We demonstrated high-performance gas sensors based on graphene oxide (GO) sheets partially reduced via low-temperature thermal treatments. Hydrophilic graphene oxide sheets uniformly suspended in water were first dispersed onto gold interdigitated electrodes. The partial reduction of the GO sheets was then achieved through low-temperature, multi-step annealing (100, 200, and 300 degrees C) or one-step heating (200 degrees C) of the device in argon flow at atmospheric pressure. The electrical conductance of GO was measured after each heating cycle to interpret the level of reduction. The thermally-reduced GO showed p-type semiconducting behavior in ambient conditions and was responsive to low-concentration NO2 and NH3 gases diluted in air at room temperature. The sensitivity can be attributed mainly to the electron transfer between the reduced GO and adsorbed gaseous molecules (NO2/NH3). Additionally, the contact between GO and the Au electrode is likely to contribute to the overall sensing response because of the adsorbates-induced Schottky barrier variation. A simplified model is used to explain the experimental observations.

We demonstrate a high-performance gas sensor using partially reduced graphene oxide ͑GO͒ sheets obtained through low-temperature step annealing ͑300°C at maximum͒ in argon flow at atmospheric pressure. The electrical conductance of GO was measured after each heating cycle to interpret the level of reduction. The thermally reduced GO showed p-type semiconducting behavior in ambient conditions and were responsive to low-concentration NO 2 diluted in air at room temperature. The sensitivity is attributed to the electron transfer from the reduced GO to adsorbed NO 2 , which leads to enriched hole concentration and enhanced electrical conduction in the reduced GO sheet.

Graphene is worth evaluating for chemical sensing and biosensing due to its outstanding physical and chemical properties. We first report on the fabrication and characterization of gas sensors using a back-gated field-effect transistor platform with chemically reduced graphene oxide (R-GO) as the conducting channel. These sensors exhibited a 360% increase in response when exposed to 100 ppm NO(2) in air, compared with thermally reduced graphene oxide sensors we reported earlier. We then present a new method of signal processing/data interpretation that addresses (i) sensing devices with long recovery periods (such as required for sensing gases with these R-GO sensors) as well as (ii) device-to-device variations. A theoretical analysis is used to illuminate the importance of using the new signal processing method when the sensing device suffers from slow recovery and non-negligible contact resistance. We suggest that the work reported here (including the sensor signal processing method and the inherent simplicity of device fabrication) is a significant step toward the real-world application of graphene-based chemical sensors.

A new gas‐sensing platform for low‐concentration gases (NO2, H2, and CO) comprises discrete SnO2 nanocrystals uniformly distributed on the surface of multiwalled carbon nanotubes (CNTs). The resulting hybrid nanostructures are highly sensitive, even at room temperature, because their gas sensing abilities rely on electron transfer between the nanocrystals and the CNTs.

INTRODUCTIONSelf-assembly of block copolymer (BCP) thin films has been explored extensively as a strategy to make periodic nanostructures. 1À4 Because these nanoscale features can be formed reproducibly and at low-cost, there is tremendous interest in transferring such patterns to functional materials. In particular, BCP films are promising for microelectronics and data storage applications where highly dense and periodic nanoscale patterns are needed over a large area. 5À8 BCP films can self-organize to form nanostructures of various morphologies with tunable length scales. Furthermore, by guiding BCP self-assembly using surface topography, highly regular patterns can be generated over macroscopic area with low defect density. 9,10 Since BCP films with a single layer of laterally ordered domains have a thickness on the order of the domain size, they are generally too thin for transferring patterns into the underlying substrate using plasma etching. Because carbon-based polymer blocks erode quickly in a plasma, the masking BCP film is completely removed before features with significant depth can be transferred. For example, polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA), one of the most widely studied BCPs (including in lithography experiments), has an overall poor etch resistance, and the etch contrast between the blocks is only about two. 11 As a result, the depth that can be etched is only on the order of the thickness of the film at best, which is tens of nanometers in most cases. Significant effort has been invested in developing BCPs containing etch-resistant blocks such as polystyrene-block-polydimethylsiloxane (PS-b-PDMS) 12,13 or polystyrene-block-poly(ferrocenylsilane) (PS-b-PFS), 14À17 but many of these BCPs have poor wetting properties or are difficult to remove after the etching process. The synthesis of these polymers can also be challenging. Furthermore, organometallic blocks (such as PFS) are undesirable for microelectronics manufacturing, a major potential application of BCPs, because the uncontrolled diffusion of metals in a semiconductor can degrade the performance of microelectronic devices.For the reasons stated above, a BCP that is easy to synthesize, applicable over large areas, and resistant to plasma etching remains elusive. To etch high aspect-ratio structures, a common scheme is to first transfer the BCP pattern to an intermediate hard mask layer that provides greater etch resistance. The insertion of a hard mask layer adds complexity and cost to the fabrication process due to complications from stress and adhesion as well as the risk of damaging the underlying substrate during deposition. The interfacial interaction between the hard mask and the BCP may also change dramatically how the BCP self-assembles. Furthermore, transferring the pattern with high fidelity into the hard mask layer still requires etch contrast between the polymer blocks. Consequently, strong etch contrast between the BCP blocks is highly desired, regardless of the overall pattern transfer scheme.In this ...