Kinetic energy spectra of O⁻ from dissociative electron attachment (DEA) to NO were measured at 7.6, 8.0, 9.0 and 10.0 eV electron energy using a spectrometer with hemispherical energy selectors for both the incident electrons and the resulting ions. The measurements were performed at 10°, 30°, 90° and 135°. The capacity of the spectrometer to detect both slow and fast ions was verified and the spectra were corrected for the analyser response function. Under these conditions only a signal corresponding to O⁻ in the ground state and N in the first excited state was observed, a signal from the remaining two energetically accessible channels was absent. These observations confirm the original conclusion of Chantry (1968 Phys. Rev. 172 125) and reduce the range of possible explanations for the diametrically different observations of Orient and Chutjian (1995 Phys. Rev. Lett. 74 5017). Allan, Michael
An electron emission device exhibits a high electron emission efficiency. The device includes an electron supply layer of metal or semiconductor, an insulator layer formed on the electron supply layer, and a thin-film metal electrode formed on the insulator layer. The insulator layer is made of a polycrystal dielectric substance and has a film thickness of 50 nm or greater and has a polycrystal phase with an average grain size of 5 to 100 nm as a major component and an amorphous phase as a minor component. When an electric field is applied between the electron supply layer and the thin-film metal electrode, the electron emission device emits electrons.
Attosecond spectroscopy holds great promise as a time-resolved general probe of electron correlation dynamics, which is central to important many-body phenomena from superconductivity to chemical bond formation. Double ionization processes are envisioned to be a direct probe of electron correlation by studying the time-resolved momentum correlation of two electrons. However, the time delay between two photoelectrons arising from double ionization has not been measured directly in the attosecond time domain, so it remains to be seen what such measurements can reveal concerning the details of electron correlation.. Recently, using a newly developed three-dimensional (3D) electron-electron coincidence imaging technique and an attosecond two-electron angular streaking method, we show the emission time delay between two electrons can be measured from zero attoseconds to more than one femtosecond. Surprisingly, in benzene, the double ionization rate decays as the time delay between the first and ...
The present invention relates to a flat display screen, comprising a cathode with electron emission microtips associated with a grid for extracting electrons from the microtips, the cathode/grid comprising conductive grid or cathode lines adapted to being sequentially addressed, and cathode or grid columns perpendicular to the lines and adapted to being addressed individually and simultaneously during the addressing of a line, and the screen comprising a return electrode adapted to being biased to a return potential corresponding to a no electron emission potential, each grid or cathode line being connected, via at least one resistive element, to the return electrode.
An electron emission device comprises an electron emission electrode with a pointed end and a counter electrode positioned opposite to the pointed end, both formed by fine working of a conductive layer laminated on an insulating substrate.
Professor Helen J. Cooper is an expert in the gas-phase ion chemistry of peptides and proteins. She is a world-leader in the field of electron capture dissociation mass spectrometry and is responsible for establishing the University of Birmingham as a centre of excellence in mass spectrometry research. Professor Cooper has published extensively in peer-reviewed journals and serves on a number of national and international committees including the Editorial Board for the Journal of the American Society for Mass Spectrometry and the British Mass Spectrometry Society.
We investigate the dynamics of low-energy electron-induced reactions in condensed thin films of methanol (CH$_3$OH) through electron stimulated desorption (ESD) and post-irradiation temperature programmed desorption (TPD) experiments. ESD experiments indicate that the anions which desorb from the methanol thin film during electron irradiation are predominantly formed through the dissociation of temporary negative ions formed by electron capture by methanol molecules, a process known as dissociative electron attachment (DEA). However, based on investigation of reaction products remaining in the methanol thin film post-irradiation through TPD experiments, DEA is not the obvious primary mechanism by which methoxymethanol (CH$_3$OCH$_2$OH) and ethylene glycol (HOCH$_2$CH$_2$OH) are formed. Evidence indicates formation of these molecules may be driven by both DEA and electron impact excitation. To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.J35.8. ...
Secondary electron emission is one of the most fundamental problems in spacecraft charging. An accurate prediction of secondary electron yield at low-energ
Compound Formulas - Ionic Ionic 1 Valence Electrons: ELECTRONS AVAILABLE FOR BONDING 2 Definition Valence electrons are electrons in the outmost shell (energy level). They are the electrons
Vanadium has five valence electrons. Valence electrons are the electrons that an element gives up or gains during a chemical bond with another element. Vanadium can be found five elements in from the...
The valence electron configuration of Pb is [Xe] 4f14 5d10 6s2 6p2, or 2, 8, 18, 32, 18, 4 electrons per shell. It has four valence electrons in the outermost shell. Lead is placed in group 14 or...
The current density of light-induced electron emission using a low-powered laser is measured. By placing a small amount of isopropyl alcohol on the arrays
This challenging PhD project is devoted to nonlinear electron emission triggered by surface plasmon polaritons. Surface plasmon polaritons are longitudinal electron density waves that can be excited by a femtosecond laser pulse and that propagate along the surface of a noble metal. It is the aim to understand the electron emission in the presence of extremely intense plasmonic excitations, and to manipulate the electron emission pathways by forming plasmonic foci both in the presence and absence of nanoparticles. The distinction between light- and plasmon-induced emission processes in time and space is accomplished in a femtosecond time-resolved photoemission microscopy experiment.. As the project relies on several modern experimental methods, the PhD student will gain a profound knowledge in a variety of techniques. Low Energy Electron Microscopy and Photoemission Electron Microscopy in conjunction with femtosecond laser pulses form the experimental basis for the project. Samples are prepared ...
Autor: Tyutyukov, N. et al.; Genre: Zeitschriftenartikel; Im Druck veröffentlicht: 2008; Titel: Energy spectra and electric and magnetic properties of 1D stacks of conjugated pi-electron systems with defect surface states. I. pi systems with tamm surface states
The need to identify complex molecules in real-world samples has propelled mass spectrometry into a $3 billion industry, growing 8% annually. The fragmentation of molecules within a mass spectrometer is necessary to accurately reveal their identity. The current approach (called CID for collision-induced dissociation) uses a sledgehammer that complicates identification by producing complex patterns with considerable noise. Our technology use low-energy electrons as a scalpel to cut molecules with precision. We can switch between three complementary methods of fragmentation in milliseconds to provide multiple sets of fingerprints to correctly identify molecules as large as whole proteins. These methods are well established, but have been restricted to expensive research instruments because of the difficulty of confining enough low-energy electrons in small volumes necessary for efficient fragmentation. We have solved this limitation by sculpting magnetic fields to confine electrons in a hockey ...
Transmission electron microscopy (TEM) at low accelerating voltages is useful to obtain images with low irradiation damage. For a low accelerating voltage, linear information transfer, which determines the resolution for observation of single-layered materials, is largely limited by defocus spread, which improves when a narrow energy spread is used in the electron source. In this study, we have evaluated the resolution of images obtained at 60 kV by TEM performed with a monochromated electron source. The defocus spread has been evaluated by comparing diffractogram tableaux from TEM images obtained under nonmonochromated and monochromated illumination. The information limits for different energy spreads were precisely measured by using diffractograms with a large beam tilt. The result shows that the information limit reaches 0.1 nm with an energy width of 0.10 eV. With this monochromated source and a higher-order aberration corrector, we have obtained images of single carbon atoms in a graphene ...
We present an experimental and theoretical study of resonant inelastic x-ray scattering (RIXS) in the carbon disulphide CS 2 molecule near the sulfur K-absorption edge. We observe a strong evolution of the RIXS spectral profile with the excitation energy tuned below the lowest unoccupied molecular orbital (LUMO) absorption resonance. The reason for this is twofold. Reducing the photon energy in the vicinity of the LUMO absorption resonance leads to a relative suppression of the LUMO contribution with respect to the emission signal from the higher unoccupied molecular orbitals, which results in the modulation of the total RIXS profile. At even larger negative photon-energy detuning from the resonance, the excitation-energy dependence of the RIXS profile is dominated by the onset of electron dynamics triggered by a coherent excitation of multiple electronic states. Furthermore, our study demonstrates that in the hard x-ray regime, localization of the S 1s core hole occurs in CS2 during the RIXS ...
The European Physical Journal D (EPJ D) presents new and original research results in Atomic, Molecular, Optical and Plasma Physics
The nonlinear interaction of an intense femtosecond laser pulse with matter can lead to the emission of a train of sub-laser-cycle--attosecond--bursts of short-wavelength radiation1, 2. Much effort has been devoted to producing isolated attosecond pulses, as these are better suited to real-time imaging of fundamental electronic processes3, 4, 5, 6. Successful methods developed so far rely on confining the nonlinear interaction to a single sub-cycle event7, 8, 9. Here, we demonstrate for the first time a simpler and more universal approach to this problem10, applied to nonlinear laser-plasma interactions. By rotating the instantaneous wavefront direction of an intense few-cycle laser field11, 12 as it interacts with a solid-density plasma, we separate the nonlinearly generated attosecond pulse train into multiple beams of isolated attosecond pulses propagating in different and controlled directions away from the plasma surface. This unique method produces a manifold of isolated attosecond pulses, ideally
The supply of absolute electron-impact cross sections for molecular targets and radicals is extremely important for developing plasma reactors and testing different types of etching gases. Current demand for such models is high as the industry aims to replace traditional plasma processing gases with less polluting species. New theoretical electron impact cross sections at typical etching plasma energies (sub 10 eV) are presented for the CFx (x=1-3) active radical species in a form suitable for plasma modeling. The available experimental and theoretical data are summarized for two potential feed gases, CF3I and C2F4. This data cover recommended cross sections for electron scattering (total, excitation, momentum transfer, and elastic integral), electron impact dissociation, and dissociative electron attachment, wherever possible. Numerical values are given as tables in the paper and are also placed in the electronic archive. (c) 2006 American Institute of Physics.. ...
Electron capture ionization is the ionization of a gas phase atom or molecule by attachment of an electron to create an ion of the form A. The reaction is A + e − → M A − {\displaystyle {\ce {{A}+e^{-}->[{M}]A^{-}}}} where the M over the arrow denotes that to conserve energy and momentum a third body is required (the molecularity of the reaction is three). Electron capture can be used in conjunction with chemical ionization. Electron-capture mass spectrometry (EC-MS) is a type of mass spectrometry that uses electron capture ionization to form negative ions from chemical compounds with positive electron affinities. The approach is particularly effective for electrophiles. In contrast to electron ionization, EC-MS uses low energy electrons in a gas discharge. EC-MS will cause less fragmentation of molecules compared to electron ionization. Resonance electron capture is also known as nondissociative EC. The compound attaches an electron to form a radical anion. The energy of the electrons are ...
I understand what you say but what about NH3BH3 where N has N+ and B has B-. As you said above, When it comes to ions on the molecular level all charges are expressed in electron (or proton - they are identical, just differ in the sign) charges. Thus - compared with the neutral atoms - Cl- has a single excess electron, while Na+ is missing one electron If I draw the Lewis structure of this molecule NH3, here N has 5 valence electrons and H has 1 valence electron so N makes 3 covalent bonds with 3 H and still it has a lone pair of electrons. So N full fills its octet. On the other hand, If we look at the Lewis structure BF3, here B has 3 valence electrons and F has 7 valence electrons. As a result, B makes three covalent bonds with F and B does not full fill its octet. It needs two more electrons to fills its octet. Now N gives the electron pair to B, making N+ and B- ( a coordinate covalent bond formed between NH3 and BF3 ...
The combination of collision-activated dissociation, (CAD) and electron capture dissociation, (ECD) yielded a 125% increase in protein identification. The S-score was developed for measuring the information content in MS/MS spectra. This measure made it possible to single out good quality spectra that were not identified by a search engine. Poor quality MS/MS data was filtered out, streamlining the identification process.. A proteomics grade de novo sequencing approach was developed enabling to almost completely sequence 19% of all MS/MS data with 95% reliability in a typical proteomics experiment.. A new tool, Modificomb, for identifying all types of modifications in a fast, reliable way was developed. New types of modifications have been discovered and the extent of modifications in gel based proteomics turned out to be greater than expected.. PhosTShunter was developed for sensitive identification of all phosphorylated peptides in an MS/MS dataset.. Application of these programs to human milk ...
Assistant Professor of Physics Samantha Fonseca dos Santos and her research collaborator from Laboratoire Génie des Procédés (Centrale-Supélec et Matériaux) in France were selected to receive a 2018 Thomas Jefferson Fund award, in partnership with the French Embassy in the U.S. and the FACE Foundation (French-American Cultural Exchange), under the "Make Our Planet Great Again" initiative. The program which was launched by the French government to develop top-level research projects in France, and with French partners, to address climate change. Their project, Electron-driven reactivity of NOx molecules by electron impact: the NO2/N2O prototype for control and reduction of atmospheric pollution, focuses on understanding the underlying mechanism behind the destruction of nitrogen oxide molecules by electron collision. Specifically, the team will investigate the process of rovibrational excitations and dissociative electron attachment of these molecules, which is important for monitoring these ...
Low-energy electron diffraction and induced damage in hydrated DNA," Thomas M. Orlando, Doogie Oh, Yanfeng Chen, Alexandr B. Aleksandrov, J. Chem. Phys., 2008, 128, 195102.. "Inelastic electron scattering and energy-selective negative ion reactions in molecular films on silicon surfaces," Christopher D. Lane, Thomas M. Orlando, Applied Surface Science, 2007, 253(16), 6646-6656.. "Analysis of organoselenium and organic acid metabolites by laser desorption single photon ionization mass spectrometry," Yanfeng Chen, M. Cameron Sullards, Tiffany T. Hoang, Sheldon W. May, Thomas M. Orlando, Anal. Chem., 2006, 78(24), 8386-8394.. "Zone specificity in low energy electron stimulated desorption of Cl+ from reconstructed Si(111)-7x7 : Cl surfaces," Doogie Oh, Matthew T. Sieger, Thomas M. Orlando, Surf. Sci., 2006, 600(19), L245-L249.. "Highly efficient electron stimulated desorption of 0+ from gadolinia-doped ceria surfaces," Haiyan Chen, Alex Aleksandrov, Shaowu Zha, Meilin Liu, Thomas M. Orlando, J. ...
Auger therapy (AT) is a form of radiation therapy for the treatment of cancer which relies on a large number of low-energy electrons (emitted by the Auger effect) to damage cancer cells, rather than the high-energy radiation used in traditional radiation therapy. Similar to other forms of radiation therapy, Auger therapy relies on radiation-induced damage to cancer cells (particularly DNA damage) to arrest cell division, stop tumor growth and metastasis and kill cancerous cells. It differs from other types of radiation therapy in that electrons emitted via the Auger effect (Auger electrons) are released in large numbers with low kinetic energy. Because of their low energy, these electrons damage cells over a very short range: less than the size of a single cell, on the order of nanometers. This very short-range delivery of energy permits highly targeted therapies, since the radiation-emitting nuclide is required to be inside the cell to cause damage to its nucleus. However, this is a technical ...
Why do atoms form bonds? Formation of chemical bonds is due to number of valence electrons Formation of chemical bonds is due to number of valence electrons Why do valence electrons play such an important role? Why do valence electrons play such an important role? How many electrons do atoms want to have in their outermost energy level? - Because elements react to get the stable electron structure of a noble gas 8
Ab initio SCF calculations have been performed for nitrobenzene, m-dinitrobenzene and sym-trinitrobenzene. A minimal basis set (STO-3G) was used for the calculations. The details of the electronic population analyses for all three compounds will be discussed, as will the assignment of ionization potentials for nitrobenzene ...
Covalent Bond: A chemical bond formed when electrons are shared between two atoms.Usually each atom contributes one electron to form a pair of electrons thatare shared by both atoms. See more at coordinate bond, double bond, polar bond.watch Covalent Bond to learn more. Valence Electrons The electrons in the outermost shell are the valence electrons the electrons on an atom that can be gained or lost in a chemical reaction. Since filled d or f sub shells are seldom disturbed in a chemical reaction, we can define valence electrons as follows: The electrons on an […]. ...
Minimization of component activation is highly desirable at accelerator-based positron sources. Electrons in the 8- to 14-MeV energy range impinging on a target produce photons energetic enough to create electron-positron pairs; however, few of the photons are energetic enough to produce photoneutrons. Slow positron production by low-energy electrons impinging on a multilayer tungsten target with and without electromagnetic extraction between the layers was studied by simulation. The neutron background from 14-MeV electrons is expected to be significantly lower than that encountered with higher-energy electron beams. Numerical results are presented and some ideas for a low-activation slow-positron source are discussed.
Jülich physicists have succeeded in accelerating the determination of material properties as well as making it more efficient. They have developed a special electron source which greatly simplifies the measurement of material surfaces and shortens the time needed for a measurement from days to minutes.
We report a study of the atomic and electronic structures of the ordered Ag2Ge surface alloy containing ⅓ monolayer of Ge. Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and angle-resolved photoelectron spectroscopy (ARPES) data reveal a symmetry breaking of the expected √3 × √3 periodicity, which is established for other Ag2M alloys (M = Bi, Sb, Pb, and Sn). The deviation from a simple √3 × √3 structure manifests itself as a splitting of diffraction spots in LEED, as a striped structure with a 6× periodicity including a distortion of the local hexagonal structure in STM, and as a complex surface band structure in ARPES that is quite different from those of the other Ag2M alloys. These results are interesting in view of the differences in the atomic and electronic structures exhibited by different group IV elements interacting with Ag(111). Pb and Sn form √3 × √3 surface alloys on Ag(111), of which Ag2Pb shows a surface band structure with a clear ...
The deposition of TiOx (x ≤ 2) structures on Au(111) by chemical vapor deposition (CVD) in ultrahigh vacuum (UHV) has been investigated with high-resolution core level photoelectron spectroscopy (PES), low-energy electron diffraction (LEED) and scanning tunnelingmicroscopy (STM). Using titanium tetra-isopropoxide as single source precursor it is possible to form different TiOx phases on the surface after deposition: at low coverages, we observe large two-dimensional (2D) honeycomb-lattice Ti2O3 islands with a (2 × 2) registry with the substrate. Higher coverages are dominated by the formation of three-dimensional (3D) TiO2 structures. The TiO2 structures are atomically well ordered provided that the deposition temperature is high enough (500 °C). The ordered structure exhibits a LEED pattern characteristic for a rectangular surface unit cell. By performing the deposition at different temperatures it is possible to tune the balance between the 2D and 3D phases: Growth at 500 °C significantly ...
article{8036eae6-1912-4fdd-bbcc-53dbce045bea, abstract = {The adsorption of water on two silicon surfaces [reconstructed planar (100)2×1 and single domain stepped (100)2×1 cut 5° towards (011)] was studied using low-energy electron diffraction and digital imaging electron stimulated desorption ion angular distributions (ESDIAD) as a function of temperature (145-700 K) and coverage. Water has been shown previously to chemisorb dissociatively to form surface OH groups. At 300 K the H + ESDIAD pattern for the planar surface is a nearly symmetric halo, indicating that OH is oriented with its bond vector inclined away from the surface normal, while at low temperatures (200 K) a four-lobed pattern that preserves substrate symmetry is observed. This reversible temperature dependence is related to librations and rotations of the OH complexes. ESDIAD from the stepped surface exhibits a two-lobed pattern, with enhanced emission towards the steps, consistent with bonding of OH to single-domain terrace ...
We report long-lived, highly spatially localized plasmon states on the surface of nanoporous gold nanoparticles-nanosponges-with high excitation efficiency. It is well known that disorder on the nanometer scale, particularly in two-dimensional systems, can lead to plasmon localization and large field enhancements, which can, in turn, be used to enhance nonlinear optical effects and to study and exploit quantum optical processes. Here, we introduce promising, three-dimensional model systems for light capture and plasmon localization as gold nanosponges that are formed by the dewetting of gold/ silver bilayers and dealloying. We study light-induced electron emission from single nanosponges, a nonlinear process with exponents of n approximate to 5...7, using ultrashort laser pulse excitation to achieve femtosecond time resolution. The long-lived electron emission process proves, in combination with optical extinction measurements and finite-difference time-domain calculations, the existence of ...
Larson, D.R., J.A. Gosse, D. Holowka, B. Baird and W.W. Webb: Temporally Resolved Interactions Between Antigen-stimulated IgE Receptors and Lyn Kinase on Living Cells. J. Cell Sci. 171(3): 527-536, 2005. (DOI). Joralemon, M.J., N.L. Smith, D. Holowka, B. Baird and K.L. Wooley: Antigen-decorated Shell Crosslinked Nanoparticles: Synthesis, Characterization and Antibody Interactions. Bioconjugate Chem. 16(5): 1246-1256, 2005. (DOI). Holowka, D., J.A. Gosse, A.T. Hammond, X. Han, P. Sengupta, N.L. Smith, A. Wagenknecht-Wiesner, M. Wu, R.M. Young and B. Baird: Lipid Segregation and IgE Receptor Signaling: A Decade of Progress. Biophys. Biochim. Acta. 1746(3): 252-259, 2005. (DOI). Gosse, J.A., A. Wagenknecht-Wiesner, D. Holowka and B. Baird: Transmembrane Sequences are Determinants of Immunoreceptor Signaling. J. Immunol. 175: 2123-2131, 2005.. Senaratne, W., C. Harnett, P. Sengupta, B. Baird, H.G. Craighead and C.K. Ober: Molecular Templates for Bio-specific Recognition by Low-Energy Electron Beam ...
In 1913 Niels Bohr proposed a model to describe how energy levels are organized around an atom. According to the theory, an electron travels from one energy level to the next, a bit like changing lanes in traffic and you overtake on the outer lane. If you want to travel slower, you go on the inside lane.. When an electron absorbs enough light energy, it travels up an energy level onto the faster lane. However, it may quickly becomes unstable and starts to loose energy. When this happens, the electron moves back down an energy level. Its called decay and the electron emits a photon of red light.. In this theory, energy levels are given as n=1, n=2, n=3 and n=4. If an electron moves from n=1 to n=3, the amount of energy aborbed is 2 energy level. If it goes from level 4 to 3, then it looses 1 energy level.. Dont confuse energy levels with orbitals. One energy level can cover over a few orbitals.. ...
In cancer radiation therapy predetermined doses of high-energy radiation are administered to reduce tumours. More than 60 % of the patients diagnosed with cancer are treated with radiation therapy. A detailed understanding of the fundamental mechanisms of DNA radiation damage is of utmost importance with respect to the question of how the damage can be increased by therapeutics used in radiation therapy. On a molecular level a large extent of the cell damage is ascribed to the production of secondary low-energy electrons along the high-energy radiation track that induce DNA single and double strand breaks. The physico-chemical mechanisms of DNA radiation damage can currently only be described for idealized small model systems (such as individual nucleobases) and it is not known, which DNA nucleotide sequences and higher-order DNA structures are most susceptible to damage. Very recent ground-breaking advances in DNA nanotechnology allow for the first time the detailed study of the interaction of ...
Because of the random movement, there is zero net current when there is no electric field. However when a metal wire is connected across two terminals of a voltage source with positive and negative terminals, the source places an electric field across the metal wire. Free electrons are forced to move toward the positive terminal under the influence of this field. This movement of electrons is called current. The free electrons are available in metallic conductors because in conductors the valance band and conduction band overlap and electrons from valance band can go to the conduction band. In the case of insulators the gap between the valance band and conduction band is quite large and hence electrons cannot jump from valance band to conduction band and hence there are no free electrons. Because of the free electrons in conductors, electric current passes through conductors ...
The BaO{sup +} cation is of interest from the perspectives of electronic structure and the potential for cooling to ultra-cold temperatures. Spectroscopic data for the ion have been obtained using a two-color photoionization technique. The ionization energy for BaO was found to be 6.8123(3) eV. The ground state of BaO{sup +} was identified as X{sup 2}Σ{sup +}, and both vibrational and rotational constants were determined. Vibrationally resolved spectra were recorded for A{sup 2}Π, the first electronically excited state. These data yielded the term energy, vibrational frequency, and the spin-orbit interaction constant. Relativistic electronic structure calculations were carried out using multi-reference configuration interaction (MRCI), coupled cluster and density functional theory methods. Transition moments for the pure vibrational and A{sup 2}Π-X{sup 2}Σ{sup +} transitions were predicted using the MRCI method. ...
The electronic configuration of an atom is given by listing its subshells with the number of electrons in each subshell, as shown in Table 1. Study th
We report a series of unique and simple donor-acceptor-donor molecular systems that provide compelling insights into the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap. In this system, thiophene and pyrazine-acene were employed as a donor and an acceptor, respectively. More specifically, acceptor moieties are a combination of phenazine, bisphenazine, and thiadiazole. These donor and acceptor units are well-known primarily for generating low band gap polymers, however a systematic study on why these donor-acceptor combinations are successful has yet to be investigated. In this study, we attempt to gain a fundamental understanding about how these specific donor and acceptors impact the energetics of the resulting molecular systems. A combination of theoretical and experimental methods was used to explore the impact of geometry on the HOMO and LUMO energies. One of the most critical findings is that the dihedral angle between the donor and acceptor ...
CONICET Digital, el repositorio institucional del CONICET, un servicio gratuito para acceder a la producción científico-tecnológica de investigadores, becarios y demás personal del CONICET.
Modern electron microscope can provide information at the atomic scale in the spatial dimemsion. The next generation of instruments will also provide temporal resolutions in the fs regime. This project will investigate solutions to providng temporal resoltuions from the ms to micro s timescale to bridge the gap between the limits imposed by current detectors and possible future pulsed electron sources.. ...
DIAGRAM) Since SEMs give us an image of the surface of a specimen, preparation of specimens for scanning electron microscopy differs from that of transmission electron microscopy. Larger specimens can be placed in an SEM than can be placed in a TEM (e.g. whole insects) as the beam does not have to pass through the specimen but over it. Specimens must be coated with a metal that reflects electrons, such as gold; this coating of a conductive substance amplifies the electron signal and also prevents the electrons from charging the specimen. [12] Electrons are fired from the electron gun into the vacuum and accelerated before they pass through one or two condenser lenses that focus the electron beam. The beam then passes through magnetic coils controlled by a scanning generator that direct it in a predetermined scanning motion over the surface of the specimen. As electrons hit the surface of the specimen they bounce off - these are known as secondary electrons. The secondary electrons are detected ...
0034] Next, a vacuum of a pressure of for example 10-5 torr may be generated within the vacuum container 5 using a vacuum pump 7. Then, in a next step (S2), a high energy electron beam 9 is directed onto the pulverized mixture of refractory metals comprised in the crucible 3. The electron beam 9 is emitted by a cathode 11 and is accelerated and controlled by an anode 13, the cathode 11 and the anode 13 being connected to a control 15. The electrons emitted by the cathode 11 are accelerated using the anode 13 to very high energies in the range of between 20 keV and 50 keV. Furthermore, the anode 13 may be controlled such as to focus the electron beam 9 onto the refractory metals comprised in the crucible 3 such that the electron beam 9 may be scanned along a surface of the refractory metal powder 1 in order to homogeneously heat the powder within the crucible 3. Upon impact of the high energy electrons of the electron beam 9, the refractory metal powder 1 is heated to such high temperatures of ...
ii) secondary electrons are electrons that came from the material itself AFTER the absoption of the primary electron. So you shoot a bunch of primary electrons at a material, the primary get absorbed, and electrons came out. The secondary electrons may be MORE in number than the primary, depending on the energy of the primary electrons and the secondary emission yield (SEY) of the material. If a material has a SEY of 4 at a particular energy, then a primary electron hitting the material at that very same energy can cause the emission of 4 secondary electrons. Of course, these secondary electrons have energies way lower than the incident primary. This technique is most often used in SEM, Auger spectroscopy, etc ...
Exploring ultrafast charge migration is of great importance in biological and chemical reactions. We present a scheme to monitor attosecond charge migration in molecules by electron diffraction with spatial and temporal resolutions from ab initio numerical simulations. An ultraviolet pulse creates a coherent
TY - GEN. T1 - Dynamic model of electron beam induced deposition (EBID) of residual hydrocarbons in electron microscopy. AU - Rykaczewski, Konrad. AU - White, Ben. AU - Browning, Jenna. AU - Marshall, Andrew D.. AU - Fedorov, Andrei G.. PY - 2006. Y1 - 2006. N2 - 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 microscopes imaging quality. Later, it has been demonstrated that with appropriate control of the electron beam this ...
Since Xe has an expanded octet you know it can hold more than 8 electrons. To find how many electrons the expanded octet can hold you should first add up the total number of valence electrons of your compound, then draw your lewis structure as you usually would. You will notice that you are missing electrons from your total valence electrons once youve filled all the octets of the other atoms. Since you know Xe has an expanded octet, you can add the remaining electrons as lone pairs there ...