RESEARCH PAPER Aggregation and fractal formation of Au and TiO 2 nanostructures obtained by fs-pulsed laser deposition: experiment and simulation Emanuele Cavaliere & Giulio Benetti & Giuseppe Luca Celardo & Damiano Archetti & Pasqualantonio Pingue & Gabriele Ferrini & Luca Gavioli Received: 20 June 2017 /Accepted: 21 August 2017 # Springer Science+Business Media B.V. 2017 Abstract In the synthesis of nanostructures by pulsed laser deposition (PLD), a crucial role is played by the environmental deposition pressure and the substrate tem- perature. Due to the high temperature of nanoparticles (NPs) at landing, other factors may determine the struc- ture of the resulting aggregates. Here, Au and TiO 2 nanostructures are obtained by non-thermal fs-PLD in ambient conditions. On Si(100), only TiO 2 NPs form fractals with areas up to ~ 1 × 10 6 nm 2 , while on quartz Au NPs also form fractals with areas up to ~ 5 × 10 3 nm 2 , a much smaller size with respect to the TiO 2 case. The aggregation is described by a simple diffusive model, taking into account isotropic diffusion of the NPs, allowing quantitative simulations of the NPs and fractal area. The results highlight the key role of substrate ther- mal conductivity in determining the formation of fractals. Keywords Fractals . Nanoparticles . Gold . Titanium oxide . Femtosecond lasers . Monte Carlo simulations . Diffusion model Introduction Pulsed laser deposition (PLD) is an advanced method for synthesis of nanoparticles (NPs) (Sanz et al. 2010; Noël et al., 2007; Chakravarty et al. 2010; Eliezer et al. 2004; Alonso et al. 2009; Kazakevich et al. 2006) or fractal structures (Musaev et al. 2009; Ong et al. 2008; Lavisse et al. 2012; Cavaliere et al. 2013; Peli et al. 2016; Celardo et al. 2017) under different environmen- tal conditions, ranging from vacuum to water, and employing either ns or fs laser pulses. The role of environmental pressure in the plume size and composi- tion has been highlighted (Amoruso et al. 2008), and recently, we have demonstrated that formation of TiO 2 fractal structures can be explained by considering a diffusion limited aggregation model applied to NPs (Celardo et al. 2017). However, to obtain controlled nanostructures (Flaherty et al. 2007 ) applicable in catalysis (Remediakis et al., 2005), photo-assisted oxidation J Nanopart Res (2017) 19:311 DOI 10.1007/s11051-017-4009-1 Giulio Benetti, Gabriele Ferrini, and Luca Gavioli contributed equally. E. Cavaliere : G. Benetti : G. L. Celardo : D. Archetti : G. Ferrini : L. Gavioli (*) Interdisciplinary Laboratories for Advanced Materials Physics (i-LAMP) and Dipartimento di Matematica e Fisica, Università Cattolica del Sacro Cuore, Via dei Musei 41, I-25121 Brescia, Italy e-mail: luca.gavioli@unicatt.it G. Benetti Laboratory of Solid State Physics and Magnetism, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium G. L. Celardo Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Apartado Postal J-48, 72570 Puebla, Mexico D. Archetti Warwick Centre for Predictive Modelling, School of Engineering, University of Warwick, Coventry CV4 7AL, UK P. Pingue Laboratorio NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Piazza San Silvestro 12, 56127 Pisa, Italy