Barrier Inhomogeneity and Electrical Properties of InN Nanodots/Si Heterojunction Diodes

The electrical transport behavior of n-n indium nitride nanodot-silicon (InN ND-Si) heterostructure Schottky diodes is reported here, which have been fabricated by plasma-assisted molecular beam epitaxy. InN ND structures were grown on a 20 nm InN buffer layer on Si substrates. These dots were found to be single crystalline and grown along [0 0 0 1] direction. Temperature-dependent current density-voltage plots (J-V-T) reveal that the ideality factor (eta) and Schottky barrier height (SBH) (Phi(B)) are temperature dependent. The incorrect values of the Richardson constant (A**) produced suggest an inhomogeneous barrier. Descriptions of the experimental results were explained by using two models. First one is barrier height inhomogeneities (BHIs) model, in which considering an effective area of the inhomogeneous contact provided a procedure for a correct determination of A**. The Richardson constant is extracted similar to 110 A cm(-2) K(-2) using the BHI model and that is in very good agreement with the theoretical value of 112 A cm(-2) K(-2). The second model uses Gaussian statistics and by this, mean barrier height Phi(0) and A** were found to be 0.69 eV and 113 A cm(-2) K(-2), respectively.

Enhanced efficiency of tri-layered dye solar cells with hydrothermally synthesized titania nanotubes as light scattering outer layer

In the present study dye sensitized solar cells (DSSCs) have been fabricated with a tri-layer photo anode consisting of hydrothermally prepared titania nano tubes (TNT) having a diameter of 9-10 nm and length of several micrometers as outer layer, P25 TiO2 powder as transparent light absorbing middle layer and a compact TiO2 inner layer to improve the adhesion of different layers on a transparent conducting oxide coated substrate. In comparison to cells fabricated using TNTs or P25 alone, the tri-layer DSSCs exhibit an enhanced efficiency of 7.15% with a current density of 17.12 mA cm(-2) under AM 1.5 illumination. The enhancement is attributed to the light scattering generated by TNTs aggregates, reduction in electron transport resistance at the TiO2/dye/electrolyte interface and an improvement in electron life-time. (c) 2012 Elsevier B.V. All rights reserved.

High-Performance Metal-Insulator-Metal Capacitors Using Europium Oxide as Dielectric

We report the first demonstration of metal-insulator-metal (MIM) capacitors with Eu2O3 dielectric for analog and DRAM applications. The influence of different anneal conditions on the electrical characteristics of the fabricated MIM capacitors is studied. FG anneal results in high capacitance density (7 fF/mu m(2)), whereas oxygen anneal results in low quadratic voltage coefficient of capacitance (VCC) (194 ppm/V-2 at 100 kHz), and argon anneal results in low leakage current density (3.2 x 10(-8) A/cm(2) at -1 V). We correlate these electrical results with the surface chemical states of the films through X-ray photoelectron spectroscopy measurements. In particular, FG anneal and argon anneal result in sub-oxides, which modulate the electrical properties.

Morphology dependent electrochemical performance of sputter deposited Sn thin films

This study deals with tailoring of the surface morphology, microstructure, and electrochemical properties of Sn thin films deposited by magnetron sputtering with different deposition rates. Scanning electron microscopy and atomic force microscopy are used to characterize the film surface morphology. Electrochemical properties of Sn thin film are measured and compared by cyclic voltammetry and charge-discharge cycle data at a constant current density. Sn thin film fabricated with a higher deposition rate exhibited an initial discharge capacity of 798 mAh g(-1) but reduced to 94 mAh g(-1) at 30th cycle. Film deposited with lower deposition rate delivered 770 mAh g(-1) during 1st cycle with improved capacity retention of 521 mAh g(-1) on 30th cycle. Comparison of electrochemical performances of these films has revealed important distinctions, which are associated with the surface morphology and hence on rate of deposition. (C) 2012 Elsevier Ltd. All rights reserved.

Synthesis and characterization of high molecular weight polyaniline for organic electronic applications

High molecular weight polyaniline (PANI) was synthesized by a combined procedure incorporating various synthesis methods. Temperature and open circuit potential of the reaction mixture were collected to monitor the reaction progress. The polymer is characterized by various techniques including gel permeation chromatography, dynamic light scattering, infrared spectroscopy, solid-state nuclear magnetic resonance, and differential scanning calorimetry for elucidating the molecular architecture obtained by this method. As-synthesized PANI was found to possess high molecular weight, reduced branching, reduced cross-linking, and to predominantly consist of linear polymer chains. This polymer was also found to be more stable in solution form. JV characteristics of as-synthesized PANI films indicate a high current density which is due to increased free pathways and less traps for the charge transport to occur in PANI films. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers

Substrate temperature influenced physical properties of silicon MOS devices with TiO2 gate dielectric

DC reactive magnetron sputtering technique was employed for deposition of titanium dioxide (TiO2) films. The films were formed on Corning glass and p-Si (100) substrates by sputtering of titanium target in an oxygen partial pressure of 6x10-2 Pa and at different substrate temperatures in the range 303 673 K. The films formed at 303 K were X-ray amorphous whereas those deposited at substrate temperatures?=?473 K were transformed into polycrystalline nature with anatase phase of TiO2. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic bonding configuration of TiO2. The surface morphology of the films was significantly influenced by the substrate temperature. MOS capacitor with Al/TiO2/p-Si sandwich structure was fabricated and performed currentvoltage and capacitancevoltage characteristics. At an applied gate voltage of 1.5 V, the leakage current density of the device decreased from 1.8?x?10-6 to 5.4?x?10-8 A/cm2 with the increase of substrate temperature from 303 to 673 K. The electrical conduction in the MOS structure was more predominant with Schottky emission and Fowler-Nordheim conduction. The dielectric constant (at 1 MHz) of the films increased from 6 to 20 with increase of substrate temperature. The optical band gap of the films increased from 3.50 to 3.56 eV and refractive index from 2.20 to 2.37 with the increase of substrate temperature from 303 to 673 K. Copyright (c) 2012 John Wiley & Sons, Ltd.

Effect of thickness variation of hole injection and hole blocking layers on the performance of fluorescent green organic light emitting diodes

In this paper we present the effect of thickness variation of hole injection and hole blocking layers on the performance of fluorescent green organic light emitting diodes (OLEDs). A number of OLED devices have been fabricated with combinations of hole injecting and hole blocking layers of varying thicknesses. Even though hole blocking and hole injection layers have opposite functions, yet there is a particular combination of their thicknesses when they function in conjunction and luminous efficiency and power efficiency are maximized. The optimum thickness of CuPc (Copper(II) phthalocyanine) layer, used as hole injection layer and BCP (2,9 dimethyl-4,7-diphenyl-1,10-phenanthroline) used as hole blocking layer were found to be 18 nm and 10 nm respectively. It is with this delicate adjustment of thicknesses, charge balancing is achieved and luminous efficiency and power efficiency were optimized. The maximum luminous efficiency of 3.82 cd/A at a current density of 24.45 mA/cm(2) and maximum power efficiency of 2.61 lm/W at a current density of 5.3 mA/cm(2) were achieved. We obtained luminance of 5993 cd/m(2) when current density was 140 mA/cm(2). The EL spectra was obtained for the LEDs and found that it has a peaking at 524 nm of wavelength. (C) 2012 Elsevier B.V. All rights reserved.

Electrical transport studies of MBE grown InGaN/Si isotype heterojunctions

The temperature dependent electrical transport behavior of n-n InGaN/Si heterostructures grown by plasma-assisted MBE was studied. Structural characteristics of the as-grown InGaN epilayers were evaluated high resolution X-ray diffraction and composition of InGaN was estimated from photoluminescence spectra using standard Vegard's law. Current density-voltage plots (J-V-T) revealed that the ideality factor (eta) and Schottky barrier height (SBH) (Phi(b)) are temperature dependent and the incorrect values of the Richardson's constant (A**) produced, suggests an inhomogeneous barrier at the heterostructure interface. The higher value of the ideality factor compared to the ideal value and its temperature dependence suggest that the current transport is mainly dominated by thermionic field emission. (C) 2012 Elsevier B.V. All rights reserved.

Electrocatalytic oxidation of 1,2-propanediol on electrodeposited Pd-poly(3,4-ethylenedioxythiophene) nanodendrite films in alkaline medium

Electrochemical deposition of Pd on conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) coated carbon paper electrode results in the formation of a stable dendritic film of Pd. In the absence of the PEDOT under-layer, Pd deposition is smooth and non-dendritic. Both Pd-PEDOT/C and Pd/C electrodes are studied for electrooxidation of 1,2-propanediol (PD) in an alkaline electrolyte. Owing to enhanced surface area and surface defects on dendritic Pd, the Pd-PEDOT/C electrode exhibits greater catalytic activity than the Pd/C electrode. Cyclic voltammetry studies suggest that peak current density increases with an increase in concentrations of PD and NaOH in the electrolyte. Repetitive cyclic voltammetry and amperometry studies indicate that Pd-PEDOT/C electrode possesses a high electrochemical stability with greater catalytic activity than Pd/C electrode toward electrooxidation of PD. (C) 2012 Elsevier Ltd. All rights reserved.

Growth and photovoltaic performance of SnS quantum dots

Tin sulphide (SnS) quantum dots of size ranging from 2.4 to 14.4 nm are prepared by chemical precipitation method in aqueous media. Growth of the SnS particles is monitored by controlling the deposition time. Both XRD and SAED patterns confirm that the particles possess orthorhombic structure. The uncapped SnS particles showed secondary phases like Sn2S3 and SnS2 which is visible in the SAED pattern. From the electrochemical characterization. HOMO-LUMO levels of both TiO2 and SnS are determined and the band alignment is found to be favorable for electron transfer from SnS to TiO2. Moreover, the HOMO-LUMO levels varied for different particle sizes. Solar cell is fabricated by sensitizing porous TiO2 thin film with SnS QDs. Cell structure is characterized with and without buffer layer between FTO and TiO2. Without the buffer layer, cell showed an open circuit voltage (V-oc) of 504 mV and short circuit current density (J(sc)) of 2.3 mA/cm(2) under AM1.5 condition. The low fill factor of this structure (15%) is seen to be increased drastically to 51%, on the incorporation of the buffer layer. The cell characteristics are analyzed using two different size quantum dots. (C) 2012 Elsevier B.V. All rights reserved.

Efficient field emission properties of ZnO (core)/graphite (shell) nanowires

In this work the field emission studies of a new type of field emitter, zinc oxide (ZnO) core/graphitic (g-C) shell nanowires are presented. The nanowires are synthesized by chemical vapor deposition of zinc acetate at 1300 degrees C Scanning and transmission electron microscopy characterization confirm high aspect ratio and novel core-shell morphology of the nanowires. Raman spectrum of the nanowires mat represents the characteristic Raman modes from g-C shell as well as from the ZnO core. A low turn on field of 2.75 V/mu m and a high current density of 1.0 mA/cm(2) at 4.5 V/mu m for ZnO/g-C nanowires ensure the superior field emission behavior compared to the bare ZnO nanowires. (C) 2012 Elsevier B.V. All rights reserved.

Synthesis and characterization of nickel/barium hexa-aluminate composite coatings

Electrodeposition of nickel/barium hexa-aluminate (Ni/BHA) composite coatings has been carried out from a Watt's bath on mild steel substrate. BHA powders with plate habit were synthesized by solution combustion synthesis followed by heat treatment to ensure complete conversion to the hexa-aluminate phase. Heat treated material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with X-ray analysis. The dispersion behaviour and stability of BHA suspensions with cationic and anionic surfactants at room temperature were studied by dynamic light scattering under different pH. The influence of BHA concentration in the electrolytic bath, deposition temperature, pH, current density and duty cycle on particle incorporation in the coatings were studied and conditions for maximum particle incorporation were established. Coatings with a roughness of about 0 center dot 4 mu m were produced by using this technique. Effect of BHA content on microhardness was also investigated. A reasonably good thickness of the coatings was achieved in a given set of conditions.

Electron field emission from reduced graphene oxide on polymer film

Field emission of reduced graphene oxide coated on polystyrene film is studied in both parallel and perpendicular configurations. Low turn-on field of 0.6 V/lm and high emission current density of 200 mA/cm(2) are observed in perpendicular configuration (along the cross section), whereas a turn-on field of 6 V/lm and current density of 20 mu A/cm(2) are obtained in parallel configuration (top surface). The emission characteristics follow Fowler-Nordheim (FN) tunneling and the values of enhancement factor estimated from FN plots are 5818 (perpendicular) and 741 (parallel). Furthermore, stability and repeatability of the field emission characteristics in perpendicular configuration are presented. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4788738]

Effect of iodine concentration on the photovoltaic properties of dye sensitized solar cells for various I-2/LiI ratios

In the present study, the effect of iodine concentration on the photovoltaic properties of dye sensitized solar cells (DSSC) based on TiO2 nanoparticles for three different ratios of lithium iodide (LiI) and iodine (I-2) has been investigated. The electron transport properties and interfacial recombination kinetics have been evaluated by electrochemical impedance spectroscopy (EIS). It is found that increasing the concentration of lithium iodide for all ratios of iodine and lithium iodide decreases the open-circuit voltage (V-oc) whereas short circuit current density (J(sc)) and fill factor (FF) shows improvement. The reduction in V-oc and increment in J(sc) is ascribed to the higher concentration of absorptive Li+ cations which shifts the conduction band edge of TiO2 positively. The increase in FF is due to the reduction in electron transport resistance (R-omega) of the cell. In addition for all the ratios of LiI/I-2 increasing the concentration of I-2 decreases the V-oc which is attributed to the increased recombination with tri-iodide ions (I-3(-)) as verified from the low recombination resistance (R-k) and electron lifetime (tau) values obtained by EIS analysis. (C) 2012 Elsevier Ltd. All rights reserved.

Electrocatalytic oxidation of C-3-aliphatic alcohols on electrodeposited Pd-PEDOT nanodendrites in Alkaline medium

Nanodendritic Pd is electrodeposited on poly(3,4-ethylenedioxythiophene) (PEDOT) coated carbon paper electrode. Electrodeposited Pd is non-dendritic in the absence of PEDOT. The electrooxidation of C-3-aliphatic alcohols, namely, propanol (PA), 1,2- propanediol (1, 2-PD), 1, 3-propanediol (1, 3-PD), and glycerol (GL) is studied in 1.0 M NaOH. The catalytic activity of nanodendritic Pd is greater than that of non-dendritic Pd for oxidation of the four alcohols molecules. Among those molecules the oxidation rate increases as: PA< 1, 2-PD < 1, 3-PD < GL. The cyclic voltammetric oxidation current peak appearing in the reverse direction of the sweep is greatly influenced by the nature of alcohol. The reduction of oxide film on Pd surface is attributed to affect the magnitude of backward peak current density. The amperometry and repeated cyclic voltammetry data suggest a high stability of nanodendritic Pd in alkaline medium. Glycerol is expected to be an appropriate alcohol for application as a fuel in alkaline fuel cells at nanodendritic electrodeposited Pd.