Electron Charging Research Articles

A Korteweg–de Vries Burgers-like equation for weakly nonlinear dust ion-acoustic waves in a charge-varying dusty plasma with nonthermal electrons

A weakly nonlinear analysis is carried out to derive a Korteweg–de Vries Burgers-like equation for small but finite amplitude dust ion-acoustic (DIA) waves in a charge varying dusty plasma with non thermally distributed electrons. The correct expression for the nonthermal electron charging current is used. Interestingly, it may be noted that due to electron nonthermality and finite equilibrium ion streaming velocity, the present dusty plasma model can admit compressive as well as rarefactive DIA solitary waves. Furthermore, there may exist DIA shocks which have either monotonic or oscillatory behavior and the properties of which depend sensitively on the number of fast nonthermal electrons. Our results should be useful to understand the properties of localized DIA waves that may occur in space dusty plasmas.

Large-amplitude electrostatic solitary structures in dusty plasmas with vortex-like variable charge dust distribution and non-isothermal trapped electrons

AbstractThe recent analysis of large-amplitude solitary potentials in a charge varying dusty plasma with trapped dust particles (Tribeche, M. 2005 Phys. Plasmas12, 072304) is extended to include the electron trapping self-consistently. The non-isothermal trapped electron charging is investigated based on the orbit motion limited approach. It is found that the nonlinear localized potential structure enlarges when the electrons deviate from isothermality. The effect of this deviation is more significant under certain conditions. The dust particles are locally expelled and pushed out of the region of soliton localization as the electrons evolve far away from their thermodynamic equilibrium.

Superconductivity, antiferromagnetism and ferromagnetism in periodic table of D.I. Mendeleev

Definite regularity in the distribution of ferromagnetic, antiferromagnetic and superconducting elements is observed in the periodic table starting with the 4th period. Elements with superconductivity, by which d-shells start to fill up, are at the beginning of each period; then follow antiferromagnetics and ferromagnetics (in 4th period and lanthanides), or elements without any of the three listed order types (5th period and 6th period), in which the d (f)-shells continue to fill up almost exceedingly; then again appear superconductors by filling the p-shell up to the number is equal to 4. We calculated the radii of the external d (f)- and p-orbitals and the nearest to them orbitals with the Slater method. These trends were explained by distinction of degree of division of the external d (f)- or p-orbitals of the neighboring atoms in the crystal. Largest division occurs in ferromagnetics. In antiferromagnetics it is smaller than in ferromagnetics. It is demonstrated that in the superconducting crystals the external dor p-shells approach the nucleus of neighboring atoms are much closely those for ferromagnetic or antiferromagnetic crystals. Furthermore the external d- or p-shells of some elements in the 5th and 6th periods approach the deeper shells of neighboring atoms. Hence the electron in this shell is situated in neighboring atoms in a different electric field from its own. This fact is open to speculation that the separation of spin and charge in electron, disposed on the external d- or p-orbitals, is quite possible. The charges without spin become bosons. Spins that have the magnetic moments are ordered antiparallel in pairs. Magnetic field transfers this pair in a parallel state and a magnetic flux component along of magnetic field from the pair is equal to one fluxon (the quant of the magnetic flux).

Nonvolatile Thin Film Transistor Memory with Ferritin

The low-temperature polycrystalline silicon (poly-Si) thin film transistor (LTPS-TFT) flash memory is a potential candidate as a key component of the system on panel (SOP). We have proposed the “bio-nano-process” for the fabrication of nanodots by using biotechnology. In this study, we have successfully fabricated and developed a LTPS-TFT flash memory with biomineralized inorganic nanodots for the first time. High-density homogeneous nanodots were made to adsorb on a silicon film by using ferritin protein without the use of vacuum systems at high temperature. Electron charging and discharging in the dots were clearly confirmed from the transient behavior of the transfer curve at room temperature. This fabrication technique is promising for the development of a flash memory for a SOP.

Single electron charging in deterministically positioned InAs/InP quantum dots

We demonstrate precise control of electron charging within a single deterministically positioned InAs/InP quantum dot emitting in the telecommunications band around 1500 nm. Photolumine-scence emission as a function of vertical electric field is used to monitor the electron number within the dot. From Stark shift spectroscopy, we extract strength and orientation for the built-in dipole moment that suggests a uniform InAs dot composition and a configuration in which the electron lies above the hole at zero electric field. The scalable gating technology we employ to electrically contact individual prepositioned quantum dots promises arrays of initialized single spins that can be used for fiber-based quantum information applications.

Measurement of Electrostatic Latent Image on Photoconductors by Use of Electron Beam Probe

A novel method that makes possible the measurement of an electrostatic latent image on a photoconductor is proposed. An electrostatic latent image is formed by electron charging and by laser exposing of a photoconductor within a vacuum chamber. The electrostatic latent image is measured by detecting secondary electrons generated by the scanning of an electron beam probe. When a primary electron beam hits the photoconductor, secondary electrons are generated. Secondary electrons generated in a charged area travel to an electron detector. In contrast, secondary electrons generated in an exposed area are pulled back to the photoconductor, thereby decreasing the number of secondary electrons that reach the detector. The exposed and charged areas are determined in this way. The significant feature of this method is that the means of charging, exposing, and detecting are all incorporated in the same system, making real-time measurement possible. This method has good performance with high-resolution measurement on the order of microns.

Electron Charged States of Pt-silicide Nanodots as Evaluated by Using an AFM/Kelvin Probe Technique

Electron Charged States of Pt-silicide Nanodots as Evaluated by Using an AFM/Kelvin Probe Technique

On the effect of nuclear bridge modes on donor–acceptor electronic coupling in donor–bridge–acceptor molecules

We report a theoretical study of intra-molecular electronic coupling in a symmetric DBA (donor–bridge–acceptor) complex, in which a donor electronic site is coupled to an acceptor site by way of intervening orbitals of a molecular bridge unit. In the off-resonant (deep tunneling) regime of electronic transport, the lowest unoccupied molecular orbitals (MO’s) of the DBA system are split into distinguishable donor/acceptor and bridge orbitals. The effect of geometrical changes at the bridge on the donor/acceptor electronic energy manifold is studied for local stretching and bending modes. It is demonstrated that the energy splitting in the manifold of donor/acceptor unoccupied MOs changes in response to such changes, as assumed in simple McConnell-type models. Limitations of the simple models are revealed where the electronic charging of the bridge orbitals correlates with increasing donor/acceptor orbital energy splitting only for stretching but not for bending bridge modes.

Charging dynamics of discrete gold nanoparticle arrays self-assembled within a poly(styrene-b-4-vinylpyridine) diblock copolymer template

The kinetics of charging and discharging of charge carriers in a memory device based on gold nanoparticles in self-assembled block copolymer of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) has been studied. Hole trapping is observed to be more efficient than electron trapping and is attributed to a lower electron injection current (due to presence of Schottky barrier between the gold electrode and P4VP layer). At higher electric fields (>0.4 MV/cm), quasi-two-dimensional charge transport through the arrays of gold nanoparticles in P4VP nanodomains is observed. The contribution of electrode work function was demonstrated with improved electron charging by the replacement of gold electrode with aluminum.

Surface States and the Charge of a Dust Particle in a Plasma

We investigate electron and ion surface states of a negatively charged dust particle in a gas discharge and identify the charge of the particle with the electron surface density bound in the polarization-induced short-range part of the particle potential. On that scale, ions do not affect the charge. They are trapped in the shallow states of the Coulomb tail of the potential and act only as screening charges. Using orbital-motion limited electron charging fluxes and the particle temperature as an adjustable parameter, we obtain excellent agreement with experimental data.

Deep Dielectric Charging of Spacecraft Polymers by Energetic Protons

The majority of research in the field of spacecraft charging concentrates on electron charging effects with little discussion of charging by protons. For spacecraft orbiting in the traditional LEO and GEO environments, this emphasis on electrons is appropriate since energetic electrons are the dominant species. However, for spacecraft in orbits within the inner radiation belts, or for interplanetary and lunar space probes, proton charging effects may also be of concern. To examine bulk spacecraft charging effects in these environments, several typical highly insulating spacecraft polymers were exposed to energetic protons with energies from 1 to 10 MeV to simulate protons from the solar wind and from solar energetic proton events. Results indicate that effects in proton-charged dielectrics are distinctly different than those observed due to electron charging. In most cases, the positive surface potential continued to increase for periods on the order of minutes to a day, followed by long-time-scale decay at rates similar to those observed for electron charging. All samples charged to positive potentials, with substantially lower magnitudes than for equivalent electron fluence. Possible explanations for the different behavior of the measured surface potentials from proton irradiation are discussed; these are related to the evolving internal charge distribution from energy-dependent electron and proton transport, electron emission, charge migration due to dark current and radiation-induced conductivity, and electron capture by embedded protons.

Nonequilibrium aspects of armchair graphene nanoribbon conduction

Electron quantum transport is theoretically studied for finite-size armchair graphene nanoribbons biased within source and drain metallic electrodes, using an extended-Hückel-based Green's function coupled to a three-dimensional Poisson solver. The analysis evidences dynamic nonequilibrium electron charging phenomena that can affect the conduction mechanism by provoking electronic structure alterations. The origin of such process can be traced in a tracking relationship between the device's local density of states and the electrochemical potentials of the contacts. Such effect has no equivalent in the semiclassical limit.

Resistance Fluctuations and Aharonov–Bohm-Type Oscillations in Antidot Arrays in the Quantum Hall Regime

Resistance fluctuation phenomenon in antidot lattices in the quantum Hall regime are studied. Magnetoresistance of finite antidot array systems in the quantum Hall plateau transition regime exhibits two types of oscillatory effect. One is the aperiodic resistance fluctuations (RFs) and the other is the Aharonov-Bohm (AB)-type oscillations. Their dependences on the magnetic field and the gate voltage are quite distinct. While the aperiodic RFs are attributed to the complex evolution of the conducting network of compressible channels, the AB-type oscillations are interpreted in terms of edge states formed around individual antidots. The self-consistent screening effect is important for the both phenomenon, whereas, the single electron charging effect plays a minor role in the present case.

Sequential tunneling and inelastic cotunneling in nanoparticle arrays

We investigate transport in weakly coupled metal nanoparticle arrays, focusing on the regime where tunneling is competing with strong single electron charging effects. This competition gives rise to an interplay between two types of charge transport. In sequential tunneling, transport is dominated by independent electron hops from a particle to its nearest neighbor along the current path. In inelastic cotunneling, transport is dominated by cooperative multielectron hops that each go to the nearest neighbor but are synchronized to move charge over distances of several particles. In order to test how the temperature-dependent cotunnel distance affects the current-voltage (I-V) characteristics, we perform a series of systematic experiments on highly ordered close-packed nanoparticle arrays. The arrays consist of ∼5.5 nm diameter gold nanocrystals with tight size dispersion, spaced ∼1.7 nm apart by interdigitating shells of dodecanethiol ligands. We present I-V data for monolayer, bilayer, trilayer, and tetralayer arrays. For stacks 2–4 layers thick we compare in-plane measurements with data for vertical transport perpendicular to the array plane. Our results support a picture whereby transport inside the Coulomb blockade regime occurs by inelastic cotunneling, while sequential tunneling takes over at large bias above the global Coulomb blockade threshold Vt(T) and at high temperatures. For the smallest measurable voltages, our data was fitted well by recent predictions for the temperature dependence zero-bias conductance due to multiple cotunneling. At finite but small bias, the cotunnel distance is predicted to set the curvature of the nonlinear I-V characteristics, in good agreement with our data. The absence of significant magnetic-field dependence up to 10 T in the measured I-V characteristics further supports the picture of inelastic cotunneling events where individual electrons hop no further than the nearest neighbor. At large bias, above the global Coulomb blockade threshold, the I-V characteristics follow power-law behavior with temperature-independent exponent close to two, predicted for sequential tunneling along branching paths that optimize the overall charging energy cost.

Control of electronic charged states of Si-based quantum dots for floating gate application

Si quantum dots (QDs) individually charged with a few electrons or holes show characteristic potential profiles with a dimple around the center of the dot which can be interpreted in terms of Coulomb repulsion among the charges retained in the dot. By an introduction of Ge core in Si dots, holes can be well-confined in the Ge core while electrons are stored in the Si clad because of the energy band discontinuity at the interface between the Si clad and the Ge core. The influence of ionized impurity doping to Si-QDs on their electron charging and discharging characteristics has also been studied. For metal-oxide-semiconductor (MOS) capacitors and n-channel MOS field-effect-transistors (n-MOSFETs) with Si-QDs floating gates, distinct multiple-step charging to and discharging from the Si-QDs floating gate have been confirmed at room temperature, which are regulated presumably by redistribution of injected electrons in the Si-QDs floating gate for further electron injection and emission.

Impact of impurity doping into Si quantum dots with Ge core on their electrical charging characteristics

Si quantum dots (Si-QDs) with impurity doped Ge core were self-assembled on thermally-grown SiO 2 from thermal decomposition of alternately pure SiH 4 and GeH 4 diluted with He. δ-doping into the dots were carried out during Ge core formation. Changes in the surface potential caused by electron charging to and discharging from individual Si-QD with and without impurity doped Ge core were studied by using a Kelvin probe technique in atomic force microscopy (AFM). We have demonstrated that the biases applied to a tip for electron injection to and for extraction from dots are reduced appreciably by boron and phosphorus doping, respectively. Such bias reduction is interpreted in terms that a negatively charged state originated from ionized B acceptor(s) results from electron injection to the valence band and that a positively charged state due to ionized P donor(s) is caused by electron extraction from the conduction band. Because of a deep potential well for holes in the Ge core, Si-QDs with B-doped Ge core shows superior retention in positive charged state to coreless B-doped Si-QDs.

High Carrier Density and Capacitance in TiO2 Nanotube Arrays Induced by Electrochemical Doping

The paper describes the electronic charging and conducting properties of vertically oriented TiO 2 nanotube arrays formed by anodization of Ti foil samples. The resulting films, composed of vertically oriented nanotubes approximately 10 mum long, wall thickness 22 nm, and pore diameter 56 nm, are analyzed using impedance spectroscopy and cyclic voltammetry. Depending on the electrochemical conditions two rather different electronic behaviors are observed. Nanotube array samples in basic medium show behavior analogous to that of nanoparticulate TiO 2 films used in dye-sensitized solar cells: a chemical capacitance and electronic conductivity that increase exponentially with bias potential indicating a displacement of the Fermi level. Nanotube array samples in acidic medium, or samples in a basic medium submitted to a strong negative bias, exhibit a large increase in capacitance and conductivity indicating Fermi level pinning. The contrasting behaviors are ascribed to proton intercalation of the TiO 2. Our results suggest a route for controlling the electronic properties of the ordered metal-oxide nanostructures for their use in applications including supercapacitors, dye-sensitized solar cells, and gas sensing.

Ion beam synthesis and charge storage behavior of Au nanocrystals in thin SiO2 layers

Au nanocrystals (NCs) were synthesized in a thin SiO2 layer by ion implantation and annealing in a tight distribution close to the Si/SiO2 interface. Between the NCs and the Si substrate a thin tunneling oxide forms self-organized during annealing totally depleted from Au NCs. Memory behavior is demonstrated by electron charging and discharging on metal–oxide–semiconductor capacitors. Lenticular liquid Au:Si droplets nucleate at the Si/SiO2 interface from silicon regions supersaturated by Au close to the oxide. Au NCs embedded in SiO2 above these droplets are stabilized during annealing due to a modified detailed balance of Au atom detachment and attachment. Capacitance-voltage and spreading resistance measurements reveal the impact of the Au contamination in the Si substrate. Structure and distribution of Au droplets and NCs are characterized by x-ray diffraction and transmission electron microscopy.

Localized Charging Properties of Si Nanocrystals Embedded in a SiO2 Layer by Scanning Capacitance Microscopy

In this work, we characterized charging properties of silicon nanocrystals (NCs) using scanning capacitance microscopy (SCM). The size of the NCs produced by pyrolysis method is in the range of 10–50 nm with a density of around 1011/cm2. Using a conducting tip, a charge was injected directly into the NCs, and the charging characteristics of a NC were analyzed through the dC/dV–V curve shift and SCM images. Bias voltage stress to a NC cause the variation of capacitance due to the electron charging, which is reflected in SCM images. By measuring consecutive dC/dV–V curve shift after NC charging, we also analyzed retention characteristics of a NC. In temperature dependence experiment, NC reveals the characteristics of good chargeability at high temperature. Capacitance spectroscopy and related SCM images show that SCM can be an adequate tool for more detailed analysis of the charging and discharging effects of each NC.

Progress on Charge Distribution in Multiply-Stacked Si Quantum Dots/SiO2 Structure as Evaluated by AFM/KFM

Multiply-stacked structures of Si quantum dots (Si-QDs) in gate oxide are attracting much attention because of their potential importance to improve retention characteristics in a high density charge storage. In this work, we have fabricated 6-fold stacked Si-QDs with 2nm-thick SiO2 interlayers, whose areal dot density and average dot size were 5.7×1011cm-2 in each dot layer and -5nm in height, and studied progress on electron distribution in 6-fold stacked Si-QDs with 2nm-thick SiO2 interlayers from the measurements of temporal changes in the surface potential after electron charging and discharging locally at room temperature using an AFM/Kelvin probe technique in clean room air. First, by scanning an area of 2×2μm2 with the AFM tip biased at +3V with respect to the substrate in a tapping mode, the area was negatively charged due to electron injection from the substrate to the dot through the bottom tunnel oxide and subsequently, the central part of 100×100nm2 in the pre-charged area was scanned with the tip biased at -3V to emit the electrons from the Si-QDs to the substrate. As a result, the negative charging level was markedly reduced in the central part in comparison to its peripheral region. And then, the surface potential of the negatively-charged peripheral region was decay monotonously with time as a result of progressive electron tunneling to the substrate. In contrast to this, the temporal change in the surface potential of the central part shows that the electron charging proceeds with time until the surface potential becomes almost the same as that in the peripheral region. This result can be interpreted in terms of lateral spreading of electrons stored in the Si-QDs layer due to the potential difference between the central part and its peripheral region more negatively charged.