Electron Energy Dissipation Research Articles

Slow electrons in condensed matter: The large polaron.

We discuss the interactions and energy dissipation of subexcitation electrons in homogeneous and isotropic condensed materials in the framework of a perturbative, generalized polaron theory. The polaron structure includes only Fourier components of the Coulomb interaction with momentum transfers \ensuremath{\Elzxh}q less than the polaron momentum p, thus limiting the treatment to long-range coupling. The coupling between the electron and rovibrational modes of the material is represented by off-diagonal form factors. The energy contributed to the polaron by virtual excitations is represented by the real part of a perturbation term, whose imaginary part represents energy dissipated (irreversibly) into other excitations. Quantitative knowledge of the relevant parameters remains undeveloped.

On dose correction in electron beam lithography

Ideal proximity exposure compensation is shown to occur when the dose correction factors are obtained by considering the electron energy dissipation distribution at the lowest plane in the resist. In such an ideal situation, the simulation of resist profiles in line patterns shows that the resist edge slope becomes nearly equal to what can be obtained with a single beam line.

Charge storage in MOS structures as affected by avalanche- and photoinjection

Experimental data are presented for charge storage in dry SiO 2 of silicon MOS structures, which accompanies electron avalanche- and photoinjection. Dependencies of the effect on prehistory, temperature and field were investigated. Dominant positive charging of nonhydrated structures at 300 K and a field ⋍ 2 MV/cm were observed. Its characteristic time was found by means of pulse photoinjection. The results obtained are discussed in terms of indirect energy dissipation of hot electrons in SiO 2.

OH production in the collision-free UV photolysis of aliphatic nitro compounds

The low-pressure gas phase photolysis of some simple nitroalkanes (C nH 2n+ 1NO 2) at ≈ 282 nm leads to OH radical formation for n > 1. The results indicate a transition state involving a five-membered ring, as suggested previously for the thermal dissociation of these compounds. This result is supported by isotopic substitution studies, and by the fact that the rotational distribution of nascent OH radicals is essentially independent of the parent molecule. The low quantum yield (0.5–2%) and the absence of parent fluorescence show that another dissociation channel (or radiationless process) is the major route of electronic energy dissipation.

Studies of energy dissipation in resist films by a Monte Carlo simulation based on the Mott cross section

The present paper applies a more accurate Mott cross section, which is calculated by the partial wave expansion to a Monte Carlo simulation of the electron energy dissipation process in resist films on substrates. Calculated spatial distributions of absorbed energy in a PMMA film on an Au substrate at 10 and 20 keV have shown an appreciable difference between the old and new models. A comparison between the two models will be made for developed resist profiles. Discussions also extend to a correction of the scattering probability near the resist–substrate boundary. This correction is significant when there is a large difference in atomic number between a film and a substrate.

Hot phonon effects in heterolayers

The theory of hot phonon effects in heterolayers is presented, in particular for electrons in gallium arsenide. The acoustic mode and optical mode cases are distinct. For the former, at low temperature, a phonon flux is radiated out of the heterolayer, and can be partially absorbed in a neighboring layer. For the latter, the phonon excitation buffers the electron energy dissipation and reduces the power scale in the dependence of electron temperature on power input. Also it adds appreciably to the total energy per electron and lengthens the thermalization ttime. Theoretical results are compared with experimental data.

Breakdown simulation of electronegative gases in non-uniform field

Gas breakdown in electronegative gases and short non-uniform field gap is studied with a set of equations taking into account the spatio-temporal changes of the conductivity along the discharge axis and the variation of the neutral species density due to hydrodynamic processes. This simulation from a precise configuration to a general conclusion shows how the spark formation is controlled by electron energy dissipation, and in particularly the fraction of this energy which dissipates as thermal energy and by the attachment process via the field redistribution.

Spatial energy dissipation profiles, W values, backscatter coefficients, and ranges for low-energy electrons in methane

In the energy range from 25 eV to 5 keV the spatial energy dissipation of electrons in methane has been studied experimentally by ionization chamber measurements as well as theoretically by Monte Carlo calculations. Using the measured and calculated spatial ionization and energy transfer distributions, the average energy W required to produce an ion pair, practical ranges, and backscatter coefficients with respect to ionization, energy, and particle number have been determined. The standard deviations of the measured W values are less than 1% for energies T ≧ 30 eV . Because of this, the differential ω values could also be derived from the energy dependence of the experimental W values. The agreement between our experimental and theoretical data is very satisfactory over the whole energy range. The theoretical results were therefore used to determine some other quantities useful in the fields of microdosimetry, such as, for instance, the energy absorption within thin layers of mass per area between 0.1 μg/cm 2 and 50 μg/cm 2 and the probability of ionization along an electron track.

Chemistry and evolution of Titan's atmosphere

Abstract The chemistry and evolution of Titan's atmosphere is reviewed in the light of the scientific findings from the Voyager mission. It is argued that the present N2 atmosphere may be Titan's initial atmosphere rather than photochemically derived from an original NH3 atmosphere. The escape rate of hydrogen from Titan is controlled by photochemical production from hydrocarbons. CH4 is irreversibly converted to less hydrogen rich hydrocarbons, which over geologic time accumulate on the surface to a layer thickness of ∼0.5 km. Magnetospheric electrons interacting with Titan's exosphere may dissociate enough N2 into hot, escaping N atoms to remove ∼0.2 of Titan's present atmosphere over geologic time. The energy dissipation of magnetospheric electrons exceeds solar e.u.v. energy deposition in Titan's atmosphere by an order of magnitude and is the principal driver of nitrogen photochemistry. The environmental conditions in Titan's upper atmosphere are favorable to building up complex molecules, particularly in the north polar cap region.

Chemistry and evolution of Titan's atmosphere

The chemistry and evolution of Titan's atmosphere is reviewed in the light of the scientific findings from the Voyager mission. It is argued that the present N 2 atmosphere may be Titan's initial atmosphere rather than photochemically derived from an original NH 3 atmosphere. The escape rate of hydrogen from Titan is controlled by photochemical production from hydrocarbons. CH 4 is irreversibly converted to less hydrogen rich hydrocarbons, which over geologic time accumulate on the surface to a layer thickness of ∼0.5 km. Magnetospheric electrons interacting with Titan's exosphere may dissociate enough N 2 into hot, escaping N atoms to remove ∼0.2 of Titan's present atmosphere over geologic time. The energy dissipation of magnetospheric electrons exceeds solar e.u.v. energy deposition in Titan's atmosphere by an order of magnitude and is the principal driver of nitrogen photochemistry. The environmental conditions in Titan's upper atmosphere are favorable to building up complex molecules, particularly in the north polar cap region.

Inductive Effect of Substituents and their Influence on the Rate of Temperature Quenching of Eu3+ Luminescence in mixed Ligand Europium β- Diketonates

Abstract The mechanism of dissipation of electronic excitation energy of rare earth element (REE) ions into the vibration components of the closer and the farther surroundings is a problem of considerable theoretical and practical interest. Temperature quen ching of REI luminescence in chelates was studied in a number of papers/1 – 6/ which revealed the importance of the energy position of the lower triplet levels of the organic ligand and the resonance excited level of the REE ion. As the temperature is raised.

Collisional drift waves in a plasma with electron temperature inhomogeneity

A fluid theory of collisional electrostatic drift waves in a plasma slab with magnetic shear is presented. Both electron temperature and density gradients are included. The equations are solved analytically in all relevant regions of the parameter space defined by the magnetic shear strength and the perpendicular wavelength and explicit expressions for the growth rates are given. For shear strengths appropriate for present-day tokamak discharges the temperature gradient produces potential wells which localize the mode in the electron resistive region, well inside the ion sound turning points. Mode stability arises from a competition between the destabilizing influence of the time dependent thermal force and the stabilizing influence of electron energy dissipation. Convective energy loss is not important for shear parameters of present-day fusion devices.

Lateral spreads of energy dissipation profiles of 20-kV electrons in polymethylmethacrylate: Functional representation and its application to proximity effect

Monte Carlo calculations have been used extensively to study the energy dissipation of electrons penetrating into solid materials both in the direction of the initial electron trajectory and lateral to it. Knowing the lateral energy dissipation is important for the prediction of proximity effects in electron-beam lithography and limiting resolution in scanning electron microscopy. The Weibull probability density functions are shown to approximate the lateral energy dissipation profiles determined by Monte Carlo calculations of 20-keV electrons in polymethylmethacrylate (PMMA), and their application to simple line and square patterns of electron-beam exposure are also discussed.

Substrate thickness considerations in electron beam lithography

A comprehensive theoretical and experimental study of the spatial distribution of electron energy dissipation in a very thin polymer film for dot, line, and parallel line exposures over a wide range of substrate thickness and exposure dosage is reported. The two Monte Carlo models used in the theoretical calculations are reviewed and the theoretical results obtained are discussed. Experimental fabrication of thin substrates and effective techniques of electron beam lithography on such substrates are described. The concept of equienergy dissipation contours is discussed and then used to compare experimental data with theory. Good agreement between experiment and theory has been obtained. With substrate thickness as a variable, the fundamental influence of electron scattering on the resolution of electron beam lithography has been verified.

Non-radiative transitions as Förster's energy transfer to solvent vibrations

New experimental evidence is given to the approach suggested by the authors to non-radiative transitions in rare earth and transition metal ions as radiationless energy transfer from ion to ligand and solvent molecule vibrations. Using non-radiative transitions in Yb 3+ as an example the participation of combinations of vibrations in the electronic energy dissipation was investigated. Dy 3+ in solutions was used to show the role of anharmonicity in non-radiative transitions. It was proved that the semi-empirical calculations of non-radiative transition rates by Förster's formula gave also good results for Mn 2+ ions luminescence which is an example of “strong” vibronic interaction. The suggested approach permits to explain the anomalous low probability of the 5D 1− 5D 0 non-radiative transition in the Eu 3+ ion.

Electron scattering and line profiles in negative electron resists

Starting with a depth-dose theory of electron energy dissipation in negative electron resists and a quasimonoenergetic Gaussian scattering theory, we derive theoretical expressions for single-line profiles using the exposure parameters of the Bell Laboratories electron-beam exposure system (EBES). These profiles are calculated by convoluting the Gaussian scattering distribution with the experimentally determined relationship between resist thickness remaining after development and input electron dose. Calculated profiles for the negative electron resist P(GMA-co-EA) agree well with experimental results for the range of feature sizes exposed on EBES. Since features on EBES are built up by multiple passes, the theory is extended to line profiles separated by the address structure of EBES. The calculated resist profiles are in reasonably good agreement with experimental results. The observed profile heights are somewhat greater than predicted by theory since the developed gel is not perfectly rigid and gel interaction takes place between neighboring profiles. The results show the importance of good gel rigidity and high contrast for negative electron resists used in high resolution applications. The range of validity of the trends predicted by the quasimonoenergetic theory for increasing film thickness and operating voltage are extended using a Monte Carlo approach which includes the effects of energy loss. The calculated trends have led to the choice of optimum exposure conditions for EBES.

946. Calculation of heating of an anode with natural heat conduction at local dissipation of electron energy: E I Sokolovskiy,Rep of Ryazan Radiotech Inst, No 35, 1973, 97–106 ( in Russian)

946. Calculation of heating of an anode with natural heat conduction at local dissipation of electron energy: E I Sokolovskiy,Rep of Ryazan Radiotech Inst, No 35, 1973, 97–106 ( in Russian)

Energy Relaxation Process inn-Type InSb under Strong Longitudinal Magnetic Fields

The energy relaxation process in n -type InSb at liquid helium temperatures under the presence of strong longitudinal magnetic fields has been analysed taking into account the existence of an impurity band. The impurity band is found to act as a thermal reservoir of the conduction band electrons, which strongly affects the energy relaxation process. The observed saturation in the magnetic field dependence of the energy relaxation time is ascribed to the reduction of the rate of energy dissipation of conduction band electrons to the lattice, which arises from the interaction between electrons in the conduction and the impurity band.

The self-focusing of electromagnetic beams in a strongly ionized magnetoplasma

The paper presents an investigation of the self-focusing of Gaussian electromagnetic beams propagating in a strongly ionized plasma along a static magnetic field. The nonlinearity in the dielectric tensor of the plasma arises because of the heating and consequent redistribution of electrons along the wavefront. At low values of magnetic field the main source of electron energy dissipation is thermal conduction; for large magnetic fields the carrier mean free path becomes comparable to or greater than the Larmor radius of the electrons, and the collisional loss of energy becomes dominant. This investigation reveals that the length of self-focusing of the beam in the extraordinary as well as ordinary mode of propagation is reduced by the application of the magnetic field, for low values of the magnetic field (ωc double less-than sign ω). For higher values of the magnetic field the self-focusing of the extraordinary mode is further enhanced while that of the ordinary mode is reduced.

Investigation of kilovolt electron energy dissipation in solids

A new technique to determine the depth distribution of energy loss, the so-called depth-dose function, is described for electrons whose energies ranged from 15 to 30 keV at normal and 45° incident angles. This method is based on a series of measurements of currents induced by the penetration of energetic electrons through a metal-oxide-semiconductor-structure (Al–SiO2–Si) specimen whose metal electrode is formed by an aluminum layer deposited in a stepwise manner. The experimental depth-dose function and range-energy relation are compared with other experimental and theoretical results. A particular interest was taken in the comparison of the experimental results with those predicted by our Monte Carlo calculations to confirm the good agreement between them. Furthermore, the ratio of the product of mobility and lifetime to the mean electron excitation energy in SiO2 was also determined to be μτ/EA = 0.10 × 10−11 cm/V2, which may be ranked between the values reported by Everhart and Hoff and by Goodman. The effects of space charge in SiO2 are also discussed.