Electron-ion Energy Research Articles

Critical dopant concentrations govern integer and fractional charge-transfer phases in doped P3HT

The conjugated polymer poly(3-hexylthiophene) (P3HT) p-doped with the strong acceptor tetrafluorotetracyanoquinodimethane (F4TCNQ) is known to undergo ion-pair (IPA) formation, i.e. integer-charge transfer, and, as only recently reported, can form ground state charge-transfer complexes (CPXs) as a competing process, yielding fractional charge transfer. As these fundamental charge-transfer phenomena differently affect doping efficiency and, thus, organic-semiconductor device performance, possible factors governing their occurrence have been under investigation ever since. Here, we focus on the role of a critical dopant concentration deciding over IPA- or CPX-dominated regimes. Employing a broad, multi-technique approach, we compare the doping of P3HT by F4TCNQ and its weaker derivatives F2TCNQ, FTCNQ, and TCNQ, combining experiments with semi-classical modeling. IPA, CPX, and neutral-dopant ratios (estimated from vibrational absorption spectroscopy) together with electron affinity and ionization energy values (deduced from cyclic voltammetry) allow calculating the width of a Gaussian density of states (DOS) relating to the highest occupied molecular orbital in P3HT. While a broader DOS indicates energetic disorder, we use grazing-incidence x-ray diffraction to assess spatial order. Our findings consider the proposal of nucleation driving IPA formation and we hypothesize a certain host-dopant stoichiometry to be key for the formation of a crystalline CPX phase.

Electron thermal internal transport barriers triggered by the effect of ion shielding

The formation of electron thermal internal transport barriers (eITBs) is investigated by critical gradient threshold analysis for recent EAST experiments with dominant RF heating and low torque injection. The ratio of electron temperature to ion temperature, τ = T e/T i, is identified to be the key parameter that triggers eITB in the hot electron mode through electron turbulence suppression by the effect of ion shielding. The critical gradient of electron-temperature-gradient turbulence can be greatly increased with τ due to strong electron heating and weak electron–ion energy coupling. The formation and evolution of eITB is found to be determined by the critical temperature gradient of electron turbulence.

Piezoresistive Behavior of Polypyrrole:Carboxymethyl Cellulose Composites.

The unique properties of conducting polymers make them ideally suited for applications in organic electronics, photovoltaics, and energy storage systems. Depending on the specific application, they can outperform metal-based electronics by cost, mechanical flexibility, molecular design opportunities, and environmental impact. Many composites of conducting polymers with polyanions can be processed in water. However, the facile processing of such composites comes at a cost of reduced conductivity. In this manuscript, electronic conductivity dependence on composition for a composite of polypyrrole (PPy) with carboxymethyl cellulose (CMC) has been studied. Secondary ion mass spectrometry and electron energy loss spectroscopy mapping indicate the formation of a nanostructure forming PPy-rich nanospheres with a CMC-rich surface coverage. This structure requires inter-particle electron conduction to occur via quantum tunneling. Variations in the tunneling distance are dependent on the applied pressure, giving rise to a pressure-dependent electronic conductivity and thus piezoresistance. This behavior opens new applications of conducting polymer composites in pressure-sensitive electronic devices, providing metal-free alternatives to quantum tunneling composites.

Measurements of ion-electron energy-transfer cross sectionin high-energy-density plasmas.

We report on measurements of the ion-electron energy-transfer cross sectionutilizing low-velocity ion stopping in high-energy-density plasmas at the OMEGA laser facility. These measurements utilize a technique that leverages the close relationship between low-velocity ion stopping and ion-electron equilibration. Shock-driven implosions of capsules filled with D^{3}He gas doped with a trace amount of argon are used to generate densities and temperatures in ranges from 1×10^{23} to 2×10^{24}cm^{-3} and from 1.4 to 2.5 keV, respectively. The energy loss of 1-MeV DD tritons and 3.7-MeV D^{3}He alphas that have velocities lower than the average velocity of the thermal electrons is measured. The energy loss of these ions is used to determine the ion-electron energy-transfer cross section, which is found to be in excellent agreement with quantum-mechanical calculations in the first Born approximation. This result provides an experimental constraint on ion-electron energy transfer in high-energy-density plasmas, which impacts the modeling of alpha heating in inertial confinement fusion implosions, magnetic-field advection in stellar atmospheres, and energy balance in supernova shocks.

Spectroscopic, biological activity studies, and DFT calculations, of Pd(II) and Pt(II) complexes of 4-Methylene-3-phenyl-3,4-dihydroquinazoline-2(1H)-thione

Four palladium (II) and platinum(II) complexes with the formula [MCl2(HPhqS)2] and [M(PhqS)2] (MII = Pd and Pt), were synthesized by treating Na2PdCl4 or K2PtCl4 with 2 mol of 4-Methylene-3-phenyl-3,4-dihydroquinazoline-2(1H)-thione (HPhqS) with or without the present base. The geometry around the Pd(II) and Pt(II) ions was a square planner and the HPhqS ligand was bonded as monodentate through the sulfur atom in complexes (1) and (2), while as bidentate chelating ligand through the nitrogen and sulfur atoms in complexes (3) and (4) as revealed by the data collection from spectroscopic studies. The prepared compounds were fully characterized by different physicochemical and spectroscopic methods. Furthermore, the free HPhqS ligand and its complexes were evaluated in vitro in regard to their antimicrobial activity against five bacteria species (Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, staphylococcus epidermidis and staphylococcus aureus). Moreover, the cytotoxic activity of the compounds was examined against breast (MCF-7) and lung (A549) cancer cell lines, and the [PdCl2(LH)2] (1) and [PtCl2(LH)2] (2) appeared a highest inhibitory effect against MCF-7 cell lines with IC50 = 4.291 ± 0.181 μM and 3.479 ± 0.162 μM, respectively, in comparison to the standard control and other complexes. The prepared ligand accompanied by the synthesized complexes were optimized using B3LYP method and 6–311++G(d,p) biases sets for the ligand and SDD basis set for the central metal. Different quantum parameters including electron affinity, ionization energy, dipole moment, hardness and vibrational frequencies were calculated for the ligand and its complexes. The total energy calculated for the two tautomeric structures of the ligand HPhqS showed a slightly higher value of the thione form over the thiol form. In addition, the trans-[PdCl2(HPhqS)2] complex possessed the highest dipole moment values while the cis-[PtCl2(HPhqS)2] showed non. In general, the obtained theoretical results showed a good match to the experimental findings.

Langmuir analysis of electron beam induced plasma in environmental TEM

The characterisation of the gas state under electron impact is of high importance for the understanding of materials in-situ environmental transmission electron microscopy (ETEM) experiments. We report on the formation of a dilute plasma state of Ar and He based on the development of a Langmuir probe as a plasma diagnostic tool for the differentially pumped volume at the TEM sample position in the octagon. In order to keep stray magnetic field influences of the objective lens small, and thus the results readily interpretable within existing theory, the experiments are performed in Lorentz mode. The applicability of Langmuir type analysis for the identification of plasma parameters, such as ion density, plasma temperature, sheath extension and electron energy distribution is examined. The systematic study as a function of gas pressure and beam current reveals cold plasma characteristics with electron temperatures of around 0.4 eV and ion and electron densities that are orders of magnitude below the expected values from ionisation cross sections. The loss of charged particles appears to be due to surface collisions at the electrically conducting pole piece surfaces as well as at the conductive parts of the TEM holder.

Schottky barrier heights and mechanism of charge transfer at metal-Bi2OS2 interfaces

Strong Fermi-level pinning (FLP) always occurs at the two-dimensional (2D) semiconductor-metal interface due to the complex interfacial charge transfer. By using monolayer (ML) Bi2OS2, an emerging 2D semiconductor with the highest electron mobility, the Schottky barrier heights (SBHs) and origin of charge transfer at Bi2OS2-metal interfaces are systematically studied based on density functional theory calculations. In 3D metal-Bi2OS2 interfaces, the formation of chemical bonding and the effect of Pauli exchange repulsion are found to be responsible for the strong interfacial charge transfer, resulting in strong FLP, and the direction of charge transfer induced by the two factors is opposite. Besides, an extra interfacial charge transfer is expected to equilibrate the Fermi level when the work functions (WFs) of metal electrodes are out of the range of electron affinity energy and ionization energy of semiconductors. For 2D metal-ML Bi2OS2 interfaces, surprisingly, the FLP is found to be entirely suppressed, and thereby, the 2D metal-Bi2OS2 contacts obey the conventional Schottky-Mott model. Such intriguing behavior arises from the 2D metal electrodes chosen in this work can effectively shield the effect of Pauli exchange repulsion. Consequently, wide-range and linear-tunable SBHs can be obtained and the conversion from n-type Ohmic contact to p-type Ohmic contact can be achieved by using 2D metal electrodes with different WFs. This study not only provides a theoretical foundation for selecting favorable metal electrodes in devices based on ML Bi2OS2, but also helps to enhance the understanding of the mechanism of interface interaction between metals and 2D semiconductors.

A deep insight of solubility behavior, mechanical quantum, thermodynamic, and mechanical properties of Pebax-1657 polymer blends with various types of vinyl polymers: A mechanical quantum and molecular dynamics simulation study

Molecular dynamics (MD) simulations are a key method frequently used to develop and design new blend polymers and predict their properties. In this study, frontier molecular orbital (FMO) and mechanical quantum (MQ) methods were used to determine the partial charges, energy values, phase behavior, regioselectivity, chemical reactivity, and surface properties of Pebax-1657 (Px) and three vinyl group polymers. Subsequently, the blend compatibility, miscibility, and mechanical behavior of poly (vinyl fluoride) (PVF), poly (vinyl chloride) (PVC), and poly (vinyl acetate) (PVAc) with Px were analyzed for a range of combinations using atomistic simulation systems. Accordingly, MD simulations were performed for the Px/PVAc, Px/PVC, and Px/PVF blend models with different composition ratios (80/20, 70/30, and 60/40, by weight) at a temperature T = 298 K and pressure P = 1 bar. For all the systems, the electron affinity (A) and ionization energy (I) were determined to calculate the global softness (σ), global hardness (η), polarizability, chemical potential (µ), and electrophilicity index (ω). The softness decreased in the following order: PVC > Px > PVF > PVAc. It can be deduced that PVC and PVAc are the most polarizable and exhibit the lowest chemical reactivities. Additionally, PVF and PVC exhibited the highest and lowest chemical hardness values, respectively. Accordingly, based on the calculated solubility parameters, PVAc, PVC, and PVF were miscible with Px and reached the same glass transition temperature (Tg). Moreover, the χ (chi) parameters of the Px-PVAc, Px-PVC, and Px-PVF polymer blends were ranked as follows: Px-PVF (∼2.66) > Px-PVC (∼1.59) > Px-PVAc (∼0.64), suggesting that Px-PVAc and Px-PVF exhibited high and low miscibility, respectively. Furthermore, the mechanical properties of Px-PVAc, Px-PVC, and Px-PVF blend polymers reduced when the content of PVAc, PVC, and PVF exceeded 30% wt.

Method to determine the electron–ion temperature relaxation rate from test particle distributions

A method to calculate the electron–ion energy exchange rate from the forces on and velocities of an ensemble of test particles is described. The essence of the method is that the energy exchange rate is related to the covariance between the distribution of velocities of test particles and the forces acting on them. The energy exchange rate is related to the electron–ion temperature relaxation rate in the limit of a low test particle speed. A proof of concept is conducted with first-principles molecular dynamics simulations.

Electronegativity: A continuing enigma

AbstractThere continues to be confusion concerning the concept of electronegativity. Pauling's original approach, focusing upon an atom in a molecule, continues to be widely invoked. There has also been a more recent tendency to view electronegativity as the negative of the chemical potential and to extend it to molecules. However, this leads to results that are incompatible with chemical experience. A more effective approach, which gives results in overall agreement with Pauling's values, is to relate electronegativity to the average valence electron ionization energies of atoms.

Mass Spectrometric Studies of Valine Molecules by Electron Shock in the Gas Phase

Relevance. Valine is one of the eight amino acids not synthesised by the human body, necessary for the synthesis and growth of body tissues, muscle coordination; regulation of nervous processes, nitrogen metabolism, and stabilisation of the hormonal background. Since α-amino acids contain an asymmetric carbon atom, they can exist as optical isomers (mirror antipodes) that play an essential role in protein biosynthesis. The structure of matter and the physical processes that occur in it are studied using the method of mass spectrometry and spectral analysis. This indicates the relevance of the problem that was studied in this paper. Purpose. Mass spectrometric studies of the formation of ionic products of single and dissociative ionisation of the valine molecule (C5 H11NO2) with electrons according to the method of beams intersecting within the energy range of bombarding electrons 6-70 eV. To consider the mechanisms of formation of the most intense ion fragments during dissociative ionisation by electron shock. Methods. The experiment was conducted on an installation with a monopole mass spectrometer of the MX-7304A type, which belongs to the class of dynamic mass analysers with electron shock ionisation in the range of mass numbers 0-120 Da. The mass spectra of molecules were investigated at different temperatures of the source of molecules in the range of 300-600 K. Results. The obtained results are compared with the mass spectra of the D-, L-, and DL-enantiomeric forms of the valine molecule with data from the NIST and SDBS databases. The features of the processes of formation of ion fragments of valine molecules by electronic shock are analysed in detail, and the dynamics of the yield of ion fragments in the range of evaporation temperatures of the initial substance of 300-440 K is also studied. The total relative ionisation cross-section of the molecule under study was measured according to mass spectrometric method with an ionising electron energy of 5-60 eV. Based on the results of experimental studies, a threshold section of the dependence of the total relative cross-section of valine ionisation is determined and given in this paper. Conclusions. A detailed analysis of the processes of formation of fragment ions in the mass spectra allows demonstrating the influence of the structural forms of valine enantiomers on the redistribution of relative intensities of product ions

Nonthermal acceleration of atoms as a mechanism of fast lattice heating in ion tracks

Atomic heating in a solid takes place after an impact of a swift heavy ion within a time of electronic cooling there, i.e., ∼100 fs. This implies an extremely fast electron–ion energy exchange (“electron–phonon coupling”) necessary for the production of detected ion tracks. In contrast, laser irradiation experiments and calculations show too slow electron–phonon energy exchange to cause structural changes detected in swift heavy ion tracks in solids. We demonstrate that this contradiction can be resolved by taking into account that electron–phonon coupling is not the sole mechanism of energy exchange between electrons and ions in condensed matter. Excitation of the electronic system alters the potential energy surface of atoms, causing them to accelerate and increase their kinetic energy at ultrashort times.

Electron-Ion Temperature Relaxation in Warm Dense Hydrogen Observed With Picosecond Resolved X-Ray Scattering

Angularly resolved X-ray scattering measurements from fs-laser heated hydrogen have been used to determine the equilibration of electron and ion temperatures in the warm dense matter regime. The relaxation of rapidly heated cryogenic hydrogen is visualized using 5.5 keV X-ray pulses from the Linac Coherent Light (LCLS) source in a 1 Hz repetition rate pump-probe setting. We demonstrate that the electron-ion energy transfer is faster than quasi-classical Landau-Spitzer models that use ad hoc cutoffs in the Coulomb logarithm.

Nonlocal pseudopotential energy density functional for orbital-free density functional theory

Orbital-free density functional theory (OF-DFT) is an electronic structure method with a low computational cost that scales linearly with the number of simulated atoms, making it suitable for large-scale material simulations. It is generally considered that OF-DFT strictly requires the use of local pseudopotentials, rather than orbital-dependent nonlocal pseudopotentials, for the calculation of electron-ion interaction energies, as no orbitals are available. This is unfortunate situation since the nonlocal pseudopotentials are known to give much better transferability and calculation accuracy than local ones. We report here the development of a theoretical scheme that allows the direct use of nonlocal pseudopotentials in OF-DFT. In this scheme, a nonlocal pseudopotential energy density functional is derived by the projection of nonlocal pseudopotential onto the non-interacting density matrix (instead of “orbitals”) that can be approximated explicitly as a functional of electron density. Our development defies the belief that nonlocal pseudopotentials are not applicable to OF-DFT, leading to the creation for an alternate theoretical framework of OF-DFT that works superior to the traditional approach.

Photoionization Spectroscopic and Theoretical Study on the Molecular Structures of cis- and trans-3-Chlorothioanisole.

Resonance-enhanced two-photon ionization (R2PI) and mass-analyzed threshold ionization (MATI) spectra are measured for the cis- and trans-3-chlorothioanisole (3ClTA). The first electronic excitation energy (E1) and the adiabatic ionization energy (IE) of the cis-rotamer are determined to be 33 959±3 and 65 326±5 cm–1, respectively, and those of the trans-rotamer are determined to be 34102±3 and 65 471±5 cm–1, respectively. Density functional theory (DFT) calculations confirm that both the cis- and trans-rotamers of 3ClTA are stable and coexist in their respective S0, S1, and D0 states. Both rotamers adopt planar structures with cis- being slightly more stable than trans- in the respective S0, S1, and D0 states. The conformation, substitution, and isotope effects on the molecular structure, active vibrations, and electronic transition and ionization energies of 3ClTA are analyzed.

Першопринципні методи обчислення лінійного коефіцієнта термічного розширення квазібінарних евтектичних систем

To calculate the linear coefficient of thermal expansion (LCTE) and its temperature dependence, a combination of the method of a priori pseudopotential and quasi-harmonic approximation (author's methods) is used. After approximating the results obtained for metal-like materials (carbides, borides, silicides), the LCTE is presented in an analytical form. In the case of quasi-binary eutectic systems based on carbides, borides, silicides, to estimate the interaction energy of the elements of two components, the concept of a virtual crystal (with a virtual cell) along the line of contact of two components is introduced. A virtual cell is assigned a volume average between the volume of a unit cell of two components, taking into account their concentration ratio. The components that make up the eutectic retain their crystal structure, their LCTE can be estimated as for pure components. Without taking into account the influence of interphase interaction, the LCTE of the eutectic system is determined using the rule of mixtures based on the LCTE components, taking into account their volume fraction. Taking into account the influence of the interface on thermal expansion is estimated by the virtual cell assigned to it. To determine the LCTE of the eutectic system, a ratio is proposed that connects the LCTE components and the docking boundaries through the concentration ratio. This method more realistically describes the structure of a quasi-binary eutectic. There is a consistency between the calculated and experimental data. Keywords: electron-ion system energy, interatomic interaction potential, quasiharmonic approximation, linear coefficient of thermal expansion, eutectic temperature.

Striations in moderate pressure dc driven nitrogen glow discharge

Plasma stratification has been studied for more than a century. Despite the many experimental studies reported on this topic, theoretical analyses and numerical modeling of this phenomenon have been mostly limited to rare gases. In this work, a one-dimensional fluid model with detailed kinetics of electrons and vibrationally excited molecules is employed to simulate moderate-pressure (i.e. a few Torrs) dc discharge in nitrogen in a 15.5 cm long tube of radius 0.55 cm. The model also considers ambipolar diffusion to account for the radial loss of ions and electrons to the wall. The proposed model predicts self-excited standing striations in nitrogen for a range of discharge currents. The impact of electron transport parameters and reaction rates obtained from a solution of local two-term and a multi-term Boltzmann equation on the predictions are assessed. In-depth kinetic analysis indicates that the striations result from the undulations in electron temperature caused due to the interaction between ionization and vibrational reactions. Furthermore, the vibrationally excited molecules associated with the lower energy levels are found to influence nitrogen plasma stratification and the striation pattern strongly. A balance between ionization processes and electron energy transport allows the formation of the observed standing striations. Simulations were conducted for a range of discharge current densities from ∼0.018 to 0.080 mA cm−2, for an operating pressure of 0.7 Torr. Parametric studies show that the striation length decreases with increasing discharge current. The predictions from the model are compared against experimental measurements and are found to agree favorably.

Ion\u2013electron energy transfer in kinetic and fluid modelling of the tokamak scrape-off layer

Using the 1D kinetic electron code SOL-KiT, simulations of the divertor tokamak scrape-off layer were carried out to explore the presence of kinetic effects in energy transfer between the ions and electrons. During steady-state conditions, it was found that the ion–electron energy transfer is well described by a fluid model, with only minimal differences seen when electrons are treated kinetically. During transient regimes (featuring a burst of energy into the scrape-off layer), we see evidence of enhanced energy exchange when calculated kinetically as compared to a fluid model. The kinetic correction represents an additional 8–55% ion–electron energy transfer across the domain, depending on the pre-transient plasma collisionality. Compared to the total energy going into the plasma during the transient, the correction is less than 1%, so its impact on plasma profiles may be small. The effect is seen to increase in strength along the domain, peaking in front of the divertor target. The overall discrepancy (integrated along the domain) increases during the transient energy burst and disappears on a similar timescale. However, at the target the effect peaks later and takes several multiples of the transient duration to relax. This effect may be only partially explained by an additional population of cold electrons arising from neutral ionization.

Cold Electron Ionization (EI) Is Not a Supplementary Ion Source to Standard EI. It is a Highly Superior Replacement Ion Source.

GC-MS usually employs a 70 eV electron ionization (EI) ion source, which provides mass spectra with detailed fragment ion information that are amenable for library search and identification with names and structures at the isomer level. However, conventional EI often suffers from low intensity or the absence of molecular ions, which reduces detection and identification capabilities in analyses. In an attempt to enhance the molecular ions, several softer ion sources are being used to supplement standard EI, including chemical ionization (CI), atmospheric pressure chemical ionization (APCI), field ionization (FI), photoionization (PI), and low electron energy EI. However, the most advantageous way to enhance molecular ions is to use cold EI, which employs 70 eV EI of cold molecules in supersonic molecular beams. Cold EI yields classical EI mass spectra with highly enhanced molecular ions, which still provides high detectability and library-searchable mass spectra. In this paper, we explain and discuss why cold EI is not a supplementary ion source to standard EI, but rather it is a highly superior replacement to standard EI. With cold EI, there is no need for standard EI or any other supplemental ion source. We describe 16 benefits and unique features of cold EI that not only yield better results for existing applications but also significantly extend the range of compounds and applications amenable for GC-MS analysis.

Photoionization of zwitterionic liquids

The electronic structures of three zwitterionic liquids (Zw-IL) have been studied using high-level ab initio method: equation-of-motion coupled-cluster (IP-EOM-CCSD) method. This method was found to match experimental UV photoelectron spectrum (UPS) of related N-methylimidazole better than Outer-valence Green’s Function (OVGF) method or Symmetry Adapted Cluster-Configuration Interaction (SAC-CI) method. Zw-IL gas phase photoelectron spectra have been simulated in the valence ionization regions based on the vertical ionization energies calculated. Valence ionizations have been attributed to specific molecular orbitals to specific functional groups The calculated electronic structures and valence ionization energies of Zw-ILs can be related to their polarizability which in turn influences the AC conductivity. AC conductivity is one of the principal properties of Zw-ILs which makes them very useful as electrolyte materials in lithium ion batteries or electric capacitors.