Surface Technology with Cold Microplasmas Klages, Claus-Peter; Hinze, Alena; Lachmann, Kristina ...
Plasma processes and polymers,
April 23, 2007, Letnik:
4, Številka:
3
Journal Article, Conference Proceeding
Recenzirano
Various new plasma‐based surface technological processes are made feasible by localizing atmospheric‐pressure discharges to predefined volumes with sub‐millimeter linear dimensions. So‐called Plasma ...Printing processes use cold discharges in microcavities formed temporarily by contacting a substrate with a suitably designed kind of plasma stamp. Aside from dielectric barrier discharges driven by mid‐frequency (MF) AC voltages, cold microplasmas can also be sustained in arrangements without a dielectric barrier, if RF excitation is used. The modification or coating of internal surfaces in already sealed microfluidic systems promises the achievement of a wide range of physico‐chemical surface properties which are difficult to attain by wet‐chemical or low‐pressure plasma processes. Using a proper electrode arrangement, the coating or modification can be localized to a selected segment of a microfluidic system.
The present paper reports on a new approach for the DBD‐based plasma‐enhanced chemical vapor deposition of MAA coatings at atmospheric pressure, using a plasma‐copolymerization with VTMS in order to ...render the deposits water‐stable. The aim of this work is the optimization of the conditions for generating a highly stable surface with a maximum number of functional carboxylic groups. Therefore, the concentrations of the monomers in the process gas have been varied as well as the plasma conditions. The MAA/VTMS plasma‐copolymer layers were characterized by ATR FT‐IR spectroscopy directly after the preparation as well as after exposure to aqueous solutions and the influence of annealing the layers has been investigated. The amount of carbon present within carboxylic groups was quantified by XPS measurements. As one of the applications of the new type of coatings, its reversible binding properties for gDNA out of blood lysates have been evaluated using a PCR reaction.
Paper-based microfluidic systems are of great interest for cheap, disposable point-of-care diagnostic devices, especially for the use in the developing countries. The development of reliable and ...cost-effective fabrication methods is therefore of great importance. We present two novel methods and experimental setups for the area-selective creation of hydrophilic channels and hydrophobic barriers utilizing atmospheric-pressure microplasmas based on dielectric barrier discharges within the pores of the paper substrate. One approach is based on a local plasma etching process which is able to remove a hydrophobic coating from the paper fibers, while a second, alternative method uses patterned plasma polymerization to deposit a hydrophobic coating on the fiber structure. Both methods utilize microstructured electrodes to shape the plasma discharge volume to allow the fabrication of microfluidic structures in the substrate. We report on the influence of various processing parameters on the fabrication process and compare the minimal structure dimensions obtained so far and maximum wicking distances achieved. Both fabrication methods led to promising results with structure dimensions of around 400 µm, but the plasma etching process turned out to be superior due to lower cost, faster processing, and better structure edge definition.
A porous plasma stamp has been developed allowing selective plasma treatment and coating of flat surfaces by using a dielectric barrier discharge arrangement at atmospheric pressure. The stamp ...consists of a porous sinter metal plate covered with photoresist. The photoresist is structured to form cavities in which the plasma is burning. The cavity footprint is the desired structure to be reproduced or “plasma printed” on the substrate. It is shown that flat substrate surfaces can be treated in the same scale as the cavity dimensions and that the treated areas are defined by the footprint of the cavities with a precision in micrometer scale. This work describes in detail the manufacturing process of the plasma stamp and furthermore shows that the stamp can be used to plasma‐coat surfaces selectively because the stamp cavities can continuously be filled with process gases through the porous metal plate. Applying process gas containing polymerizable monomers to a porous material will close the pores after a certain plasma treatment time. As a consequence this work also addresses the issue of cleaning the stamp to keep it intact for a long term usage.
A porous plasma stamp has been developed to area‐selectively coat flat surfaces at atmospheric pressure using dielectric barrier discharges. The stamp can continuously be filled with coating gases through porous sinter metal. The areas to be coated can have every shape and their dimensions can be scaled down to 100 μm with an accuracy of 10 μm.
A novel plasma stamp has been developed allowing selective plasma treatment and coating of flat surfaces using dielectric barrier discharges at atmospheric pressure. The stamp consists of a flat ...carrier material covered with photoresist. The resist is structured to form cavities in which the plasma is burning. The cavity footprint is the desired structure to be reproduced or “plasma printed” on the substrate. Cavities can have any geometry and widths down to 10 µm. It is shown that the substrate surfaces can be activated in the same scale as the cavity dimensions and that the treated areas reproduce the footprint of the cavities. To be able to coat surfaces selectively, the stamp consists of multiple resist layers forming a channel network. Using this network, the cavities can be filled with process gas containing polymerizable monomers. This plasma stamp technology introduces a new MEMS process with high potential for production processes and bioscience applications.
Microplasma stamps based upon the principle of dielectric barrier discharges are applied to a new type of area‐selective surface modification process at atmospheric pressure. This process integrates ...the surface treatment and lateral microstructuring within one process step. For this purpose, the plasma is ignited in cavities which are formed temporarily by compressing the microplasma stamp and the substrate to be treated. In this work, we investigate the influence of the cavity design and the ignition conditions on the surface treatment. Furthermore, peptide synthesis on area‐selectively treated poly(propylene) surfaces is presented as an application.
In technical applications strain gauges are widely used. Apart from conventional polymer foil based strain gauges that are glued to the work piece surface, sputtered strain gauges are already ...commercially used in special applications. Those sputter strain gauges are typically made of NiCr alloy and the sensor layer is as sensitive to strain as the ones used in the glued strain gauges with a gauge factor of 2, but neglecting problems of creeping and swelling of the involved polymer materials. Diamond-like carbon (DLC) films offer significantly higher strain sensitivity, but usually they are also very sensitive to temperature effects. Using metal doped diamond-like carbon (Me-DLC), higher strain sensitivity than conventional metal based systems, in combination with thermal compensation, is possible. The influence of different process parameters on the gauge factor and temperature coefficient of resistance (TCR) of DLC and Me-DLC films produced in industrial sputtering systems was investigated. Gauge factors up to 13 in combination with a high negative TCR in the range of a few thousand ppm/K were reached with sputtered DLC films. The substrate bias voltage in particular showed a strong influence on the resulting gauge factor of the films. For Me-DLC films different deposition methods (dc and rf sputtering) and various doping metals (Ag, Ni, Ti, and W) were investigated. Using dc sputtering of the Me-DLC films only Ni-DLC showed gauge factors slightly higher than 2. Furthermore, only for Ni-DLC zero crossing of the TCR was observed by variation of the metal content. Using rf excitation especially Ni-DLC films showed gauge factors exceeding values of 15 in combination with a TCR close to zero.
► Influence of deposition parameters on gauge factor and TCR for sputtered DLC films. ► Comparison of gauge factor and TCR for different Me-DLC films. ► Significant differences in gauge factors for dc and rf sputtered Ni-DLC films. ► TCR is independent of whether dc or rf sputtering was used for Ni-DLC. ► Discussion with several referenced models about reason for behavior of Ni-DLC.
Amino group containing films of maximum 30 nm thickness were deposited on gold‐coated wafers using atmospheric pressure dielectric barrier discharges (DBD) and process gases consisting of ...aminopropyl‐trimethoxysilane (APTMS) as precursor in combination with various carrier gases including nitrogen, helium, argon, or a mixture of ammonia and nitrogen. With CD‐XPS a concentration NH2/C of up to almost 6% was found. Storage of the films in air for four weeks generally led to a considerable reduction of the primary amino group concentration; however, in the case of the films produced using ammonia in nitrogen as carrier gas the concentration remained stable at just under 4%. Oxidation products according to XPS and IR data include amides and nitriles though imines may also be present.
Chemical derivatization analysis of polyethylene surfaces plasma-treated in the afterglow regions of dielectric barrier discharges in mixtures of nitrogen and hydrogen was studied, using nucleophilic ...instead of electrophilic reagents which have commonly been used in studies of polymer surfaces exposed to discharges in nitrogen or nitrogen-containing gases. Vapors of strongly nucleophilic 2-mercaptoethanol and 4-(trifluoromethyl)-phenylhydrazine (TFMPH), respectively, were used for derivatization. XPS spectroscopy was subsequently applied in order to quantify the amount of sulfur and fluorine, respectively, introduced to the surface due to the presence of electrophilic moieties generated by the plasma treatment. Using FTIR-ATR spectroscopy following TFMPH derivatization, a quantitative determination of the hydrazone groups formed was possible, based on a comparison with spectra of a low-molecular weight model hydrazone. The results of these investigations confirm conclusions from earlier studies showing that the formation of electrophilic groups such as imines on polymers treated in afterglows of nitrogen–hydrogen DBDs must not be disregarded.
In this paper, we demonstrate the development of plasmonically active PMMA optical fiber probes by the attachment of gold nanoparticles to the probe surface functionalized by means of flowing ...post-discharges from dielectric barrier discharge (DBD) plasmas for the first time. Polymer optical fiber (POF) probes (U shape to improve absorbance sensitivity) were subjected to reactive gas atmospheres in the post-discharge region of a coaxial DBD plasma reactor run at atmospheric pressure in different gases (Ar, Ar + 10 % O
2
, O
2
, N
2
, N
2
+ 0.5 % H
2
). Plasma treatments in Ar or N
2
gave rise to water-stable electrophilic functional groups on PMMA surface, whereas the amine groups generated by N
2
-containing plasmas were not stable. Subsequently, PMMA surfaces were treated with hexamethylene diamine (HMDA) to obtain stable amine groups through the reaction of electrophilic groups. Gold nanoflowers (AuNF, 37 nm, peak 570 nm) binding to the amine functionalized fiber probes was monitored in real-time by recording the optical absorbance changes at 570 nm with the help of a UV–vis spectrometer. Absorbance response from Ar or N
2
plasma treated probes are 100 and 60 times, respectively, that of untreated control probes. A 25 fold improvement in absorbance response was obtained for Ar plasma treated POF in comparison with only HMDA treated POF. The shelf life of the hence fabricated plasmonically active probes was found to be at least 3 months. In addition, plasmonic activity of U-bent fiber probes treated in Ar plasma is better than the conventional wet-chemical activation by environmentally hazardous acid pre-treatment approaches.
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