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

44 CHAPTER 2. EXPERIMENTAL METHODS25210 [deg]20180 [deg]1515010400800 [nm]12001600Figure 2.5: Spectroscopic Ψ and ∆ spectra, acquired at incidence of θ = 50 ◦ on a ≈ 6 nmfilm of gold supported on a nanopatterned LiF(110) substrate (fig. 2.10(b)).2.2.2 Spectroscopic Reflectometry and TransmittanceWe now briefly introduce the other optical methods employed in this thesis for the opticalcharacterizations, namely reflectivity and transmissivity. Compared to ellipsometry, spectroscopicreflectivity (SR) and transmissivity (ST) are much simpler techniques, requiringa less elaborated experimental apparatus and allowing a more direct interpretation ofthe data; however, these measurements are also more affected by systematic errors andprovide less informations on the optical properties of the samples.I 0θI R100I 01.0I TTa.Intensity [a.u.]500.80.6TransmittanceI TI 0θb. c.0400800 [nm]120016000.4Figure 2.6: Panels a, b: sketches of reflectivity (a) and transmissivity (b) experiments,at incidence θ. Panel c: example of baseline (red curve) and transmitted intensity (blackcurve) at normal incidence, and the corresponding transmittance obtained from their ratio(blue curve). The light source was the Xe lamp of the M2000-U ellipsometer; the samplewas a ≈ 6 nm Au film deposited on a nanopatterned Lif(110) substrate (fig. 2.10(b)).The basic principle behind SR and ST experiments is quite straightforward. Theintensity of a light beam is measured, as a function of the wavelength or energy, before(I 0 , called baseline) and after the interaction with the sample under scrutiny; in case ofSR, the intensity I R of the reflected beam is measured (fig. 2.6(a)), while in case of STthe intensity I T of the transmitted beam is acquired (fig. 2.6(b)). The ratios betweenthe intensities of the reflected or transmitted beam and the incident beam are called theabsolute reflectance R or transmittance T: