KAUST Catalysis Center, Physical Science and Engineering Division, King Abdullah University of Science and Technology , Thuwal 23955-6900, Kingdom of Saudi Arabia.
ACS Nano. 2017 Sep 26;11(9):9215-9222. doi: 10.1021/acsnano.7b04323. Epub 2017 Aug 15.
Two-dimensional (2D) transition-metal dichalcogenide (TMDC) semiconductors are important for next-generation electronics and optoelectronics. Given the difficulty in growing large single crystals of 2D TMDC materials, understanding the factors affecting the seed formation and orientation becomes an important issue for controlling the growth. Here, we systematically study the growth of molybdenum disulfide (MoS) monolayer on c-plane sapphire with chemical vapor deposition to discover the factors controlling their orientation. We show that the concentration of precursors, that is, the ratio between sulfur and molybdenum oxide (MoO), plays a key role in the size and orientation of seeds, subsequently controlling the orientation of MoS monolayers. High S/MoO ratio is needed in the early stage of growth to form small seeds that can align easily to the substrate lattice structures, while the ratio should be decreased to enlarge the size of the monolayer at the next stage of the lateral growth. Moreover, we show that the seeds are actually crystalline MoS layers as revealed by high-resolution transmission electron microscopy. There exist two preferred orientations (0° or 60°) registered on sapphire, confirmed by our density functional theory simulation. This report offers a facile technique to grow highly aligned 2D TMDCs and contributes to knowledge advancement in growth mechanism.
二维(2D)过渡金属二卤化物(TMDC)半导体对于下一代电子学和光电子学至关重要。鉴于生长大尺寸 2D TMDC 材料单晶的困难,了解影响晶种形成和取向的因素对于控制生长变得非常重要。在此,我们通过化学气相沉积法系统地研究了钼二硫化物(MoS)单层在 c 面蓝宝石上的生长,以发现控制其取向的因素。我们表明,前驱体的浓度,即硫和氧化钼(MoO)之间的比例,对晶种的大小和取向起着关键作用,从而控制 MoS 单层的取向。在生长的早期阶段需要高的 S/MoO 比来形成易于与衬底晶格结构对齐的小晶种,而在下一个横向生长阶段应降低该比例以扩大单层的尺寸。此外,我们通过高分辨率透射电子显微镜表明,晶种实际上是结晶的 MoS 层。通过我们的密度泛函理论模拟证实,在蓝宝石上存在两个优先取向(0°或 60°)。本报告提供了一种生长高取向二维 TMDC 的简便技术,并为生长机制的知识进步做出了贡献。