Photodetachment of H- in a static electric field

We derive a formula using closed-orbit theory for the photodetachment cross-section of H^- in the presence of a static electric field when there is an arbitrary angle θ_L between the laser polarization direction and the static electric field. This formula generalizes the previous result for laser polarization parallel to the static electric field, the effect of laser polarization direction appears as a factor cos²(θ_L) in the amplitude of the oscillation. A photodetachment cross-section formula valid above and below detachment threshold is proposed.     

Generation of low-density plasma by two-step photoionization of barium and its evolution in electric field

Two-color, two-step resonant photoionization has been used to produce low-density (∼10⁶ – 10⁷cm⁻³) barium photoplasma in an atomic beam. The two-photon induced specific absorption coefficient at 355nm for the photoionization process has been measured. The motion of the finite size photoplasma bounded by vacuum is experimentally studied in a static electric field in parallel-plate electrode configuration. It is observed that at sufficiently high electric fields all electrons leave the plasma and the evolution of the left over ion bunch is understood on the basis of independent particle motion.     

DFT study on the influence of electric field on surface‐enhanced Raman scattering from pyridine–metal complex

The influence of a static external electric field on surface‐enhanced Raman scattering is investigated by calculating the Raman spectra and excited state properties of pyridine–Au₂₀ complex with the density functional theory and time‐dependent density functional theory method. The external electric field with orientation parallel (positive) or antiparallel (negative) to the permanent dipole moment is respectively applied on the complex. This field slightly changes the equilibrium geometry and polarizabilities, which results in shifted vibration frequencies and selectively enhanced Raman intensities. The changes of charge transfer (CT) excited states in response to the electric field are visualized by employing the charge difference densities. Further, the energy of charge transfer transition is tuned by electric field to be resonant or not with the incident light, leading to the Raman intensities are enhanced or not enhanced. At the same time, the intensities of vibration modes are sensitive to the orientation of the field. The positive electric field enhances the totally symmetric ring breathing mode (~1009 cm⁻¹) but suppresses the trigonal ring breathing mode (~1051 cm⁻¹). On the contrary, the mode at 1051 cm⁻¹ is more enhanced than the mode at 1009 cm⁻¹ when the negative electric field is applied on the complex. The Raman spectra could be modulated by tuning the strength and direction of the electric field. Copyright © 2013 John Wiley & Sons, Ltd.     

A wire trap for neutral atoms

We present new ways of trapping a neutral atom with static electric and magnetic fields. We discuss the interaction of a neutral atom with the magnetic field of a current carrying wire and the electric field of a charged wire. Atoms can be trapped by the 1/r magnetic field of a current-carrying wire in a two-dimensional trap. The atoms move in Kepler-like orbits around the wire and angular momentum prevents them from being absorbed at the wire. Trapping was demonstrated in an experiment by guiding atoms along a 1 m long current-carrying wire. Stable traps using the interaction of a polarizable atom with the electric field of a charged wire alone are not possible because of the 1/r ² form of the interaction potential. Nevertheless, we show that one can build a microscopic trap with a combination of a magnetic field generated by a current in a straight wire and the static electric field generated by a concentric charged ring which provides the longitudinal confinement. In all of these traps, the neutral atoms are trapped in a region of maximal field, in theirhigh-field seeking state.Dedicated to H. Walther on the occasion of his 60th birthday     

Atom interferometry measurement of the electric polarizability of lithium

Using an atom interferometer, we have measured the static electric polarizability of ⁷Li α=(24.33 ±0.16)×10^-30 m³ = 164.2±1.1 atomic units with a 0.66% uncertainty. Our experiment, which is similar to an experiment done on sodium in 1995 by Pritchard and co-workers, consists in applying an electric field on one of the two interfering beams and measuring the resulting phase-shift. With respect to Pritchard's experiment, we have made several improvements which are described in detail in this paper: the capacitor design is such that the electric field can be calculated analytically; the phase sensitivity of our interferometer is substantially better, near 16 mrad/ ; finally our interferometer is species selective so that impurities present in our atomic beam (other alkali atoms or lithium dimers) do not perturb our measurement. The extreme sensitivity of atom interferometry is well illustrated by our experiment: our measurement amounts to measuring a slight increase Δv of the atom velocity v when it enters the electric field region and our present sensitivity is sufficient to detect a variation Δv/v ≈6 ×10^-13.     

Electric-field-enhanced metal-induced crystallization of hydrogenated amorphous silicon at room temperature

A novel simple method of crystallization of hydrogenated amorphous silicon (a-Si:H) thin films is described. Namely, we studied a metal-induced crystallization enhanced by a dc electric field in sandwich p⁺–i–n⁺structures. The samples were fabricated from wide-bandgap a-Si:H with high hydrogen content (13–51 at. % H). Macroscopic islands of a-Si:H (up to ∼1 mm in diameter) in the region between upper (CrNi) and lower (ITO) contacts crystallize instantaneously when a sufficiently high dc electric field (≳10⁵ V cm^-1) is applied. The crystallization sets in at room temperature and ambient atmosphere and is spatially selective. A proposed microscopic mechanism of such an easy macroscopic crystallization consists in easy diffusion of Ni and/or Ni silicides (representing nucleation sites) through a dense network of voids in hydrogen-rich a-Si:H. Received: 30 November 2000 / Accepted: 3 May 2001 / Published online: 27 June 2001     

Organic thin films based on a dicyanovinyl-quaterthiophene: Influence of electrode configuration on third-order nonlinear optical properties measured by electroabsorption spectroscopy

Electroabsorption (EA) studies at room temperature on organic thin films based on a dicyanovinyl-quaterthiophene 4T-V(CN)₂ are reported. An electric field modulation is applied to the samples for two different electrode geometries, i.e. sandwich and coplanar versus the organic layer. Changes in optical absorption coefficient of 4T-V(CN)₂ based thin films are measured and analyzed to determine the character of the optical transition in the visible range (400-800 nm). Depending on the experimental electrode configuration, magnitude of electroabsorption responses are different, possibly due to different distribution of the externally applied electric field. The results indicate a higher resolution of EA response for the sandwich electrode configuration and confirm the charge transfer exciton character of 4T-V(CN)₂ in contrast to the unsubstituted quaterthiophene 4T. Finally, a third-order nonlinear susceptibility χ⁽³⁾ (−ω; ω, 0, 0) of 16 × 10⁻¹² e.s.u. is obtained.     

Non-linear response and electron-electron interactions in mesoscopic metal rings

A time-dependent electric field gives rise to a stationary non-equilibrium current I ⁽²⁾ around a mesoscopic metal ring threaded by a magnetic flux. We show that this current, which is proportional to the intensity of the field, is closely related to the exchange part of the interaction contribution to the equilibrium persistent current, and that the corresponding non-linear conductivity directly measures the weak localization correction to the polarization. We explicitly calculate the disorder average of I ⁽²⁾ in the diffusive regime as function of the frequency of the electric field and the static flux piercing the ring, and suggest an experiment to test our theory. Received: 5 September 1997 / Accepted: 4 November 1997     

Dissociation of bipolaron in non-degenerate polymer chain at high electric fields

We investigate the dynamics of bipolaron in non-degenerate polymer (e.g. PPV) in an external electric field by using a nonadiabatic evolution method, which allows transition between instantaneous electronic states. When the applied electric field exceeds a critical value, a bipolaron is found to dissociate like the case of polaron due to the lattice distortion not being able to follow the fast moving electrons. The critical value is estimated to be of order ¹⁰⁶ V/cm${10}^6\text{ V}/\text{cm}$. This result is consistent with experiment in that a large increase in current in PPV occurs at high fields. At a given electric field, the saturation velocity of bipolaron will decrease with the increase of non-degenerate parameters te$t_e$.     

Preparation and field emission properties of carbon nanotubes cold cathode using melting Ag nano-particles as binder

A new preparation process for carbon nanotubes (CNTs) cold cathode was studied through the replacement of traditional organic or inorganic binder with Ag nano-particles. This method has the advantages of low preparation temperature and fine electrical contact between CNTs paste and substrate. A mixture paste of CNTs, Ag nano-particles and other organic solvents was spreaded on Si substrate. By melting and connecting of Ag nano-particles after sintered 30 min at 250 °C, a flat CNTs films with good field emission properties was obtained. The measurements reveal that the turn on electric field and the threshold electric field of as-prepared CNTs cathode are 2.1 and 3.9 V/μm respectively and the field emission current density is up to 41 mA/cm² at an applied electric field of 4.7 V/μm.     

Effect of high electric field on the dc conduction of TeO2-V2O5-MoO3 amorphous bulk material

Effect of high electric field on the dc conductivity of TeO₂-V₂O₅-MoO₃ amorphous bulk samples with different molar ratio of each component was investigated with gap-type electrode arrangement. At low electric fields, the current-voltage (I–V) characteristics has a linear shape, while at high electric fields (>10³ V/cm), bulk samples show nonlinear behavior (nonohmic conduction) and current-voltage characteristics shows increasing deviation from Ohm’s law with increasing current density. High-field effect of Pool-Frenkel type was observed at electrical fields about 10³−10⁴ V/cm. In addition, positive deviation from Pool-Frenkel effect was observed when a field higher than about 10⁴ V/cm was applied.     

On the role of combined static hyperfine interactions for the interpretation of in-beam nuclear Larmor-precession measurements

Differential perturbed angular-distribution measurements have been performed for¹⁰⁷Cd and¹⁰⁹Cd in silver hosts. The data have been obtained at various target temperatures with and wthout applied magnetic fields. The theory of static, combined electric and magnetic hyperfine interaction has been applied for comparison of the zero-field quadrupole data and the external field Larmor-precession data.It is concluded that this combined interaction of the external magnetic field and the damage-induced, electric field gradients quantitatively accounts for the observed dependence of Larmor-precession amplitudes on time, temperature and field strength. The significance of the experimental time range for the appearance and thus for the interpretation of this dependence is demonstrated.     

Enhanced light emission in Si-nanoclusters arrays

An array of silicon nanoclusters aimed at producing light emission upon injection of electrons and holes from external sources is studied by Monte Carlo simulations. The conditions for obtaining a significant charge accumulation in the emitting nanoclusters are investigated as a function of array geometry and applied electric fields. It is found that if a stationary state, reached for an applied field F₀, is suddenly perturbed by a field F₁≫F₀, a significant increase in electron-hole pairs population can be obtained with respect to the case of a single field of constant intensity F₁, leading to enhanced light emission when the conductivity of the array is above 6×10^-10 [ Ω cm] ^-1. The excess population thus created gets fully recombined on the time scale of milliseconds, suggesting a device that can produce enhanced light emission in the range of kilohertz.     

Exact polarizability of low-dimensional excitons

Wannier excitons polarized by a static electric field and confined to low-dimensional structures are studied. Effective non-integer dimensions are included by considering hydrogenic states in α-dimensional space, with α as a parameter. Exact expressions for lowest order energy and wave function corrections are obtained as a function of α. For the 1s state, we demonstrate that the exciton polarizability decreases with reduced dimensionality and eventually vanishes as (α−1)⁴ as the 1D limit is approached. The low-dimensional 2s and 2p polarizabilities are also decreased but remain finite in the 1D limit.     

Characteristics of SrBi2Ta2O9 ferroelectric films in an in situ applied low electric field prepared by metalorganic decomposition

SrBi₂Ta₂O₉ (SBT) films were prepared on Pt/TiO₂/SiO₂/Si substrates at 750 °C in oxygen by metalorganic decomposition method. A low electric field was in situ applied during the film crystallization. It was first found that a low electric field and its direction have significant influence on the microstructures and ferroelectric properties of SBT films. Under a positive electric field (assuming that the bottom electrode is electrically grounded), the films show stronger c-axis-preferred orientation than without electric field and under a negative electric field. As a possible origin is proposed that the interface-induced nucleation growth between SBT and Pt coated substrate with application of low electric field plays a key role. Above all, an in situ applied low electric field during the film crystallization is a promising technique controlling film orientation for film preparation by wet chemical method.     

Angular Velocity Distribution of the Electric Microfield in Plasma

In theory of the spectral line shapes, the conventional scheme use two approximations for the local electric field (microfield) due to all charged particles of the plasma. The quasi‐static approximations for the ions and the impact approximation for the electrons. The first approximation consists to say that the electric field is constant during the characteristic time. In this work we shall transpose the idea of the first approximation, to the angular velocity of the microfield whereas its strength is kept constant and equal to its mean value. We shall use the Holtsmark approach and the independent particles model (due to Margeneau and Lewis) to compute the static distribution function of the angular velocity of the microfield. In the first approach (Holtsmark), the distribution shows a Lorentzian behavior, whereas the second approach (Margenau and Lewis) shows a gaussian behavior. Subsequently, we have applied the obtained static distribution to show the effect on the broadening of Lyman‐alpha line for a plasma composed of He⁺ ions. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear optical rectification in asymmetric double triangular quantum wells

The nonlinear optical rectification (OR) in the asymmetric double triangular quantum wells (DTQWs) is investigated theoretically. The dependence of OR on the right-well width of the DTQWs is studied, and the influence of the applied electric field on OR is also taken into account. The analytical expression of the OR susceptibility is analyzed by using the compact density-matrix approach and the iterative method and the numerical calculations are presented for the typical GaAs/Al_xGa_1-xAs asymmetric DTQWs. The results show that the OR susceptibility obtained in this coupled system can reach the magnitude of 10^-3 m/V, 2-3 orders of magnitude higher than that in single quantum systems. Moreover, the OR susceptibility is not a monotonic function of the width of the right well, but has complex relationship with it. The calculated results also reveal that an applied electric field has a great influence on the OR susceptibility. Applying an appropriate electric field to a quasi-symmetric or symmetric DTQW can result in a larger OR susceptibility as compared with that obtained in an optimal asymmetric DTQW without electric field.     

Two-colour laser excitation as a way to set an absolute energy scale in photodetachment-microscopy based electron spectrometry

A two-colour laser technique is developed for photodetachment microscopy, by means of microwave modulation of a CW single-mode dye laser. A phase modulation regime is achieved through an electro-optical LiNbO₃ crystal excited at the frequency 1.95 GHz. The two first sidebands created are selected by rejection of the other orders through a plane Fabry-Perot interferometer. With the resulting two-colour radiation, the photodetachment microscopy technique is applied to a beam of ³²S⁻ ions. It is shown that the superposition of the two resulting interference patterns can be used as a ‘spectral vernier’ to remove the uncertainty on the electric field and absolute energy scale. Without any initial assumption on the value F of the electric field in the laser-ion interaction region, a measure of F and of the electron affinity ^eA of Sulfur can be obtained. Putting 16 recordings of two-colour photodetachment interferograms together, with the only condition that F be the same for all experiments, one gets ^eA(³²S) = 16752.978(11) cm⁻¹, which is quite compatible, even though not as accurate, with the most recently recommended value ^eA(³²S) = 16752.9760(42) cm⁻¹. A proposal is made for going from an incoherent to a coherent two-colour photodetachment scheme, which would make photodetachment interferograms sensitive to a new degree of freedom.     

Infrared laser stark shift spectroscopy in ammonia

The Stark effect in ammonia has been theoretically and experimentally analyzed using lead salt tunable diode laser absorption spectroscopy and CO₂ laser absorption spectroscopy of several absorption lines around 1050 cm^–1 applied to an all-optical sensor for measuring of electric field strength. Measurements of the Stark splitting effect of theaR(5,K) ammonia lines forK=1–5 as well as for the sR(3,K) lines forK=0–3 have been made at Doppler broadening pressures and for several different electric field strengths. Theoretical electric field dependent energy levels have been evaluated by diagonalization of a 6×6 energy matrix constructed using both electric field independent and dependent terms. From the theoretical analysis the resolution can be predicted and optimized both in the Doppler broadened and in the pressure broadened regimes. The predicted resolution is 0.5% at an electric field strength of 20 kV/cm. The theoretical calculations and the experimental data recorded with the tunable diode laser system were compared with independent measurements made with a CO₂ laser system. The agreement between experimentally recorded and theoretically calculated spectra is good which indicates that the theoretical model is satisfactory for our purposes. The contribution from the normally forbidden ssR(5, 3) ammonia line to the absorption at theP(12) CO₂ laser line in the 9 m band is briefly discussed.     

Electrical properties of highly (111)-oriented lead zirconate thin films

Antiferroelectric PbZrO₃ thin films were grown on Pt/Ti/SiO₂/Si substrates with predominant (111) orientation using a sol-gel process. The Pt/PbZrO₃/Pt film capacitor showed well-saturated hysteresis loops at an applied voltage of 5 V with remanent polarisation (P_r) and coercive electric field (E_c) values of 8.97 μC/cm² and 162 kV/cm, respectively. The leakage current density of the highly (111)-oriented PbZrO₃ film was less than 1.0×10⁻⁷ A/cm² over electric field ranges from 0 to 105 kV/cm. The conduction current depended on the voltage polarity. The PbZrO₃/Pt interface forms a Schottky barrier at electric fields from 20 to 160 kV/cm. The dielectric relaxation current behaviour of Pt/PbZrO₃/Pt capacitor obeys the well-known Curie-Von Schweidler law at electric field of 20-80 kV/cm, the currents have contributions of both dielectric relaxation current and leakage current.