Electron excitation and the optical potential in electron microscopy

Ritchie, R.H.; Howie, A.

doi:10.1080/14786437708244948

Cited by 409 publications

(256 citation statements)

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“…The coefficients for the parametrization of (ω e ,q), written as a set of Drude-like functions, 51,57 are shown in Refs. 38 and 42.…”

Section: A Monte Carlo Modeling Of Photons High-energy Electrons Amentioning

confidence: 99%

“…Scattering of a high-energy electron is treated with the complex dielectric function (CDF) formalism 38,51,57,58 : the cross sections σ i (E e ) for electron scattering within solid diamond are obtained from optical data, 53,54 extended for the case of finite momentum transfer q. The cross section is then calculated from the complex dielectric function (ω e ,q) as…”

Section: A Monte Carlo Modeling Of Photons High-energy Electrons Amentioning

confidence: 99%

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Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

2013

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Diamond irradiated with an ultrashort intense laser pulse in the regime of photon energies from soft up to hard x rays can undergo a phase transition to graphite. This transition is induced by an excitation of electrons from the valence band or from atomic deep shells of the material into its conduction band, which is followed by a transient rapid change of the interatomic potential. Such a nonthermal phase transition occurs on a femtosecond time scale, shortly after or even during the laser pulse. In this work we show that the duration of the graphitization depends on the incoming photon energy: the higher the photon energy is, the longer the secondary electron cascading which promotes the electrons into the conduction band will take. The transient kinetics of the electronic and atomic processes during the graphitization is analyzed in detail. The damage threshold fluence is calculated in the broad photon energy range and is found to be always ∼0.7 eV/atom in terms of the average dose absorbed per atom. It is confirmed that the temporal characteristics of a femtosecond laser pulse (at a fixed pulse duration and fluence) do not significantly influence the transient damage kinetics. Finally, the influence of an additional surface layer of high-Z material on the damage within diamond is discussed.

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“…The coefficients for the parametrization of (ω e ,q), written as a set of Drude-like functions, 51,57 are shown in Refs. 38 and 42.…”

Section: A Monte Carlo Modeling Of Photons High-energy Electrons Amentioning

confidence: 99%

Section: A Monte Carlo Modeling Of Photons High-energy Electrons Amentioning

confidence: 99%

Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

2013

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“…For the sake of simplicity, in this work we use the simple quadratic dispersion relation introduced by Ritchie and Howie [25], with its parameters for liquid water [24], since the model is easier to implement in this way and it gives results of the same level of accuracy as other approximations used in our methodology.…”

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confidence: 99%

Semiempirical Model for the Ion Impact Ionization of Complex Biological Media

et al. 2013

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We present a semiempirical model for calculating the electron emission from any organic compound after ion impact. With only the input of the density and composition of the target we are able to evaluate its ionization cross sections using plausible approximations. Results for protons impacting in the most representative biological targets (such as water or DNA components) show a very good comparison with experimental data. Because of its simplicity and great predictive effectiveness, the method can be immediately extended to any combination of biological target and charged particle of interest in ion beam cancer therapy. DOI: 10.1103/PhysRevLett.110.148104 PACS numbers: 87.53.Àj, 79.20.Àm, 87.14.gk, 87.56.Àv Secondary electron emission is a key step in the mechanism of radiation damage to biomolecular systems induced by ion impact. As a matter of fact, ion beam cancer therapy exploits the particular properties of ion tracks, in which the ionization yield reaches a maximum near the end of their trajectories (the Bragg peak), allowing a precise and narrow energy deposition in deep-seated tumors, minimizing the radiation effects in healthy surrounding tissues [1]. These ejected electrons can produce further ionizations, initiating an avalanche effect, leading to the energy transfer to sensitive biomolecular targets, such as DNA or proteins. But not only is the number of emitted electrons relevant, but also their energy spectrum, since, although high energy electrons are those capable of producing further ionizations, it has been shown that low energy electrons (below ionization threshold) can also produce damage to biomolecules by dissociative electron attachment [2,3].In order to reach a deeper understanding of ion beam cancer therapy from a fundamental point of view, a great amount of data is needed regarding several and very diverse processes, since the whole mechanism implies steps in very different energy, space, and time scales. Therefore, the problem must be studied within a multiscale approach [4], a fact that motivates an interdisciplinary effort within the European COST Action Nano-IBCT (Nanoscale insights into ion beam cancer therapy) to build a comprehensive database [5]. In this context, ionization data for a wide variety of projectile and organic target combinations, covering a broad range of incident and ejected energies, is needed in order to get insight into micro-and nanometric aspects of radiation damage to biomolecular systems. The aim of this Letter is to present a simple theoretical method that provides the above mentioned required ionization data with the use of little input information, based on the dielectric formalism [6] and some physically motivated approximations. Results are here presented for proton impact, although the methodology can be immediately extended to heavier ions, electrons, and other charged particles.Although several simple theoretical and semiempirical methods already exist nowadays to calculate the energy spectra of secondary electrons [7] (and are currently in us...

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“…These primary excitation processes include interband transitions, surface and bulk plasmons, the latter being dominant. The dielectric function E is used to describe both single and collective excitations [27]. The energy loss function for a bulk plasmon can be written following the Drude model [28,29] [33] shows that the cross-section profiles describe the K-edge roughly for an edge where the fine structures are important, such as BN.…”

Section: Calculation Of a Spectrummentioning

confidence: 99%