Thèses sur le sujet « Electronic Properties - Metal Clusters »
Pour voir les autres types de publications sur ce sujet consultez le lien suivant : Electronic Properties - Metal Clusters.
Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres
Consultez les 50 meilleures thèses pour votre recherche sur le sujet « Electronic Properties - Metal Clusters ».
À côté de chaque source dans la liste de références il y a un bouton « Ajouter à la bibliographie ». Cliquez sur ce bouton, et nous générerons automatiquement la référence bibliographique pour la source choisie selon votre style de citation préféré : APA, MLA, Harvard, Vancouver, Chicago, etc.
Vous pouvez aussi télécharger le texte intégral de la publication scolaire au format pdf et consulter son résumé en ligne lorsque ces informations sont inclues dans les métadonnées.
Parcourez les thèses sur diverses disciplines et organisez correctement votre bibliographie.
1
Raparla, Mrudula. « Study of the structural and electronic properties of aluminum nano clusters by DFT ». To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Texte intégral
2
Stoll, Tatjana. « Ultrafast electronic, acoustic and thermal properties of metal nanoparticles and clusters ». Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10332/document.
Texte intégralRésumé :
Nous avons étudié par spectroscopie pompe-sonde résolue en temps la réponse optique ultrarapide d'agrégats de très petite taille (< 2 nm), pour lesquelles une transition d'un comportement de type solide à un comportement moléculaire est attendue. Les modifications des processus de thermalisation interne (interactions électrons-électrons et électrons phonons) avec la réduction de taille ont été étudiées dans des nanosphères d'argent triées en masse entourées de silice, et dans des échantillons d'or atomiquement définis stabilisées par des surfactants. Ces expériences ont mis en évidence les effets de confinement quantique des états électroniques sur la cinétique électronique. L'étude des vibrations acoustiques de nanoparticules dans le même régime de taille a été effectuée. Les vibrations observées dans les agrégats d'or sont dominées par leur mode de respiration radial avec une période proportionnelle à leur diamètre, an analogie avec les nanoparticules plus grandes. Le mode de respiration observé sur les nanoobjets bimétalliques de type cœur/couronne Pt-Au et Ni-Ag est en accord quantitatif avec les estimations du modèle élastique macroscopique, malgré une épaisseur de couronne monoatomique. La spectroscopie résolue en temps a également été utilisée pour étudier le transfert de chaleur à travers l'interface d'une nanoparticule sphérique. Dans ce but, l'évacuation de la chaleur dans des nanoparticules d'or, nues ou enrobées de silice, en solution colloïdale a été étudiée expérimentalement et modélisée de manière quantitative grâce à la prise en compte de la contribution de l'environnement (échauffement du solvant) au signal optiqueWe used ultrafast time-resolved pump-probe spectroscopy to experimentally investigate the optical response of small metal nano-objects in the few nanometer range (< 2 nm), where a transition from a small solid behaviour to a molecular one is expected. The modification of the intrinsic thermalization processes (electron-electron and electron-phonon interactions) has been studied both on glass-embedded mass-selected silver samples and chemically synthesized ligand-stabilized atomic-defined gold clusters. Electron gas internal thermalization and cooling with the lattice are shown to be affected by size reduction and the concomitant discretization of electronic states. The acoustic response in the same small size range has been investigated. Vibrations of gold clusters were characterized by a quasi-breathing mode scaling with their size, in analogy with larger nanoparticles. The breathing mode of bimetallic core/shell Pt-Au and Ni-Ag nanospheres appeared to be in good quantitative agreement with predictions of continuous elastic models, despite the monoatomic thickness of the layer shell. The same time-resolved approach was used to investigate heat transfer through the nanoparticles interfaces. In this context, heat evacuation of bare or silica-encapsulated gold
3
Irawan, Thomas Christoph Eng Fuk. « Geometric and electronic properties of size selected metal clusters on surfaces ». Berlin Pro Business, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?id=2899406&prov=M&dok_var=1&dok_ext=htm.
Texte intégral
4
VERONESE, MARCO. « ELECTRONIC AND MAGNETIC PROPERTIES OF IMPURITIES AND CLUSTERS ON METAL SURFACES ». Doctoral thesis, Università degli studi di Trieste, 2004. http://thesis2.sba.units.it/store/handle/item/12556.
Texte intégralRésumé :
2002/2003La struttura elettronica ed il magnetismo di atomi singoli e impurezze di metalli di transizione deposti su superfici metalliche sono stati studiati per mezzo di tecniche dicroiche di assorbimento dei raggi X (XMCD) e misure di magnetizzazione, in alti campi magnetici ed a temperature criogeniche. Le caratteristiche uniche delle XMCD nell'investigare sia momenti magnetici di spin che orbitali con selettività chimica sono state applicate a sistemi estremamente diluiti, con concentrazione di superficie dell'ordine di 1012 atomi cm-2 , fino al limite di atomi isolati. Questo genere di misure è stato applicato ai sistemi di impurezze di superficie soltanto in ultimi anni grazie alla disponibilità di sorgenti di radiazione di sincrotrone di elevata brillanza. Ad oggi queste misure rappresentano un esempio di punta nello studio sul magnetismo delle impurezze di superficie. l risultati sono riportati per tre gruppi di sistemi: Impurezze di V e Mn sulla superficie dei metalli alcalini (Cs, K, Na); atomi isolati di Mn, V, Fe, Co sulla superficie Cu(100) ed atomi isolati di Co su Pt(111 ).Inoltre è presentato uno studio della distribuzione dei momenti magnetici di uno strato monoatomico di manganese accoppiato alla superficie Fe(1 00). Il manganese su potassio è stato indicato possedere una configurazione elettronica simile a quella atomica d5 . Questa configurazione elettronica è particolarmente stabile per i piccoli cambiamenti di ibridazione indotti dal cambiamento della densità elettronica nei dai metalli alcalini. Se l'ibridazione è ulteriormente aumentata come nel caso di atomi di M n deposti su Al(1 00) le caratteristiche spettroscopiche che si evidenziano in strutture di multipletti atomici negli spettri sono soppresse e con esse il magnetismo. Le impurezze di vanadio sulle superfici alcaline mostrano una configurazione elettronica che non più così simile a quella degli atomi liberi, come ad esempio le configurazioni d o d4 .11 momento orbitale è trovato essere piccolo, minore di 0.5 f.ls, rispetto al momento orbitale delle configurazioni puramente atomiche, ma in similitudine con esse è allineato antiparallelamente al momento di spin. Inoltre il momento orbita le diminuisce risalendo lungo la colonna dei metalli alcalini (gruppo 1 A della tabella periodica degli elementi), cioè andando dal Cs al Li, mentre la densità elettronica è aumentata. Questo effetto è legato all'aumento dell'ibridazione dovuta alla maggiore densità elettronica. l momenti magnetici misurati sono dell'ordine di 3 f.ls e non possono essere spiegati con parametri puramente atomici. Due meccanismi possibili vengono proposti per spiegare l'estinzione parziale del momento orbitale: l'effetto di un debole campo cristallino e l'effetto dell'ibridazione in concomitanza con maggiore larghezza dello stato regato di Friedel nel caso dei primi elementi della serie dei metallo di transizione 3d. Gli atomi isolati di Fe sulla superficie del Cu(1 00) mostrano una grande anisotropia magnetica, di 1,5 me V/atomo ed un momento magnetico orbitale aumentato rispetto al Fedi volume. Il substrato di Cu non contribuisce considerevolmente all'anisotropia come nel caso del Co su platino. All'opposto gli atomi isolati di Co su Cu(100) non mostrano alcuni dicroismo e quindi alcun magnetismo. Questo risultato è spiegato in termini di effetto Kondo, poiché i singoli atomi di Co sono stati trovati per essere un sistema di Kondo con T K=88 K. Un confronto dei dati sperimentali per impurezze di V, M n, Fe e Co su Cu(1 00) con il comportamento magnetico calcolato dei adatomi lungo la serie 3d, mostra un buon accordo generale, ma con deviazioni importanti per le impurezze di Co e di V. Atomi singoli atomi di Co sulla superficie del Pt(111) hanno una straordinaria anisotropia magnetica di circa 9,2 meV/atomo (circa 1000 volte quella del Co di volume) ed ad oggi la più alta energia di anisotropia magnetica misurata per un sistema magnetico. L'origine di un effetto cosi' grande risiede in un momento orbitale aumentato dalla ridotta coordinazione del singolo atomo, alla rottura di simmetria sulla superficie ed all'effetto dell'ibridazione del platino, conseguenza di un mescolamento di stati 3d-5d tra Co ePt, che porta il substrato a contribuire all'anisotropia magnetica totale.
The electronic structure and the magnetism of transition metal single atoms and magnetic impurities on metal surfaces have been studied by means of x-ray absorption dichroic techniques (XMCD, and magnetization measurements) in high magnetic fields and at low temperatures. The unique capabilities of XMCD to probe the both spin and orbital magnetic moments with element selectivity have been applied to diluted systems with low surface concentration (1012 atoms cm-2 ) down to the limit of isolated atoms. This kind of measurements have been applied to surface impurity systems only in the last few year thanks to the availability of high flux and brilliance synchrotron radiation sources. At the present these measurements represent the state of the art in the study of the magnetism of surface impurities. Results are reported for three different classes of systems: Mn and V impurities on the surface of alkali metals (Cs, K, N a); M n, V, Fe, Co single atoms on the Cu(1 00) surface an d Co single atoms on the Pt(111) surface. Furthermore results have been presented, regarding the magnetic moment distribution of a Mn monolayer coupled to the Fe(1 00) surface. Manganese on potassium has been shown to possess an atomic like magnetic d5 electronic configuration. This electronic configuration is particularly stable for small hybridization changes induced by alkali metals of increased electronic density. lf the hybridization is further increased as on Al(100) the spectroscopic features related to atomic multiplets are suppressed together with magnetism. Vanadium impurities on alkali metal surfaces also show atomic multiplet features. The electronic configuration is not an atomic-like configuration as d3 or d4 . The orbital moment is found to be small, less than 0.5 !-ls with respect to the purely atomic configurations and to be antiparallel to the spin. lt decreases along the alkali metals column (group 1A) of the periodic table, as the electronic density is increased, i.e. going from Cs to Li. This effect is related to an increased hybridization with the substrate due to the larger electronic density. The measured magnetic moments are of the order of 3)-ls, and cannot be explained with simple atomic parameters. Two possible mechanisms have been proposed to explain the partial quenching of the orbital moment, the effect of a weak crystal field and the effect of hybridization through the larger width of Friedel resonant bound state for the early elements of 3d transition metal series. Fe single atoms on Cu(100) surface have a large ot1f of plane magnetic anisotropy of 1.5 meV/atom and enhanced orbital magnetic moment with the respect to the bulk. The Cu substrate does not contribute considerably to the anisotropy as in the case of Co o n Pt. At the apposite Co single atoms on Cu(1 00) surface do not show any dichroism an d hence magnetism. This result ca n be explained on the basis of the Kondo effect, since Co single atoms have been found to be a Kondo system with T K=88 K. A comparison of the experimental data for V, Mn, Fe, Co impurities on Cu(100) with the calculated magnetic behavior of adatoms along the 3d series, gives an overall reasonable agreement, with important deviations for V and Co impurities. Co single atoms on the Pt(111) surface have an extraordinary large out of plane magnetic anisotropy of about 9.2 meV/atom due to the interplay between an enhanced orbital moment, consequence reduced coordination of the single atom, at the surface, and the effect of Pt hybridization, consequence of a d-d mixing between Co and Pt orbitals. This result is of particular relevance since this magnetic anisotropy is the highest measured, by now, for any system.
XVI Ciclo
1971
Versione digitalizzata della tesi di dottorato cartacea.
5
Rittmann, Jochen [Verfasser], et Thomas [Akademischer Betreuer] Möller. « Electronic Properties of Transition Metal Doped Silicon Clusters / Jochen Rittmann. Betreuer : Thomas Möller ». Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2011. http://d-nb.info/1016730470/34.
Texte intégral
6
Fernández, Villanueva Estefanía. « Theoretical Study of the Geometrical, Electronic and Catalytic properties of Metal Clusters and Nanoparticles ». Doctoral thesis, Universitat Politècnica de València, 2020. http://hdl.handle.net/10251/135277.
Texte intégralRésumé :
[ES] Dado su tamaño subnanométrico, los clusters metálicos están regidos por el confinamiento cuántico, lo que les hace más "moleculares" y menos "metálicos". En consecuencia, manifiestan propiedades que difieren con respecto a las de partículas más grandes del mismo elemento, y que a menudo son ventajosas para la catálisis de reacciones específicas. Además, su menor tamaño los hace más económicos, con una mayor superficie expuesta. Todo ello hace que los clusters sean opciones muy interesantes en catálisis, y su estudio, síntesis y aplicación ha crecido continuamente desde su descubrimiento en los años 90.
Esta tesis se ha centrado principalmente en el cobre, del que se presenta, en primer lugar, un estudio fundamental sobre la disociación de oxígeno por clusters de diferentes tamaños. Después, se explora computacionalmente la catálisis de las oxidaciones de CO y propeno, confirmando que los clusters de Cu5 (o inferior) son prometedores para reacciones de oxidación. Las dos reacciones utilizadas son buenos ejemplos de la aplicación potencial en industria, sea para reducir emisiones de CO o para producir epóxido de propeno, que es un intermedio importante en la producción de plásticos y adhesivos, entre otros. Además, también se estudió la influencia de dos soportes en los clusters de cobre y su capacidad de oxidación: N-grafeno como un sistema más inerte y ceria como uno que puede participar activamente en reacciones de oxidación.
Finalmente, se incluyen otros dos estudios más específicos, sobre la capacidad de los clusters de Pt3 y Pd3 para catalizar reaciones de acoplamiento C-C como la reacción de Heck, importante para la síntesis de productos de la química fina, y sobre la reacción CO + NO en clusters de Pt, motivado por su uso potencial como catalizadores para la conversión de esas especies en los menos perjudiciales CO2 y N2 en motores de combustión interna.[CAT] Atès que són de grandària subnanomètrica, els clusters metàl·lics estan regits pel confinament quàntic, el qual els fa més "moleculars" i menys "metàl·lics". En conseqüència, manifesten propietats que són diferents a les de partícules més grans del mateix element, i que sovint són avantatjoses per a la catàlisi de reaccions específiques. A més a més, la seua menor grandària fa que siguen més econòmics, amb una major superfície exposada. Així, els clusters són una opció molt interesant en catàlisi, i el seu estudi, síntesi i aplicació ha cres-cut contínuament des del seu descobriment als anys 90. Aquesta tesi s'ha centrat principalment en el coure, del qual es presenta, en primer lloc, un estudi fonamental sobre la dissociació de l'oxígen per clusters de diferents grandàries. Després, s'explora computacionalment la catàlisi de les oxidacions de CO i de propè, confirmant que els clusters de Cu5 (o inferior) són prometedors per a reaccions d'oxidació. Les dues reaccions utilitzades són bons exemples de l'aplicació potencial en indústria, siga per reduir emissions de CO o per produir epòxid de propè, que és un intermedi important en la producció de plàstics i adhesius, entre altres. A més, també es va estudiar la influència de dos suports en els clusters de coure i la seua capacitat d'oxidació: N-grafè com a un sistema més inert i cèria com a un que pot participar activament en reaccions d'oxidació. Finalment, s'inclouen altres dos estudis més específics, sobre la capacitat dels clusters de Pt3 y Pd3 per catalitzar reaccions d'acoblament C-C com la reacció de Heck, important per a la síntesi de productes de la química fina, i sobre la reacció CO + NO als clusters de Pt, motivat pel seu ús potencial com a catalitzadors per a la conversió d'eixes espècies en els menys perjudicials CO2 i N2 als motors de combustió interna.
[EN] Due to their subnanometric size, metal clusters belong to the regime affected by quantum confinement, which makes them more "molecular" and less "metallic". As a result, they exhibit properties that differ with respect to those of larger particles of the same element, and which are often advantageous in the catalysis of specific reactions. Besides, their smaller size makes them more economic and with a higher surface exposed. All of this renders metal clusters very interesting options for catalysis, and their study, synthesis and application has steadily increased since their discovery in the 90s. In this work we have largely focused on copper, of which a fundamental study on the oxygen dissociation by clusters of different sizes is first presented. Then, the catalysis of the CO and propene oxidation reactions is theoretically explored, confirming that Cu5 (or smaller) clusters are promising systems for oxidation reactions. The two reactions used are good examples of the potential application in industry, either to reduce CO emissions or to produce propene epoxide, an important intermediate in the production of plastics and adhesives, among others. In addition, the influence of two supports in the copper clusters and their oxidation capability is explored: on N-graphene as a more inert system and on ceria as one that can actively participate in oxidation reactions. Finally, two other more specific studies are included, regarding the capability of Pt3 and Pd3 clusters to undergo C-C coupling reactions such as the Heck reaction, important for the synthesis of many products of fine chemistry, and regarding the CO + NO reaction on Pt clusters, motivated by their potential use as catalysts for the conversion of those species in less harmful CO2 and N2 in internal combustion engines.
En primer lugar me gustaría agradecer al Ministerio de Economía y Competitividad de España (MINECO) por la financiación de esta tesis mediante el programa Severo Ochoa (SVP-2013-068146), incluyendo los costes adicionales de mi estancia de investigación (EEBB-I-17-12057).
Fernández Villanueva, E. (2019). Theoretical Study of the Geometrical, Electronic and Catalytic properties of Metal Clusters and Nanoparticles [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/135277
TESIS
7
Hoffmann, Sabrina [Verfasser], Heinz [Akademischer Betreuer] Hövel et Shaukat [Akademischer Betreuer] Khan. « Structure and electronic properties of supported noble metal clusters / Sabrina Hoffmann. Betreuer : Heinz Hövel. Gutachter : Shaukat Khan ». Dortmund : Universitätsbibliothek Dortmund, 2013. http://d-nb.info/1099912806/34.
Texte intégral
8
Sinha, Roy Rajarshi. « Ab initio simulation of optical properties of noble-metal clusters ». Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0017/document.
Texte intégralRésumé :
L'intérêt de la recherche fondamentale pour les morceaux nanométriques de métaux nobles est principalement dû à la résonance localisée des plasmons de surface (LSPR) dans l'absorption optique. Différents aspects, liés à la compréhension théorique de la LSPR dans le cas de clusters de métaux nobles de taille dite intermédiaire, sont étudiés dans ce manuscrit. Afin d'avoir une vision plus large nous utilisons deux approches : l'approche électromagnétique classique et le formalisme ab initio en temps réel de la théorie de la fonctionnelle de la densité dépendant du temps (RT-TDDFT). Une comparaison systématique et détaillée de ces deux approches souligne et quantifie les limitations de l'approche électromagnétique lorsqu'elle est appliquée à des systèmes de taille quantique. Les différences entre les excitations plasmoniques collectives et celles impliquant les électrons d, ainsi que leurs interactions, sont étudiées grâce au comportement spatial des densités correspondantes. Ces densités sont obtenues en appliquant une transformée de Fourier dans l'espace à la densité obtenue par les simulations DFT utilisant une perturbation delta-kick. Dans ce manuscrit, des clusters de métaux nobles nus et protégés par des ligands sont étudiés. En particulier, motivé par de récents travaux sur les phénomènes d'émergence de plasmon, l'étude par TD-DFT de nano-alliages Au-Cu de taille tout juste inférieure à 2nm à fourni de subtiles connaissances sur les effets d'alliages sur la réponse optique de tels systèmesThe fundamental research interest in nanometric pieces of noble metals is mainly due to the localized surface-plasmon resonance (LSPR) in the optical absorption. Different aspects related to the theoretical understanding of LSPRs in `intermediate-size' noble-metal clusters are studied in this thesis. To gain a broader perspective both the real-time \ai formalism of \td density-functional theory (RT-TDDFT) and the classical electromagnetics approach are employed. A systematic and detailed comparison of these two approaches highlights and quantifies the limitations of the electromagnetics approach when applied to quantum-sized systems. The differences between collective plasmonic excitations and the excitations involving $d$-electrons, as well as the interplay between them are explored in the spatial behaviour of the corresponding induced densities by performing the spatially resolved Fourier transform of the time-dependent induced density obtained from a RT-TDDFT simulation using a $\delta$-kick perturbation. In this thesis, both bare and ligand-protected noble-metal clusters were studied. In particular, motivated by recent experiments on plasmon emergence phenomena, the TDDFT study of Au-Cu nanoalloys in the size range just below 2~nm produced subtle insights into the general effects of alloying on the optical response of these systems
9
Zhang, Chaofan. « Multicomponent Clusters/Nanoparticles : An Investigation of Electronic and Geometric Properties by Photoelectron Spectroscopy ». Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-205651.
Texte intégralRésumé :
Clusters/nanoparticles are aggregates of a “small” number of building blocks, atoms or molecules, ranging from two up to millions of atoms. Two main groups of clusters have been studied using photoelectron spectroscopy based on synchrotron radiation. They are dry/wet alkali-halide clusters, including pure water clusters, and metal-based nanoparticles. For the dry alkali halide clusters, analysis of the data and theoretical modeling has allowed us insights into the local electronic properties at nanoscale: a change of polarizability of ions in the alkali-halide clusters due to the varying environment has been suggested. The study of the wet salt clusters shows that the alkali-halides are already solvated at the nanoscale reached by water clusters doped with salt vapor. The photoelectron angular distribution of water cluster shows lower anisotropy parameters as compared to the separate monomers. A model based on intracluster scattering has been built to partly explain the reduction. In the last part of the thesis, metal-based multi-component nanoparticles have been produced by self-assembly processes using reactive magnetron sputtering. Depending on the specific metal element, oxidation processes have been applied before or after the aggregation. Clearly radial distributions such as core-shell and “sandwich-like” structures have unambiguously determined by photoelectron spectroscopy.
10
Woodruff, Daniel. « Organometallic and metal-amide precursors for transition metal and lanthanide cluster complexes with interesting electronic an magnetic properties ». Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/organometallic-and-metalamide-precursors-for-transition-metal-and-lanthanide-cluster-complexes-with-interesting-electronic-an-magnetic-properties(d35cea40-6e84-4d19-ba6a-7a7fe1e4a135).html.
Texte intégralRésumé :
This project exploited the Brönsted basicity of the organometallic/metal-amide compounds,MnCp2 and Ln[N(SiMe3)2]3·LiCl(THF)3 (Ln = Gd, Tb and Dy) in attempts to synthesizepolymetallic cluster compounds via deprotonation of X-H (X = N or S) bond containing proligands.The chemical, electronic and magnetic properties of the resulting compounds werestudied with a variety of methods.The reaction of Ln[N(SiMe3)2]3·LiCl(THF)3 (Ln = Gd, Tb and Dy) with EtSH yieldsa series of [{Ln(N(SiMe3)2)(μ2-SEt)2}4(μ3-SEt)][Li(THF)4] “Ln4” squares in which theterbium and dysprosium analogues show SMM behaviour in zero field, with the dysprosiumanalogue displaying a fast relaxation process which can be “switched off” by the applicationof a 2000 Oe external field.Reactions of MnCp2 with Me3SiNP(NHR)3 (R = nPr, Cy, tBu) afforded a series ofcompounds; [CpMn{Me3SiN=P(NHnPr)2(μ-NnPr)}]2, [Mn{Me3SiN=P(NHCy)2(NCy)}2]and [CpMn{Me3SiN=P(NHtBu)2(NtBu)}]. Q-band EPR studies of these complexes revealthat altering the R group attached to the ligand causes a variation in coordination geometryaround the manganese centers and as such alters the electronic properties of the manganesecentres present in each complex.In order to avoid the synthesis of potentially unstable organometallic/metal-amideprecursors, one pot synthetic methodologies were developed to allow the isolation a series ofμ8-oxo centred Li7M cubes [MLi7(μ8-O)(μ-hpp)6]+ (M = Co, Mn and Zn). Addition ofstiochiometric amounts of water to the initial reaction mixture produced the Li7M cubes inhigh yields.Extension of the one pot synthetic strategy to the use of DyCl3 and YbCl3 inreactions with Li-TMP (TMP = 2,2,6,6-tetramethylpipiridine) afforded the lanthanidedimers [Ln(TMP)2(μ-OEt)]2 (Ln = Dy and Yb) in which the EtO- ligands were formed via insitu ether cleavage and the dysprosium analogue shows SMM behaviour under a 7000Oeapplied field.
11
Mikkelä, M. H. (Mikko-Heikki). « Experimental study of nanoscale metal clusters using synchrotron radiation excited photoelectron spectroscopy ». Doctoral thesis, University of Oulu, 2013. http://urn.fi/urn:isbn:9789526200798.
Texte intégralRésumé :
Abstract
In this work an experimental study of size varied, neutral, and free metal clusters using synchrotron radiation excited photoelectron spectroscopy was performed. The combined core-level and valence photoelectron spectroscopic investigation indicates metallic properties for nanoscale Rb, K, Sn, and Bi clusters. In the case of Sn the experimental results suggest a metal-to-insulator transition occurring at the studied size range. In addition to the experimental results the technical implementation of the cluster production set-up is presented and jellium-model-based simulations are compared with the experimental results of the Rb and K clusters.
12
López, Fernández Xavier. « Theoretical Study of the Basicity and the Redox Properties of Heteropolyanions ». Doctoral thesis, Universitat Rovira i Virgili, 2003. http://hdl.handle.net/10803/9069.
Texte intégralRésumé :
La tesi que porta per títol "Theoretical Study of the Basicity and the Redox Properties of Heteropolyanions" ofereix informació complementària a la comunitat científica relacionada amb la química de coordinació amb metalls de transició en general, i particularment a experts en òxids metàl·lics d'elevada nuclearitat, o polioxometal·lats (POMs). Els POMs poden encapsular selectivament espècies iòniques i catalitzar força reaccions orgàniques, també són agents blanquejadors de la polpa de fusta respectuosos amb el medi ambient, funcionen com a membranes, sensors, etc. En el futur, podrien ser aplicats amb èxit en medecina ja que estan sent testats com a agents antivirals. La llista de possibles aplicacions és interminable. Sigui com sigui, molts grups estan treballant per explotar les propietats d'aquests òxids metàl·lics. Per tant, un coneixement acurat de les propietats fonamentals dels POMs és necessari si els experimentalistes volen desenvolupar noves tecnologies.La pràctica totalitat dels resultats presentats en la memòria han estat obtinguts amb mètodes de càlcul mecano-quàntics d'alt nivell. La tècnica més àmpliament utilitzada ha estat el mètode relacionat amb la teoria del funcional de la densitat. Aquesta eina, d'ús rutinari des de fa uns pocs anys, s'ha convertit en la preferida per al càlcul de sistemes de gran mida com els POMs. Els principals temes abordats en aquest treball estan relacionats amb l'estructura electrònica d'alguns heteropolianions (HPAs). Aquests es caracteritzen per posseir dos tipus estructurals d'àtoms a part dels lligands oxo: el(s) central(s) i els perifèrics. Dintre d'aquest subgrup dels POMs, s'han investigat les propietats de les dues estructures més comuns: l'anió de Keggin (XM12O40n) i el de WellsDawson (X2M18O62m), així com alguns derivats. Han estat estudiades sèries amb diferents metalls perifèrics (anomenats addenda), metalls centrals (heteroàtoms), isòmers i estructures, de manera que s'han traçat conclusions valuoses i extrapolables a altres sistemes no estudiats. Aquesta classe de POMs presenta una seqüència d'orbitals moleculars peculiar. Els seus orbitals frontera han estat analitzats detalladament per un grup ampli de compostos. S'ha posat especial èmfasi en conèixer la relació entre els orbitals metàl·lics (normalment buits) i les propietats redox dels HPAs. Un dels èxits del treball ha estat explicar de forma inequívoca i general les tendències en els potencials de reducció segons la composició química d'una espècie, així com el comportament dels electrons metàl·lics―(des)localització. Val a dir que, en la gran majoria dels casos, s'ha trobat una concordància molt bona amb les dades experimentals.
El segon gran tema abordat en la tesi és la basicitat dels HPAs. En un compost tipus XxMmOyn existeixen diverses posicions oxo, les quals no sempre són equivalents químicament. La seva basicitat pot ésser, doncs, diferent. Un estudi realitzat sobre una sèrie de compostos amb metalls mesclats ha donat escales relatives de basicitat, estimades a partir de la funció potencial electrostàtic, així com a partir d'energies de protonació. S'ha mostrat que els lligands oxo bicoordinats a metalls solen ser els més bàsics, mentre que els oxígens terminals són, generalment, els menys bàsics. Els processos de dimerització en anions de Keggin solen tenir lloc en medi àcid. Aquests passen per una protonació dels monòmers i s´han abordat en dos casos. L'objectiu era mostrar possibles mecanismes de reacció del procés.
El tractament teòric dels POMs és encara en la seva etapa inicial, probablement per les dificultats intrínseques associades al càlcul d'aquestes espècies. Aquestes són, des del punt de vista computacional, molècules grans. A més, degut a que són òxids de metalls de transició, acostumen a ser anions altament carregats amb, de vegades, estats electrònics de capa oberta. Els resultats recopilats en la tesi són una prova de que el DFT ha estat hàbilment aplicat a l'estudi dels POMs.
The thesis titled "Theoretical Study of the Basicity and the Redox Properties of Heteropolyanions" offers complementary information to the scientific community concerned to coordination chemistry with transition metals in general, and particularly to experts in high-nuclearity metal oxide compounds. They are the so-called polyoxometalates (POMs). POM species can encapsulate selectively some ionic species as well as catalyse many organic reactions. They are also environmentally-friendly wood pulp bleaching agents, they work as membranes, sensors, etc. In the close future, they could be successfully applied to medicine since they were tested as antiviral agents. The full list of possible applications is endless. Be that as it may, many groups are working with the aim of exploiting the properties of these metal oxides. Thus, an accurate knowledge of their fundamental properties is necessary if experimentalists are to develop new POM-related technologies.
The great majority of the results presented in the thesis were obtained by means of high-performance quantum-mechanics computational methods. The most amply utilised tool in this study was the method derived from the density function theory. This tool, only recently utilised routinely, has arisen as the preferred one for computing molecular systems of large size as POMs are. The main topics studied in this work are related to the electronic structure of some heteropolyanions (HPAs). They are characterised by possessing two structural types of atoms, a part from oxo ligands: the central and the peripheral atoms. Within this subset of POMs, the two most common structures were studied: the Keggin (XM12O40n) and the WellsDawson (X2M18O62m) anions, and some of their derivatives, as well. Large series of compounds with varying peripheral atoms (also known as addenda), central metals (heteroatoms), isomers and frameworks, so that we traced valuable conclusions, extrapolable to other systems not studied here. This class of POMs features a particular molecular orbitals sequence. Their frontier orbitals were carefully analysed for a wide set of compounds. We especially stressed the connection between the metal orbitals (normally empty) and the redox properties of HPAs. One of the successes of the work was to explain unequivocally and in a general way the trends in the reduction potentials depending on the chemical composition of a given species, as well as the behaviour of metal electrons―(de)localisation. It is worth noting that, in virtually all cases, we found a fair accordance of our results with experimental data.
The second great topic studied in the thesis is the basicity of HPAs. In a compound like XxMmOyn there exist different oxo positions which are not always chemically equivalent. Their basicity might be, then, different. The study carried out for a series of mixed-addenda molecules gives relative basicity scales, estimated from the electrostatic potential function and from protonation energies. It has been showed that the oxo ligands coordinated to two metals are more basic than terminal position, which in general are the least basic. The dimerisation processes in Keggin anions take place, normally, in acidic media. They occur after protonation of the monomers and were investigated for two cases. The goal was to show possible reaction mechanisms for the process.
The theoretical treatment of POMs is still in its initial steps, probably due to the intrinsic difficulties associated to the calculation of such species. They are, from a computational point of view, large molecules. In addition, because they are transition-metal oxides, they are highly charged anions that, sometimes, display open-shell electronic states. The compilation of results of the thesis is a proof that the DFT have been skilfully applpied to the study of POMs.
13
Thang, Yang [Verfasser], Rainer [Akademischer Betreuer] Beckert et Lothar [Akademischer Betreuer] Dunsch. « Metal nitride cluster as a template to tune the electronic and magnetic properties of rare-earth metal containing endohedral fullerenes / Yang Thang. Gutachter : Rainer Beckert ; Lothar Dunsch ». Jena : Thüringer Universitäts- und Landesbibliothek Jena, 2014. http://d-nb.info/1048047288/34.
Texte intégral
14
Sameera, W. M. C. « Electronic structure of transition metal ions and clusters ». Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/1389/.
Texte intégralRésumé :
This thesis uses density functional theory (DFT) to explore the electronic structure and reaction mechanisms of open-shell transition metal ions and clusters. The early part of the thesis (Chapters 2 and 3) is devoted to high-valent metal-oxo species, both mono- and bimetallic, while Chapter 4 describes some aspects of copper-catalysed carbon-carbon bond formation. Finally, Chapter 5 highlights the role of DFT in computing magnetic and spectroscopic properties of exchange-coupled iron clusters. Whilst the chemistry contained in the thesis is rather diverse, the underlying theme of open-shell transition metal ions is common to all chapters. Moreover, we are primarily concerned with the ways in which interactions between two or more adjacent open-shells (either two metals or a metal and a ligand radical) control structure and reactivity. After a brief introduction to relevant theoretical aspects in Chapter 1, we use Chapter 2 to establish a link between the electronic structure of the high-valent Mn(V)=O porphyrin monomer species and their ability to perform oxidation reactions. The reaction profiles for oxidation of a range of substrates depend critically on the electronic structure of the isolated oxidant. Where the electronic ground state is genuinely best described as Mn(V)=O, the interaction between oxidant and substrate is repulsive at large separations, only becoming attractive when the incoming nucleophile approaches close enough to drive an electron out of oxide p manifold. In contrast, where the ground state is better described as an oxyl radical form, Mn(IV)-O.+, the oxidation occurs in sequential one-electron steps, the first of which is barrierless. In Chapter 3, we extend these ideas to bimetallic systems, where the presence of two high-valent manganese centres allows the system to oxidise water. Specifically, we focus on two model systems which have been shown to oxidise water, a Mn-porphyrin-based system synthesised by Naruta and a Mn-based system reported by McKenzie where the ligands contain a mixture of pyridine and carboxylate donors. In both cases, we again find that the emergence of oxyl radical character is the key to the reaction chemistry. However, the radical character is ‘masked’ in the electronic ground states, either by transfer of an electron from the porphyrin ring (Naruta) or by formation of a di-μ-oxo bridge (McKenzie system). In Chapter 4 we turn our attention to copper chemistry, and the role of copper complexes in catalysing atom transfer radical additions (Kharasch additions). In this reaction, the copper cycles between Cu(I) and Cu(II) oxidation states, and the result is the formation of a new C-C bonds. This Chapter makes extensive use of hybrid QM/MM techniques to model the environment of the copper centre in the target polypyrazolylborate-copper complexes (TpxCu). Finally, in Chapter 5 we consider the electronic structure, magnetic and spectroscopic properties of a pair of exchange-coupled Fe3 clusters, [Fe3(μ3-O)(μ-4-O2N-pz)6X3]2- (where pz = pyrazolato, X = Cl, Br). Our primary goal was to establish how well broken-symmetry DFT is able to reproduce the observed Mössbauer spectroscopic parameters, which are extensively used to identify the chemical environments of iron species and, in the case of mixed-valence clusters, to establish the degree of delocalisation of the additional electrons. In recent years DFT has proved able to compute these parameters with encouraging accuracy, but it is not clear to what extent the known deficiencies in broken-symmetry wavefunctions will compromise this ability. Our work suggests that neither the isomer shift nor the quadrupole splitting are strongly influenced by the nature of the coupling between the metal ions, suggesting that broken-symmetry solutions can be used as a basis for computing these parameters in more complex clusters.
15
Sowrey, Frank Edward. « Electronic and magnetic coupling in triangular metal clusters ». Thesis, University of East Anglia, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338298.
Texte intégral
16
Thompson, Jeffrey M. « The electronic structure and spectra of small metal clusters / ». Thesis, Connect to this title online ; UW restricted, 1998. http://hdl.handle.net/1773/9648.
Texte intégral
17
KerherveÌ, Gwilherm. « Production and properties of metal clusters on alumina ». Thesis, University of Liverpool, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288300.
Texte intégral
18
Wu, Lu. « STRUCTURES AND ELECTRONIC STATES OF SMALL GROUP 3 METAL CLUSTERS ». UKnowledge, 2014. http://uknowledge.uky.edu/chemistry_etds/32.
Texte intégralRésumé :
Group 3 metal clusters are synthesized by laser vaporization in a pulsed cluster beam source and identified with laser ionization time-of-flight mass spectrometry. The adiabatic ionization energies and vibrational frequencies of these clusters are measured using mass-analyzed threshold ionization (MATI) spectroscopy. Their structures and electronic states are determined by combining the MATI spectra with quantum chemical calculations and spectral simulations. This dissertation focuses on the study of several small molecules, which include LaO2, La2, M2O2, M3O4, M3C2, and La3C2O, where M = Sc, Y, and La. Except for La2, these molecules exhibit strong ionic characters between the metal and oxygen or carbon atoms and can be described as [O-][La2+][O-], [M2+]2[O2-]2, [M8/3+]3[O2-]4, [M2+]3[C3-]2, and [La8/3+]3[C3-]2[O2-]. The interactions between the metal atoms form covalent bonds, which can be described by a triple bond in La2, a two-center two electron bond in M2O2, a three-center one electron bond in M3O4, and a three-center three electron bond in M3C2. In addition, the electron in the non-bonding highest occupied molecular orbital (HOMO) is localized in the La 6s orbital in LaO2 and La3C2O. The ground states of these molecules are all in low electron-spin states with the spin multiplicities of 1 or 2. Although the ground electronic state of LaO2 is a linear structure, the excited quartet state of the molecule is determined to be a bent structure. M2O2 and M3O4 have the planar rhombic and cage-like structures, respectively; whereas M3C2 has a trigonal bipyramid structure. La3C2O is formed by oxygen binding with two La atoms of La3C2. Ionization removes a metal-based (n+1)s electron in all neutral molecules, and the resultant ions have similar geometries to those of the corresponding neutral states. In the case of La2, additional ionization of a La 5d electron is also observed.
19
Mete, Ersen. « Electronic Properties Of Transition Metal Oxides ». Phd thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1069699/index.pdf.
Texte intégralRésumé :
Transition metal oxides constitute a large class of materials with variety of very interesting properties and important technological utility. A subset with perovskite structure has been the subject matter of the current theoretical investigation with an emphasis on their electronic and structural behavior. An analytical and a computational method are used to calculate physical entities like lattice parameters, bulk moduli, band structures, density of electronic states and charge density distributions for various topologies. Results are
discussed and compared with the available experimental findings.
20
Andersson, Tomas. « Free Metal Clusters Studied by Photoelectron Spectroscopy ». Doctoral thesis, Uppsala universitet, Yt- och gränsskiktsvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-183031.
Texte intégralRésumé :
Clusters are aggregates of a finite number of atoms or molecules. In the present work, free clusters out of metallic parent materials have been created and studied by synchrotron radiation-based photoelectron spectroscopy. The clusters have been formed and studied in a beam and the electronic structure of the clusters has been investigated. Conclusions have been drawn about the spatial distribution of atoms of different elements in bi-component clusters, about the development of metallicity in small clusters, and about the excitation of plasmons. Bi-component alloy clusters of sodium and potassium and of copper and silver have been produced. The site-sensitivity of the photoelectron spectroscopy technique has allowed us to probe the geometric distribution of the atoms of the constituent elements by comparing the responses from the bulk and surface of the clusters. In both cases, we have found evidence for a surface-segregated structure, with the element with the largest atoms and lowest cohesive energy (potassium and silver, correspondingly) dominating the surface and with a mixed bulk. Small clusters of tin and lead have been probed to investigate the development of metallicity. The difference in screening efficiency between metals and non-metals has been utilized to determine in what size range an aggregate of atoms of these metallic parent materials stops to be metallic. For tin this has been found to occur below ~40 atoms while for lead it happened somewhere below 20-30 atoms. The excitation of bulk and surface plasmons has been studied in clusters of sodium, potassium, magnesium and aluminium, with radii in the nanometer range. The excitation energies have been found to be close to those of the corresponding macroscopic solids. We have also observed spectral features corresponding to multi-quantum plasmon excitation in clusters of Na and K. Such features have in macroscopic solids been interpreted as due to harmonic plasmon excitation. Our observations of features corresponding to the excitation of one bulk and one surface plasmon however suggest the presence of sequential excitation in clusters.
21
Bürgel, Christian. « Functionality of noble-metal clusters ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2009. http://dx.doi.org/10.18452/15887.
Texte intégralRésumé :
In dieser Dissertation wurden die ungewöhnlichen und einzigartigen Eigenschaften von Edelmetall-Clustern untersucht, die durch Quantum-Confinement im Sub-Nanometer-Bereich entstehen. Dabei zeigt sich, dass die chemischen und physikalischen Eigenschaften und damit die Funktionen nicht vom Festkörper abgeleitet werden können und stark von der Anzahl der Atome abhängen. Die erzielten theoretischen Ergebnisse wurden in enger Zusammenarbeit mit experimentell arbeitenden Partnergruppen erzielt. Dabei hat sich gezeigt, dass durch die enge Kooperation zwischen Theorie und Experiment ein tiefes Verständnis von fundamentalen Prozessen und den zugrunde liegenden Mechanismen erlangt werden kann. Im Rahmen dieser Dissertation wurden die Reaktivität von geladenen Goldoxid-Clustern in der Gasphase, die ultraschnelle Dynamik von Edelmetall-Clustern und deren Komplexen sowie die optischen Eigenschaften von kleinen, deponierten Silber-Clustern untersucht und damit Beiträge geliefert, die einzigartigen Eigenschaften von Edelmetall-Clustern im Zusammenhang mit der heterogenen Katalyse und Nano-Optik besser zu verstehen.In this thesis, the unique novel properties of noble metal clusters which arise in the sub-nanometer size regime due to quantum confinement have been theoretically explored. It has been demonstrated that by adding or removing a single atom the chemical and physical properties and functionality of noble-metal clusters can strongly change. The theoretical results have been derived in close cooperation with experimental findings of partner groups demonstrating that by joint theoretical and experimental efforts thorough understanding of fundamental processes and underlying mechanisms can be achieved. This thesis addresses the reactivity of charged gas-phase gold-oxide clusters in the context of the heterogeneous gold nano-catalysis, the ultrafast dynamical properties of noble-metal clusters and their complexes, and the optical properties of silver clusters at surfaces.
22
Li, Fen. « Zeolite-supported noble metal clusters : synthesis, characterization, and catalytic properties / ». For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
Texte intégral
23
Yoshii, Takao. « Structures and Electronic Properties of Carbon Clusters and Related Compounds ». Kyoto University, 2001. http://hdl.handle.net/2433/150661.
Texte intégral
24
Gore, Jonathan Geoffrey. « The electronic properties of mixed metal oxides ». Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308532.
Texte intégral
25
Cussen, Edmund John. « The electronic properties of mixed metal oxides ». Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301436.
Texte intégral
26
Blake, Graeme Robert. « The electronic properties of mixed metal iridates ». Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298679.
Texte intégral
27
Gennard, Steven John. « Electronic structure properties of metal oxide surfaces ». Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400570.
Texte intégral
28
Regoutz, Anna. « Structural and electronic properties of metal oxides ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6f425890-b211-4b35-b438-b8de18f7ae64.
Texte intégralRésumé :
Metal oxides are of immense technological importance. Their wide variety of structural and electronic characteristics leads to a flexibility unrivalled by other groups of materials. However, there is still much debate about the fundamental properties of some of the most widely used oxides, including TiO2 and In2O3. This work presents high quality, in-depth characterisation of these two oxides in pure and doped form, including soft and hard X-ray photoelectron spectroscopy and X-ray diffraction. Bulk samples as well as thin film samples were prepared analysed. For the preparation of thin films a high quality sol-gel dip-coating method was developed, which resulted in epitaxial films. In more detail the organisation of the thesis is as follows: Chapter 1 provides an introduction to key ideas related to metal oxides and presents the metal oxides investigated in this thesis, In2O3, Ga2O3, Tl2O3, TiO2, and SnO2. Chapter 2 presents background information and Chapter 3 gives the practical details of the experimental techniques employed. Chapters 4 presents reciprocal space maps of MBE-grown In2O3 thin films and nanorods on YSZ substrates. Chapters 5 and 6 investigate the doping of In2O3 bulk samples with gallium and thallium and introduce a range of solid state characterisation techniques. Chapter 7 describes the development of a dip-coating sol-gel method for the growth of thin films of TiO2 and shows 3D reciprocal space maps of the resulting films. Chapter 8 concerns hard x-ray photoelectron spectroscopy of undoped and Sn-doped TiO2. Chapter 9 interconnects previous chapters by presenting 2D reciprocal space maps of nano structured epitaxial samples of In2O3 grown by the newly developed sol-gel based method. Chapter 10 concludes this thesis with a summary of the results.
29
Cobb, Stephen Hal. « Gas-phase characterization of the molecular electronic structure of metal clusters and metal cluster oxidation ». Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/30417.
Texte intégral
30
Abreu, Marissa B. « Electronic Principles Governing the Stability and Reactivity of Ligated Metal and Silicon Encapsulated Transition Metal Clusters ». VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/3732.
Texte intégralRésumé :
A thorough understanding of the underlying electronic principles guiding the stability and reactivity of clusters has direct implications for the identification of stable clusters for incorporation into clusters-assembled materials with tunable properties. This work explores the electronic principles governing the stability and reactivity of two types of clusters: ligated metal clusters and silicon encapsulated transition metal clusters. In the first case, the reactivity of iodine-protected aluminum clusters, Al13Ix- (x=0-4) and Al14Iy- (y-0-5), with the protic species methanol was studied. The symmetrical ground states of Al13Ix- showed no reactivity with methanol but reactivity was achieved in a higher energy isomer of Al13I2- with iodines on adjacent aluminum atoms – complementary Lewis acid-base active sites were induced on the opposite side of the cluster capable of breaking the O-H bond in methanol. Al14Iy- (y=2-5) react with methanol, but only at the ligated adatom site. Reaction of methanol with Al14- and Al14I- showed that ligation of the adatom was necessary for the reaction to occur there – revealing the concept of a ligand-activated adatom. In the second case, the study focused heavily on CrSi12, a silicon encapsulated transition metal cluster whose stability and the reason for that stability has been debated heavily in the literature. Calculations of the energetic properties of CrSin (n=6-16) revealed both CrSi12 and CrSi14 to have enhanced stability relative to other clusters; however CrSi12 lacks all the traditional markers of a magic cluster. Molecular orbital analysis of each of these clusters showed the CNFEG model to be inadequate in describing their stability. Because the 3dz2 orbital of Cr is unfilled in CrSi12, this cluster has only 16 effective valence electrons, meaning that the 18-electron rule is not applicable. The moderate stability of CrSi12 can be accounted for by the crystal-field splitting of the 3d orbitals, which pushes the 3dz2 orbital up in energy. CrSi14, on the other hand, has 18 effective valence electrons on Cr, minimal 3d-orbital splitting, and does follow the 18-electron rule. A repetition of these calculations with WSin (n=6-16) showed similar results, except WSi12 shows all the markers of a magic cluster, due to the greater crystal-field splitting of 5d orbitals.
31
Dogbevia, Moses K. « Gas phase transition metal-cluster catalysis / ». abstract and full text PDF (free order & ; download UNR users only), 2005. http://0-wwwlib.umi.com.innopac.library.unr.edu/dissertations/fullcit/3209128.
Texte intégralRésumé :
Thesis (Ph. D.)--University of Nevada, Reno, 2005."August, 2005." Includes bibliographical references. Online version available on the World Wide Web. Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2005]. 1 microfilm reel ; 35 mm.
32
Millburn, Julie Elizabeth. « Structural and electronic properties of transition metal oxides ». Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364166.
Texte intégral
33
Jones, Christopher Wynne. « Structural and electronic properties of mixed metal oxides ». Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235645.
Texte intégral
34
Rochford, Luke A. « Structural, electronic and magnetic properties of metal phthalocyanines ». Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/60649/.
Texte intégralRésumé :
Metal phthalocyanines (MPcs) prepared as single crystals, polycrystalline powders and thin films have been analysed using a combination of surface science techniques, diffraction based structural characterisation and magnetic characterisation. Vanadium oxide phthalocyanine (VOPc) prepared as thin films on the (111) surface of gold, silver and copper is analysed by (STM) low energy electron diffraction (LEED) and ultraviolet photoemission spectroscopy (UPS). Similar surface and electronic structure is observed on gold and silver, but profoundly different assembly and electronic properties were observed on copper. The effect of increasing the substrate temperature during growth on the structure and morphology of iron phthalocyanine (FePc) and manganese phthalocyanine (MnPc) is investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). An evaporated copper iodide (CuI) structural template layer is also used to alter the arrangement of FePc molecules in thin films. The single crystal structure of fluorinated copper phthalocyanine (F16CuPc) is re-determined using synchrotron X-ray diffraction. Thin films of F16CuPc grown on graphene oxide supports are analysed using X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). This allows assignment of both crystal structure and texture in polycrystalline thin films of a variety of thicknesses. F16CuPc is also analysed using superconducting quantum interference (SQUID) magnetometry in both powder and thin film morphologies. 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) structural template layers are used to alter the orientation of crystallites and the effect of this on the magnetic properties are analysed.
35
Njoki, Peter Njunge. « Metal and alloy nanoparticles synthesis, properties and applications / ». Diss., Online access via UMI:, 2007.
Trouver le texte intégral
36
Fahlquist, Henrik. « Transition Metal Hydride Complexes and Hydrogenated Gallium Clusters : Synthesis and Structural Properties ». Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-89760.
Texte intégralRésumé :
Synthesis and structural characterisation of metal hydrides in two important systems are presented. The first system presented is low valent cobalt and nickel complex hydrides with the compositions BaMg5Co2H10, RbMg5CoNiH10, SrMg2CoH7and Sr4Mg4Co3H19 featuring nickel with oxidation state of 0 and cobalt with oxidation state +I and -I. The second system presented is polyanionic gallium complex hydrides with the compositions RbGaH2, RbxK(1−x)GaH2 (0.5≤x≤1), CsxRb(8−x)Ga5H15 (0≤x≤8) and Cs10Ga9H25 featuring novel hydrogenous polyanionic gallium hydride clusters mimicking common hydrocarbons. The syntheses of the compounds were performed at elevated temperatures and at moderate hydrogen pressures (50-100 bar). The structural investigations were mainly done by X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD). The metal-hydrogen bond was investigated by vibrational spectroscopy using Fourier Transform IR-spectroscopy (FTIR) and Inelastic Neutron Scattering (INS).By subtle changes in the compositions of the hydrides it was possible to induce major changes in band gaps, oxidation states and structures.At the time for the doctoral defence the following papers were unpublished and had a status as follows: Paper 1: Manuscript; Paper 2: Accepted; Paper 5: Manuscript
37
Aylward, Nigel Nunn. « Studies of electronic and structural properties of molecular clusters of prebiotic importance ». Thesis, Queensland University of Technology, 2006. https://eprints.qut.edu.au/16328/1/Nigel_Aylward_Thesis.pdf.
Texte intégralRésumé :
This thesis applies the ab initio techniques of computational chemistry to studies of molecular clusters containing covalent (strong) or van der Waals (weak) bonds formed in chemistry and biochemistry in the temperature range 10-300 K. Van derWaals complexes with an enthalpy of formation from reactants of less than 25 kJ mol-1 and covalent clusters are described in this thesis.
The first group of van der Waals complexes involved the molecule carbon monoxide that possesses a small permanent dipole that could lead to dipole - induced dipole interaction and dipole - dipole interaction with another reactant in addition to dispersion. The substrates investigated were methanimine and cyanogen where endergonic unstable molecules were formed, and the clustering of carbon monoxideon a porphin surface leading to the formation of carbon - carbon fragments. TheFaraday effect was invoked to suggest that this was the original method by which thechirality of the D-sugars was selected. Coordination of imino-compounds on thesame surface involving induction and electrostatic interactions could lead to the preferential formation of L-aziridones, hydrolysable to L-amino-acids.The preferred formation of D-ribose, and the more stable D-2-deoxyribose, andnucleotides polymerisable to deoxyribonucleic acids was described.
The second group of van der Waals complexes involved the polymerisation of acetylene molecules, to di- and tri-acetylene complexes where the exchange interaction involved the quadrupole moment of the acetylene radical reacting with acetylene or diacetylene. The reaction of carbon monoxide was extended to include its interaction with diacetylene. The entire potential energy surface for the interaction with diacetylene was investigated. The reaction was shown to be endergonic to produce a reactive species, here postulated to rearrange with a reasonable activation energy toform an aldehyde. The energetics of the formation of diacetylene, triacetylene andhigher polymers was briefly investigated. The reactivity of the acetylene polymeraldehydes with other substrates was briefly investigated.
This work has apparently laid a firm basis both, qualitative and quantitative, tounderstand some of the weakest interactions in nature involving the simplest ofreactions that have been important in atmospheric chemistry.
38
Aylward, Nigel Nunn. « Studies of electronic and structural properties of molecular clusters of prebiotic importance ». Queensland University of Technology, 2006. http://eprints.qut.edu.au/16328/.
Texte intégralRésumé :
This thesis applies the ab initio techniques of computational chemistry to studies of molecular clusters containing covalent (strong) or van der Waals (weak) bonds formed in chemistry and biochemistry in the temperature range 10-300 K. Van derWaals complexes with an enthalpy of formation from reactants of less than 25 kJ mol-1 and covalent clusters are described in this thesis. The first group of van der Waals complexes involved the molecule carbon monoxide that possesses a small permanent dipole that could lead to dipole - induced dipole interaction and dipole - dipole interaction with another reactant in addition to dispersion. The substrates investigated were methanimine and cyanogen where endergonic unstable molecules were formed, and the clustering of carbon monoxideon a porphin surface leading to the formation of carbon - carbon fragments. TheFaraday effect was invoked to suggest that this was the original method by which thechirality of the D-sugars was selected. Coordination of imino-compounds on thesame surface involving induction and electrostatic interactions could lead to the preferential formation of L-aziridones, hydrolysable to L-amino-acids.The preferred formation of D-ribose, and the more stable D-2-deoxyribose, andnucleotides polymerisable to deoxyribonucleic acids was described. The second group of van der Waals complexes involved the polymerisation of acetylene molecules, to di- and tri-acetylene complexes where the exchange interaction involved the quadrupole moment of the acetylene radical reacting with acetylene or diacetylene. The reaction of carbon monoxide was extended to include its interaction with diacetylene. The entire potential energy surface for the interaction with diacetylene was investigated. The reaction was shown to be endergonic to produce a reactive species, here postulated to rearrange with a reasonable activation energy toform an aldehyde. The energetics of the formation of diacetylene, triacetylene andhigher polymers was briefly investigated. The reactivity of the acetylene polymeraldehydes with other substrates was briefly investigated. This work has apparently laid a firm basis both, qualitative and quantitative, tounderstand some of the weakest interactions in nature involving the simplest ofreactions that have been important in atmospheric chemistry.
39
Tallarida, Massimo. « Electronic properties of semiconductor surfaces and metal, semiconductor interfaces ». [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2005/196/index.html.
Texte intégral
40
Warren, Rachel Frances. « Optical, electronic and structural properties of metal halide intercalates ». Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333365.
Texte intégral
41
Seo, Jiwon. « Electronic and magnetic properties of transition metal oxide heterostructures ». Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611390.
Texte intégral
42
Nazarzadehmoafi, Maryam. « Electronic properties of metal-In 2 O 3 interfaces ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2017. http://dx.doi.org/10.18452/17771.
Texte intégralRésumé :
Das Verhalten der elektronischen Eigenschaften von gespaltenen, aus der Schmelze gezüchteten In2O3-(111) Kristallen wurde bei Deposition von Edelmetallen, In und Sn mittels winkelaufgelöster Photoelektronen-Spektroskopie untersucht. Die Stöchiometrie, strukturelle Qualität und Kristall-Orientierung, die Oberflächenmorphologie und die Elektronenkonzentration wurden jeweils mittels energiedispersiver Röntgenspektroskopie, Laue-Beugung, Raster Tunnel-Mikroskopie (STM) und Hall-Effekt untersucht. Die Ähnlichkeit der fundamentalen und Oberflächen-Bandlücken kann auf das fast flache Verhalten der Bänder auf der gespaltenen Oberfläche der Kristalle zurückgeführt werden. Die Grenzflächen von Ag und Au/In2O3 zeigen Schottky-Verhalten, während ein ohmscher in Cu, In und Sn /In2O3-Kontakten beobachtet wurde. Aufgrund der Übereinstimmung zwischen optischen und Oberflächen-Bandlücken, der Bildung eines Gleichrichterkontaktes und des Auftretens der Oberflächenphotospannung auf der frischen Kristalloberfläche kann gefolgert werden, dass SEAL nicht eine intrinsische Eigenschaft der gespaltenen Oberfläche der untersuchten Kristalle ist. Des Weiteren wurden bei dicker Au- und Cu-Beschichtung von In2O3 bei Raumtemperatur Shockley-artige Oberflächenzustände beobachtet. Zusätzlich wurde die erste Phase des Wachstums von Cu und In auf In2O3 von der Ausbildung eines 2-dimensionalen Elektrongases (2DEG) begleitet, welches bei dickeren Schichten verschwand, die von dem auf reinen Oberflächen von dünnen In2O3- Filmen gemessenen 2DEG verschieden sind. Nach Messung der Austrittarbeit von In2O3 und den jeweils untersuchten Metallen in situ und unter Verwendung der Schottky-Mott-Regel trat außer bei Ag/In2O3 eine deutliche Abweichung auf. Die experimentellen Ergebnisse stimmen auch mit fortgeschrittenen Theorien, die auf dem Elektronegativitätskonzept und MIGS–Modellen basieren, nicht überein.The behavior of the electronic properties of as-cleaved melt-grown In2O3 (111) single crystals was studied upon noble metals, In and Sn deposition using angle-resolved photoemission spectroscopy. The stoichiometry, structural quality and crystal orientation, surface morphology, and the electron concentration were examined by energy dispersive X-ray spectroscopy, Laue diffraction, scanning tunneling microscopy (STM), and Hall-effect measurement, respectively. The similarity of the measured-fundamental and surface-band gaps reveals the nearly flat behavior of the bands at the as-cleaved surface of the crystals. Ag and Au/In2O3 interfaces show Schottky behavior, while an ohmic one was observed in Cu, In, and Sn/In2O3 contacts. From agreement of the bulk and surface band gaps, rectifying contact formation as well as the occurrence of photovoltage effect at the pristine surface of the crystals, it can be deduced that SEAL is not an intrinsic property of the as-cleaved surface of the studied crystals. Moreover, for thick Au and Cu overlayer regime at room temperature, Shockley-like surface states were observed. Additionally, the initial stage of Cu and In growth on In2O3 was accompanied by the formation of a two dimensional electron gas (2DEG) fading away for higher coverages which are not associated with the earlier-detected 2DEG at the surface of In2O3 thin films. The application of the Schottky-Mott rule, using in situ-measured work functions of In2O3 and the metals, showed a strong disagreement for all the interfaces except for Ag/In2O3. The experimental data also disagree with more advanced theories based on the electronegativity concept and metal-induced gap states models.
43
李軼 et Yat Li. « Syntheses, structural characterization and electrochemistry of tetraosmium carbonyl clusters and catalytic properties of tetraosmium-gold mixed-metal clusters ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243356.
Texte intégral
44
Li, Yat. « Syntheses, structural characterization and electrochemistry of tetraosmium carbonyl clusters and catalytic properties of tetraosmium-gold mixed-metal clusters / ». Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25155064.
Texte intégral
45
Krämer, Tobias. « Electronic structure of open-shell transition metal complexes ». Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:1f4a1330-281d-4696-b3e6-62b76fb41d65.
Texte intégralRésumé :
This thesis presents electronic structure calculations on problems related to the bonding in inorganic coordination compounds and clusters. A wide range of molecules with the ability to exist in different structural forms or electronic states has been selected and density functional theory is systematically applied in order to gain detailed insight into their characteristics and reactivity at the electronic level. First, we address the question of redox non-innocent behaviour of bipyridine in a series of 1st row transition metal complexes. Complexes of the type [M(2,2'-bipyridine)(mes)₂]0 (M = Cr, Mn, Fe, Co, Ni; mes = 2,4,6-Me₃C6H₂) and their one-electron reduced forms have been explored. The results clearly show that the anions are best described as complexes of the monoanionic bipyridine radical (Sbpy = 1/2), giving a rationale for the observed structural changes within the ligand. Likewise, we have identified dianionic bipyridine in both the complexes [Zn2(4,4'-bpy)(mes)₄]²− and [Fe(2,2'-bpy)₂]²−. In no case have we found evidence for significant metal-to-ligand backbonding. The subject of redox-noninnocence is further revisited in a comparative study of the two complexes [M(o-Clpap)₃] (M = Cr, Mo; o-Clpap = 2-[(2-chloro-phenyl)azo]-pyridine), and their associated electron transfer series. The results indicate that all electron transfer processes are primarily ligand-based, although in the case of the Mo analogue these are coupled to substantial electron density changes at the metal. The ability of pap to form radical anions finds a contrasting case in the di- nuclear Rh complex [Rh₂(μ-p-Clpap)₂ (cod)Cl₂], where the two ligand bridges act as acceptors of strong dπ∗ backbonding from a formally Rh–I centre. We then direct our attention to the endohedral Zintl clusters [Fe@Ge10]³− and [Mn@Pb12]³−, which reveal peculiar topologies. We have probed the electronic factors that influence their geometric preferences, and propose a model based on the shift of electron density from the endo- hedral metal to the cage to account for the observed geometries. Subsequently, we reassess the electronic structure of the xenophilic clusters Mn₂(thf)₄(Fe(CO)₄)₂ and [Mn(Mn(thf)₂)₃(Mn(CO)₄)₃]–. We conclude that these are best viewed as exchange coupled MnII centres bridged by closed- shell carbonylate fragments. In the closing chapter the reduction of NO₂– to NO by the complex [Cu(tct)(NO₂)]+ (tct = cis,cis-1,3,5-tris(cinnamylideneamino)cyclohexane) is studied, a process that mimics the enzyme-catalysed reaction. Two viable pathways for the reaction have been traced and key inter-mediates identified. Both direct release of NO or via decomposition of a Cu-NO complex are kinetically and thermodynamically feasible.
46
Schelter, Eric John. « Cyanide clusters of ReII with 3d metal ions and their magnetic properties : incorporating anisotropic ions into metal-cyanide clusters with high spin magnetic ground states ». Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/2205.
Texte intégralRésumé :
Clusters of metal ions that possess large numbers of magnetically coupled unpaired electrons have attracted much interest in recent years due to their fascinating magnetic behavior. With an appreciable component of magnetic anisotropy, these large-spin paramagnetic molecules can exhibit an energy barrier to inversion of their magnetic dipole, leading to spontaneous magnetization and magnetic hysteresis below a critical temperature. Since this behavior is a property of an individual clusters rather than a collection of molecules, this phenomenon has been dubbed ??Single Molecule Magnetism??. Our approach to the study of new high-spin systems has been to exert a measure of synthetic control in the preparation of clusters. Specifically we are employing highly anisotropic metal ions with the anticipation that these ions would engender large overall magnetic anisotropy in the resulting clusters. The first step in this process was the development of the chemistry of two new d5 ReII (S = ??) complexes, namely [ReII(triphos)(CH3CN)3][PF6]2 and [Et4N][ReII(triphos)(CN)3]. The magnetic, optical and electrochemical properties were studied and theoretical models were developed to describe the origin of the large temperature independent paramagnetism that was observed. Next, we successfully employed transition metal cyanide chemistry using the ReII building blocks to prepare a family of isostructural, cubic clusters of the general formula {[MCl]4[Re(triphos)(CN)3]4} M = Mn, Fe, Co, Ni, Cu, Zn whose 3d ions adopt local tetrahedral geometries. Within the clusters, magnetic exchange is observed between the paramagnetic ions, which has been modeled using an Ising exchange model to account for the dominating anisotropy of the ReII ion. Despite the high pseudo-symmetry of the clusters (Td), this work has yielded a rare example of a metal-cyanide single molecule magnet, {[MCl]4[Re(triphos)(CN)3]4} with an S = 8 ground state, D = -0.39 cm-1 and an effective energy barrier for magnetization reversal of Ueff = 8.8 cm-1. The elucidation of this family of isostructural clusters has also allowed us to pursue fundamental work on the structure/property relationships of the exotic, paramagnetic ReII ion. As the clusters are soluble, stable compounds, the future of this chemistry lies in the development of a true building-block approach to ??super-clusters?? that exhibit very high ground state spin values.
47
Drewery, J. S. « The electronic transport properties of amorphous metallic alloys ». Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233897.
Texte intégralRésumé :
Amorphous metals have been studied extensively recently and possess many interesting electronic properties. This thesis aims to examine some of these, with particular reference to the conductivity and Hall effect in such alloys. In an extensive review of recent theoretical and experimental work, the author attempts to examine (i) whether the data can be explained using the 'semi-classical' theory of transport, with the inbuilt assumption that the electron loses memory of all collisions before that immediately preceding the time of observation, or whether 'quantum interference' and 'electron correlation phenomena must be considered, and (ii) whether it is possible to provide a simple physical picture of such quantum interference phenomena which leads to results commensurate with those of formal theories and with experimental results. A good probe of electron correlation effects is the temperature dependence of the Hall coefficient. In conjunction with the conductivity a good idea of the importance of such phenomena can be obtained. The succeeding chapters discuss the rebuilding of a radio frequency sputtering system suitable for production of thin amorphous metal films, and the methods used in making high precision measurements of the properties mentioned, between 1.25 and 300K. A results chapter reports data taken on the Cu-Ti and Ni-Zr systems, which were chosen as representative transition metal - transition metal alloy systems showing a wide range of behaviour. Extensive analysis of these data is undertaken, in terms of quantum interference and other theories. The effects of clustering of magnetic centres, and of superconductivity, in Ni-Zr films, is discussed. It is shown that the results are in broad agreement with these theories and first evidence is presented that electron correlation phenomena may be affected by inelastic electron scattering at intermediate temperatures. Confirmation of a simple relationship between the change in Hall coefficient and of conductivity due to electron correlation, predicted by theory, is provided. A short conclusion makes suggestions for future experimental work.
48
Chapman, Richard G. « Structure and electronic properties of expanded alkali fluids ». Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329925.
Texte intégral
49
Mulley, James Stephen. « Electronic, spectroscopic and interface properties of two transition metal oxides ». Thesis, University of Reading, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.533743.
Texte intégral
50
Branford, William Richard. « Relationship of structural and electronic properties in transition metal oxides ». Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407974.
Texte intégral