Sachser Roland, Reith Heiko, Huzel Daniel, Winhold Marcel, Huth Michael
Physikalisches Institut, Goethe-Universität , Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany.
ACS Appl Mater Interfaces. 2014 Sep 24;6(18):15868-74. doi: 10.1021/am503407y. Epub 2014 Sep 11.
In the majority of cases, nanostructures prepared by focused electron beam induced deposition employing an organometallic precursor contain predominantly carbon-based ligand dissociation products. This is unfortunate with regard to using this high-resolution direct-write approach for the preparation of nanostructures for various fields, such as mesoscopic physics, micromagnetism, metaoptical phenomena in the visible spectral range, or others. Following early attempts of postprocessing Pt-based structures prepared by focused electron beam induced deposition at several hundred degrees Celsius in a reactive gas atmosphere, recent work has focused on developing in situ purification processes by using a stationary O2 flux in combination with electron irradiation to oxidize the carbonaceous component of the deposits. Here we show that this purification process is driven by the catalytic activity of Pt and in fact does not rely on the parallel electron irradiation process to function, if the O2 exposure is done in a pulsed fashion. We suggest a multistep cleaning mechanism which results in pure, nanoporous Pt. By suitably chosen beam parameters, high-resolution Pt dot and line structures with dimensions below 10 nm can thus be conveniently obtained. In temperature-dependent resistance measurements, we find the typical metallic behavior of Pt. In low-temperature magnetoresistance measurements, we see clear evidence for weak antilocalization effects and deduce a dephasing length of 234 nm at 1.2 K. We consider this to be a promising starting point for developing this approach into a versatile preparation technique for Pt-based mesoscopic structures, in particular since the purification process can be run in parallel on different deposits. We furthermore anticipate that our results will spur further research on purification approaches for nanostructures prepared by focused electron beam induced deposition containing a catalytically active metal species such as Pd-, Fe-, or Co-based deposits.
在大多数情况下，采用有机金属前驱体通过聚焦电子束诱导沉积制备的纳米结构主要包含碳基配体解离产物。对于将这种高分辨率直写方法用于制备适用于各种领域（如介观物理学、微磁学、可见光谱范围内的超光学现象等）的纳米结构而言，这是令人遗憾的。在早期尝试于反应性气体气氛中在几百摄氏度下对通过聚焦电子束诱导沉积制备的铂基结构进行后处理之后，近期的工作集中于通过使用稳定的氧气通量与电子辐照相结合来氧化沉积物中的碳质成分，从而开发原位纯化工艺。在此我们表明，如果以脉冲方式进行氧气暴露，这种纯化过程是由铂的催化活性驱动的，实际上并不依赖于并行的电子辐照过程来发挥作用。我们提出了一种多步清洁机制，该机制可产生纯净的纳米多孔铂。通过适当选择束参数，因此可以方便地获得尺寸低于10 nm的高分辨率铂点和线结构。在与温度相关的电阻测量中，我们发现了铂的典型金属行为。在低温磁电阻测量中，我们看到了弱反局域化效应的明确证据，并推断出在1.2 K时的退相干长度为234 nm。我们认为这是将该方法发展成为一种用于制备基于铂的介观结构的通用制备技术的有前景的起点，特别是因为纯化过程可以在不同的沉积物上并行进行。我们还预计，我们的结果将激发对通过聚焦电子束诱导沉积制备的包含催化活性金属物种（如钯基、铁基或钴基沉积物）的纳米结构的纯化方法的进一步研究。
