2D materials, with their extraordinary physical and chemical properties, have gained extensive interest for physical, chemical and biological sensing applications. However, 2D material-based devices, such as field effect transistors (FETs) often show high contact resistance and low output signals, which severely affect their sensing performance. In this study, a new strategy is developed to combine metallic and semiconducting polymorphs of transition-metal dichalcogenides (TMDCs) to solve this critical issue. Such a phase engineering methodology to integrate large-scale and spatially assembled multilayers of 2H MoTe 2 FETs with coplanar metallic 1T′ MoTe 2 contacts is applied. Such in-plane heterophase-based FETs exhibit an ohmic contact behavior with an extremely low contact resistance due to the coplanar and seamless connections between 2H and 1T′ phases of MoTe 2 . These 1T′/2H/1T′ based FETs are successfully demonstrated for detecting NH 3 with high current outputs increased up to microamp levels without using any conventional interdigital electrodes, which is compatible with the current CMOS circuits for practical applications. Furthermore, the as-fabricated sensors can detect NH 3 gas concentrations down to 5 ppm at room temperature. This study demonstrates a new strategy of applying the heterophase MoTe 2 -based nanoelectronics for high-performance sensing applications.
Tuning the optical and electrical
properties of two-dimensional
(2D) hexagonal boron nitride (hBN) is critical for its successful
application in optoelectronics. Herein, we report a new methodology
to significantly enhance the optoelectronic properties of hBN monolayers
by substitutionally doping with sulfur (S) on a molten Au substrate
using chemical vapor deposition. The S atoms are more geometrically
and energetically favorable to be doped in the N sites than in the
B sites of hBN, and the S 3p orbitals hybridize with the B 2p orbitals,
forming a new conduction band edge that narrows its band gap. The
band edge positions change with the doping concentration of S atoms.
The conductivity increases up to 1.5 times and enhances the optoelectronic
properties, compared to pristine hBN. A photodetector made of a 2D
S-doped hBN film shows an extended wavelength response from 260 to
280 nm and a 50 times increase in its photocurrent and responsivity
with light illumination at 280 nm. These enhancements are mainly due
to the improved light absorption and increased electrical conductivity
through doping with sulfur. This S-doped hBN monolayer film can be
used in the next-generation electronics, optoelectronics, and spintronics.
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