Electron Charging Research Articles

Optical investigation of the natural electron doping in thin MoS2 films deposited on dielectric substrates

Two-dimensional (2D) compounds provide unique building blocks for novel layered devices and hybrid photonic structures. However, large surface-to-volume ratio in thin films enhances the significance of surface interactions and charging effects requiring new understanding. Here we use micro-photoluminescence (PL) and ultrasonic force microscopy to explore the influence of the dielectric environment on optical properties of a few monolayer MoS2 films. PL spectra for MoS2 films deposited on SiO2 substrates are found to vary widely. This film-to-film variation is suppressed by additional capping of MoS2 with SiO2 and SixNy, improving mechanical coupling of MoS2 with surrounding dielectrics. We show that the observed PL non-uniformities are related to strong variation in the local electron charging of MoS2 films. In completely encapsulated films, negative charging is enhanced leading to uniform optical properties. Observed great sensitivity of optical characteristics of 2D films to surface interactions has important implications for optoelectronics applications of layered materials.

The characteristic of elongated Coulomb-blockade regions in a Si quantum-dot device coupled via asymmetric tunnel barriers

We investigate the peculiar electrical characteristics of Si quantum-dot devices coupled with asymmetric source/drain tunnel barriers. When the thick and thin tunnel barriers connect the quantum-dot to the source and drain, respectively, an elongated Coulomb-blockade region is created and enables a precise, reliable, and systematic control of both Coulomb-blockade oscillation and negative-differential-conductance oscillation by means of bias voltages. The distinctive phenomenon is attributed to the renormalization of the electron charging energy requirements for the Coulomb blockade. In-depth analyses on the transport characteristics and transport mechanisms are discussed.

Electron Excitation Memory Induced by Light Irradiation of Hydrogenated Si Nanocrystals Embedded in SiO2

We demonstrate an electron excitation effect in silicon nanocrystals (SiNCs) embedded in a SiO2 layer treated with hydrogen atoms for passivation of interface defects. Using electron spin resonance (ESR) measurements of quasi-conduction electrons (QCE) excited at lower temperatures, we observed the enhancement of the number of QCE in SiNCs by light irradiation. The electron excitation effect is retained at temperatures lower than 250 K after stopping the light irradiation. The dependence on the size of SiNCs and on excitation laser wavelength suggest that the main memory process is caused by photo-induced electron charging induced through electron excitation of interface states between SiNCs and SiO2.

Mechanism of Electronic Charging of Coal Mine Dust

The electronic charging of mine dust can cause coal-dust explosion and increase the risk of pneumoconiosis, so it is necessary to take more attention to the study of its electronic charging properties. The mechanism of electronic charging of coal mine dust was investigated in this paper. It was found that the formation and polarity of dust are determined by the energy band structure and of the two contacting sides; then a mathematical model of work function is established in mesoscopic level. The experiments conclude that the work function decreases with the particle size for the dust with same properties, moreover large particles are positively charged and small particles are negatively charged. Finally, the experimental verification of the main particles charged model drive unipolar and bipolar charged modes and confirm the correctness of microstructure and mesoscopic analyses, which furthermore lay the foundation for further research. DOI: http://dx.doi.org/10.11591/telkomnika.v11i9.3237

Electron interaction, charging, and screening at grain boundaries in graphene

Electronic, transport, and spin properties of grain boundaries (GBs) are investigated in electrostatically doped graphene at finite electron densities within the Hartree and Hubbard approximations. We demonstrate that depending on the character of the GBs, the states residing on them can have a metallic character with a zero group velocity or can be fully populated losing the ability to carry a current. These states show qualitatively different features in charge accumulation and spin polarization. We also demonstrate that the semiclassical Thomas-Fermi approach provides a satisfactory approximation to the calculated self-consistent potential. The conductance of GBs is reduced due to enhanced backscattering from this potential.

Design of a Single-Electron Memory Operating at Room Temperature

Single-electronic transistors (SETs) are considered as the attractive component for the next generation of transistors due to their ultrasmall size and low power consumption. Because SETs with single island cannot work at high temperature normally, more researchers begin to carry out research on the SETs with N-dimension multi-islands. In this paper, we introduce a new architecture of single-electron memory; ideally the memory should operate in combination of SETs with a nanowire of two-dimensional regular array of multiple tunnel junctions (MTJs). This structure is analyzed and studied with Monte Carlo simulator, SIMON. The Coulomb blockade effect and thermionic effect play an important role in carrier conduction in the system at room temperature. Nanowire MTJs are used as an electrometer to sense the memory-node charge. The well-defined parameter in tunnel junction circuits helps to obtain the charging of single electrons in these circuits at room temperature.

Consumer Contactless Transactions Using ARM9 Processor

Traditionally, mobile bills are paid either by cash, or credit/debit cards by standing in the queues at the operator’s showroom. Else it’s paid using some recharge coupons. This paper is a part of industrial project for users helping them to participate in value added services offered by mobile operators. Using their RFID tags, users can carry out transactions such as bill payments (postpaid), content downloads, recharge their prepaid connections, etc.., Mobile users can perform cash-less transactions. All this with easy-to-use, simple but intuitive touch of their handset to ‘target icons’. This solution with anytime, anywhere electronic talk time charging and bill payment in self service mode offers Mobile Network Operators a quantum leap in operational efficiency of their revenue assurance systems. It simplifies and speeds up day-to-day mobile transactions by their customers.

Plasma Damage Mechanism of Electron Beam Curing Process for Spin on Dielectrics

This letter presents the plasma damage mechanism of electron beam curing process for spin on dielectrics. Device damage is studied using the antenna gate metal-oxide-semiconductor field-effect transistor (MOSFET) in terms of the threshold voltage variation as a function of electron beam conditions such as ambient and cathode voltage. Threshold voltages of nMOSFET are decreased by an electron beam curing process without antenna ratio dependency. The electron energy and interlayer dielectric thickness between active devices and metal layers largely affect the variation of threshold voltage. From the experimental results, it is concluded that device damage induced by an electron beam curing process is characterized as radiation damage rather than electron charging damage. For the damage free electron beam curing process, it is essential to control the penetration depth of high-energy electrons by adjusting the cathode voltage while considering the dielectric thickness over active devices.

Secondary electron emission from lunar soil: Yields, energy distributions, and charging effects

We report the electron emission and charging of sub-mature lunar highland soil 61241 by electron impact under ultra-high vacuum for 40–2000eV electrons. The energy distribution of emitted secondary electrons was measured as a function of primary electron energy under neutral charging conditions, and electron energy loss spectroscopy was used to determine the ∼8eV band gap. Total electron yields were obtained with low electron fluxes. Imaging the soil with a Scanning Auger Microprobe using 10keV electrons revealed differential grain motion induced by charging in ultra-high vacuum.

Dynamic Trap Formation and Elimination in Colloidal Quantum Dots.

Using first-principles simulations on PbS and CdSe colloidal quantum dots, we find that surface defects form in response to electronic doping and charging of the nanoparticles. We show that electronic trap states in nanocrystals are dynamic entities, in contrast with the conventional picture wherein traps are viewed as stable electronic states that can be filled or emptied, but not created or destroyed. These traps arise from the formation or breaking of atomic dimers at the nanoparticle surface. The dimers' energy levels can reside within the bandgap, in which case a trap is formed. Fortunately, we are also able to identify a number of shallow-electron-affinity cations that stabilize the surface, working to counter dynamic trap formation and allowing for trap-free doping.

Formation and Characterization of Hybrid Nanodots Floating Gate for Optoelectronic Application

ABSTRACTWe have fabricated a hybrid nanodots floating gate (FG) in which Si quantum dots (QDs) and silicide nanodots (NDs) are stacked with a very thin SiO2 interlayer in order to satisfy both multiple valued capability and charge storage capacity for a sufficient memory window and to open up novel functionality for optoelectronic application. In electron charging and discharging characteristics measured with application of pulsed gate biases to MOS capacitors with a hybrid NDs FG, stepwise changes in the rates for electron injection and emission were revealed with increasing pulse width at room temperature. Also, nMOSFETs with a hybrid NDs FG show unique hysteresis with stepwise changes in the drain current - gate voltage characteristics. The observed characteristics can be interpreted in terms that the electron injection and storage into silicide-NDs proceed through the discrete charged states of Si-QDs. For MOS capacitors with a triple-stacked hybrid NDs FG fabricated by adding another Si-QDs, by subgap light irradiation from the back side of the Si substrate, a distinct infrared optical response in C-V characteristics was detected at room temperature. The result is attributable to the shift of charge centroid in the hybrid NDs FG as a result of transfer of photoexcited electrons from silicide NDs to Si-QDs.

The Research and Implementation of a Kind of Simulating Manual Electronic Charging Machine Tester

To solve the test problems of electronic charging machine, and to change the original test module based on artificial test. This paper described the research and implementation of a kind of electronic charging machine tester with an embedded system controlling step motor. The tester could imitate manual swiping and achieve swiping automatically. It used LCD and LED display technology, and could display the tester’s working condition and the number of swiping. The realization of this kind of tester will get rid of the original testing way of car charging machine and change the test method, meanwhile improving work efficiency.

Dust-acoustic shock waves in a charge varying electronegative magnetized dusty plasma with suprathermal electrons

The combined effects of an oblique magnetic field and electron suprathermality on weak dust-acoustic (DA) waves in a charge varying electronegative dusty plasmas with application to the Halley Comet are investigated. The correct suprathermal electron charging current is derived based on the orbit-motion limited approach. A weakly nonlinear analysis is carried out to derive a Korteweg-de Vries-Burger equation. The electron suprathermality, the obliqueness, and magnitude of the magnetic field are found to modify the dispersive properties of the DA shock structure. Our results may aid to explain and interpret the nonlinear oscillations that may occur in the Halley Comet plasma.

Radical versus Nucleophilic Mechanism of Formaldehyde Polymerization Catalyzed by (WO3)3 Clusters on Reduced or Stoichiometric TiO2(110)

(WO(3))(3) clusters deposited on the (110) rutile TiO(2) surface are excellent catalysts for the formaldehyde (CH(2)O) polymerization reaction (J. Phys. Chem. C 2010, 114, 17017). The present B3LYP study unravels the possible paths of this catalyzed reaction. According to the stoichiometry of the r-TiO(2) surface, the (WO(3))(3) clusters can be neutral, singly charged, or doubly charged. We find that only neutral (WO(3))(3) and anionic (WO(3))(3)(-) clusters are reactive toward CH(2)O molecules. In both cases it is possible to determine more than one mechanism on the basis of a nucleophilic attack of the formaldehyde O atom to the W ions of the cluster. The reaction proceeds through successive attacks of other CH(2)O molecules and the formation of acetal and polyacetal intermediates, which inhibits the chain propagation. Only in the case of the anionic (WO(3))(3)(-) catalyst is a totally different reaction path possible at low temperatures. This path involves the formation of radical species where the unpaired electron is localized on the organic moiety bound to the cluster. The polymer chain propagation follows a radical mechanism with low activation barriers. Thus, a cluster's electron charging speeds up the formaldehyde polymerization at low temperatures. On the basis of these unexpected results, we conclude that electron-rich supports and low working temperatures are the keys to kinetic control of the reaction favoring a fast radical chain propagation mechanism.

Periodic negative differential conductance in a single metallic nanocage

We report a bi-polar multiple periodic negative differential conductance (NDC) effect on a single cage-shaped Ru nanoparticle measured using scanning tunneling spectroscopy. This phenomenon is assigned to the unique multiply-connected cage architecture providing two (or more) defined routes for charge flow through the cage. This, in turn, promotes a self- gating effect, where electron charging of one route affects charge transport along a neighboring channel, yielding a series of periodic NDC peaks. This picture is established and analyzed here by a theoretical model.

Time-Dependent Scattering of Ultrathin Gold Film under Potential Perturbation

Shifts of the plasmon scattering band of ultrathin gold films under the effect of dynamic applied potential were studied in single wavelength measurements. The effect on scattering of applied potential was ascribed to electronic charging and discharging of the gold film. Scattering transients in response to square-wave potential modulation had an exponential form which depended on the potential step width, the modulation frequency and the nature of the ions. The presence of an AC signal component induced by ±10 mV potential modulated at 2 kHz indicated the capability of very thin gold film to respond to high frequency voltage.

Bursts of energetic electron induced large surface charging observed by Chang'E-1

A relationship between surface charging and bursts of energetic electron (BEE) event is presented in this paper. In a 200km lunar polar orbit, during quiet time, 0.1–2.0MeV BEE events were observed by High Energetic Particles Detectors (HPD) on board Chang'E-1, on December 22, 2007, when the spacecraft was within the inner terrestrial magnetosheath. At the same time, a large surface charging of ∼−5.4kV was observed by Chang'E-1, which was evidenced by increasing the ions energy observed by Solar Wind Ion Detectors (SWIDs). We found that the surface charging is strongly correlated with BEE events, and the potentials of spacecraft surface charging was experientially expressed as U≈3.6×10−5·fT (kV). The BEE events did occur in the solar wind, geomagnetic tail and magnetosheath alternately, whereas the surface charging during the BEE events is in the magnetosheath or transition region of boundaries. Though the observed surface charging was fewer than the BEE events, it is expected that the occurrence of the charging events caused by the bursts of energetic electrons should be more frequent than the Chang'E-1 observations. Meanwhile, the spacecraft charging indicates the lunar surface can be charged to negative kilovolt-scale by the BEE events even in quiet times.

H2O2-Mediated Oxidation of Zero-Valent Silver and Resultant Interactions among Silver Nanoparticles, Silver Ions, and Reactive Oxygen Species

The H(2)O(2)-mediated oxidation of silver nanoparticles (AgNPs) over a range of pH (3.0-14.0) is investigated here, and an electron charging-discharging model capable of describing the experimental results obtained is developed. AgNPs initially react with H(2)O(2) to form Ag(+) and superoxide, with these products subsequently reacting to reform AgNPs (in-situ-formed AgNPs) via an electron charging-discharging mechanism. Our experimental results show that the AgNP reactivity toward H(2)O(2) varies significantly with pH, with the variation at high pH (>10) due particularly to the differences in the reactivity of H(2)O(2) and its conjugate base HO(2)(-) with AgNPs whereas at lower pH (3-10) the pH dependence of H(2)O(2) decay is accounted for, at least in part, by the pH dependence of the rate of superoxide disproportionation. Our results further demonstrate that the in-situ-formed AgNPs resulting from the superoxide-mediated reduction of Ag(+) have a different size and reactivity compared to those of the citrate-stabilized particles initially present. The turnover frequency for AgNPs varies significantly with pH and is as high as 1776.0 min(-1) at pH 11.0, reducing to 144.2 min(-1) at pH 10.0 and 3.2 min(-1) at pH 3.0.

Dust ion-acoustic solitary waves in a dusty plasma with nonextensive electrons

The dust-modified ion-acoustic waves of Shukla and Silin are revisited within the theoretical framework of the Tsallis statistical mechanics. Nonextensivity may originate from correlation or long-range plasma interactions. Interestingly, we find that owing to electron nonextensivity, dust ion-acoustic (DIA) solitary waves may exhibit either compression or rarefaction. Our analysis is then extended to include self-consistent dust charge fluctuation. In this connection, the correct nonextensive electron charging current is rederived. The Korteweg-de Vries equation, as well as the Korteweg-de Vries-Burgers equation, is obtained, making use of the reductive perturbation method. The DIA waves are then analyzed for parameters corresponding to space dusty plasma situations.

Low voltage and variable-pressure scanning electron microscopy of fractured composites

Uncoated fracture surfaces of carbon–epoxy composites are investigated using a variable-pressure environmental scanning electron microscope (VP-ESEM), under optimized conditions for topographic description, image quality and sample preservation. Always using freeware or open source programs, parameters for low-voltage and low vacuum are stipulated with the support of Monte Carlo simulations combined to topographic measurements, tailoring the VP-ESEM setup for visualization of fine relief details. Based on topographic information from atomic force microscope (AFM) images, finest fracture steps were measured. These were the references to optimize and define boundaries for applied beam voltages and chamber pressures, restricted by the beam penetration depth and gas–electron interactions, guided by Monte Carlo simulations and signal-to-noise measurements. For VP mode, ideal chamber pressure was found around 30–40Pa at 3keV beam voltage and 6mm working distance. Lower pressures will cause noise due to electron charging and gas excess provokes resolution degradation and noise due to positive charging and electron beam scattering, raising the skirt radius. When a larger working distance is necessary, it can be compensated by adjusting the detector bias and the probe current, or even lowering chamber pressure, but the signal-to-noise ratio will certainly change. Monte Carlo simulations provided a good approach to optimize imaging conditions under low vacuum and low voltage for fractographic analysis of carbon–epoxy composites.