Antimony Tri-Sulfide (Sb2S3) Nanowires Synthesis and Characterization
Authors: Tsai An-Ni , Wang Chiu-Yen 
Published: February 2020

During the past decade, one-dimensional (1D) nanostructures such as wires, rods, belts, and tubes have been explored extensively in nanotechnology due to their excellent properties, which may lead to unique applications in various nanoscale device. It is known that nanowires with high aspect ratios can provide a low-scattering transport path of the carriers and the electron and hole energy states become discrete due to the spatial confinement, which are highly beneficial for achieving high-performance electrical or optical properties.
Antimony tri-sulfide (Sb2S3) is a low-toxic and earth-abundant semiconductor and important binary chalcogenide, that with an energy band gap varying between 1.78 and 2.2 eV has attracted particular attention and . Owing to its good photovoltaic properties, high thermoelectric power, suitable valence band position, and broad spectrum the response. Sb2S3 used in technological applications such as photo-catalysis, photovoltaics, and thermoelectric devices[1-2] . It has a direct band gap with large absorption coefficient (>104 cm−1) in the visible region. Especially, it has wide application in optical property because of wide band gap and the other point is the thermoelectric property of Sb2S3. The Sb2S3 of NWs show excellent light-to-heat performance. In this work, Sb2S3 nanowires (NWs) were fabricated by a vacuum hydraulic pressure injection process using anodic aluminum oxide (AAO) as templates. The AAO quality depends on the purity of Al substrate. The higher Al purity, such as 99.999% (5N), the better quality of AAO with uniform pore diameter can be obtained. The AAO templates with, 70 nm, and 100 nm diameters are manufactured by anodizing a pure aluminum (Al) substrate (99.999%) in acid solutions of oxalic acid (COOH)2. It will help us to easily get a large quantity and uniform Sb2S3 NWs. The nanomaterials arrayed photoelectric devices have great potential to obtain high sensitivity, fast response, and low energy consumption. The highly ordered array nanostructure can be achieved with high-aspect-ratio template. Porous anodic aluminium oxide played a significant role for the fabrication of Sb2S3, which controlled the diameter of NWs. Compare to the other synthesis, vacuum hydraulic pressure injection process is easy way to fabricate heterogeneous structure. First, antimony tri-sulfide powder was prepared by Sb/S=2/3 in a vacuum quartz tube and make the powder homogeneous mixing. Then, it was melted at 650 oC for 20 min and homogenized at 520 oC for 1 day. Then, the Sb2S3 of ingot was slowly cooling to room temperature. After Sb2S3 ingot was obtained, mechanical polishing was conducted to remove surface oxide. Second, the ingot of Sb2S3 was placed between the two plates of AAO template. Next, the entire chamber was vacuumed and heated to 600 oC again, holding the temperature for 5 min, load 50 kgf / cm2 for 1 min to press. Then, the melting Sb2S3 is pressed into the AAO template to form Sb2S3 nanowire array. Finally, the entire chamber was cooled down under air atmosphere and etch the AAO of Sb2S3. It will obtain the nanowires. Moreover, we will observe the different condition of NWs by controlling the time of etching. The time of etching decides the cleanness of NWs. As the time is longer the mass of bundles will decrease. Also, the difference of acid solutions is one of the important condition of etching the NWs, such as phosphoric acid (H3PO4), chromic acid (H2CrO4). In this work, we use chromic acid to etching the AAO to obtain the NWs. The temperature of the acid solution also affect the rate of etching speed. The temperature of etching is kept at around 60 oC. Combination of above conditions, the diameter of NWs is around 70 nm, the length of NWs is about 6 µm. Furthermore, The morphologies and crystal structures of Sb2S3 NWs were characterized by using optical microscopy (OM), field-emission scanning electron microscope (FE-SEM), X-Ray diffraction (XRD), UV-Vis spectrophotometry, Raman spectroscopy and transmission electron microscopy (TEM). The composition was analyzed with energy dispersive x-ray spectroscopy (EDS) attached the SEM. In the future, we can fabricate the heterogeneous structure of Sb system and Sb2S3 NWs to increase the diversity of the research on electrical and optical applications.
Ref.
[1] Kai Zhang, Tao Luo, Haoran Chen, Zheng Lou and Guozhen Shen, Au-nanoparticles-decorated Sb2S3 nanowirebased flexible ultraviolet/visible photodetectors.. J. Mater. Chem. C, 2017, 5, 3330-3335.
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