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

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88 CHAPTER 5. MODELLING AND ANALYSIS OF THE OPT. PROP.[001]30Counts [%]2010ab01.02.0Aspect ratio1510Counts [%]105Counts [%]5c0510 15NP lenght [nm]20d0510 15NP width [nm]20Figure 5.10: Panel a: AFM image of a nanopatterned LiF(110) sample with Λ ≈ 30 nm,following the grazing deposition of ≈ 3 nm of gold at T = 100 ◦ C and annealing atT = 400 ◦ C (“rectangular” configuration). Panels b, c, d: statistical distributions of theNP in-plane aspect ratio and semiaxes along and across the LiF ridges, respectively. Thecontinuous lines are best-fit lognormal probability density functions. See text for details.along and across the LiF ridges, were characterized by very similar parameters, exhibitinga mean and a standard deviation of a x = a y = (8.5 ± 3.0) nm, corresponding to anaspect ratio of 1.0 ± 0.3. Mean NP spacings of d y = (20 ± 5) nm along the chains andd x = (30±5) nm across the ripples were found, indicating that the particles can be statisticallythought as laying on a rectangular mesh. We will refer to this class of samplesas the “rectangular” arrays.Optical characterizationIn analogy with the previous cases, the optical response of the samples under scrutinyhas been investigated by means of polarized light reflectivity, with the plane of incidenceeither along (||) or across (⊥) the LiF ridges, in order to selectively discriminate thecontributions of the individual L and T plasmonic modes (see §4.2.3).In fig. 5.11 and fig. 5.12 we report, as open circles, R S (panels (b)) and R P (panels (c))spectra measured for the “square” and the “rectangular” samples, respectively, at θ = 50 ◦of incidence. For each polarization, the longitudinal and transverse LSP modes have beenexcited by fixing the plane of incidence in parallel or perpendicular configuration: L mode(black lines) excited in RS ⊥ , T mode (red lines) excited in R||S , and vice versa for R P.The in-plane optical anisotropy of the system is particularly accentuated for the“square” configuration, reported in fig. 5.11: looking at R S , the L and T modes areexcited by setting the plane of incidence perpendicular (⊥, fig. 5.11(c)) and parallel (||,fig. 5.11(b)) to the LiF ridges, respectively, and are found at λ S L = (597 ± 3) nm and= (542 ± 3) nm, separated by ≈ 55 nm; the full widths at half maximum (Γ) ofλ S T
5.2. 2-DIMENSIONAL ARRAYS OF GOLD NANOPARTICLES 890.060.04R P||0.30R S┴R PR S0.200.020.100.00a.200 400 600 800 1000 1200 1400 [nm]c.200400600800 [nm]10001200140017 nmps11.5 nmps40 nme.41 nm0.20R S||0.015R p┴R S0.15R P0.0100.100.005b.200400600800 [nm]100012001400d.0.000200400600800 [nm]100012001400Figure 5.11: “Square” sample. Left panels: p-polarized (a) and s-polarized (b) reflectivityspectra measured with the plane of incidence parallel (||) the LiF ridges. Right panels: s-polarized (c) and p-polarized (d) reflectivity spectra measured with the plane of incidenceperpendicular (⊥) the LiF ridges. Red curves: excitation of transverse LSP mode (R ||S ,RP ⊥); black curves: excitation of longitudinal LSP mode (R⊥ S , R|| P). The continuouslines represent the corresponding reflectivities calculated according the model describedin §5.2.1. The dashed curves were computed with the same morphological parameterslike the previous ones but neglecting the dispersion of the depolarization factors. Panel e:schematic diagram representing the NPs arrangement and shape employed in the opticalcalculations.the L and T resonances are also markedly different, reading Γ S L = (150 ± 5) nm andΓ S T = (94±3) nm.In case of p-polarized light the EM excitation is orthogonal with respect to s polarization,therefore, for a given optical geometry (|| or ⊥), the LSP modes are exchanged:the L mode is observed in || geometry (fig. 5.11(a)), while the T mode in ⊥ geometry(fig. 5.11(d)). The LSP characteristics obtained from R P are λ P L = (597 ± 3) nm andΓ P L = (167±5) nm for the L mode, λP T = (539±3) nm and ΓP T = (95±5) nm for the Tmode; the slight differences from the corresponding R S values are due to the fact that in
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Università degli studi di GenovaFa
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4 CONTENTS5.2.2 Optical anisotropy
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6 Introductionconfining the EM ener
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8 Introduction
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10 CHAPTER 1. THEORYEλBkFigure 1.1
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12 CHAPTER 1. THEORYfrom which, sep
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14 CHAPTER 1. THEORY≈ ω 0 like
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16 CHAPTER 1. THEORYε 1 (λ) = N 2
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18 CHAPTER 1. THEORYThe correspondi
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20 CHAPTER 1. THEORYso the induced
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22 CHAPTER 1. THEORYε MG −ε aε
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24 CHAPTER 1. THEORYUV range, this
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26 CHAPTER 1. THEORYwhich is called
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28 CHAPTER 1. THEORYwhere Γ 0 = v
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30 CHAPTER 1. THEORYpoints of the c
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32 CHAPTER 1. THEORYand then monoto
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34 CHAPTER 1. THEORYposition, has t
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36 CHAPTER 1. THEORYfieldorequivale
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Page 40 and 41: 40 CHAPTER 2. EXPERIMENTAL METHODSt
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Page 46 and 47: 46 CHAPTER 2. EXPERIMENTAL METHODSs
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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
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