A Comparison of PE Surfaces Modified by Plasma Generated Neutral Nitrogen Species and Nitrogen Ions

The surface modification of polyethylene (PE) by neutral nitrogen species (ground and excited state N₂ as well as atomic N; modified nitrogen plasma treatment) has been compared to the effect of nitrogen ion bombardment using X-ray Photoelectron Spectroscopy (XPS) and contact angle measurements. XPS results indicate that a greater nitrogen concentration was grafted during the modified nitrogen plasma treatment of PE, an effect that was attributed to surface sputtering during ion beam modification. The distribution of nitrogen-containing functionalities was strongly dependent upon the treatment strategy; the modified nitrogen plasma treatment lead predominantly to imine groups being formed at the PE surface, while amine groups were the dominant species produced during ion beam modification. The presence of electron irradiation during the modified nitrogen plasma treatment of PE did not modify the rate of nitrogen incorporation or change the nature of N-containing functional groups produced but did lead to a systematic decrease in contact angle.     

Synthèse assistée par plasma d'un revêtement de h-bn: composition et vieillissement

A thin film containing h-BN was deposited on a silicon substrate from the reaction between a flowing nitrogen plasma and B₂H₆. The influence of various durations of pre-treatment and post-treatment by the nitrogen plasma on the chemical composition of the coating and on its ageing in open air was studied by FTIR and XPS.     

XANES and XPS characterization of hard amorphous CSixNy thin films grown by RF nitrogen plasma assisted pulsed laser deposition

Amorphous carbon silicon nitride thin films were grown on (100) oriented silicon substrates by pulsed laser deposition (PLD) assisted by an RF nitrogen plasma source. Up to about 30 at. % nitrogen and up to 20 at. % silicon were found in the hard amorphous thin films by XPS in dependence on the composition of the mixed graphite / Si₃N₄ PLD target. The universal nanohardness was measured to be at maximum load force of 0.1 mN up to 23 GPa for thin CSi_xN_y films with reference value of 14 GPa for single crystalline silicon. X-ray photoelectron spectroscopy (XPS) of CSi_xN_y film surfaces showed a clear correlation of binding energy and intensity of fitted features of N 1s, C 1s, and Si 2p peaks to the composition of the graphite / Si₃N₄ target and to nitrogen flow through the plasma source, indicating soft changes of binding structure of the thin films due to variation of PLD parameters. Auger electron spectroscopy (AES) of Si KL₂₃L₂₃;¹D Auger transition gave a detailed view of bonding structure of Si in the CSi_xN_y films. The intensity of π* and σ* resonances at the carbon K-edge X-ray absorption near-edge structure (XANES) of the CSi_xN_y films measured at BESSY I corresponded to the nanohardness of the CSi_xN_y films, thus giving insight into chemical binding structure of superhard amorphous materials.     

One-Step Synthesis of Silicon Oxynitride Films Using a Steady-State and High-Flux Helicon-Wave Excited Nitrogen Plasma

A steady-state and high-flux helicon-wave excited N₂ plasma was used to oxynitride Si substrates for the synthesis of silicon oxynitride (SiON) films. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) have been extensively used to characterize surface quality of the SiON films, and it is found that a large amount of nitrogen (N) can be incorporated into the films. The result of XPS depth profiles shows that the N concentration is high near the surface and the oxide/Si interface. In the UPS spectra, absence of the reappearance of surface states suggests a resistance to clustering of the oxynitride layer. The N₂ flux and Ar mixture quantity can facilitate tuning of the dissociation characteristics in N₂ discharge. By modulating the N₂ fractions, the N⁺ density reaches maximum at a N₂/(N₂ + Ar) flow-rate ratio of 0.5, resulting in incorporation of more N atoms into the SiON films. Considering the easy control of N₂ plasma, our work opens up a new avenue for achieving high-yield SiON films at low temperature.     

Mechanochemical reaction of TiO<Subscript>2</Subscript> with β-alanine for the preparation of visible light active nitrogen doped titania: adsorption and kinetic studies

Nitrogen doped TiO₂ (TiO_2−xN_x) with a homogenous anatase phase was synthesized, using β-alanine as a nitrogen precursor and ethanol as a oxygen depriving agent in the concentration range of 0.05, 0.10, 0.15 and 0.2 at% and were characterized by Powder X-ray Diffraction (PXRD), X-ray Photoelectron Spectra (XPS), Scanning Electron Microscope (SEM), Fourier Transform Infrared (FT-IR) and UV–visible Diffused Reflectance Spectroscopic (DRS) techniques. Ethanol deprives the surface oxygen, thereby generating oxygen defects whose concentration was evaluated by FTIR, Photoluminescence (PL) and Electron Spin Resonance (ESR) studies. FTIR analysis reveal that concentration of oxygen vacancies/defects (V_o) decreases as the nitrogen concentration increases leading to the reduction in the Ti–O bond length. This results in a shift of the IR absorption peak towards a low wave number as predicted by simple physical harmonic oscillator model. The Ti 2p_3/2 XPS spectra of TiO_2−xN_x shifts to lower binding energies due to the increase in the electron densities around the Ti atoms indicating the formation of Ti³⁺ in the doped samples. N₂ adsorption–desorption isotherms measurements show a slight increase in the Brunner–Emmet–Teller (BET) surface area, pore diameter, mesopore volume, while the crystallite size and the morphology were also effected by the nitrogen doping. The equilibrium adsorption of Toluene molecules on the photocatalyst surface follows Langmuir theory and the rate controlling step could be the surface reaction of the adsorbed Toluene molecules.     

UV-ozone modification of plasma-polymerised acetonitrile films for enhanced cell attachment

Plasma polymerisation is of great interest for modifying the surface properties of biomedical devices in order to control, for example, protein adsorption and cell attachment. In this paper we present results for plasma-polymerised acetonitrile deposited onto silicon or polystyrene substrates. The chemistry of films deposited under a range of experimental conditions was studied by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). XPS provided evidence that the elemental composition of the films varied with rf power to flow rate parameter (W/F) with films produced at higher W/F being deficient in nitrogen. FTIR revealed that the plasma deposited film contained a wide range of nitrogen functional groups including amine, imine and nitrile. Oxidation of the films by exposure to radiation from a low pressure mercury vapour lamp in an air ambient increased the surface oxygen levels from 3 to 17 at.% after 300 s exposure. XPS also revealed that the oxidation process proceeded via the formation of carbonyl groups at short exposure times (<60 s) while longer treatment times (>60 s) resulted in an increase in the concentration of carboxyl groups. To assess their potential to support cell growth, polystyrene culture dishes coated with plasma deposited films and UV-ozone oxidised films were seeded with 1BR.3.N human fibroblast cells and incubated for up to 72 h. Un-oxidised plasma-polymerised acetonitrile films were found to give comparable cell attachment densities as tissue culture polystyrene. The greatest cell attachment density was found with plasma polymer films which had been UV-ozone treated for the longest time (300 s). Enhanced attachment to this surface was attributed to the high level of carboxylic groups found on this substrate.     

An XPS and STM study of the size effect in NO adsorption on gold nanoparticles

The effect of the gold particle size, temperature of the model gold catalyst, and NO pressure on the composition of the adsorption layer was studied by in situ XPS and STM methods. Adsorption of nitric oxide was carried out on gold nanoparticles with a mean size of 2?C7 nm prepared on the thin film surface of alumina. In high-vacuum conditions (P _NO ?? 10^?5 Pa), only atomically adsorbed nitrogen is formed on the surface of gold nanoparticles. At about 1 Pa pressure of NO and in the temperature range from 325 to 475 K, atomically adsorbed nitrogen coexists with the N₂O adsorption complex. The surface concentration of the adsorbed species changes with a change in both the mean gold particle size and adsorption temperature. The saturation coverage of the surface with the nitrogen-containing complexes is observed for the sample with a mean size of gold particles of 4 nm. The surface of these samples is mainly covered with atomically adsorbed nitrogen, the saturation coverage of adsorbed nitrogen of about ??0.6 monolayer is attained at T = 473 K. The change in the composition of the adsorption layer with temperature of the catalysts agrees with the literature data on the corresponding temperature dependence of the selectivity of N₂ formation observed in the catalytic reduction of NO with carbon monoxide on the Au/Al₂O₃ catalyst. The dependences of the composition of the adsorption layer on the mean size of Au nanoparticles (size effect) and temperature of the catalyst are explained by the sensitivity of NO adsorption to specific features of the gold surface.     

Amination of Poly(ethylene-terephthalate) polymer surface for biochemical applications

Amine functionalization of Poly(ethylene-terephthalate) (PET) films for covalent binding of peptides is described. Ammonia plasma treatments have been used to graft nitrogen-containing functional groups onto the PET surface. The samples were then analyzed by X-ray photoelectron spectroscopy (XPS) and a parametric study was performed to define the best plasma grafting conditions. For biological tests, samples were sterilized by steam autoclaving: this induces a four to fivefold loss of the nitrogen functional groups on the polymer surface. XPS does not differentiate easily between the various nitrogen groups present on the surface so it is difficult to estimate the amount of surface amine groups available for direct coupling of bioactive molecules (proteins, peptides, nucleic acids, ...). To obtain a direct measurement of the amines present, we assayed for cysteine fixation through its carboxylic group by detection of the thiolaminoacid by XPS. We obtained cysteine fixation, showing the presence of grafted primary amine functions on PET surface after ammonia plasma treatment. Radiochemical assays were also made to quantify the amount of amine groups on plasma treated PET. XPS, cysteine fixation and radiochemical assays all show the presence of amine functions on ammonia plasma treated PET.     

Surface Modification of Polypropylene Non-Woven Fabrics by Atmospheric-Pressure Plasma Activation Followed by Acrylic Acid Grafting

Polypropylene (PP) non-woven fabrics have been activated by an atmospheric-pressure plasma treatment using surface dielectric barrier discharge in N₂ and ambient air. Subsequently, the plasma activated samples were grafted using catalyst-free water solution of acrylic acid. Surface properties of the activated and polyacrylic acid post-plasma grafted non-woven were characterised by scanning electron microscopy, Fourier transform infrared spectroscopy, electron spin resonance spectroscopy, surface energy and dyeability measurements. The grafted non-woven exhibit improved water transport and dyeing properties. The plasma activation in nitrogen plasma gas was more efficient than in air.     

Reaction scheme of ammonia synthesis in the ECR plasmas

The reaction scheme of ammonia synthesis in the ECR plasma apparatus teas investigated from both identifications of the species in the plasmas and the adsorbed species on the surface of a steel substrate placed in the plasmas. The adsorbed species were considerably different when different kinds of plasmas are used. NH, species were adsorbed on the steel substrate surface in the nitrogen-hydrogen plasma, and N₂ molecules were adsorbed in the nitrogen plasma. By the application of a negative bias potential on the substrate, the adsorption of N atom or Fe-N bond formation was identified on the steel substrate surface. When the stainless steel wall of the chamber was covered with aluminum foil, the yield of NH,, radicals, which were on both the substrate and in the plasma, decreased. By exposure of the substrate, on which N₂ molecules or N atoms adsorbed, to the hydrogen plasma, N₂ and N disappeared from the steel substrate surface, forming ammonia. Moreover, the adsorption of NH,, radicals disappeared when the stainless steel wall surface was covered with aluminum foil. Thus, the surface of the stainless steel wall acts as a catalyst in ammonia formation. The formation of ammonia in the nitrogen-hydrogen ECR plasma, in which the steel substrate served as the catalyst, is not only through the dissociative adsorption of excited nitrogen molecules but also through the dissociative adsorption of nitrogen molecular ions.     

Biaxially Oriented Polypropylene (BOPP) Surface Modification by Nitrogen Atmospheric Pressure Glow Discharge (APGD) and by Air Corona

We compare two surface treatments of biaxially-oriented polypropylene (BOPP), which are carried out in the same dielectric barrier discharge (DBD) apparatus, namely air corona, and N₂ atmospheric pressure glow discharge (APGD). Changes in the surface energy and chemistry are investigated by contact angle measurements, by X-ray photoelectron spectroscopy (XPS) and by attenuated total reflectance infrared spectroscopy (ATR-FTIR). It is shown that N₂ APGD treatment leads to a higher surface energy than air corona treatment, and to the formation of mostly amine, amide, and hydroxyl functional groups at the polypropylene surface. Finally, hydrophobic recovery of the treated film is studied; for both treatment types, the increased surface energy is found to decay in a similar manner with increasing storage time after treatment.     

Silicon Dioxide Coating of Titanium Dioxide Nanoparticles from Dielectric Barrier Discharge in a Gaseous Mixture of Silane and Nitrogen

The coating of titanium dioxide nanoparticles with silicon dioxide has been carried out by dielectric barrier discharge (DBD) plasma treatments to enhance the thermostability of Titania for applications at high temperature processes. During the first coating processing step, a closed film of silicon nitride was produced via plasma treatment in a gaseous mixture of silane and nitrogen, while atmospheric surface contaminations got mainly removed. In the second processing step, the DBD plasma treatment in oxygen or air was used to convert the silicon nitride mainly into silicon dioxide. Remaining carbon impurities at the interfaces between titanium dioxide and silicon nitride after the nitrogen/silane plasma treatment were subsequently removed simultaneously. Atomic force microscopy and X-ray photoelectron spectroscopy were employed to study the DBD plasma treatments of the TiO₂ nanoparticles.     

Effect of excitation states of nitrogen on the surface nitridation of iron and steel in d.c. glow discharge plasma

The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow‐discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N₂*) or nitrogen molecule ions (N₂⁺). The optical emission spectra suggested that the formation of N₂*‐rich or N₂⁺‐rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N₂⁺‐rich plasma had a much higher nitrogen concentration than that by a N₂*‐rich plasma, likely due to the larger chemical activity of the N₂⁺ species as well as the N₂⁺ sputtering bombardment to the cathode surface. The strong reactivity of the N₂⁺ species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N₂⁺‐rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N₂*‐rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination. Copyright © 2010 John Wiley & Sons, Ltd.     

Introduction of Primary Amino Groups on Poly(ethylene terephthalate) Surfaces by Ammonia and a Mix of Nitrogen and Hydrogen Plasma

With the aim of introducing primary amino groups on the surface of poly(ethylene terephthalate) (PET), two methods were compared—the use of ammonia or a combination of nitrogen and hydrogen low-pressure microwave plasma. Several plasma parameters were optimized on the reactor to increase the –NH₂ surface density, which was estimated by colorimetric titration and X-ray photoelectron spectroscopy (XPS). These techniques show that whatever the plasma treatment, almost 2 –NH₂/nm2 are incorporated on PET films. Emission spectroscopy highlighted a correlation between the density of primary amino groups and the ratio between an NH peak intensity and an Ar peak intensity (I_NH/I_Ar). Variation in surface hydrophilicity with aging in air after plasma treatment was monitored with contact angle measurements and showed a hydrophobic recovery. This was confirmed by XPS, which suggests also that surfaces treated by NH₃ plasma are more stable than surfaces treated by N₂/H₂.     

Effects of cyclonic plasma deposited organosilicon nano-coating on 316 stainless steel and its surface characterization

Cyclonic atmospheric pressure plasma is developed to synthesize the organosilicon nano-coating on 316 L stainless steel surface with hexamethyldisilazane (HMDSN) and HMDSN/N₂ monomers. The modified 316 L stainless steel surface characteristics of cyclonic plasma deposited organosilicon nano-coating were evaluated by the static contact angle measurement, FTIR, SEM, AFM, and XPS detections. The chemical analysis with FTIR and XPS depicts that cyclonic plasma deposited nano-coating obtains the relatively inorganic characteristics. The surface morphological determination with SEM and AFM refers cyclonic plasma deposited 316 L stainless steel surface roughness alteration with switching monomer inputs. This study shows the potential of chamber-less deposition to create the plasma deposited organosilicon nano-coating for 316 L stainless.     

Covalent attachment of trypsin on plasma polymerized allylamine

This paper focuses on the immobilization of a proteolytic enzyme, trypsin, on plasma polymerized allylamine (ppAA) films. The later have been deposited onto silicon substrate by means of radiofrequency glow discharge. The covalent attachment of the enzyme was achieved in three steps: (i) activation of the polymer surface with glutaraldehyde (GA) as a linker, (ii) immobilization of trypsin and (iii) imino groups reduction treatment. The effects and efficiency of each step were investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Fluorescent spectroscopy was used to evaluate the change of the biological activity following the immobilization steps. The results showed that enzyme immobilization on GA-modified substrate increases the enzyme activity by 50% comparing to adsorbed enzymes, while the imino reduction treatment improves the enzyme retention by about 30% comparing to untreated samples. In agreement with XPS and AFM data, UV–vis absorption spectroscopy, used to quantify the amount of immobilized enzyme, showed that allylamine plasma polymer presents a high adsorption yield of trypsin. Although the adsorbed enzymes exhibit a lower activity than that measured for enzymes grafted through GA linkers, the highest catalytic activity obtained was for the enzymes that underwent the three steps of the immobilization process.     

Deposition of polysiloxane‐like nanofilms onto an aluminium alloy by plasma polymerized hexamethyldisiloxane: characterization by XPS and contact angle measurements

In this work, aluminium (Alclad 2024‐T3) substrates were cleaned by an r.f. (13.56 MHz) plasma, using argon (Ar), oxygen (O₂) and a mixture of O₂/Ar (50:50) gases. The effectiveness of plasma cleaning was checked in situ using X‐ray photoelectron spectroscopy (XPS) and ex situ using water contact angle measurements. XPS O/Al surface atomic ratios are in excellent agreement with those of the crystalline boehmite and the pseudoboehmite. Oxygen O 1s peak‐fitting was used to quantify the proportion of hydroxyl ions and the functional composition on the aluminium surface: the surface cleaned with O₂ plasma contains 50% of aluminium hydroxides, the ones cleaned with Ar plasma and with Ar/O₂ plasma contain, respectively, 25 and 37% hydroxyl ions. The binding energy separation between Al 2p and O 1s is characteristic of AlO(OH). Thin SiO_x films were subsequently deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen. In the absence of oxygen, a hydrophobic (Θ≥ 100° ) film characteristic of polydimethylsiloxane (PDMS) is formed: polysiloxane‐like thinner films (SiO_x) are obtained with the introduction of oxygen. XPS and contact angle measurements confirmed both the composition and the structure of these films. More importantly, contact angle measurements using different liquids and interpreted with the van Oss‐Good‐Chaudhury theory allowed determination of the surface free energy of the deposited films: the calculated values of surface tension of the film formed from HMDSO/O₂: (50/50) are in excellent agreement with those of reference silica‐based materials such as a silicon wafer and cleaned glass. Copyright © 2007 John Wiley & Sons, Ltd.     

Low energy ion bombardment of Ti and TiNx films

The influence of low energy ion bombardment on TiN_x film growth and film properties was investigated. The discharge was characterized using Langmuir probe technique as well as energy resolved mass spectrometry with a plasma monitor (Hiden HAL 301 S/EQP). The deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Increasing the N₂ gas flow as well as increasing the negative substrate voltage at constant gas flow effect an increase of the N/Ti ratio in the films determined by XPS. The influence of the energy flux to the surface due to ion bombardment was mainly recognized in the substructure of the films. In addition, pure Ti films were modified by nitrogen ion bombardment after deposition using an ion gun. An increase of the N/Ti ratio was observed with increasing ion energy. Finally saturation is reached.     

Surface modification of aromatic polyamide film by oxygen plasma

The surface of poly(p-phenylene terephthalamide) (PPTA) films was modified by oxygen plasma, and the modified film surface was analyzed by an advancing contact meter and X-ray photoelectron spectroscopy (XPS). The advancing contact measurement showed that the oxygen plasma treatment made the surface of the PPTA film hydrophilic. The XPS analyses also showed the increase in the O/C and N/C atom ratio, especially the O/C atom ratio, at the PPTA film surface by the oxygen plasma treatment. A main oxygen functionality formed by the oxygen plasma treatment is a carboxylic acid group, and a main nitrogen functionality formed is a protonated amino group. The formation of the oxygen and nitrogen functionalities formed by the oxygen plasma treatment is not restricted to the surface of the PPTA film, but penetrates at least 35 Å deep from the film surface. The formation of these carboxylic acid and protonated amino groups is a result of the bond scission of the amide linkages in the PPTA film. Interactions of photons in the oxygen plasma rather than interactions of electrons and activated oxygen atoms contribute greatly to the bond scission. © 1995 John Wiley & Sons, Inc.     

Surface modification of SPEU films by ozone induced graft copolymerization to improve hemocompatibility

Surface modification of segmented poly(ether urethane) (SPEU) by graft copolymerization with N,N′-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl) ammonium (DMMSA), a zwitterionic sulfobetaine structure, was conducted. A simple two-step procedure for grafting of DMMSA onto the surface of SPEU film was used. The surface was first treated with ozone to introduce active hydroperoxide groups. The active surface was then exposed to the DMMSA solution in the sealed tube. Grafted SPEU film was characterized by ATR–FTIR, XPS and contact angle measurement. ATR–FTIR and XPS investigations confirmed the graft copolymerization. The monomer concentration, copolymerization temperature and time were varied to maximize the efficiency of DMMSA grafting. The equilibrium water content (EWC) and contact angle measurements showed that the hydrophilicity of the film had been greatly improved. The blood compatibility of the grafted films was evaluated by platelet adhesion in platelet rich plasma (PRP), deposits in blood control and protein adsorption in bovine fibrinogen using SPEU film as the control. No platelet adhesion and no thrombus were observed for the grafted films incubated in PRP for 300 min and in blood for 120 min, respectively. The protein adsorption was reduced on the grafted films after incubation in bovine fibrinogen for 120 min. These results proved that improved blood compatibility was obtained by grafting this new zwitterionic sulfobetaine structure monomer onto SPEU film.