In situ observation of laser induced crystallisation in group IV semiconductors.
Bibliographic record
Abstract
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.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.003 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".