The characteristics of organic light emitting diodes with Al doped zinc oxide grown by atomic layer deposition as a transparent conductive anode

Al doped zinc oxide (AZO) films, deposited by atomic layer deposition (ALD) were investigated for applying a transparent conductive oxide (TCO) layer as an anode for organic light emitting diode (OLED) devices. AZO films with a thickness of 100 nm were deposited at various Al atomic ratios ranging from 0 to 5% at a deposition temperature (250 °C). The optimum electrical properties: the carrier mobility, the resistivity, and the sheet resistance for the 2% AZO film were found to be 16.2 cm² V^?1 s^?1, 1.5 × 10^?3 cm^?3, and 217 Ω/sq, respectively. The red OLED devices were fabricated using AZO anodes utilizing the various Al atomic ratios; the electrical and optical characteristics were then investigated. The best luminance, quantum efficiency, and current efficiency were found in the OLED device using the 2% AZO TCO; the results were 16599 cd/m², 8.2%, and 7.5 cd/A, respectively.     

Strain rate sensitivity of a high strain rate superplastic TiNp/2014 Al composite

The effects of deformation temperature and strain in hot rolling deformation on strain rate sensitivity of the TiN_p/2014 Al composite were studied by tensile tests conducted out at 773, 798, 818 and 838 K with the strain rates from 1.7 ×10^?3 to 1.7 × 10⁰ s^?1. It is shown that the curves of m value of the TiN_p/2014Al composite deformed at different temperatures can be divided into two stages with the variation of strain rate, and the critical strain rates are 10^?1 s^?1. The optimum deformation temperature of the TiN_p/2014 Al composite is near incipient melting temperature of 816 K and the optimum strain rate is a little higher than the critical strain rate. The effect of deformation temperature on strain rate sensitivity is relative to liquid phase helper accommodation. The effect of strain in hot rolling deformation on strain rate sensitivity attributes to change of microstructure and deformation mechanism.     

Critical Al content to form external-alumina scales on Cu–Al alloys

The oxidation of Cu–6.8Al (at.%) alloy has been studied at 800 and 900 °C in 1 × 10⁵ Pa pure O₂. The scales formed at 800 °C are composed of a thin outer CuO layer and an inner protective Al₂O₃ layer. On the contrary, at 900 °C different samples of the alloy present two kinds of different oxidation behavior: one is protective, very similar to that at 800 °C, while the other is intermediate between protective and non-protective, with formation of very thick scale on the partial surface, which is mainly composed of copper oxides. The different behavior presented on a single sample is probably caused by local inhomogeneities of the alloy. It is deduced that at 900 °C the critical Al content to form external-alumina scale on Cu–Al alloy is about 6.8 at.%.     

Chemical synthesis of cobalt oxide thin film electrode for supercapacitor application

Cobalt oxide thin film electrode was grown on copper substrate from an aqueous alkaline bath containing cobalt chloride as a cobalt source by adopting simple and inexpensive chemical deposition method and characterized for structural and morphological studies. The supercapacitive properties of cobalt oxide electrode were studied in aqueous KOH electrolyte solution. The effect of electrolyte concentration on specific capacitance and the stability of cobalt oxide electrode were studied. The highest specific capacitance achieved with cobalt oxide films was 118 F g^?1. The specific energy (E), specific power (P) and coulomb efficiency (η%) were 5.8 Wh kg^?1, 0.33 kW kg^?1 and 93.44%, respectively.     

Structural,electrical and optical properties of p-type transparent conducting SnO2:Al film derived from thermal diffusion of Al/SnO2/Al multilayer thin films

Highly transparent, p-type conducting SnO₂:Al films derived from thermal diffusion of a sandwich structure Al/SnO₂/Al multilayer thin films deposited on quartz substrate have been prepared by direct current and radio-frequency magnetron sputtering using Al and SnO₂ targets. The deposited films were annealed at various temperatures for different durations. The effect of thermal diffusing temperature and time on the structural, electrical and optical performances of SnO₂:Al films has been studied. X-ray diffraction results show that all p-type conducting films possessed polycrystalline SnO₂ with tetragonal rutile structure. Hall-effect results indicate that 450 °C for 4 h were the optimum annealing parameters for p-type SnO₂:Al films, resulting in a relatively high hole concentration of 7.2 × 10¹⁸ cm^?3 and a low resistivity of 0.81 Ω cm. The transmission of the p-type SnO₂:Al films was above 80%.     

Formation and oxidation resistance of Hf and Al modified silicide coating on Nb–Si based alloy

Codeposition of Si, Al and Hf were prepared by pack cementation at 1300 °C for 10 h. The results show that the coating is composed of a thick (Nb, X)Si₂ outer layer, a (Ti, Nb)₅Si₄ middle layer and a thin discontinuous (Cr, Al)₂(Nb, Ti) inner layer. The mass gain of the coating is only 4.12 mg/cm² after isothermal oxidation at 1250 °C for 100 h. Some “oxide pegs” form at the interface of the oxide scale and coating. The coating exhibits good cyclic oxidation resistance due to the improved adhesion between the oxide scale and coating.     

Perylenetetracarboxylic di-imide-based bottom-contact devices: A study on two kinds of source/drain electrodes,ITO and MoW

High-performance bottom-contact devices based on an air-stable n-type organic semiconductor N,N-bis(4-trifluoromethoxybenzyl)-perylene-3,4,9,10-tetracarboxylic di-imide, were fabricated, and the effects of crystal packing on indium tin oxide and molybdenum–tungsten alloy were shown in two different electric characteristics. The estimated work function of indium tin oxide and molybdenum–tungsten alloy were 4.7 and 5.0 eV. The calculated lowest unoccupied molecular orbital energy level of the organic material was 3.7 eV. Transistors with indium tin oxide bottom electrodes exhibited a high mobility of 3.37 × 10^?2 cm² V^?1 s^?1, an on/off current ratio of 6.5 × 10⁵ and threshold voltage of ?4.0 V.     

Controlling of silicon–insulator–metal junction by organic semiconductor polymer thin film

Electrical and photovoltaic properties of a metal–semiconductor–insulator–polymer–metal diode were investigated. The n-Si/SiO₂/MEH-PPV/Al diode shows a rectifying behavior with the rectification ratio of 2.22 × 10⁵ at ±5 V and exhibits a non-ideal behavior due to the series resistance and oxide-organic layers. The organic semiconductor makes a contribution to the I–V characteristics of the diode and the trap-charge limited space charge and space charge limited current mechanisms were observed for the diode. The current–voltage characteristics of the n-Si/SiO₂/MEH-PPV/Al diode under different illumination intensities give an open circuit voltage (V_oc) along with a short circuit current (I_sc). This suggests that the n-Si/SiO₂/MEH-PPV/Al diode is a photovoltaic device with V_oc = 0.456 V and J_sc = 7.89 × 10^?8 A/cm² values under 100 mW/cm² illumination intensity. The photoconductivity mechanism of the diode is controlled by monomolecular recombination. The interface state density D_it values with time constant τ_it of the diode under dark and illumination conditions were found to be 2.53 × 10¹⁰ eV^?1 cm^?2 with 5.09 × 10^?5 s and 2.50 × 10¹⁰ eV^?1 cm^?2 with 8.27 × 10^?5 s, respectively. The obtained results indicate that the n-Si/SiO₂/MEH-PPV/Al diode is a photo-sensitive diode.     

Composition and annealing effects in solution-processable functionalized graphene oxide/P3HT based solar cells

Characterization of a solution-processable functionalized graphene oxide (SPFGraphene oxide) was investigated by FT-IR spectroscopy and the result of elemental analysis showed that the isocyanate treatment results in the functionalization groups in SPFGraphene oxide. Doping SPFGraphene oxide to P3HT based solar cells induces absorbing spectra more strongly and a great quenching of the photoluminescence of the P3HT. With an increase in the SPFGraphene oxide content, the overall performances of the hybrid devices increases first, reaching the peak efficiency for the 10 wt% SPFGraphene oxide content, and then decreases. After annealing at 160 °C for different time durations, the device containing 10 wt% of SPFGraphene oxide for 10 min shows the best performance with a power conversion efficiency of 1.046%, an open-circuit voltage of 0.73 V, a short-circuit current density of 3.98 mA cm^?2 and a fill factor of 0.36 under simulated AM1.5G conditions at 100 mW cm^?2; The similar content one for 20 min shows η value of 1.013%, which is lower than the former one to a small extent for longer annealing duration. The graphene has the potential to act as the next-generation material in the photovoltaic devices and other applications for ease of preparation, low price, large surface area, high conductivity and excellent transparency.     

Initial oxide-film growth on Mg-based MgAl alloys at room temperature

The initial, thermal oxidation of bare, Mg-based MgAl alloys (containing up to 7.31 at.% Al) at 304 K in the partial oxygen pressure range of 10⁻⁶ ⩽ pO₂ ⩽ 10⁻⁴ Pa was investigated by angle-resolved X-ray photoelectron spectroscopy and real-time in situ spectroscopic ellipsometry. The chemical constitution of the initially grown oxide film resembles that of a MgO-type of oxide with, adjacent to the alloy/oxide interface, Al enrichments in both the oxide film and the subsurface region of the alloy substrate. The Al-to-Mg content of the oxide films is governed by the alloy composition in the subsurface region, which deviates from the bulk alloy composition due to sputter cleaning prior to oxidation. Continued oxide-film growth proceeds by the transformation of a defective surface-oxide structure into “bulk” oxide upon reacting with outwardly diffusing Mg cations under the influence of a surface-charge field. The effective rate of depletion of Mg from the alloy subsurface region is governed by the competing processes of preferential oxidation of Mg and interfacial segregation of Mg.     

A novel hydrogen peroxide biosensor based on the specific binding of horseradish peroxidase with polymeric thiophene-3-boronic acid monolayer in hydrophilic room temperature ionic liquid

In the present work, we have developed a novel hydrogen peroxide (H₂O₂) biosensor based on electropolymerization of thiophene-3-boronic acid film (TBA) in ionic liquid via glucosidic bond with glycoprotein horseradish peroxidase (HRP). A thin film of poly (thiophene-3-boronic acid) (PTBA) has been synthesized by electropolymerization using room temperature ionic liquids (RTIL) as the growth medium and the supporting electrolyte. Horseradish peroxidase (HRP) in this study shows affinity interaction with the formed PTBA thin film. With the aid of hydroquinone (H₂Q) mediator, the biosensor has a fast response of less than 7 s with linear range of 5.0 × 10^?6 to 1.75 × 10^?4 M and a detection limit of 0.5 μM. The developed biosensor exhibits fast response, a low detection limit, high stability and very good reproducibility.     

Synthesis and properties of phenothiazylene vinylene and bithiophene-based copolymers for organic thin film transistors

A series of new phenothiazylene vinylene and thiophene copolymers (P1, P2, and P3) have been synthesized via Yamamoto and Stille coupling reactions. The number-averaged molecular weights (M_n) of P1, P2, and P3 were found to be 12,000, 10,000, and 8200, with polydispersity indices of 3.5, 1.4, and 1.6, respectively. The UV–visible absorption spectra of the polymers contain two strong absorption bands in the ranges 306–325 nm and 430–480 nm, which arise from the absorptions of the phenothiazine segments and the conjugated main chains respectively. Solution-processed field-effect transistors (FETs) fabricated with these polymers exhibit p-type organic thin film transistor characteristics. The field-effect mobilities for P1, P2, and P3 were measured to be 1.8 × 10^?4, 5.7 × 10^?4, and 2.5 × 10^?7 cm² V^?1s^?1, respectively, with the corresponding on/off ratios of 5 × 10², 1 × 10⁴, and 5 × 10².     

Superplastic deformation of a heat-resistant Al–Cu–Mg–Ag–Mn alloy

The superplastic behavior and deformation mechanism of a heat-resistant Al–Cu–Mg–Ag–Mn alloy prepared by ingot metallurgy was investigated by using optical microscopy, scanning electron microscopy and transmission electron microscopy. It is shown that the Al–Cu–Mg–Ag–Mn alloy shows good superplastic properties at temperatures higher than 450 °C and strain rates lower than 10^?2 s^?1. A maximum elongation-to-failure of 320% was observed at 500 °C and 5 × 10^?4 s^?1, where the corresponding strain rate sensitivity index m is 0.58 and the flow stress σ is 5.7 MPa. Microstructure studies revealed that the observed superplastic behavior resulted from severe grain elongation rather than grain boundary sliding. It is suggested that this phenomenon may provide a new concept for developing superplastic materials.     

Preparation of self-organized porous anodic niobium oxide microcones and their surface wettability

Porous anodic niobium oxide with a pore size of ～10 nm was formed at 10 V in glycerol electrolyte containing 0.6 mol dm^?3 K₂HPO₄ and 0.2 mol dm^?3 K₃PO₄ at 433 K. After prolonged anodizing for 5.4 ks, niobium oxide microcones develop on the surface. X-ray diffraction patterns of the anodized specimens revealed that the initially formed anodic oxide is amorphous, but an amorphous-to-crystalline transition occurs during anodizing. As a consequence of the preferential chemical dissolution of the initially formed amorphous oxide, due to different solubility of the amorphous and crystalline oxides, crystalline oxide microcones appear on the film surface after prolonged anodizing. The surface is superhydrophilic. After coating with fluorinated alkylsilane, the surface becomes superhydrophobic with a contact angle of 158° for water. The surface is also oil repellent, with a contact angle as high as 140° for salad oil.     

Microwave study of chemically synthesized conducting polyaniline on alumina

Polyaniline (PANI) thin film on alumina was prepared by the chemical oxidation of aniline with ammonium peroxydisulphate in acidic aqueous medium. DC conductivity, microwave transmission and reflection, microwave conductivity, shielding effectiveness and microwave dielectric constant of the conducting PANI films are reported. DC conductivity was between 0.15 × 10^?3 and 3.13 × 10^?3 S/cm. Microwave conductivity was between 0.2 and 10 S/cm. The PANI films coated on alumina gave shielding effectiveness value of ?1 to ?4 db. The ?′ was between 2 and 350 whereas ?″ was between 437 and 60. Measurements have been carried over the frequency range of 8.2–18 GHz.     

Iridium(III) complexes with cyclometalated styrylbenzoimidazole ligands: Synthesis,electrochemistry and as highly efficient emitters for organic light-emitting diodes

Two phosphorescent iridium complexes (psbi)₂Ir(acac) and (ppbi)₂Ir(acac) (psbi = 1-phenyl-2-styryl-1H-benzo[d]imidazole, ppbi = 1-phenyl-2-(1-phenylprop-1-en-2-yl)-1H-benzo[d]imidazole, acac = acetylacetonate) were synthesized, and their photophysical, electrochemical and electroluminescent properties were also studied. Organic light-emitting devices with these two complexes as dopant emitters having the structure ITO/NPB (10 nm)/TCTA (20 nm)/x%Ir:CBP (y nm)/BCP (10 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The device based on (psbi)₂Ir(acac) exhibited a maximum brightness of 56,162 cd m^?2, while the device based on (ppbi)₂Ir(acac) gave a maximum brightness of 31,232 cd m^?2. At high brightness of 1000 cd m^?2 and 10,000 cd m^?2, high current efficiencies of 25.7 cd A^?1 and 20.7 cd A^?1 were achieved, respectively, for the (psbi)₂Ir(acac)-based EL device. For the EL device based on (ppbi)₂Ir(acac), current efficiencies of 20.1 cd A^?1 at 1000 cd m^?2 and 14.2 cd A^?1 at 10,000 cd m^?2 were observed.     

Phase separation kinetics in a Fe–Cr–Al alloy

The α–α′ phase separation kinetics in a commercial Fe–20 wt.% Cr–6 wt.% Al oxide dispersion-strengthened PM 2000? steel have been characterized with the complementary techniques atom probe tomography and thermoelectric power measurements during isothermal aging at 673, 708, and 748 K for times up to 3600 h. A progressive decrease in the Al content of the Cr-rich α′ phase was observed at 708 and 748 K with increasing time, but no partitioning was observed at 673 K. The variation in the volume fraction of the α′ phase well inside the coarsening regime, along with the Avrami exponent 1.2 and activation energy 264 kJ mol^?1, obtained after fitting the experimental results to an Austin–Rickett type equation, indicates that phase separation in PM 2000? is a transient coarsening process with overlapping nucleation, growth, and coarsening stages.     

High temperature oxidation of Mo–Si–B alloys: Effect of low and very low oxygen partial pressures

The oxidation mechanism of a Mo–Si–B alloy in two different oxygen partial pressure ranges was investigated between 820 and 1200 °C. Oxygen partial pressures between 10^?19 and 10^?12 bar were applied in order to suppress Mo oxide formation. Weight gain kinetics were determined resulting from simultaneous external and internal oxidation. Silica scale formation was found to lead to a droplet shape because of the high evaporation rates of B₂O₃ and limited wetting of the silica. In the oxygen partial pressure range 10^?6–10^?4 bar Mo–Si–B alloys suffer from severe degradation due to continuous formation of volatile MoO₃. Catastrophic oxidation was observed as a consequence of the formation of a highly porous and non-protective silica scale.     

Nitric oxide sensing by cytochrome c bonded to a conducting polymer modified glassy carbon electrode

A nitric oxide biosensor based on cytochrome c (an heme protein) covalently immobilized to poly(5-amino-1-naphthol) by using cyanuric chloride as a bridge was developed. The immobilization was studied by cyclic voltammetry and quartz crystal microbalance. The nitric oxide detection as a function of poly(5-amino-1-naphthol) amount was recorded, and the best result was obtained with the electrode prepared by 70 cycles. The sensitivity and detection limit were 0.015 μA cm^?2/μmol L^?1 and 2.85 μmol L^?1, respectively.     

Microstructure and grain boundary relaxation in ultrafine-grained Al/Al oxide composites

The microstructure and grain boundary relaxation in ultrafine-grained Al/Al oxide composites were studied by electron microscopy observation and internal friction measurement, respectively. Both the microstructure and the internal friction behavior of the composites were strongly influenced by the thermomechanical treatment parameters. All the Al particles were still covered by the native amorphous oxide shells in those composites sintered at T < 823 K, and no indication of Al grain boundary relaxation was detected. Some Al oxide shells were cracked, resulting in the formation of a few Al–Al grain boundaries between adjacent particles in the sample sintered at 823 K, and one internal friction peak centered at ～440 K was detected. All the oxide shells were broken into small fragments in those samples sintered at T ? 843 K, and two internal friction peaks were detected, one prominent peak at ～440 K and one weak peak at ～540 K. A microstructure with a bimodal grain size distribution of Al was formed via partial recrystallization after thermomechanical treatment of the sample sintered at 893 K, and two internal friction peaks with comparable intensity were detected. The internal friction peaks were associated with the relaxation of Al grain boundary in the composites.