| Résumé | Electron-beam modification of a precursor material can be utilized to fabricate metallic structures on single-digit nanometer dimensions. Whereas, reliable fabrication of magnetic nanostructures is essential for study of fundamental processes in magnetism, cobalt fluoride (CoF2) precursor is a candidate for such fabrication of magnetic (cobalt) nanostructures. We have studied in situ electron beam patterning of CoF2 using a JEOL 3000F transmission electron microscope. The microscope is equipped with a Gatan Image Filter allowing for electron-energy-loss chemical analysis, and equipped for electron holography for mapping of magnetic fields. Our results on electron beam (<10 nm probe) modification of cobalt fluoride show that electron dose typically of 900 C/cm² is needed for complete removal of fluorine at temperature 570 K. However, cobalt particles about 3 nm in diameter start to form at electron doses on the order of 200 C/cm². Nucleation of cobalt particles initiates at the grain boundaries of the CoF2 precursor. The Co particles grow during exposure resulting, after complete exposure, in structures composed of separated, faceted cobalt particles typically 5 - 15 nm in size. The cobalt particles are either c-axis parallel or perpendicular to the substrate plane. Elevated sample temperature during exposure was necessary to eliminate buildup of microscope-related contamination. Cooling the sample to liquid nitrogen temperature during exposure also resulted in elimination of microscope contamination, but the resulting cobalt structures were composed of individual, separated particles. We believe that the non-continuous nature of the final cobalt structures stems from the surface energetics of high surface energy metal (cobalt) on low surface energy substrate (amorphous carbon). A real-time high-resolution TEM movie of the exposure process will be presented to provide insight to the exposure process. |
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