Single-walled carbon nanotubes (SWNTs) possess extraordinary electrical properties, with many possible applications in electronics. Dense, horizontally aligned arrays of linearly configured SWNTs represent perhaps the most attractive and scalable way to implement this class of nanomaterial in practical systems. Recent work shows that templated growth of tubes on certain crystalline substrates yields arrays with the necessary levels of perfection, as demonstrated by the formation of devices and full systems on quartz. This paper examines advanced implementations of this process on crystalline quartz substrates with different orientations, to yield strategies for forming diverse, but well-defined horizontal configurations of SWNTs. Combined experimental and theoretical studies indicate that angle-dependent van der Waals interactions can account for nearly all aspects of alignment on quartz with X, Y, Z, and ST cuts, as well as quartz with disordered surface layers. These findings provide important insights into methods for guided growth of SWNTs, and possibly other classes of nanomaterials, for applications in electronics, sensing, photodetection, light emission, and other areas.

A chemiresistive sensor array was created from single-walled carbon nanotubes (SWCNTs) by non-covalent modification with late first-row transition metal complexes of meso-tetraphenylporphyrin. The responses to vapors of various volatile organic compounds (VOCs) were strong and were subjected to statistical analyses that enabled the successful classification of representative VOCs into five different categories (aliphatic hydrocarbons, alcohols, ketones, aromatic hydrocarbons, and amines) with 98% accuracy. With the exception of amines, which are capable of strong charge transfer interactions, the basis of classification appears to correlate with the differences in the solubility properties of the porphyrin compounds in the various VOCs as solvents. This feature suggests that an analyte with greater intermolecular affinity for the SWCNT-porphyrin composite will induce a greater response. These results further demonstrate the potential for porphyrin-functionalized SWCNT-based electronic noses for applications in inexpensive, portable chemical sensors for the identification of VOCs.