Repulsive Centers Research Articles

Relaxation features of own photoconductivity in p-GaSe single crystals

The effects of the electric field, temperature, and initial value of the dark resistivity on the relaxation processes of intrinsic photoconductivity in single crystals of gallium monoselenide (p-GaSe) are studied. It is shown that although in all the samples under study, in the processes of establishment and disappearance of photoconductivity, the process of attachment of nonequilibrium charge carriers by attracting and repulsive centers in weak and stronger electric fields is, accordingly, inevitable, however, in samples of high-resistivity crystals, it is also necessary to take into account the significant influence of random macroscopic defects caused by layering.

How Adsorbed Oxygen Atoms Inhibit Hydrogen Dissociation on Tungsten Surfaces.

Hydrogen molecules dissociate on clean W(110) surfaces. This reaction is progressively inhibited as the tungsten surface is precovered with oxygen. We use density functional theory and ab initio molecular dynamics to rationalize, at the atomic scale, the influence of the adsorbed O atoms on the H2 dissociation process. The reaction probability is calculated for kinetic energies below 300 meV and different O nominal coverages. We show that the adsorbed O atoms act as repulsive centers that modulate the dynamics of the impinging H2 molecules by closing dissociation pathways. In agreement with existing experimental information, H2 dissociation is absent for an O coverage of half a monolayer. The results show that the influence of O adsorbates on the dissociation dynamics on W(110) goes much beyond the blocking of possible H adsorption sites. Adsorbed O atoms create a sort of chemical shield at the surface that prevents further approach and dissociation of the H2 molecules.

Computer vision-based classification of concrete spall severity using metaheuristic-optimized Extreme Gradient Boosting Machine and Deep Convolutional Neural Network

This paper presents alternative solutions for classifying concrete spall severity based on computer vision approaches. Extreme Gradient Boosting Machine (XGBoost) and Deep Convolutional Neural Network (DCNN) are employed for categorizing image samples into two classes: shallow spall and deep spall. To delineate the properties of a concrete surface subject to spall, texture descriptors including local binary pattern, center symmetric local binary pattern, local ternary pattern, and attractive repulsive center symmetric local binary pattern (ARCS-LBP) are employed as feature extraction methods. In addition, the prediction performance of XGBoost is enhanced by Aquila optimizer metaheuristic. Meanwhile, DCNN is capable of performing image classification directly without the need for texture descriptors. Experimental results with a dataset containing real-world concrete surface images and 20 independent model evaluations point out that the XGBoost optimized by the Aquila metaheuristic and used with ARCS-LBP has achieved an outstanding classification performance with a classification accuracy rate of roughly 99%.

Electronic and optical properties of an electro-magnetic non-uniform narrow quantum ring under repulsive scattering centre

ABSTRACT Non-uniform height semiconductor quantum rings are studied in order to determine their electronic and optical absorption properties. Theoretical modelling of the structure includes an analytical description of the non-regular multi-hilled confining potential as well as the presence of repulsive scattering centre and external crossing electric and magnetic fields. We have discussed the features of localised and extended (rotational, Aharonov–Bohm-like) states in the presence of the magnetic field. A modification of the spectrum, with the appearance of a Stark-like behaviour, and its corresponding modification related to the repulsive potential is analysed when the electric field effect is considered. In double-hilled structures, these properties of the energy spectrum are of main importance in explaining the apparent optical transparency induced within a certain range of the electric field strength. The presence of the repulsive centre is found to cause a moderate redshift of the light absorption response.

Zwitterion membranes for selective cation separation via electrodialysis

Lithium extraction from saline water by electrodialysis is an energy-efficient process. Herein, we examined a synergetic impact of amino isophthalic acid (AIPA) and the fixed quaternized groups to produce stable, cost-effective, and efficient zwitterion membranes (ZIMs) via a sol-gel process. We developed different membranes such as QAIPA-10, QAIPA-15, and QAIPA-20 by varying the amount of AIPA from 10 to 20 wt% in the base membrane. It was found that when the amount of AIPA increases, the Li+ flux also improved from 1.66 × 10−10 mol cm−2 s−1 to 33.46 × 10−10 mol cm−2 s−1, respectively. By comparing the membranes based on the various amounts of AIPA, the membrane with 20 wt% (QAIPA-20) had a higher Li+ flux and reasonable permselectivity due to the high WU, CEC as compared with the QAIPA-10, QAIPA-15 and base membranes. To further explore the performance of the QAIPA-20, we also studied various cation systems such as Na+/Mg2+, K+/Mg2+, and H+/Fe2+, respectively. The obtained results proved that AIPA strongly dictates the cation transport channels, hydrophilicity, and repulsive centers of the ZIMs. We may conclude that QAIPA-20 is effective for lithium extraction, water desalination, and acid recovery.

Channel hot carrier induced volatile oxide traps responsible for random telegraph signals in submicron pMOSFETs

The effect of channel hot carrier stress has been investigated in pMOSFETs with respect to channel hole trapping by the gate oxide traps and the resultant Random Telegraph Signals (RTS) observed at the output. Process- and stress- induced oxide traps have been identified through RTS measurements. These traps are believed to be E′ centers, acting as hole-attractive or repulsive centers, causing RTS through correlated carrier number and mobility fluctuations. Generation of E′ centers as well as activation of the passivated oxide defects as a result of stress are thought to be the reasons behind observing the stress-induced RTS. Two of the observed defects: one process-induced and one stress-induced trap have disappeared and reappeared randomly with stress. We report the reaction of the defects with hydrogen to be responsible for the volatile nature of the traps. Hydrogen is either bound to the Si/SiO2 interface or trapped at the oxide defects. Applying the stress releases these hydrogen species, which then drift towards the gate through the oxide layer and react with the oxide defects to passivate them. Reaction with another hydrogen de-passivates the defect releasing H2. This is the first article that reports hydrogen to deactivate and reactivate oxide traps responsible for RTS.

Two Types of <inline-formula> <tex-math notation="LaTeX">${E}^{\prime}$ </tex-math> </inline-formula> Centers as Gate Oxide Defects Responsible for Hole Trapping and Random Telegraph Signals in pMOSFETs

We report on the investigation of random telegraph signals (RTSs) in pMOSFETs at variable temperatures to identify and characterize the hole traps residing at the oxide–semiconductor interface. Attractive center defects as well as a repulsive center defect are identified with trap location, capture cross section, remote Coulomb scattering coefficient, capture barrier energy, trap binding enthalpy, relaxation energy, and change in entropy with hole emission. The attractive centers responsible for RTS were a pair of dissociated three-coordinated silicon (D-III-Si) defects while the repulsive center was identified as a puckered/back-projected oxygen vacancy defect, [a pair of under-coordinated silicon (III-Si) and over-coordinated oxygen (III-O) defects]. Both contain ${E}\gamma ^{\prime }$ centers. This is the first time when such detailed analysis is reported on the hole traps in SiO2 which are responsible for RTS.

Qualitative and Numerical Analysis of a Cosmological Model Based on an Asymmetric Scalar Doublet with Minimal Couplings. I. Qualitative Analysis of the Model

A qualitative analysis of a cosmological model based on the asymmetric scalar doublet classical + phantom scalar field with minimal interaction is performed. It is shown that depending on the parameters of the model, the corresponding dynamical system can have 1, 3, or 9 stationary points corresponding to attractive or repulsive centers (1--5) and saddle points (0--4). A physical analysis of the model is performed.

Photodetachment dynamics near an attractive Coulomb center

We consider the photodetachment of a single-charged anion near an attractive Coulomb center. The photoelectron dynamics is analyzed in detail by following the classical trajectories and using semiclassical methods. Both the geometry of the trajectories and the caustics are shown to be different from those in the photodetachment dynamics near a repulsive Coulomb center. Based on semiclassical methods, the corresponding quantum interferences in both differential and total cross sections are calculated and discussed with respect to an anion in either an s-symmetry or a p-symmetry state before photodetachment. The total photodetachment cross sections of the present system are compared with those near a repulsive Coulomb center and in a uniform electric field.

Force field analysis suggests a lowering of diffusion barriers in atomic manipulation due to presence of STM tip.

We study the physics of atomic manipulation of CO on a Cu(111) surface by combined scanning tunneling microscopy and atomic force microscopy at liquid helium temperatures. In atomic manipulation, an adsorbed atom or molecule is arranged on the surface using the interaction of the adsorbate with substrate and tip. While previous experiments are consistent with a linear superposition model of tip and substrate forces, we find that the force threshold depends on the force field of the tip. Here, we use carbon monoxide front atom identification (COFI) to characterize the tip's force field. Tips that show COFI profiles with an attractive center can manipulate CO in any direction while tips with a repulsive center can only manipulate in certain directions. The force thresholds are independent of bias voltage in a range from 1 to 10mV and independent of temperature in a range of 4.5 to 7.5K.

Rate constant of capture of electron charge carriers on a screened repulsive center

The rate constant of capture of electron charge carriers on a screened repulsive center are performed. Approximate expressions for the potential barrier width, the capture cross section, and rate constant are derived. It is shown that the increase in the concentration of free charge carriers in silver azide from 1016 to 1020 cm−3 results in an increase in the capture rate constant by four orders of magnitude. It is also shown that, with increasing concentration of free carriers, the temperature dependence of the rate constant weakens and the effective activation energy of capture in silver azide decreases from 0.18 to 0.01 eV.

Defect assessment and leakage control in Ge junctions

In this work, the temperature behavior of the transport mechanisms present in Ge p+n junctions selectively grown in shallow trench isolation (STI) substrates is investigated. Special attention is given to the impact of electrically active defects on the current–voltage (I–V) and capacitance–voltage (C–V) characteristics. Moreover, deep level transient spectroscopy (DLTS) is performed in order to evaluate the electrical properties of the traps. The results show that the presence of threading dislocations and associated deep acceptors has a marked impact on the electrical characteristics. The DLTS response seems to be related to electron repulsive centers with an acceptor character located at ∼0.33–0.40eV below the conduction band. This mid-gap position yields very effective Shockley–Read–Hall centers and can explain the generation lifetime reduction and leakage increase observed in non-annealed Ge in STI Si diodes.

Photodetachment near a repulsive center: Closed-orbit theory for the total cross section

The total photodetachment cross section of a negative ion near a repulsive center is studied based on the closed-orbit theory. An analytical expression, written as a product of the zero-field photodetachment cross section and a modulation function, is obtained for energy above and below threshold. The expression also incorporates the different wave sources produced by different negative ions. The present results are shown to be accurate by comparing with quantum calculations based on the exact Coulomb Green's function. We also compared the photodetachment cross section near a repulsive center with that in a homogeneous electric field and found interesting connections between the two.

Electric Field Control of the Photodetachment of H− Ion near a Repulsive Center

The influence of electric field on the photodetachment of H− ion near a repulsive center is investigated for the first time. The classical motion of the detached electron has been studied and the photodetachment cross section has been derived. It is found that the electric field has significant effect on the photodetachment of H− ion near a repulsive center. If the electric field is put upward, the electric field force acting on the detached electron has an opposite direction with the Coulomb repulsive force. Under this condition, the motion of the detached electron is relatively complex. Both the number of the closed orbits and the oscillating structure of the photodetachment cross section depend on the electric field strength. If the electric field is put downward, the electric field force acting on the detached electron has the same direction with the Coulomb repulsive force. Under this circumstance, the electric field can always strengthen the oscillation in the photodetachment cross section. Therefor...

Photodetachment of H− ion near two repulsive centers

Based on a theoretical model for the photodetachment of negative ion near a repulsive center, we study the photodetachment of H− ion near two repulsive centers. Using the semiclassical closed orbit theory, we study the classical motion of the detached electron and calculate the photodetachment cross section of H− ion near two repulsive centers. It is found that the repulsive centers have significant effects on the photodetachment of H− ion. The photodetachment cross section of our system is strongly oscillatory compared to the photodetachment near one repulsive center. The calculation results suggest: if one repulsive center is kept fixed, with the decrease of the distance between two repulsive centers, the oscillating amplitude in the cross section becomes enlarged and the photodetachment cross section exhibits a multi-periodic oscillatory structure. In order to show the correspondence between the oscillation in the photodetachment cross section and the detached electron's classical closed orbits clearly, we make a Fourier transformation for the scaled photodetachment cross section of this system. Each peak in the Fourier transformed cross section corresponds to the scaled action of one closed orbit. We hope that our study will be useful in directing the future experimental research of the photodetachment processes of multiply charged anions.

Spatial interferences of photodetachment near a repulsive center

We study the detached-electron flux distributions from the photodetachment of a negative ion near a repulsive center. Using a semiclassical approach, we calculate the electron flux on spherical detectors with various radii. The classically allowed angular range of the interference patterns on the spherical screen increases as the detached-electron energy is increased. In the classically allowed range, we find that there are always two trajectories going from the negative ion to the observation point on the screen, inducing quantum interference patterns. We have also extended the formulas into the tunneling region. The interference patterns also reflect the quantum angular distribution of electrons leaving the ion. A scaling property for the detached-electron flux is investigated. The accuracy of our semiclassical formulas is established by comparison with a quantum treatment using the exact Coulomb Green's function.

Vortex kinks in superconducting films with periodically modulated thickness

We report magnetoresistance measurements in Nb films having a periodic thickness modulation. The cylinder shaped thicker regions of the sample, which form a square lattice, act as repulsive centers for the superconducting vortices. For low driving currents along one of the axes of the square lattice, the resistivity ρ increases monotonously with increasing magnetic field B and the ρ–B characteristics are approximately piecewise linear. The linear ρ versus B segments change their slope at matching fields where the number of vortices is an integer or a half integer times the number of protruding cylinders in the sample. Numerical simulations allow us to associate the different segments of linear magnetoresistance to different vortex-flow regimes, some of which are dominated by the propagation of discommensurations (kinks).

Influence of periodically propagating impurity and accompanying time variation of impurity spread on excitation profile of doped quantum dots

We investigate the excitation behavior of a repulsive impurity-doped quantum dot induced by the simultaneous oscillations of the impurity coordinate and spatial stretch of the impurity domain. We have considered repulsive Gaussian impurity centers. The ratio of two oscillations (η) has been exploited to understand the nature of the excitation rate. Indeed, it has been found that the said ratio could orchestrate the excitation in a most elegant way. In conjunction with the ratio, the dopant location also plays some important role towards modulating the excitation rate. The present study also indicates attainment of stabilization in the excitation rate as soon as η exceeds a threshold value irrespective of the dopant location. Moreover, prior to the onset of stabilization, we also envisage maximization/minimization in the excitation rate at some typical η values depending on the dopant location. The critical dissection of the characteristics of various impurity parameters provides important insight into the physics underlying the excitation process.

Separation of suspended particles in microfluidic systems by directional locking in periodic fields

We investigate the transport and separation of overdamped particles under the action of a uniform external force in a two-dimensional periodic energy landscape. Exact results are obtained for the deterministic transport in a square lattice of parabolic, repulsive centers that correspond to a piecewise-continuous linear-force model. The trajectories are periodic and commensurate with the obstacle lattice and exhibit phase-locking behavior in that the particle moves at the same average migration angle for a range of orientation of the external force. The migration angle as a function of the orientation of the external force has a Devil's staircase structure. The first transition in the migration angle was analyzed in terms of a Poincare map, showing that it corresponds to a tangent bifurcation. Numerical results show that the limiting behavior for impenetrable obstacles is equivalent to the high Peclet number limit in the case of transport of particles in a periodic pattern of solid obstacles. Finally, we show how separation occurs in these systems depending on the properties of the particles.

Information entropy and level-spacing distribution based signatures of quantum chaos in electron doped 2D single carrier quantum dots

Information entropy and level-spacing distribution in single carrier two-dimensional quantum dots are analyzed as functions of the location of a repulsive impurity centre and the strength of its interaction with the carrier electron. Quantum adiabatic switching is used to monitor the transition to quantum chaos with two different choices of the unperturbed hamiltonian.