Jinwei Wei,Bo Liang,Qingpeng Cao,Hangxu Ren,Youming Zheng,Xuesong Ye
Asymmetric transfer characteristics and hysteresis behaviors are two puzzling electronic transport properties in graphene field effect transistor (GFET). Herein, we presented systematic investigations on these phenomena by varying gate voltage sweeping rates and testing chemical atmospheres. Three different doping mechanisms for GFET were proposed to illustrate these behaviors: electric field doping, molecule chemical doping, and electrochemical doping by redox reactions . In ambient environment, the plateau's emergence in asymmetric transfer curve of GFET was attributed to the counteraction between n-type electric field doping and p-type O 2 /H 2 O electrochemical doping. The hysteresis effect difference in backward sweeping varied as a function of gate voltage sweeping rate, which has been offered a qualitative explanation in the context of thermodynamics and kinetics. In NH 3 , the degree of hysteresis effect in GFET increased with the vapor concentration rising up, while NO 2 atmosphere induced opposite behavior. Generally, the interplay of the three doping mechanisms accounts for the total Fermi level modulation and carrier migration behavior near the Dirac point. For instance, the electrochemical doping could occur spontaneously because the electric effect doping or chemical doping raised the graphene Fermi level high enough with respect to the electrochemical O 2 /H 2 O redox potential.
Herein, an efficient method for in-situ assembly of silver (Ag) nanoparticles on glycine functionalized graphene (Gly-Gr) has been proposed, which only requires a simple one-step hydrothermal reaction. The microstructure of the material (Ag-Gly-Gr) was characterized by a series of methods, such as FT-IR, XRD, and TEM. For comparison, glycine functionalized graphene (Gly-Gr) was prepared by the same way without adding silver nitrate. The electrochemical sensor (Ag-Gly-Gr/GCE or Gly-Gr/GCE) was prepared by coating the glassy carbon electrode (GCE) surface with dispersive droplets of the related material. The outcomes of the electrochemical impedance test showed that the charge transfer resistance of Ag-Gly-Gr/GCE was less than that of Gly-Gr/GCE and GCE. Compared with the other two sensors, Ag-Gly-Gr/GCE showed a more sensitive response for bergenin. By studying the influence of the pH and sweep rate on the peak potential, the dynamics parameters were discussed to understand the electrochemical reaction mechanism of bergenin. The strategy for quantitative analysis of bergenin was further established at the working potential of 0.8 V (vs SCE). The peak current of bergenin displayed a linear dependence for concentration in 0.01–1 μM with a detection limit of 3.0 nM. Additionally, the analytical availability of Ag-Gly-Gr/GCE was demonstrated by determining bergenin in real-life samples.
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