Copper nanoparticles encapsulated in multi-shell carbon cages

• Published in: Applied physics. A, Materials science & processing Vol. 78; no. 1; pp. 73 - 77
• Main Authors: SCHAPER, A. K, HOU, H, GREINER, A, SCHNEIDER, R, PHILLIPP, F
• Format: Journal Article
• Language: English
• Published: Berlin Springer 2004
• Subjects: ANNEALING PROCESSES; Cages; Carbon; Copper; Cross-disciplinary physics: materials science; rheology; ENCAPSULATION; Exact sciences and technology; Materials science; MELTING POINT; Melting points; Methods of nanofabrication; MICROSTRUCTURES; Nanomaterials; Nanostructure; PARTICLES; Physics; Shells; Encapsulation; Radiation effects; Annealing; Phase transformations; Experimental study; Nanoparticles; Electron beams; Transmission electron microscopy; Order degree; Transition elements; Copper; Microstructure; Chemical synthesis
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-003-2199-0

Nanoparticles are attracting increasing interest because of their high potential for a great number of practical applications, such as optical and electronic devices, nanoscale storage, and delivery systems. Using Cu-phthalocyanine as precursor material, we have synthesized multi-shell graphitic carbon nanospheres without and with metal encapsulation, depending on the pyrolysis conditions. The encapsulated elemental copper nanocrystals achieved using that route were of the order of 50 nm in size. The particles were characterized in detail by high-resolution transmission electron microscopy (HRTEM) and by energy filtering microscopy (EFTEM). The concentric graphitic carbon shells of the as-grown particles were clearly discernable. After in situ high-temperature annealing, an increase in the degree of order was observed. Under high-voltage electron irradiation and heating, a melting point reduction of the enclosed nanosized copper of more than 200 K could be detected, as compared to the melting point 1083 C of bulk copper. Time-resolved imaging revealed the displacement of the melting copper by migration through the carbon shells, leaving intact carbon cages with a central hole. At intermediate stages of this process the transformation into a hexagonal morphology of the copper nanocrystals was observed.