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1
Merli, P. G., e V. Morandi. "Low-Energy STEM of Multilayers and Dopant Profiles". Microscopy and Microanalysis 11, n. 1 (28 gennaio 2005): 97–104. http://dx.doi.org/10.1017/s1431927605050063.
Testo completoAbstract (sommario):
A conventional scanning electron microscope equipped with a LaB6 source has been modified to operate in a scanning transmission mode. Two detection strategies have been considered, one based on the direct collection of transmitted electrons, the other on the collection of secondary electrons resulting from the conversion of the transmitted ones. Two types of specimens have been mainly investigated: semiconductor multilayers and dopant profiles in As-implanted Si. The results show that the contrast obeys the rules of mass–thickness contrast whereas the resolution is always defined by the probe size independently of specimen thickness and beam broadening. The detection strategy may affect the bright field (light regions look brighter) or dark field (heavy regions look brighter) appearance of the image. Using a direct collection of the transmitted electrons, the contrast can be deduced from the angular distribution of transmitted electrons and their collection angles. When collecting the secondary electrons to explain the image contrast, it is also necessary to take into account the secondary yield dependence on the incidence angle of the transmitted electrons.
2
Howie, A. "Threshold Energy Effects in Secondary Electron Emission". Microscopy and Microanalysis 6, n. 4 (luglio 2000): 291–96. http://dx.doi.org/10.1017/s1431927602000521.
Testo completoAbstract (sommario):
AbstractIn large bandgap semiconductors and insulators, the threshold energies for e–h pair production and ionization damage can lie above the vacuum level. For low energy imaging, a window is then opened whose width is potentially sensitive to local changes in work function, doping level, or acidity. Recent progress and future opportunities for damage-free imaging of these properties using low energy electrons are discussed in the light of the underlying physics, as well as of recent instrumental developments in low energy electron microscopy (LEEM), environmental scanning electron microscopy (ESEM), photoelectron emission microscopy (PEEM), scanned probe microscopy (SPM), and projection electron microscopy.
3
Howie, A. "Threshold Energy Effects in Secondary Electron Emission". Microscopy and Microanalysis 6, n. 4 (luglio 2000): 291–96. http://dx.doi.org/10.1007/s100050010042.
Testo completoAbstract (sommario):
Abstract In large bandgap semiconductors and insulators, the threshold energies for e–h pair production and ionization damage can lie above the vacuum level. For low energy imaging, a window is then opened whose width is potentially sensitive to local changes in work function, doping level, or acidity. Recent progress and future opportunities for damage-free imaging of these properties using low energy electrons are discussed in the light of the underlying physics, as well as of recent instrumental developments in low energy electron microscopy (LEEM), environmental scanning electron microscopy (ESEM), photoelectron emission microscopy (PEEM), scanned probe microscopy (SPM), and projection electron microscopy.
4
Hembree, G. G., J. Unguris, R. J. Celotta e D. T. Pierce. "Magnetic microstructure imaging by secondary electron spin polarization analysis". Proceedings, annual meeting, Electron Microscopy Society of America 44 (agosto 1986): 634–35. http://dx.doi.org/10.1017/s0424820100144619.
Testo completoAbstract (sommario):
Recent research has shown that the low energy secondary electrons generated from ferromagnetic material are spin polarized. The secondary electron polarization yields a signal which is directly proportional to the magnitude and direction of the magnetization within the volume of material in which the electrons were generated. This signal can be used in a scanning electron microscope to image the microstructure of magnetic domains on the surface of ferromagnetic materials.We have incorporated a new compact spin polarization analyzer into a commercial UHV SEM. A schematic diagram of the apparatus is shown in Fig. 1. The secondary electrons are extracted from the sample and are then focused into a hemispherical energy analyzer which filters out the high energy electrons.
5
Tivol, William F. "How to Calculate the Temperature Rise Due to Beam Heating". Microscopy Today 7, n. 7 (settembre 1999): 24–27. http://dx.doi.org/10.1017/s1551929500064774.
Testo completoAbstract (sommario):
The temperature of a specimen rises when the electron beam interacts with it, producing ionization and excitation of atoms and breaking molecular bonds. Energy loss in bulk materials is ultimately converted to heat, but for small particles some of the energy escapes. Of the energy lost by the electrons in the incident beam, that which is absorbed by the specimen and degraded to heat includes oscillations of valence electrons, the kinetic energy of low-energy secondary electrons, and radiationless recombination of ionized atoms or moiecuies. Energy not absorbed includes brehmsstrahlung, characteristic x-rays, and the kinetic energy of higher-energy secondary electrons. Glaeser (1979) estimated that 50% of the energy loss is confined to a distance of about 5 nm from the track of the incident electron, while the other 50% is largely due to secondary electrons having 0.5 to 5 keV kinetic energy.
6
Cipriani, Maicol, Styrmir Svavarsson, Filipe Ferreira da Silva, Hang Lu, Lisa McElwee-White e Oddur Ingólfsson. "The Role of Low-Energy Electron Interactions in cis-Pt(CO)2Br2 Fragmentation". International Journal of Molecular Sciences 22, n. 16 (20 agosto 2021): 8984. http://dx.doi.org/10.3390/ijms22168984.
Testo completoAbstract (sommario):
Platinum coordination complexes have found wide applications as chemotherapeutic anticancer drugs in synchronous combination with radiation (chemoradiation) as well as precursors in focused electron beam induced deposition (FEBID) for nano-scale fabrication. In both applications, low-energy electrons (LEE) play an important role with regard to the fragmentation pathways. In the former case, the high-energy radiation applied creates an abundance of reactive photo- and secondary electrons that determine the reaction paths of the respective radiation sensitizers. In the latter case, low-energy secondary electrons determine the deposition chemistry. In this contribution, we present a combined experimental and theoretical study on the role of LEE interactions in the fragmentation of the Pt(II) coordination compound cis-PtBr2(CO)2. We discuss our results in conjunction with the widely used cancer therapeutic Pt(II) coordination compound cis-Pt(NH3)2Cl2 (cisplatin) and the carbonyl analog Pt(CO)2Cl2, and we show that efficient CO loss through dissociative electron attachment dominates the reactivity of these carbonyl complexes with low-energy electrons, while halogen loss through DEA dominates the reactivity of cis-Pt(NH3)2Cl2.
7
Suga, Hiroshi, Takafumi Fujiwara, Nobuhiro Kanai e Masatoshi Kotera. "Secondary Electron Image Contrast in the Scanning Electron Microscope". Proceedings, annual meeting, Electron Microscopy Society of America 48, n. 1 (12 agosto 1990): 410–11. http://dx.doi.org/10.1017/s042482010018080x.
Testo completoAbstract (sommario):
An image contrast given in the scanning electron microscope(SEM) is due to differences in a detected number of secondary electrons (SE) coming from the specimen surface. The difference arises from the topographic, compositional and voltage features at the specimen surface. Two kinds of approaches have been taken for the quantification of SE images. One is to simulate electron trajectories in vacuum toward the detector, assuming the typical angular and energy distributions of electrons emitted from the specimen surface. However, the typical angular and energy distributions are not always applicable if a topographic or a compositional feature is present at the surface. The other is to simulate electron trajectory in the specimen. It is possible to obtain angular, energy, and spatial distributions of electrons emitted from the specimen surface. However, in order to discuss the SEM contrast based on these data, one has to assume that, for example, all slow electrons (<50eV) may be collected by the SE detector, or fast electrons ((>50eV) electrons may take a straight trajectory in the vacuum specimen chamber of the SEM. In a practical SEM picture of, for example, an etch-pit, different crystallographic plane surface shows different contrast even if the angle of the primary electron incidence toward all those surfaces is the same. This is because of the acceptance of the signal detection system. In a present study we combined two electron trajectory simulations mentioned above and calculated electron trajectories both in and out of the specimen, to simulate the trajectory from the point of the signal generated until the signal is detected.Although several simulation models of electron scatterings in a specimen have been reported to estimate the SE intensity at the surface, the model should be available to trace low energy (<50eV) electron trajectories. The model used here is basically the same as that reported in previous papers, and only a brief explanation is given in the following. Here, we made several assumptions as; [l]the energy loss of the primary and excited fast electrons is proportion to the number of SEs generated in the specimen, [2]the generated SE has an energy distribution as described by the Streitwolf equation, [3]the energy of the generated SEs are transferred to free electrons of the atom by the elastic-binary-collision, then one SE excited by the primary electron produces a ternary electron after the collision, and each one of the SE and the ternary electron produces higher order electrons in a cascade fashion. The simulation continues until the energy of each electron is less than the surface potential barrier. Angular and energy distributions and number of electrons emitted at the surface agree quite well with each experimental result in a typical case.
8
Mikmeková, Šárka, Haruo Nakamichi e Masayasu Nagoshi. "Contrast of positively charged oxide precipitate in out-lens, in-lens and in-column SE image". Microscopy 67, n. 1 (8 dicembre 2017): 11–17. http://dx.doi.org/10.1093/jmicro/dfx117.
Testo completoAbstract (sommario):
Abstract Modern scanning electron microscopes are usually equipped with multiple detectors and enable simultaneous collection of two or even three secondary electron images. The secondary electrons become divided between the detectors in dependence on their initial kinetic energy and emission angle. In this study, sharing of the secondary electrons by out-lens, in-lens and in-column detectors has been systematically investigated. Energy filtering of the signal electrons is demonstrated by separation of the voltage and the topographical contrast in the micrographs obtained by out-lens and in-lens/in-column detectors. The presence of two detectors inside the electron column enables further filtering of the low kinetic energy secondary electrons, which results to unusual contrasts and phenomena. In this paper, inversion of the contrast sign between a positively charged oxide particle and conductive steel matrix (i.e. voltage contrast) in SE images collected under specific imaging conditions is demonstrated.
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TURTON, S., M. KADODWALA e ROBERT G. JONES. "POSSIBLE "HOT" MOLECULE DESORPTION BY ELECTRON STIMULATED DECOMPOSITION OF DIHALOETHANES ON Cu(111)". Surface Review and Letters 01, n. 04 (dicembre 1994): 535–38. http://dx.doi.org/10.1142/s0218625x94000606.
Testo completoAbstract (sommario):
The desorption of ethene from physisorbed 1, 2-dichloroethane (DCE) and 1-bromo-2-chloroethane (BCE) on Cu(111) has been observed on irradiating the surface with electrons. The techniques used were low energy electron diffraction (LEED), Auger electron spectroscopy (AES), ultraviolet photoelectron spectroscopy (UPS), and mass spectrometric detection of the desorbed species. At 110 K physisorbed DCE and BCE underwent electron capture from low energy (<1 eV ) electrons in the secondary electron yield of the surface followed by decomposition and desorption of ethene alone. The decomposition was found to be first order in the surface coverage of the physisorbed DCE/BCE. No other molecular species desorbed from the surface, a stoichiometric amount of chemisorbed halogen was deposited and no carbon was detectable at the end of the desorption. The formation of the negative ions of these molecules by electron capture of low energy electrons in the secondary electron emission from the surface and the possible dynamics by which the negative ions undergo decomposition leaving the ethene product with sufficient energy to desorb, are discussed.
10
Hembree, Gary G., Frank C. H. Luo e John A. Venables. "Auger electron spectroscopy and microscopy in STEM". Proceedings, annual meeting, Electron Microscopy Society of America 49 (agosto 1991): 464–65. http://dx.doi.org/10.1017/s0424820100086623.
Testo completoAbstract (sommario):
Spatial resolution in Auger electron spectroscopy (AES) is primarily a function of the excitation beam current distribution. For highest resolution the question of how to produce such a small probe of electrons is coupled with how to extract the secondary electrons efficiently from the sample. Kniit and Venables have shown the optimum configuration for highest resolution AES is a combination of a magnetic immersion lens, additional solenoids (“parallelizers“) to shape the weak magnetic field in the low energy electron transport region and a concentric hemispherical analyzer (CHA) to disperse and detect the secondary electrons. This combination has been incorporated into a new ultra-high vacuum STEM at ASU, along with the low energy electron optics required to interface the magnetic collection system with the CHA.
11
Joens, Steve. "Hitachi S-4700 ExB Filter Design and Applications". Microscopy and Microanalysis 7, S2 (agosto 2001): 878–79. http://dx.doi.org/10.1017/s1431927600030464.
Testo completoAbstract (sommario):
Electron beam - specimen interactions and SEM signals have been well understood and documented for many years. These interactions result in a variety of electron signals including the most common, secondary and backscattered electron. Each electron signal produces unique characteristic information about the sample surface, subsurface, and elemental composition. Important information can be gained by controlling and filtering electron signals collected by the electron detector system.The S-4700 Cold Field Emission SEM incorporates a set of electrodes and plates positioned in the objective lens upper pole piece in close proximity to the upper secondary detector (figure 1). When a positive voltage is applied to the electrode plates, a high yield of secondary and backscattered electrons spiral up the column of the objective lens. The backscattered electrons are filtered with the ExB producing a SE rich signal. The information from this type of signal provides absolute detail from the sample surface, but can be prone to charging with some highly nonconductive samples. Figure 2a shows the effect of charging while observing uncoated Teflon ™. The image becomes distorted with bright intermittent horizontal lines. Surface detail is enhanced due to the high contribution of SEs from the sample surface.When the electrode voltage is set negative, through the instrument GUI, the low energy secondary electrons are repelled providing a signal rich in backscattered electrons. The information from this type of signal provides compositional information and inherently reduces charging. The uncoated Teflon ™ sample in figure 2b shows all charging affects have been eliminated.
12
Panchenko, O. F., e L. K. Panchenko. "Relaxation of Highly Non Equilibrium Charge Carriers in Crystals by Low-Energy Electron Influence". Solid State Phenomena 115 (agosto 2006): 261–66. http://dx.doi.org/10.4028/www.scientific.net/ssp.115.261.
Testo completoAbstract (sommario):
The cascade process describing the energy loss and relaxation or multiplication of highly non-equilibrium secondary electrons and holes in crystalline platinum irradiated by lowenergy electrons is studied. The pair-creation scattering rates are evaluated in the framework of the statistical model taking into account the electron band structure of platinum. Kinetic equations for the excited electron and hole energy distributions are solved numerically in the isotropic scattering approximation for some primary (excitation) energies Ep which do not exceed the plasma energy.
13
Drucker, J. S., M. Krishnamurthy, G. G. Hembree, Luo Chuan Hong e J. A. Venables. "High-spatial-resolution secondary and Auger imaging in a STEM". Proceedings, annual meeting, Electron Microscopy Society of America 47 (6 agosto 1989): 208–9. http://dx.doi.org/10.1017/s0424820100153014.
Testo completoAbstract (sommario):
Secondary electrons form the main signal in a standard SEM, and machines incorporating Auger electron spectroscopy and imaging have become widely commercialized. However, these approaches to low energy (0-2000eV) electron spectroscopy and imaging do not work at the highest spatial resolution, since there are geometrical and electromagnetic conflicts as the focal length of the probe forming lens is reduced. As discussed elsewhere in more detail, the solution is to make the magnetic probe forming lens of the SEM/STEM also function as the first stage of the electron collection and analysis system.A new lOOkV field emission STEM has been constructed for the NSF HREM facility, which incorporates provision for using these low energy electrons from both sides of a thin sample. The outline design has been described previously. The microscope, codenamed MIDAS, is of UHV construction throughout with ∽10−10 mbar at the sample position, and extensive surface preparation facilities. The region of the column concerned with secondary and Auger electrons is shown diagrammatically, but to scale, in fig. 1. This region consists of the objective lens, O, bounded by analyser chambers AC1 and AC2, onto which the electron detectors are mounted.
14
Hembree, Gary G., Frank C. H. Luo e John A. Venables. "Secondary and Auger Electron Spectroscopy and Energy-Selected Imaging in a UHV-STEM". Proceedings, annual meeting, Electron Microscopy Society of America 48, n. 2 (12 agosto 1990): 382–83. http://dx.doi.org/10.1017/s0424820100135514.
Testo completoAbstract (sommario):
A new UHV-STEM has been developed for the NSF-HREM facility at Arizona State University. In this instrument low energy (0-2 keV) electrons can be collected through the objective lens from both sides of thin (STEM) samples, or from the input side of bulk (SEM) samples. As explained in more detail elsewhere, we use magnetic parallelizers to control the angular compression of the emitted secondary and Auger electrons, which spiral around the B-field lines. The parallelizers have axial fields of about 100 G, and compress all these emitted electrons into a cone of less than 6 deg. The sample may be biassed negatively by a few hundred volts, which enables us to compress the cone angle further and to observe the sample using biassed secondary electron imaging (b-SEI). At the exit aperture of the parallelizer the low energy electrons are deflected slightly off-axis by a Wien (E × B) filter to separate them from the the 100 keV beam.
15
Jaber, Ahmad M. D. (Assa’d), Ammar Alsoud, Saleh R. Al-Bashaish, Hmoud Al Dmour, Marwan S. Mousa, Tomáš Trčka, Vladimír Holcman e Dinara Sobola. "Electron Energy-Loss Spectroscopy Method for Thin-Film Thickness Calculations with a Low Incident Energy Electron Beam". Technologies 12, n. 6 (7 giugno 2024): 87. http://dx.doi.org/10.3390/technologies12060087.
Testo completoAbstract (sommario):
In this study, the thickness of a thin film (tc) at a low primary electron energy of less than or equal to 10 keV was calculated using electron energy-loss spectroscopy. This method uses the ratio of the intensity of the transmitted background spectrum to the intensity of the transmission electrons with zero-loss energy (elastic) in the presence of an accurate average inelastic free path length (λ). The Monte Carlo model was used to simulate the interaction between the electron beam and the tested thin films. The total background of the transmitted electrons is considered to be the electron transmitting the film with an energy above 50 eV to eliminate the effect of the secondary electrons. The method was used at low primary electron energy to measure the thickness (t) of C, Si, Cr, Cu, Ag, and Au films below 12 nm. For the C and Si films, the accuracy of the thickness calculation increased as the energy of the primary electrons and thickness of the film increased. However, for heavy elements, the accuracy of the film thickness calculations increased as the primary electron energy increased and the film thickness decreased. High accuracy (with 2% uncertainty) in the measurement of C and Si thin films was observed at large thicknesses and 10 keV, where . However, in the case of heavy-element films, the highest accuracy (with an uncertainty below 8%) was found for thin thicknesses and 10 keV, where . The present results show that an accurate film thickness measurement can be obtained at primary electron energy equal to or less than 10 keV and a ratio of . This method demonstrates the potential of low-loss electron energy-loss spectroscopy in transmission electron microscopy as a fast and straightforward method for determining the thin-film thickness of the material under investigation at low primary electron energies.
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Jung, Jiwon, Moo-Young Lee, Jae-Gu Hwang, Moo-Hyun Lee, Min-Seok Kim, Jaewon Lee e Chin-Wook Chung. "Low-energy electron beam generation in inductively coupled plasma via a DC biased grid". Plasma Sources Science and Technology 31, n. 2 (1 febbraio 2022): 025002. http://dx.doi.org/10.1088/1361-6595/ac43c2.
Testo completoAbstract (sommario):
Abstract Low-energy electron beam generation using a DC biased grid was investigated in an inductively coupled plasma (ICP). The electron beam was measured in argon gas at various pressures, ICP source powers, and substrate voltages (V sub). At a low ICP source power (50 W), an electron beam was generated even at small values of V sub (10 V), however at a high ICP source power (200 W), an electron beam was only generated when a higher voltage (30 V) was applied due to the short sheath thickness on the grid surface. The sheath on the grid surface is an important factor for generating electron beams because low-energy electrons are blocked. If the sheath thickness to small, a high voltage should be applied to generate an electron beam, as accelerate regions cannot exist without the sheath. At high pressure, since electrons experience numerous neutral collisions, a high substrate voltage is needed to generate an electron beam. However, if the applied substrate voltage becomes too high (40 V) at high pressure, high-energy electrons result in secondary plasma under the grid. Therefore, maintaining a low pressure and low ICP source power is important for generating electron beams.
17
Ebel, Maria F., Robert Svagera, Horst Ebel, Robert Hobl, Michael Mantler, Johann Wernisch e Norbert Zagler. "Determination of Thickness and Composition of Thin AlxGa1-xAs Layers on GaAs by Total Electron Yield (TEY)". Advances in X-ray Analysis 38 (1994): 127–37. http://dx.doi.org/10.1154/s0376030800017729.
Testo completoAbstract (sommario):
The measurement of the total electron yield (TEY) emitted from a solid specimen when irradiated by monochromatic x-rays is used for quantitative information on the specimen. For this purpose one has to determine the increase of TEY in the course of a variation of the photon energy from below to above the absorption edges of the specimen elements. These increases are the analytical quantities and are correlated with the composition of the specimen. The detected electrons are photo, Auger and secondary electrons. Most of them lost some of their original kinetic energy due to inelastic collisions along their path from the atom of origin to the surface. Low energy electrons are especially found in the secondary electron peak with electron energies of less than 20eV. Electrically nonconductive specimens under x-irradiation tend to positive surface charging.
18
Alizadeh, Elahe, Dipayan Chakraborty e Sylwia Ptasińska. "Low-Energy Electron Generation for Biomolecular Damage Inquiry: Instrumentation and Methods". Biophysica 2, n. 4 (17 novembre 2022): 475–97. http://dx.doi.org/10.3390/biophysica2040041.
Testo completoAbstract (sommario):
Technological advancement has produced a variety of instruments and methods to generate electron beams that have greatly assisted in the extensive theoretical and experimental efforts devoted to investigating the effect of secondary electrons with energies approximately less than 100 eV, which are referred as low-energy electrons (LEEs). In the past two decades, LEE studies have focused on biomolecular systems, which mainly consist of DNA and proteins and their constituents as primary cellular targets of ionizing radiation. These studies have revealed that compared to other reactive species produced by high-energy radiation, LEEs have distinctive pathways and considerable efficiency in inducing lethal DNA lesions. The present work aims to briefly discuss the current state of LEE production technology and to motivate further studies and improvements of LEE generation techniques in relation to biological electron-driven processes associated with such medical applications as radiation therapy and cancer treatment.
19
Cowley, J. M. "High Resolution Scanning Electron Microscopy of Surfaces". Proceedings, annual meeting, Electron Microscopy Society of America 48, n. 1 (12 agosto 1990): 296–97. http://dx.doi.org/10.1017/s0424820100180239.
Testo completoAbstract (sommario):
Electron beams of small diameter, generated with field emission guns may be used to investigate surfaces in many different ways. Images may be formed in the scanning mode by use of the elastically, or quasi-elastically scattered electrons or by the detection of secondary radiation including low energy secondary electrons, Auger electrons and X-rays. Except in the case of low-energy secondary electrons, high spatial resolution has not yet been achieved by detection of the secondary radiations so these imaging modes will not be discussed here.The scanning modes used with the detection of elastic or quasi-elastic electrons in a dedicated STEM instrument are analogous to those used in conventional TEM instruments for surface studies, such as profile imaging and reflection electron microscopy. In each case, the practical limitations of current STEM systems tend to limit the quality of the imaging but the flexibility of the STEM detector system has provided several important advantages. In scanning reflection microscopy (SREM) the resolution attained is comparable with that for REM. The important advantage over REM is that microdiffraction patterns may be obtained from any surface features as small as the resolution limit for imaging. Also it is relatively easy to make use of the surface channelling conditions in order to enhance the contrast of surface steps or other surface features.
20
Thorman, Rachel M., Ragesh Kumar T. P., D. Howard Fairbrother e Oddur Ingólfsson. "The role of low-energy electrons in focused electron beam induced deposition: four case studies of representative precursors". Beilstein Journal of Nanotechnology 6 (16 settembre 2015): 1904–26. http://dx.doi.org/10.3762/bjnano.6.194.
Testo completoAbstract (sommario):
Focused electron beam induced deposition (FEBID) is a single-step, direct-write nanofabrication technique capable of writing three-dimensional metal-containing nanoscale structures on surfaces using electron-induced reactions of organometallic precursors. Currently FEBID is, however, limited in resolution due to deposition outside the area of the primary electron beam and in metal purity due to incomplete precursor decomposition. Both limitations are likely in part caused by reactions of precursor molecules with low-energy (<100 eV) secondary electrons generated by interactions of the primary beam with the substrate. These low-energy electrons are abundant both inside and outside the area of the primary electron beam and are associated with reactions causing incomplete ligand dissociation from FEBID precursors. As it is not possible to directly study the effects of secondary electrons in situ in FEBID, other means must be used to elucidate their role. In this context, gas phase studies can obtain well-resolved information on low-energy electron-induced reactions with FEBID precursors by studying isolated molecules interacting with single electrons of well-defined energy. In contrast, ultra-high vacuum surface studies on adsorbed precursor molecules can provide information on surface speciation and identify species desorbing from a substrate during electron irradiation under conditions more representative of FEBID. Comparing gas phase and surface science studies allows for insight into the primary deposition mechanisms for individual precursors; ideally, this information can be used to design future FEBID precursors and optimize deposition conditions. In this review, we give a summary of different low-energy electron-induced fragmentation processes that can be initiated by the secondary electrons generated in FEBID, specifically, dissociative electron attachment, dissociative ionization, neutral dissociation, and dipolar dissociation, emphasizing the different nature and energy dependence of each process. We then explore the value of studying these processes through comparative gas phase and surface studies for four commonly-used FEBID precursors: MeCpPtMe3, Pt(PF3)4, Co(CO)3NO, and W(CO)6. Through these case studies, it is evident that this combination of studies can provide valuable insight into potential mechanisms governing deposit formation in FEBID. Although further experiments and new approaches are needed, these studies are an important stepping-stone toward better understanding the fundamental physics behind the deposition process and establishing design criteria for optimized FEBID precursors.
21
Feng, Guobao, Yun Li, Xiaojun Li, Heng Zhang e Lu Liu. "Characteristics of electron evolution during initial low-pressure discharge stage upon microwave circuits". AIP Advances 12, n. 11 (1 novembre 2022): 115129. http://dx.doi.org/10.1063/5.0130735.
Testo completoAbstract (sommario):
High-power microwave-induced low-pressure discharges seriously threaten the reliability of space payload systems. Under extremely low-pressure conditions, the evolution of ionized and secondary electrons at the initial stage of discharge is crucial to figure out the discharge process. Therefore, this paper investigates the development of multiple electrons in the discharge process under a highly low-pressure environment using numerical simulation. A three-dimensional simulation model based on the Monte Carlo algorithm is established by considering various electron-gas collisions and secondary electron emissions from different material surfaces. The evolution characteristics of various electrons' populations, energy, and distribution patterns during the discharge process are analyzed. In addition, the influence of the critical conditions at different air pressures on the electron evolution during the discharge process and the intrinsic causes are also investigated. This study is significant in revealing the transition characteristics between multipactor and low-pressure discharge and exploring their inherent mechanisms.
22
Boamah, Mavis D., Kristal K. Sullivan, Katie E. Shulenberger, ChanMyae M. Soe, Lisa M. Jacob, Farrah C. Yhee, Karen E. Atkinson, Michael C. Boyer, David R. Haines e Christopher R. Arumainayagam. "Low-energy electron-induced chemistry of condensed methanol: implications for the interstellar synthesis of prebiotic molecules". Faraday Discuss. 168 (2014): 249–66. http://dx.doi.org/10.1039/c3fd00158j.
Testo completoAbstract (sommario):
In the interstellar medium, UV photolysis of condensed methanol (CH3OH), contained in ice mantles surrounding dust grains, is thought to be the mechanism that drives the formation of “complex” molecules, such as methyl formate (HCOOCH3), dimethyl ether (CH3OCH3), acetic acid (CH3COOH), and glycolaldehyde (HOCH2CHO). The source of this reaction-initiating UV light is assumed to be local because externally sourced UV radiation cannot penetrate the ice-containing dark, dense molecular clouds. Specifically, exceedingly penetrative high-energy cosmic rays generate secondary electrons within the clouds through molecular ionizations. Hydrogen molecules, present within these dense molecular clouds, are excited in collisions with these secondary electrons. It is the UV light, emitted by these electronically excited hydrogen molecules, that is generally thought to photoprocess interstellar icy grain mantles to generate “complex” molecules. In addition to producing UV light, the large numbers of low-energy (<20 eV) secondary electrons, produced by cosmic rays, can also directly initiate radiolysis reactions in the condensed phase. The goal of our studies is to understand the low-energy, electron-induced processes that occur when high-energy cosmic rays interact with interstellar ices, in which methanol, a precursor of several prebiotic species, is the most abundant organic species. Using post-irradiation temperature-programmed desorption, we have investigated the radiolysis initiated by low-energy (7 eV and 20 eV) electrons in condensed methanol at ∼ 85 K under ultrahigh vacuum (5 × 10−10 Torr) conditions. We have identified eleven electron-induced methanol radiolysis products, which include many that have been previously identified as being formed by methanol UV photolysis in the interstellar medium. These experimental results suggest that low-energy, electron-induced condensed phase reactions may contribute to the interstellar synthesis of “complex” molecules previously thought to form exclusively via UV photons.
23
Morgan, S. W., e M. R. Phillips. "Time Dependent Study of the Positive ion Current in the Environmental Scanning Electron Microscope (ESEM)". Microscopy and Microanalysis 7, S2 (agosto 2001): 788–89. http://dx.doi.org/10.1017/s1431927600030014.
Testo completoAbstract (sommario):
The Environmental Scanning Electron Microscope (ESEM) is capable of image generation in a gaseous environment at sample chamber pressures of up to 20 torr. in an ESEM, low energy secondary electrons emitted from a sample surface, by virtue of the primary electron beam, are accelerated towards the positively biased metallic ring (typically +30 to +550V) Gaseous Secondary Electron Detector (GSED). As these electrons accelerate towards the ring they undergo ionizing collisions with gas molecules producing positive ions and additional electrons known as environmental secondary electrons. The environmental electrons further ionize the gas on their way to the ring producing a cascade amplification of the original signal. The amplified signal induced in the ring is used to form an image. The electric field generated between the GSED ring and the grounded stage causes the positive ions produced in the cascade to drift towards the sample, effectively neutralizing negative charge build up on the surface of a non-conducting sample.
24
Bronold, F. X., e H. Fehske. "Invariant embedding approach to secondary electron emission from metals". Journal of Applied Physics 131, n. 11 (21 marzo 2022): 113302. http://dx.doi.org/10.1063/5.0082468.
Testo completoAbstract (sommario):
Based on an invariant embedding principle for the backscattering function, we calculate the electron emission yield for metal surfaces at very low electron impact energies. Solving the embedding equation within a quasi-isotropic approximation and using the effective mass model for the solid experimental data are fairly well reproduced provided (i) incoherent scattering on ion cores is allowed to contribute to the scattering cascades inside the solid and (ii) the transmission through the surface potential takes into account Bragg gaps due to coherent scattering on crystal planes parallel to the surface as well as randomization of the electron’s lateral momentum due to elastic scattering on surface defects. Our results suggest that in order to get secondary electrons out of metals, the large energy loss due to inelastic electron–electron scattering has to be compensated for by incoherent elastic electron–ion core scattering, irrespective of the crystallinity of the sample.
25
Lochmann, Christine, Thomas F. M. Luxford, Samanta Makurat, Andriy Pysanenko, Jaroslav Kočišek, Janusz Rak e Stephan Denifl. "Low-Energy Electron Induced Reactions in Metronidazole at Different Solvation Conditions". Pharmaceuticals 15, n. 6 (2 giugno 2022): 701. http://dx.doi.org/10.3390/ph15060701.
Testo completoAbstract (sommario):
Metronidazole belongs to the class of nitroimidazole molecules and has been considered as a potential radiosensitizer for radiation therapy. During the irradiation of biological tissue, secondary electrons are released that may interact with molecules of the surrounding environment. Here, we present a study of electron attachment to metronidazole that aims to investigate possible reactions in the molecule upon anion formation. Another purpose is to elucidate the effect of microhydration on electron-induced reactions in metronidazole. We use two crossed electron/molecular beam devices with the mass-spectrometric analysis of formed anions. The experiments are supported by quantum chemical calculations on thermodynamic properties such as electron affinities and thresholds of anion formation. For the single molecule, as well as the microhydrated condition, we observe the parent radical anion as the most abundant product anion upon electron attachment. A variety of fragment anions are observed for the isolated molecule, with NO2− as the most abundant fragment species. NO2− and all other fragment anions except weakly abundant OH− are quenched upon microhydration. The relative abundances suggest the parent radical anion of metronidazole as a biologically relevant species after the physicochemical stage of radiation damage. We also conclude from the present results that metronidazole is highly susceptible to low-energy electrons.
26
Berezin, Andrei Vsevolodovich, Aleksandr Duhanin Aleksandr Duhanin, Oleg Sergeevich Kosarev, Mikhail Borisovich Markov, Sergey Vladimirovich Parot'kin, Yuri Viktorovich Pomazan e Ilya Alekseyevich Tarakanov. "On the simulation of gas ionization by fast electrons". Keldysh Institute Preprints, n. 46 (2021): 1–12. http://dx.doi.org/10.20948/prepr-2021-46.
Testo completoAbstract (sommario):
The gas-dynamic parameters of an ionized medium formed during impact ionization of a rarefied gas by fast electrons are considered. The concentration, drift velocity, and specific energy of low-energy secondary electrons are constructed by an approximate solution of the kinetic equation. Approximations of the spatial homogeneity of the kinetic equation and the isotropy of the initial distribution of secondary electrons during impact ionization are used. Additional approximations are related to the structure of the distribution function of secondary electrons and averaging of the cross sections.
27
Kawata, Jun, e Kaoru Ohya. "Secondary Electron Emission from Rough-Textured Beryllium Surface under Oblique Incidence of Low-Energy Electrons". Journal of the Physical Society of Japan 63, n. 10 (15 ottobre 1994): 3907–8. http://dx.doi.org/10.1143/jpsj.63.3907.
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Hembree, G. G., Luo Chuan Hong, P. A. Bennett e J. A. Venables. "Transfer optics for high spatial resolution electron spectroscopy". Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 666–67. http://dx.doi.org/10.1017/s0424820100105394.
Testo completoAbstract (sommario):
A new field emission scanning transmission electron microscope has been constructed for the NSF HREM facility at Arizona State University. The microscope is to be used for studies of surfaces, and incorporates several surface-related features, including provision for analysis of secondary and Auger electrons; these electrons are collected through the objective lens from either side of the sample, using the parallelizing action of the magnetic field. This collimates all the low energy electrons, which spiral in the high magnetic field. Given an initial field Bi∼1T, and a final (parallelizing) field Bf∼0.01T, all electrons emerge into a cone of semi-angle θf≤6°. The main practical problem in the way of using this well collimated beam of low energy (0-2keV) electrons is that it is travelling along the path of the (100keV) probing electron beam. To collect and analyze them, they must be deflected off the beam path with minimal effect on the probe position.
29
Kumar, Anil, David Becker, Amitava Adhikary e Michael D. Sevilla. "Reaction of Electrons with DNA: Radiation Damage to Radiosensitization". International Journal of Molecular Sciences 20, n. 16 (16 agosto 2019): 3998. http://dx.doi.org/10.3390/ijms20163998.
Testo completoAbstract (sommario):
This review article provides a concise overview of electron involvement in DNA radiation damage. The review begins with the various states of radiation-produced electrons: Secondary electrons (SE), low energy electrons (LEE), electrons at near zero kinetic energy in water (quasi-free electrons, (e−qf)) electrons in the process of solvation in water (presolvated electrons, e−pre), and fully solvated electrons (e−aq). A current summary of the structure of e−aq, and its reactions with DNA-model systems is presented. Theoretical works on reduction potentials of DNA-bases were found to be in agreement with experiments. This review points out the proposed role of LEE-induced frank DNA-strand breaks in ion-beam irradiated DNA. The final section presents radiation-produced electron-mediated site-specific formation of oxidative neutral aminyl radicals from azidonucleosides and the evidence of radiosensitization provided by these aminyl radicals in azidonucleoside-incorporated breast cancer cells.
30
Venables, J. A., G. G. Hembree e C. J. Harland. "Electron spectroscopy in SEM and STEM". Proceedings, annual meeting, Electron Microscopy Society of America 48, n. 2 (12 agosto 1990): 378–79. http://dx.doi.org/10.1017/s0424820100135496.
Testo completoAbstract (sommario):
Low energy electrons, in the energy range 0-2 keV, are very useful in surface science. Both secondary (0-100 eV nominally) and Auger (50-2 keV) electrons can be used as analytic signals in ultra-high vacuum (UHV) scanning (SEM) and scanning transmission (STEM) electron microscopes. This paper briefly reviews some ongoing projects, which are aimed at improving the spatial resolution and information content of these signals.Both secondary electron imaging (SEI) and Auger electrons spectroscopy (AES) have a long history. Reviews of AES and its microscopic counterpart scanning Auger microscopy (SAM) have been given previously in this International Conference Series; over the intervening period AES/SAM instruments have become widely available commercially. Simply biassing the sample up to a few hundred volts (-ve) has lead to a new technique (biassed-SEI) which is sensitive at the sub-monolayer level. In general biassing the sample is a useful additional experimental variable. It can be used to visualize thin films and surface topography, including steps; it can also be used to distinguish spectral features (eg Auger peaks) from the sample from those due to stray electrons, and to place such features in the best energy region for the electron spectrometer.
31
Rigler, Mark, e William Longo. "High Voltage Scanning Electron Microscopy Theory and Applications". Microscopy Today 2, n. 5 (agosto 1994): 12–13. http://dx.doi.org/10.1017/s1551929500066256.
Testo completoAbstract (sommario):
A variety of energy emissions occur as a result of primary beam interaction with the specimen surface. Secondary electrons, x-rays, visible photons, near IR photons, and Auger electrons are emitted during inelastic scattering of electrons. Backscattered electrons (BSE) are emitted during elastic scattering of primary electrons. Backscattered electrons are those electrons which pass through the electron cloud of an atom and change direction without much energy loss. BSEs may diffuse into the sample or may escape from the sample surface. In practice, the primary electron beam penetrates deeply into low Z (atomic number) materials and produces few BSEs while high Z materials retard primary beam penetration and emit large numbers of BSEs. According to Murata et al., the higher the atomic number, the smaller the mean free path between electron scattering events (i.e. 528 Å for Al vs. 50 Å for Au at 30 KeV) and the higher the probability of scattering.
32
Fitting, H. J., E. Schreiber e I. A. Glavatskikh. "Monte Carlo Modeling of Electron Scattering in Nonconductive Specimens". Microscopy and Microanalysis 10, n. 6 (dicembre 2004): 764–70. http://dx.doi.org/10.1017/s1431927604040735.
Testo completoAbstract (sommario):
Very low energy electrons in a solid should behave like Bloch electrons and will interact with perturbations of the atomic lattice, that is, with phonons. So we use the acoustic phonon scattering for replacing the elastic binary encounter approximation of the Mott scattering for electrons with low energies E < 100 eV. For ballistic electrons (1 eV < E < Eg) and higher energies up to 1 keV we determined the acoustic phonon scattering and the impact ionization rate by means of the “backscattering-versus-range” proof and respective η(E0) − R(E0) diagrams. Electron trajectories demonstrate the relatively short range of primary electrons (PE) with energies E > 50 eV due to strong impact ionization losses (cascading) and the much greater range of secondary electrons (SE) with E < 50 eV, finally as a consequence of less effective phonon losses. The field-dependent transport parameters allow us to model the self-consistent charge transport and charging-up of insulating SiO2 layers during electron bombardment maintained by the current components of primary electrons jPE, secondary electrons jSE, and associated ballistic holes jBH, as well as by Fowler–Nordheim field injection jFN from the substrate. The resulting distributions of currents j(x,t), charges ρ(x,t), electric fields F(x,t), and the potential V(x,t) across the dielectric layer explain the phenomena of field-enhanced and field-blocked secondary electron emission with rates δ [gel ] 1.
33
Sanche, L�on. "Nanoscopic aspects of radiobiological damage: Fragmentation induced by secondary low-energy electrons". Mass Spectrometry Reviews 21, n. 5 (settembre 2002): 349–69. http://dx.doi.org/10.1002/mas.10034.
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Zheng, Yi, e Léon Sanche. "Mechanisms of Nanoscale Radiation Enhancement by Metal Nanoparticles: Role of Low Energy Electrons". International Journal of Molecular Sciences 24, n. 5 (28 febbraio 2023): 4697. http://dx.doi.org/10.3390/ijms24054697.
Testo completoAbstract (sommario):
Metal nanoparticles are considered as highly promising radiosensitizers in cancer radiotherapy. Understanding their radiosensitization mechanisms is critical for future clinical applications. This review is focused on the initial energy deposition by short-range Auger electrons; when high energy radiation is absorbed by gold nanoparticles (GNPs) located near vital biomolecules; such as DNA. Auger electrons and the subsequent production of secondary low energy electrons (LEEs) are responsible for most the ensuing chemical damage near such molecules. We highlight recent progress on DNA damage induced by the LEEs produced abundantly within about 100 nanometers from irradiated GNPs; and by those emitted by high energy electrons and X-rays incident on metal surfaces under differing atmospheric environments. LEEs strongly react within cells; mainly via bound breaking processes due to transient anion formation and dissociative electron attachment. The enhancement of damages induced in plasmid DNA by LEEs; with or without the binding of chemotherapeutic drugs; are explained by the fundamental mechanisms of LEE interactions with simple molecules and specific sites on nucleotides. We address the major challenge of metal nanoparticle and GNP radiosensitization; i.e., to deliver the maximum local dose of radiation to the most sensitive target of cancer cells (i.e., DNA). To achieve this goal the emitted electrons from the absorbed high energy radiation must be short range, and produce a large local density of LEEs, and the initial radiation must have the highest possible absorption coefficient compared to that of soft tissue (e.g., 20–80 keV X-rays).
35
Proto, Andrea, e Jon Gudmundsson. "The Influence of Secondary Electron Emission and Electron Reflection on a Capacitively Coupled Oxygen Discharge". Atoms 6, n. 4 (28 novembre 2018): 65. http://dx.doi.org/10.3390/atoms6040065.
Testo completoAbstract (sommario):
The one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 is applied to explore the role of secondary electron emission and electron reflection on the properties of the capacitively-coupled oxygen discharge. At low pressure (10 mTorr), drift-ambipolar heating of the electrons dominates within the plasma bulk, while at higher pressure (50 mTorr), stochastic electron heating in the sheath region dominates. Electron reflection has negligible influence on the electron energy probability function and only a slight influence on the electron heating profile and electron density. Including ion-induced secondary electron emission in the discharge model introduces a high energy tail to the electron energy probability function, enhances the electron density, lowers the electronegativity, and increases the effective electron temperature in the plasma bulk.
36
Feng, Guobao, Huiling Song, Yun Li, Xiaojun Li, Guibai Xie, Jian Zhuang e Lu Liu. "Gas Desorption and Secondary Electron Emission from Graphene Coated Copper Due to E-Beam Stimulation". Coatings 13, n. 2 (6 febbraio 2023): 370. http://dx.doi.org/10.3390/coatings13020370.
Testo completoAbstract (sommario):
The gas desorption and secondary electron multiplication induced by electron bombardment tend to induce severe low-pressure discharge effects in space microwave device cavities. Nevertheless, few studies have focused on both secondary electron emission and electron-stimulated gas desorption (ESD). Although the suppression of secondary electrons by graphene was found to be better in our previous study, it is still unclear whether the surface modification of graphene, which brings about different interfacial states, can also be manifested in terms of ESD. The deep mechanism of gas desorption and secondary electron emission from this extremely thin two-dimensional material under electron bombardment still needs further investigation. Therefore, this paper investigates the mechanism of graphene modification on Cu metal surface on the gas release and secondary electron emission properties under electron bombardment. The surface states of graphene-modified Cu were characterized, and the ESD yield and secondary electron yield of Cu/GoCu were investigated using a self-researched platform and analyzed using molecular dynamics simulations and electron Monte Carlo simulations. The results of the study showed that the most released component on the Cu surface under the bombardment of electrons was H2O molecules, while the most released component on the GoCu surface was H2 molecules. The graphene-modified samples showed a significant suppression effect on the secondary electron yield and ESD only in the low-energy region below 400 eV. This study can provide a valuable reference for suppressing low-pressure discharge and multipactor phenomena in space microwave components.
37
Cochran, Raymond F. "Characterization of the low accelerating voltage performance of a microchannel plate based detector system for scanning microscopy". Proceedings, annual meeting, Electron Microscopy Society of America 49 (agosto 1991): 364–65. http://dx.doi.org/10.1017/s042482010008612x.
Testo completoAbstract (sommario):
The Galileo SEM2000 microchannel plate (MCP) detector collects onaxis symmetrical secondary electron images at accelerating voltages as low as 200 eV and beam currents less than 5 picoamps. Symmetrical images are particularly useful in metrology and for viewing features that are shielded by topology from an off-axis detector. Backscatter images from the same on-axis orientation can be obtained at accelerating voltages below 500 eV and beam currents less than 10 picoamps.The ability to image secondary and backscattered electrons in the same orientation, together with extremely high detection efficiency for low energy electrons make it a valuable tool for direct analysis of beam-sensitive or dielectric samples. Additional topographic enhancement can be obtained by A-B signal processing at accelerating voltages as low as 200 eV.
38
Hauchard, Christelle, e Paul A. Rowntree. "Low-energy electron-induced decarbonylation of Fe(CO)5 films adsorbed on Au(111) surfaces". Canadian Journal of Chemistry 89, n. 10 (ottobre 2011): 1163–73. http://dx.doi.org/10.1139/v11-073.
Testo completoAbstract (sommario):
The decarbonylation of Fe(CO)5 adsorbed in monolayer and multilayer films on Au(111)/mica substrates has been induced by 0–20 eV electrons and studied by grazing incidence IR spectroscopy. Our results show that the cross sections for the initial stages of this process in as-deposited films range from 60–300 Å2 and show considerable variations with the incident electron energy. The high sensitivity to low-energy electrons is believed to be the result of secondary reactions of anion fragments in the film with the neighbouring Fe(CO)5 moieties, leading to increasingly massive heteronuclear Fen(CO)m species and progressive CO elimination. Continued exposure to the electron beam leads to the slower degradation of these newly created species into an Fe-rich deposit containing traces of CO. These traces are removed by subsequent heating to ~300 K. Fe(CO)5 films that have been subjected to temperatures exceeding 125 K have no measurable sensitivity to the electron beam in the 0–20 eV regime; this is believed to be due to the structural transformation of the as-deposited thin film structure into 3D aggregates. This structural motif presents a very limited quantity of the adsorbed Fe(CO)5 to the incident beam, and may also form a protective layer of the robust Fen(CO)m species during the initial stages of exposure to the electrons.
39
Sanche, Léon. "Role of secondary low energy electrons in radiobiology and chemoradiation therapy of cancer". Chemical Physics Letters 474, n. 1-3 (maggio 2009): 1–6. http://dx.doi.org/10.1016/j.cplett.2009.03.023.
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Zheng, Yi, Pierre Cloutier, Darel J. Hunting e Léon Sanche. "Radiosensitization by Gold Nanoparticles: Comparison of DNA Damage Induced by Low and High-Energy Electrons". Journal of Biomedical Nanotechnology 4, n. 4 (1 dicembre 2008): 469–73. http://dx.doi.org/10.1166/jbn.2008.3282.
Testo completoAbstract (sommario):
Our previous studies on high energy (60 keV) electron bombardment of thin films of pGEM-3Zf(-) plasmid DNA with and without bound gold nanoparticles (GNP) showed that the presence of these particles greatly increases the formation of single-(SSB) and double-strand (DSB) breaks. To study the basic mechanisms underlying this DNA sensitization, we performed similar experiments with low energy (1, 10, 100 eV) and 60 keV electrons. The exposure response curves were recorded for the formation of SSB, DSB and loss of supercoiled DNA. The yields of SSB and DSB for pure DNA, salted DNA and GNP-DNA complexes with a molecular ratio of 1:1 were measured by agarose gel electrophoresis. The yields recorded for the GNP-DNA complexes were consistently enhanced by a factor of about 2 or more compared to those obtained with the salted DNA sample. Furthermore, the yields for low-energy electron damage were at least one order of magnitude larger than those produced by high-energy electrons. The results suggest that the radiosensitizing action of GNP takes place via two mechanisms: (1) an increase of the absorption of ionizing radiation close to the DNA, which in turns leads to a considerable increase in the production of short range secondary electrons that have a high probability of damaging DNA, and (2) an increase in the sensitivity of DNA to fragmentation induced by low energy electron impact near the site of binding of the GNP.
41
Romand, K. J., F. Gaillard, M. Charbonnier e D. S. Urch. "Fundamentals of X-ray Spectrometric Analysis Using Low-Energy Electron Excitation". Advances in X-ray Analysis 34 (1990): 105–21. http://dx.doi.org/10.1154/s0376030800014373.
Testo completoAbstract (sommario):
In the field of material analysis and characterization interest has considerably shifted over the last few decades from bulk to surface and very thin film problems. At the present state a wide range of surface analytical techniques - such as x-ray photoelectron (XPS), Auger electron (AES), secondary ion mass (SIMS), ion scattering (ISS) spectroscopies - have become available but every one of them exhibits specific analytical features and information content. Within the context of this paper the main parameter to be considered is the information depth i.e the layer thickness from which the majority of information-bearing particles escape and hence are detected. For XPS and AES, this parameter is associated with the mean-free path of photoelectrans or Auger electrons and typically is in the range from 0.5 to 4 nm. In SIMS the ejected secondary ions are emitted from the outer 2 or 3 atomic layers (i.e. from about 1 nm) while the single-collision binary process occuring in ISS is restricted to atoms from the top most atomic layer (0.2-0.3 nm).
42
MIKHAILOV, V. V. "LOW ENERGY ELECTRON AND POSITRON SPECTRA IN THE EARTH ORBIT MEASURED BY MARIA-2 INSTRUMENT". International Journal of Modern Physics A 17, n. 12n13 (20 maggio 2002): 1695–704. http://dx.doi.org/10.1142/s0217751x02011199.
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Liu, Yiheng, Kai He, Gang Wang, Guilong Gao, Xin Yan, Yanhua Xue, Ping Chen et al. "Simulation of the impact of using a novel neutron conversion screen on detector time characteristics and efficiency". AIP Advances 12, n. 4 (1 aprile 2022): 045206. http://dx.doi.org/10.1063/5.0073025.
Testo completoAbstract (sommario):
To directly measure the DT neutrons from inertial confinement fusion with a high time resolution, a new type of neutron conversion composed of a CH2 conversion layer, a metal moderation layer, and a CsI secondary electron emission layer is proposed. The conversion screen is based on the principle that recoil protons produced by elastic scattering of the neutrons in CH2 interact with CsI to generate secondary electrons. The moderation layer can filter the energy spectrum of protons to prevent low-energy protons from reaching CsI, which shortens the duration of the secondary electron pulse and improves the temporal resolution of the conversion screen. Based on the Monte Carlo method, both the neutron impulse and background γ-rays response of this conversion screen were calculated. The simulation indicates that the temporal resolution of the conversion screen can reach up to 4.9 ps when the thickness of the gold layer is 100 µm. The detection efficiency of secondary electrons/neutrons can reach 7.4 × 10−3. The detection efficiency of the neutron conversion screen for secondary electrons/γ-rays is an order of magnitude lower than the neutron impulse response, and the response time of γ-rays is 20 ps earlier than the neutron pulses. This means that using this conversion screen is beneficial to distinguish between neutrons and γ-rays and has a good signal-to-noise ratio.
44
Rodneva, S. M., e D. V. Guryev. "Theoretical Analysis of the Radiation Quality and the Relative Biological Efficiency of Tritium". MEDICAL RADIOLOGY AND RADIATION SAFETY 69, n. 2 (aprile 2024): 65–72. http://dx.doi.org/10.33266/1024-6177-2024-69-2-65-72.
Testo completoAbstract (sommario):
Introduction 1. Tritium and reference radiation 1.1 Tritium isotope and its energy spectrum 1.2 Reference radiation 2. Methods for determining the quality of radiation and RBE 2.1 Radiation quality in microdosimetry 2.2 RBE by the number of DNA double-strand breaks 2.3 RBE by fraction of secondary low-energy electrons 3. Analysis of calculations of radiation quality and tritium RBE 3.1 Estimation of tritium emission quality factors 3.2 Evaluation of the RBE of tritium radiation during its action on DNA 3.3 Estimation of the RBE of tritium from the fraction of secondary low-energy electrons 3.4 Quality factors and RBE of tritium with respect to reference emissions Conclusion
45
Mohamad Nor, Nurul Hidayah, Nur Afira Anuar, Wan Ahmad Tajuddin Wan Abdullah, Boon Tong Goh e Mohd Fakharul Zaman Raja Yahya. "A Geant4 Simulation on the Application of Multi-layer Graphene as a Detector Material in High-energy Physics". Sains Malaysiana 51, n. 10 (31 ottobre 2022): 3423–36. http://dx.doi.org/10.17576/jsm-2022-5110-25.
Testo completoAbstract (sommario):
The excellent properties of graphene, such as its high thermal conductivity, high electrical conductivity, and high electron density, make it an ideal candidate as a detector material in high-energy physics applications. In this work, we demonstrate the feasibility of multi-layer graphene (MLG) as a detector material in a high-energy environment. The Geant4 software package was used to estimate the energy of the deposited electrons within various thicknesses of MLG, ranging from 3 to 20 nm. The efficiency of the MLG as a detector material was further analyzed from the scattering angle and the yield of the secondary particles produced from the electron interaction with the material. The incident electron’s kinetic energy used herein ranged between 30 keV and 1 GeV, at a particle fluence of 1×107 e/cm2. The results show that the deposited energy was relatively low for the interaction with 1 MeV electrons, and dramatically increased as the thickness increases beyond 15 nm. This result was further supported by the highest yield of gamma radiation recorded by the interaction with a kinetic energy larger than 1 MeV, for thickness larger than 15 nm. The results suggest that the MLG works best as a charged particle detector in low energy ranges, while for high energy ranges, a thickness over 15 nm is suggested. The findings demonstrate that a MLG with a thickness larger than 15 nm could potentially be used as a detector material in high-energy conditions.
46
Akhdar, Hanan, Reem Alanazi, Nadyah Alanazi e Abdullah Alodhayb. "Secondary Electrons in Gold Nanoparticle Clusters and Their Role in Therapeutic Ratio: The Outcome of a Monte Carlo Simulation Study". Molecules 27, n. 16 (19 agosto 2022): 5290. http://dx.doi.org/10.3390/molecules27165290.
Testo completoAbstract (sommario):
Gold nanoparticles (GNPs) are used in proton therapy radio-sensitizers to help increase the dose of radiation to targeted tumors by the emission of secondary electrons. Thus, this study aimed to investigate the link between secondary electron yields produced from a nanoshell of GNPs and dose absorption according to the distance from the center of the nanoparticles by using a Monte Carlo model. Microscopic evaluation was performed by modeling the interactions of secondary electrons in a phase-space file (PSF), where the number of emitted electrons was calculated within a spherical GNP of 15 nm along with the absorbed dose near it. Then, the Geant4-DNA physics list was used to facilitate the tracking of low-energy electrons down to an energy below 50 eV in water. The results show a remarkable change in the number of secondary electrons, which can be compared at concentrations less than and greater than 5 mg/mL, with increased secondary electron production exhibited around NPs within a distance of 10–100 nm from the surface of all nanospheres. It was found that there was a steep dose enhancement drop-off up to a factor of dose enhancement factor (DFE) ≤ 1 within a short distance of 100 nm from the surface of the GNPs, which revealed that the dose enhancement existed locally at nanometer distances from the GNPs. Overall, our results indicate that the physical interactions of protons with GNP clusters should not be considered as being directly responsible for the radio-sensitization effect, but should be regarded as playing a major role in NP properties and concentrations, which has a subsequent impact on local dose enhancement.
47
H Kelley, Michael. "Uses of Spin-polarised Electrons in Fundamental Electron-Atom Collision Processes and the Analysis of Magnetic Microstructures". Australian Journal of Physics 43, n. 5 (1990): 565. http://dx.doi.org/10.1071/ph900565.
Testo completoAbstract (sommario):
Two experimental programs are discussed which exploit the use of polarised electrons for studies of fundamental processes and physical properties. In one program, collisions between spin�polarised electrons and optically pumped sodium atoms provide a very detailed characterisation of the spin-dependent interactions important in low-energy electron-atom collisions. The results of these measurements provide a critical test for the reliability of state-of-the�art electron scattering calculations. In the second program, the spin polarisation of secondary electrons ejected by high� energy electron impact is used to determine the magnetic structure of ferromagnetic materials with very high spatial resolution (-60 nm). This ability to perform such studies with high resolution has been exploited both in studies of the basic magnetic properties of ferromagnetic materials and in studies of how these basic properties affect the magnetic structure and performance of devices used for magnetic information storage.
48
Do Rego, A. M. Botelho, M. Rei Vilar, J. Lopes da Silva, M. Heyman e M. Schott. "Electronic excitation and secondary electron emission studies by low-energy electrons backscattered from thin polystyrene film surfaces". Surface Science Letters 178, n. 1-3 (dicembre 1986): A653. http://dx.doi.org/10.1016/0167-2584(86)90161-1.
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Do Rego, A. M. Botelho, M. Rei Vilar, J. Lopes Da Silva, M. Heyman e M. Schott. "Electronic excitation and secondary electron emission studies by low-energy electrons backscattered from thin polystyrene film surfaces". Surface Science 178, n. 1-3 (dicembre 1986): 367–74. http://dx.doi.org/10.1016/0039-6028(86)90313-4.
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Rosenberg, R. A., J. M. Symonds, K. Vijayalakshmi, Debabrata Mishra, T. M. Orlando e R. Naaman. "The relationship between interfacial bonding and radiation damage in adsorbed DNA". Phys. Chem. Chem. Phys. 16, n. 29 (2014): 15319–25. http://dx.doi.org/10.1039/c4cp01649a.
Testo completoAbstract (sommario):
Illustration showing that secondary electrons have a higher damage probability for thiolated DNA as opposed to unthiolated DNA, due to the former's higher density of LUMO states, which leads to more efficient capture of the low energy electrons.