Conductive Surface Layer Research Articles

Hydrogenated ZnO thin film with p-type surface conductivity from plasma treatment

Fabrication of a ZnO p-n homojunction within a single structure by a simple process is a challenging task. In this work, an intrinsic p-type surface conductive layer of ZnO with a controlled concentration of holes over n-type conductive bulk was obtained by a one-step room-temperature process via hydrogen plasma treatment. Non-contact surface sensitive techniques, such as Kelvin probe force microscopy and conductive force atomic microscopy, confirmed the existence of surface p-type conductivity through analyzing the distribution and concentration of charge carriers on the topmost surface of hydrogenated ZnO. A theoretical framework was constructed to provide a rationale of the p-type surface conductivity and justify its relation to the treatment time. It is believed that this finding will open a new possibility for the fabrication of ZnO based p-n junction devices.

Optical and electrical properties of synthetic single-crystal diamond under high-fluence ion irradiation

The modification of the (111) face of synthetic diamond under high-fluence (≥1018 ion/cm2) 30-keV Ar+ irradiation is studied experimentally. It is found that ion irradiation at room temperature results in the formation of a low-conductivity surface layer. Heat treatment when the target temperature is increased to 400°C results in a more than ten-fold exponential drop in the layer resistance, as compared to its value at room temperature. If the temperature of the irradiated diamond is increased from 30 to 400°C the layer resistance of the ion-induced conductive layer drops by more than two orders of magnitude to the level corresponding to the conductivity of graphite-like materials. The Raman spectra of the ion-induced conductive surface layer reflect the processes of structural disorder—sp 2-carbon ordering and strong changes in the optical transmittance of diamond after ion irradiation.

Effect of surface roughness and H–termination chemistry on diamond's semiconducting surface conductance

The H-terminated surface of diamond when activated with NO2 produces a surface conduction layer that has been used to make FETs. Variations in processing can significantly affect this conduction layer. This article discusses the effect of diamond surface preparation and H termination procedures on surface conduction. Surface preparations that generate a rough surface result in a more conductive surface with the conductivity increasing with surface roughness. We hypothesize that the increase in conductance with roughness is the result of an increase of reactive sites that generate the carriers. Roughening the diamond surface is just one way to generate these sites and the rough surface is believed to be a separate property from the density of surface reactive sites. The presence of C in the H2 plasma used for H termination decreases surface conductance. A simple procedure for NO2 activation is demonstrated. Interpretation of electrical measurements and possible alternatives to activation with NO2 are discussed. Using Kasu's oxidation model for surface conductance as a guide, compounds other than NO2 have been found to activate the diamond surface as well.

Spin galvanic effect at the conducting SrTiO3 surfaces

The (001) surface of SrTiO3 were transformed from insulating to conducting after Ar+ irradiation, producing a quasi two-dimensional electron gas (2DEG). This conducting surface layer can introduce Rashba spin orbital coupling due to the broken inversion symmetry normal to the plane. The spin splitting of such a surface has recently been demonstrated by magneto-resistance and angular resolved photoemission spectra measurements. Here, we present experiments evidencing a large spin-charge conversion at the conducting surface. We use spin pumping to inject a spin current from NiFe film into the surface, and measure the resulting charge current. The results indicate that the Rashba effect at the surface can be used for efficient charge-spin conversion. The conversion efficiency measured by the ratio of the spin flow density to the charge flow density is about 0.23 nm. This value is on the same order as the interfaces in metallic multilayers and 2DEG of LaAlO3/SrTiO3. In this point of view, the conducting SrTiO3 surface provides another solution for oxide spintronics.

Copper-Coated Liquid-Crystalline Elastomer via Bioinspired Polydopamine Adhesion and Electroless Deposition.

This study explores the functionalization of main-chain nematic elastomers with a conductive metallic surface layer using a polydopamine binder. Using a two-stage thiol-acrylate reaction, a programmed monodomain is achieved for thermoreversible actuation. A copper layer (≈155 nm) is deposited onto polymer samples using electroless deposition while the samples are in their elongated nematic state. Samples undergo 42% contraction when heated above the isotropic transition temperature. During the thermal cycle, buckling of the copper layer is seen in the direction perpendicular to contraction; however, transverse cracking occurs due to the large Poisson effect experienced during actuation. As a result, the electrical conductivity of the layer reduced quickly as a function of thermal cycling. However, samples do not show signs of delamination after 25 thermal cycles. These results demonstrate the ability to explore multifunctional liquid-crystalline composites using relatively facile synthesis, adhesion, and deposition techniques.

Direct determination of the barrier height of Au ohmic-contact on a hydrogen-terminated diamond (001) surface

The barrier height ϕB of Au ohmic-contact on hydrogen-terminated p-type surface conductive layer (SCL) made on a boron-doped diamond (001) substrate has been directly determined by X-ray photoelectron spectroscopy (XPS). For this purpose, thin layer (thickness~3.6nm) of Au was deposited on the p-type SCL. The formation of nm-size Au-islands was identified by scanning electron microscopy. It became therefore evident that C 1s XPS spectra originate from diamond in the gap areas among Au-islands but not from diamond underneath the Au-islands. Two-dimensional energy band simulation was performed to show that the diamond band diagram in the gap areas among Au-islands become effectively identical to that of diamond underneath the Au-islands when SCL is eliminated only in the gap areas. In order to eliminate SCL in the gap area only, a VUV/ozone irradiation process was applied on the Au-island-covered sample. C 1s and Au 4f7/2 XPS spectra were measured for the sample before and after the VUV/ozone irradiation process. The peak binding energies and widths of C 1s and Au 4f7/2 XPS spectra are carefully considered to reach to the conclusion that ϕB=0.29±0.13eV. For the boron-doped present substrate, the current flow mechanism at the Au ohmic-contacts is expected to be thermionic emission and specific contact resistance RC is thus evaluated to be the order of 10−4Ωcm2.

Electrochemical Property of Boron-Doped Heteroepitaxial Diamond Treated By Different Oxidation Method

Boron-doped diamond electrode is expected to realize high sensitive electrochemical sensors because of its unique properties such as wide potential window and low background current. Many studies of diamond electrochemistry have been already reported but most of these works were carried out using polycrystalline diamond. Because several crystal faces and many grain boundary exists, electrochemical reactions at the surface of polycrystalline diamond becomes complex. On the other hand, epitaxial diamond (nearly single crystal) is structurally uniform, we believe that boron-doped epitaxial diamond will be more ideal material in order to realize highly-sensitive and highly-reliable sensor. Furthermore, it is useful to clarify basic electrochemical reactions at the surface of diamond. Several studies have been already reported using boron-doped homoepitaxial diamond. In the case of homoepitaxial growth, HPHT (high pressure high temperature) diamond is used for substrate but available size of HPHT diamond is small and also costs much. On the other hand, heteroepitaxial growth is much easier to fabricate diamond in large size at low cost. From the viewpoint of practical use, studies on boron-doped heteroepitaxial diamond will be important. In this study, fundamental electrochemical property of hydrogen-terminated and oxygen-terminated boron-doped heteroepitaxial diamond was evaluated. There are several methods to change the surface termination of diamond from hydrogen to oxygen such as heat mixed acid, oxygen plasma, UV irradiation, anodic oxidation treatment. The treatment conditions were optimized at each method and the oxidation peak shift of potassium ferrocyanide was compared. First, non-doped epitaxial diamond(100) was grown on Ir(100)/MgO(100) substrate in thickness of 100 μm by direct current plasma enhanced chemical vapor deposition (PE-CVD) method. After the growth, Ir/MgO substrate was removed by acid treatment in order to fabricate free-standing diamond platelet. Finally, boron-doped epitaxial diamond was grown on non-doped epitaxial diamond at boron concentration of 5000 ppm. Oxidation peak potential of potassium ferrocyanide (5mM in 0.1 M sodium sulfate) was measured by cyclic voltammetry after oxidation treatment under defined condition. To optimize oxidation treatment condition, this operation was repeated until the peak potential becomes constant. For heat mixed acid treatment, sample was dipped in mixed acid (60% nitric acid:95% sulfuric acid = 3:1) at 523 K for 15 min. For anodic oxidation treatment, 0.5 M sulfuric acid was used for electrolyte and the potential was kept at 3.0 V for 5 s. From the X-ray diffraction measurement, single sharp peak at around 120 degrees which is due to diamond(004) was detected from 2theta-omega spectrum and four-fold symmetry peaks were detected from diamond{111} pole figure which indicates that the diamond was epitaxially grown on Ir/MgO substrate. When the sample was terminated by hydrogen, sharp oxidation and reduction peaks were observed from the cyclic voltammogram and its peak separation was around 70 mV which reflects a quasi-reversible reaction (very close to reversible reaction). Shift of oxidation peak was observed after both heat mixed acid and anodic oxidation treatment. By repeating heat mixed acid treatment for four times (total 60 min treatment), oxidation peak became constant and its potential was 0.42 V vs Ag/AgCl. On the other hand, repeating anodic oxidation treatment for six times (total 30 s treatment), the peak became constant at potential of 1.52 V. Heat mixed acid treatment is a well-known method to remove surface conductive layer of diamond but the peak potential at optimized treatment condition was extremely different between two methods which indicates that termination structure differs. Termination structures analyzed by X-ray photoelectron spectroscopy will be discussed. Furthermore, the results of other methods such as oxygen plasma and UV irradiation treatment will be also discussed.

Mixed Ionic/Electronic Conducting Surface Layers Adsorbed on Colloidal Silica for Flow Battery Applications.

PSS). Using a combination of small angle neutron scattering (SANS), electron microscopy, and thin-film conductivity, we show that the synthesis scheme provides a flexible platform to form conductive PSS-SiO2 nanoparticle dispersions. Based on these measurements, we demonstrate that these particles are stable when dispersed in propylene carbonate. Using a combination of rheology and dielectric spectroscopy, we show that these stable dispersions facilitate electrical percolation at concentrations below their mechanical percolation threshold, and this percolation is maintained under flow. These results demonstrate the potential for strategies which seek to decouple mechanical and electrical percolation to allow for the development of higher performance conductive additives for slurry based flow batteries.

Graphitization of a diamond surface upon high-dose ion bombardment

Results from structural and morphological studies, measurements of the sheet electrical resistance, and estimating resistivity ρm of a graphite-like conducting surface layer formed upon high-dose irradiation of the (111) face of a synthetic diamond with Ar+ ions at an energy of 30 keV and a target temperature of 400°C are presented. It is found that the orienting effect of the diamond lattice is visible in the suppression of the formation of graphite crystallites with axis c perpendicular to the surface. The thickness of the modified layer is 40–50 nm, and its sheet resistance is 0.5 kΩ/sq. Resistivity ρm = 20–25 μΩ m of the modified layer lies within the range of ρ values of graphite and glassy carbon materials.

Hydrophilic Organic Electrodes on Flexible Hydrogels.

Prompted by the rapidly developing field of wearable electronics, research into biocompatible substrates and coatings is intensifying. Acrylate-based hydrogel polymers have gained widespread use as biocompatible articles in applications such as contact and intraocular lenses. Surface treatments and/or coatings present one strategy to further enhance the performance of these hydrogels or even realize novel functionality. In this study, the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is deposited from the vapor phase onto hydrated hydrogel substrates and blended with biocompatibilizing coconstituents incorporating polyethylene glycol (PEG) and polydimethyl siloxane (PDMS) moieties. Plasma pretreatment of the dehydrated hydrogel substrate modifies its surface topography and chemical composition to facilitate the attachment of conductive PEDOT-based surface layers. Manipulating the vapor phase polymerization process and constituent composition, the PEDOT-based coating is engineered to be both hydrophilic (i.e. to promote biocompatibility) and highly conductive. The fabrication of this conductively coated hydrogel has implications for the future of wearable electronic devices.

Screening limited switching performance of multilayer 2D semiconductor FETs: the case for SnS.

Gate tunable p-type multilayer tin mono-sulfide (SnS) field-effect transistor (FET) devices with SnS thickness between 50 and 100 nm were fabricated and studied to understand their performance. The devices showed anisotropic inplane conductance and room temperature field effect mobilities ∼5-10 cm2 V-1 s-1. However, the devices showed an ON-OFF ratio ∼10 at room temperature due to appreciable OFF state conductance. The weak gate tuning behavior and finite OFF state conductance in the depletion regime of SnS devices are explained by the finite carrier screening length effect which causes the existence of a conductive surface layer from defect induced holes in SnS. Through etching and n-type surface doping by Cs2CO3 to reduce/compensate the not-gatable holes near the SnS flake's top surface, the devices exhibited an order of magnitude improvement in the ON-OFF ratio, and a hole Hall mobility of ∼100 cm2 V-1 s-1 at room temperature is observed. This work suggests that in order to obtain effective switching and low OFF state power consumption, two-dimensional (2D) semiconductor based depletion mode FETs should limit their thickness to within the Debye screening length of the carriers in the semiconductor.

EDM of Insulating Ceramics by Electrical Conductive Surface Layer Control

Electrical discharge machining (EDM) is available and effective for precise, complex shaping. Recently, by using the assisting electrode method, EDM can be applied to insulating ceramics. In this method, a pulse discharge that is longer than the set pulse duration is generated. With this long pulse discharge, an electrical conductive layer is formed on the surface of the insulating ceramic, which maintains stable machining. In this paper, we describe how to control this electrical conductive surface layer. The layer control sequence is applied to the wire electrical discharge milling method (WED-milling) with a wire guide on a hemisphere tip in order to realize 3D machining of insulating ceramics.

Effects of Eddy Current in Electrical Connection Surface of Laminated Cores on High-Speed PM Motor Supported by Active Magnetic Bearings

For the high-speed permanent magnet (PM) motor supported by active magnetic bearings (AMBs), the iron cores of radial AMBs and the motor are made of laminations in order to reduce eddy-current loss. However, the surfaces of laminations are usually not smooth enough, so further surface manufacturing is required, by which the surfaces of each lamination are connected and a conductive layer is formed on the laminations surface. In the varying magnetic field, these conductive surface layers will generate additional eddy currents, which will increase the machine loss and affect the distribution of original magnetic field. In this paper, these effects on magnetic bearing and PM motor are investigated by the finite-element method.

Isotope analysis of diamond-surface passivation effect of high-temperature H2O-grown atomic layer deposition-Al2O3 films

The Al2O3 film formed using an atomic layer deposition (ALD) method with trimethylaluminum as Al precursor and H2O as oxidant at a high temperature (450 °C) effectively passivates the p-type surface conduction (SC) layer specific to a hydrogen-terminated diamond surface, leading to a successful operation of diamond SC field-effect transistors at 400 °C. In order to investigate this excellent passivation effect, we carried out an isotope analysis using D2O instead of H2O in the ALD and found that the Al2O3 film formed at a conventional temperature (100 °C) incorporates 50 times more CH3 groups than the high-temperature film. This CH3 is supposed to dissociate from the film when heated afterwards at a higher temperature (550 °C) and causes peeling patterns on the H-terminated surface. The high-temperature film is free from this problem and has the largest mass density and dielectric constant among those investigated in this study. The isotope analysis also unveiled a relatively active H-exchange reaction between the diamond H-termination and H2O oxidant during the high-temperature ALD, the SC still being kept intact. This dynamic and yet steady H termination is realized by the suppressed oxidation due to the endothermic reaction with H2O. Additionally, we not only observed the kinetic isotope effect in the form of reduced growth rate of D2O-oxidant ALD but found that the mass density and dielectric constant of D2O-grown Al2O3 films are smaller than those of H2O-grown films. This is a new type of isotope effect, which is not caused by the presence of isotopes in the films unlike the traditional isotope effects that originate from the presence of isotopes itself. Hence, the high-temperature ALD is very effective in forming Al2O3 films as a passivation and/or gate-insulation layer of high-temperature-operation diamond SC devices, and the knowledge of the aforementioned new isotope effect will be a basis for further enhancing ALD technologies in general.

Device Simulation of Hydrogen-Terminated Diamond Mosfet and Extraction of Small-Signal Parameters

Diamond has exceptional properties suitable for electronic and photonic devices. In particular, hydrogen-terminated diamond (HTD) FET devices have been studied recently for potential radio-frequency (RF) applications by exploiting its high conductivity at diamond surface, high thermal conductivity and simple fabrication process [1-3]. However, the device simulation of such FET device is rarely reported because the surface conductive mechanism is not fully understood. In this work, a new device structure including a surface adsorbate layer (ADL) is presented and a possible explanation of the formation of surface conductive layer is provided. Based on our theory, the 2D device simulation is achieved using Sentaurus Technology Computer-Aided Design software; both the capacitance-voltage (C-V) and DC current-voltage (I-V) properties of the HTD MOSFET can be understood well. It is found that the current mainly flow at diamond surface when the drain-source voltage (VDS) is small but meander into the bulk when |VDS| becomes larger. The working mode of the device can change from enhancement to depletion as the gate length (Lg) shrinks, and the threshold voltage becomes very sensitive to Lg when Lg≤0.2μm. The off-state leakage current increases drastically when Lg is approaching 50nm, causing the on/off current ratio dropping from 106 to 103. In addition, the radio-frequency (RF) small-signal equivalent circuit of the device is generated and the frequency responses of the circuit components are studied. For devices with small gate length (<0.2μm), the non-quasi-static (NQS) effect happens at the frequency over 10GHz, making the HTD device suitable for applications in microwave range. The simulated transition frequency fT is around 170GHz when Lg=50nm, but it is greatly affected by the source/drain series resistance. Finally, a strategy is presented to extract the values of circuit components from simulated two-port parameters, which works well up to 2GHz. [1] M. Schwitters, M. P. Dixon, A. Tajani, D. J. Twitchen, J. I. S. E. Coe, H. El-Haji et al., Diamond-MESFETs-synthesis and integration, IEEE European Radar Conference, (2005) pp.1-4. [2] M. Kasu, K. Ueda, H. Ye, Y. Yamauchi, S. Sasaki, T. Makimoto, High RF output power for H-terminated diamond FETs, Diamond and Related Materials, 15(2006) pp.783-786. [3] J. L. Liu, C. M. Li, R. H. Zhu, J. C. Guo, L. X. Chen, J. J. Wei et al., RF characteristic of MESFET on H-terminated DC arc jet CVD diamond film, Applied Surface Science, 284 (2013) pp.798-803.

One-Step Synthesis of Novel Mesoporous Three-Dimensional GeO2 and Its Lithium Storage Properties

In order to meet the requirements of high energy density as well as high power performance, a worldwide effort has been made to develop novel high-performance electrode materials to keep pace with the fast increasing market demands. Various compounds that form intermetallic phases (so-called “alloys”) with lithium have been proposed as alternative anode materials, such as silicon (Si) [1-2], tin (Sn) [3] and germanium (Ge) [4]. Compared to Si, less attention has been paid so far on Ge due to its higher costs. Nevertheless, its good lithium diffusivity (400 times higher than in silicon) and high electronic conductivity (ca. 104 times higher than silicon) enable it as a promising anode material for the next-generation LIBs. Currently, researchers report on different structures of Ge-based materials, such as nanotubes [5], nanowires [6], porous structures [7] and Ge-based composite materials [4]. So far, only a few studies focus on GeO2 as anode material. GeO2 is of interest for application as negative electrode material due to its high theoretical reversible capacity (1125 mAh g-1 based on 4.25 mol Li per mol Ge), low operation voltage (0.7 V to 0 V vs. Li/Li+) and higher thermal stability compared to Ge.[8] The reaction of GeO2 with Li involves two steps: 1) GeO2 + 4Li à Ge + 2Li2O; 2) xLi + Ge ⇌ LixGe (x ≤ 4.25). While the first reaction can be considered as to a large part electrochemically irreversible, resulting in a large irreversible charge loss by formation of Li2O, the lithiation/de-lithiation reaction in step 2) can be regarded as reversible, providing the discharge capacity of GeO2. The high irreversible capacity during the first lithiation process is also well-known for SnO2-based anodes and is one of the main reasons hindering so far the application in commercial lithium-ion batteries.[9] In general, the synthesis of GeO2 can be achieved by different methods, including hydrolysis reactions from a Ge precursor, chemical vapor deposition (CVD) and sputter processes. In this work, novel mesoporous three-dimensional GeO2 was successfully synthesized by a facile one-step synthesis method followed by mixing with graphene using a spray drying process. The as-prepared GeO2 shows a bean-like morphology with a particle size of 400 to 500 nm in length and 200 to 300 nm in diameter (Figure 1a-d). In a further step, we take the advantages of graphene (low-dimensional carbon material with high electronic conductivity; excellent mechanical properties; graphene can contribute to the capacity) to further enhance the electrochemical performance of b-GeO2. As illustrated in Figure 2, it can be clearly observed that the GeO2 particles are tightly anchored on or wrapped within the graphene sheets. Notably, during the mixing process, GeO2 particles are still homogenously dispersed within or firmly encapsulated by the graphene sheets. The b-GeO2 without any additional conductive surface layer shows a high reversible capacity for lithium storage of 845 mAh g-1 after 100 cycles, with nearly no capacity fading. When graphene was employed to be mixed with GeO2 via a spray drying method, the electrochemical performance is further significantly improved. The b-GeO2/graphene composite electrode gives a higher de-lithiation capacity of 1,021 mAh g-1 for 200 cycles at 0.2C and a high rate capability of up to 5C. This superior electrochemical performance benefits from its uniformly dispersed mesoporous structure, in which the GeO2 particles are homogeneously distributed on or within the conductive graphene sheets. Figure 1. Low-resolution (a, b) and high-resolution-resolution (c, d) SEM images of b GeO2. Figure 2. (a, b) SEM images of the b-GeO2/graphene composite prepared by spray drying method.

Electrochemical Transfer Doping: A Novel Phenomenon Seen in Diamond, Gallium Nitride, and Carbon Nanotubes

Intrinsic diamond with its band gap of 5.5 eV is an extremely good insulator. However, for undoped, hydrogen-terminated diamond exposed to air, a p-type conductive surface layer appears that is mediated by adsorbates from the ambient atmosphere.1 Since its discovery, several explanations of this effect have been proposed, none has received wide acceptance and the mechanism remained controversial. Recent studies have shown indisputably that the conductivity arises as result of electron exchange between atmospheric oxygen and diamond through an electrochemical redox reaction occurring in an adsorbed water layer: 4H+ + 4e- + O2 = 2H2O This results in the formation of a hole accumulation layer on the surface.2,3 This novel phenomenon, referred to as “surface transfer doping” depends only on the band line up of the semiconductor with respect to the ambient. For diamond, the Fermi level is higher than the electron chemical potential of oxygen redox couple, which results in electron transfer into water layer and generation of p-type surface conductivity. See Figure 1. The electron chemical potential (Fermi energy) of the redox couple, which can be estimated from the Nernst equation. Since water layers form spontaneously on surfaces exposed to humid air, electrochemical transfer doping is a very general phenomenon that has been unrecognized so far. Since its discovery in diamond, the effect has been observed in other technologically important materials such as in single-walled semiconducting carbon nanotubes, graphene, gallium nitride and zinc oxide.4 The process not only affects the electrical properties but also optical properties of the semiconductor. For example, in both GaN and ZnO, electron exchange between oxygen redox couple and mid-gap states results in dramatic changes in the ubiquitous yellow and green luminescence respectively. This phenomenon opens the door to novel and robust class of devices and processes. 1. M. I. Landstrass, and K. V. Ravi, Appl. Phys. Lett., 55 (1989) 975. 2. F. Maier, M. Riedel, B. Mantel, J. Ristein, L. Ley, Phys. Rev. Lett. 85, 3472 (2000) 3. V. Chakrapani, J. C. Angus, A. B. Anderson, S. D. Wolter, B. R. Stoner and G. U. Sumanasekera, Science 318, 1424 (2007) 4. V. Chakrapani, C. Pendyala, K. Kash, A. B. Anderson, M. K. Sunkara, J. C. Angus, J. Am. Chem. Soc. 130, 12944 (2008) Figure 1

High-fluence ion-beam modification of a diamond surface at high temperature

The results of experimental investigation into modification of the (111) face of a synthetic diamond crystal under high-fluence 30-keV Ar+ irradiation are presented. It is found that irradiation at a temperature of 400°C leads to the formation of a conductive surface layer, which is detected in the Raman spectra as a broad band with a maximum close to the position characteristic of the G peak of graphite at 1580 cm−1. In addition, the intensity of the narrow peak of diamond at 1332 cm−1 decreases by an order of magnitude. Ion irradiation is accompanied by the suppression of the initial photoluminescence and gives rise to weak photoluminescence with a spectrum characteristic of gem diamonds.

Dynamics of energy coupling and thermalization in barrier discharges over dielectric and weakly conducting surfaces on µs to ms time scales

The paper presents experiments characterizing discharge development and energy coupling in a surface dielectric barrier discharge (SDBD), atmospheric air plasmas over dielectric and weakly conducting surfaces, over a wide range of time scales and electrical conductivities. The experiments are done using nanosecond pulse (NS) both single polarity and alternating polarity) and ac voltage waveforms. Discharge development and mechanisms of coupling with quiescent air are analysed using nanosecond gate camera imaging, schlieren imaging, and laser differential interferometry. It is shown that NS SDBD plasmas generate stochastic, localized, near-surface perturbations on a long time scale (>100 μs) after the discharge pulse. These perturbations, entirely different from compression waves generated on a short time scale (~1–10 μs), are caused by discharge contraction and originate from the ends of the filaments. Surface conductivity has almost no effect on discharge behaviour if RC time of the conducting surface layer is much longer compared to the characteristic time of NS or ac voltage waveforms. In the opposite limit of short RC time, the conducting layer acts as an extension of the high-voltage electrode. Discharge contraction significantly increases energy stored on the dielectric surface, which in this case exceeds energy dissipated as Joule heat. The stored energy is dissipated if the discharge pulse is followed by an opposite polarity pulse. In a single polarity discharge, on the other hand, surface charge accumulation limits energy coupled to the plasma by subsequent pulses. The results demonstrate that surface plasma actuator control authority may be significantly increased by using an alternating polarity pulse waveform, which is more effective than the removal of surface charge between the pulses using a weakly conducting surface.

Enhanced cyclability of LiNi0.5Mn1.5O4 cathode in carbonate based electrolyte with incorporation of tris(trimethylsilyl)phosphate (TMSP)

In this work, tris (trimethylsilyl) phosphate (TMSP) is used as an electrolyte additive to improve the cycling performance of Li/LiNi0.5Mn1.5O4 cell upon cycling at high voltage, 4.9 V vs. Li/Li+ at room temperature and elevated temperature (55 °C). The effects of TMSP on the cathode interface and the cycling performance of Li/LiNi0.5Mn1.5O4 cell were investigated via the combination of electrochemical methods, including cycling test, cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). It is found that cells with electrolyte containing TMSP have better capacity retention than that of the cells without TMSP upon cycling at high voltage at room temperature and elevated temperature. The functional mechanism of incorporation of TMSP to the electrolyte to improve the cycling performance is conducted with ex-situ analysis approaches, including X-ray diffraction (XRD), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and ICP-MS. The surface analysis results reveal that more stable and more conductive surface layer is formed on the LiNi0.5Mn1.5O4 electrode with TMSP containing electrolyte, which is a leading factor for the enhanced the cycling performance of Li/LiNi0.5Mn1.5O4 cells upon cycling at high voltage at room temperature and elevated temperature.