Abstract
A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid.
Highlights
10 mV to as much as 50 mV within a distance of several hundreds of nanometers from the surface
To more manipulate the contact area ratio, and to increase the total exposure area so as to enhance the generated power, the investigation considers the system shown in Fig. 1(a), in which a monolayer graphene is placed in contact with a microfludic chip composed of Figure 2. ky-dependent low-energy bands near Dirac point: (a) in absence of liquid (w/L = 0) with enlarged unit cell for RE = 300, and in presence of liquid with RE = 300 and V0 = 0.1 γ0 (~0.25 eV) at: (b) w/L = 0.2 and (c) w/L = 0.4. (d–f) corresponding density of states (DOS) for cases (a~c)
The charge carriers in the graphene are sensitive to the external field and can be transported rapidly, while no free carriers exist at the Fermi energy
Summary
10 mV to as much as 50 mV within a distance of several hundreds of nanometers from the surface. Moon et al.[31] investigated the electrical power generated by liquid flows over an ITO surface, and showed that the voltage exhibited a quadratic dependence on the contact area. The adsorption energy of the hydrated Na+ ion within a NaCl aqueous solution is around 0.1 eV43 These surface adsorbates induce a doping effect to modulate the π-electronic structures of the graphene[44,45], and impacts the transport properties (e.g., the conductance and the mobility). This study performs a theoretical investigation into the electronic properties of graphene in the presence of liquid for various values of the contact area ratio. To investigate the resulting behavior of the charge carriers in the graphene, a tight-binding model[17] is used to calculate the low-energy dispersions and density of states (DOS) near the Fermi level. The theoretical results provide a useful insight into the optimal value of w/L, i.e., the value of w/L at which the maximum number of charge carriers are prospectively induced for transport
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