Doping of bulk silicon and III–V materials has paved the foundation of the current semiconductor industry. Controlled doping of 2D semiconductors, which can also be used to tune their bandgap and ...type of carrier thus changing their electronic, optical, and catalytic properties, remains challenging. Here the substitutional doping of nonlike element dopant (Mn) at the Mo sites of 2D MoS2 is reported to tune its electronic and catalytic properties. The key for the successful incorporation of Mn into the MoS2 lattice stems from the development of a new growth technology called dual‐additive chemical vapor deposition. First, the addition of a MnO2 additive to the MoS2 growth process reshapes the morphology and increases lateral size of Mn‐doped MoS2. Second, a NaCl additive helps in promoting the substitutional doping and increases the concentration of Mn dopant to 1.7 at%. Because Mn has more valance electrons than Mo, its doping into MoS2 shifts the Fermi level toward the conduction band, resulting in improved electrical contact in field effect transistors. Mn doping also increases the hydrogen evolution activity of MoS2 electrocatalysts. This work provides a growth method for doping nonlike elements into 2D MoS2 and potentially many other 2D materials to modify their properties.
A dual‐additive chemical vapor deposition method achieves the growth of large lateral size 2D MoS2 substitutionally doped with Mn. The doping of Mn on the Mo sites in MoS2 is confirmed by scanning transmission electron microscopy imaging and various spectroscopic characterizations. As a result, the Mn‐doped MoS2 exhibits improved electrical contact and better hydrogen evolution reaction activity.
Explosive detection has been receiving much attention for homeland security and global anti-terrorism. Most explosives are organic nitro-group-containing compounds. Numerous analytical methods have ...been applied for explosive detection, including mass spectrometry, X-ray imaging, ion mobility spectroscopy, and so on. However, these analytical methods are always time-consuming, expensive and inconvenient for practical applications. Fluorescence spectroscopy sensing technologies have provided an alternative detection method, but an aggregation-caused quenching (ACQ) effect of non-AIE based fluorescent materials limits their potential. Aggregation-induced emission (AIE) is, however, considered as an ideal solution to effectively overcome the above-mentioned ACQ effect, and AIE-active polymeric materials have been extensively applied for explosive detection. This review is to summarize the latest developments of AIE-active polymeric materials for the explosive detection in a more exhaustive and systematic way. First, the physics and chemistry of AIE-active polymers and mechanisms of explosive detection are overviewed. Then, the synthesis of AIE-active conjugated and non-conjugated polymers and their explosive detection are summarized with a special emphasis on establishing a relationship between the structures of AIE-active polymers and their sensing performance. At the end, perspectives and outlooks of AIE-active polymers for explosive detection are commented on.
This review is to summarize the latest progress on aggregation-induced-emission (AIE)-active polymers for explosive detection.
Carbon nanotubes have a helical structure wherein the chirality determines whether they are metallic or semiconducting. Using in situ transmission electron microscopy, we applied heating and ...mechanical strain to alter the local chirality and thereby control the electronic properties of individual single-wall carbon nanotubes. A transition trend toward a larger chiral angle region was observed and explained in terms of orientation-dependent dislocation formation energy. A controlled metal-to-semiconductor transition was realized to create nanotube transistors with a semiconducting nanotube channel covalently bonded between a metallic nanotube source and drain. Additionally, quantum transport at room temperature was demonstrated for the fabricated nanotube transistors with a channel length as short as 2.8 nanometers.
Inorganic chalcogenides are traditional high-performance thermoelectric materials. However, they suffer from intrinsic brittleness and it is very difficult to obtain materials with both high ...thermoelectric ability and good flexibility. Here, we report a flexible thermoelectric material comprising highly ordered Bi
Te
nanocrystals anchored on a single-walled carbon nanotube (SWCNT) network, where a crystallographic relationship exists between the Bi
Te
<Formula: see text> orientation and SWCNT bundle axis. This material has a power factor of ~1,600 μW m
K
at room temperature, decreasing to 1,100 μW m
K
at 473 K. With a low in-plane lattice thermal conductivity of 0.26 ± 0.03 W m
K
, a maximum thermoelectric figure of merit (ZT) of 0.89 at room temperature is achieved, originating from a strong phonon scattering effect. The origin of the excellent flexibility and thermoelectric performance of the Bi
Te
-SWCNT material is attributed, by experimental and computational evidence, to its crystal orientation, interface and nanopore structure. Our results provide insight into the design and fabrication of high-performance flexible thermoelectric materials.
Inorganic chalcogenides are traditional high-performance thermoelectric materials. However, they suffer from intrinsic brittleness and it is very difficult to obtain materials with both high ...thermoelectric ability and good flexibility. Here, we report a flexible thermoelectric material comprising highly ordered Bi2Te3 nanocrystals anchored on a single-walled carbon nanotube (SWCNT) network, where a crystallographic relationship exists between the Bi2Te3 <\\bar{1}2\bar{1}0\> orientation and SWCNT bundle axis. This material has a power factor of ~1,600 μW m−1 K−2 at room temperature, decreasing to 1,100 μW m−1 K−2 at 473 K. With a low in-plane lattice thermal conductivity of 0.26 ± 0.03 W m−1 K−1, a maximum thermoelectric figure of merit (ZT) of 0.89 at room temperature is achieved, originating from a strong phonon scattering effect. The origin of the excellent flexibility and thermoelectric performance of the Bi2Te3–SWCNT material is attributed, by experimental and computational evidence, to its crystal orientation, interface and nanopore structure. Our results provide insight into the design and fabrication of high-performance flexible thermoelectric materials.
Monolithic carbon aerogel composites with low density have been prepared from phenolic resin as a reactive precursor and ultralight and hyper-elastic carbon fiber felt as a soft reinforcement by a ...low-cost ambient pressure drying approach. During carbonization, the felt shrinks collaboratively with the phenolic aerogel so that the typical shrinkage mismatch between fibers and matrix can be overcome. Therefore, a robust, crack-free and large-size carbon fiber reinforced carbon aerogel composite was obtained, which has a low density (0.16 g cm−3), high compressive strength (0.93 MPa), extremely low thermal conductivity (0.03 Wm−1K−1) and outstanding ultrahigh temperature thermal insulation performance.
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Revealing the active phase and structure of catalyst nanoparticles (NPs) is crucial for understanding the growth mechanism and realizing the controlled synthesis of carbon nanotubes (CNTs). However, ...due to the high temperature and complex environment during CNT growth, precise identification of the active catalytic phase remains a great challenge. We investigated the phase evolution of cobalt (Co) catalyst NPs during the incubation, nucleation, and growth stages of CNTs under near-atmospheric pressure using an in situ close-cell environmental transmission electron microscope (ETEM). Strict statistical analysis of the electron diffractograms was performed to accurately identify the phases of the catalyst NPs. It was found that the NPs belong to an orthorhombic Co3C phase that remained unchanged during CNT growth, with errors in lattice spacing <5% and in angle <2°, despite changes in their morphology and orientation. Theoretical calculations further confirm that Co3C is the thermodynamically preferred phase during CNT growth, with the supply of carbon atoms through the surface and NP–CNT interfacial diffusion.
Abstract
Atomically thin 2D materials have received intense interest both scientifically and technologically. Bismuth oxyselenide (Bi
2
O
2
Se) is a semiconducting 2D material with high electron ...mobility and good stability, making it promising for high‐performance electronics and optoelectronics. Here, an ambient‐pressure vapor–solid (VS) deposition approach for the growth of millimeter‐size 2D Bi
2
O
2
Se single crystal domains with thicknesses down to one monolayer is reported. The VS‐grown 2D Bi
2
O
2
Se has good crystalline quality, chemical uniformity, and stoichiometry. Field‐effect transistors (FETs) are fabricated using this material and they show a small contact resistivity of 55.2 Ω cm measured by a transfer line method. Upon light irradiation, a phototransistor based on the Bi
2
O
2
Se FETs exhibits a maximum responsivity of 22 100 AW
−1
, which is a record among currently reported 2D semiconductors and approximately two orders of magnitude higher than monolayer MoS
2
. The Bi
2
O
2
Se phototransistor shows a gate tunable photodetectivity up to 3.4 × 10
15
Jones and an on/off ratio up to ≈10
9
, both of which are much higher than phototransistors based on other 2D materials reported so far. The results of this study indicate a method to grow large 2D Bi
2
O
2
Se single crystals that have great potential for use in optoelectronic applications.
1D materials have attracted significant research interest due to their unique quantum confinement effects and edge‐related properties. Atomically thin 1D nanoribbons are particularly interesting ...because it is a valuable platform with the physical limits of both thickness and width. Here, a catalyst‐free growth method is developed and the growth of Bi2O2Se nanostructures with tunable dimensionality is achieved. Significantly, Bi2O2Se nanoribbons with a thickness down to 0.65 nm, corresponding to a monolayer, are successfully grown for the first time. Electrical and optoelectronic measurements show that Bi2O2Se nanoribbons possess decent performance in terms of mobility, on/off ratio, and photoresponsivity, suggesting their promise for devices. This work not only reports a new method for the growth of atomically thin nanoribbons but also provides a platform to study properties and applications of such nanoribbon materials at a thickness limit.
Atomically thin nanoribbons represent a valuable platform to exploit the property of materials with physical limits of both thickness and width. A catalyst‐free chemical vapor deposition approach is developed to grow Bi2O2Se nanoribbons down to the monolayer. Electrical and optoelectronic measurements show that Bi2O2Se nanoribbons possess decent performance in terms of mobility, on/off ratio, and photoresponsivity, suggesting their promise for devices.
Homogeneous single‐layer graphene films are fabricated using an electrophoretic deposition technique, and their field‐emission properties are investigated. The graphene films show high density, ...uniform thickness, numerous edges normal to the film surface, and good interface contact and adhesion with the substrate, and consequently show excellent field‐emission properties.
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