Step-Edge-Guided Nucleation and Growth of Aligned WSe sub(2) on Sapphire via a Layer-over-Layer Growth Mode

• Published in: ACS nano Vol. 9; no. 8; pp. 8368 - 8375
• Main Authors: Chen, Liang, Liu, Bilu, Ge, Mingyuan, Ma, Yuqiang, Abbas, Ahmad N, Zhou, Chongwu
• Format: Journal Article
• Language: English
• Published: 05-08-2015
• Subjects: Alignment; Chemical vapor deposition; Flakes; Grain boundaries; Molybdenum disulfide; Nucleation; Sapphire; Two dimensional
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.5b03043

Two-dimensional (2D) materials beyond graphene have drawn a lot of attention recently. Among the large family of 2D materials, transitional metal dichalcogenides (TMDCs), for example, molybdenum disulfides (MoS sub(2)) and tungsten diselenides (WSe sub(2)), have been demonstrated to be good candidates for advanced electronics, optoelectronics, and other applications. Growth of large single-crystalline domains and continuous films of monolayer TMDCs has been achieved recently. Usually, these TMDC flakes nucleate randomly on substrates, and their orientation cannot be controlled. Nucleation control and orientation control are important steps in 2D material growth, because randomly nucleated and orientated flakes will form grain boundaries when adjacent flakes merge together, and the formation of grain boundaries may degrade mechanical and electrical properties of as-grown materials. The use of single crystalline substrates enables the alignment of as-grown TMDC flakes via a substrate-flake epitaxial interaction, as demonstrated recently. Here we report a step-edge-guided nucleation and growth approach for the aligned growth of 2D WSe sub(2) by a chemical vapor deposition method using C-plane sapphire as substrates. We found that at temperatures above 950 degree C the growth is strongly guided by the atomic steps on the sapphire surface, which leads to the aligned growth of WSe sub(2) along the step edges on the sapphire substrate. In addition, such atomic steps facilitate a layer-over-layer overlapping process to form few-layer WSe sub(2) structures, which is different from the classical layer-by-layer mode for thin-film growth. This work introduces an efficient way to achieve oriented growth of 2D WSe sub(2) and adds fresh knowledge on the growth mechanism of WSe sub(2) and potentially other 2D materials. Keywords: tungsten diselenides; transition metal dichalcogenides; TMDCs; chemical vapor deposition; sapphire; aligned growth; layer-over-layer