Microstructural and optical properties of Sn4Sb6S13 nanocrystals deposited on PAA templates
Graphical abstract
Introduction
In recent years, the ternary SnxSbySz compounds have attracted a lot of attention due to their excellent optical and electrical properties in different technological applications in various fields, including thermoelectric energy conversion [1], solar cells [[2], [3], [4]], and sensors [[5], [6], [7], [8]]. Moreover, tin antimony sulfur (TAS) Sn4Sb6S13 nanomaterial can offer novel opportunities for thermo-electronic and solar energy applications due to their cheaper cost, low toxicity and high absorbance [[9], [10], [11]].
Nowadays, the porous anodic alumina (PAA) layer with highly ordered pore arrangement structure and controlled pores diameters can be used as support for growing nanomaterials on which gas sensor and photovoltaic applications are based [[12], [13], [14], [15], [16], [17]]. PAA template has been used as a suitable substrate for depositing various nanomaterials and alloys with various sizes, shapes, and nature, such as Si nanocrystals (NCs) and nanowires (NWs), SnO2 nanotubes (NTs), Ti particles, Ni-Fe alloys, Cu and Ni nanowires (NWs), CdSe NRs, and LiCoO2 NRs [[18], [19], [20], [21], [22], [23], [24], [25], [26]]. The deposition of TAS nanocrystals on PAA template might be used in applications such as photocatalysis and solar energy technology. Due to the porous surface, the PAA substrate is able to accommodate more nanomaterials than planar surface substrates. The effect of the nanoporous alumina substrate on the growth of Sn4Sb6S13 nanocrystals and on their morphological and optical properties has not been studied yet. In this context, we study the effect of PAA template and the deposition temperature on the growth of the TAS compounds and their microstructural and optical properties. In this work, we report the PAA synthesis process by using electrochemical anodization. We also describe the growth of TAS nanocrystals on the PAA template by means of a vacuum thermal evaporation method. This research aims at studying the influences of the porous substrate and the deposition temperature on microstructural, morphological and optical properties of the TAS film. X-Ray diffraction (XRD) and Raman spectroscopy are used to supply information on the stresses, microstrain and crystalline quality of the TAS/PAA. The surface morphology of TAS films on PAA substrates is presented by using the scanning electron microscope (SEM) and atomic force microscopy (AFM). Energy dispersive X-ray (EDX) analysis is performed to determine the elemental compositions of PAA and TAS/PAA layers. UV–vis–NIR spectroscopy is used to measure the evolution of total reflectivity of the TAS film deposited on PAA substrate as a function of deposition temperature. In this study, we have performed ellipsometric measurements to determine the optical parameters (n and k), dielectric constants (εr and εi), and thickness of the TAS/PAA structures deposited at various temperatures.
Section snippets
Elaboration of the PAA templates
PAA films were synthesized on aluminum foils (Al purity > 99.999 %) by electrochemical anodization in a two-step process using 10% sulfuric acid solution under a constant voltage of 25 V for 45 min at 10 °C [18,27,28]. The initial PAA films obtained in the first step were completely removed from the Al substrate using an acid mixture solution (H2SO4: 28 %, H3PO4: 60 %, HNO3: 12 %). The second anodization step was performed under the same conditions as the first step in order to obtain PAA
SEM and EDX analysis
In Fig. 1(a), the top view SEM images of as-prepared PAA layer on aluminum foil are shown. The surface morphology of the PAA layer exhibits hexagonal pore arrays with high regularity and average pores diameter of about 30 nm. The SEM micrographs of the TAS films prepared on PAA substrate at various deposition temperatures (from 30 to 200 °C) are shown in Fig. 1(b–f). A partially smooth surface with the presence of some voids was observed for the TAS film deposited at 30 °C (Fig. 1(b)). As
Conclusion
TAS nanocrystals were successfully deposited on the PAA templates at various temperatures via the vacuum thermal evaporation method. Using SEM and AFM microscopes, we found that the PAA template pores were hexagonally arranged with an average pore size of 30 nm. The TAS thin films deposited on PAA at different temperatures caused an evolution in the crystal sizes and shapes, which exhibit an elongated TAS nanocolumn array with average diameter in the range of 17-19 nm. The XRD and Raman
Author statement
I hereby assure that the contents of this article are original and have neither been published elsewhere in any language fully or partly, nor under review for publication anywhere.
Declaration of Competing Interest
None.
Acknowledgements
The author is grateful to the Tunisian Ministry of Higher Education and Scientific Research for its financial support.
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