In this thesis Brillouin spectroscopy is exploited as a nondestructive investigation technique to characterize tungsten thin films deposited by PLD technique (Pulsed Laser Deposition). The speed of the acoustic modes of the layered material (supported film) is measured by shining a laser light, collecting the scattered light and analyzing its spectrum. The scattering is due to thermal agitation and probes its vibrational component at a specific wave vector. From the measured velocity it is possible to calculate the elastic properties of the material, such as density and elastic constants, using Christoffel equations that define the relationship between these variables. The study focuses on tungsten thin films, a material used in nuclear fusion as a first wall material and as a coating for optical mirrors. Films were grown either in vacuum or in gaseous atmosphere, and their properties were characterized. The films morphology was investigated by the scanning electron microscope (SEM), using cross-section to accurately measure the thickness, which results non-uniform in PLD deposition. It was possible to obtain the complete elastic characterization of some films, and to identify specific correlations between the properties measured with the Brillouin technique and the microstructures of different films, or different film thickness within the same sample.
In questa tesi la spettroscopia Brillouin viene utilizzata come tecnica di indagine non distruttiva al fine di caratterizzare film sottili di tungsteno deposti mediante la tecnica PLD (Pulsed Laser Deposition). La velocità dei modi acustici del materiale stratificato (film supportato) viene misurata illuminando con un laser il campione analizzato, raccogliendo la luce diffusa e analizzandone lo spettro. Lo scattering è dovuto all’agitazione termica e ne sonda la componente vibrazionale a uno specifico vettore d’onda. Dalle velocità misurate è possibile calcolare le proprietà elastiche del materiale, come densità e costanti elastiche, sfruttando le equazioni di Christoffel che definiscono il legame tra queste grandezze. Lo studio si concentra sui film sottili di tungsteno, materiale utilizzato nel campo della fusione nucleare come materiale di prima parete e come rivestimento di specchi ottici. Sono stati caratterizzati film deposti sia in vuoto, sia con diverse pressioni di gas, calcolandone le proprietà. La morfologia dei film è stata investigata utilizzando il microscopio elettronico a scansione (SEM), utilizzando le cross-section per misurare esattamente gli spessori, che nelle deposizioni con PLD risultano non uniformi. È stato possibile ottenere la caratterizzazione elastica completa di alcuni film, e identificare precise correlazioni tra le proprietà misurate con la tecnica Brillouin e le microstrutture dei diversi film, o i diversi spessori all’interno dello stesso campione.
Caratterizzazione di film di tungsteno, ottenuti mediante la tecnica PLD, attraverso la spettroscopia Brillouin
GIULIANI, ANDREA
2010/2011
Abstract
In this thesis Brillouin spectroscopy is exploited as a nondestructive investigation technique to characterize tungsten thin films deposited by PLD technique (Pulsed Laser Deposition). The speed of the acoustic modes of the layered material (supported film) is measured by shining a laser light, collecting the scattered light and analyzing its spectrum. The scattering is due to thermal agitation and probes its vibrational component at a specific wave vector. From the measured velocity it is possible to calculate the elastic properties of the material, such as density and elastic constants, using Christoffel equations that define the relationship between these variables. The study focuses on tungsten thin films, a material used in nuclear fusion as a first wall material and as a coating for optical mirrors. Films were grown either in vacuum or in gaseous atmosphere, and their properties were characterized. The films morphology was investigated by the scanning electron microscope (SEM), using cross-section to accurately measure the thickness, which results non-uniform in PLD deposition. It was possible to obtain the complete elastic characterization of some films, and to identify specific correlations between the properties measured with the Brillouin technique and the microstructures of different films, or different film thickness within the same sample.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/37001