Exploration on the growth of Bi₂O₂Se films and nanosheet by an ALD-assisted CVD method

The emerging two-dimensional bismuth selenium oxide (2D Bi₂O₂Se) has attracted great attention due to its high mobility and excellent air stability. Bi₂O₂Se with different morphologies, including the film and the nanosheet can be obtained by the chemical vapor deposition (CVD) method. However, the growth mode during the synthesis process is still unclear. In this work, we present systematic studies to understand the growth of Bi₂O₂Se films and nanosheet. The atomic layer deposition (ALD) method is first used to prepare the bismuth precursor for the CVD growth of Bi₂O₂Se. The amount of the precursor can be effectively controlled by the ALD method, and it is helpful to understand the growth of the Bi₂O₂Se. It is found that the Bi₂O₂Se films can be fabricated at a relatively low temperature. The films on the mica substrates follow the layer-by-layer growth mode and those on silicon substrates exhibit a three-dimensional growth mode. The Bi₂O₂Se nanosheets can be obtained at higher temperatures on mica substrate and the topography is affected greatly by the concentration of the precursor. The vapor–solid reaction is considered to play the major role during the growth process with low temperature and the vapor–vapor reaction prevails during the growth at higher temperature. In summary, we have provided a new preparation strategy and investigated the growth process of the emerging 2D Bi₂O₂Se. The study about the large-scale films and high-quality nanosheets may open up a new path for the urgent need for the preparation and the device fabrication of Bi₂O₂Se.