Probable Energy Loss Research Articles

Microwave Absorption in Ge After Bombardment of Helium Ions Beam

AbstractIn this work, the effect of Ge sample bombardment by energy Ei = 1.2 MeV mono‐energetic He+ ions within the fluence range of 1013–1.2 × 1015 cm−2 on the microwave reflection/transmission modification in the frequency range of 26–38 GHz is investigated. It is shown for the first time that such Ge treatment allows achieving a drastic increase in its interaction with microwaves. After the 1 µm thick undersurface area of Ge, accounting for less than 10−3 of its bulk, underwent the fluence of 1.2 × 1015 cm−2, the increase of the microwave absorption coefficient from 0.06 to 0.78 and decrease of the microwave reflection coefficient from 0.7 to 0.18 are observed. This is caused by the occurrence of dangling atomic bonds in nanoscale cavities inside the material. Most probable energy loss mechanisms of microwaves in modified Ge are suggested. Modified semiconductor structures can be used as microwave‐absorbing coverings, devices employing a periodic structure of materials or a gradient of its properties.

On the Impact Parameter Dependence of the Ionization Energy Loss of Fast Negatively Charged Particles in an Oriented Crystal

When a fast charged particle passes through matter, it loses some of its energy to the excitation and ionization of atoms. This energy loss is called ionization energy loss. In rather thin layers of matter, the value of such energy loss is stochastic. It is distributed in accordance with the law, which was first received by L.D. Landau. In amorphous substances, such a distribution (or spectrum), known as the Landau distribution, has a single maximum that corresponds to the most probable value of particle energy loss. When a particle moves in crystal in a planar channeling mode, the probability of close collisions of the particle with atoms decreases (for a positive particle charge) or increases (for a negative charge), which leads to a change in the most probable energy loss compared to an amorphous target. It has recently been shown that during planar channeling of negatively charged particles in a crystal, the distribution of ionization energy loss of the particles is much wider than in the amorphous target. In this case, this distribution can be two-humped, if we neglect the incoherent scattering of charged particles on the thermal oscillations of the crystal atoms and the electronic subsystem of the crystal. This paper explains the reason for this distribution of ionization energy loss of particles. The ionization energy loss distribution of high-energy negatively charged particles which move in the planar channeling mode in a silicon crystal are studied with the use of numerical simulation. The dependence of this distribution on the impact parameter of the particles with respect to atomic planes is considered. The dependence of the most probable ionization energy loss of particles on the impact parameter is found. It is shown that, for a large group of particles, the most probable ionization energy loss during planar channeling in a crystal is lower than in an amorphous target.

Impact of the experimental approach on the observed electronic energy loss for light keV ions in thin self-supporting films

Energy spectra of keV ions interacting with self-supporting foils of Au and W were recorded with a Time-of-Flight Medium-Energy Ion Scattering system in different backscattering and transmission geometries in an otherwise identical experimental setup. For He ions transmitted through Au spectra of detected particles depending on geometry show two distinct components, i.e. different energy loss distributions in the film, whereas for protons no such phenomenon was observed. The two components in the spectrum of transmitted He could be attributed to impact parameter dependent energy loss, being more prominent for He than for protons. The main origin of the necessary impact parameter selection along different trajectories is expected to be texture in the Au-foils. Electronic stopping powers obtained from both, most probable energy loss in transmission and best fits to spectrum width in backscattering are in agreement within experimental uncertainties. This observation applied for all investigated combinations of projectile and target material.

Analytic saddlepoint approximation for ionization energy loss distributions

We present a saddlepoint approximation for ionization energy loss distributions, valid for arbitrary relativistic velocities of the incident particle 0<v/c<1, provided that ionizing collisions are still the dominant energy loss mechanism. We derive a closed form solution closely related to Moyal’s distribution. This distribution is intended for use in simulations with relatively low computational overhead. The approximation generally reproduces the Vavilov most probable energy loss and full width at half maximum to better than 1% and 10%, respectively, with significantly better agreement as Vavilov’s κ approaches 1.

Most probable and average energy losses of the beam of monoenergetic charge particles with average and low energies at multiple scattering

The results of statistical modeling of the discrete process of multiple inelastic scattering are presented. This process is modeled to find the most probable and average energy losses of a beam of charged particles (electrons and protons) passing through a material layer with a given thickness. The proposed approach is based on determining the most probable energy loss at single small-angle scattering, on including the effect of the statistical probability on this quantity at multiple scattering, and on determining the average number of inelastic interactions for particles in a film with a known thickness. The dependence of the particle energy lost during interaction with atomic electrons on their relative motion is taken into account for low-energy particles. A new interpretation is offered for the parameter J in the logarithmic term in the formulas for the average and most probable energy losses of charged particles. A computational scheme for this parameter as an average potential energy of atomic electrons is given.

Dynamics of the most probable energy loss by relativistic ions

Simple but very general formulas determining the parameters of the statistical distribution of inelastic energy losses (in particular, their most probable values) by relativistic ions as functions of the velocity and path length in a substance have been derived on the basis of the generalization of the classical Landau approach and steepest descent method. These expressions are more accurate than the well-known formulas and significantly expand the domains of applicability of the latter. Comparison with the numerical results confirms the high accuracy of the resulting analytical representations in wide intervals of the parameters and reveals their limitation.

Determination of the difference between the mean and the most probable energy loss of low-energy proton beams traversing thin solid foils

Precise determinations of the energy loss of ion beams in solid targets in the low-energy range (typically a few keV/u) using the transmission technique, require, among other things, a fine analysis of the energy distributions of the transmitted ion beams. In particular, it is known that possible asymmetries in the energy distributions – and related differences between the mean and the most probable energy loss – may be a source of discrepancies or uncertainties in stopping power determinations. We have performed detailed analyses of the energy-loss distributions of proton beams traversing various thin foils (12–24nm) of metallic elements (Al, Au and Bi) including mono and polycrystalline foils. The differences between the mean and the most probable energy losses in these conditions were analyzed. The analysis has been extended to the first three moments of the energy loss spectra and the results have been compared with theoretical predictions. The magnitude of the differences so obtained were in all cases very small and give good support to the use of the transmission method for precise energy loss determinations in the few-keV region.

Deflection efficiency and energy loss distributions for high energy protons in a bent crystal

Energy loss distributions and the deflection efficiency of 450 GeV protons during their passage through a (111) bent silicon crystal have been calculated by computer simulation. The path dependent stopping power and local electron density averaged along the particle trajectories were used to construct the energy loss spectra for the considered crystal layers. It was shown that the most probable energy loss for deflected particles and their straggling increase during the passage through the crystal part with increasing curvature. The observed characteristics of the calculated energy loss distributions for deflected and undeflected particles are in good agreement with experiment.

Optimal strategies for imaging thick biological specimens: exit wavefront reconstruction and energy-filtered imaging.

In transmission electron microscopy (TEM) of thick biological specimens, the relationship between the recorded image intensities and the projected specimen mass density is distorted by incoherent electron-specimen interactions and aberrations of the objective lens. It is highly desirable to develop a strategy for maximizing and extracting the coherent image component, thereby allowing the projected specimen mass density to be directly related to image intensities. For this purpose, we previously used exit wavefront reconstruction to understand the nature of image formation for thick biological specimens in conventional TEM. Because electron energy-loss filtered imaging allows the contributions of inelastically scattered electrons to be removed, it is potentially advantageous for imaging thick, biological samples. In this paper, exit wavefront reconstruction is used to quantitatively analyse the imaging properties of an energy-filtered microscope and to assess its utility for thick-section microscopy. We found that for imaging thick biological specimens (> 0.5 microns) at 200 keV, only elastically scattered electrons contribute to the coherent image component. Surprisingly little coherent transfer was seen when using energy-filtering at the most probable energy loss (in this case at the first plasmon energy-loss peak). Furthermore, the use of zero-loss filtering in combination with exit wavefront reconstruction is considerably more effective at removing the effects of multiple elastic and inelastic scattering and microscope objective lens aberrations than either technique by itself. Optimization of the zero-loss signal requires operation at intermediate to high primary voltages (> 200 keV). These results have important implications for the accurate recording of images of thick biological specimens as, for instance, in electron microscope tomography.

Electron Energy Loss Distributions in Solid and Gaseous Hydrocarbons

The dipole oscillator strength distributions for solid and for gas phase cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, and benzene were constructed from experimentally derived optical constants and from atomic X-ray absorption cross sections. Monte Carlo simulations of the energy loss by electrons of initial energy from 10 keV to 1 MeV in these media were performed using cumulative inelastic cross sections obtained from a formulation incorporating the constructed dipole oscillator strength distributions. In the solid phase, the energy loss distributions, the most probable energy losses, and the mean energy losses for electrons show little effect due to the conjugation of $pi bonds. However, there are large differences between the gases, and there is a considerable effect due to condensation. The most probable and the mean energy losses for 1 MeV incident electrons in solid cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, and benzene are in the ranges 22-24 and 47-48 eV, respectively. Comparison with data for water suggests that the values for the solid phases of hydrocarbons are acceptable approximations for the liquid phase. Density normalized stopping powers, inelastic mean free paths, and ranges for electrons in the various hydrocarbons are also presented. 36 refs., 4 figs., 7 tabs.

The energy spectrum of electrons passing through film targets and some of its applications to electron beam engineering

The problem of analytical description of the energy spectrum of transmitted electrons was solved on the basis of the two-channel model of energy losses: inelastic scattering on valence electrons and inelastic scattering on core electrons of target atoms. Based on the correspondence between the velocity of probable energy losses of each channel and the well known Landau and Thomson-Widdington correlations, the generalized form of the energy losses law is presented which describes the most probable energy losses by kilovolt electrons in films with arbitrary thickness. A semiempirical approach taking into account the straggling of energy losses based on use of the universal function obtained was developed, which characterizes the inelastic discrete losses of each transmitted electron group with energy E. On the basis of these results the analytical description of the energy distribution of transmitted electrons is given for beryllium, aluminium, copper, silver and gold films and correlation is made between the calculated distribution and experimental spectra. Some possibilities of using the results obtained for application to electron probe methods are shown.

Electron Energy-Loss Distributions in Solid, Dry DNA

Experimentally derived optical constants and X-ray attenuation cross sections were used to construct the complete dipole oscillator strength distribution for solid, dry DNA. Monte Carlo simulations of the energy loss by electrons of initial energy 5 keV to 1 MeV in DNA were performed using cumulative inelastic cross sections obtained from a formulation incorporating the constructed dipole oscillator strength distribution. The energy-loss distribution, the most probable energy loss and the mean energy loss for electrons in DNA are compared to those for liquid water, gaseous water and gaseous hexane. For the most part, the calculations show that electron energy loss in DNA is very similar to that in liquid water; however, it is quite different from both gaseous water and gaseous hexane. The mean energy losses for a 1 MeV incident electron in DNA, liquid water, gaseous water and gaseous hexane are 57.9, 56.8, 50.9 and 38.4 eV, respectively. The large differences found between the predictions for DNA and for the gaseous media bring into serious question calculations of radiation-induced damage in DNA which make use of cross sections for gaseous media. Stopping powers and continuous-slowing-down approximation ranges for the media for electrons are also presented.

Quantification of the electron beam damage of thin films

Owing to diverse possible mechanisms of the e-beam damage, some changes either in the crystalline structure, chemical composition or film thickness occur as the proper “damage” of the virgin state. Changes in the chemical bonds are often connected with some change in thickness or structure so that the other two are the most important items to be detected, preferably in real time of the electron-microscopical or electron-spectroscopical examination. We propose to measure the film thickness on the basis of the most probable energy loss due to the electron pass through the film and back, i.e. on the basis of the position of the broad background maximum in the electron spectra of stratified specimens. A change in crystallinity can be sensed through the elastic peak intensity. Placing a measurement window between these features in the energy scale and measuring the energy filtered background during the irradiation, we get a pronounced dependence of the signal on the dose which unambiguously reveals the damage limit in the form of a curve knee. In some cases, two stages of damage are detectable.

Position-dependent stopping powers of the (100) surfaces of NaCl-type crystals for MeV light ions

Energy losses of MeV H and He ions after interaction of clean surfaces of several NaCl-type crystals at glancing-angle of incidence are investigated. From the most probable energy losses of ions reflected from the surface atomic plane, position-dependent stopping powers of the (100) surfaces of NaCl, KCl, KBr, SnTe, PbSe and PbTe for MeV H and He ions are determined. The results are explained by a sum of the stopping caused by dynamic response of valence electrons to fast ions in vacuum and that due to single ion-electron collisions.

Energy loss of axially channeled antiprotons

A detailed study of energy spectra (channeled fraction, most probable energy loss, shape of the spectra) of low energy antiprotons moving in a thin crystal, under axial channeling conditions is performed using a Monte Carlo computer simulation. The results of calculations for antiprotons are compared with those for protons. It was observed that the channeled fraction of the antiproton beam is considerably smaller than that for protons due to strong dechanneling. This fraction as a function of incident angle shows a maximum at angles near ψ = 0.5 ψ L. Whereas for protons, well aligned with a crystal axis, the energy loss is onsiderably reduced as compared to the random beam, for antiprotons the energy loss is nearly the same as for those in a random direction. The spectra for antiprotons are wider than those for protons and have a high-loss tail. In general the directional effects in energy spectra are less pronounced for antiprotons than for protons.

Axial channelling of low-energy antiprotons

Monte Carlo computer simulation of the passage of antiprotons and protons through a silicon crystal under axial channelling conditions is performed. The energy spectra and angular distribution of channelled protons and antiprotons moving along the (110) direction are calculated and compared. The projectile energy range is from 300 keV to several megaelectronvolts. It is shown that the energy loss corresponding to the maximum of the antiproton spectrum is close to the energy loss of particles moving in a random direction. Moreover, the most probable energy loss of the channelled part of the antiproton beam is slightly less than the random energy loss. The Barkas correction to the energy loss has little effect on the energy spectra of channelled particles and can hardly be studied with this type of experiment. The angular distributions of protons and antiprotons differ considerably. The characteristic features of the angular distribution may serve as evidence of channelling of low-energy antiprotons.

High-resolution measurements of ion energy loss in thin films

The energy loss distribution of ∼ 100 keV H + and He + transmitted through thin carbon films (6–16 nm) has been measured with an energy resolution of ∼ 30 eV in ∼10 −7 Torr. We find the following: (1) the energy loss distribution is fitted by either a symmetric or an asymmetric Gaussian; (2) the film thickness derived from the most probable energy loss ( ΔE p) with the tabulated stopping powers agrees within 10% for H + and He +; (3) ΔE p increases by approximately 20% per μC/mm 2 of H + and He + bombardment, and this effect appears not to be scaled with the nuclear stopping power.

Energy loss by electrons in gaseous saturated hydrocarbons

The stopping powers, the inelastic mean free paths, the ranges, and the distributions of energy loss events for electrons in some gaseous alkanes have been calculated from experimentally based dipole oscillator strength distributions. The results show very little difference between the members of the homologous series of straight-chain hydrocarbons, C{sub n}H{sub 2n+2} where n = 2, 4, 6, and 8. For instance, the integrated path length of a 1-MeV electron in ethane of unit density is 0.38 cm and increases to 0.40 cm in octane of the same density. The stopping power of a 1-MeV electron in unit density hexane is 0.2 eV/nm, and the inelastic mean free path is 220 nm. The corresponding values for the other alkanes differ by less than 10%. The distribution of energy loss events along the track of a high-energy electron in these gaseous hydrocarbons is not significantly affected by the value of n, and it is insensitive to the incident electron energy from 10 keV to 1 MeV. The most probable energy loss along the track of a 1-MeV electron is 14 eV in ethane, 15 eV in butane and hexane, and 16 eV in octane. The mean energy loss is 25 eVmore » in butane, hexane, and octane and is 1 eV less in ethane.« less

Electron Microscope Tomography (Emt): Reconstruction Algorithms, Imaging and Mass Loss of Thick Sections

We previously reported EMT reconstructions of thick (&gt;0.5 μm) sections using electron spectroscopic imaging at the most probable electron energy loss (ΔEp). We2 calculated values of contrast and signal-to-noise ratio (SNR) for images formed with electrons taken throughout the spectrum. We observed maximal SNR just below ΔEp, and found that changes in the electron beam voltage and mass thickness (t/λ) led to predictable changes in the EELS.We have begun a study of mass loss due to electron exposure of thick epon sections. Uranyl and lead stained sections were put on formvar covered grids and carbon coated on each side. Clear epon regions were analyzed. During each exposure series the beam was kept at crossover; the beam current was changed from its lowest value (0.5 μamp) to its highest value (55 μamp). As reported elsewhere, mass loss occurs early and plateaus. Calculations were based on EELS collected at different times during each series (Figure 1a). Measured positions of ΔEp at different times (min) of maximum beam current irradiation are shown in Figure 1 b. Mass thickness, t/λ = In (total area/zero loss area), shows a linear relationship with ΔEp (Figure 1c). Using λ = 115 nm in epon, we calculate the initial thickness of the sections to be 0.5, 0.75, 1.0 μm and the mass loss to be ∼37 nm. If mass loss is independent of the specimen thickness, then the 50% loss observed with thinner specimen becomes a trivial 4-7% loss in sections of 0.5 to 1.0 μm.

Energy distribution of electrons transmitted through thin foils

The energy distributions of electrons transmitted through thin foils are investigated especially with regard to the possibilities of an analytical representation of these spectra. Most probable energy losses are quantified and compared with mean energy losses. A mathematical description of the energy spectra is presented and its applicability in the electron acceleration energy region between ≈15 and 40 keV is proved by comparison with experimentally found distributions. Due to the simple form of the respective formulae several physical phenomena such as energy deposition by electrons in solids, scattering phenomena, etc., can easily be investigated and quantified.