Table of contents

Graphene has attracted great attention owing to its superb properties as an anode of organic or polymer light-emitting diodes (OLEDs or PLEDs). However, there are still barriers for graphene to replace existing indium tin oxide (ITO) due to relatively high sheet resistance and work function mismatch. In this study, PLEDs using molybdenum oxide (MoO_x) nanoparticle-doped graphene are demonstrated on a plastic substrate to have a low sheet resistance and high work function. Also, this work shows how the doping amount influences the electronic properties of the graphene anode and the PLED performance. A facile and scalable spin coating process was used for doping graphene with MoO_x. After doping, the sheet resistance and the optical transmittance of five-layer graphene were ∼180 Ω sq⁻¹ and ∼88%, respectively. Moreover, the surface roughness of MoO_x-doped graphene becomes smoother than that of pristine graphene. Furthermore, a nonlinear relationship was observed between the MoO_x doping level and device performance. Therefore, a modified stacking structure of graphene electrode is presented to further enhance device performance. The maximum external quantum efficiency (EQE) and power efficiency of the PLED using the MoO_x-doped graphene anode were 4.7% and 13.3 lm W⁻¹, respectively. The MoO_x-doped graphene anode showed enhanced device performance (261% for maximum EQE, 255% for maximum power efficiency) compared with the pristine graphene.

Metal films with broadband optical transparency are desirable in many optoelectronic devices, such as displays, smart windows, light-emitting diodes and infrared detectors. As bare metal is opaque to light, this issue of transparency attracts great scientific interest. In this work, we proposed and demonstrated a feasible and universal approach for achieving broadband optical transparent (BOT) metals by utilizing all-dielectric resonant cavities. Resonant dielectrics provide optical cavity modes and couple strongly with the surface plasmons of the metal film, and therefore produce a broadband near-unity optical transparent window. The relative enhancement factor (EF) of light transmission exceeds 3400% in comparison with that of pure metal film. Moreover, the transparent metal motif can be realized by other common metals including gold (Au), silver (Ag) and copper (Cu). These optical features together with the fully retained electric and mechanical properties of a natural metal suggest that it will have wide applications in optoelectronic devices.

ReS₂ and ReSe₂ have recently been enthusiastically studied owing to the specific in-plane electrical, optical and structural anisotropy caused by their distorted one-layer trigonal (1 T) phase, whereas other traditional transition-metal dichalcogenides (TMDCs, e.g. MoS₂ and WSe₂) have a hexagonal structure. Because of this special property, more and versatile nano-electronics and nano-optoelectronics devices can be developed. In this work, 2D materials in the series ReS_2−xSe_x (0 ≤ x ≤ 2) have been successfully grown by the method of chemical vapor transport. The direct and indirect resonant emissions of the complete series of layers can be simultaneously detected by polarized micro-photoluminescence (μPL) spectroscopy when the thickness of the ReS_2−xSe_x is greater than ∼70 nm. When it is less than 70 nm, only three direct excitonic emissions—E₁^ex, E₂^ex and E_S^ex—are detected. For the thick (bulk) ReS_2−xSe_x, more stacking of the ReX₂ monolayers even flattens and shifts the valence-band maximum from Γ to the other K- or M-related points, thus leading to the coexistence of direct and indirect resonant light emissions from the c-plane ReX₂. The transmittance absorption edge of each bulk ReX₂ (a few microns thick) usually has a lower energy than those of the direct E₁^ex and E₂^ex excitonic emissions to form indirect absorption. The coexistence of direct and indirect emissions in ReX₂ is a unique characteristic of a 2D layered semiconductor possessing triclinic low symmetry.

A novel fabrication method using controlled sacrificial etching of the mask is utilized to fabricate tapered vertical GaAs nanowire arrays. Experimental measurements of the absorption characteristics show that the tapered nanowires absorb over a broadband range as compared to cylindrical ones. The broadband characterization is verified by using optical modeling and results from improved coupling of the nanowires due to distinct radial HE modes being excited separately in the taper and the cylindrical part. The absorption is found to be more broadband as compared to conical nanowires studied so far.

Well-ordered periodic nanostructures are excellent substrates for many surface-enhanced Raman spectroscopy (SERS) applications. Conventional fabrication approaches such as high precision electron beam lithography or focused ion beam produce high resolution nano-features with great reproducibility at the expense of low throughput. In this work, a highly sensitive and scalable AAO-nano-fibre (ANF) SERS substrate is demonstrated by optimising the second anodisation time of the standard two-step anodisation of aluminium and performing an additional wet etching step on the resulting AAO substrate. The optimised ANF substrate exhibits SERS sensitivity that surpasses the AAO nanoholes and the metal-film-on-nanoparticles substrates. A detection limit of 0.1 nM is achieved with a signal-to-noise ratio of 2.6–3 using a low excitation power of 0.1 mW. The ANF substrate exhibits an enhancement factor of 9.28 × 106 and a standard deviation of no more than 8%. The results indicate that the highly sensitive and scalable ANF substrate is a promising substrate for commercial SERS application.

We report on the observation of an unexpected sudden increase of resistance in bilayer graphene nanomesh (GNM) in the temperature range 270 ∼ 300 K that is strongly dependent on the magnetic field strength. We conjecture that the sharp increase in resistance originates from ripple scattering as induced by substrate roughness. The observed result is evidence of extrinsic corrugation in bilayer GNM as an additional scattering source that contributes to significant resistance. The observed weak localization in the GNM indicates intervalley scattering induced by lattice defects acts as resonant scatterers attribute to the high D peak. Magnetotransport measurement strongly supports that the charge inhomogeneity related to the intrinsic disorder in bilayer GNM and the positive magnetoresistance shows a linear behavior with magnetic field strength. Potentially, the observed phenomena, therefore, point to a clear pathway towards practical application of bilayer GNM and to the design of a graphene magnetic sensor that can be manipulated by a magnetic field and a new generation of spintronics.

We developed a simple and controlled method to synthesize FeCo₂O₄@MnO₂ core–sheath nanoarchitecture (CSN) grown on Ni foam. Ultrathin FeCo₂O₄ nanoflakes with an average thickness of 10 nm served as the scaffold to deposit the MnO₂ nanosheets. The MnO₂ nanosheets were able to vertically grow on FeCo₂O₄ nanoflakes to form a sheath via a hydrothermal reaction. The nanocomposites' thickness could be tailored from 80 nm–550 nm by changing the reaction times. Electrochemical measurements demonstrated that FeCo₂O₄@MnO₂ CSN with an optimal thickness of about 400 nm achieved an areal capacitance of 3.077 F cm⁻² at 2 mA cm⁻², which is much higher than individual FeCo₂O₄ nanoflakes (0.295 F cm⁻²) and MnO₂ nanosheets (1.065 F cm⁻²). An aqueous asymmetric supercapacitor (ASC) was assembled using FeCo₂O₄@MnO₂ CSN as its positive electrode and activated carbon (AC) as its negative electrode. The FeCo₂O₄@MnO₂⫽AC ASC exhibited a capacitance of 0.538 F cm⁻² at 5 mA cm⁻² with a potential window of 1.65 V, and an excellent cycling stability (99.1% retention even after 5000 cycles). Furthermore, the maximum energy density and power density of FeCo₂O₄@MnO₂⫽AC ASC was 0.203 mWh cm⁻² at 3.44 mW cm⁻² and 28.6 mW cm⁻² at 0.061 mWh cm⁻², respectively.

Spray pyrolysis (SP) easily affords nano or sub-micro phosphor particles even on an industrial scale. However, control of the coordination environment around the emitting ion is inefficient, and the final solid matrix will dictate the symmetry of the emitter. Moreover, the fast heat treatment typical of SP usually results in heterogeneous symmetry sites. This paper aimed to obtain inorganic matrices incorporated with phosphors by SP while keeping the symmetry of the emitting ion unchanged along the pyrolysis process. Nanoparticles consisting of Eu³⁺-doped YVO₄ phosphors with average diameter of 15 nm were prepared by the co-precipitation method and were subsequently incorporated into the alumina matrix by SP, to yield YVO₄:Eu³⁺/γ-Al₂O₃ composite particles with mean size of 600 nm. X-ray powder diffraction confirmed that the vanadate particles were incorporated into the alumina matrix, and that the γ-Al₂O₃ phase emerged. The band due to the ${{{\rm{VO}}}_{4}}^{3+}$ → Eu³⁺ transition intensified as a consequence of the incorporation of YVO₄:Eu³⁺ into alumina—the suppression effects caused by the surface properties of the YVO₄:Eu³⁺ phosphor nanoparticles diminished, while the structure of Eu³⁺ remained unchanged in the matrix.

Hollow silica nanoparticles (HSNPs) were synthesized using a microreactor-assisted system with a hydrodynamic focusing micromixer. Due to the fast mixing of each precursor in the system, the poly(acrylic acid) (PAA) thermodynamic-locked (TML) conformations were protected from their random aggregations by the immediately initiated growth of silica shells. When altering the mixing time through varying flow rates and flow rate ratios, the different degrees of the aggregation of PAA TML conformations were observed. The globular and necklace-like TML conformations were successfully captured by modifying the PAA concentration at the optimized mixing condition. Uniform HSNPs with an average diameter ∼30 nm were produced from this system. COMSOL numerical models was established to investigate the flow and concentration profiles, and their effects on the formation of PAA templates. Finally, the quality and utility of these uniform HSNPs were demonstrated by the fabrication of antireflective thin films on monocrystalline photovoltaic cells which showed a 3.8% increase in power conversion efficiency.

Self-assembled monolayers (SAMs) on Au(111) are able to control the functionality of a gold surface. We use scanning tunnelling microscopy (STM) in air and contact angle measurements to compare the morphology and the chemistry of three alkylthiol SAMs differing by their tail groups: 1,9-nonanedithiol (NDT), 1,4-butanedithiol (BDT) and 11-mercaptoundecanol (MUOH). STM reveals very different morphologies: a hexagonal lattice for MUOH and parallel rows for NDT and BDT. In the case of NDT, we find that the thiol tail groups may form disulfide bridges with long immersion times. The availability of the –SH group for chemical reactions is demonstrated by attaching gold nanoparticles (AuNPs). When the thiol tail group is available, AuNPs readily attach as shown with atomic force microscopy (AFM). When disulfide bridges are formed, the gold surface is not able to bind nanoparticles.

The wet-chemical approach is of great significance for the synthesis of two-dimensional (2D) bismuth telluride nanoplatelets as a potential thermoelectric (TE) material. Herein, we proposed a simple and effective solution method with the assistance of aniline for the fabrication of bismuth telluride nanoplatelets at a low temperature of 100 °C. The choice of aniline with its dual function avoided the simultaneous use of a capping regent and a toxic reductant. The as-synthesized nanoplatelets have a large size of more than 900 × 500 nm² and a small thickness of 15.4 nm. The growth of bismuth telluride nanoplatelets are related to the Bi/Te ratio of precursors indicating that a larger content of the Bi precursor is more conducive to the formation of 2D nanoplatelets. The bismuth telluride nanoplatelets pressed into a pellet show a smaller electrical resistivity (∼6.5 × 10⁻³ Ω · m) and a larger Seebeck coefficient (−135 μV K⁻¹), as well as a lower thermal conductivity (0.27 W m⁻¹ K⁻¹) than those of nanoparticles. The next goal is to further reduce the electrical resistivity and optimize the TE performance by disposing of the residual reactant of aniline adsorbed on the surface of the nanoplatelets.

The characterization of nanowires (NWs) often requires the use of scanning electron beam techniques because of their high spatial resolution. However, the impact of the high energetic electron beam on the physical parameters under investigation is rarely taken into account. In this work, a combination of optical and electrical techniques is involved for the measurement of the electron beam dose (EBD) dependence of cathodoluminescence intensity, exciton diffusion length and electrical resistance in ZnO NWs. Large EBD dependences of these key parameters are observed and their reversibility is investigated. The results are discussed in terms of bulk and surface reversible modifications. In particular, the behaviors of surface recombination velocity and surface space charge under electron beam exposure are determined and simulated. This study points out that caution must be taken and experimental protocols must be well defined when measuring physical parameters of NWs using electron beam techniques.

Exfoliated hexaniobate nanosheets E-H₂K₂Nb₆O_17−x (E-HKNO) with broad light absorption (up to 850 nm) and high adsorption properties were prepared via ion exchange and transient annealing processes with micron-size K₄Nb₆O₁₇ powders as the precursor. The as-prepared E-HKNO nanosheets show excellent visible light photodegradation performances when compared to degussa P25, which was evaluated in terms of degradation of Rhodamine B (Rh B). High adsorption and broad light absorption characteristics could be attributed to the exfoliation behavior and the reduction of surface Nb⁵⁺ to Nb⁴⁺, which was confirmed by x-ray photoelectron spectroscopy (XPS) and Raman spectra. From the Mott–Schottky analysis, the E-HKNO is an n-type semiconductor and has a higher flat band voltage (−0.46 V versus RHE at pH = 7), compared with K₄Nb₆O₁₇. In addition, the electrochemical impedance spectroscopy (EIS) indicates that the E-HKNO nanosheets have an increased semiconductor–electrolyte charge transfer resistance, which is not conducive to the separation of photogenerated carriers (e⁻-h⁺). Accordingly, a small amount of holes scavenger (EDTA) was added to improve the photodegradation performance of the E-HKNO, since the holes scavenger can inhibit the recombination of the photogenerated carriers. This work provides not only a facile method for the preparation of an efficient E-HKNO nanosheets photocatalyst, but also new insights for further enhancing the photodegradation performance by adding trace scavenger.