Primary Beam Energy Research Articles

In SituStudy of Live Specimens in an Environmental Scanning Electron Microscope

In this paper we introduce new methodology for the observation of living biological samples in an environmental scanning electron microscope (ESEM). The methodology is based on an unconventional initiation procedure for ESEM chamber pumping, free from purge-flood cycles, and on the ability to control thermodynamic processes close to the sample. The gradual and gentle change of the working environment from air to water vapor enables the study of not only living samples in dynamic in situ experiments and their manifestation of life (sample walking) but also its experimentally stimulated physiological reactions. Moreover, Monte Carlo simulations of primary electron beam energy losses in a water layer on the sample surface were studied; consequently, the influence of the water thickness on radiation, temperature, or chemical damage of the sample was considered.

Radiation protection, radiation safety and radiation shielding assessment of HIE-ISOLDE

The high intensity and energy ISOLDE (HIE-ISOLDE) project is an upgrade to the existing ISOLDE facility at CERN. The foreseen increase in the nominal intensity and the energy of the primary proton beam of the existing ISOLDE facility aims at increasing the intensity of the produced radioactive ion beams (RIBs). The currently existing ISOLDE facility uses the proton beam from the proton-synchrotron booster with an energy of 1.4 GeV and an intensity up to 2 μA. After upgrade (final stage), the HIE-ISOLDE facility is supposed to run at an energy up to 2 GeV and an intensity up to 4 μA. The foreseen upgrade imposes constrains, from the radiation protection and the radiation safety point of view, to the existing experimental and supply areas. Taking into account the upgraded energy and intensity of the primary proton beam, a new assessment of the radiation protection and radiation safety of the HIE-ISOLDE facility is necessary. Special attention must be devoted to the shielding assessment of the beam dumps and of the experimental areas. In this work the state-of-the-art Monte Carlo particle transport simulation program FLUKA was used to perform the computation of the ambient dose equivalent rate distribution and of the particle fluxes in the projected HIE-ISOLDE facility (taking into account the upgrade nominal primary proton beam energy and intensity) and the shielding assessment of the facility, with the aim of identifying in the existing facility (ISOLDE) the critical areas and locations where new or reinforced shielding may be necessary. The consequences of the upgraded proton beam parameters on the operational radiation protection of the facility were studied.

Cathodoluminescence of Powder Layers of Nanometer-Sized Y2O3:Eu and Micrometer-Sized ZnO:Zn Phosphor Particles

We present a simple method to measure the cathodoluminescence of charging and non-charging phosphor powder layers at low primary electron beam energy. The method is based on comparing a non-charging surface of a conducting material such as copper or indium tin oxide with charging surfaces of non-conducting phosphors. The phosphors that were investigated were ZnO:Zn, which is slightly conductive and supposed not to charge upon electron bombardment, and Y2O3:Eu, which charges at sufficiently high current density. It was found that the luminous efficacies of ZnO:Zn and Y2O3:Eu at 5 keV primary beam energy were 23 and 16 lm/w respectively, larger than reported in the literature. This is partly explained by calculating the efficacy from the summation of the luminances measured in the reflected and transmitted mode. This method also minimizes the inaccuracy introduced by the effect of the coating weight. The ratio between luminances measured in reflection and transmission is described in terms of a one-dimensional light scattering theory.

Bringing Deconvolution Algorithmic Techniques to the Electron Microscope

The Scanning Electron Microscope (SEM) as a three dimensional imaging tool is increasingly popular for studies in neurobiology. Serial slicing methods based on diamond-knife cutting are, however, reaching practical limitations in terms of achievable z-resolution and voxel isotropy. While Focused-Ion Beam SEM serial block face imaging can improve the z-resolution to 5nm, this technology is restricted in terms of the total volume of material that can be processed. In this work we describe the Multi Energy Confocal Scanning Electron Microscope or “MECSEM” method that achieves high isotropic resolution by a combination of backscatter image sequence acquisition and deconvolution (DC). The method is built on improved understanding of beam-sample interaction for classically prepared samples. Furthermore the point spread function (PSF) of backscatter electrons (BSE) in these materials appears to be well confined laterally. As the range of penetration in the sample is dependent on the energy of the primary beam, acquiring an image sequence with increasing landing energies leads to the acquisition of images from increasing depth. The lateral confinement of BSE PSFs allows for restricting the DC to a layer separation task (z direction). As the structure of the PSF is difficult to obtain experimentally it will be considered unknown leading to a blind DC problem requiring the recovery of both depth layers and PSFs. To verify the reconstruction results we combine this technique with classical FIB-SEM serial block imaging using the through the lens detector in BSE mode on an FEI Helios 650 DualBeam. The z-resolution was controlled by varying the primary beam energy. The comparison with finer FIB reconstruction shows identical structures on the studied samples proving the reliability of the 3D technique, while the achieved depth using DC can reach up to 180nm.

Quantitative analysis of cathodoluminescence phenomena in InGaN/GaN QW by Monte Carlo method

In this paper, cathodoluminescence from InGaN/GaN single quantum wells grown on the facets of the GaN nano-pyramids has been quantitatively studied by Monte Carlo method. The influence of primary electron beam energy and the nanopyramid angle on generation of electron–hole pairs in individual parts of nanostructure has been studied by Monte Carlo simulations. The evolution of the GaN- and InGaN-related cathodoluminescence spectral lines with primary electron beam energy and angle of incidence has been assessed from the recombination rates in individual parts of the structure and compared with cathodoluminescence spectra measured at various beam energies. The possibility to determine the diffusion length of generated carriers in the structures like InGaN/GaN quantum wells using developed Monte Carlo simulator and CL measurements has been demonstrated.

Enhancement of the electron-stimulated desorption from amorphous aluminum oxide films on silicon during an increase in the substrate temperature

The effect of high-temperature electron-stimulated desorption (ESD) from 20-nm-thick Al2O3 films deposited onto silicon wafers is studied. The ESD effect is found to be significantly enhanced upon heating. The films are found to decompose during ion beam irradiation of a heated substrate resulting in pure Al appearance. This process is accompanied by the formation of islands and almost pure silicon surface regions at a certain critical irradiation dose. Outside the irradiation zone, a 20-nm-thick Al2O3 film remains continuous even upon heating to 700°C and holding for 90 min. The effect of the primary electron beam energy on ESD from a 20-nm-thick Al2O3 film on silicon is investigated, and the parameters at which ESD takes place or absent are determined.

O2+ probe‐sample conditions for ultra low energy SIMS depth profiling of nanometre scale Si0.4Ge0.6/Ge quantum wells

The O2+ probe‐sample conditions and subsequent data analysis required to obtain high depth resolution SIMS depth profiles from Si1−xGex/Ge quantum well structures (0.6 ≤ x ≤ 1) are presented. For primary beam energies Ep >500 eV and x approaching 1, a significant decrease in the Ge+ ionisation probability resulted in unrepresentative and unquantifiable depth profiles. For Ep ≤ 500 eV, a monotonic increase in the Ge+ signal with x was observed resulting in profiles representative of the sample structure and enabling x to be found. A depth scale was also established using a point‐by‐point approach taking into account the local erosion rate, which is a function of x. Both the composition and the thickness of the Si1−xGex and Ge layers were found to be in excellent agreement with those obtained using X‐ray and transmission electron microscopy. Copyright © 2012 John Wiley & Sons, Ltd.

Leakage Current Simulation of Insulating Thin Film Irradiated by a Nonpenetrating Electron Beam

We perform numerical simulations of the leakage current characteristics of an insulating thin film of SiO2 negatively charged by a low-energy nonpenetrating focused electron beam. For the formation of leakage current, electrons are demonstrated to turn from diffusion to drift after clearing the minimum potential barrier due to electron-hole separation. In the equilibrium state, the leakage current increases approximately linearly with the increasing primary beam current and energy. It also increases with the increasing film thickness and trap density, and with the decreasing electron mobility, in which the film thickness has a greater influence. Validated by some existing experiments, the simulation results provide a new perspective for the negative charging effects of insulating samples due to the low-energy focused electron beam.

Improved parametrization ofK+production inp−Becollisions at low energy using Feynman scaling

This paper describes an improved parametrization for proton-beryllium production of secondary ${K}^{+}$ mesons for experiments with primary proton beams from 8.89 to $24\text{ }\text{ }\mathrm{GeV}/c$. The parametrization is based on Feynman scaling in which the invariant cross section is described as a function of ${x}_{F}$ and ${p}_{T}$. This method is theoretically motivated and provides a better description of the energy dependence of kaon production at low beam energies than other parametrizations such as the commonly used modified Sanford-Wang model. This Feynman scaling parametrization has been used for the simulation of the neutrino flux from the Booster Neutrino Beam at Fermilab and has been shown to agree with the neutrino interaction data from the SciBooNE experiment. This parametrization will also be useful for future neutrino experiments with low primary beam energies, such as those planned for the Project X accelerator.

LUNAR DUST GRAIN CHARGING BY ELECTRON IMPACT: DEPENDENCE OF THE SURFACE POTENTIAL ON THE GRAIN SIZE

The secondary electron emission is believed to play an important role for the dust charging at and close to the lunar surface. However, our knowledge of emission properties of the dust results from model calculations and rather rare laboratory investigations. The present paper reports laboratory measurements of the surface potential on Lunar Highlands Type regolith simulants with sizes between 0.3 and 3 μm in an electron beam with energy below 700 eV. This investigation is focused on a low-energy part, i.e., ≤100 eV. We found that the equilibrium surface potential of this simulant does not depend on the grain size in our ranges of grain dimensions and the beam energies, however, it is a function of the primary electron beam energy. The measurements are confirmed by the results of the simulation model of the secondary emission from the spherical samples. Finally, we compare our results with those obtained in laboratory experiments as well as those inferred from in situ observations.

Molecular depth profiling by wedged crater beveling.

Time-of-flight secondary ion mass spectrometry and atomic force microscopy are employed to characterize a wedge-shaped crater eroded by a 40-keV C(60)(+) cluster ion beam on an organic film of Irganox 1010 doped with Irganox 3114 delta layers. From an examination of the resulting surface, the information about depth resolution, topography, and erosion rate can be obtained as a function of crater depth for every depth in a single experiment. It is shown that when measurements are performed at liquid nitrogen temperature, a constant erosion rate and reduced bombardment induced surface roughness is observed. At room temperature, however, the erosion rate drops by ∼(1)/(3) during the removal of the 400 nm Irganox film and the roughness gradually increased to from 1 nm to ∼4 nm. From SIMS lateral images of the beveled crater and AFM topography results, depth resolution was further improved by employing glancing angles of incidence and lower primary ion beam energy. Sub-10 nm depth resolution was observed under the optimized conditions on a routine basis. In general, we show that the wedge-crater beveling is an important tool for elucidating the factors that are important for molecular depth profiling experiments.

SU‐E‐T‐678: Monte Carlo Investigation on Dose Perturbations in the Lung Due to Constant Magnetic Fields during MRIgRT

Purpose: Magnetic resonance image‐guided radiotherapy (MR‐IGRT) has emerged as a promising new technology to reduce tumor position uncertainty during photon radiotherapy treatments of lung cancer. MRIGRT improves upon traditional IGRT techniques by providing real‐time intrafraction imaging of tumor motion. However, the use of MRI during beam delivery complicates treatment planning since the magnetic field will perturb the radiation dose distribution especially in fields prescribed in heterogeneous regions of the body such as the lung. In this study we used Monte Carlo methods to investigate the magnetic field effects on dose distributions near interfaces of high‐ and low‐density regions where the influence of magnetic fields will be significant. Methods: The Monte Carlo code EGS4nrc was used for all simulations performed in this study. We investigated dose distributions from both Co‐60 and 6‐MV photon beam energy spectra in simple heterogeneous phantoms. The phantoms consisted of alternating slabs of PMMA and air or lung material with different thicknesses. Homogeneous transverse magnetic fields of varying strengths were applied to the phantom during the simulations. Results: Large perturbations in the dose distributions near PMMA‐air or PMMA‐lung interfaces were recorded when a transverse magnetic field was applied to the phantom, which can be attributed to electron return effect. It was demonstrated that the size of the perturbation at an interface depends not only on the magnetic field strength, but also on the primary photon beam energy spectrum and the length of the air cavity within the phantom. Conclusions: Preliminary results demonstrated that magnetic fields alter the delivered dose distributions near interfaces of high‐ and low‐density regions. Therefore, accurate planning for MR‐IGRT treatments of lung cancer may need to consider magnetic field effects on the dose distribution. Future work will use Monte Carlo methods to investigate dose perturbations due to magnetic fields in 4D patient geometry.

Scattering effects and damping of electrons in Pt(1 1 1) and Cu(1 1 1)

In this work an analysis of experimental and theoretical data associated with the scattering and attenuation of electrons in the Pt(1 1 1) and Cu(1 1 1) crystalline samples is presented. The information about the crystalline structure of the first few atomic layers was obtained by the directional elastic peak electron spectroscopy (DEPES) at the primary electron beam energies E p from 1.5 keV to 2.0 keV. The comparison of the experimental and theoretical DEPES distributions indicates a qualitative agreement between experiment and theory. The relative signal values associated with the intensity maxima were found to be different. The latter effect suggest that the electron attenuation in the crystalline samples can have an anisotropic character. A qualitative analysis of the characteristic pattern around the [1 1 1] direction concerning the calculation of the scattering factors was performed. The collective scattering of electrons by atoms located around the threefold symmetry axis resulting in the so called ring focusing effect is discussed.

The charging stability of different silica glasses studied by measuring the secondary electron emission yield

This paper reports that the charging properties of lead silica, Suprasil silica and Infrasil silica are investigated by measuring the secondary electron emission (SEE) yield. At a primary electron beam energy of 25 keV, the intrinsic SEE yields measured at very low injection dose are 0.54, 0.29 and 0.35, respectively for lead silica, Suprasil and Infrasil silica glass. During the first e-beam irradiation at a high injection current density, the SEE yields of lead silica and Suprasil increase continuously and slowly from their initial values to a steady state. At the steady state, the SEE yields of lead silica and Suprasil are 0.94 and 0.93, respectively. In Infrasil, several charging and discharging processes are observed during the experiment. This shows that Infrasil does not reach its steady state. Two hours later, all samples are irradiated again in the same place as the first irradiation at a low current density and low dose. The SEE yields of lead silica, Suprasil and Infrasil are 0.69, 0.76 and 0.55, respectively. Twenty hours later, the values are 0.62, 0.64 and 0.33, respectively, for lead silica, Suprasil and Infrasil. These results show that Infrasil has poor charging stability. Comparatively, the charging stability of lead silica is better, and Suprasil has the best characteristics.

Investigations of Co/Cu(1 1 0) by AES and DEPES

Auger electron (AES) and directional elastic peak electron spectroscopies (DEPES) were used to find the growth mode of Co on Cu(110) and the crystalline structure within the first few atomic layers. The Co growth at RT is characterized by the at first linear and then exponential decay of the Auger signal from the substrate hCu (CuM2,3VV, 66eV). A detailed analysis of the Auger signal suggests that at an early stage of the Co growth the formation of the second layer occurs before the completion of the first monolayer. Further deposition leads to the simultaneous nucleation of subsequent layers before the complete covering of the substrate. The DEPES profiles recorded along the two Cu[100] and Cu1¯10 azimuths at the primary electron beam energy Ep=1.0keV for equivalent quantities of 3ML and 5ML of Co show distribution of the intensity maxima similar to that for the clean Cu(110) sample, which indicates the epitaxial growth of Co. Theoretical DEPES profiles obtained by using the multiple scattering (MS) formalism at the maximal scattering order s=3 reflect the intensity maxima associated with the 100, 110, 112 and 111 directions, as it was observed in experiment.

Ion, sputter and useful ion yields for accurate quantification of Si1−xGex(0 < x < 1) using ultra low energy O2+ SIMS

AbstractIt has been previously demonstrated that accurate measurement of x in the Si1−xGex (x ≤ 0.3) alloy can be achieved using a variety of O2+ SIMS conditions. With SiGe device technology still developing to exploit its full potential, the useful matrices now extend from 0 ≤ x ≤ 1. Using the previously established conditions, we have found that roughening of the material occurs when x approaches 1. To overcome this limitation we have developed a set of conditions that enables the whole Si1−xGex (0 ≤ x ≤ 1) range to be quantified. This is achieved by using an O2+ primary beam energy of ≤ 500 eV at near‐normal incidence. Here, we present a comprehensive study of the measured (Si and Ge) ion, useful ion and sputter yield behavior as a function of matrix composition and incident beam energy (250 eV–1 keV), from which these new conditions have been established. For the extended Si1−xGex (0 ≤ x ≤ 1) range and primary beam energies used here, the measured Si and Ge ion yields were found to be well described by quartic, cubic or quadratic dependences as a function of x. The useful ion yields and sputter yields all showed moderate matrix effects, with the former decreasing monotonically for increasing x except in the case of Ge at 250 eV. Here, the useful Ge ion yield was found to be invariant with x while its measured ion yield (for all x) was observed to be proportional to its sputter yield. Copyright © 2010 John Wiley & Sons, Ltd.

The status of the positron beam facility at NEPOMUC

The NEutron induced POsitron source MUniCh NEPOMUC provides a high intensity positron beam with 9·108 moderated positrons per second with a primary beam energy of 1keV. After remoderation, the positron beam is magnetically guided to five experimental setups: a coincident Doppler-broadening spectrometer (CDBS), a positron annihilation induced Auger-electron spectrometer (PAES), a pulsed low-energy positron system (PLEPS) as well as an interface for providing a pulsed beam with further improved brightness. An apparatus for the production of the negatively charged positronium ion Ps− is currently in operation at the open multi-purpose beam port, where additional experiments can be realized. Within this contribution, an overview of the positron beam facility NEPOMUC with its instrumentation at the research reactor FRMII is given.

Radioactive ion beam facilities at INFN LNS

Radioactive ion beams are produced at INFN- Laboratori Nazionali del Sud (LNS) by means of the two operating accelerators, the Tandem and the Superconducting Cyclotron (CS), originally designed to accelerate stable beams. Both the ISOL (Isotope Separation On Line) and the IFF (In-Flight Fragmentation) methods are exploited to produce RIBs in two different ways at different energies: in the first case, the Cyclotron is the primary accelerator and the Tandem accelerates the secondary beams, while in the second case radioactive fragments are produced by the Cyclotron beam in a thin target with energies comparable to the primary beam energy. The ISOL facility is named EXCYT (Exotics at the Cyclotron and Tandem) and was commissioned in 2006, when the first radioactive beam (8Li) has been produced. The IFF installation is named FRIBs (in Flight Radioactive Ion Beams), and it has started to produce radioactive beams in 2001, placing a thin target in the extraction beam line of the Cyclotron. The development of both facilities to produce and accelerate radioactive ion beams at LNS, is briefly described, with some details on the future prospects that are presently under consideration or realization.

Atomic spectrometry update. Industrial analysis: metals, chemicals and advanced materials

There is considerable interest in the non-destructive analysis of archaeological or historical materials (glasses, ceramics, paintings, materials etc.). The use of solid sampling techniques that cause minimal damage is therefore still gaining in popularity. This is especially true for laser-based techniques such as LIBS and laser ablation, although the many variants of the X-ray-based techniques are also still proving very popular. Non-destructive analysis is also the ideal scenario for forensic scientists and therefore many of these applications are using similar techniques. The increasing trend to use multiple analytical techniques, ideally simultaneously, to cause minimal damage and to obtain the maximal number of results in the shortest time, is also noted. The technique of LIBS, which offers minimal sample damage and a “stand-off” capability is still gaining in popularity, although there are still question marks regarding its quantitative capabilities for some sample types. There is also considerable interest in the growing area of thin films and depth-profiling. Substantial research is on-going to develop methods to improve depth-resolution and several different approaches have been described in the literature. These approaches often use SIMS with either a lower energy primary beam or a primary beam consisting of polyatomic molecules.

The Backscattering Correction Factor in AES: A New Outlook

There is currently renewed interest in the backscattering correction for Auger electron spectroscopy (AES). There are several reasons for this interest. First, the energy of the primary-beam energy reaches 25 keV in modern AES instruments and Shimizu’s predictive formulae based on calculations for primary energies between 3 keV and 10 keV are of uncertain validity at higher energies. Second, it has been shown recently that the present definition of the backscattering factor is based on a simplified model of electron transport that breaks down for low primary energies and/or more grazing-incidence angles. A new term, the backscattering correction factor (BCF) has therefore been introduced that is based on an advanced model of electron transport. Third, much progress has been recently made in the theory of electron transport and the data for electron-scattering parameters which should improve the reliability of calculated backscattering correction factors. Finally, the BCF from the advanced theoretical model has been found to depend on numerous parameters defining the solid, the selected Auger transition, and the experimental configuration. Since the derivation of a simple predictive formula for the BCF does not seem to be feasible, a computer-controlled database has been developed to provide BCFs for a user-specified material and experimental configuration. Examples are given of BCFs from the advanced and simplified models for Ag M4N45N45 Auger electrons from silver.