Processing and characterization of copper-fullerene systems

[摘要] Nanocrystalline copper-fullerene thin films were simultaneously co-deposited by copper evaporation and fullerene sublimation, and annealed over a range from 200 to 800$spcirc$C for 8 hours in flowing argon. Scanning electron microscopy, transmission electron microscopy, electron probe micro analysis, x-ray diffraction and extended x-ray absorption fine structure analysis were used to characterize the films before and after annealing. These analyses show that fullerenes were dispersed at a microscopic level in the uniform thin films by the co-deposition technique. The fullerenes were observed to segregate at the copper grains boundaries. The copper grains were refined with the nanosize fullerene particles during the co-deposition. Comparing to the pure copper thin films, grain growth in the fullerene-copper thin films was significantly suppressed by the dispersed fullerenes when the annealing temperature was lower than 400$spcirc$C. Grain growth occurred when the films annealed above 400$spcirc$C where the fullerenes were separated from the copper matrix. Furthermore, a model for a Cu-C$sb{60}$ system was proposed to provide a better understanding of the interactions between copper atoms and fullerene molecules. This model suggests that fullerene segregation and its concentrations at the copper grain boundaries are the two major factors in determining the microstructures of the copper-fullerene thin films during co-deposition and annealing. The Zener pinning theory was used to explain the copper grain size stabilization with the fullerene dispersion. It was revealed that the stabilized grain size is a function of the grain boundary saturation concentrations of the fullerenes. The oxidation of the films, the formation of holes and hillocks were also explored.Bulk copper-fullerene composites were processed by powder metallurgy with dry and wet mixing techniques. Fullerene dispersion was achieved at an intergranular level. Hot isostatic pressing was applied during sintering to control porosity. The copper grain sizes at sintering temperatures over a range from 850 to 1050$spcirc$C for 2 hours in flowing argon were determined with metallographic technique. The relationships between grain growth, sample porosity and fullerene addition were discussed.

[发布机构] Rice University

[效力级别] Engineering