Vertically aligned carbon nanotubes, MoS2\u2013rGo based optoelectronic hybrids for NO2 gas sensing

Foad Ghasemi

doi:10.1038/s41598-020-68388-2

Abstract

A simple method is developed through drop-casting techniques to assemble a molybdenum disulfide (MoS2)-reduced graphene oxide (rGO) hybrid on vertically aligned carbon nanotubes (VACNTs) to perform as an optoelectronic device for nitrogen dioxide (NO2) gas sensing at room temperature. The VACNT not only forms an ohmic contact with the hybrid material, but also yields a weak charge impurity scattering in the rGo layers across the channel. These features dramatically affect the optical response of the device to the light through which improve the photoresponsivity by up to 236% and the response time by up to 40% compared to the Au contacted device. Next, the fabricated MoS2–rGo/VACNTs device is employed as a resistor gas sensor for NO2 under in situ exposure to the light at room temperature. Under laser illumination, the sensor demonstrates a high sensitivity of ~ 41% at an inlet NO2 concentration of 100 ppm with a complete recovery time of ~ 150 s which shows comparable improvements relative to the sensor performance in dark condition.

Highlights

A simple method is developed through drop-casting techniques to assemble a molybdenum disulfide (MoS2)-reduced graphene oxide hybrid on vertically aligned carbon nanotubes (VACNTs) to perform as an optoelectronic device for nitrogen dioxide ( NO2) gas sensing at room temperature
The scanning electron microscopy (SEM) image of VACNTs demonstrates the dense growth of nanotubes with a vertically aligned arrangement where the lengths of the nanotubes are measured to be around 1–2 μm (Fig. 1b)
In the growth process of VACNTs, Ni film acts as a catalyst which remains on the top of the nanotubes upon completion of the growth

Summary

Introduction

A simple method is developed through drop-casting techniques to assemble a molybdenum disulfide (MoS2)-reduced graphene oxide (rGO) hybrid on vertically aligned carbon nanotubes (VACNTs) to perform as an optoelectronic device for nitrogen dioxide ( NO2) gas sensing at room temperature. In situ exposure to light during gas detection process results in the photo-generated carriers within the channel of the optical-sensitive device It can enhance the gas response of the sensor by two reasons: first, the photogenerated carriers provide the required energy for desorbing the ambient molecules ( O2, and H2O) from the surface of the material. An optoelectronic NO2 gas sensor was reported based on the single layer M oS2 layers with graphene contacts by Pham et al.[11] Their results showed the device sensitivity of ~ 25% at 0.2 ppm N O2 gas with recovery time of about 200 s in situ exposure to red light at room temperature. In most reported works, the operating temperatures are above room temperature because they mostly showed poor responses and incomplete recovery times at near room temperature

Methods

Results

Conclusion