We report a systematic study of large-scale growth of high-quality WSe2 atomic layers directly on SiO2/Si substrates using a convenient method. Various parameters, especially growth temperatures, flow rate of carrier gas and tube pressure, are investigated in affecting the properties of as-grown WSe2 flakes in terms of their sizes, shapes and thickness. The pre-annealing step is demonstrated to be a key role in achieving the large-scale growth. Under an optimized condition, the lateral size of triangular single-crystal monolayer WSe2 is up to 30 μμm and the area of the monolayer thin film can be up to 0.25 mm2. And some other interesting features, such as nanoflowers, are observed, which are a promising for catalyzing research. Raman spectrum and microphotoluminescence indicate distinct layer dependent efficiency. Auger electron spectroscopy (AES) studies demonstrate the atomic concentration of the as-grown WSe2. Electrical transport further shows that the pp-type WSe2 field-effect transistors exhibit excellent electrical properties with carrier mobility of ∼∼64 cm2⋅2⋅V−1⋅−1⋅s−1−1 and current on/off ratio over 105. These results are comparable to the exfoliated materials.
