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. 2022 Jun 6;12(26):16732-16744.
doi: 10.1039/d2ra02030k. eCollection 2022 Jun 1.

Adsorption of gas molecules on buckled GaAs monolayer: a first-principles study

Rifat Shahriar  1 , Orchi Hassan  1 , Md Kawsar Alam  1
Affiliations

Adsorption of gas molecules on buckled GaAs monolayer: a first-principles study

Rifat Shahriar et al. RSC Adv. .

Abstract

The design of sensitive and selective gas sensors can be significantly simplified if materials that are intrinsically selective to target gas molecules can be identified. In recent years, monolayers consisting of group III-V elements have been identified as promising gas sensing materials. In this article, we investigate gas adsorption properties of buckled GaAs monolayer using first-principles calculations within the framework of density functional theory. We examine the adsorption energy, adsorption distance, charge transfer, and electron density difference to study the strength and nature of adsorption. We calculate the change in band structure, work function, conductivity, density of states, and optical reflectivity for analyzing its prospect as work function-based, chemiresistive, optical, and magnetic gas sensor applications. In this regard, we considered the adsorption of ten gas molecules, namely NH3, NO2, NO, CH4, H2, CO, SO2, HCN, H2S, and CO2, and noticed that GaAs monolayer is responsive to NO, NO2, NH3, and SO2 only. Specifically, NH3, SO2 and NO2 chemisorb on the GaAs monolayer and change the work function by more than 5%. While both NO and NO2 are found to be responsive in the far-infrared (FIR) range, NO shows better spin-splitting property and a significant change in conductivity. Moreover, the recovery time at room temperature for NO is observed to be in the sub-millisecond range suggesting selective and sensitive NO response in GaAs monolayer.

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Conflict of interest statement

There are no conflicts of interest to declare.

Figures

Fig. 1
Fig. 1. Optimized structure of GaAs monolayer showing the lattice constant of 4.042 Å, bond length 2.398 Å, buckling height of 0.55 Å, and the four adsorption sites.
Fig. 2
Fig. 2. The band structure of pristine GaAs monolayer with a band gap of 1.046 eV.
Fig. 3
Fig. 3. Top and side view of the most energetically favorable adsorption configuration of the adsorbed molecules (a) NH3, (b) NO2, (c) NO, (d) H2, (e) CO, (f) CH4, (g) SO2, (h) HCN, (i) H2S, and (j) CO2 molecules on the GaAs monolayer. The balls of the colors green, violet, blue, red, black, yellow, and white represent Ga, As, N, O, C, S, and H.
Fig. 4
Fig. 4. Electron density difference plots of (a) NH3, (b) NO2, (c) NO, (d) H2, (e) CO, (f) CH4, (g) SO2, (h) HCN, (i) H2S, and (j) CO2 adsorbed GaAs monolayer. Here the blue (yellow) color denotes electron accumulation (depletion). Isovalue is 0.01 electrons per Å3.
Fig. 5
Fig. 5. Phonon dispersion curves of (a) NH3, (b) NO2, (c) NO, (d) H2, (e) CO, (f) CH4, (g) SO2, (h) HCN, (i) H2S, and (j) CO2 adsorbed GaAs monolayer.
Fig. 6
Fig. 6. The band structures of (a) pristine, and (b) NH3, (c) NO2, (d) NO, (e) H2, (f) CO, (g) SO2, (h) HCN, (i) H2S, and (j) CO2 adsorbed GaAs monolayer. The blue (red) color indicates up (down) spin. NO adsorption substantially decreases the band gap to 0.64 eV, while other gas adsorbed structures have a band gap reasonably similar to the pristine band gap of 1.046 eV.
Fig. 7
Fig. 7. The orbital projected density of states of (a) NH3, (b) NO2, (c) NO, (d) H2, (e) CO, (f) SO2, (g) HCN, (h) H2S, and (i) CO2 adsorbed GaAs monolayer. The blue (red) color indicates up (down) spin. NO adsorption substantially decreases the band gap to 0.64 eV, while other gas adsorbed structures have a band gap reasonably similar to the pristine band gap of 1.046 eV.
Fig. 8
Fig. 8. The reflectivity of pristine and gas adsorbed GaAs monolayer. The reflectivity of NO and NO2 adsorbed monolayers are higher than the pristine and other gas adsorbed monolayers in the 0–1 eV range. In the 4–6 eV range, the reflectivity curves are on top of each other, indicating that the value of reflectivity is the same for all structures in this range.
Fig. 9
Fig. 9. (a) Spin resolved density of states in NO adsorbed GaAs monolayer; (b) the isosurface of showing spin density in NO adsorbed GaAs monolayer. Blue color represents up spin and red represents down spin. Isovalue is 0.005e per Angstrom3.
Fig. 10
Fig. 10. Initial, transition, and final state for CO diffusion on GaAs monolayer.
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