Accumulation Of Negative Charge Research Articles

Triboelectrification-Induced Large Electric Power Generation from a Single Moving Droplet on Graphene/Polytetrafluoroethylene

Recently, several reports have demonstrated that a moving droplet of seawater or ionic solution over monolayer graphene produces an electric power of about 19 nW, and this has been suggested to be a result of the pseudocapacitive effect between graphene and the liquid droplet. Here, we show that the change in the triboelectrification-induced pseudocapacitance between the water droplet and monolayer graphene on polytetrafluoroethylene (PTFE) results in a large power output of about 1.9 μW, which is about 100 times larger than that presented in previous research. During the graphene transfer process, a very strong negative triboelectric potential is generated on the surface of the PTFE. Positive and negative charge accumulation, respectively, occurs on the bottom and the top surfaces of graphene due to the triboelectric potential, and the negative charges that accumulate on the top surface of graphene are driven forward by the moving droplet, charging and discharging at the front and rear of the droplet.

Defect‐induced electrostatic charging of nitrogen films

Electrostatic charging of nanostructured N2 films was studied employing optical and a current set of emission spectroscopy methods: cathodoluminescence CL, thermally and photon‐stimulated exoelectron emission TSEE, PSEE as well as thermally and photon‐stimulated luminescence TSL, PSL. Concurrently with thermally stimulated yield of electrons the yield of nitrogen particles was detected, so‐called “postdesorption.” An enhancement of the optical emission stemmed from the neutralization reaction N4+ + e → N2* + N2* → N2 + N2 + hν was observed with an exposure to an electron beam. The experiments performed with a variable voltage applied to an electrode for current detection demonstrated significant accumulation of negative charge. The TSEE current in the low‐temperature range was detected at negative voltages up to −30 V. An accumulation of trapped electrons (up to 1016 cm−3) was detected. A possible contribution of N3− in electrostatic charging was assumed.Thermally stimulated yield of negatively charged particles from a N2 film subjected to an electron beam.

Processing of n+/p−/p+ strip detectors with atomic layer deposition (ALD) grown Al2O3 field insulator on magnetic Czochralski silicon (MCz-si) substrates

Detectors manufactured on p-type silicon material are known to have significant advantages in very harsh radiation environment over n-type detectors, traditionally used in High Energy Physics experiments for particle tracking. In p-type (n+ segmentation on p substrate) position-sensitive strip detectors, however, the fixed oxide charge in the silicon dioxide is positive and, thus, causes electron accumulation at the Si/SiO2 interface. As a result, unless appropriate interstrip isolation is applied, the n-type strips are short-circuited. Widely adopted methods to terminate surface electron accumulation are segmented p-stop or p-spray field implantations. A different approach to overcome the near-surface electron accumulation at the interface of silicon dioxide and p-type silicon is to deposit a thin film field insulator with negative oxide charge. We have processed silicon strip detectors on p-type Magnetic Czochralski silicon (MCz-Si) substrates with aluminum oxide (Al2O3) thin film insulator, grown with Atomic Layer Deposition (ALD) method. The electrical characterization by current–voltage and capacitance−voltage measurement shows reliable performance of the aluminum oxide. The final proof of concept was obtained at the test beam with 200GeV/c muons. For the non-irradiated detector the charge collection efficiency (CCE) was nearly 100% with a signal-to-noise ratio (S/N) of about 40, whereas for the 2×1015neq/cm2 proton irradiated detector the CCE was 35%, when the sensor was biased at 500V. These results are comparable with the results from p-type detectors with the p-spray and p-stop interstrip isolation techniques. In addition, interestingly, when the aluminum oxide was irradiated with Co-60 gamma-rays, an accumulation of negative fixed oxide charge in the oxide was observed.

Pt3 Co Octapods as Superior Catalysts of CO2 Hydrogenation.

As the electron transfer to CO2 is a critical step in the activation of CO2 , it is of significant importance to engineer the electronic properties of CO2 hydrogenation catalysts to enhance their activity. Herein, we prepared Pt3 Co nanocrystals with improved catalytic performance towards CO2 hydrogenation to methanol. Pt3 Co octapods, Pt3 Co nanocubes, Pt octapods, and Pt nanocubes were tested, and the Pt3 Co octapods achieved the best catalytic activity. Both the presence of multiple sharp tips and charge transfer between Pt and Co enabled the accumulation of negative charges on the Pt atoms in the vertices of the Pt3 Co octapods. Moreover, infrared reflection absorption spectroscopy confirmed that the high negative charge density at the Pt atoms in the vertices of the Pt3 Co octapods promotes the activation of CO2 and accordingly enhances the catalytic activity.

Pt3Co Octapods as Superior Catalysts of CO2 Hydrogenation

AbstractAs the electron transfer to CO2 is a critical step in the activation of CO2, it is of significant importance to engineer the electronic properties of CO2 hydrogenation catalysts to enhance their activity. Herein, we prepared Pt3Co nanocrystals with improved catalytic performance towards CO2 hydrogenation to methanol. Pt3Co octapods, Pt3Co nanocubes, Pt octapods, and Pt nanocubes were tested, and the Pt3Co octapods achieved the best catalytic activity. Both the presence of multiple sharp tips and charge transfer between Pt and Co enabled the accumulation of negative charges on the Pt atoms in the vertices of the Pt3Co octapods. Moreover, infrared reflection absorption spectroscopy confirmed that the high negative charge density at the Pt atoms in the vertices of the Pt3Co octapods promotes the activation of CO2 and accordingly enhances the catalytic activity.

Dynamic secondary electron emission characteristics of polymers in negative charging process

We studied the dynamic secondary electron emission (SEE) characteristics of a polyimide sample in negative charging process under electron bombardment. The time evolution of secondary electron yield (SEY) has been measured with a pulsed electron gun. The dynamic SEY, as well as the surface potential have been analyzed using a capacitance model. The shift in surface potential caused by the negative charge accumulation on the sample reduces the landing energy of the primary electrons (PEs), which in turn alters the SEY. The charging process tends to be stable when the landing energy of PEs reaches the secondary crossover energy where the corresponding SEY is 1. The surface potential has an approximately negative exponential relationship with the irradiation time. The total accumulated charge at the stable state is found to be proportional to the product of the sample capacitance and the difference between initial incident energy and the secondary crossover energy. The time constant of the exponential function is proportional to the ratio of final accumulated charge to the incident current.

Electrical detection of dengue virus (DENV) DNA oligomer using silicon nanowire biosensor with novel molecular gate control

In this paper, a silicon nanowire biosensor with novel molecular gate control has been demonstrated for Deoxyribonucleic acid (DNA) detection related to dengue virus (DENV). The silicon nanowire was fabricated using the top–down nanolithography approach, through nanostructuring of silicon-on-insulator (SOI) layers achieved by combination of the electron-beam lithography (EBL), plasma dry etching and size reduction processes. The surface of the fabricated silicon nanowire was functionalized by means of a three-step procedure involving surface modification, DNA immobilization and hybridization. This procedure acts as a molecular gate control to establish the electrical detection for 27-mers base targets DENV DNA oligomer. The electrical detection is based on the changes in current, resistance and conductance of the sensor due to accumulation of negative charges added by the immobilized probe DNA and hybridized target DNA. The sensitivity of the silicon nanowire biosensors attained was 45.0µAM−1, which shows a wide-range detection capability of the sensor with respect to DNA. The limit of detection (LOD) achieved was approximately 2.0fM. The demonstrated results show that the silicon nanowire has excellent properties for detection of DENV with outstanding repeatability and reproducibility performances.

Photochemical synthesis, characterization, photoinduced electron transfer, charging and discharging in copper-titania colloid

Abstract One of major goals in photocatalysis and photochemistry is to understand photoinduced charge transfer. Colloidal solutions serve as convenient model systems for mechanistic studies of charge transfer. For the first time, colloid Cu(0)-V O -TiO 2 was prepared by the “one-pot” photochemical synthesis from copper nitrate and titanium isopropoxide precursors in ethanol under UV–vis light. The Cu(0)-V O -TiO 2 colloid shows the surface plasmon resonance (SPR) absorption band of metallic copper and contains oxygen vacancy V O . Kinetics of the synthesis of Cu(0)-V O -TiO 2 colloid follows the zeroth-order kinetic rate law, while synthesis of Cu 2 O colloid under the same conditions follows the first order rate law. Under UV–vis light, Cu(0)-V O -TiO 2 colloid undergoes repeated accumulation of negative charge on metallic copper after photoexcitation of TiO 2 , and discharge of electrons from metallic copper occurs in the dark.

Working Principles of Perovskite Photodetectors: Analyzing the Interplay Between Photoconductivity and Voltage‐Driven Energy‐Level Alignment

Organic–inorganic lead halide perovskites have recently received significant attention as active materials for high‐performance photovoltaics and photodetectors. However, the understanding of their operation mechanism remains limited. High‐gain, low‐voltage CH3NH3PbI3 photodetectors in various architectures are demonstrated herein. Photomultiplication in all structures with direct contact of fluorine‐doped tin oxide (FTO) and perovskite with the highest responsivity 208 A W−1 corresponding to an incident photon‐to‐current efficiency of 47 000% is observed. Studying the dynamics and temperature dependence, a slow process with an activation energy of 420 ± 90 meV in the time scale of seconds is found, which is essential to photocurrent multiplication. A model based on ion migration to explain the observed transients and the photomultiplication is developed. The accumulation of negative ionic charge at the FTO/perovskite interface under reverse bias lowers the FTO work function allowing for direct hole injection into the perovskite valence band. Under illumination, the conductivity of perovskite is increased and the device behaves similar to a photoconductor.

Surface charge dynamics and OH and H number density distributions in near-surface nanosecond pulse discharges at a liquid / vapor interface

The present work provides insight into surface charge dynamics and kinetics of radical species reactions in nanosecond pulse discharges sustained at a liquid-vapor interface, above a distilled water surface. The near-surface plasma is sustained using two different discharge configurations, a surface ionization wave discharge between two exposed metal electrodes and a double dielectric barrier discharge. At low discharge pulse repetition rates (~100 Hz), residual surface charge deposition after the discharge pulse is a minor effect. At high pulse repetition rates (~10 kHz), significant negative surface charge accumulation over multiple discharge pulses is detected, both during alternating polarity and negative polarity pulse trains. Laser induced fluorescence (LIF) and two-photon absorption LIF (TALIF) line imaging are used for in situ measurements of spatial distributions of absolute OH and H atom number densities in near-surface, repetitive nanosecond pulse discharge plasmas.Both in a surface ionization wave discharge and in a double dielectric barrier discharge, peak measured H atom number density, [H] is much higher compared to peak OH number density, due to more rapid OH decay in the afterglow between the discharge pulses. Higher OH number density was measured near the regions with higher plasma emission intensity. Both OH and especially H atoms diffuse out of the surface ionization wave plasma volume, up to several mm from the liquid surface. Kinetic modeling calculations using a quasi-zero-dimensional H2O vapor / Ar plasma model are in qualitative agreement with the experimental data. The results demonstrate the experimental capability of in situ radical species number density distribution measurements in liquid-vapor interface plasmas, in a simple canonical geometry that lends itself to the validation of kinetic models.

Defect creation via dissociative recombination of ionic centers in solid Ne matrices

Recombination of the intrinsic ionic centers Ne2+ (self-trapped holes) with the detrapped electrons in solid Ne matrices and relaxation channels have been studied. The experiments were performed employing combination of the cathodoluminescence (CL) with current and optical activation spectroscopy techniques. CL spectra were recorded simultaneously in the VUV and visible range. Yields of spectrally resolved thermally and photon-stimulated luminescence (TSL, PSL) and thermally and photon-stimulated exoelectron emission (TSEE, PSEE) were measured in the time-correlated manner. It was found that the recombination reaction proceeds with irreversible dissociation of the transient Ne2∗∗ centers and the dissociative recombination (DR) products exit the matrix cage. Products of the DR reaction are found to be in 3s and 3p states. The detection of “defect” components in the TSL and PSL points to the defect formation via DR in Ne matrices. The temperature range of the electron traps stability is elucidated. A long-lasting “afteremission” of electrons and afterglow of VUV photons observed on switching off the irradiation suggest the accumulation of the uncompensated negative charge.

Mechanistic pathways of mercury removal from the organomercurial lyase active site.

Bacterial populations present in Hg-rich environments have evolved biological mechanisms to detoxify methylmercury and other organometallic mercury compounds. The most common resistance mechanism relies on the H+-assisted cleavage of the Hg–C bond of methylmercury by the organomercurial lyase MerB. Although the initial reaction steps which lead to the loss of methane from methylmercury have already been studied experimentally and computationally, the reaction steps leading to the removal of Hg2+ from MerB and regeneration of the active site for a new round of catalysis have not yet been elucidated. In this paper, we have studied the final steps of the reaction catalyzed by MerB through quantum chemical computations at the combined MP2/CBS//B3PW91/6-31G(d) level of theory. While conceptually simple, these reaction steps occur in a complex potential energy surface where several distinct pathways are accessible and may operate concurrently. The only pathway which clearly emerges as forbidden in our analysis is the one arising from the sequential addition of two thiolates to the metal atom, due to the accumulation of negative charges in the active site. The addition of two thiols, in contrast, leads to two feasible mechanistic possibilities. The most straightforward pathway proceeds through proton transfer from the attacking thiol to Cys159 , leading to its removal from the mercury coordination sphere, followed by a slower attack of a second thiol, which removes Cys96. The other pathway involves Asp99 in an accessory role similar to the one observed earlier for the initial stages of the reaction and affords a lower activation enthalpy, around 14 kcal mol−1, determined solely by the cysteine removal step rather than by the thiol ligation step. Addition of one thiolate to the intermediates arising from either thiol attack occurs without a barrier and produces an intermediate bound to one active site cysteine and from which Hg(SCH3)2 may be removed only after protonation by solvent-provided H3O+. Thiolate addition to the active site (prior to any attack by thiols) leads to pathways where the removal of the first cysteine becomes the rate-determining step, irrespective of whether Cys159 or Cys96 leaves first. Comparisons with the recently computed mechanism of the related enzyme MerA further underline the important role of Asp99 in the energetics of the MerB reaction. Kinetic simulation of the mechanism derived from our computations strongly suggests that in vivo the thiolate-only pathway is operative, and the Asp-assisted pathway (as well as the conversion of intermediates of the thiolate pathway into intermediates of the Cys-assisted pathway) is prevented by steric factors absent from our model and related to the precise geometry of the organomercurial binding-pocket.

Experimental and Computational Characterization of the Transition State for C–X Bimetallic Oxidative Addition at a Cu–Fe Reaction Center

The heterobimetallic complex (IPr)Cu-Fp (IPr = N,N′-bis(2,6-diisopropylimidazol-2-ylidene, Fp = FeCp(CO)2) was identified previously as a nonprecious metal catalyst for C–H borylation. To better understand the nature of the bimetallic reaction pathways operative in this system, we have conducted a thorough mechanistic study of alkyl halide activation by the Cu–Fe heterobimetallic reaction center. Use of cyclopropylmethyl halide substrates as radical clocks established that alkyl halide activation occurs by a two-electron mechanism for alkyl bromides and chlorides but not iodides. Eyring analysis of the activation of benzyl chloride allowed for experimental determination of activation parameters, including a large and negative entropy of activation (ΔS⧧ = −36 eu). A Hammett study with para-substituted benzyl chlorides revealed a reaction constant of ρ = 1.6, indicating accumulation of negative charge in the transition state on the alkyl halide carbon. The Ru analogue, (IPr)Cu-Rp (Rp = RuCp(CO)2), was found to react approximately 17–25 times more slowly with selected benzyl chlorides than (IPr)Cu-Fp, indicating that the relative nucleophilicities of the free metal carbonyl anions are predictive of the relative reactivities of their heterobimetallic counterparts. Synthesis and characterization of the new Ag and Au analogues, (IPr)Ag-Fp and (IPr)Au-Fp, are reported along with the observation that these more covalent congeners are significantly less reactive toward alkyl halides. DFT calculations were used to model a transition state for the Cu–Fe reaction, which was identified as stereoinvertive at the alkyl halide carbon. NBO calculations indicate crucial roles played by the CO ligands within the Fp group: they both act as redox noninnocent ligands and also provide structural templating to stabilize the transition state as the metal–metal bond breaks.

Theory of Nanosecond High-Power Microwave Breakdown on the Atmosphere Side of the Dielectric Window

This paper deals with the theory of plasma development in the nanosecond high-power microwave breakdown at the dielectric/air interface. Utilizing the Poisson and Boltzmann equations, the basic physics are explored and investigated. Corresponding to the incident electric field, electrons moving back and forth bring about the negative charge accumulation at the interface. This process generates an extra electric field, strengthening the total amplitude. Simultaneously, deviations of electrons and ions lead to a sheath region providing a space charge field. Secondary electrons are strongly accelerated in the sheath region, eventually leading to an ionization avalanche in a very short time. Both the densities and energies of particles reach the maximums near the sheath region, and that is why the illumination is most significant near the interface. The theory is in good accordance with an experiment conducted under the same conditions.

4‐Acetylthio‐2,2‐dimethyl‐3‐oxobutyl Group as an Esterase‐ and Thermo‐Labile Protecting Group for Oligomeric Phosphodiesters

Abstract(4‐Acetylthio‐2,2‐dimethyl‐3‐oxobutyl)‐protected oligomeric phosphodiesters 1 and 2 were synthesized and removal of the protecting groups in the presence and absence of hog liver esterase was followed at pH 7.5 and 37 °C. Phosphotriesters 1 and 2 were successfully converted into the desired fully deprotected phosphodiesters 3 and 4, respectively. Some cleavage of internucleosidic P–O bonds took place, which reduced the yield of 3 and 4. Non‐enzymatic removal of the protecting group was only modestly retarded by accumulation of negative charge on the molecule. With 1, the half‐lives for the departure of the first and second protecting groups were 7.8 and 10.7 h, respectively, and with 2, 6.2 and 7.2 h, respectively. After 4 d, 70 % of both starting materials 1 and 2 were converted into the unprotected phosphodiester. The presence of hog liver esterase (2.6 units mL–1) resulted in fast removal of the first protecting group (τ1/2 2.7 min and 36 min with 1 and 2, respectively), but the appearance of fully deprotected 3 and 4 was accelerated only by a factor of 2, consistent with dramatic retardation of the enzymatic reaction upon accumulation of the negative charge.

Charging and discharging of single colloidal particles at oil/water interfaces.

The physical behavior of solid colloids trapped at a fluid-fluid interface remains in itself an open fundamental issue. Here, we show that the gradients of surface tension can induce particles to jet towards the oil/water interface with velocities as high as ≈ 60 mm/s when particle suspensions come in contact with the interface. We hypothesize that rubbing between the particles and oil lead to the spontaneous accumulation of negative charges on the hemisphere of those interfacial particles that contact the oil phase by means of triboelectrification. The charging process is highly dependent on the sliding distances, and gives rise to long-ranged repulsions that protect interfacial particles from coagulating at the interface by the presence of electrolyte. These triboelectric charges, however, are compensated within several hours, which affect the stability of interfacial particles. Importantly, by charging different kinds of colloidal particles using various spreading solvents and dispersion methods, we have demonstrated that charging and discharging of single colloidal particles at oil/water interfaces impacts a broad range of dynamical behavior.

Detection of pre-electrical breakdown of IZO/α-NPD/Alq3/Al light-emitting diodes by electric-field-induced optical second-harmonic generation measurement

By using the electric-field-induced optical second-harmonic generation (EFISHG), we measured the EFISHG–time (EFISHG–t) characteristics to study pre-electrical breakdown of indium–zinc-oxide (IZO)/N,N′-di[(1-naphthyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine (α-NPD)/tris(8-hydroxy-quinolinato)aluminum(III) (Alq3)/Al organic light-emitting diodes (OLEDs). A series of EFISHG pulses were identified as a pre-electrical breakdown phenomenon, before OLEDs were electrically broken. Analyzing the results revealed the additional negative charge accumulation at the α-NPD/Alq3 interface which caused by the generation of EFISHG pulses. We concluded that the EFISHG–t measurement is available as a method for detecting pre-electrical breakdown phenomena of OLEDs.

Serotype-Specific Identification of Dengue Virus by Silicon Nanowire Array Biosensor

In this work, we demonstrated a silicon nanowire (SiNW) biosensing platform capable of simultaneously identifying different Dengue serotypes on a single sensing chip. Four peptide nucleic acids (PNAs), specific to each Dengue serotypes (DENV-1 to DENV-4), were spotted on different areas of the SiNW array surface, and the covalently immobilized PNA probes were then interacted with different Dengue serotypes target to establish the specificity of detection. Detection scheme is based on the changes in resistances due to accumulation of negative charges contributed by the hybridized DNA target. The results show that resistance changes only occur in regions where the Dengue target hybridizes with its complementary probe. What is more, a mixture of two different Dengue serotypes obtained from a one-step duplex RT-PCR was applied to the multiplex SiNW surface to validate SiNW capability to identify multiple Dengue serotypes on a single sensing platform. Through this study, we have established the multiplex SiNW biosensor as a promising device to detect multiple Dengue infections with high specificity.

The ferroelectricity of Bi0.9Pb0.1FeO3 films grown on atomic flat SrRuO3/SrTiO3 substrates

Bi0.9Pb0.1FeO3 (BPFO) films were grown on SrRuO3 (SRO)/SrTiO3 (STO) substrates. The surface morphology of BPFO films is highly dependent on that of the SRO layer. Though the step height of STO (100) substrate is equal to one unit cell of STO crystal, the height and width of steps on the surface of SRO and BPFO are larger, which supports a step bunching growth mode on both the SRO layer and BPFO films. At zero bias voltage, the BPFO film exhibits a natural dipole polarization toward the SRO layer, which is believed to be due to the negative charge accumulation at the BPFO/SRO interface, and manifests of 71° and 109° but 180° domain walls. Doping of Pb distorted the BPFO crystal lattice to near cubic that weakens the electric anisotropy and forms a two-step flipping process. To complete a 180° dipole flipping procedure, the dipole moment first rotates 71° to adjacent states followed by a 109° rotation to the final 180° state.

Degradation of AlGaN/GaN HEMT devices: Role of reverse-bias and hot electron stress

This paper describes a deep investigation of the degradation mechanisms induced by off-state and on-state stress in AlGaN/GaN HEMTs. Concerning reverse-bias degradation, results underline that the exposure to reverse-bias stress can induce (i) a recoverable change in the gate current due to the accumulation of negative charges under the gate, (ii) and a permanent degradation of gate characteristics due to the generation of vertical parasitic leakage paths through the AlGaN layer. Further analysis of the kinetics of this degradation mechanism, correlated with time-resolved Electroluminescence (EL) measurements, allowed to define a model that explains the time-dependence of the phenomenon and the role of gate voltage as accelerating factor, providing an interpretation for both recoverable and permanent modifications of the main device characteristics induced by reverse-bias stress. On the other hand, on devices that have shown an improved robustness against the reverse-bias gate degradation, we investigated the origin of the degradation under on-state stress. In this case, results obtained with a combined electrical and optical analysis, showed that on-state stress may induce a significant decrease in drain saturation current and Electroluminescence (EL) signal, with a degradation rate that strongly depends on the EL intensity measured before stress, which is representative of the presence of hot-electrons in the channel. On-state degradation can be ascribed to a decrease in the electric-field, due to the trapping of electrons within the barrier or at the surface induced by hot-electrons. Therefore, by using the EL signal as measure of the stress accelerating factor, it was possible to derive an acceleration law for hot-electron degradation on GaN HEMTs.