All Solution‐Based Fabrication of Copper Oxide Thin Film/Cobalt‐Doped Zinc Oxide Nanowire Heterojunctions

Versatile and intriguing solution‐based processes are utilized to synthesize nanostructured materials for device applications to reduce material production and device fabrication costs. This study presents results on the fabrication and characterization of copper oxide (CuO) coated cobalt‐doped zinc oxide nanowires (Co‐doped ZnO NWs)‐based heterojunction diodes prepared by a two‐step synthesis route through combined hydrothermal growth and sol–gel spin coating. Highly dense, well‐ordered, undoped, and Co‐doped ZnO NWs were successfully grown by hydrothermal method. Complementary CuO thin films were synthesized by sol–gel method and subsequently coated onto both undoped and Co‐doped ZnO NWs through spin‐coating technique. Enhanced diode properties with a rectification ratio of 10³ at ±2 V and an ideality factor of n = 2.4 (in dark) were obtained for Co‐doped ZnO NWs‐based heterojunction diodes. The obtained results demonstrated that the investigated heterojunction diode structure fabricated by facile and cost‐effective solution‐based processes can be a promising candidate for the next generation optoelectronic devices.     

A study of microwave transmission,reflection, absorption,and shielding effectiveness of conducting polypyrrole films

Microwave transmission, reflection, and absorption behavior and the shielding effectiveness of electrochemically synthesized polypyrrole films with dc conductivities ranging from 0.001 to 50 S/cm are presented. Results show that the electrical conductivity of the doped polypyrrole films has a significant effect on transmission, reflection, and absorption of microwaves. Heavily doped, conducting films were highly reflective, whereas lightly doped, semiconducting films had very high transmission. Intermediate conductivity polypyrrole samples were highly absorptive. The agreement between experimental data and theoretical modeling provided confidence to extend the modeling to include the effect of sample thickness on the transmission, reflection, and absorption properties of films with a wide range of conductivity values, hence, providing valuable information for the design of microwave devices and fundamental understanding of the material properties. A method of measuring the far-field sheilding effectiveness of polypyrrole films is also presented. Results of shielding experiments indicated the potential for such applications. © 1994 John Wiley & Sons, Inc.     

Temperature dependence of electrical conduction in pure and doped polypyrrole

Summary Pure polypyrrole and polypyrrole in salt form were synthesized using NaOH as reducing agent in aqueous HCl, respectively. Electrical conduction in these pure and doped polypyrrole samples was studied through the I-V characteristics of these materials. I-V characteristic curves for both pure and doped polypyrrole were found to be linear. The conductivity of chlorine-doped polypyrrole is about 10⁴ times that of pure polypyrrole. An attempt has been made to study the dependence of conductivity on temperature, in order to understand the application of these systems. It has been observed from the variation of conductivity vs. temperature curve in both the samples that the conductivity increases with the increase in temperature. This behaviour is indicative of semiconducting nature of the samples with a variation in electrical conductivity of each, which is a strong function of doping and temperature of the environment. Activation energies for both the samples have been found to be in millielectron-volt range, 101.94 meV and 121.68 meV for pure and doped polypyrrole, respectively. An effort has also been made to understand the charge transport in these conductive polymers through models.     

Recent Advances in Electrochemical Performances of Graphene Composite (Graphene-Polyaniline/Polypyrrole/Activated Carbon/Carbon Nanotube) Electrode Materials for Supercapacitor: A Review

The latest trend in the direction of miniaturized portable electronic devices has brought up necessitate for rechargeable energy sources. Among the various non conventional energy devices, the supercapacitor is the promising candidate for gleaning the energy. Supercapacitor, as a new energy device that colligates the gap between conventional capacitors and batteries, it has attracted more attention due to its high power density and long cycle life. Many researchers work on, synthesizing new electrode material for the development of supercapacitor. The electrode material possesses salient structure and electrochemical properties exhibit the efficient performance of the supercapacitor. Graphene has high carrier mobility, thermal conductivity, elasticity and stiffness and also has a theoretical specific capacitance of 2630 m²g^??1 corresponds to a specific capacitance of 550 Fg^??1. This article summarizes and reviews the electrochemical performance and applications of various graphene composite materials such as graphene/polyaniline, graphene/polypyrrole, graphene/metal oxide, graphene/activated carbon, graphene/carbon nanotube as an electrode materials towards highly efficient supercapacitors and also dealt with symmetric, asymmetric and hybrid nature of the graphene based supercapacitor.     

Thermal stability of polypyrroles

The effect of dopants and level of doping on the thermal stability of polypyrrole at 90, 120 and 150°C in dry air and nitrogen was investigated by monitoring the decay of conductivity. Polymers doped with aromatic anions (p-toluene sulphonate and p-chlorobenzene sulphonate) exhibit better stability than polymers doped with an aliphatic anion (dodecyl sulphate). The conductivity decay appears to follow diffusion controlled kinetics. After an initial decrease in conductivity, polypyrrole doped with p-toluene sulphonate anion maintains a constant conductivity at 150°C in air for at least 4 weeks. Dedoping results in materials of lower conductivity but greater thermal stability. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were found to be useful techniques to characterize and investigate thermal stability. Oxidation of polypyrrole films, monitored by DSC, shows diffusion controlled kinetics. Although both oxidation and conductivity decay show typical diffusion kinetics, oxidation is a necessary but not sufficient condition for the decay.     

Trends in sputter deposited tungsten oxide structures for electrochromic applications: A review

Electrochromic devices (ECD) show reversible color change under applied electric field and are predicted to become indispensable in many applications such as low power displays, smart windows to develop energy-saving buildings as well as light-adapting mirrors in high-end cars and aircrafts. Despite the assiduous research work, ECD faces several challenges for practical usage including delamination, durability, lifetime and their integration into multifunctional devices. To improve the performance, different techniques have already been used to deposit single-layered thin film, or a stack of promising EC layers on several substrates including transparent conductive oxides (TCO) coated glass and different conducting polymers. These layers can be flat enough or have a definite shape or structure to satisfy the needs of the designed device. Based on their low resistivity and high transparency, fluorine and indium doped tin oxides (FTO, ITO) are mostly used as TCOs whereas polyaniline, polypyrrole and ethylenedioxythiophene are the trending future polymers. In this review, the critical parameters of magnetron sputtering are delineated for the deposited tungsten oxide (WO₃) films focused on ITO and FTO layered glass. The main focus of interest is to highlight the recent progress and future trends in this technique, structure introduced with sputtered electrochromic film and their carefully review along with effect of altering these parameters on physical, optical, electrochemical, durability and thus overall performance of the ECD. Finally, it will be intended to underline the future perspectives in realizing smart EC devices with various factual characteristics.     

Electroactive polymer blends

The rapid development of two new classes of electrically active polymer materials, electronically conducting and electroactive polymers and ion-conducting polymers respectively, offers new possibilities for application of both classes of material, especially in combination with each other. While some of these combinations have been attempted before, they all met serious problems due to poor interpenetration of the two polymers. The recent availability of solubilized and soluble electroactive and conductive polymers has greatly advanced the possibilities of reducing the interpenetration problem. Some experimental studies using the combination of solubilized electroactive polypyrrole with poly(ethylene oxide) in an electroactive polymer blend electrode for solid-state polymer batteries are discussed. The opportunities for using polymer blends for solid-state electrochemical polymeric devices, and avenues for the development of materials for such devices, are also reviewed.     

Transient memristive device based on lead-free double perovskite for secured data storage and artificial learning systems

Modern day electronic devices are fascinated by various indispensable activities for various schemes. Transient devices are one of those systems useful for disposable electronics. However, choice of materials is an integral part, because the material should be compatible with the required device application and can show transient nature at the same time. Most importantly, the material for the aforesaid application should not possess any environmental hazard. In this work, we have for the first time integrated non-toxic double perovskite material in transient memristive application. The Cs₂AgBiBr₆ integrated in between Au and indium doped tin oxide (ITO) electrode serves as the functional material and the proposed device exhibited dual-functional switching characteristics. The device could retain the reproducible and stable resistive memory feature along with high-density storage capacity. The threshold switching behavior is useful to realize selector device in cross-bar resistive memory architecture. Thus, the same device can be utilized simultaneously for both the application. In addition, the device could also demonstrate some basic synaptic functions. Finally, the modulation of device resistance could be ascribed to the establishment/dissolution of conductive path related to Br^? vacancy and Ag filaments. Interestingly, the device could also display transient behavior as the Cs₂AgBiBr₆ film and the device undergo rapid decomposition within 60 s in H₂O.     

Production and characterisation of composite relaxor ferroelectric multi-layer structures

The drive for miniaturisation of passive capacitor and filter devices requires dielectric materials with higher relative permittivities than can be attained using normal ferroelectrics. Relaxor ferroelectrics possess the required high relative permittivities but are incapable of being chemically doped to give a temperature stable capacitance. Work is presented detailing the design and development of a new class of temperature stable high volumetric efficiency multi-layer capacitors. Various compositions of high relative permittivity relaxor ferroelectrics are co-sintered in to a multi-layer capacitor with controllable temperature characteristics. The materials used are all doped perovskite Pb(Mg_1/3Nb_2/3)O₃ (PMN) compositions. The ceramic powder-processing route required to make such structures is summarised with reference to the unique device fabrication problems encountered. Dielectric measurements of the prototype devices are presented. ©     

Fast electrochemistry of conductive polymer nanotubes: synthesis, mechanism, and application

Conductive polymers exhibit several interesting and important properties, such as metallic conductivity and reversible convertibility between redox states. When the redox states have very different electrochemical and electronic properties, their interconversion gives rise to changes in the polymers' conformations, doping levels, conductivities, and colors, useful attributes if they are to be applied in displays, energy storage devices, actuators, and sensors. Unfortunately, the rate of interconversion is usually slow, at best on the order a few hundred milliseconds, because of the slow transport of counterions into the polymer layer to balance charge. This phenomenon is one of the greatest obstacles toward building rapidly responsive electrochemical devices featuring conductive polymers. One approach to enhancing the switching speed is decreasing the diffusion distance for the counterions in the polymer. We have found that nanotubular structures are good candidates for realizing rapid switching between redox states because the counterions can be readily doped throughout the thin nanotube walls. Although the synthesis of conductive polymer nanotubes can be performed using electrochemical template synthesis, the synthetic techniques and underlying mechanisms controlling the nanotube morphologies are currently not well established. We begin this Account by discussing the mechanisms for controlling the structures from hollow nanotubes to solid nanowires. The applied potential, monomer concentration, and base electrode shape all play important roles in determining the nanotubes' morphologies. A mechanism based on the rates of monomer diffusion and reaction allows the synthesis of nanotubes at high oxidation potentials; a mechanism dictated by the base-electrode shape dominates at very low oxidation potentials. The structures of the resulting conductive polymer nanotubes, such as those of poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole, can be characterized using scanning electron microscopy and transmission electron microscopy. We also discuss these materials in terms of their prospective use in nanotube-based electrochemical devices. For example, we describe an electrochromic device incorporating PEDOT nanotubes that exhibits an ultrafast color switching rate (<10 ms) and strong coloration. In addition, we report a supercapacitor based on PEDOT nanotubes that can provide more than 80% of its own energy density, even at power demands as high as 25 kW/kg.     

Protein Nanofibrils Balance Colours in Organic White-Light-Emitting Diodes

In this review we discuss our efforts in using protein nanowires (amyloid fibrils) as structural templates for use in organic electronics applications, mainly focusing on organic light-emitting diodes (OLEDs). We discuss different ways of functionalising amyloid fibrils. In one method, the amyloid fibril is used to organise luminescent polymers. We also discuss an alternative preparative method, resulting in amyloid-like materials functionalised with phosphorescent organometallic complexes. We discuss the incorporation of such materials in organic electronics devices, such as OLEDs. When amyloid fibrils are integrated into the OLED active layer, consisting of an electroluminescent blue-emitting polyfluorene, the efficiency of the device increases by a factor of 10. Furthermore, when amyloid fibrils incorporating phosphorescent metal complexes are used, the phosphorescent guest functions more efficiently than in the corresponding case where naked metal complexes are used. By preparing amyloid fibrils incorporating green- and red-emitting phosphorescent complexes, and combining these with blue-emitting polyfluorene, we can fabricate devices for white-light emission. The origin of the effects of the biomaterial on device performance is discussed.     

Direct‐current and alternating‐current analysis of the humidity‐sensing properties of nickel oxide doped polypyrrole encapsulated in mesoporous silica SBA‐15

Nickel oxide (NiO) doped polypyrrole (PPy) was encapsulated in mesoporous SBA‐15. All of the synthesized samples were characterized by infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy. They were investigated as humidity‐sensor materials at room temperature. The sensor showed excellent humidity sensitivity in the relative humidity range 11–95%. The humidity‐sensing properties were very much improved by encapsulation of the NiO‐doped PPy into mesoporous silica SBA‐15. Finally, the sensitivity mechanism was investigated by direct‐current (dc) and alternating‐current (ac) analysis. The dc circuit with the instantaneous polarity reversion method was designed by us to study the dc response in different humidity environments. The conductive mechanism was established through the dc and ac investigation, and the conductive particles were identified as ions and electrons. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Simple and rapid synthesis of NiO/PPy thin films with improved electrochromic performance

Nickel oxide/polypyrrole (NiO/PPy) thin films were deposited by a two step process in which the NiO layer was electrodeposited potentiostatically from an aqueous solution of NiCl₂·6H₂O at pH 7.5 on fluorine doped tin oxide (FTO) coated conducting glass substrates, followed by the deposition of polypyrrole (PPy) thin films by chemical bath deposition (CBD) from pyrrole mixed with ammonium persulfate (APS). The NiO/PPy films were further characterized for their structural, optical, morphological and electrochromic properties. X-ray diffraction study indicates that the films composed of polycrystalline NiO and amorphous PPy. Infrared transmission spectrum reveals chemical bonding between NiO and PPy. Rectangular faceted grains were observed from scanning electron microscopy results. The electrochromic (EC) property of the film was studied using cyclic voltammogram (CV), chronoamperometry (CA) and optical modulation. The NiO/PPy presents superior EC properties than their individual counterparts. The coloration/bleaching kinetics (response time of few ms) and coloration efficiency (358 cm²/C) were found to be improved appreciably. The dramatic improvement in electrochemical stability (from about 500 c/b cycles for PPy to 10,000 c/b cycles for NiO/PPy) was observed. This work therefore demonstrates a cost-effective and simple way of depositing highly efficient, faster and stable NiO/PPy electrodes for EC devices.     

Electronic Structures and Device Applications of Transparent Oxide Semiconductors: What Is the Real Merit of Oxide Semiconductors?

The main objective of this review is to provide an idea how to create new functions in oxides and how to find suitable applications only oxides can realize. Oxides have crystal and electronic structures largely different from those of conventional semiconductors such as Si and GaAs. Therefore, we should design suitable applications according to the inherent properties of oxide semiconductors if we intend to develop practical optoelectronic devices using oxides. In this review, we first briefly describe the characteristic features of oxide semiconductors from the viewpoints of crystal and electronic structures. Then three materials and related device applications are shown as examples. N-type amorphous oxide semiconductors (AOSs) can have electron transport properties superior even to silicon if they are in amorphous states. We propose that AOSs are favorable materials for active layers in low-temperature thin film device technology and demonstrate high-performance thin film transistors fabricated at room temperature on flexible plastic sheets. The second example is transparent p-type semiconductors. Employing chalcogen orbitals and layered crystal structures, large hole mobilities, degenerate p-type conduction, and room-temperature stable excitions are rendered in wide bangap materials. Room-temperature operation of excitonic blue light-emitting diodes was thereby demonstrated. The last is 12CaO·7Al₂O₃ in which the use of subnanometer-sized cages and anions clathrated in the cages creates many chemical, optical, and electronic functions.     

Enhanced Piezoelectric Performance of Electrospun Polyvinylidene Fluoride Doped with Inorganic Salts

A novel approach to preparing electrospun polyvinylidene fluoride (PVDF) nanofibers is proposed, with high piezoelectric performance. PVDF nanofibers are doped with inorganic salts without the use of any postpolarization treatment. Twenty‐six salts are doped into the nanofibers and their piezoelectric properties are studied. The salts are classified into three groups based on their differing piezoelectric enhancement effects. A piezoelectric nanogenerator fabricated with an optimized electrospun PVDF nanofiber mat shows a piezovoltage seven times greater than that of a device based on undoped nanofibers. The simple and low‐cost approach to fabricate these piezoelectric nanofiber mats may broaden the range of industrial applications of these materials in energy‐harvesting devices and portable sensors.     

Synthesis of ZnO rod arrays on aluminum recyclable paper and effect of the rod size on power density of eco-friendly nanogenerators

In this work, we demonstrated a novel and effective approach on the use of low-cost electrodes, an eco-friendly substrate and zinc oxide (ZnO) micro or nanorods (MRs or NRs, respectively) for building triboelectric devices (TENGs). The reported strategy focuses on using low-cost materials and fabrication processes. For the first time and without any pre-treatment, an aluminum recyclable paper from the milk carton (named ARP) was used as a substrate and TENG bottom electrode. A systematic study on the growing of ZnO structures on ARP by chemical bath deposition has been carried out. We found that the ZnO rods size, and resistivity of the TENG upper electrode considerably influence the power density of the device. Such sustainable, low-priced ZnO-based TENGs can produce up to 1.6μW/cm² output power density when operated at 50?Hz. The fabrication of an eco-friendly nanogenerator demonstrates the possibility of manufacturing low-cost, flexible, and large-area energy harvesting devices for future applications.     

Bismuth based oxide electrolytes— structure and ionic conductivity

Bismuth oxide systems exhibit high oxide ion conductivity and have been proposed as good electrolyte materials for applications such as solid oxide fuel cells and oxygen sensors. However, due to their instability under conditions of low oxygen partial pressures there has been difficulty in developing these materials as alternative electrolyte materials compared to the state-of-the-art cubic stabilised zirconia electrolyte. Bismuth oxide and doped bismuth oxide systems exhibit a complex array of structures and properties depending upon the dopant concentration, temperature and atmosphere. In this paper we comprehensively review the structures, thermal expansion, phase transitions, electrical conductivity and stability of bismuth oxide and doped bismuth oxide systems. ©     

Homoepitaxial Diamond Devices

Diamond has been proposed as an excellent material for high-temperature, high-power, and high-frequency applications. The interest in diamond electronics is due to its large electric breakdown field, high-saturated current velocity and high-thermal conductivity. As silicon and gallium arsenide devices begin to reach their performance limits, there is a need to develop new, better performing materials such as diamond. Significant progress in the development of diamond as a semiconducting material has been made and diamond has been implemented into numerous conventional and novel device designs. In this work homoepitaxial diamond material properties and device performance are reviewed. In summary, the large activation energy of boron-doped p-type diamond and phosphorus-doped n-type diamond severely limits diamond's use in conventional semiconductor device designs. The large activation energy reduces the number of charge carriers, which limits the current handling capability and produces temperature-dependent device performance. To overcome diamond's limitations, novel devices, such as enhancement mode field effect transistors (FETs) that use a hydrogenated surface conducting layer or pulsed doped devices with almost complete ionization, have been investigated. These devices require further development. The initial results show promise for high-temperature, high-frequency, and high-power applications.     

Linear sensing actuators of polypyrrole nanofiber scaffolds

In the search for renewable materials for linear actuators, polypyrrole (PPy) glucose-glycerin nanofiber scaffolds were used here to provide the actuator with a basic fibrillary structure, mimicking natural muscles. Each nanofiber was coated with a chemically synthesized PPy film, getting conductive nanofiber scaffolds (CNS), used then as electrodes to attain a second polypyrrole doped with dodecylbenzensulfonate (PPyDBS) coat forming PPyDBS-CNS material structure. PPyDBS bulk films obtained by electropolymerization on stainless steel under the same condition were used to compare the linear actuation properties of both materials. Cyclic voltammetry, square potential waves, and square potential currents, in combination with linear actuation measurements, studied the samples. Three different potential ranges (PRs) were selected for those methodologies: 1.0 to −0.55 V (PR1), 0.8 to −0.4 V (PR2), and 0.65 to −0.55 V (PR3), revealing that PPyDBS-CNS has anion-driven actuation independent of the applied PR1–3, while in comparison PPyDBS films had in PR3 mixed ion actuation. The best strain from PPyDBS, 24.6%, was attained at PR1, and from PPyDBS-CSN, 17.5% strain in the same PR. Further characterizations are conducted, such as scanning electron microscopy, Fourier transform infrared spectroscopy, and element determination using energy dispersive x-ray spectroscopy.     

Synthesis In Situ, Characterization, and Photostability of Europium β-Diketone Chelates in Organically Modified Silicates (ORMOSILs)

Europium β-diketonates have desirable optical properties, and transparent inorganic materials that have been doped with these chelates seem to be promising for potential applications in luminescence-display devices, integrated optical device sources, and new visible lasers. However, these chelates may be decomposed or not dissolved in sol—gel precursor solutions and, thus, cannot be doped in gel glasses that have been prepared via traditional sol—gel processing. An in situ synthesis technique has been used for the first time to synthesize five binary and ternary coordination compounds of europium β-diketonates in transparent organically modified silicates (ORMOSILs) during heat treatment or during the process of sol-to-monolithic ORMOSIL conversion. ORMOSILs that have been doped with in situ europium β-diketonates exhibit rather-high fluorescence intensity and good monochromati-city. These materials result in enhanced red-light emission under ultraviolet excitation. The chelates that have been synthesized in situ in the ORMOSILs reveal better photostability, in comparison to that of the pure chelates that have been dissolved in ethanol solutions.