Ammonia Plasma Treatment Research Articles

Effects of Ammonia Plasma Treatment on the Electrical Properties of Plasma-Enhanced Chemical Vapor Deposition Amorphous Hydrogenated Silicon Carbide Films

Amorphous hydrogenated silicon carbide (a-SiC:H) films were deposited from a mixture of silane and methane gases using the plasma-enhanced chemical vapor deposition (PECVD) process. The properties of the film, following ammonia plasma treatment, are reported. A lower silane flow rate reduces the refractive index, but increases the carbon content and the optical band gap. Increasing the carbon concentration of the a-SiC:H films reduces the dielectric constant. The films were treated with ammonia plasma for various treatment periods. The original film has a smooth surface with a roughness of 0.231 nm, but increasing the ammonia plasma treatment period gradually roughens the surface. The chemical bonding nature of the a-SiC:H films with higher silicon content was investigated by X-ray photoelectron spectroscopy. Various nitrogen ionization species reacted with Si to promote the formation of silicon nitride. As a result, although the dielectric constant of the a-SiC:H films increased slightly, the leakage current density declined as the ammonia plasma treatment time increased.

Fabrication and surface modification of macroporous poly(L-lactic acid) and poly(L-lactic-co-glycolic acid) (70/30) cell scaffolds for human skin fibroblast cell culture.

The fabrication and surface modification of a porous cell scaffold are very important in tissue engineering. Of most concern are high-density cell seeding, nutrient and oxygen supply, and cell affinity. In the present study, poly(L-lactic acid) and poly(L-lactic-co-glycolic acid) (70/30) cell scaffolds with different pore structures were fabricated. An improved method based on Archimedes' Principle for measuring the porosity of scaffolds, using a density bottle, was developed. Anhydrous ammonia plasma treatment was used to modify surface properties to improve the cell affinity of the scaffolds. The results show that hydrophilicity and surface energy were improved. The polar N-containing groups and positive charged groups also were incorporated into the sample surface. A low-temperature treatment was used to maintain the plasma-modified surface properties effectively. It would do help to the further application of plasma treatment technique. Cell culture results showed that pores smaller than 160 microm are suitable for human skin fibroblast cell growth. Cell seeding efficiency was maintained at above 99%, which is better than the efficiency achieved with the common method of prewetting by ethanol. The plasma-treatment method also helped to resolve the problem of cell loss during cell seeding, and the negative effects of the ethanol trace on cell culture were avoided. The results suggest that anhydrous ammonia plasma treatment enhances the cell affinity of porous scaffolds. Mass transport issues also have been considered.

Improving cell affinity of ­poly(D,L‐lactide) film modified by anhydrous ammonia plasma treatment

AbstractAnhydrous ammonia gaseous plasma treatment was used for improving cell affinity of the poly(D,L‐lactide) film surface. The contact angle was measured and the surface energy was calculated through harmonic mean equations. The surface chemical composition of the sample was identified by X‐ray photoelectron spectroscopy (XPS) analysis. It was demonstrated that the O‐containing and N‐containing groups such as hydroxyl and amine were incorporated onto the surface of films. The effect of preserving methods for maintaining the hydrophilicity was also investigated. The result indicated that preserving at low temperature (0–4 °C) was sufficient to maintain the improvements. It could resolve the problem of hydrophilicity being partially lost with preserving time after plasma treatment. Mouse 3T3 fibroblast cells were used as model cells to compare the cell affinity of the modified films and control. The ammonia plasma treatment could promote the cells attachment and cells growth. After 4 days culture, the plasma treated films yielded almost two magnitude cells compared with the control. Copyright © 2002 John Wiley & Sons, Ltd.

Adhesion properties of aluminium-metallized/ammonia plasma-treated polypropylene: Spectroscopic analysis (XPS, EXES) of the aluminium/polypropylene interface

The purpose of this work was to investigate the influence of a low-pressure, low-frequency ammonia plasma treatment on the wettability of polypropylene (PP) thin films and its consequences on the adhesion properties of such treated films to thermally evaporated aluminium coatings. The wettability was determined by contact angle measurements while the adherence was evaluated by a U-Peel test especially suited to thin flexible substrates with thin metallic layers. Furthermore, an image processing system was used to measure the percentage of the peeled-off metal. Measurements carried out on NH3 plasma-treated PP films revealed a sharp increase in the wettability and in the adhesion properties for treatment times as short as 1s. Electron-induced X-ray emission spectroscopy and X-ray photoelectron spectroscopy showed the formation of new chemical bonds at Al/NH3 plasma-treated PP film interfaces. The new types of bonds have been characterized by well-defined chemical states (C–NHx, CO–NH, Al–N–C) in the N 1s (and C 1s) spectra. The interfacial complexes Al–N–C and Al–N–CO are formed by the NH3 plasma treatment which creates at the PP surface active sites (N(C–NHx) and N(CO–NH)) which react with the evaporated aluminium atoms. These interfacial bonds play an important role in the enhancement of the metal/polymer adhesion.

Low pressure plasma treatment of poly(3-hydroxybutyrate): toward tailored polymer surfaces for tissue engineering scaffolds.

Thin films of poly(3-hydroxybutyrate) were modified by microwave ammonia plasma treatment. The results of the modification were studied by means of contact angle goniometry, ellipsometry, Fourier transform infrared-attenuated total reflection spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. To prove the presence of amino groups on the poly(3-hydroxybutyrate) surface, chemical labeling with 4-trifluoromethyl benzaldehyde was performed before X-ray photoelectron spectroscopy analysis. Under the applied plasma conditions, a hydrophilic surface with a good long-term stability was obtained.

The effect of ammonia plasma treatment on low- k methyl-hybrido-silsesquioxane against photoresist stripping damage

The integration process, low- k hybrid-organic-siloxane-polymers (HOSP) and photoresist stripping process have been investigated. The dielectric properties of HOSP films are degradated after photoresist removal. This is because photoresist stripping processes destroy the functional groups and induce moisture uptake in HOSP films. In this study, NH 3-plasma treatment was used for HOSP films to form a thin nitrogen-containing layer, preventing HOSP films from O 2 plasma ashing and chemical wet stripper damage during photoresist removal. The leakage current is decreased significantly and the dielectric constant is maintained at a low value after photoresist removal. These experimental results show that NH 3 treatment is a promising technique to enhance the resistance of HOSP films to the photoresist stripping process.

Plasma-Induced Surface Functionalization of Polymeric Biomaterials in Ammonia Plasma

Plasma-chemical modification is frequently used to improve the adaption of polymer surfaces to biological environments. In this regard amino functional groups play a key role. They provide an excellent basis for subsequent modifications with specific biomolecules. It would be of great value to get an amino functionalization independent of the specific material in use. The paper reports on an investigation concerning the feasibility of such an universal plasma functionalization procedure. Two different downstream microwave plasma sources were taken to apply a procedure, which was developed for high-grade modification of polystyrene (PS), to a number of other polymers including polyetheretherketone (PEEK), polyethyleneterephthalate (PET), polyethylenenaphthalate (PEN), polycarbonate (PC), polyethylene (PE), polymethylmethacrylate (PMMA) and fluorinated polymers. In many cases, very similar results were obtained. At maximum 5% of the surface were covered by nitrogen functional groups. In some cases, about 50% of total nitrogen functional groups were amino groups. The results suggest that a downstream ammonia plasma treatment indeed is a fairly universal method for high performance amino functionalization of polymeric biomaterials.

Plasma-Induced Surface Functionalization of Polymeric Biomaterials in Ammonia Plasma

Plasma-chemical modification is frequently used to improve the adaption of polymer surfaces to biological environments. In this regard amino functional groups play a key role. They provide an excellent basis for subsequent modifications with specific biomolecules. It would be of great value to get an amino functionalization independent of the specific material in use. The paper reports on an investigation concerning the feasibility of such an universal plasma functionalization procedure. Two different downstream microwave plasma sources were taken to apply a procedure, which was developed for high-grade modification of polystyrene (PS), to a number of other polymers including polyetheretherketone (PEEK), polyethyleneterephthalate (PET), polyethylenenaphthalate (PEN), polycarbonate (PC), polyethylene (PE), polymethylmethacrylate (PMMA) and fluorinated polymers. In many cases, very similar results were obtained. At maximum 5% of the surface were covered by nitrogen functional groups. In some cases, about 50% of total nitrogen functional groups were amino groups. The results suggest that a downstream ammonia plasma treatment indeed is a fairly universal method for high performance amino functionalization of polymeric biomaterials.

An oxygen free 6061 aluminum alloy surface produced by ammonia dc plasma and sputtering processes

An oxygen free polycrystalline 6061 aluminum alloy surface was obtained for the first time in an UHV environment ( 1×10 −9 to 3×10 −9 Torr) after dc ammonia plasma treatment in a separate vacuum system. The specimen was first sputtered and processed in the plasma chamber for about 1 h, transferred after air exposure into the UHV chamber, then cleaned by 2.8 keV Ar + ion bombardment for about 10 min to remove the air-grown oxide. An oxygen free 6061 aluminum surface was observed using Auger electron spectroscopy. Regrowth of the oxide layer in the UHV environment was monitored versus time. A possible cleaning mechanism by the ammonia plasma is proposed. This oxygen free surface is key to achieving thin film growth/deposition on aluminum or its alloys.

Antithrombotic and fibrinolytic system of human endothelial cells seeded on PTFE: the effects of surface modification of PTFE by ammonia plasma treatment and ECM protein coatings

The aim of this study was to determine the effects of ECM protein coatings and surface modification of PTFE on the ability of seeded human endothelial cells (EC) to secrete prostacyclin (PGI 2), plasminogen inhibitor-1 (PAI-1) and tissue plasminogen activator (t-PA). PTFE surfaces were modified by a novel surface modification technique based on ammonia plasma. Fibronectin, collagen type-1 and gelatin-coated ammonia plasma modified PTFE and unmodified PTFE surfaces were employed and compared in this study. All ammonia plasma modified surfaces showed similar secretions of PGI 2 compared to non-modified PTFE surfaces. With the exception of gelatin-coated modified PTFE, seeded EC seeded on all modified PTFE showed lower levels of PAI-1 secretion compared to those seeded on unmodified PTFE. The specific activity of t-PA secreted by EC seeded on ammonia plasma modified and fibronectin coated modified PTFE showed increases of 100 and 30%, respectively, when compared to their unmodified counterparts. Our studies show that EC seeded on modified PTFE have ability to secrete PGI 2 that modulates the early phase of thrombus formation. Furthermore, superior t-PA profile, along with lower levels of PAI-1 suggest that ammonia plasma modification and use of appropriate ECM proteins can modulate antithrombotic and fibrinolytic properties of in vitro endothelialized vascular prostheses. Accordingly, these surfaces may be suitable to further develop protocols and other strategies for arterial and venous reconstruction.

Light Emission Analysis of Dielectric Breakdown in Stressed Damascene Copper Interconnection

Visible light emission observed in biased comb-type capacitors with a copper (Cu) damascene structure appears to be caused by electroluminescence. Photon emission probably occurs via energy states related to dangling bonds formed at a chemical-mechanical polished (CMP) surface. These energy states also appear to degrade the time-dependent dielectric breakdown (TDDB) characteristics and to increase line-to-line leakage currents. Ammonia (NH3) plasma treatment of a Cu-CMP surface dramatically improved TDDB and decreased the leakage currents. We attribute this to a reduced energy-state density through the termination of dangling bonds by hydrogen generated from the NH3 plasma.

Polyelectrolyte adsorption on NH3-Plasma-Treated poly(tetrafluoroethylene-co-hexafluoropropylene)

A two-step procedure for a permanently hydrophilic surface modification of poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP, fluorinated ethylene propylene) was studied. In the first step a cationic polymer surface was created by low-pressure ammonia plasma treatment introducing nitrogen-containing functional groups. Afterwards, the anionic poly(sodium 4-styrenesulfonate) was adsorbed onto the plasma-treated FEP surface. The adsorption was assumed to be controlled by ionic interactions. The modification effects and their long-term behavior were evaluated by means of water contact angle goniometry. Furthermore, electrokinetic measurements and X-ray photoelectron spectroscopy were used for surface characterization.

Preparation of cellulose triacetate pervaporation membrane by ammonia plasma treatment

Homogeneous cellulose triacetate membranes were prepared by the solution-casting method. The surface of this membrane was modified with gaseous plasma of a 10-W discharge power in the presence of ammonia gas at 0.15 Torr pressure. The percentage of weight loss of the CTA membranes was found to be 0.7 for 20 min of treatment time in the ammonia plasma. The contact angle measurement indicated that hydrophilicity of the surface increases. ATR-FTIR spectral analysis showed that the hydrophilicity is mainly derived from the amino groups on the modified surface. SEM studies indicate that no considerable change of surface morphology occurred up to 5 min of treatment time, but a considerable change of surface morphology resulted for treatment of 10 and 20 min. The modified membranes were used for pervaporation studies for separation of an isopropanol–aqueous mixture. These membranes showed excellent selectivity for water. The water flux increases with an increase in treatment time for all concentrations of isopropanol in the feed. The isopropanol flux decreases for initial treatment time (2 and 5 min), but showed an increasing trend for a higher treatment time (10 and 20 min). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 258–265, 2000

PdCl2 anchorage onto the surface of polystyrene films via oxygen and ammonia plasma treatment

The surface properties of polystyrene as a possible catalytic support for active coordinative species were investigated. To improve the surface properties, discharge treatments in the presence of oxygen and ammonia were carried out. The polymer surface was studied before and after the plasma treatments. Contact angles for the polymer surface were measured in order to determine the surface free energy. Polymer-bound complex catalysts were prepared by anchoring PdCl 2 on the surface of the polystyrene samples. The chemical compositions were studied by X-ray Photoelectron Spectroscopy (XPS). Plasma treatments in the presence of oxygen or ammonia caused an increase in the surface free energy of polystyrene, as a consequence of the higher concentration of oxygenated or nitrogenated functional groups, respectively, on the polymer surface. Contact angle measurements are in agreement with the corresponding values obtained by XPS. After treatment with PdCl 2 , the amount of palladium anchored to the polymer surface treated with ammonia is greater than in the case of the oxygen plasma treatments; this may be explained on the basis of the higher nucleophilic character of the amine groups. No palladium was detected in the untreated polystyrene surface.

PdCl2 anchorage onto the surface of polystyrene films via oxygen and ammonia plasma treatment

The surface properties of polystyrene as a possible catalytic support for active coordinative species were investigated. To improve the surface properties, discharge treatments in the presence of oxygen and ammonia were carried out. The polymer surface was studied before and after the plasma treatments. Contact angles for the polymer surface were measured in order to determine the surface free energy. Polymer-bound complex catalysts were prepared by anchoring PdCl2 on the surface of the polystyrene samples. The chemical compositions were studied by X-ray Photoelectron Spectroscopy (XPS). Plasma treatments in the presence of oxygen or ammonia caused an increase in the surface free energy of polystyrene, as a consequence of the higher concentration of oxygenated or nitrogenated functional groups, respectively, on the polymer surface. Contact angle measurements are in agreement with the corresponding values obtained by XPS. After treatment with PdCl2, the amount of palladium anchored to the polymer surface treated with ammonia is greater than in the case of the oxygen plasma treatments; this may be explained on the basis of the higher nucleophilic character of the amine groups. No palladium was detected in the untreated polystyrene surface. © 2000 Society of Chemical Industry

Ammonia RF-Plasma on PTFE Surfaces: Quantification of the Species Created on the Surface by Vapor - Phase Chemical Derivatization

AbstractA cylindrically-configured plasma treatment system in Radio Frequency Glow Discharges fed with ammonia was used with the aim of modifying the internal surface of ePTFE arterial prostheses to improve their biocompatibility. In order to understand the effects of this treatment on the PTFE polymer surface, we have first realized RF-plasma treatment experiments on PTFE films. Preliminary XPS analyses have shown that about 15% of the surface atoms were substituted by nitrogen (N/C ratio of 0.3) whereas the F/C ratio decreased from 2 to 0.6, therefore leading to the conclusion that several chemical species are created onto the surface upon an ammonia plasma treatment. As X-Ray Photoelectron Spectroscopy (XPS) analysis does not allow the direct determination of the nature of the N-species grafted on the surface (chemical shifts are not different enough), vapor phase chemical derivatization was carried out on PTFE films to quantify the concentration of these new surface moities grafted on the polymer surface.

Adhesion Quantification of Post-CMP Copper to Amorphous SiN Passivation by NanoIndentation

ABSTRACTIn this study, film interfacial fracture is induced by nanoindentation to quantify the practical work of adhesion of a post-CMP copper film to an amorphous silicon nitride passivation film. Poor adhesion of electrodeposited copper to SiN passivation is observed following CMP due to copper oxide growth prior to plasma enhanced silicon nitride deposition. Four point bend testing has shown that failure by brittle fracture of test structures occurs at the Cu/CuO interface. Hydrogen, ammonia, and nitrogen plasma treatments of the post-CMP copper surface can be used to remove the oxide, shown by auger electron spectroscopy, and to increase the surface roughness of copper, shown by atomic force microscopy. Both effects can be used to improve the Cu/SiN adhesion. Nanoindentation with a conical indenter (1.59 μm tip radius) was used to induce SiN film delaminations from Cu, the sizes of which were measured and correlated with the practical work of adhesion.[1,2] In order to more reliably and repeatably produce these delaminations a TiW (10wt% Ti) superlayer was sputter deposited on to the test structures.[2,3] Mechanical properties, including elastic modulus and hardness of SiN, electrodeposited copper, and TiW measured by nanoindentation are also reported here.

Electrokinetic surface characterization of biomedical polymers — a survey

The application of streaming potential measurements in support of the development of blood compatible polymers is reviewed. Current knowledge about the relevance of interfacial charge of materials with respect to thrombogenicity of and coagulation activation by medical devices is discussed. Potentialities of streaming potential measurements for the characterization of biomedical polymers comprise the distinction between interfacial charge formation processes, the derivation of acid–base characteristics of surface functions, and the estimation of the relative contribution of known molecular surface sites to the interfacial charge density. Frequently, polymer surfaces consist of different types of surface sites. Beyond sites with Bronsted-acidic or -basic character the preferential adsorption of electrolyte ions onto indifferent surface sites may substantially contribute to the interfacial charge. Examples are given for the detection of acidic and basic properties of hemodialysis membranes of different shape made of poly(sulfone)/poly(vinylpyrrolidone) and cellulose derivates. For partially amine-modified cellulose flat membranes the percentage of basic surface sites is derived from the shift of the isoelectric point. Further, the use of streaming potential measurements is demonstrated in the optimization of surface modifications of cardiovascular implant materials by low pressure plasma treatments. The introduction of basic groups into the poly(tetrafluoroethylene) implant surfaces by ammonia plasma treatments manifests itself in the shift of the isoelectric point. A correlation between hydrophobicity and charge formation of the polymer–solution interface by preferential ion adsorption is confirmed for polymers without dissociating functions. This is based on the comparison of water contact angles for a series of poly(styrene) derivates of different hydrophobicity and the maximum zeta potential of these polymer films in potassium hydroxide solutions. Advanced applications of streaming potential measurements for the characterization of biomedical polymers are comprise the in situ characterization of protein adsorption processes onto polymer solids. This approach is demonstrated for the adsorption of the blood plasma proteins albumin and fibrinogen onto a fluorocarbon polymer substrate. The potentialities of a recently developed microslit electrokinetic setup are illustrated which permits to study simultaneously zeta potential and surface conductivity of flat polymer–liquid interfaces. Data gained by the microslit electrokinetic setup reveal the dramatic increase of the surface conductivity of a fluorocarbon polymer–solution interface caused by fibrinogen adsorption.

Enhanced growth of animal and human endothelial cells on biodegradable polymers

Biodegradable polymers such as poly( L-lactic acid) (PLLA), poly(glycolic acid) (PGA) and PGA coated with PLLA are being employed for cell transplantation and for in vivo regeneration of vascular tissue. Ingrowth and organization of fibrovascular tissue inside polymer scaffolds lead to the occlusion of the regenerated blood vessel. In order to provide regulatory mechanisms to control the development of an inner capsule, endothelialization of these materials is necessary. To achieve this, we employed a novel ammonia plasma technique to surface modified PLLA substrates. Human endothelial cell (HUVEC) and rabbit microvascular endothelial cell (RbMVEC) growth was studied on modified PLLA and control PLLA. Our studies show that modified PLLA and fibronectin (Fn)-coated modified PLLA exhibited statistically significant improvement in HUVEC and RbMVEC growth ( P<0.001) when compared to PLLA and Fn-coated PLLA. Therefore, ammonia plasma treatment gives us the unique capability of modifying prosthetic biomaterials of various constructs with the eventual transplantation of mammalian cells to be used in tissue engineering or as biological implants.

X-ray photoelectron spectra of adhesion-enhanced a-Si:H on stainless steel induced by plasma treatments

An investigation by X-ray photoelectron spectroscopy (XPS) of adhesion mechanisms of a-Si:H films on stainless steel substrates after hydrogen (H2), nitrogen (N2) and ammonia (NH3) plasma treatments of the surface is presented. It is shown that adhesion is increased by N2 treatment. This effect is related to chemical bonding states at the interface. The improvement is attributed to the formation of silicon nitride at the interface and to the existence of Fe–Fe metallic bonds which contribute to a hardening of the substrate.