Atmospheric pressure non-equilibrium (cold) plasma jet technology received enormous attention in surface processing of materials in the last two decades, and still continues nowadays to attract growing interest. In addition to the advantages of the atmospheric pressure operation such as the potential cost reduction of apparatuses as well as their easier handling and maintenance, due to the distinctive remote operation, plasma jets give the unique possibility of placing the substrate outside the source boundaries. Consequently, the processing of complex three-dimensional objects and the integration into existing production lines are expected to be much easier. However, while appealing, plasma jet technology has the drawback that great efforts are required for process optimization, since many factors can affect, for instance, the physical and chemical proprieties of the so-called “plasma plume” emanating from the devices and propagating in open space towards the substrate to be treated. The aim of this paper is to provide a critical literature review on the utilization of atmospheric pressure non-equilibrium plasma jets in surface processing of materials. Starting from the description and classification of the multitude of devices used in this applicative field so far, the attention will be drawn on some very important aspects to be taken into account in process optimization. The discussion will be focused on basic concepts and peculiarities closely related to the remote operation of the plasma sources, which include the characteristics and dynamics of the plasma plume interacting with the substrate and the surrounding atmosphere. Since the plasma jet approach allows the surface modification of small localized regions of the sample, the strategies implemented to enlarge the treated area will be also addressed. Finally, a brief overview will be given of the available applications and recent developments in the field of etching, thin film deposition and treatment.

Atmospheric pressure non-equilibrium plasma jet technology: general features, specificities and applications in surface processing of materials

Disorder, which qualitatively describes some measure of irregularities in spatial patterns, is ubiquitous in many-body systems, equilibrium and non-equilibrium states of matter, network structures, biological systems and wave–matter interactions. In photonics, the introduction of order and disorder for device applications has traditionally been treated separately. However, recent developments in nanofabrication and design strategies have enabled the use of materials that lie between the extremes of order and disorder that can yield innovative optical phenomena owing to their engineered disordered patterns. Here, we review recent achievements in the emerging field of engineered disorder in photonics by outlining milestones in the control of the spectrum, transport, wavefront and topology of light in disordered structures. We show that engineered disorder has begun to transform the traditional landscape of photonics by introducing a greatly enhanced design freedom and, hence, has great potential for the rational design of the next generation of materials. In photonics, the introduction of order and disorder has traditionally been treated separately. However, recent developments in nanofabrication and design strategies have enabled the use of materials that lie between the extremes of order and disorder that can yield innovative optical phenomena. This Review surveys the basics and recent achievements of engineered disorder in photonics.

Engineered disorder in photonics

Palladium nanoparticles have proven to be exceptionally suitable materials for the optical detection of hydrogen gas due to the dielectric function that changes with the hydrogen concentration. The development of a reliable, low-cost, and widely applicable hydrogen detector requires a simple optical readout mechanism and an optimization of the lowest detectable hydrogen concentration. The so-called "perfect absorber"-type structures, consisting of a layer of plasmonic palladium nanoantennas suspended above a metallic mirror layer, are a promising approach to realizing such sensors. The absorption of hydrogen by palladium leads to a shift of the plasmon resonance and, thus, to a change in the far-field reflectance spectrum. The spectral change can be analyzed in detail using spectroscopic measurements, while the reflectance change at a specific wavelength can be detected with a simple photometric system of a photodiode and a monochromatic light source. Here, we systematically investigate the geometry of cavity-coupled palladium nanostructures as well as the optical system concept, which enables us to formulate a set of design rules for optimizing the hydrogen sensitivity. Employing these principles, we demonstrate the robust detection of hydrogen at concentrations down to 100 ppm. Our results are not limited to hydrogen sensing but can be applied to any type of plasmonic sensor.

Design Principles for Sensitivity Optimization in Plasmonic Hydrogen Sensors.

Fabrication of Nearly‐Hyperuniform Substrates by Tailored Disorder for Photonic Applications

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/adom.202100787

Tailored Disorder in Photonics: Learning from Nature

Arrays of nanoparticles exploited in light scattering applications commonly only feature either a periodic or a rather random arrangement of its constituents. For the periodic case, light scattering is mostly governed by the strong spatial correlations of the arrangement, expressed by the structure factor. For the random case, structural correlations cancel each other out and light scattering is mostly governed by the scattering properties of the individual scatterer, expressed by the form factor. In contrast to these extreme cases, it is shown here that hyperuniform disorder in self-organized large-area arrays of high refractive index nanodisks enables both structure and form factor to impact the resulting scattering pattern, offering novel means to tailor light scattering. The scattering response from the authors’ nearly hyperuniform interfaces can be exploited in a large variety of applications and constitutes a novel class of advanced optical materials.

/pdf/tailored-light-scattering-through-hyperuniform-disorder-in-7o5ispn1lr.pdf

Tailored Light Scattering through Hyperuniform Disorder in Self-Organized Arrays of High-Index Nanodisks

Etch Mechanism and Temperature Regimes of an Atmospheric Pressure Chlorine-Based Plasma Jet Process

We study the light-trapping properties of surface textures generated by a bottom-up approach, which utilizes monolayers of densely deposited nanospheres as a template. We demonstrate that just allowing placement disorder in monolayers from identical nanospheres can already lead to a significant boost in light-trapping capabilities. Further absorption enhancement can be obtained by involving an additional nanosphere size species. We show that the Power Spectral Density provides limited correspondence to the diffraction pattern and in turn to the short-circuit current density enhancement for large texture modulations. However, in predicting the optimal nanosphere size distribution, we demonstrate that full-wave simulations of just a c-Si semi-infinite halfspace at a single wavelength in the range where light trapping is of main importance is sufficient to provide an excellent estimate. The envisioned bottom-up approach can thus reliably provide good light-trapping surface textures even with simple nanosphere monolayer templates defined by a limited number of control parameters: two nanosphere radii and their occurrence probability.

/pdf/strategy-for-tailoring-the-size-distribution-of-nanospheres-uxdr4aplt2.pdf

Peter M. Piechulla

Papers

Fabrication of Nearly‐Hyperuniform Substrates by Tailored Disorder for Photonic Applications

Tailored Light Scattering through Hyperuniform Disorder in Self-Organized Arrays of High-Index Nanodisks

Etch Mechanism and Temperature Regimes of an Atmospheric Pressure Chlorine-Based Plasma Jet Process

Strategy for tailoring the size distribution of nanospheres to optimize rough backreflectors of solar cells.

Antireflective Huygens’ Metasurface with Correlated Disorder Made from High-Index Disks Implemented into Silicon Heterojunction Solar Cells