Block Co-polymer on Graphene: Doping of Graphene and a Robust Chemical Sensor
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Block Co-polymer on Graphene: Doping of Graphene and a Robust Chemical Sensor Shirui Guo1, Maziar Ghazinejad2, Cengiz S. Ozkan2*, Mihrimah Ozkan3* 1
Department of Chemistry, 2Department of Mechanical Engineering, 3Department of Electrical Engineering, University of California, Riverside, CA, 92521 ABSTRACT It is essential to control the electronic properties of a graphene field effect transistor (GFET). And the ability to accurately control the intrinsic electrical transport properties and to locally change the carrier density will be significant for graphene devices. We succeeded in achieving and controlling the Dirac point (neutrality point) simply by doping block co-polymer (BCP) covered GFET with CF4 plasma. By exposing polymer covered GFET to CF4 plasma for a short time the electronic transport was altered significantly. The hexagonal structure of BCP produces patterns with nanoscale spacing for heterogeneous patterns which provides a new approach to tune the electron and the hole conductivity simultaneously. Exploitation of fluorine doping provides a general route to control electronic property of any polymer coated GFET. The BCP protected GFET could detect 1mM NaF solution in “dry” condition in 60s. The sensing property demonstrates that BCP protected GFET could be a good candidate for stable and sensitive chemical or biological sensor. Furthermore, the distinct property of two functional groups within BCP facilitates the selective sensing property. These findings pave the way for developing more stable and sensitive sensors under ambient conditions. INTRODUCTION Graphene has attracted a lot of attention due to its remarkable intrinsic electronic properties.1 The ballistic transport of electrons, along with mobilities exceeding 15 000 cm2/V·s and an ambipolar field effect, make graphene a particularly good candidate for the next generation of semiconductor devices.[1] Electrical transport in graphene can be tuned between hole and electron conduction by shifting the Fermi level with an applied field effect, and the ability to tailor the electronic properties of graphene is one of the most important potential ways to facilitate the use of graphene for future applications.[2] Moreover, the ability to accurately control the intrinsic electrical transport properties and to locally change the carrier density will be quite significant for graphene devices. Many methods have been developed to achieve this goal, including opening the band gap by using graphene nanoribbons or nanomeshes, utilizing bilayer graphene for a narrow band gap, and doping graphene to make it n-type or p-type. Among these methods, the doping effect is perhaps the most promising as a way to modify the electronic properties of graphene. Through doping or the chemical functionalization of graphene, the Fermi level can be changed, and that can cause a shift of the neutrality point and a change in hole or electron mobility. Many materials have been utilized to modify the electronic properties of graphene via surface doping, including metals (Ca, Ag
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