Correlation of the applied electrical field and CO adsorption/desorption behavior on Al-doped graphene

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Abstract

Recently, Al-doped graphene was proposed as a highly sensitive CO gas sensor material. In this work, the correlation of the applied electric field F and the adsorption/desorption behavior of a CO molecule on Al-doped graphene was studied by density functional theory calculations. The results indicate that a negative F strengthens the adsorption of the CO on the Al-doped graphene, while the adsorption is reduced when a positive F is present. Furthermore, desorption of the CO molecule from the graphene layer commences when F0.03a.u. is applied, which can be used to reactivate the sensor material for repetitious application.

Introduction

Graphene-based devices have been demonstrated as promising candidates to detect toxic gas molecules, such as NO2, CO and NH3, with ultra-low concentration in ambient environments [1], [2], [3]. Recently, a theoretical analysis with density functional theory (DFT) suggested that Al-doped graphene is extremely sensitive to CO molecule adsorption, which induces a large variation of electrical conductivity [3]. Detecting the electrical conductivity variation of the sensor in practical applications, an electric field F would be present [1]. In general, F affects the electronic properties of low-dimensional systems significantly, including 1D quantum wires [4], carbon nanotubes [5], [6], and graphene [7]. Such phenomena have been studied with the tight-binding model [8], experiments [9], [10] and DFT simulation, respectively [7]. Results showed that the band structure and density of state (DOS) are very sensitive to the orientation and the intensity of F[7], [8].

The first theoretical work with quantum mechanical calculations on F inducing adsorption/desorption was undertaken for N2 molecules on an Fe(111) surface [11]. Recent simulation works about the effects of F on (1) the adsorption and dissociation of oxygen on Pt(111) [12], (2) the electronic structure of Au–XO(0,−1,+1) (X=C,N and O) [13], and (3) vibrational frequencies of CO on Pt(111) [14] showed that F changes their electronic orbitals, thus inducing some new physical phenomena  [15].

Therefore, it is of interest to investigate how F influences the adsorption/desorption behavior of CO on Al-doped graphene. In this work, favorable adsorption configurations of CO on Al-doped graphene under different F are determined by DFT calculation, and the effects of F on the corresponding interaction between CO and Al-doped graphene are also discussed.

Section snippets

Calculation details

All DFT calculations are performed using Dmol3 code [16], [17]. In general, calculations based on the local density approximation (LDA) overestimate the binding energy but underestimate the atomic equilibrium distances [18], [19]. Thus, a uniform generalized gradient approximation (GGA) with the revised Perdew–Burke–Ernzerhof (PBE) method is used as the exchange correlation function [20]. The DFT semicore pseudopotentials (DSPP) core treatment [21] is implemented for relativistic effects, which

Results and discussion

Ead values of the CO/graphene systems with all possible adsorption configurations in the presence of F is listed in Table 1. Based on the calculated Ead values, the corresponding favorite adsorption configurations under different F are present in Fig. 1 where the CO molecule always takes the top site of the doped Al atom. From Table 1, the most stable structures obtained from the initial arrangements of T–B–T, H–T–H, H–B–H, B(O atom)–T–H, B(O upwards) and H(O upwards) when F=0.03a.u., T–B–T,

Conclusion

In conclusion, the adsorption of a CO molecule on an Al-doped graphene with the presence of electrical field F is investigated by DFT calculations. It is found that the adsorption of CO on Al-doped graphene is weakened under a positive F while it is strengthened by applying a negative F. Furthermore, the desorption of CO from Al-doped graphene occurs when F=0.03a.u., which indicates that the used materials could be reactivated by applying a highly positive F.

Acknowledgements

This work was financially supported by National Key Basic Research and Development Program (Grant No. 2010CB631001) and Australia Research Council Discovery Program DP0665539.

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