sulfides, selenides and tellurides) have very interesting properties such as high transparency in the broad middle and far infrared regions, strong nonlinear properties and large optical gaps, which can be exploited from the scientific and technological viewpoints in developing applications as waveguides and optical fibers, solid electrolytes and active layers in electronic devices [1–3]. Recently, Serbena et al. [3] demonstrated that an amorphous P 10 Se 90 (a-P 10 Se 90 ) alloy could be used as an efficient hole injection layer for devices based on organic materials. Such alloy was produced by mechanical alloying (MA) [4] and some of its physical properties (atomic structure, vibrational modes and optical gap) were investigated by Oliveira et al. [5]. It is interesting to note that binary amorphous alloys formed by Se and P (P x Se 100 − x ) can be produced in a large compositional range, from pure Se to P 54 Se 46 and from P 64 Se 36 to P 84 Se 16 [6,7]. Such large range opens the possibility of investigating other compositions besides a-P 10 Se 90 , in order to develop possible applications of these alloys. Thus, here we investigated an amorphous alloy with the composition P 20 Se 80 (a-P 20 Se 80 ), which was also produced by MA, and we focused on properties directly related to technological applications. Specifically, we determined the thermal diffusivity and the optical absorption and optical gap of this alloy. Such properties can be obtained by means of photoacoustic (PA) measurements. Since the PA signal depends directly on the optical absorption coefficient [8], it is possible to obtain optical properties through PA spectroscopy (PAS) measurements. In addition, the PA signal also depends on the way heat diffuses through the sample [8–10], allowing us to obtain photothermal properties such as thermal diffusivity. PA techniques demand minimum sample preparation, they are nondestructive and allow investigations on several kinds of materials, including nonhomogeneous ones [8–10]. In this article we used two apparatuses to perform PA measurements. The first one is the open photoacoustic cell (OPC) configuration, which was used here to determine the thermal diffusivity α s of a-P 20 Se 80 . The second apparatus, a PAS configuration, was used to investigate the optical properties and to obtain the optical gap E g of a-P 20 Se 80 . The results obtained indicate that a-P 20 Se 80 has the highest reported thermal diffusivity among amorphous alloys produced by MA. Its optical gap is located in the near infrared region, and the alloy has a strong absorption in the UV and visible regions. The theoretical fundamentals used to analyze the PA measurements and to obtain α s and E g are described in Section 2. Section 3 describes the experimental apparatuses employed to make the measurements. Results obtained are shown in Section 4, and Section 5 presents the conclusions obtained. 2. Theoretical background 2.1. Thermal diffusivity measurements Fig. 1 presents the OPC apparatus used to determine the thermal diffusivity of the samples investigated. In this configuration, a planar sample is fixed on the top of a microphone, sealing it. The other surface of the sample is illuminated by the light coming from a light source Journal of Non-Crystalline Solids 426 (2015) 43–46 ⁎ Corresponding author. E-mail address: kleber@fisica.ufpr.br (K.D. Machado). http://dx.doi.org/10.1016/j.jnoncrysol.2015.06.025 0022-3093/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol