This value is less than that of SWNT2 (1.42 eV) but still in the same order of magnitude for a qualitative comparison. In the 2-point measurements of Zhou et al. [50], the contact resistance is included in their IVs, which might induce a barrier due to metal–semiconductor-metal junction
effects. This is excluded or at least minimized in our 4-point measurements, as the contact resistance is subtracted in our configuration. Furthermore, the Protein Tyrosine Kinase inhibitor estimated contact resistance R c of SWNT2 is less than 3R Q , which is reasonably too small to be considered as invasive or to induce a significant contact barrier [40]. Interestingly, from measurements on suspended (no substrate effects) and ‘ultraclean’ metallic SWNTs, a Mott insulating state was reported, buy OICR-9429 with energy gaps between 10 and 100 meV [51]. Specifically, for SWNTs with diameters similar to SWNT2, the energy barrier was between 70 and 80 meV, which is in good agreement with the measured barriers for SWNT2. However, to explore the nature of the insulating state in SWNT2, gating experiments are needed,
which is again beyond the scope of this letter. Figure 7 Low-bias current versus PARP inhibitor voltage graph of sample SWNT2 measured at 2, 5, and 10 K. Finally, the appearance of completely different properties for SWNT1 (TLL/CB) and SWNT2 (transition to an insulating state) at low temperatures and their relation with the observed strong interaction with the quartz substrate is currently not understood. Further theoretical and experimental efforts are underway to elucidate these effects. Conclusions In conclusion, a method is introduced to isolate and measure the electrical properties of individual SWNTs aligned on Proteasome inhibitor an ST-cut quartz substrate, from room temperature down to 2 K. The diameter and chirality of the measured SWNTs are accurately defined from
resonant Raman spectroscopy and AFM. A significant up-shift in the G-band of the Raman spectra of the SWNTs is observed, which increases with increasing SWNTs diameter and indicates a strong interaction with the quartz substrate. A semiconducting SWNT (diameter 0.84 nm) shows Tomonaga-Luttinger liquid and Coulomb blockade behaviors at low temperatures. Another semiconducting SWNT (diameter of 0.68 nm) exhibits a transition from the semiconducting state to an insulating state at low temperatures. These results elucidate some of the electrical transport properties of SWNTs on ST-cut quartz substrates, which can be useful for prospective device applications. Acknowledgements This study was supported by Nano-Integration Foundry (NIMS) in ‘Nanotechnology Platform Project’ operated by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. ESS would like to acknowledge the support and hospitality of NIMS during his visit as a Guest Researcher. References 1.