# Self-Organizing Sub-μm Surface Structures Stimulated by Microplasma Generated Reactive Species and Short-Pulsed Laser Irradiation

## TL;DR

A new method combines plasma and laser treatments to create structured copper surfaces for better CO2 reduction catalysts.

## Contribution

A novel catalyst functionalization approach using plasma and laser to control surface structure and chemical composition.

## Key findings

- Combining plasma and laser treatments creates nanoscale structures and Cu(II) species on copper surfaces.
- Pulsed laser dewetting forms copper nanoparticles, with size controlled by layer thickness.
- Gas flow during treatment disrupts particle formation, but higher laser energy can counteract this.

## Abstract

Catalysts are critical components for chemical reactions
in industrial
applications. They are able to optimize selectivity, efficiency, and
reaction rates, thus enabling more environmentally friendly processes.
This work presents a novel approach to catalyst functionalization
for the CO2 reduction reaction by combining the reactive
species of an atmospheric pressure plasma jet with the electric fields
and energy input of a laser. This leads to both a nanoscale structuring
as well as a controllable chemical composition of the surface, which
are important parameters for optimizing catalyst performance. The
treatment is conducted on thin copper layers deposited by high power
pulsed magnetron sputtering on silicon wafers. Because atomic oxygen
plays a key role in oxidizing copper, two photon absorption fluorescence
is used to investigate the atomic oxygen density in the interaction
zone of the COST plasma jet and a copper surface. The used atmospheric
pressure plasma jet provides an atomic oxygen density at the surface
in a distance of 8 mm to the jet nozzle of approximately or a flux of . Pulsed laser-induced dewetting is used
to form nanoparticles from the deposited copper layer to enhance catalytic
performance. Varying the layer thickness allows control of the size
of the particles. A gas flow directed on the sample during the combined
treatment disturbs the particle formation. This can be prevented by
increasing the laser energy to compensate for the cooling effect of
the gas flow. Investigating the surface using X-ray photoemission
spectroscopy reveals that the untreated copper layer surface consists
mostly of metallic copper and Cu(I) oxide. Irradiating the sample
only with the laser did not change the composition. The combination
of plasma and laser treatment is able to produce Cu(II) species such
as CuO, whose concentration increases with treatment time. The presented
process allows the tuning of the ratio of C2O/CuO, which
is an interesting parameter for further studies on copper catalyst
performance.