Conversion of n-Type CuTCNQ into p-Type Nitrogen-Doped CuO and the Implication for Room-Temperature Gas Sensing

Abstract

Sensors to detect toxic and harmful gases are usually based on metal oxides that are operated at elevated temperature. However, enabling gas detection at room temperature (RT) is a significant ongoing challenge. Here, we address this issue by demonstrating that microrods of semiconducting CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) with nanostructured features can be employed as conductometric gas sensors operating at 50 °C for detection of oxidizing and reducing gases such as NO 2 and NH 3 . The sensor is evaluated at RT and up to 200 °C. It was found that CuTCNQ is transformed into a N-doped CuO material with p-type conductivity when annealed at the maximum temperature. This is the first time that such a transformation, from a semiconducting charge transfer material into a N-doped metal oxide, is detected. It is shown here that both the surface chemistry and the type of majority charge carrier within the sensing layer are critically important for the type of response toward oxidizing and reducing gases. A detailed physical description of the NO 2 and NH 3 sensing mechanism at CuTCNQ and N-doped CuO is provided to explain the differences in the response. For the N-doped CuO sensor, detection limits of 1 ppm for NO 2 and 10 ppm for NH 3 are achieved.

Superhydrophobic Fabrics for Oil/Water Separation Based on the Metal–Organic Charge‐Transfer Complex CuTCNAQ

“…In recent studies it has been shown that charge‐transfer complexes based on metal‐TCNQ demonstrate applicability in a wide range of areas beyond their traditional uses in memristive and field‐emission applications. It is well known that MTCNQ and MTCNQF 4 (M=Cu, Ag) are good candidates for molecular switching devices and field emission, but it has been shown that their electronic and chemical properties can be utilized for applications as diverse as heterogeneous catalysis, photocatalysis, gas sensing, and antibacterial textiles . Indeed, nanostructured CuTCNQ and CuTCNQF 4 on rigid substrates have also been shown to be superhydrophobic, and could, in principle, be used in contaminant‐ and humidity‐tolerant electronic devices.…”

Floating Back-Gate Field Effect Transistor Fabricated Using a Single Nanowire of Charge Transfer Complex as a Channel

“…To understand the mechanism and reason behind enhancement of current due to positive gate voltage of the NW FET, a gate-controlled metal–semiconductor barrier modulation is proposed to interpret the carrier transport in Cu:TCNQ. Cu:TCNQ NW is an n-type semiconductor. , Figure represents the energy band diagram along the horizontal axis showing the effect of bias applied in between S, D, and G. Flow of I DS from D to S through the channel will be determined by the available energy states in the channel material. Application of V DS > 0 lowers all the energy levels in the D by an amount qV DS , which results in current flow from D to S. Applied V g > 0 lowers the energy levels in the channel region relative to the two contacts S and D. This enhances the available energy state in the channel material, resulting in enhancement in I DS .…”

Gas‐Sensing Activity of Amorphous Copper Oxide Porous Nanosheets

“…As a common metal oxide, p‐type semiconductor copper oxide (CuO) with a narrow band gap (1.2 eV) is more and more widely used in the field of gas sensing due to its advantage of low cost, facile synthesis, high reproducibility and nontoxicity . Up to present, crystalline CuO (c‐CuO) nanoparticles, nanorods, nanowires, nanobelts and three‐dimensional hierarchical porous structures have been successfully synthesized . Among them, hierarchically porous structured CuO nanostructures displayed excellent gas sensing properties due to its large specific surface area and abundant accessible pores, which could increase the adsorption and desorption of target gas molecules.…”