Tuning
the structural and electronic properties of atomically thin two-dimensional
(2D) materials via defect and vacancy engineering is the key to enabling
their potential use in various applications, including electronics,
energy, and sensing devices. Vacancies are, for instance, becoming
highly promising for the enhanced interaction of gases and biomolecules
with
2D materials in energy and sensing applications. However, the deterministic
generation of desirable vacancies with tunable concentrations remains
a challenge in 2D materials due to the limitations in the current
growth methods, such as the complex reaction chemistries and gas flow
dynamics. Therefore, engineering defects and vacancies in 2D materials
have been mainly limited to destructive top-down processes such as
heating, ion bombardments, and laser postprocessing. Here, we introduce
a single-step bottom-up synthesis approach for the growth of monolayer
MoSe2 crystals with tunable vacancy concentrations. This
method utilizes the spatiotemporal properties and adjustable power
densities of the lasers to control the vaporization dynamics of the
stoichiometric MoSe2 powders. Such a mechanism in the vaporization
allows us to grow tunable stoichiometry monolayer MoSe2–x
crystals on the substrates. The localized and time-controlled
(250 ms to 2 s) vaporization of the MoSe2 powder by a CO2 laser enables the formation of monolayer crystals with controlled
vacancy concentrations ranging from ∼1 to 20%. The effects
of laser power, laser irradiation time, and background pressure on
the tuning range and subsequent properties of the crystals are investigated
and quantified using Raman and photoluminescence spectroscopy, scanning
transmission electron microscopy (STEM), and time-correlated single-photon
counting (TCSPC). This bottom-up synthesis is a promising approach
that allows the deterministic vacancy tuning for future electronics
and, in particular, gas and biosensing applications without the need
for further postprocessing and potential structural disruption of
the crystals.