To see the other types of publications on this topic, follow the link: Electron spectroscopy.
Dissertations / Theses on the topic 'Electron spectroscopy'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Electron spectroscopy.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Tavener, P. "Electron spectroscopy of electrode materials." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370304.
Full text
2
Gagnon, Justin. "Attosecond Electron Spectroscopy." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-125375.
Full text
3
Taylor, M. E. "Substrate and electrode effects in inelastic electron tunnelling spectroscopy." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235265.
Full textAbstract:
Inelastic Electron Tunnelling Spectroscopy is a powerful and versatile technique for obtaining vibrational densities of states of amorphous materials and adsorbed molecules. The experimental device, or tunnel junction, consists of two metal electrodes separated by a thin (2nm) layer of the material under study. This thesis looks at features in the tunnelling spectrum due to electrode phonons, and also at the effects of substrate roughness on the spectrum. Two coupled linear chains are used to model the vibrational behaviour of joined lattices in order to consider the penetration of phonons of one material into the other; penetration does not occur unless the two chains have very similar properties. Work with Al-I-Al-Pb tunnel junctions confirms the model results, as no sign is seen of lead phonon peaks in the tunnelling spectrum. However, other workers have seen lead peaks in Al-I-Ag-Pb junctions, and invoked phonon penetration in explanation. Microscopic examination of similarly prepared silver films reveals that they are pinholed; and this, it is argued, gives rise to the lead peaks. Results are presented on the magnitudes of electrode phonon structure in tunnelling spectra, and models for the occurrence of these features are reviewed. It is argued, from comparison of the experimental data with bulk self energies from superconducting tunnelling, that the electron-phonon coupling responsible is characteristic of the bulk metal; interaction does not take place in the barrier. This is consistent with the linear chain model. The effects of roughening tunnel junctions with calcium fluoride substrates are studied. Little change is noted with undoped junctions, but investigation of formate-doped junctions confirms the loss in dopant peak intensity seen by other workers and some variation is noticed in the rate of loss of intensity between C-H and CO2 modes. The mechanism which best explains these observations is that roughening encourages penetration of the organic layer by atoms of the top electrode metal.
4
Flavell, W. R. "Electron spectroscopy of metal oxides." Thesis, University of Oxford, 1986. https://ora.ox.ac.uk/objects/uuid:6b72b77e-5bf5-4b48-bf89-77d5a2d78350.
Full textAbstract:
The validity of the classical dielectric theory of HREELS is investigated. Group theory is employed to obtain a tabulation of SO phonon modes expected to appear strongly in the spectra of given faces of many common crystal structures. The effects of crystalline anisotropy and surface defects are considered in detail. The theoretical investigation is used in conjunction with experiment to obtain a more detailed understanding of the HREELS of rutile (110), (100) and (001) surfaces than has been obtained previously. XPS, UPS and HREELS are used to investigate the surface composition and electronic structure of Sn-doped In2O3 ceramics (containing 1-6 at.% Sn) and thin films. XPS of the well-equilibrated ceramics reveals substantial tin enrichment in the surface atomic layer, with a heat of segregation of ~-20kJmol-1, and provides evidence for a sub-surface region partly depleted in tin. UPS and HREELS results are consistent with a free-carrier concentration close to the surface considerably below the bulk nominal value. XPS of the thin films reveals considerably less surface tin segregation, suggesting that thermal equilibrium is not attained during film production. Vacuum annealing dramatically increases the free carrier concentration, as shown by the shift in the surface plasmon frequency in HREELS. There is a substantial discrepancy between the bulk plasmon frequency predicted from HREELS, and that measured directly from optical transmission. The shift and attenuation of the HREELS plasmon is compared with a model where the surface layer is completely depleted of free carriers. Surface depletion layers have been created on rutile (001), and Sb-doped SnO2 ceramics containing 0.1 and 1 at.% Sb, by adsorption of Cl2 and NO2. The surface coverage of adsorbate is monitored by XPS. Shifts in work function and valence band edge are measured by UPS. HREELS of Cl2-dosed Sb-doped SnO2 show changes consistent with a depletion layer model.
5
Chaudhry, M. A. "Electron and X-ray spectroscopy of electron-atom collisions." Thesis, University of Stirling, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379507.
Full text
6
Todd, Billy Dean. "Electron-excited Auger-electron coincidence spectroscopy off solid surfaces." Thesis, Todd, Billy Dean (1989) Electron-excited Auger-electron coincidence spectroscopy off solid surfaces. PhD thesis, Murdoch University, 1989. https://researchrepository.murdoch.edu.au/id/eprint/51561/.
Full textAbstract:
An experimental and theoretical investigation has been conducted in an attempt to perform electron-excited coincidence Auger-electron spectroscopy off solid surfaces.
The experimental apparatus was designed and built to achieve time and energy resolutions of ~2ns and ~l-2eV respectively. The entire experimental system was shown to have functioned as designed.
Experiments measuring the Auger electron in coincidence with its ionizing (core-loss) electron were attempted on samples of amorphous silicon and iron sulphide with negative results. The measurements placed upper bounds on the coincidence trues-to-accidentals ratio of 0.09 and 0.02 for silicon and iron sulphide respectively.
A comprehensive theoretical model was developed to calculate the expected true coincidence count rate as well as the trues-to-accidentals ratio for silicon. The model predicts that the true coincidence count rate and trues-to-accidentals ratio are several orders of magnitude too low for the experiment to be feasible with the existing experimental apparatus. It demonstrates that the main problem is the high value of the secondary electron background which increases the accidental coincidence background rate to an unacceptable level. For completeness the model was further modified and applied to the Auger-photoelectron coincidence experiment performed by Haak et al [1978,1984] and predicts the feasibility of this experiment.
Finally, suggestions for future electron-excited Auger-electron coincidence experiments are provided with the aim of achieving successful coincidence measurements off solid surfaces.
7
Al, Sawi A. N. "Study of the electronic structure of InSb by electron spectroscopy." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3007631/.
Full text
8
Moreira, Leandro Malard. "Raman spectroscopy of graphene:: probing phonons, electrons and electron-phonon interactions." Universidade Federal de Minas Gerais, 2009. http://hdl.handle.net/1843/ESCZ-7ZFGDY.
Full textAbstract:
Since the identification of mono and few graphene layers in a substrate in 2004, intensive work has been devoted to characterize this new material. In particular, Raman spectroscopy played an important role in unraveling the properties of graphene systems. Moreover resonant Raman scattering (RRS) in graphene systems was shown to be an important tool to probe phonons, electrons and electronphononinteractions. In this thesis, by using different laser excitation energies, we obtain important electronic and vibrational properties of mono- and bi-layer graphene. For monolayer graphene, we determine the phonon dispersion near the Dirac point for the in-plane transverse optical (iTO) mode and the in-plane longitudinal acoustic (iLA) mode. These results are compared with recent theoretical calculations for the phonon dispersion around the K point. For bilayer graphene we obtain the Slonczewski-Weiss-McClure band parameters. These results show that bilayer graphene has a strong electron-hole asymmetry, which is larger than in graphite. In a gating experiment, we observe that the change in Fermi level of bilayer graphene gives rise to a symmetry breaking, allowing the observation of both the symmetric (S) and anti- symmetric (AS) phonon modes. The dependence of the energy and damping of these phonons modes on the Fermi level position is explained in terms of distinct couplings of the S and AS phonons with intraand inter-band electron-hole transitions. Our experimental results confirm the theoretical predictions for the electron-phonon interactions in bilayer graphene. We also study the symmetry properties of electrons and phonons in graphene systems as a function of the number of layers, by a group theory approach. We derive the selection rules for the electron-radiation and for the electron-phonon interactions at all points in the Brillouin zone. By considering these selection rules, we address the double resonance Raman scattering process. The selection rules for monolayer and bilayer graphene in the presence of an applied electric field perpendicular to the sample plane are also discussed.Desde a identificação de uma ou poucas camadas de grafeno em um substrato em 2004, trabalhos intensivos tem sido feitos para se caracterizar esse novo material. Em particular, a Espectroscopia Raman Ressonante tem sido muito importante para elucidar propriedades físicas e químicas em sistemas de grafeno. A Espectroscopia Raman Ressonante também tem se mostrado como uma ferramenta importante para se estudar fônons, elétrons e interações elétron-fônon em grafeno. Nesta tese, ao usarmos diferentes energias de laser de excitação, nós obtivemos propriedades importantes sobre as estruturas eletrônicas e vibracionais para uma e duas camadas de grafeno. Para uma monocamada de grafeno, nós determinamos a dispersão de fônons perto do ponto de Dirac para o modo óptico transversal no plano (iTO) e para o modo acústico longitudinal no plano (iLA). Comparamos nossos resultados experimentais como cálculos teóricos recentes para a dispersao de fônons nas proximidades do ponto K. Para a bicamada de grafeno, nós obtivemos os parâmetros de estrutura eletrônica do modelo de Slonczewski-Weiss-McClure. Nossos resultados mostram que a bicamada de grafeno possue uma forte assimetria elétron-buraco, que por sua vez é mais forte que no grafite. Em experimentos aplicando uma tensão de porta, variamos o nível de Fermi em uma bicamada de grafeno, o que levou uma quebra de simetria, deixando assim ambos os modos de vibração simétricos (S) e anti-simétricos (AS) ativos em Raman. A dependência da energia e do amortecimento desses modos de fônons com a energia de Fermi é explicada através do acoplamento elétron-buraco intra- ou inter- banca. Nossos resultados experimentais deram suporte às previsões teóricas para interações elétron-fónon em uma bicamada de grafeno.
9
Finch, D. C. "FTIR spectroscopy of electron irradiated polymers." Thesis, Brunel University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381899.
Full text
10
Tulloch, Simon. "Astronomical spectroscopy with electron multiplying CCDs." Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522382.
Full text
11
Pickard, Christopher James. "Ab initio electron energy loss spectroscopy." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627420.
Full text
12
Dogbe, John Kofi. "Comparing cluster and slab model geometries from density functional theory calculations of si(100)-2x1 surfaces using low-energy electron diffraction." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3258835.
Full text
13
Ji, Tao. "Inelastic electron tunneling spectroscopy in molecular electronic devices from first-principles." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=96883.
Full textAbstract:
In this thesis, we present the first-principle calculations of inelastic electron tunneling spectroscopy(IETS) in single molecular break junctions. In a two-probe electrode-molecule-electrode setup, density functional theory(DFT) is used for the construction of the Hamiltonian and the Keldysh non-equilibrium Green's function(NEGF) technique will be employed for determining the electron density in non-equilibrium system conditions. Total energy functional, atomic forces and Hessian matrix can be obtained in the DFT-NEGF formalism and self-consistent Born approximation(SCBA) is used to integrate the molecular vibrations (phonons) into the framework once the phonon spectra and eigenvectors are calculated from the dynamic matrix. Geometry optimization schemes will also be discussed as an indispensable part of the formalism as the equilibrium condition is crucial to correctly calculate the phonon properties of the system.To overcome the numerical difficulties, especially the large computational time demand of the electron-phonon coupling problem, we develop a numerical approximation for the electron self-energy due to phonons and the error is controlled within numerical precision. Besides, a direct IETS second order I-V derivative expression is derived to reduce the error of numerical differentiation under reasonable assumptions. These two approximations greatly reduce the computation requirement and make the calculation feasible within current numerical capability.As the application of the DFT-NEGF-SCBA formalism, we calculate the IETS of the gold-octanedithiol(ODT) molecular junction. The I-V curve, conductance and IETS from ab-inito calculations are compared directly to experiments. A microscopic understanding of the electron-phonon coupling mechanism in the molecular tunneling junctions is explained in this example. In addition, comparisons of the hydrogen-dissociative and hydrogen-non-dissociative ODT junctions as well as the different charge transfer behaviors are presented to show the effects of thiol formation in the ODT molecular junction.Dans cette thèse, nous présentons des calculs ab initio de la spectroscopie à effet tunnel par électron inélastique (IETS)appliqués à des jonctions moléculaires. Dans le cadre d'une configuration électrode-molécule-électrode,la théorie de la fonctionnelle de la densité (DFT) est utilisée pour construire l'hamiltonien et les fonctions de Green hors-équilibres(NEGF) sont employées pour déterminer la densité électroniquedans des conditions hors-équilibre. Le cadrede la DFT-NEGF nous permet de calculer des quantités telles que la fonctionnelle d'énergie totale,les forces atomiques ainsi que la matrice de Hessian. L'approximationauto-consistante de Born (SCBA) est employée afin d'intégrer les vibrations moléculaires (phonons) dans le formalisme DFT-NEGF,une fois que le spectre des phonons et les vecteurs propres ont été calculés à partir de la matrice dynamique. Des méthodes d'optimisations géométriques sont aussi discutées en tant que part indispensable du formalisme,étant donné que la condition d'équilibre mécanique est essentielle afin de calculer correctement les propriétés des phonons du système.Afin de surmonter les difficultés numériques, particulièrement concernant la grande demandecomputationnelle requise pour le calcul du couplage électron-phonon, nous développons une approximation numérique pour la self-énergie associée aux phonons. De plus, en employant quelques hypothèses raisonables, nous dérivons une expression pour l'IETS calculée à partir de laseconde dérivée de la courbe I-V dans le butde réduire l'erreur associée à la différentiation numérique. L'utilisation de ces deux approximations diminuent grandement les exigences computationnelles et rendent les calculs possibles avec les capacités numériques actuelles.Comme application du formalisme DFT-NEGF-SCBA, nous calculons l'IETS de la jonction moléculaire or-octanedithiol(ODT)-or. La courbe I-V, la conductance et l'IETS obtenues par calculs ab initio sontdirectement comparées aux données expérimentales. Une compréhension microscopique du couplage électron-phonon pour une jonction moléculaire à effet tunnel est élaborée dans cet exemple. De plus, des comparaisons entre les jonctions ODT à hydrogène dissociatif et à hydrogène non-dissociatif ainsi queles différents comportements de transfert de charges sont présentés afin de montrer les effets de la formation du thiol dans la jonction moléculaire ODT.
14
Kemp, Jeremy. "Electron spectroscopy and electronic structure of first row transition metal oxides." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257736.
Full text
15
Murooka, Yoshie. "Parallel electron energy loss spectroscopy of electron hole drilling in calcite." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361611.
Full text
16
Eljarrat, Ascunce Alberto. "Quantitative methods for electron energy loss spectroscopy." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/349214.
Full textAbstract:
This thesis explores the analytical capabilities of low-loss electron energy loss spectroscopy (EELS), applied to disentangle the intimate configuration of advanced semiconductor heterostructures. Modern aberration corrected scanning transmission electron microscopy (STEM) allows extracting spectroscopic information from extremely constrained areas, down to atomic resolution. Because of this, EELS is becoming increasingly popular for the examination of novel semiconductor devices, as the characteristic size of their constituent structures shrinks. Energy-loss spectra contain a high amount of information, and since the electron beam undergoes well-known inelastic scattering processes, we can trace the features in these spectra down to elementary excitations in the atomic electronic configuration.
In Chapter 1, the general theoretical framework for low-loss EELS is described. This formulation, the dielectric model of inelastic scattering, takes into account the electrodynamic properties of the fast electron beam and the quantum mechanical description of the materials. Low-loss EELS features are originated both from collective mode (plasmons) and single electron excitations (e.g. band gap), that contain relevant chemical and structural information. The nature of these excitations and the inelastic processes involved has to be taken into account in order to analyze experimental data or to perform simulations. The computational tools required to perform these tasks are presented in Chapter 2. Among them, calibration, deconvolution and Kramers-Kronig analysis (KKA) of the spectrum constitute the most relevant procedures, that ultimately help obtain the dielectric information in the form of a complex dielectric function (CDF). This information may be then compared to the one obtained by optical techniques or with the results from simulations. Additional techniques are explained, focusing first on multivariate analysis (MVA) algorithms that exploit the hyperspectral acquisition of EELS, i.e. spectrum imaging (SI) modes. Finally, an introduction to the density functional theory (DFT) simulations of the energy-loss spectrum is given.
In Chapter 3, DFT simulations concerning (Al, Ga, In)N binary and ternary compounds are introduced. The prediction of properties observed in low-loss EELS of these semiconductor materials, such as the band gap energy, is improved in these calculations. Moreover, a super-cell approach allows to obtain the composition dependence of both band gap and plasmon energies from the theoretical dielectric response coefficients of ternary alloys. These results are exploited in the two following chapters, in which we experimentally probe structures based on group-III nitride binary and ternary compounds. In Chapter 4, two distributed Bragg reflector structures are examined (based upon AlN/GaN and InAlN/GaN multilayers, respectively) through different strategies for the characterization of composition from plasmon energy shift. Moreover; HAADF image simulation is used to corroborate he obtained results; plasmon width, band gap energy and other features are measured; and, KKA is performed to obtain the CDF of GaN. In Chapter 5, a multiple InGaN quantum well (QW) structure is examined. In these QWs (indium rich layers of a few nanometers in width), we carry out an analysis of the energy-loss spectrum taking into account delocalization and quantum confinement effects. We propose useful alternatives complementary to the study of plasmon energy, using KKA of the spectrum.
Chapters 6 and 7 deal with the analysis of structures that present pure silicon-nanocrystals (Si-NCs) embedded in silicon-based dielectric matrices. Our aim is to study the properties of these nanoparticles individually, but the measured low-loss spectrum always contains mixed signatures from the embedding matrix as well. In this scenario, Chapter 6 proposes the most straightforward solution; using a model-based fit that contains two peaks. Using this strategy, the Si-NCs embedded in an Er-doped SiO2 layer are characterized. Another strategy, presented in Chapter 7, uses computer-vision tools and MVA algorithms in low-loss EELS-SIs to separate the signature spectra of the Si-NCs. The advantages and drawbacks of this technique are revealed through its application to three different matrices (SiO2, Si3N4 and SiC). Moreover, the application of KKA to the MVA results is demonstrated, which allows to extract CDFs for the Si-NCs and surrounding matrices.Este trabajo explora las posibilidades analíticas que ofrece la técnica de espectroscopia electrónica de bajas pérdidas (low-loss EELS), capaces de revelar la configuración estructural de los más avanzados dispositivos semiconductores. El uso de modernos microscopios electrónicos de transmisión-barrido (STEM) nos permite obtener información espectroscópica a partir de volúmenes reducidos, hasta llegar a resolución atómica. Por ello, EELS es cada vez mas popular para la observación de los dispositivos semiconductores, a medida que los tamaños característicos de sus estructuras constituyentes se miniaturiza. Los espectros de pérdida de energía contienen mucha información: dado que el haz de electrones sufre unos bien conocidos procesos de dispersión inelástica, podemos trazar relaciones entre estos espectros y excitaciones elementales en la configuración atómica de los elementos y compuestos constituyentes de cada material. Se describe un marco teórico para el estudio del low-loss EELS: el modelo dieléctrico de dispersión inelástica, que toma en consideración las propiedades electrodinámicas del haz de electrones y la descripción mecano-cuántica de los materiales. Adicionalmente, se describen en detalle las herramientas utilizadas en el análisis de datos experimentales o la simulación teórica de espectros. Monitorizando las energías de band gap y plasmon en los datos experimentales de low-loss EELS se obtiene información directa sobre propiedades electrónicas de los materiales. Además, usando análisis Kramers-Kronig en los espectros se obtiene información dieléctrica que puede ser comparada con las simulaciones o con otras técnicas (ópticas). Se demuestra el uso de estas herramientas con una serie de estudios sobre estructuras basadas en nitruros del grupo-III. Por otro lado, el uso de algoritmos para el análisis multivariante permite separar las contribuciones individuales que se miden mezcladas en espectros de estructuras complicadas. Hemos utilizado estas avanzadas herramientas para el análisis de estructuras basadas en silicio que contienen nano-cristales embebidos en matrices dieléctricas.
17
Lehmann, Dietmar. "Phonon Spectroscopy and Low-Dimensional Electron Systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1138734990743-55381.
Full textAbstract:
The generation and propagation of pulses of nonequilibrium acoustic phonons and their interaction with semiconductor nanostructures are investigated. Such studies can give unique information about the properties of low-dimensional electron systems, but in order to interpret the experiments and to understand the underlying physics, a comparison with theoretical models is absolutely necessary. A central point of this work is therefore a universal theoretical approach allowing the simulation and the analysis of phonon spectroscopy measurements on low-dimensional semiconductor structures. The model takes into account the characteristic properties of the considered systems. These properties are the elastic anisotropy of the substrate material leading to focusing effects and highly anisotropic phonon propagation, the anisotropic nature of the different electron-phonon coupling mechanisms, which depend manifestly on phonon wavevector direction and polarization vector, and the sensitivity to the confinement parameters of the low-dimensional electron systems. We show that screening of the electron-phonon interaction can have a much stronger influence on the results of angle-resolved phonon spectroscopy than expected from transport measurements. Since we compare theoretical simulations with real experiments, the geometrical arrangement and the spatial extension of phonon source and detector are also included in the approach enabling a quantitative analysis of the data this way. To illustrate the influence of acoustic anisotropy and carrier confinement on the results of phonon spectroscopy in detail we analyse two different applications. In the first case the low-dimensional electron system acts as the phonon detector and the phonon induced drag current is measured. Our theoretical model enables us to calculate the electric current induced in low-dimensional electron systems by pulses of (ballistic) nonequilibrium phonons. The theoretical drag patterns reproduce the main features of the experimental images very well. The sensitivity of the results to variations of the confining potential of quasi-2D and quasi-1D electrons is demonstrated. This provides the opportunity to use phonon-drag imaging as unique experimental tool for determining the confinement lengths of low-dimensional electron systems. By comparing the experimental and theoretical images it is also possible to estimate the relative strength of the different electron-phonon coupling mechanisms.In the second application the low-dimensional electron system acts as the phonon pulse source and the angle and mode dependence of the acoustic phonon emission by hot 2D electrons is investigated. The results exhibit strong variations in the phonon signal as a function of the detector position and depend markedly on the coupling mechanism, the phonon polarization and the electron confinement width. We demonstrate that the ratio of the strengths of the emitted longitudinal (LA) and transverse (TA) acoustic phonon modes is predicted correctly only by a theoretical model that properly includes the effects of acoustic anisotropy on the electron-phonon matrix elements, the screening, and the form of the confining potential. A simple adoption of widely used theoretical assumptions, like the isotropic approximation for the phonons in the electron-phonon matrix elements or the use of simple variational envelope wavefunctions for the carrier confinement, can corrupt or even falsify theoretical predictions.We explain the `mystery of the missing longitudinal mode' in heat-pulse experiments with hot 2D electrons in GaAs/AlGaAs heterojunctions. We demonstrate that screening prevents a strong peak in the phonon emission of deformation potential coupled LA phonons in a direction nearly normal to the 2D electron system and that deformation potential coupled TA phonons give a significant contribution to the phonon signal in certain emission directionsDie vorliegende Arbeit beschäftigt sich mit der Ausbreitung von akustischen Nichtgleichgewichtsphononen und deren Wechselwirkung mit Halbleiter-Nanostrukturen. Güte und Effizienz moderner Halbleiter-Bauelemente hängen wesentlich vom Verständnis der Wechselwirkung akustischer Phononen mit niederdimensionalen Elektronensystemen ab. Traditionelle Untersuchungsmethoden, wie die Messung der elektrischen Leitfähigkeit oder der Thermospannung, erlauben nur eingeschränkte Aussagen. Sie mitteln über die beteiligten Phononenmoden und eine Trennung der einzelnen Wechselwirkungsmechanismen ist nur näherungsweise möglich ist. Demgegenüber erlaubt die in der Arbeit diskutierte Methode der winkel- und zeitaufgelösten Phononen-Spektroskopie ein direktes Studium des Beitrags einzelner Phononenmoden, d.h. in Abhängigkeit von Wellenzahlvektor und Polarisation der Phononen. Im Mittelpunkt der Arbeit steht die Fragestellung, wie akustische Anisotropie und Ladungsträger-Confinement die Ergebnisse der winkel- und zeitaufgelösten Phononen-Spektroskopie beeinflussen und prägen. Dazu wird ein umfassendes theoretisches Modell zur Simulation von Phononen-Spektroskopie-Experimenten an niederdimensionalen Halbleitersystemen vorgestellt. Dieses erlaubt sowohl ein qualitatives Verständnis der ablaufenden physikalischen Prozesse als auch eine quantitative Analyse der Messergebnisse. Die Vorteile gegenüber anderen Modellen und Rechnungen liegen dabei in dem konsequenten Einbeziehen der akustischen Anisotropie, nicht nur für die Ausbreitung der Phononen, sondern auch für die Matrixelemente der Wechselwirkung, sowie eine saubere Behandlung des Confinements der Elektronen in den niederdimensionalen Systemen. Dabei werden die Grenzen weit verbreiteter Näherungsansätze für die Elektron-Phonon-Matrixelemente und das Elektronen-Confinement deutlich aufgezeigt. Für den quantitativen Vergleich mit realen Experimenten werden aber auch solche Größen, wie die endliche räumliche Ausdehnung von Phononenquelle und Detektor, die Streuung der Phononen an Verunreinigungen oder die Abschirmung der Elektron-Phonon-Kopplung durch die Elektron-Elektron-Wechselwirkung berücksichtigt.Im zweiten Teil der Arbeit wird der theoretische Apparat auf typische experimentelle Fragestellungen angewandt. Im Falle der Phonon-Drag-Experimente an GaAs/AlGaAs Heterostrukturen wird der durch akustische Nichtgleichgewichtsphononen in zwei- und eindimensionalen Elektronensystemen induzierte elektrische Strom (Phonon-Drag-Strom) als Funktion des Ortes der Phononenquelle bestimmt. Das in der Arbeit hergeleitete theoretische Modell kann die experimentellen Resultate für die Winkelabhängigkeit des Drag-Stromes sowohl für Messungen mit und ohne Magnetfeld qualitativ gut beschreiben. Außerdem wird der Einfluss unterschiedlicher Confinementmodelle und unterschiedlicher Wechselwirkungsmechanismen studiert. Dadurch ist es möglich, aus Phonon-Drag-Messungen Rückschlüsse auf die elektronischen und strukturellen Eigenschaften der niederdimensionalen Elektronensysteme zu ziehen (Fermivektor, effektive Masse, Elektron-Phonon-Kopplungskonstanten, Form des Confinementpotentials). Als weiteres Anwendungsbeispiel wird das Problem der Energierelaxation (aufgeheizter)zweidimensionaler Elektronensysteme in GaAs Heterostrukturen und Quantentrögen untersucht. Für Elektronentemperaturen unterhalb 50 K werden die Gesamtemissionsrate als Funktion der Temperatur und die winkelaufgelöste Emissionsrate (als Funktion der Detektorposition) berechnet. Für beide Größen wird erstmals eine gute Übereinstimmung zwischen Theorie und Experiment gefunden. Es zeigt sich, dass akustische Anisotropie und Abschirmungseffekte zu überraschenden neuen Ergebnissen führen können. Ein Beispiel dafür ist der unerwartet große Beitrag der mittels Deformationspotential-Wechselwirkung emittierten transversalen akustischen Phononen, der bei einer Emission der Phononen näherungsweise senkrecht zum zweidimensionalen System beobachtet werden kann
18
Bawagan, Alexis Delano Ortiz. "Evaluation of wavefunctions by electron momentum spectroscopy." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26958.
Full textAbstract:
Electron momentum spectroscopy (EMS) provides experimental atomic and molecular electronic structure information in terms of the binding energy spectrum and the experimental momentum profile (XMP), which is a direct probe of the electron momentum distribution in specific molecular orbitals. The measured XMPs permit a detailed quantitative evaluation of theoretical ab initio wavefunctions in quantum chemistry and also provide a means to investigate traditional concepts in chemical reactivity at the fundamental electronic level.
This thesis reports high momentum resolution EMS measurements of the valence orbitals of H₂0, D₂0, NH₃ and H₂CO obtained using an EMS spectrometer of the symmetric, non-coplanar type operated at an impact energy of 1200eV. The measured experimental momentum profiles for the valence orbitals of each molecule have been placed on a common intensity scale, which has allowed a stringent quantitative comparison between experiment and theory. These studies now confirm earlier preliminary investigations that suggested serious discrepancies between experimental and theoretical momentum distributions. Exhaustive consideration of possible rationalizations of these discrepancies indicate that double zeta quality and even near Hartree-Fock quality wavefunctions are insufficient in describing the outermost valence orbitals of H₂0 and NH₃. Preliminary results for H₂CO also indicate that near Hartree-Fock wavefunctions are incapable of describing the outermost 2b₂ orbital. Interactive and collaborative theoretical efforts have therefore led to the development of new Hartree-Fock limit and also highly correlated (CI) wavefunctions for H₂0, NH₃ and H₂CO. It is found that highly extended basis sets including diffuse functions and the adequate inclusion of correlation and relaxation effects are necessary in the accurate prediction of experimental momentum profiles as measured by electron momentum spectroscopy.
New EMS measurements are also reported for the outermost valence orbitals of NF₃, NH₂CH₃, NH (CH₃)₂, N (CH₃)₃ and para-dichlorobenzene. These exploratory studies have illustrated useful chemical applications of EMS. In particular, EMS measurements of the outermost orbitals of the methylated amines have revealed chemical trends which are consistent with molecular orbital calculations. These calculations suggest extensive electron density derealization of the so-called nitrogen 'lone pair' in the methylated amines in comparison to the 'lone pair' in NH₃. EMS measurements of the non-degenerate π₃ and π₂ orbitals of para-dichlorobenzene show different experimental momentum profiles consistent with arguments based on inductive and resonance effects. These experimental trends, both in the case of the amines and para-dichlorobenzene, were qualitatively predicted by molecular orbital calculations using double zeta quality wavefunctions. However more accurate prediction of the experimental momentum profiles of these molecules will need more extended basis sets and the inclusion of correlation and relaxation effects as suggested by the studies based on the smaller molecules.
An integrated computer package (HEMS) for momentum space calculations has also been developed based on improvements to existing programs. Development studies testing a new prototype multichannel (in the ɸ plane) EMS spectrometer are described.Science, Faculty of
Chemistry, Department of
Graduate
19
Sleigh, Anne Katherine. "Inelastic electron tunnelling spectroscopy of adsorbed molecules." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.346406.
Full text
20
Tarbutt, Michael Roy. "Spectroscopy of few-electron highly charged ions." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365339.
Full text
21
Paoli, M. P. "Electron-volt neutron spectroscopy of condensed matter." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235080.
Full text
22
Nicholls, Rebecca Jane. "Electron energy loss spectroscopy of fullerene materials." Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:2fd55ddf-ca30-4b9a-a37f-61b024a3f22f.
Full textAbstract:
This thesis is comprised of two closely related studies of fullerenes. The first part is an investigation of C60 and C70 nanocrystals using both experimental and simulated electron energy loss (EEL) spectra. Through a detailed comparison of particular features in EEL spectra collected from these materials in a transmission electron microscope, with simulated spectra, it is established that differences in spectra from different materials can be linked to particular aspects of the structural models. For example, in the case of C60 differences in experimental spectra from different samples can be linked to differences in the bond lengths within the molecules of different samples. In the case of C70, it is found that features within the spectrum which have previously been attributed to the ten equatorial atoms do not have this origin in a crystal. The second part is an experimental investigation of endohedral fullerenes Nd@C82 and Sc3N@C80. The effect of temperature on the EEL spectrum is investigated and, in the case of Nd@C82, the effect of the presence of different isomers is also investigated. Spectra are successfully obtained from the encapsulated atoms, and the importance of careful experiments in terms of avoiding contamination is highlighted.
23
Hubbard, Penny Louise. "Molecular and electron dynamics with muon spectroscopy." Thesis, University of East Anglia, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268573.
Full text
24
Arlow, J. S. "Auger electron spectroscopy on cylindrical single crystals." Thesis, University of Warwick, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373070.
Full text
25
Eriksen, S. "Electron spectroscopy of rutile-type metal oxides." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38301.
Full text
26
Natusch, Michael Kurt Heinrich. "Detection limits in electron energy-loss spectroscopy." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624128.
Full text
27
Sivaraya, Sivapathasundaram. "Hot electron spectroscopy studies of indirect tunnel barriers." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301961.
Full text
28
Wright, Helen Elizabeth. "Studies of the electronic structure of metals and alloys by electron spectroscopy." Thesis, University of Liverpool, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329397.
Full text
29
Newell, Mark Alistair. "Physical and electronic structure of simple metal systems studied by electron spectroscopy." Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333499.
Full text
30
Rafferty, Brian Edward. "Probing electronic structure near the bandgap region using electron energy loss spectroscopy." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627334.
Full text
31
Pietzsch, Annette. "Towards femtosecond time resolved electron spectroscopy for chemical analysis: core level photoelectron spectroscopy on solids at free electron lasers." München Verl. Dr. Hut, 2008. http://d-nb.info/990811220/04.
Full text
32
Rolke, James M. "Orbital electron density from electron momentum spectroscopy : comparison with AB initio calculations." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25146.pdf.
Full text
33
Magerl, Elisabeth. "Attosecond photoelectron spectroscopy of electron transport in solids." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-130576.
Full text
34
Clark, S. A. "Studies of molecular orbitals by electron momentum spectroscopy." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30626.
Full textAbstract:
The binding energies and momentum distributions of all of the valence orbitals of (CH₃)₂O, PH₃, CH₄ and SiH₄ have been measured by high momentum resolution electron momentum
spectroscopy. The binding energy spectra have been compared to Green's function and configuration interaction calculations from the literature and with new calculations performed in collaboration with co-workers at Indiana University and Universitat Braunschweig.
For PH₃, CH₄ and SiH₄, near Hartree-Fock limit calculations of the momentum distributions and very accurate calculations of the ion-neutral overlap using MRSD-CI wavefunctions to describe the ion and target have been performed in collaboration with co-workers at Indiana University.
Good agreement is obtained between the (CH₃)₂O measurements and the momentum distributions calculated from relatively simple wavefunctions, except in the case of the outermost orbital. The effects of diffuse and polarization functions in the basis sets, and also the influence of molecular geometry, have been investigated. Comparison of the momentum distributions of the outermost orbitals of H₂O, CH₃OH and (CH₃)₂O demonstrates a delocalization of charge density with methyl substitution.
The measured momentum distributions of PH₃, CH₄ and SiH₄ are compared with near Hartree-Fock limit calculations as well as ion-neutral overlap calculations in which the ion and neutral wavefunctions are described by multireference, singly and doubly excited, configuration interaction calculations. In each case, the experimental results are well modelled by the near Hartree-Fock limit calculations, and there is little difference between the Hartree-Fock limit and ion-neutral overlap calculations. A significant splitting of the
4a₁ (inner valence) pole strength is observed for PH₃, but the inner valence strength is largely contained in the main peak for both CH₄ and SiH₄. Green's function calculations quantitatively reproduce these results.
Ion-neutral overlap calculations using MRSD-CI wavefunctions to describe the ion and target have been performed for HF, HCl, Ne and Ar. These are compared with previously published EMS measurements of the momentum distributions. Very poor agreement between theory and experiment is obtained for HF and HCl. The theoretical and experimental results for all of the hydrides CH₄-HF and SiH₄-HCl as well as Ne and Ar are reviewed.Science, Faculty of
Chemistry, Department of
Graduate
35
Walls, Michael Gerard. "Electron energy-loss spectroscopy of surfaces and interfaces." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254503.
Full text
36
Drummond-Brydson, Richard. "Electron energy loss spectroscopy in solid-state chemistry." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237906.
Full text
37
Hackenberg, Wolfgang. "Hot electron luminescence spectroscopy in GaAs and InP." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309213.
Full text
38
Kumari, Sudesh. "ELECTRON AND ION SPECTROSCOPY OF METAL HYDROCARBON COMPLEXES." UKnowledge, 2014. http://uknowledge.uky.edu/chemistry_etds/30.
Full textAbstract:
Metal-hydrocarbon complexes were prepared in a laser-vaporization molecular beam source and studied by single-photon zero electron kinetic energy (ZEKE) and mass-analyzed threshold ionization (MATI) spectroscopy. The ionization energies and vibrational frequencies of the metal complexes were measured from the ZEKE and MATI spectra. Metal-ligand bonding and low-lying electronic states of the neutral and ionized complexes were analyzed by combining the spectroscopic measurements with quantum chemical calculations and spectral simulations.
In this dissertation, the metal complexes of mesitylene, aniline, cyclooctatetraene, benzene, ethene, and propene were studied. For each complex, different effects from metal coordination have been identified. Although metal-bis(mesitylene) sandwich complexes may adopt eclipsed and staggered conformations, the group VI metal-bis(mesitylene) complexes are determined to be in the eclipsed form. In this form, rotational conformers with the methyl group dihedral angles of 0 and 60° are identified for the Cr complex, whereas the 0° rotamer is observed for the Mo and W species. The unsuccessful observation of the 60° rotamer for the Mo and W complexes is the result of its complete conversion to the 0° rotamer in both He and He/Ar carriers. For group III metal aniline complexes, the ZEKE spectrum of each complex exhibits a strong origin band, a short M+-aniline stretching progression, and several low-frequency ligand based vibrational modes. The intensities of most of the transitions can be explained by the Franck-Condon (FC) principle within the harmonic approximation. However, the intensity of the low frequency out-of-plane ring deformation mode is greatly overestimated by the FC calculations and may be caused by the anharmonic nature of the mode. Although aniline offers two possible binding modes for the metal atoms, a п binding mode is identified with the metal atom over the phenyl ring. For Ce, Pr, and Nd(cyclooctatetraene) complexes multiple band systems are observed. This is assigned to the ionization of several low-lying electronic states of the neutral complex. This observation is different from the Gd(cyclooctatetraene) complex, for which a single band system is observed. The presence of the multiple low-energy electronic states is caused by the splitting of the partially filled lanthanide 4f orbitals in the ligand field. The ZEKE spectrum of the Gd(benzene) complex exhibits a strong origin band, whereas the spectrum of Lu(benzene) displays a weak one. The benzene ring is planar in the Gd complex, but bent in the Lu complex. Dehydrogenation and C-C coupling products are observed in the reaction of La atom and ethene/propene. For the La and ethene reaction, La(C2H2) and La(C4H6) complexes are identified. With propene, C-H bond activation leads to the formation of the La(C3H4) and H-La(C3H5) complexes, whereas the C-C coupling yields the La(trimethylenemethane) complex. In addition, the La(CHCCH3) and La(CHCHCH2) isomers of La(C3H4) are observed, which are produced by the 1,2- and 1,3-hydrogen elimination of propene.
39
Findlay, Peter Charles. "Free electron laser spectroscopy of narrow gap semiconductors." Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/528.
Full text
40
Eustace, David Andrew. "Spin polarisation effects in electron energy loss spectroscopy." Thesis, University of Glasgow, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438978.
Full text
41
Davies, Julia Ann. "Electron spectroscopy of selected atmospheric molecules and hydrocarbons." Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283221.
Full text
42
Kibble-Wilson, H. A. B. "Inelastic electron tunnelling spectroscopy of glasses and clusters." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377226.
Full text
43
Cotter, M. D. "Surface studies of ionic oxides by electron spectroscopy." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47008.
Full text
44
Chan, Ho Bun 1969. "Tunneling spectroscopy of the two-dimensional electron gas." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9387.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999.Includes bibliographical references (p. 155-161).
We measure the single particle density of states (DOS) of a two-dimensional electron system (2DES) in a GaAs/AlGaAs heterostructure. Using a technique that we call "Time Domain Capacitance Spectroscopy" (TDCS), we measure the complete current-voltage characteristics for tunneling into the 2DES without making ohmic contacts to it. TDCS detects the tunneling current in regimes difficult to access by conventional methods, such as when the in-plane conductance is low. For the first time we detect the contributions of localized states to the tunneling current. The DOS of an interacting 2DES in the diffusive limit displays logarithmic energy dependence near the Fermi level. Using TDCS, we measure the voltage dependence of the tunneling conductance of a semiconductor 2DES and observe the logarithmic Coulomb anomaly for the first time in 2D systems other than thin metal films. As we increase the density, this suppression in tunneling conductance narrows and recedes. Nevertheless suppression reappears when we apply a magnetic field perpendicular to the 2D plane. We find that the tunneling conductance depends linearly on voltage near zero bias for all magnetic field strengths and electron densities. Moreover, the slopes of this linear gap are strongly field dependent. The data are suggestive of a new model of the tunneling gap in the presence of disorder and screening. We also use TDCS to study the interactions among electronic spins. By applying excitations less than kT, we observe that equilibrium tunneling into spin-polarized quantum Hall states (v=l, 3, 1/3) occurs at two distinct tunneling rates for samples of very high mobility. Some electrons tunnel into the 2DES at a fast rate while the rest tunnel at a rate up to 2 orders of magnitude slower. Such novel double-rate tunneling is not observed at even-integer filling fractions where the 2DES is not spin-polarized. The dependence of the two rates on magnetic field, temperature and tunnel barrier thickness suggests that slow in-plane spin relaxation, possibly related to formation of Skyrmions, leads to a bottleneck for tunneling of electrons.
by Ho Bun Chan.
Ph.D.
45
Hamidizadeh, Yasaman. "Inelastic electron tunnelling spectroscopy using nanoscale tunnel junctions." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/26225.
Full textAbstract:
Inelastic Electron Tunnelling Spectroscopy (IETS) [1-5] provides a means to characterise the phonon spectrum of a molecule by measuring the phonon-assisted tunnelling current through a potential barrier impregnated with target molecules. Traditionally, this technique has used Metal - Insulator - Metal (MIM) junctions, and the molecules of interest are adsorbed on to the insulator during junction fabrication. At low applied voltage V, tunnelling through the barrier is elastic. However, inelastic tunnelling caused by electron interaction with vibrational states in the adsorbed molecules can create additional conduction channels, occurring when V reaches a value of hω/e, where ω is a molecular vibrational mode. These lead to peaks in the d^2 I / dV^2 vs. V characteristics for each additional channel, giving a spectrum of the molecular vibration modes. As energy separations in the vibrational spectrum are relatively small compared to the electronic spectrum, the full vibrational spectrum is measured only at T < 30K. However, it may be possible to measure part of the spectrum even at room temperature, raising the possibility of a molecular detector. This project is concerned with fabricating nanoscale tunnel junctions based on Si nanowires (NWs) made by electron-beam lithography (EBL), for the purpose of IETS measurements, at 300K. A Si/SiO2 tunnel barrier/Al structure is used, where the Al NW crosses an oxidised Si NW. This allows the fabrication of tunnel junctions down to 50nm x 120nm in area and tunnelling occurs across a 10nm thick SiO2 layer. The reduction in device dimensions to the nanoscale may increase the sensitivity of the device to molecules adsorbed on the tunnel junction. Furthermore, the use of Silicon on insulator (SOI) material allows modulation of the tunnel junction using the back gate formed by the SOI substrate, control the Fermi energy and electron concentration in the NW, and hence the IETS characteristics of the device. In principle, an IETS sensor may be possible using such a configuration. In principle, a switchable IETS measurements are performed at 300K for ammonium hydroxide (NH4OH), acetic acid (CH3COOH), and propionic acid (C3H6O2) molecules. The I-V , dI/dV - V , and d2^I/dV^2-V characteristics of the tunnel junction are measured before and after the adsorption of molecules on the junction using vapour treatment or immersion. Peaks can be observed in the d^2I/dV^2-V characteristics in all the cases following molecules adsorption. These peaks may be attributed to vibrational modes of N-H and C-H bonds. Simulation of IETS characteristics modelled based on a combination of elastic, inelastic tunnelling and Schottky barriers at the Si / SiO2 / Al interface in the device. A comparison has been made between the simulation results and experimental measurements which showed very good agreement. This device modelling can be used to predict experimental characteristics and allow thermal broadening of the IETS peaks to be investigated.
46
Mistry, Andrew Kishor. "In-beam gamma and electron spectroscopy of ²⁵³No." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2003299/.
Full textAbstract:
The (S)ilicon (A)nd (Ge)rmanium (sage) spectrometer has been employed, together with the ritu gas-filled separator and the great focal plane spectrometer with Total Data Readout (TDR) at the University of Jyv¨askyl¨a to analyse the heavy actinide nucleus 253No (Z=102). Initially, the neutron-deficient odd-A isotope 177Au (Z=79) is studied using the recoil-decay tagging technique, enabling testing and demonstration of γ ray and conversion electron coincidence analysis techniques using sage. This has allowed for conversion coefficient measurements on a number of low-lying states. The main focus of the study is on 253No with combined in-beam γ ray and electron spectroscopy through the recoil-tagging technique. Orbitals emanating from the next shell closure above 208Pb are sensitive to measurement in the deformed heavy midshell region. Thus probing the single-particle structure of regional midshell heavy nuclei allows for exploration of the island of enhanced stability toward the next closed nucleon shells. Using 253No data from sage has enabled γ-electron coincidences to be established for level scheme construction with transition energies determined. Recoil-tagged prompt γ ray and internal conversion electron spectra are compared to Monte Carlo simulations to confirm the rotational structure nature of the bands. Internal conversion coefficient measurements establish the multipolarity of transitions within the bands. Measurement of the B(M1+E2’)/B(E2) interband-intraband ratio confirms the assignment of the bandhead configuration, with results presented strongly supporting the 9/2−[734]ν observed in previous studies. An isomeric state is measured with T1/2=28.6±2.3 µs confirmed through a decay via a 167 keV M2 transition resulting from the 5/2+[622]ν configuration. A 608±20 µs slower isomer has also been tentatively measured, potentially with decay through a non-yrast structure. Excited 249Fm states following the α-decay of 253No are also measured through the recoil-decay tagging technique.
47
Deborde, Jean-Laurent. "Lateral electron tunneling spectroscopy between low-dimensional electron systems in GaAs,AlGaAs heterostructures." Tönning Lübeck Marburg Der Andere Verl, 2009. http://d-nb.info/995773491/04.
Full text
48
Pierce, William Renton. "High-resolution transmission electron microscopy and electron energy loss spectroscopy of doped nanocarbons." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/highresolution-transmission-electron-microscopy-and-electron-energy-loss-spectroscopy-of-doped-nanocarbons(dd1340ba-4a31-49e5-a421-9dd47ea35256).html.
Full textAbstract:
Graphene, a one-atom thick sheet of carbon, is the thinnest, strongest and most electrically conductive material ever discovered. Alongside carbon nanotubes it is part of the group of nanocarbons whose unique properties have sparked huge interest in possible applications, including electronic devices, solar cells and biosensors. Doping of these materials allows for the modification of their optical and electronic properties,which is crucial to realising these applications. Studying the properties of these doped materials at atomic resolution and finding controllable and industrially scalable routes to doping, such as low energy ion implantation, are thus essential if they are to becomethe materials of the future. In this thesis, highly localised optical enhancements in metal doped graphene are studied using energy-filtered transmission electron microscopy in a monochromated and aberration corrected electron microscope. The ideal conditions for imaging the low energy loss region of graphene using EFTEM are discussed and new methods to compensate for image artifacts when using this technique at high resolution are presented. Density functional theory is used to reveal new visible spectrum plasmon excitations in the electron energy loss spectra of boron and nitrogen doped nanocarbons. Atomic resolution scanning transmission electron microscopy and nanoscale electron energy loss spectroscopy are used to investigate controllable and defect-free substitutional doping of suspended graphene films through low energy ion implantation. Computational methods for filtering high angle annular dark field images are shown and software for the automated processing and spectroscopic analysis of these images is developed.
49
Saubi, Benjamin Haubiih. "Studies in ferromagnetism using electron polarization analysis." Thesis, University of Sussex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249391.
Full text
50
Roth, Friedrich. "Electronic structure of selected aromatic hydrocarbon systems investigated with electron energy-loss spectroscopy." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-106800.
Full textAbstract:
Organic materials with fascinating/intriguing electronic properties have been the driving force for many research activities in the past, and in particular for important progress in materials science covering both new functional materials as well as theoretical developments. In addition, charge transfer, i. e., the addition or removal of charges to or from molecules in organic solids is one route to modify and control their electronic properties. Recently, the discovery of superconductivity in several alkali metal intercalated hydrocarbon systems (picene, phenanthrene, coronene and 1,2;8,9-dibenzopentacene) with rather high transition temperatures has opened a new chapter in organic material science as well as solid-state physics.
The search for a microscopic understanding of the mechanism that drives materials superconducting always has initiated a large number of scientific activities, and there are numerous examples where these activities have provided major advancement. A basic foundation of this understanding is the knowledge of the electronic properties of the material under investigation.
In this context, this thesis reports first, very detailed insight into the electronic structure of both undoped as well as potassium doped picene, coronene and 1,2;8,9-dibenzopentacene using electron energy-loss spectroscopy (EELS) as main experimental method. Additionally, also photoemission spectroscopy experiments have been performed to investigate the occupied electronic density of states close to the chemical potential. In order to learn more about the electronic structure we have compared the results we obtained from EELS and photoemission spectroscopy with theoretical calculations based on Density functional theory (DFT) using the local-density approximation (LDA).
We identify the peculiar case of very close lying conduction bands that upon doping harbour the electrons that form the Cooper-pairs in the superconducting state. Moreover, the presented data display substantial changes in the electronic excitation spectrum upon doping, whereas in the doped case the appearance of one new peak (for picene) and several new peaks (for coronene and 1,2;8,9-dibenzopentacene) in the former optical gap is reported. By using a Kramers–Kronig analysis (KKA) it is possible to gain information about the nature of this doping introduced excitations. In particular, in case of picene, the new low energy feature can be assigned to a charge carrier plasmon. Interestingly, this plasmon disperses negatively upon increasing momentum transfer, which deviates significantly from the traditional picture of metals based on the homogeneous electron gas. The comparison with calculations of the loss function of potassium intercalated picene shows how this finding is the result of the competition between metallicity and electronic localization on the molecular units.
Furthermore, core level excitation measurements show the reduction of the lowest lying C 1s excitation feature, which clearly demonstrates that potassium intercalation leads to a filling of the conduction bands with electrons. Additionally, the measurements of potassium intercalated 1,2;8,9-dibenzopentacene clearly indicate the formation of particular doped phases with compositions K_xdibenzopentacene (x = 1, 2, 3), whereas the data suggest that K_1dibenzopentacene has an insulating ground state with an energy gap of about 0.9 eV, while K_2dibenzopentacene and K_3dibenzopentacene might well be metallic, because of the absent of an energy gap in the electronic excitation spectra.
Interestingly, a comparison of the photoemission as well as EELS spectra of undoped 1,2;8,9-dibenzopentacene and pentacene reveal that the electronic states close to the Fermi level and the electronic excitation spectra of the two materials are extremely similar, which is due to the fact, that the additional two benzene rings in 1,2;8,9-dibenzopentacene virtually do not contribute to the delocalized pi molecular orbitals close to the Fermi level. This close electronic similarity is in contrast to the behavior upon potassium doping, where evidence for a Mott state has been reported in the case of pentacene.
A comparison of the low energy excitation spectra of chrysene with picene (phenacenes) as well as tetracene with pentacene (acenes) crystals reveal a significant difference between the former and the latter two materials. While for the phenacenes (zigzag arrangement) the excitation onset is characterized by up to five weak excitation features with only small anisotropy and without visible Davydov splitting within the a*, b*-planes, the acene (linear arrangement) spectra are dominated by a large excitation close to the onset and a sizable Davydov splitting. The presented data show further that the spectral shape of the pentacene excitation spectrum provides clear evidence for a large admixture of molecular Frenkel-type excitons with charge-transfer excitations resulting in excited states with a significantly mixed character. This conclusion is in good agreement with recent advanced calculations which predicted a charge-transfer admixture to the lowest singlet excitation which is significantly dependent upon the length of the acene molecules. Moreover, also for picene and chrysene we observe differences which point towards an increased charge-transfer contribution to the singlet excitation spectrum in the former.
Finally, investigations of the electronic properties of undoped and potassium doped chrysene, a close relative of picene, show that the doping introduced changes are in a similar range such as observed in case of picene. Interestingly, due to the analogy between the observed changes in the electronic structure upon potassium doping between chrysene and picene and further similarity in the crystal structure we speculate that chrysene is a promising candidate for another aromatic hydrocabon superconductor.