The synthesis and properties of nanocrystalline electrode materials by mechanical alloying

In this work, we have experimentally studied the structure and electrochemical properties of nanocrystalline TiFe- and LaNi₅-type alloys. These materials were prepared by mechanical alloying (MA) followed by annealing. The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics. It was found that the respective replacement of Fe in TiFe by Ni and/or by Cr, Co, Mo, Zr improved not only the discharge capacity but also the cycle life of these electrodes. In the nanocrystalline TiFe_0.25Ni_0.75, powder discharge capacity up to 155 mA h g⁻¹ was measured (at 40 mA g⁻¹ discharge current). On the other hand, a partial substitution of Ni by Al or Mn in LaNi_5−xM_x alloy leads to an increase in discharge capacity. The alloying elements such as Al, Mn and Co greatly improved the cycle life of LaNi₅ material. For example, in the nanocrystalline LaNi_3.75Mn_0.75Al_0.25Co_0.25 powder, discharge capacity up to 258 mA h g⁻¹ was measured (at 40 mA g⁻¹ discharge current). The studies show, that electrochemical properties of Ni–MH batteries are the function of the microstructure and the chemical composition of used electrode materials.     

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.     

Carbon fiber formation in electrical discharges in hydrocarbons

The process of synthesis of carbon fiber from hydrocarbon vapours in low-current electrical-discharge plasma was investigated in the paper. The carbon fibers were effectively synthesised in discharge of positive polarity generated between a stainless steel needle and a plate made of nickel alloy, for the discharge current ranged from 1 mA up to 3 mA. The experiments were carried out at normal pressure in cyclohexane vapours with argon as carrier gas. The diameter of produced fibers varied from about 20 to 70 μm. The growth rate of the fiber was about 0.25 mm/s.     

Low temperature synthesis of layered LiNiO2 cathode material in air atmosphere by ion exchange reaction

The layered LiNiO₂ cathode material for lithium ion battery was synthesized by ion-exchange reaction at low temperature in air atmosphere. The influence of synthesis conditions on the electrochemical performance of the resulting LiNiO₂ was investigated. The LiNiO₂ samples were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and infrared (IR) analysis. The results indicate that low temperature fabricated LiNiO₂ powders keep a single layered hexagonal structure and homogenous spheric shape like the raw material NiOOH. Charge and discharge tests show that the resultant LiNiO₂ exhibits good electrochemical properties. The first charge and discharge capacities of the sample are 183.4 mA h g^− 1 and 169.5 mA h g^− 1 at 0.5 mA cm^− 2, respectively. Galvanic charge/discharge and cyclic voltammetry tests reflect that LiNiO₂ electrode exhibits good cycle reversibility.     

Fabrication of thin-film transistor based on self-assembled single-walled carbon nanotube network

Thin-film transistor based on controllable electrostatic self-assembled monolayer single-wall carbon nanotubes (SWNTs) network has been fabricated by varying the density of nanotubes on the silicon substrate. The densities of SWNTs network have been investigated as a function of concentration and assembly time. It has been observed that the density of SWNTs network increases from 0.6 µm⁻² to 2.1 µm⁻², as the average on-state current (I_on) increases from 0.5 mA to 1.47 mA. The device has a current on/off ratio (I_on/I_off) of 1.3×10⁴ when I_on reaches to 1.34 mA.     

Structural and electrochemical properties of LiNi0.5Mn0.5 − xAlxO2 (x = 0, 0.02, 0.05, 0.08, and 0.1) cathode materials for lithium-ion batteries

Layered LiNi_0.5Mn_0.5 ? xAl_xO₂ (x = 0, 0.02, 0.05, 0.08, and 0.1) series cathode materials for lithium-ion batteries were synthesized by a combination technique of co-precipitation and solid-state reaction, and the structural, morphological, and electrochemical properties were examined by XRD, FT-IR, XPS, SEM, CV, EIS, and charge–discharge tests. It is proven that the aliovalent substitution of Al for Mn promoted the formation of LiNi_0.5Mn_0.5 ? xAl_xO₂ structures and induced an increase in the average oxidation number of Ni, thereby leading to the shrinkage of the lattice volume. Among the LiNi_0.5Mn_0.5 ? xAl_xO₂ materials, the material with x = 0.05 shows the best cyclability and rate ability, with discharge capacities of 219, 169, 155, and 129 mAh g^? 1 at 10, 100, 200, and 400 mA g^? 1 current density respectively. Cycled under 40 mA g^? 1 in 2.8–4.6 V, LiNi_{0. 5}Mn_0.45Al_0.05O₂ shows the highest discharge capacity of about 199 mAh g^? 1 for the first cycle, and 179 mAh g^? 1 after 40 cycles, with a capacity retention of 90%. EIS analyses of the electrode materials at pristine state and state after first charge to 4.6 V indicate that the observed higher current rate capability of LiNi_{0. 5}Mn_0.45Al_0.05O₂ can be understood due to the better charge transfer kinetics.     

Effect of Eu and Pb doping on the dosimetric properties of LiCAF

LiCaAlF₆ (LiCAF) crystals doped with two different ions (europium and lead) have been investigated as potential new dosimetric materials. The stability of thermally stimulated luminescence (TSL) glow peaks in LiCAF:Eu was evaluated by means of the initial rise technique. The decay times at room temperature of the traps related to the dosimetric glow peaks were found to range between 40 and 2 × 10⁴ years confirming the good dosimetric characteristics of this crystal. The glow curve of LiCAF:Pb is dominated by a peak at approximately 300 °C emitting in the UV region (³P_0,1–¹S₀ transition of Pb²⁺) superimposed to a very broad structure at lower temperature (20–200 °C) featuring recombination at an intrinsic defect centre. The anomalous behavior of the low temperature structure during thermal cleaning procedures prevented any reliable numerical analysis of the TSL glow peak at 300 °C.     

A simple dye-sensitized solar cell sealing technique using a CO2 laser beam excited by 60 Hz AC discharges

Dye-sensitized solar cells (DSSCs) use two glass substrates (photo electrode and counter electrode) coated with fluorine-doped tin oxide (FTO) to harvest light into the cell and to collect electrons. The space between the photo electrode and the counter electrode are filled with a liquid type electrolyte for electron transfer into the cell. Therefore, an appropriate sealing method is required to prevent the liquid electrolyte leaking out. In this paper, a simple CO₂ laser beam with TEM₀₀ mode excited by a 60 Hz AC discharge was used to seal two glass substrates coated with FTO for the fabrication of DSSCs. The sealing technique improved the durability and stability of the DSSCs. The optimal conditions for the sealing of the DSSCs are related to the pin-hole diameter, the discharge current and the moving velocity of the target. Especially, the CO₂ laser beam is used as a heat source that is precisely controlled by the pin-hole, which plays an important role in adjusting its spot size. From these results, the maximum laser power was found to be 40 W at 18 Torr and 35 mA. In order to achieve the best sealing quality, the following parameters are required: a pin-hole diameter of 4 mm, input voltage of 10.73 kV, discharge current of 9.31 mA, moving velocity of 1 mm/s and distance from the target surface of 26.5 cm. Scanning electron microscope images show that the sealing quality obtained using the CO₂ laser beam is superior to that obtained using a hot press or soldering iron.     

Rapid synthesis of LiCr0.15Mn1.85O4 by glycine–nitrate method

LiCr_0.15Mn_1.85O₄ spinel has been successfully synthesized by glycine–nitrate method (GNM). The presence of pure spinel phase was confirmed by long term XRPD measurements and the Rietveld structural refinement. Lattice parameter was estimated to be 8.2338 Å. Average particle size of prepared powder material is below 500 nm. The BET surface area is 9.6 m² g^− 1. As a cathode material for lithium batteries LiCr_0.15Mn_1.85O₄ shows initial discharge capacity of 110 mA h g^− 1 and capacity retention of 83% after 50 cycles.     

InAs/GaSb strained layer superlattice detectors with nBn design

We have investigated the electrical and optical properties of an nBn based Type-II InAs/GaSb strained layer superlattice detector as a function of absorber region background carrier concentration. Temperature-dependent dark current, responsivity and detectivity were measured. At T = 77 K and V_b = 0.1 V, with two orders of magnitude change in doping concentration, the dark current density increased from ～0.3 mA/cm² to ～0.3 A/cm². We attribute this to a depletion region that exists at the AlGaSb barrier and the SLS absorber interface. The device with non-intentionally doped absorption region demonstrated the lowest dark current density (0.3 mA/cm² at 0.1 V) with a specific detectivity D¹ at zero bias equal to 1.2 × 10¹¹ Jones at 77 K. The D¹ value decreased to 6 × 10¹⁰ cm Hz^1/2/W at 150 K. This temperature dependence is significantly different from conventional PIN diodes, in which the D¹ decreases by over two orders of magnitude from 77 K to 150 K, making nBn devices a promising alternative for higher operating temperatures.     

Luminescence and defect studies of YAlO3:Dy3+, Sm3+ single crystals exposed to 100 MeV Si7+ ion beam

Ionoluminescence (IL) and photoluminescence (PL) spectra for different rare earth ions (Sm³⁺ and Dy³⁺) activated YAlO₃ single crystals have been induced with 100 MeV Si⁷⁺ ions with fluence of 7.81×10¹² ions cm^?2. Prominent IL and PL emission peaks in the range 550–725 nm in Sm³⁺ and 482–574 nm in Dy³⁺ were recorded. Variation of IL intensity in Dy³⁺ doped YAlO₃ single crystals was studied in the fluence range 7.81×10¹²–11.71×10¹² ions cm^?2. IL intensity is found to be high in lower ion fluences and it decreases with increase in ion fluence due to thermal quenching as a result of an increase in the sample temperature caused by ion beam irradiation. Thermoluminescence (TL) spectra were recorded for fluence of 5.2×10¹² ions cm^?2 on pure and doped crystals at a warming rate of 5 °C s^?1 at room temperature. Pure crystals show two glow peaks at 232 (Tg₁) and 328 °C (Tg₂). However, in Sm³⁺ doped crystals three glow peaks at 278 (Tg₁), 332 (Tg₂) and 384 °C (Tg₃) and two glow peaks at 278 (Tg₁) and 331 °C (Tg₂) in Dy³⁺ was recorded. The kinetic parameters (E, b s) were estimated using glow peak shape method. The decay of IL intensity was explained by excitation spike model.     

Kinetics of microplasma atmospheric ion generation correlated with discharge current

The conditions necessary for achieving a stable bipolar ion generation (in the order of 10⁶ ion/cm³) and lower ozone concentration (less than 50 ppb) using a surface discharge microplasma device (SMD) by adjusting the applied voltage and frequency were experimentally determined and investigated. Measurements of the discharge current characteristics of the SMD revealed saturation against the frequency (1.5–2.5 kHz, depending on the applied voltage). The ion and ozone concentrations both increased in step with the discharge current in the lower frequency region. The ion concentration reached equilibrium in the frequency range of 200–500 Hz, and the point of equilibrium within that range depended on the applied voltage. The ozone concentration did not reach equilibrium under our experimental conditions (ozone concentration < 100 ppb). The kinetics of the ion/ozone generation rate with a focus on the plasma reaction and recombination of bipolar ions is discussed.     

Highly efficient flexible organic light-emitting devices utilizing F4-TCNQ/m-MTDATA multiple quantum well structures

Flexible organic light-emitting devices (FOLEDs) based on multiple quantum well (MQW) structures, which consist of alternate layers of 2,3,5,6-Tetrafluoro-7,7,8,8,-tetracyano-quinodimethane (F4-TCNQ) and 4,4′,4″-tris-(3-methylphenylphe-nylamino)tripheny-lamine (m-MTDATA) have been fabricated. The Alq₃-based device with double quantum well (DQW) structure exhibits the remarkable electroluminescent (EL) performances for the brightness of 23,500 cd/m² at 14 V and the maximum current efficiency of 7.0 cd/A at 300.3 mA/cm², respectively, which are greatly improved by 114% and 56% compared with the brightness of 10,958 cd/m² at 14 V and the maximum current efficiency of 4.5 cd/A at 174.0 mA/cm² for the conventional device without MQW structures. These results demonstrate that the EL performances of FOLEDs could be greatly improved by utilizing the novel MQW structures, and the reason for this improvement has also been explained by the effect of interfacial dipole and interfacial doping between F4-TCNQ and m-MTDATA in this article.     

Facile synthesis of low-dimensional SnO2 nanostructures: An investigation of their performance and mechanism of action as anode materials for lithium-ion batteries

Owing to high-energy density of rechargeable lithium-ion batteries (LIBs), they have been investigated as an efficient electrochemical power sources for various energy applications. High theoretical capacities of tin oxide (SnO₂) anodes have led us a path to meet the ever-growing demands in the development of high-performance electrode materials for LIBs. In this paper, a facile approach is described for the synthesis of porous low-dimensional nanoparticles and nanorods of SnO₂ for application in LIBs with the help of Tween-80 as a surfactant. The SnO₂ samples synthesized at different reaction temperatures produced porous nanoparticles and nanorods with average diameters of ~7–10 nm and ~70–110 nm, respectively. The SnO₂ nanoparticle electrodes exhibit a high reversible charge capacity of 641.1 mAh/g at 200 mA/g after 50 cycles, and a capacity of 340 mAh/g even at a high current density of 1000 mA/g during the rate tests, whereas the porous nanorod electrodes delivers only 526.3 mAh/g at 200 mA/g after 50 cycles and 309.4 mAh/g at 1000 mA/g. It is believed that finer sized SnO₂ nanoparticles are much more favorable to trap more Li⁺ ion during electrochemical cycling, resulting in a large irreversible capacity. In contrast, rapid capacity fading was observed for the porous nanorods, which is the result of their pulverization resulting from repeated cycling.     

Rechargeability improvement of δ-type chemical manganese dioxide with the co-doping of Bi and Ni in alkaline electrolyte

δ-MnO₂ with the doping of Ni and Bi was prepared through a simple chemical precipitation/oxidation method. Its structure was confirmed by the X-ray diffraction tests. The results of cyclic voltammetry and galvanostatic charge–discharge tests showed that both the doping of Bi and Ni benefited the electrochemical activity of the MnO₂ electrode. Compared to the un-doped electrode, the Bi-doped one showed larger discharge capacity and the Ni-doped one showed higher discharge potential and better cycleability. With the co-doping of 5 wt% Bi and 10 wt% Ni, the discharge capacity of the MnO₂ electrode reached 252 mA h g^?1 at a 0.2C rate and 116 mA h g^?1 at a 1C rate, respectively. Its capacity remained in 105 mA h g^?1 after 50 cycles at a 1C rate, but the capacity of a commercial electrolytic MnO₂ electrode was only 37 mA h g^?1.     

Reduction of Escherichia coli O157:H7 on beef surfaces using low-voltage direct electric current and the impact on sensory properties

Low-voltage direct current was applied to beef, inoculated with Escherichia coli O157:H7 on the surface covered with a thin film of 0.15 M NaCl solution. Experiments were conducted with 15, 30, and 45 mA/cm² currents; 1, 10 and 100 kHz frequencies; 30, 50 and 70% duty cycles, and 2, 8 and 16 min treatment durations. Increase in current intensity, frequency, duty cycle, and treatment duration increased the % reduction of E. coli. A maximum reduction of 98.9% was achieved. Sensory color analysis showed significant differences between treated and untreated beef. The maximum temperature rise of NaCl solution was 31.9 °C.     

Thermo,Iono and photoluminescence properties of 100 MeV Si7+ ions bombarded CaSiO3:Eu3+ nanophosphor

This paper reports on the thermo (TL), iono (IL) and photoluminescence (PL) properties of nanocrystalline CaSiO₃:Eu³⁺ (1–5 mol %) bombarded with 100 MeV Si⁷⁺ ions for the first time. The effect of different dopant concentrations and influence of ion fluence has been discussed. The characteristic emission peaks ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions was recorded in both PL (1×10¹¹–1×10¹³ ions cm^?2) and IL (4.16×10¹²–6.77×10¹² ions cm^?2) spectra. It is observed that PL intensity increases with ion fluence, whereas in IL the peaks intensity increases up to fluence 5.20×10¹² ions cm^?2, then it decreases. A well resolved TL glow peak at ～304 °C was recorded in all the ion bombarded samples at a warming rate of 5 °C s^?1. The TL intensity is found to be maximum at 5 mol% Eu³⁺ concentration. Further, TL intensity increases sub linearly with shifting of glow peak towards lower temperature with ion fluence.     

Thermoluminescence,photoluminescence and EPR studies on Mn2+ activated yttrium aluminate (YAlO3) perovskite

Thermoluminescence (TL) measurements were carried out on undoped and Mn²⁺ doped (0.1 mol%) yttrium aluminate (YAlO₃) nanopowders using gamma irradiation in the dose range 1–5 kGy. These phosphors have been prepared at furnace temperatures as low as 400 °C by using the combustion route. Powder X-ray diffraction confirms the orthorhombic phase. SEM micrographs show that the powders are spherical in shape, porous with fused state and the size of the particles appeared to be in the range 50–150 nm. Electron Paramagnetic Resonance (EPR) studies reveal that Mn ions occupy the yttrium site and the valency of manganese remains as Mn²⁺. The photoluminescence spectrum shows a typical orange-to-red emission at 595 nm and suggests that Mn²⁺ ions are in strong crystalline environment. It is observed that TL intensity increases with gamma dose in both undoped and Mn doped samples. Four shouldered TL peaks at 126, 240, 288 and 350 °C along with relatively resolved glow peak at 180 °C were observed in undoped sample. However, the Mn doped samples show a shouldered peak at 115 °C along with two well defined peaks at ～215 and 275 °C. It is observed that TL glow peaks were shifted in Mn doped samples. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped, and Mn doped samples were determined at different gamma doses using the Chens glow peak shape method and the results are discussed in detail.     

Near-white emitting QD-LED based on hydrophilic CdS nanocrystals

In this work we report fabrication of a nanocrystal (NC)-based hybrid organic–inorganic LED with structure of ITO/PEDOT:PSS/PVK/CdS-NCs/(Al or Mg:Ag). The hydrophilic CdS NCs were synthesized using a novel aqueous thermochemical method at 80 °C and sizes (around 2 nm) were controlled by thioglycolic acid (TGA) as the capping agent. The favorite feature of these NCs is their relatively high emission intensity and broad, near-white emission. The hydrophilic CdS NCs were successfully spin coated using Triton X-100 as the wetting agent. The fabricated LEDs demonstrated a turn on voltage about 7 V for Al metallic contact. The electroluminescence was a broad spectrum at 540 and 170 nm width, which was about 50 nm red shifted compared to photoluminescence spectra. The CIE color coordinates of the LED at (0.33, 0.43) demonstrated a near white light LED with an emission on green–yellow boundary of white. Annealing of the device up to 190 °C had a positive effect on the performance, possibly due to better contacts between layers. Replacing Al contacts with Mg:Ag reduced the turn-on voltage to 6 V and changed CIE color coordinate to (0.32, 0.41). The EL peak was also shifted to 525 nm, with a brightness of 15 Cd/m² at working voltage of 15 V. The current efficiency and external quantum efficiency of device were 0.08 Cd/A and 0.03% at current densities higher than 10 mA/cm².     

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).