Functional Materials Letters

The interplay between the linear elastic deformation up to 20% and the unique electronic properties of graphene nanostructures offers an attractive prospect to manipulate their properties by strain. Here we review the recent progress on the electronic response of graphene to the in-plane strains, including the strain-modulated electronic structure and the strain-modulated spin, valley and superconducting transports. A generalized Hamiltonian for a graphene was constructed subjected to arbitrary in-plane strains. The Hamiltonian is helpful to design and optimize the graphene-based nano-electromechanical systems (NEMS).

Multiferroic BiCoO₃ nanoflowers were synthesized by a hydrothermal process. The BiCoO₃ nanoflowers show superior bipolar resistive switching characteristics. The typical current–voltage (I–V) characteristics of the Ag/BiCoO₃/Ag structures exhibit an extreme change in resistance between high resistance state (HRS) or "OFF" state and low resistance state (LRS) or "ON" state with ON/OFF ratio ~ 10⁵.

Photovoltaic (PV) effect of polycrystalline Bi_0.975La_0.025Fe_0.975Ni_0.025O₃ (BLFNO) film grown on Pt(111)/Ti/SiO₂/Si(001) substrate using sol–gel method has been investigated. The BLFNO film possesses good ferroelectric property and large twice-remanent polarization. It is found that PV response exhibited a strong dependence on the potential of top indium tin oxide (ITO) and bottom Pt electrode. The open circuit voltage is -0.67 V when the potential of ITO electrode is higher than that of Pt electrode and 0.45 V when the potential of ITO electrode is lower than that of Pt electrode. This can be interpreted by the variation of barrier heights at both ITO/BLFNO and BLFNO/Pt interfaces.

Antimony sulfide (Sb₂S₃) films on indium-doped tin oxide (ITO) glass substrates are easily synthesized by a solvothermal method from Sb ultrathin films and S powder as antimony and sulfur source, respectively. The crystalline Sb₂S₃ films were characterized using X-ray powder diffraction (XRD) and Raman spectroscopy. The Sb₂S₃ films are composed of micro-flakes of Sb₂S₃. The composite of Sb₂S₃ film and ITO substrate were used to fabricate the solar cell device (ITO/Sb₂S₃:P3HT/Au), and I–V measurement of the device was performed. Under the optimized condition, the solar conversion efficiency is 0.0026% at 1 sun illumination.

The uniform ball-like luminescence down-shifting (LDS) Sm(TTA)₃Phen materials have been synthesized by microwave ultrasonic method. Microwave ultrasonic plays a synergistic effect of microwave with ultrasonic, including thermal effect, dipole vortex and air bombard make the particles aggregation reach to the lowest energy. Through this method, we successfully synthesised 1–4 μm ball-like uniform Sm(TTA)₃Phen clusters. The Sm(TTA)₃Phen can transfer violet light to red-orange flourescence with a feature large Stokes shift and completely avoid self-absorption losses.

Basalt fiber reinforced porous aggregates-geopolymer based cellular material (BFRPGCM) was prepared. The stress–strain curve has been worked out. The ideal energy-absorbing efficiency has been analyzed and the application prospect has been explored. The results show the following: fiber reinforced cellular material has successively sized pore structures; the stress–strain curve has two stages: elastic stage and yielding plateau stage; the greatest value of the ideal energy-absorbing efficiency of BFRPGCM is 89.11%, which suggests BFRPGCM has excellent energy-absorbing property. Thus, it can be seen that BFRPGCM is easy and simple to make, has high plasticity, low density and excellent energy-absorbing features. So, BFRPGCM is a promising energy-absorbing material used especially in civil defense engineering.

Y₂O₃:Eu³⁺, Tb³⁺ nanopowders were prepared by co-precipitation method with NH₄HCO₃ as precipitant. The nanopowders with different calcined temperatures and Eu³⁺/Tb³⁺ doped ratio were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrophotometer. The results showed that the nanopowders calcined at 1100°C for 2 h had a uniform distribution, high purity and good dispersibility. The particle size was in the range of 60–80 nm. The excitation spectra of Eu³⁺/Tb³⁺ co-doped phosphors were wide. The phosphors could emit the green light at the peak of 543 nm and the red light at the peak of 611 nm simultaneously under 276 nm or 300 nm excited. Because of the energy transfer between Tb³⁺ and Eu³⁺, the 543 nm emission of Tb³⁺ ion was weakened while the 611 nm emission of Eu³⁺ enhanced. The emissive colors of Y₂O₃:Eu³⁺, Tb³⁺ nanopowders could be adjusted from yellow-green to orange-red by changing the Eu³⁺/Tb³⁺ doping ratio.

Quasi-two-dimensional (Q2D) Nb₂O₅ nanoflakes were synthesized by combined sol–gel/exfoliation method with the average thickness of 10–25 nm. Their structural, surface- and electro-chemical properties were closely studied and analyzed by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), conductive atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy techniques.

Bi_(1.98-x)In_0.02Na_xTe_2.7Se_0.3 (x = 0, 0.02, 0.04, 0.06) and Bi₂Te_2.7Se_0.3 alloys were prepared by vacuum melting and hot pressing methods. The phase structure of the bulk samples were characterized by X-ray diffraction. Effects of indium and sodium co-substitutions for bismuth on the electrical and thermal transport properties were investigated in the temperature range of 298–473 K. Indium and sodium co-doping can enhance the carrier concentration, and accordingly the electrical conductivity can be improved effectively. The Seebeck coefficients of the co-doped samples have not been derogated strongly. The power factors are enhanced for the Bi_(1.98-x)In_0.02Na_xTe_2.7Se_0.3 (x = 0.02) within the whole testing temperature range. The Bi_(1.98-x)In_0.02Na_xTe_2.7Se_0.3 (x = 0.02) samples have the lower thermal conductivity due to reduction in lattice thermal conductivity, which leads to a great improvement in the thermoelectric figure of merit ZT. The highest ZT of the sample can reach 0.87 at 398 K.

The passive direct methanol fuel cell (DMFC) is a promising candidate power source for portable applications but has to deal with many technical challenges before practical use. This study presents a preliminary investigation on the use of a woven carbon fiber fabric (WCFF) for constructing a gradient porous structure based on the traditional design. The WCFF, carbon paper and carbon-black micro porous layer (MPL) combine into a carbon-based assembly which acts as a mass-transfer-controlling medium at the anode of a passive DMFC. Results show that this novel setup is able to significantly improve the cell performance and facilitate high-concentration operation. A maximum power density of 16.4 mWcm^-2 is obtained when two layers of the WCFF are used at a methanol concentration of 8M. This work provides an effective method for using concentrated methanol with no need for major change of the fuel cell configuration.

The electric-pulse-driven resistance change of metal/oxides/metal structure, which is called resistive switching effect, is a fascinating phenomenon for the development of next generation non-volatile memory. In this work, an outstanding bipolar resistive switching behavior of Ag/MoS₂/fluorine-doped tin oxide (FTO) device is demonstrated. The device can maintain superior reversible stability over 100 cycles with an OFF/ON-state resistance ratio of about 10³ at room temperature.

Graphene-wrapped CuInS₂ composites were synthesized via a facile hydrothermal approach. The as-synthesized products were characterized by scanning electron microscope and transmission electron microscopy and the reduction of GO were confirmed by Raman spectroscopy. Graphene-wrapped CuInS₂ composites exhibit excellent electrocatalytic activity for the triiodide reduction due to the improved conductivity and the synergetic catalysis of CuInS₂ and graphene. The graphene-wrapped CuInS₂ composites were exploited as counter electrode for dye-sensitized solar cells and therefore achieved a power conversion efficiency of 6.4%, which is comparable to that of Pt CE (6.9%).

Zinc oxide (ZnO) nanorods (ZNRs) and hierarchical ZnO nanosheet–spheres (ZNSs) were prepared through a simple aqueous chemical growth process and a low-temperature solid-phase method, respectively. The prepared ZNRs and ZNSs were mixed to obtain a composite structure by using a circumference oscillator. After structure and morphology characterizations via X-ray diffraction and scanning electron microscopy, the mixture of ZNRs and ZNSs was used as a photoanode in dye-sensitized solar cells (DSSCs). Photovoltaic performance and optimal mixture ratio were investigated. The results indicated that the photovoltaic properties of DSSCs depended on the microstructures, morphologies and mixture ratios of the electrodes. In addition, the mixture of ZNRs and ZNSs (molar ratio of 1:12) yielded an overall light conversion efficiency of 6.02%, with a fill factor of 65.0%, a short-circuit current of 13.49 mA/cm², and an open-circuit voltage of 0.69 V. These values are higher than those of pure ZNRs or pure ZNSs.

Novel flower-like Fe₂O₃/Ag nanocomposites were synthesized by a simple direct subsidence loading method. The composition and morphology of the obtained samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SEAD) techniques. The Ag nanoparticles which loaded on the surface of petals exhibit spherical morphology. Further, the magnetic and electrical conductive properties reveal the well controllable performance. Room temperature magnetic measurement of the flower-like nanocomposites demonstrated its ferromagnetic properties and the saturation magnetization (Ms) decreased from 0.6 to 0.11 emu/g.

Tin oxide (SnO₂) thin films were deposited by radio-frequency (RF) magnetron sputtering on silicon and glass substrates at different oxygen-to-argon gas-flow ratio (O₂-to-Ar = 0%, 10%, 20%, 30% and 50%). All films were deposited at room temperature and fixed working pressures, 10 mTorr. X-ray diffraction (XRD) measurement suggests that all films were crystalline in nature except film deposited only in argon environment. The transparency of all of the films was more than 85% in the visible range except the film deposited only in the argon environment. Atomic force microscopy results showed that the surface of all the films were highly flat and smooth. The optical bandgap, estimated by Tauc plot was increased with oxygen environment. Blue shift was observed in the absorption edge and was accounted to decrease in the oxygen vacancies and dangling bonds.

Ba(Sn_0.02Ti_0.98)O₃ thin films (BTS) were prepared by sol–gel route and deposited by spin-coating on commercial Pt/Ti/SiO₂/Si substrates. By modifying the annealing conditions from 750°C at 1 h to 950°C at 15 min, the relative tunability n_r at 100°C in the paraelectric state increased from 45 to 70% while the DC dielectric permittivity ε′(0) increased as well. The evolutions of ε′(E) and n_r(E) are explained from Devonshire thermodynamic formalism. The very high value of tunability of 70% is explained by the grain size increase of our BTS thin films and the decrease of the dead layer effect when the annealing conditions are optimized.