Electron Transmission Studies Research Articles

Low-energy electron interaction and focused electron beam-induced deposition of molybdenum hexacarbonyl (Mo(CO)6).

Motivated by the potential role of molybdenum in semiconductor materials, we present a combined theoretical and experimental gas-phase study on dissociative electron attachment (DEA) and dissociative ionization (DI) of Mo(CO)6 in comparison to focused electron beam-induced deposition (FEBID) of this precursor. The DEA and DI experiments are compared to previous work, differences are addressed, and the nature of the underlying resonances leading to the observed DEA processes are discussed in relation to an earlier electron transmission study. Relative contributions of individual ionic species obtained through DEA and DI of Mo(CO)6 and the average CO loss per incident are calculated and compared to the composition of the FEBID deposits produced. These are also compared to gas phase, surface science and deposition studies on W(CO)6 and we hypothesize that reductive ligand loss through electron attachment may promote metal–metal bond formation in the deposition process, leading to further ligand loss and the high metal content observed in FEBID for both these compounds.

Theory of valley-dependent transport in graphene-based lateral quantum structures

Modulation of electronic states in two-dimensional (2D) materials can be achieved by using in-plane variations of the band gap or the average potential in lateral quantum structures. In the atomic configurations with hexagonal symmetry, this approach makes it possible to tailor the valleytronic properties for potential device applications. In this work, we present a multi-band theory to calculate the valley-dependent electron transport in graphene-based lateral quantum structures. As an example, we consider the structures with a single interface that exhibits an energy gap or potential discontinuity. The theoretical formalism proceeds within the tight-binding description, by first deriving the local bulk complex band structures in the regions of a constant gap or potential and, next, joining the local wave functions across the interface via a cell-averaged current operator to ensure the current continuity. The theory is applied to the study of electron reflection off and transmission through an interface. Both reflection and transmission are found to exhibit valley-contrast behavior that can be used to generate valley-polarized electron sources. The results vary with the type of interfaces, as well as between monolayer and bilayer graphene based structures. In the monolayer case, the valley contrast originates from the band warping and only becomes sizable for incident carriers of high energy; whereas in AB-stacked bilayer graphene, the vertical interlayer coupling emerges as an additional important cause for valley contrast, and the favorable carrier energy is also found to be drastically lower. Our numerical results clearly demonstrate the propitious valleytronic properties of bilayer graphene structures.

Incident energy and charge deposition dependences of electron transmission through a microsized tapered glass capillary

An experimental study of electron transmission and guiding through a tapered glass capillary has been performed. Electrons were transmitted for tilt angles up to ∼6.5° and ∼9.5° (laboratory angles) for incident energies of 500 and 1000eV, respectively. It is found that elastic and inelastic contributions give rise to distinguishable peaks in the transmitted profile. For 500eV elastic transmission dominates the profile, while for 1000eV both elastic and inelastic contributions are present. The transmission for both energies was studied as a function of the charge (time) deposition and found to be strongly dependent. Results suggest fundamental differences between 500 and 1000eV incident electrons. For 500eV the transmission slowly increases suggesting charge up of the capillary wall, reaching relative stability with infrequent breakdowns for all angles investigated. For 1000eV for tilt angles near zero degrees the time dependent profile shows oscillations in the transmission, which never reached a stable condition, while for the larger angle investigated the transmission reached near equilibrium. Inelastic processes dominated the transmission for 1000eV even at very small tilt angles, but was generally elastic (due to Coulomb deflection) for 500eV even for the largest tilt angle measured.

Study of electron transmission through a metallic capillary

SynopsisIn this work we study the transmission of charged particles through a single cylindrically shaped metallic capillary of microscopic dimensions with a large aspect ratio. We used electrons as projectiles. Our results suggest the existence of guiding of the electron beam by a metallic capillary.

Study of electron transmission through a platinum tube

We have measured 200eV electron transmission through a single platinum tube of a diameter of 3.3mm. We find that the transmission of electrons can be detected even at large tilt angles, where the tube is not transparent geometrically. The transmission drops down exponentially with increasing the tilt angle. The energy spectrum of detected electrons behind the tube contain contributions at lower energies due to both inelastic scattering and secondary electron emission. The spectrum is qualitatively in good agreement with the calculations performed for the flat Pt surface in order to understand and model the electron interaction processes that define the transmission and the energy spectrum at the exit.

Raman sensitivity to crystal structure in InAs nanowires

We report electron transmission and Raman spectroscopy study of InAs nanowires. We demonstrate that the temperature dependent behavior of optical phonon energies can be used to determine the relative wurtzite fraction in the InAs nanowires. Furthermore, we propose that the interfacial strain between zincblende and wurtzite phases along the length of the wires manifests in the temperature-evolution of the phonon linewidths. From these studies, temperature-dependent Raman measurements emerge as a non-invasive method to study polytypism in such nanowires.

Analytic study of electron transmission through serial mesoscopic metallic rings

We investigate the electron transmission through a structure of serial mesoscopic metallic rings coupled to two external leads. A set of analytical expressions based on the quantum waveguide transport and the transfer matrix method are derived and used to discuss the effects of geometric configurations on transmission probabilities. It is found that in the contact ring case the existence of an applied magnetic flux is necessary to create transmission gaps, while in the non-contact ring case transmission gaps always appear irrespective of whether there is an applied magnetic flux or not. The transmissions for periodic rings with a defect ring and periodic rings built by two sorts of rings are also briefly studied. It is also found that the transmission periodicity with wave vector must be ensured by the commensurability of two characteristic lengths, i.e., of the half perimeter of a ring and the connecting wire between two adjacent rings. The special points of wave vector and magnetic flux which give rise to the transmission resonance and antiresonance are analyzed in detail.

Electronic transport through a CNT-Pseudopeptide-CNT hybrid material

We present electron transmission studies on a pseudopeptide fragment (P) linking two (10,0) semi-infinite carbon nanotubes (CNTs). Calculations are performed using the non-equilibrium Green function formalism (NEGF) implemented within the tight-binding molecular dynamics density functional theory code FIREBALL. Results are compared with the transmission for an ideal (10,0) infinite CNT and a hydrogen passivated CNT-pseudopeptide-CNT (CNT–P–CNT) structure. The transmission spectrum indicates that the pseudopeptide fragment acts as a good bridge for hole transfer and strongly suppresses electron transfer.

Electron transmission studies of diamond films

Diamond is an attractive cold emitter candidate because of specific negative-electron-affinity (NEA) surfaces and good electron transport properties. In this study, transmission electron spectroscopy is used to examine the low-energy electron transport and emission properties of thin CVD diamond films. After injecting electrons into diamond films using an external electron gun, the transmission of low-energy secondary electrons is examined. In particular, the intensity and energy distribution of the transmitted electrons are measured as a function of the film properties (thickness, doping concentration) and incident beam properties (energy, intensity). Electron transmission through a heavily-doped, 5μm thick film exhibits a larger energy spread and lower intensity than electron transmission through a medium-doped, 2μm thick film. However, the transmission yields are relatively low for both films compared to the reflected yield measurements. Furthermore, the incident beam parameters influence the transmitted electron distribution in ways that cannot be explained by our secondary emission model. On the other hand, the results of the study concerning the transmission of high-energy electrons confirm the theoretical predictions of electron penetration depths in diamond. These initial electron transmission measurements from thin diamond films indicate that the transport process is quite complex, and the study reveals several issues that need to be examined further before the cold emission capabilities of diamond can be assessed.

Ideal spin filters: A theoretical study of electron transmission through ordered and disordered interfaces between ferromagnetic metals and semiconductors

It is predicted that certain atomically ordered interfaces between some ferromagnetic metals (F) and semiconductors (S) should act as ideal spin filters that transmit electrons only from the majority spin bands or only from the minority spin bands of the F to the S at the Fermi energy, even for F with both majority and minority bands at the Fermi level. Criteria for determining which combinations of F, S and interface should be ideal spin filters are formulated. The criteria depend only on the bulk band structures of the S and F and on the translational symmetries of the S, F and interface. Several examples of systems that meet these criteria to a high degree of precision are identified. Disordered interfaces between F and S are also studied and it is found that intermixing between the S and F can result in interfaces with spin anti-filtering properties, the transmitted electrons being much less spin polarized than those in the ferromagnetic metal at the Fermi energy. A patent application based on this work has been commenced by Simon Fraser University.

Two-dimensional electron gas in a magnetic field and point potentials

This paper presents a brief review of the electron properties in two-dimensional systems which contain zero-range scatterers which are subjected to a magnetic field. The electron spectrum is described for a periodic arrangement of point scatterers and rational magnetic flux per unit cell. Delocalized states on the Landau levels are constructed for the case of positional disorder. The electron localization in a one-dimensional disordered set of scatterers is studied. Application to the study of electron transmission through quantum dots and ballistic channels is reviewed.

Monte Carlo study of electron transmission and backscattering from metallic thin films.

A Monte Carlo trajectory model that describes electron transport in semi-infinite metallic solids also gives quantitative agreement with experiment for the transmission fraction for thin films of Be, Al, Cu, and Au and for the energy distribution in Al, both as a function of primary energy ${\mathit{E}}_{\mathit{p}}$ and of film thickness t. Significantly, the results enabled the construction of universal curves of transmission and backscattered fractions versus reduced film thickness ${\mathit{t}}_{\mathit{n}}$=t/${\mathit{x}\mathit{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{p}}$ for each element, where ${\mathit{x}\mathit{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{p}}$ is the mean depth of penetration of primary electrons in the semi-infinite solids. As ${\mathit{x}\mathit{\ifmmode\bar\else\textasciimacron\fi{}}}_{\mathit{p}}$ may also be fitted to empirical curves, these results may be used to predict transmission and backscattering for thin films without future resort to lengthy numerical calculations. \textcopyright{} 1996 The American Physical Society.

Ultraviolet photoelectron, electron transmission and ab initio study of the factors determining the stability of imines

The electronic structure of several alkyl-, N-bis(trimethylsilyl)methyl-(BTMSM), and C-phenyl-substituted imines 1–11 have been determined by ab initio 3-21G* calculations. The calculations reproduce with good accuracy the available geometry of methylenimine, 1, obtained by microwave spectroscopy and ab initio 6-31G** calculations as well as the outermost energy levels experimentally determined by ultraviolet photoelectron spectroscopy for several derivatives. The analysis of the results of the calculations indicate that alkyl substitution of 1 at the nitrogen atom reduces the charge separation at the double bond increasing stabilisation, while substitution at the carbon atom has the opposite effect. Steric hindrance of the substituent(s) and the energy gaps between filled (nitrogen lone pair, HOMO and πCN) and virtual (πCN*) orbitals play a secondary role on stability.

A dissociative electron attachment, electron transmission, and electron energy-loss study of the temporary negative ion of acetylene

The three title electron-impact techniques are used to study the ground and excited states of acetylene negative ion and their decay processes. The π* resonance at 2.6 eV predissociates into C2H− and H. Four narrow resonances are observed in the transmission spectrum in the 7.5–9.5 eV region and assigned to Feshbach and core-excited shape resonances with double occupation of Rydberg orbitals and ground state positive ion core. These four resonances decay into low-lying Rydberg states of neutral acetylene, the first two undergo quasiresonant autodetachment ejecting low energy (<0.7 eV) electrons, and the lowest also dissociates to yield C−2. One additional resonance is observed in the C−2 yield, which is not observable in other decay channels. The shapes of the dissociative attachment bands differ qualitatively from the band shapes of the parent and grandparent states, indicating either a strong v dependence of the dissociation rate or the admixture of σ* orbitals in some of the dissociating anion states.

ChemInform Abstract: Electron Transmission Study of the Temporary Negative Ion States of Selected Benzenoid and Conjugated Aromatic Hydrocarbons.

AbstractET spectroscopy is utilized to determine the vertical electron affinities and to characterize the temporary anion states of benzene, naphthalene, anthracene, tetracene, styrene, cis‐ and trans‐stilbene.

Electron transmission study of the temporary negative ion states of selected benzenoid and conjugated aromatic hydrocarbons

Electron transmission spectroscopy is utilized to determine the vertical electron affinities and to characterize the temporary anion states of a series of alternant hydrocarbons including benzene, naphthalene, anthracene, tetracene, styrene, and cis- and trans-stilbene. The vibrational structure present in the low lying resonances is interpreted in light of the charge distributions of the temporarily occupied orbitals. The energies of the anion states are compared with the predictions of PPP, PPP-CI, and HAM calculations, the pairing theorem and with the results from optical absorption measurements on the ground state anions in rigid glasses.

ChemInform Abstract: ELECTRON TRANSMISSION STUDY OF THE NEGATIVE ION STATES OF P‐BENZOQUINONE, BENZALDEHYDE, AND RELATED MOLECULES

Chemischer InformationsdienstVolume 15, Issue 46 Physical Organic Chemistry ChemInform Abstract: ELECTRON TRANSMISSION STUDY OF THE NEGATIVE ION STATES OF P-BENZOQUINONE, BENZALDEHYDE, AND RELATED MOLECULES A. MODELLI, A. MODELLISearch for more papers by this authorP. D. BURROW, P. D. BURROWSearch for more papers by this author A. MODELLI, A. MODELLISearch for more papers by this authorP. D. BURROW, P. D. BURROWSearch for more papers by this author First published: November 13, 1984 https://doi.org/10.1002/chin.198446040AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume15, Issue46November 13, 1984 RelatedInformation

Electron transmission study of the negative ion states of p-benzoquinone, benzaldehyde, and related molecules

Par cette methode avec des electrons de 0-6 eV, localisation des resonances de forme en phase gazeuse de p-benzoquinone et de ses derives dimethyl-2,6 et di-t-butyl-2,6, d'acetophenone, de benzaldehydes p-substitues, de cyclohexanone et cyclohexene-2one-1. Ordre des orbitales normalement vacantes

Theoretical study of electron transmission through N 2

The objective of the present work is to unfold the population of the vibrational levels from the experimental electron transmission spectra of N 2 . This is accomplished by comparing these spectra with theoretical spectra which have been obtained using computed resonant vibrational excitation cross sections and assuming a Boltzmann distribution for the population of the vibrational levels of the N 2 target molecule. The cross sections are calculated using an accurate non-local energy-dependent complex potential for the vibrational motion in the resonance state. These “non-local cross sections” are compared with “local cross sections” (obtained with the so-called boomerang model). It is shown that the two types of cross sections may differ from each other and that non-local cross sections are needed to unfold accurately the vibrational populations from expiremental spectra.

Electron-transmission study of the temporary anion states of substituted pyridines

Electron-transmission spectroscopy has been employed in a study of the temporary negative-ion states of 2-, 3- and 4-methylpyridine, 2-, 3- and 4-chloropyridine, 2-, 3- and 4-aminopyridine, 2-, 3- and 4-acetylpyridine and 2- and 4-vinylpyridine. The effect of substitution on the normally unoccupied orbitals, as well as that of replacement of a CH group by a nitrogen atom, is found to be related to the coefficient of the molecular orbital at the site of substitution. The latter effect, however, is much less pronounced for the unfilled than for the filled orbitals. We attribute this to changes in geometry of the aza derivatives and to the greater diffuseness of the anion wavefunction compared with that of the cation. A simple Hückel MO treatment, the equivalent of the LCBO method for filled orbitals, is applied to the unfilled orbitals of the vinylpyridines and acetylpyridines, and yields the energies of these short-lived anion states quite satisfactorily.