Abstract
In order to take full advantage of novel functional materials in the next generation of sensorial devices scalable processes for their fabrication and utilization are of great importance. Also understanding the processes lending the properties to those materials is essential. Among the most sought-after sensor applications are low-cost, highly sensitive and selective metal oxide based gas sensors. Yet, the surface reactions responsible for provoking a change in the electrical behavior of gas sensitive layers are insufficiently comprehended. Here, we have used near-edge x-ray absorption fine structure spectroscopy in combination with x-ray microscopy (NEXAFS-TXM) for ex-situ measurements, in order to reveal the hydrogen sulfide induced processes at the surface of copper oxide nanoparticles, which are ultimately responsible for triggering a percolation phase transition. For the first time these measurements allow the imaging of trace gas induced reactions and the effect they have on the chemical composition of the metal oxide surface and bulk. This makes the new technique suitable for elucidating adsorption processes in-situ and under real operating conditions.
Highlights
In recent years micro- and nano-scaled particles of various morphologies and sizes have been investigated in order to utilize their unique properties for a multitude of technological applications, including energy conversion and storage[1], plasmonics[2], drug delivery[3], catalysis[4,5] and gas sensing[6]
To address both applied as well as fundamental issues of generation metal oxide based sensors we present a new route for synthesizing Cu2O nanoparticles with high yield, and demonstrate how to interface and to use them as sensor material
Because of the highly complex nature of gas-solid interactions and the current lack of possibilities to directly monitor surface reactions the behavior of solid-state gas sensors based on functional metal oxides is inadequately understood
Summary
In recent years micro- and nano-scaled particles of various morphologies and sizes have been investigated in order to utilize their unique properties for a multitude of technological applications, including energy conversion and storage[1], plasmonics[2], drug delivery[3], catalysis[4,5] and gas sensing[6]. One appealing technology in that regard is the inkjet printing process, which provides a precise and scalable method to deposit functional nanoparticles onto arbitrary structures Using this technique colloidal suspensions of metal oxide inks may be deposited and used as a gas sensitive layer on low-power consuming, micro-machined silicon-based structures. We employ the novel approach to track the fundamental changes in CuO caused by the interaction with H2S using the NEXAFS-TXM method to shed light onto fundamental surface processes To address both applied as well as fundamental issues of generation metal oxide based sensors we present a new route for synthesizing Cu2O nanoparticles with high yield, and demonstrate how to interface and to use them as sensor material. This demonstrates the suitability of the NEXAFS-TXM method to provide a spatially resolved analysis of the chemical bonds formed during gas-surface interaction, which are at the heart of gas detection using semiconducting metal-oxides as functional material
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