Research Topics

• Elastic and optical properties of glassy systems via Brillouin Spectroscopy

One of the most evident changes at the glass transition is related to the variation of the elastic (mechanical) properties; the deformable liquid transforms into a rigid solid. Molecular crystals and polymers are used as model systems for the study of freezing processes. In these model systems it is possible to reduce the number of degrees of freedom able to induce the glass transition (as in the case of plastic crystals) and also to suppress any crystallization risk tailoring the polymer chains. High Resolution Brillouin Spectroscopy reveals as a very powerful technique to study this kind of materials. This experimental method gives information of the evolution of the elastic properties and, as an optical technique, also of the refractive index of the samples investigated. Amber, a natural glass obtained after thousands of years, is one of the subjects of investigation.Temperature evolution of elastic constants and refractive index shows typical glass behaviour. Propanol is under study too. (Related research project)

Temperature and frequency dependence of the longitudinal elastic constant and hypersonic attenuation before and after the glass transition (Tg) as shown by the Brillouin Spectroscopy     (Courtesy of Prof. Dr. J. K. Krüger)           Temperature dependence of the main relaxation time until the glass transition temperature

 

 

 

 

 

 

 

 

 

 

 

Research Topics

• Acoustic characterization of materials with applications in SAW devices

One of the most important applications of piezoelectric materials is related to the existence of surface acoustic waves (SAWs) which can be stimulated by elctrical fields resulting in high frequency filters. This technology is presently applied to cellular phones with clear success. It is evident that a non destructive and contact less characterization method for SAWs plays a decisive role in order to test new materials. High Resolution Brillouin Spectroscopy is a very powerful  method to study the elatic and mechanical properties of different type of materials, including surface and bulk acoustic waves. As an optical spectroscopy, this technique has the advantage of being non destructive and contact less. Film samples of Al_1-xGa_xN are the subject of investigation. The concentration evolution of the bulk and  surface acoustic waves reveals that these materials are very promising for their application in SAW-devices. (Related research project)