Energy Spectrum Of Auger Electrons Research Articles

Isolated CuO and medium strong acid on CuO/Nb2O5-H catalyst for efficient enhancement of triethylamine selective catalytic oxidation

The selective catalytic oxidation (SCO) of triethylamine (TEA) to harmless N2, CO2, and H2O is an appropriate elimination technology. It is necessary to develop the catalysts capable of working under mild condition and with excellent N2 selectivity for this reaction. In this article, the CuO/Nb2O5-H catalysts with various loadings were characterized and employed for the SCO of TEA. The 15 %CuO/Nb2O5-H demonstrated the most noticeable catalytic performance. At 220 °C, the conversion of TEA reached 100.0 %, and the selectivity of N2 was 96.0 %. XPS, UV–vis results demonstrated the presence of isolated CuO species in the catalyst and auger electron energy spectra proved the content of Cu2+ species over 85 %. Pyridine-IR and NH3-TPD demonstrated the presence of a substantial number of acidic sites in Nb2O5-H. Based on the in-situ DRIFTs results, the adsorption of TEA on the acidic sites of Nb2O5-H at low temperature is considered as the initial step in the process, followed by C-N bond activation, cleavage, and adsorption of the -NH* intermediates. The -NH* was oxidized to N2 by highly dispersed copper oxide species on the catalyst surface at 220 °C.

Relaxation of Ne1+ 1s02s22p6 np produced by resonant excitation of an ultraintense ultrafast x-ray pulse

The creation and relaxation of double K-hole states 1s02s22p6 np (n ≥ 3) of Ne1+ in the interaction with ultraintense ultrafast x-ray pulses are theoretically investigated. The x-ray photon energies are selected so that x-rays first photoionize 1s22s22p6 of a neon atom to create a single K-hole state of 1s2s2p6 of Ne1+, which is further excited resonantly to double K-hole states of 1s02s22p6 np (n ≥ 3). A time-dependent rate equation is used to investigate the creation and relaxation processes of 1s02s22p6 np, where the primary microscopic atomic processes including photoexcitation, spontaneous radiation, photoionization and Auger decay are considered. The calculated Auger electron energy spectra are compared with recent experimental results, which shows good agreement. The relative intensity of Auger electrons is very sensitive to the photon energy and bandwidth of x-ray pulses, which could be used as a diagnostic tool for x-ray free electron laser and atom experiments.

An approach to assessing the contribution of the high LET effect in strategies for Auger endoradiotherapy

Purpose: The interest in exploiting Auger emitters in cancer therapy stems from their high linear energy transfer (LET) – type radiation damage. However, the design of Auger-emitter labelled vehicles, that target the Auger cascade specifically to tumour cells, is challenging, especially to bring the decay event close enough to DNA to inflict high LET– type damage in DNA. Here we suggest a possible approach to evaluate tumour-targeting Auger-labelled conjugates by assessing the impact of a radioprotector known to be effective in protecting low LET radiation, but ineffective in protecting against high LET-type radiation. However, the efficacy of the radioprotector is not known in the context of irradiation by low energy electrons from randomly distributed Auger emitters. Given some similarity between the energy spectrum of Auger electrons and that of secondary electrons from soft X-rays, we report the results of radioprotection experiments with 25 kVp X-rays. Materials and methods: Clonogenic survival curves for cultured human keratinocytes were established for three different irradiation conditions: 137Cs γ-rays, 25 keV X-rays (effective energy 15.5 keV) and 320 kVp X-rays, and the effect of including a new methylproamine analogue, denoted “2PH”, before and during irradiation, was investigated. Results: The extent of radioprotection by 2PH was essentially the same for all radiation conditions, although RBE was higher (about 1.7) for soft X-rays. This suggests that the effects of randomly distributed Auger emitters will be largely subject to radioprotection. Conclusions: It is reasonable to expect that use of methylproamine analogues will help to ascertain the relative contributions of the high-LET effects (not protected), compared to other components, including bystander effects, that are subject to radioprotection. This could be a useful tool in evaluating Auger endoradiotherapy strategies.

Ramsey interferometry for resonant Auger decay through core-excited states

We theoretically investigate the electron dynamics in Ne atoms involving core-excited states through the Ramsey scheme with a pair of time-delayed x-ray pulses. Irradiation of Ne atoms by the $\ensuremath{\sim}1$ femtosecond x-ray pulse simultaneously populates two core-excited states, and an identical but time-delayed x-ray pulse probes the dynamics of the core-excited electron wave packet which is subject to the resonant Auger decay. The energy-integrated total Auger electron yield and energy-resolved Auger electron spectra in the time domain show periodic structures due to the temporal evolution of the wave packet, from which we can obtain the counterpart in the frequency domain through the Fourier transformation. The Auger electron energy spectra in the time as well as frequency domains show the interference patterns between the two Auger electron wave packets released into the continuum from the superposition of two core-excited states at different times. These spectra are important to clarify the individual contribution of the different Auger decay channels upon core excitation by the x-ray pulse.

A Model to Realize the Potential of Auger Electrons for Radiotherapy

Auger-electron-emitting radioisotopes provide a unique tool that enables the targeted irradiation of a small volume in their immediate vicinity. Over the last forty years, Auger emission has been established as a promising form of molecular radiotherapy, and it has recently made the transition from the laboratory to the clinic. In this paper we review the physical processes of Auger emission in nuclear decay and present a new model being developed to evaluate the energy spectrum of Auger electrons from radioisotopes.

Atomic radiations in the decay of medical radioisotopes: a physics perspective.

Auger electrons emitted in nuclear decay offer a unique tool to treat cancer cells at the scale of a DNA molecule. Over the last forty years many aspects of this promising research goal have been explored, however it is still not in the phase of serious clinical trials. In this paper, we review the physical processes of Auger emission in nuclear decay and present a new model being developed to evaluate the energy spectrum of Auger electrons, and hence overcome the limitations of existing computations.

Atomic Radiation in Nuclear Decay

Auger electrons emitted in nuclear decay offer a unique tool to kill cancer cells at the scale of a DNA molecule. Over the last forty years many aspects of this promising therapeutic tool have been explored, however it is still not in the phase of large scale clinical trials. In this paper we review the physical processes of Auger emission in nuclear decay and present a new model being developed to evaluate the energy spectrum of Auger electrons, and hence overcome the limitations of existing computations. Unstable atomic nuclei release excess energy through var- ious radioactive decay processes by emitting radiation in the form of particles (neutrons, alpha, beta particles) or electromagnetic radiation (gamma-ray photons). Most of the applications using nuclear isotopes are based on the fact that the interaction of the radiations passing through material will depend on their type (photons, neutral or charged particles) and the transferred energy. Most ra- dioisotopes used in clinical therapy emitparticles, which are ionizing radiations. The biological effect is often char- acterized by Relative Biological Effectiveness (RBE) - which is related to Linear Energy Transfer, LET. LET is expressed in units ofkeV/µm,which isameasureofthe en- ergy deposited along the particle track. A new class of ra- dionuclides (1), including 149 Tb, 211 At, 211 Po, 213 Bi, 223 Ra, 225 Ac, 226 Th, 227 Ac, and 230 U, which emit® particles have been considered for therapy. The LET for most therapeu- tic® emitters ranges from 25 to 230 keV/µm. On the other hand, electrons and positrons emitted in nucleardecay, and in the internal conversion processes, referred to here asparticles, have kinetic energies ranging from tens of keV to several MeV and their LET is much lower, typi- cally» 0.2 keV/µm. A third type of ionizing radiation is Auger electrons (2), named after the French physicist Pierre Victor Auger. When an inner-shell electron is removed from an atom, the vacancy will be filled by an electron from the outer shells and the excess energy will be released as an X-ray photon, or by the emission of an Auger electron. Referred to as atomic radiations, X-ray and Auger electron emission are competing processes. The atomic transition rate and the energy of emitted X-rays and/or Auger electrons depend on the atomic number, the electron shells involved, and the electron configuration of the atom. The full relaxation of the inner-shell vacancy is a multi step process, resulting in a cascade of atomic radiations. The energy of atomic radi- ation is typically in the range from a few eV to 100 keV. Due to their short range (nm toµm), Auger electrons with relatively low energies can have a much higher LET. For

Matrix Effects in Metals and Alloys During AES Investigations

The Auger relative sensitivity factors of pure materials are frequently used for quantitative analysis of Auger electron energy spectra in the case of multicomponent samples, too. However, this procedure takes no account of the matrix effects. In the present work the matrix dependence of the two most important parameters, namely the electron mean free path and the backscattering factor are taken into consideration. The values of these two factors are calculated for Ni, Cr, Si, and Al in the case of 24 different majority materials. On the basis of this a new evaluation method of AES spectra are worked out for multicomponent samples. The efficiency of this evaluation method was checked by means of two multicomponent standard samples.

Modified relative sensitivity factors for Auger spectra

The quantitative evaluation method of Auger electron energy spectra using the relative sensitivity factors of pure materials is widely used for complex multicomponent samples. Nevertheless, the traditional “relative sensitivity factors” method leaves matrix effects out of consideration. In the present work new, modified values of the relative sensitivity factors can be calculated for the most common elements in different matrices. In this new method the most important matrix effects are taken into consideration, namely the electron inelastic mean free path and the backscattering factor.

MC model of Auger spectra from highly charged ion beam surface interaction

Abstract A Monte Carlo code is described which simulates angle resolved Auger electron energy spectra from highly charged ion surface interaction. The combined effect of the Doppler spread of laboratory emission energy and electron scattering by the solid, together with the broad inherent line width, is found to have considerable influence on the spectral lines. As a new feature, low or high energy shoulders can appear. By comparison between simulated and measured spectra information on the kinematic and electronic state of the projectile ions in the moment of electron emission can be extracted. The standard method of spectrum analysis, which is based on the assumption of direct escape of the electrons, is evaluated with respect to the simulated spectra.

He-like ions colliding on H2 an analysis of the 1s23131' electron spectra

The authors present energy spectra of Auger electrons due to autoionisation of doubly excited Be-like states with configuration 1s23l31' produced in collisions of the He-like N5+ and O6+ ions on H2 at impact energies ranging from 24 to 108 keV. The spectra are analysed using theoretically predicted energy levels and lifetimes. The theoretical values of Bachau et al (1989) are in excellent agreement with the experimental data. It is found that interferences between transitions from different states have to be taken into account to reproduce structures in the measured spectra satisfactorily. The fits yield populations for the various states. Changing the impact energy shows clear variations in the relative populations, especially an increase of the high L states with increasing impact velocity.

Auger electron and characteristic energy loss spectra for electro-deposited americium-241

Auger electron energy spectra for electro-deposited americium-241 on platinum substrate were obtained using a cylindrical mirror analyzer. Characteristic energy loss spectra for this sample were also obtained at primary electron beam energies of 990 and 390 eV. From these measurements PI, PII, and PIII energy levels for americium-241 are determined. Auger electron energies are compared with theoretically calculated values. Minimum detectability under the present condition of sample preparation and equipment was estimated at approximately 1.2×10−8 g/cm2 or 3.9×10−8 Ci/cm2. Minimum detectability for plutonium-239 under similar conditions was estimated at about 7.2×10−10 Ci/cm2.

Auger electron emission from the decay of collisionally-excited atoms sputtered from Al and Si

Atom collisions of several keV may result in inner-shell excitations. The energy spectra of Auger electrons from excitations induced by ion bombardment of solid materials are different from those stimulated by X-rays or electrons. Auger electron spectra produced by ion bombardment of solids contain features similar to spectra obtained from atoms undergoing Auger transitions in the gas phase, i.e., atomic-like spectra. An interpretation of the atomic-like spectra from ion-bombarded solids is that a significant portion of the atoms undergoing Auger de-excitation have previously been sputtered from the solid. Auger decay in the gas phase can occur if the inner-shell lifetime is sufficiently long for the excited atom to escape. Results from our Monte Carlo calculations of the origin, movement, and decay of ion-bombardment induced 2p inner-shell excitations of Al and Si will be presented. These calculations indicate that a significant portion of the Auger emission originates from sputtered atoms; the kinetic energy of atoms sputtered while experiencing inner-shell excitation far exceeds the average kinetic energy of sputtered atoms, and so, Auger electron emission may constitute a probe of the high energy collision cascade. Calculated dependence of the Auger electron intensity on the incident angle of the ion beam will be compared with measurements, and the effect of inner-shell lifetime on the calculated Auger electron intensity will be discussed.

A modulation technique for discrimination against ion induced auger electrons in micro‐area AES

AbstractBeam brightness modulation Auger spectrometry is shown to be an effective means of eliminating ion induced Auger electrons from Auger electron energy spectra. Modulating the incident electron beam intensity causes the true electron induced Auger electron emission to be modulated at the beam modulation frequency which can be easily separated from the unmodulated ion induced Auger electrons by means of frequency sensitive detection using a lock‐in amplifier. This technique is particularly useful when depth profiling with a high energy ion beam (∼5 kV) and a low current (small spot) electron beam (<100 nA).

Electron Spectroscopy of Exploding Fast Molecular lons

We have measured Auger electrons emitted from atomic (C+-, N+-, O+)- and molecular (N2+-, CO+)-projectiles (ca. 80 keV A-1) excited under single collision conditions in thin gaseous targets (N2, CO2). The dominant lines in the observed spectra can be attributed to the decay of Li-and Be-like configurations using intermediate coupling Dirac-Fock calculations. Molecular projectiles (N2+ and CO+) loose their binding electrons in the collisions and the molecular fragments explode via Coulomb repulsion, imposing their kinematics on the deexcitation radiation. This results in an additional kinematic line broadening in the Auger electron energy spectra. It can be well separated from all other contributions to the total linewidth by comparing the spectra of atomic and molecular projectiles of equivalent velocity.

Auger Electron Spectroscopy of fcc Metal Surfaces

The energy spectra of Auger electrons from clean Au, Ag, Cu, Pd, and Ni surfaces have been determined. Uniform deposition of a second metal onto clean metal surfaces has made it possible to assess the depth of the surface region which contributes to the Auger peaks in the secondary electron energy distribution characteristic. These results indicate that the mean escape depth for Auger electrons in Ag (without significant loss of energy) varies between 4 and 8 Å for energies of 72 and 362 eV, respectively. It has been shown (using Auger electron spectroscopy for detection of surface imuprities and low-energy electron diffraction for determining surface structure) that a clean Au (100) surface is reconstructed into a (1×5) structure, while clean Ag (100), Cu (100), and Pd (100) surfaces are characterized by bulk atomic arrangement. The combination of these two techniques has also been effectively applied to the interpretation of the structure and composition of CuAu surface alloys.

Analysis of Materials by Electron-Excited Auger Electrons

The energy spectra of Auger electrons emitted from many elements and alloys have been observed. Differentiation of the secondary electron-energy distribution by perturbation and synchronous detection techniques, and suppression of the effects of low-energy secondaries, were used to obtain well-defined spectra. The Auger lines afford a sensitive indicator for light elements, though spectra for elements as heavy as gold have been obtained. Because the method examines only a superficial layer of the sample, it is useful for detecting contamination, surface migration, or segregation, and for diffusion studies. Cleaning of the surfaces is critical for useful analysis. Quantitative analysis is hindered by noise and the lack of known surface conditions for calibration.

Use of LEED Apparatus for the Detection and Identification of Surface Contaminants

A low-energy electron diffraction (LEED) system has been used to study the energy spectra of Auger electrons from clean and alkali-covered Ge and Si surfaces. Auger bands characteristic of the substrates were observed for the clean surfaces and the deposition of submonolayer coverages of K and Cs introduced new bands characteristic of the respective alkali. It is shown that a surface impurity in a quantity as small as 0.1 monolayer can be detected and identified by this measurement.