(20) However, the CVD technique is quite challenging and is strongly dependent on the precursorsвЂ™ chemistry and process parameters. Currently, the superior WS 2 layers containing the big crystalline domains up to several hundreds of Ојm were obtained by CVD. In contrast, chemical vapor deposition (CVD) (17) and direct atomic layer deposition (ALD) (18,19) easily provide wafer-scale coverage with a precise thickness control. Bulk crystal exfoliation cannot satisfy this requirement since it does not provide precise control over the thickness and material properties (16) as well as not scalable to industrial standards. (14,15) In this regard, the controllable WS 2 synthesis with a given structure over a large area is an essential task for practical applications. While the large-area films with a terrace-terminated structure and a given number of monolayers are most relevant for optoelectronic applications, an edge-terminated film structure with a large number of dangling bonds is desirable for catalysis applications. (13) Each of these applications requires a specific film structure. (7,8) Moreover, it also demonstrated good catalytic, (9,10) gas-sensing, (11,12) and chemical-sensitive properties. (5,6) Relatively high mobility and tunable band gap in the visible optical range make this material promising for use in electronic and optoelectronic devices. Theoretical calculations predict that WS 2 should possess the highest carrier mobility among other semiconducting 2D TMDs due to the reduced effective carrier mass. (4) In addition to this, an indirect-to-direct band gap transition occurs on decreasing the thickness down to a single monolayer. (1в€’3) 2H-WS 2 is a semiconductor with the band gap varying from 1.3 to 2.1 eV, depending on the number of layers. Tungsten disulfide is a representative of the class of two-dimensional (2D) transition-metal dichalcogenides (TMDs), which are characterized by a layered structure with adjacent layers bonded with van der Waals forces. Most valuably, it was shown that the growth of the thinnest WS 2 film (3вЂ“4 monolayers) is most challenging due to the amorphous intergrain phase formation, and further investigations focused on preventing the intergrain phase formation should be conducted. These results show that the thickness of the ALD-grown seed layer may strongly affect the resultant WS 2 structure and properties. cm) within the investigated thickness range.The observed structural evolution affected the film resistivity, which was found to decrease from в€ј10 6 to 10 3 (ОјО© The increase in the seed-film thickness of up to 4.7 nm resulted in a visible grain size decrease down to 15вЂ“20 nm, which was accompanied by defect suppression. The signs of incomplete sulfurization, namely, oxysulfide phase presence, were found by X-ray photoemission spectroscopy analysis. Transmission electron microscopy indicated that the thinnest (1.9 nm) film contains rather big (up to 50 nm) WS 2 grains in the amorphous matrix.

In this work, we investigated the influence of atomic layer deposition (ALD)-grown WO 3 seed-film thickness on the structural and electrical properties of WS 2 nanosheets obtained via a sulfurization technique. Therefore, their synthesis over a large area, allowing control over their thickness and structure, is an essential task. Mo interdiffusion is therefore responsible for the pronounced donor character of the initially inert oxide, and largely modifies its adsorption and reactivity behavior.Ultrathin WS 2 films are promising functional materials for electronic and optoelectronic devices. For example, exposure of O 2 results in the formation of superoxo species on the oxide surface, as revealed from STM measurements. While near-interface Mo transfers extra electrons back to the substrate, generating an interface dipole that gives rise to the observed band shift, near-surface species are able to exchange electrons with adsorbates bound to the oxide surface. The subsequent changes in the Mo oxidation state have been followed with high-resolution XPS measurements. The Mo substitutes divalent Ca species in the rocksalt lattice and is able to release electrons to the system. This evolution is explained with a temperature-induced diffusion of Mo ions from the metal substrate to the oxide and their accumulation in the interface region of the film. Upon annealing or reducing the thickness of the film, a rigid shift of the CaO bands to lower energy is revealed. The electronic structure of CaO films of 10вЂ“60 monolayer thickness grown on Mo(001) has been investigated with synchrotron-mediated x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM).

Xps peak shift film thickness