Alkanethiolate-protected copper nanoparticles: Spectroscopy, electrochemistry, and solid-state morphological evolution

Copper nanoparticles protected by alkanethiolate monolayers were prepared in a one-phase system using superhydride as the reducing reagent. The as-produced nanoparticles were typically found within the size range of 1-2 nm in diameter and of spherical shape. UV-vis and FTIR spectroscopies were carried out to investigate the particle optoelectronic properties and the molecular conformations of the protecting monolayers. Electrochemistry was used to study their quantized charging properties in solutions where the nanoparticle molecular capacitance was evaluated. When the particles were subject to mild-temperature thermal annealing in solid state, large (> 10 nm) nanocrystals emerged with well-define facets and distinct surface morphologies. While the majority of the nanocrystals were spherical, other crystal shapes such as hexagons, pentagons, diamonds, triangles, and even rods were very visible. Discussion of the molecular mechanism for the shape evolution is presented.