Fabrication of high coercivity magnetic nanostructures by electron beam induced deposition with dual metal-organic gases

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We modified our UHV-FE-SEM, by which we could introduce one kind of gas in its camber, to an EBID instrument with dual gases introduction system. Electron beam induced deposition with a mixture gas of Fe (C_5H_5)2 and Fe (CO)_5 was carried out to fabricate nanostructures with different iron concentrations using this instrument. It was found that the iron concentration could be controlled by changing the ratio of partial pressure of Fe (C_5H_5)_2 and Fe (CO)_5. Electron holography was employed to evaluate the remanent magnetic flux density Br for the nanostructures with various compositional ratios of iron to carbon, indicating that the Br value is related to the iron concentration.A mixture gas of Fe (CO)_5 and (CH_3)_3 (C_5H_5)Pt was used as a precursor and post-annealing at 600℃ for 2 hour was performed to accomplish the crystallization process. Nanorods were composed of a chain of crystalline Fe-Pt alloy nanoparticles encapsulated within a carbon-containing sheath. The nanoparticles were identified to be face centered tetragonal FePt phase L10 by electron diffraction and HRTEM. The residual magnetic flux density Br of the nanorods was evaluated from electron holography, showing a strong ferromagnetic character.The addition of water vapor to Fe (CO)_5 could effectively reduce carbon content and the addition of enough water vapor resulted in the formation of carbon-free crystalline Fe_3O_4 nanorods. However, in the case of W (CO)_6, the resulting nanorods were composed of a carbon-rich amorphous matrix and tungsten oxide nanocrystals embedded in a matrix. This result suggested that the effect of the catalytic property of iron on the EBID process with water vapor use might be important.