Investigation of reactions between trace gases and functional CuO nanospheres and octahedrons using NEXAFS-TXM imaging

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.

Low-Power Odor-Sensing Network Based on Wake-Up Nodes

“…To detect H2S we employ copper(II) oxide (CuO) nanosphere-based functional layers [11] deposited onto micro-machined hotplates [12] via inkjet printing [13]. CuO is known to feature a highly specific reaction towards H2S even at room temperature [14], which ultimately leads to a break-down in electrical resistivity via a percolation phase transition [9,10].…”

Cu2O@PNIPAM core–shell microgels as novel inkjet materials for the preparation of CuO hollow porous nanocubes gas sensing layers

“…13,14 It can be also used as precursor particles for fabricating CuO materials. 15 Due to the possibility to achieve highly selective detection of the toxic gas using Cu 2 O and CuO as sensing material, both Cu 2 O and CuO are of great interest in material research. [16][17][18] Consequently, the deposition of Cu 2 O nanoparticles onto various substrates is of great importance in the construction of gas sensors, which has significant impact on the performance of the sensing layers.…”

“…22 Moreover, a combination of inkjet printing technology with so-called hotplate devices allows for quickly testing novel nano-sized gas sensitive materials. 15,[23][24][25] The strict requirements for the properties of the ink system top the list of challenges needed to be overcome for inkjet printing of Cu 2 O nanoparticles. On the one hand, the stability of the ink system should meet the requirement to attain monodispersed patterns on the substrates without aggregation and can be long-term stored without deterioration.…”

A general approach to obtain soft x-ray transparency for thin films grown on bulk substrates

“…b) Author to whom correspondence should be addressed: eisebitt@mbiberlin.de electrical or magnetic fields and without detrimental effects associated with photoemission-induced charging, and (iii) the technical advantages of operating symmetrically around the optical axis, allowing for high spatial resolution in full-field approaches. Examples for such soft x-ray transmission techniques with spatial resolutions approaching approximately 10 nm are Transmission X-ray Microscopy (TXM), 1,2 Scanning Transmission X-ray Microscopy (STXM), 3 Fourier Transform X-ray Holography (FTH), 4 and Coherent Diffractive Imaging (CDI). 5 As the exit wave of the incident radiation after passage through the sample is detected, all these approaches require suitable soft x-ray transparency of the sample to be investigated.…”