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Atomically thin narrow-bandgap layered PdSe2 has attracted much attention due to its rich and unique electrical properties. For silicon-compatible device integration, direct wafer-scale preparation of high-quality PdSe2 thin film on a silicon substrate is highly desired. Here, we present the low-temperature synthesis of large-area polycrystalline PdSe2 films grown on SiO2/Si substrates by plasma-assisted metal selenization and investigate their charge carrier transport behaviors. Raman analysis, depth-dependent X-ray photoelectron spectroscopy, and cross-sectional transmission electron microscopy were used to reveal the selenization process. The results indicate a structural evolution from initial Pd to intermediate PdSe2-x phase and eventually to PdSe2. The field-effect transistors fabricated from these ultrathin PdSe2 films exhibit strong thickness-dependent transport behaviors. For thinner films (4.5 nm), a record high on/off ratio of 104 was obtained. While for thick ones (11 nm), the maximum hole mobility is about 0.93 cm2 V-1 S-1, which is the record high value ever reported for polycrystalline films. These findings suggest that our low-temperature-metal-selenized PdSe2 films have high quality and show great potential for applications in electrical devices.

Cobalt was chosen as the doping element for BiFeO3 (BFO), and pure BFO and a series of BiFe1−x Co x O3 (x = 0.03, 0.05, 0.07, 0.09) nanoparticles, correspondingly labeled as nBFCO (n = 3, 5, 7, 9), were successfully prepared and investigated based on the sol-gel method in this paper. The synthesized nanoparticles were characterized by x-ray diffraction, field emission scanning electron microscopy, Brunauer−Emmett−Teller surface area, x-ray photoelectron spectroscopy and ultraviolet-visible light absorption. With the increase in the doping level of cobalt in BFO, a competing structure wandering between rhombohedral and orthorhombic structures was observed in the experiment. For instance, the microstructure characterization clearly indicates coexistence of the rhombohedral and orthorhombic structures in 7BFCO. Meanwhile, the bandgap of BFO was significantly reduced from 2.04 eV to 1.78 eV. The photocatalytic degradation of Rhodamine B of samples in an aqueous solution was investigated under different wavelengths of light. We found that 7BFCO was the optimal proportion for acquiring the photocatalytic and magnetic activity in this work, e.g. the photocatalytic efficiency can reach 98.2%. The underlying physics based on the lattice structure, size effects and energy gap is also discussed.

Photodetectors based on two-dimensional/three-dimensional (2D/3D) semiconducting heterostructures have attracted tremendous attention in recent years due to their novel performance. Here, we found that the photodetection performance of the graphene (Gr)/Si 2D/3D heterostructure can be very broadly enhanced by introducing an optimized ultrathin WS2 film prepared by sulfidation as an interfacial layer. The fabricated Gr/WS2(10.9 nm)/Si photodetector shows a wide spectralresponse from 400 to 1800 nm with a maximum photoresponsivity of 8.96 × 104 A W−1 and photodetectivity of 8.86 × 1011 Jones at 690 nm, which are more than three orders of magnitude higher than that of the Gr/Si photodetector. Such a high photoresponsivity can be attributed to the strong photogain induced by the hole trap states that exist in the WS2 film. With the increase in the WS2 film thickness, the photoresponsivity increases firstly owing to the increase of hole trap states, and then decreases due to the decrease in light transmittance through WS2. The device also shows a high responsivity of 0.735 A W−1 at 1550 nm by forming type-II interlayer excitation. Our results indicate that 2D transition metal dichalcogenides (TMDCs) could be a good candidate functioning as an interfacial layer for high performance Gr/Si photodetectors, which provide a facile way for enhancing the photodetection performance of van der Waals 2D/3D heterostructure photodetectors.

Semiconducting two-dimensional (2D) layered materials have shown great potential in next-generation electronics due to their novel electronic properties. However, the performance of field effect transistors (FETs) based on 2D materials is always environment-dependent and unstable under gate bias stress. Here, we report the environment-dependent performance and gate-induced instability of few-layer p-type WSe2-based FETs. We found that the hole mobility of the transistor drastically reduces in vacuum and further decreases after in situ annealing in vacuum compared with that in air, which can be recovered after exposure to air. The on-current of the WSe2 FET increases with positive gate bias stress time but decreases with negative gate bias stress time. For the double sweeping transfer curve, the transistor shows prominent hysteresis, which depends on both the sweeping rate and the sweeping range. Large hysteresis can be observed when a slow sweeping rate or large sweeping range is applied. In addition, such gate-induced instability can be reduced in vacuum and further reduced after in situ vacuum annealing. However, the gate-induced instability cannot be fully eliminated, which suggests both gases adsorbed on the device and defects in the WSe2 channel and/or the interface of WSe2/SiO2 are responsible for the gate-induced instability. Our results provide a deep understanding of the gate-induced instability in p-type WSe2 based transistors, which may shed light on the design of high-performance 2D material-based electronics.

Due to the ultra-thin nature and moderate carrier mobility, semiconducting two-dimensional (2D) materials have attracted extensive attention for next-generation electronics. However, the gate bias stress instability and hysteresis are always observed in these 2D materials-based transistors that significantly degrade their reliability for practical applications. Herein, the origin of gate bias stress instability and hysteresis for chemical vapor deposited monolayer WS2 transistors are investigated carefully. The transistor performance is found to be strongly affected by the gate bias stress time, sweeping rate and range, and temperature. Based on the systematical study and complementary analysis, charge trapping is determined to be the major contribution for these observed phenomena. Importantly, due to these charge trapping effects, the channel current is observed to decrease with time; hence, a rate equation, considering the charge trapping and time decay effect of current, is proposed and developed to model the phenomena with excellent consistency with experimental data. All these results do not only indicate the validity of the charge trapping model, but also confirm the hysteresis being indeed caused by charge trapping. Evidently, this simple model provides a sufficient explanation for the charge trapping induced gate bias stress instability and hysteresis in monolayer WS2 transistors, which can be also applicable to other kinds of transistors.

Since the discovery of graphene in 2004, it has become a worldwide hot topic due to its fascinating properties. However, the zero band gap and weak light absorption of graphene strictly restrict its applications in optoelectronic devices. In this regard, semiconducting two-dimensional (2D) materials are thought to be promising candidates for next-generation optoelectronic devices. Infrared (IR) light has gained intensive attention due to its vast applications, including night vision, remote sensing, target acquisition, optical communication, etc. Consequently, the generation, modulation, and detection of IR light are crucial for practical applications. Due to the van der Waals interaction between 2D materials and Si, the lattice mismatch of 2D materials and Si can be neglected; consequently, the integration process can be achieved easily. Herein, we review the recent progress of semiconducting 2D materials in IR optoelectronic devices. Firstly, we introduce the background and motivation of the review. Then, the suitable materials for IR applications are presented, followed by a comprehensive review of the applications of 2D materials in light emitting devices, optical modulators, and photodetectors. Finally, the problems encountered and further developments are summarized. We believe that milestone investigations of IR optoelectronics based on 2D materials beyond graphene will emerge soon, which will bring about great industrial revelations in 2D material-based integrated nanodevice commercialization.

In this study, using gadolinium (Gd) as a dopant, Gd-WO3/Ag/Gd-WO3 (WGd–Ag–WGd) transparent conductive films with improved electrochromic (EC) and energy storage performance were fabricated on glass substrates by reactive sputtering. The EC performance and sheet resistance of WGd–Ag–WGd are shown to be sensitive to the concentration of the Gd dopant. The optimized structure for transparent conducting (TC) coating is obtained to be Gd-WO3 (52 nm)/Ag (12 nm)/Gd-WO3 (42 nm) with a luminous transmittance of 82.7% and a sheet resistance of 3.4 Ω sq−1 at a modest Gd doping concentration of 0.29 at%. Such a film (sample size of 1 cm × 3 cm) exhibits luminous transmittance modulation (ΔTlum = 49.6%), high coloration efficiency (71.4 cm2 C−1 at 633 nm), fast switching time (1.6 s for coloring and 3.2 s for bleaching time), and long-term cycling stability (2000 cycles) with an applied potential of ±1.0 V. By combining the film structure characterization and electrochemical analysis, such a decent performance can be attributed to the embedded island structured monoclinic Gd2O3 on the surface of WO3 which enhanced charge capacity and reaction kinetics compared with undoped amorphous WO3 films. Moreover, the WGd–Ag–WGd films showed superior capacitive capability with a maximum specific capacitance of 124.7 F g−1 at 2 A g−1, suggesting their potential application in electrochemical energy storage (ECES) devices.

Due to the efficient photocarrier separation and collection coming from their distinctive band structures, superlattice nanowires (NWs) have great potential as active materials for high-performance optoelectronic devices. In this work, InGaZnO NWs with superlattice structure and controllable stoichiometry are obtained by ambient-pressure chemical vapor deposition. Along the NW axial direction, perfect alternately stacking of InGaO(ZnO)

Because of their fascinating properties, two-dimensional (2D) nanomaterials have attracted a lot of attention for developing next-generation electronics and optoelectronics. However, there is still a lack of cost-effective, highly reproducible, and controllable synthesis methods for developing high-quality semiconducting 2D monolayers with a sufficiently large single-domain size. Here, utilizing a NaOH promoter and W foils as the W source, we have successfully achieved the fabrication of ultralarge single-domain monolayer WS2 films via a modified chemical vapor deposition method. With the proper introduction of a NaOH promoter, the single-domain size of monolayer WS2 can be increased to 550 μm, while the WS2 flakes can be well controlled by simply varying the growth duration and oxygen concentration in the carrier gas. Importantly, when they are fabricated into global backgated transistors, WS2 devices exhibit respectable peak electron mobility up to 1.21 cm2 V-1 s-1, which is comparable to those of many state-of-the-art WS2 transistors. Photodetectors based on these single-domain WS2 monolayers give an impressive photodetection performance with a maximum responsivity of 3.2 mA W-1. All these findings do not only provide a cost-effective platform for the synthesis of high-quality large single-domain 2D nanomaterials, but also facilitate their excellent intrinsic material properties for the next-generation electronic and optoelectronic devices.

Spinel oxides (AB2O4) with unique crystal structures have been widely explored as promising alternative catalysts for efficient oxygen evolution reactions; however, developing novel methods to fabr...

Amorphous indium—gallium—zinc oxide (a-IGZO) materials have been widely explored for various thin-film transistor (TFT) applications; however, their device performance is still restricted by the intrinsic material issues especially due to their non-crystalline nature. In this study, highly crystalline superlattice-structured IGZO nanowires (NWs) with different Ga concentration are successfully fabricated by enhanced ambient-pressure chemical vapor deposition (CVD). The unique superlattice structure together with the optimal Ga concentration (i.e., 31 at.%) are found to effectively modulate the carrier concentration as well as efficiently suppress the oxygen vacancy formation for the superior NW device performance. In specific, the In1.8Ga1.8Zn24O7 NW field-effect transistor exhibit impressive device characteristics with the average electron mobility of ~ 110 cm2·V−1·s−1 and on/off current ratio of ~ 106. Importantly, these NWs can also be integrated into NW parallel arrays for the construction of high-performance TFT devices, in which their performance is comparable to many state-of-the-art IGZO TFTs. All these results can evidently indicate the promising potential of these crystalline superlattice-structured IGZO NWs for the practical utilization in next-generation metal-oxide TFT device technologies.

Due to the superior optoelectronic properties of halide perovskites, it has attracted wide attentions during the past decade, especially in the field of energy. When the dimension of halide perovskites reduces, novel properties will appear, such as large exciton binding energy, high photoluminescence quantum yield, and enlarged band gap. This way, low dimensional halide perovskites, especially two-dimensional (2D) halide perovskites, have attracted intensive attention in recent years and showed promising applications, including photodetectors, light emitting diodes (LEDs), and solar cells. Various methods were then developed for the synthesis of 2D halide perovskites and studying the exciting optoelectronic properties. The optoelectronic devices based on 2D halide perovskites showed excellent performance, particularly high sensitive photodetection, high electroluminescence with sharp emission peak, and environmental stable solar cells with decent power conversion efficiency. In this case, 2D halide perovskites become superstar materials in perovskites research area. In this review, we summarize the recent progresses in the synthesis and energy applications of 2D halide perovskites, and challenges and future directions in the field.

Recently, due to the excellent and tunable optoelectrical properties, quasi-two-dimensional (quasi-2D) layered perovskites have attracted tremendous attention for next-generation optoelectronic devices. However, fabricating high-quality 2D perovskite films, especially with low trap density, is still a challenge. Here, we successfully incorporate different concentrations of FA and Cs cations (i.e. mixed cations) into the quasi-2D perovskites of (iBA)2(MA)3Pb4I13 (FA = formamidinium; iBA = iso-butylamine; MA = methylamine) to modulate their thin film qualities, improving their subsequently fabricated device performances. When configured into photodetectors on rigid substrates, the optimal mixed cation-incorporated (iBA)2(MA)3Pb4I13 perovskites exhibit impressive photodetection properties, which are comparable or even better than those of other 2D perovskite-based photodetectors previously reported. Once fabricated as a flexible photodetector on polyimide, the quasi-2D perovskite device demonstrates further improved performances, yielding a good responsivity of 400 mA W−1, a high detectivity up to 1.68 × 1012 Jones and fast response speeds (rise and decay time constants of 43 and 22 ms, respectively) under 532 nm illumination. Importantly, the obtained devices possess excellent mechanical flexibility and durability with photocurrent maintaining 82% of the initial value even after 9000 bending cycles. This work can provide valuable design guidelines of 2D perovskites to obtain high-performance flexible photodetectors for next-generation optoelectronics.

Rational design of active and stable bifunctional electrocatalysts for both hydrogen evolution and oxygen evolution reactions is critical for the realization of renewable energy technologies. Although direct growth of active two-dimensional (2D) nanosheets on the current collector is an effective method to improve the exposure of active sites, the inefficient electron transfer and weak electron interaction between 2D nanosheets and current collectors greatly limit their overall electrochemical performance. Herein, a unique sandwich structure of CoMnP/Ni2P/NiFe is successfully designed via introducing a Ni2P interlayer between CoMnP nanosheets and nickel–iron (NiFe) foam to achieve an excellent bifunctional electrocatalyst in alkaline media. The metallic Ni2P interlayer does not only improve the electron transfer from the current collector of NiFe foam to the catalyst of CoMnP, but also enhances the intrinsic activity of each active site via strong electron interaction. Electrochemical studies show that the resulting electrocatalyst exhibits superior electrocatalytic activity, such as giving a low cell voltage of only 1.48 V at 10 mA cm−2 stably for a long time when applied as both the cathode and anode in alkaline solutions. These results evidently indicate the superior electrochemical characteristics of this sandwich structure, which may provide a new insight into the design of electrocatalysts for different utilizations.

Due to their excellent physical and chemical properties, one-dimensional (1D) transparent metal-oxide nanostructures, especially nanowires (NWs), are widely considered to be promising candidates for next-generation high-performance electronics. Meanwhile, with increasing industrial demand for electronics which can reliably function in harsh environments, such as high humidity, high temperature, and robust operating environments, 1D metal-oxide nanostructures with wide bandgaps and high stabilities are attracting increasing interest for devices operating in extreme conditions. In this article, we provide a comprehensive review on the recent advances in high-performance transparent metal-oxide NWs and their corresponding device applications in harsh electronics. We begin with a brief introduction of different methodologies for the controllable synthesis of high-quality metal-oxide NWs, followed by an evaluation of the physical limitations of these nanomaterials and approaches for addressing their electrical contact issues. Importantly, the operating principles of transistors, photodetectors and gas sensors based on these 1D metal-oxide nanostructures as well as some excellent examples will be thoroughly discussed for harsh environment operation. The final section describes the challenges for the practical utilization of 1D metal-oxide nanostructures for industrial applications and concludes with an outlook on the future development of these NWs for harsh electronics.

Because of the excellent electrical properties, III-V semiconductor nanowires are promising building blocks for next-generation electronics; however, their rich surface states inevitably contribute large amounts of charge traps, leading to gate bias stress instability and hysteresis characteristics in nanowire field-effect transistors (FETs). Here, we investigated thoroughly the gate bias stress and hysteresis effects in InAs nanowire FETs. It is observed that the output current decreases together with the threshold voltage shifting to the positive direction when a positive gate bias stress is applied, and vice versa for the negative gate bias stress. For double-sweep transfer characteristics, the significant hysteresis behavior is observed, depending heavily on the sweeping rate and range. On the basis of complementary investigations of these devices, charge traps are confirmed to be the dominant factor for these instability effects. Importantly, the hysteresis can be simulated well by utilizing a combination of the rate equation for electron density and the empirical model for electron mobility. This provides an accurate evaluation of carrier mobility, which is in distinct contrast to the overestimation of mobility when using the transconductance for calculation. All these findings are important for understanding the charge trap dynamics to further enhance the device performance of nanowire FETs.

Semiconducting two-dimensional (2D) layered materials have shown great potential in next-generation electronics due to their novel electronic properties. However, the performance of field effect transistors (FETs) based on 2D materials is always environment-dependent and unstable under gate bias stress. Here, we report the environment-dependent performance and gate-induced instability of few-layer p-type WSe

Graphene/WS

Due to the energy crisis, the development of high-performance photoelectrocatalysts is becoming a hot research area in recent years. Among the materials studied, BiFeO3 (BFO) exhibits excellent photoelectrocatalytic performance due to its moderate bandgap and unique band structure. In this paper, both pure BFO and La-doped BFO were synthesized by solgel method. The average size of the BFO nanoparticles was tuned from 65 to 440 nm. For the La-doped BFO, the average size of the nanoparticles was reduced from 95 to 40 nm with the increase in doping level from 0 to 30%. Next, the photoelectrocatalytic performance of the pure BFO nanoparticles were enhanced with the reduction in nanoparticle size, which was possibly caused by increased surface-to-volume ratio. For the increase in doping of La, the corresponding photoelectrocatalytic performance was first enhanced and then degraded. To understand the obtained results, a mechanism was proposed, which can be attributed to the competition between geometric size effects and surface effects. Our findings provided a controlled way to tune the photoelectrocatalytic performance of BFO system, which is crucial for practical applications.

Van der Waals heterostructure shows promising applications in next generation optoelectronics. As a kind of van der Waals heterostructure, graphene/silicon (Gr/Si) based heterostructure devices have been demonstrated as high performance photodetectors. Here, we studied the origin of the high performance of Gr/Si photodetectors based on photocurrent mapping technology. According to photocurrent mapping, the photocurrent in the Gr/Si and Gr/SiO2/Si area nearing the Si window edge is higher than that in other positions, which is attributed to the highly effective collection efficiency of photocarriers. A device with size of Gr/Si region (r=7.4 μm) and Gr/SiO2/Si region (L=6.1 μm) shows high sensitivity and a broadband photoresponse in the range from 420 to 1000 nm with the peak sensitivity of 52 A/W at 780 nm, and fast response speed with rise time of 16 μs and decay time of 52 μs. Our study provides a strategy for the design of high photoresponsivity Gr/Si based devices.

As an important semiconductor nanomaterial, InP nanowires (NWs) grown with a typical vapor–liquid–solid mechanism are still restricted from their low electron mobility for practical applications. Here, nonpolar-oriented defect-free wurtzite InP NWs with electron mobility of as high as 2000 cm2 V–1 s–1 can be successfully synthesized via Pd-catalyzed vapor–solid–solid growth. Specifically, PdIn catalyst particles are involved and found to expose their PdIn{210} planes at the InP nucleation frontier due to their minimal lattice mismatch with nonpolar InP{2110} and {1100} planes. This appropriate lattice registration would then minimize the overall free energy and enable the highly crystalline InP NW growth epitaxially along the nonpolar directions. Because of the minimized crystal defects, the record-high electron mobility of InP NWs (i.e., 2000 cm2 V–1 s–1 at an electron concentration of 1017 cm–3) results, being close to the theoretical limit of their bulk counterparts. Furthermore, once the top-gated d...

Recently, owing to the excellent electrical and optical properties, n-type In2O3 nanowires (NWs) have attracted tremendous attention for application in memory devices, solar cells, and ultra-violet photodetectors. However, the relatively low electron mobility of In2O3 NWs grown by chemical vapor deposition (CVD) has limited their further utilization. In this study, utilizing in-situ Ga alloying, highly crystalline, uniform, and thin In2xGa2−2xO3 NWs with diameters down to 30 nm were successfully prepared via ambient-pressure CVD. Introducing an optimal amount of Ga (10 at.%) into the In2O3 lattice was found to effectively enhance the crystal quality and reduce the number of oxygen vacancies in the NWs. A further increase in the Ga concentration adversely induced the formation of a resistive β-Ga2O3 phase, thereby deteriorating the electrical properties of the NWs. Importantly, when configured into global back-gated NW field-effect transistors, the optimized In1.8Ga0.2O3 NWs exhibit significantly enhanced electron mobility reaching up to 750 cm2·V–1·s–1 as compared with that of the pure In2O3 NW, which can be attributed to the reduction in the number of oxygen vacancies and ionized impurity scattering centers. Highly ordered NW parallel arrayed devices were also fabricated to demonstrate the versatility and potency of these NWs for next-generation, large-scale, and high-performance nanoelectronics, sensors, etc.

Two-dimensional (2D) nanomaterials have recently attracted considerable attention due to their promising applications in next-generation electronics and optoelectronics. In particular, the large-scale synthesis of high-quality 2D materials is an essential requirement for their practical applications. Herein, we demonstrate the wafer-scale synthesis of highly crystalline and homogeneous monolayer WS2 by an enhanced chemical vapor deposition (CVD) approach, in which precise control of the precursor vapor pressure can be effectively achieved in a multi-temperature zone horizontal furnace. In contrast to conventional synthesis methods, the obtained monolayer WS2 has excellent uniformity both in terms of crystallinity and morphology across the entire substrate wafer grown (e.g., 2 inches in diameter), as corroborated by the detailed characterization. When incorporated in typical rigid photodetectors, the monolayer WS2 leads to a respectable photodetection performance, with a responsivity of 0.52 mA/W, a detectivity of 4.9 × 109 Jones, and a fast response speed (< 560 μs). Moreover, once fabricated as flexible photodetectors on polyimide, the monolayer WS2 leads to a responsivity of up to 5 mA/W. Importantly, the photocurrent maintains 89% of its initial value even after 3,000 bending cycles. These results highlight the versatility of the present technique, which allows its applications in larger substrates, as well as the excellent mechanical flexibility and robustness of the CVD-grown, homogenous WS2 monolayers, which can promote the development of advanced flexible optoelectronic devices.

With distinct ion insertion-induced tinting behavior, tungsten oxide (WO3) has been intensively studied as a representative electrochromic (EC) material for many years. To enhance its EC properties, strategies including nanostructuring, plasmonic engineering, and metal ion doping have been adopted. Here, we show that rare earth element of gadolinium (Gd) doping can effectively improve the coloration efficiency (η) of a sputtered amorphous WO3 (∼30% enhancement at the maximum of eye-sensitive wavelength of 520 nm for 0.57 wt% doping). By combining the film structural characterization and electrochemical analysis, such an increment can be attributed to the monoclinic Gd2O3 nanoislands formed on WO3 surface which enhanced charge capacity and reaction kinetics of the film. The large transmittance modulation (76% at 800 nm), high coloration efficiency (68.3 cm2 C−1 at 633 nm) and fast switching speed (7.8 and 10.4 s for coloration and bleach time, respectively) were achieved for the modest Gd-doped WO3 film (0.9%). However, further increasing of Gd doping results in decreasing of η, which could be attributed to the excess amount of Gd2O3 that inhibits the penetration of electrolyte into the active material. We believe that the understanding of the Gd-doping effect on the electrochemical behaviours of WO3 may shed light on selecting the proper doping elements and their concentration for energy-saving smart windows.

Because of sluggish kinetics of the oxygen evolution reaction (OER), designing low-cost, highly active, and stable electrocatalysts for OER is important for the development of sustainable electrochemical water splitting. Here, {112} high-index facet exposed porous Co3O4 nanosheets with oxygen vacancies on the surface have been successfully synthesized via a simple hydrothermal method followed by NaBH4 reduction. As compared with the pristine and other faceted porous Co3O4 nanosheets (e.g., {110} and {111}), the as-prepared {112} faceted porous nanosheets exhibit a much lower overpotential of 318 mV at a current density of 10 mA cm–2. Importantly, these nanosheets also give excellent electrochemical stability, displaying an insignificant change in the required overpotential at a current density of 10 mA cm–2 even after a 14 h long-term chronoamperometric test. All these superior OER activity and stability could be attributed to their unique hierarchical structures assembled by ultrathin porous nanosheets, ...

The emerging of graphene has stimulated the exploration of two-dimensional (2D) nanomaterials. As a kind of important semiconducting 2D materials, WS2 shows great potentials in electronics, optoelectronics, and photonics, etc.; however, the synthesis of high quality, large area, uniform and epitaxial 2D WS2 monolayer films is still a challenge. Herein, we report the epitaxial growth of WS2 on sapphire with excellent electrical and optoelectronic properties via an enhanced chemical vapor deposition method. With the assistance of Na2WO4 as well as the investigation of related growth mechanism, large single crystal triangular WS2 monolayer flakes with well-defined orientations are achieved. The corresponding single crystal domain size is larger than 1 mm together with the centimeter-scale continuous film realized. Once fabricated into transistors, the monolayers exhibit excellent device properties, such as high mobility and large on/off current ratio. Also, these devices give respectable photoresponse properties when operated in the photoconductive mode. The peak responsivity can reach 4.6 A W−1. All these results demonstrate the high quality of as-synthesized WS2 monolayers, indicating the bright future of this synthesis technology for 2D materials towards practical applications.

van der Waals heterostructures built from two-dimensional (2D) materials have attracted wide attention because of their fascinating electrical and optoelectronic properties. Here, we report a highly responsive and broadband photodetector based on WS2–graphene van der Waals epitaxial heterostructures, which were fabricated by directly growing single crystalline few layer WS2 nanosheets on a polycrystalline graphene film. Upon light illumination, the current apparently reduces because of the transfer of photogenerated electrons from WS2 into the underlying p-type graphene and a photo-gating effect induced by the remaining holes, which is in stark contrast to ordinary semiconducting photoconductors. Thanks to the strong and broadband absorption of WS2, the WS2–graphene heterostructure photodetector exhibits a high responsivity with a maximum of 950 A W−1 at 405 nm and a wide spectrum response ranging from 340 to 680 nm. The high performance can be attributed to the internal built-in electric field at the WS2–graphene interface, which leads to the efficient separation of photogenerated electron–hole pairs. The WS2–graphene heterostructure photodetector may have potential applications in low cost, broadband, and flexible optoelectronics.

Because of tunable bandgap and high carrier mobility, ternary III-V nanowires (NWs) have demonstrated enormous potential for advanced applications. However, the synthesis of large-scale and highly-crystalline InxGa1−xSb NWs is still a challenge. Here, we achieve high-density and crystalline stoichiometric InxGa1−xSb (0.09 -orientation via chemical vapor deposition. The as-prepared NWs show excellent electrical and optoelectronic characteristics, including the high hole mobility (i.e. 463 cm2 V−1 s−1 for In0.09Ga0.91Sb NWs) as well as broadband and ultrafast photoresponse over the visible and infrared optical communication region (1550 nm). Specifically, the In0.28Ga0.72Sb NW device yields efficient rise and decay times down to 38 and 53 μs, respectively, along with the responsivity of 6000 A W−1 and external quantum efficiency of 4.8 × 106 % towards 1550 nm regime. High-performance NW parallel-arrayed devices can also be fabricated to illustrate their large-scale device integrability for next-generation, ultrafast, high-responsivity and broadband photodetectors., The application of ternary nanowires (NWs) in optoelectronics has been hindered by difficulties in producing high quality NWs on silicon substrates. Here, the authors report on InxGa1-xSb NWs exhibiting simultaneously high hole mobility, responsivity, and fast response times in the infrared regime.

Two-dimensional (2D) materials have attracted wide attention due to their exotic properties. In particular, the lack of dangling bonds makes it possible to build highly lattice mismatched heterostructures composed of 2D materials and conventional semiconductors. Here, we report that by simply stacking a chemical vapor deposition grown monolayer WS2 film onto the surface of a room temperature sputtered ZnO film, significant enhanced ultra-violet (UV) photoresponse can be achieved. In this heterostructure of ZnO–WS2, the ZnO film acts as a light harvesting layer while the WS2 monolayer functions as a carrier transport layer which facilitates the photocarrier transport and reduces its recombination. Such a mechanism was confirmed by the observation of further photoresponsivity improvement of the ZnO–WS2 heterostructure under vacuum which removes the surface absorbates and thereby increases the carrier mobility of WS2. The strategy presented here can be applied to other wide band-gap semiconductors, shedding light on high sensitivity and flexible UV photodetectors based on van der Waals heterostructures.

Nanostructured WO3 films prepared by an industry compatible method with large surface area and strong adhesive force to the substrate are highly desired for electrochromic (EC) applications. Here, we report the preparation of a kind of WO3 nanoisland films on indium-doped tin oxide (ITO)-coated glass substrates by Ag-induced reactive sputtering deposition combined with a post-etching treatment. Our study demonstrates that compared with the bare WO3 film, the nanoisland film exhibits apparently enhanced EC performance, including high luminous transmittance (92.8%) in a bleached state, high luminous coloration efficiency (126.4 cm2/C), relatively fast color-switching time (7.1 s for coloring and 12.1 s for bleaching), decent long-term cycling stability (2000 cycles) and improved self-bleaching ability. Electrochemical kinetics analysis indicates that such enhanced EC performance relies on large lithium-ion diffusion coefficient (2.37 × 10−10 cm2/s), a good ability of charge storage (10.82 mF/cm2), and low charge-transfer resistance (196 Ω) of the nanoisland microstructure. The results shed light on exploring a novel method to prepare high EC performance WO3 film.

Graphene/WS2 (G/WS2) van der Waals (vdW) heterostructures are utilized as saturable absorbers (SAs) in compact mode-locked fiber lasers operating in the telecommunication L-band for the first time. The interlayer coupling is confirmed by Raman and photoluminescence spectra. In comparison with pure WS2, the heterostructure exhibits excellent nonlinear optical properties in terms of larger modulation depth and lower saturation intensity due to the strong interlayer coupling. By incorporating the G/WS2-based SA into an all-anomalous-dispersion fiber laser, stable conventional-soliton pulses with a pulse duration down to 660 fs can be realized at 1601.9 nm, manifesting better output performance compared to pure WS2. In addition, through shifting the cavity dispersion to the net-normal dispersion, the G/WS2 SA can also be applied for dissipative-soliton generation. Resultant output pulses feature the central wavelength of 1593.5 nm and the pulse duration of 55.6 ps. Our results indicate that the G/WS2 vdW heterostructure is a promising candidate as SA for pulsed laser applications, which pave the way for the development of novel ultrafast photonic devices with desirable performance.

We demonstrate a compact erbium-doped fiber ring laser mode-locked by a WS 2 saturable absorber (SA), which operates in the telecommunication L-band. The monolayer WS 2 is synthesized by an enhanced chemical vapor deposition (CVD) method and transferred onto the end face of a fiber connector to form a fiber-compatible WS 2 SA. Stable soliton pulses centered at 1602.2 nm with a pulse duration of 1.19 ps are achieved in the laser. Our research results show that monolayer WS 2 is a promising material for L-band ultrashort pulse generation.

Quasi two-dimensional (2D) layered organic–inorganic perovskite materials (e.g., (BA)2(MA)n−1PbnI3n+1; BA = butylamine; MA = methylamine) have recently attracted wide attention because of their superior moisture stability as compared with three-dimensional counterparts. Inevitably, hydrophobic yet insulating long-chained organic cations improve the stability at the cost of hindering charge transport, leading to the unsatisfied performance of subsequently fabricated devices. Here, we reported the synthesis of quasi-2D (iBA)2(MA)n−1PbnI3n+1 perovskites, where the relatively pure-phase (iBA)2PbI4 and (iBA)2MA3Pb4I13 films can be obtained. Because of the shorter-branched chain of iBA as compared with that of its linear equivalent (n-butylamine, BA), the resulting (iBA)2(MA)n−1PbnI3n+1 perovskites exhibit much enhanced photodetection properties without sacrificing their excellent stability. Through hot-casting, the optimized (iBA)2(MA)n−1PbnI3n+1 perovskite films with n = 4 give the significantly improved crys...

Multiwall carbon nanotubes (CNTs) were synthesized by the annealing of carbonaceous solid at a low-temperature (450 °C). The average diameter of the CNTs is about 50 nm. The length of the CNTs ranges from 200 nm to nearly 1 μm. The as-synthesized CNTs are crystallized. Cobalt nanoparticle is capped at the tip of the CNT. The carbonaceous solid, which contains cobalt nanoparticles, was obtained by the sol–gel autocombustion method. The growth of CNTs occurred in the annealing process, while the combustion process only produced carbonaceous solid and cobalt nanoparticles. The cobalt nanoparticles catalyze the decomposition of carbonaceous solid into carbonaceous gas species, and also catalyze the growth of CNTs during the annealing process.

Single-crystalline GeS nanoribbons were synthesized by chemical vapor deposition for the first time. Structural characterization revealed that the nanoribbons grow along the [01] direction with a thickness of 20–50 nm, a width of several micrometers and a length of hundreds of micrometers. The GeS nanoribbons show a p-type behavior verified from the field effect transport measurement. The nanoribbon photodetectors respond to the entire visible incident light with a response edge at around 750 nm consistent with the band gap absorption of GeS. A strong nonlinear light-intensity-dependent response was observed between the measured illumination intensity from 0.25 to 212 μW cm−2. Under 530 nm light illumination, the maximum responsivity and external quantum efficiency are 139.9 A W−1 and 32730%, respectively. These results indicate that GeS nanoribbon is a promising semiconducting nanomaterial for high performance broadband visible-light sensing applications.