  Two-dimensional layered ReX2 (X = Se, S) has attracted researcher's great
interest due to its unusual in-plane anisotropic optical and electrical
properties and great potential in polarization-sensitive optoelectronic
devices, while the clean, energy-saving, and ecological synthesis of
highly-crystalline ReSe2 with controlled domains remains challenging yet
promising. Here, we develop a novel space-confined solid-phase approach for the
growth of high-quality two-domain 1T'-ReSe2 with tunable optoelectronic
properties by using pure Re powder film as Re precursor. The results show that
ReSe2 can be grown at a temperature as low as 550 oC in a small-tube-assisted
space-confined reactor, with its size and shape well-tailored via temperature
control. A solid-phase two-domain ReSe2 growth mechanism is proposed, as
evidenced by combining in-situ optical monitoring, ex-situ electron microscope
and elemental mapping, and polarized optical imaging. Moreover, we have
fabricated two-domain ReSe2 transistors, which exhibit switchable transport
behavior between n-type and ambipolar character via grain boundary orientation
control. This modulation phenomenon is attributed to the different doping
levels between the grain boundary and the single domain. Furthermore, the
as-fabricated two-domain ReSe2 photodetectors exhibit a highly gate-tunable
current on-off ratio (with a maximum value of ~8.2x10^3), a
polarization-sensitive photo-response, and a high-speed response time (~300
us), exceeding most of the previously reported ReX2 photodetectors. Our work
thus provides a new, low-consumption, energy-saving growth strategy toward
high-quality, domain-controlled ReX2 for highly tunable and high-performance
optoelectronics.
