凯发

Graphene is showing promise for many technological applications due to its extraordinary electrical, mechanical, thermal, and optical properties. Especially, graphene has the highest surface-to-volume ratio that allows the total exposure of all its atoms to the environment. Graphene sensors possess the ability to detect a single interacting molecule. When a molecule, acting as an electron donor/acceptor, is attached to graphene, the resistance of graphene is significantly modified. The high carrier mobility inherently ensures low electrical noise and energy consumption in graphene sensors. Graphene sensors have shown a high sensitivity for various types of gas, such as NO2, CO, CO2, H2, NH3 and VOCs [1, 2]. The key issues to deal with practical applications of graphene sensors are slow reversibility, low response, and poor selectivity [3]. In this work, we fabricate graphene sensors by a simple and low-cost method for the detection of formaldehyde (HCHO), the most common air pollutant indoor. Our sensors have been integrated with CMOS chips for smart building management. 

Graphene is synthesized by chemical vapor deposition (CVD) [4], and transferred onto a micro hot plate (µhp) by a polymer-based method (Fig. 1). To increase the graphene adsorption ability by three functionalization routes: (1) Deposition of 2,3,5,6-Tetrafluoro-hydroquinone (TFQ) molecules on graphene. (2) Binding graphene with amine groups. (3) Doping graphene by Pt or Pd nano particles. The Raman measurements reveal that the first rout is a damage-free modification [5]. The graphene sensor with damage-free functionalization shows a high sensitivity and good selectivity. The sensor selectivity is further improved by using molecularly imprinted polymer (MIP) technique. The TFQ-functionalized sensor is tested to investigate its response, ∆R/R0 = (R- R0)/R0, where R0 and R are the resistance of the sensor before and after exposure to HCHO. Fig. 2 plots sensing cycle experiments for a HCHO concentration of 1 ppm. The best sensor exhibits a response time of 15 s and a sensitivity of 20% [6]. The possible response mechanism is that the acid hydroxyl groups in TFQ interact with HCHO molecules to form weak and reversible intermediate complexes, which are positively charged. They deplete holes in the p-type semiconducting graphene, while increases the graphene resistance. Our sensors demonstrate not only a high sensitivity, but also a fast response and good selectivity for HCHO. Moreover, our sensors can also be used to detect the other gases and bio-molecules by changing functionalization routs.