Flexible Foil of Hybrid TaS₂/Organic Superlattice: Fabrication and Electrical Properties

Abstract

2D transitional metal dichalcogenide (2D-TMDC) materials, as inorganic graphene analogs (IGAs), have been intensively investigated for their novel chemical and physical properties when the thickness is reduced to a few atomic layers, such as MoS 2 , WS 2 , among others. [1] Tantalum disulfide, TaS 2 , one of the TMDC materials, has attracted growing attention recently. In the bulk state, TaS 2 occupies 2H or 1T structure, which is composed of covalently bonded STaS layers. 1T-TaS 2 with Ta in octahedral coordination with S atoms exhibits semiconducting behavior, and it has a commensurate charge density wave (CCDW) phase under 180 K. Adjusted by pressure, the superconductivity of 1T-TaS 2 develops in the CCDW state and survives to very high pressure. [2][3][4] 2H-TaS 2 with Ta in trigonal prismatic coordination with S atoms exhibits metallic behaviors with CDW phase transition (T CDW = 75 K) and superconductivity (T c = 0.8 K). [5][6][7][8] The electrical conductivity of single-crystal 2H-TaS 2 can reach 6.8 × 10 4 S m −1 at room temperature. [9] When the thickness is reduced to a few layers, interesting phenomena have been found, such as gate-tunable phase transition [10] and enhanced superconductivity, [11] which are promising properties for applications like electrical oscillators, [12] fast memories, [13] hydrogen evolution catalyst. [14] Until now, 2D TaS 2 has been mainly synthesized by the mechanical exfoliation method, [15] which is time consuming and of poor reproductivity and low yield. It has been noticed that the exfoliation of TaS 2 seems rather difficult and the atomically thin layers are unstable in ambient environments due to easy oxidation. [16] Complex encapsulation techniques are therefore required to help preserve the samples in air. [16] The chemical vapor deposition method [17] proves to be swift and effective in fabrication of high-quality 2D materials, but large-area synthesis of full-coverage atomically thin material is still in progress. For device applications, solution-based chemical synthesis is particularly important, as the product can be easily integrated into electronic devices.There is a new solution-based strategy to synthesize 2D materials in the form of inorganic/organic superlattice, in which the inorganic layers may get close to the low-dimensional state due to the spatial separation by the organic molecules. In our previous papers, we synthesized a hybrid superlattice with alternating 2D [TiS 2 ] monolayers and organic cations through an electrochemical reaction process. [18] The isolation of the [TiS 2 ] TaS 2 nanolayers with reduced dimensionality show interesting physics, such as a gate-tunable phase transition and enhanced superconductivity, among others. Here, a solution-based strategy to fabricate a large-area foil of hybrid TaS 2 /organic superlattice, where [TaS 2 ] monolayers and organic molecules alternatively stack in atomic scale, is proposed. The [TaS 2 ] layers are spatially isolated with remarkably weakened interlayer bonding, resulting in lattice vibration ...

Photocatalytic activity of twist-angle stacked 2D TaS2

“…Its initial metallicity and, thus, electrical conductivity can lead to potential applications such as a light-responsive active electrode in the HER and photosensing. Albeit the study of TaS 2 is mainly focused on the superconductivity [22][23][24] , field emission 25,26 , photo-induced features of the material for HER and photosensing have not been explored yet. Aiming to enhance the photoresponse performance of the TaS 2 , the quality and dimensions of the material must be considered.…”

Regulating Intercalation of Layered Compounds for Electrochemical Energy Storage and Electrocatalysis

“…c) Schematic diagram of solution-based synthesis processes of intercalated TaS 2 HA x NMF y . Reproduced with permission [199]. Copyright 2015, Wiley.…”

High thermoelectric performance in flexible TiS₂/organic superlattices

“…In addition, through the cation-dipole effect, neutral polar organic solvents, such as N-methyl formamide (NMF) 29) and DMSO, 17) can also enter the interlayer to participate in the superlattice during the electrochemical intercalation process, and can be controlled by a solvent exchange to optimize structures and performances. 14),17) The polar solvents that can be used for exchange range from small molecules, such as water 21) and ethylene glycol (EG), to polymers, such as polyethylene glycol (PEG), 14) which is a feasible way to synthesize inorganic/polymer superlattices.…”

“…Lewis bases represented by transition metal compounds with unfulfilled d orbitals can react with a variety of electron donors, including nitrogen atoms with the lone pair electrons and carbon rings with extended ³ bond. The synthesis strategy of superlattice based on Lewis acid-base reactions has been applied in TaS 2 29) and SnSe 2 . 31) In order to facilitate the thermoelectric performance testing, the TiS 2 /organic superlattice powder further selfassembles into tailorable free-standing foils with an alternatively stacked structure through the co-intercalation of the solvents and exfoliation of nanosheets.…”