Morphology and plasmonic properties of self-organized arrays of ...

More documents

Recommendations

Info

74 CHAPTER 4. SELF-ORGANIZED NPS ARRAYS: OPTICAL PROP.640LSPR [nm]600560T modeL mode5205.06.0t Au[nm]7.0Figure 4.14: Wavelength position of longitudinal (solid red squares) and transverse (openblack squares) LSP resonances for gold nanoparticles on LiF(110) samples with similarripples periodicities and the different amounts t Au of deposited gold (see fig. 4.13).effects: increasing t Au , the NPs aspect ratio increases, inducing a red-shift of the L modeand a slight blue shift of the T mode (fig. 1.15). Instead, the increase of reflectivity canbe related mainly to the overall increase of the NPs volume, which promotes more intenseinduced dipoles (α ∝ v, see (1.42)) and consequently an enhanced optical response.
Chapter 5Modelling and analysis of theoptical propertiesIn this chapter we will focus on the development of a theoretical modelling framework,allowing us to account for the optical response of the 2D arrays of gold nanoparticlesdescribed in the previous chapters. A theoretical support to the experimental data is offundamental importance in order to achieve a comprehensive understanding of the originsof the optical properties of these systems, and thus to engineer the optical response byselecting a priori the proper morphological characteristics.In the next sections, we will first characterize the optical properties of the LiF templates,and then we will cover in detail the arrays of gold NPs, overlooking instead on thenanowires.5.1 Lithium fluoride nanostructuresWe start by extracting the optical constant of the nanopatterned LiF substrates. Adetailed characterization of the substrates characteristics is in fact extremely importantfor an proper modelling of the Au NPs arrays. In §4.1 we reported the ellipsometricspectra measured on the LiF(110) substrates prior to and after the further depositionof LiF, so here we proceed, as customary in ellipsometry, by constructing a model todescribe the samples and then fit the optical constants against the experimental data.All the calculation have been performed using the WVASE software supplied with theellipsometer.5.1.1 LiF substratesWe first consider the LiF(110) substrates in the as-received state. In the previous chapterwe saw that the samples exhibit negligible in-plane birefringence, despite the anisotropicatomic environments along the [001] and [1¯10] crystal directions. We can therefore applyan isotropic dielectric model for the bare substrate. Lithium fluoride is an insulator witha very wide band gap, and in the energy range between ∼1 eV and ∼5 eV it behaves likea transparent, non absorbing material; then, we can approximate its optical constants,in the visible and near-IR range, using a Cauchy parametrization of the refractive index(see equation (1.20)). We can further improve the model by accounting for the surface75
Page 1:
Università degli studi di GenovaFa
Page 4 and 5:
4 CONTENTS5.2.2 Optical anisotropy
Page 6 and 7:
6 Introductionconfining the EM ener
Page 8 and 9:
8 Introduction
Page 10 and 11:
10 CHAPTER 1. THEORYEλBkFigure 1.1
Page 12 and 13:
12 CHAPTER 1. THEORYfrom which, sep
Page 14 and 15:
14 CHAPTER 1. THEORY≈ ω 0 like
Page 16 and 17:
16 CHAPTER 1. THEORYε 1 (λ) = N 2
Page 18 and 19:
18 CHAPTER 1. THEORYThe correspondi
Page 20 and 21:
20 CHAPTER 1. THEORYso the induced
Page 22 and 23:
22 CHAPTER 1. THEORYε MG −ε aε
Page 24 and 25: 24 CHAPTER 1. THEORYUV range, this
Page 26 and 27: 26 CHAPTER 1. THEORYwhich is called
Page 28 and 29: 28 CHAPTER 1. THEORYwhere Γ 0 = v
Page 30 and 31: 30 CHAPTER 1. THEORYpoints of the c
Page 32 and 33: 32 CHAPTER 1. THEORYand then monoto
Page 34 and 35: 34 CHAPTER 1. THEORYposition, has t
Page 36 and 37: 36 CHAPTER 1. THEORYfieldorequivale
Page 38 and 39: 38 CHAPTER 1. THEORY
Page 40 and 41: 40 CHAPTER 2. EXPERIMENTAL METHODSt
Page 44 and 45: 44 CHAPTER 2. EXPERIMENTAL METHODS2
Page 46 and 47: 46 CHAPTER 2. EXPERIMENTAL METHODSs
Page 50 and 51: [001][100]50 CHAPTER 3. SELF-ORGANI
Page 52 and 53: 52 CHAPTER 3. SELF-ORGANIZED NPS AR
Page 76 and 77: 76 CHAPTER 5. MODELLING AND ANALYSI
Page 98 and 99: 98 CHAPTER 6. COMPOSITE MEDIA BASED
Page 100 and 101: 100 CHAPTER 6. COMPOSITE MEDIA BASE
Page 102 and 103: 102 CHAPTER 6. COMPOSITE MEDIA BASE
Page 104 and 105: 104 Conclusionsparticular cases of
Page 106 and 107: 106 Acknowledgements
Page 108 and 109: 108 BIBLIOGRAPHY[14] Shouheng Sun,
Page 110 and 111: 110 BIBLIOGRAPHY[44] Q A Pankhurst,
Page 112 and 113: 112 BIBLIOGRAPHY[74] Prashant K. Ja
Page 114 and 115: 114 BIBLIOGRAPHY[103] Tobias Kraus,
Page 116 and 117: 116 BIBLIOGRAPHY[137] F. Brouers, J
Page 118 and 119: 118 BIBLIOGRAPHY[169] Christy L. Ha
Page 120 and 121: 120 BIBLIOGRAPHY[201] G. Baldacchin
show all

Morphology and plasmonic properties of self-organized arrays of ...

Create successful ePaper yourself

Delete template?

Save as template?