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

Introduction Inorganic nanoparticle properties  Large surface / volume ratio  Quantum confinement effect The control over the particle shape, size and concentration 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

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

 type of the PE  pH value of the PE assembly  Thickness controllable in nanometer range pH=2.5 pH=3.0 pH=3.5 Substrate effect number of polyelectrolyte bilayers PEM thickness (nm) Properties of the PEM film Weak polyelectrolyte - PAA [COO - ]= f (pH)

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

In-situ Ag nanoparticle synthesis n Ag nanoparticle Ag + NaBH 4 solution Ag acetate solution pH=5.5 HAADF - STEM image pH = 2.5 pH = 3.0 pH = 3.5 PEM film PS substrate Ag nanoparticle

Volume fraction and size of the Ag nanoparticles in PEM are pH- dependent 1.1∙ ± ∙ ± ∙ ± Ag particle concentrations (particles/cm 3 ) Average Ag particle diameter (nm) Ag volume fraction (%) pH value of PEM assembly pH=2.5 pH=3.0 pH=3.5

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

n ,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 Absorbance (arbitrary units) Wavelength (nm) Volume fraction and size of the Ag nanoparticles in PEM are n- dependent pH=2.5 n=1 4.1* ± ∙ ± Ag particle concentrations (particles/cm 3 ) Average Ag particle diameter (nm) Ag volume fraction (%) Number of the reaction cycles pH=2.5 n=3 Red shift

In-situ ZnS nanoparticle synthesis n ZnS nanoparticle Zn 2+ Na 2 S solution Zn acetate solution pH=5.5 NaCl solution pH = 2.5 n = 1 d a = 3.2 ± 0.3 nm ZnS nanoparticles in PEM pH = 3.0 n = 1 d a = 4.1 ± 0.9 nm 20 nm

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

UV-vis absorption spectrum absorbance (a.u.)/ nm wavelength (nm) pH n Red shift absorbance (a.u.) wavelength (nm) Quantum confinement effect

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