Tomáš Homola

Plasma Treatment of Glass Surfaces Using Diffuse Coplanar Surface Barrier Discharge in Ambient Air

We report a study on the treatment of flat glass surfaces by ambient air atmospheric pressure plasma, generated by a dielectric barrier discharge of coplanar arrangement of the electrode system—the diffuse coplanar surface barrier discharge (DCSBD). The plasma treatment of glass was performed in both static and dynamic modes. With respect to wettability of the glass surface, treatment in static mode resulted in non-uniform surface properties, whereas dynamic mode provided a fully uniform treatment. A water contact angle measurement was used to determine the efficiency of plasma treatments in dynamic mode and also to investigate a hydrophobic recovery of plasma treated glass surfaces. The X-ray photoelectron spectroscopy measurements showed a decrease of overall carbon concentrations after plasma treatment. A deconvolution of C1s peak, showed that a short plasma treatment led to decrease of C–C bonds concentration and increases of C–O and O–C=O bond concentrations. An enhancing influence of the glass surface itself on DCSBD diffuse plasma was observed and explained by different discharge onsets and changes in the electric field distribution.

Low temperature temporal and spatial atomic layer deposition of TiO2 films

Titanium dioxide films were grown by atomic layer deposition (ALD) using titanium tetraisopropoxide as a titanium precursor and water, ozone, or oxygen plasma as coreactants. Low temperatures (80–120 °C) were used to grow moisture barrier TiO2 films on polyethylene naphthalate. The maximum growth per cycle for water, ozone, and oxygen plasma processes were 0.33, 0.12, and 0.56 A/cycle, respectively. X-ray photoelectron spectrometry was used to evaluate the chemical composition of the layers and the origin of the carbon contamination was studied by deconvoluting carbon C1s peaks. In plasma-assisted ALD, the film properties were dependent on the energy dose supplied by the plasma. TiO2 films were also successfully deposited by using a spatial ALD (SALD) system based on the results from the temporal ALD. Similar properties were measured compared to the temporal ALD deposited TiO2, but the deposition time could be reduced using SALD. The TiO2 films deposited by plasma-assisted ALD showed better moisture barri...

Atmospheric Plasma Surface Activation of Poly(Ethylene Terephthalate) Film for Roll-To-Roll Application of Transparent Conductive Coating

An effective surface activation is crucial for high-speed roll-to-roll coating of functional films for printed electronics applications. In this article, we report a study of surface treatment of three types of poly(ethylene terephthalate) (PET) films by an argon/oxygen atmospheric pressure plasma and an ambient air atmospheric pressure plasma to obtain the required wettability for subsequent slot die coating of transparent conductive polymer layer using a poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) ink. Prior to plasma treatment, the PET surfaces, which differ in manufacturing process of their preparation, were characterized by X-ray photoelectron spectroscopy. The surface changes after the plasma treatments were characterized by water contact angle measurement and atomic force microscopy. We found that the water contact angles of the three types of untreated PET surfaces were 80.9°, 75.9°, and 66.3°, respectively, and the water contact angles after argon/oxygen plasma treatment at treatment speed of 1 m · min−1 decreased to 36.2°, 31.9°, and 40.9°, respectively. These conditions were stable from 1 up to 4 days, which are longer than reported values of 15–60 min and sufficient for roll-to-roll coating processes.

Photoelectrocatalytic activity of ZnO coated nano-porous silicon by atomic layer deposition

In the present study, ZnO thin film was grown on nano-porous silicon by atomic layer deposition (ALD) whereas porous silicon was prepared by a stain etching method for three different durations, 4 min (PS1), 8 min (PS2) and 12 min (PS3). SEM analysis shows that ZnO nanoparticles with a size of 20–50 nm were uniformly distributed on nano-porous silicon. AFM analysis shows that the surface roughness of the nanoporous silicon increases continuously with the increase of porous silicon etching time. In contradiction, the surface roughness is almost equal for ZnO/PS1, ZnO/PS2 and ZnO/PS3. XRD analysis shows that the ZnO nanoparticles exhibited a hexagonal wurtzite structure. XPS characterization was used to analyze the chemical composition and states present in the ZnO coated porous silicon. The DRS UV-Visible absorbance spectrum reveals that ZnO/PS3 very strongly absorbs visible light around 526 nm. ZnO coated porous silicon, especially ZnO/PS3, exhibited higher photocatalytic activity compared to ZnO coated glass towards methylene blue dye degradation. Likewise, the negative biased ZnO/PS3 exhibited superior photocatalytic activity compared to unbiased and positive biased ZnO/PS3. The enhanced solar photocatalytic and photoelectrocatalytic activity is attributed to the visible light absorption of ZnO/PS and the effective injection of photogenerated electrons from porous silicon to ZnO even if porous silicon is not directly involved in any redox reactions.

Attachment of Poly(l-lactide) Nanoparticles to Plasma-Treated Non-Woven Polymer Fabrics Using Inkjet Printing.

Active dressings that based on fabric materials are an area of interest for the treatment of wounds. Poly(l-lactide) nanoparticles containing the antimicrobial agent octenidine can be controllably lysed by toxins released by pathogenic bacteria thus releasing antimicrobial material in response to the presence of the bacterial toxins and so counteracting the infection. We developed an integrated engineering solution that allows for the stable immobilisation of nanoparticles on non-woven fabrics. The process involves coating nanoparticles on non-woven polymer surfaces by using an inkjet printing process. In order to improve the adhesion and retention of the nanoparticles on the fabric, surface pretreatment of the non-woven fabric using plasma jet treatment can be applied to increase its surface energy.

Atomic layer deposition of cerium oxide for potential use in diesel soot combustion

The particulate soot emission from diesel motors has a severe impact on the environment and peoples health. The use of catalytic convertors is one of the ways to minimize the emission and decrease the hazard level. In this paper, the activity of cerium oxide for catalytic combustion of diesel soot was studied. Thin films of cerium dioxide were synthesized by atomic layer deposition using tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)cerium [Ce(thd)4] and ozone as precursors. The characteristics of the films were studied as a function of deposition conditions within the reaction temperature range of 180–350 °C. Thickness, crystallinity, elemental composition, and morphology of the CeO2 films deposited on Si (100) were characterized by ellipsometry, x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and field emission scanning electron microscopy, respectively. The growth rate of CeO2 was observed to be 0.30 A/cycle at temperatures up to 250 °C with a slight increase to 0.37 A/...

Sub-image searching through intersection of local descriptors

The complexity of search in current business intelligence systems, academic research, or even the home audiovisual databases grows up rapidly. Users require searching by the content of their data. For example, the user sees a cathedral while watching a movie and by taking a snapshot, his or her private collection of holiday photos can be searched for images containing that cathedral, as demonstrated in Figure 1. In practice, it is not sufficient to store data and search in it by exact match but rather by means of similarity, i.e. retrieving data items similar to a query item. Similarity searching is especially requested in multimedia databases, digital right management systems, computer aided diagnosis, but also in natural sciences and psychology. In these fields, theoretical primal background for querying by similarity is already defined.

Proximity-Based order-respecting intersection for searching in image databases

As the volume of non-textual data, such images and other multimedia data, available on Internet is increasing. The issue of identifying data items based on query containment rather than query equality is becoming more and more important. In this paper, we propose a solution to this problem. We assume local descriptors are extracted from data items, so the aforementioned problem reduces to finding data items that share as many as possible local descriptors with the query. In particular, we define a new e-intersection for this purpose. Local descriptors usually contain the location of the descriptors, so the proposed solution takes them into account to increase effectiveness of searching. We evaluate the e-intersection on two real-life image collections using SIFT and SURF local descriptors from both effectiveness and efficiency points of view. Moreover, we study the influence of individual parameters of the e-intersection to query results.

Atmospheric dry hydrogen plasma reduction of inkjet-printed flexible graphene oxide electrodes

This study concerns a low-temperature method for dry hydrogen plasma reduction of inkjet-printed flexible graphene oxide (GO) electrodes, an approach compatible with processes envisaged for the manufacture of flexible electronics. The processing of GO to reduced graphene oxide (rGO) was performed in 1-64 s, and sp2 /sp2 +sp3 carbon concentration increased from approximately 20 % to 90 %. Since the plasma reduction was associated with an etching effect, the optimal reduction time occurred between 8 and 16 s. The surface showed good mechanical stability when deposited on polyethylene terephthalate flexible foils and significantly lower sheet resistance after plasma reduction. This method for dry plasma reduction could be important for large-area hydrogenation and reduction of GO flexible surfaces, with present and potential applications in a wide variety of emerging technologies.

MDPV: metric distance permutation vocabulary

Sub-image content-based similarity search forms an important operation in current image archives since it provides users with images that contain a query image as their part. Such a search can conveniently be implemented using the bag-of-features model. Its integral part is a construction of visual vocabulary. Most existing algorithms to create a visual vocabulary suffer from high computational (e.g. k-means) or supervisor-guidance (e.g. visual-bit classifier, or sparse coding) requirements. In this paper, we propose a novel approach to visual vocabulary construction called metric distance permutation vocabulary. It is based on permutations of metric distances to create compact visual words. Its major advantage over prior techniques is time and space efficiency of vocabulary construction and quantization process during querying, while achieving comparable or even better effectiveness (query result quality). Moreover, this basic concept is extended to combine more independent permutations. Both the proposals are experimented on well-known real-world data-sets and compared to other state-of-the-art techniques.