Coulomb Effects Research Articles

Controlling the fluoridophilicity of sulfonium boranes via chelation, Coulombic and hydrophobic effects

We describe the synthesis and properties of a series of sulfonium boranes featuring a dimesitylboryl unit and a dimethylsulfonium or methylphenyl sulfonium moiety connected by an ortho- or para-phenylene linker. Acid-base and fluoride anion tritration experiments carried out in aqueous media indicate that [o-(Mes2B)C6H4(SMePh)]+ is the most Lewis acidic derivative. Structural and computational analysis indicate that the favorable properties of this cationic borane derive from the proximity of the sulfonium and boryl units which enhances the Coulombic stabilization of the ensuing zwitterions o-(Mes2XB)C6H4(SMePh) with X = OH or F. Another important factor is the overall hydrophobicity of the sulfonium borane which, we propose, promotes anion desolvation, a factor also favoring B-X bond formation. Finally, the crystal structure of o-(Mes2FB)C6H4(SMePh) shows that the zwitterion is further stabilized by formation of a BF→S chelate motif.

Gate-Tunable Topological Flat Bands in Trilayer Graphene Boron-Nitride Moiré Superlattices.

We investigate the electronic structure of the flat bands induced by moiré superlattices and electric fields in nearly aligned ABC trilayer graphene (TLG) boron-nitride (BN) interfaces where Coulomb effects can lead to correlated gapped phases. Our calculations indicate that valley-spin resolved isolated superlattice flat bands that carry a finite Chern number C=3 proportional to the layer number can appear near charge neutrality for appropriate perpendicular electric fields and twist angles. When the degeneracy of the bands is lifted by Coulomb interactions, these topological bands can lead to anomalous quantum Hall phases that embody orbital and spin magnetism. Narrow bandwidths of ∼10 meV achievable for a continuous range of twist angles θ≲0.6° with moderate interlayer potential differences of ∼50 meV make the TLG-BN systems a promising platform for the study of electric-field tunable Coulomb-interaction-driven spontaneous Hall phases.

Composition and charge state influence on the ion-neutral collision cross sections of protonated N-linked glycopeptides: an experimental and theoretical deconstruction of coulombic repulsion vs. charge solvation effects.

Ion mobility spectrometry (IMS) is of significant interest as a platform for glycoanalysis. While much attention has been focused on the resolution of isomeric carbohydrates and glycoconjugates, another appealing aspect of IMS is the ability to sort different classes of biomolecules into distinct regions of mass vs. mobility space. This capability has potential to greatly simplify glycoproteomic analyses, as glycosylated and non-glycosylated peptides can be rapidly partitioned in the gas phase. Nevertheless, the physical and chemical characteristics of glycopeptides that dictate their mass vs. mobility loci have yet to be systematically investigated. This report presents an IMS study of model protonated glycopeptide ions with systematically varied oligosaccharide topologies, polypeptide sequences, and charge states. In all, over 110 ion-neutral collision cross sections (CCSs) were measured and analyzed in the context of the physicochemical characteristics of the analytes. Glycan size and composition emerged as a decisive factor in dictating the CCS space occupied by the glycopeptides and exerted this influence in a charge state dependent fashion. Furthermore, elongation of the glycan group was found to either increase or decrease glycopeptide CCSs depending on the ion charge state and the size of the glycan. Molecular dynamics (MD) simulations of the gas phase structures and CCSs of selected glycopeptides revealed that the experimental observations were consistent with a glycan size and charge state dependent interplay between destabilizing coulombic repulsion effects (tending to result in more extended structures) and stabilizing charge solvation effects in which the glycan plays a major role (tending to result in more compact structures). Taken together, these IMS and MD findings suggest the possibility of predicting and delineating glycopeptide-enriched regions of mass vs. mobility space for applications in glycoproteomics.

Drain Conductance Oscillations in Poly-Si Junctionless Nanowire Thin-Film Transistors

The drain conductance oscillations are simultaneously observed in the trigated and double-gated poly-Si junctionless (JL) nanowire thin-film transistors (TFTs). The strongest oscillations appear at ${V} _{\text {GS}}$ of 1 V and $V_{\text {DS}}$ of 4–5 V/6–7 V in 0.35- $\mu \text{m}$ /5- $\mu \text{m}$ poly-Si JL nanowire TFTs. To explain the drain conductance oscillations, in addition to the separated sub-bands and Coulomb blockade effect, the space-charge-potential barrier/grain boundary (GB) potential barrier in the channel and the kink effect in the output characteristics should be considered. The space-charge-potential barrier is affected by the unstable trapped electrons at GB and leads to the drain conductance oscillations. Due to the kink effect, an anomalous increase of the current in the output characteristics can enhance the conductance oscillations. Moreover, the channel of the double-gated device shows higher degree of crystallinity by solid-phase crystallization. Compared with the trigated device without solid-phase crystallization, less GB potential barriers in the channel of the double-gated device lead to a higher mobility in the channel, and these electrons can easily destroy the stability of the trapped electrons at the GBs, resulting in the stronger drain conductance oscillations. Therefore, the physical mechanisms are proposed to understand the drain conductance oscillations well in poly-Si JL nanowire TFTs.

Some MoS2-based materials for sodium-ion battery

Sodium-ion batteries (SIB) play a promising role in the area of energy storage device researching. MoS2-based materials are considered as one of the most attractive materials for high-performance SIBs owing to their high capacity, high cycle stability and excellent Coulomb effect. This review has summarized the synthesis of MoS2-based materials (MoS2, MoS2/carbon-based materials, MoS2/metal oxides, MoS2/metal sulfides) to emphasize their electrochemical behaviors in SIBs.

Coulomb effect induced intrinsic degradation in OLED

Abstract Intrinsic degradation in 100 nm AlQ3 OLED device with strong luminescence was observed while nearly no degradation in 50 nm AlQ3 device with weak luminescence was observed for the same operation time. Based on the EL and PL measurements, it was suggested that penetration of AlQ3 molecules into NPB layer resulted in the increase of electron leakage current, and thus significant loss of current efficiency. A plausible Coulomb effect induced intrinsic degradation mechanism was therefore proposed to explain the experimental results.

Coulomb potential effects in strong-field atomic ionization under elliptical polarization

We experimentally and theoretically investigate strong-field ionization of noble-gas atoms in elliptically polarized laser fields at 2000 nm. The ellipticity dependence of the ion yields has been measured at a series of intensities and compared to various theoretical model predictions [i.e., the Ammosov-Delone-Krainov (ADK), strong-field approximation (SFA), and Coulomb-Volkov distorted-wave approximation (CVA) models]. The SFA and ADK calculations match each other, which alludes to the negligible contribution of nonadiabatic effect. In the meantime, they both deviate significantly from the measurements. On the other hand, the good agreement between CVA calculations and measurements reveals the salient role played by the Coulomb potential in atomic ionization. The Coulomb potential effect is further confirmed by comparison of CVA calculations and measurements at 800 nm. Our work demonstrates the significant Coulomb potential effect on the ionization yields, the experimental evidence of which has rarely been documented.

Coulomb-Volkov S-matrix theory of ionisation

In this paper we outline the recently derived Coulomb-Volkov (CV) S-matrix theory and present the results of calculations of the energy and the momentum spectra of the electrons emitted from ionisation of Ar atoms by an intense long-wavelength laser field. The results are compared with the corresponding calculations using the usual (plane-wave) SFA S-matrix theory, up to the second order of the series. We introduce a modified stationary phase method with a parametric integration to evaluate the high-dimensional integrals that occur in the second order of the ionisation amplitudes. The final-state Coulomb effect is found to be dominant at the lower energies, where the two theories differ greatly. In contrast, at high energies, the two theories produce qualitatively similar (in the logarithmic scale) distributions. It is found that despite the similarity of the positions of the ‘forward rescattering’ (or ‘soft collision’) peaks shown by the second order CV- and the SFA-amplitude, the line-shapes produced by them are qualitatively different. For example, the CV-spectrum shows a peak at 0.1 Up with a characteristic line-shape that is convex on one side and steeply rising on the other side; this is qualitatively similar to the line-shape of the peak observed experimentally earlier at the same energy. In contrast, the SFA-spectrum shows at the same energy a pointed peak with a line-shape that is concave on both sides. The characteristic line-shape of the low energy LES-peak(s) thus appears to suggest itself as a signature of the final-state Coulomb interaction in strong-field ionisation processes.

Influence of temperature and carrier density on the photoluminescence intensity of semiconductor carbon nanotubes

The role of temperature and carrier density in the photoluminescence (PL) properties of single-walled carbon nanotubes (SWNTs) is theoretically studied by solving the Bethe-Salpeter equation. Especially, the calculation of PL peak position and height for various carrier densities shows a good agreement with experimental results. The peak position and width show a moderate dependence while the intensity presents a strong dependence on temperature and density where a blue shift and intensity enhancement at low temperature are seen. These results help confirming the role of Coulomb effects on the optical transition in SWNTs.

Coulomb effects in the absorbance spectra of two-dimensional Dirac materials

A wide range of materials like graphene, topological insulators, and transition-metal dichalcogenides (TMDs) share an interesting property: the low-energy excitations behave as Dirac particles. This emergent behavior of Dirac quasiparticles defines a large class of media that are usually called Dirac materials. In this work we build the foundations of a way to study the linear optical properties of these two-dimensional media. Our approach is based on a Dirac-like formulation of the standard semiconductor Bloch equations used in semiconductor physics. We provide an explicit expression of the linear absorbance, which we call the relativistic Elliott formula, and use it to quantify the variation of the continuum absorbance spectrum with the strength of the Coulomb interaction (the Sommerfeld factor). Our calculations also show how the Coulomb enhancements scales with the band gap and vanishes for zero band gap, shedding light on the behavior of graphene for low-light intensities. The results presented are in good quantitative agreement with published experimental results. Our theory can help researchers to explore the nonlinear interactions of intense, ultrashort pulses with TMDs, and the framework is flexible enough to be adapted to different experimental situations, such as cavities, multilayers, heterostructures, and microresonators.

Electronic and optical properties of charge carriers in a GaSb quantum ring in a GaAs/Al0.6Ga0.4As quantum well

We present a study of the electronic and optical properties of charge carriers in a GaSb quantum ring inside a GaAs/Al0.6Ga0.4As quantum well as a function of the well width. After calculating the strain field using the continuum elasticity model, we analyzed the changes in the wavefunctions and energies of electron and hole with and without Coulomb interaction, using the effective mass approximation. The exciton total energy and binding energy, as well as the oscillator strength and radiative lifetime, are also examined as a function of the quantum well width. An interplay between the Coulomb interaction and the confinement effect was found, whereby the Coulomb effects are more important for wide quantum wells and the confinement effect becomes dominant for narrow ones—especially for 5 nm quantum wells, where a drastic change of the wavefunction accompanied by an increase of the exciton lifetime and transition energy was observed. A good agreement with the experimental results of Hodgson et al [2016 J. Appl. Phys. 119, 044305] was found for narrow quantum wells. For wide wells, however, our results differed from Hodgson’s results. This is attributed to the weak Coulomb effect induced by the single electron–hole pair in our calculations instead of the multiple-pair case in Hodgson’s results.

Mathematical modeling of pneumatic semi-rotary actuator with friction

In this paper, the problem of modeling a pneumatic semi-rotary actuator for precise control in the presence of friction for future robotic manipulator applications is addressed. Precise commercial pneumatic components have become increasingly available and are widely applied in the processes and manufacturing industry. The robustness of pneumatic actuator solutions is limited by the precision of the system controller positioning, which depends on sophisticated algorithms that must deal with the highly nonlinear nature of the pneumatic system operation by means of the use of controllers that require suitable system knowledge. In this study, aiming at obtaining such a suitable model for a class of pneumatic semi-rotary actuator, the pressure dynamics in its chambers is modeled. The overall modeling task involves a detailed experimental identification of the curves of the mass flow rate related to the control voltage of the servovalve and its relationship with the pressures in the piston chambers. Moreover, friction was formulated with the LuGre model on account of its ability to represent different effects that comprise friction phenomena, including Coulomb, viscous and static friction effects, resulting in a comprehensive mathematical model for supporting future development of a nonlinear controller. Finally, validation in open loop was performed with comparisons between experimental and simulation results.

Coulomb effects on the photoexcited quantum dynamics of electrons in a plasmonic nanosphere

With recent experiments investigating the optical properties of progressively smaller plasmonic particles, quantum effects become increasingly more relevant, requiring a microscopic description. Using the density matrix formalism we analyze the photo-excited few-electron dynamics of a small nanosphere. Following the standard derivation of the bulk plasmon we particularly aim on elucidating the role of the Coulomb interaction. Calculating the dielectric susceptibility spectrum in the linear optical response we find discrete resonances resulting from a collective response mediated by the Coulomb interaction between the electrons. In the nonlinear regime, the occupations of the system exhibit oscillations between the interacting eigenstates. Our approach provides an ideal platform to study and explain nonlinear and quantum plasmonics, revealing that the photo-excited dynamics of plasmonic nano spheres has similarities with and combines characteristics of both, the well-known two-level Rabi dynamics, and the collective many-electron behavior typical of plasmons.

Coulomb Corrections in Photoelectron Spectra in the Adiabatic Limit

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Interface Roughness, Carrier Localization, and Wave Function Overlap in c -Plane (In,Ga)N/GaN Quantum Wells: Interplay of Well Width, Alloy Microstructure, Structural Inhomogeneities, and Coulomb Effects

In this work we present a detailed analysis of the interplay of Coulomb effects and different mechanisms that can lead to carrier localization effects in c-plane InGaN/GaN quantum wells. As mechanisms for carrier localization we consider here effects introduced by random alloy fluctuations as well as structural inhomogeneities such as well width fluctuations. Special attention is paid to the impact of the well width on the results. All calculations have been carried out in the framework of atomistic tight-binding theory. Our theoretical investigations show that independent of the here studied well widths, carrier localization effects due to built-in fields, well width fluctuations and random alloy fluctuations dominate over Coulomb effects in terms of charge density redistributions. However, the situation is less clear cut when the well width fluctuations are absent. For large well width (approx. > 2.5 nm) charge density redistributions are possible but the electronic and optical properties are basically dominated by the spatial out-of plane carrier separation originating from the electrostatic built-in field. The situation changes for lower well width (< 2.5 nm) where the Coulomb effect can lead to significant charge density redistributions and thus might compensate a large fraction of the spatial in-plane wave function separation observed in a single-particle picture. Given that this in-plane separation has been regarded as one of the main drivers behind the green gap problem, our calculations indicate that radiative recombination rates might significantly benefit from a reduced quantum well barrier interface roughness.

Capturing Photoelectron Motion with Guiding Centers.

Electron motion in combined strong laser and Coulomb fields is central to laser-matter interactions. By mapping this problem onto the motion of a guiding center, we derive a reduced model which naturally embeds important Coulomb effects such as focusing and asymmetry, and clearly distinguishes direct versus rescattered electron ionization processes. We demonstrate the power of this tool by unraveling the bifurcation in photoelectron momentum distributions seen in experiments.

Anti-Flt1 peptide and cyanine-conjugated gold nanoparticles for the concurrent antiangiogenic and endothelial cell proton treatment.

Anti-Flt1 peptide of GNQWFI binds to vascular endothelial growth factor receptor 1 (VEGFR1 or Flt1) and prevents binding of VEGF, inhibiting VEGFR1-mediated endothelial cell migration and tube formation. Bare gold nanoparticle (AuNP) was known to have anti-angiogenic properties by specific binding with VEGF. In this study, anti-Flt1 peptide (GGNQWFI) and cyanine were chemically conjugated to AuNPs (Flt1@AuNP-cyanine 5.5 or Flt1@AuNP-hydrocyanine 5.5 [HCy5.5]) to enhance antiangiogenic properties with targeting to VEGFR-1 as well as producing Coulomb nanoradiator therapeutic effect on the retinal endothelial cells. Anti-Flt1 AuNP complex showed binding with VEGFR-1 and showed more protein-induced fluorescence enhancement (PIFE) by various VEGFs compared with bare AuNPs, suggesting enhanced antiangiogenic properties compared to bare AuNP. Nonfluorescent Flt1@AuNP-HCy5.5 successfully reacted with reactive oxygen species (ROS) produced from Fenton reactions or a proton-induced Coulomb nanoradiator, enabling quenching-free oxidant fluorescence ROS imaging in HRMECs under oxidative stress. Flt1@AuNP-HCy5.5 alone induced 50% greater cytotoxicity for HRMECs compared to bare AuNPs and 80% greater cell death by the Au-nanoradiator effect. In conclusion, this study describes a new therapeutic anti-Flt1 gold nanocomplex with enhanced antiangiogenic properties and nanoradiator-mediated cytotoxicity on retinal endothelial cells. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1272-1283, 2019.

Effect of bump structural friction on the performance of bump foil bearing and rotor dynamic behavior: Experimental study

Air foil bearings are a kind of self-acting lubricated bearing, which have potential applications in high-speed turbomachinery. Air foil journal bearings have simple structure that consists of top foil, bump foil, and bearing sleeve, and use gas as working fluid. However, the relative motion of top foil and bump foil, bump foil and bearing sleeve occurs when dynamic pressure is generated as long as there is spinning of shaft. Thus, the friction between each part of bearing should be considered when modeling. Many papers have theoretically shown the effect of Coulomb friction between top foil and top foil, bump foil and bearing sleeve on the static and dynamic performances of air foil journal bearing by developing many bump foil structural models. The results show that this foil structural Coulomb friction can significantly make bump foil stiffer. However, the improvement of the Coulomb friction effect through experiments is quite difficult and there is no study regarding this so far. The purpose of this paper is to certify the Coulomb effect on bearing performance by using experimental method. Two bump foil journal bearings are manufactured with different bearing sleeve surface roughnesses. Foil structure stiffness, bearing lift-off speed, and rotor dynamic behavior supported by two sets of bearings are measured and compared.

Coulomb effect in laser-induced recollision excitation

Coulomb effect in laser-induced recollision excitation

Investigation of Incomplete Fusion events: Recent Results

The dynamics of incomplete fusion processes has been extensively investigated and is found to compete with complete fusion at low incident energies (i.e. ≤ 7.0 MeV/A). Recent reports suggest that the probability of incomplete fusion depends on Qα of the projectile, and found to be originated from the high input angular momentum provided into the system due to non-central collisions. Apart from the well documented existence of low energy incomplete fusion, a strong contradiction on previously established mass-asymmetry systematics has been noticed recently. It has been found that the incomplete fusion fraction increases with entrance channel mass-asymmetry for the individual projectiles. Further, a strong dependence of incomplete fusion on the Coulomb effect (ZP ZT ) has been observed and is found to increase linearly with ZP ZT, a significantly important approach to understand the breakup fusion reactions. For better insights into the onset and strength of incomplete fusion in terms of various entrance channel parameters and to understand the role of high angular momenta in the onset of incomplete fusion, a quality data have been obtained in a variety of experiments performed at the Inter-University Accelerator Center (IUAC), New Delhi, India. Some of the recent results are presented in this paper, conclusively demonstrating the effect of entrance channel parameters on the onset and strength of incomplete fusion, and the usefulness of incomplete fusion to populate high-spin states in final reaction products.