Faculty of Sciences Thickness-dependent refractive index in - PowerPoint PPT Presentation

Faculty of Sciences Thickness-dependent refractive index in plasmonic nanocomposites C. Guyot and M. Voué Physics of Materials and Optics corentin.guyot@umons.ac.be 18 th annual workshop of the IEEE Benelux chapter - Mons 2015

Content • Introduction • Materials & methods • Results & discussion – Topography of the nanocomposite films (AFM) – Optical properties (SE) – Multivariate analysis – SVM classification • Conclusions Université de Mons C. Guyot | Physics of Materials and Optics Unit 2

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Dielectric Plasmonic Metal NPs matrix nanocomposites Interaction Polyvinyl with light Silver NPs alcohol (PVA) Collective “In situ synthesis” : growth of NPs in a oscillations of doped polymer matrix by a thermal the free e - annealing Optical response : Localized plasmon resonance Université de Mons C. Guyot | Physics of Materials and Optics Unit 3

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Interest for Ag-PVA • Tunable absorption in the visible range • Optical enhancing properties • Antibacterial or anti- fouling properties • Non-linear optical properties • Random lasers with dyes G. V. Ramesh, S. Porel and T. P. Radhakrishnan Chem. Soc. Rev., 2009, 38, 2646 – 2656 (e.g. Rhodamine G) Université de Mons C. Guyot | Physics of Materials and Optics Unit 4

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Spectroscopic Ellipsometry (SE) • Non destructive optical method • Change of polarization state after reflexion Optical properties ( 𝑜, 𝑙 ) • and thicknesses of the layers • Optical model needed 𝜍 = 𝑠 𝑞 = tan Ψ𝑓 𝑗Δ 𝑠 𝑡 = 𝑔(𝑜 𝑗 , 𝑙 𝑗 , 𝑈 𝑗 ) Université de Mons C. Guyot | Physics of Materials and Optics Unit 5

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS 110°C 60 min 𝐵𝑕 + + 𝑄𝑊𝐵 → 𝐵𝑕 0 − 𝑄𝑊𝐵 Samples PVA concentration (in water) 2% 8% Dry film thickness ±30 nm ±300 nm Silver to polymer ratio (w:w) 2.5% 25% 2.5% 25% THIN FILMS THICK FILMS Université de Mons C. Guyot | Physics of Materials and Optics Unit 6

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS PVA Ag-PVA 25% ± 30 nm ± 30 nm ± 300 nm 𝐓 𝐛 = 𝟏. 𝟒𝟑 𝐨𝐧 𝐓 𝐛 = 𝟏. 𝟔𝟘 𝐨𝐧 𝐓 𝐛 = 𝟏. 𝟕𝟕 𝐨𝐧 Université de Mons C. Guyot | Physics of Materials and Optics Unit 7

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Spectroscopic ellipsometry 𝛽 = cos 2Ψ 𝛾 = sin 2Ψ cos(Δ) Determination of : Optical properties (𝑜, 𝑙) • • Thickness of the layers NPs = homogeneous sphere, radius a and permittivity 𝜗 1 in a polymer matrix 𝜗 𝑛 𝜗 1 − 𝜗 𝑛 𝛽 = 4𝜌𝑏 3 𝜗 𝑛 𝜗 1 + 2𝜗 𝑛 Resonance when 𝜗 1 = −2𝜗 𝑛 𝑜 𝑄𝑊𝐵 = 1.5 𝜗 𝑛 = 𝑜 𝑄𝑊𝐵 2 = 2.25 ⇒ 𝜗 1 = −4.5 Resonance at 405 nm or 3.1 eV Université de Mons C. Guyot | Physics of Materials and Optics Unit 8

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Spectroscopic ellipsometry Optical model Unknown 𝐔, 𝒐(𝝁), 𝒍(𝝁) Dielectric matrix : Cauchy law (2 param.) LSPR : Lorentzian absorption (3 param.) • 𝐵 Amplitude of the resonance 6 parameters • Λ 0 Position of the resonance peak • Γ 0 Full-width at half maximum (FWHM) Université de Mons C. Guyot | Physics of Materials and Optics Unit 9

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Question : links between the resonance parameters and the experimental parameters ? Approach : Multivariate analysis (4 classes, N > 90) %Ag (w:w) 2.5% 25% 2% Thin low (tl) Thin high (tH) %PVA 8% Thick low (Tl) Thick high (TH) Thickness versus A : OK Université de Mons C. Guyot | Physics of Materials and Optics Unit 10

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS A Overlapping in the 𝚫 𝟏 − 𝚳 𝟏 plane ? 𝚳 𝟏 Different optical behavior between THIN and THICK films ? ? 𝚫 𝟏 Université de Mons C. Guyot | Physics of Materials and Optics Unit 11

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Box-and-whiskers plots (50% of the data in the box) 𝚳 𝟏 𝚫 𝟏 𝐁 L 0 : small blue- G 0 : more A : strongly correlated to [Ag] shift (thin to Thick) complicated Université de Mons C. Guyot | Physics of Materials and Optics Unit 12

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Support Vector Machines (SVM) or Large Margin Classifiers Separable data Overlapping data Good Best classifier Best classifier Good Margin Margin OK but … Misclassification = Cost Best classifier = largest margin Université de Mons C. Guyot | Physics of Materials and Optics Unit 13

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Back to the resonance data … Δ : 2.5% Ag/PVA ratio Ο : 25% Ag/PVA ratio (A) Thick films (B) Thin films 0.46 0.44 0.45 0.43 0.44 0.42 0 (µm) 0 (µm) 0.43 0.41 0.40 0.42 0.39 0.05 0.10 0.15 0.20 0.25 0.30 0.00 0.05 0.10 0.15 0.20 0 (µm) 0 (µm) • Possibility to discriminate the high and low doping level films • Very efficient way : only 3 samples per plot are misclassified Slopes of the optimum classifiers have opposite sign : Thick (−0.36) and • thin films +0.30 Université de Mons C. Guyot | Physics of Materials and Optics Unit 14

I NTRODUCTION | M ATERIALS & METHODS | R ESULTS & DISCUSSION | C ONCLUSIONS Conclusion • Optical properties of nanocomposites (Ag/PVA) determined from SE data • Influence of thickness and the Ag concentration on refractive index • Different behavior of thin and thick films at a given doping level (Ag + ) • Possible explanation : different growth mechanisms resulting in different spatial distributions of the NPs (2D vs 3D) Thin films Thick films Silicon Silicon 3D-like matrix 2D-like matrix Université de Mons C. Guyot | Physics of Materials and Optics Unit 15

Thank you for your attention This work is financially supported by the F.N.R.S. (FRFC project nr 1926111) Université de Mons C. Guyot | Physics of Materials and Optics Unit 16