School of Engineering, Brown University, Providence, RI 02912, USA.
Nanoscale. 2012 Sep 7;4(17):5293-9. doi: 10.1039/c2nr31260c. Epub 2012 Jul 25.
Crystalline diamond nanowires have been grown in a chemical vapor deposition (CVD) process under 900 °C and atmospheric pressure--an extraordinary find in diamond growth. These diamond nanowires are straight, thin and long, and uniform in diameter (60-90 nm) over their entire lengths of tens of microns. Extensive characterizations including electron microscopy and Raman spectroscopy were performed to confirm that the diamond nanowire has highly crystalline cubic diamond structure encased inside a graphitic or carbonaceous shell. Such a core-shell structure suggests a potential formation mechanism in the framework of an effectively lowered Gibbs free energy due to nano-capillary and surface charge pressure. The capillary pressure (inversely proportional to the wire radius) can be sufficiently high to allow the diamond phase to be thermodynamically favorable in the inner core while the outer shell takes on the graphitic phase. The properties of diamond can manifest themselves differently in the nanowire morphology. Examples include single-photon emission of nitrogen-vacancy and electron field-emission. Whereas the former has received much attention in the literature, the latter turned out to be just as impressive and is show-cased here for the first time.
在 900°C 和常压下的化学气相沉积（CVD）工艺中已经生长出了晶态金刚石纳米线——这是在金刚石生长中的一项非凡发现。这些金刚石纳米线笔直、纤细且修长，直径在整个数十微米的长度上保持均匀（60-90nm）。进行了广泛的特性分析，包括电子显微镜和拉曼光谱，以确认金刚石纳米线具有高度晶态的立方金刚石结构，被石墨或碳质壳包裹着。这种核壳结构表明，由于纳米毛细管和表面电荷压力，在有效降低吉布斯自由能的框架内存在一种潜在的形成机制。毛细管压力（与线半径成反比）可以足够高，以使金刚石相在内部核心中具有热力学优势，而外壳则呈现石墨相。金刚石的性质在纳米线形态中可以表现出不同的特性。例如，氮空位的单光子发射和电子场发射。虽然前者在文献中受到了广泛关注，但后者同样令人印象深刻，并且这里是首次展示。
