We explore the formation kinetics, optical absorption spectra, and particle size distributions of copper nanoparticles (CuNPs) formed by direct laser ablation from the bulk metal via a process we refer to as Laser Ablation Synthesis in Solution (LASiS). Comparisons are made between CuNPs formed in pure water versus those formed in the presence of 1 Â 10 À4 M solutions of the N-donor ligands 4,4 0 -bipyridine (4,49Bipy) and 1H-5-(4-pyridyl)tetrazole (T-4Py). CuNPs formed in pure water and in the presence of 4,49Bipy display similar UV-visible absorption spectra and very similar particle size distributions. In comparison, CuNPs formed in the presence of T-4Py display significantly different absorption properties, with the surface plasmon resonance transition blue-shifted by ,55 nm, and a much smaller and narrower particle size distribution compared with the former samples. Based on previous literature reports, it is possible to ascribe these differences to differences in the CuNP surface oxidation states for samples prepared in the presence of T-4Py. However, an analysis of the formation kinetics of all three samples indicates near-identical behaviour.

We report on studies that demonstrate how the chemical composition of the surface of copper nanoparticles (CuNPs) – in terms of percentage copper(I/II) oxides – can be varied by the presence of N-donor ligands during their formation via laser ablation. Changing the chemical composition thus allows systematic tuning of the surface plasmon resonance (SPR) transition. The trialed ligands include pyridines, tetrazoles, and alkylated tetrazoles. CuNPs formed in the presence of pyridines, and alkylated tetrazoles exhibit a SPR transition only slightly blue shifted with respect to CuNPs formed in the absence of any ligand. On the other hand, the presence of tetrazoles results in CuNPs characterized by a significant blue shift of the order of 50–70 nm. By comparing these data also with the SPR of CuNPs formed in the presence of carboxylic acids and hydrazine, this work demonstrates that the blue shift in the SPR is due to tetrazolate anions providing a reducing environment to the nascent CuNPs, thus preventing the formation of copper(II) oxides. This conclusion is further supported by the fact that both AFM and TEM data indicate only small variations in the size of the nanoparticles, which is not enough to justify a 50–70 nm blue-shift of the SPR transition. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies further confirm the absence of Cu(II)-containing CuNPs when prepared in the presence of tetrazolate anions.