Single ZnO Nanowire-Based Gas Sensors to Detect Low Concentrations of Hydrogen.

Marlene Cardoza-Contreras,José Romo-Herrera,R García-Gutiérrez,Luis Ríos,Oscar Contreras,T Zepeda

doi:10.3390/s151229816

Abstract

Low concentrations of hazardous gases are difficult to detect with common gas sensors. Using semiconductor nanostructures as a sensor element is an alternative. Single ZnO nanowire gas sensor devices were fabricated by manipulation and connection of a single nanowire into a four-electrode aluminum probe in situ in a dual-beam scanning electron microscope-focused ion beam with a manipulator and a gas injection system in/column. The electrical response of the manufactured devices shows response times up to 29 s for a 121 ppm of H2 pulse, with a variation in the nanowire resistance appreciable at room temperature and at 373.15 K of approximately 8% and 14% respectively, showing that ZnO nanowires are good candidates to detect low concentrations of H2.

Highlights

Conductometric gas sensors are electronic devices with a simple structure where their operation principle is based on the variation of electrical conductance of their sensor element; this can occur due to the electron exchange between the surface and conduction band as the result of oxidation/reduction when its surface is exposed by chemical gases
This will lead to an electron depletion layer, and there is no conduction on the semiconductor surface, and the remaining free charge carriers are concentrated in the bulk of the nanowire
In this work we studied the conductometric response of single ZnO nanowires tested as gas sensor elements in order to explore their capability to detect very low concentrations of H2 at room temperature and at 373.15 K

Summary

Introduction

Conductometric gas sensors are electronic devices with a simple structure where their operation principle is based on the variation of electrical conductance of their sensor element; this can occur due to the electron exchange between the surface and conduction band as the result of oxidation/reduction when its surface is exposed by chemical gases. Semiconductors are one of the most commonly used materials for sensor elements, since naturally, in ambient air, a thin layer of native oxide is formed on a semiconductor’s surface, and in the presence of a reducing gas, the interaction of oxygen-adsorbed species on its surface and the objective gas molecules causes the chemical reduction of its surface This phenomenon modifies the amount of active charge carriers in the semiconductor and, its conductance. ZnO is a direct wide-band-gap semiconductor (3.37 eV at RT), naturally grown as an n-type semiconductor, that according to the literature has an intrinsic behavior that results from intrinsic crystal defects such as oxygen vacancies and/or zinc interstitials Materials with this feature are good candidates in the fabrication of fast-response and highly sensitive gas sensor devices for reducing atmosphere when n-type nanostructures are used as sensor elements. In this work we studied the conductometric response (electrical resistance) of single ZnO nanowires tested as gas sensor elements in order to explore their capability to detect very low concentrations of H2 at room temperature and at 373.15 K

Experimental Section

Results and Discussion

Conclusions