Development and application of a holistic model for the steady state growth of porous anodic alumina films

A holistic model was developed and applied to anodic alumina films galvanostatically grown in sulphuric acid solution at different anodising conditions thus characterised by different structural characteristics. The O²⁻ and Al³⁺ species transport numbers near the metal|oxide interface were determined that depended on both temperature and current density. The rate of film thickness growth was found to be proportional to the O²⁻ anionic current through the barrier layer near the metal|oxide interface. The results introduced a new growth mechanism theory embracing the rarefaction of barrier layer oxide lattice towards the metal|oxide interface. The oxide density near the metal|oxide is closely independent of anodising conditions and is related to the transformation of Al lattice to a transient oxide lattice about 37% rarer than that of γ-Al₂O₃ that is further suitably transformed to denser, amorphous or nanocrystalline material as this oxide is shifted to the oxide|electrolyte interface and becomes the pore wall material. This gradual lattice density variability can explain many peculiar properties of anodic alumina films.     

Scaling of Dopant Segregation Schottky Barrier Using Metal Strip Buried Oxide MOSFET and its Comparison with Conventional Device

In this paper, a Schottky barrier silicon-on-insulator (SOI) MOSFET with asymmetric doping (dopant segregated) at the source/drain side and a metal strip in the BOX (Buried oxide) layer has been proposed. The asymmetric doping reduces the off-state leakage (I_OFF) and improves the on-state drive current (I_ON) in comparison to the conventional structure. The metal strip inside the BOX improves the subthreshold swing and I_ON/I_OFF current ratio. The simulation study of a conventional device using an image force barrier lowering model and without image force barrier lowering is presented. The channel length scaling leads to a high on-current in the conventional device. The thermionic emission and tunneling current are increased with barrier lowering and hence a high leakage current in the off-state region. Moreover, the proposed device is compared with the conventional device. The proposed device shows high I_ON/I_OFF ratio of 10⁷-10⁸ at V_DS = 0.1 V and Subthreshold Swing (SS) of 66 mV/dec.     

Facile Fabrication of Binder-Free CoZn LDH/CFP Electrode with Enhanced Capacitive Properties for Asymmetric Supercapacitor

CoZn layered double hydroxide (LDH) or Co(OH)₂ pseudocapacitive material has been prepared on the current collector of carbon fiber paper (CFP) using an eco-friendly one-step electrodeposition. Benefiting from its unique structural feature, the binder-free CoZn LDH/CFP electrode material realizes high specific capacitance of 1156 Fg^?1 at a current density of 1 Ag^?1 and excellent rate capability of 80% retention with 16 fold current density increment, which is much better than that of Co(OH)₂ (617 Fg^?1, 65%). Notably, the CoZn LDH/CFP can retain an outstanding electrochemical stability with a capacitance degradation of only 6% after 6000 charge–discharge cycles at 32 Ag^?1. Moreover, an asymmetric supercapacitor (ASC) using CoZn LDH/CFP as a positive electrode and AC/CFP as a negative electrode has been assembled. The ASC exhibits a superior energy density of 30.0 Whkg^?1 at a power density of 800 Wkg^?1 with a specific capacitance up to 84.4 Fg^?1 and a potential window wide to 1.6 V. These encouraging results indicate that CoZn LDH/CFP composite material has a great potential for next-generation energy conversion/storage devices.

     

Characterization of leakage current on diamond Schottky barrier diodes using thermionic-field emission modeling

A diamond vertical Schottky barrier diode (SBD) with nonepitaxial crystallites (NCs) exhibits high leakage current in both its forward and its reverse characteristics. A shunt path current through the grain boundary of the NCs is the dominant mechanism. The defectless device shows a low leakage current of less than 10^− 11 A/cm², and the device yield corresponds to the density of the NCs. The reverse leakage current of the defectless device increases with the reverse field. The leakage current of the diamond SBD is in good agreement with the tunneling model described by thermionic-field emission (TFE) rather than the conventionally used barrier-lowering model. The TFE current dominates when the reverse electric field is larger than 1.2 MV/cm, and current density reaches 10^− 6 A/cm², even at 1.6 MV/cm, which is lower than the avalanche limit.     

Structural and electrical properties of H-terminated diamond field-effect transistor

A dielectric barrier separating hydrogen induced p-type channel and Al gate metal contact of diamond FET has been investigated. The separation barrier is necessary to prevent tunneling current between the H-induced channel and the gate contact. In this investigation, CV measurements, fitting of forward IV characteristics, TEM and SIMS profiles have been used to obtain a more detailed picture of this barrier layer. While the composition of this layer is not clear, TEM and SIMS measurements indicate that this layer may be connected to a diamond phase or aluminium oxide. Using material properties of these materials, thickness of the separation layer extracted from the CV measurements was between 5–10 nm and the channel sheet change density was above 1 × 10¹³ cm^? 2. This thickness is in good agreement with the TEM observations. Frequency dependent CV measurements showed almost no frequency dependence, and no UV light dependence has been observed. Temperature dependent CV measurements showed a decrease of the dielectric constant at 100 °C. Fitting of the forward tunnelling current indicated a thickness of the barrier layer of about 5 nm with a barrier height of 2.4 eV.     

Spatially resolved electronic inhomogeneities of graphene due to subsurface charges

We probe the local inhomogeneities in the electronic properties of exfoliated graphene due to the presence of charged impurities in the SiO₂ substrate using a combined scanning tunneling and electrostatic force microscope. Contact potential difference measurements using electrostatic force microscopy permit us to obtain the average charge density but it does not provide enough resolution to identify individual charges. We find that the tunneling current decay constant, which is related to the local tunneling barrier height, enables one to probe the electronic properties of graphene distorted at the nanometer scale by individual charged impurities. We observe that such inhomogeneities do not show long-range ordering and their surface density obtained by direct counting is consistent with the value obtained by macroscopic charge density measurements. These microscopic perturbations of the carrier density significantly alter the electronic properties of graphene, and their characterization is essential for improving the performance of graphene based devices.     

The Role of Charge Localization in Current-Driven Dynamics

We explore the role of charge localization in current-triggered, resonance-mediated, dynamical events in molecular junctions. To that end we use a simple model for a molecular rattle, a Li⁺C₉H⁻₉ zwitterion attached between two metal clusters. By varying the size of the metal clusters we systematically vary the degree of delocalization of the electronic orbitals underlying the resonant current, and thus can draw general conclusions regarding the effect of delocalization on dynamical processes induced by resonance inelastic current in molecular electronics. In the small cluster limit, we find interesting quantum dynamics in the nuclear subspace, corresponding to coherent tunneling of the wave packet through the barrier of an asymmetric double-well potential. These dynamics are rapidly damped with increasing charge delocalization in extended systems.     

High Dielectric Constant ZrO<Subscript>2</Subscript> Films by Atomic Layer Deposition Technique on Germanium Substrates

Germanium has been reconsidered as a potential substitute channel material for high-performance MOSFETs due to its intrinsic high mobilities for both electrons (3900 cm² s^-1V^-1) and holes (1900 cm² s^-1V^-1). In the present work we have fabricated Pt/Ti metal bilayered ALD-ZrO ₂/n-Ge based MOS capacitors. The ZrO₂ thin film was deposited on n-Ge (100) substrates by using ZrEMA and oxygen precursors at 300 ^°C in a PEALD system. The Pt/Ti bilayer metallization was carried out using e-beam evaporation and PMA using a RTA system at 350 ^°C in the forming gas. The thickness of the ZrO₂ gate stack was measured to be 3.61 nm using an ellipsometer. The electrical study was done by analyzing capacitance voltage and current voltage measurements. The flat-band shift was found to be 0.22 V, Q_eff was 3.55×10¹² cm^-2 and D_it was 8.53×10¹² cm^-2 eV^-1. Current voltage characteristics have been analyzed to know the conduction mechanism in fabricated MOS devices.     

Ex situ and in situ characterization studies of spin-coated TiO2 film electrodes for the electrochemical ozone production process

An electrode composed of silicon/titanium oxide/platinum/titanium dioxide (Si/TiO_X/Pt/TiO₂) was fabricated by spin-coating TiO₂ multilayers on a Si/TiO_X/Pt substrate and was used in electrochemical ozone production (EOP). EOP was realized when the Si/TiO_X/Pt substrate was completely covered with the TiO₂ film and a current efficiency of 7% was achieved at a low current density of 26.7 mA cm⁻² in 0.01 M HClO₄ at 15 °C. The TiO₂ film was found to be of an anatase-type TiO₂ and that to comprise aperture structures from the X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations. Moreover, the fabricated TiO₂ film was found to be an n-type semiconductor by photoelectrochemical measurements. The high efficiency at a low current density of EOP on the TiO₂ n-type semiconductor was explained to result from the electron transfer through the TiO₂/HClO₄ interface as tunneling current. When the tunneling current passes through a depletion layer of TiO₂, the electrode potential is necessarily high enough to facilitate EOP.     

Detection of oxygen ion drift in Pt/Al2O3/TiO2/Pt RRAM using interface-free single-layer graphene electrodes

Resistive switching random access memory (RRAM) with oxygen ion drift under electric (E)-field has been intensively studied. However, the findings are insufficient because redox reaction by oxygen ion drift occurs beneath the top electrode, and it is difficult to analyze with a nondestructive method. Therefore, an effective method to circumvent this difficulty is suggested in this study with a Pt/Al₂O₃/TiO₂/Pt device using a single layer graphene (SLG) top electrode. Based on results from spectroscopic analyses, the SLG serves as not only an interface free electrode, but also as a highly effective indicator for proving O⁻ ion drift motion in response to the E-field in RRAM. The origin of asymmetric resistive switching is due to a redox reaction at the interface by oxygen ion drift. The endurance and operation-current distribution are significantly improved with increased thickness of the Al₂O₃ insertion layer, which provides carrier tunneling barrier height. The resistance ratio of the high resistance state (HRS) to the low resistance state (LRS) is greater than one order of magnitude in a log scale within 1800 cycles. This result demonstrates that control of a localized charge tunneling barrier is a key factor for reliable resistive switching of the scaled-down RRAM.     

Modeling a perforated bipole trickle bed electrochemical reactor for the generation of alkaline peroxide

This paper describes the modeling of a novel perforated bipole electrochemical reactor with trickle-bed cathodes employed in the electrosynthesis of alkaline peroxide solutions. The model engages an electronic analogue of the 3D electrode/bipoles to solve the coupled material, energy and voltage (charge) balances that estimate the potential, current density, composition, pressure and temperature profiles through the reactor. The predictions of this model are compared to the performance of a bench scale experimental reactor operating at superficial current densities up to 5 kA m⁻². With eddy diffusion through the diaphragm as the single adjustable parameter the model shows good agreement with peroxide current efficiency but underestimates the electrochemical specific energy consumption by about 2 kWh/kg H₂O₂ at 5 kAm⁻².     

1/f Spin noise and a single spin detection with STM

We propose a novel mechanism for single spin detection based on the 1/f spin current noise. We postulate that the 1/f spin noise for the tunneling current is similar to the ubiquitous 1/f noise in magnetic systems. Magnetic coupling between tunneling electrons and localized spin S then leads to the peak at Larmor frequency in the power spectrum of the electric current fluctuations I²_ω. The elevated noise in the current spectrum will be spatially localized near the magnetic site. The difference in the power spectra taken at the Larmor frequency and elsewhere would reveal the peak in the spectrum. We argue that the signal-to-noise ratio for this mechanism is on the order of one. In addition, we discuss the asymmetric line shapes observed regularly with this measurement. We show that such line shapes are in accordance with the random sampling done with the tunneling electrons. Yet this predicts a line width at least one order of magnitude larger than observed experimentally, which is likely to be due to electrostatic repulsion between the tunneling electrons and temporal correlations in the tunneling process.     

Nanosecond reversible solid state switches capable of handling MJ of energy

The theoretical applicability of the Schottky thermionic emission model to electronic transport at tin dioxide grain boundaries is addressed. Firstly, the theoretical behaviour of the barrier height ?_(v) versus applied voltage V is determined for a single grain boundary. Next we predict the current density–voltage characteristics as a function of temperature, demonstrating good correlation between experimental and theoretical results. The model carried out has the advantage that it contains no adjustable parameters. Agreement with experimental results from optimised polycrystalline ceramics gives strong evidence for the double-depletion-layer/thermionic-emission model. Moreover, this study emphasises the importance of the direct large-bandgap of doped SnO₂ in surge-arrester applications, and gives credibility to the analogy between the apparent behaviour of doped SnO₂ and doped ZnO varistors. Doped polycrystalline tin oxide ceramic is the first material to compete with doped ZnO in the medium and high voltage applications for surge arresters.     

Applied of central composite design for the optimization of removal yield of the ketoprofen (KTP) using electrocoagulation process

ABSTRACT

In this paper, the modeling and the optimization of the removal efficiency of ketoprofen (KTP) by the electrocoagulation process were studied. The central composite design experiments (CCD) method was used to study the main effects and the interaction effects between operational parameters and to optimize the value of each parameter. According to the regression equation obtained, the current density appears to be one of the most important parameters (b₂ = +22.11) controlling the removal efficiency of KTP. The positive sign of b₂ coefficient suggests that the increase of current density increases the yield of removal. The second signi?cant parameter with a negative effect was the initial KTP concentration (b₃ = ?16.27). This result suggests that the removal efficiency was inversely proportional to the initial concentration. In addition, according to the model, the most influencing interactions were pH-current density, pH-initial concentration, and current density-initial concentration. The model obtained by CCD led to the following optimal conditions for KTP removal e?ciency (96.70%): pH = 7, i = 24.04 mA cm^?2, and C₀ = 5 mg L^?1.     

Effect of TiO2 Thin Film with Different Dopants in Bringing Au-Metal into a Contact with n-Si

In this work, effects of TiO₂ contribution together with two different doping as graphene oxide (GO) and rubidium fluoride (RbF) are investigated at the interface of Au/n-Si metal–semiconductor (MS) diode. Diode characteristics are mainly evaluated from current–voltage measurements and values of barrier height and ideality factor are compared to the diodes with and without doping in interface layer. Although existence of interface layer increases these values, there is a decrease with adapting GO and RbF to the TiO₂ structure. In addition, series and shunt resistance values are calculated with interface layer, and resistance effect is also discussed by Norde’s and Cheung’s functions. Forward biased carrier transport mechanism is evaluated under the presence of interface states by thermionic emission model and density of interface trap states is also discussed. At the reverse biased region, field effected thermionic emission model is found to be dominant flow mechanism, and leakage current behavior is explained by Schottky effect. Solar simulator with different illumination intensities is used to investigate photo-generated carrier contribution and photo-response of the diodes.

     

Five-layer reverse tape casting of IT-SOFC

Tape casting is a well-established method for manufacturing thin ceramic layers with controllable thickness and porosity. This study investigates the potential of 10Sc1CeSZ material for the electrolyte and anode layers for intermediate-temperature solid oxide fuel cells (IT-SOFC) in an anode-supported cell (ASC) geometry. In order to use La_0.6Sr_0.4Co_0.2Fe_0.8 Oxide (LSCF) cathode material, a Gd_0.2Ce_0.8 Oxide (GDC) barrier layer is needed; however, thermal expansion coefficient mismatch results in delamination of the GDC from the electrolyte during high temperature sintering when fabricated by conventional tape casting procedures. For the first time, ASCs have been manufactured by a five-layer tape casting technique; barrier layer, novel composite layer, electrolyte, anode functional layer, and anode substrate. Ni-ScCeSZ composite cells were tested between 650 and 800°C in H₂:N₂ fuel (85% H₂) on the anode and air on the cathode to yield a maximum power density of .46 W/cm². These results demonstrate the feasibility of this new five-layer tape casting technique to produce IT-SOFC.     

Effects of diamond-like carbon in TPD-Alq3 doped PVK organic light-emitting devices

Effects of an ultrathin (~ 1 nm) diamond-like carbon (DLC) layer in single-layer organic light-emitting devices (OLEDs) that consist of ITO/(TPD-Alq₃ doped PVK)/Al were investigated. DLC layers deposited by using Nd:YAG laser at laser wavelengths of 355 nm were high in sp³ content and resistivity (DLC_UV) while that of 1064 nm laser were lower in sp³ content and resistivity (DLC_IR), as characterized by Raman spectroscopy and resistivity measurements. Although emission were obtained for all the devices, only the device of ITO/DLC_UV/(TPD-Alq₃ doped PVK)/Al exhibited enhanced current density and brightness with lower turn-on voltage as compared to a standard device. Devices of ITO/DLC_IR/(TPD-Alq₃ doped PVK)/Al and ITO/(TPD-Alq₃ doped PVK)/DLC_UV/Al showed poor current and brightness characteristics but failed at higher applied voltage. The enhance performance of device with high resistivity/sp³ DLC film suggests the mechanisms of barrier reduction by sufficiently thin insulating layer which increase the probability of tunneling of carriers at ITO and PVK interface.     

Ab initio computations of electronic,mechanical, lattice dynamical and thermal properties of ZrP2O7

A systematical ab initio analysis of ZrP₂O₇ is presented in this work. Density functional theory (DFT) computations were performed for the electronic, mechanical, lattice dynamical and thermal properties of ZrP₂O₇. The lattice constants determined from the theoretical calculation are consistent with the experimental results. Based on the analyses on the electronic density of states, charge density and electron localization function of ZrP₂O₇, heterogeneous bonding nature is revealed and confirmed by the phonon density of states. We also reported the second-order elastic constants and polycrystalline mechanical properties of ZrP₂O₇ for the first time. According to the calculated polycrystalline moduli, the minimum thermal conductivity of ZrP₂O₇ is estimated to be 1.15 W m⁻¹ K⁻¹. Our theoretical results illustrate that ZrP₂O₇ is a promising candidate as thermal barrier coating and high temperature binding material.     

2D/2D SnS2/MoS2 layered heterojunction for enhanced supercapacitor performance

Two-dimensional (2D) SnS₂/MoS₂ heterojunction with a 2D/2D novel structure was used as electrode material for enhanced supercapacitor performance. Compared with the sole SnS₂, the as-prepared 2D/2D SnS₂/MoS₂ layered heterojunction has exhibited great improvement in supercapacitor properties. This novel structure can effectively prevent agglomeration and stacking in electrochemical process, and 2D/2D structure is beneficial to intercalation and desorption of ions in electrochemical processes. The experiment result shows that MoSn₅ (samples with 5% MoSn5 mole ratios) display a specific capacitance of 466.6 F/g at the current density of 1 A/g in 0.5 mol/L potassium hydroxide solution, an impressive cycling stability with 88.2% capacitance retention at current density of 4 A/g. In addition, the as-fabricated symmetric supercapacitor exhibited high energy density of 115 Wh kg⁻¹ at the power density of 2230 Wh kg⁻¹. This work provides a fundamental investigation of 2D/2D layered material synergistic effect on the electrochemical process.     

Effects of the annealing atmosphere on the microstructure and properties of BiFe0.99Zn0.01O3 films

BiFe_0.99Zn_0.01O₃ (BFZO) films were annealed in different atmospheres (Air, N₂ and O₂) on ITO/glass substrates. The influences of the different annealing atmospheres on the oxygen vacancy concentration, microstructure, ferroelectric behavior, leakage current, leakage mechanism, aging and dielectric performance of the BFZO films were studied. The crystallization and grain development for the sample annealed in an O₂ atmosphere improved, and the concentrations of the Fe²⁺ and oxygen vacancies were the lowest among the samples studied herein. The BFZO film had the lowest leakage current density and the best ferroelectric performance in an O₂ annealing atmosphere among the samples studied herein, and the leakage was due to the F-N tunneling effect mechanism. From the perspective of the volume effect, the aging model was established, and the aging mechanism of the BFZO films was discussed in depth. Compared with Air and N₂, the annealed film in O₂ exhibited no obvious aging.