Two-dimensional (2D) semiconductor nanomaterials hold great promises for future electronics and optics. In this paper, a 2D nanosheets of ultrathin GaSe has been prepared by using mechanical cleavage ...and solvent exfoliation method. Single- and few-layer GaSe nanosheets are exfoliated on an SiO2/Si substrate and characterized by atomic force microscopy and Raman spectroscopy. Ultrathin GaSe-based photodetector shows a fast response of 0.02 s, high responsivity of 2.8 AW–1 and high external quantum efficiency of 1367% at 254 nm, indicating that the two-dimensional nanostructure of GaSe is a new promising material for high performance photodetectors.
The first GaS nanosheet-based photodetectors are demonstrated on both mechanically rigid and flexible substrates. Highly crystalline, exfoliated GaS nanosheets are promising for optoelectronics due ...to strong absorption in the UV–visible wavelength region. Photocurrent measurements of GaS nanosheet photodetectors made on SiO2/Si substrates and flexible polyethylene terephthalate (PET) substrates exhibit a photoresponsivity at 254 nm up to 4.2 AW–1 and 19.2 AW–1, respectively, which exceeds that of graphene, MoS2, or other 2D material-based devices. Additionally, the linear dynamic range of the devices on SiO2/Si and PET substrates are 97.7 dB and 78.73 dB, respectively. Both surpass that of currently exploited InGaAs photodetectors (66 dB). Theoretical modeling of the electronic structures indicates that the reduction of the effective mass at the valence band maximum (VBM) with decreasing sheet thickness enhances the carrier mobility of the GaS nanosheets, contributing to the high photocurrents. Double-peak VBMs are theoretically predicted for ultrathin GaS nanosheets (thickness less than five monolayers), which is found to promote photon absorption. These theoretical and experimental results show that GaS nanosheets are promising materials for high-performance photodetectors on both conventional silicon and flexible substrates.
A cross-linked silica and polyvinyl alcohol (PVA) hybrid material was prepared via a sol–gel process for use as a highly transparent, thermostable and mechanically strong coating. The effect of the H ...2 O/TEOS ratio on the properties of the silica/PVA hybrid films, such as transmittance, thermal stability, mechanical strength, adhesive strength and hygrothermal resistance, is discussed herein. A strong chemical interaction between PVA and silica is indicated by the weakening of the C–OH peak and the formation of a Si–O–C peak in the XPS results. This interaction is further confirmed by the decrease in the PVA crystallinity from 23.29% to 2.56%, and the reduction in the silica/PVA melting point from 204.3 °C to 122.0 °C. This excellent compatibility between PVA and silica makes silica/PVA disperse well in solution with a dendritic-like or spherical morphology, and leads to a 97% increase in visible light transmittance. Therefore, compared with pure PVA, the obtained silica/PVA hybrid films are transparent. Even though the mass percentage of silica in the material is beyond 50 wt%, its Young's modulus is much improved from 0.17 ± 0.03 GPa to 2.52 ± 0.10 GPa, its ultimate tensile strength is enhanced from 40.1 ± 9.27 MPa to 80.3 ± 2.5 MPa, and its adhesive strength is increased from 475 N (1.52 MPa) to 712 ± 90 N (2.29 MPa) and it can almost maintain super hygrothermal resistance after 15 hygrothermal aging cycles. It is believed that the obtained silica/PVA hybrid could be used as a high-performance coating with excellent transparency, thermostability and mechanical strength.
Carrier doping of MoS2 nanoflakes was achieved by functional self-assembled monolayers (SAMs) with different dipole moments. The effect of SAMs on the charge transfer between the substrates and MoS2 ...nanoflakes was studied by Raman spectroscopy, field-effect transistor (FET) measurements, and Kelvin probe microscope (KFM). Raman data and FET results verified that fluoroalkyltrichlorosilane-SAM with a large positive dipole moment, acting as hole donors, significantly reduced the intrinsic n-doping characteristic of MoS2 nanoflakes, while 3-(trimethoxysilyl)-1-propanamine-SAMs, acting as electron donors, enhanced the n-doping characteristic. The additional built-in electric field at the interface between SiO2 substrates and MoS2 nanoflakes induced by SAMs with molecular dipole moments determined the charge transfer process. KFM results clearly demonstrated the charge transfer between MoS2 and SAMs and the obvious interlayer screening effect of the pristine and SAM-modified MoS2 nanoflakes. However, the KFM results were not fully consistent with the Raman and FET results since the externally absorbed water molecules were shown to partially shield the actual surface potential measurement. By eliminating the contribution of the water molecules, the Fermi level of monolayer MoS2 could be estimated to modulate in a range of more than 0.45–0.47 eV. This work manifests that the work function of MoS2 nanoflakes can be significantly tuned by SAMs by virtue of affecting the electrostatic potential between the substrates and MoS2 nanoflakes.
Considering the unique layered structure and novel optoelectronic properties of individual MoS2 and MoSe2, as well as the quantum coherence or donor–acceptor coupling effects between these two ...components, rational design and artificial growth of in-plane mosaic MoS2/MoSe2 lateral heterojunctions film on conventional amorphous SiO2/Si substrate are in high demand. In this article, large-area, uniform, high-quality mosaic MoS2/MoSe2 lateral heterojunctions film was successfully grown on SiO2/Si substrate for the first time by chemical vapor deposition (CVD) technique. MoSe2 film was grown along MoS2 triangle edges and occupied the blanks of the substrate, finally leading to the formation of mosaic MoS2/MoSe2 lateral heterojunctions film. The composition and microstructure of mosaic MoS2/MoSe2 lateral heterojunctions film were characterized by various analytic techniques. Photodetectors based on mosaic MoS2/MoSe2 lateral heterojunctions film, triangular MoS2 monolayer, and multilayer MoSe2 film are systematically investigated. The mosaic MoS2/MoSe2 lateral heterojunctions film photodetector exhibited optimal photoresponse performance, giving rise to responsivity, detectivity, and external quantum efficiency (EQE) up to 1.3 A W–1, 2.6 × 1011 Jones, and 263.1%, respectively, under the bias voltage of 5 V with 0.29 mW cm–2 (610 nm), possibly due to the matched band alignment of MoS2 and MoSe2 and strong donor–acceptor delocalization effect between them. Taking into account the similar edge conditions of transition metal dichalcogenides (TMDCs), such a facile and reliable approach might open up a unique route for preparing other 2D mosaic lateral heterojunctions films in a manipulative manner. Furthermore, the mosaic lateral heterojunctions film like MoS2/MoSe2 in the present work will be a promising candidate for optoelectronic fields.
High-precision gas sensors operated at room temperature are attractive for various real-time gas monitoring applications, with advantages including low energy consumption, cost effectiveness and ...device miniaturization/flexibility. Studies on sensing materials, which play a key role in good gas sensing performance, are currently focused extensively on semiconducting metal oxide nanostructures (SMONs) used in the conventional resistance type gas sensors. This topical review highlights the designs and mechanisms of different SMONs with various patterns (
e.g.
nanoparticles, nanowires, nanosheets, nanorods, nanotubes, nanofilms,
etc.
) for gas sensors to detect various hazardous gases at room temperature. The key topics include (1) single phase SMONs including both n-type and p-type ones; (2) noble metal nanoparticle and metal ion modified SMONs; (3) composite oxides of SMONs; (4) composites of SMONs with carbon nanomaterials. Enhancement of the sensing performance of SMONs at room temperature can also be realized using a photo-activation effect such as ultraviolet light. SMON based mechanically flexible and wearable room temperature gas sensors are also discussed. Various mechanisms have been discussed for the enhanced sensing performance, which include redox reactions, heterojunction generation, formation of metal sulfides and the spillover effect. Finally, major challenges and prospects for the SMON based room temperature gas sensors are highlighted.
A comprehensive review on designs and mechanisms of semiconducting metal oxides with various nanostructures for room-temperature gas sensor applications.
Graphene, with amazing physical and chemical properties, exhibits great potential for next-generation electronic devices. Promising achievements were obtained in recent years. Nevertheless, there are ...challenges before the industrialization of graphene-based electronic devices (G-EDs), which present opportunities as well. Mass-production of graphene and the growing G-EDs are the major issues. In this perspective, we briefly outline the notable advances in the production of graphene and the development of diverse G-EDs. Then we probe into the critical challenges on the way of G-EDs and provide corresponding strategies. Finally, we give our expectations of G-EDs in the near future.
The electrocatalytic hydrogen evolution reaction (HER) has attracted increasing attention in the field of hydrogen-based economy, whereat developing cheap and efficient catalysts to reduce the use of ...Pt-based catalysts is highly required. Tin disulfide (SnS2) as a new rising star has exhibited intriguing properties in energy storage and conversion applications, while showing slow progress in HER due to the inherent poor activity. Herein, we demonstrate the successful structural engineering and simultaneous integration of trace amount Pt in SnS2 nanosheets via a facile and effective in situ cycling voltammetry activation process, leading to the efficiently synergistic HER. Defect-rich SnS2 nanosheets decorated with a trace amount (0.37 wt %) of Pt exhibit greatly enhanced HER activity due to the synergy between them, revealing low onset potential of 32 mV and overpotential of 117 mV at 10 mA/cm2, small Tafel slope of 69 mV/dec, and large exchange current density of 394.46 μA/cm2. Present work provides an intriguing strategy for developing ultralow loading Pt electrocatalysts with high HER performance.
Carbon fiber reinforced composites have stimulated increasing attention due to their excellent mechanical properties. However, the interface tends to be weak because carbon fiber does not naturally ...have a good wettability and adsorption with most polymers matrix, which could not effectively transfer the load from the matrix to the fibers. Here we proposed to chemically functionalize carbon fiber (CF) by poly (amido amine) (PAMAM), which has more concentration of amino groups than traditional coupling agents. The chemical bond formation between acid-treated CF and PAMAM was confirmed. The PAMAM functionalization did not change the surface morphology while significantly increased the wettability of CF surface. The interfacial shear strength has an increase of 85% compared to that without functionalization. The interfacial enhancement mechanism was also explored in details.
In order to increase the response speed of the InSe‐based photodetector with high photoresponsivity, graphene is used as the transparent electrodes to modify the difference of the work function ...between the electrodes and the InSe. As expected, the response speed of InSe/graphene photodetectors is down to 120 μs, which is about 40 times faster than that of an InSe/metal device. It can also be tuned by the back‐gate voltage from 310 μs down to 100 μs. With the high response speed, the photoresponsivity can reach as high as 60 A W−1 simultaneously. Meanwhile the InSe/graphene photodetectors possess a broad spectral range at 400–1000 nm. The design of 2D crystal/graphene electrical contacts can be important for high‐performance optoelectronic devices.
By using graphene as the transparent electrodes to modify the difference of the work function between the electrodes and the InSe, the response time of an InSe‐based photodetector can be down to 120 μs. It can also be tuned by the back‐gate voltage from 310 μs down to 100 μs. Simultaneously, the photoresponsivity can reach as high as 60 A W−1.
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