Synthesis of TaS₂ Nanotubes From Ta₂O₅ Nanotube Templates

Abstract

The discovery that layered transition metal dichalcogenide (TMD) materials such as WS 2[1] and MoS 2 [2] can form nanotubes and other inorganic fullerene-type structures has generated considerable interest in the study and synthesis of nanomaterials consisting of two-dimensional (2D), layered structures. [3][4][5] One unique property of TMD nanomaterials includes superior tribological behavior; [6] other applications include use as solid lubricants, [7] catalysts for hydrosulfurization, [8] and hydrogen-storage devices. [9] Control over the nanoscale architecture could also greatly accelerate investigations of finite size effects on complex electronic properties such as superconductivity and charge-density wave (CDW) behavior. For example, tantalum disulfide (TaS 2 ) displays three polytypes where Ta atoms are covalently bonded between two layers of S atoms in trigonal prismatic (2H), octahedral (1T), or mixed (6R) coordinations. [10] Investigations of structureproperty relationships of TaS 2 nanomaterials have been limited, however, because they can neither be produced in high yield nor with control over the crystalline structure.Tubular TaS 2 nanomaterials have been synthesized by the hydrogen reduction of TaS 3 precursors [11] but the crystal structure could not be determined because of sample degradation under the electron beam. Other nanostructures of TaS 2 include fullerene-like TaS 2 nanoparticles produced by a gas-phase reaction [12] and TaS 2 nanoplates formed by laser ablation [13] or from molecular precursors. [14] 2H-TaS 2 nanowires synthesized from elemental Ta and S by chemical vapor transport exhibited a superconductivity transition temperature (T c ¼ 3.4 K) higher than that of bulk 2H-TaS 2 (0.8 K). [15] Recently, we demonstrated synthetic control over the size, shape, and polytype of surface-patterned TaS 2 nanostructures by converting nanopatterned tantalum oxide (Ta 2 O 5 ) to TaS 2 using a gas-phase reaction. [14] Here we report how large quantities of crystalline TaS 2 multi-walled nanotubes can be synthesized starting from Ta 2 O 5 nanotube templates. We achieved control over the length, diameter, and the number of TaS 2 layers within the nanotube. Our template-based approach produced a high yield of structurally uniform nanotubes, which opens up possibilities for potential scalable applications. Also, we observed that the electronic properties were different from the bulk, where the T c of the TaS 2 nanotubes was elevated, and the CDW transition temperature (T CDW ) was suppressed. Figure 1a depicts the scheme for converting Ta 2 O 5 nanotubes to multi-walled TaS 2 nanotubes. First, largearea arrays (%3.5 Â 10 10 tubes cm À2 ) of amorphous Ta 2 O 5 communications [ Ã ] Prof.Figure 1. a) Scheme of chemical conversion process to synthesize TaS 2 nanotubes starting from Ta 2 O 5 nanotube templates. b) SEM image of Ta 2 O 5 nanotube arrays formed after anodizing the Ta film. c) TEM image of a Ta 2 O 5 nanotube. d) Photograph of bulk quantities of TaS 2 nanotubes.1096

Synthesis of Coral-Like Tantalum Oxide Films via Anodization in Mixed Organic-Inorganic Electrolytes

“…Many methods could be used to synthesize them. As for the preparation of nano tantalum oxide, the anodization is a very popular and efficient approach that has been widely investigated under different conditions [6]–[11], [19]–[22]. The tantalum oxide films with compact structure could be synthesized in different fluoride–free electrolytes such as mineral acids, organic acids, salt solutions and oxidizing agents at anodization voltages typically between 100 V and 200 V over a wide range of temperatures, which were well documented in the literature [23].…”

“…Of late, various nano materials with different morphologies were successfully fabricated, e.g. nanotube [6]–[11], nano pyramidal arrays [12], nano dimple arrays [13], nano hollow spheres [14], [15] and nano coral-like materials [16]–[18]. Many methods could be used to synthesize them.…”

“…Normally, the introduction of fluoride ion was believed to be essential to the formation of nano morphologies [8]. The structures of nano pores and nanotube could be achieved when the anodization process was performed in the highly corrosive electrolyte such as the mixture of HF and H 2 SO 4 [6]–[11], [21]–[22]. However, only in the concentrated H 2 SO 4 was it possible to obtain the nanotubular morphology [6]–[11].…”

“…The structures of nano pores and nanotube could be achieved when the anodization process was performed in the highly corrosive electrolyte such as the mixture of HF and H 2 SO 4 [6]–[11], [21]–[22]. However, only in the concentrated H 2 SO 4 was it possible to obtain the nanotubular morphology [6]–[11]. Moreover, it was reported that relatively low concentrations of organic additives would be of benefit to the growth of nanotube [9].…”

Noble-Metal Chalcogenide Nanotubes

“…They have also been suggested as scanning probe tips [18], catalysts [19], reinforcements for composite materials [20], photo-transistors [21], gas storage and host materials [22,23], etc. Later, other transition-metal chalcogenide (TMC) NTs have been reported such as TiS 2 , NbS 2 , ReS 2 , TiSe 2 and TaS 2 [24][25][26][27][28]. Subsequently, many more TMC NTs can be expected due to the large manifold of the layered TMC materials [29,30].…”