M.Logar, B.Jančar and D.Suvorov

1. Synthesis of metallic Ag and semiconducting ZnS nanoparticles in self-assembled polyelectrolyte templates M.Logar, B.Jančar and D.Suvorov Institute Jožef Stefan, Advanced materials department, Slovenia

2. The control over the particle shape, size and concentration Introduction Inorganic nanoparticle properties • Large surface / volume ratio • Quantum confinement effect In-situ nanoparticle synthesis methodology • nanoparticles are synthesized in-situ in polymer template • the surrounding polymer chains limits particle aggregation • the size and volume fraction of the particles in composite films is manipulated by varying the synthesis conditions

3. Polyelectrolyte multilayer (PEM)template formation Layer-by-layer self- assembly method Driving force for the multilayer buildup Electrostatic interaction between appositively charged polyelectrolyte PAA PAH

4. Properties of the PEM film • type of the PE • pH value of the PE assembly Weak polyelectrolyte - PAA [COO- ]= f (pH) • Thicknesscontrollable in nanometer range pH=3.5 250 200 pH=3.0 150 PEM thickness (nm) pH=2.5 Substrate effect 100 50 0 0 5 10 15 number of polyelectrolyte bilayers

5. In-situ synthesis of inorganic nanoparticles O C O- m+ Metal salt solution pH=5.5 Metal ion Ag+, Zn 2+ Reduction/sulfidication Recharge Inorganic nanoparticle Ag, ZnS

6. In-situ Ag nanoparticle synthesis Ag acetate solution pH=5.5 n Ag+ Ag nanoparticle NaBH4 solution pH = 2.5 pH = 3.0 pH = 3.5 Ag nanoparticle PEM film PS substrate HAADF - STEM image

7. pH=2.5 pH=3.5 pH=3.0 Volume fraction and size of the Ag nanoparticles in PEM are pH- dependent pH value of PEM assembly Ag volume fraction (%) Average Ag particle diameter (nm) Ag particle concentrations (particles/cm3) 2.5 4.5±1.5 6.9∙1018 33 3.0 27 6.1±1.6 5.2∙1018 3.5 22 7.4±2.5 1.1∙1018

8. UV-vis absorption spectrum 0,022 0,020 0,018 0,016 pH value of PEM assembly SPR wavelenght Λmax (nm) FWHM (nm) 0,014 Absorbance [a.u.]/nm 0,012 0,010 2.5 110 440 0,008 3.0 427 97 0,006 3.5 414 90 0,004 0,002 0,000 200 400 600 800 Wavelenght [nm] Red shift Surface plasmon resonance effect pH=2.5 pH=3 pH=3.5

9. 4,0 3,5 3,0 Absorbance (arbitrary units) 2,5 n 2,0 1,5 1,0 0,5 0,0 200 400 600 800 1000 1200 Wavelength (nm) pH=2.5 n=1 pH=2.5 n=3 Volume fraction and size of the Ag nanoparticles in PEM are n- dependent Red shift Number of the reaction cycles Ag volume fraction (%) Average Ag particle diameter (nm) Ag particle concentrations (particles/cm3) 1.0 33 4.5±1.5 6.9∙1018 3.0 65 6.7±1.6 4.1*1018

10. In-situ ZnS nanoparticle synthesis pH = 2.5 n = 1 da= 3.2 ± 0.3 nm NaCl solution 20 nm Zn acetate solution pH=5.5 pH = 3.0 n = 1 da= 4.1 ± 0.9 nm Zn 2+ n Na2S solution ZnS nanoparticles in PEM ZnS nanoparticle 20 nm

11. ZnS nanoparticle crystal structure pH = 2.5 n = 2 da= 3.7 ± 0.4 nm Wurtzite - hexagonal [100] [110] [111] [202] Sphalerite - cubic SAED pattern BF – TEM image

12. UV-vis absorption spectrum 0.025 0.8 0.020 0.7 absorbance (a.u.)/ nm 0.6 0.015 0.5 absorbance (a.u.) 0.4 0.3 0.010 220 240 260 280 300 320 wavelength (nm) 0.2 0.1 0.0 220 240 260 280 300 320 wavelength (nm) Quantum confinement effect Red shift Red shift pH n

13. Conclusions The thickness of PEM template is controlled in nanometer range by: • pH value of the PE solution and • number of adsorbed layers With the In-situ synthesis method the control over the inorganic particle volume fraction and size is obtained by: • pH value of the PEM assembly and • number of the reaction cycles - By increasing the pH value and number of the reaction cycles larger size and lower volume fraction of inorganic nanoparticles in composite films were obtained Control over the optical properties of the composite film