A new approach to the elastic tunneling current in metal-insulator-metal diodes

A new formulation of the elastic coherent tunneling current has been developed. Electron transport is described by quasifree electrons in the metals and by an effective one-particle barrier in the insulator. This phenomenological theory needs three parameters to characterize the barrier (barrier height φ, tunneling length s and an asymmetric parameter V_b). Four independent quantities containing these three parameters have been experimentally determined to check the consistency of this theory and an excellent agreement has been found. Finally, the theory is extended to a trapezoidal barrier explaining the experimental results obtained on AlIAl diodes.     

Scattering theory of Bardeen's formalism for tunneling: new approach to near-field microscopy

We propose a new theoretical approach to near-field microscopy, which allows one to deal with scanning tunneling microscopy and scanning near-field optical microscopy with a unified formalism. Under the approximation of weak tip-sample coupling, we show that Bardeen's perturbation formula, originally derived for electron tunneling, can be derived from a scattering formalism which extends its validity to electromagnetic vector fields. This result should find broad applications in near-field imaging and spectroscopy.     

A new approach to obtain the non-Condon factors in closed form for two one-dimensional harmonic oscillators

A simple algebraic approach to calculate general Franck-Condon overlaps is extended to evaluate non-Condon factors for two one-dimensional harmonic oscillators. The method is based on the use of eigenstates of the harmonic oscillator annihilation operator which allows to obtain in terms of a multi-dimensional Hermite polynomial the overlap of harmonic oscillator functions associated with different Born-Oppenheimer potentials. The presented approach is self-contained, only basic concepts of quantum mechanics associated with the harmonic oscillator system are needed. The obtained expression for the Franck-Condon overlaps is similar to the Ansbacher’s formula and equivalent to the one calculated by Malkin and Man’ko. However our final expression has the advantages that only real numbers are involved and it is straightforward to get the limit case of equal frequencies. Concerning the non-Condon factors two approaches leading to different formulas are considered, both of which reduce to triple sums of products of three Hermite polynomials.     

Diffusion in a symmetric bistable potential: A variational approach

An approximation procedure for the solution of stochastic nonlinear equations, which was derived from a variational principle in a previous paper, is applied to the problem of a particle that diffuses in a symmetric bistable potential starting from the point of unstable equilibrium. The second moment and variance for the particle's position are calculated as functions of the timet. Good agreement is found with results recently obtained by Baibuzet al. from an approximate evaluation of a path integral expression for the probability density.     

A theoretical approach to saturation effects in lasers

Exact numerical solution of a one-dimensional three-level lasing system (homogeneously broadened) is used to establish the relevance of spatially independent rate equations. It is shown that these equations can be applied not only for unsaturated lasing media but also for highly saturated media. However the loss term and the correlation term have to be modified.     

A new approach for dynamic modeling of widely tunable GCSR lasers

A new dynamic model is developed for simulating the widely tunable grating assisted codirectional coupler with rear sampled grating reflector （GCSR） lasers. The gain section of the device is calculated in timedomain using traveling-wave method, while the transmission spectrum of the coupler and the reflection spectrum of the reflector are firstly simulated in frequency-domain, and then transformed into time-domain via digital filter approach. Both static and dynamic performances based on this model agree well with the published results. Compared with previous works, this new model is more efficient and applicable, especially in the dynamic simulation.     

A new variational method to calculate escape rates in bistable systems

We apply the Rayleigh-Ritz variational principle to the inverse of the Smoluchowsky operator in order to calculate the lowest non-vanishing eigenvalue of the Smoluchowsky equation. In contrast to former variational calculations the new method is very insensitive to the choice of the test function. We obtain the asymptotic expansion of the eigenvalue in the limit of vanishing diffusion.     

Investigation of the performance and band-to-band tunneling effect of a new double-halo-doping carbon nanotube field-effect transistor

Carbon nanotube field-effect transistors (CNTFETs) can be fabricated with Ohmic- or Schottky-type contacts. We focus here on Ohmic CNTFETs. The CNTFETs suffer from band-to-band tunneling which in turn causes the ambipolar conduction. In this paper, to suppress the ambipolar behavior of CNTFETs and improve the performance of these devices, we have proposed application of symmetric double-halo (DH)-doping in CNTFETs. In this new structure, the source-side halo doping reduces the drain-induced barrier lowering (DIBL) and the drain-side halo reduces the band-to-band tunneling effect. Simulation results show in the DH-CNTFET, subthreshold swing below the 60 mV/decade conventional limit can be achieved. Also it decreases significantly the leakage current and drain conductance and increases on–off current ratio and voltage gain as compared to conventional CNTFET.     

理想气体压强公式的一种推导方法

本文从球形容器中理想气体入手，用一种简单易懂且不失一般性的方法，推导出理想气体压强公式。     

A new approach of binary addition and subtraction by non-linear material based switching technique

Here, we refer a new proposal of binary addition as well as subtraction in all-optical domain by exploitation of proper non-linear material-based switching technique. In this communication, the authors extend this technique for both adder and subtractor accommodating the spatial input encoding system.     

A new approximation method to obtain vibration eigenfunctions suitable for a new oscillator model

A new oscillator model has been proposed by introducing some modifications in the Morse potential function. Its efficacy is tested by taking a number of electronic states of diatomic molecules. For comparison the Hulbert-Hirschfelder model potential is also used. A new approximation method to find the vibrational eigenfunctions suitable for the new oscillator model has been reported. Langer’s method has been used to determine the wavefunctions. Franck-Condon factors andr-centroids are reported for the observed bands ofD ¹Π —X ¹Σ system of SnO molecule.     

Resonant tunneling in the fractional quantum Hall effect: superperiods and braiding statistics

We study theoretically resonant tunneling of composite fermions through their quasibound states around a fractional quantum Hall island, and find a rich set of possible transitions of the island state as a function of the magnetic field or the backgate voltage. These have possible relevance to a recent experimental study, and reveal many subtleties involved in deducing fractional braiding statistics.     

Resonant tunneling in truly axial symmetry Mn12 single-molecule magnets: sharp crossover between thermally assisted and pure quantum tunneling

Magnetization measurements of a truly axial symmetry molecular nanomagnet with a spin ground state of S = 10 show resonant tunneling. This compound has the same magnetic anisotropy as but the molecules are better isolated and the crystals have less disorder and a higher symmetry. Hysteresis loop measurements at several temperatures reveal a well-resolved step fine structure which is due to level crossings of excited states. All step positions can be modeled by a simple spin Hamiltonian. The results establish a sharp crossover between thermally assisted and pure quantum tunneling, as had been previously predicted.     

Stochastic resonance in bistable systems with nonlinear dissipation and multiplicative noise: A microscopic approach

We have studied the stochastic resonance (SR) of bistable systems coupled to a bath with a nonlinear system–bath interaction, by using the microscopic, generalized Caldeira–Leggett (CL) model. The adopted CL model yields the non-Markovian Langevin equation with nonlinear dissipation and state-dependent (multiplicative) diffusion which preserve the fluctuation–dissipation relation (FDR). Results of our simulations are given as follows: (1) the spectral power amplification (SPA) exhibits SR not only for a$a$ and b$b$ but also for τ$\tau$ while the stationary probability distribution function is independent of them where a$a$ and b$b$ denote magnitudes of multiplicative and additive noises, respectively, and τ$\tau$ expresses the relaxation time of Ornstein–Uhlenbeck (OU) colored noise; (2) the SPA for coexisting additive and multiplicative noises has a single-peak but two-peak structure as functions of a$a$, b$b$ and/or τ$\tau$. Results (1) and (2) are qualitatively different from previous ones obtained by phenomenological Langevin models where the FDR is not held or indefinite. These show an importance of the FDR in a study on SR of open bistable systems.     

A bistable, self-latching inverter by the monolithic integration of resonant tunnelling diode and high electron mobility transistor

This paper reports that the structures of AlGaAs/InGaAs high electron mobility transistor (HEMT) and AlAs/GaAs resonant tunnelling diode (RTD) are epitaxially grown by molecular beam epitaxy (MBE) in turn on a GaAs substrate. An Al_0.24Ga_0.76As chair barrier layer, which is grown adjacent to the top AlAs barrier, helps to reduce the valley current of RTD. The peak-to-valley current ratio of fabricated RTD is 4.8 and the transconductance for the 1-μm gate HEMT is 125mS/mm. A static inverter which consists of two RTDs and a HEMT is designed and fabricated. Unlike a conventional CMOS inverter, the novel inverter exhibits self-latching property.     

A green function approach to the relaxation time of phonon assisted tunneling

Although many elegant formulations of the phonon assisted tunneling problem have been given, the calculation of the relaxation time itself always has been based on the “golden rule”, which requires the artifice of a fictitious static field. In this communication the relaxation time is given by means of linear response theory, unitary transformations and an application of the Bogoliubov inequality. The artifice of a static field is no longer required.     

Waveguide holograms: A new approach to hologram integration

A new class of holography is proposed, in which (1) the evanescent part of a guided wave, or (2) the guided wave in a thin-film hologram is utilized as the reference wave and/or the illuminating one. The hologram was designated as “wave-guide hologram” and has advantages in the possibility of integration, wide field of view, and compactness and high reliability of the reconstructing system. The possibility of the waveguide hologram has been proved through reconstruction experiments with a guided wave of a waveguide hologram recorded with a plane reference wave.