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

将可在其腔内引入一种气体的超高压fe - sem改造为双气体引入系统的EBID仪器。利用该仪器在Fe (C_5H_5)2和Fe (CO)_5的混合气体中进行了电子束诱导沉积，制备了不同铁浓度的纳米结构。结果表明，通过改变Fe (C_5H_5)_2和Fe (CO)_5的分压比，可以控制铁的浓度。利用电子全息技术对不同铁碳比纳米结构的剩余磁通密度Br进行了测量，结果表明，Br值与铁浓度有关。以Fe (CO)_5和（CH_3）_3 (C_5H_5)Pt的混合气体为前驱体，在600℃下退火2小时完成结晶过程。纳米棒由包裹在含碳护套内的结晶铁铂合金纳米颗粒链组成。通过电子衍射和HRTEM鉴定了纳米颗粒为面心方形FePt相L10。用电子全息法测定了纳米棒的剩余磁通密度Br，表明纳米棒具有强铁磁性。在Fe (CO)_5中加入水蒸气可以有效地降低碳含量，加入足够的水蒸气可以形成无碳结晶Fe_3O_4纳米棒。然而，在W (CO)_6的情况下，得到的纳米棒是由富含碳的非晶基体和嵌入在基体中的氧化钨纳米晶体组成的。这一结果表明，铁的催化性能对使用水蒸气的EBID过程可能有重要影响。

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.