Properties of thin poly(tetrafluoroethylene) films deposited on solid substrates by electron beam polymerization from vapor phase

The deposition of thin poly(tetrafruoroethylene) films on silicon substrates via the polymerization of tetrafluoroethylene from the vapor phase by means of an electron beam with an electron energy of 20–40 eV and the current density varied in the range 1–10⁴ μA/cm² has been studied. It has been shown that a variation in the current density during deposition allows one to widely vary the properties of the films being formed, in particular, their heat resistance. The crosslinked poly(tetrafluoroethylene) films prepared at a current density of 10² to 10³ μA/cm² demonstrate heat resistance up to 400–450°C. This opens wide prospects for the use of these films as dielectric layers in microelectronics.     

Electrodeposition of nanostructured diamond-like films by oxidation of lithium acetylide

Diamond-like carbon (DLC) films have been deposited by anodic oxidation of 4 M solution of lithium acetylide in dimethylsulfoxide on the surface of stainless steel or nickel electrode at room temperature and moderate anodic current densities (0.2–2.0 mA/cm²) in the range of electrode potentials 0.3–2.5 V (vs. sat. Ag|AgCl reference electrode). Electrodeposited DLC coatings represented complete and optically transparent films of a thickness 50–100 nm having dark island inclusions with a diameter 0.8–5.0 μm. The concentration and average size of these particles increased with the prolongation of deposition time. Micro-Raman spectra obtained by the focusing of laser beam onto these dark inclusions are characterized by a broad peak centered at 1500 cm⁻¹ and weak peak at 1200 cm⁻¹. With a defocused laser beam, there appear two well-distinguished peaks on the integrated Raman spectra – at 1530 and 1130 cm⁻¹. Analysis of Raman spectra with the use of a Breit–Wigner–Fano lineshape and spectrum deconvolution indicates that the electrodeposited films consist of diamond-like nanostructured carbon with a high content (70–80%) of sp³ phase.     

Analysis of polymer films by diffuse reflectance FTIR spectroscopy: Characterization of terminal carboxyl functionalities

Fourier transform infrared (FTIR) spectroscopy in the diffuse reflectance mode was used to study polyethylene terephthalate (PET) films. The polymer film (12 μm, molecular weight M₁ = 18,000) was placed on a finely powdered KBr matrix, used as a reference. Infrared spectra exhibited a new band at 1684 cm^?1, not usually reported in the literature. This band is assigned to the C? O stretching vibration of a terminal acidic function in the presence of internal hydrogen bonds. In the carbonyl region, artifacts created by specular reflection are also discussed. The assignment of the band at 1684 cm^?1 is confirmed by transmission measurements on the overtone of carbonyl group (3335 cm^?1), using polymer films with thicknesses greater than 200 μm and by comparison with polymer of different molecular weight. These acidic functions can be used to monitor the rate of polymerization. It is therefore possible to obtain information on the polymerization rate of PET films, using diffuse reflectance and transmission analysis, directly on the solid. © 1992 John Wiley & Sons, Inc.     

Vacuum lithography—A completely dry lithography using plasma processing

The purpose of this paper is to describe a thoroughly dry lithography using plasma polymerization and plasma etching. The new lithography is named vacuum lithography because all processes are performed at reduced pressures. Resist films were formed in bell-jar-type and argon-flow-type reactors. The controllability of plasma polymerization is discussed with respect to the type of reactor and gas mixture. A pattern was delineated in the resist using an electron beam, and it was developed by plasma etching with a mixture of argon and oxygen. It was found that the quality of the plasma-polymerized resist depends strongly on the polymer structure and on the plasma etching conditions. In this experiment, the recorded values of sensitivity and value of plasma-polymerized methyl methacrylate were 700 µC/cm² and 1, respectively.     

The Formation of Terminal Double Bonds in Vinyl Chloride Polymerization

The determination of double bonds in PVC is achieved with an increased accuracy in comparison with earlier methods by the addition of iodine monochloride (Wijs reaction) to PVC coupled with x-ray fluorescence analysis to determine the iodine content of the polymer. The number of double bonds per unit weight of polymer increases on increasing the polymerization temperature and is proportional to the number of polymer molecules. It is not affected, however, by the presence of the chain transfer agent tetrahydrofuran (THF). At the technically important polymerization temperatures of 30 to 80°C and in the absence of the chain transfer agent, 0.9 double bonds per polymer molecule are found. The number of double bonds per polymer molecule is lowered using the chain transfer agent THF. These results support the theory that the chain transfer to monomer and possibly the termination reaction are coupled with the formation of terminal double bonds. Contributions by internal double bonds formed by dehydrochlorination of the polymer during polymerization are excluded by investigating the Cl^θ content of the water phase in the oxygen-free VC suspension polymerization. No hydrogen chloride is formed. In IR spectra of PVC, the stretching vibration of the double bonds is detected at 1667 cm^?1 by the correlation of the double bond contents and the intensities of the absorption bands. The stretching vibration at 1667 cm^?1is in accordance with those of model compounds with a 1-chloro-2-alkene structure.     

Improved Process for Producing Well-Adhered/Abrasion-Resistant Optical Coatings on an Optical Plastic Substrate

Abstract

A well-adhered and abrasion-resistant coating on a typical optical substrate [polymethylmethacrylate (PMMA)] can be achieved by polymerizing organosilane in a low-temperature polymerization process. The substrate surface can be initially modified with hydrophilic functionalities in a radio-frequency plasma of argon/water vapor mixture in the pressure range 0.05-0.15 mbar to attach hydroxyl functionalities covalently to the substrate surface, which act as “anchorage sites” for polymerizing organosilane. This modified surface is then coated with polyvinyltrimethoxysilane at a power loading in the 20-60 W range and a flow rate of monomer in the 0.7-2.0 cm³-min^?1 range. The polymeric films deposited in this manner on PMMA substrates consistently passed adhesion and abrasive tests even after prolonged storage and thermal cycling in boiling water for at least 10 minutes as exposure to extreme differential thermal expansion conditions. The posttreatment of deposited films with plasmas of inert gases for stress relief had an insignificant effect on peel-off tests and, therefore, it was believed to be not as important as surface modification prior to coatings. The optical properties are essentially not affected by the organosilane coatings irrespective of film thickness, and the coated substrates are virtually transparent above 400 nm.     

Morphology of polythiophene and polyphenyl films produced via surface polymerization by ion-assisted deposition

Conducting polymer films are grown by either mass-selected or non-mass-selected, hyperthermal thiophene ions coincident on a surface with a thermal beam of organic monomers of either alpha-terthiophene (3T) or p-terphenyl (3P) neutrals. Previous experiments verified polymerization of both 3T and 3P by 200 eV C(4)H(4)S(+) during surface polymerization by ion-assisted deposition (SPIAD). A wide variety of structures are observed by scanning electron microscopy to form in the SPIAD polythiophene and polyphenyl films. These structures include microscale islands, lamellar structures, fractal-like growth patterns, and nanoscale crystallites. Some of the deposited films diffract X-rays while others show electron micrographs of crystallites. The variation of these patterns with deposition conditions clearly indicate that ion-induced polymerization mediates film morphology through control of ion energy and ion/neutral ratio. Furthermore, these ion-assisted events mediate important thermal processes such as sublimation.     

Effects of the polarizability and packing density of transparent oxide films on water vapor permeation

The tin oxide and silicon oxide films have been deposited on polycarbonate substrates as gas barrier films, using a thermal evaporation and ion beam assisted deposition process. The oxide films deposited by ion beam assisted deposition show a much lower water vapor transmission rate than those by thermal evaporation. The tin oxide films show a similar water vapor transmission rate to the silicon oxide films in thermal evaporation but a lower water vapor transmission rate in IBAD. These results are related to the fact that the permeation of water vapor with a large dipole moment is affected by the chemistry of oxides and the packing density of the oxide films. The permeation mechanism of water vapor through the oxide films is discussed in terms of the chemical interaction with water vapor and the microstructure of the oxide films. The chemical interaction of water vapor with oxide films has been investigated by the refractive index from ellipsometry and the OH group peak from X-ray photoelectron spectroscopy, and the microstructure of the composite oxide films was characterized using atomic force microscopy and a transmission electron microscope. The activation energy for water vapor permeation through the oxide films has also been measured in relation to the permeation mechanism of water vapor. The diffusivity of water vapor for the tin oxide films has been calculated from the time lag plot, and its implications are discussed.     

Aluminum Antimonide Thin Films: Structure and Properties

Protocols for sputtering stoichiometric aluminum antimonide thin films were developed by calculating aluminum and antimony vapor condensation flux densities. Aluminum and antimony were sputtered separately. The high chemical reactivity of nanosized aluminum and antimony films made it possible to reduce the synthesis temperature considerably (far below the melting point of the compound). The synthesis involved thermal annealing. The reaction between aluminum and antimony films started at 470°С. Optimal AlSb formation parameters comprise annealing at 540°С for at least 10 h. Film synthesis steps were studied by X-ray powder diffraction, optical, electron, and atomic force microscopy. The composition was monitored by energy dispersive X-ray spectra. The films were found to have hole conductivity; the 300-K charge density and charge mobility in the films are 1 × 10¹⁹ cm^–3 and 1 × 10² cm²/(V s), respectively.     

Composite thin films of poly(phenylene oxide)/poly(styrene) and PPO/silver via vapor phase deposition

We report fabrication of thin (100～300 nm) poly(phenylene oxide) (PPO) films and their composites with poly (styrene) (PS) and silver (Ag) nanoparticles using a one‐step electron beam‐assisted vapor phase co‐deposition technique. Surface morphology and the structure of the deposited polymer thin film composites were characterized by FTIR, Raman, X‐ray spectroscopy, and contact angle measurements. As‐deposited PPO films and PPO/Ag composites were of porous nature and contrary to solvent casting techniques were free from nodular growth. In the case of PPO/PS thin film polymer composites, however, film morphology displayed nodular growth of PPO with nodule diameters of about ～200 nm and height of approximately 50 nm. Unique morphological changes on the porous PPO thin film surface were noticed at different Ag filling ratios. Further, the capacitance of PPO/Ag composites (<16 wt%) were measured under radio‐frequency conditions and they were functional up to 100 MHz with an average capacitance density of about 2 nF/cm². The fabricated PPO‐based composite systems are discussed for their potential applications including embedded capacitor technology. Copyright © 2008 John Wiley & Sons, Ltd.     

Application of proton beams to radiation-induced graft polymerization for making amidoxime-type adsorbents

MeV proton beams have been successfully applied as ionizing radiation to induce graft polymerization of acrylonitrile to prepare amidoxime-type adsorbents on polyethylene film substrates. Dependence of degree of grafting (DG) on the pre-irradiation proton energy, beam current and fluence has been examined with use of FTIR absorption measurements and RBS. The DG is observed to be proportional to the deposited energy, and saturate at a fluence of the order of 10¹³ cm⁻² which is more than one order of magnitude smaller than the saturation fluence for molecular hydrogen release from the substrate. It is shown that graft polymerization could be possible deep into a substrate with thickness of hundreds of μm, indicating a possibility to control distribution of functional groups with a spatial variation of the order of a micron.     

Microstructural and Potential Dependence Studies of Urease-Immobilized Gold Nanoparticles–Polypyrrole Composite Film for Urea Detection

Gold nanoparticle–polypyrrole nanocomposite film was electrochemically deposited in a single-step polymerization of pyrrole in the presence of 3-mercaptopropionic acid (MPA)-capped gold nanoparticles (GNPs) and p-toluenesulfonic acid (pTSA) on the surface of an indium tin oxide (ITO)-coated glass plate. The carboxyl functional groups surrounding the GNPs within the polymer matrix were utilized for the immobilization of urease enzyme through carbodiimide coupling reaction for the construction of a Urs/GNP(MPA)–PPy/ITO-glass bioelectrode for urea detection in Tris–HCl buffer. The resulting bioelectrode film was characterized by atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), contact angle measurement, Fourier transform infrared spectroscopy (FTIR), and electrochemical techniques. The potentiometric response of the bioelectrode made of polymer nanocomposite films of two different thicknesses prepared at 100 and 250 mC cm^?2 charge densities, respectively, was studied towards the urea concentration in Tris–HCl buffer (pH 7.4). The thin polymer nanocomposite film-based bioelectrode prepared at 100 mC cm^?2 charge density exhibited a comparatively good potentiometric response than a thick 250 mC cm^?2 charge density film with a linear range of urea detection from 0.01 to 10 mM with a sensitivity of 29.7 mV per decade.     

Thickness and temperature‐dependent study of Co/Si interface

Thin films of cobalt (10, 40, and 100 nm) are deposited on Si substrate by electron beam physical vapor deposition technique. After deposition, 4 pieces from each of the wafers of silicon substrate were cut and annealed at a temperature of 200°C, 300°C, and 400°C for 2 hours each, separately. X‐ray diffraction, atomic force microscopy, and transmission electron microscopy (TEM) are used to study the structural and morphological characteristics of the deposited films. To obtain TEM images, Co films are deposited on Cu grids; so far, no such types of TEM images of Co films are reported. Structural studies confirm nanocrystalline nature with hexagonal close packed structure of the deposited Co film at lower thickness, while at higher thickness, film structure transforms to amorphous with lower surface roughness value. The particle sizes in all the cases are in the range of 3 to 5 nm. Micro‐Raman spectroscopy is also used to study the phase formation and chemical composition as a function of thickness and temperature. The results confirm that the grown films are of good quality and free from any impurity. Studies show the silicide formation at the interface during deposition. The appearance of new band at 1550 cm⁻¹ as a result of annealing indicates the structural transformation from CoSi to CoSi₂, which further enhances at higher annealing temperatures.     

Electrically conductive composite prepared by template polymerization of pyrrole into a complexed polymer

Electrically conducting polymer composite films have been synthesized by the exposure of poly(4-vinylpyridine) complexed with cupric ions to pyrrole and water vapor. To immobilize a stoichiometric amount of the oxidant inside the polymer matrix, the ratio of poly(4-vinylpyridine)/cupric ion = 1.8 was chosen. Polypyrrole was formed in this tailored structure by a template polymerization process. Opaque polymer composite films with electrical conductivity up to 60 (Ω cm)^?1 have been obtained by this method, However, slightly colored transparent composite thin films with a conductivity as high as 50 (Ω cm)^?1 were also produced. The electrically conducting polymer composite films and the metal-polymer complex have been characterized by XPS and IR spectroscopy, elemental analysis, EDX, and scanning electron microscopy. The polymerization process was also followed by use of a quartz crystal microbalance. © 1994 John Wiley & Sons, Inc.     

Electrochemical deposition of copper in polyaniline films — number density and spatial distribution of deposited metal clusters

The electrochemical deposition of copper in reduced polyaniline (PAN) films is studied at different polymer layer thicknesses. A saturation in the number density, n₀, of active sites for metal deposition is found at 0.5 μm PAN thickness (n₀=10⁸ cm⁻²). The surface spatial distribution of the deposited copper crystals is analysed in two cases. It is found that nucleation exclusion zones play an appreciable role in the course of the deposition process in thin PAN films. In contrast, a random distribution and a larger number of deposited crystals are obtained in thicker PAN layers.     

Analysis of Low-k Organosilicon and Low-Density Silica Films Deposited in HMDSO Plasmas

Low-dielectric constant (low-k) films have been prepared by plasma-enhanced chemical vapor deposition from hexamethyldisiloxane (HMDSO). The films are analyzed by ellipsometry, infrared absorption spectroscopy while their electrical properties are deduced from C–V and I–V measurements performed on metal/insulator/silicon structures. First, it is shown that the carbon-containing silicon oxide films deposited in HMDSO and HMDSO/Ar plasmas have a dielectric constant equal to 3.0 ± 0.1 and are thermally stable at 400°C. The leakage current densities measured for an electric field of 1 MV/cm are less than 10^–9 A/cm² and the breakdown fields are in the range of 6–7 MV/cm. Then, a low-density silica film was obtained by exposing a film deposited in an HMDSO plasma to an O₂ plasma. The dielectric constant of this low-density silica film is 3.5 and its breakdown field is close to 6 MV/cm.     

Preparation of ultrathin films of aromatic polymides by vapor deposition polymerization from N-silylated aromatic diamines or aromatic tetracarboxylic dithioanhydride

A novel method for the preparation of ultrathin films of aromatic polyimides was developed through vapor deposition polymerization from combinations of monomer pairs of either N,N′-bis (trimethylsilyl)-substituted aromatic diamines and pyromellitic dianhydride or aromatic diamines and pyromellitic dithioanhydride. Both diamine component and tetracarboxylic dianhydride component were evaporated simultaneously at a stoichiometric molar ratio under vacuum, giving a deposited film on a substrate, which consisted of a polyamic acid derivative formed by the ring-opening polyaddition. The deposit was then converted to polyimide by thermal imidization at a relatively lower temperature, compared with a conventional method using the parent diamine and tetracarboxylic dianhydride. The properties of polyimide ultrathin films such as thermal stability, chemical resistance, and dielectric behavior were almost the same as those of the polyimide films prepared by a conventional method.     

50 keV H+ ion beam irradiation of Al doped ZnO thin films: Studies of radiation stability for device applications

Thin films of Al doped ZnO (Al:ZnO) were deposited on two substrates (Si and glass) at room temperature and 300°C using DC magnetron sputtering. These films were bombarded with 50 keV H⁺ beam at several fluences. The pristine and ion beam irradiated films were analysed by X‐ray diffraction, Raman spectroscopy, scanning electron microscopy, and UV‐Vis spectroscopy. The X‐ray diffraction analysis, Hall measurements, Raman and UV‐Vis spectroscopy confirm that the structural and transport properties of Al:ZnO films do not change substantially with beam irradiation at chosen fluences. However, in comparison to film deposited at room temperature, the Al:ZnO thin film deposited at 300°C shows increased transmittance (from 70% to approximately 90%) with ion beam irradiation at highest fluence. The studies of surface morphology by scanning electron microscopy reveal that the ion irradiation yields smoothening of the films, which also increases with ion fluences. The films deposited at elevated temperature are smoother than those deposited at room temperature. In the paper, we discuss the interaction of 50 keV H⁺ ions with Al:ZnO films in terms of radiation stability in devices.     

Emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. II. Effects of reaction conditions on polymer particle size and number

The size, distribution, and number of PTFE particles formed by radiation-induced emulsifier-free polymerization were measured by electron microscope and automatic particle analyzer (centrifugation method). From the electron micrographs we found that the particles are formed within 5 min. The change in the number of polymer particles (n_p) with reaction time (t) depends on the relative concentration of growing polymer chains to stabilizing species produced by the radiolysis of water and monomer; that is, it was governed by TFE pressure/dose rate ratio and classified into three cases: case I, dn_p/dt = 0 (e.g., at 3 × 10⁴ rad/hr and 20 kg/cm²); case II, dn_p/dt < 0 (e.g., at dose rate below 1.9 × 10⁴ rad/hr and 20 kg/cm²); case III, dn_p/dt > 0 (e.g., at 3 × 10⁴ rad/hr and 2 kg/cm²). The polymer molecular weight above 10⁶ is almost independent of the particle size. The polymerization loci are mainly on the surface of polymer particles dispersed in the aqueous phase in cases I and II except in the initial stage. In case III new particles are formed successively during polymerization. Therefore the polymerization loci are mainly in the aqueous phase. Especially in case I, we concluded that after the generation of particles the propagation proceeds mainly on the surface of polymer particles like the core shell model proposed by Granico and Williams.