Material research: New chemistry for ultra-thin gas sensors

Date:
July 1, 2020
Source:
Ruhr-University Bochum
Summary:
The application of zinc oxide layers in industry is manifold and
ranges from the protection of degradable goods to the detection of
toxic nitrogen oxide gas. Such layers can be deposited by atomic
layer deposition (ALD) which employs typically chemical compounds,
or simply precursors, which ignite immediately upon contact with
air, i.e. are highly pyrophoric.



FULL STORY ==========================================================================
A Bochum-based team has developed a new process for zinc oxide layers
that can be used for nitrogen oxide sensors as well as protection layer
on plastic.


==========================================================================
The application of zinc oxide layers in industry is manifold and ranges
from the protection of degradable goods to the detection of toxic nitrogen oxide gas. Such layers can be deposited by atomic layer deposition (ALD)
which employs typically chemical compounds, or simply precursors, which
ignite immediately upon contact with air, i.e. are highly pyrophoric. An interdisciplinary research team at Ruhr-Universita"t Bochum (RUB) has
now established a new fabrication process based on a non-pyrophoric zinc precursor that can be processed at temperatures low enough to allow
plastics to be coated. The team published their report in the journal
"Small," where it was featured as the cover story in the edition from
4 June 2020.

The application of zinc oxide layers in industry is manifold and ranges
from the protection of degradable goods to the detection of toxic nitrogen oxide gas. Such layers can be deposited by atomic layer deposition (ALD)
which employs typically chemical compounds, or simply precursors, which
ignite immediately upon contact with air, i.e. are highly pyrophoric. An interdisciplinary research team at Ruhr-Universita"t Bochum (RUB) has
now established a new fabrication process based on a non-pyrophoric zinc precursor that can be processed at temperatures low enough to allow
plastics to be coated. The team published their report in the journal
Small, where it was featured as the cover story in the edition from 4
June 2020.

Depositing ultra-thin layers In order to produce a sensor for nitrogen
dioxide (NO2), a thin layer of nanostructured zinc oxide (ZnO) must be
applied to a sensor substrate and then integrated into an electrical
component. Professor Anjana Devi's team used ALD to apply ultra-thin
ZnO layers on such sensor substrates.

In general, ALD processes are used in industry to miniaturise electrical components using ultra-thin layers, some of which are only a few atomic
layers thick, while at the same time increasing their efficiency. For
that, suitable precursors are required that react at surfaces to form
such a thin film. "The chemistry behind ALD processes is therefore
essential and has a huge impact on the resulting thin films," points
out Anjana Devi.

Safe handling and highest quality To date, industrial manufacturers
have been producing ZnO thin films by deploying an extremely reactive,
highly pyrophoric zinc precursor via ALD. "The key for the development
of a safe alternative ALD process for ZnO at RUB was to develop a new, non-pyrophoric precursor that is safe to handle and is able to deposit
ZnO thin films of the highest quality," explains Lukas Mai, lead author
of the study. "The challenge was to find alternative chemistries
to replace the pyrophoric compounds that are generally used in the
industry for ZnO." The unique aspect of the new process is that it
can be performed at very low process temperatures, thus facilitating
deposition onto plastics. Consequently, the new process can be used
not only for the manufacture of gas sensors, but also of gas barrier
layers. In the packaging industry, such layers are applied on plastics
to protect degradable goods such as food or pharmaceuticals from air.


========================================================================== Story Source: Materials provided by Ruhr-University_Bochum. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Lukas Mai, Felix Mitschker, Claudia Bock, Alessia Niesen, Engin
Ciftyurek, Detlef Rogalla, Johannes Mickler, Matthias Erig, Zheshen
Li, Peter Awakowicz, Klaus Schierbaum, Anjana Devi. Zinc Oxide:
From Precursor Chemistry to Gas Sensors: Plasma‐Enhanced
Atomic Layer Deposition Process Engineering for Zinc Oxide Layers
from a Nonpyrophoric Zinc Precursor for Gas Barrier and Sensor
Applications (Small 22/2020).

Small, 2020; 16 (22): 2070122 DOI: 10.1002/smll.202070122 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200701100010.htm

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