Synthesis of tungsten ditelluride thin films and highly crystalline nanobelts from pre-deposited reactants

Tungsten ditelluride (WTe2) is a layered transition metal dichalcogenide (TMD) that has attracted increasing research interest in recent years. WTe2 has demonstrated large non-saturating magnetoresistance, potential for spintronic applications and promise as a type-II Weyl semimetal. The majority of works on WTe2 have relied on mechanically exfoliated flakes from chemical vapour transport (CVT)-grown crystals for their investigations. While producing high-quality samples, this method is hindered by several disadvantages including long synthesis time, high-temperature annealing and an inherent lack of scalability. In this work, a synthesis method is demonstrated that allows the production of large-area polycrystalline films of WTe2. This is achieved by the reaction of pre-deposited films of W and Te at a relatively low temperature of 550 °C. Sputter X-ray photoelectron spectroscopy reveals the rapid but self-limiting nature of the oxidation of these WTe2 films in ambient conditions. The WTe2 films are composed of areas of micrometre-sized nanobelts that can be isolated and offer potential as an alternative to CVT-grown samples. These nanobelts are highly crystalline with low defect densities indicated by transmission electron microscopy and show promising initial electrical results.