Quasi-free Electrons Research Articles

Efficient coupling of picosecond laser pulses with (CCl4)n clusters: Linear vs circular polarization

Ionic outcome and electron energy distribution, upon interaction of carbon tetrachloride clusters ((CCl4)n) with picosecond laser pulses of 1064 nm was investigated, to understand influence of linear and circular polarization on the mechanism of laser-cluster interaction. Contrary to the perception regarding higher proficiency of circular polarized laser pulses in collisional heating of ionized cluster, higher yield of multiply charged atomic ions (up to C5+ (I.E. ~ 392 eV) and Cl10+ (I.E. ~ 456.7 eV)) was obtained for linear polarization. Though marginally higher peak and mean electron energy were recorded for circular polarized laser pulses, with electron energy distribution extending up to ~ 300–350 eV. Present studies provide insight about the crucial steps of complex laser-cluster interaction mechanism, where inverse Bremsstrahlung energization of quasi-free electrons and screening effect within the ionized cluster are found to play a decisive role in determining efficiency of laser-cluster interaction.

Accurate Electron Drift Mobility Measurements in Moderately Dense Helium Gas at Several Temperatures

We report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26K≤T≤300K for densities lower than those at which states of electrons localized in bubbles appear. By heuristically including multiple-scattering effects into classical kinetic formulas, as previously done for neon and argon, an excellent description of the field E, density N, and temperature T dependence of μ is obtained. Moreover, the experimental evidence suggests that the strong decrease of the zero-field density-normalized mobility μ0N with increasing N from the low up to intermediate density regime is mainly due to weak localization of electrons caused by the intrinsic disorder of the system, whereas the further decrease of μ0N for even larger N is due to electron self-trapping in cavities. We suggest that a distinction between weakly localized and electron bubble states can be done by inspecting the behavior of μ0N as a function of N at intermediate densities.

The Lightest 2D Nanomaterial: Freestanding Ultrathin Li Nanosheets by In Situ Nanoscale Electrochemistry.

As the lightest solid element and also the simplest metal, lithium (Li) is one of the best representations of quasi-free electron model in both bulk form and the reduced dimensions. Herein, the controlled growth of 2D ultrathin Li nanosheets is demonstrated by utilizing an in situ electrochemical platform built inside transmission electron microscope (TEM). The as-grown freestanding 2D Li nanosheets have strong structure-anisotropy with large lateral dimensions up to several hundreds of nanometers and thickness limited to just a few nanometers. The nanoscale dynamics of nanosheets growth are unraveled by in situ TEM imaging in real-time. Further density-functional theory calculations indicate that oxygen molecules play an important role in directing the anisotropic 2D growth of Li nanosheets through controlling the growth kinetics by their facet-specific capping. The plasmonic optical properties of the as-grown Li nanosheets are probed by cathodoluminescence spectroscopy equipped within TEM, and a broadband visible emission is observed that contains contributions of both in-plane and out-of-plane plasmon resonance modes.

Transient evolution of quasifree electrons of plasma in liquid water revealed by optical-pump terahertz-probe spectroscopy

The fundamental properties of laser-induced plasma in liquid water, such as the ultrafast electron migration and solvation, have not yet been clarified. We use 1650-nm femtosecond laser pulses to induce the plasma in a stable free-flowing water film under the strong field ionization mechanism. Moreover, we adopt intense terahertz (THz) pulses to probe the ultrafast temporal evolution of quasifree electrons of the laser-induced plasma in water on the subpicosecond scale. For the first time, the THz wave absorption signal with a unique two-step decay characteristic in time domain is demonstrated, indicating the significance of electron solvation in water. We employ the Drude model combined with the multilevel intermediate model and particle-in-a-box model to simulate and analyze the key information of quasifree electrons, such as the frequency-domain absorption characteristics and solvation ratio. In particular, we observe that the solvation capacity of liquid water decreases with the increase of pumping energy. Up to ∼50 % of quasifree electrons cannot be captured by traps associated with the bound states as the pumping energy increases to 90 μJ / pulse. The ultrafast electron evolution in liquid water revealed by the optical-pump/THz-probe experiment provides further insights into the formation and evolution mechanisms of liquid plasma.

Confined water radiolysis in aluminosilicate nanotubes: the importance of charge separation effects.

Imogolite nanotubes are potentially promising co-photocatalysts because they are predicted to have curvature-induced, efficient electron-hole pair separation. This prediction has however not yet been experimentally proven. Here, we investigated the behavior upon irradiation of these inorganic nanotubes as a function of their water content to understand the fate of the generated electrons and holes. Two types of aluminosilicate nanotubes were studied: one was hydrophilic on its external and internal surfaces (IMO-OH) and the other had a hydrophobic internal cavity due to Si-CH3 bonds (IMO-CH3), with the external surface remaining hydrophilic. Picosecond pulse radiolysis experiments demonstrated that the electrons are efficiently driven outward. For imogolite samples with very few external water molecules (around 1% of the total mass), quasi-free electrons were formed. They were able to attach to a water molecule, generating a water radical anion, which ultimately led to dihydrogen. When more external water molecules were present, solvated electrons, precursors of dihydrogen, were formed. In contrast, holes moved towards the internal surface of the tubes. They mainly led to the formation of dihydrogen and of methane in irradiated IMO-CH3. The attachment of the quasi-free electron to water was a very efficient process and accounted for the high dihydrogen production at low relative humidity values. When the water content increased, electron solvation dominated over attachment to water molecules. Electron solvation led to dihydrogen production, albeit to a lesser extent than quasi-free electrons. Our experiments demonstrated the spontaneous curvature-induced charge separation in these inorganic nanotubes, making them very interesting potential co-photocatalysts.

Особенности излучательных свойств квантово-размерных частиц узкозонных полупроводников

For colloidal quantum-size particles (QP) of narrow-gap semiconductors, in contrast to quantum dots of wide-gap CdSe, in QP-PbS there take place an anomalous temperature dependence of the photoluminescence intensity. Also, in the planar microstructure containing QP-InSb, long-wavelength radiation (more than 3 µm) and photoconductivity (over 20 µm) was observed. Under certain conditions, the radiation intensity and photoconductivity demonstrate a resonance maximum. The effects were explained in the model of a one-dimensional quantum oscillator, which energy substantially depends on the effective mass of its quasi-free electron. This leads to competition between the manifestations of long-wave radiation and photoluminescence, and hence, to the anomalous temperature dependence of photoluminescence. It is assumed that QP-InSb in a planar microstructure can be sources and receivers of terahertz radiation, which properties depend on the crystal structure of quantum-sized particles determined by the parameters of their synthesis.

Active principle in potentised medicines: Nanoparticle versus quantum domain – An overview

Background: The fact that homoeopathic medicines act even at very high dilutions has created a confusion amongst scientists. This led to different models such as formation of nanoparticles and memory of water. The basic question 'what is responsible for physiological activity of homoeopathic medicines' is yet to be answered conclusively. Objective: The objective of this overview was to find out if formation of nanoparticles or creation of quantum domain in the medium is responsible for the physiological activity of homoeopathic medicines. Methods: This overview is based on the experiments done between 2004 and 2019. Results: The succussion of the medicine has the following effects: i. At high potency, due to the mechanical energy transferred to the system, the size of the substrate reduces to nanodimension increasing membrane permeability. Furthermore, they affect several electrical properties of an electroactive polymer and enhance thermovoltage generation. ii. In the presence of an ambient electromagnetic field, domains composed of the vehicular polar molecules are formed, which bear the signature of the dissolved solute. The domains are sources of quasi-free electrons which are manifested in voltage generation separating two different polar media. The structured water also explains the ultraviolet–visible (UV-Vis) spectra. Conclusion: In high potency, formation of nanoparticles explains the effect of homoeopathic medicines on properties such as permeability, electrical properties of polymers and thermovoltage generation, whereas formation of domains in the vehicle medium explains properties such as voltage generation separating two different polar media and UV-Vis spectra.

Size effects of tin oxide quantum dot gas sensors: from partial depletion to volume depletion

The grain size effect is one of the fundamental characteristics of semiconductor gas sensors. However, it has not been fully understood due to the absence of studies on the volume-depleted grains. In this work, the gas-sensitive SnO2 quantum dots (QDs) from partial depletion to volume depletion are prepared to discuss the size effects. A facile aqueous-based method is used to prepare the size-controllable SnO2 QDs of 2.0–12.6 nm. The resistance shows a monotonically negative size effect while the response reaches the optimization when the grain radius is comparable to the depletion layer width. It is suggested that the design of highly sensitive gas sensors should consider the equal importance of the control of grain size and depletion layer width. The computational results illustrate size-dependent energy level of donors and number of quasi-free electrons, which are responsible for the negative size effect of resistivity in the volume-depleted SnO2 crystallites. This work provides a comprehensive understanding of grain size effects from partial depletion to volume depletion in semiconductor gas sensors.

Temporal Development of a Laser-Induced Helium Nanoplasma Measured through Auger Emission and Above-Threshold Ionization.

Femtosecond pump-probe electron and ion spectroscopy is applied to study the development of a helium nanoplasma up to the nanosecond timescale. Electrons, bound by the deep confining mean-field potential, are elevated toward the vacuum level in the nanoplasma expansion. Subsequent electron recombination gives rise to transitions between He^{+} states, resulting in autoionization. The time-resolved analysis of the energy transfer to quasifree electrons reveals a transient depletion of the Auger emission, which allows for a temporal gate to map the distribution of delocalized electrons in the developing mean field. Furthermore, we trace the recombination of delocalized electrons near the vacuum level into highly excited Rydberg states. Transient above-threshold ionization is introduced as a diagnostic tool to resolve the dynamics. Thus, the development of the electron distribution in the nanoplasma mean-field potential can be monitored via the features observed in the emission spectra.

Exact solution of the 1D time-dependent Schrödinger equation for the emission of quasi-free electrons from a flat metal surface by a laser

We solve exactly the one-dimensional Schrödinger equation for ψ(x, t) describing the emission of electrons from a flat metal surface, located at x = 0, by a periodic electric field E cos(ωt) at x > 0, turned on at t = 0. We prove that for all physical initial conditions ψ(x, 0), the solution ψ(x, t) exists, and converges for long times, at a rate , to a periodic solution considered by Faisal et al (2005 Phys. Rev. A 72 023412). Using the exact solution, we compute ψ(x, t), for t > 0, via an exponentially convergent algorithm, taking as an initial condition a generalized eigenfunction representing a stationary state for E = 0. We find, among other things, that: (i) the time it takes the current to reach its asymptotic state may be large compared to the period of the laser; (ii) the current averaged over a period increases dramatically as ℏω becomes larger than the work function of the metal plus the ponderomotive energy in the field. For weak fields, the latter is negligible, and the transition is at the same frequency as in the Einstein photoelectric effect; (iii) the current at the interface exhibits a complex oscillatory behavior, with the number of oscillations in one period increasing with the laser intensity and period. These oscillations get damped strongly as x increases.

Abstract 482: Multiple chemical action cancer therapeutics

Abstract Radiation-produced quasi-free electrons (i.e., low energy electrons in solutions) causes DNA damage. However, there are no evidence that radiation-produced partially solvated electrons (i.e., presolvated or, prehydrated electrons) and fully solvated electrons (i.e., aqueous or solvated electrons) cause strand breaks. However, recent work on azidoDNA-model systems show that radiation-produced electrons can be converted to highly damaging aminyl radicals (RNH•) which do have the potential to cause strand breaks. Experimental studies in our labs (both in vitro and in vivo) have shown that 2-deoxy-D-glucose (2-DG), a glucose mimic and glycolytic inhibitor, enhances radiation-induced damage selectively in tumor cells while protecting normal cells and against infection. Thereby suggesting that 2-DG can be used as a differential radiomodifier to improve the efficacy of cancer radiotherapy. Based on these experimental results and data mining models, we show that the azido derivative of 2DG; 2-Azido-2-deoxy-D-glucose (2-AZ-2-DG) has unique azido chemistries. The neutral aminyl radical produced from 2-AZ-2-DG under reductive environment undergoes facile conformational change from the stable chair form to the reactive boat form. Subsequently, this aminyl radical causes H-atom abstraction from C5 of the sugar moiety via proton-coupled electron transfer process. Further, a promise as multivalent drug to augment multipronged cellular damage including site-specific DNA radiation damage and also counter infections persisting in several cancer cases. Our long range goals are to harness these unique chemistries in gold based nanotools for X-PDT (X-ray induced photodynamic therapy). Citation Format: Rao Papineni, Amithava Adhikary. Multiple chemical action cancer therapeutics [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 482.

Towards ultra-high gradient particle acceleration in carbon nanotubes

Charged particle acceleration using solid-state nanostructures is attracting new attention in recent years as a method of achieving ultra-high acceleration gradients in the order of TV/m. The use of carbon nanotubes (CNTs) has the potential to overcome limitations of using natural crystals, e.g. channelling aperture and thermo-mechanical robustness. In this work, we present preliminary particle-in-cell simulation results of laser and beam interaction with a single CNT, modelled as 20 parallel plates of Carbon ions and electrons. This is the equivalent to a 10-layers tube in 3D. We further discuss simulation of anisotropic particles to model 2D quasi-free electrons in CNT walls. Further research ideas are outlined along with the presentation of a possible proof-of-principle experiment.

Laser picoscopy of valence electrons in solids.

Valence electrons contribute a small fraction of the total electron density of materials, but they determine their essential chemical, electronic and optical properties. Strong laser fields can probe electrons in valence orbitals1-3 and their dynamics4-6 in the gas phase. Previous laser studies of solids have associated high-harmonic emission7-12 with the spatial arrangement of atoms in the crystal lattice13,14 and have used terahertz fields to probe interatomic potential forces15. Yet the direct, picometre-scale imaging of valence electrons in solids has remained challenging. Here we show that intense optical fields interacting with crystalline solids could enable the imaging of valence electrons at the picometre scale. An intense laser field with a strength that is comparable to the fields keeping the valence electrons bound in crystals can induce quasi-free electron motion. The harmonics of the laser field emerging from the nonlinear scattering of the valence electrons by the crystal potential contain the critical information that enables picometre-scale, real-space mapping of the valence electron structure. We used high harmonics to reconstruct images of the valence potential and electron density in crystalline magnesium fluoride and calcium fluoride with a spatial resolution of about 26 picometres. Picometre-scale imaging of valence electrons couldenable direct probing of the chemical, electronic, optical and topological properties of materials.

Kinematically complete experimental study of Compton scattering at helium atoms near the threshold

Compton scattering is one of the fundamental interaction processes of light with matter. Already upon its discovery [1] it was described as a billiard-type collision of a photon kicking a quasi-free electron. With decreasing photon energy, the maximum possible momentum transfer becomes so small that the corresponding energy falls below the binding energy of the electron. Then ionization by Compton scattering becomes an intriguing quantum phenomenon. Here we report a kinematically complete experiment on Compton scattering at helium atoms below that threshold. We determine the momentum correlations of the electron, the recoiling ion, and the scattered photon in a coincidence experiment finding that electrons are not only emitted in the direction of the momentum transfer, but that there is a second peak of ejection to the backward direction. This finding links Compton scattering to processes as ionization by ultrashort optical pulses [2], electron impact ionization [3,4], ion impact ionization [5,6], and neutron scattering [7] where similar momentum patterns occur.

Interaction of (CCl4)n clusters with nanosecond and picosecond laser pulses at discrete wavelengths spanning from IR to UV region: A comparative study using TOFMS

Using time-of-flight mass spectrometer (TOFMS), photochemistry of carbon tetrachloride clusters ((CCl4)n) has been investigated upon interaction with nanosecond and picosecond Nd:YAG laser pulses (266, 355, 532 and 1064 nm) spanning over intensity range of ∼1.2 × 109 to 7.9 × 1012 W/cm2. At all the laser wavelengths upon interaction of (CCl4)n clusters with laser pulse, multiphoton excitation leads to excessive fragmentation of cluster constituents, which are subsequently ionized by multiphoton absorption process. Depending on laser wavelength and pulse duration, at 266 and 355 nm these clusters exhibit dominant ion signal corresponding to singly charged fragment ions i.e. Cl+, CCl+, CCl2+ and CCl3+ in the mass spectra. In addition, for studies carried out at 266 nm using picosecond laser pulses minor ion signal corresponding to C2Cl+ and C2Cl2+ were also observed. Generation of these ions has been ascribed to intra-cluster radical chemistry resulting in generation of neutral precursors, which subsequently are multiphoton ionized. At 532 and 1064 nm, dominant ion signal corresponding to multiply charged atomic ions of carbon (up to C4+/C5+) and chlorine (up to C11+) have been observed. Though multiphoton absorption is the primary process driving the photochemistry of (CCl4)n clusters, observation of multiply charged atomic ions at 532 and 1064 nm has been ascribed to dominant role played by quasi-free electrons which are confined within the ionized cluster, in efficient coupling of laser energy at longer laser wavelengths via inverse Bremsstrahlung process.

1D Quantum Simulations of Electron Rescattering with Metallic Nanoblades

Electron rescattering has been well studied and simulated for cases with ponderomotive energies of the quasi-free electrons, derived from laser–gas and laser–surface interactions, lower than 50 eV. However, with advents in longer wavelengths and laser field enhancement metallic surfaces, previous simulations no longer suffice to describe more recent strong field and high yield experiments. We present a brief introduction to and some of the theoretical and empirical background of electron rescattering emissions from a metal. We set upon using the Jellium potential with a shielded atomic surface potential to model the metal. We then explore how the electron energy spectra are obtained in the quantum simulation, which is performed using a custom computationally intensive time-dependent Schrödinger equation solver via the Crank–Nicolson method. Finally, we discuss the results of the simulation and examine the effects of the incident laser’s wavelength, peak electric field strength, and field penetration on electron spectra and yields. Future simulations will investigate a more accurate density functional theory metallic model with a system of several non-interacting electrons. Eventually, we will move to a full time-dependent density functional theory approach.

Reaction of Electrons with DNA: Radiation Damage to Radiosensitization.

This review article provides a concise overview of electron involvement in DNA radiation damage. The review begins with the various states of radiation-produced electrons: Secondary electrons (SE), low energy electrons (LEE), electrons at near zero kinetic energy in water (quasi-free electrons, (e−qf)) electrons in the process of solvation in water (presolvated electrons, e−pre), and fully solvated electrons (e−aq). A current summary of the structure of e−aq, and its reactions with DNA-model systems is presented. Theoretical works on reduction potentials of DNA-bases were found to be in agreement with experiments. This review points out the proposed role of LEE-induced frank DNA-strand breaks in ion-beam irradiated DNA. The final section presents radiation-produced electron-mediated site-specific formation of oxidative neutral aminyl radicals from azidonucleosides and the evidence of radiosensitization provided by these aminyl radicals in azidonucleoside-incorporated breast cancer cells.

An Integral Method for Processing Xenon Used as a Working Medium in the RED-100 Two-Phase Emission Detector

An integral method is described for processing xenon used as a working medium in the RED-100 two-phase emission detector constructed in the NRNU MEPhI to study the process of elastic coherent neutrino scattering off atomic nuclei. The developed technology for purifying xenon and the detector has made it possible to increase the lifetime of quasi-free electrons in the 205-kg liquid xenon from ≤0.1 to ≥400 μs in fields of 50−500 V/cm. The entire procedure takes approximately 1000 h. The method can be used to process working media for new-generation two-phase emission detectors designed to conduct basic research, in particular, searching for dark matter in the form of weakly interacting massive particles, detecting boron solar neutrinos, and searching for neutrinoless double-beta decay.

Molecular orbitals of delocalized electron clouds in neuronal domains

We have further developed the two-brains hypothesis as a form of complementarity (or complementary relationship) of endogenously induced weak magnetic fields in the electromagnetic brain. The locally induced magnetic field between electron magnetic dipole moments of delocalized electron clouds in neuronal domains is complementary to the exogenous electromagnetic waves created by the oscillating molecular dipoles in the electro-ionic brain. In this paper, we mathematically model the operation of the electromagnetic grid, especially in regard to the functional role of atomic orbitals of dipole-bound delocalized electrons. A quantum molecular dynamic approach under quantum equilibrium conditions is taken to illustrate phase differences between quasi-free electrons tethered to an oscillating molecular core. We use a simplified version of the many-body problem to analytically solve the macro-quantum wave equation (equivalent to the Kohn-Sham equation). The resultant solution for the mechanical angular momentum can be used to approximate the molecular orbital of the dipole-bound delocalized electrons. In addition to non-adiabatic motion of the molecular core, ‘guidance waves’ may contribute to the delocalized macro-quantum wave functions in generating nonlocal phase correlations. The intrinsic magnetic properties of the origins of the endogenous electromagnetic field are considered to be a nested hierarchy of electromagnetic fields that may also include electromagnetic patterns in three-dimensional space. The coupling between the two-brains may involve an ‘anticipatory affect’ based on the conceptualization of anticipation as potentiality, arising either from the macro-quantum potential energy or from the electrostatic effects of residual charges in the quantum and classical subsystems of the two-brains that occurs through partitioning of the potential energy of the combined quantum molecular dynamic system.

Auger emission from the Coulomb explosion of helium nanoplasmas.

The long-time correlated decay dynamics of strong-field exposed helium nanodroplets is studied by means of photoelectron spectroscopy. As a result of the adiabatic expansion of the laser-produced, fully inner-ionized nanoplasma, delocalized electrons in the deep confining mean field potential are shifted towards the vacuum level. Meanwhile, part of the electrons localize in bound levels of the helium ions. The simple hydrogenlike electronic structure of He+ results in clear signatures in the experimentally observed photoelectron spectra, which can be traced back to bound-free and bound-bound transitions. Auger electron emission takes place as a result of the transfer of transition energy to weakly bound electrons in the quasifree electron band. Hence, the spatial and temporal development of the nanoplasma cloud is encoded in the experimental spectra, whereas the electronic properties of He+ help resolve the different contributions.