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Ce travail de thèse porte sur l’étude théorique de la fragmentation de petits agrégats carbonés et d’hydrocarbures neutres par le modèle statistique Micarocanonical Metropolis Monte Carlo (MMMC). Ce modèle décrit, à contrainte d’énergie fixée, l’espace des phases associé à tous les degrés de liberté accessibles au système (partitions des masses, mouvements de translation et de rotation, spin et moment angulaire des fragments, etc.). Les ingrédients de base du modèle (énergies de dissociation, géométries, fréquences de vibration etc.) doivent être obtenus par un calcul ab initio. Ils ont été calculés à l’aide de la théorie de la fonctionnelle de la densité (DFT) au niveau de calcul B3LYP/6-311+G(3df). Les probabilités obtenues des voies de fragmentation en fonction de l’énergie d’excitation, ont été comparées aux données expérimentales obtenues auprès du Tandem. Des faisceaux de haute vitesse (projectile de Cn+ à v = 2.6 u.a. et de CnH+ à v = 4.5 u.a.) entraient en interaction avec les noyaux d’hélium. Tous les rapports de branchement des voies de fragmentation des Cn (n ≤ 9) et des CnH (n ≤ 4) résultant de capture électroniques ont été mesurés. La distribution d’énergie d’excitation de l’agrégat parent a du être ajustée pour que les mesures expérimentales soient reproduites d’une façon optimale, à l’aide de deux algorithmes : Non-Negative Least Squares et backtracing Bayesien. La comparaison des probabilités théoriques et expérimentales montre un bon accord global. Les deux algorithmes de minimisation ont convergé vers des distributions d’énergie déposée présentant des pics. Ces pics pourraient être la signature d’états moléculaires spécifiques jouant un rôle dans la fragmentation du cluster. / This thesis deals with the theoretical study of the fragmentation of small neutral carbon and hydrocarbon clusters using a statistical model called Microcanonical Metropolis Monte Carlo (MMMC). This model describes, at a given energy, the phase space associated with all the degrees of freedom accessible to the system (partition of the mass, translation and rotation, spin and angular momentum of the fragments, etc.). The basic ingredients of the model (cluster geometries, dissociation energies, harmonic frequencies, etc.) are obtained, for both the parent cluster and the fragments, by an ab initio calculation. These parameters were calculated using the density functional theory (DFT) at the B3LYP/6-311+G(3df) level. The results obtained for the probabilities of the fragmentation channels as a function of the excitation energy, were compared with the experimental data obtained at the Orsay Tandem. High velocity cluster beams (v = 2.6 u.a. Cn+ and v = 4.5 u.a. CnH+ projectiles) interacted with helium atoms. All the branching ratios of the fragmentation channels of Cn (n ≤ 9) and CnH (n ≤ 4) resulting from electron captures were measured. The deposited energy distributions were adjusted so that the experimental measurements were optimally reproduced. Two algorithms were used: Non-Negative Least Squares and Bayesien backtracing. The comparison of the theoretical and experimental probabilities shows a good global agreement. Both algorithms result in deposited energy distributions showing peaks. These peaks could be the signatures of specific molecular states which may play a role in the cluster fragmentation.

In this thesis, graphene (i.e. monolayer carbon film) and carbon clusters supported on a transition metal surface are systematically studied by local probe techniques, with respect to their structures, electronic properties and formation mechanisms. The main tools used are low-temperature scanning tunnelling microscopy and spectroscopy (STM and STS), which are introduced in Chapter 2. The mechanism of the resonance tunnelling at electron energies higher than the work function of the surface is discussed in detail, and a qualitative explanation of the Gundlach oscillations in the corresponding spectroscopy is presented. Epitaxial graphene synthesised on the Rh(111) surface by ethylene dehydrogenation is investigated by STM in Chapter 4. Such carbon film exhibits a hexagonal Moiré pattern due to a lattice mismatch between graphene and the rhodium substrate. The periodicity and local registries of the graphene/Rh(111) superstructure are carefully analysed. Based on a thorough discussion about the “commensurate vs. incommensurate” nature of the Moiré pattern in surface science field, the graphene/Rh(111) system is identified to have a non-simple-commensurate superstructure. The surface electronic properties and geometric buckling of graphene/Rh(111) are investigated by resonance tunnelling spectroscopy (RTS) and density functional theory (DFT) calculations in Chapter 5. Spectroscopy measurements reveal a modulation of the electronic surface potential (or work function Φ) across the supercell of epitaxial graphene. Based on the microscopy/spectroscopy data and the extended DFT calculations, we examined the electronic coupling of the various local C-Rh registries, and identified both experimentally and theoretically the local atomic configurations of maximum and minimum chemical bonding between graphene and the rhodium substrate. We studied in Chapter 6 the growth mechanism of graphene on Rh(111) at elevated temperatures. This part starts by investigating the dehydrogenation of ethylene into ethylidyne. When the dehydrogenation process is complete, monodispersed carbon species, identified as 7C6, are found to dominate the cluster population on the rhodium terraces. A significant coalescence of the 7C6 clusters into graphene islands occurs at temperatures higher than 873 K. The structural and electronic properties of the 7C6 carbon clusters are examined by high-resolution STM and STS, and compared with coronene molecules, i.e. the hydrogenated analogues of 7C6. DFT calculations are further used to explain the stability of 7C6 supported on the Rh(111) surface, and also the structural characteristics of such magic-sized carbon clusters.

<div>Laser-produced plasmas (LPP) have been used in a wide range of applications such as in pulsed laser deposition (PLD), extreme ultraviolet lithography (EUVL), laser-induced breakdown spectroscopy (LIBS), and many more. In the collision of two laser-produced plasmas, the two counter-streaming plasmas may face a degree of stagnation which influences the subsequent development of the compound plasma plume. The plume development of the stagnation layer can deviate quite noticeably from typical laser-plasma behavior. For instance, an enhanced degree of collisionality is expected, especially when the plasma collision transpires in a low pressure ambient. Colliding plasma can be intentionally implemented or conversely may occur naturally. In EUV lithography colliding plasma could service as an efficient EUV source with inherent debris mitigation. Conversely, colliding plasma could manifest in an inertial fusion energy (IFE) chamber leading to contamination, disrupting successful device operation.</div><div><br></div><div>Various techniques such as optical emission spectroscopy (OES), CCD plume imaging, laser-induced fluorescence (LIF), laser-induced incandescence (LII), and scanning electron microscopy (SEM) may be used to study laser-produced plasmas and their associated byproducts. These techniques will be used extensively throughout this work to aid in developing an understanding of the various physical and chemical phenomena occurring in these plasmas.</div><div><br></div><div><div>Chapter 1 provides introductory knowledge regarding LPPs with a specific exploration into colliding plasma and its relevance to a broad body of scientific knowledge. Additionally, the principles behind the various experimental techniques are capitulated.</div><div><br></div><div>Chapter 2 presents the laboratory facilities available at our Center for Materials Under eXtreme Environment (CMUXE) which can be used to study LPP. The various equipment (chambers, lasers, spectrograph, etc.) are discussed in detail.</div><div><br></div><div>Chapter 3 begins the series of substantive chapters which comprise the original research of this thesis. Here, the early formation (< 1 μs) of colliding carbon plasmas produced from the ablation of graphite is explored. The influence of plume hydrodynamics on the temporary lateral confinement of the stagnation layer is discussed with attention to the three different laser intensities studied. Additionally, species in the plasma were identified using OES and monochromatic plume imaging. A large increase in Swan emission from C2 dimers is observed in the stagnation layer, suggesting formation of C2 and/or re-excitation of C2 produced ab initio during laser ablation. Results were compared with HEIGHTS computational modeling to verify observations and to validate the code package for a new plasma regime.</div><div><br></div><div>Chapter 4 functions as a continuation from Chapter 3, looking into the intermediate time (1-10 μs) dynamics of colliding carbon plasma. To observe transient molecular species of carbon, C2 and C3, LIF was employed. By acquiring plume images through LIF, the various mechanisms by which C2 and C3 appear at different times in the plasma lifetime may be discerned. Using optical time-of-flight (OTOF), more information of carbon species populations may be determined to construct space-time contours which offer corroborative information regarding the spatiotemporal development of the stagnation layer.</div></div><div><br></div><div><div>Chapter 5 presents work on colliding Sn plasma for application as a EUV light source. The accumulation of material along the stagnation layer makes colliding plasmas a suitable preplasma in a dual pulse laser scheme. Dual-pulse EUV concepts call for the formation of a preplasma from the stagnation of two Sn plasmas. This preformed plasma is then subject to a second, pumping laser purposed to optimize the conversion efficiency (CE) of laser energy into EUV output. Characterization of the stagnation layer was obtained through optical emission spectroscopy while CE data is obtained using an absolutely calibrated EUV photodiode. HEIGHTS computational modeling then provides prediction of EUV emission upon using a CO2 laser for preplasma reheat.</div><div><br></div><div>Chapter 6 explores the collision between two dissimilar plasmas. Laser-produced plasma of Si and C are created in a manner which enables the two plasmas to collide. The ensuing development of the colliding plasma regime is then discussed in terms of relevant plume hydrodynamics. Analysis of the colliding regime is accomplished using fast-gated plume imaging and optical time-of-flight.</div><div><br></div><div>The final chapter, Chapter 7, provides a concise summary of the results presented in the preceding chapters. Additionally, recommended research directives are presented which are designed with consideration for the current facilities and capabilities at CMUXE.</div></div>

Ziel der Arbeit ist die theoretische Analyse von Kohlenstoff-Clustern der Größe 100 - 500 Atome. Die experimentellen Beobachtungen sind bei dieser geringen Anzahl der Atome schwierig. Anderseits sind Kenntnisse über solche Cluster sehr wichtig, z.B. für die Keimbildung von Diamant auf Substraten, oder für die Kohlenstoff-Nanotechnologie (Fullerene, Nanotubes), oder für strukturelle Defekte in Kohlenstoff-Systemen. Es wurden gekrümmte Grenzflächen im Diamant simuliert. Zuerst mit einem empirischen Potential. Es wurde danach eine Methode entwickelt, bei der die schwach gestörten Gebiete einem empirischen Potential gehorchen, und die stark gestörten Gebiete, wo eine genaue Berechnung erforderlich ist, durch eine quantenmechanische Näherung beschrieben wurden. Somit kann man mit guter Genauigkeit große Systeme, bestehend aus einigen 10 (hoch)4 Atomen, simulieren, bei denen nur lokal quantenmechanische Methoden erforderlich sind. Mit diesem Hybrid-Code wurden weiterhin Diamantkeime auf Silizium gerechnet. Es wurden Aussagen bezüglich der Stabilität des Diamants auf dem Siliziumsubstrat, der kritischen Keimgröße, der Änderungen, die der Keim erfährt, gemacht. Ein anderes Gebiet ist die molekulardynamische Simulation bezüglich der Stabilität und des Transformationsverhaltens von Kohlenstoff-Nanoteilchen. Es wurden als »Rohstoffe» sowohl Diamant- und Graphitkristalle sphärischer, ellipsoidischer oder quadratischer Form benutzt, als auch amorpher Kohlenstoff. Es wurde demonstriert, daß sich Diamant unter höherer Temperatur und Bestrahlung in Kohlenstoffzwiebeln transformiert. Es wurde der innere Kern, bestehend aus zwei Schalen, der Kohlenstoffzwiebel simuliert. Es wurde, nach meinem Wissen, zum ersten Mal gezeigt, daß zwischen den Schalen der Kohlenstoffzwiebel Quer-Verbindungen (cross-links) existieren. Diese waren von den Experimentatoren vermutet worden. Sie bilden die Initiatoren der Diamantkeime der Kohlenstoffzwiebel bei ihrer ohne äußeren Druck möglichen Transformation in Diamant. Die Zentren der Kohlenstoffzwiebeln befinden sich bereits in der Entstehung der Zwiebel unter einem Selbstdruck. Bei den größeren Kohlenstoffzwiebeln beträgt der experimentell bestimmte Abstand zwischen den Schalen von außen nach innen von 3.34 Å bis 2.2 Å. Anlagen: nano1.mpg (91,8 MB); nano2.mpg (131 MB) Nutzung: Referat Informationsvermittlung der SLUB / The scope of this work is the analysis of carbon clusters of about 100 - 500 atoms. The experimental studies are at such small clusters heavy. Knowledges about thus clusters are very important, for example in the field of the nucleation of diamond on substrates, or for the carbon nano-technology (fullerene, nanotubes), or for local defects in carbon systems. There were simulated curved interfaces in diamond. Firstly with an empirical potential. Than I developed a method, in wich the defects and the structure around them are treated by a quantum mechanical algorithm and the rest with a near to ideal structure with an empirical potential. So, it is possible an accurate calculation of great systems of about 10 (high)4 atoms on wich only locally quantum mechanical methods are necessary. With this hybrid-code diamond nuclei on silicon substrate were simulated. The stability of the diamond nuclei on the silicon substrate, the critical radius of the nuclei and the changes of the nuclei during his transformation was investigated. Another field of investigations is the molecular dynamics simulation of free carbon clusters. The initial structures had spherical, ellipsoidical or square form and consists of diamond and graphite or a free form in the case of amorphous carbon. It was demonstrated that diamond transforms at higher temperatures and under irradiation in carbon onions. The genesis of the nucleus of a carbon onion with two shells was here for the first time simulated. The existence of the cross-links between the shells of a carbon onion was demonstrated. These existence was expected from the experimentators. The cross-links are the initiators of the transformation of carbon onions to diamond. The center of carbon onions is under self-pressure, because the distance between the outer shells is about 3.34 Å and between the inner shells about 2.2 Å. Appendix: nano1.mpg (91,8 MB); nano2.mpg (131 MB) Usage: Referat Informationsvermittlung/ SLUB

Ziel der Arbeit ist die theoretische Analyse von Kohlenstoff-Clustern der Größe 100 - 500 Atome. Die experimentellen Beobachtungen sind bei dieser geringen Anzahl der Atome schwierig. Anderseits sind Kenntnisse über solche Cluster sehr wichtig, z.B. für die Keimbildung von Diamant auf Substraten, oder für die Kohlenstoff-Nanotechnologie (Fullerene, Nanotubes), oder für strukturelle Defekte in Kohlenstoff-Systemen. Es wurden gekrümmte Grenzflächen im Diamant simuliert. Zuerst mit einem empirischen Potential. Es wurde danach eine Methode entwickelt, bei der die schwach gestörten Gebiete einem empirischen Potential gehorchen, und die stark gestörten Gebiete, wo eine genaue Berechnung erforderlich ist, durch eine quantenmechanische Näherung beschrieben wurden. Somit kann man mit guter Genauigkeit große Systeme, bestehend aus einigen 10 (hoch)4 Atomen, simulieren, bei denen nur lokal quantenmechanische Methoden erforderlich sind. Mit diesem Hybrid-Code wurden weiterhin Diamantkeime auf Silizium gerechnet. Es wurden Aussagen bezüglich der Stabilität des Diamants auf dem Siliziumsubstrat, der kritischen Keimgröße, der Änderungen, die der Keim erfährt, gemacht. Ein anderes Gebiet ist die molekulardynamische Simulation bezüglich der Stabilität und des Transformationsverhaltens von Kohlenstoff-Nanoteilchen. Es wurden als »Rohstoffe» sowohl Diamant- und Graphitkristalle sphärischer, ellipsoidischer oder quadratischer Form benutzt, als auch amorpher Kohlenstoff. Es wurde demonstriert, daß sich Diamant unter höherer Temperatur und Bestrahlung in Kohlenstoffzwiebeln transformiert. Es wurde der innere Kern, bestehend aus zwei Schalen, der Kohlenstoffzwiebel simuliert. Es wurde, nach meinem Wissen, zum ersten Mal gezeigt, daß zwischen den Schalen der Kohlenstoffzwiebel Quer-Verbindungen (cross-links) existieren. Diese waren von den Experimentatoren vermutet worden. Sie bilden die Initiatoren der Diamantkeime der Kohlenstoffzwiebel bei ihrer ohne äußeren Druck möglichen Transformation in Diamant. Die Zentren der Kohlenstoffzwiebeln befinden sich bereits in der Entstehung der Zwiebel unter einem Selbstdruck. Bei den größeren Kohlenstoffzwiebeln beträgt der experimentell bestimmte Abstand zwischen den Schalen von außen nach innen von 3.34 Å bis 2.2 Å. Anlagen: nano1.mpg (91,8 MB); nano2.mpg (131 MB) Nutzung: Referat Informationsvermittlung der SLUB / The scope of this work is the analysis of carbon clusters of about 100 - 500 atoms. The experimental studies are at such small clusters heavy. Knowledges about thus clusters are very important, for example in the field of the nucleation of diamond on substrates, or for the carbon nano-technology (fullerene, nanotubes), or for local defects in carbon systems. There were simulated curved interfaces in diamond. Firstly with an empirical potential. Than I developed a method, in wich the defects and the structure around them are treated by a quantum mechanical algorithm and the rest with a near to ideal structure with an empirical potential. So, it is possible an accurate calculation of great systems of about 10 (high)4 atoms on wich only locally quantum mechanical methods are necessary. With this hybrid-code diamond nuclei on silicon substrate were simulated. The stability of the diamond nuclei on the silicon substrate, the critical radius of the nuclei and the changes of the nuclei during his transformation was investigated. Another field of investigations is the molecular dynamics simulation of free carbon clusters. The initial structures had spherical, ellipsoidical or square form and consists of diamond and graphite or a free form in the case of amorphous carbon. It was demonstrated that diamond transforms at higher temperatures and under irradiation in carbon onions. The genesis of the nucleus of a carbon onion with two shells was here for the first time simulated. The existence of the cross-links between the shells of a carbon onion was demonstrated. These existence was expected from the experimentators. The cross-links are the initiators of the transformation of carbon onions to diamond. The center of carbon onions is under self-pressure, because the distance between the outer shells is about 3.34 Å and between the inner shells about 2.2 Å. Appendix: nano1.mpg (91,8 MB); nano2.mpg (131 MB) Usage: Referat Informationsvermittlung/ SLUB