Showing papers in "Journal of Applied Physics in 2008"
TL;DR: In this article, a review of mostly recent activities can be found, with a brief summary of the historical perspective of the multiferroic magnetoelectric composites since its appearance in 1972.
Abstract: Multiferroic magnetoelectric materials, which simultaneously exhibit ferroelectricity and ferromagnetism, have recently stimulated a sharply increasing number of research activities for their scientific interest and significant technological promise in the novel multifunctional devices. Natural multiferroic single-phase compounds are rare, and their magnetoelectric responses are either relatively weak or occurs at temperatures too low for practical applications. In contrast, multiferroic composites, which incorporate both ferroelectric and ferri-/ferromagnetic phases, typically yield giant magnetoelectric coupling response above room temperature, which makes them ready for technological applications. This review of mostly recent activities begins with a brief summary of the historical perspective of the multiferroic magnetoelectric composites since its appearance in 1972. In such composites the magnetoelectric effect is generated as a product property of a magnetostrictive and a piezoelectric substance. A...
3,288 citations
TL;DR: In this paper, an exact solution for the electromagnetic field due to an electric current in the presence of a surface conductivity model of graphene is obtained in terms of dyadic Green's functions represented as Sommerfeld integrals.
Abstract: An exact solution is obtained for the electromagnetic field due to an electric current in the presence of a surface conductivity model of graphene. The graphene is represented by an infinitesimally thin, local, and isotropic two-sided conductivity surface. The field is obtained in terms of dyadic Green’s functions represented as Sommerfeld integrals. The solution of plane wave reflection and transmission is presented, and surface wave propagation along graphene is studied via the poles of the Sommerfeld integrals. For isolated graphene characterized by complex surface conductivity σ=σ′+jσ″, a proper transverse-electric surface wave exists if and only if σ″>0 (associated with interband conductivity), and a proper transverse-magnetic surface wave exists for σ″<0 (associated with intraband conductivity). By tuning the chemical potential at infrared frequencies, the sign of σ″ can be varied, allowing for some control over surface wave properties.
2,304 citations
TL;DR: In this article, a review of the developments in dielectric elastomer actuator technology for several applications is presented, highlighting some of its advantages over existing actuator technologies, identifying some of the challenges associated with its development, and examining the main focus of research within this field.
Abstract: This paper reviews the developments in dielectric elastomer actuator technology for several applications. Dielectric elastomers are a variety of electroactive polymer that deform due to the electrostatic interaction between two electrodes with opposite electric charge. Dielectric elastomers have been subject of much interest and research over the past decade. In earlier years, much of the focus was on actuator configurations, and in more recent years the focus has turned to investigating material properties that may enhance actuator performance. This review outlines the operating principle and actuation mechanisms behind this actuator technology, highlights some of its advantages over existing actuator technologies, identifies some of the challenges associated with its development, and examines the main focus of research within this field, including some of the potential applications of such an actuator technology.
677 citations
TL;DR: The equations of motion of the Euler-Bernoulli and Timoshenko beam theories were reformulated using the nonlocal differential constitutive relations of Eringen [International Journal of Engineering Science 10, 1−16 (1972) as mentioned in this paper.
Abstract: The equations of motion of the Euler–Bernoulli and Timoshenko beam theories are reformulated using the nonlocal differential constitutive relations of Eringen [International Journal of Engineering Science 10, 1–16 (1972)]. The equations of motion are then used to evaluate the static bending, vibration, and buckling responses of beams with various boundary conditions. Numerical results are presented using the nonlocal theories to bring out the effect of the nonlocal behavior on deflections, buckling loads, and natural frequencies of carbon nanotubes.
642 citations
TL;DR: In this article, the authors demonstrate that the surface passivation of Al2O3 can be related to a satisfactory low interface defect density in combination with a strong field-effect passivation induced by a negative fixed charge density.
Abstract: Al2O3 is a versatile high-κ dielectric that has excellent surface passivation properties on crystalline Si (c-Si), which are of vital importance for devices such as light emitting diodes and high-efficiency solar cells. We demonstrate both experimentally and by simulations that the surface passivation can be related to a satisfactory low interface defect density in combination with a strong field-effect passivation induced by a negative fixed charge density Qf of up to 1013 cm−2 present in the Al2O3 film at the interface with the underlying Si substrate. The negative polarity of Qf in Al2O3 is especially beneficial for the passivation of p-type c-Si as the bulk minority carriers are shielded from the c-Si surface. As the level of field-effect passivation is shown to scale with Qf2, the high Qf in Al2O3 tolerates a higher interface defect density on c-Si compared to alternative surface passivation schemes.
518 citations
TL;DR: An extensive review of the results from literature on electron beam induced deposition is given in this article, where the authors categorize the data according to the specific parameter that can have an effect on the final deposit properties, such as the physical dimensions, the composition, the morphology or the conductivity.
Abstract: An extensive review is given of the results from literature on electron beam induced deposition. Electron beam induced deposition is a complex process, where many and often mutually dependent factors are involved. The process has been studied by many over many years in many different experimental setups, so it is not surprising that there is a great variety of experimental results. To come to a better understanding of the process, it is important to see to which extent the experimental results are consistent with each other and with the existing model. All results from literature were categorized by sorting the data according to the specific parameter that was varied (current density, acceleration voltage, scan patterns, etc.). Each of these parameters can have an effect on the final deposit properties, such as the physical dimensions, the composition, the morphology, or the conductivity. For each parameter-property combination, the available data are discussed and (as far as possible) interpreted. By combining models for electron scattering in a solid, two different growth regimes, and electron beam induced heating, the majority of the experimental results were explained qualitatively. This indicates that the physical processes are well understood, although quantitatively speaking the models can still be improved. The review makes clear that several major issues remain. One issue encountered when interpreting results from literature is the lack of data. Often, important parameters (such as the local precursor pressure) are not reported, which can complicate interpretation of the results. Another issue is the fact that the cross section for electron induced dissociation is unknown. In a number of cases, a correlation between the vertical growth rate and the secondary electron yield was found, which suggests that the secondary electrons dominate the dissociation rather than the primary electrons. Conclusive evidence for this hypothesis has not been found. Finally, there is a limited understanding of the mechanism of electron induced precursor dissociation. In many cases, the deposit composition is not directly dependent on the stoichiometric composition of the precursor and the electron induced decomposition paths can be very different from those expected from calculations or thermal decomposition. The dissociation mechanism is one of the key factors determining the purity of the deposits and a better understanding of this process will help develop electron beam induced deposition into a viable nanofabrication technique.
494 citations
TL;DR: In this article, the level of surface passivation in thin Al2O3 films was determined by techniques based on photoconductance, photoluminescence, and infrared emission.
Abstract: Thin Al2O3 films with a thickness of 7–30 nm synthesized by plasma-assisted atomic layer deposition (ALD) were used for surface passivation of crystalline silicon (c-Si) of different doping concentrations. The level of surface passivation in this study was determined by techniques based on photoconductance, photoluminescence, and infrared emission. Effective surface recombination velocities of 2 and 6 cm/s were obtained on 1.9 Ω cm n-type and 2.0 Ω cm p-type c-Si, respectively. An effective surface recombination velocity below 1 cm/s was unambiguously obtained for nearly intrinsic c-Si passivated by Al2O3. A high density of negative fixed charges was detected in the Al2O3 films and its impact on the level of surface passivation was demonstrated experimentally. The negative fixed charge density results in a flat injection level dependence of the effective lifetime on p-type c-Si and explains the excellent passivation of highly B-doped c-Si by Al2O3. Furthermore, a brief comparison is presented between the ...
449 citations
TL;DR: In this article, the authors investigated the thermal conductivity and viscosity of copper nanoparticles in ethylene glycol and found that the measured increase in thermal conductivities was twice the value predicted by the Maxwell effective medium theory.
Abstract: This study investigates the thermal conductivity and viscosity of copper nanoparticles in ethylene glycol. The nanofluid was prepared by synthesizing copper nanoparticles using a chemical reduction method, with water as the solvent, and then dispersing them in ethylene glycol using a sonicator. Volume loadings of up to 2% were prepared. The measured increase in thermal conductivity was twice the value predicted by the Maxwell effective medium theory. The increase in viscosity was about four times of that predicted by the Einstein law of viscosity. Analytical calculations suggest that this nanofluid would not be beneficial as a coolant in heat exchangers without changing the tube diameter. However, increasing the tube diameter to exploit the increased thermal conductivity of the nanofluid can lead to better thermal performance.
416 citations
TL;DR: In this paper, a model is developed for a parallel-plate waveguide formed by graphene, where the graphene is represented by an infinitesimally thin, local two-sided surface characterized by a surface conductivity obtained from the Kubo formula.
Abstract: A model is developed for a parallel-plate waveguide formed by graphene. The graphene is represented by an infinitesimally thin, local two-sided surface characterized by a surface conductivity obtained from the Kubo formula. Maxwell’s equations are solved for the model fields guided by the graphene layers. It is shown that despite the extreme thinness of its walls, a graphene parallel-plate waveguide can guide quasi-transverse electromagnetic modes with attenuation similar to structures composed of metals, while providing some control over propagation characteristics via the charge density or chemical potential. Given the interest in developing graphene electronics, such waveguides may be of interest in future applications.
415 citations
TL;DR: In this article, a spherical quantum dot with parabolic confinement subjected to an external electric field with the presence of an impurity, the linear and third-order nonlinear optical absorption coefficients as well as refractive index changes have been calculated.
Abstract: In the present work, the case of a spherical quantum dot with parabolic confinement subjected to an external electric field with the presence of an impurity, the linear and third-order nonlinear optical absorption coefficients as well as refractive index changes have been calculated. The numerical method we are using for the calculation of the energy levels and the corresponding wave functions is the potential morphing method in the effective mass approximation. As our results indicate an increase of the electric field and/or the position of the impurity and/or the quantum dot radius redshifts the peak positions of the total absorption coefficient and total refractive index changes. Additionally, an increase of the position of the impurity and/or the quantum dot radius decreases the total absorption coefficient and increases the total refractive index changes. An increase also of the electric field decreases the total absorption coefficient but does not significantly affect the peak values of the total refractive index changes. Finally, an increase of the optical intensity considerably changes the total absorption coefficient as well as the total refractive index changes.
411 citations
TL;DR: In this paper, the effect of sample size on deformation behavior was investigated on columns with diameters between 8μm and 140nm, fabricated from sputtered amorphous Pd77Si23 films on Si substrates by focused ion beam machining.
Abstract: Uniaxial compression tests were performed on micron-sized columns of amorphous PdSi to investigate the effect of sample size on deformation behavior. Cylindrical columns with diameters between 8μm and 140nm were fabricated from sputtered amorphous Pd77Si23 films on Si substrates by focused ion beam machining and compression tests were performed with a nanoindenter outfitted with a flat diamond punch. The columns exhibited elastic behavior until they yielded by either shear band formation on a plane at 50° to the loading axis or by homogenous deformation. Shear band formation occurred only in columns with diameters larger than 400nm. The change in deformation mechanism from shear band formation to homogeneous deformation with decreasing column size is attributed to a required critical strained volume for shear band formation.
TL;DR: In this paper, CdSe quantum dots (QDs) were applied onto nanostructured TiO2 films for different times by using a chemical bath deposition method in order to produce QD-sensitized solar cells (QDSSCs).
Abstract: CdSe quantum dots (QDs) were adsorbed onto nanostructured TiO2 films for different times by using a chemical bath deposition method in order to produce QD-sensitized solar cells (QDSSCs). Surface modification was done by coating ZnS onto the CdSe QDs. The optical absorption and current-voltage characteristics of these devices were studied. The size of the CdSe QDs increased with increasing adsorption time, and there was an optimum CdSe adsorption time for achieving the best photovoltaic conversion efficiency. The photovoltaic properties of short-circuit current density, open-circuit voltage, and photovoltaic conversion efficiency were significantly improved after modifying the surface with ZnS. Under a solar illumination of 100 mW/cm2, an efficiency as high as 2.02% was achieved for the CdSe QDSSCs that were made by using this method.
Abstract: The transport properties of magnetic tunnel junctions with different (110)-textured Heusler alloy electrodes such as Co2MnSi, Co2FeSi or Co2Mn0.5Fe0.5Si, AlOx barrier, and Co–Fe counterelectrode are investigated. The bandstructure of Co2Mn1−xFexSi is predicted to show a systematic shift in the position of the Fermi energy EF through the gap in the minority density of states while the composition changes from Co2MnSi toward Co2FeSi. Although this shift is indirectly observed by x-ray photoemission spectroscopy, all junctions show a large spin polarization of around 70% at the Heusler alloy/Al–O interface and are characterized by a very similar temperature and bias voltage dependence of the tunnel magnetoresistance. This suggests that these transport properties of these junctions are dominated by inelastic excitations and not by the electronic bandstructure.
TL;DR: In this paper, the physical properties of coplanar waveguide resonators and their relation to the materials properties for use in circuit quantum electrodynamics (QED) were analyzed.
Abstract: High quality on-chip microwave resonators have recently found prominent new applications in quantum optics and quantum information processing experiments with superconducting electronic circuits, a field now known as circuit quantum electrodynamics (QED). They are also used as single photon detectors and parametric amplifiers. Here we analyze the physical properties of coplanar waveguide resonators and their relation to the materials properties for use in circuit QED. We have designed and fabricated resonators with fundamental frequencies from 2 to 9 GHz and quality factors ranging from a few hundreds to a several hundred thousands controlled by appropriately designed input and output coupling capacitors. The microwave transmission spectra measured at temperatures of 20 mK are shown to be in good agreement with theoretical lumped element and distributed element transmission matrix models. In particular, the experimentally determined resonance frequencies, quality factors, and insertion losses are fully and consistently explained by the two models for all measured devices. The high level of control and flexibility in design renders these resonators ideal for storing and manipulating quantum electromagnetic fields in integrated superconducting electronic circuits.
TL;DR: In this paper, photonic crystals were utilized to simulate enhanced light-trapping in a-Si:H thin-film solar cells, where a one dimensional photonic crystal or distributed Bragg reflector with alternating dielectric layers acts as low loss backreflector.
Abstract: We utilize photonic crystals to simulate enhanced light-trapping in a-Si:H thin film solar cells A one dimensional photonic crystal or distributed Bragg reflector with alternating dielectric layers acts as low loss backreflector A two dimensional photonic crystal between the absorber layer and the Bragg reflector diffracts light at oblique angles within the absorber The photonic crystal geometry is optimized to obtain maximum absorption The photonic crystal provides lossless diffraction of photons, increasing the photon path length within the absorber layer The simulation predicts significantly enhanced photon harvesting between 600 and 775nm below the band edge, and an absorption increase by more than a factor of 10 near the band edge The optical path length ratio can exceed the classical limit predicted for randomly roughened scattering surfaces at most wavelengths near the band edge The optical modeling is performed with a rigorous scattering matrix approach where Maxwell’s equations are solved
TL;DR: A review of three types of energy harvesting with focus on devices at or below the cm3 scale is presented in this paper, where the harvesting technologies discussed are based on the conversion of temperature gradients, mechanical vibrations, and radiofrequency waves.
Abstract: As sensors for a wide array of applications continue to shrink and become integrated, increasing attention has been focused on creating autonomous devices with long-lasting power supplies. To achieve this, energy will have to be harvested from the sensors’ environment. An energy harvesting device can power the sensor either directly or in conjunction with a battery. Presented herein is a review of three types of energy harvesting with focus on devices at or below the cm3 scale. The harvesting technologies discussed are based on the conversion of temperature gradients, mechanical vibrations, and radiofrequency waves. Operation principles, current state of the art, and materials issues are presented. In addition, requirements and recent developments in power conditioning for such devices are discussed. Future challenges specific to miniaturization are outlined from both the materials and device perspectives.
TL;DR: In this article, the relationship between phase diagrams and the electrical properties of (Bi1/2Na 1/2)TiO3 (BNT)-based solid solutions was demonstrated.
Abstract: In this study, we demonstrated the relationship between the phase diagrams and the electrical properties of (Bi1/2Na1/2)TiO3 (BNT)-based solid solutions. In this study, (1−x)(Bi1/2Na1/2)TiO3–xNaNbO3 and (1−x)(Bi1/2Na1/2)TiO3–xKNbO3 (abbreviated to BNT-NN100x and BNT-KN100x) ceramics were prepared by a conventional ceramic fabrication process, and (1−x)(Bi1/2Na1/2)TiO3–x(Bi1/2K1/2)TiO3 (abbreviated to BNKT100x) ceramic was prepared for comparison. We revealed the phase transition temperatures, such as the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature Tm of the maximum dielectric constant, from the temperature dependence of dielectric properties using poled and unpoled specimens. As a result, it was shown that the BNT-based solid solutions form three types of phase diagrams. In addition, we clarified the relationship between the phase diagrams and the electrical properties of BNT-NN100x, BNT-KN100x, and BNKT100x. The piezoelectric properties we...
TL;DR: In this paper, the luminance loss, voltage rise, and emissive layer photoluminescence quenching that occur in electrically aged blue electrophosphorescent organic light emitting devices (OLEDs) are studied by examining the luminances loss, and voltage rise dependence on time and current density are consistent with defect formation due primarily to exciton polaron annihilation reactions.
Abstract: Operational degradation of blue electrophosphorescent organic light emitting devices (OLEDs) is studied by examining the luminance loss, voltage rise, and emissive layer photoluminescence quenching that occur in electrically aged devices. Using a model where defect sites act as deep charge traps, nonradiative recombination centers, and luminescence quenchers, we show that the luminance loss and voltage rise dependence on time and current density are consistent with defect formation due primarily to exciton-polaron annihilation reactions. Defect densities ∼1018cm−3 result in >50% luminance loss. Implications for the design of electrophosphorescent OLEDs with improved lifetime are discussed.
TL;DR: In this paper, the effect of heterovalent Ca, Sr, Pb, and Ba substitution on the crystal structure, dielectric, local ferroelectric, and magnetic properties of the BiFeO3 multiferroic perovskite was studied.
Abstract: In this work, we studied the effect of heterovalent Ca, Sr, Pb, and Ba substitution on the crystal structure, dielectric, local ferroelectric, and magnetic properties of the BiFeO3 multiferroic perovskite. Ceramic solid solutions with the general formula Bi0.7A0.3FeO3 (A is a doping element) were prepared and characterized by x-ray diffraction, dielectric, piezoresponse force microscopy (PFM), and magnetic measurements. It is shown that the crystal structure of the compounds is described within the space group R3c, permitting the spontaneous polarization, whose existence was confirmed by the PFM data. Magnetic properties of the solid solutions are determined by the ionic radius of the substituting element. Experimental results suggest that the increase in the radius of the A-site ion leads to the effective suppression of the spiral spin structure of BiFeO3, resulting in the appearance of net magnetization.
TL;DR: In this paper, a spin transfer switching in the TbCoFe∕CoFeB∕MgO∕ CoFeB ∕TbCo FeB free layer with a large coercive field of 1.2kOe and a large thermal stability factor of 107 at room temperature was studied.
Abstract: Spin transfer (ST) switching in the TbCoFe∕CoFeB∕MgO∕CoFeB∕TbCoFe magnetic tunnel junction (MTJ) was studied. The TbCoFe∕CoFeB free layer with a large coercive field of 1.2kOe and a large thermal stability factor of 107 at room temperature was switched by a 100ns pulse current with a current density of 4.7MA∕cm2. This is the first report of ST switching in a MTJ with perpendicular magnetic anisotropy. The temperature dependence of the coercive field was also investigated to estimate the magnetic anisotropy in the case of rising temperature due to the Joule heating effect. The measured coercive field at 87°C, which was the simulated temperature during the switching pulse current, was about 0.34kOe. The ratio of the switching current density to the coercive field under the switching current in the MTJ with the TbCoFe∕CoFeB free layer is smaller than that in a typical MTJ with an in-plane magnetized CoFeB free layer. This result indicates that a MTJ with perpendicular magnetic anisotropy is advantageous for ...
TL;DR: In this article, the room temperature ferroelectric and piezoelectric properties of lead-free ceramics were studied based on the measured properties, and two groups were categorized into two groups: group I and group II compositions displaying mixed ferro-electric and antiferroelectric properties at room temperature.
Abstract: Lead-free piezoelectric ceramics, 1� xyBi 0.5 Na 0.5 TiO 3 -xBaTiO 3 -yK 0.5 Na 0.5 NbO 3 0.05x 0.07 and 0.01y 0.03, have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and piezoelectric properties of these ceramics were studied. Based on the measured properties, the ceramics were categorized into two groups: group I compositions having dominant ferroelectric order and group II compositions displaying mixed ferroelectric and antiferroelectric properties at room temperature. A composition from group II near the boundary between these two groups exhibited a strain as large as 0.45% at an electric field of 8k V/ mm. Polarization in this composition was not stable in that the piezoelectric coefficient d33 at zero electric field was only about 30 pm/ V. The converse piezoelectric response becomes weaker when the composition deviated from the boundary between the groups toward either the ferroelectric or antiferroelectric compositions. These results were rationalized based on a field induced antiferroelectric-ferroelectric phase transition. © 2008 American Institute of Physics. DOI: 10.1063/1.2838472
TL;DR: In this article, the effects of surface tension and surface modulus on diffusion-induced stresses within spherical nanoparticles were examined and both the magnitude and distribution of stresses can be significantly affected by surface mechanics if the particle diameter is in the nanometer range.
Abstract: We examine the effects of surface tension and surface modulus on diffusion-induced stresses within spherical nanoparticles. We show that both the magnitude and distribution of stresses can be significantly affected by surface mechanics if the particle diameter is in the nanometer range. In particular, a tensile state of stress may be significantly reduced in magnitude or even be reverted to a state of compressive stress with decreasing particle radius. This reduction in tensile stress may be responsible for the observed resilience to fracture and decrepitation of nanoparticles used in various industrial applications.
TL;DR: In this article, the authors show that one of the fundamental premises used to justify the use of PLD, that material is transferred from an ablation target to the film without stoichiometry deviations, is incorrect even when no volatile elements are involved.
Abstract: Epitaxial oxide thin films are at the heart of new “oxide electronic” applications, such as excitonic ultraviolet light-emitting diodes and resistive switching memories Complex oxide films are often grown by pulsed laser deposition (PLD) because the technique is believed to be material agnostic Here, we show that one of the fundamental premises used to justify the use of PLD, that material is transferred from an ablation target to the film without stoichiometry deviations, is incorrect even when no volatile elements are involved Even more importantly, the commonly used solution of increasing the laser energy density above a material-specific threshold value to obtain stoichiometric films cannot be used in the case of low carrier density systems such as SrTiO3, where even minute 1018 cm−3 order cation nonstoichiometry can have a dramatic effect on transport Lattice parameter deviations in oxide films, which are often incorrectly ascribed to oxygen loss, correlate very well with cation nonstoichiometry
TL;DR: In this paper, focused surface acoustic waves (SAWs) were generated on 128° rotated Y-cut X-propagating lithium niobate (LiNbO3) for enhancing the actuation of fluids and the manipulation of particle suspensions at microscale dimensions.
Abstract: We report the use of focused surface acoustic waves (SAWs) generated on 128° rotated Y-cut X-propagating lithium niobate (LiNbO3) for enhancing the actuation of fluids and the manipulation of particle suspensions at microscale dimensions. In particular, we demonstrate increased efficiency and speed in carrying out particle concentration/separation and in generating intense micromixing in microliter drops within which acoustic streaming is induced due to the focused SAW beneath the drop. Concentric circular and elliptical single-phase unidirectional transducers (SPUDTs) were used to focus the SAW. We benchmark our results against a straight SPUDT which does not cause focusing of the SAW. Due to the increased wave intensity and asymmetry of the wave, we found both circular and elliptical SPUDTs concentrate particles in under 1 s, which is one order of magnitude faster than the straight SPUDT and several orders of magnitude faster than conventional microscale devices. The concentric circular SPUDT was found ...
TL;DR: In this article, the correlation between the electroforming procedure and the resulting bipolar switching behavior is discussed, and the dependence of electroforming behavior on atmosphere is also identified, from which they define symmetric or asymmetric electroforming.
Abstract: Electroforming effects on the composition, structure, and electrical resistance of Pt/TiO2/Pt switching cells are investigated. The correlation between the electroforming procedure and the resulting bipolar switching behavior is discussed. The dependence of electroforming behavior on atmosphere is also identified, from which we define symmetric or asymmetric electroforming. The symmetry of electroforming is a key factor determining the resulting bipolar switching characteristics. From the experimental results we suggest a possible mechanism for electroforming in Pt/TiO2/Pt in terms of the formation of oxygen gas and vacancies in the vicinity of the anode.
TL;DR: In this article, the authors present conceptual designs of an emerging class of logic gates, including NOT, NOR, and NAND, that use traveling spin waves (SWs) in the gigahertz range and that are based on a Mach-Zehnder-type SW (MZSW) interferometer.
Abstract: We present conceptual designs of an emerging class of logic gates, including NOT, NOR, and NAND, that use traveling spin waves (SWs) in the gigahertz range and that are based on a Mach–Zehnder-type SW (MZSW) interferometer. In this MZSW interferometer, logical input and output signals are achievable by the application of currents in order to control the phases that are accumulated by propagating SWs and by either destructive or constructive SW interference, respectively. In this article, the operation mechanism underlying a NOT gate function using a single MZSW interferometer is described and demonstrated numerically. The MZSW interferometer can itself become a NOT gate and be combined in its parallel and serial configurations to form NAND and NOR gates, respectively, which represent emerging classes of universal logic functions for microwave information signal processing.
TL;DR: In this article, the electric field emission behavior of vertically aligned few-layer graphene was studied in a parallel plate-type setup, and it was found to be a good field emitter, characterized by turn-on fields as low as 1V/μm and field amplification factors up to several thousands.
Abstract: The electric field emission behavior of vertically aligned few-layer graphene was studied in a parallel plate–type setup. Few-layer graphene was synthesized in the absence of any metallic catalyst by microwave plasma enhanced chemical vapor deposition with gas mixtures of methane and hydrogen. The deposit consists of nanostructures that are several micrometers wide, highly crystalline stacks of four to six atomic layers of graphene, aligned vertically to the substrate surface in a high density network. The few-layer graphene is found to be a good field emitter, characterized by turn-on fields as low as 1 V/μm and field amplification factors up to several thousands. We observe a clear dependence of the few-layer graphene field emission behavior on the synthesis parameters: Hydrogen is identified as an efficient etchant to improve field emission, and samples grown on titanium show lower turn-on field values and higher amplification factors when compared to samples grown on silicon.
TL;DR: In this article, a series of structure transformations depend upon the doping level of Bi1−xLaxFeO3 ceramics with x=0, 0.8La0.2 and Bi0.7La 0.3 have been synthesized by solid state reaction starting from metal oxides.
Abstract: Bi1−xLaxFeO3 ceramics with x=0, 0.1, 0.2, and 0.3 have been synthesized by solid state reaction, starting from metal oxides. A series of structure transformations is found to depend upon the doping level. Below 10% La doping, Bi1−xLaxFeO3 maintains the rhombohedral structure of BiFeO3. However, for Bi0.8La0.2FeO3 and Bi0.7La0.3FeO3, the structures change to the orthorhombic and tetragonal, respectively. La doping significantly reduces electric leakage and leads to successful observation of electrical polarization hysteresis loops. Doping with La also enhances the ferromagnetic moment, due to the broken cycloid spin structure caused by the changes in the crystalline structure.
TL;DR: It is found that the charged particles play a minor role in the inactivation process when He/N2(3%) is used as working gas, but the active species, including O, O3, and metastable state O2∗, can play a crucial role inThe inactivation of the bacteria.
Abstract: The roles of various plasma agents in the inactivation of bacteria have recently been investigated. However, up to now, the effect of the charged particles on the inactivation of bacteria is not well understood. In this paper, an atmospheric pressure plasma jet device, which generates a cold plasma plume carrying a peak current of 300 mA, is used to investigate the role of the charged particles in the inactivation process. It is found that the charged particles play a minor role in the inactivation process when He/N2(3%) is used as working gas. On the other hand, when He/O2(3%) is used, the charged particles are expected to play an important role in the inactivation of bacteria. Further analysis shows that the negative ions O2− might be the charged particles that are playing the role. Besides, it is found that the active species, including O, O3, and metastable state O2∗, can play a crucial role in the inactivation of the bacteria. However, the excited He∗, N2 C Π3u, and N2+ B Σ2u+ have no significant direct effect on the inactivation of bacteria. It is also concluded that heat and UV play no or minor role in the inactivation process.
TL;DR: In this paper, the magnetic anisotropy of FeCo core-shell MNPs is tuned by composition and/or shape variation to achieve the maximum specific loss power (SLP) at biocompatible fields.
Abstract: Magnetic nanoparticles (MNPs) offer promise for local hyperthermia or thermoablative cancer therapy. Magnetic hyperthermia uses MNPs to heat cancerous regions in an rf field. Metallic MNPs have larger magnetic moments than iron oxides, allowing similar heating at lower concentrations. By tuning the magnetic anisotropy in alloys, the heating rate at a particular particle size can be optimized. Fe–Co core-shell MNPs have protective CoFe2O4 shell which prevents oxidation. The oxide coating also aids in functionalization and improves biocompatibility of the MNPs. We predict the specific loss power (SLP) for FeCo (SLP ∼450W∕g) at biocompatible fields to be significantly larger in comparision to oxide materials. The anisotropy of Fe-Co MNPs may be tuned by composition and/or shape variation to achieve the maximum SLP at a desired particle size.