Formation of environmentally stable hole-doped graphene films with instantaneous and high-density carrier doping via a boron-based oxidant

Large-area graphene films have substantial potential for use as next-generation electrodes because of their good chemical stability, high flexibility, excellent carrier mobility, and lightweight structure. However, various issues remain unsolved. In particular, high-density carrier doping within a short time by a simple method, and air stability of doped graphene films, are highly desirable. Here, we demonstrate a solution-based high-density (>1014 cm−2) hole doping approach that promises to push the performance limit of graphene films. The reaction of graphene films with a tetrakis(pentafluorophenyl)borate salt, containing a two-coordinate boron cation, achieves doping within an extremely short time (4 s), and the doped graphene films are air stable for at least 31 days. X-ray photoelectron spectroscopy reveals that the graphene films are covered by the chemically stable anions, resulting in an improved stability in air. Moreover, the doping reduces the transmittance by only 0.44 ± 0.23%. The simplicity of the doping process offers a viable route to the large-scale production of functional graphene electrodes

Impedance Characteristics of Monolayer and Bilayer Graphene Films with Biofilm Formation and Growth

Biofilms are the result of bacterial activity. When the number of bacteria (attached to materials’ surfaces) reaches a certain threshold value, then the bacteria simultaneously excrete organic polymers (EPS: extracellular polymeric substances). These sticky polymers encase and protect the bacteria. They are called biofilms and contain about 80% water. Other components of biofilm include polymeric carbon compounds such as polysaccharides and bacteria. It is well-known that biofilms cause various medical and hygiene problems. Therefore, it is important to have a sensor that can detect biofilms to solve such problems. Graphene is a single-atom-thick sheet in which carbon atoms are connected in a hexagonal shape like a honeycomb. Carbon compounds generally bond easily to graphene. Therefore, it is highly possible that graphene could serve as a sensor to monitor biofilm formation and growth. In our previous study, monolayer graphene was prepared on a glass substrate by the chemical vapor deposition (CVD) method. Its biofilm forming ability was compared with that of graphite. As a result, the CVD graphene film had the higher sensitivity for biofilm formation. However, the monolayer graphene has a mechanical disadvantage when used as a biofilm sensor. Therefore, for this new research project, we prepared bilayer graphene with high mechanical strength by using the CVD process on copper substrates. For these specimens, we measured the capacitance component of the specimens’ impedance. In addition, we have included a discussion about the possibility of applying them as future sensors for monitoring biofilm formation and growth