[show abstract][hide abstract] ABSTRACT: Surface oxidation of the duplex stainless steel DSS alloy 2205 was studied by X-ray photoelectron spectroscopy (XPS) and SEM imaging. The experiments were performed on the alloy after controlled oxidation with oxygen atoms created in an inductively coupled plasma. Experiments were performed at temperatures from room temperature up to 700 °C. Compositions of the modified oxidized surfaces were obtained from XPS survey scans, and the chemistries of selected elements from higher energy resolution scans of appropriate peaks. The morphologies of the surfaces were obtained using field emission scanning electron microscopy at different magnifications, up to 10,000×. Different Fe/Cr/Mn oxidized layers and different oxide thicknesses were observed and correlated with temperature.
[show abstract][hide abstract] ABSTRACT: For plasma polymerized (PP) thin films, many practical optical, electronic, sensing, and bio-applications are closely related to their surface properties. In particular, the surfaces of many PP films have a strong affinity for oxygen and moisture. Therefore, three different types of monomers which do not contain oxygen were selected to fabricate PP films, in order to understand the mechanisms for surface oxygen absorption. These monomers were a hydrocarbon, benzene (B); ferrocene (FC), containing Fe ions which have a great affinity for oxygen; and octafluorocyclobutane (OFCB), containing the strong electronegative (and thus oxygen repellent) element fluorine. X-Ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FTIR) spectroscopy, and electron spin resonance (ESR) were used to explore the chemical composition and structure of the resulting PP films. XPS depth-profiling was also used to investigate the oxygen content in the bulk of the films by analyzing the film surface after various amounts of argonetching. The initial oxygen content on the surface of the PP-FC films was the largest of the three while PP-OFCB films only contained a trace quantity. PP-B films had an intermediate concentration. Affinity for oxygen for this latter film was determined to be due to residual activated species including free radicals and dangling bond sites on the film surface. Depth profiling disclosed little oxygen a short distance into the PP-B films, indicating that the oxygen was attracted after deposition upon exposure to ambient conditions. Although the PP-B film exhibited a high concentration of free radicals as determined by ESR, the dense and crosslinked bulk structure shielded these active centers in the film by prohibiting oxygen diffusion. For the PP-FC films, although a decrease in the amount of oxygen was observed after etching, a substantial concentration of oxygen exists with the depth, indicating incorporation of oxygen during the initial deposition. Because of the chemical nature of fluorine, the as-deposited PP-OFCB films did not exhibit significant affinity towards oxygen. However, a slightly oxygen enriched film surface was present after argonetching due to changes in the surface chemistry and structure. These results demonstrate that the formation and distribution of oxygen on and within the PP films are strongly dependent upon the chemical composition and structure of the films.
Journal of Materials Chemistry 01/2009; 19(15). · 5.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: The refractive index is a key characteristic of polymer materials in optical applications. For organic polymers, typical refractive indices are in the range of 1.35 to 1.65. Extending the refractive index beyond the limits is of fundamental scientific interest and would enhance the utility of polymers in many applications. Polymeric thin films fabricated by plasma enhanced chemical vapor deposition (PECVD) have been investigated in the fields of electronics and optics and their utility is becoming more widespread in a variety of applications. Outstanding attributes of the PECVD photonic films include a smooth surface, dense crosslinking structure, robustness, environmental resistance, optical transparency in either visible or IR regions, and good adhesion to many optical window and substrate materials. In recent years, our laboratory has fabricated novel polymer optical coatings and films by PECVD. One focus of this research has been to expand the achievable maximum refractive index. This goal has been sought using two approaches including increasing the conjugation and crosslinking of chemical moieties of the bulk film and incorporation of metal ions into the structure. The techniques of XPS, FTIR, HRSEM, and ellipsometry were used to characterize both the optical properties and the chemical structure of plasma polymerized benzene, ferrocene, and metal-phthalocyanine thin films. The structure-property relationship and the effect of PECVD processing conditions are also discussed in this presentation.
[show abstract][hide abstract] ABSTRACT: This communication describes the formation of high index of refraction polymer thin films using a novel plasma polymerization deposition process. A flowing afterglow plasma reactor was modified to enable sublimation of solid samples into the gas phase for subsequent plasma polymerization. Thin films of plasma polymerized ferrocene were deposited on substrates and subsequently characterized. The refractive index as a function of processing conditions was obtained. Relatively high values of n (∼1.73 at 589nm) were obtained. The chemical nature of the polymer thin films was characterized using FTIR and XPS spectroscopy. This work demonstrates that plasma polymerization is an enabling technology for the fabrication of photonic thin films that utilize solid state precursors.
[show abstract][hide abstract] ABSTRACT: Polymer dielectric films fabricated by plasma enhanced chemical vapor deposition (PECVD) have unique properties due to their dense crosslinked bulk structure. These spatially uniform films exhibit good adhesion to a variety of substrates, excellent chemical inertness, high thermal resistance, and are formed from an inexpensive, solvent-free, room temperature process. In this work, we studied the dielectric properties of plasma polymerized (PP) carbon-based polymer thin films prepared from two precursors, benzene and octafluorocyclobutane. Two different monomer feed locations, directly in the plasma zone or in the downstream region (DS) and two different pressures, 80 Pa (high pressure) or 6.7 Pa (low pressure), were used. The chemical structure of the PECVD films was examined by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. The dielectric constant (εr) and dielectric loss (tan δ) of the films were investigated over a range of frequencies up to 1 MHz and the dielectric strength (breakdown voltage) (Fb) was characterized by the current-voltage method. Spectroscopic ellipsometry was performed to determine the film thickness and refractive index. Good dielectric properties were exhibited, as PP-benzene films formed in the high pressure, DS region showed a Fb of 610 V/μm, an εr of 3.07, and a tan δ of 7.0 × 10− 3 at 1 kHz. The PECVD processing pressure has a significant effect on final film structure and the film's physical density has a strong impact on dielectric breakdown strength. Also noted was that the residual oxygen content in the PP-benzene films significantly affected the frequency dependences of the dielectric constant and loss.
Material Research Innovations 08/2006; 10(3):331-lxxxivPublisher: Maney Publishing
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[show abstract][hide abstract] ABSTRACT: Photonic thin films have been grown on a variety of substrates using plasma-enhanced chemical vapor deposition (PECVD) of organic monomers, namely benzene and octafluorocyclobutane (OFCB). Films produced by both homo-polymerization and co-polymerization have been prepared and analyzed. In order to introduce significant contributions from OFCB into co-polymerized films, the OFCB was introduced directly into the plasma zone and the benzene flow was reduced to a low, stable level using a high-accuracy metering valve. The films have been characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and variable-angle spectroscopic ellipsometry (VASE), with an emphasis on XPS. Apart from determining the atomic composition of the films with XPS, it was extremely valuable in determining the chemistry of the films. Studies of the mechanisms of the homo- and co-polymerization reactions have aided in the fabrication of photonic films.
[show abstract][hide abstract] ABSTRACT: We have developed plasma copolymerization techniques to fabricate photonic films with two (or more) monomers, whose composition can be controlled to manipulate the optical properties of the films. Spectroscopic ellipsometry confirmed that by changing monomer feed ratios (benzene and octafluorocyclobutane), films in the nanometer thickness range with refractive indices between those of the homopolymerized films could be fabricated. Spectroscopic analysis of the chemical structure of the copolymerized films using FTIR and XPS confirmed a nonlinear variation of chemical composition as a function of the monomer feed ratios. However, the refractive index of these films changes linearly with the film composition (characterized as the fluorine/carbon ratio). Facile control of optical thickness was demonstrated by fabricating multilayer antireflecting (AR) coatings on substrates of differing refractive indices. Very good agreement between the design and experimental spectra was obtained. This growth process creates a new way to prepare gradient-index (GRIN) films in the nanometer range, with a Δn greater than 0.3 and with well-controlled properties.
Chemistry of Materials - CHEM MATER. 03/2004; 16(7).
[show abstract][hide abstract] ABSTRACT: Fabrication methodologies of thin, optical quality polymer films are important given the current interest in photonics. Plasma enhanced chemical vapor deposition (PECVD) has been previously investigated as a useful technique to polymerize various organic precursors. In the work presented here, we have studied the simultaneous plasma copolymerization of two monomers, benzene and octafluorocyclobutane (OFCB), and explored the structure of the final films using FTIR and XPS in order to tailor the resulting optical properties. There is a complex relationship between the film structures and the input parameters including monomer feed ratio and feed location. In plasma copolymerization, the gas phase initiation of the monomers is strongly dependent upon the bond dissociation energy of their structural moieties. The change of the monomer feed ratio leads to different trends with respect to various CFn(n=1–3) structural units, resulting in differences in the final film structure. Defluorination of the copolymer films was significantly enhanced by the addition of a small amount of benzene. The main fluorine-containing structural unit was the CF moiety for the copolymerized film, which is different from both homopolymerized OFCB and conventional PTFE polymers where the main fluorine-containing structural unit is CF2. Retention of conjugation and aromaticity in the resultant films was also observed.
[show abstract][hide abstract] ABSTRACT: A systematic study has been made on the influence of doped rare-earth metal ions (Er3+ and Nd3+) on the molecular interaction present in thin films fabricated from chitosan-acetic acid solutions (chitosan/HAc). FT-IR spectroscopy (including NIR, MIR and FIR) coupled with X-ray photoelectron spectroscopy (XPS) indicate a weak complexation between the metal ions and amine groups of chitosan. Specifically, the FIR spectra show broad bands near 550, 480 and 250 cm−1 for the doped films suggestive of metal ion-ligand vibrations. XPS indicates multiple chemical states of N with an increased percentage of a higher binding energy state nitrogen caused by a weak interaction with the doped metal ions. Slight differences in microroughness between the doped and undoped films as observed by X-ray reflectometry may also be related to the doping. The NIR and MIR spectra do not show any significant changes for all the doped and undoped films, implying that the basic molecular conformation of chitosan is not changed by the weak complexation.
[show abstract][hide abstract] ABSTRACT: Different polymeric photonic films, including 1/4 wavelength high/low refractive index layer stacks and anti-reflective coatings have been prepared by means of plasma enhanced chemical vapor deposition. All these films show a dense bulk structure and a smooth, pin-hole free surface. By controlling the processing parameters, the films can be prepared in accordance with any optical design allowing for selection of notch (bandgap) locations and depths. The ability to deposit polymer films with any refractive index between 1.35-1.65 by copolymerization techniques and to deposit on a variety of substrates yields an effective tool at fabricating a wide variety of non-conventional polymer photonic elements. Due to the highly crosslinked structure of the polymer, these films possess excellent chemical resistance, environment survivability, and good adhesion with substrates. IR and UV-Vis spectroscopies, ellipsometry, SEM, XPS, and AFM have been applied to explore the relationships between structure and the optical properties of the resultant thin films.
[show abstract][hide abstract] ABSTRACT: A multilayer optical interference film has been developed using plasma-enhanced chemical vapor deposition (PECVD) of different organic precursor materials. A relatively large refractive index contrast for polymers (>0.2) is achieved by sequential plasma polymerization (PP) of octafluorocyclobutane (OFCB) and benzene. Gas-phase molecules of both precursors, excited by an argon plasma in a flowing afterglow reaction chamber, are deposited on a variety of substrates to form dense, pinhole-free, cross-linked polymer films. The PP-OFCB film yields a refractive index of 1.40, whereas PP-benzene exhibits a refractive index of 1.61 at 500 nm. We report here on the chemical (FTIR and XPS), optical (variable angle spectroscopic ellipsometry and UV−Vis spectrometry), and morphological (scanning electron microscopy) characterization of individually polymerized films of each component. These data are used to design a multilayer film with a notch at 1 μm. A ten-bilayer stack (alternating high and low refractive index) was fabricated by sequential deposition of high and low refractive index layers at approximately 1/4λ optical thickness. Optical spectra of the experimental stack exhibit a notch wavelength within several nanometers of the design wavelength indicating good thickness control.
Chemistry of Materials - CHEM MATER. 12/2002; 15(1).
[show abstract][hide abstract] ABSTRACT: Spatially grading the refractive index profile on length scales commensurate with light is the basis for high performance optical filters. A step profile of refractive index can be used to form l/4 and l/2 stacks while a gradient allows for elimination of higher harmonics and ripples associated with interference filters. These types of optical films, stacks and rugates, have been pioneered using inorganic materials, such as SiO2 and TiO2. We report here on progress in the development of similar structures using organic components using plasma enhanced chemical vapor deposition of monomeric precursors. The limitation to date has been the inability to obtain any value of refractive index between those afforded by plasma polymerized benzene (n=1.65) and octafluorocyclobutane (n=1.35). Previous attempts have led to a biased incorporation of benzene resulting in only high refractive index films even with appreciable flow rates of the low index monomer. By adjustment of critical processing parameters including precursor flow rates, plasma power, monomer input environment, and reactor geometry, we have successfully controlled the variation of the refractive indices in the deposited films. Spectroscopy, ellipsometry, atomic force microscopy and scanning electron microscopy have been applied to explore relationships among the processing parameters, the structure and the optical properties of the resulting thin films.
[show abstract][hide abstract] ABSTRACT: The ability to spatially grade the refractive index profile is the basis for photonic band gap structures. The ability to control the refractive index profile in a non-conventional manner, i. e. a sinusoidal profile, expands the design space typically associated with conventional ABAB stack designs. These types of optical films, rugates, have been pioneered using inorganic materials, such as SiO2 and TiO2. The first step in our development of a methodology to fabricate rugate-like structures of polymeric materials using plasma enhanced chemical vapor deposition (PECVD), namely the formation of ABAB stacks, is presented here. Polymer films with low and high refractive indices have been alternatively deposited on different substrates using precursor monomers in the flowing afterglow of a low pressure argon plasma. The refractive index (n) of films made from octafluorocyclobutane is approximately 1.35, while a value of n=1.65 is achieved using benzene. The PECVD films possess a highly cross-linked and dense internal structure with a smooth and pin-hole free surface. Spectroscopy, ellipsometry, atomic force microscopy and scanning electron microscopy have been applied to explore relationships among the processing parameters, the physical structure and the optical properties of the resulting thin films. We also discuss the initial attempts to spatially grade the refractive index profile by simultaneously varying the deposition rate of the two precursors
[show abstract][hide abstract] ABSTRACT: The number of applications employing polymeric optical materials is growing rapidly due to recent advances in telecommunications, display, and laser markets. For a number of these applications, organic dyes (chromophores) are added to the polymer host to add linear or nonlinear optical properties to the system. In homogeneous systems, dye diffusion is not an issue; however in multiple stacks of polymer films with different dye concentrations or in films with a spatially varying dye concentration, diffusion becomes important. We report here on initial studies to control the diffusion of the dye, zinc octabromylporpyhrin (ZnOBP), doped in poly(dimethylsiloxane) films, from diffusing into other layers in multiple stack systems. Plasma enhanced chemical vapor deposition (PECVD) was utilized to deposit thin films (60–240nm) of hexamethyldisiloxane (HMDS) at the interface of two separate polymer layers, one with and one without ZnOBP. The diffusion of the chromophore to the outside surface of the undoped layer was examined with and without the plasma polymerized barrier layer. The thin but highly crosslinked interlayer is found to be an effective barrier to diffusion as measured using X-ray photoelectron spectroscopy to track bromine diffusion.
[show abstract][hide abstract] ABSTRACT: Sulfonated C60, 5,10,15,20-tetra kis 4-[meso-tetra-methyl (4-pyridinyl)] porphyrin (C60(SO3−)n–TMePyP4+) complex films have been prepared by electrostatic self-assembly of each chromophore from solution. When these complex films are formed on a thin film of chitosan polymer, the stacked bilayer films exhibit nearly twice the absorption as those prepared on conventional silanized substrates. X-ray photoelectron spectroscopy measurements disclose a strong interaction between the C60(SO3−)n and TMePyP4+. Atomic force microscopy results of the surface morphology, hardness, and the chemical functionality are used to explain the differences between substrate treatments.
Thin Solid Films 01/2000; 372:85-93. · 1.60 Impact Factor