OVERVIEW ON THE MAJOR RESEARCH ACTIVITIES ON CARBON NANOTUBES BEING DONE IN AMERICA, EUROPE AND ASIA - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 249

might ind applications in integrated nanophotonic circuits, quantum optics
and on-chip optical interconnects.
Figure 9.4 3D schematic representation of the device comprising a CNT-based FET
integrated with a planar λ /2 microcavity. Figure redrawn from Xia et al . 36
One main hurdle in the widespread application of CNTs in electronics is
still represented by the current inability to produce large amounts of identical
nanostructures. A solution to this problem has been proposed, which suggests
the use of uniform CNTs as key components in thin-ilm transistors (TFTs).
In this context, CNTs were self-assembled into micrometre-wide strips that
formed regular arrays of dense and highly aligned CNTs covering the entire
chip. 41 The initial limitation, due to the presence of heterogeneous mixtures
of metallic tubes with concomitant low on/off currents, was overcome by
pre-selection of the tubes, thus obtaining purely semiconducting CNT-based
TFTs which, as a result, exhibited high current lows. This work was realised
between two main groups of research, namely, Avouris's group and Hersam's
(reported in another session), thus merging excellent skills towards common
ambitious goals.
Another successful array has been reported through the assembly of
aligned SWCNTs via lithography techniques. 42 More precisely, CNTs were
initially derivatised with hydroxamic acid groups, which presented the double
advantage of enhancing SWCNTs' water dispersibility while increasing their
interaction with metal oxide surfaces (i.e., hafnium oxide [HfO 2 ]) (Fig. 9.5) .
Subsequently, the tubes were arranged and aligned into trenches of SiO 2
ilms with HfO 2 at the bottom. Thermal treatment at 600 ° C reconstituted
pristine, pure SWCNTs, to which palladium source−drain electrodes were
connected perpendicularly to the trench length. The array exhibited electrical
properties comparable to those reported for suspended CNT-based devices,
without deterioration following the alignment of the tubes, thus representing
valuable starting points for large-scale arrays.