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Identifier

000397112

Title

Μελέτη υπερταχέων διαδικασιών σε κολλοειδείς νανοκρυστάλλους Αργύρου χρησιμοποιώντας υπερταχεία φασματοσκοπία λέιζερ

Alternative Title

Study of ultrafast dynamics in colloidal nanocrystals Ag using ultrafast laser spectroscopy

Author

Καραλάκη, Μαρία

Reviewer

Λάππας, Α.
Λουκάκος, Π.

Thesis advisor

Ρακιτζής, Πέτρος

Abstract

The present study examines three forms of nanoparticle colloidal silver; solution in water, thin films with PDDA and thin films without PDDA. Conductivity electrons can be modeled as free electrons, a fact that allows a relatively simple simulation of the dynamic relaxation of the electrons distribution, as thoroughly described on Chapter 1. Contrary to different metal systems, in noble metal systems the surface plasmon effect takes place. Moreover, in silver nanoparticles systems, the surface plasmon effect ranges extensively, with its ceiling wavelength approximately at 400 nm. Our experiments were conducted based on the pump-probe technique, which is a two colors technique. Particularly, the electron distribution is excited by a pulse, which is created by a pump, while electron relaxation in thermalization is controlled using a probe. Changes in the detector’s intensification caused by the sample’s excitement are recorded. The experimental setup is described in detail on Chapter 2. The experimental setup is based on ultrafast pulses created by a Ti: Sapphire oscillator. The frequency of the pump pulse is twice as big as the frequency of the initial laser (392 nm) which allows to the surface plasmon to be excited. The probe beam is created using a Ti: Sapphire crystal, which produces white light while remaining optically non-linear. The results of the experiment are meticulously discussed on Chapter 3. The objective of the present study is to gain a deep insight into the mechanisms of electron trapping and relaxation. We found that the surfactant is responsible for trapping of electrons at the surface states at the boundary of the nanocrystals as well as for hindering the heat diffusion from the nanocrystals towards the environment due to the low thermal conductivity of the nanocrystals.

Language

Greek

Subject

Ultrafast dynamics

Υπερταχείες διαδικασίες

Issue date

2015-11-20

Collection

School/Department--School of Sciences and Engineering--Department of Physics--Post-graduate theses

Type of Work--Post-graduate theses

Views

522

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