Controlled Synthesis、Identification And Research Of Horizontal Arrays Of Single-walled Carbon Nanotubes

Single-walled carbon nanotubes(SWCNTs) can be metallic or semiconducting depending on their chirality. Metallic SWCNTs(m-SWCNTs) can be used as nanoscale electrodes and interconnects, and semiconducting SWCNTs(s-SWCNTs) can be served as active channels with extraordinary mobility and high ON/OFF ratios. Besides, the bandgaps of s-SWCNTs are dependent on their diameters. However, the as-synthesized SWCNTs are always a mixture of m-SWCNTs and s-SWCNTs with a bandgap distribution. So the key challenge for SWCNTs in high-performance field effect transistors(FETs) is the requirement of a tight distribution of s-SWCNTs, and a methodology to achieve rapid and large-scale evaluation of a purity of s-SWCNTs should be developed. Besides, we also need to improve other techniques, such as the density of SWCNTs arrays, transfer of SWCNTs, performances of SWCNTs devices.Here we demonstrate that horizontally aligned SWCNTs are synthesized on stable temperature-cut(ST-cut) quartz by chemical vapor deposition(CVD). The large-area SWCNTs with intramolecular junctions also have been grown by a “blowing” technique during the growth process.We show that the Schottky barrier between metal electrode and s-SWCNT can be clearly observed in scanning electron microscopy(SEM) images as a bright segment with length up to micrometers, due to the space charge distribution in the depletion region. The lengths of the bright segments are notably different for various s-SWCNTs, and we found that the lengths increase with the diameters of s-SWCNTs, which means a linear relationship between the lengths of bright segments and the inverse of the bandgap of s-SWCNTs. This approach enables direct and efficient evaluation of the bandgap distributions of s-SWCNTs and will play key roles on the road toward a tight distribution of semiconductor bandgaps, or even single bandpgap(single chirality). Moreover, it can also be applied for a wide variety of semiconducting nanomaterials, adding a new function to conventional SEM.We developed a metal-film-assisted method to realize an ultra-clean transfer of SWCNTs mediated by poly(methyl methacrylate)(PMMA). The surfaces of SWCNTs and substrates are much cheaner than those obtained the conventional transfer, which is veryfied by atomic force microscope(AFM), Raman spectra and transmission electron microscope(TEM) characterizations. This technique is efficient, nondestructive, and scalable. We also fabricate complex nanostructures by multiple transfers, such as cross-stacked SWCNT networks and SWCNT/graphene stack structures. Schottky barriers at the contact point of m-SWCNT and s-SWCNT can be clearly observed, which means a good contact between SWCNTs can be formed by our method. Moreover, the relatively low workly temperature of this technique is compatible with the transfer of flexible electronics.We fabricate the SWCNTs cross-junction devices via metal-filmed-assisted technique, showing a good contact between SWCNTs from different layers. Furthermore, we also fabricate the high-performance FET using m-SWCNTs as electrodes and s-SWNCT as conductive channel.