# Enhanced Room-Temperature Optoelectronic NO2 Sensing Performance of Ultrathin Non-Layered Indium Oxysulfide via In Situ Sulfurization

## TL;DR

Researchers developed a new 2D material that can detect nitrogen dioxide efficiently at room temperature using light.

## Contribution

A novel non-layered 2D indium oxysulfide material is synthesized and shown to enable room-temperature optoelectronic NO2 sensing with high performance.

## Key findings

- The material shows a 1.2 response factor for 10 ppm NO2 under blue light at room temperature.
- It exhibits linear response from 0.1 to 10 ppm NO2 with improved reversibility and selectivity.
- The material has a bandgap of 2.53 eV and maintains n-type semiconducting behavior.

## Abstract

The detection of trace nitrogen dioxide (NO2) is critical for environmental monitoring and industrial safety. Among various sensing technologies, chemiresistive sensors based on semiconducting metal oxides are prominent due to their high sensitivity and fast response. However, their application is hindered by inherent limitations, including low selectivity and elevated operating temperatures, which increase power consumption. Two-dimensional metal oxysulfides have recently attracted attention as room-temperature sensing materials due to their unique electronic properties and fully reversible sensing performance. Meanwhile, their combination with optoelectronic gas sensing has emerged as a promising solution, combining higher efficiency with minimal energy requirements. In this work, we introduce non-layered 2D indium oxysulfide (In2SxO3−x) synthesized via a two-step process: liquid metal printing of indium followed by thermal annealing of the resulting In2O3 in a H2S atmosphere at 300 °C. The synthesized material is characterized by a micrometer-scale lateral dimension with 6.3 nm thickness and remaining n-type semiconducting behavior with a bandgap of 2.53 eV. It demonstrates a significant response factor of 1.2 toward 10 ppm NO2 under blue light illumination at room temperature. The sensor exhibits a linear response across a low concentration range of 0.1 to 10 ppm, alongside greatly improved reversibility, selectivity, and sensitivity. This study successfully optimizes the application of 2D metal oxysulfide and presents its potential for the development of energy-efficient NO2 sensing systems.