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The synthesis of stoichiometric two-dimensional (2D) transition-metal dichalcogenides (TMDC) over large areas remains challenging. Using a combination of X-ray diffraction and X-ray absorption spectroscopy, we demonstrate the advantages of using a thin amorphous layer of S-rich MoS2(MoS4in this paper) for the growth of well-ordered crystalline MoS2films via annealing at 900 °C. In contrast to the crystallization of stoichiometric amorphous MoS2, the crystallization of the as-deposited amorphous MoS4phase shows the strong preferred ordering of layered MoS2on a Si/SiOxnontemplating substrate with the dominant (002) crystallographic plane and accompanying Kiessig fringes, which indicate the improved crystallinity of the MoS2layers. A similar effect can only be achieved by the templated crystallization of an amorphous MoS2thin film deposited on a c-plane sapphire substrate. We suggest that the crystal growth improvement originates from the lower coordination number (CN) of the Mo atoms in the MoS4amorphous phase (CN = 4) in comparison with that of amorphous MoS2(CN = 6) and the gradual release of free sulfur atoms from the thin film during crystallization.

The continuous emission of nitrous oxides contributes to the overall air pollution and deterioration of air quality. In particular, an effective NO2sensor capable of low concentration detection for continuous monitoring is demanded for safety, health, and wellbeing. The sensing performance of a metal oxide-based sensor is predominantly influenced by the availability of surface area for O2adsorption and desorption, efficient charge transport, and size or thickness of the sensing layer. In this study, we utilized anodic one-dimensional (1D) TiO2nanotube layers of 5 μm thick which offer large surface area and unidirectional electron transport pathway as a platform to accommodate thin SnO2coatings as a sensing layer. Conformal and homogeneous SnO2coatings across the entire inner and outer TiO2nanotubes were achieved by atomic layer deposition with a controlled thickness of 4, 8, and 16 nm. The SnO2-coated TiO2nanotube layers attained a higher sensing response than a reference Figaro SnO2sensor. Specifically, the 8 nm SnO2-coated TiO2nanotube layer has recorded up to ten-fold enhancement in response as compared to the blank nanotubes for the detection of 1 ppm NO2at an operating temperature of 300 °C with 0.5 V applied bias. This is attributed to the SnO2/TiO2heterojunction effect and controlled SnO2thickness within the range of the Debye length. We demonstrated in this work, a tailored large surface area platform based on 1D nanotubes with thin active coatings as an efficient approach for sensing applications and beyond.