Giant Temperature Coefficient of Resistance in Carbon Nanotube/Phase‐Change Polymer Nanocomposites

Abstract

The temperature coeffi cient of resistance of a carbon nanotube nanocomposite with the non-conductive phase-change hydrogel Poly(N-isopropylacrylamide) is studied. This nanocomposite is found to achieve the largest reported temperature coeffi cient of resistance, ≈ − 10%/ ° C, observed in carbon nanotube-polymer nanocomposites to date. The giant temperature coefficients of resistance results from a volume-phase-transition that is induced by the humidity present in the surrounding atmosphere and that enhances the temperature dependence of the resistivity via direct changes in the tunneling resistance that electrons experience in moving between nearby carbon nanotubes. The bolometric photoresponses of this new material are also studied. The nanocomposite's enhanced responses to temperature and humidity give it great potential for sensor applications and uncooled infrared detection.

Uncooled Carbon Nanotube Photodetectors

“…The highest TCR for SWCNT-polymer composites was reported by Xu et al, [86] who attained 10%/K, even larger than that (3%/K) of vanadium oxide. In this work SWCNTs were incorporated into poly(N-isopropylacrylamide) (PNIPAm) to make SWCNT-PNIPAm composites.…”

“…The TCR of SWCNT films has been increased from 0.1%/K to 10%/K using this approach. [86] In 2008, [95] an IR bolometer based on suspended SWCNT-PC composite was reported by The IR bolometer based on this composite operated at room temperature, with a responsivity of ~ 150V/W, but a relatively slow response time of ~1 seconds (see Fig. 9c).…”

“…As far as the first aspect is concerned, many methods have been explored such as the variation of the CNT film thickness, [54] sorting the CNTs by electronic type, [33] investigating the optimal diameter distribution of CNTs, [94] and engineering the activation energy for charge transport at inter-tube junctions by embedding CNTs into a polymer matrix. [84][85][86][95][96][97] As for the second aspect, the focal point is how to suspend the device efficiently through various techniques. [82,88] During the last decade, CNT-based bolometric detectors have made substantial progress and the performances of these detectors is continuously being improved.…”

Midinfrared Surface Plasmons in Carbon Nanotube Plasmonic Metasurface

“…Starting from the pioneering work of Itkis et al [39] many studies were performed to increase the efficiency of SWCNT-based bolometers. Embedding SWCNTs to the polymer [40][41][42] leads to the growth of the composite TCR up to 10% K −1 which is greater than the TCR of commercially used vanadium oxide [43] and silicon and also improves the mechanical stability of the device. The drawback of the composite bolometers is the longer response time determined by a larger amount of material which has to be heated.…”

Carbon nanotube microbolometers on suspended silicon nitride via vertical fabrication procedure

“…Carbon nanotubes (CNTs) have recently been studied as an alternative material to VOx and a-Si with a reported TCR of less than $1%. 3,4 Commonly observed responsivity is in the neighborhood of a few hundred V/W with time constants ranging from 5 to 100 ms. 3,4 In this work, we designed and developed a vertical layer-by-layer fabrication approach that uses silicon nitride (Si 3 N 4 ) coated silicon wafers as substrates. The Si 3 N 4 layer served to both electrically isolate the pixels from the Si substrate, as well as to enable the suspension of the thin CNT membrane over the silicon substrate and form suspended microbolometer pixels anchored on the corners.…”