Atomic layer deposition-enabled single layer of tungsten trioxide across a large area

Abstract Reduction from multi-layer to one fundamental layer thickness represents a variety of exotic properties and distinctive applications of such two-dimensional (2D) semiconductor as tungsten trioxide (WO 3 ). This transition without damaging single layer on a large spatial resolution remained elusive until the atomic layer deposition (ALD) technique was utilized. Here we report for the first time the ALD-enabled atomic-layer-precision development of a single layer WO 3 with thickness of 0.7 ± 0.07 nm across a large area by using ( t BuN) 2 W(NMe 2 ) 2 as tungsten precursor and H 2 O as oxygen precursor, without affecting the underlying SiO 2 /Si substrate. Versatility of ALD is in tuning recipe in order to achieve the complete WO 3 with desired number of WO 3 layers including monolayer. Governed by self-limiting surface reactions, the ALD-enabled approach is versatile, scalable and applicable for a broader range of 2D semiconductors and various device applications. Photodetector based on monolayer WO 3 exhibited extremely ultra-fast photo-response of ∼1.0 ms.