Chemical Investigation on Various Aromatic Compounds Polymerization in Low Pressure Helium Plasma

Remarkable properties of plasma polymer films are greatly dependent not only on the chemical structure of precursor but also on the reactor design and the deposition conditions. In many industrial applications it is a challenge to control the plasma polymer structure. In this paper we investigate the chemical transformation of various aromatic compounds, such as activation and fragmentation of substituent-part, aromatic ring opening, during plasma polymerization process. Polymerized films are deposited in a low-frequency capacitively coupled plasma-enhanced chemical vapour deposition reactor, working at low pressure. The chemical composition of plasma-polymerized films is elucidated by Fourier-transform infrared spectroscopy, solid-state carbon-13 nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. Based on spectroscopic measurements, the intermediary reactions during film growth may be presumed.     

Deposition of plasma conjugated polynitrile thin films and their optical properties

The plasma polymerization of 4-phenylbenzonitrile was carried out with the objective of synthesizing a novel conjugated polynitrile thin film with a better optical property. The structure, compositions and morphology of the plasma-polymerized 4-phenylbenzonitrile (PPBPCN) thin films were investigated by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). A fine, homogenous PPBPCN film with a large π-conjugated system and a high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained when a low discharge power of 30 W was used during film formation. For the first time, a blue emission with relatively high photoluminescence intensity for PPBPCN thin films was observed.     

低介电常数聚喹啉衍生物薄膜的合成与表征

采用等离子体聚合技术合成了一种新型的低介电常数聚喹啉衍生物薄膜: 聚3-氰基喹啉(PP3QCN)薄膜. 借助于傅里叶变换红外光谱(FT-IR)、紫外-可见(UV-Vis)吸收光谱、X光电子能谱(XPS)和原子力显微镜(AFM)对薄膜结构进行了系统表征. 结果表明, 等离子体聚合条件对沉积膜的化学结构、表面组成、膜形态以及介电性能均有影响. 在较低的等离子体放电功率(10 W)条件下, 可得到具有较高芳环保留率和较大π-共轭体系的高质量聚3-氰基喹啉薄膜材料; 而在较高功率(25 W)条件下, 聚合过程中会出现比较严重的单体分子破碎, 形成较多非π-共轭体系的聚合物, 从而导致聚3-氰基喹啉的共轭度降低. 聚3-氰基喹啉薄膜的介电性能测试结果表明, 低放电功率(10 W)条件下制得的聚3-氰基喹啉薄膜具有比较低的介电常数值, 仅为2.45.     

Effects of surface properties of different substrates on fine structure of plasma-polymerized SiOCH films prepared from hexamethyldisiloxane (HMDSO)

In this study, Doppler broadening energy spectroscopy (DBES) combined with slow positron beam was used to discuss the effect of substrate types on the fine structure of a plasma-polymerized SiOCH layer as a function of depth. From the SEM pictures, the SiOCH films formed on different substrates showed hemispherical macrostructures, and the deposition rate was dependent on the mean pore size. It appears that the morphology of the plasma-polymerized SiOCH films was associated with the porosity-related characteristics of the substrate such as the size/shape of pores. As deposited on the MCE-022 substrate (mixed cellulose esters membrane with a mean pore size of 0.22 μm) with a nodular structure, the SiOCH films had pillar-like structures and high gas permeabilities. DBES results showed that the SiOCH films deposited on different substrates were composed of three layers: the SiOCH bulk layer, the transition layer, and the substrate. It was observed that the microstructure of the SiOCH films was affected layer by layer; a higher surface pore size in the substrates induced thicker transition layers with higher microporosities and led to thinner bulk layers having higher S parameter values during the plasma polymerization. It was also observed that the change in O(2)/N(2) selectivity was consistent with the DBES analysis results. The gas separation performance and DBES analysis results agreed with each other.     

Composite plasma-polymerized organosiloxane-based material for hydrocarbon vapor selectivity

Films synthesized by plasma enhanced chemical vapor deposition from a mixture of octamethyltrisiloxane and hexamethylcyclotrisiloxane have been studied regarding to their preparation, deposition, chemical composition and membrane properties according to hydrocarbon vapor selectivities of solubility.

Composition of the plasma glow discharge in neutral species has been studied by mass spectrometry whereas structural information of the deposited membranes has been extracted from Fourier transform infra-red (FTIR) spectroscopy. In the deposition conditions presented here leading to plasma-polymerized films, heavy radicals mostly contribute to their growth and their chemical composition. Depending on the precursors ratio in the plasma, i.e. linear and cyclic clusters ratio in the deposited material, solubility of selectivity against nitrogen of the deposited material varies from 50 up to 150 for hexane vapor.     

Plasma Polymerization on Metals

An ellipsometric technique is described for accurately measuring the film thickness of plasma-polymerized polymers on metallic substrates. The index of refraction n and absorption index Kof the plasma polymer film can also be studied by ellipsometry. Films of plasma polystyrene and polyepichlorohydrin were deposited on evaporated aluminum substrates and their thickness and optical constants determined. Plasma polystyrene films from 20 to 1600 Å thick have optical constants n = 1.63 and K =0 independent of film thickness. Plasma polyepichlorohydrin films over the same range of thickness give n ? 1.70 and K? 0.01. By utilizing the ellipsometric method the effect of plasma polymer film thickness on surface energy properties was determined. Advancing contact angle measurements and surface energy analysis detail the polar γSV^P dispersion γSV^Pcontributions to the solid-vapor surface tension γSV = γSV^d + γSV^P Polystyrene and polyepichlorohydrin films on etched aluminum. For thin plasma polystyrene films (600 Å), anomalies in the calculated surface energy are discussed and related to possible surface nonuniformity caused by film growth. Thicker films of plasma polystyrene are shown to have normal surface energy properties as does plasma poly-epichlorohydrin over the entire range of film thickness measured. The adhesive and cohesive properties of plasma polystyrene and polyepichlorohydrin films are discussed as estimated from a lap-shear bond strength study. Etched aluminum coated with various thicknesses of these two polymers and bonded with an epoxy-phenolic adhesive shows a decreasing shear strength with increasing plasma film thickness but begins to level off at ～1600 psi for films >1600 Å thick.     

Characterization of diffusion-controlled mass transport through nanoporous and nanothin films plasma polymerized on a sputtered platinum electrode

We demonstrate the diffusion mode of various redox chemical species through a plasma-polymerized nanothin coating with nanometer-sized pores on a sputtered platinum (Pt) electrode. In this work, hexamethyldisiloxane plasma-polymerized films (PPFs) were added onto the sputtered platinum film, both of which were sequentially deposited in the same vacuum chamber. Results of atomic force microscopy, X-ray photoelectron spectroscopy, and electrochemical studies showed that the PPF provided the platinum electrode with a coating with a complete surface coverage. Sub-nanometer-sized pores (less than 1 nm) responsible for a highly crosslinked polymer network in the PPF coatings offered diffusivity-controlled permeation of redox molecules (i.e., size-exclusivity) rather than solubility-controlled permeation (i.e., chemoselectivity). Consequently, variation of the plasma power could give control over the size of the nanometer-sized cavities.     

Deposition of π-Conjugated Polycyanate Ester Thin Films and Their Dielectric Properties

Two kinds of novel π-conjugated polycyanate esters, namely the plasma-polymerized 4-methoxyphenol cyanate ester (PPMPCE) and the plasma-polymerized 4-phenylphenol cyanate ester (PPPPCE), were successfully prepared by plasma polymerization for the first time. The structure and compositions of both plasma polycyanate esters were investigated by Fourier Transform Infrared (FT-IR), X-ray Photoelectron Spectroscopy (XPS) and UV–Visible Absorption Spectra (UV–Vis). The results show that extensively conjugated C=N double bonds were formed in the plasma-deposited cyanate ester thin films, the plasma polymerization of both monomers proceeded mainly via the opening of π-bonds of the O–C≡N functional groups which are further on being formed into a large π-conjugated system, this unique process is noticeably different from the conventional thermal polymerization reaction of cyanate ester monomers. Further dielectric measurement shows that PPPPCE thin film gives a lower dielectric constant comparing to that of the PPMPCE film, and the dielectric constant of both plasma deposited thin films decreased with an increase in measurement frequency.     

Structure–Property Relationship of Thin Plasma Deposited Poly(allyl alcohol) Films

Poly(allyl alcohol) films with a thickness of about 150 nm were deposited by pulse plasma polymerization onto different substrates (inorganic and organic). The structure/property relationships of these samples were studied in dependence on the duty cycle (DC) of the plasma by a broad combination of different techniques and probes. For the first time volume sensitive methods (FTIR and dielectric spectroscopy) are combined with surface analytics by employing XPS for that system. FTIR spectroscopy gives qualitatively the same dependence of the concentration of the OH groups on DC like XPS. The observed differences are discussed considering the different analytical depths of both the methods. The dielectric measurements show that the plasma deposited films are not thermally stable but undergo a post plasma chemical reaction during heating. The results obtained by dielectric spectroscopy are discussed in detail with the data from FTIR and XPS measurements.     

Attachment and phospholipase A2-induced lysis of phospholipid bilayer vesicles to plasma-polymerized maleic anhydride/SiO2 multilayers

This article describes a method by which intact vesicles can be chemically attached to hydrolyzed maleic anhydride films covalently bound to plasma-polymerized SiO2 on Au substrates. Surface plasmon field-enhanced fluorescence spectroscopy (SPFS) combined with surface plasmon resonance spectroscopy (SPR) was used to monitor the activation of plasma-deposited maleic anhydride (pp-MA) film with EDC/NHS and the subsequent coupling of lipid vesicles. The vesicles were formed from a mixture of phosphatidylcholine and phosphatidylethanolamine lipids, with a water-soluble fluorophore encapsulated within. Vesicle attachment was measured in real time on plasma films formed under different pulse conditions (plasma duty cycle). Optimum vesicle attachment was observed on the pp-MA films containing the highest density of maleic anhydride groups. Phospholipase A2 was used to lyse the surface-bound vesicles and to release the encapsulated fluorophore.     

Low-temperature deposition of tin(IV) oxide films for thin-film power sources

Thin films of tin(IV) oxide were deposited in a Picosun R-150 installation from tetraethyltin using remote inductively coupled plasma at temperatures lower than 200°C with the aim of developing a material for thin-film current sources. The thickness and morphology of the films were studied by spectral ellipsometry and scanning electron microscopy. Both the thickness and roughness of the films considerably decrease with an increase in the synthesis temperature in the interval 100–180°C. The films are X-ray amorphous. As shown by X-ray photoelectron spectroscopy, tin in the films is in oxidation state +4.     

Surface Modification of Textile Fibers and Cords by Plasma Polymerization

In this paper we report on the treatment of industrial fibers and cords by means of plasma polymerization techniques. Coatings of plasma-polymerized pyrrole or acetylene were deposited on aramid fibers, aramid cords and polyester cords. The equipment was a custom-built semi-continuous reactor operated on a pulsed DC glow discharge. The fibers and cords were tested for adhesion to various polymers such as tire cord skim stock rubber compounds and epoxy adhesives. Standard industrial pull-out force adhesion measurement techniques were used. The deposition conditions of the plasma polymer films were varied within wide limits. It was found that, in general, films deposited under low-power and high-pressure conditions performed better than films prepared under high-power and low-pressure conditions. For some systems pulsing of the discharge power improved the performance further. For all systems studied, the optimized plasma polymer surface modification outperformed current industrial standards. The plasma-polymerized coatings were characterized by various techniques and the excellent performance results are explained in a tentative model based on the molecular structure of the films. This structure was found to be strongly dependent on the discharge conditions.     

Graphene nanostructures with plasma-polymerized pyrrole as an adsorbent layer for biosensors

We report on a novel nanoarchitecture for use in highly bioactive electrochemical biosensors. It consists of multilayers of nanostructured plasma-polymerized pyrrole (ppPY) and nanosheets of electrically conductive graphene. The ppPY films were deposited by plasma-enhanced chemical vapor deposition on a graphene surface to form nanostructured composites (G-ppPY). The G-ppPY films were then coated with protein (BSA as a model) by adsorption, and then with DNA. The adsorption of protein and DNA on the nanocomposite was studied by electrochemical impedance spectroscopy and with a quartz crystal microbalance. Results demonstrated that the adsorption of biomolecules on G-ppPY films causes a higher variation in its electrochemical properties and adsorbed amount than that on a plain ppPY surface. This indicates that the presence of graphene can enhance the electrochemical activity of ppPY without reducing the sensitivity of biomolecular adsorption.

Plasma polymerization of ethylene glycol monomethylether and water-vapor permeability

Plasma polymerization of ethylene glycol monomethylether (EGMME) was investigated by elemental analysis, infrared spectroscopy, and ESCA. The surface and permeation properties for the formed polymers were discussed. EGMME was plasma-polymerized to yield films. The films contained a large amount of oxygen-containing groups such as hydroxy, carbonyl, carboxylate ester, and ether groups. The formation of polymers having hydroxy groups was favorable in plasma polymerization at low W/FM values. Their surface energy was high (63.2–57 dyn/cm) and decreased with increasing the W/FM value. The plasma-polymers from EGMME had slightly high water-vapor permeability and low oxygen and nitrogen permeabilities. The plasma-polymers, conclusively, are characterized to have high selectivity in water-vapor permeation.     

Plasma-polymerized polyaniline films: Synthesis and characterization

The radio-frequency plasma polymerization technique was used to polymerize aniline onto polymer substrates including perfluorinated ethylene propylene copolymer. The plasma-polyaniline films were characterized by ultraviolet/visible absorption spectroscopy, Fourier transform infrared spectroscopy, electron spin resonance, X-ray photoelectron spectroscopy, scanning electron microscopy, and contact angle measurements. Preliminary conductivity measurements were also carried out. It was demonstrated that the chemical and physical characteristics of the plasma-polymerized poly-aniline films changed significantly with discharge conditions, indicating the possibility for tailoring the structure and properties of the polyaniline films by optimizing the discharge conditions. In particular, the contents of quinoid sequences and aliphatic crosslinking moieties were found to increase with increasing power input and/or discharge duration. By contrast, the number of free radicals trapped in the polyaniline films and their mobility were shown to increase with decreasing the power input and/or discharge duration within the plasma conditions covered in this study. Furthermore, a correlation was found between surface hydrophilicity of the resultant plasma-polyaniline films and the atomic ratio of C to N. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 633–643, 1998     

乙醇在Mn薄膜／Rh（100）上吸附和分解的研究

应用高分辨电子能量损失谱（HREELS）和热脱附谱（TDS）,研究了Mn薄膜／Rh(100)上乙醇的吸附和分解,提出了表面吸附和分解的反应工,在300K时,蒸镀的Mn在清洁Rh(100)表面上以层层模式生长;在130－300K间,在25mLMn/Rh(100)表面上吸附20L乙醇的TDS结果与乙醇在Rh(100)表面上的结果一致在155K处,脱附出多层凝聚态吸附的乙醇;升温到255K,脱附出H2和CH4,继续升温,出现了与乙醇在R (100)表面上不一致的现象,在470K,同时出现了第2个H2和CH4的脱附峰,在500K,脱附极少量的CO;在950K附近,脱附出大量CO。     

Integration of microfabricated needle-type glucose sensor devices with a novel thin-film Ag/AgCl electrode and plasma-polymerized thin film: mass production techniques

We developed an integrated array of needle-type biosensors employing a novel process of fabrication, comprising conventional semiconductor fabrication and micromachining technology. Amperometric sensing electrodes with plasma-polymerized films and a thin-film Ag/AgCl reference electrode were directly integrated on a glass substrate with thin-film process, e.g., sputtering. An enzyme was immobilized on the electrode via the plasma-polymerized film, which was deposited directly on the substrate using a dry process. The novel thin-film Ag/AgCl reference electrode showed stable potentials in concentrated chloride solutions for a long period. The plasma-polymerized film is considered to play an important role as an interfacial design between the sensing electrode and the immobilized enzyme considering that the film is extremely thin, adheres well to the substrate (electrode) and has a highly cross-linked network structure and functional groups, such as amino groups. The results showed increments of the sensor signal, probably because the plasma-polymerized film allowed a large amount of enzyme to be immobilized. The greatest advantage is that the process can permit the mass production of high-quality biosensors at a low cost.     

Control of attachment of bovine serum albumin to pulse plasma-polymerized maleic anhydride by variation of pulse conditions

This letter describes how the irreversible attachment of bovine serum albumin (BSA) to films of plasma-polymerized maleic anhydride can be measured by an indirect antibody-binding assay and how this attachment appears to be strongly affected by the polymerization conditions. Surface plasmon resonance (SPR) was used to follow the binding of the antibody, anti-bovine serum albumin (aBSA), to protein-modified plasma-polymerized maleic anhydride films. It was found that BSA could be irreversibly bound to polymers made under pulse plasma conditions, but BSA did not bind to polymers made under continuous wave conditions. Moreover, the degree of antibody binding, which is directly related to the quantity of BSA on the polymer, correlated with the plasma duty cycle (t(on)/t(on) + t(off)): lower duty cycle pulse plasma conditions gave greater BSA attachment. We speculate that BSA is being covalently bound to the polymer via the reaction of amine groups on lysine residues in BSA with the retained anhydride group functionality in the polymer.     

A transparent boron-nitrogen thin film formed by plasma CVD out of the discharge region

A transparent boron-nitrogen thin film of thickness 550 nm was successfully deposited out of the discharge region by rf plasma CVD. The deposition was performed with diborane (4.8 vol % in N₂) as the reactant gas and argon as the carrier gas by an inductively coupled reactor at a frequency of 13.56 MHz. The transparent films could be obtained at a low pressure of about 30 Pa, at a discharge power level of 30 W, and at room temperature without heating the substrate. The thin films obtained by rf plasma are compared with those obtained by microwave plasma. Both the refractive index and the deposition rate for the films deposited by microwave plasma are discussed according to the deposition conditions.     

Amperometric glucose biosensor based on mediated electron transfer between immobilized glucose oxidase and plasma-polymerized thin film of dimethylaminomethylferrocene on sputtered gold electrode.

We propose an electron transfer-mediated amperometric enzyme biosensor based on plasma-polymerized thin film of dimethylaminomethylferrocene (DMAMF) on a sputtered gold electrode. The DMAMF plasma-polymerized film is deposited directly onto the surface of the electrode under dry conditions. The resulting thin film not only has redox sites but also is extremely thin (approximately 20 nm), adheres well onto the substrate (electrode), has a flat surface and a highly-crosslinked network structure, and is hydrophilic in nature. Glucose oxidase is densely immobilized onto the surface of DMAMF plasma-polymerized film on the gold electrode. From the electrochemical measurement, the biosensor can cover the wide range of glucose concentration (1.3 - 81 mM) at +350 mV of applied potential. The current response of the glucose biosensor was decreased by less than 5% in an aerobic solution as compared to that in an anaerobic solution. These show that the DMAMF plasma-polymerized films play a role as the electron transfer mediators between the reaction center of enzyme and the electrode.