Additional External Field Research Articles

Vibrations and dissociation of molecules in strong electric fields: N2, NACl, H2O and SF6

The static deformations and vibrations of the title compounds with an applied static electric field have been studied by density functional theory calculations. It is found that for diatomic molecules, bond length and vibrational frequency as a function of the field can be fit very well all the way up to the dissociation limit by an analytical formula derived from a Morse potential model including an additional external field term. Polyatomic molecules show more complex behaviour with a single mode becoming soft at the dissociation limit. The frequency of the soft mode near the critical field is again described well by the analytical model. The vibrational analysis shows that in polyatomic molecules dissociation proceeds as a heterolytic fragmentation process, which can break the symmetry of the molecule in the applied field.

Investigation of micromagnetism and magnetic reversal of Ni nanoparticles using a magnetic force microscope

Isolated Ni nanoparticles were studied in situ by atomic and magnetic force microscopy in the presence of an additional external field up to 300 Oe. By comparing topographic and magnetic images, and also by computer modeling of magnetic images, it was established that particles smaller than 100 nm are single-domain and easily undergo magnetic reversal in the direction of the applied external magnetic field. For large magnetic particles, the external magnetic field enhances the magnetization uniformity and the direction of total magnetization of these particles is determined by their shape anisotropy. Characteristics of the magnetic images and magnetic reversal of particles larger than 150 nm are attributed to the formation of a vortex magnetization structure in these particles.

Vertical polarization of quantum magnets in high density arrays of nickel dots with small height-to-diameter ratio

Using interferometric lithography and postexposure processing we have fabricated high density (1.3×1010/in.2) magnetic nickel dot arrays on silicon substrates. The dots have the shape of truncated cones and are 75 nm in height and about 120 nm in diameter. The arrays are characterized using magnetic force microscopy (MFM). We demonstrate that such shallow dots with a small height-to-diameter ratio of only 0.63, show single-domain behavior with vertical, out-of-plane magnetization, i.e., along their short axis. The coercive field of these dots is drastically enlarged due to shape anisotropy and is exceeding the dot interaction strength by about one order of magnitude. Local manipulation of the magnetization state using an additional external field and the stray field of the MFM tip is demonstrated.

Corrosion of used nuclear fuel in aqueous perchlorate and carbonate solutions

The corrosion of used fuel was investigated using electrodes constructed from fuel pins discharged from the Pickering, Bruce and Darlington CANDU reactors, and compared to the corrosion behaviour observed on unirradiated UO 2 and SIMFUEL. Experiments were carried out in solutions of NaClO 4 (pH∼ 9.5) in the presence and absence of (a) substantial concentrations of sodium carbonate, and (b) additional external gamma fields. Used fuel electrodes reached oxidizing corrosion potentials ( E CORR) rapidly compared with unirradiated UO 2 electrodes. However, optical and SEM examinations showed no evidence for rapid oxidative dissolution. This reaction, expected to be fast since high values of E CORR are observed, appears to be blocked by the accumulation of secondary phases in grain boundaries. The oxidation and dissolution behaviour of used fuel is determined predominantly by (i) the dose rate in solution near the fuel surface, (ii) the extent of burnup (which determines the degree of fission product doping), and (iii) the degree of non-stoichiometry.

Influence of a constriction on the longitudinal resistance of a 2DEG: effects of electrical fields and edge states

The breakdown of the quantum Hall effect in constricted GaAlAs heterostructures is studied. For constriction widths w > 100 microm very sharp resistance changes are observed. The influence of an additional external field, supplied with an in-plane gate, is to increase the breakdown current if the external field is applied parallel to the Hall field. A model calculation for a confined system of non-interacting electrons in a strong magnetic field and a Hall field shows characteristic features in the density of states which, however, cannot explain the experimental observations.

Master equation for two-photon transitions

The authors utilize Liouville-space and projection operator methods, introducing additional atomic projection operators, and derive master equations for an atom coupled to a radiation reservoir and to an additional external field via multi-photon interactions; the explicit forms of the equations are studied in detail for two-photon processes. The coupling coefficients of the equations are expressed in terms of effective operators for two-photon transitions. The expressions for the probability of transfer of coherence via two-photon transitions and for the dephasing due to elastic interactions with the reservoir are obtained quantum mechanically for the first time.

Internal field emission of microelectronic MIS structures

High field effects in special (ultraviolet (UV) treated, with graded-band-gap insulating layer multitips) MIS structures are considered. These structures have low interface barriers or high internal contact electric fields. A superposition of internal and additional external fields leads to a release of mobile ions, in particular protons. The dependence of the emission current on the properties of MIS structures and field strength are studied. The Poole-Frenkel mechanism is found to be responsible for the ionic component of the emission current. The parameters of this process have been determined. A new method for studying the kinetic characteristics of the internal electron emission taking into account carrier trapping processes has been developed. This technique makes it possible to determine the carrier effective masses as well as the interface barrier heights in MIS structures containing graded band-gap SiO x N y or other complex layers. The last part of the report is dedicated to field photoemission in MIS structures with emitter arrays containing tunnel-thin insulator films and a Schottky barrier. Along with Fowler-Nordheim photoemission, an anomalous photocurrent of the opposite polarity (infrared photocurrent) has been observed.

Internal field emission of microelectronic MIS structures

Abstract High field effects in special (ultraviolet (UV) treated, with graded-band-gap insulating layer multitips) MIS structures are considered. These structures have low interface barriers or high internal contact electric fields. A superposition of internal and additional external fields leads to a release of mobile ions, in particular protons. The dependence of the emission current on the properties of MIS structures and field strength are studied. The Poole-Frenkel mechanism is found to be responsible for the ionic component of the emission current. The parameters of this process have been determined. A new method for studying the kinetic characteristics of the internal electron emission taking into account carrier trapping processes has been developed. This technique makes it possible to determine the carrier effective masses as well as the interface barrier heights in MIS structures containing graded band-gap SiOxNy or other complex layers. The last part of the report is dedicated to field photoemission in MIS structures with emitter arrays containing tunnel-thin insulator films and a Schottky barrier. Along with Fowler-Nordheim photoemission, an anomalous photocurrent of the opposite polarity (infrared photocurrent) has been observed.

Investigation of solid surfaces by nuclear spin polarized alkali atoms

Nuclear spin polarized alkali atom beams are used to investigate metal surfaces. The surface diffusion of the alkali atoms on the surface results in a randomly fluctuating electric field gradient. The relaxation is measured in dependence of the surface temperature. Using an additional external RF field, also NMR measurement can be performed. Besides some fluctuating components of the EFG which cause the relaxation process, there is also a static part of the EFG. This results in an energy splitting of the nuclear spin states and can be detected by the NMR experiments.

Theory of Parametric Interactions in Semiconductors Under a Simultaneous Action of Two High-Power Electromagnetic Radiation Fields. I. Generalized Quantum Distribution Functions

The parametric excitation problem is considered for a semiconductor taken in the two-band model in which there exist resonant interband transitions due to an additional external high-intensity electromagnetic wave field with the frequency being in resonance with the band gap.In the first part of the investigation the basic Hamiltonian of the problem is obtained in the language of new quasi-particles arising from the interaction between the electrons and the interband resonant field. The so-called generalized quantum distribution functions of quasi-particles are introduced, the equations of motion for them are derived and solved using the formalism developed in [1].

Charged bose gas in astrophysics

We study theoretically a gas consisting of charged bosons (ions) over the flat dielectric surface at low temperatures and its tendency to form a state with a Bose-Einstein condensate. For the stability of a system, an additional external electric field, which keeps charges at the dielectric surface, is introduced. The formalism is developed in the framework of a self-consistent-field approach, which combines the quasiclassical description in terms of the Wigner distribution functions and the quantum-mechanical approach by employing the Gross-Pitaevskii equation. We predict a formation of the state with a Bose-Einstein condensate and determine the near-critical physical characteristics of the system. It is shown that the thermal and condensate components become spatially separated under these conditions. We discuss the limitations of the developed semiclassical approach and prospects for the pure quantum-mechanical treatment of the problem.