WS₂ Nanotubes, 2D Nanomeshes, and 2D In-Plane Films through One Single Chemical Vapor Deposition Route

Abstract

We demonstrate a versatile, catalyst free chemical vapor deposition process on insulating substrates capable of producing in one single stream one-dimensional (1D) WO3–x suboxides leading to a wide range of substrate-supported 2H-WS2 polymorphs: a tunable class of out-of-plane (of the substrate) nanophases, with 1D nanotubes and a pure WS2, two-dimensional (2D) nanomesh (defined as a network of webbed, micron-size, few-layer 2D sheets) at its extremes; and in-plane (parallel to the substrate) mono- and few-layer 2D domains. This entails a two-stage approach in which the 2WO3 + 7S → 2WS2 + 3SO2 reaction is intentionally decoupled. First, various morphologies of nanowires or nanorods of high stoichiometry, WO2.92/WO2.9 suboxides (belonging to the class of Magnéli phases) were formed, followed by their sulfurization to undergo reduction to the aforementioned WS2 polymorphs. The continuous transition of WS2 from nanotubes to the out-of-plane 2D nanomesh, via intermediary, mixed 1D-2D phases, delivers tunable functional properties, for example, linear and nonlinear optical properties, such as reflectivity (linked to optical excitations in the material), and second harmonic generation (SHG) and onset of saturable absorption. The SHG effect is very strong across the entire tunable class of WS2 nanomaterials, weakest in nanotubes, and strongest in the 2D nanomesh. Furthermore, a mechanism via suboxide (WO3–x ) intermediate as a possible path to 2D domain growth is demonstrated. 2D, in-plane WS2 domains grow via “self-seeding and feeding” where short WO2.92/WO2.9 nanorods provide both the nucleation sites and the precursor feedstock. Understanding the reaction path (here, in the W–O–S space) is an emerging approach toward controlling the nucleation, growth, and morphology of 2D domains and films of transition-metal dichalcogenides.

“Hot” in Plasmonics: Temperature‐Related Concepts and Applications of Metal Nanostructures

“…Together with 2D materials, metal surfaces/interfaces of single layer thickness, are among the thinnest possible sources of SHG. However, in metal surfaces, the typical frequency conversion efficiency is of ≈10 −15 .…”

Tungsten disulfide: synthesis and applications in electrochemical energy storage and conversion

“…Generally, WO 3 is always the first choice as a cheap and easily handled precursor with relatively low melting and evaporation temperature [70]. WO 3 can be easily volatized to the sub-oxide WO 3-x [71], rendering the growth of WS 2 by CVD operable in the low pressure and atmospheric pressure systems [72,73]. However, the aforementioned proposed mechanisms were applicable to the growth of WS 2 nanotubes.…”

“…However, the aforementioned proposed mechanisms were applicable to the growth of WS 2 nanotubes. Till recently, Liu et al [71] demonstrated the possible mechanism of using WO 3−x as the intermediate to guide the growth of 2D WS 2 . Their results manifested the growth of 2D in-plane WS 2 followed the principle of "self-seeding and feeding", in which short WO 3-x nanorods were acted as both the nucleation sites and the precursor material (Fig.…”

“…Schematic evolution with sulfurization time (Δt) of the WO 3-x cores into 2D WS 2 nanosheets. Reproduced with permission from Ref [71]…”

Interface Kinetics Assisted Barrier Removal in Large Area 2D-WS2 Growth to Facilitate Mass Scale Device Production

“…Rong’s group [ 28 ] achieved precise control over S introduction time by utilizing a two-zone furnace and obtained very large area WS 2 films of 370 μm domain size. Recently, Liu et al [ 36 ] reported sequential synthesis of several one-, and two-dimensional nanomaterials by intentionally creating initial low sulfur conditions, to divide the growth process in two stages: the first stage is a partial reduction and the second one is sulfurization. By this, they could exploit a WO 3- x intermediate route, and were able to grow large size WS 2 (150 µm).…”