Development of Method to Form New-Function Thin Film by Fullerene Plasma

The endohedral metallofullerene K@CィイD260ィエD2 was successfully formed by the energy and flux control of KィイD1+ィエD1 and CィイD1-ィエD1ィイD260ィエD2 ions flowing into substrates in experiments of the thin-film formation with a potassium-fullerene (KィイD1+ィエD1-CィイD1-ィエD1ィイD260ィエD2) plasma. Since the K@CィイD260ィエD2 production ratio to CィイD260ィエD2 was at most 30% and usually 5〜10% or less, however, it was difficult to clarify the relation between the plasma effect and encapsulation mechanism. From the above-mentioned viewpoint, the experiments were carried out by a sodium-fullerene (NaィイD1+ィエD1-CィイD1-ィエD1ィイD260ィエD2) plasma, where the diameter of NaィイD1+ィエD1 is smaller than that of KィイD1+ィエD1. The following results were obtained. According to the mass analysis of thin films formed on the substrates, the large mass-spectrum peak (Na(@)CィイD260ィエD2) corresponding to the Na-endohedral fullerene is observed. The average intensity ratio of Na(@)CィイD260ィエD2 to CィイD260ィエD2 is turned out to be 30〜50%. Moreover, the Na(@)CィイD260ィエD2 production ratio to CィイD260ィエD2 in a narrow region of the substrate attains to 200% or more. When the substrate bias is changed, the average spectrum-peak intensity of Na(@)CィイD260ィエD2 is found to give the maximum value at a specific voltage. The composition and structure of the thin film are directly investigated by the high-resolution electron microscope (HREM) observation. A lot of CィイD260ィエD2 molecules with dark shadows around the centers are observed over the image of the thin film in the narrow region of the substrate. The round material imaged by the HREM is considered to be CィイD260ィエD2 encapsulating Na inside the cage, because the NaィイD1+ィエD1 diameter almost corresponds to the dark shadow diameter. It can be said that a large amount of production of the Na-CィイD260ィエD2 compound materials containing Na@CィイD260ィエD2 facilitates the constituent analysis and structure observation for the purpose of clarifying their physical and chemical properties. This work is also important in the sense of establishing the method of forming fullerene-based thin films with new functions.