High-density arrays of perfectly aligned single-walled carbon nanotubes (SWNTs) consisting almost exclusively of semiconducting nanotubes were grown on ST-cut single crystal quartz substrates. Raman spectroscopy together with electrical measurements of field effect transistors (FETs) fabricated from the as-grown samples showed that over 95% of the nanotubes in the arrays are semiconducting. The mechanism of selective growth was explored. It is proposed that introducing methanol in the growth process, combined with the interaction between the SWNTs and the quartz lattice, leads to the selective growth of aligned semiconducting nanotubes. Such a high density of horizontally aligned semiconducting SWNTs can be readily used in high current nanoFETs and sensors. This method demonstrates great promise to solve one of the most difficult problems which limits application of carbon nanotubes in nanoelectronicsthe coexistence of metallic and semiconducting nanotubes in samples produced by most, if not all, growth methods.

Herein we report a CVD approach to prepare high-density and perfectly aligned arrays of long SWNTs on stable temperature (ST)-cut quartz substrates using copper as catalyst and ethanol as carbon source. Compared with earlier reports, we have demonstrated that the aligned nanotube arrays can be grown on ST quartz substrate without the need of thermal annealing. The density can reach >50 nanotubes per micron and the length can be a few millimeters. Additionally, we have obtained direct proof on the "tip-growth" mechanism for the aligned nanotubes and important evidence that explained the termination of the growth.

Horizontally aligned single-walled carbon nanotubes (SWNTs) are highly desired for SWNT device applications. A large variety of metals including Fe, Co, Ni, Cu, Pt, Pd, Mn, Mo, Cr, Sn, Au, Mg, and Al successfully catalyzed the growth of such tubes on stable temperature (ST)-cut quartz by lattice guidance. In addition, Mg and Al were presented to produce random and aligned SWNTs for the first time. A hypothesis is proposed in which the precipitated carbon shell on the outer surface of the metal catalysts guides the alignment along the crystal lattice but not the catalysts themselves. By elucidating the role of the catalysts, an understanding of the aligned growth mechanism on quartz is further improved. Moreover, a simple “scratch” method by a razor blade such as the carbon steel and tungsten carbide (with 9% cobalt) is presented to pattern the “catalysts” without any complex processing steps such as lithography for the aligned SWNT growth.

The photovoltage produced by local illumination at the Schottky contacts of carbon nanotube field-effect transistors varies substantially with gate voltage. This is particularly pronounced in ambipolar nanotube transistors where the photovoltage switches sign as the device changes from p-type to n-type. The detailed transition through the insulating state can be recorded by mapping the open-circuit photovoltage as a function of excitation position. These photovoltage images show that the band-bending length can grow to many microns when the device is depleted. In our palladium-contacted devices, the Schottky barrier for electrons is much higher than that for holes, explaining the higher p-type current in the transistor. The depletion width is 1.5 μm near the n-type threshold and smaller than our resolution of 400 nm near the p-type threshold. Internal photoemission from the metal contact to the carbon nanotube and thermally assisted tunneling through the Schottky barrier are observed in addition to the photocurrent that is generated inside the carbon nanotube.

Carbon nanotubes and graphene are candidate materials for nanoscale electronic devices. Both materials show weak acoustic phonon scattering and long mean free paths for low-energy charge carriers. However, high-energy carriers couple strongly to optical phonons, which leads to current saturation and the generation of hot phonons. A non-equilibrium phonon distribution has been invoked to explain the negative differential conductance observed in suspended metallic nanotubes, while Raman studies have shown the electrical generation of hot G-phonons in metallic nanotubes. Here, we present a complete picture of the phonon distribution in a functioning nanotube transistor including the G and the radial breathing modes, the Raman-inactive zone boundary K mode and the intermediate-frequency mode populated by anharmonic decay. The effective temperatures of the high- and intermediate-frequency phonons are considerably higher than those of acoustic phonons, indicating a phonon-decay bottleneck. Most importantly, inclusion of scattering by substrate polar phonons is needed to fully account for the observed electronic transport behaviour.

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An electroless deposition method comprised of seed formation and subsequent seeded growth is developed for the decoration of surface-grown single-walled carbon nanotubes (SWCNTs) with gold nanoparticles of controlled size and interparticle distance. The density of the gold nanoparticles is determined by the density of seeds. Gold seeds are used for the SWCNT arrays grown on SiO(x)/Si substrates. For the dense SWCNT arrays on quartz, palladium seeds are used because it is much easier to obtain higher quantities of seeds. Attributed to both the seed formation specified on SWCNTs and the succedent efficient seeded growth process, the gold nanoparticles deposit on SWCNTs with very high selectivity. This electroless method shows no selectivity on types, defects, and conductivity of the SWCNTs, and thus ensures the uniform decoration of all SWCNTs on the wafer. Most importantly, this method provides the possibility to realize the optimal configurations of gold nanoparticles on SWCNTs for obtaining maximal surface-enhanced effects and consequently surface-enhanced Raman spectrum (SERS) of each SWCNT. Thus, both the in situ Raman detection of every SWCNT including those nonresonant with laser energy and the observation of the radial breathing modes of SWCNTs originally undetectable with resonance Raman spectroscopy are achieved. Further investigations over the effect of the laser wavelength and the interparticle distance on the SERS enhancement factors of SWCNTs prove that the coupled surface plasmon resonance absorption of the high-density gold nanoparticles decorated on SWCNTs contributes most to the strong surface enhancement.

This research examines the influence of consumer online brand community engagement (OBCE) at a time of product-harm crisis on consumers' cognitive responses and behavioral reactions toward the affected brand's super-recovery effort. Data were collected from members of Samsung's online brand community in China during the brand's Galaxy Note 7 battery crisis. The results show that OBCE has a direct as well as indirect effect on repurchase intention through the mediation of consumer forgiveness. In contrast, brand superrecovery effort has a weak direct effect on repurchase intention, and its effect is mainly indirect through consumer forgiveness. The findings suggest that higher levels of consumer brand engagement and forgiveness can offset the negative consequences of brand scandals, highlighting the importance of fostering customer engagement in the brand's online communities. The findings have important implications for both theory and practice.