Influence Of Electronic Excitation Research Articles

Electron Irradiation of Two-dimensional MoS2: Insights into the Influence of Electronic Excitations from First-principle Calculations

Electron Irradiation of Two-dimensional MoS2: Insights into the Influence of Electronic Excitations from First-principle Calculations

Transport coefficients and heat fluxes in non-equilibrium high-temperature flows with electronic excitation

The influence of electronic excitation on transport processes in non-equilibrium high-temperature ionized mixture flows is studied. Two five-component mixtures, N2/N2+/N/N+/e− and O2/O2+/O/O+/e−, are considered taking into account the electronic degrees of freedom for atomic species as well as the rotational-vibrational-electronic degrees of freedom for molecular species, both neutral and ionized. Using the modified Chapman-Enskog method, the transport coefficients (thermal conductivity, shear viscosity and bulk viscosity, diffusion and thermal diffusion) are calculated in the temperature range 500–50 000 K. Thermal conductivity and bulk viscosity coefficients are strongly affected by electronic states, especially for neutral atomic species. Shear viscosity, diffusion, and thermal diffusion coefficients are not sensible to electronic excitation if the size of excited states is assumed to be constant. The limits of applicability for the Stokes relation are discussed; at high temperatures, this relation is violated not only for molecular species but also for electronically excited atomic gases. Two test cases of strongly non-equilibrium flows behind plane shock waves corresponding to the spacecraft re-entry (Hermes and Fire II) are simulated numerically. Fluid-dynamic variables and heat fluxes are evaluated in gases with electronic excitation. In inviscid flows without chemical-radiative coupling, the flow-field is weakly affected by electronic states; however, in viscous flows, their influence can be more important, in particular, on the convective heat flux. The contribution of different dissipative processes to the heat transfer is evaluated as well as the effect of reaction rate coefficients. The competition of diffusion and heat conduction processes reduces the overall effect of electronic excitation on the convective heating, especially for the Fire II test case. It is shown that reliable models of chemical reaction rates are of great importance for accurate predictions of the fluid dynamic variables and heat fluxes.

Influence of electronic excitations on structural, optical and electrical properties of undoped and antimony doped tin oxide thin films

Study reports on the influence of swift heavy ion irradiation (SHII) induced electronic excitations (EEs) on structural, optical and electrical properties of undoped SnO2 (TO) and antimony doped SnO2 (ATO) thin films. EEs in the thin films were induced by 70MeV Si ion irradiation. It is noticed from the structural analysis that the crystallinity of TO and ATO almost remains unchanged upon Si ion beam irradiation. However, morphological studies by atomic force microscopy and scanning electron microscopy show surface modification upon irradiation. Interestingly, transport measurements show that the pristine ATO film possesses high conductivity which further increases upon irradiation for a fluence of 1×1012ions/cm2, followed with drastic decrease in conductivity and carrier concentration at higher fluences of irradiation. Band gap modification in TO and ATO films are also reported with irradiation fluence and found to be in agreement with quantum confinement (QC) model for TO; while with Burstein-Moss shift (BMS) model for ATO films. However, the modifications at higher fluence can be ascribed to the band tail states due to very high disorder in the lattice as revealed by very high value of Urbach energy in corroboration with transmittance investigations, which also exhibits a significant decrease in transmittance in both films at irradiation fluence ≥1×1013ions/cm2.

Theoretical investigation of thermophysical properties in two-temperature argon-helium thermal plasma

The thermophysical properties of argon-helium thermal plasma have been studied in the temperature range from 5000 to 40 000 K at atmospheric pressure in local thermodynamic equilibrium and non-local thermodynamic equilibrium conditions. Two cases of thermal plasma considered are (i) ground state plasma in which all the atoms and ions are assumed to be in the ground state and (ii) excited state plasma in which atoms and ions are distributed over various possible excited states. The influence of electronic excitation and non-equilibrium parameter θ = Te/Th on thermodynamic properties (composition, degree of ionization, Debye length, enthalpy, and total specific heat) and transport properties (electrical conductivity, electron thermal conductivity, and thermal diffusion ratio) have been studied. Within the framework of Chapman-Enskog method, the higher-order contributions to transport coefficient and their convergence are studied. The influence of different molar compositions of argon-helium plasma mixture on convergence of higher-orders is investigated. Furthermore, the effect of different definitions of Debye length has also been examined for electrical conductivity and it is observed that electrical conductivity with the definition of Debye length (in which only electrons participate in screening) is less than that of the another definition (in which both the electrons and ions participate in screening) and this deviation increases with electron temperature. Finally, the effect of lowering of ionization energy is examined on electron number density, Debye length, and higher-order contribution to electrical conductivity. It is observed that the lowering of the ionization energy affects the electron transport-properties and consequently their higher-order contributions depending upon the value of the non-equilibrium parameter θ.

ChemInform Abstract: Spectroscopic Studies of Collision-Induced Desorption from Surfaces

It is now possible to perform spectroscopic studies of particles desorbed from surfaces by energetic collisions. In this discussion, experiments are described which allow measurement of the energy and angle of ejection of atoms in specific electronic states. The states are detected by directing a pulsed laser beam over the sample surface and ionizing the desorbing atom via multiphoton resonance absorption. The results are then compared to molecular dynamics computer simulations of the ion-bombardment event. For this set of calculations, a special extension of the classical model has been developed which allows the influence of electronic excitation to be included

Influence of electronic excitations on the thermodynamics of small carbon clusters: the example of C3 +

We illustrate the influence of the thermalization of electrons on the linear-cyclic isomerization of small carbon clusters by model Monte Carlo calculations of C3 + at 3500 K. It is shown that the inclusion of the electronic degrees of freedom, in such systems with several low-lying excited states, can significantly change the relative isomer populations and energy distributions, as compared with equivalent electronic ground-state simulations.

State-to-state dissociation rate coefficients in electronically excited diatomic gases

In the present Letter, state dependent dissociation rate coefficients in diatomic gases with non-equilibrium vibrational and electronic excitation and chemical reactions are studied. A widely used Treanor–Marrone model is generalized to take into account state-to-state vibrational and electronic distributions. The influence of electronic excitation on the rate of dissociation from various electronic states of CO molecules is estimated.

Radiation effects in insulators: past, present, future

Interest in the structure and chemical and physical properties of irradiated ionic crystals in the 1960s and 1970s lead to the initiation of this series of conferences with REI-1 at Arco, Lago di Garda (Italy) in 1981. The early programs focused on treatment of collisional events in insulators (mainly from ions) and the physical and chemical properties of defects. Studies were about evenly distributed among halides, oxides, glasses and organic polymers. Radiation effects in nuclear waste materials and “hot” chemistry were important subjects during the mid to late 1980s but interest in these areas has decreased. In recent years, the addition of laser-induced effects has grown and the interest in polymers has focused on tailoring surfaces for specific applications, e.g. biomedical. Researches on covalent-bonded materials (SiC and diamond), complex oxides (spinels, etc.) and nanoclusters have become more prevalent. Theoretical and modeling treatments have moved from treatment of single collision events to molecular dynamics modeling of events associated with cascades. Many fundamental questions remain that will be studied by increasingly improved experimental techniques and modeling. The modeling studies will progress from describing events that occur during the first few picoseconds to description of microstructural developments. There should be renewed interest in secondary effects such as the influence of electronic excitation on defect diffusion and stability. The future of ion beam produced nanoclusters rests upon a demonstration of its ability to satisfy the demands of some unique application.

Effect of the Excited 4fLevel of Eu(Fod)3(HFod—Heptafluorodimethyloctanedione) on the Kinetics and Thermodynamics of Complex Formation in Solutions. Participation of fElectrons in Coordination Bonds

Complexation of aromatic and aliphatic ketones with Eu(Fod)3chelate (HFod is heptafluorodimethyloctanedione) is studied in the ground state using chemiluminescence and in the excited state using kinetic luminescence spectroscopy. The increase in the stability of [Eu(Fod)3 *· ketone] complexes is explained by the accepting power of Eu(III) chelate increasing as a result of the growing contribution of a covalent component of the coordination bonds due to the participation of 4f orbitals. The influence of electronic excitation of Eu(Fod)3on thermodynamic isotopic effects of complexation with acetone is established.

Molecular dynamics simulations of particle-metal surface grazing scattering under the influence of electronic excitations: Case of Si–Cu surface

A molecular dynamics (MD) study is carried out in order to investigate the role of inelastic processes on the trajectories of the particles scattered at grazing incidence from crystal surfaces. Two important electronic processes are taken into account. One is the momentum transfer associated with the electronic excitations, i.e., the electronic stopping power. The other is the fluctuation of this excitation process, which results in the energy and angular straggling. A charge exchange model is assumed to be the basis of the excitation process. In this model, the electronic system is excited by means of an electron exchange between the particle and the surface. As a result, the charge state of the particle is unstable and fluctuates. The charge fluctuations are treated semi-classically and they are unified into the classical equation of motion as a fluctuation force. The electronic stopping power and other parameter values needed in the MD simulations are determined from molecular orbital calculations of a SiCu5 cluster, and the simulations are performed for 1 keV Si beams incident on an ideal Cu{111} surface at an angle of incidence 4°. The MD simulations excluding the thermal vibrations of the target atoms reveal that the effect due to charge fluctuations yields an angular straggling of 1°, compared to 0.5° without. When room temperature thermal vibrations are included, ≥ 10% of the particles are transiently trapped in the attractive potential minima near the surface, i.e., skipping motion. This finding and the calculated energy distribution appear to agree with the experimental observations.

ChemInform Abstract: Effect of Kinetic and Electronic Energy on the Reactions of Mn+ with H2, HD, and D2.

AbstractThe influence of electronic excitation on the title reactions has been studied using guided ion beam mass spectroscopy.

Temperature dependence of phonon-frequencies and — Linewidths for weakly anharmonic molecular crystals

Results of model calculations of the shift of phonon frequencies and of phonon widths with temperature and pressure are compared with experimental results for α-N2 , NH3 , benzene, naphthalene and anthracene. The molecular crystals are assumed to be perfect, neglecting the influence of electronic excitations, impurities and lattice defects. A short description of harmonic models, often used for the lattice dynamics of molecular crystals preceeds the treatment of the models of anharmonic crystal vibrations. Within the framework of the theory shifts and widths are in qualitative, often in quantitative agreement with experiment. At low temperatures the width of external and low energy internal phonons can be nearly always explained by a population relaxation effect.

Trapping, detrapping and replacement of keV hydrogen implanted into graphite

Trapping and detrapping of low energy hydrogen isotopes in graphite is relevant to the collection of fuel particles in graphite probes for diagnostics of particle fluxes and energies in the plasma boundary layer, and to the recycling of fuel particles. The measurement of saturation concentrations by depth profiling of D may be influenced by detrapping of deuterium by the analyzing ion-beam. Detrapping yields have been measured for 1 and 8 keV deuterium implanted to saturation concentrations in papyex and pyrolytic graphite at room temperature by 790 keV H +, 400–2500 keV 3He +, and 400–1600 keV 14N + ions. Initial detrapping yields of 1 keV implanted deuterium by 790 keV 3He + and 14N + are 4 and 56 D-atoms/ion, respectively. The detrapping yiled for 14N +-ions increases with increasing energy similar to the electronic stopping power of the ions indicating the influence of electronic excitation on the detrapping mechanism. Detrapping by 790 keV H + was found to be negligible. Papyex and pyrolytic graphite show similar behavior. Careful determination of the deuterium saturation concentration from the D concentration profile by D( 3He, α)H nuclear reaction method and taking detrapping into account yields a value of 0.4 D-atoms/C-atom. Furthermore, the replacement of hydrogen by deuterium at equal ranges (8keV H +, 7keV D +) has been measured in pyrolytic graphite with elastic recoil detection (ERD) by 2.6–2.8 MeV 4He ions. The H/D isotopic replacement behavior in saturated layers is similar to that found in metals at low temperatures and in low- Z coatings as TiC at room temperature.