Showing papers on "Electric field published in 2007"
TL;DR: It is demonstrated that the electronic gap of a graphene bilayer can be controlled externally by applying a gate bias and can be changed from zero to midinfrared energies by using fields of less, approximately < 1 V/nm, below the electric breakdown of SiO2.
Abstract: We demonstrate that the electronic gap of a graphene bilayer can be controlled externally by applying a gate bias. From the magnetotransport data (Shubnikov-de Haas measurements of the cyclotron mass), and using a tight-binding model, we extract the value of the gap as a function of the electronic density. We show that the gap can be changed from zero to midinfrared energies by using fields of less, approximately < 1 V/nm, below the electric breakdown of SiO2. The opening of a gap is clearly seen in the quantum Hall regime.
1,557 citations
Journal Article•
TL;DR: In this paper, the electronic gap of a graphene bilayer can be controlled externally by applying a gate bias, and the gap can be changed from zero to mid-infrared energies by using fields of less, approximately < 1 V/nm, below the electric breakdown of SiO2.
Abstract: We demonstrate that the electronic gap of a graphene bilayer can be controlled externally by applying a gate bias. From the magnetotransport data (Shubnikov-de Haas measurements of the cyclotron mass), and using a tight-binding model, we extract the value of the gap as a function of the electronic density. We show that the gap can be changed from zero to midinfrared energies by using fields of less, approximately < 1 V/nm, below the electric breakdown of SiO2. The opening of a gap is clearly seen in the quantum Hall regime.
1,365 citations
TL;DR: It is demonstrated that the magnetocrystalline anisotropy of ordered iron-platinum and iron-palladium intermetallic compounds can be reversibly modified by an applied electric field when immersed in an electrolyte.
Abstract: A large electric field at the surface of a ferromagnetic metal is expected to appreciably change its electron density. In particular, the metal's intrinsic magnetic properties, which are commonly regarded as fixed material constants, will be affected. This requires, however, that the surface has a strong influence on the material's properties, as is the case with ultrathin films. We demonstrated that the magnetocrystalline anisotropy of ordered iron-platinum (FePt) and iron-palladium (FePd) intermetallic compounds can be reversibly modified by an applied electric field when immersed in an electrolyte. A voltage change of -0.6 volts on 2-nanometer-thick films altered the coercivity by -4.5 and +1% in FePt and FePd, respectively. The modification of the magnetic parameters was attributed to a change in the number of unpaired d electrons in response to the applied electric field. Our device structure is general and should be applicable for characterization of other thin-film magnetic systems.
1,062 citations
TL;DR: Gate-modulated low-temperature Raman spectra reveal that the electric field effect (EFE), pervasive in contemporary electronics, has marked impacts on long-wavelength optical phonons of graphene and demonstrate optically the particle-hole symmetry about the charge-neutral Dirac point.
Abstract: Gate-modulated low-temperature Raman spectra reveal that the electric field effect (EFE), pervasive in contemporary electronics, has marked impacts on long-wavelength optical phonons of graphene. The EFE in this two-dimensional honeycomb lattice of carbon atoms creates large density modulations of carriers with linear dispersion (known as Dirac fermions). Our EFE Raman spectra display the interactions of lattice vibrations with these unusual carriers. The changes of phonon frequency and linewidth demonstrate optically the particle-hole symmetry about the charge-neutral Dirac point. The linear dependence of the phonon frequency on the EFE-modulated Fermi energy is explained as the electron-phonon coupling of massless Dirac fermions.
1,061 citations
TL;DR: The experimentally realized coherent control of a single-electron spin in a quantum dot using an oscillating electric field generated by a local gate to establish the feasibility of fully electrical manipulation of spin qubits.
Abstract: Manipulation of single spins is essential for spin-based quantum information processing Electrical control instead of magnetic control is particularly appealing for this purpose, because electric fields are easy to generate locally on-chip We experimentally realized coherent control of a single-electron spin in a quantum dot using an oscillating electric field generated by a local gate The electric field induced coherent transitions (Rabi oscillations) between spin-up and spin-down with 90 degrees rotations as fast as approximately 55 nanoseconds Our analysis indicated that the electrically induced spin transitions were mediated by the spin-orbit interaction Taken together with the recently demonstrated coherent exchange of two neighboring spins, our results establish the feasibility of fully electrical manipulation of spin qubits
852 citations
TL;DR: The appropriate conditions under which the selective binding of macromolecules is accurately sensed with NW-FET sensors are shown.
Abstract: Nanowire field effect transistors (NW-FETs) can serve as ultrasensitive detectors for label-free reagents. The NW-FET sensing mechanism assumes a controlled modification in the local channel electric field created by the binding of charged molecules to the nanowire surface. Careful control of the solution Debye length is critical for unambiguous selective detection of macromolecules. Here we show the appropriate conditions under which the selective binding of macromolecules is accurately sensed with NW-FET sensors.
679 citations
TL;DR: In this article, the charge carrier transport and recombination in two types of thermally treated bulk-heterojunction solar cells is reviewed: in regioregular poly(3-hexylthiophene) (RRP3HT) mixed with 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) and in the blend of poly[2-methyl-5-(3,7-dimethyl octyloxy)-phenylene vinylene] (MD
Abstract: The charge carrier transport and recombination in two types of thermally treated bulk-heterojunction solar cells is reviewed: in regioregular poly(3-hexylthiophene) (RRP3HT) mixed with 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) and in the blend of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) mixed with PCBM. The charge carrier mobility and bimolecular recombination coefficient have been comparatively studied by using various techniques including Time-of-Flight (ToF), Charge Extraction by Linearly Increasing Voltage (CELIV), Double Injection (DI) transients, Current–Voltage (I–V) technique. It was found that the carrier mobility is at least an order of magnitude higher in RRP3HT/PCBM blends compared to MDMO-PPV/PCBM. Moreover, all used techniques demonstrate a heavily reduced charge carrier recombination in RRP3HT/PCBM films compared to Langevin-type carrier bimolecular recombination in MDMO-PPV/PCBM blends. As a result of long carrier lifetimes the formation of high carrier concentration plasma in RRP3HT/PCBM blends is demonstrated and plasma extraction methods were used to directly estimate the charge carrier mobility and bimolecular recombination coefficients simultaneously. A weak dependence of bimolecular recombination coefficient on the applied electric field and temperature demonstrates that carrier recombination is not dominated by charge carrier mobility (Langevin-type recombination) in RRP3HT/PCBM blends. Furthermore, we found from CELIV techniques that electron mobility in RRP3HT/PCBM blends is independent on relaxation time in the experimental time window (approx. hundreds of microseconds to tens of milliseconds). This reduced carrier bimolecular recombination in RRP3HT/PCBM blends implies that the much longer carrier lifetimes can be reached at the same concentrations which finally results in higher photocurrent and larger power conversion efficiency of RRP3HT/PCBM solar cells. Copyright © 2007 John Wiley & Sons, Ltd.
550 citations
TL;DR: It is proposed that the spatial summation of LFP and MUA is determined by the size of these signals' generators and the nature of neural events underlying them, rather than by biophysical properties of gray matter.
435 citations
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TL;DR: In this paper, a theoretical model for the formation of hot corona around strongly magnetized neutron stars was developed, and it was shown that the corona self-organizes quickly (on a millisecond timescale) into a quasi-steady state, with voltage 108-109 V along the magnetic lines.
Abstract: We develop a theoretical model that explains the formation of hot coronae around strongly magnetized neutron stars—magnetars. The starquakes of a magnetar shear its external magnetic field, which becomes nonpotential and threaded by an electric current. Once twisted, the magnetosphere cannot untwist immediately because of its self-induction. The self-induction electric field lifts particles from the stellar surface, accelerates them, and initiates avalanches of pair creation in the magnetosphere. The created plasma corona maintains the electric current demanded by ∇ × and regulates the self-induction EMF by screening. This corona persists in dynamic equilibrium: it is continually lost to the stellar surface on the light crossing time ~10-4 s and replenished with new particles. In essence, the twisted magnetosphere acts as an accelerator that converts the toroidal field energy to particle kinetic energy. Using a direct numerical experiment, we show that the corona self-organizes quickly (on a millisecond timescale) into a quasi-steady state, with voltage 108-109 V along the magnetic lines. The voltage is maintained near the threshold for e± discharge. The heating rate of the corona is ~1036 ergs s-1, in agreement with the observed persistent, high-energy output of magnetars. We deduce that a static twist that is suddenly implanted into the magnetosphere will decay on a timescale of 1-10 yr. The particles accelerated in the corona impact the solid crust, knock out protons, and regulate the column density of the hydrostatic atmosphere of the star. The transition layer between the atmosphere and corona may be hot enough to create additional e± pairs. This layer can be the source of the observed 100 keV emission from magnetars. The corona emits curvature radiation and can supply the observed IR-optical luminosity.
390 citations
[...]
TL;DR: In this paper, the conductivity of massive = 2 hypermultiplet fields at finite baryon number density in an = 4 SU(Nc) super-Yang-Mills theory plasma in the large Nc, large 't Hooft coupling limit was derived.
Abstract: We use the AdS/CFT correspondence to compute the conductivity of massive = 2 hypermultiplet fields at finite baryon number density in an = 4 SU(Nc) super-Yang-Mills theory plasma in the large Nc, large 't Hooft coupling limit. The finite baryon density provides charge carriers analogous to electrons in a metal. An external electric field then induces a finite current which we determine directly. Our result for the conductivity is good for all values of the mass, external field and density, modulo statements about the yet-incomplete phase diagram. In the appropriate limits it agrees with known results obtained from analyzing small fluctuations around equilibrium. For large mass, where we expect a good quasi-particle description, we compute the drag force on the charge carriers and find that the answer is unchanged from the zero density case. Our method easily generalizes to a wide class of systems of probe branes in various backgrounds.
388 citations
TL;DR: The results presented in this work show for the first time that an electric field used to macroscopically align polymer nan ofibers can also align polymer chains parallel to the fiber axis, indicating that anisotropic structural properties can be induced in polymer nanofibers during the electrospinning process.
Abstract: The results presented in this work show for the first time that an electric field used to macroscopically align polymer nanofibers can also align polymer chains parallel to the fiber axis. This important result indicates that anisotropic structural properties (mechanical, electrical, etc.) can be induced in polymer nanofibers during the electrospinning process. Such uniaxially oriented nanofibers exhibit a variety of potential applications in biomedicine, microelectronics, and optics. A simple technique of vertical electrospinning with an electric field induced, stationary collection was employed to obtain the molecular orientation in polymer nanofibers. This manuscript describes the orientation process via electrospinning and verifies this molecular orientation in the polymer nanofibers using three independent methods: polarized Fourier transform infrared spectroscopy, polarized Raman scattering, and X-ray diffraction.
TL;DR: Experimental studies have confirmed the hypothesis that the application of nanosecond pulses induces a type of programmed cell death, apoptosis, in biological cells, and shown that the similarity law allows one not only to predict cell viability based on pulse parameters, but has also been shown to be applicable for inducing platelet aggregation.
Abstract: Electrical models for biological cells predict that reducing the duration of applied electrical pulses to values below the charging time of the outer cell membrane (which is on the order of 100 ns for mammalian cells) causes a strong increase in the probability of electric field interactions with intracellular structures due to displacement currents. For electric field amplitudes exceeding MV/m, such pulses are also expected to allow access to the cell interior through conduction currents flowing through the permeabilized plasma membrane. In both cases, limiting the duration of the electrical pulses to nanoseconds ensures only nonthermal interactions of the electric field with subcellular structures. This intracellular access allows the manipulation of cell functions. Experimental studies, in which human cells were exposed to pulsed electric fields of up to 300 kV/cm amplitude with durations as short as 3 ns, have confirmed this hypothesis and have shown that it is possible to selectively alter the behavior and/or survival of cells. Observed nanosecond pulsed effects at moderate electric fields include intracellular release of calcium and enhanced gene expression, which could have long term implications on cell behavior and function. At increased electric fields, the application of nanosecond pulses induces a type of programmed cell death, apoptosis, in biological cells. Cell survival studies with 10 ns pulses have shown that the viability of the cells scales inversely with the electrical energy density, which is similar to the "dose" effect caused by ionizing radiation. On the other hand, there is experimental evidence that, for pulses of varying durations, the onset of a range of observed biological effects is determined by the electrical charge that is transferred to the cell membrane during pulsing. This leads to an empirical similarity law for nanosecond pulse effects, with the product of electric field intensity, pulse duration, and the square root of the number of pulses as the similarity parameter. The similarity law allows one not only to predict cell viability based on pulse parameters, but has also been shown to be applicable for inducing platelet aggregation, an effect which is triggered by internal calcium release. Applications for nanosecond pulse effects cover a wide range: from a rather simple use as preventing biofouling in cooling water systems, to advanced medical applications, such as gene therapy and tumor treatment. Results of this continuing research are leading to the development of wound healing and skin cancer treatments, which are discussed in some detail.
TL;DR: In this paper, a single molecule tip-enhanced resonance Raman spectra from brilliant cresyl blue (BCB) submonolayers adsorbed on a planar Au surface with Ag tips was presented.
Abstract: We present single molecule tip-enhanced resonance Raman spectra from brilliant cresyl blue (BCB) submonolayers adsorbed on a planar Au surface with Ag tips A gap of 1 nm between a Ag tip and the Au substrate was employed to create a highly enhanced electric field and to generate Raman scattering from an area of ∼100 nm2 Three lines of evidence are presented to prove the single molecule sensitivity of our experiments: (1) Extremely diluted samples were used Estimations show that at most a few molecules were excited by the Ag tip (2) Spectroscopic fluctuations, including intensity fluctuations, frequency shifts, and line shape changes were observed A histogram analysis of the intensity fluctuations of two different BCB coverages was carried out The results clearly show the features of single molecule behavior (3) Discrete signal losses also were observed This is because of photochemical processes involving single molecules Besides BCB, which shows a strong resonant absorption at 633 nm (the wavele
TL;DR: In this article, the stability, band structures of few-layer graphite films, and their dependence on electric field applied along the c-axis are examined within the density functional theory. And they predict that those of Bernal type and also rhombohedral type tri-and tetra-layer graphs exhibit stability.
TL;DR: In this article, the authors showed that the half-metallicity in zigzag edge graphene nanoribbons (ZGNR) can be realized when an external electric field is applied across the ribbon.
Abstract: At B3LYP level of theory, we predict that the half-metallicity in zigzag edge graphene nanoribbon (ZGNR) can be realized when an external electric field is applied across the ribbon. The critical electric field decreases with the increase of the ribbon width to induce the half-metallicity. Both the spin polarization and half-metallicity are removed when the edge state electrons fully transferred from one side to the other under very strong electric field. The electric field range under which ZGNR remains half-metallic increases with the ribbon width. Our study demonstrates a rich field-induced spin polarization behavior, which may lead to some important applications in spinstronics.
TL;DR: It is shown that obtaining the appropriate boundary conditions is essential for capturing the underlying device physics in LEECs and that accumulation and depletion of mobile ions near the electrodes create high interfacial electric fields that enhance the injection of electronic carriers.
Abstract: The interplay between ionic and electronic charge carriers in mixed conductors offers rich physics and unique device potential. In light-emitting electrochemical cells (LEECs), for example, the redistribution of ions assists the injection of electronic carriers and leads to efficient light emission. The mechanism of operation of LEECs has been controversial, as there is no consensus regarding the distribution of electric field in these devices. Here, we probe the operation of LEECs using electric force microscopy on planar devices. We show that obtaining the appropriate boundary conditions is essential for capturing the underlying device physics. A patterning scheme that avoids overlap between the mixed-conductor layer and the metal electrodes enabled the accurate in situ measurement of the electric-field distribution. The results show that accumulation and depletion of mobile ions near the electrodes create high interfacial electric fields that enhance the injection of electronic carriers.
TL;DR: The room-temperature control of magnetization reversal with an electric field in an epitaxial nanostructure consisting of ferrimagnetic nanopillars embedded in a ferroelectric matrix is demonstrated and a proposed electric field to assist magnetic recording in multiferroic systems with high perpendicular magnetic anisotropy is proposed.
Abstract: We demonstrate the room-temperature control of magnetization reversal with an electric field in an epitaxial nanostructure consisting of ferrimagnetic nanopillars embedded in a ferroelectric matrix. This was achieved by combining a weak, uniform magnetic field with the switching electric field to selectively switch pillars with only one magnetic configuration. On the basis of these experimental results, we propose to use an electric field to assist magnetic recording in multiferroic systems with high perpendicular magnetic anisotropy.
TL;DR: All-electrical methods are used to inject, transport, and detect spin-polarized electrons vertically through a 350-micron-thick undoped single-crystal silicon wafer, yielding a conduction electron spin lifetime (T1) lower bound in silicon of over 500 ns at 60 K.
Abstract: We use all-electrical methods to inject, transport, and detect spin-polarized electrons vertically through a 350-micron-thick undoped single-crystal silicon wafer. Spin precession measurements in a perpendicular magnetic field at different accelerating electric fields reveal high spin coherence with at least 13pi precession angles. The magnetic-field spacing of precession extrema are used to determine the injector-to-detector electron transit time. These transit time values are associated with output magnetocurrent changes (from in-plane spin-valve measurements), which are proportional to final spin polarization. Fitting the results to a simple exponential spin-decay model yields a conduction electron spin lifetime (T1) lower bound in silicon of over 500 ns at 60 K.
TL;DR: These threshold fields correspond to changes in somatic potential of ∼70 μV, below membrane potential noise levels for neurons, demonstrating the emergent properties of neuronal networks can be more sensitive than measurable effects in single neurons.
Abstract: The sensitivity of brain tissue to weak extracellular electric fields is important in assessing potential public health risks of extremely low frequency (ELF) fields, and potential roles of endogenous fields in brain function. Here we determine the effect of applied electric fields on membrane potentials and coherent network oscillations. Applied DC electric fields change transmembrane potentials in CA3 pyramidal cell somata by 0.18 mV per V m−1 applied. AC sinusoidal electric fields have smaller effects on transmembrane potentials: sensitivity drops as an exponential decay function of frequency. At 50 and 60 Hz it is ∼0.4 that for DC fields. Effects of fields of ≤ 16 V m−1 peak-to-peak (p-p) did not outlast application. Kainic acid (100 nm) induced coherent network oscillations in the beta and gamma bands (15–100 Hz). Applied fields of ≥ 6 V m−1 p-p (2.1 V m−1 r.m.s.) shifted the gamma peak in the power spectrum to centre on the applied field frequency or a subharmonic. Statistically significant effects on the timing of pyramidal cell firing within the oscillation appeared at distinct thresholds: at 50 Hz, 1 V m−1 p-p (354 mV m−1 r.m.s.) had statistically significant effects in 71% of slices, and 0.5 V m−1 p-p (177 mV m−1 r.m.s.) in 20%. These threshold fields are consistent with current environmental guidelines. They correspond to changes in somatic potential of ∼70 μV, below membrane potential noise levels for neurons, demonstrating the emergent properties of neuronal networks can be more sensitive than measurable effects in single neurons.
TL;DR: In this paper, an electrically tunable negative permeability metamaterial consisting of a periodic array of split ring resonators infiltrated with nematic liquid crystals is demonstrated, which can be continuously and reversibly adjusted by an applied electric field, and the maximum shift is about 210MHz with respect to the resonance frequency around 11.08GHz.
Abstract: An electrically tunable negative permeability metamaterial consisting of a periodic array of split ring resonators infiltrated with nematic liquid crystals is demonstrated. It shows that the transmitted resonance dip of the metamaterial can be continuously and reversibly adjusted by an applied electric field, and the maximum shift is about 210MHz with respect to the resonance frequency around 11.08GHz. Numerical simulation shows that the permeability is negative near the resonance frequency, and the frequency range with negative permeability can be dynamically adjusted and widened by about 200MHz by the electric field. It provides a convenient means to design adaptive metamaterials.
TL;DR: In this article, the electronic structure of a spherical quantum dot with parabolic confinement that contains a hydrogenic impurity and is subjected to a DC electric field is studied, and the calculated electronic structure is further used for determining the nonlinear optical rectification coefficient of the quantum dot structure.
Abstract: The electronic structure of a spherical quantum dot with parabolic confinement that contains a hydrogenic impurity and is subjected to a DC electric field is studied. In our calculations we vary the position of the impurity and the electric field strength. The calculated electronic structure is further used for determining the nonlinear optical rectification coefficient of the quantum dot structure. We show that both the position of the impurity and the strength of the electric field influence the nonlinear optical rectification process.
TL;DR: A novel mechanism by which the nonlinear properties of single neurons “amplify” the effect of small electric fields is demonstrated, providing a precise mechanism for a functional role of endogenous field oscillations in brain function and introducing a framework for considering the effects of environmental fields and design of low-intensity therapeutic neurostimulation technologies.
Abstract: Despite compelling phenomenological evidence that small electric fields (<5 mV/mm) can affect brain function, a quantitative and experimentally verified theory is currently lacking. Here we demonstrate a novel mechanism by which the nonlinear properties of single neurons "amplify" the effect of small electric fields: when concurrent to suprathreshold synaptic input, small electric fields can have significant effects on spike timing. For low-frequency fields, our theory predicts a linear dependency of spike timing changes on field strength. For high-frequency fields (relative to the synaptic input), the theory predicts coherent firing, with mean firing phase and coherence each increasing monotonically with field strength. Importantly, in both cases, the effects of fields on spike timing are amplified with decreasing synaptic input slope and increased cell susceptibility (millivolt membrane polarization per field amplitude). We confirmed these predictions experimentally using CA1 hippocampal neurons in vitro exposed to static (direct current) and oscillating (alternating current) uniform electric fields. In addition, we develop a robust method to quantify cell susceptibility using spike timing. Our results provide a precise mechanism for a functional role of endogenous field oscillations (e.g., gamma) in brain function and introduce a framework for considering the effects of environmental fields and design of low-intensity therapeutic neurostimulation technologies.
TL;DR: This work combines the DFT results at various external electric field strengths with a previously developed model of electrochemical reactions which fully accounts for the effect of the electrode potential to find that the local electric field only slightly affects the output of the model.
Abstract: By varying the external electric field in density functional theory (DFT) calculations we have estimated the impact of the local electric field in the electric double layer on the oxygen reduction reaction (ORR). Potentially, including the local electric field could change adsorption energies and barriers substantially, thereby affecting the reaction mechanism predicted for ORR on different metals. To estimate the effect of local electric fields on ORR we combine the DFT results at various external electric field strengths with a previously developed model of electrochemical reactions which fully accounts for the effect of the electrode potential. We find that the local electric field only slightly affects the output of the model. Hence, the general picture obtained without inclusion of the electric field still persists. However, for accurate predictions at oxygen reduction potentials close to the volcano top local electric field effects may be of importance.
TL;DR: In this paper, a review of the techniques for the generation and measurement of ultrashort pulses in the frequency range from about 0.1 to 10 THz is presented, which is restricted to table-top systems based on short-pulse lasers in the visible or in the near-infrared.
Abstract: In this paper techniques for the generation and measurement of ultrashort pulses in the frequency range from about 0.1 to 10 THz are reviewed. The methods for generation are restricted to table-top systems based on short-pulse lasers in the visible or in the near-infrared. Three techniques are dealt with in detail: photoconductive switches, difference frequency generation and plasma sources. Definitions and methods to measure the pulse width are given, among them cross-correlation and measurements of the electric field of these pulses as a function of time by photoconductive switches and electro-optic sampling.
TL;DR: In this paper, apple juice extracted from golden delicious fruits was pasteurized using a pulsed electric field (PEF) treatment and compared with a conventional high temperature short time (HTST) method.
TL;DR: The theoretical results, strikingly different from the standard 2D electron gas, are explained using a "Lorentz boost," and as an "instability of a relativistic quantum field vacuum."
Abstract: A new effect in graphene in the presence of crossed uniform electric and magnetic fields is predicted. Landau levels are shown to be modified in an unexpected fashion by the electric field, leading to a collapse of the spectrum, when the value of electric to magnetic field ratio exceeds a certain critical value. Our theoretical results, strikingly different from the standard 2D electron gas, are explained using a "Lorentz boost," and as an "instability of a relativistic quantum field vacuum." It is a remarkable case of emergent relativistic type phenomena in nonrelativistic graphene. We also discuss few possible experimental consequence.
TL;DR: In this article, the angular dependence of the electrons' spin precession on their direction of motion with respect to the crystal lattice was measured by optically monitoring the spin-up and spin-down states.
Abstract: Spin–orbit coupling is a manifestation of special relativity. In the reference frame of a moving electron, electric fields transform into magnetic fields, which interact with the electron spin and lift the degeneracy of spin-up and spin-down states. In solid-state systems, the resulting spin–orbit fields are referred to as Dresselhaus and Rashba fields, depending on whether the electric fields originate from bulk or structure inversion asymmetry, respectively. Yet, it remains a challenge to determine the absolute value of both contributions in a single sample. Here, we show that both fields can be measured by optically monitoring the angular dependence of the electrons’ spin precession on their direction of motion with respect to the crystal lattice. Furthermore, we demonstrate spin resonance induced by the spin–orbit fields. We apply our method to GaAs/InGaAs quantum-well electrons, but it should be universally useful to characterize spin–orbit interactions in semiconductors, and therefore could facilitate the design of spintronic devices.
TL;DR: A novel dielectrophoresis switching with vertical electrodes in the sidewall of microchannels for multiplexed switching of objects has been designed and tested and can be integrated with other particle detection components to enable microfluidic flow cytometry systems.
Abstract: A novel dielectrophoresis switching with vertical electrodes in the sidewall of microchannels for multiplexed switching of objects has been designed, fabricated and tested. With appropriate electrode design, lateral DEP force can be generated so that one can dynamically position particulates along the width of the channel. A set of interdigitated electrodes in the sidewall of the microchannels is used for the generation of non-uniform electrical fields to generate negative DEP forces that repel beads/cells from the sidewalls. A countering DEP force is generated from another set of electrodes patterned on the opposing sidewall. These lateral negative DEP forces can be adjusted by the voltage and frequency applied. By manipulating the coupled DEP forces, the particles flowing through the microchannel can be positioned at different equilibrium points along the width direction and continue to flow into different outlet channels. Experimental results for switching biological cells and polystyrene microbeads to multiple outlets (up to 5) have been achieved. This novel particle switching technique can be integrated with other particle detection components to enable microfluidic flow cytometry systems.
TL;DR: In this article, a technique for the determination of the equivalent currents distribution from a known radiated field is described, based on the representation of the radiating structure by means of a set of equivalent currents over a 3D surface that can be fitted to the arbitrary geometry of the antenna.
Abstract: A technique for the determination of the equivalent currents distribution from a known radiated field is described. This Inverse Radiation Problem is solved through an Integral Equation algorithm that allows the characterization of antennas of complex geometry both for near field to far field (NF-FF) transformation purposes as well as for diagnostic tasks. The algorithm is based on the representation of the radiating structure by means of a set of equivalent currents over a three-dimensional (3D) surface that can be fitted to the arbitrary geometry of the antenna. The innovative formulation uses an integral equation involving the electric field due to the currents tangential components to the represented antenna 3D surface. For that purpose, both the magnetic and electric equivalent currents are considered in the integral equations. Regularization techniques are also introduced to improve the convergence of the proposed iterative solution. The paper concludes with several results related to the practical verification of the Equivalence Principle and the characterization of a horn antenna.
Book•
01 Jan 2007
TL;DR: In this paper, the authors present an overview of the main components of a two-dimensional Curvilinear Beams with translation symmetry (Lomax-Kirstein method).
Abstract: PREFACE. Introduction. I.1 Outline of the Book. I.2 List of Symbols. I.3 Electromagnetic Fields and Potentials. I.4 Principle of Least Action. Lagrangian. Generalized Momentum. Lagrangian Equations. I.5 Hamiltonian. Hamiltonian Equations. I.6 Liouville Theorem. I.7 Emittance. Brightness. PART I ELECTRON BEAMS. 1 Motion of Electrons in External Electric and Magnetic Static Fields. 1.1 Introduction. 1.2 Energy of a Charged Particle. 1.3 Potential-Velocity Relation (Static Fields). 1.4 Electrons in a Linear Electric Field e0E kx. 1.5 Motion of Electrons in Homogeneous Static Fields. 1.6 Motion of Electrons in Weakly Inhomogeneous Static Fields. 1.6.1 Small Variations in Electromagnetic Fields Acting on Moving Charged Particles. 1.7 Motion of Electrons in Fields with Axial and Plane Symmetry. Busch's Theorem. 2 Electron Lenses. 2.1 Introduction. 2.2 Maupertuis's Principle. Electron-Optical Refractive Index. Differential Equations of Trajectories. 2.3 Differential Equations of Trajectories in Axially Symmetric Fields. 2.4 Differential Equations of Paraxial Trajectories in Axially Symmetric Fields Without a Space Charge. 2.5 Formation of Images by Paraxial Trajectories. 2.6 Electrostatic Axially Symmetric Lenses. 2.7 Magnetic Axially Symmetric Lenses. 2.8 Aberrations of Axially Symmetric Lenses. 2.9 Comparison of Electrostatic and Magnetic Lenses. Transfer Matrix of Lenses . 2.10 Quadrupole lenses. 3 Electron Beams with Self Fields. 3.1 Introduction. 3.2 Self-Consistent Equations of Steady-State Space-Charge Electron Beams. 3.3 Euler's Form of a Motion Equation. Lagrange and Poincare' Invariants of Laminar Flows. 3.4 Nonvortex Beams. Action Function. Planar Nonrelativistic Diode. Perveance. Child-Langmuir Formula. r- and T-Modes of Electron Beams. 3.5 Solutions of Self-Consistent Equations for Curvilinear Space-Charge Laminar Beams. Meltzer Flow. Planar Magnetron with an Inclined Magnetic Field. Dryden Flow. 4 Electron Guns. 4.1 Introduction. 4.2 Pierce's Synthesis Method for Gun Design. 4.3 Internal Problems of Synthesis. Relativistic Planar Diode. Cylindrical and Spherical Diodes. 4.4 External Problems of Synthesis. Cauchy Problem. 4.5 Synthesis of Electrode Systems for Two-Dimensional Curvilinear Beams with Translation Symmetry (Lomax-Kirstein Method). Magnetron Injection Gun. 4.6 Synthesis of Axially Symmetric Electrode Systems. 4.7 Electron Guns with Compressed Beams. Magnetron Injection Gun. 4.8 Explosive Emission Guns. 5 Transport of Space-Charge Beams. 5.1 Introduction. 5.2 Unrippled Axially Symmetric Nonrelativistic Beams in a Uniform Magnetic field. 5.3 Unrippled Relativistic Beams in a Uniform External Magnetic Field. 5.4 Cylindrical Beams in an Infinite Magnetic Field. 5.5 Centrifugal Electrostatic Focusing. 5.6 Paraxial-Ray Equations of Axially Symmetric Laminar Beams. 5.7 Axially Symmetric Paraxial Beams in a Uniform Magnetic Field with Arbitrary Shielding of a Cathode Magnetic Field. 5.8 Transport of Space-Charge Beams in Spatial Periodic Fields. PART II MICROWAVE VACUUM ELECTRONICS. 6 Quasistationary Microwave Devices. 6.1 Introduction. 6.2 Currents in Electron Gaps. Total Current and the Shockley-Ramo Theorem. 6.3 Admittance of a Planar Electron Gap. Electron Gap as an Oscillator. Monotron. 6.4 Equation of Stationary Oscillations of a Resonance Self-Excited Circuit. 6.5 Effects of a Space-Charge Field. Total Current Method. High-Frequency Diode in the r-Mode. Llewellyn-Peterson Equations. 7 Klystrons. 7.1 Introduction. 7.2 Velocity Modulation of an Electron beam. 7.3 Cinematic (Elementary) Theory of Bunching. 7.4 Interaction of a Bunched Current with a Catcher Field. Output Power of A Two-Cavity Klystron. 7.5 Experimental Characteristics of a Two-Resonator Amplifier and Frequency-Multiplier Klystrons. 7.6 Space-Charge Waves in Velocity-Modulated Beams. 7.7 Multicavity and Multibeam Klystron Amplifiers. 7.8 Relativistic Klystrons. 7.9 Reflex Klystrons. 8 Traveling-Wave Tubes and Backward-Wave Oscillators (O-Type Tubes). 8.1 Introduction. 8.2 Qualitative Mechanism of Bunching and Energy Output in a TWTO. 8.3 Slow-Wave Structures. 8.4 Elements of SWS Theory. 8.5 Linear Theory of a Nonrelativistic TWTO. Dispersion Equation, Gain, Effects of Nonsynchronism, Space Charge, and Loss in a Slow-Wave Structure. 8.6 Nonlinear Effects in a Nonrelativistic TWTO. Enhancement of TWTO Efficiency (Velocity Tapering, Depressed Collectors). 8.7 Basic Characteristics and Applications of Nonrelativistic TWTOs. 8.8 Backward-Wave Oscillators. 8.9 Millimeter Nonrelativistic TWTOs, BWOs, and Orotrons. 8.10 Relativistic TWTOs and BWOs. 9 Crossed-Field Amplifiers and Oscillators (M-Type Tubes). 9.1 Introduction. 9.2 Elementary Theory of a Planar MTWT. 9.3 MTWT Amplification. 9.4 M-type Injected Beam Backward-Wave Oscillators (MWO, M-Carcinotron). 9.5 Magnetrons. 9.6 Relativistic Magnetrons. 9.7 Magnetically Insulated Line Oscillators. 9.8 Crossed-Field Amplifiers. 10 Classical Electron Masers and Free Electron Lasers. 10.1 Introduction. 10.2 Spontaneous Radiation of Classical Electron Oscillators. 10.3 Stimulated Radiation of Excited Classical Electron Oscillators. 10.4 Examples of Electron Cyclotron Masers. 10.5 Resonators of Gyromonotrons (Free and Forced Oscillations). 10.6 Theory of a Gyromonotron. 10.7 Subrelativistic Gyrotrons. 10.8 Elements of Gyrotron Electron Optics. 10.9 Mode Interaction and Mode Selection in Gyrotrons. Output Power Systems. 10.10 Gyroklystrons. 10.11 Gyro-Traveling-Wave Tubes. 10.12 Applications of Gyrotrons. 10.13 Cyclotron Autoresonance Masers. 10.14 Free Electron Lasers. Appendixes. 1. Proof of the 3/2 Law for Nonrelativistic Diodes in the r-Mode. 2. Synthesis of Guns for M-Type TWTS and BWOS. 3. Magnetic Field in Axially Symmetric Systems. 4. Dispersion Characteristics of Interdigital and Comb Structures. 5. Electromagnetic Field in Planar Uniform Slow-Wave Structures. 6. Equations of Free Oscillations of Gyrotron Resonators. 7. Derivation of Eqs. (10.66) and (10.67). 8. Calculation of Fourier Coefficients in Gyrotron Equations. 9. Magnetic Systems of Gyrotrons. References. Index.