Letteratura scientifica selezionata sul tema "Secondary low-energy electrons"
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Articoli di riviste sul tema "Secondary low-energy electrons"
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
Tesi sul tema "Secondary low-energy electrons"
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Sedmidubská, Barbora. "The role of the low-energy electrons in the process of radiosensitization". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASF069.
Testo completoAbstract (sommario):
Dans la chimioradiothérapie concomitante, il y a un effort pour augmenter son efficacité et atténuer la toxicité pour les cellules saines. Cela peut être atteint par le biais du synergisme et de la délivrance ciblée de médicaments (DCM). La DCM est un transport sélectif des médicaments vers des sites d'intérêt, protégeant ainsi les tissus sains de la toxicité des agents chimiothérapeutiques. Le synergisme est l'effet maximal de la chimioradiothérapie résultant des interactions complexes entre les deux modalités de traitement, comme l'interaction d'un agent radiosensibilisant avec des électrons de basse énergie (EBE) générés dans les tissus irradiés. Dans ce contexte, la thèse se concentre sur le processus de radiosensibilisation afin d'étudier le potentiel et les mécanismes radiosensibilisants des molécules sélectionnées basés sur leur interaction avec les EBE ; l'objectif est d'obtenir de nouvelles informations permettant de concevoir des radiosensibilisateurs plus efficaces et moins toxiques. La partie théorique traite des radiosensibilisateurs existants et leurs composés modèles du point de vue de l'interaction avec les EBE. La partie expérimentale combine des expériences d'attachement électronique en phase gazeuse et des calculs ab initio des affinités électroniques des molécules étudiées, des expériences de radiolyse pulsée en solution, ainsi que l'irradiation par microtron avec évaluation par la spectroscopie de résonance magnétique nucléaire. Sur la base de l'étude des interactions avec les EBE (secondaires), le potentiel radiosensibilisant a été confirmé pour l'agent antiviral favipiravir ; une interaction significative a été prouvée pour le radiosensibiliseur chimiothérapeutique RRx-001, ainsi qu'une forte interaction des électrons solvatés avec les fullerénols comme une plate-forme radiosensibilisante destinée à la DCMIn concomitant chemoradiotherapy (CCRT), there is an effort to increase its effectiveness and alleviate toxicity for healthy cells. It may be achieved via synergism and targeted drug delivery (TDD). TDD is the selective drug transport to sites of interest, protecting healthy tissue from chemotherapeutic toxicity. The synergism, the highest chemoradioterapeutic effect, results from complex interactions between both treatment modalities, as the interaction of the radiosensitizing chemo-drug with secondary low-energy electrons (LEEs) arising in irradiated tissue. In light of that work focuses on the radiosensitization process to investigate the radiosensitizing potential and mechanisms of selected molecules based on interaction with LEE; there is an aim to obtain new information to design more effective radiosensitizers with lower toxicity. The theoretical part deals with existing radiosensitizers and their model compounds from the point of view of interaction with LEEs. The experimental part combines electron attachment experiments in the gas phase and ab initio calculations of electron affinities of studied molecules, pulse radiolysis experiments in solution, and microtron irradiation with NMR spectroscopic evaluation. Based on the study of interaction with (secondary) LEEs, the radiosensitizing potential was confirmed for the antiviral agent favipiravir; significant interaction was proven for radiosensitizing chemotherapeutic RRx-001 as well, so as a strong interaction of solvated electrons with fullerenols as a radiosensitizing carrier drug for TGM in CCRT
Konkomitantní chemoradioterapie je jedna z důležitých metod léčby rakoviny. Stále existuje snaha zvýšit její účinnost a udržet toxicitu pro zdravé buňky na snesitelné úrovni. Její největší výhodou je synergický efekt plynoucí z mnoha komplexních interakcí mezi oběma léčebnými přístupy (tzn. chemoterapie a radioterapie). Bylo ukázáno, že jednou z příčin synergismu může být interakce chemosložky (tzv. radiosensitizéru) se sekundárními nízkoenergetickými elektrony vznikajícími v hojném počtu během radiolýzy v ozářené tkáni. V této práci se zaměřuji na proces radiosensitizace s cílem prozkoumat radiosensitizační potenciál molekul a odhalit radiosensitizační mechanismy na bázi jejich interakce s nízkoenergetickými elektrony. Motivací této práce bylo získat nové informace pro návrh nových a více účinných radiosensitizérů s menší toxicitou. Práce sestává z teoretické a experimentální části. Teoretická část je postavena na rešerši již existujících radiosensitizérů a jejich modelových sloučenin z pohledu interakce s nízkoenergetickými elektrony. Experimentální část kombinuje experimenty elektronového záchytu v plynné fázi na dvou experimentálních zařízeních, experimenty pulsní radiolýzy v roztoku, dále ozařování na mikrotronu s NMR spektroskopickým vyhodnocením a ab-initio výpočty elektronových afinit studovaných molekul a jejích fragmentů. V této práci bylo studováno antivirotikum favipiravir, pro který jsme na základě interakce s nízkoenergetickými elektrony potvrdili jeho radiosensitizační potenciál. Také byl zkoumán mechanismus radiosensitizace již potvrzeného radiosensitizéru a zároveň chemoterapeutika RRx-001 z pohledu jeho možné interakce se sekundárními nízkoenergetickými elektrony, která byla v této práci potvrzena. Nakonec byla odhalena silná interakce solvatovaných elektronů s fullerenoly studovanými pro použití v rámci platformy, která by prokazovala citlivost na nízkoenergetické elektrony a užívala by se pro dodávání léků v rámci konkomitantní chemoradiační terapii
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Pierron, Juliette. "Modèle de transport d'électrons à basse énergie (~10 eV- 2 keV) pour applications spatiales (OSMOSEE, GEANT4)". Thesis, Toulouse, ISAE, 2017. http://www.theses.fr/2017ESAE0024/document.
Testo completoAbstract (sommario):
L’espace est un milieu hostile pour les équipements embarqués à bord des satellites. Les importants flux d’électrons qui les bombardent continuellement peuvent pénétrer à l’intérieur de leurs composants électroniques et engendrer des dysfonctionnements. Leur prise en compte nécessite des outils numériques 3D très performants, tels que des codes de transport d’électrons utilisant la méthode statistique de Monte-Carlo, valides jusqu’à quelques eV. Dans ce contexte, l’ONERA a développé, en partenariat avec le CNES, le code OSMOSEE pour l’aluminium. De son côté, le CEA a développé, pour le silicium, le module basse énergie MicroElec dans le code GEANT4. L’objectif de cette thèse, dans un effort commun entre l’ONERA, le CNES et le CEA, est d’étendre ces codes à différents matériaux. Pour ce faire, nous avons choisi d’utiliser le modèle des fonctions diélectriques, qui permet de modéliser le transport des électrons à basse énergie dans les métaux, les semi-conducteurs et les isolants. La validation des codes par des mesures du dispositif DEESSE de l’ONERA, pour l’aluminium, l’argent et le silicium, nous a permis d’obtenir une meilleure compréhension du transport des électrons à basse énergie, et par la suite, d’étudier l’effet de la rugosité de la surface. La rugosité, qui peut avoir un impact important sur le nombre d’électrons émis par les matériaux, n’est habituellement pas prise en compte dans les codes de transport, qui ne simulent que des matériaux idéalement plats. En ce sens, les résultats de ces travaux de thèse offrent des perspectives intéressantes pour les applications spatialesSpace is a hostile environment for embedded electronic devices on board satellites. The high fluxes of energetic electrons that impact these satellites may continuously penetrate inside their electronic components and cause malfunctions. Taking into account the effects of these particles requires high-performant 3D numerical tools, such as codes dedicated to electrons transport using the Monte Carlo statistical method, valid down to a few eV. In this context, ONERA has developed, in collaboration with CNES, the code OSMOSEE for aluminum. For its part, CEA has developed for silicon the low-energy electron module MicroElec for the code GEANT4. The aim of this thesis, in a collaborative effort between ONERA, CNES and CEA, is to extend those two codes to different materials. To describe the interactions between electrons, we chose to use the dielectric function formalism that enables to overcome of the disparity of electronic band structures in solids, which play a preponderant role at low energy. From the validation of the codes, for aluminum, silver and silicon, by comparison with measurements from the experimental set-up DEESSE at ONERA, we obtained a better understanding of the transport of low energy electrons in solids. This result enables us to study the effect of the surface roughness. This parameter, which may have a significant impact on the electron emission yield, is not usually taken into account in Monte Carlo transport codes, which only simulate ideally flat materials. In this sense, the results of this thesis offer interesting perspectives for space applications
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Lemelin, Vincent. "Mesure de sections efficaces absolues vibrationnelles pour la collision d’électrons de basse énergie (1-19 eV) avec le tétrahydrofurane (THF) condensé". Mémoire, Université de Sherbrooke, 2016. http://hdl.handle.net/11143/9467.
Testo completoAbstract (sommario):
Résumé: Ce mémoire de maîtrise est une étude des probabilités d’interactions (sections efficaces) des électrons de basse énergie avec une molécule d’intérêt biologique. Cette molécule est le tétrahydrofurane (THF) qui est un bon modèle de la molécule constituant la colonne vertébrale de l’ADN; le désoxyribose. Étant donné la grande quantité d’électrons secondaires libérés lors du passage des radiations à travers la matière biologique et sachant que ceux-ci déposent la majorité de l’énergie, l’étude de leurs interactions avec les molécules constituant l’ADN devient rapidement d’une grande importance. Les mesures de sections efficaces sont faites à l’aide d’un spectromètre à haute résolution de pertes d’énergie de l’électron. Les spectres de pertes d’énergie de l’électron obtenus de cet appareil permettent de calculer les valeurs de sections efficaces pour chaque vibration en fonction de l’énergie incidente de l’électron. L’article présenté dans ce mémoire traite de ces mesures et des résultats. En effet, il présente et explique en détail les conditions expérimentales, il décrit la méthode de déconvolution qui est utilisée pour obtenir les valeurs de sections efficaces et il présente et discute des 4 résonances observées dans la dépendance en énergie des sections efficaces. En effet, cette étude a permis de localiser en énergie 4 résonances et celles-ci ont toutes été confirmées par des recherches expérimentales et théoriques antérieures sur le sujet des collisions électrons lents-THF. En outre, jamais ces résonances n’avaient été observées simultanément dans une même étude et jamais la résonance trouvée à basse énergie n’avait été observée avec autant d’intensité que cette présente étude. Cette étude a donc permis de raffiner notre compréhension fondamentale des processus résonants impliqués lors de collisions d’électrons secondaires avec le THF. Les valeurs de sections efficaces sont, quant à elles, très prisées par les théoriciens et sont nécessaires pour les simulations Monte Carlo pour prédire, par exemple, le nombre d’ions formées après le passage des radiations. Ces valeurs pourront justement être utilisées dans les modèles de distribution et dépôt d’énergie au niveau nanoscopique dans les milieux biologiques et ceux-ci pourront éventuellement améliorer l’efficacité des modalités radiothérapeutiques.Abstract: This master’s thesis is a study of interactions probabilities (cross sections) of low-energy electrons with an important biomolecule. The studied molecule is tetrahydrofuran (THF) which is a good model for the DNA backbone constituent deoxyribose. Knowing the important quantity of secondary electrons generated by the radiations passage through the biological matter and knowing that these low-energy electrons are responsible for the majority of the energy deposited, the study of their interactions with DNA constituents becomes rapidly important. Cross sections measurements are performed with a high-resolution electron energy loss spectrometer. The electron energy loss spectra obtained from this spectrometer allow cross sections calculations for each vibration mode as a function of electron incident energy. The article presented in this master thesis describes in details the experimental methods, it presents energy loss spectra and it shows and discusses results obtained in this project. The energy dependence of the cross sections allows the observation of multiple resonances in many vibration modes of THF. Effectively, this study allows the energy localisation of 4 resonances, which have all been confirmed by previous experimental and theoretical studies on the electron-THF collisions. Additionally, these resonances have never been observed simultaneously in the same study and the resonance found at low incident energy has never been observed with as much intensity as this present work. This study allowed a better understanding of the fundamental processes occurring in collisions of low-energy electrons with THF. The cross sections values are highly prized by theorists and they are essential for Monte Carlo simulations. These values will be used in models for energy distribution and deposition in biological matter at nanoscopic scales, thereby they will eventually improve the efficiency of radiotherapeutic modalities.
Capitoli di libri sul tema "Secondary low-energy electrons"
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Gomati, M. M. El, A. M. D. Assa’d, T. El Gomati e M. Zadrazil. "On the measurement of low energy backscattered and secondary electron coefficients". In Electron Microscopy and Analysis 1997, 265–68. Boca Raton: CRC Press, 2022. http://dx.doi.org/10.1201/9781003063056-68.
Testo completo
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Joy, David C. "Secondary Electrons and Imaging". In Monte Carlo Modeling for Electron Microscopy and Microanalysis, 134–73. Oxford University PressNew York, NY, 1995. http://dx.doi.org/10.1093/oso/9780195088748.003.0008.
Testo completoAbstract (sommario):
Abstract Secondary electrons (SE), discovered by Austin and Starke in 1902, are defined as being those electrons emitted from the specimen that have energies between 0 and 50 eV. Because of their low energy, secondary electrons are readily deflected and collected by the application of an electrostatic or magnetic field; as a consequence, the great majority of all scanning electron microscope (SEM) images have been taken using the SE signal. Secondaries can be generated through a variety of interactions in the specimen (Wolff, 1954; Seiler, 1984), a typical event being a knock-on collision in which the incident electron imparts some fraction of its energy to a free electron in the specimen. This is followed by a cascade process in which these secondaries diffuse through the solid, multiplying and losing energy as they travel, until they either sink back into the sea of conduction electrons or reach the surface with sufficient energy to emerge as true SE. For SE with energies of a few tens of electron volts, the inelastic mean free path (MFP) is small, in the range 10 to 40 A, so each secondary typically travels only a short distance before sharing some of its energy in an inelastic event. However, for most materials, the inelastic MFP reaches a minimum at about 20 to 30 eV; for energies below that value, it increases rapidly, because there are no large cross-section inelastic scattering events through when energy can be transferred. The elastic MFP also falls with energy but becomes approximately constant at a few tens of angstroms for energies below about 30 eV. SE with energies below this value are therefore strongly elastically scattered even though inelastic scattering is insignificant. Consequently, as the cascade develops from some point below the surface of the irradiated specimen, only a finite fraction will actually reach the surface and escape to be collected. We can thus see that there is a region beneath the surface-the so-called SE escape depth, perhaps 50 to 150 A in extent-beyond which no SE generated can reach the surface and escape.
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Riviere, J. C. "Electron excitation: electron energy loss spectroscopy (ELS), core electron energy loss spectroscopy (CEELS), and high resolution electron energy loss spectroscopy (HREELS)". In Surface Analytical Techniques, 125–66. Oxford University PressOxford, 1990. http://dx.doi.org/10.1093/oso/9780198513704.003.0005.
Testo completoAbstract (sommario):
Abstract In none of these loss spectroscopies is spatial resolution required, but they do require electron sources capable of variable primary energy down to very low energies, with good stability. The need in HREELS for careful screening of the whole analytical system of source and analyser from strong magnetic fields has already been emphasized, as has the practice of minimizing currents of unwanted secondary electrons by coating internal surfaces with a low secondary emitter such as carbon.
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Krishnan, Kannan M. "Probes: Sources and Their Interactions with Matter". In Principles of Materials Characterization and Metrology, 277–344. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198830252.003.0005.
Testo completoAbstract (sommario):
Probes are generated using laboratory sources, or in large user facilities. Photon sources include incandescence and plasma discharge lamps. Electron beams are generated using thermionic or field-emission sources. RF plasma sources generate ions that are accelerated and used for scattering experiments. Specimens should be probed first with light, as it causes the least damage. Electron interaction with matter causes beam broadening, atomic displacements, sputtering, or radiolysis leading to mass loss and local contamination. Neutrons are heavier than electrons, penetrate more deeply in materials, and require more sample for analysis. Protons (positive charge, heavier than electrons) go a longer way in the specimen without significant broadening. Ions in solids undergo kinematic collisions with conservation of energy and momentum; they also lose energy continuously as they propagate. In the back-scattering geometry, they form important methods of Rutherford backscattering spectroscopy (RBS) and low-energy ion scattering spectroscopy (LEISS). Medium energy ions generate secondary ions by sputtering that can be analyzed by mass spectrometers to determine specimen composition (SIMS). Alternatively, its composition is analyzed (ICP-MS), by creating an aqueous dispersion and converting it to a plasma. Finally, interaction of high-energy ions with core electrons can lead to inner shell ionization and characteristic X-ray emission (PIXE).
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Madhavan, Jayachandran. "Transition metal oxides-MXene nanocomposite: The next frontier in supercapacitors". In Materials Research Foundations, 117–44. Materials Research Forum LLC, 2024. http://dx.doi.org/10.21741/9781644903292-6.
Testo completoAbstract (sommario):
The steady depletion of non-renewable energy sources along with global warming, has emphasized environment friendly energy systems worldwide. Consequently, there has been a significant increase in demand for efficient energy storage devices, particularly for highly efficient energy storage devices such as supercapacitors and secondary batteries. Comparing with energy storage devices supercapacitor possess a very high-power density, a decent energy density and have an excellent cyclic stability. However, their limited energy density restricts them from being integrated with our daily energy needs. Electrode material based on transition metal oxide (TMO) are particularly intriguing due to their exceptional blend of structural, mechanical, electrical, and electrochemical capabilities. TMO are promising electrode materials for supercapacitors owing to its high capacitance and energy density attributed to rich redox chemistry, as well as their high reversibility, rapid charge-discharge operations, minimal expense owing to availability, and ecological sustainability. However, the significant obstacles that need to be surmounted are inadequate electrical conductivity, rate capability, poor cycle life, and low power density. To overcome these hindrances nanocomposite of TMO with 2D layered materials such as MXenes which provides high electronic conductivity and large surface area for better activation of TMO to enhance the charge storage capabilities. This chapter systematically aims on the most recent developments in MXene-TMO heterostructure electrode materials for supercapacitors and highlights their merits.
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Traynor, C. A., e J. B. Anderson. "Parallel Monte Carlo calculations to determine energy differences among similar molecular structures". In Quantum Monte Carlo, 59. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.0062.
Testo completoAbstract (sommario):
Abstract This study combines correlated sampling with Green’s function sampling in QMC for highly accurate calculations of potential energy differences among similar molecular structures. The method is exact for nodeless systems. It is illustrated with calculations for the molecular ion Ht to determine the minimum-energy structure and the potential energy surface in that region. The key to Green’s function sampling is the use of geometrically similar structures all related to a primary structure by a single length parameter. The movement of walkers in the secondary system (or systems) is geometrically similar to that in the primary, the electron configurations are geometrically similar, and the sampling of positions is completely correlated. Since the potential energies are not the same for secondary walkers, the multiplication terms V/ E differ, and the weights of secondary walkers diverge from those of the primary walkers as the calculations proceed. Division of secondary walkers with high weights, and elimination of those with low weights, is matched to that of the primary systems. Importance sampling may be incorporated with a single trial function or with scaled trial functions. The results for Ht showed the minimum energy structure for the equilateral triangle to be very close to 1.6500 bohr in side length. The calculations for 12 different structures at the same time required about the same calculation effort as for a single structure when scaled trial functions were used. Energy differences were obtained with high accuracy for structures differing by up to about 10% in size. For those differing more than about 10%, the accuracies in energy differences were much lower.
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Pappu, Samhita, Tata N. Rao, Sarada V. Bulusu e Katchala Nanaji. "Introduction to Green Supercapacitors: Fundamentals, Design, Challenges, and Future Prospects". In Low-carbon Supercapacitors, 1–33. Royal Society of Chemistry, 2023. http://dx.doi.org/10.1039/bk9781837672479-00001.
Testo completoAbstract (sommario):
Many efforts have been dedicated to the design of high-energy and power-based green energy storage systems. In this context, supercapacitors with tailored electrode and device architectures are found to be highly appropriate. Recent years have seen supercapacitors attracting worldwide interest due to their critical role in replacing conventional fuels in the transportation sector and also owing to their promising electrochemical characteristics like long cycle life, high power density, and low toxicity. Supercapacitors bridge the gap between conventional dielectric capacitors and primary or secondary Li-ion batteries in terms of their energy and power densities. However, the basic electrochemistry based on how different types of supercapacitors work is less established. Therefore, the underlying charge storage mechanisms, redox reactions, and processes may be confusing. A good supercapacitor electrode material should possess certain characteristics such as large specific surface area and porosity, good surface wettability, high electrical conductivity, tuning of textural parameters, and thermodynamic stability to deliver good electrochemical properties. This chapter discusses the fundamentals of supercapacitors, their classification, and storage mechanisms. This is followed by a brief discussion of various electrode materials used among the different supercapacitor types and their corresponding synthesis and electrochemical progress. Furthermore, the chapter also details the challenges and scope of each of the classifications.
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Fatima, Tatheer, Tanzeela Fazal e Nusrat Shaheen. "Electro-Peroxone and Photoelectro-Peroxone Hybrid Approaches: An Emerging Paradigm for Wastewater Treatment". In Wastewater Treatment [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.102921.
Testo completoAbstract (sommario):
Electrochemical advanced oxidation practices (EAOPs), remarkably, electro-peroxone (EP), photoelectro-peroxone (PEP), and complementary hybrid EP approaches, are emerging technologies on accountability of complete disintegration and elimination of wide spectrum of model pollutants predominantly biodegradable, recalcitrant, and persistent organic pollutants by engendering powerful oxidants in wastewater. A concise mechanism of EP and PEP approaches along with their contribution to free radical formation are scrutinized. Furthermore, this chapter provides a brief review of EP, PEP, and complementary hybrid EP-based EAOPs that have pragmatically treated laboratory-scale low- and high-concentrated distillery biodigester effluent, refractory pharmaceutical, textile, herbicides, micropollutant, organic pollutant, acidic solution, landfill leachates, municipal secondary effluents, hospital, and industries-based wastewater. Afterward, discussion has further extended to quantitatively evaluate energy expenditures in terms of either specific or electrical energy consumptions for EP and PEP practices through their corresponding equations.
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Mohanbabu, A., S. Maheswari, N. Vinodhkumar, P. Murugapandiyan e R. Saravana Kumar. "Advancements in GaN Technologies: Power, RF, Digital and Quantum Applications". In Nanoelectronic Devices and Applications, 1–28. BENTHAM SCIENCE PUBLISHERS, 2024. http://dx.doi.org/10.2174/9789815238242124010003.
Testo completoAbstract (sommario):
Quantum well devices based on III-V heterostructures outperform Field Effect Transistors (FETs) by harnessing the exceptional properties of the twodimensional electron gas (2DEG) in various material interface systems. In high-power electronics, III-V-based Gallium Nitride (GaN) HEMTs can have a great influence on the transport industry, consumer, RADAR, sensing systems, RF/ power electronics, and military systems. On the other hand, the devices made of HEMTs and MIS-HEMTs work in enhancement mode, having very low leakage current, which can conserve energy for more efficient power conversion, microwave/ power transistors and highspeed performance for wireless communication. The existing physics of the wellestablished AlGaN heterostructure system imposes constraints on the further progress of GaN-based HEMTs. Some of the scopes include: Initially, the semiconductor materials made of SiC, GaN, and AlGaN allow a device that is resistant to severe conditions, such as high-power /voltage-high temperature, to operate due to its effective dielectric constant and has a very good thermal conductivity, which makes this device well-suited for military applications. Secondly, with the urgent need for high-speed internet multimedia communication across the world, high transmission network capacity is required. GaN-based HEMT devices are suitable candidates for achieving high-speed limits, high gain and low noise performance. In conclusion, GaN and related interface materials exhibit chemical stability and act as robust semiconductors, exhibiting remarkable piezoelectric polarization effects that lead to a high-quality 2DEG. Integrating free-standing resonators with functionalized GaNbased 2DEG formation reveals the potential for designing advanced sensors.
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Zhuang, Yanling, Shujuan Liu e Qiang Zhao. "Organic Resistive Memories for Neuromorphic Electronics". In Advanced Memory Technology, 60–120. Royal Society of Chemistry, 2023. http://dx.doi.org/10.1039/bk9781839169946-00060.
Testo completoAbstract (sommario):
With the rapid development of big data, advanced data storage technologies with lower power consumption, faster switching speed, higher integration density and larger storage capacity have become the target of storage electronics in the future. However, traditional Si-based CMOS technology and von Neumann architecture will reach their limits, which cannot satisfy the needs of ultra-high density, ultra-small size, and in-memory computing. Due to their low cost, fast speed, easy handling, high energy efficiency, good scalability and flexibility, organic resistive memories are expected to be candidates for high-density storage, logic computing, and neuromorphic computing. In this chapter, we summarize the research progress of organic resistive switching materials and devices. Firstly, the device structure, storage type and switching mechanism are introduced in detail. Secondly, the design strategies and memory properties of various organic resistive switching materials including organic small molecules, organometallic compounds, polymers, and biomaterials are systematically summarized, while the key performance parameters of the memories are also specifically mentioned. Next, the applications of memristors in neuromorphic computing such as artificial synapses, image recognition, and in-memory arithmetic and logic computing are also discussed. Finally, the current challenges and future directions in developing organic resistive memory materials and their neuromorphic devices are outlined.
Atti di convegni sul tema "Secondary low-energy electrons"
1
Nyyssonen, Diana. "Collection of low-energy secondary electrons and imaging in a low-voltage SEM". In SPIE's 1996 International Symposium on Microlithography, a cura di Susan K. Jones. SPIE, 1996. http://dx.doi.org/10.1117/12.240145.
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Kunz, R. R., T. E. Allen e T. M. Mayer. "Thin Film Growth and Deposition by Low Energy Electron Stimulated Surface Chemistry". In Microphysics of Surfaces, Beams, and Adsorbates. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/msba.1987.tua2.
Testo completoAbstract (sommario):
Direct materials processing by focused particle beams has received considerable attention in recent years. The electron beam, traditionally used for resist exposure in electron beam lithography applications, is among the candidates for direct materials modification. High energy electrons (>1keV) are not very chemically active due to small cross sections for inelastic scattering processes such as bond dissociation and attachment. Low energy electrons are expected to be much more efficient at stimulating chemical processes. In particular, secondary electrons produced by particle or photon bombardment of surfaces with kinetic energies of approx. 2-10 eV have large cross sections for attachment and dissociative electron attachment to many electronegative molecules. We have begun a general investigation of chemical reactivity and mechanisms of electron-adsorbate interactions leading to film growth and deposition. Prospects for applications to focussed beam, direct write materials processing are being explored.
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Kash, J. A., e J. C. Tsang. "Non-equilibrium Carriers in GaAs: Secondary Emission During the First Four Picoseconds". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/up.1986.tuc2.
Testo completoAbstract (sommario):
When electrons and holes are optically injected into GaAs by a short pulse laser with photon energy well above the direct gap, the initial monoenergetic carrier distribution is rapidly changed by both carrier-carrier scattering and electron-LO phonon scattering. The effect of each mechanism on the carrier distributions is very different. Electron-LO phonon scattering causes the carriers to lose energy to the lattice. On the other hand, carrier-carrier scattering efficiently redistributes energy within the carriers and produces a carrier distribution that can be characterized by a well-defined temperature common to both electrons and holes, but different than the lattice temperature. In addition 1,2τe–LO ≃ 165 fsec and is independent of carrier concentration for n < 1018cm−3, while τc–c depends1 on concentration n roughly as τc–c ≃ 2 × 104 sec /n cm3. Thus, the relative importance of each mechanism depends upon the carrier concentrations. The initial relaxation of the optically injected carriers is dominated by τe–LO at low n, and by τc–c at high n. The two rates are equal at n ≃ 1.25 × 1017cm−3.
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Rolsma, Peter B., John N. Lee e Tae-Kwan Oh. "Experimental Investigation of Photoemitter Membrane Spatial Light Modulator Performance Limit". In Spatial Light Modulators and Applications. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/slma.1988.the7.
Testo completoAbstract (sommario):
A photoemitter membrane light modulator (PEMLM) is enhanced by adding a visible light photocathode to the basic structure [1]. The basic structure consists of four parts; a microchannel plate (MCP), a grid, a deformable membrane, and a transparent electrode as shown in Figure 1. Previously the input of the MCP was used as a photocathode to convert an ultraviolet (uv) image into an electron distribution. The MCP then amplifies this distribution by secondary emission, similar to a photomultiplier tube. At the output of the MCP the electron energies are low. The purpose of the grid that is added to the MCP output, is to control the electron energy. If the energy is low the electrons will be deposited onto the membrane. If they are high, excess secondary emission at the membrane will occur and electrons will be removed from the membrane. Thus, images are added or subtracted by changing the grid voltage. The rate at which these functions and other possible functions occur, is dependent upon the rate of electron generation by the MCP, up to the point of MCP saturation. This electron generation is the product of the light intensity and photocathode quantum efficiency. Using the MCP input as a photocathode requires a strong uv light because of a low quamtum efficiency (≃10-7), even at short wavelengths. To avoid the problems of working with uv, a cesium-antimony(Cs3Sb) photocathode for the PEMLM is being fabricated. This will allow the use of red light for a write beam. Previously, high frame rates were not achieved because of the limits of the light source. With the Cs3Sb photocathode frame rates should be increased to the MCP strip current limit.
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Rykaczewski, Konrad, Ben White, Jenna Browning, Andrew D. Marshall e Andrei G. Fedorov. "Dynamic Model of Electron Beam Induced Deposition (EBID) of Residual Hydrocarbons in Electron Microscopy". In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-14955.
Testo completoAbstract (sommario):
Adsorbed species surface diffusion Electron beam induced deposition (EBID) of residuals carbon can be either a contamination problem or can provide a basis for 3-D nanofabrication and nanoscale metrology. In this process a solid deposit is formed at the point of impact of the electron beam due to the decomposition of residual hydrocarbon species adsorbed on the solid substrate. The first observation of EBID can be traced to miscroscopists who noticed the growth of thin films of carbon while imaging using an electron microscope. The process was referred to as "contamination" because of its adverse effects on the microscope's imaging quality. Later, it has been demonstrated that with appropriate control of the electron beam this problematic contamination can be exploited to deposit three dimensional nanostructures with the spatial resolution down to 10nm. Numerous researchers have experimentally explored various factors influencing EBID growth rate and geometry of the deposit. To date, the most comprehensive theoretical model predicting the shape of the deposit in EBID is due to Silvis-Cividjian[1]. However, this model accounts for electron transport only. A few, fairly rudimentary models have also been developed for mass transport in EBID, but usually limited to rather simplistic treatment of electron transport. To this end, we have developed a comprehensive dynamic model of EBID coupling mass transport, electron transport and scattering, and species decomposition to predict deposition of carbon nano-dots. The simulations predict the local species and electron density distributions, as well as the 3-D profile and the growth rate of the deposit. Since the process occurs in a high vacuum environment surface diffusion is considered as the primary transport mode of surface-adsorbed hydrocarbon precursor. Transport, scattering, and absorption of primary electron as well as secondary electron generation are treated using the Monte Carlo methods. Low energy secondary electrons (SE) are the major contributors to hydrocarbon decomposition due to their energy range matching peak dissociation reaction cross section energies for precursor molecules. The local SE flux at the substrate and at the free surface of the growing deposit is computed using the Fast Secondary Electron (FSE) model. When combined with the total dissociation reaction corssection and the local hydrocarbon surface concentration, this allows us to compute the local deposition rate. The deposition rates are then used to predict the shape profile evolution of the deposit. Simulation results are compared with an AFM imaging of carbon EBID.
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Feschenko, A. V. "Bunch shape monitors using low energy secondary electron emission". In Accelerator instrumentation fourth annual workshop. AIP, 1992. http://dx.doi.org/10.1063/1.44336.
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Tao, Runming, Bryan Steinhoff, Yang-Tse Cheng e Jianlin Li. "Manufacturing Cathodes via Dry-Processing for Lithium-Ion Batteries". In ASME 2024 19th International Manufacturing Science and Engineering Conference. American Society of Mechanical Engineers, 2024. http://dx.doi.org/10.1115/msec2024-125340.
Testo completoAbstract (sommario):
Abstract Conventional lithium-ion battery (LIB) electrodes are prepared through a wet slurry process with n-methyl pyrrolidone solvent, especially for cathodes. The wet slurry process encounters several disadvantages such as binder migration, electrode cracking in thick electrodes, energy intense heat-dry NMP solvent removal, and costly NMP recovery. The cost and energy consumption of coating and drying of electrode are about 11.5 % and > 46 % in LIB manufacturing, respectively. Thereby, it is essential to develop a facile roll-to-roll solvent-free LIB electrode processing for reducing the cost and energy consumption. Recently, the Maxwell-type dry processing (DP) shines new lights on LIB manufacturing, which mainly bases on dry mixing (DM) of electrode component powder followed by calendering into electrode films and laminating onto current collectors, realizing the rapid manufacturing of LIB electrodes in a powder-to-film manner for industries. This report shares some recent progress on the DP from our group. We aim to further advance the manufacturing science of DP by correlating the processing conditions with electrode properties and performance. Particularly, we investigate the effect of DM, and compression on the polytetrafluoroethylene (PTFE) binder fiberization, porosity, mechanical properties, electrical conductivity and electrochemical behaviors of electrodes. The DM study suggests that PTFE fiberization heavily relies on the degree of DM. Insufficient DM results in poor PTFE fiberization while outrageous DM damages the formed PTFE fibers. Both negatively affect the mechanical behaviors of the electrodes and their rate capability. However, moderate DM is highly beneficial. In addition, our study of the porosity impact reveals that LiNi0.8Mn0.1Co0.1O2 (NMC) secondary particles can be broken into primary particles due to compression, especially at low porosity. Those fractured NMC secondary particles exhibit lower modulus. We propose that a moderate porosity of around 32% favors the electronic conductivity, charge transfer impedance and rate capability. The study of the cathodic electrolyte interphase layer of PTFE-based DPed electrode confirms that side reactions of PTFE binder due to the formation of LiF in LiClO4-based electrolyte.
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Fukamachi, Asuna, Masato Watanabe, Akitoshi Okino, Kwang-Cheol Ko e Eiki Hotta. "Application of low-energy secondary emission electron gun for VOC treatment". In 2006 International Symposium on Discharges and Electrical Insulation in Vacuum. IEEE, 2006. http://dx.doi.org/10.1109/deiv.2006.357387.
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Miyake, Hiroaki, Kumi Nitta, Shinichiro Michizono e Yoshio Saito. "Secondary electron emission on degradation sample and development of new measurement system with low electron energy". In 2008 XXIII International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV 2008). IEEE, 2008. http://dx.doi.org/10.1109/deiv.2008.4676853.
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Toliyat, Amir, e Alexis Kwasinski. "Energy storage sizing for effective primary and secondary control of low-inertia microgrids". In 2015 IEEE 6th International Symposium on Power Electronics for Distributed Generation Systems (PEDG). IEEE, 2015. http://dx.doi.org/10.1109/pedg.2015.7223077.
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