The enhancement of microporosity in HMDSO-derived plasma polymer films through sequential cycles of plasma polymerization and etching has been demonstrated using positron spectroscopy techniques. These thin films exhibit a labyrinthine nanoporous architecture, characterized by an interconnected pore network with bottlenecks. The configuration of the plasma reactor significantly influences the final nanoporous structure, governed by the balance between ion-induced densification and chemical oxidation of residual hydrocarbons. By fine-tuning the plasma parameters and reactor design, small nanopores within the Si–O–Si cage structure are optimized to approximately 0.3 nm. These structural units are acting as interconnections of larger nanopores around 0.65 nm, functionalized with Si–OH groups along the pore walls. The high precision of positron annihilation spectroscopy enables clear differentiation between samples, with complementary insights provided by ellipsometry and Rutherford backscattering spectroscopy. Further optimization of the intrinsic microporosity was achieved through near-plasma chemical surface engineering, effectively mitigating ion-induced densification. Given the application potential of superhydrophilic SiOx-like thin films, the thermal stability of the nanoporous network was evaluated at moderate temperatures, revealing excellent structural integrity. These findings support the use of plasma polymer films fabricated via polymerization of hexamethyldisiloxane followed by etching as advanced membrane materials, where well-defined, defect-free microporous structures are essential.

Is plasma truly a "fourth state of matter"? And if not, does this change how we would approach its chemical reactivity? In equilibrium systems, temperature (T) is the main control parameter for chemical reactions. Here, we argue that in non-equilibrium plasmas the main driving quantity is the entropy change (Delta S) associated with the externally supplied energy. Therefore, plasma-chemical activation is analyzed for (i) low and (ii) highly collisional plasmas, and (iii) plasmas with significant heating. In all cases, the governing parameter is the energy available per molecule, reflecting the entropy exported through electron-impact and thermally driven reactions. Based on this, analytical expressions of Arrhenius- and Saha-like form are derived that describe plasma gas conversion, for example, for CO2 and CH4.

Per- and polyfluoroalkyl substances (PFAS) are widely used due to their unique properties combining liquid repellency with low friction and high thermal, mechanical and chemical stability. PFAS coatings, however, contribute to the release of long-lasting chemicals, components of which break down very slowly over time. They are thus increasingly detected as environmental pollutants, and some are linked to negative effects on human health. Therefore, alternative coating materials and technologies are required, meeting PFAS properties for specific applications. Most of all, plasma technology offers a promising and green way to deposit ultrathin, fluorine-free coatings firmly bond to material surfaces with adjusted chemical and nanostructural properties, while considering safety and sustainability of the entire lifecycle of the used materials.

Reactive oxygen species (ROS) are promising green candidates for tackling challenges ranging from antimicrobial resistance to water decontamination. Metal oxide nanomaterials structured as thin films, deposited at room temperature (RT) using plasma technology, can deliver ROS to the environment by catalyzing oxygen and water following a chemodynamics approach. This study proposes thin film plasma polymerization as a strategy to precisely control ROS delivery, unravel ROS formation mechanism at the catalytic interface, and ensure ROS‐driven chemistry. A proper combination of semiconductors, specifically silver oxide and titanium oxide, is used as a model system for ROS production. This specific coupling of semiconductors produces ROS in the dark due to charge separation without ion leaching. Plasma surface functionalization with nanoporous SiOx‐like films in the 1–100 nm range allows selective control of the delivery of radicals with different characteristic lifetimes such as superoxide anion and singlet oxygen based on the thickness of the functional layer. As proof of promising applications, results regarding radicals' detection are correlated with the antimicrobial activity of the ROS‐releasing system. Thin film plasma surface functionalization allows control of ROS delivery, ensuring that the material efficacy is due to ROS and not by other direct redox chemistry or leaching processes.

Enhanced wettability and adhesion of fibrous materials requires surface functionalization, e.g. for fiber-reinforced composites. Plasma functionalization as an environmentally friendly process is thus investigated using roll-to-roll low pressure plasma processing for large area treatment such as e.g. fabrics. Hydrocarbon gases (C2H4) mixed with a reactive gas (CO2) are examined to optimize oxygen functionality, regarding plasma-surface interaction, deposition rates, and penetration into the fibrous structure, while limiting heat load. Power input increases deposition rates by generating more reactive and film-forming species, while optimal substrate positioning is crucial to achieve uniform coatings and desired wettability, particularly for roll-to-roll processing. The influence of potential air leakage and substrate outgassing is assessed, revealing significant impacts on deposition rates. These findings offer valuable insights for optimizing plasma polymerization processes for industrial applications.

AbstractSurface functionalization technologies of fibrous or porous materials are often considered relatively unstable with a shelf life of several weeks or months at most, evoked by heterogeneous treatment of their internal surface areas. Here, it is demonstrating that the fine balance of plasma etching, deposition, and oxidation involving different reactive species, strongly enhances penetration depth within complex structures. On this basis, capillary wicking is maintained over >10 years after plasma functionalization of a scaffold material used for biomedical engineering. Electrospun membranes of poly(ε‐caprolactone) are coated with an oxygen‐functional hydrocarbon layer, deposited in a competitive ablation and plasma polymerization process with CO2 and C2H4 as reactive gases. Chemical analysis immediately after coating, 9 months later, and after storing at ambient conditions for over 10 years, indicate a stable surface coating. Using defined geometries such as a cavity and an undercut, the underlying plasma interaction mechanisms are revealed, showing different synergies of energetic particles, depositing species with different surface reactivities, and oxidizing species. A concerted action of such species during plasma functionalization is key to enabling long‐term wetting properties. This has a major implication for the surface functionalization of scaffolds, textiles, membranes, or foams used in diverse fields.

Molecular-level understanding of liquid-solid interfaces is key to the development of many physical, biological and chemical systems. In this context, functional plasma polymer films (PPFs) offer tunable surfaces ranging from hydrophilic to hydrophobic behavior. In this study, smooth hydrophilic PPFs with average surface roughness below 0.3 nm were fabricated from hexamethyldisiloxane (HMDSO) precursor by varying the substrate-plasma separation. The reference method consisted of direct plasma exposure (DPE) of mica and silicon substrates, while an alternative near-plasma chemistry (NPC) approach allowed film formation at a controlled distance, filtering out high-energy ions. Secondary ion mass spectroscopy revealed chemical and structural differences between the PPFs. Despite these, both films exhibited similar negative zeta potential in aqueous solution at neutral pH. The interfacial interactions at the PPF-liquid interface were accessed at different length scales using atomic force microscopy, colloidal probe microscopy, and the extended surface force apparatus. Both deposited films exhibited a degree of porosity and exceptionally low adhesion in water. DPE-PPF interactions were consistent with electrostatic double-layer theory, supporting its suitability as a model system for fundamental surface force studies. In contrast, NPC-PPF surfaces exhibited additional repulsive forces at 20 +/- 10 nm in water, suggesting an additional mechanism beyond ordinary double-layer repulsion.

The Gibbs free energy is a valuable thermodynamic potential to predict the spontaneity of reactions and the feasibility of chemical processes. At thermodynamic equilibrium a system's Gibbs free energy reaches its minimum, and its entropy is maximized. At this point, the entropy becomes unavailable for performing useful chemical work. Hence, temperature, T , is generally used to drive chemical reactions, especially in gas conversion processes. However, in systems far from equilibrium, changes in entropy can be harnessed to drive chemical reactions. In a non-thermal plasma, non-equilibrium conditions can be sustained with electron temperature exceeding gas temperature (T-e >> T-gas). More importantly, the chemical reaction rates are affected by the energy input into the plasma while the observed temperatures remain constant. Here, a new concept is introduced proposing the effective (average) energy input - which is related to a change in entropy at different (constant) temperatures under non-equilibrium conditions - as the fundamental parameter controlling gas phase reactions. Using this theoretically derived formalism, electron-driven reactions related to T e can be distinguished from thermally driven reactions by plasma gas heating related to T gas . This approach can explain observed conversion and efficiency trends, as demonstrated for plasma-based methane pyrolysis, and point towards further efficiency improvements for gas conversion processes under non-equilibrium plasma conditions e.g. as an important source for hydrogen.

Plasma polymer deposition processes are well-studied and optimized on flat substrates. Understanding the role of substrate geometry is crucial for optimizing deposition on non-planar substrates. We investigated the altered transport of film-forming species into two 3D geometries, cavities with a slit opening and a cavity with an undercut, to assess the contribution of ions to the deposition and etching and to estimate the sticking coefficient of depositing species for the CO2/C2H4/Ar gas mixture. Profilometry and ellipsometry were employed to obtain film thicknesses. It revealed a significant extension of the deposition inside the cavities attributed to film- forming species with a low sticking coefficient. These depositing species contain less oxygen because a spatially resolved ATR-FTIR analysis revealed an increasing proportion of hydrocarbons further inside the cavity. Inside the cavities with a slit, the film thickness exceeded its value on the flat Si surface outside. This difference indicated that ions responsible for etching collide during their flight toward the growing film inside the slit. However, it also suggests that some ionic species contribute to the deposition because directional species become more prominent under the slit than outside due to the geometrical shielding of thermalized species represented by the structure's angular aperture. Monte Carlo simulations inside the cavity with different slits confirmed that diffusion alone did not explain the experimentally obtained profiles, as the model considering thermalized deposition and etching particles is not able to reproduce the narrow film thickness profiles obtained in the cavities with a slit. The model with directional particles demonstrated significantly better agreement.

PVD Coatings Enable Textile Wires and Sensors - Process control by adjusted energy ranges Plasma sputtering deposition is a Physical Vapor Deposition (PVD) method based on a weakly ionized gas, the plasma, that ablates atoms from a solid target material at vacuum conditions to deposit the sputtered atoms on a substrate. In this way, the plasma has two functions, i) the generation of high-energy ions of several 100 eV accelerated to the target for sputtering, and ii) to support film growth by plasma-surface interaction with particles bearing lower energies around similar to 10 eV. For both processes, energy thresholds are present, which will be discussed in this article. Plasma sputtering deposition has wide spread industrial applications. As one example, the metallization of polymer fibers is demonstrated to obtain electrically conductive textile sensors and wires.

Dust contamination is a frequent problem when processing materials at the nanoscale by plasma technology. Various approaches have thus been applied to protect samples, however, requiring to adjust plasma properties which also imposes limitations on the process window. We therefore propose near-plasma chemical (NPC) surface engineering as a way to avoid dust contamination during and after plasma operation without altering the plasma environment by simply locating a polymeric mesh above the samples in the plasma sheath. Because of the electric potential acquired by the mesh, heavy charged particles cannot pass the open area of the mesh, avoiding their contact with the samples positioned below. Samples fabricated by NPC surface engineering are dust-free independently on the size or the origin of the powder nanoparticles. This neat approach can support many high-precision, dust-free applications of plasma technology on an industrial scale.

As a new trend in plasma surface engineering, plasma conditions that allow more-defined chemical reactions at the surface are being increasingly investigated. This is achieved by avoiding high energy deposition via ion bombardment during direct plasma exposure (DPE) causing destruction, densification, and a broad variety of chemical reactions. In this work, a novel approach is introduced by placing a polymer mesh with large open area close to the plasma-sheath boundary above the plasma-treated sample, thus enabling near-plasma chemistry (NPC). The mesh size effectively extracts ions, while reactive neutrals, electrons, and photons still reach the sample surface. The beneficial impact of this on the plasma activation of poly (tetrafluoroethylene) (PTFE) to enhance wettability and on the plasma polymerization of siloxanes, combined with the etching of residual hydrocarbons to obtain highly porous SiOx coatings at low temperatures, is discussed. Characterization of the treated samples indicates a predominant chemical modification yielding enhanced film structures and durability.

Hexamethyldisiloxane (HMDSO) low-pressure plasmas are known for their versatility in the deposition of plasma polymer films (PPFs) with different properties and applications. Although they have been studied for decades, the reaction mechanisms of plasma polymer formation leave open questions, particularly when deposition on 3D materials with complex geometries such as cavities and undercuts is considered. In the present study, two configurations named "cavity" and "undercut" have been selected to study the influence of diffusion of film-forming species and surface reactivity in HMDSO plasmas without and with O2 admixture. A varying spatial chemical composition of the plasma polymer deposit along the penetration depth of the studied configurations indicates different sticking probabilities of the film-forming species. Furthermore, although ion-induced effects are usually only considered for direct plasma exposure, the obtained results and additional etching experiments reveal that the contribution of high-energy particles might still be considered underneath small openings. Finally, the relevance of oxidizing chemical reactions at the surface inside the configurations is clarified when O2 is added to the plasma.

ZusammenfassungSputtern oder Kathodenzerstäubung ist eine Methode der physikalischen Gasphasenabscheidung (physical vapor deposition, PVD), die auf der Wechselwirkung mit einem Plasma, ein teilweise ionisiertes Gas, unter Vakuumbedingungen beruht. Durch Plasmawechselwirkung werden Atome von einem festen Material, dem Target, abgetragen (gesputtert) und auf einem Substrat abgeschieden. Auf diese Weise erfüllt das Plasma zwei Funktionen: i) die Erzeugung hochenergetischer Ionen von mehreren 100 eV, die auf das Target beschleunigt werden, und ii) die Unterstützung des Schichtwachstums durch Wechselwirkung mit Plasmateilchen niedrigerer Energie, etwa um 10 eV. Für beide Prozesse gibt es angepasste Energiebereiche sowie Schwellenwerte, die in diesem Artikel eingehender betrachtet werden. Sputtern ist ein etabliertes Verfahren mit breiter industrieller Anwendung. Hier wird als Beispiel die Metallisierung von Polymerfasern aufgezeigt, um elektrisch leitfähige textile Sensoren und hochfeste textile Kabel zu ermöglichen.

Increasing complications due to bacterial and viral infections require novel antimicrobial approaches. One emerging strategy is that based on catalysts able to selectively deliver reactive oxygen species (ROS) without leaching of other substances. In particular, metal oxide thin films activated by daylight can produce ROS by simply catalyzing oxygen and water molecules. This study examines plasma technology, combining deposition and oxidation processes, as well as plasma polymerization, to obtain functionalized AgOx-doped titanium oxide (TiOx) catalytic materials. The high-energy conditions in the reactive, ionized gas enable the intrinsic formation of a large number of reactive sites at defects and interfaces between the metal oxide nanostructures. Furthermore, plasma functionalization with nanoporous SiOx films (up to 100 nm thick) allows to precisely control the ROS delivery as well as unravel ROS formation mechanism at the metal oxide interface. Combining fluorescence spectroscopy and electron paramagnetic resonance, the controlled delivery of superoxide anion and singlet oxygen has been tuned based on the thickness of the nanoporous functional layer. ROS delivery by functionalized catalytic plasma coating has been related to excellent antimicrobial activity against E. coli bacteria as well as murine hepatitis virus, while avoiding cytotoxic and sensitization effects.

Outside Front Cover: Molecular dynamics simulations are carried out for inspecting neutral chemical reactions in an Ar/CH 4 plasma.Mass spectra at temperature in the range 300-1000K are calculated.Detailed pathways leading to large C n H m molecule (n > 5) formation are obtained.Structure of linear and alicyclic/ aromatic species is is identifi ed and evolution against temperature is determined.

Plasma polymers (PPs) can easily modify material surfaces to improve their bio-applicability due to match-made surface-free energy and functionality. However, cell adhesion to PPs typically composed of various functional groups has not yet been fully understood. We explain the origin of strong resistance to trypsin treatment previously noted for nonendothelial cells on amine PPs. It is caused mainly by nonspecific adhesion of negatively charged parts of transmembrane proteins to the positively charged amine PP surface, enabled by thin glycocalyx. However, endothelial cells are bound primarily by their thick, negatively charged glycocalyx and sporadically by integrins in kinetic traps, both cleaved by trypsin. Cell scratching by atomic force microscopy tip confirmed the correlation of trypsin resistance to the strength of cell adhesion.

In a low-temperature plasma, the electrons pick up energy from the electric field in collisions with atoms and molecules, gaining high kinetic energy that must be sufficient for ionizing reactions to sustain the plasma. For molecular gases, an average energy per heavy gas particle is thus available in the plasma, the specific energy input, yielding plasma activation by inelastic collisions. Following a distribution law, the probability for the activation mechanism can be described by an Arrhenius-like equation. The potential of this approach is demonstrated on the basis of plasma polymerization and plasma CO2 conversion. For perspective, energy efficiencies are discussed as a function of conversion indicating the optimum that can be achieved by electron impact activation compared with additional ways of energy transfer, probably depending on certain constraints.

Materials with the desirable surface wettability are of key importance in diverse applications. However, most of the existing chemical processes used for surface wettability control are often energy-inefficient, pollute the environment, and rely on harsh processing conditions. Therefore, highly-selective, green, and low-cost alternative fabrication techniques are in urgent demand. Low-temperature plasma processing is one such promising approach that satisfies the above requirements. In this review, we present recent advances in plasma processing to control surface wettability for diverse emerging applications in the environment, energy, and biomedicine fields. The underlying mechanisms of the plasma surface engineering, key features of the fabrication processes, and water-surface interactions are discussed. This review aims to guide further development of the plasma processing to effectively control the surface wettability of various surfaces. This effort is poised to contribute to the development of advanced functional materials targeting a broad range of applications.