Preparation of copper nanoparticles for metal-metal bonding by aqueous reduction with d-glucose and PVP

Copper nanoparticles (CuNPs) for metal-metal bonding were prepared by aqueous reduction with d-glucose and polyvinylpirrolidone (PVP). Increasing the cupric concentration in the range 0.1–1.0 M resulted in a progressive increase in CuNPs size from 30 nm to 200 nm. Fourier-transform infrared spectroscopy (FTIR) revealed as the PVP groups responsible for capping were CN and CO at low cupric concentration and only CO at higher concentration. X-ray absorption fine structure (XAFS) revealed as the reduction occurred in two steps, with a fast reduction of CuO to Cu2O and a slower reduction of Cu2O. The reaction kinetics was modeled as a series of two irreversible first order reactions based on XAFS results. LC-MS highlighted as d-glucose oxidized to gluconate, glycerate, glycolate and oxalate. Increasing the d-glucose concentration did not affect the kinetics but resulted in smaller CuNPs. The electrical resistivity of the CuNPs material sintered at 300 °C was 36 µΩ cm.