Evidence for surface initiated solidification in Ge films upon picosecond laser pulse irradiation
Amorphous Ge films on Si films have been melted by single 30 ps laser pulses at λ=583 nm and a solidification process has been followed by means of real time reflectivity (RTR) measurements with nanosecond time resolution. Evidence is provided for the occurrence of surface initiated solidification f...
| Autores: | , , , , , , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2001 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/64529 |
| Acceso en línea: | http://hdl.handle.net/10261/64529 |
| Access Level: | acceso abierto |
| Sumario: | Amorphous Ge films on Si films have been melted by single 30 ps laser pulses at λ=583 nm and a solidification process has been followed by means of real time reflectivity (RTR) measurements with nanosecond time resolution. Evidence is provided for the occurrence of surface initiated solidification for films with thicknesses in the 80-130 nm range. This process occurs at high fluences following complete melting of the film and of a thin layer of the Si substrate which undergoes mixing with the liquid Ge. The release of the solidification enthalpy of the latter layer together with its lower solidification temperature favored by constitutional undercooling are proposed as the origin of the initial gradient inversion required for such a process. This scenario leads also to the formation of a secondary solidification front counterpropagating towards the film surface, as suggested by optical simulations of the experimental RTR transients. A transition from a surface initiated solidification process towards a bulk solidification process is shown to occur when increasing the film thickness beyond 130 nm. The results further show that, besides the film thickness, the pulse duration has a major influence on the type of solidification process induced. © 2001 American Institute of Physics. |
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