Band engineering of carbon nanotube field-effect transistors via selected area chemical gating

Abstract

This letter presents an approach to engineer the band structure of carbon nanotube field-effect transistors via selected area chemical gating. By exposing the center part, or the contacts, of nanotube devices to oxidizing or reducing gases, a good control over the threshold voltage and subthreshold swing has been achieved. Our experiments reveal that NO 2 shifts the threshold voltage positively, while NH 3 shifts it negatively for both center-exposed and contact-exposed devices. However, modulations to the subthreshold swing are in opposite directions for center-exposed and contact-exposed devices: NO 2 lowers the subthreshold swing of the contact-exposed devices, but increases that of the center-exposed devices. In contrast, NH 3 reduces the subthreshold swing of the center-exposed devices, but increases that of the contact-exposed devices.

Sensing Mechanisms of Carbon Nanotube Based NH3 Gas Detectors

“…www.intechopen.com Interestingly, Liu et al also employed PMMA as a passivation layer. They observed changes in the transfer characteristics upon exposure to NH 3 and NO 2 for both contact-passivated device and channel passivated devices, suggesting that both the CNT channel and the CNT/metal contacts play a role in the detection process (Liu, et al, 2005). The obvious ambiguity in those reports could arise from the permeable passivation materials used.…”

“…Therefore, we can unambiguously conclude that NH 3 gas induced SB modulation is a dominant mechanism for our CNT gas sensors at room temperature. Actually, PMMA was widely employed as a passivation material to protect the CNT/metal contact regions for gas , Liu, et al, 2005 and protein sensing (Heller, et al, 2008). However, two major problems exist due to the polymer nature of PMMA.…”

Carbon nanomaterials for electronics, optoelectronics, photovoltaics, and sensing

“…However, the lack of definitive proof regarding the sensing mechanism inspired a series of subsequent studies focusing on the mechanism of chemical sensing by CNT FETs. 466 Through these studies, the range of analytes was expanded to include alcohols, 467 oxygen, 468 benzene, 469 hydrogen, 470 and water. 471 While some papers confirmed bulk doping as the underlying mechanism, 466 others reported that the observed resistance change was a contact effect and not a bulk doping phenomenon.…”

Biomimetic Cortical Nanocircuits

“…In comparison, interconnects made of top-down fabricated metal electrodes may never reach a width of 1-2l nm due to issues like the finite grain size and instability related to the grain wall migration. Following Zhou's previous work on carbon nanotube p-n junctions [56], mechanical switches, and chemical sensors [57], Zhou's group has carried out significant work, including the demonstration of the complementary nanotube inverter [58], band engineering of nanotube transistors via selected-area chemical doping [59], and template-free directional growth of nanotubes on a-and r-plane sapphire substrates [60,61].…”