title: Optimization of second harmonic generation of gold nanospheres and nanorods in aqueous solution: the dominant role of surface area.
abstract: Size and shape of gold nanoparticles (AuNPs) have a strong influence on their second order nonlinear optical properties. In this work, we propose a systematic investigation of surface and shape effects in the case of small gold nanoparticles. Colloidal solutions on AuNPs with different sizes and shapes have been synthesized, i.e. nanospheres (diameters 3.0; 11.6; 15.8; 17.4; 20.0 and 43 nm) and nanorods (aspect ratios 1.47; 1.63 and 2.30). The first hyperpolarizability β values of these AuNPs have been measured by harmonic light scattering (HLS) at 1064 nm. For nanospheres and nanorods, we found that their β values are governed by a purely local, dipolar contribution, as confirmed by their surface area dependence. As an important consequence of these surface effects, we have revisited the previously reported aspect ratio dependence of β values for gold nanorods, and evidenced the predominant influence of nanoparticle area over aspect ratio considerations.
authors.affiliation: Laboratoire de Photonique Quantique et Moléculaire, UMR 8537, Ecole Normale Supérieure de Cachan, CentraleSupélec, CNRS, Université Paris-Saclay, 94235 Cachan, France. ledoux@lpqm.ens-cachan.fr.
authors.forename: Hoang Minh
authors.initials: HM
authors.lastname: Ngo
authors.affiliation: Department of Chemistry, University of Science, Vietnam National University, Ho Chi Minh City, Vietnam.
authors.forename: Phuong Phong
authors.initials: PP
authors.lastname: Nguyen
authors.affiliation: Laboratoire de Photonique Quantique et Moléculaire, UMR 8537, Ecole Normale Supérieure de Cachan, CentraleSupélec, CNRS, Université Paris-Saclay, 94235 Cachan, France. ledoux@lpqm.ens-cachan.fr.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Ledoux-Rak