Combining Plasma Treatment Research Articles

ZnO Microcrystals for Light Emitting Diode and Photovoltaic Applications with Integration on Flexible Substrates

AbstractWe report a new integration approach to produce arrays of ZnO microcrystals for optoelectronic and photovoltaic applications. Demonstrated applications are n-ZnO/p-GaN heterojunction LEDs and photovoltaic cells. The integration process uses an oxygen plasma treatment in combination with a photoresist pattern on Magnesium doped GaN substrates to define a narrow sub-100nm width nucleation region. ZnO is synthesized in the defined areas by a hydrothermal technique using zinc acetate and hexamethylenetetramine precursors. Nucleation is followed by lateral epitaxial overgrowth producing single crystal disks of ZnO. The process provides control over the dimension and location of the ZnO crystals. The quality of the patterned ZnO is high; the commonly observed defect related emission in the electroluminescence spectra is suppressed and a single near-band-edge UV peak is observed. Transfer printing of the ZnO microcrystals onto a flexible substrate is also demonstrated in the context of transparent flexible electronics.

Vertically aligned carbon nanotube based electrodes: Fabrication, characterisation and prospects

We present a methodology to fabricate carbon nanotube based electrodes using plasma enhanced chemical vapour deposition. The metal catalyst nanoparticles used to promote nanotube growth are removed using a water plasma treatment in combination with an acid attack. The final integrated microelectrode-based devices present excellent electrocatalytic properties that make them suitable for electrochemical applications. The presented methodology enables the construction of highly regular and dense vertically aligned carbon nanotube (VACNT) forests that can be confined within the patterned bounds of a desired surface. These VACNT electrodes display very low capacitive currents and are amenable to further chemical modifications.

Patterned Growth and Transfer of ZnO Micro and Nanocrystals with Size and Location Control

A method to fabricate and transfer crystalline ZnO with control over location, orientation, size, and shape is reported. The process uses an oxygen plasma treatment in combination with a photoresist pattern on magnesium-doped GaN substrates to define narrow nucleation regions and attachment points with 100 nanometer scale dimensions. Lateral epitaxial overgrowth follows nucleation to produce single-crystalline ZnO shown in the figure.

Integration of ZnO Microcrystals with Tailored Dimensions Forming Light Emitting Diodes and UV Photovoltaic Cells

This article reports a new integration approach to produce arrays of ZnO microcrystals for optoelectronic and photovoltaic applications. Demonstrated applications are n-ZnO/p-GaN heterojunction LEDs and photovoltaic cells. The integration process uses an oxygen plasma treatment in combination with a photoresist pattern on magnesium doped GaN substrates to define a narrow sub-100 nm width nucleation region. Nucleation is followed by lateral epitaxial overgrowth producing single crystal disks of ZnO with desired size over 2 in. wafers. The process provides control over the dimensions (<1% STD) and the location (0.7% STD pitch variation) of the ZnO crystals. The quality of the patterned ZnO is high; the commonly observed defect related emission in the electroluminescence spectra is completely suppressed, and a single near-band-edge UV peak is observed.

Immobilization of soluble eggshell membrane protein on polyethylene film surface: Effect on the culture of NIH3T3 in vitro

AbstractPolyethylene (PE) film surface is modified by combining plasma treatment and soluble eggshell membrane protein (SEP) immobilization. Contact angle measurements, attenuated total reflectance infrared spectroscopy, and X‐ray photoelectron spectroscopy confirm that SEP adheres tightly to the PE film surface. Mouse 3T3 fibroblasts are used as model cells to evaluate the biocompatibility of PE film surfaces before and after modification. Plasma pretreatment can incorporate polar groups onto the surface, benefitting tight immobilization of SEP. The hydrophilicity of the PE film surface modified by combining plasma treatment and SEP immobilization is increased as evidenced by contact angle measurements, and the biocompatibility of the surface is greatly improved as shown by cell culture. The surface of the modified material can endure rinsing with 10% acetic acid (a good solvent of SEP), which would be an advantage for further application as a biomaterial. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1340–1345, 2006

Hydrophilic surface-grafted poly(tetrafluoroethylene) membranes using in pervaporation dehydration processes

Preparation of hydrophilic poly(tetrafluoroethylene) (PTFE) membranes was performed by means of combined hydrogen plasma and ozone treatment and surface-initiating grafting polymerization. Acrylamide (AAm) and sodium 4-styrenesulfonate (NaSS) were used as monomers in grafting polymerization. Grafted PTFE membrane exhibited high hydrophilicity with a water contact angle of 38° and showed superior performance of pervaporation dehydration for various aqueous solutions of organic compounds. A high permeation flux of 422 g/m 2 h and a high separation factor of 4491 were observed with PTFE-g-PSSA membrane in pervaporation dehydration of a 90 wt.% aqueous solution of isopropanol (IPA) at 65 °C. The PTFE-g-PSSA membrane also exhibits advantages of wide application scopes, low temperature-sensitivity, good membrane stability, and operation durability in pervaporation dehydration processes.

Plasma Treatment and Surface Analysis of Polyimide Films for Electroless Copper Buildup Process

We report here a detailed characterization of the surface chemical states and morphology of polyimide (PI) films following modifications by plasma treatment and electroless copper deposition. and Ar plasma treatments have been successfully used to achieve morphological and chemical modification of the PI surface so that electroless copper plating can occur. The adhesion strength of the electroless copper to the PI surface was measured and correlated with the plasma-induced chemical and physical modifications of the PI surface. The plasma causes primarily chemical changes to the PI surface through creation of nitrogen moieties (i.e., ) on the surface. The Ar plasma treatment brings about mainly physical changes to the surface (i.e., surface roughening). The combined-plasma treatment (Ar plasma followed by plasma) combines the desirable chemical and physical effects of each treatment, yielding a PI surface with higher roughness for physical anchoring of the copper and surface bonding sites (nitrogen and oxygen sites). During the electroless copper surface activation step with tin chloride and palladium chloride, tin bonds mainly with the oxygen on the surface, whereas palladium reacts with tin chloride as well as with the surface nitrogen. A direct relationship has been observed between surface palladium concentration and the abundance of the sites on the surface. This suggests that the nitrogen radicals created during the plasma are incorporated into the surface and serve as bonding sites for the palladium. In the subsequent electroless Cu deposition, there was a direct correlation between the palladium surface concentration and Cu coverage. The adhesion strength of the electroless copper to the PI correlated well to the surface modifications and plasma treatment conditions. For the first time, a specific bonding configuration on the PI surface is shown to promote adsorption of palladium, which in turn promotes covalent bonding with Cu. The relative importance of surface roughness and chemical bonding on the adhesion strength is discussed.

Transport and adhesion properties of an unlined and a liquid‐crystalline polymer–lined vinyl ester thermoset exposed to severe environments

AbstractThe application of liquid‐crystalline polymers (LCP) as lining materials for fiber‐reinforced plastics was investigated. The lining consisted of one uniaxially and one biaxially oriented LCP and, for comparison, a fluorinated ethylene propylene copolymer. The lining was attached to a glass‐fiber–reinforced vinyl ester thermoset. The laminates were examined with respect to their chemical resistance, transport/barrier properties, and lining/matrix adhesion behavior. The transport properties were determined by gravimetric desorption measurements and cup tests. It was shown that the LCP was suitable as a lining in organic solvent and nonoxidizing acid environments. Diffusivities, equilibrium concentrations, and transmission rates of water, methanol, toluene, and trichloroethylene were obtained in the LCP, the fluorinated ethylene propylene copolymer, and also, in the case of the vinyl ester, of hydrochloric acid. In general, the diffusivity and transmission rate in the LCP were one to several orders of magnitude lower than those of the fluorinated ethylene propylene copolymer and the vinyl ester. The reinforcement in the glass‐fiber–reinforced plastic led to an increase in the water and methanol diffusivities and transmission rates, which was probably attributable to liquid capillary diffusion. The lap‐shear bonding strength between the LCP and the vinyl ester was poor, but it was improved almost sixfold by a combined abrasive and oxygen plasma treatment. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 797–806, 2005

Enhanced cell affinity of poly ( d, l-lactide) by combining plasma treatment with collagen anchorage

Surface properties of poly ( d, l-lactide) (PDLLA) were modified by combining plasma treatment and collagen modification. The changes of surface properties were characterized by contact angles, surface energy, X-ray photoelectron spectra and scanning electron microscopy. The mouse 3T3 fibroblasts were used as model cells to evaluate the cell affinity of PDLLA before and after modification. Effects of different modification methods including plasma treatment, collagen coating and combining plasma treatment with collagen anchorage were investigated and compared. The results showed that the hydrophilicity and surface-free energy were improved and reduced, respectively, after each modification. Plasma pre-treatment could improve the roughness as it incorporated the polar groups and positively charged groups onto the sample surface; so the plasma pre-treated surface would benefit in anchoring more collagen tightly. As a result, cell affinity of PDLLA modified by combining plasma treatment with collagen anchorage was greatly improved. The modified materials could endure rinsing by PBS, which would facilitate further application when the modified materials were used as cells scaffold in tissue engineering.

Application of a novel vacuum-arc ion-plating technology for the design of advanced wear resistant coatings

For the design of a new generation of wear resistant coatings a PVD-technology was used, which combines plasma surface treatment and ion-plating methods in a single process. On the basis of an PVD-apparatus with modern modules of plasma-technical equipment it has taken advantage of special plasma-physical effects to improve the microstructure of the thin-film coating systems. Wear resistant complexes were designed according to the principle of the multifunctional structure as multilayered composite coating systems. Dry cutting tests were carried out with various HSS and carbide tools coated by the above plasma-technology. The higher efficiency and reliability of these surface refined cutting tools compared with conventionally coated tools were attributed to the improved microscopic structure of the new wear resistant complexes. First results of the application of this novel technology for combined plasma treatment and coating of a broad field of various tools and machine units will be discussed.

Effect of a combined gamma irradiation and parylene plasma treatment on the hydrolytic degradation of synthetic biodegradable sutures

The aim of this study was to alter the hydrolytic degradation property of synthetic absorbable suture fibers so that their mass loss would occur at a shorter time without significantly compromising their tensile strength loss profile. A two-step treatment concept (gamma-irradiation followed by Parylene plasma deposition) was introduced for achieving this aim. Vicryl and Maxon were used as the model compounds to test this new concept. After the treatment, the in vitro hydrolytic degradation properties of Vicryl and Maxon were evaluated by weight loss, tensile breaking strength, heat of fusion and melting temperature, intrinsic viscosity, surface wettability, and surface morphology. The results suggested that gamma-irradiation at a dosage level between 0.2-2.0 Mrad for Vicryl sutures and about 2.0 Mrad for Maxon sutures were the most effective dosages to accelerate the suture mass loss. The subsequent Parylene plasma deposition treatment statistically significantly improved the retention of tensile strength for both gamma-irradiated Vicryl and Maxon sutures and hence counteracted the undesirable gamma-irradiation induced acceleration of tensile strength loss. However, this second-step Parylene plasma treatment extended the suture mass loss to longer periods. These findings were consistent with the observed surface wettability, surface morphology, intrinsic viscosity, and thermal properties. A thin hydrophobic Parylene skin layer wrapped around a suture was responsible for the slower rate in mass and strength loss. This outer skin layer acted as a barrier to not only water but also degradation fragments.

Surface modification of Kevlar® fiber by a combination of plasma treatment and coupling agent treatment for silicone rubber composite

To improve the adhesion between poly(p-phenylene terephthalamide), PPTA, fiber and silicone rubber, the surface modification of PPTA was investigated. Combining plasma treatment and coupling agent treatment with the silicone adhesive was found to be effective in improving adhesion. The combination process made the pull-out force of the PPTA yarn/silicone rubber composite 2.5 times higher, compared with the plasma treatment or the coupling agent treatment alone. The plasma treatment led to the elimination of carbonized layer from the PPTA yarn surface and the formation of oxygen functionalities including C-O and C=O groups. The elimination of the carbonaceous deposits from the PPTA surface and the interaction between the silicone adhesive and the oxygen functionalities created by the plasma treatment contribute to the improvement of adhesion with silicone rubber.

TOWARDS DESIGNER SURFACES

There are thought to be great technical and economic benefits potentially available through the application of multiple surface engineering technologies in new market sectors. This is illustrated through the combined plasma and PVD treatment of low alloy steel substrates. Unique opportunities exist, through the advent of high energy beam technologies, to liquid phase thermochemically alloy aluminium and titanium materials which can then be combined with plasma or PVD techniques to enhance the performance of engineering components by many orders of magnitude. The most recent work in this field suggests that roller element bearings in titanium alloys will soon be within the bounds of design capability and advances towards the design and manufacture of titanium gears could well be possible in the longer term.