One-step Gas-phase Synthesis of Core-shell Nanoparticles via Surface Segregation.

A great amount of research effort has been devoted to theproduction of core-shell nanoparticles for applications in variousfields including biomedical imaging, catalysis, and plasmonics.Such attention to core-shell nanoparticles arise from the fact thatthey can exhibit enhanced physical and/or chemical properties.Furthermore, core-shell particles with distinctly new propertiescompared to those of the constituent materials can be designedby tuning, for example, their size, shell thickness, and structure [1,2].Although chemical synthesis techniques are currently the mostpopular methods for fabricating core-shell nanoparticles,interface and surface contaminations are often an unavoidableissue in the solution-based approaches. Aerosol based methodsare cleaner alternatives and have been used to produce core-shellnanoparticles [3-6]. Here we present aerosol core-shellnanoparticles generated via spark discharge generation (SDG) [7].Cu-Ag core shell nanoparticles were fabricated via surfacesegregation using SDG accompanied by sintering directly in thegas phase. The surface segregation employed in this methodrefers to the phenomenon of the enrichment of one componentof a mixture in the surface region and is attributed to theinterplay between the atomic radii, cohesive energy, and surfaceenergy of the core and shell materials [8].Depending on the sintering temperature, the SDG-generatednanoparticles form Janus-like or core-shell structures. Themorphology, crystallinity, and composition of the SDG-generatedbimetallic nanoparticles were investigated by scanning electronmicroscopy, high-resolution transmission electron microscopy,and energy-dispersive X-ray spectroscopy. Molecular dynamicssimulations were carried out to investigate the structuralevolution of Cu-Ag nanoparticles during heating and coolingprocesses corresponding to the sintering. This appealingly simpleone-step gas-phase synthesis method presented here can beemployed for other bimetallic systems. (Less)