Characterization of thin polymer‐like films formed by plasma polymerization of methylmethacrylate: A neutron reflectivity study

The microstructure of the plasma‐polymerized methylmethacrylate (ppMMA) films is characterized using neutron reflectivity (NR) as a function of the plasma reaction time or film thickness. Variation in the crosslink density normal to the substrate surface is examined by swelling the film with a solvent, d‐nitrobenzene (dNB). In the presence of dNB, uniform swelling is observed throughout the bulk as well as at the air surface, and silicon oxide interfaces. The results indicate that the MMA film prepared by plasma polymerization (ppMMA) has a uniform crosslink density from air surface to substrate surface. Additionally, the scattering length density of the plasma‐polymerized MMA film (SLD ≈ 0.750 × 10⁻⁶ Å⁻²) is much lower than that of a conventional PMMA film (SLD = 1.177 × 10⁻⁶ Å⁻²). The increase in film thickness following dNB sorption is 7.5% and at least 36% for the ppMMA and PMMA films, respectively. This suggests that the films formed by plasma polymerization are different from conventional polymers in chemical structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2522–2530, 2004     

Reusable thin film photocatalyst of Fe‐doped TiO2 deposited by ECR plasma

The paper presents an improved method of depositing nanocrystalline thin films of Fe‐doped TiO₂ to be used as a reusable cyclic photocatalyst for degrading the organic pollutants. The technique of electron cyclotron resonance plasma‐enhanced chemical vapor deposition was employed with titanium tetra‐isopropoxide (C₁₂H₂₈O₄Ti) and ferrocene (C₁₀H₁₀Fe) as precursors of Ti and Fe, respectively. Optical emission spectroscopy was used to identify the reactive species, to determine the electron temperature and the ion density during deposition. The films were characterized using optical absorption and photoluminescence spectra, whereas the morphological analysis was carried out with scanning electron microscopy. Strong adhesion of the deposited films with the substrate ruled out any possibility of TiO₂ particles being leached out. It was confirmed by observing the degradation rate of the same film repeatedly. Cyclic use of the film for the catalytic reactions thus makes the process much user friendly for the water treatment. Copyright © 2014 John Wiley & Sons, Ltd.     

Single‐phase TiO2 formation by plasma oxidation of titanium thin films

Synthesis of titanium oxide film by plasma oxidization of the metallic films is investigated. Argon/oxygen gas mixture in the pressure range 30 × 10^?2 mbar is used for plasma processing at a frequency of 250 kHz. The plasma‐oxidized films are annealed in a tube furnace in argon atmosphere to establish crystalline‐phase formation. X‐ray diffraction and Raman spectroscopic results manifest peaks corresponding to rutile TiO₂. Ultraviolet‐Visible (UV‐Vis) spectroscopic analysis confirms the bandgap of rutile TiO₂, and photoluminescence spectra exhibit peaks due to oxygen defects. Homogeneity across the film's thickness and the nature of the film substrate interface is studied by depth profiling acquired using secondary ion mass spectrometry. Copyright © 2015 John Wiley & Sons, Ltd.     

Perfluoro(methylcyclohexane) plasma polymer thin film: Growth,surface morphology,and properties investigated by scanning thermal microscopy

Scanning thermal microscopy (SThM) has been used for the visualization and characterization of an ultrathin plasma polymer film of perfluoro(methylcyclohexane) at a submicrometer level. The morphology, molecular dynamics, and lateral homogeneity of the ultrathin film have all been examined precisely with SThM. The growth of the plasma polymer film on a silicon wafer (Si‐wafer) has also been precisely determined using a new burning‐hole technique. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1392–1400, 2005     

Synthesis by plasma and characterization of bilayer aniline–pyrrole thin films doped with iodine

The synthesis by plasma and characterization of aniline–pyrrole bilayer polymers doped in situ with iodine were studied. The objective was to study the electrical conductivity of thin films composed of alternating layers of different polymers. The results indicated that the plasma technique is capable of forming chemically bonded layered polymers with several possible combinations. The electric conductivity was studied during heating–cooling cycles so the dependence of the bilayer polymers on temperature could be observed. The behavior was related with the Arrhenius model, with average activation energies of 0.4 ± 0.1 eV in the heating steps and 0.5 ± 0.1 eV in the cooling steps. The difference in both steps shows the influence of the aniline in the bilayer polymer network because polyaniline presents changes in the structure during heating processes. The bilayer aniline–pyrrole polymers had greater electric conductivity at room temperature than that shown by the separate homopolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1850–1856, 2002     

Study of the Interface Microstructures of CVD Diamond Films by TEM

 The characteristics of the interface microstructures between a CVD diamond film and the silicon substrate have been studied by transmission electron microscopy and electron energy loss spectroscopy. The investigations are performed on plan-view TEM specimens which were intentionally thinned only from the film surface side allowing the overall microstructural features of the interface to be studied. A prominent interfacial layer with amorphous-like features has been directly observed for CVD diamond films that shows a highly twinned defective diamond surface morphology. Similar interfacial layers have also been observed on films with a <100> growth texture but having the {100} crystal faces randomly oriented on the silicon substrate. These interfacial layers have been unambiguously identified as diamond phase carbon by both electron diffraction and electron energy loss spectroscopy. For the CVD diamond films that exhibit heteroepitaxial growth features, with the {100} crystal faces aligned crystallographically on the silicon substrate, such an interfacial layer was not observed. This is consistent with the expectation that the epitaxial growth of CVD diamond films requires diamond crystals to directly nucleate and grow on the substrate surface or on an epitaxial interface layer that has a small lattice misfit to both the substrate and the thin film material.     

Substrate temperature effects on film chemistry in plasma depositions of organics. II. Polymerizable precursors

The influence of substrate temperature during plasma deposition on the chemistry of the organic films formed was examined. Plasma ionization of precursor gases that are polymerizable by conventional mechanisms was studied. Film chemistry was analyzed by x-ray photoelectron spectroscopy (XPS). Monomers that polymerize by a free radical mechanism [2-hydroxyethyl methacrylate (HEMA) and hexafluorobutadiene (HFB)] form more regular polymers (i.e. with less molecular rearrangement) by plasma deposition at low substrate temperatures than monomers that polymerize by ionic mechanisms [ethylene oxide (EO) and tetrahydrofuran (THF)]. In all cases, lowering the substrate temperature during deposition produces films with elemental composition virtually identical to that of the precursor gas. Comparison of high-resolution XPS spectra of the deposited films with those for model polymers suggests that functional groups in the monomers used to generate the plasma are incorporated to a greater extent at low substrate temperatures. The effect of plasma power on the degree of precursor structure retention obtained when reduced substrate temperatures are employed was also examined. Plasma deposition of HEMA at low substrate temperatures and low plasma power produces thin films which are, by core level XPS, indistinguishable from HEMA polymerized by conventional methods. EO and THF films coated at low substrate temperatures on glass, polyethylene, or polytetrafluoroethylene varied widely in surface chemistry due to differences in film uniformity. Film quality (uniformity) is enhanced for these low reactivity precursors by pretreating substrates with an argon plasma. © 1992 John Wiley & Sons, Inc.     

Synthesis and luminescence properties of hybrid organic-inorganic transparent titania thin film activated by in-situ formed lanthanide complexes

Stable transparent titania thin films were fabricated at room temperature by combining thenoyltrifluoroacetone (TTFA)-modified titanium precursors with amphiphilic triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO, P123) copolymers. The obtained transparent titania thin films were systematically investigated by IR spectroscopy, PL emission and excitation spectroscopy and transmission electron microscopy. IR spectroscopy indicates that TTFA coordinates the titanium center during the process of hydrolysis and condensation. Luminescence spectroscopy confirms the in-situ formation of lanthanide complexes in the transparent titania thin film. TEM image shows that the in-situ formed lanthanide complexes were homogeneously distributed throughout the whole thin film. The quantum yield and the number of water coordinated to lanthanide metal center have been theoretically determined based on the luminescence data.     

Nanoscale structure and morphology of thin films of poly(2-chloroxylylene) synthesized by the CVD method on different liquids

Poly(2-chloroxylylene) (PCX) thin films are obtained on the surface of liquids with different density and surface tension values. Morphology of these films is different showing increasing roughness and hydrophobicity in correlation with aforementioned physical parameters. A detailed study by means of vibrational spectroscopy, XRD and TEM of the structure of PCX at the interface with the liquid is reported. The results here obtained prove the possibility to tailor the surface of thin solid films of PCX changing the liquid substrate thus addressing the surface functionalities.     

Substrate temperature effects on film chemistry in plasma deposition of organics. III. Analysis by static secondary ion mass spectrometry

Static secondary ion mass spectrometry (SIMS) was used to examine the effect of reducing the substrate temperature during the radio frequency plasma deposition of organic films. Studies of two polymerizable plasma precursors (2-hydroxyethyl methacrylate and acrylic acid) and one nonpolymerizable precursor (acetone) deposited without substrate cooling and with liquid nitrogen cooling are presented. Acetone deposited with methanol/dry ice cooling was also investigated. Spectra of polymerizable precursors were analyzed by comparison to spectra for the corresponding conventionally-polymerized polymer films [i.e., poly(hydroxyethyl methacrylate) and poly(acrylic acid)]. Acetone spectra were interpreted by reference to SIMS analysis of plasma-deposited films prepared from isotopically-labelled acetone and to reference homopolymers. Comparison of the SIMS spectra of films deposited at different substrate temperatures indicates that a reduction in substrate temperature generally results in higher intensity of peaks characteristic of oxygenated ion structures. SIMS also suggests that the reduction of substrate temperature results in less polymer unsaturation and fewer structures which form by hydrogen redistribution during the deposition process. These results support the hypothesis that deposition at low substrate temperatures leads to an increase in the proportion of precursor incorporated into the film without substantial fragmentation. Corroborative results from high resolution x-ray photoelectron spectroscopy (XPS) and assays for precursor functional groups by chemical derivatization reactions in conjunction with XPS are also presented. © 1992 John Wiley & Sons, Inc.     

Multilayer graphene/amorphous carbon hybrid films prepared by microwave surface‐wave plasma CVD: synthesis and characterization

Hybrid films of multilayer graphene (MG) containing amorphous carbon (a‐C) were synthesized on Al substrates by microwave surface‐wave plasma chemical vapor deposition. Raman scattering and surface transmission electron microscopy showed that the carbon films contained a large quantity of MG when a radio frequency (RF) substrate bias was not applied. Amorphization of graphene in the carbon film was promoted by applying an RF bias, which generated Ar⁺ in the plasma. The bandgaps of the films were found to increase as the Raman intensity ratios between the 2D‐band (at 2700 cm^?1) and D‐band (at 1350 cm^?1) decreased, indicating the formation of a‐C. The MG/a‐C all‐sp² phase of carbon hybrid films exhibited an increase in current density under 5 mW/cm² of AM1.5G solar simulated irradiation as the RF bias increased because of Ar⁺‐induced amorphization of the graphene. Copyright © 2016 John Wiley & Sons, Ltd.     

Catalytic effect of iron wires on the syntheses of ammonia and hydrazine in a radio-frequency discharge

The catalytic effect of iron wires on plasma syntheses of ammonia and hydrazine has been studied in the nitrogen-hydrogen plasma prepared using rf discharge at a pressure of 650 Pa (5 Torr). The product was mainly ammonia including a small amount of hydrazine. When iron wires were placed in the plasma downstream of the gas flow, the yields of both products increased, about two times in ammonia and two orders of magnitude in hydrazine. The yields increased with increasing number of wires (the surface area of the catalyst). The dissociative adsorption of nitrogen molecules and/or molecular ions on the iron surface and the formation of NH_x by the reaction with hydrogen in the plasma followed by the formation of NH₃ or N₂H₄ are considered as a reaction scheme. This is supported by the identification of NH₃ with XPS of the surface of iron wires.Partly presented at the 10th International Symposium on Plasma Chemistry, August 4–9, 1991, Bochum, Germany.     

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.     

Amorphous silicon carbonitride thin‐film coatings produced by remote nitrogen microwave plasma chemical vapour deposition using organosilicon precursor

Amorphous silicon carbonitride (a‐SiCN) films were produced by remote nitrogen plasma chemical vapour deposition (RP‐CVD) from bis(dimethylamino)methylsilane precursor. The effect of substrate temperature (T _S) on the kinetics of RP‐CVD, chemical structure, surface morphology and some properties of the resulting films is reported. The T _S dependence of film growth rate implies that RP‐CVD is an adsorption‐controlled process. Fourier transform infrared spectroscopic examination revealed that an increase in T _S from 30 to 400°C involves the elimination of organic moieties from the film and the formation of Si─C and Si─N network structure. The films were characterized in terms of their surface roughness and basic physical and optical properties, such as density and refractive index, respectively. Reasonably good relationships between the structural parameters represented by relative integrated intensity of infrared absorption bands from the Si─C and Si─N bonds (controlled by T _S) and the film properties are determined. Due to their small surface roughness, high density and high refractive index, the a‐SiCN films produced at T _S ≥ 350°C would seem to be useful protective coatings for metals and optical devices.     

Attachment and ionization in a self-consistent treatment of the electron kinetics of a collision-dominated rf plasma

This paper deals with the self-consistent determination of the rf field amplitude for sustaining the steady-state collision-dominated weakley ionized plasmas in the bulk of the rf discharge and of the time-resolved behavior of the isotropic part of the distribution function as well as of relevant macroscopic quantities in plasmas whose particle loss is dominantly determined by electron attachment. The strict timeresolved treatment is based on the nonstationary Boltzmann equation of the electrons and its numerical solution including, apart from electron number conservative collision processes, the electron attachment and ionization. The investigations are related to an rf plasma in a model gas and in SF₆ and are performed for reduced rf field frequencies around 10 MHz Torr^–1 which are of particular interest from the point of application of rf discharges for plasma processing. The numerical results show that a large field amplitude of around 160 V cm^–1 Torr^–1 is necessary to maintain the discharge and that the isotropic distribution, the relevant collision frequencies for attachment and ionization, and the electron density undergo a large modulation during a period of the rf field.     

A zirconium modified Co/SiO2 Fischer-Tropsch catalyst prepared by dielectric-barrier discharge plasma

Co/SiO₂ and zirconium promoted Co/Zr/SiO₂ catalysts were prepared using dielectric-barrier discharge (DBD) plasma instead of the conventional thermal calcination method. Fischer-Tropsch Synthesis (FTS) performances of the catalyst were evaluated in a fixed bed reactor. The results indicated that the catalyst treated by DBD plasma shows the higher FTS activity and yield of heavy hydrocarbons as compared with that treated by the conventional thermal calcination method. Increase in CO conversion was unnoticeable on the Co/SiO₂ catalyst, but significant on the Co/Zr/SiO₂ catalyst, both prepared by DBD plasma. On the other hand, heavy hydrocarbon selectivity and chain growth probability (α value) were enhanced on all the catalysts prepared by the DBD plasma. In order to study the effect of the DBD plasma treatment on the FTS performance, the catalysts were characterized by N₂-physisorption, H₂-temperature programed reduction (H₂-TPR), H₂-temperature-programmed desorption (H₂-TPD) and oxygen titration, transmission electron microscope (TEM) and X-ray diffraction (XRD). It was proved that, compared with the traditional calcination method, DBD plasma not only could shorten the precursor decomposition time, but also could achieve better cobalt dispersion, smaller Co₃O₄ cluster size and more uniform cobalt distribution. However, cobalt reducibility was hindered to some extent in the Co/SiO₂ catalyst prepared by DBD plasma, while the zirconium additive prevented significantly the decrease in cobalt reducibility and increased cobalt dispersion as well as the FTS performance.     

Surface modification of Kapton film by plasma treatments

Kapton films were treated with seven plasmas: Ar-, N₂-, O₂-, CO-, CO₂-, NO-, and NO₂- plasmas. Surface properties and chemical composition of the plasma-treated Kapton films were investigated from the contact angle measurement, and the IR and XPS spectra. The plasmas, especially NO- and NO₂-plasma, made the Kapton film surface hydrophilic. The XPS and IR spectra showed that the plasma led to the modification of the imide groups in the Kapton film to secondary amide and carboxylate groups.     

Preparation of films from aluminum acetylacetonate by plasma sputtering

Aluminum acetylacetonate has been reported as a precursor for the deposition of alumina films using different approaches. In this work, alumina‐containing films were prepared by plasma sputtering this compound, spread directly on the powered lowermost electrode of a reactor, while grounding the substrates mounted on the topmost electrode. Radiofrequency power (13.56 MHz) was used to excite the plasma from argon atmosphere at a working pressure of 11 Pa. The effect of the plasma excitation power on the properties of the resulting films was studied. Film thickness and hardness were measured by profilometry and nanoindentation, respectively. The molecular structure and chemical composition of the layers were analyzed by Fourier transform infrared spectroscopy and energy dispersive spectroscopy. Surface micrographs, obtained by scanning electron microscopy, allowed the determination of the sample morphology. Grazing incidence X‐ray diffraction was employed to determine the structure of the films. Amorphous organic layers were deposited with thicknesses of up to 7 µm and hardness of around 1.0 GPa. The films were composed by aluminum, carbon, oxygen and hydrogen, their proportions being strongly dependent on the power used to excite the plasma. A uniform surface was obtained for low‐power depositions, but particulates and cracks appeared in the high‐power prepared materials. The presence of different proportions of aluminum oxide in the coatings is ascribed to the different activations promoted in the metalorganic molecule once in the plasma phase. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of CF4 plasma chemistry by power modulation

The dominant chemical reaction kinetics occurring in the plasma environment are studied by small periodic power modulation and analyzed using transfer functions. A CF₄/Ar rf plasma at 500 mTorr was chosen to validate this experimental methodology because the kinetics of the CF, system have been well studied previously.(1) The experimental results demonstrated that the modulation technique can determine dominant reactions in the plasma. The experimental results also confirmed the importance of surface recombination reactions and provided quantitative total sticking coefficients for F, CF₂ and CF: _F=0.02, _CF2=0.05, and CF0.20. The results also indicated that an activated intermediate may be a precursor to the formation of both CF₂ and CF from CF₄. Energetic considerations and excited-.state lifetime calculations suggest that this activated intermediate may be an internally excited CF₃* radical.