Durrer Lukas, Greenwald Jason, Helbling Thomas, Muoth Matthias, Riek Roland, Hierold Christofer
Micro and Nanosystems, Department of Mechanical and Process Engineering, ETH Zürich, Zurich, Switzerland.
Nanotechnology. 2009 Sep 2;20(35):355601. doi: 10.1088/0957-4484/20/35/355601. Epub 2009 Aug 12.
Sensors and devices made from single-walled carbon nanotubes (SWNTs) are most often electrically probed through metal leads contacting the semiconducting SWNTs (s-SWNTs). Contact barriers in general and Schottky barriers (SBs) in particular are usually obtained at a metal-semiconductor interface. The unique one-dimensional structure (1D) of SWNTs allows tailoring of the SB heights through the contact metal type and the size of the s-SWNT bandgap. A large workfunction reduces the SB height (e.g. using Pd as the metal contact material). The bandgap of an SWNT is inversely proportional to its diameter. Ohmic contacts--the preferable choice--are achieved for s-SWNTs with diameters greater than 2 nm on Pd metal leads. SWNT device reproducibility, on the other hand, requires a narrow distribution of the SWNT diameters. Here, we present a method to fabricate SWNTs with a large and adjustable mean diameter (1.9-2.4 nm) and very narrow diameter distribution (+/- 0.27 nm at mean diameter 1.9 nm). The results are achieved through a size separation of the ferritin catalyst particles by sedimentation velocity centrifugation prior to their use in the chemical vapor deposition (CVD) formation of SWNTs.
由单壁碳纳米管（SWNTs）制成的传感器和器件通常通过与半导体单壁碳纳米管（s - SWNTs）接触的金属引线进行电探测。一般的接触势垒，特别是肖特基势垒（SBs），通常在金属 - 半导体界面处形成。SWNTs独特的一维结构（1D）允许通过接触金属类型和s - SWNT带隙大小来调整SB高度。较大的功函数会降低SB高度（例如使用Pd作为金属接触材料）。SWNT的带隙与其直径成反比。对于直径大于2 nm的s - SWNTs，在Pd金属引线上可实现欧姆接触——这是更优选择。另一方面，SWNT器件的可重复性要求SWNT直径分布狭窄。在此，我们提出一种方法来制造平均直径大且可调节（1.9 - 2.4 nm）、直径分布非常窄（平均直径1.9 nm时为±0.27 nm）的SWNTs。这些结果是通过在用于SWNTs化学气相沉积（CVD）形成之前，通过沉降速度离心对铁蛋白催化剂颗粒进行尺寸分离而实现的。
