Charge Buildup Research Articles

The murburn precepts for photoreception

Murburn concept is a redox mechanistic scheme involving interactive equilibriums of discretized or organized protein/substrate molecules, unbound ions and radicals (or reactive species); which may afford selective/specific electron transfers, particularly at phospholipid interfaces. Earlier, we have applied murburn concept to provide thermodynamically and kinetically viable explana-tions for various physiological/bioenergetic routines like xenobiotic metabolism, unusual dose responses, aerobic respiration, thermogenesis, homeostasis, trans-membrane potential, oxygenic photosynthesis, etc. While proposing the murburn model for photophosphorylation, we had projected that the murburn mechanism could also be relevant for photoreception physiology. Herein, we expand on this aspect and present the basic scheme and evidence in support of the murburn model of photorecep-tion, with retinal/opsin as the salient photon-impingement response-transducing element. In alignment with our earlier murburn schemes, we propose that diffusible reactive oxygen species (DROS, as exemplified by superoxide, which is currently deemed a toxic product of all-trans retinal and NADPH oxidase interactions) is produced in rod/cone cells upon photoactivation and it plays a crucial role in the visual cycle. This is supported by several facts: (i) Layers of photoreceptive neural cells precede the rod/cone cells (with respect to the presentation to oncoming light ray/photon), (ii) There exists high oxygen demand in the retina, (iii) Copious DROS are detected in functional retina, (iv) NAD(P)H/reductase is involved in the cycle, and (v) Events occur at sub-micrometer dimensioned phospholipid disks stacked to stabilize DROS and minimize free protons (quite like the thylakoids that harbor carotenoids in chloroplasts and cyanobacteria). In the new scheme, photo-electric activation leads to charge sepa-ration and hyperpolarization in rod/cone cells due to negative charge build-up. This electro-chemical signaling serves as the front-runner to trigger an action potential relay along a neuron and the superoxide mediated phosphorylation of GDP bound to transducin serves as the initiator of signal transduction cascade. The newly proposed scheme allows a simple electrical connec-tivity of the retina-photoreceptors with the brain via the optic nerve, is anatomically correlated with the structure and resolution of the retina, and is kinetically viable.

Experimental Study of Flood Gun

Using the flood gun is a common and effective way to eliminate the charge buildup, which is mainly used in electron optics based devices such as CD-SEM, X-Ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), Secondary Ion Mass Spectrometry (SIMS), Electron Probe Micro Analysis (EPMA) and Ion Implanter. The characteristics of the beam play a decisive role in eliminating the effect of charge buildup, which directly determines the effect of using the related equipment. It is difficult to measure accurately and comprehensively the performance of the beam by using the current testing methods for the flood gun. In this paper, a method for measuring beam spot by using a Faraday cup aperture is proposed, and a test system is set up based on this method. Experiments on this test system have successfully achieved accurate and comprehensive measurement of the beam spot performance. The in-depth analysis of the beam spot performance has a guiding significance for the optimization of structural design and installation of the flood gun. At the same time, it contributes to the prediction of the experiment.

Numerical Simulation of Spacecraft Charging Attributed to Ionospheric Plasma in Polar and Equatorial Environment

The presence of spacecraft in ionospheric plasma can change plasma properties, vice versa plasma can lead to charge buildup on spacecraft. The level of charging, through electric potential of spacecraft, initially depends on plasma density. However, simulations done on four LEO satellites, i.e. ERS 1, MIDORI, ASCA and FUSE 1, showed that charging level depends on plasma electron temperature rather than plasma density which satisfied the Boltzmann’s relation in the absence of high-energy electrons from aurora. The higher the plasma electron temperature the more spacecraft exposed to negative charging. It is assumed that plasma ions and electrons are collisionless or in Maxwellian distribution. It is found that there is no strong relation between density and charging level. Furthermore, there exists insignificant different of charging between polar and equatorial satellites. It means that the placement of satellite in polar or equatorial region, as long as the presence of auroral electrons is excluded, will suffer similar level of charging which is less than 5V (negative). Since spacecraft are exposed to negative charge, electric field generated by spacecraft potential, together with mesothermal motion effects, deflects ion trajectory into donwstream region leading to ion void region. The ion density is reduced compared to electron density, but there is no significant different of ion void feature between polar and equatorial satellites.and capacity building of beneficiaries.

XPS guide: Charge neutralization and binding energy referencing for insulating samples

This guide deals with methods to control surface charging during XPS analysis of insulating samples and approaches to extracting useful binding energy information. The guide summarizes the causes of surface charging, how to recognize when it occurs, approaches to minimize charge buildup, and methods used to adjust or correct XPS photoelectron binding energies when charge control systems are used. There are multiple ways to control surface charge buildup during XPS measurements, and examples of systems on advanced XPS instruments are described. There is no single, simple, and foolproof way to extract binding energies on insulating material, but advantages and limitations of several approaches are described. Because of the variety of approaches and limitations of each, it is critical for researchers to accurately describe the procedures that have been applied in research reports and publications.

Prevention of copper corrosion on post-FIB wet stained sample using UV charge-neutralization method

This paper presents the study of various charge neutralization methods to prevent copper corrosion on post-FIB wet stained sample. Conventional fast and economic wet staining on post-FIB copper processed sample can sometimes cause unwanted artifact such as copper corrosion due to build-up of charges on non-grounded, long copper interconnect structures during FIB milling. Some charge neutralization methods such as probe-pin grounding, conductive paint application and UV treatment were investigated on an ET structure. The recommended method, using UV treatment, is applied to the die area on a bulk Si wafer and on a SOI (Si-on-insulator) wafer to compare the effect of this method in preventing the copper corrosion effect.

Triboelectric charging of polyethylene powders: Comparison of same-material and different-material contributions to the charge build-up

The understanding of triboelectric charging of industrially important powders can help in avoiding or controlling the particle agglomeration and wall sheeting. We developed a new experimental approach to study both same-material particle-particle (PP) and different-material particle-wall (PW) charging of nascent polyethylene (PE) particles born by catalytic polymerization. We constructed a simple tribocharger consisting of a metal box divided inside into several compartments filled with the PE sample and attached to the vibration shaker. The particle charge distribution was characterized by a self-constructed electrostatic separator. This way, we investigated the charging dynamics of PE particles colliding with other PE particles as well as with metal walls of the box compartments. Both PP and PW charging were measured either separately, or in sequence, and in combination of simultaneous PP and PW. The different-material PW charging produced unipolarly charged particles and was much faster than the same-material PP charging leading to bipolar particle charge distribution.

Electrostatic charge generation on material surfaces from the evaporation of liquids

Electrostatic charging is a ubiquitous but poorly understood phenomenon. One of the difficulties with studying electrostatics is separating the different types of charging (triboelectric, inductive, or gas phase ion adsorption). We constructed an experiment to test how liquid film evaporation affects the charge on an insulator surface. Our results showed that when a liquid evaporates in an electric field, it leaves a charge on the substrate surface. It was also determined that the magnitude and polarity of the charge depends on the local electrostatic potential of the substrate and sufficient charge buildup leads to a dielectric breakdown of air, a potential source of hazardous sparks. We reveal through careful experiments that the charge is transferred via induction from electrical ground through the liquid film and onto the substrate's surface. Ambient fields were shown to be able to cause this type of charging, suggesting that failing to account for this phenomenon may explain the lack of reproducibility in previous electrostatic charging studies.

Ionizing-Radiation Response and Low-Frequency Noise of 28-nm MOSFETs at Ultrahigh Doses

Total ionizing dose (TID) mechanisms are investigated in 28-nm MOSFETs via dc static and low-frequency noise measurements. nMOSFETs and pMOSFETs are irradiated up to 1 Grad(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and annealed at high temperatures. TID sensitivity depends on the channel length, the channel width, and the bias condition. Halo implantations improve the radiation tolerance of shorter-channel transistors. Worst case bias for TID-induced degradation is found with high electric field applied to the gate during irradiation, due to increased charge trapping in the upper corner of the shallow trench isolation (STI) and in the gate oxide. DC and low-frequency noise measurements show that, at doses up to ~100 Mrad(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), radiation-induced degradation is primarily due to the positive charge buildup in the STI oxides. At ultrahigh doses approaching 1 Grad(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), TID degradation is influenced by charge buildup in the gate oxide and traps at or near the gate/dielectric interface and/or along the STI sidewalls. Worst case degradation is found in narrower and longer-channel devices, due to the enhanced charge buildup in the STI oxide and along its interfaces.

Comparison of plasma-enhanced kinetics between floating and grounded states

There are increasing evidences that charges should make nanoparticles liquid-like or enhance diffusion in nanoparticles. Considering these, there is a possibility that plasma enhanced dewetting, which had been attributed to the bombardments of high energy electrons or ions, should be attributed to charges. In order to clarify whether plasma enhanced kinetics come from bombardments of electrons or ions or from the charge buildup, two series of experiments were made. One is the comparison of dewetting kinetics of Sn and Au films in the inductively-coupled plasma between floating and grounded states. The other is the comparison of recrystallization kinetics of the Fe-1%Si sheet sample in the inductively-coupled plasma between floating and grounded states. Both dewetting and recrystallization kinetics were much more enhanced in the floating state than in the grounded state. These results show that the charge buildup is responsible for the plasma enhanced kinetics.

Water Poisons H2 Activation at the Au-TiO2 Interface by Slowing Proton and Electron Transfer between Au and Titania.

Understanding the dynamic changes at the active site during catalysis is a fundamental challenge that promises to improve catalytic properties. While performing Arrhenius studies during H2 oxidation over Au/TiO2 catalysts, we found different apparent activation energies (Eapp) depending on the feedwater pressure. This is partially attributed to changing numbers of metal-support interface (MSI) sites as water coverage changes with temperature. Constant water coverage studies showed two kinetic regimes: fast heterolytic H2 activation directly at the MSI (Eapp ∼ 25 kJ/mol) and significantly slower heterolytic H2 activation mediated by water (Eapp ∼ 45 kJ/mol). The two regimes had significantly different kinetics, suggesting a complicated mechanism of water poisoning. Density functional theory (DFT) showed water has minor effects on the reaction thermodynamics, primarily attributable to intrinsic differences in surface reactivity of different Au sites in the DFT model. The DFT model suggested significant surface restructuring of the TiO2 support during heterolytic H2 adsorption; evidence for this phenomenon was observed during in situ infrared spectroscopy experiments. A monolayer of water on the hydroxylated TiO2 surface increased the H2 dissociation activation barrier by ∼0.2 eV, in good agreement the difference in experimentally measured values. DFT calculations suggested H2 activation goes through a proton-coupled electron-transfer-like mechanism. During proton transfer to a basic support hydroxyl group, electron density is distributed through the gold nanorod and partially localized on the protonated support hydroxyl group. Water slows H2 activation by slowing this H+ transfer, forcing negative charge buildup on the Au and increasing the transition state energy.

Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction

Organic photovoltaic (OPV) efficiencies continue to rise, raising their prospects for solar energy conversion. However, researchers have long considered how to suppress the loss of free carriers by recombination-poor diffusion and significant Coulombic attraction can cause electrons and holes to encounter each other at interfaces close to where they were photogenerated. Using femtosecond transient spectroscopies, we report the nanosecond grow-in of a large transient Stark effect, caused by nanoscale electric fields of ∼487 kV/cm between photogenerated free carriers in the device active layer. We find that particular morphologies of the active layer lead to an energetic cascade for charge carriers, suppressing pathways to recombination, which is ∼2000 times less than predicted by Langevin theory. This in turn leads to the buildup of electric charge in donor and acceptor domains-away from the interface-resistant to bimolecular recombination. Interestingly, this signal is only experimentally obvious in thick films due to the different scaling of electroabsorption and photoinduced absorption signals in transient absorption spectroscopy. Rather than inhibiting device performance, we show that devices up to 600 nm thick maintain efficiencies of >8% because domains can afford much higher carrier densities. These observations suggest that with particular nanoscale morphologies the bulk heterojunction can go beyond its established role in charge photogeneration and can act as a capacitor, where adjacent free charges are held away from the interface and can be protected from bimolecular recombination.

Simulating of charge build-up in irradiated MOS/SOI transistors

The charge build-up in the interface of silicon / buried oxide in n-channel MOS/SOI transistors depending on their geometric parameters and electrical modes during ionizing irradiation is calculated with the use of the software Silvaco. It is shown that the electrical mode is most “harsh”, when during irradiation the voltage of +5 V is applied to drain and source electrodes and 0 V is applied to substrate, gate and channel feeding. The amount of the built-up charge can be substantially reduced by applying a negative bias to the substrate and by decreasing the thickness of the buried oxide layer.

An air-stable anionic two-dimensional semiconducting metal-thiolate network and its exfoliation into ultrathin few-layer nanosheets.

The black, small-bandgap semiconducting framework Eu-dfdmat features extensive Eu3+-sulfur bridges from the linear linker 2,5-difluoro-3,6-dimercaptoterephthalate (dfdmt). Each Eu center is chelated to four dfdmt linkers to form an anionic coordination sphere involving four carboxyl O and four mercapto S centers (EuO4S4), wherein the charge buildup can be alleviated by the electron-withdrawing fluoro groups. The extensive metal-linker bonding, together with a trace of Eu2+ species, appears to boost electronic interaction in the 2D net, generating a small band gap of 1.31 eV (946 nm), albeit a modest conductivity (e.g., 10-6 S m-1). The crystals also exhibit persistent EPR signals indicative of organic radicals (g = 2.002). The Eu-dfdmt solid are stable in air and can be exfoliated into ultrathin nanosheets (ca. 5 nm; 6-8 layers).

A quantitative study of ion guiding between two glass plates

SynopsisThe transmission of a 1 keV Ar+ beam between two glass plates was studied. We present experimental data with the goal to provide quantitative information about the buildup and decay of charge on the glass plates and how this correlates with the observed guiding.

Aqueous solution-processed AlOx dielectrics and their biased radiation response investigated by an on-site technique

The effect of annealing temperature on the properties of aqueous solution-processed AlOx thin films is reported in this paper. Specifically, the stability of AlOx based Metal Oxide Semiconductor (MOS) capacitor devices under bias-stress (BS) and biased radiation stress (BRS) were assessed by an on-site technique with bias stress time up to 105 s. A 662-keV Cs137 γ-ray radiation source was used, with circa 92 Gy, for biased radiation stress experiments. In order to better understand the origin of degradation mechanisms, the build-up of charge and generation of defects during the BS and BRS were analyzed by calculation of the variation of oxide trap density (ΔNot) in AlOx bulk and interface trap density (ΔNit) at the oxide/semiconductor interface. It is been found that high annealing temperature (>250 °C) can result in the formation of AlOx thin films with reduced impurities, low leakage current, and satisfactory BS as well as BRS stability. The results of ΔNot and ΔNit vs stress time indicate that AlOx bulk oxide traps dominate the shift of flat-band voltage (VFB) under BRS. Furthermore, ΔNot and ΔNit decrease slightly under positive biased radiation stress (PBRS), while the increase in ΔNot and ΔNit concentrations observed under negative biased radiation stress (NBRS), exhibits a mechanism which differs from the traditional two-stage process theory.

Comparison of Plasma Effect on Dewetting Kinetics of Sn Films Between Grounded and Floating Substrates

When metal thin films deposited typically by sputtering is heated to sufficiently high temperature, thin films tend to disintegrate into individual isolated spherical particles, whose phenomenon is called thermal dewetting. If such metal films are exposed to plasma, however, the dewetting kinetics is enhanced dramatically. One possibility for enhanced dewetting kinetics is the ion bombardment on the film surface from plasma. The other possibility is the excess charge buildup on the film surface provided from plasma. If enhanced dewetting kinetics is due to charge buildup, it can provide an evidence for charge-enhanced kinetics, which has been suggested as a hypothesis to explain the evolution of void-free dense films in non-classical crystallization where the building block is charged nanoparticles. To clarify which is responsible for plasma enhanced dewetting, the dewetting behavior of 100 nm thick Sn films on silicon substrates with native oxide surface was compared between floating and grounded films in the inductively-coupled plasma environment. The dewetting kinetics on the floating film was much higher than that on the grounded film. These results indicate that the charge buildup is responsible for the plasma enhanced dewetting kinetics.

Ion Manipulation in Open Air Using 3D-Printed Electrodes.

Ambient ionization techniques provide a way to sample materials via creation of ions in the air. However, transferring and focusing of these ions is typically done in the reduced pressure environment of the mass spectrometer. Spray-based ambient ionization sources require relatively large distances between the source and mass spectrometer inlet for effective desolvation, resulting in a small fraction of the ions being collected. To increase the efficiency of ion transfer from atmosphere to vacuum, 3D-printed focusing devices made of conductive carbon nanotube doped polymers have been designed and evaluated for ion focusing in air. Three main classes of electrodes are considered: (i) conic section electrodes (conical, ellipsoidal, and cylindrical), (ii) simple conductive and non-conductive apertures, and (iii) electrodes with complex geometries (straight, chicane, and curved). Simulations of ion trajectories performed using the statistical diffusion simulation (SDS) model in SIMION showed a measure of agreement with experiment. Cross-sectional images of ion beams were captured using an ion detecting charge-coupled device (IonCCD). After optimization, the best arrangements of electrodes were coupled to an Agilent Ultivo triple quadrupole to record mass spectra. Observations suggest that electrode geometry strongly influences ion trajectories in air. Non-conductive electrodes also assisted in focusing, due to charge buildup from ion deposition. We also observed minimal spreading of the ion packet after exiting the focusing electrodes indicating that atmospheric collisions do not reduce collimation of the beam. The study suggests that high pressures need not be viewed as a hindrance to ion transport, but as a potentially useful force.

Effect of electric field non-uniformity on the differences between I-V characteristics of QWIP devices fabricated on the same wafer

Capacitance versus voltage, C–V, measurements are used to identify the origin of the difference between current versus voltage, I–V, characteristics of quantum well infrared photodetector, QWIP, devices fabricated simultaneously on the same wafer, i.e., same epitaxial layers. The devices have similar I–V curves at low bias but differ significantly at higher voltages. It is shown that the charge buildup inside the multiple quantum well structure is responsible for changing the conduction mechanism at voltages lower than that would be expected if the entire structure was subjected to a uniform electric field. This charge buildup varies from device to device, indicating local characteristics dependence. Although a non-uniform electric field is established, as identified by C–V measurements, none of the known fingerprints related to the formation and propagation of electric field domains are present in the I–V curves, i.e., no plateau or negative differential conductivity were observed.

InGaAs/graphene infrared photodetectors with enhanced responsivity

High responsivity is a vital aim of photodetectors research. Based on the photogating effect, ultra-high responsivity can be realized by combining the high mobility of graphene and strong light absorption of other materials. Due to long carrier lifetime and low mobility, quantum dots(QDs) are usually used to form hybrid photodetectors with graphene. However, hybrid photodetectors of graphene with materials possessing higher mobility are rarely studied at present. In this paper, the hybrid photodetector of graphene and InGaAs is studied. We fabricated and measured pure InGaAs photodetectors, hybrid photodetectors of the whole graphene on InGaAs surface and hybrid photodetectors of graphene nanoribbons(GNRs) on InGaAs surface. It is found that, compared to pure InGaAs photodetectors, the responsivity of the whole graphene on InGaAs surface devices increases by 14.7 times, which is 7.66 A W−1, and the response time is twice faster. We also found that the negative back voltage can increase the photocurrent by modulating the Fermi energy of graphene and barrier height of the hybrid photodetectors. The illuminated area effect on various devices area was discussed in this study. In terms of theoretical mechanization, as high mobility materials, both graphene and InGaAs could generate and transport carriers in this hybrid photodetector under optical illumination. The photoexcited holes in InGaAs enter graphene while the photoexcited electrons in graphene enter InGaAs due to the built-in field, which leads to a charge build-up on both sides of the junction and a strong photogating effect on the channel conductance. The results of this study are of novel significance for the development of infrared detectors based on graphene.

Segmented ion-trap fabrication using high precision stacked wafers

We describe the use of laser-enhanced etching of fused silica in order to build multilayer ion traps. This technique offers high precision of both machining and alignment of adjacent wafers. As examples of designs taking advantage of this possibility, we describe traps for realizing two key elements of scaling trapped ion systems. The first is a trap for a cavity-QED interface between single ions and photons, in which the fabrication allows shapes that provide good electrostatic shielding of the ion from charge buildup on the mirror surfaces. The second incorporates two X-junctions allowing two-dimensional shuttling of ions. Here, we are able to investigate designs which explore a trade-off between pseudopotential barriers and confinement at the junction center. In both cases, we illustrate the design constraints arising from the fabrication.