Matrix-Assisted Pulsed Laser Evaporation Deposition of Pd Nanoparticles: The Role of Solvent

The formation of Pd nanoparticles (NPs) by matrix-assisted pulsed laser evaporation (MAPLE) of a palladium acetate solution has been studied as a function of the carrier solvent, laser-pulse number, metal precursor concentration and post-deposition thermal heating. Structural and compositional analyses demonstrate that: (i) the conventional MAPLE process can induce self-reduction of the metal salt precursor, thereby leading to the formation of metallic Pd(0) NPs; (ii) the solvent critically determines the size, morphology, and size distribution of the resulting NPs; and (iii) the cumulative effects of laser-pulse number and solute concentration are less influential than the type of solvent used. For diethyl ether-derived samples, a bimodal distribution of NP sizes spanning from ∼1 nm up to 20 nm was obtained. Conversely, by using acetone, a mono-modal distribution of sizes in the ∼1 nm–6 nm range (mean diameter of 1.5±0.7 nm) and a more uniform and densepacked surface coverage (NP coverage was twice as dense as the one obtained with diethyl ether) resulted in. These observations point out that solvents with low dynamical viscosity coefficients and high volatility favor the formation of larger and more broadly dispersed NPs. A general theoretical picture has been proposed to describe the NP formation pathways on account of the solvent properties and the mechanisms underlying the MAPLE process enabled by the technique.