Ultrasensitive Boron-Nitrogen-Codoped CVD Graphene-Derived NO2 Gas Sensor

Abstract

Recent trends in 2D materials like graphene are focused on heteroatom doping in a hexagonal honeycomb lattice to tailor the desired properties for various lightweight atomic thin-layer derived portable devices, particularly in the field of gas sensors. To design such gas sensors, it is important to either discover new materials with enhanced properties or tailor the properties of existing materials via doping. Herein, we exploit the concept of codoping of heteroatoms in graphene for more improvements in gas sensing properties and demonstrate a boron- and nitrogen-codoped bilayer graphene-derived gas sensor for enhanced nitrogen dioxide (NO₂) gas sensing applications, which may possibly be another alternative for an efficient sensing device. A well-known method of low-pressure chemical vapor deposition (LPCVD) is employed for synthesizing the boron- and nitrogen-codoped bilayer graphene (BNGr). To validate the successful synthesis of BNGr, the Raman, XPS, and FESEM characterization techniques were performed. The Raman spectroscopy results validate the synthesis of graphene nanosheets, and moreover, the FESEM and XPS characterization confirms the codoping of nitrogen and boron in the graphene matrix. The gas sensing device was fabricated on a Si/SiO₂ substrate with prepatterned gold electrodes. The proposed BNGr sensor unveils an ultrasensitive nature for NO₂ at room temperature. A plausible NO₂ gas sensing mechanism is explored via a comparative study of the experimental results through the density functional theory (DFT) calculations of the adsorbed gas molecules on doped heteroatom sites. Henceforth, the obtained results of NO₂ sensing with the BNGr gas sensor offer new prospects for designing next-generation lightweight and ultrasensitive gas sensing devices.

Figure 1

(a) Optical microscopy image of the BNGr nanosheet. (b) Raman spectra of Gr and BNGr nanosheets. (c) FESEM image of the BNGr nanosheet. (d) EDX spectrum of the small region of the BNGr nanosheet with elements B, N, and C present in the nanosheet.

Figure 2

(a) Survey scan spectra of the BNGr nanosheet. Deconvoluted (b) N 1s core-level spectra, (c) B 1s core-level spectra, and (d) C 1s core-level spectra of the BNGr nanosheet on the Si/SiO₂ substrate.

Figure 3

(a) UV–vis spectra of Gr and BNGr nanosheets on the quartz substrate. (b) I–V measurements of Gr and BNGr nanosheets on the Si/SiO₂ substrate.

Figure 4

(a) Response versus time plots for 1–80 ppb NO₂ for the BNGr sensor. (b) Response versus ppb concentration of NO₂ for the BNGr sensor. (c) Comparison of sensor responses of Gr and BNGr sensors for 1 ppb NO₂. (d) Response curve of the BNGr sensor for five consecutive cycles of 1 ppb NO₂.

Figure 5

Optimized configurations (top and side views) for NO₂ gas molecule adsorption on (a, c) Gr and (b, d) BNGr. C, N, O, and B atoms are shown as blue, brown, red, and green solid spheres, respectively.

Figure 6

Charge density difference plots of the NO₂ gas molecule on (a) Gr surface and (b) BNGr surface.

Figure 7

Schematic band diagram of the NO₂ gas sensing mechanism on the bilayer graphene nanosheet.