Showing papers in "Journal of Physics D in 2015"

The 2015 super-resolution microscopy roadmap

Abstract: Far-field optical microscopy using focused light is an important tool in a number of scientific disciplines including chemical, (bio)physical and biomedical research, particularly with respect to the study of living cells and organisms. Unfortunately, the applicability of the optical microscope is limited, since the diffraction of light imposes limitations on the spatial resolution of the image. Consequently the details of, for example, cellular protein distributions, can be visualized only to a certain extent. Fortunately, recent years have witnessed the development of 'super-resolution' far-field optical microscopy (nanoscopy) techniques such as stimulated emission depletion (STED), ground state depletion (GSD), reversible saturated optical (fluorescence) transitions (RESOLFT), photoactivation localization microscopy (PALM), stochastic optical reconstruction microscopy (STORM), structured illumination microscopy (SIM) or saturated structured illumination microscopy (SSIM), all in one way or another addressing the problem of the limited spatial resolution of far-field optical microscopy. While SIM achieves a two-fold improvement in spatial resolution compared to conventional optical microscopy, STED, RESOLFT, PALM/STORM, or SSIM have all gone beyond, pushing the limits of optical image resolution to the nanometer scale. Consequently, all super-resolution techniques open new avenues of biomedical research. Because the field is so young, the potential capabilities of different super-resolution microscopy approaches have yet to be fully explored, and uncertainties remain when considering the best choice of methodology. Thus, even for experts, the road to the future is sometimes shrouded in mist. The super-resolution optical microscopy roadmap of Journal of Physics D: Applied Physics addresses this need for clarity. It provides guidance to the outstanding questions through a collection of short review articles from experts in the field, giving a thorough discussion on the concepts underlying super-resolution optical microscopy, the potential of different approaches, the importance of label optimization (such as reversible photoswitchable proteins) and applications in which these methods will have a significant impact.

Progress in magnetic domain observation by advanced magneto-optical microscopy

Abstract: The observation of magnetic domains by magneto-optical microscopy, based on the Kerr and the Faraday effect, is one of the most prominent techniques for the visualization of distributions of magnetization within magnetic materials. The method has gained increased attention due to the possibility to visualize field and current induced phenomena in nanostructured magnetic materials on fast time-scales. Fundamental concepts and recent advances in methodology are discussed in order to provide guidance on the usage of wide-field magneto-optical microscopy in applied magnetism. Recent applications of magneto-optical microscopy in bulk and thin film materials are reviewed at the end.

A review of plasma-liquid interactions for nanomaterial synthesis

Abstract: Over the past few decades, a new branch of plasma research, nanomaterial (NM) synthesis through plasma–liquid interactions (PLIs), has been developing rapidly, mainly due to the various, recently developed plasma sources operating at low and atmospheric pressures. PLIs provide novel plasma–liquid interfaces where many physical and chemical processes take place. By exploiting these physical and chemical processes, various NMs ranging from noble metal nanoparticles to graphene nanosheets can easily be synthesized. The currently rapid development and increasingly wide utilization of the PLI method has naturally lead to an urgent need for the presentation of a general review. This paper reviews the current status of research on PLIs for NM synthesis. The focus is on a comprehensive understanding of the synthesis process and perceptive opinions on current issues and future challenges in this field.

Molten pool behaviour and its physical mechanism during selective laser melting of TiC/AlSi10Mg nanocomposites: simulation and experiments

Abstract: Simulation of temperature evolution and thermal behaviour of the molten pool during selective laser melting (SLM) of TiC/AlSi10Mg nanocomposites was performed, using a finite volume method. Some important physical phenomena, such as a transition from powder to solid, nonlinearities produced by temperature-dependent material properties and fluid flow, were taken into account in the calculation. The effects of Marangoni convection and SLM processing parameters, such as laser power and scan speed, on temperature evolution behaviour, molten pool dimensions and liquid lifetime were thoroughly investigated. The simulation results showed that Marangoni convection played a crucial role in intensifying the convective heat transfer and changing the molten pool geometry. The temperature of laser–powder interaction zone, the molten pool dimensions and liquid lifetime increased with increasing laser power or decreasing scan speed. The maximum temperature gradient within the molten pool increased significantly with increasing the applied laser power, but increased slightly as a higher scan speed was applied. The experimental study on the interlayer bonding and densification behaviour and the surface morphologies and balling effect of the SLM-processed TiC/AlSi10Mg nanocomposites parts was performed. The experimental results validated the thermal behaviour and underlying physical mechanism of the molten pool obtained in the simulations.

Interband cascade lasers

Abstract: We review the current status of interband cascade lasers (ICLs) emitting in the midwave infrared (IR). The ICL may be considered the hybrid of a conventional diode laser that generates photons via electron–hole recombination, and an intersubband-based quantum cascade laser (QCL) that stacks multiple stages for enhanced current efficiency. Following a brief historical overview, we discuss theoretical aspects of the active region and core designs, growth by molecular beam epitaxy, and the processing of broad-area, narrow-ridge, and distributed feedback (DFB) devices. We then review the experimental performance of pulsed broad area ICLs, as well as the continuous-wave (cw) characteristics of narrow ridges having good beam quality and DFBs producing output in a single spectral mode. Because the threshold drive powers are far lower than those of QCLs throughout the λ = 3–6 µm spectral band, ICLs are increasingly viewed as the laser of choice for mid-IR laser spectroscopy applications that do not require high output power but need to be hand-portable and/or battery operated. Demonstrated ICL performance characteristics to date include threshold current densities as low as 106 A cm−2 at room temperature (RT), cw threshold drive powers as low as 29 mW at RT, maximum cw operating temperatures as high as 118 °C, maximum cw output powers exceeding 400 mW at RT, maximum cw wallplug efficiencies as high as 18% at RT, maximum cw single-mode output powers as high as 55 mW at RT, and single-mode output at λ = 5.2 µm with a cw drive power of only 138 mW at RT.

Perpendicular-anisotropy magnetic tunnel junction switched by spin-Hall-assisted spin-transfer torque

Abstract: We investigate the magnetization switching induced by spin-Hall-assisted spin-transfer torque (STT) in a three-terminal device consisting of a perpendicular-anisotropy magnetic tunnel junction (MTJ) and an β-W strip. Magnetization dynamics in free layer of MTJ is simulated by solving numerically a modified Landau–Lifshitz–Gilbert equation. The influences of spin-Hall write current (density, duration and direction) on the STT switching are evaluated. We find that the switching speed of a STT-MTJ can be significantly improved (reduced to <1 ns) by using a sufficiently large spin-Hall write current density (~25 MA cm−2) with an appropriate duration (~0.5 ns). Finally we develop an electrical model of three-terminal MTJ/β-W device with Verilog-A language and perform transient simulation of switching a 4 T/1MTJ/1β-W memory cell with Spectre simulator. Simulation results demonstrate that spin-Hall-assisted STT-MTJ has advantages over conventional STT-MTJ in write speed and energy.

Quantum dot optoelectronic devices: lasers, photodetectors and solar cells

Abstract: Nanometre-scale semiconductor devices have been envisioned as next-generation technologies with high integration and functionality. Quantum dots, or the so-called ‘artificial atoms’, exhibit unique properties due to their quantum confinement in all 3D. These unique properties have brought to light the great potential of quantum dots in optoelectronic applications. Numerous efforts worldwide have been devoted to these promising nanomaterials for next-generation optoelectronic devices, such as lasers, photodetectors, amplifiers, and solar cells, with the emphasis on improving performance and functionality. Through the development in optoelectronic devices based on quantum dots over the last two decades, quantum dot devices with exceptional performance surpassing previous devices are evidenced. This review describes recent developments in quantum dot optoelectronic devices over the last few years. The paper will highlight the major progress made in 1.3 μm quantum dot lasers, quantum dot infrared photodetectors, and quantum dot solar cells.

III–V nanowires and nanowire optoelectronic devices

Abstract: III–V nanowires (NWs) have been envisioned as nanoscale materials for next-generation technology with good functionality, superior performance, high integration ability and low cost, because of their special growth modes and unique 1D structure. In this review, we summarize the main challenges and important progress of the fabrication and applications of III–V NWs. We start with the III–V NW growth, that significantly influences the NW morphology and crystal quality. Attention is then given to the fabrication of some advanced III–V structures composed of axial and radial junctions. After that, we review the advantages, challenges, and major breakthroughs of using III–V NWs as solar energy harvesters and light emitters. Finally, we attempt to give a perspective look on the future development trends and the remaining challenges in the research field of III–V NWs.

Measurements of the exchange stiffness of YIG films using broadband ferromagnetic resonance techniques

Abstract: Measurements of the exchange stiffness D and the exchange constant A of Yttrium Iron Garnet (YIG) films are presented. YIG films with thicknesses from 0.9 to 2.6 µm were investigated with a microwave setup in a wide frequency range from 5 to 40 GHz. The measurements were performed with the external static magnetic field applied in-plane and out-of-plane. The method of Schreiber and Frait (1996 Phys. Rev. B 54 6473), based on the analysis of the perpendicular standing spin wave mode frequency dependence on the applied out-of-plane magnetic field, was used to obtain the exchange stiffness D. This method was modified to avoid the influence of internal magnetic fields during the determination of the exchange stiffness. Furthermore, the method was also adapted for in-plane measurements. The results obtained using all methods are compared and values of D between (5.18 ± 0.01) 10−17 T m2 and (5.40 ± 0.02) 10−17 T m2 were obtained for different thicknesses. From this, the exchange constant was calculated to be A = (3.7 ± 0.4) pJm−1.

Mechanical properties and fracture behavior of single-layer phosphorene at finite temperatures

Abstract: Phosphorene, a new two-dimensional (2D) material beyond graphene, has attracted great attention in recent years due to its superior physical and electrical properties. However, compared to graphene and other 2D materials, phosphorene has a relatively low Young's modulus and fracture strength, which may limit its applications due to possible structure failures. For the mechanical reliability of future phosphorene-based nanodevices, it is necessary to have a deep understanding of the mechanical properties and fracture behaviors of phosphorene. Previous studies on the mechanical properties of phosphorene were based on first principles calculations at 0 K. In this work, we employ molecular dynamics simulations to explore the mechanical properties and fracture behaviors of phosphorene at finite temperatures. It is found that temperature has a significant effect on the mechanical properties of phosphorene. The fracture strength and strain reduce by more than 65% when the temperature increases from 0 K to 450 K. Moreover, the fracture strength and strain in the zigzag direction is more sensitive to the temperature rise than that in the armchair direction. More interestingly, the failure crack propagates preferably along the groove in the puckered structure when uniaxial tension is applied in the armchair direction. In contrast, when the uniaxial tension is applied in the zigzag direction, multiple cracks are observed with rough fracture surfaces. Our present work provides useful information about the mechanical properties and failure behaviors of phosphorene at finite temperatures.

Fabrication of aluminium nanostructures for plasmonics

Abstract: Metallic nanostructures are the building blocks for nanoplasmonics and for subsequent applications in nanooptics. For several decades, plasmonics have been almost exclusively studied in the visible region by using nanostructures made of noble metals exhibiting plasmonic properties in the near infrared to visible range. This notwithstanding, emerging applications will require the extension of nanoplasmonics toward higher energies, particularly in the UV range. Therefore, alternative metals, often described as poor metals are emerging to achieve that goal. Among all these metals, aluminium appears to be one of the most appealing for extending plasmonics towards ultraviolet energies. Aluminium is cheap, widely available, compatible with optoelectronic devices and exhibits plasmonic properties over a wide range of energies, from the infrared to the deep UV. Our aim is to present a review of current research centred on the fabrication of aluminium nanostructures. Mastering the geometry of aluminium nanostructures is extremely important in order to tune their plasmonic properties and target a given application. First we give an introduction to the nanofabrication of aluminium nanostructures within the context of plasmonics. The review then focuses on the possible geometries that such structures may take when fabricated with specific fabrication techniques. Each technique is detailed and the plasmonic properties of the aluminium nanostructures are briefly described. When possible, an example of an application is given. Finally, the future applications of aluminium plasmonics are highlighted and a conclusion with perspectives is given.

Microwave assisted magnetic recording technologies and related physics

Abstract: Microwave assisted magnetic recording (MAMR) has been proposed as one of the prospective recording technologies for forthcoming tera-bit-class magnetic recording. In this paper, the technological and related physical issues of MAMR are reviewed. MAMR is the combined technology of microwave assisted switching (MAS) and spin torque oscillator (STO). MAS is a magnetization switching technology in which magnetization switches through excitation of its precessional motion by a radio frequency (rf) field. The MAS behavior in which nonlinear large angle precession is excited has been a challenging issue from scientific and technological viewpoints. Recently developed theories successfully predict the MAS behavior of a single macrospin in which all spins in a magnet are assumed to behave coherently. For a magnetic element with a size larger than the exchange length, spatially non-uniform magnetization precession modes become dominant instead of the coherent precession mentioned above, resulting in significant enhancement of the MAS effect. This size dependent MAS effect is experimentally very well verified for nanosized dots with perpendicular magnetization. Meanwhile, the STO is used as an rf field generator in MAMR technology. The aforementioned large angle magnetization precession dynamics are also a crucial problem for the stable operation of STO. While various types of STOs have been proposed so far, the optimum structure of STO for MAMR is still under investigation. The combination of the MAS and STO may provide frequency domain recording architecture which enables us to realize a new recording scheme, such as multilevel recording.

Direct observation of the thickness distribution of ultra thin AlOx barriers in Al/AlOx/Al Josephson junctions

Abstract: We have directly measured the thickness distribution of the tunnel barriers in state-of-the-art Al/AlOx/Al tunnel junctions. From the distribution we can conclude that less than 10% of the junction area dominates the electron tunnelling. The barriers have been studied by transmission electron microscopy, specifically using atomic resolution annular dark field (ADF) scanning transmission electron microscopy (STEM) imaging. The direct observation of the local barrier thickness shows a Gaussian distribution of the barrier thickness variation along the junction, from ~1 to ~2nm. We have investigated how the thickness distribution varies with oxygen pressure (Po) and oxidation time (to) and we find, in agreement with resistance measurements, that an increased to has a larger impact on barrier thickness and its uniformity compared to an increased Po.

Probing the transport of plasma-generated RONS in an agarose target as surrogate for real tissue: dependency on time, distance and material composition

Abstract: We report a simple experimental approach to follow the transport of helium (He) plasma-generated reactive oxygen and nitrogen species (RONS) through millimetre thick agarose targets. These RONS may be either primary RONS, generated directly by the plasma jet, or secondary RONS generated for example at the surface of, or within, the material. Our experiment involves placing an agarose film over a quartz cuvette filled with deionized water. The agarose film is exposed to a He plasma jet and the UV absorption profile (of the deionized water) is recorded in real-time. Plasma exposure time, source-target distance and agarose film thickness and composition are varied to explore their effects on the depth of RONS delivery by the plasma jet. We conclude that plasma UV plays a minor role in the transport of RONS; whereas direct plasma contact and the He gas flow promote the transport of RONS into tissue. Our data indicate an accumulation of RONS within the agarose film (during plasma exposure) and a subsequent (time-lagged) release into the deionized water. Our approach can be readily adapted to other plasma sources; it can accommodate more complex biological materials, and has the potential to provide new insights into plasma-induced phenomena within real tissues.

Electromagnetohydrodynamic (EMHD) micropump of Jeffrey fluids through two parallel microchannels with corrugated walls

Abstract: By employing the perturbation method, the approximate analytical solutions of velocity and volume flow rate are presented for electromagnetohydrodynamic (EMHD) flow of an electrically conducting, incompressible and viscous Jeffrey fluid between two slit microparallel plates with corrugated walls. The corrugations of the two walls are described as periodic sinusoidal waves with small amplitude either in phase or half-period out of phase. The effects of the corrugations on the EMHD flow velocity are analyzed by using numerical computation. The variations of velocity profiles and mean velocity parameter and their dependences on the Reynolds number Re, Hartmann number Ha, dimensionless wave number λ of the wall perturbation, the dimensionless relaxation time λ1ω and retardation time λ2ω are explained graphically.

Giant magnetocaloric effect in Gd2NiMnO6 and Gd2CoMnO6 ferromagnetic insulators

Abstract: We have investigated the magnetocaloric effect in double perovskite Gd2NiMnO6 (GNMO) and Gd2CoMnO6 (GCMO) samples by magnetic and heat capacity measurements. Ferromagnetic ordering is observed at ~130 K (~ 112 K) in GNMO (GCMO), while the Gd exchange interactions seem to dominate for T < 20 K. In GCMO, below 50 K, antiferromagnetic behaviour due to the 3d–4f negative exchange interaction is observed. A maximum entropy (−ΔS M) and adiabatic temperature change of ~35.5 J Kg−1 K−1 (~ 24 J Kg−1 K−1) and 10.5 K (6.5 K) is observed in GNMO (GCMO) for a magnetic field change of 7 T at low temperatures. Absence of magnetic and thermal hysteresis and their insulating nature make them promising for low temperature magnetic refrigeration.

Influence of film composition in quaternary Heusler alloy Co2(Mn,Fe)Si thin films on tunnelling magnetoresistance of Co2(Mn,Fe)Si/MgO-based magnetic tunnel junctions

Abstract: The influence of off-stoichiometry on the half-metallic character of quaternary Heusler alloy thin films of Co2(Mn,Fe)Si (CMFS) was investigated by studying the composition dependence of the tunnelling magnetoresistance (TMR) ratio of fully epitaxial CMFS/MgO/CMFS magnetic tunnel junctions (CMFS MTJs) having Co2(Mnα'Feβ')Si0.84 electrodes with various Mn and Fe compositions. It was found that with (Mn + Fe)-rich electrodes had higher TMR ratios than ones with (Mn + Fe)-deficient electrodes at 4.2 and 290 K. These results indicate that the suppression of Co antisites at nominal Mn/Fe sites is critical to obtaining half-metallic quaternary Co2(Mn,Fe)Si in a similar way as in ternary alloy Co2MnSi. CMFS MTJs with Mn-rich and lightly Fe-doped CMFS electrodes showed giant TMR ratios of 2610% at 4.2 K and 429% at 290 K. These results suggest that Co-based Heusler alloy thin films would be highly applicable to spintronic devices because of their half-metallicity and material diversity arising from not only ternary alloy but also quaternary alloy systems.

Numerical investigation of the formation of Trichel pulses in a needle-plane geometry

Abstract: This paper presents a numerical investigation of the formation of the Trichel pulses in negative dc corona discharge for a needle-plane configuration in atmospheric air. A 2D axisymmetric model of the problem considering three charged species and consisting of a hyperboloid needle with a tip radius of 35 μm and needle-plane spacing of 6 mm over the voltage range of −3.5 kV to −12 kV has been studied. A commercial finite element package COMSOL was used for simultaneously solving three convection-diffusion equations along with Poisson's equation. In order to obtain a better understanding of the processes which lead to the pulse formation, a close look is taken at one of the pulses. The distributions of the major charged species and the timeline of peak-values of charged species densities and electric field are presented. Through tracing the evolution of the locations of the peak densities of the charged species some new insights have been provided. The configuration of the model was chosen so that the simulation results could be compared with the experimental data published by Lama and Gallo. The numerical results were in acceptable agreement with the experimental values. Some explanations are given for the discrepancies between experimental and simulation results. It is also shown, that as the frequency of the pulses increases with voltage, the transition from Trichel pulse discharge to glow discharge initiates and full glow discharge is reached at −12 kV.

Magnetic resonance tracking of fluorescent nanodiamond fabrication

Abstract: Magnetic resonance techniques (electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR)) are used for tracking the multi-stage process of the fabrication of fluorescent nanodiamonds (NDs) produced by high-energy electron irradiation, annealing, and subsequent nano-milling. Pristine commercial high pressure and high temperature microdiamonds (MDs) with mean size 150 mu m contain similar to 5 x 10(18) spins/g of singlet (S = 1/2) substitutional nitrogen defects P1, as well as sp(3) C-C dangling bonds in the crystalline lattice. The half-field X-band EPR clearly shows (by the appearance of the intense `forbidden' g = 4.26 line) that high-energy electron irradiation and annealing of MDs induce a large amount (similar to 5 x 10(17) spins/g) of triplet (S = 1) magnetic centers, which are identified as negatively charged nitrogen vacancy defects (NV-). This is supported by EPR observations of the `allowed' transitions between Zeeman sublevels of the triplet state. After progressive milling of the fluorescent MDs down to an ultrasubmicron scale (<= 100 nm), the relative abundance of EPR active NV- defects in the resulting fluorescent NDs (FND) substantially decreases and, vice versa, the content of C-inherited singlet defects correlatively increases. In the fraction of the finest FNDs (mean particle size <20 nm), which are contained in the dried supernatant of ultracentrifuged aqueous dispersion of FNDs, the NV- content is found to be reduced by one order of magnitude whereas the singlet defects content increases up to similar to 2 x 10(19) spins/g. In addition, another triplet-type defect, which is characterized by the g = 4.00 `forbidden' line, appears. On reduction of the particle size below the 20 nm limit, the `allowed' EPR lines become practically unobservable, whereas the `forbidden' lines remain as a reliable fingerprint of the presence of NV- centers in small ND systems. The same size reduction causes the disappearance of the characteristic hyperfine satellites in the spectra of the P1 centers. We discuss the mechanisms that cause both the strong reduction of the peak intensity of the `allowed' lines in EPR spectra of triplet defects and the transformation of the P1 spectra.

Waveguide-coupled surface plasmon resonance sensor structures: Fano lineshape engineering for ultrahigh-resolution sensing

Abstract: We analyze in detail the plasmon-induced transparency and Fano resonance exhibited by a waveguide-coupled surface plasmon resonance sensor structure. It is shown that the results of electromagnetic calculations made for the structure agree very well with those of mechanical calculations made for two coupled harmonic oscillators. This implies that an analogy holds between the present electromagnetic system and the coupled-oscillator system. The analogy established allows us to conclude that the plasmon-induced transparency and Fano resonance are caused by the coupling between a surface plasmon polariton and a planar waveguide mode. Sensing action of the Fano resonance is also analyzed in detail. From the calculation of the figure of merit for the sensitivity by intensity, it is shown that there is an optimum condition for the coupling of the modes to achieve a maximum sensitivity. Under the optimum condition, the figure of merit is found to be three orders of magnitude higher than that of a conventional surface plasmon sensor.

Momentum, heat, and neutral mass transport in convective atmospheric pressure plasma-liquid systems and implications for aqueous targets

Abstract: There is a growing interest in the study of plasma-liquid interactions with application to biomedicine, chemical disinfection, agriculture, and other fields. This work models the momentum, heat, and neutral species mass transfer between gas and aqueous phases in the context of a streamer discharge; the qualitative conclusions are generally applicable to plasma-liquid systems. The problem domain is discretized using the finite element method. The most interesting and relevant model result for application purposes is the steep gradients in reactive species at the interface. At the center of where the reactive gas stream impinges on the water surface, the aqueous concentrations of OH and ONOOH decrease by roughly 9 and 4 orders of magnitude respectively within 50 m of the interface. Recognizing the limited penetration of reactive plasma species into the aqueous phase is critical to discussions about the therapeutic mechanisms for direct plasma treatment of biological solutions. Other interesting results from this study include the presence of a 10 K temperature drop in the gas boundary layer adjacent to the interface that arises from convective cooling. Though the temperature magnitudes may vary among atmospheric discharge types (different amounts of plasma-gas heating), this relative difference between gas and liquid bulk temperatures is expected to be present for any system in which convection is significant. Accounting for the resulting difference between gas and liquid bulk temperatures has a significant impact on reaction kinetics; factor of two changes in terminal aqueous species concentrations like H2O2, NO, and NO are observed in this study if the effect of evaporative cooling is not included.

Threshold current reduction for the metal-insulator transition in NbO 2−x -selector devices: the effect of ReRAM integration

Abstract: The threshold current for inducing the metal–insulator transition in a NbO2−x selector element is shown to be affected by the properties of an adjacent memory element when integrated into a hybrid selector-memory device structure. Experimental results are reported for homogeneous NbO2−x/Nb2O5−y and heterogeneous NbO2−x/HfO2 device structures, and show that the threshold current is lower in both hybrid structures than in the selector element alone, and is lower in the heterogeneous structure than in the homogeneous structure. Finite element modeling of the selector-memory structure shows that this results primarily from current confinement produced by the filamentary conduction path in the resistive-switching memory layer (i.e. Nb2O5−y or HfO2), an observation that further implies a smaller diameter filament in HfO2 than in Nb2O5−y. The thermal and electrical conductivities of the memory layer are also shown to influence the threshold current, but to a lesser extent.

Photonic crystals with plasmonic patterns: novel type of the heterostructures for enhanced magneto-optical activity

Abstract: A multilayer structure consisting of a magnetophotonic crystal with a rare-earth iron garnet microresonator layer and plasmonic grating deposited on it was fabricated and studied in order to combine functionalities of photonic and plasmonic crystals. The plasmonic pattern allows excitation of the hybrid plasmonic-waveguide modes localized in dielectric Bragg mirrors of the magnetophotonic crystal or waveguide modes inside its microresonator layer. These modes give rise to the additional resonances in the optical spectra of the structure and to the enhancement of the magneto-optical effects. The Faraday effect increases by about 50% at the microresonator modes while the transverse magneto-optical Kerr effect demonstrates pronounced peculiarities at both hybrid waveguide modes and microresonator modes and increases by several times with respect to the case of the bare magnetophotonic crystal without the metal grating.

Yellow–red emission from (Ga,In)N heterostructures

Abstract: (Ga,In)N-based light emitting devices are very efficient in producing blue light and to a lesser extent green. Extending their spectral range to longer wavelengths while maintaining high efficiency is a challenge due to material and physical issues related to high-In content (Ga,In)N alloys. We review the current status of yellow and red emitters (light emitting diodes and laser diodes) based on this material system. We also describe the state-of-the-art of devices mixing blue–yellow or red–blue–green coloured light, such as monolithic phosphor-free white light emitting diodes and full-colour micro-displays.

ZnO:Ca nanopowders with enhanced CO2 sensing properties

Abstract: Calcium doped ZnO (CZO) nanopowders with [Ca]/[Zn] atomic ratios of 0, 0.01, 0.03 and 0.05 were prepared via a sol-gel route and characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy (FT-IR). Characterization data showed that undoped and Ca-doped ZnO samples have a hexagonal wurtzite structure with a slight distortion of the ZnO lattice and no extra secondary phases, suggesting the substitution of Ca ions in the ZnO structure.Chemo-resistive devices based on a thick layer of the synthesized CZO nanoparticles were fabricated and their electrical and sensing properties towards CO2 were investigated. Sensing tests have demonstrated that Ca loading is the key factor in modulating the electrical properties and strongly improving the response of ZnO matrix towards CO2. An increased CO2 adsorption with Ca loading has been also evidenced by FT-IR, providing the basis for the formulation of a plausible mechanism for CO2 sensing operating on these sensors.

Sign of inverse spin Hall voltages generated by ferromagnetic resonance and temperature gradients in yttrium iron garnet platinum bilayers

Abstract: We carried out a concerted effort to determine the absolute sign of the inverse spin Hall effect voltage generated by spin currents injected into a normal metal. We focus on yttrium iron garnet (YIG)∣platinum bilayers at room temperature, generating spin currents by microwaves and temperature gradients. We find consistent results for different samples and measurement setups that agree with theory. We suggest a right-hand-rule to define a positive spin Hall angle corresponding to the voltage expected for the simple case of scattering of free electrons from repulsive Coulomb charges.

Near field thermal memory based on radiative phase bistability of VO2

Abstract: We report the concept of a near-field memory device based on the radiative bistability effect in the system of two closely separated parallel plates of SiO2 and VO2 which exchange heat by thermal radiation in vacuum. We demonstrate that the VO2 plate, having metal-insulator transition at 340 K, has two thermodynamical steady-states. One can switch between the states using an external laser impulse. We show that due to near-field photon tunneling between the plates, the switching time is found to be only 5 ms which is several orders lower than in case of far field.

A purely flexible lightweight membrane-type acoustic metamaterial

Abstract: This paper proposes a purely flexible lightweight membrane-type acoustic structure, wherein one kind of flexible lightweight rubber material takes the roles of mass and stiffness and another type of lightweight flexible EVA (ethylene–vinyl acetate copolymer) or plastic material functions as the localized stiffness for each unit. Because both the scatterers and base are constituted by the same material, this type of structure breaks the limitation that the metamaterials and phononic crystals need different materials with relatively large density and elasticity modulus ratios to play the roles of the scatterers and base respectively. Based on the band structures with different units, mass block shapes and size parameters, it is suggested that the shapes of the mass block can significantly affect the band structure. In addition, this type of structure could not only open a full band gap in the low-frequency range below 500 Hz, but also obtain an ultra-low-frequency bending wave band gap in the range below 100 Hz. Finally, we take into account the semi-infinite medium as a component, and calculate the sound transmission loss (STL) to evaluate the interaction between the structure and air. An experimental validation employing the cylindrical mass structure was developed to directly support the simulation results. Since the structures proposed in this study have achieved a purely flexible lightweight design, there exists an important promotion effect to realize the engineering applications of the acoustic metamaterials in practice.

A dielectric barrier discharge terminally inactivates RNase A by oxidizing sulfur-containing amino acids and breaking structural disulfide bonds

Abstract: RNases are among the most stable proteins in nature. They even refold spontaneously after heat inactivation, regaining full activity. Due to their stability and universal presence, they often pose a problem when experimenting with RNA. We investigated the capabilities of nonthermal atmospheric-pressure plasmas to inactivate RNase A and studied the inactivation mechanism on a molecular level. While prolonged heating above 90 °C is required for heat inactivating RNase A, direct plasma treatment with a dielectric barrier discharge (DBD) source caused permanent inactivation within minutes. Circular dichroism spectroscopy showed that DBD-treated RNase A unfolds rapidly. Raman spectroscopy indicated methionine modifications and formation of sulfonic acid. A mass spectrometry-based analysis of the protein modifications that occur during plasma treatment over time revealed that methionine sulfoxide formation coincides with protein inactivation. Chemical reduction of methionine sulfoxides partially restored RNase A activity confirming that sulfoxidation is causal and sufficient for RNase A inactivation. Continued plasma exposure led to over-oxidation of structural disulfide bonds. Using antibodies, disulfide bond over-oxidation was shown to be a general protein inactivation mechanism of the DBD. The antibody's heavy and light chains linked by disulfide bonds dissociated after plasma exposure. Based on their ability to inactivate proteins by oxidation of sulfur-containing amino acids and over-oxidation of disulfide bonds, DBD devices present a viable option for inactivating undesired or hazardous proteins on heat or solvent-sensitive surfaces.