Utilization of surface plasmon resonance of Au/Pt nanoparticles for highly photosensitive ZnO nanorods network based plasmon field effect transistor

Hydrothermally processed highly photosensitive ZnO nanorods based plasmon field effect transistors (PFETs) have been demonstrated utilizing the surface plasmon resonance coupling of Au and Pt nanoparticles at Au/Pt and ZnO interface. A significantly enhanced photocurrent was observed due to the plasmonic effect of the metal nanoparticles (NPs). The Pt coated PFETs showed I_on/I_off ratio more than 3 × 10⁴ under the dark condition, with field-effect mobility of 26 cm² V⁻¹ s⁻¹ and threshold voltage of −2.7 V. Moreover, under the illumination of UV light (λ = 350 nm) the PFET revealed photocurrent gain of 10⁵ under off-state (−5 V) of operation. Additionally, the electrical performance of PFETs was investigated in detail on the basis of charge transfer at metal/ZnO interface. The ZnO nanorods growth temperature was preserved at 110 °C which allowed a low temperature, economical and simple method to develop highly photosensitive ZnO nanorods network based PFETs for large scale production.     

Synthesis of defect-rich, (001) faceted-ZnO nanorod on a FTO substrate as efficient photocatalysts for dehydrogenation of isopropanol to acetone

Highly oriented ZnO nanorod was successfully synthesised on Ag nanoseed coated FTO substrate via a microwave hydrolysis approach. It was found that the morphology and the optical properties of the ZnO nanorod are strongly influenced by the power of the microwave irradiation used during the growth process. The aspect ratio of the nanorods changed from high to low with the increasing of microwave power. It was also found that the optical band gap of the ZnO nanorod red shifted with the increasing of the microwave power, reflecting an excellent tune ability of the optical properties of ZnO nanorods. The photocatalytic activity of these unique nanorod was evaluated by a dehydrogenation process of isopropanol to acetone in the presence of ZnO nanorod. It was found that the ZnO nanorod exhibited an excellent catalytic performance by showing an ability to accelerate the production of 0.031 mol L⁻¹ of acetone within only 35 min or 0.9 mmol L⁻¹ min⁻¹ from isopropyl alcohol dehydrogenation. It was almost no conversion from isopropyl alcohol when ZnO nanorods was absence during the reaction. In this report, a detailed mechanism of ZnO nanorod formation and the relationship between morphology and optical energy band gap are described.     

Enhanced power efficiency of ZnO based organic/inorganic solar cells by surface modification

We present series of strategies to enhance efficiency of ZnO nanorods based organic/inorganic solar cells with spin-coated P3HT:PCBM blend as active layer. The performance of the as-fabricated devices is improved by controlling the size of ZnO nanorods, annealing temperature and time of active layer, surface modification of ZnO with PSBTBT. Optimized device of ITO/ZnO nanorod/P3HT:PCBM/Ag device with PSBTBT surface modification and air exposure reaches an efficiency of 2.02% with a short-circuit current density, open-circuit voltage and fill factor of 13.23 mA cm⁻², 0.547 V and 28%, respectively, under AM 1.5 irradiation of 100 mW m⁻², the increase in efficiency is 7-fold of the PSBTBT surface modified ITO/ZnO nanorods/P3HT:PCBM/Ag device compared with the unmodified one, which is own to the increased interface contact, expanded light absorption, tailored band alignment attributed to PSBTBT. We found exposure to air and surface modification is crucial to improve the device performance, and we discussed the mechanisms that affect the performance of the devices in detail.     

Characteristics of ZnO MSM UV photodetector with Ni contact electrodes on poly propylene carbonate (PPC) plastic substrate

In this study, we report the fabrication of ZnO metal-semiconductor-metal UV photodetector (MSM UV PD) by deposition ZnO thin film on poly propylene carbonate (PPC) plastic substrate using direct current (DC) sputtering technique, and Nickel (Ni) contact as electrodes. The structural, optical and electrical properties of the ZnO thin film were investigated by using atomic force microscopy (AFM), X-Ray diffraction (XRD) measurement, and photoluminescence (PL). The electrical characteristics of the detector were investigated using the current–voltage (I–V) measurements, the dark- and photo-currents were found to be 1.04 and 93.80 μA, respectively. Using forward dark conditions at 5 volt; the barrier height Φ_B was calculated to be 0.675 eV. Under incident wavelength of 385 nm, it was found that the maximum responsivity (R) of the Ni/ZnO/Ni MSM PD was found to be 1.59 A/W.     

Mid-infrared photoconductive properties of heavily Bi-doped PbTe p–n homojunction diode grown by liquid-phase epitaxy

We fabricated a heavily Bi-doped (x_Bi ≈ 2 × 10¹⁹ cm⁻³) PbTe p–n homojunction diode that detects mid-infrared wavelengths by the temperature difference method (TDM) under controlled vapor pressure (CVP) liquid phase epitaxy (LPE). The photocurrent density produced by the heavily Bi-doped diode sample is approximately 20 times and 3 times greater than that produced by an undoped and heavily In-doped sample, respectively. By varying the ambient temperature from 15 K to 225 K, the detectable wavelength is tunable from 6.18 μm to 4.20 μm. The peak shift of the detectable wavelength is shorter in the heavily Bi-doped sample than in the undoped sample, consistent with our previously proposed model, in which Bi–Bi nearest donor–acceptor pairs are formed in the heavily Bi-doped PbTe liquid phase epitaxial layer. Current–voltage (I–V) measurements of the heavily Bi-doped diode sample under infrared exposure at 77 K indicated a likely leak in the dark current, arising from the deeper levels. From the dark I–V measurements, the activation energy of the deep level was estimated as 0.067 eV, close to the energy of the deep Tl-doped PbTe acceptor layer. We conclude that the deep level originates from the Tl-doped p-type epitaxial layer.     

Controllable synthesis of rice-shape Alq3 nanoparticles with single crystal structure

We report the controllable growth of rice-shape nanoparticles of Alq₃ by an extremely facile self-assembly approach. Possible mechanisms have been proposed to interpret the formation and controlled process of the single crystal nanoparticles. The field-emission performances (turn-on field 7 V μm⁻¹, maximum current density 2.9 mA cm⁻²) indicate the potential application on miniaturized nano-optoelectronics devices of Alq₃-based. This facile method can potentially be used for the controlled synthesis of other functional complexes and organic nanostructures.     

Experimental investigation on the structural,dielectric, ferroelectric and piezoelectric properties of La doped ZnO nanoparticles and their application in dye-sensitized solar cells

Pure and lanthanum (La) doped ZnO nanorods were synthesized via co-precipitation method. The structure and morphology of as grown ZnO and La-ZnO nanoparticles were studied using transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) methods. The values of remnant polarization and coercive field were found to be 0.027 μC/cm² and 1.33 kV/cm, respectively, for as grown La-ZnO nanostructures. High Curie temperature (276 °C) for doped ZnO was observed in dielectric study. Piezoelectric coefficient at room temperature was found to be 101.30 pm/V. I-V characteristics were studied for both pure and doped ZnO nanoparticles. Photo-anodes of dye-sensitized solar cells (DSSCs) were made using ZnO and La-ZnO nanorods. The conversion efficiency and short circuit current density of La-ZnO nanorods based DSSC were 0.36% and 1.31 mA/cm², respectively, which were found to be largely enhanced when compared with that of pure ZnO based DSSC (0.20% and 0.94 mA/cm²).     

The effect of annealing in forming gas on the a-IGZO thin film transistor performance and valence band cut-off of IGZO on SiNx

In this investigation, the carrier concentration gradient between channel and contact region is achieved to improve the Thin film Transistors (TFT) performance by employing annealing at 350 °C in forming gas (N₂ + 5% H₂). The contact region is covered with Mo metal and the channel region is only exposed to forming gas to facilitate the diffusion controlled reaction. The TFT using a-IGZO active layer is fabricated in ambient of Ar:O₂ in ratio 60:40 and the conductivity of the order of 10⁻³ S/cm is measured for as-deposited sample. The electrical conductivity of an annealed sample is of the order of 10² S/cm. The device performance is determined by measuring merit factors of TFT. The saturation mobility of magnitude 18.5 cm²V⁻¹ s⁻¹ has been determined for W/L (20/10) device at 15 V drain bias. The extrapolated field effect mobility for a device with channel width (W) 10 μm is 19.3 cm²V⁻¹ s⁻¹. The on/off current ratio is 10⁹ and threshold voltage is in the range between 2 and 3 V. The role of annealing on the electronic property of a-IGZO is carried out using X-ray photoelectron spectroscopy (XPS). The valance band cut-off has been approximately shifted to higher binding energy by 1 eV relative to as-deposited sample.     

High quality nitrogen-doped zinc oxide thin films grown on ITO by sol–gel method

Highly transparent N-doped ZnO thin films were deposited on ITO coated corning glass substrate by sol–gel method. Ammonium nitrate was used as a dopant source of N with varying the doping concentration 0, 0.5, 1.0, 2.0 and 3.0 at%. The DSC analysis of prepared NZO sols is observed a phase transition at 150 °C. X-ray diffraction pattern showed the preferred (002) peak of ZnO, which was deteriorated with increased N concentrations. The transmittance of NZO thin films was observed to be ~88%. The bandgap of NZO thin films increased from 3.28 to 3.70 eV with increased N concentration from 0 to 3 at%. The maximum carrier concentration 8.36×10¹⁷ cm⁻³ and minimum resistivity 1.64 Ω cm was observed for 3 at% N doped ZnO thin films deposited on glass substrate. These highly transparent ZnO thin films can be used as a window layer in solar cells and optoelectronic devices.     

Correlation between sintering temperature and properties of ZnO ceramic varistors

The effect of sintering temperature on ZnO varistor properties is investigated in the range of 700–1400 °C. The increase of sintering temperature does not influence the well-known peaks related to hexagonal wurtzite structure of ZnO ceramics, whereas the average grain size is increased from (1.08 to 2.1 μm). With increasing sintering temperature up to 1200 °C, the nonlinear region is clearly observed in the I–V characteristics, whereas this region is completely absent only for the sample sintered at 1400 °C. As the sintering temperature increased, the breakdown field decreased over a wide range from 2838.7 to 6.41 V/cm, while the nonlinear coefficient is increased in the range of (23.86–47.76). Furthermore, the barrier height decreased from 1.76 to 0.974 eV, whereas electrical conductivity is improved. On the other hand, the optical band gap is gradually decreased in the range of 3.08–2.70 eV with increasing sintering temperature. These results showed a strong correlation between sintering temperature and the properties of ZnO ceramic varistor.     

Investigation of a graded channel InGaAs/GaAs heterostructure transistor

An InGaAS/GaAs heterostructure transistor utilizing a gradedIn_xGa_1 − xAs channel grown by low-pressure metal-olorganic chemical vapor deposition has been demonstrated. A negative differential resistance (NDR) phenomenon is observed. Electron mobilities are significantly improved by using the graded InGaAs channel. For the In composition varying fromx =  0.25 (at the buffer–channel interface) to x =  0.1 (at the spacer–channel interface) structure, a peak extrinsic transconductance of 24.6 S mm ^− 1(atV_DS =  6.5 V,V_GSstep =  − 0.5 mV) and a saturation current density as high as 555 mA mm ^− 1for a gate length of 1.5 μ m are obtained.     

Microstructure and varistor properties of ZnO–V2O5–MnO2 ceramics with Ta2O5 addition

The effect of Ta₂O₅ addition on microstructure, electrical properties, and dielectric characteristics of the quaternary ZnO–V₂O₅–MnO₂ vaistor ceramics was investigated. Analysis of the microstructure indicated that the quaternary ZnO–V₂O₅–MnO₂–Ta₂O₅ ceramics consisted of mainly ZnO grain and minor secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, TaVO₅, and Ta₂O₅. As the amount of Ta₂O₅ increased, the sintered density increased from 94.8 to 97.2% of the theoretical density (5.78 g/cm³ for ZnO), whereas the average grain size decreased from 7.7 to 6.0 μm. The ceramics added with 0.05 mol% Ta₂O₅ exhibited the highest breakdown field (2715 V/cm) and the highest nonlinear coefficient (20). However, further increase caused α to abruptly decrease. The Ta₂O₅ acted as a donor due to the increase of electron concentration in accordance with the amount of Ta₂O₅. The donor concentration increased from 1.97×10¹⁸ to 3.04×10¹⁸cm^?3 with increasing the amount of Ta₂O₅ and the barrier height exhibited the maximum value (0.95 eV) at 0.05 mol% Ta₂O₅.     

Electrically forced microthreading of highly viscous dielectric liquids

The behaviour of three high viscosity (4875, 12 125 and 58 560 mPa s), dielectric liquids was investigated at flow rates of 10⁻¹⁰, 10⁻¹² and 10⁻¹⁴ m³ s⁻¹ and the applied voltage range 6–15 kV. In these experiments, due to the low electrical conductivity of the liquids (10⁻¹³ S m⁻¹) and therefore the ensuing high electrical relaxation time, classical electrohydrodynamic atomization conditions are not satisfied. Only dripping and unstable jetting were observed at 4875 mPa s. A transition from no jetting to stable microthreading was observed for the 12 125 and 58 560 mPa s samples. The relics accompanying the transition were found to change from discrete droplets to a continuous filament. Stable microthreading, which generates uniform filaments, was obtained for the 12 125 mPa s sample at flow rates 10⁻¹⁰ and 10⁻¹² m³ s⁻¹ and in the case of the 58 560 mPa s sample at all the flow rates investigated. The high viscosity assisted stable microthreading with the filament diameter decreasing with increasing applied voltage and more dramatically decreasing with reducing flow rate.     

Device linearity improvement and current enhancement utilizing high-to-low doping-channel FETs

We report device linearity improvement and current enhancement in both a heterostructure FET (HFET) and a camel-gate FET (CAMFET) using InGaAs/GaAs high-low and GaAs high-medium-low doped channels, respectively. In an HFET, a low doped GaAs layer was employed to build an excellent Schottky contact. In a GaAs CAMFET, a low doped layer together withn⁺andp⁺layers formed a high-performance majority camel-diode gate. Both exhibit high effective potential barriers of >1.0 V and gate-to-drain breakdown voltages of >20.0 V (atI_g=1.0 mA mm⁻¹). A thin, high doped channel was used to enhance current drivability and to improve the transconductance linearity. A 2×100 μm²HFET had a peak transconductance of 230 mS mm⁻¹and a current density greater than 800 mA mm⁻¹. The device had a transconductance of more than 80 percent of the peak value over a wide drain current range of 200 to 800 mA mm⁻¹. A 1.5×100 μm²CAMFET had a peak transconductance of 220 mS mm⁻¹and a current density greater than 800 mA mm⁻¹. Similarly, the device had a transconductance of more than 80 percent of the peak value over a wide drain current range of 160 to 800 mA mm⁻¹. The improvement of device linearity and the enhancement of current density suggest that high-to-low doped-channel devices for both an HFET and a CAMFET are suitable for high-power large signal circuit applications.     

Controlled fabrication of Si nanostructures by high vacuum electron beam annealing

Silicon nanostructures, called Si nanowhiskers, have been successfully synthesized on Si(1 0 0) substrate by high vacuum electron beam annealing (EBA). Detailed analysis of the Si nanowhisker morphology depending on annealing temperature, duration and the temperature gradients applied in the annealing cycle is presented. A correlation was found between the variation in annealing temperature and the nanowhisker height and density. Annealing at 935 °C for 0 s, the density of nanowhiskers is about 0.2 μm⁻² with average height of 2.4 nm grow on a surface area of 5×5 μm, whereas more than 500 nanowhiskers (density up to 28 μm⁻²) with an important average height of 4.6 nm for field emission applications grow on the same surface area for a sample annealed at 970 °C for 0 s. At a cooling rate of −50 °C s⁻¹ during the annealing cycle, 10–12 nanowhiskers grew on a surface area of 5×5 μm, whereas close to 500 nanowhiskers grew on the same surface area for samples annealed at the cooling rate of −5 °C s⁻¹. An exponential dependence between the density of Si nanowhiskers and the cooling rate has been found. At 950 °C, the average height of Si nanowhiskers increased from 4.0 to 6.3 nm with an increase of annealing duration from 10 to 180 s. A linear dependence exists between the average height of Si nanowhiskers and annealing duration. Selected results are presented showing the possibility of controlling the density and the height of Si nanowhiskers for improved field emission properties by applying different annealing temperatures, durations and cooling rates.     

Pressure induced structural change in PbPc studied by infrared and UV–visible spectroscopy and theoretical calculation

Lead phthalocyanine (PbPc) has a non-planar ‘shuttle-cock’ structure with a C_4v molecular symmetry and forms a one-dimensional column in the crystal. We measured infrared and UV–visible spectra for the PbPc crystal under high hydrostatic pressure by using a diamond anvil cell. The IR spectrum of PbPc shows three strong peaks in the 1000–1200 cm⁻¹ region. With increasing pressure, the intensity ratio of the middle peak to the other two peaks increased. This result suggests a structural transformation of the PbPc molecule from the shuttle-cock structure toward the planar structure with increasing pressure. In the UV–visible spectra, two remarkable changes were observed under high pressure: the peak intensity of the band at 2.7 eV was decreased, and the band at 1.5 eV was shifted to lower energy and broadened. The former feature suggests that the highest occupied molecular orbital (HOMO) band is not filled perfectly in the solid-state of PbPc under ambient pressure, and that the filling of the HOMO band occurs with increasing pressure. The change on the low energy band at 1.5 eV due to increasing pressure can be attributed to an increase in the intermolecular interaction.     

Studies on structural and magnetic properties of Co-doped pyramidal ZnO nanorods synthesized by solution growth technique

Large-area arrays of highly oriented Co-doped ZnO nanorods with pyramidal hexagonal structure are grown on silica substrates by wet chemical decomposition of zinc–amino complex in an aqueous medium. In case of undoped ZnO with an equi-molar ratio of Zn²⁺/hexamethylenetetramine (HMT), highly crystalline nanorods were obtained, whereas for Co-doped ZnO, good quality nanorods were formed at a higher Zn²⁺/HMT molar ratio of 4:1. Scanning electron microscope (SEM) studies show the growth of hexagonal-shaped nanorods in a direction nearly perpendicular to the substrate surface with a tip size of ～50 nm and aspect ratio around 10. The XRD studies show the formation of hexagonal phase pure ZnO with c-axis preferred orientation. The doping of Co ions in ZnO nanorods was confirmed by observation of absorption bands at 658, 617 and 566 nm in the UV–vis spectra of the samples. The optical studies also suggest Co ions to be present both in +2 and +3 oxidation states. From the photoluminescence studies, a defect-related emission is observed in an undoped sample of ZnO at 567 nm. This emission is significantly quenched in Co-doped ZnO samples. Further, the Co-doped nanorods have been found to show ferromagnetic behavior at room temperature from vibrating sample magnetometer (VSM) studies.     

Magnetism in nanocrystalline SiC films

Magnetism been studied in two series of nanocrystalline SiC films obtained by the method of direct deposition of ions with an energy of ~100 eV at temperatures 1150 °С and 1200 °С. There were separated the contributions of diamagnetism, paramagnetism and superparamagnetism+ferromagnetism. Magnetization value of the films correlates with the deposition temperature. In the films deposited at higher temperatures the value of magnetization was by 1.5 times lower. It was concluded that induced magnetism in nanocrystalline SiC films is caused by interaction of magnetic moments of neutral V_SiV_C divacancies in separate nanocrystals. The estimated concentration of neutral V_SiV_C divacancies in nanocrystalline SiC films is ~10²⁰ сm⁻³.     

Fiber curvature sensor based on spherical-shape structures and long-period grating

A novel curvature sensor based on optical fiber Mach–Zehnder interferometer (MZI) is demonstrated. It consists of two spherical-shape structures and a long-period grating (LPG) in between. The experimental results show that the shift of the dip wavelength is almost linearly proportional to the change of curvature, and the curvature sensitivity are −22.144 nm/m⁻¹ in the measurement range of 5.33–6.93 m⁻¹, −28.225 nm/m⁻¹ in the range of 6.93–8.43 m⁻ and −15.68 nm/m⁻¹ in the range of 8.43–9.43 m⁻¹, respectively. And the maximum curvature error caused by temperature is only −0.003 m⁻¹/°C. The sensor exhibits the advantages of all-fiber structure, high mechanical strength, high curvature sensitivity and large measurement scales.     

Hydrophilic polyaniline nanofibrous architecture using electrosynthesis method for supercapacitor application

An electrosynthesis process of hydrophilic polyaniline nanofiber electrode for electrochemical supercapacitor is described. The TGA–DTA study showed polyaniline thermally stable up to 323 K. Polyaniline nanofibers exhibit amorphous nature as confirmed from XRD study. Smooth interconnected fibers having diameter between 120–125 nm and length typically ranges between 400–500 nm observed from SEM and TEM analysis. Contact angle measurement indicated hydrophilic nature of polyaniline fibers. Optical study revealed the presence of direct band gap with energy 2.52 eV. The Hall effect measurement showed room temperature resistivity ∼3 × 10⁻⁴ Ω cm and Hall mobility 549.35 cm⁻²V⁻¹ s⁻¹_. The supercapacitive performance of nanofibrous polyaniline film tested in 1 M H₂SO₄ electrolyte and showed highest specific capacitance of 861 F g⁻¹ at the voltage scan rate of 10 mV/s.