Recognizing Physisorption and Chemisorption in Carbon Nanotubes Gas Sensors by Double Exponential Fitting of the Response.

Andrea Calvi,Silvio Modesti,Andrea Goldoni,Alberto Ferrari,Luca Sbuelz

doi:10.3390/s16050731

Abstract

Multi-walled carbon nanotubes (CNTs) have been grown in situ on a substrate and used as gas sensors. For this purpose, the voltage response of the CNTs as a function of time has been used to detect and at various concentrations by supplying a constant current to the system. The analysis of both adsorptions and desorptions curves has revealed two different exponential behaviours for each curve. The study of the characteristic times, obtained from the fitting of the data, has allowed us to identify separately chemisorption and physisorption processes on the CNTs.

Highlights

Resistive-type gas sensors are devices that detect a change in the concentration of a chemical specimen through the variation of an electric signal
Since the theoretical calculations suggest that both chemisorption and physisorption are active processes, but still doubts remain from the experimental point of view [27], the aim of this paper is to understand whether or not it is possible to recognize the kind of adsorption process from the analysis of the resistivity response induced by the gas
The second branch is due to the relaxation of the carbon nanotubes (CNTs) sensor, which starts when the gas valve is closed

Summary

Introduction

Resistive-type gas sensors are devices that detect a change in the concentration of a chemical specimen through the variation of an electric signal. In the past two decades, many studies were performed on the sensing properties of semiconducting oxides such as ZnO, SnO2 and In2 O3. Those sensors showed issues regarding the long-term stability and the capability to operate at room temperature [6]. A large effort has been put into developing carbon nanotubes (CNTs [7,8]) based sensors. These sensors are very promising since they are characterized by short response and recovery times, high sensitivity and stability and wide temperature operating range [5]

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Conclusion