Gregor Filipič

Uniform surface growth of copper oxide nanowires in radiofrequency plasma discharge and limiting factors

The uniform growth of copper oxide nanowires on the top of copper plate has been investigated during the exposure to radiofrequency plasma discharge in respect to plasma properties and its localization. The copper samples of 10 mm radius and 1 mm in thickness were exposed to argon-oxygen plasma created at discharge power of 150 W. After 10 min, almost uniform growth of nanowires was achieved over large surface. There were significant distortions in nanowire length and shape near the edges. Based on the experimental results, we developed a theoretical model, which took into account a balance in heat released at the flow of the current to the nanowire and rejected from the nanowire. This model established a dependence of the maximal length of the nanowire at dependence on the plasma parameters, where the limiting factor for nanowire growth and distortions in distribution are ballistic effects of ions and their local fluxes. In contrast, the plasma heating by potential interactions of species has very little influence on the length and smaller deviations in flux are allowed for uniformity of growth.

Growth dynamics of copper oxide nanowires in plasma at low pressures

The growth time dynamics of the copper oxide nanowires (NWs) in radiofrequency plasma discharge were investigated. Grounded copper samples were treated in argon-oxygen plasma with the discharge power of 150 W for sequenced times up to 20 min. After the treatment, the samples were analysed with scanning electron microscopy and image processing to obtain the length and aspect ratio of the NWs. A growth mode with the saturation was observed in dependence to NW length, where the maximal length of 5 μm was achieved in 20 min. However, the best NW aspect ratio had maximum of about 40 after 10 min of plasma treatment. To describe and understand nanowire growth mechanism, a theoretical model was developed and it is in agreement with the experiment. The model results indicate that different densities of the ion current to the side and top area of NW modify the NW growth in height and width. The NW growth is enhanced by presence of ions, and thus this implies that it can be controlled by discharge power. This explains much faster growth of copper oxide nanowires in plasma environment compared to prolonged thermal treatments.

Safety aspects of atmospheric pressure helium plasma jet operation on skin: In vivo study on mouse skin

Biomedical applications of plasma require its efficacy for specific purposes and equally importantly its safety. Herein the safety aspects of cold plasma created with simple atmospheric pressure plasma jet produced with helium gas and electrode discharge are evaluated in skin damage on mouse, at different duration of exposure and gas flow rates. The extent of skin damage and treatments are systematically evaluated using stereomicroscope, labelling with fluorescent dyes, histology, infrared imaging and optical emission spectroscopy. The analyses reveal early and late skin damages as a consequence of plasma treatment, and are attributed to direct and indirect effects of plasma. The results indicate that direct skin damage progresses with longer treatment time and increasing gas flow rates which reflect changes in plasma properties. With increasing flow rates, the temperature on treated skin grows and the RONS formation rises. The direct effects were plasma treatment dependent, whereas the disclosed late—secondary effects were more independent on discharge parameters and related to diffusion of RONS species. Thermal effects and skin heating are related to plasma-coupling properties and are separated from the effects of other RONS. It is demonstrated that cumulative topical treatment with helium plasma jet could lead to skin damage. How these damages can be mitigated is discussed in order to provide guidance, when using atmospheric pressure plasma jets for skin treatments.

Protein retention on plasma-treated hierarchical nanoscale gold-silver platform.

Dense arrays of gold-supported silver nanowires of about 100 nm in diameter grown directly in the channels of nanoporous aluminium oxide membrane were fabricated and tested as a novel platform for the immobilization and retention of BSA proteins in the microbial-protective environments. Additional treatment of the silver nanowires using low-temperature plasmas in the inductively-coupled plasma reactor and an atmospheric-pressure plasma jet have demonstrated that the morphology of the nanowire array can be controlled and the amount of the retained protein may be increased due to the plasma effect. A combination of the neutral gold sublayer with the antimicrobial properties of silver nanowires could significantly enhance the efficiency of the platforms used in various biotechnological processes.

Nanoherding : plasma-chemical synthesis and electric-charge-driven self organization of SiO2 nanodots

We report on the chemical synthesis of the arrays of silicon oxide nanodots and their self-organization on the surface via physical processes triggered by surface charges. The method based on chemically active oxygen plasma leads to the rearrangement of nanostructures and eventually to the formation of groups of nanodots. This behavior is explained in terms of the effect of electric field on the kinetics of surface processes. The direct measurements of the electric charges on the surface demonstrate that the charge correlates with the density and arrangement of nanodots within the array. Extensive numerical simulations support the proposed mechanism and prove a critical role of the electric charges in the self-organization. This simple and environment-friendly self-guided process could be used in the chemical synthesis of large arrays of nanodots on semiconducting surfaces for a variety of applications in catalysis, energy conversion and storage, photochemistry, environmental and biosensing, and several others.

Recent Advances in the Methods for Designing Superhydrophobic Surfaces

The investigations of superhydrophobicity and self-cleaning surfaces have been given a lot of attention in the last few decades. The surfaces having water contact angle larger than 90° are termed as hydrophobic surfaces and those which exhibit contact angle higher than 150° are said to be superhydrophobic. Such surfaces were first observed in nature in various plants and animals, for example, lotus leaf-like structures. Water repellence of various materials have shown great influences on various applications such as self-cleaning, anti-ageing, water-oil separation, water corrosion in electrical industry, water proof textiles, controlled transportation of fluids, etc. Generally, surface micro/nanostructuring combined with low surface energy of materials leads to extreme anti-wetting properties. The hundreds of research articles and more than 450 patents on the subject of nature mimicking self-cleaning surfaces prove the potential of this topic. Self-cleaning property depends on both surface morphology and surface chemistry. For achieving superhydrophobic surfaces, we can, typically, either increase the roughness of the intrinsically hydrophobic material or tune desired roughness and morphology on hydrophilic surfaces. Depending on such parameters a water droplet on the surface attains either Wenzel or Cassie-Baxter state. For the preparation of superhydrophobic surfaces, various physical and chemical methods have been successfully used. Methods such as hydrothermal process, using various templates, plasma surface modifications, physical and chemical vapour deposition, layer by layer deposition, electrospinning and sol-gel processing have been used for achieving desired roughness and surface chemistry on various

Microplasma Induced Cell Morphological Changes and Apoptosis of Ex Vivo Cultured Human Anterior Lens Epithelial Cells – Relevance to Capsular Opacification

Inducing selective or targeted cell apoptosis without affecting large number of neighbouring cells remains a challenge. A plausible method for treatment of posterior capsular opacification (PCO) due to remaining lens epithelial cells (LECs) by reactive chemistry induced by localized single electrode microplasma discharge at top of a needle-like glass electrode with spot size ~3 μm is hereby presented. The focused and highly-localized atmospheric pressure microplasma jet with electrode discharge could induce a dose-dependent apoptosis in selected and targeted individual LECs, which could be confirmed by real-time monitoring of the morphological and structural changes at cellular level. Direct cell treatment with microplasma inside the medium appeared more effective in inducing apoptosis (caspase 8 positivity and DNA fragmentation) at a highly targeted cell level compared to treatment on top of the medium (indirect treatment). Our results show that single cell specific micropipette plasma can be used to selectively induce demise in LECs which remain in the capsular bag after cataract surgery and thus prevent their migration (CXCR4 positivity) to the posterior lens capsule and PCO formation.

Investigation on band gap energy and effect of various surface plasma treatments on nano structured SnO2 semiconductor

For any semiconducting metal oxides, dielectric properties of nanomaterial play an important role, which determines various activities such as sensing, catalytic activity, adsorption, etc. These properties depend on the chemical composition, method of synthesis and surface characteristics. Various physical and chemical properties of nanomaterials can be tuned by choosing various chemical treatments or novel synthetic routes. Among various metal oxide semiconductors, SnO2 is extensively used for gas sensing applications. Surface plasma treatment is one of the advanced techniques used for improving the sensing properties of SnO2. Surface modification can be done by treating with high energy reactive species in plasma by collision and chemical reaction. In this work, we discuss how impregnation of foreign atoms changes the band gap energy of SnO2 thick films, which is an imperative for any semiconducting material. Chemically synthesized SnO2 thick film was treated with plasma gases and using different plasma parameters. The performances variations were measured by using different characterization techniques including SEM, TEM, Raman, UV-VIS spectroscopy, etc.