Inelastic Interactions Of Electrons Research Articles

E-Beam Lithography Simulation Techniques

This review describes general approaches for the simulation exposure and development stages of e-beam lithography (EBL). The general models of elastic and inelastic electron interactions with matter, which are used for the simulation of the EBL exposure stage, are presented. The empirical and theoretical models of the resist’s dissolution in wet developers are provided for the simulation of the EBL profile development stage. Also, the kinetic transport and Monte-Carlo simulation algorithms are described.

Local temperature rise during the electron beam characterization Calculation model for the AlxGa1-xN at low dimensions

Abstract During the characterization by electron beam techniques including scanning electron microscope (SEM) and cathodoluminescence at low dimensions, some undesirable phenomena (unwanted effects) can be created, like the thermal effects (or electron beam damage), and these effects can damage the sample. This limits the information one can get from a sample or reduces image spatial resolution. In order to understand these effects, significant efforts have been made but these studies focused on the thermal properties, without a detailed study of the causes of nanoscale heating in the bulk of samples during the SEM-characterization. Additionally, it is very difficult to measure experimentally the heating because there are many variables that can affect the results, such as the current beam, accelerating energy, thermal conductivity and size of samples. Taking into account all the factors and in order to determine the local temperature rise during the electron beam characterization of AlGaN at low dimensions, we have used a hybrid model based on combined molecular dynamics and Monte Carlo calculation of inelastic interaction of electrons with matter to calculate the temperature elevation during the SEM-characterization which can be taken into account during the characterization of AlGaN at low dimension by electron beam techniques.

EV-TEM: Transmission electron microscopy in a low energy cathode lens instrument

We are developing a transmission electron microscope that operates at extremely low electron energies, 0–40eV. We call this technique eV-TEM. Its feasibility is based on the fact that at very low electron energies the number of energy loss pathways decreases. Hence, the electron inelastic mean free path increases dramatically. eV-TEM will enable us to study elastic and inelastic interactions of electrons with thin samples. With the recent development of aberration correction in cathode lens instruments, a spatial resolution of a few nm appears within range, even for these very low electron energies. Such resolution will be highly relevant to study biological samples such as proteins and cell membranes. The low electron energies minimize adverse effects due to radiation damage.

Limitations (and merits) of PENELOPE as a track-structure code

Purpose: To outline the limitations of PENELOPE (acronym of PENetration and Energy LOss of Positrons and Electrons) as a track-structure code, and to comment on modifications that enable its fruitful use in certain microdosimetry and nanodosimetry applications.Methods: Attention is paid to the way in which inelastic collisions of electrons are modelled and to the ensuing implications for microdosimetry analysis.Results: Inelastic mean free paths and collision stopping powers calculated with PENELOPE and two well-known optical-data models are compared. An ad hoc modification of PENELOPE is summarized where ionization and excitation of liquid water by electron impact is simulated using tables of realistic differential and total cross sections.Conclusions: PENELOPE can be employed advantageously in some track-structure applications provided that the default model for inelastic interactions of electrons is replaced by suitable tables of differential and total cross sections.

Inertial confinement fusion fast ignition with ultra-relativistic electron beams

AbstractInertial confinement fusion fast ignition at very high relativistic electron beam energy is systematically explored through a possible combination of various stopping mechanisms including strong Langmuir turbulence, elastic, and inelastic electron interactions with target particles. A specific attention is given to final state interaction through catalysis by negative pion.

Surface electron band structure and very low-energy electron diffraction reflectivity for Al(111)

The two-dimensional 2D layer Green's function scattering method is used to calculate the energy of surface states and resonances at $\overline{\ensuremath{\Gamma}}$ for Al(111) for both below and above the vacuum level. The surface-barrier potential is represented by an empirical form. The above vacuum-level surface electron band structure for this surface has not been calculated before and it is important in understanding many surface phenomena. The geometric structure of the Al(111) surface is known from intensity analysis in low-energy electron diffraction at energies 60--450 eV. The details of the surface barrier for Al(111) were obtained from a match with the below vacuum-level experimental energy position of the first Rydberg surface resonance and the Shockley surface state at ${\mathbit{k}}_{\ensuremath{\parallel}}=0(\overline{\ensuremath{\Gamma}})$. The calculation was then extended to the above vacuum-level case for 0--27 eV with the inclusion of inelastic electron interactions. Tamm-type resonances at 6.9 eV and possibly also at 8.3 eV, a Shockley-type resonance at $14.0\ifmmode\pm\else\textpm\fi{}0.5\text{ }\text{eV}$ and a series of Rydberg (image) resonances near 24 eV all above vacuum level are found at ${\mathbit{k}}_{\ensuremath{\parallel}}=0$. The same 2D layer Green's function scattering method using the same input data was then used to calculate the intensity of the 00 beam for ${\mathbit{k}}_{\ensuremath{\parallel}}=0$ (normal incidence) in very low-energy electron diffraction (VLEED) from this surface in the energy range 0--65 eV. Features in the VLEED intensities are found due to the Shockley and Rydberg resonances. Experimental data from over 26 years ago found surface features near the energies found in this work. Beam intensities from low-energy electron microscope measurements at normal incidence and new data from other surface spectroscopies could provide experimental confirmation of the resonances predicted in this work.

Inelastic Electron Interaction with Chloroform Clusters embedded in Helium Droplets

The inelastic electron interaction (ionization/attachment) with chloroform embedded in helium droplets has been studied utilizing a two-sector field mass spectrometer. Positive mass spectra have been recorded at the electron energy of 70 eV and are compared with previous results in the gas phase and with other systems embedded in helium droplets. Moreover, the negative ion mass spectrum has been recorded at the electron energy of 1.5 eV. Both negative and positive mass spectra show that chloroform clusters are easily formed by embedding single molecules in the helium droplets. Moreover, for anions appearing in the mass spectrum, the ion yield has been determined as function of the electron energy. While no parent anion of chloroform can be observed in the gas phase, the present cluster environment allows the stabilization of the transient negative ion. The influence of the helium droplet upon the ionization or attachment process of the embedded chloroform is discussed.

Inelastic electron holography as a variant of the Feynman thought experiment

Using a combination of electron holography and energy filtering, interference fringes produced after inelastic interaction of electrons with hydrogen molecules are examined. Surprisingly, the coherence of inelastic scattering increases when moving from the surface of a hydrogen-containing bubble to the vacuum. This phenomenon can be understood in terms of the Feynman two-slit thought experiment with a variable ambiguity of the which-way registration.

Memory effect on the inelastic interaction of electrons moving parallel to a solid surface

It is generally assumed that two successive inelastic interactions between an electron and a solid are independent of each other. In other words, the electron has no memory of its previous interaction. However, the previous interaction of the electron generates a potential that should influence its succeeding inelastic interaction. The aim of this work is to establish a model to account for the memory effect of an electron between two successive inelastic interactions. On the basis of the dielectric response theory, formulae for differential inverse inelastic mean free paths (DIIMFPs) and inelastic mean free paths (IMFPs) considering the memory effect were derived for electrons moving parallel to a solid surface by solving the Poisson equation and applying suitable boundary conditions. These mean free paths were then calculated with the extended Drude dielectric function for a Cu surface. It was found that the DIIMFP and the IMFP with the memory effect for electron energy E lay between the corresponding values without the memory effect for electron energy E and previous energy E0. The memory effect increased with increasing electron energy loss, E0 − E, in the previous inelastic interaction. Copyright © 2005 John Wiley & Sons, Ltd.

Inelastic interactions of electrons with cylindrical interfaces

A theory was developed to deal with inelastic interactions for an electron moving parallel to the axis of a cylindrical structure. Formulas for the differential inverse inelastic mean free path (DIIMFP) and the total inverse inelastic mean free path (IIMFP) were derived using dielectric response theory. A sum-rule-constrained extended Drude dielectric function with spatial dispersion was applied to calculate DIIMFPs and IIMFPs for a solid wire and a cavity in solid. The calculated results showed that surface excitations occurred as the electron moved near the boundary either inside or outside the solid, whereas volume excitations arose only for electron moving inside the solid. It was found that the probability for surface excitations increases and that for volume excitations decreases for an electron moving close to the surface. Near the surface, the decrease in volume excitations is compensated by the increase in surface excitations. For a cavity in solid, the IIMFP inside the solid can be approximated by a constant value equal to the IIMFP for the infinite solid, except in the immediate vicinity of the cavity boundary.

Inelastic electron interaction (attachment/ionization) with deoxyribose.

We have investigated experimentally the formation of anions and cations of deoxyribose sugar (C(5)H(10)O(4)) via inelastic electron interaction (attachment/ionization) using a monochromatic electron beam in combination with a quadrupole mass spectrometer. The ion yields were measured as a function of the incident electron energy between about 0 and 20 eV. As in the case of other biomolecules (nucleobases and amino acids), low energy electron attachment leads to destruction of the molecule via dissociative electron attachment reactions. In contrast to the previously investigated biomolecules dehydrogenation is not the predominant reaction channel for deoxyribose; the anion with the highest dissociative electron attachment (DEA) cross section of deoxyribose is formed by the release of neutral particles equal to two water molecules. Moreover, several of the DEA reactions proceed already with "zero energy" incident electrons. In addition, the fragmentation pattern of positively charged ions of deoxyribose also indicates strong decomposition of the molecule by incident electrons. For sugar the relative amount of fragment ions compared to that of the parent cation is about an order of magnitude larger than in the case of nucleobases. We determined an ionization energy value for C(5)H(10)O(4) (+) of 10.51+/-0.11 eV, which is in good agreement with ab initio calculations. For the fragment ion C(5)H(6)O(2) (+) we obtained a threshold energy lower than the ionization energy of the parent molecular ion. All of these results have important bearing for the question of what happens in exposure of living tissue to ionizing radiation. Energy deposition into irradiated cells produces electrons as the dominant secondary species. At an early time after irradiation these electrons exist as ballistic electrons with an initial energy distribution up to several tens of electron volts. It is just this energy regime for which we find in the present study rather characteristic differences in the outcome of electron interaction with the deoxyribose molecule compared to other nucleobases (studied earlier). Therefore, damage induced by these electrons to the DNA or RNA strands may start preferentially at the ribose backbone. In turn, damaged deoxyribose is known as a key intermediate in producing strand breaks, which are the most severe form of lesion in radiation damage to DNA and lead subsequently to cell death.

Monte Carlo Simulation of Electron Transport and X-Ray Generation. I. Electron Elastic and Inelastic Scattering

We present different theoretical approaches to determine differential cross sections for elastic and inelastic interactions of electrons. These cross sections are the basic ingredients for accurate Monte Carlo simulation of electron transport in matter. The considered models range from simple analytical approximations employed in early calculations to purely numerical differential cross sections described by large databases calculated with state-of-the-art theory.

Inelastic transport of tunnel and field-emitted electrons through a single atom

The desorption of individual hydrogen atoms from a Ge~111! surface with the tip of a scanning tunneling microscope is used as a prototype system for investigating the inelastic transport of electrons through a single atom. A method based on the analysis of the desorption time averaged over the spatial extent of the hydrogen site has enabled the localization and the efficiency of the inelastic electron interaction to be studied. Both the localization and the efficiency show very different features in the tunnel and field emission regimes.

Inelastic interactions of tunnel electrons with surfaces.

Inelastic interactions of electrons emitted from the tip of a scanning tunnelling microscope (STM) are used to desorb individual hydrogen atoms from a Ge(111) surface. It is observed that the inelastic interactions depend not only on the electron energy and the current intensity but also on the electron emission regime of the STM tip. Quite surprisingly, it is found that tunnel electrons interact inelastically much less efficiently than field emitted electrons even though the electrons are in resonance with the Ge-H unoccuppied orbital.

Inelastic electron interactions in overlayers on substrates

The inelastic interaction of electrons with overlayers on substrates is investigated within the framework of dielectric response theory. A general formula for the position-dependent inelastic differential inverse mean free path (DIIMFP), for electron transport in a layered system has been derived. The position dependence reveals specific details of the changes between bulk, interface and surface excitation modes. Numerical calculations of the DIIMFP and the IIMFP have been made for the case of a Au film deposited on a Si substrate, for which experimental optical constants and an extended Drude dielectric function have been used.

Inelastic interaction of electrons with lattice waves in many-valley-model semiconductors at low temperature

Inelastic interaction of electrons with lattice waves in many-valley-model semiconductors at low temperature

Inelastic Electron Interactions in the Energy Range 50 eV to 10 keV in Insulators: Alkali Halides and Metal Oxides

AbstractCalculations of electron inelastic mean free paths and stopping powers for several alkali halides (KF, KCl, KBr, and KI) and metal oxides (BeO, MgO, SiO2, and Al2O3) have been performed in the 50 eV to 10 keV energy range. The complex dielectric formalism, improved to include the energy gap, was used for estimating the valence part of the transport characteristics, whereas the part related to electron‐core interactions was evaluated according to Gryzinski's theory. An extended comparison of these calculations with the available experimental data as well as with other theoretical predictions is presented. Trends of the energy dependence of the inelastic mean free path and stopping power in alkali halides are studied. The role of the plasmon deexcitation process as a source for low‐energy electrons in secondary electron emission spectra is discussed. The presented data can be used in Monte‐Carlo simulations of electron transport in the considered materials.

Electron-stimulated desorption from ionic crystal surfaces

Inelastic interactions of electrons with surfaces of ionic crystals result in emission of various particles such as ions, atoms and molecules. We will review such electron-stimulated desorption processes for the particular class of ionic crystals, namely for alkali halides. In this case, a dominant fraction of the emission is in the form of halogen and alkali atoms characterized by a thermal (Maxwellian) spectrum of translational energies. For several alkali halides (potassium and rubidium chlorides, bromides, and iodides), however, a significant part of the halogen atoms is ejected with nonthermal energies, i.e. energies of the order of 0.1 eV. The results of recent systematic studies of angular-resolved kinetic energy distributions of the emitted particles will be reported and current views on the electronic mechanisms of desorption will be described. In particular, it will be shown that the ESD mechanism can be understood in terms of the model involving a surface localisation of the so called “hot-holes” created by electron bombardment of alkali halides. A role of hot holes in ESD processes will further be discussed in relation to very recent experimental results obtained for the KBr crystals doped with In impurities which act as efficient hole traps.

Hot-electron relaxation dynamics in quantum wires

Monte Carlo simulations of hot nonequilibrium electron relaxation in rectangular GaAs quantum wires of different cross sections are carried out. The simulations demonstrate that the initial stage of hot-electron cooling dynamics is determined by cascade emission of optical phonons and exhibits strong dependence on the excitation energy. The second (slow) relaxation stage is controlled by strongly inelastic electron interactions with acoustic phonons as well as by nonequilibrium (hot) optical phonons. The relaxation times obtained in our simulations are in good agreement with the results of recent luminescence experiments. At low electron concentrations where hot phonon effects are negligible the cascade emission of optical phonons may lead to the overcooling of the electron system to temperature below the lattice temperature. These electrons then slowly (during tens of picoseconds) relax to equilibrium due to the interaction with acoustic phonons. At certain excitation energies strong intersubband electron scattering by optical phonons leads to electron redistribution among subbands and intersubband population inversions. If the electron concentration exceeds 105 cm−1, hot phonon effects come into play. In contrast to bulk materials and quantum wells, hot phonon effects in quantum wires exhibit strong dependence on the initial broadening of the energy distribution of the electrons. The very initial electron gas relaxation stage in quantum wires is faster in the presence of hot phonons, while for t≳0.5 ps the hot phonon thermalization time defines the characteristic electron cooling time.

Inelastic interactions of electrons with surfaces: application to Auger-electron spectroscopy and X-ray photoelectron spectroscopy

Electron-based probes of surface properties are used frequently in surface science since strong inelastic scattering for electron energies between about 50 and 2000 eV ensures high surface sensitivity. An overview is given of developments in the understanding of inelastic electron scattering in solids with emphasis on important surface properties. Auger-electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) are the two techniques most commonly used for measurements of surface composition. We give a brief description of the development of AES and XPS and then proceed to describe the role of inelastic electron scattering in AES and XPS. Attention is given to the measurement of electron attenuation lengths, to the calculation of electron inelastic mean free paths, and to intensity measurements for quantitative AES and XPS.