Showing papers in "Journal of Physics D in 2012"

The emerging role of reactive oxygen and nitrogen species in redox biology and some implications for plasma applications to medicine and biology

Abstract: Reactive oxygen species (ROS) and the closely related reactive nitrogen species (RNS) are often generated in applications of atmospheric pressure plasmas intended for biomedical purposes. These species are also central players in what is sometimes referred to as ‘redox’ or oxidation‐reduction biology. Oxidation‐reduction biochemistry is fundamental to all of aerobic biology. ROS and RNS are perhaps best known as disease-associated agents, implicated in diabetes, cancer, heart and lung disease, autoimmune disease and a host of other maladies including ageing and various infectious diseases. These species are also known to play active roles in the immune systems of both animals and plants and are key signalling molecules, among many other important roles. Indeed, the latest research has shown that ROS/RNS play a much more complex and nuanced role in health and ageing than previously thought. Some of the most potentially profound therapeutic roles played by ROS and RNS in various medical interventions have emerged only in the last several years. Recent research suggests that ROS/RNS are significant and perhaps even central actors in the actions of antimicrobial and anti-parasite drugs, cancer therapies, wound healing therapies and therapies involving the cardiovascular system. Understanding the ways ROS/RNS act in established therapies may help guide future efforts in exploiting novel plasma medical therapies. The importance of ROS and RNS to plant biology has been relatively little appreciated in the plasma biomedicine community, but these species are just as important in plants. It appears that there are opportunities for useful applications of plasmas in this area as well. (Some figures may appear in colour only in the online journal)

The 2012 Plasma Roadmap

Abstract: Low-temperature plasma physics and technology are diverse and interdisciplinary fields. The plasma parameters can span many orders of magnitude and applications are found in quite different areas of daily life and industrial production. As a consequence, the trends in research, science and technology are difficult to follow and it is not easy to identify the major challenges of the field and their many sub-fields. Even for experts the road to the future is sometimes lost in the mist. Journal of Physics D: Applied Physics is addressing this need for clarity and thus providing guidance to the field by this special Review article, The 2012 Plasma Roadmap.

Plasma chemistry model of surface microdischarge in humid air and dynamics of reactive neutral species

Abstract: We present a numerical model of a surface microdischarge (SMD) in humid air at atmospheric pressure. Our model includes over 50 species and 600 elementary reactions and consists of two, coupled well-mixed regions: a discharge layer with both charged and neutral species and an afterglow region consisting only of neutral species. Multiple time steps employed in our model enable capturing rapid dynamic behaviour in the discharge layer as well as the relatively slow diffusion and reaction in the afterglow. A short duration, high electric field is assumed to be excited at 10 kHz in the discharge region with power density maintained at 0.05 W cm−2. Among the predicted dominant species in the afterglow are O3, N2O5, N2O, HNO3, H2, NO3, H2O2, HNO2 and NO2. The results are in qualitative agreement with Fourier transform infrared absorption spectroscopy. Our simulation results show that density of those reactive species continues to evolve significantly in time, even after ~15 min of SMD exposure. This result suggests that SMD treatments on the order of minutes or less may involve significant neutral species concentration and flux transients, potentially affecting interpretation of results.

Surface plasmon polaritons: physics and applications

Abstract: Surface plasmon polaritons (SPPs) are electromagnetic excitations existing at the interface between a metal and a dielectric material. Remarkable progress has been made in the field of SPPs in recent years. Control and manipulation of light using SPPs on the nanometre scale exhibit significant advantages in nanophotonics devices with very small elements, and SPPs open a promising way in areas involving environment, energy, biology and medicine. This paper presents an overview of current research activities on SPPs, including fundamental physics and applications. We first discuss the excitation of SPPs based on the SPP dispersion relation, coupling to SPPs by momentum matching between photons and SPPs, and propagation behaviour of SPPs. Based on the physical mechanism and the peculiar properties of SPPs, we demonstrate the major applications of SPPs, such as waveguides, sources, near-field optics, surface-enhanced Raman spectroscopy, data storage, solar cells, chemical sensors and biosensors.

Flexural wave band gaps in locally resonant thin plates with periodically attached spring-mass resonators

Abstract: The authors study the propagation of flexural waves in a locally resonant (LR) thin plate made of a two-dimensional periodic array of spring–mass resonators attached on a thin homogeneous plate. The well-known plane wave expansion method is extended to deal with such a plate system with a periodic array of lumped resonant elements. Explicit matrix formulations are developed for the calculation of complex band structures, in which the imaginary parts of Bloch wave vectors are displayed to quantify the wave attenuation performance of band gaps. It is found that resonance-type and Bragg-type band gaps coexist in the LR plate, and the bandwidth of these gaps can be dramatically affected by the resonant frequency of local resonators. In particular, a super-wide pseudo-directional gap can be formed by a combination of the resonance gap and Bragg gap; inside such a pseudo-gap, only a very narrow pass band exists. An explicit formula is further developed to facilitate the design of such a pseudo-gap. Finally, vibration transmission in finite LR plates is calculated using the finite element method. Vibration transmission gaps are observed, and the results are in good agreement with the band gap properties predicted by the complex band structures.

Plasmonics: visit the past to know the future

Abstract: Surface plasmons are collective oscillations of free electrons localized at surfaces of structures made of metals. Since the surface plasmons induce fluctuations of electric charge at surfaces, they are accompanied by electromagnetic oscillations. Electromagnetic fields associated with surface plasmons are localized at surfaces of metallic structures and significantly enhanced compared with the excitation field. These two characteristics are ingredients for making good use of surface plasmons in plasmonics. Plasmonics is a rapidly growing and well-established research field, which covers various aspects of surface plasmons towards realization of a variety of surface-plasmon-based devices. In this paper, after summarizing the fundamental aspects of surface plasmons propagating on planar metallic surfaces and localized at metallic nanoparticles, recent progress in plasmonic waveguides, plasmonic light-emitting devices and plasmonic solar cells is reviewed.

Graphene-based devices in terahertz science and technology

Abstract: Graphene is a one-atom-thick planar sheet of a honeycomb carbon crystal. Its gapless and linear energy spectra of electrons and holes lead to nontrivial features such as giant carrier mobility and broadband flat optical response. In this paper, recent advances in graphene-based devices in terahertz science and technology are reviewed. First, the fundamental basis of the optoelectronic properties of graphene is introduced. Second, synthesis and crystallographic characterization of graphene material are described, particularly focused on the authors' original heteroepitaxial graphene-on-silicon technology. Third, nonequilibrium carrier relaxation and recombination dynamics in optically or electrically pumped graphene are described to introduce a possibility of negative-dynamic conductivity in a wide terahertz range. Fourth, recent theoretical advances towards the creation of current-injection graphene terahertz lasers are described. Fifth, the unique terahertz dynamics of the two-dimensional plasmons in graphene are described. Finally, the advantages of graphene devices for terahertz applications are summarized.

Micromagnetic simulations using Graphics Processing Units

Abstract: The methodology for adapting a standard micromagnetic code to run on graphics processing units (GPUs) and exploit the potential for parallel calculations of this platform is discussed. GPMagnet, a general purpose finite-difference GPU-based micromagnetic tool, is used as an example. Speed-up factors of two orders of magnitude can be achieved with GPMagnet with respect to a serial code. This allows for running extensive simulations, nearly inaccessible with a standard micromagnetic solver, at reasonable computational times.

Eu3+/Tb3+-codoped Y2O3 nanophosphors: Rietveld refinement, bandgap and photoluminescence optimization

Abstract: In this work, Eu-doped, Tb-doped and Eu, Tb-codoped Y2O3 nanophosphors were synthesized by the combustion synthesis method The prepared phosphors were characterized by x-ray diffraction (XRD), Rietveld refinement and Fourier transform infrared (FTIR) spectroscopy XRD studies and Rietveld refinement confirmed the body-centred cubic structure of doped and codoped phosphors FTIR studies also confirmed the formation of these compounds Thermal analysis results indicated that there was no phase transition for all the phosphors in the studied temperature range In the optical properties, diffuse reflectance (DR) and photoluminescence (PL) measurements were performed DR spectra were used to determine the bandgap and it increased in the doped and codoped samples due to the crystallite size effect A strong characteristic emission from Eu3+ and Tb3+ ions was identified and the influence of doping concentration and annealing temperature on PL properties was systematically studied Transfer of energy was observed from Tb3+ to Eu3+ ions in the codoped phosphor at room temperature

Applications of quantum cascade lasers in plasma diagnostics: a review

Abstract: Over the past few years mid-infrared absorption spectroscopy based on quantum cascade lasers operating over the region from 3 to 12 µm and called quantum cascade laser absorption spectroscopy or QCLAS has progressed considerably as a powerful diagnostic technique for in situ studies of the fundamental physics and chemistry of molecular plasmas. The increasing interest in processing plasmas containing hydrocarbons, fluorocarbons, nitrogen oxides and organo-silicon compounds has led to further applications of QCLAS because most of these compounds and their decomposition products are infrared active. QCLAS provides a means of determining the absolute concentrations of the ground states of stable and transient molecular species at time resolutions below a microsecond, which is of particular importance for the investigation of reaction kinetics and dynamics. Information about gas temperature and population densities can also be derived from QCLAS measurements. Since plasmas with molecular feed gases are used in many applications such as thin film deposition, semiconductor processing, surface activation and cleaning, and materials and waste treatment, this has stimulated the adaptation of QCLAS techniques to industrial requirements including the development of new diagnostic equipment. The recent availability of external cavity (EC) QCLs offers a further new option for multi-component detection. The aim of this paper is fourfold: (i) to briefly review spectroscopic issues arising from applying pulsed QCLs, (ii) to report on recent achievements in our understanding of molecular phenomena in plasmas and at surfaces, (iii) to describe the current status of industrial process monitoring in the mid-infrared and (iv) to discuss the potential of advanced instrumentation based on EC-QCLs for plasma diagnostics.

Stretchable electronics: materials, architectures and integrations

Abstract: Stretchable electronics, ie elastic electronics that can be bent and stretched, is a new, emerging class of electronics, based on building electronic circuits or devices on stretchable substrates The potential applications range from fully conformable, stretchable, skin sensors for robotic devices, wearable electronic devices, to flesh-like biodevices One of the challenges in the development of stretchable electronics is to retain full functionality under high external strains in stretching In this paper, we review a few approaches recently developed for stretchable electronics and highlight recent research efforts on multi-directional writing for stretchable, three-dimensional structures (Some figures may appear in colour only in the online journal)

Inactivation of a 25.5 µm Enterococcus faecalis biofilm by a room-temperature, battery-operated, handheld air plasma jet

Abstract: Effective biofilm inactivation using a handheld, mobile plasma jet powered by a 12 V dc battery and operated in open air without any external gas supply is reported. This cold, room-temperature plasma is produced in self-repetitive nanosecond discharges with current pulses of ~100 ns duration, current peak amplitude of ~6 mA and repetition rate of ~20 kHz. It is shown that the reactive plasma species penetrate to the bottom layer of a 25.5 µm-thick Enterococcus faecalis biofilm and produce a strong bactericidal effect. This is the thickest reported biofilm inactivated using room-temperature air plasmas.

Comparison of electromagnetic interference shielding properties between single-wall carbon nanotube and graphene sheet/polyaniline composites

Abstract: Single-wall carbon nanotube/polyaniline (SWCNT/PANI) and graphene sheet/polyaniline (GS/PANI) composites were prepared by a simple alcohol-assisted dispersion and pressing process. The SWCNTs and GSs were synthesized by the dc arc-discharge method. The dc electrical conductivity and the electromagnetic interference (EMI) shielding effectiveness (SE) of these two kinds of composites were measured. The experimental results reveal that the conductivity and the EMI SE of the GS/PANI composite are better than that of the SWCNT/PANI composite, and the absorption proportion of the SWCNT/PANI composite is higher than that of the GS/PANI composite. The EMI shielding results (2–18 GHz) also show that both composites present an absorption-dominant mechanism and present a wide application prospect in the field of EMI shielding and microwave absorption.

Streamer inhibition for improving force and electric wind produced by DBD actuators

Abstract: The use of thin wires from 13 to 300 µm in diameter as the exposed electrode of a surface dielectric barrier discharge (SDBD) plasma actuator is experimentally investigated by electrical and optical diagnostics, electrohydrodynamic force measurements and produced electric wind characterization from time-averaged and time-resolved measurements. The streamer inhibition and glow discharge enhancement due to the use of a thin wire active electrode fully modify the topology and the temporal behaviour of the thrust and the electric wind production. With a typical plate-to-plate DBD, the electric wind velocity increases during the negative going cycle. With a wire-to-plate design, both positive and negative going-cycle discharges result in an electric wind velocity increase. The four main quantitative results are as follows: (1) for a power consumption of 1 W cm−1, the force is increased from 65 to 95 mN m−1 when a 13 µm wire is used, (2) this corresponds to a 15% electric wind velocity enhancement, (3) electromechanical efficiency can be increased from 0.1% to 0.25%, (4) these improvements are applied for definition of a new multi-DBD design plasma actuator that allows us to produce a mean velocity of 10.5 m s−1.

Structural, optical and electrical properties of spray-deposited CZTS thin films under a non-equilibrium growth condition

Abstract: Spray pyrolysed thin films of quaternary Cu2ZnSnS4 (CZTS) were successfully deposited on soda lime glass substrates at 320 °C under a non-equilibrium condition (by varying Zn, Sn and S precursor concentrations) and without additional sulfurization. The effect of deficiency and enrichment of these three elements (normalized with respect to Cu) on the film's microstrain, optical band-gap and Hall mobility was investigated. A large non-uniform microstrain of (5–6) × 10−3 and compressive nature were observed for both Zn- and Sn-enriched films from Williamson–Hall analysis of x-ray diffraction (XRD) data. However, a tensile strain of (2–3) × 10−3 was revealed in Sn-poor and S-rich samples. The optical band-gap (Eg) in stoichiometric CZTS was found to be 1.45 eV and Hall mobility (μH) in the range 87–92 cm2 V−1 s−1 was observed for S- and Zn-enriched films. The tensile nature of microstrain and inhomogeneities in Eg and μH were observed with greater magnitude due to the existence of other secondary phases, which were confirmed complementarily by FTIR spectroscopy and XRD.

Mobility enhancement and highly efficient gating of monolayer MoS 2 transistors with polymer electrolyte

Abstract: We report electrical characterization of monolayer molybdenum disulfide (MoS2) devices using a thin layer of polymer electrolyte (PE) consisting of poly(ethylene oxide) (PEO) and lithium perchlorate (LiClO4) as both a contact-barrier reducer and channel mobility booster. We find that bare MoS2 devices (without PE) fabricated on Si/SiO2 have low channel mobility and large contact resistance, both of which severely limit the field-effect mobility of the devices. A thin layer of PEO/LiClO4 deposited on top of the devices not only substantially reduces the contact resistance but also boost the channel mobility, leading up to three-orders-of-magnitude enhancement of the field-effect mobility of the device. When the PE is used as a gate medium, the MoS2 field-effect transistors exhibit excellent device characteristics such as a near ideal subthreshold swing and an on/off ratio of 106 as a result of the strong gate-channel coupling.

Spintronic oxides grown by laser-MBE

Abstract: The recent study of oxides led to the discovery of several new fascinating physical phenomena. High-temperature superconductivity, colossal magnetoresistance, dilute magnetic doping, or multiferroicity were discovered and investigated in transition-metal oxides, representing a prototype class of strongly correlated electronic systems. This development was accompanied by enormous progress regarding thin film fabrication. Within the past two decades, epitaxial thin films with crystalline quality approaching semiconductor standards became available using laser-molecular beam epitaxy. This evolution is reviewed, particularly with emphasis on transition-metal oxide thin films, their versatile physical properties, and their impact on the field of spintronics. First, the physics of ferromagnetic half-metallic oxides, such as the doped manganites, the double perovskites and magnetite is presented together with possible applications based on magnetic tunnel junctions. Second, the wide bandgap semiconductor zinc oxide is discussed particularly with regard to the controversy of dilute magnetic doping with transition-metal ions and the possibility of realizing p-type conductivity. Third, the field of oxide multiferroics is presented with the recent developments in single-phase multiferroic thin film perovskites as well as in composite multiferroic hybrids.

A tunable hybrid metamaterial absorber based on vanadium oxide films

Abstract: A tunable hybrid metamaterial absorber (MA) in the microwave band was designed, fabricated and characterized. The hybrid MA was realized by incorporating a VO2 film into the conventional resonant MA. By thermally triggering the insulator–metal phase transition of the VO2 film, the impedance match condition was broken and a deep amplitude modulation of about 63.3% to the electromagnetic wave absorption was achieved. A moderate blue-shift of the resonance frequency was observed which is promising for practical applications. This VO2-based MA exhibits many advantages such as strong tunability, frequency agility, simple fabrication and ease of scaling to the terahertz band.

Measurement of OH density and air–helium mixture ratio in an atmospheric-pressure helium plasma jet

Abstract: The absolute density of OH radicals in an atmospheric-pressure helium plasma jet is measured using laser-induced fluorescence (LIF). The plasma jet is generated in room air by applying a pulsed high voltage onto a quartz tube with helium gas flow. The time-averaged OH density is 0.10 ppm near the quartz tube nozzle, decreasing away from the nozzle. OH radicals are produced from water vapour in the helium flow, which is humidified by water adsorbed on the inner surface of the helium line and the quartz tube. When helium is artificially humidified using a water bubbler, the OH density increases with humidity and reaches 2.5 ppm when the water vapour content is 200 ppm. Two-dimensional distribution of air–helium mixture ratio in the plasma jet is also measured using the decay rate of the LIF signal waveform which is determined by the quenching rate of laser-excited OH radicals.

Multiferroic properties of Ba2+ and Gd3+ co-doped bismuth ferrite: magnetic, ferroelectric and impedance spectroscopic analysis

Abstract: Enhanced magnetoelectric coupling is observed in bismuth ferrite samples, co-doped with non-magnetic Ba and magnetic Gd ions replacing Bi and Fe, respectively. Distortion in Fe–O octahedra has a significant effect on the magnetic properties of the samples. Ferromagnetic signature is found to increase significantly in the co-doped samples with respect to the only-Gd-doped sample both at 80 and 300 K. The co-doped samples show enhanced electric polarization as well as the highest resistivity at room temperature, which might be due to the reduction in the leakage current and oxygen vacancy in the compositions. An interesting correlation between the antiferromagnetic Neel temperature (TN) of bismuth ferrite and the temperature-dependent dielectric constant is observed in all samples. Bi0.9Ba0.1Fe0.95Gd0.05O3 ceramic possesses maximum coupling between electric dipole and magnetic dipole with an estimated magnetodielectric effect MD ([er(H) − er (0)]/er (0)) ~ 380 at an applied field of 6 kOe. Impedance spectroscopy in the frequency range 40–107 Hz and temperature within 30–300 °C suggests that grain relaxation is dominant in the samples. Electrical parameters (such as capacitance and resistance) of the grains are determined using the real and imaginary parts of impedance (Z' and Z'') and the electrical modulus (M' and M'') plot. The results of electrical conductivity indicate a correlated barrier hopping conduction mechanism in the samples.

Indentation-based methods to assess fracture toughness for thin coatings

Abstract: There are many techniques to determine fracture toughness. Experimental simplicity and amenability to materials evaluation are features of general indentation testing. Sometimes indentation is the only practical means of obtaining fundamental information on critical lifetime-limiting damage modes in some ceramics and coatings. Fracture patterns are dependent on the indenter geometry and material properties. The analysis of interfacial toughness by indentation has been well documented. However, no such comprehensive review is available for the analysis of fracture toughness for thin coatings based on (nano)indentation. Therefore, this paper tends to fill this gap. The mechanisms of various crack patterns and existing models used to determine the fracture toughness have been discussed in this study.

Numerical calculation of spin wave dispersions in magnetic nanostructures

Abstract: We present the numerical calculations of spin wave dispersions in magnetic nanostructures. The dispersion is obtained by processing the space–time data calculated using the finite difference method based micromagnetic simulations. Various issues related to the calculation of the two-dimensional fast Fourier transform and methods to obtain high-quality dispersion curves are discussed. The spatial profile of the spin wave modes is also presented. The method is validated by applying it to various nanomagnetic systems including magnetic nanostripes, magnetic nanowires and confined thin film elements. Further, we calculate the magnonic dispersions in simple 1D and 2D magnonic crystals based on magnetic anti-dot arrays.

Dose-dependent killing of leukemia cells by low-temperature plasma

Abstract: The effect of low-temperature atmospheric pressure plasma towards the progression of cancerous human T-cell leukemia cells was investigated. The plasma pencil, which utilizes short duration high voltage pulses, was used to generate a low-temperature plasma (LTP) plume in ambient air. Our data showed that cell morphology and cell viability were affected in a dose-dependent manner after treatment with LTP. The outcome of this study revealed that the effect of plasma exposure was not immediate, but had a delayed effect and increasing the time of plasma exposure resulted in increased leukemia cell death.

Oxygen level: the dominant of resistive switching characteristics in cerium oxide thin films

Abstract: Currently, resistive switching mechanisms in metal oxide thin films are not clearly understood due to lack of solid evidence. In this work, the switching behaviour of the Au/CeO2/conductive glass structure was analysed, where reproducible and pronounced resistive switching characteristics were obtained. The role of oxygen vacancies in switching characteristics was investigated. The concentration of oxygen vacancies in the CeO2 thin films was controlled by post-annealing and monitored by x-ray photon spectroscopy. The reduction in the switching ratio and the intensity of the peak associated with oxygen concentration O 1s level after annealing treatment confirmed the dominating role of oxygen vacancies in switching behaviour.

Quadrupole mass spectrometry of reactive plasmas

Abstract: Reactive plasmas are highly valued for their ability to produce large amounts of reactive radicals and of energetic ions bombarding surrounding surfaces. The non-equilibrium electron driven plasma chemistry is utilized in many applications such as anisotropic etching or deposition of thin films of high-quality materials with unique properties. However, the non-equilibrium character and the high power densities make plasmas very complex and hard to understand. Mass spectrometry (MS) is a very versatile diagnostic method, which has, therefore, a prominent role in the characterization of reactive plasmas. It can access almost all plasma generated species: stable gas-phase products, reactive radicals, positive and negative ions or even internally excited species such as metastables. It can provide absolute densities of neutral particles or energy distribution functions of energetic ions. In particular, plasmas with a rich chemistry, such as hydrocarbon plasmas, could not be understood without MS. This review focuses on quadrupole MS with an electron impact ionization ion source as the most common MS technique applied in plasma analysis. Necessary information for the understanding of this diagnostic and its application and for the proper design and calibration procedure of an MS diagnostic system for quantitative plasma analysis is provided. Important differences between measurements of neutral particles and energetic ions and between the analysis of low pressure and atmospheric pressure plasmas are described and discussed in detail. Moreover, MS-measured ion energy distribution functions in different discharges are discussed and the ability of MS to analyse these distribution functions with time resolution of several microseconds is presented.

Advances in the chemical modification of epitaxial graphene

Abstract: Chemistry will play an increasingly important role in the realization of graphene applications. The chemical formation of covalent carbon–carbon bonds involving the basal plane carbon atoms offers an alternative approach to the control of the electronic properties of graphene, and potentially allows the generation of insulating and semiconducting regions in graphene wafers. This review summarizes recent progress in the covalent modification of epitaxial graphene and the effect that chemistry has on the electronic and magnetic properties of the material.

Experimental study of hard x-rays emitted from metre-scale positive discharges in air

Abstract: We investigate structure and evolution of long positive spark breakdown; and we study at which stage pulses of hard x-rays are emitted. Positive high-voltage pulses of standardized lightning impulse wave form of about 1MV were applied to about 1m of ambient air. The discharge evolution was imaged with a resolution of tens of nanoseconds with an intensified CCD camera. LaBr3(Ce + ) scintillation detectors recorded the x-rays emitted during the process. The voltage and the currents on both electrodes were measured synchronously. All measurements indicate that first a large and dense corona of positive streamers emerges from the high-voltage electrode. When they approach the grounded electrode, negative counter-streamers emerge there, and the emission of hard x-rays coincides with the connection of the positive streamers with the negative counter-streamers. Leaders are seen to form only at later stages. (Some figures may appear in colour only in the online journal)

A novel plasmonic resonance sensor based on an infrared perfect absorber

Abstract: We present an infrared perfect absorber model composed of gold nanobars and a photonic microcavity. The inevitable losses in metamaterials are taken as an advantage for high absorbance efficiency. By adjusting the structural geometry, the device can be used for refractive index sensing. In our calculation with a spacer thickness H = 90 nm it can yield more than 99% absorbance in the near-infrared frequency region. The full-width at half-maximum can be realized up to an extremely narrow value of 40.8 nm and the figure of merit can be obtained as high as 357. For sensing applications with a perfect absorber, our work can serve as a model of coupling between the localized surface plasmon within nanoparticles and the propagating surface plasmon along the planar metal layer. The novel concept has great potential to maintain its performance of localized surface plasmon in practical applications.

Microscopic mechanism for unipolar resistive switching behaviour of nickel oxides

Abstract: A microscopic mechanism for the unipolar resistive switching phenomenon in nickel oxides is proposed based on the thermal decomposition of oxygen ions from oxygen-rich clusters and their recombination with electron-depleted vacancies induced by local electric field in conductive filaments. The proposed physical feature is confirmed by x-ray photoelectron spectroscopy, transmission electron microscopy and electrical measurements in the as-deposited NiOx samples. The deduced formulae under reasonable approximations directly demonstrate the relationships of switching parameters that were widely observed and questioned in different material systems, indicating the universal validity of the proposed mechanism.

Nanoscale size effect on surface spin canting in iron oxide nanoparticles synthesized by the microemulsion method

Abstract: Uniformly sized and crystalline iron oxide nanoparticles (IONPs) with spinel structure and mean diameters of about 3, 6 and 9 nm were synthesized in high yield using the microemulsion route at room temperature. The nanoparticles (NPs) were stabilized in situ by organic surfactant molecules which acted both as a stabilizer of the microemulsion system and as a capping layer of the NP surface. NP size control was attained by careful adjustment of the preparation conditions. The structure, morphology and NP size distribution were investigated by x-ray diffraction, transmission electron microscopy and scanning electron microscopy. A particular effort was devoted in this work to study the effect of size and capping of these NPs on their magnetic structure by in-field Mossbauer spectroscopy at 4.2 K. The mean canting angle (relative to the applied field direction) of the Fe spins was observed to increase with decreasing NP size due to the enhanced surface-to-volume ratio. Comparing bare and capped NPs of the same diameter, we verified that the spin canting was not affected by the organic capping. This implied almost identical magnetic orientations of bare and capped NPs. Simultaneously, the capping material was capable of preventing agglomeration effects which can occur in case of direct particle contact. Using a core/shell model, we showed that spin canting originated from the surface shell of the NPs. Furthermore, the Mossbauer spectral parameters provided evidence for the existence of a high fraction of Fe3O4 (magnetite) in the IONP.