Highly Stretchable and Conductive Core–Sheath Chemical Vapor Deposition Graphene Fibers and Their Applications in Safe Strain Sensors

Highly stretchable and conductive core–sheath nanofibers are significant for flexible and wearable microelectronics. Core–sheath fibers were massively fabricated from ultralong chemical vapor deposition (CVD)-grown graphene bundles. They exhibited superior conductivity and excellent mechanical properties that exceeded those of the reduced graphene oxide fibers. The intrinsic dynamic fracture procedure and mechanism of the core–sheath nanofibers were investigated. Furthermore, safe strain sensors based on as-prepared core–sheath CVD graphene fibers have been demonstrated as a proof-of-concept application. The performance of strain sensors has been greatly improved by using CVD graphene fibers

Carrier Control of MoS₂ Nanoflakes by Functional Self-Assembled Monolayers

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 <i>n</i>-doping characteristic of MoS₂ nanoflakes, while 3-(trimethoxysilyl)-1-propanamine-SAMs, acting as electron donors, enhanced the <i>n</i>-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

Synthesis of Few-Layer GaSe Nanosheets for High Performance Photodetectors

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

Gate Modulation of Threshold Voltage Instability in Multilayer InSe Field Effect Transistors

We report a modulation of threshold voltage instability of back-gated multilayer InSe FETs by gate bias stress. The performance stability of multilayer InSe FETs is affected by gate bias polar, gate bias stress time and gate bias sweep rate under ambient conditions. The on-current increases and threshold voltage shifts to negative gate bias stress direction with negative bias stress applied, which are opposite to that of positive bias stress. The intensity of gate bias stress effect is influenced by applied gate bias time and the sweep rate of gate bias stress. The behavior can be explained by the surface charge trapping model due to the adsorbing/desorbing oxygen and/or water molecules on the InSe surface. This study offers an opportunity to understand gate bias stress modulation of performance instability of back-gated multilayer InSe FETs and provides a clue for designing desirable InSe nanoelectronic and optoelectronic devices

Hierarchical Assembly of Tungsten Spheres and Epoxy Composites in Three-Dimensional Graphene Foam and Its Enhanced Acoustic Performance as a Backing Material

Backing materials play important role in enhancing the acoustic performance of an ultrasonic transducer. Most backing materials prepared by conventional methods failed to show both high acoustic impedance and attenuation, which however determine the bandwidth and axial resolution of acoustic transducer, respectively. In the present work, taking advantage of the structural feature of 3D graphene foam as a confined space for dense packing of tungsten spheres with the assistance of centrifugal force, the desired structural requirement for high impedance is obtained. Meanwhile, superior thermal conductivity of graphene contributes to the acoustic attenuation via the conversion of acoustic waves to thermal energy. The tight contact between tungstate spheres, epoxy matrix, or graphene makes the acoustic wave depleted easily for the absence of air barrier. The as-prepared 3DG/W_80 wt %/epoxy film in 1 mm, prepared using ∼41 μm W spheres in diameter, not only displays acoustic impedance of 13.05 ± 0.11 MRayl but also illustrates acoustic attenuation of 110.15 ± 1.23 dB/cm MHz. Additionally, the composite film exhibits a high acoustic absorption coefficient, which is 94.4% at 1 MHz and 100% at 3 MHz, respectively. Present composite film outperforms most of the reported backing materials consisting of metal fillers/polymer blending in terms of the acoustic impedance and attenuation

Solid-State Reaction Synthesis of a InSe/CuInSe₂ Lateral p–n Heterojunction and Application in High Performance Optoelectronic Devices

Graphene-like layered semiconductors are a new class of materials for next generation electronic and optoelectronic devices due to their unique electrical and optical properties. A p–n junction is an elementary building block for electronics and optoelectronics devices. Here, we demonstrate the fabrication of a lateral p–n heterojunction diode of a thin-film InSe/CuInSe₂ nanosheet by simple solid-state reaction. We discover that InSe nanosheets can be easily transformed into CuInSe₂ thin film by reacting with elemental copper at a temperature of 300 °C. Photodetectors and photovoltaic devices based on this lateral heterojunction p–n diode show a large photoresponsivity of 4.2 A W^–1 and a relatively high light-power conversion efficiency of 3.5%, respectively. This work is a giant step forward in practical applications of two-dimensional materials for next generation optoelectronic devices

Phase-Engineering-Driven Enhanced Electronic and Optoelectronic Performance of Multilayer In₂Se₃ Nanosheets

Here, we report electronic and optoelectronic performance of multilayer In₂Se₃ are effectively regulated by phase engineering. The electron mobility is increased to 22.8 cm² V^–1 s^–1 for β-In₂Se₃ FETs, which is 18 times higher than 1.26 cm² V^–1 s^–1 of α-In₂Se₃ FETs. The enhanced electronic performance is attributed to larger carrier sheet density and lower contact resistance. Multilayer β-In₂Se₃ photodetector exhibits an ultrahigh responsivity of 8.8 × 10⁴ A/W under 800 nm illumination, which is 574 times larger than 154.4 A/W of α-In₂Se₃ photodetector. Our results demonstrate phase-engineering is a valid way to tune and further optimize electronic and optoelectronic performance of multilayer In₂Se₃ nanodevices

Electrostatic Assembly Preparation of High-Toughness Zirconium Diboride-Based Ceramic Composites with Enhanced Thermal Shock Resistance Performance

The central problem of using ceramic as a structural material is its brittleness, which associated with rigid covalent or ionic bonds. Whiskers or fibers of strong ceramics such as silicon carbide (SiC) or silicon nitride (Si₃N₄) are widely embedded in a ceramic matrix to improve the strength and toughness. The incorporation of these insulating fillers can impede the thermal flow in ceramic matrix, thus decrease its thermal shock resistance that is required in some practical applications. Here we demonstrate that the toughness and thermal shock resistance of zirconium diboride (ZrB₂)/SiC composites can be improved simultaneously by introducing graphene into composites via electrostatic assembly and subsequent sintering treatment. The incorporated graphene creates weak interfaces of grain boundaries (GBs) and optimal thermal conductance paths inside composites. In comparison to pristine ZrB₂–SiC composites, the toughness of (2.0%) ZrB₂–SiC/graphene composites exhibited a 61% increasing (from 4.3 to 6.93 MPa·m^1/2) after spark plasma sintering (SPS); the retained strength after thermal shock increased as high as 74.8% at 400 °C and 304.4% at 500 °C. Present work presents an important guideline for producing high-toughness ceramic-based composites with enhanced thermal shock properties

In-Plane Mosaic Potential Growth of Large-Area 2D Layered Semiconductors MoS₂–MoSe₂ Lateral Heterostructures and Photodetector Application

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

Effective Synergistic Effect of Dipeptide-Polyoxometalate-Graphene Oxide Ternary Hybrid Materials on Peroxidase-like Mimics with Enhanced Performance

Dipeptide-polyoxometalates (POMs)-graphene oxide (GO) ternary hybrid is an excellent peroxidase-like mimic, exhibiting enhanced peroxidase-like activity compared to POMs alone. The hybrid was readily prepared through a reprecipitation method involving electrostatic encapsulation of H₃PW₁₂O₄₀ (PW₁₂) by cationic diphenylalanine (FF) peptide and coassembly of FF@PW₁₂ spheres with graphene oxide (GO). Using 3,3′,5,5′-tetramethylbenzidine (TMB) as the chromogenic substrate, the peroxidase-like activity of FF@PW₁₂ was evaluated in the heterogeneous phase, and it is 13 times higher than that of pristine PW₁₂ in the homogeneous phase. Furthermore, ternary hybrids of FF@PW₁₂@GO containing 5 wt % GO could enhance the activity 1.7 times higher than that of FF@PW₁₂. The noncovalent interactions of hydrogen bonding and ionic interaction between GO and POMs are speculated to result in the synergistic effect for the enhancement of peroxidase-like performance. The strong interactions between rGO and PW₁₂ are evaluated by a four-probe Hall measurement via the van der Pauw method, and rGO is significantly p-doped by the doping effect of PW₁₂ with lower LUMO energy than that of the energy level of rGO and also due to the electron reservoir feature of PW₁₂. Cyclic voltammogram measurements also suggest that GO causes significant influence on the electronic structure of the reduced forms of the redox couples of PW₁₂. The nature of the TMB catalytic reaction may originate from the generation of the hydroxyl radical (^•OH) from the decomposition of H₂O₂ by ternary hybrids and the formation of peroxo species of POM. Taking advantage of the UV–vis signals of TMB being correlated to the concentration of H₂O₂, FF@PW₁₂@GO can be used to detect H₂O₂ within the limit of detection of 0.11 μM, and the detection range is 1–75 μM. The present method indeed opens up a promising route in constructing heterogeneous peroxidase-like mimics through the use of POMs via the introduction of GO for building H₂O₂ sensors