Abstract/Details

Propriétés optiques linéaires et non-linéaires de nanocomposites métal/diélectrique anisotropes

Lamarre, Jean-Michel.   Ecole Polytechnique, Montreal (Canada) ProQuest Dissertations Publishing,  2008. NR46107.

Abstract (summary)

In this thesis, we present the development and the analysis of advanced fabrication techniques allowing for the precise control of the synthesis of nanocomposites formed of gold nanoparticles embedded in a silica matrix. We have developed a three-step technique allowing us to fabricate nanocomposite films with particles of controlled size and shape.

(1) The first paper describes the sample fabrication method and their linear optical properties. The nanocomposite materials are first deposited using a PECVD/sputtering hybrid technique. In order to increase the nanoparticule size, the sample are then submitted to a 900°C thermal annealing for several hours. The modification technique used to change the particles from spheres to ellipsoids is described. This technique consists of irradiating the samples using high energy copper ions (30 MeV). The resulting structure is anisotropic since the particles' long axis are aligned with the irradiation direction. This is the first use of this technique for samples with gold particles embedded in a solid matrix. The details of the ellipsometric and spectrophotometric characterization are discussed and the linear optical properties of these materials measured by these techniques are presented. These measurements allow one to find the nanostructural parameters of the layer (gold concentration, particle size, thickness and surface roughness) from the complex refractive index of the layer. We demonstrate the effect of the annealing and the irradiation on the optical properties of the nanocomposite system notably on the control of the characteristics of the SPR absorption band. Thus, we show that the thermal annealing induce a red-shift in the SPR position while the irradiation step corresponds to a blue-shift. We also demonstrate that a final post-irradiation annealing treatment allows to re-form spherical nanoparticles.

(2) The second paper is focused on the nonlinear optical properties of Au/SiO2 nanocomposites. Polarized P-Scan et Z-Scan techniques adapted for the measurements of anisotropic samples are described. The P-Scan technique linearity in the context of high power measurements of nanocomposite samples is discussed by comparing several models (model of saturable absorption, correction for linear absorption, correction for linear and nonlinear absorption). Isotropic (spheres) and anisotropic (nanoellipsoids) nanocomposite samples were measured by the Z-Scan and P-Scan techniques. The measurements of isotropic samples yield a nonlinear absorption coefficient value of –4.8×10 -2 cm/W while the measurements of the nonlinear absorption coefficient of anisotropic samples yield values ranging between –0.9×10 -2 cm/W and –3.0×10-2 cm/W depending on the polarization direction of the measurement light. This change in polarization corresponds to a variation of the excitation of the nanoellipsoids short and long axes. Using a simple geometrical model, we show that the nonlinear absorption coefficient measured for a polarization along the ellipsoids short or long axis is equal respectively to –0.9×10-2 cm/W and –5.1×10-2 cm/W.

(3) The third paper deals with improvements to the currently used model for the nonlinear response of nanocomposite samples. These modifications allows one to model high metal concentration samples and/or samples containing anisotropic particles. The introduction of the depolarization factor in the calculation of the effective nonlinear susceptibility of nanocomposites from the generalized Maxwell-Garnett equation allows for the addition of a parameter which depends on the geometry of the nanoparticles. The modified model for high gold concentration is compared to the traditional model. We show that the use of the modified model is of prime importance for gold volume fractions exceeding 1%. The effect of each parameter of the model is evaluated and discussed (metal concentration, metal dielectric constant, matrix dielectric constant, metal nonlinear susceptibility). We demonstrate that each fabrication parameter must be carefully choosen as a function of the particle geometry in order to optimize the optical nonlinearity value. The use of this improved model for the prediction of real sample properties is discussed notably in the context of the results introduced in the preceding paper. The model we developped allows one to predict and understand the values of the nonlinear absorption coefficient measured along the nanoellipsoids short and long axes. Finally, we show that the maximum anisotropy of the nonlinear optical properties is not necessarily obtained for particles with maximum deformation. (Abstract shortened by UMI.)

Indexing (details)


Subject
Condensed matter physics;
Optics;
Materials science
Classification
0611: Condensed matter physics
0752: Optics
0794: Materials science
Identifier / keyword
Applied sciences; Pure sciences; Gold nanoparticles; Nanocomposite films
Title
Propriétés optiques linéaires et non-linéaires de nanocomposites métal/diélectrique anisotropes
Alternate title
Linear and Non-Linear Optical Properties of Anisotropic Metal/dielectric Nanocomposites
Author
Lamarre, Jean-Michel
Number of pages
240
Publication year
2008
Degree date
2008
School code
1105
Source
DAI-B 70/01, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
978-0-494-46107-5
University/institution
Ecole Polytechnique, Montreal (Canada)
University location
Canada -- Quebec, CA
Degree
Ph.D.
Source type
Dissertation or Thesis
Language
French
Document type
Dissertation/Thesis
Dissertation/thesis number
NR46107
ProQuest document ID
304805826
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
https://www.proquest.com/docview/304805826/abstract