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The fermi-level pinning effect caused by low-order contact interface influences the performance of carbon nanotube (CNT) network field-effect transistors (FETs). In this paper, ambipolar CNT network FETs subjected to van der Waals (vdW) contact are demonstrated with the negligible Fermi-level pinning effect by using a physical transfer approach. The vdW contact method allows for the metal and CNT network to retain their intrinsic states without direct chemical bonding and interface interactions, leading to low injection barrier and contact resistance (Rc). Therefore, the field-effect mobilities of vdW metal-semiconductor (MS) contact devices in regions of dominance of the holes (μp) and electrons (μn) were 18.71 and 2.4 cm2 V−1 s−1 and yielded enhancements 2 and 10 times, respectively, beyond those of devices with typically evaporated electrodes. In addition, to develop ambipolar devices with balanced output capability, two-dimensional materials (h-BN and graphene) were inserted into the MS interface to tune the injection barrier. Because the metal work function was effectively reduced by inserting the h-BN layer, devices with h-BN inserted obtained values of μp and μn of 15.85 and 5.1 cm2 V−1 s−1, respectively. For devices with graphene, because of its field-modulated band alignment capability, μn improved to 8.38 cm2 V−1 s−1, while μp dropped slightly to 17.5 cm2 V−1 s−1. Therefore, the vdW contact method is a highly efficient integration strategy for high-performance CNT network FETs, and the different insertion layers can efficiently tune the ambipolar transportation of CNT network FETs rather than using different contact metals. This research provides an avenue for the design of future CNT network-based electronics.

Effect of proton irradiation on poly(vinylidene fluoride-trifluoroethylene) 56/44 mol % copolymer has been studied using a Mach–Zehnder heterodyne interferometer, polarization hysteresis loop and dielectric constant measurements. The electrical-field-induced strain response of the copolymer after proton bombardment follows a quadratic electrostriction relationship. The electrostrictive coefficient at 5 kHz is similar to that obtained with a bimorph-based strain sensor, but at a much lower electric field. The polarization hysteresis after proton irradiation is reduced considerably and the dielectric constant exhibits typical relaxor behavior, which is suggested as the cause of the observed results.

Electrical field-induced strain response of electron-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer has been studied by a Mach–Zehnder type heterodyne interferometer in the frequency range of 3–9 kHz. The electrostrictive constant is calculated from the strain results, which is of the same order of magnitude as those obtained at 1 Hz by a bimorph-based strain sensor but at much lower electrical field. Changes in the dielectric property, phase transition behavior and crystal structure of the same copolymer have also been studied. The reversible solid–state transition between the polar and nonpolar phase in the crystalline regions of the copolymer driven by the external electric field is suggested to be responsible for the significant high electrostrictive strain of the electron-irradiated copolymer.

Both direct current (DC) and alternating current (AC) driving electroluminescence were obtained from isotype heterojunction (n-i-n: n-ZnO/i-HfO2/n-GaN) light-emitting diodes (LEDs) fabricated by a pulsed laser deposition system. The n-ZnO film maintained the same growth orientation as the n-GaN film and was of high crystalline quality even on a polycrystalline high-k HfO2 thin film. The as-produced n-i-n LEDs can emit strong visible light or dominant ultraviolet light at ∼392 nm, depending on the polarity of the applied DC voltages. The individual spectrum under either forward or reverse bias can be integrated to one spectrum by applying 50 Hz AC driving voltages (sinusoidal signals). More importantly, near white-light can be obtained by tuning the symmetric driving AC sinusoidal signals to the asymmetric ones. This simple and facile method only by applying AC asymmetric signals to achieve white light emission on one single chip may provide an easy route for the white-light solid-state lighting industry.

The atomic-scale oxide growth dynamics are directly revealed by in situ high resolution transmission electron microscopy during the oxidation of Mg surface. The oxidation process is characterized by the layer-by-layer growth of magnesium oxide (MgO) nanocrystal via the adatom process. Consistently, the nucleated MgO crystals exhibit faceted surface morphology as enclosed by {200} lattice planes. It is believed that the relatively lower surface energies of {200} lattice planes should play important roles, governing the growth mechanism. These results facilitate the understanding of the nanoscale oxide growth mechanism that will have an important impact on the development of magnesium or magnesium alloys with improved resistance to oxidation.

We report a continuously tunable resistive switching behavior in Pt/BiFeO3/Nb-doped SrTiO3 heterostructure for ferroelectric memristor application. The resistance of this memristor can be tuned up to 5 × 105% by applying voltage pulses at room temperature, which exhibits excellent retention and anti-fatigue characteristics. The observed memristive behavior is attributed to the modulation effect of the ferroelectric polarization reversal on the width of depletion region and the height of potential barrier of the p-n junction formed at the BiFeO3/Nb-doped SrTiO3 interface.

We report the epitaxial growth of multiferroic BiFeO3 (BFO) film on Si(001) substrate by pulsed laser deposition using CeO2/yttria-stabilized zirconia (YSZ) as buffer layers. The epitaxial relationships of the films were BFO(001)/CeO2(001)/YSZ(001)/Si(001) for out-of-plane and [110]BFO‖[100]CeO2‖[100]YSZ‖[100]Si for in-plane, respectively. Capacitance-voltage characteristics of a Pt/BFO/CeO2/YSZ/p-Si capacitor exhibited clockwise hysteresis loops with a large memory window of 2.5 V at sweeping voltages of ±16 V. Both the high and low capacitance values showed no obvious degradation after 104 s. The improved retention property was attributed to the use of high-k CeO2/YSZ insulating layers that effectively eliminated the charge trapping in the heterostructure.

n-ZnO/HfO2/p-GaN based heterojunction light emitting diodes were fabricated using a radio frequency magnetron sputtering system. The electroluminescence measurements revealed that dominant violet emissions centered at around 415 nm were emitted and improved performances were observed for the devices with the HfO2 intermediate layer; the color of the devices could be tuned from violet (0.18, 0.10) to cold white (0.22, 0.20) by varying the Ar/O2 flow ratio during the deposition of HfO2, which are probably ascribed to the deep level emission bands in ZnO. The results were studied by peak-deconvolution with Gaussian functions and were discussed in terms of band diagram of the heterojunctions.

We fabricate an ultraviolet (UV)/orange bicolor light emitting diode (LED) based on an n-ZnO/n-GaN isotype heterojunction, which presents a sharp ultraviolet emission centered at 367 nm and a broad orange emission centered at 640 nm under forward and reverse biases, respectively. Time dependence electroluminescence (EL) measurements reveal that this device shows good stability. The electroluminescence mechanism of the bicolor light emitting diode is discussed in terms of the material properties of the interfacial layer and the luminescence properties of the device in this work.

Organic solar cells based on vertically aligned zinc oxide nanorod arrays (ZNR) in an inverted structure of indium tin oxide (ITO)∕ZNR∕poly(3-hexylthiophene): (6,6)-phenyl C61 butyric acid methyl ester(P3HT:PCBM)∕MoO(3)∕aluminum(Al) were studied. We found that the optimum MoO(3) layer thickness condition of 20 nm, the MoO(3) can effectively decrease the probability of bimolecular recombination either at the Al interface or within the active layer itself. For this optimum condition we get a power conversion efficiency of 2.15%, a short-circuit current density of 9.02 mA∕cm(2), an open-circuit voltage of 0.55V, and a fill factor of 0.44 under 100 mW∕cm(2) irradiation. Our investigations also show that the highly crystallized ZNR can create short and continuous pathways for electron transport and increase the contact area between the ZNR and the organic materials.

ZnO nanorod strain driving transistor (SDT) with 107 scale “on”-“off” ratio has been fabricated on Kapton substrate by a single-step hydrothermal reaction. The transistor is driven by strain due to the change in Schottky barrier height caused by piezoelectric effect as well as the change of contact area between ZnO bridging nanorods. Moreover, via utilizing two SDTs on the top and bottom surfaces of the substrate as two complementary metal-oxide-semiconductor transistors, several logic operations such as inverter, NAND, NOR, XOR, MUX, and DEMUX with good rectifying behaviors have been demonstrated.

A valve-based microfluidic device was developed for droplet on-demand operation and static assay. Droplet generation with precise and expectant volume, transportation, fusion, and trapping was achieved by integration of microvalves with programed control. Based on this automatic unique function combination, a droplet team was created with a controllable proportion of components. A DNA sample was encapsulated into the aqueous droplets, selectively merged with probe droplet in the desired ratio, well mixed, and then trapped for the static fluorescence assay with a total reagent consumption of no more than 2 μl. This method would have a powerful potential for biochemical or chemical research.

A simple and effective droplet electric separator microfluidic device was developed for cell sorting. The aqueous droplet without precharging operation was influenced to move a distance in the channel along the electric field direction by applying dc voltage on the electrodes beside the channel, which made the target droplet flowing to the collector. Single droplet can be isolated in a sorting rate of ∼100 Hz with microelectrodes under a required pulse. Single or multiple mammalian cell (HePG2) encapsulated in the surfactant free alginate droplet could be sorted out respectively. This method may be used for single cell operation or analysis.

Nanomotors represent a significant step forward in nanotechnology, and prove that nanotubes and other nanostructures several hundred times smaller than the diameter of a human hair can be manipulated and assembled into true devices. In this letter, nanotubes based nanomotors are reported. The nanomotors were observed to move at a velocity of ∼0.5 m/s, which is several orders of magnitude faster than current nanomotors. Concentration difference energy was thought to provide the main motive forces to drive these nanomotors. This phenomenon which is seldom observed at macroscopic scale, is common in microscale, and can be employed to explain some motions of nano- and microscale objects.

The authors report on the field emission from controlled selective grown zinc oxide (ZnO) nanorod arrays by hydrothermal reaction. With the combined effect from a ZnO seed layer and a passivation layer for nanorod growth, ZnO nanorods could only grow on the edge of a 4 μm diameter circle. The ZnO nanorods hollow arrays present excellent electron emission characteristics duo to its typical morphology which can significantly diminish the screen effect. By calculating the electrostatic field distribution, it was found that the electrostatic field of the ZnO nanorods hollow arrays is significantly higher than that of the solid arrays.

The sequential resonant tunneling in La0.5Sr0.5CoO3−δ (LSCO) semiconductor quantum dots (QDs) arrays were observed by current-voltage measurements under room temperature. A series of spikelike current peaks are found, which are resulted from the accumulation and depletion of electrons tunneling through the QDs embedded in insulated barriers. Temperature dependent onset-voltage blueshift and number variation in current peaks are also observed. These results confirm the size-induced metal-to-semiconductor transition in LSCO.

Ultraviolet light-emitting diodes based on ZnO/NiO heterojunctions were fabricated on commercially available n + -GaN /sapphire substrates using a radio frequency magnetron sputtering system. Near band edge emission of ZnO peaking at ∼ 370 nm with a full-width at half maximum of ∼ 7 nm was achieved at room temperature when the devices were under sufficient forward bias. With the help of an electron blocking i -Mg 1 − x Zn x O ( 0 x 1 ) layer inserted between the ZnO and NiO layers, the emission intensity has been much enhanced and the threshold current drops down to ∼ 23 from ∼ 70 mA . The results were discussed in terms of the band diagrams of the heterojunctions.

N-ZnO nanorods/n-silicon heterojunction was fabricated by growth of ZnO nanorods on a n-type silicon (111) wafer with a low-temperature aqueous solution method. Capacitance-voltage measurements revealed that after annealing at 900 °C in O2 ambient for 1 h, the heterojunction changed from abrupt N-ZnO nanorods/n-silicon to graded P-ZnO/n-silicon junction. The annealed diode showed good photoresponse in both the ultraviolet and visible regions with responsivity around 0.3 and 0.5 A/W without bias. The photoresponses toward ultraviolet and visible light were enhanced when the diode was under reverse and forward bias, respectively. The results were discussed in terms of phosphorus diffusion process and the band diagrams of the heterojunctions in this work.

n-ZnO/p-silicon nanowire (SiNW) photodiodes were prepared by radio frequency reactive magnetron sputtering of n-type zinc oxide at room temperature on photoresist filled p-SiNWs, which were fabricated by electroless metal deposition method at 323 K. Our n-ZnO/p-SiNW photodiodes showed good temperature- and light-intensity dependence. They exhibited strong responsivities of 19.2 and 2.5 A/W for 254 and 1000 nm photons, respectively, under a reverse bias of 2 V with a strong peak of responsivity near 390 nm, the wavelength corresponding to the band gap of ZnO. These results present potential applications of n-ZnO/p-SiNW photodetectors in deep ultraviolet and near infrared regions.

High-valence Pr-doped BiFeO3 (BPF) multiferroic thin film was prepared by pulsed laser deposition on a Pt∕TiO2∕SiO2∕Si substrate. X-ray diffraction analysis indicates that the BPF film is of pure phase with a polycrystalline perovskite structure. The BPF film exhibited enhanced multiferroic properties: (i) a rectangular-shaped electric hysteresis loop with a large Pr of 75μC∕cm2 and a low Ec of 250kV∕cm at Emax ∼620kV∕cm, (ii) a saturated magnetic hysteresis loop with a large Ms of 58emu∕cm3, and (iii) a fatigue-free behavior after being subjected to 1.2×109 switching cycles, which were superior to, in some aspects, those of La- or Nd-doped BiFeO3 films reported before.

We report on the feasible fabrication of microfluidic devices for noncontact particle trapping. A half-wavelength resonator was constructed using standard soft lithography to generate ultrasonic standing waves through a miniature piezoelectric transducer. Microparticles (400nm to 10μm in diameter) flowing through polydimethylsiloxane microchannels were efficiently trapped to levitate in the middle depth of a resonance cavity. Such a device could potentially offer a flexible platform for particle-based assays for a large variety of applications.

A surface modification method was carried out by rf magnetron sputtering to fabricate ZnO-coated TiO2 electrodes (TiO2∕ZnO) for improving the performance of dye-sensitized solar cells. The TiO2∕ZnO electrodes had been characterized by x-ray photoelectron spectroscopy, scanning electron microscopy, UV-visible spectrophotometer, and electrochemical impedance spectroscopy. The study results revealed that the TiO2 modification suppresses interfacial recombination. Sputtering ZnO for 3min on 5μm TiO2 greatly improves all cell parameters, resulting in increasing efficiency from 4.76% to 6.55%.

The authors have prepared poly(vinylidenefluoride-trifluoroethylene) Ni∕P(VDF-TrFE) nanoscaled coaxial cables with Ni nanowires as the cores and P(VDF-TrFE) nanotubes as the shells by a two-step process. Scanning electron microscope and x-ray diffraction measurements revealed the microstructure and crystallinity of the nanocables. Electrical measurements indicated that the nanocables possessed a large specific capacitance (∼10.84pC∕mm2) and ferroelectric remnant polarization (∼10μC∕cm2) due to the composite structure. The distribution of electrical field in the nanostructure was also analyzed.

Bi1.5Zn1.0Nb1.5O7∕Ba0.6Sr0.4TiO3∕Bi1.5Zn1.0Nb1.5O7 (BZN/BST/BZN) sandwich films were deposited by radio frequency magnetron sputtering. The relative permittivity and dielectric loss of the sandwich films were measured using planar Pt∕BZN∕BST∕BZN∕Pt∕Ti∕SiO2∕Si capacitor structures. The sandwich films with thickness of about 280nm exhibited relative permittivity around 206–247 and dielectric loss tangent (tanδ) less than 0.008 at 1MHz. Films annealed at 750°C had an ∼11% relative tunability of the permittivity at a maximum applied bias field of 0.77MV∕cm. The sandwich films are not ferroelectric at room temperature.

The radiation properties of an asymmetrical two-dimensional phononic crystal resonant cavity with a point source inside are investigated experimentally. The resonant cavity is formed by two separated phononic crystals of different thickness, both of which consist of the same square array of steel rods in water. We observe highly directional acoustic wave radiation when a point acoustic source is put inside the cavity. The radiation field has a half-power beam width less than 6°. This design may serve as a highly directional acoustic source in applications.

A microstrip filter with an H-shaped fractal pattern is proposed. It is found that the microstrip filter has multiple gaps and passbands for electromagnetic waves over an ultrawide frequency range, and the band gaps shift to lower frequencies with the increasing first level length of the fractal structure, showing tunable band gap properties. Experimental observations are in good agreement with simulations by the finite-difference-time-domain method. A prototype of the microstrip filter was fabricated by conventional low-cost printed circuit board techniques.