Applied Science and Convergence Technology 2021; 30(3): 74-77
Published online May 30, 2021
Copyright © The Korean Vacuum Society.
aDepartment of Physics, Mokpo National University, Chonnam 58554, Republic of Korea
Correspondence to:E-mail: firstname.lastname@example.org
CoIn2S4. thin films were grown onto glass substrates by a spray pyrolysis method. For the growth, the substrate temperature was varied between 250 and 320 °C, and the spray rate was fixed at 6 ml/min. The grown thin films were characterized X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and optical spectroscopy. The XRD analysis showed that the thin films grown at 320 °C were well crystallized in cubic spinel structure. The FE-SEM results demonstrated that the thin films have a uniform and homogeneous surface. The direct band gap energy was first obtained from the measurement of optical absorption spectra near the fundamental absorption edge at 292 K, and was founded to be 1.59 eV. We also observed two group absorption bands in the near-infrared region, which originate in cobalt ions of the constituent elements of CoIn2S4.. The absorption bands were well assigned as due to the crystal-field transitions of Co2+ ions occupying tetrahedral sites of the cubic spinel CoIn2S4. host lattice.
Keywords: CoIn2S4., Thin films, Optical absorption, Band gap, Tetrahedral Co2+, Spray pyrolysis method
CoIn2S4, one of the type–
In the present paper, we report on the thin film growth of CoIn2S4 by the spray pyrolysis technique. The grown thin films were characterized by X-ray diffraction and field-emission scanning electron micro-scope measurements. The band gap energy at 292 K was first obtained by optical absorption spectroscopy measurements. Also, we discuss the absorption bands observed in the near-infrared region, which are originated in cobalt ions of the constituent elements of CoIn2S4. These absorption bands are analyzed in connection with
CoIn2S4 thin films were grown by the spray pyrolysis method . A spraying solution was prepared by dissolving CoCl2 (GA, Alfa Products), InCl3 (5N, Alfa Products) and thiourea (GA, Alfa Products) in 1:1 solvent solution composed of methanol (Merck-Analysis) and distilled water to give 0.2 molar solutions of each solute. Then these solutions were mixed in a volume ratio of 1:2:4, and at the same time an excess thiourea solution of 20 % was added in order to compensate the loss of sulphur caused by vaporization during the deposition. The final mixture of the solutions was magnetically stirred at 70 °C for 30 min. Then this solution has sprayed on a slide glass (Corning-2948) with a fixed spray rate of 6 ml⋅min−1 under ambient air. The substrate temperature was varied from 250 to 320 °C for film deposition.
The structural properties such as surface morphology and layer thickness of the grown thin films were characterized by using field-emission scanning electron microscope (FE-SEM, Hitachi, S-4800), and their crystalline phases and qualities were studied by X-ray diffraction (XRD, X’pert pro MPD) measurements. Also, the band gaps of CoIn2S4 and the
Figure 1 shows the XRD patterns of the CoIn2S4 thin films depending on the substrate temperature. The XRD patterns for the thin films grown at 250 °C of Fig. 1(a) shows a broad and weak peak near 2θ angle of 20~30∘, which is considered to be typical of amorphous thin films. As the substrate temperature increases, the XRD peaks become intense. For the thin films grown at the substrate temperature of 320 °C, as shown in Fig. 1(c), the XRD pattern shows a lot of planes (111), (220), (311), (400), (511), (440), (531), (533), and (444) of cubic spinel, except for the diffraction peak with a relatively weak intensity at 2θ = 22.336 originated from In2O3. It is in good agreement with that in JCPDS 03-065-5369 for CoIn2S4 crystals. The strong and sharp diffraction peaks suggest that the grown thin films were well crystallized. Also, the FE-SEM micrographs of surface and cross-section of the CoIn2S4 thin films grown at 320 °C are given in Fig. 2. The result depicts that the morphological features of the CoIn2S4 thin films have almost a uniform and homogeneous surface, and a thickness of 1.90 µm.
Figure 3 depicts optical absorption spectrum of the CoIn2S4thin films in the wavelength range of 250 to 3200 nm at 292 K. In Fig. 3 we can see some characteritics, i.e., a rapid rise in absorption near the regions of 780 and 2700 nm, and a relatively sharp absorption band in the wavelength range of 600 to 850 nm and a broad absorption band in the wavelength range of 1200 to 2400 nm. Among them, the rapid absorption near the 2700 nm-wavelength region originates in a slide glass used as a substrate, and also the arising of abrupt absorption near the 780 nm-wavelength region refers to the fundamental absorption. And the two absorption bands observed in the wavelength range of 650 to 850 nm and 1200 to 2400 nm are concerned with the
Now, we discuss the
CoIn2S4 thin films have been successfully grown on a slide glass at an optimal substrate temperature of 320 °C and a spray rate of 6 ml⋅min−1 by the spray pyrolysis method. The XRD analysis revealed that the films grown at 320 °C are well crystallized in single-phase cubic spinel structure. The FE-SEM micrographs depicted that the films have a uniform and homogeneous surface.
The nature and the magnitude of band-to-band transitions of the CoIn2S4 thin films were determined from the optical absorption spectrum analysis near the fundamental absorption edge in which the absorption effect due to the cobalt ions of the constituent elements was extracted. The result gives the direct band gap of 1.59 eV. Also, the two absorption bands observed in the near-infrared regions, which are originated in cobalt ions of constituent elements, are well assigned as due to the crystal-field transitions of Co2+ ions with the tetrahedral sites of the CoIn2S4 lattice. However, our results due to only tetrahedral Co2+ are somewhat different from those due to both octahedral and tetrahedral Co2+ reported in reflectance spectra of CoIn2S4 for x = 1.0 of Co
This research was supported by Research Funds of Mokpo National University in 2019.