In situ observation of laser induced crystallisation in group IV semiconductors.
Notice bibliographique
Résumé
The main objectives of this thesis were to study in situ the structure formation during \nlaser induced crystallisation in group IV semiconductors. We were interested to reveal the \nsequence of change in the morphology during the growth of the different microstructures, \nto unveil the shape of the growth front during its propagation, to estimate the velocities of \ncrystallisation and to shed light on the possible mechanisms of growth through estimation \nof the temperature within the films. For that, we used Dynamic Transmission Electron \nMicroscopy (DTEM) because the technique offers the required combination of spatial and \ntemporal resolutions for in situ visualisation of the phase transformation. We used freestanding \nand membrane-supported films with the goal of elucidating the influence of the \nsupporting layer on the kinetics and thermodynamics of the phase transformation. \nIn the first part of this work, we studied the crystallisation dynamics in membrane- \nSupported and self-sustained a-Ge films. We acquired time resolved images of the \nformation of the central nanocrystalline structure, the evolution of the size and the \nroughness of the crystallisation front during the two other structures growth i.e. dendritic \nand layered structure. This study allowed us to estimate the velocities of crystallisation and \nthe evolution of the temperature within the film. We found that in the central region, \nnucleation from the bulk occurs at temperatures below the melting temperature of the \ncrystalline material. We showed that the dendritic growth occurs by propagation of thin \nmetastable liquid layer in front of the growing crystalline phase and is a result of high \nthermal instabilities at the growth front. We demonstrated that the growth of the layered \nstructure takes place at temperature below the melting temperature of the crystalline \nmaterial and proceeds in azimuthal direction, i.e. orthogonal to the direction of the net heat \nflow. However, the growth mechanisms remains similar to the dendritic growth because \nthe heat diffusion can allow formation of very thin pocket-like layer to be formed and \npropagate III the azimuthal direction. These findings allowed us to overturn earlier \nhypothesis based solely on the post-mortem equilibrium investigation of the structure. \nIn the second part of the thesis we studied the crystallisation dynamics in amorphous \nsilicon. We showed that the formed structure is dependent on the fluence of the pump-Iaser. \nWe demonstrated that at the fluences used in this study the process is melt-mediated \nfavoring super-lateral growth. Nanocrystallization occurs at the periphery of the melted \nzone but with very limited extent. The crystallisation proceeds inward i.e. toward the center \nof the heated region resulting in the observed long-grained microstructure. Our observations \nare consistent with the earlier developed theory on super-lateral growth where the \nnucleation and nanocrystallisation occurs at the periphery of the heated region and the \nelongated grains are growing along the heat gradient i.e. toward the central part of the \nheated region. Our study contributed for better understanding of growth of these structures \nand permitted estimation of the evolution of the temperature within the film.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,003 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».