Multiple Regulation over Growth Direction, Band Structure,and Dimension of Monolayer WS2 by a Quartz Substrate
2020
A substrate
plays a crucial role in controlled growth and property
modulation of two-dimensional (2D) transition-metal dichalcogenides
(TMDCs). In this work, we report multiple regulation over growth direction,
band structure, and dimension of an epitaxial monolayer (1L) WS2 by an m-plane quartz substrate. The as-grown
WS2 is oriented on a 2-fold symmetric m-quartz based on an anisotropic lattice match, which is distinct
from that on c-sapphire. Owing to the large thermal
expansion coefficient, the m-quartz generates a large
compressive thermal strain in the as-grown WS2. By manipulating
this thermal strain, the band structure of 1L-WS2 can be
in situ regulated and a direct–indirect band gap transition
occurs when the thermal strain exceeds 0.5%. Moreover, the unique
atom distribution of the m-plane quartz established
an anisotropic diffusion barrier for adlayer monomers which restricted
the growth of WS2 uniaxially. By exploiting this, the dimension
of WS2 can be tailored from a 2D triangle to a one-dimensional
ribbon with controlled growth time. This work not only deepens the
understanding of the relationship between a substrate and a material
but also provides an effective way to directly regulate the as-grown
TMDCs with desirable structures and properties.
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