Preparation and electrochemical properties of lamellar MnO2 for supercapacitors

Lamellar birnessite-type MnO₂ materials were prepared by changing the pH of the initial reaction system via hydrothermal synthesis. The interlayer spacing of MnO₂ with a layered structure increased gradually when the initial pH value varied from 12.43 to 2.81, while the MnO₂, composed of α-MnO₂ and γ-MnO₂, had a rod-like structure at pH 0.63. Electrochemical studies indicated that the specific capacitance of birnessite-type MnO₂ was much higher than that of rod-like MnO₂ at high discharge current densities due to the lamellar structure with fast intercalation/deintercalation of protons and high utilization of MnO₂. The initial specific capacitance of MnO₂ prepared at pH 2.81 was 242.1 F g⁻¹ at 2 mA cm⁻² in 2 mol L⁻¹ (NH₄)₂SO₄ aqueous electrolyte. The capacitance increased by about 8.1% of initial capacitance after 200 cycles at a current density of 100 mA cm⁻².     

Hybrid manganese oxide films for supercapacitor application prepared by sol-gel technique

Hybrid films were prepared by adding various concentrations of meso-carbon microbeads (MCMB) during sol-gel processing of manganese oxide films. The heat-treated films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, electrochemical performance of the MCMB-added Mn-oxide hybrid coatings was evaluated by cyclic voltammetry (CV) and compared with its unadded counterpart. Experimental results showed that Mn-oxide films exhibited a mixture of Mn₂O₃ and Mn₃O₄ phases. The higher the heat-treatment temperature, the more Mn₂O₃ can be observed. The specific capacitance of the unadded Mn-oxide electrodes is 209 F/g. Because the MCMB particles provide more interfacial surface area for electrochemical reactions, a significant improvement can be noticed by adding MCMB in Mn-oxide coatings. The 300 °C heat-treated hybrid Mn-oxide coating with a Mn/MCMB ratio of 10/1 exhibits the highest value of 350 F/g, showing a ~ 170% increase in specific capacitance.     

Multicomponent oxide thin-film transistors fabricated by a double-layer inkjet printing process

In this work we report on the fabrication and characterization of multicomponent metal oxide thin-film transistors with a double-layer inkjet printing process. Both the active area and source-drain electrodes of the devices are printed with inks based on metal salt precursors to form Ga₂O₃-In₂O₃-ZnO and In₂O₃-SnO respectively. Electrical characterization has shown that the devices' performance, apart from the active area composition, can also be affected by the printing drop spacing. In general, devices printed with Ga:In:Zn 2:4:1 composition present the highest field effect mobility (~ 1.75-3 cm² V⁻¹ s⁻¹). More stable devices with improved switching, but with a compromise over field effect mobility (~ 0.5-0.9 cm² V⁻¹ s⁻¹) were obtained for the 2:4:2 composition.     

Antiferromagnetic manganite La1/3Ca2/3MnO3 as barrier material in superconductor/insulator/ferromagnet tunnel junctions

Current transport through thin antiferromagnetic (AF) barriers of the perovskita manganite La_1/3Ca_2/3MnO₃ (LCMO) was studied with respect to its dependence on temperature and voltage. Planar-type La_2/3Ca_1/3MnO₃(~ 80 nm)/La_1/3Ca_2/3MnO₃(~ 7 nm)/YBa₂Cu₃O_7 − δ(~ 100 nm) heterojunctions were used as basic structures. The current-voltage (I-V) measurements were carried out on test junctions with a standard area of 20 × 40 µm² in a four-terminal configuration. In spite of the carefully controlled growth conditions, barriers with the same nominal thickness showed different electrical behavior varying from elastic tunneling to Mott variable range hopping (VRH) via localized states. The different transport characteristics seem to be related to intrinsic difference in microstructure as the average surface roughness of the constituent layers may already be larger than the thickness of the barrier itself.     

Preparation and characterization of nanostructured NiO/MnO2 composite electrode for electrochemical supercapacitors

Nanostructured nickel-manganese oxides composite was prepared by the sol-gel and the chemistry deposition combination new route. The surface morphology and structure of the composite were characterized by scanning electron microscope and X-ray diffraction. The as-synthesized NiO/MnO₂ samples exhibit higher surface area of 130-190 m² g⁻¹. Cyclic voltammetry and galvanostatic charge/discharge measurements were applied to investigate the electrochemical performance of the composite electrodes with different ratios of NiO/MnO₂. When the mass ratio of MnO₂ and NiO in composite material is 80:20, the specific capacitance value of NiO/MnO₂ calculated from the cyclic voltammetry curves is 453 F g⁻¹, for pure NiO and MnO₂ are 209, 330 F g⁻¹ in 6 mol L⁻¹ KOH electrolyte and at scan rate of 10 mV s⁻¹, respectively. The specific capacitance of NiO/MnO₂ electrode is much larger than that of each pristine component. Moreover, the composite electrodes showed high power density and stable electrochemical properties.     

Low field magnetoresistance, temperature coefficient of resistance and magnetocaloric effect in Pr2/3Ba1/3MnO3:PdO composites

Electrical resistivity, magnetoresistance (MR), temperature coefficient of resistance (TCR) and magnetocaloric effect of (1 − x) Pr_2/3Ba_1/3MnO₃:x PdO (x = 0-30 mol% PdO) composite manganites are reported here. Pristine sample Pr_2/3Ba_1/3MnO₃ (PBMO) shows two insulator-metal like transitions (T_P1 ~ 194 K and T_P2 ~ 160 K) in the electrical resistivity behavior. With PdO, T_P1 becomes sharper whereas T_P2 disappears beyond 10 mol% PdO addition. The intrinsic MR gets enhanced from 22% for the pristine sample to ~ 42% for 27% PdO sample. However, the extrinsic MR is found to decrease in the composites. The TCR also increases from a negligible value for PBMO to 8% for 25 mol% PdO sample. These features have been explained on the basis of opening of new conducting channels and decrease in spin dependent scattering and the overall decrease in electrical resistivity. The magnetic entropy change and relative cooling power (RCP) for the PBMO sample are 5.3418 J.Kg-K and 304.5428 J/Kg respectively. However, these values decrease in the composites.     

MoO3 nanoparticles distributed uniformly in carbon matrix for supercapacitor applications

A highly uniform nanocomposite of MoO₃ and carbon with a weight ratio of 1:1 is prepared by employing a simple procedure of ball milling. Such composite as electrochemical pseudocapacitor materials for potential energy storage applications exhibits a high specific capacitance of ~ 179 F/g at a charge and discharge current density of 50 mA/g with excellent cycling ability over 1000 cycles. Compared with the capacitance of pure milled graphite (~ 22 F/g) and MoO₃ (< 10 F/g), an enhanced electrochemical performance of the composite with a weight ratio of 1:1 is attributed to its unique structure, in which MoO₃ nanoparticles (with a size range of 1-180 nm) are uniformly dispersed in an electrically conductive carbon host.     

Improved dielectric properties of lead lanthanum zirconate titanate thin films on copper substrates

Thin films of lead lanthanum zirconate titanate (PLZT) were directly deposited on copper substrates by chemical solution deposition and crystallized at temperatures of ~ 650 °C under low oxygen partial pressure (pO₂) to create film-on-foil capacitor sheets. The dielectric properties of the capacitors formed have much improved dielectric properties compared to those reported previously. The key to the enhanced properties is a reduction in the time that the film is exposed to lower pO₂ by employing a direct insertion strategy to crystallize the films together with the solution chemistry employed. Films exhibited well-saturated hysteresis loops with remanent polarization of ~ 20 μC/cm², dielectric constant of > 1100, and dielectric loss of < 0.07. Energy densities of ~ 32 J/cm³ were obtained at a field of ~ 1.9 MV/cm on a ~ 1 μm thick film with 250 μm Pt electrodes.     

Characteristics of sputtered Al-doped ZnO films for transparent electrodes of organic thin-film transistor

Aluminum-doped ZnO (AZO) thin-films were deposited with various RF powers at room temperature by radio frequency (RF) magnetron sputtering method. The electrical properties of the AZO film were improved with the increasing RF power. These results can be explained by the improvement of the crystallinity in the AZO film. We fabricated the organic thin-film transistor (OTFT) of the bottom gate structure using pentacene active and poly-4-vinyl phenol gate dielectric layers on the indium tin oxide gate electrode, and estimated the device properties of the OTFTs including drain current-drain voltage (I_D-V_D), drain current-gate voltage (I_D-V_G), threshold voltage (V_T), on/off ratio and field effect mobility. The AZO film that grown at 160 W RF power exhibited low resistivity (1.54 × 10^− 3 Ω·cm), high crystallinity and uniform surface morphology. The pentacene thin-film transistor using the AZO film that's fabricated at 160 W RF power exhibited good device performance such as the mobility of 0.94 cm²/V s and the on/off ratio of ~ 10⁵. Consequently, the performance of the OTFT such as larger field-effect carrier mobility was determined the conductivity of the AZO source/drain (S/D) electrode. AZO films prepared at room temperature by the sputtering method are suitable for the S/D electrodes in the OTFTs.     

Cathodic electrodeposition of Ag-doped manganese dioxide films for electrodes of electrochemical supercapacitors

Cathodic electrodeposition method has been developed for the fabrication of Ag-doped MnO₂ films from the KMnO₄ aqueous solutions containing AgNO₃ for the application in electrodes of electrochemical supercapacitors (ES). The films were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry (CV) and impedance spectroscopy. The Ag-doped MnO₂ films showed improved capacitive behaviour and lower electrical resistance compared to pure MnO₂ films. The highest specific capacitance (SC) of 770 F g^− 1 was obtained at a scan rate of 2 mV s^− 1 in the 0.5 M Na₂SO₄ electrolyte.     

Ultrathin TaOx film based photovoltaic device

Application of the economical metal oxide thin-film photovoltaic devices is hindered by the poor energy efficiency. This paper investigates the photovoltaic effect with an ultrathin tantalum oxide (TaOx) tunnel barrier, formed by the plasma oxidation of a pre-deposited tantalum (Ta) film. These ~ 3 nm TaOx tunnel barriers showed approximately 160 mV open circuit voltage and 3-5% energy efficiency, for varying light intensity. The ultrathin TaOx (~ 3 nm) could absorb approximately 12% of the incident light radiation in 400-1000 nm wavelength range; this strong light absorbing capability was found to be associated with the dramatically large extinction coefficient. Spectroscopic ellipsometry revealed that the extinction coefficient of 3 nm TaOx was ~ 0.2, two orders higher than that of tantalum penta oxide (Ta₂O₅). Interestingly, refractive index of this 3 nm thick TaOx was comparable with that of stochiometeric Ta₂O₅. However, heating and prolonged high-intensity light exposure deteriorated the photovoltaic effect in TaOx junctions. This study provides the basis to explore the photovoltaic effect in a highly economical and easily processable ultrathin metal oxide tunnel barrier or analogous systems.     

Electrochemical capacitors of flower-like and nanowire structured MnO2 by a sonochemical method

Nanostructured manganese dioxide, MnO₂, was synthesized by a sonochemical method. Nanostructured MnO₂ had the shapes of flower-like and nanowires by changing the pH in the aqueous solution, as observed via scanning electron microscopy and transmission electron microscopy. The electrochemical capacitance was studied by cyclic voltammetry. A maximum specific capacitance of 300 Fg⁻¹ was obtained for the nanowires in a potential range from 0.1 to 0.9 V vs. SCE in 1 M sodium sulfate solution at a scan rate of 5 mV s⁻¹. These materials can be useful to increase the specific capacitance by wetting behavior of electrolytes from their structural properties.     

Further work function and interface quality improvement on Al2O3 capped high-k/metal gate p-type metal-oxide-semiconductor field-effect-transistors by incorporation of fluorine

The impact of fluorine (F) incorporation into TiN/HfO₂/SiO₂ on work function has been investigated. By process scheme optimization, F implanted through sacrificial oxide layer reveals sufficient the flat-band voltage (V_FB) shift ~ 170 mV without an equivalent oxide thickness (EOT) penalty. On the contrary, apparent EOT increasing was observed if F implanted directly through Si. Moreover, F incorporation into TiN/Al₂O₃/HfO₂/SiO₂, the V_FB shift can be up to about 250 mV or 410 mV at 10 keV with a dose of 2 × 10¹⁵ cm^− 2 or 5 × 10¹⁵ cm^− 2, respectively. Effective work function has been boosted to 4.95 eV closer to the valence band edge. Besides, interface defect density also can be improved ~ 20% by F incorporation from charge pumping result.     

Wet chemical route to transparent BiFeO3 films on SiO2 substrates

BiFeO₃ nanoparticles were prepared by a wet chemical synthesis method. Transparent films were deposited on glass and quartz substrates by dip and spin coating processes from the synthesized sol. We obtained thicker films (~ 2 µm) by dip coating process and thinner films (~ 200 nm) by spin coating process. Transmission electron microscopy images confirmed that the particles are nanocrystalline in size. From the optical transmittance spectra the band gap of the BiFeO₃ nanoparticles was determined in the range of ~ 3.03-2.88 eV (~ 410-430 nm). Electrical resistivity, polarization, zero-field-cooled and field-cooled magnetizations versus temperature characteristics were also studied for these films.     

Preparation and characterization of CuIn1 − xGaxSe2 − ySy thin film solar cells by rapid thermal processing

This paper describes the synthesis and characterization of CuIn_1 − xGa_xSe_2 − yS_y (CIGSeS) thin-film solar cells prepared by rapid thermal processing (RTP). An efficiency of 12.78% has been achieved on ~ 2 µm thick absorber. Materials characterization of these films was done by SEM, EDS, XRD, and AES. J-V curves were obtained at different temperatures. It was found that the open circuit voltage increases as temperature decreases while the short circuit current stays constant. Dependence of the open circuit voltage and fill factor on temperature has been estimated. Bandgap value calculated from the intercept of the linear extrapolation was 1.1-1.2 eV. Capacitance-voltage analysis gave a carrier density of 4.0 × 10¹⁵ cm^− 3.     

Properties of atomic-vapor and atomic-layer deposited Sr, Ti, and Nb doped Ta2O5 Metal-Insulator-Metal capacitors

Atomic Vapor Deposition and Atomic Layer Deposition techniques were applied for the depositions of Ta₂O₅, Ti-Ta-O, Sr-Ta-O and Nb-Ta-O oxide films for Metal-Insulator-Metal (MIM) capacitors used in back-end of line for Radio Frequency applications. Structural and electrical properties were studied. Films, deposited on the TiN bottom electrodes, in the temperature range of 225-400 °C, were amorphous, whereas the post deposition annealing at 600 °C resulted in the crystallization of Nb-Ta-O films. Electrical properties of MIM structures, investigated after sputtering Au top electrodes, revealed that the main characteristics were different for each oxide. On one hand, Ti-Ta-O based MIM capacitors possessed the highest dielectric constant (50), but the leakages currents were also the highest (~ 10^− 5 A/cm² at − 2 V). On the other hand, Sr-Ta-O showed the lowest leakage current densities (~ 10^− 9 A/cm² at − 2 V) as well as the smallest capacitance-voltage nonlinearity coefficients (40 ppm/V²), but the dielectric constant was the smallest (20). The highest nonlinearity coefficients (290 ppm/V²) were observed for Nb-Ta-O based MIM capacitors, although relatively high dielectric constant (40) and low leakage currents (~ 10^− 7 A/cm² at − 2 V) were measured. Temperature dependent leakage-voltage measurements revealed that only Sr-Ta-O showed no dependence of leakage current as a function of the measurement temperature.     

Preparation and characteristics of nanostructured MnO2/MWCNTs using microwave irradiation method

Ball-nanostructured MnO₂/MWCNTs composite was successfully prepared by microwave irradiation. The surface morphology and structures of the composite were examined by scanning electron microscope and X-ray diffraction. Multi-walled carbon nanotubes play a role as sustainment to inhibit MnO₂ nanoplates from collapsing into nanorods. The electrochemical studies indicated that the composite had ideal capacitive performance and high specific capacitances of 298 F g^− 1, 213 F g^− 1 and 198 F g^− 1 at the current density of 2 mA·cm^− 2, 10 mA·cm^− 2 and 20 mA·cm^− 2, respectively. The formation mechanism of nanostructured MnO₂/MWCNTs and the electrochemical behaviour of composites were discussed in detail.     

The mechanism of specific capacitance improvement of supercapacitors based on MnO2 at an elevated operating temperature

Amorphous nanostructured MnO₂ film was anodically deposited onto economical duplex stainless steel substrate. The obtained MnO₂ film was characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy for microstructural, morphological, and compositional studies. The capacitive behavior was systematically investigated by cyclic voltammetry, charge-discharge cycling and electrochemical impedance spectroscopy (EIS) in 1 M Na₂SO₄ electrolyte at different operating temperatures ranging from 20 to 60 °C. The specific capacitance (SC) was improved with an increase of operating temperature, and the highest SC of 398 F/g was achieved at a scan rate of 10 mV/s and operating temperature of 60 °C. The mechanism of SC improvement at elevated operating temperature was investigated using EIS. With an increase of operating temperature, the conductivity of electrolyte was improved, and the charge-transfer resistance (R_ct) was decreased. The temperature dependence of 1/R_ct follows an Arrhenius equation. The MnO₂ film was electrochemically activated at 60 °C due to the formation of Na_yMnO₂ after discharging.     

Facile synthesis of MnO2/CNT nanocomposite and its electrochemical performance for supercapacitors

A nanocomposite of manganese dioxide coated on the carbon nanotubes (MnO₂/CNTs) was synthesized by a facile direct redox reaction between potassium permanganate and carbon nanotubes without any other oxidant or reductant addition. The morphology, microstructure and crystalline form of this MnO₂/CNT nanocomposite were characterized by scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical properties are characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge (GCD). The results show that the facile prepared MnO₂/CNTs nanocomposite shows specific capacitance of 162.2 F g⁻¹ at the current density of 0.2 A g⁻¹ and excellent charge/discharge property with 90% of its specific capacitance kept after 2000 cycles at the current density of 5 A g⁻¹.     

Structure, growth and magnetic property of hard magnetic CoPtP nanowires synthesized by electrochemical deposition

This paper reports the electrochemical synthesis and characterization of one dimensional hard magnetic CoPtP nanowires. Three electrode potentiostatic electrochemical technique was used to deposit nanowires into a nanoporous track-etched polycarbonate membrane with a nominal pore diameter 50 nm and thickness around 6-9 μm. The room temperature electrolyte used for the deposition of nanowires consists of 60 g/lt CoSO₄7H₂O, 4.1 g/lt H₂PtCl₆, 4.5 g/lt NaHPO₂ and 25 g/lt B(OH)₃. The structural morphology was observed by scanning electron microscope and transmission electron microscope. The magnetic property of the nanowires was measured by vibrating sample magnetometer before removing the template. The coercive fields were measured to be 143 kA m^− 1 and 103 kA m^− 1 for parallel (H_║) and perpendicular to the nanowire axis, respectively. The higher coercivity value for H_║ indicating nanowires' easy magnetization direction lies along the nanowires' axis. The average composition of the CoPtP nanowires was determined by electron dispersive spectroscopy and the crystallinity was measured by X-ray diffractometer.