Controlling the morphology of copper-silica nanocomposites from laser ablation in liquid

Abstract

Synthesis of copper-silica nanocomposites with controllable morphology and composition were produced with a one-step femtosecond reactive laser ablation in liquid (fs-RLAL) technique. The composite nanomaterials were generated by focusing femtosecond near-IR laser pulses onto a silicon wafer immersed in an aqueous copper(II) nitrate solution, with the solution pH adjusted using nitric acid or potassium hydroxide. Under acidic conditions (pH 3.0 and 5.4), little copper was incorporated in the predominantly silica product (1.4 and 1.5 wt.%). These acidic conditions yielded large ~30-80 nm silica particles, with some particles consisting of copper core/silica shell. In contrast, increasing the solution pH to 10.4 resulted in extremely high Cu loading of 31.5 wt.% and a composite product consisting of 1.5 nm copper clusters distributed throughout a matrix of amorphous silica and copper phyllosilicate. The relationship between the precursor solution pH and the product morphology and copper loading is attributed to the point of zero charge (PZC) of silica, in which the high solution pH allows for electrostatic adsorption to occur between the deprotonated silica clusters from the ablated silicon wafer and the copper hydroxide dimer formed in solution. File list (2) download file view on ChemRxiv CuSiO2_v7.pdf (4.09 MiB) download file view on ChemRxiv sicu_SI.pdf (1.16 MiB)

Deposition of Cubic Copper Nanoparticles on Silicon Laser-Induced Periodic Surface Structures via Reactive Laser Ablation in Liquid

“…The laser reduction of copper nitrate is primarily driven by hydrated electrons in solution, which form both from water photolysis and ejection from the silicon surface. − However, hydrated electrons are rapidly scavenged under acidic conditions, , which is expected to slow Cu 2+ reduction. Slow Cu 2+ reduction is consistent with the extremely low deposition of copper onto silica ejected from the silicon surface during RLAL under acidic conditions . In contrast, high copper loading on ejected silica species observed in RLAL under basic conditions is consistent with faster reduction.…”

“…The Si 0 doublet in both samples appears downshifted from the generally accepted 99.4 eV value for the Si 2p peak . This slight downshifting in the Si 0 doublet has been observed in silica colloids obtained from femtosecond laser ablation before ,, and likely indicates increased electron density around the Si atoms. , The high contribution of SiO x species at earlier sputter times is due to oxidation of surface Si atoms by reactive water species such as hydroxyl radicals produced during ablation. , In both samples, the rapid decrease of SiO x (orange) and increase of Si 0 doublet peaks (red) with sputter time indicate that SiO x species are rapidly etched away. These results indicate that the Ar + ion sputtering penetrates into the surface over the course of sputter time, rather than just probing the “valleys” of the LIPSS structures because SiO x would still be present on these regions due to exposure to the aqueous solution.…”

“…The Si 0 doublet in both samples appears downshifted from the generally accepted 99.4 eV value for the Si 2p peak. 40 This slight downshifting in the Si 0 doublet has been observed in silica colloids obtained from femtosecond laser ablation before 23,32,41 and likely indicates increased electron density around the Si atoms. 42,43 The high contribution of SiO x species at earlier sputter times is due to oxidation of surface Si atoms by reactive water species such as hydroxyl radicals produced during ablation.…”

“…Slow Cu 2+ reduction is consistent with the extremely low deposition of copper onto silica ejected from the silicon surface during RLAL under acidic conditions. 41 In contrast, high copper loading on ejected silica species observed in RLAL under basic conditions is consistent with faster reduction. Moreover, the formation of silicic acid in solution at pH >8 30 results in further conversion of Cu 2+ into copper phyllosilicates with strong Cu−O−Si bonds.…”

“…In contrast, high copper loading on ejected silica species observed in RLAL under basic conditions is consistent with faster reduction. Moreover, the formation of silicic acid in solution at pH >8 30 results in further conversion of Cu 2+ into copper phyllosilicates with strong Cu–O–Si bonds . This consumption of copper in solution reactions to form phyllosilicates at high pH likely inhibits copper deposition onto the Si surface, resulting in the observed low Cu loadings on the Cu-Si NSS at high pH (Figure ).…”