Plasma Polymerized Thin Films Research Articles

Determination of the optical and chemical properties of aniline doped plasma polymerized cineole thin films synthesized at various RF powers

Aniline-doped plasma polymerized cineole (PPCin) thin films were produced on glass substrates by plasma polymerization technique under varying Radio Frequency (RF) power levels. PPCin thin films were produced at 30 min deposition time and at 50, 75 and 100 W RF energies. Surface morphologies of pure and aniline-doped PPCin thin films obtained on glass substrates were investigated by AFM. It was found that the average surface roughness of pure PPCin thin films increased from 0.19 to 30.6 nm due to the dopant effect and RF energies. The optical band gap for pure polymer thin film was 3.65 eV, but with the effect of doping, these value was found to be 3.54, 3.29 and 3.93, respectively, with increasing RF energy. The extinction coefficient and refractive indices of PPCin thin films were calculated as between 0.065 and 0.92 and between 1.24 and 1.57 respectively, at the wavelength of 400 nm. Wettability analyzes of PPCin thin films were also determined using the water contact angle (WCA) measurement and all thin films were found to have hydrophilic character.

Plasma polymerized hexamethyldisiloxane thin films for corrosion protection

This study focused on the corrosion protection performance of plasma polymerized HMDSO thin films in two different corrosive medias, 0.3M NaCl and 0.3M H2SO4. The pp-HMDSO thin films were deposited on steel substrates for electrochemical tests using the potentiodynamic polarization technique, they were deposited also on aluminum and silicon substrates to investigate their resistance to corrosion, through the analysis of the degradation of microhardness and morphology, respectively, after immersion of the substrates for one week in the corrosive media. The results showed promising corrosion protection properties of the pp-HMDSO thin films.

Heparin molecularly imprinted polymer thin flm on gold electrode by plasma-induced graft polymerization for label-free biosensor

Heparin, a highly sulfated glycosaminoglycan, is an important biomaterial having biological and therapeutic functionalities such as anticoagulation, regeneration, and protein stabilization. This study addresses a label-free quartz crystal microbalance (QCM) biosensor for heparin detection based on a macromolecularly imprinted polymer (MIP) as an artificial recognition element. We demonstrate the novel strategy for MIP in the form of thin film on a gold (Au) electrode with the plasma-induced graft polymerization (PIP) technique. The procedure of PIP is as follows: (i) Hexamethyldisiloxane plasma-polymerized thin film (PPF) as a pre-coating scaffold of active species for PIP (post-polymerization) is deposited on an Au electrode. (ii) The PPF/Au electrode is soaked in an water solution containing heparin (template), (2-(methacryloxy)-ethyl)trimethylammonium chloride acrylamide (functional monomer), acrylamide, and N,N-methylenebisacrylamide (crosslinker). Double bonds of monomer and crosslinker attacked by residually active species in pre-coating PPF cause radical chain reaction. Consequently, a growing polymer network of 20 nm thickness of PIP-MIP thin film is formed and grafted on the PPF/Au surface. (iii) The PIP-MIP/PPF/Au is washed by sodium chloride solution so as to remove the template. Non-imprinted polymer (NIP) is carried out like the same procedure without a template. The AFM, XPS, and QCM measurements show that the PIP process facilitates macromolecularly surface imprinting of template heparin where the template is easily removed and is rapidly rebound to PIP-MIP without a diffusional barrier. The heparin-PIP-MIP specifically binds to heparin compared with heparin analog chondroitin sulfate C (selective factor: 4.0) and a detectable range of heparin in the presence of CS (0.1 wt%) was 0.001-0.1 wt%. The PIP-NIP does not show selectivity between them. The evaluated binding kinetics are association (ka = 350 ± 100 M−1 s−1), dissociation (kd = (5.0 ± 2.0) × 10−4 s−1), and binding (KD = 1.3 ± 0.6 μM) constants, demonstrating that the PIP-MIP as a synthetic antibody can be applied to analytical chemistry.

Organic bioelectronic plasma polymerised polyterpenol thin films: preservation of properties relevant to biomedical and organic electronic applications following exposure to sterilising doses of gamma radiation

Plasma polymers such as polyterpenol have been investigated for use as biofunctional coatings, insulating/dielectric layers in electronics, and adhesion promoting interlayers in organic electronics. The commercialisation of plasma polymers in these and other biomaterial-related applications is contingent upon their ability to resist degradation in response to sterilising and potentially damaging ionising radiation, such as gamma rays. Hence, this study focusses on the stability of plasma polymerised polyterpenol thin films following exposure to gamma radiation doses ranging from 0 to 100 kGy. Irradiated films were subjected to ellipsometry, current–voltage, dielectric, Fourier transform infrared, and atomic force microscopy characterisation. Stability of polyterpenol was evidenced by the observed lack of radiation-induced variation in its complex refractive index, optical band gap, relative permittivity, dc conductivity, surface chemical functionalities, and surface morphology.

Nanotexturing of plasma-polymer thin films using argon plasma treatment

Plasma-polyaniline films are treated by argon plasma in order to obtain nanostructured surfaces. The polymer deposition and its subsequent treatment are realized in a low pressure microwave reactor. The effects of several operating conditions, i.e., discharge power, argon pressure, processing time and substrate bias on the chemical and morphological structure of the obtained layers are examined. The chemical structure of the polymer is characterized using Fourier Transform Infra-Red spectroscopy whereas the film morphology is determined by Atomic Force Microscopy. The results show that the density and the dimensions of the nanostructures can be finely tuned by the plasma parameters. Low argon flow rate or microwave power, short treatment time and the use of substrate polarization yield high structured surfaces. We show that the formation of the nanodots is mainly ion-dependent according to the ion energy and the ion flux. Concerning the chemical structure of treated films, a moderate destruction of aromatic character and a partial loss of amine groups are observed.

Flexible Polymer/Metal/Polymer and Polymer/Metal/Inorganic Trilayer Transparent Conducting Thin Film Heaters with Highly Hydrophobic Surface.

Polymer/metal/polymer and polymer/metal/inorganic trilayer-structured transparent electrodes with fluorocarbon plasma polymer thin film heaters have been proposed. The polymer/metal/polymer and polymer/metal/inorganic transparent conducting thin films fabricated on a large-area flexible polymer substrate using a continuous roll-to-roll sputtering process show excellent electrical properties and visible-light transmittance. They also exhibit water-repelling surfaces to prevent wetting and to remove contamination. In addition, the adoption of a fluorocarbon/metal/fluorocarbon film permits an outer bending radius as small as 3 mm. These films have a sheet resistance of less than 5 Ω sq-1, sufficient to drive light-emitting diode circuits. The thin film heater with the fluorocarbon/Ag/SiNx structure exhibits excellent heating characteristics, with a temperature reaching 180 °C under the driving voltage of 13 V. Therefore, the proposed polymer/metal/polymer and polymer/metal/inorganic transparent conducting electrodes using polymer thin films can be applied in flexible and rollable displays as well as automobile window heaters and other devices.

Retention of Antibacterial Activity in Geranium Plasma Polymer Thin Films.

Bacterial colonisation of biomedical devices demands novel antibacterial coatings. Plasma-enabled treatment is an established technique for selective modification of physicochemical characteristics of the surface and deposition of polymer thin films. We investigated the retention of inherent antibacterial activity in geranium based plasma polymer thin films. Attachment and biofilm formation by Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli was significantly reduced on the surfaces of samples fabricated at 10 W radio frequency (RF) power, compared to that of control or films fabricated at higher input power. This was attributed to lower contact angle and retention of original chemical functionality in the polymer films fabricated under low input power conditions. The topography of all surfaces was uniform and smooth, with surface roughness of 0.18 and 0.69 nm for films fabricated at 10 W and 100 W, respectively. Hardness and elastic modules of films increased with input power. Independent of input power, films were optically transparent within the visible wavelength range, with the main absorption at ~290 nm and optical band gap of ~3.6 eV. These results suggest that geranium extract-derived polymers may potentially be used as antibacterial coatings for contact lenses.

Inelastic deformation of plasma polymerised thin films facilitated by transient dense plasma focus irradiation

The high degree of crosslinking present in plasma polymerised thin films, coupled with their high molecular weight, imbues these films with properties similar to those of thermosetting polymers. For instance, such films tend to be relatively hard, insoluble, and to date have not exhibited plasticity when subjected to elevated temperatures. In this paper it is demonstrated that plasma polymers can, in fact, undergo plastic deformation in response to the application of extremely short-lived thermal treatment delivered by a dense plasma focus device, as evidenced by the evolution of bubble-like structures from the thin film. This finding suggests new avenues for texturing plasma thin films, and synthesising cavities that may find utility as thermal insulators or domains for material encapsulation.

Structural, morphological, compositional and optical studies of plasma polymerized 2-furaldehyde amorphous thin films

Plasma synthesized 2-furaldehyde (PPFDH) amorphous polymer thin films of varying thicknesses were prepared in optimum conditions by a capacitively coupled parallel plate glow discharge reactor at room temperature. The structure, morphology, composition and optical properties of deposited PPFDH thin films have been investigated using X-Ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM), Energy dispersive X-Ray spectroscopy (EDS), as well as Ultraviolet–visible (UV–vis) absorption spectroscopy. XRD results confirmed the amorphous nature of the films. The smooth and uniform nature of the PPFDH thin films were observed by SEM images. FTIR analyses of monomer FDH and PPFDH thin films show that structural rearrangement has occurred due to the synthesis process taking place in the chemical structure. IR stretching bands obtained from DFT calculations of the optimized structures of monomer and polymer of 2-furaldehyde are in good agreement with the experimental results. UV–vis absorption spectra in transmittance as well as reflectance mode was utilized to compute absorption coefficient, allowed direct and indirect transition energy gaps, band edge sharpness, Urbach energy, steepness parameter, extinction coefficient, and dispersion and oscillator energy. The oscillator strength, moments of optical spectra, refractive index at infinite wavelength, high frequency dielectric constant, average oscilator strength, complex refractive index, dissipation factor, optical conductivity and skin depth were also determined by using measured UV–vis transmittance and reflectance spectra.

In situ monitoring of the effect of ionic strength and pH on plasma polymer thin films

The effect of ionic strength and pH on the structure of hydrated plasma polymerized films of allylamine (ppAAm) and acrylic acid (ppAAc) has been analyzed in situ using quartz crystal microbalance with dissipation techniques, electrochemical impedance spectroscopy, ellipsomtery, and X-ray photoelectron spectroscopy. Both materials showed a salt concentration and pH dependent uptake and release of water and ions. Depending on the type of monomer used, the effects showed reversible or non-reversible behavior. The investigation of the electrochemical properties of the film further revealed a non-homogeneous structure, especially in the case of ppAAc films, with regions of higher and lower cross-linking density. The use of complimentary techniques to characterize the films in situ allowed for a deeper understanding of processes happening inside the plasma polymerized films, which can help to optimize film preparation conditions for selected applications.

Enhancement of electrical conductivity of plasma polymerized fluorene-type thin film under iodine and chlorine dopants

Electrical and optical properties of plasma-polymerized fluorene-type (C13H10) iodine-and chlorine-doped thin films are investigated. Fluorene-type thin films are produced using a mixture of biphenyl (C12H10) and methane (CH4) inside a single capacitively coupled radio frequency plasma system. The dopants are mixed with the plasma directly as vapor during the deposition. The chemical structures of the generated functional compounds, evaluated by a Fourier transform infrared spectroscopy, exhibit a changeable extension conjugation providing high crosslinking and branching. The structural orders of the doped films are analyzed using X-ray diffraction measurements. The film thickness is measured by ellipsometry. Measured difference in thickness due to doping varies from 16nm to 50nm. The structural characterization shows that the doped films are stable and of high quality. The current–voltage characteristics of devices are obtained using two-point probe measurements. As a result of doping, electrical conductivity as high as two orders of magnitude compared to that of the undoped films is measured. In addition, ultraviolet-visible spectroscopy is used to characterize the optical properties. Optical energy band gaps of the doped films as low as 2.4eV are obtained. In conclusion, plasma processing is proven to improve the optical and electrical properties of the doped films.

Influence of the applied power on the barrier performance of silicon‐containing plasma polymer coatings using a hollow cathode‐activated PECVD process

A hollow cathode arc discharge is used for the roll‐to‐roll deposition of silicon‐containing plasma polymer thin films on a polymer substrate. It is found that the fragmentation of the used monomer hexamethyldisiloxane (HMDSO) increases with increasing plasma power. The higher fragmentation was related to a reduced hydrogen content as a result of breaking CH bonds. This allowed for a higher degree of cross‐linking. The latter has a positive effect on the barrier performance of the coatings. A hollow cathode arc discharge with separate anode allowed the deposition of a plasma polymer with a water vapor transmission rate (WVTR) of 0.16 g m−2 day−1 (measured at 38 °C and 90% r.h.) on a PET substrate while maintaining a deposition rate of approximately 450 nm m min−1.

Glow discharge plasma polymerized nanostructured polyaniline thin film optical waveguide

In this work, glow discharge continuous wave plasma polymerization technique was used to deposit nanostructured polyaniline (PANI) thin film by varying input power. The radio frequency (RF) used for plasma polymerization was 13.56 MHz and working pressure was 0.15 mbar. It was found that, changes in the input power can be used to control the properties of the plasma polymerized PANI thin films. Highly cross-linked structure with an increase in chain length was observed from FTIR spectra with input RF power, whereas the film surface morphology was found to be highly uniform, densely packed and smooth from FE-SEM images. The surface roughness of the film was found to increase with RF power. The refractive index and adhesion of the film was found to be increased while the optical band gap and surface energy decreased with input RF power. The plasma polymerized PANI film showed outstanding optical transmission loss properties and proved itself as excellent optical waveguide.

Fabrication and structural characterization of plasma polymerized polypyrrole thin film

Polypyrrole films deposited on glass or silicon substrates by plasma polymerization under different radio frequency power are investigated in this study. Targeting on electrical conduction, lower RF power for deposition is particularly chosen. The microstructures of deposited films were carefully studied by following instruments; Scanning electron microscope for surface morphology; Fourier transform infrared spectroscopy for the molecular vibrational modes; X-ray photoelectron spectroscopy for chemical binding energy; Energy-dispersive X-ray spectroscopy for elemental composition; current-voltage measure for electrical resistance. Results from these material characterizations indicate that a stronger plasma field breaks down the pyrrole rings while creates more nitrogen groups containing N−H, C−N+ or C=N+. However, a certain amount of undamaged pyrrole rings were deposited into films. These intact pyrrole rings make electrical conduction to be possible in films. From the linear regression for the measured current-voltage data, we found that lower RF power (10W) can improve the electrical conduction; however, a noticeable enhancement in conduction is achieved by the doping of iodine such that the film's electrical resistance is reduced to almost half of other un-doped pyrrole films.

Effects of radio frequency power on the microstructures and properties of plasma polymerized polypyrrole thin films

Polypyrrole films, deposited on glass or silicon substrate by plasma polymerization under different radio frequency power and pyrrole flow rates, were investigated in this study. The plasma condition was monitored by optical emission spectrometer and films' properties and functions were assessed by following instruments: surface profiler for the average thickness and deposition rate; Fourier transform infrared spectroscopy for the microstructural vibration modes; optical spectrometer for transmittance, reflectance and absorbance and contact angle for wettability. Some discoveries were found from these material characterizations. A higher power results in faster deposition rates and thicker films. All deposited films are transparent and made of fragmented pyrrole such as CN, CN, CC and NH whereas for the main part of pyrrole CCC, NCC bonds are relatively weak, which implies most carbon rings are fractured by the plasma. After material characterizations, a set of optimal process parameters, i.e. power and flow rate were chosen to deposit the pyrrole film as a diffusion barrier for chemical release. The chemical, dexamethasone 21-phosphate disodium salt, sandwiched between polypyrrole and substrate was immersed in de-ionized water over time. The concentration of released DPS in water via deposited film was found to increase with time but saturates after 48 h.

Microstructural, wetting, and dielectric properties of plasma polymerized polypyrrole thin films

ABSTRACTPolypyrrole (PPy) thin films were synthesized by plasma polymerization technique and investigated the influence of discharge power on microstructural, optical, surface wettability, and dielectric properties of grown films. As deposited PPy films were characterized by X‐ray diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR), Atomic force microscopy, UV‐VIS spectroscopy and dielectric spectroscopy. The broad XRD peak present at 2θ = 23.5° revealed the amorphous nature of grown PPy films. The FTIR spectra displayed characteristic peaks in the wavenumbers regions 3300–3400 cm−1 and 1635–1700 cm−1 and respective peaks intensities decreased slightly as a function of discharge powers. Significant modifications in surface morphology of the films were observed as a function of discharge powers and PPy films synthesized at higher discharge power of 50 W demonstrated characteristic surface morphology composed of characteristic vertical cone shaped clusters provided with rms roughness of 3.42 nm. The UV‐VIS absorption spectra evidenced that the optical density values varied as a function of discharge power. The evaluated band gap energies decreased with an increase of discharge power and found to be 2.53 eV for PPy films prepared at higher discharge power of 50 W. The surface wettability studies evidenced that as prepared PPy films were found to be hydrophilic in nature. The dielectric measurements were carried out for “ITO/polymer/ITO” structures in the frequency range 10 mHz to 100 kHz. As evidenced from dielectric spectroscopic measurements, PPy films synthesized at 50 W were demonstrated conductivity value of 6.0 × 10−12 S/m. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43982.

Influence of Plasma Polymerized Dielectric Buffer Layer and Gold Film on the Excitation of Long-Range Surface Plasmon Resonance

Recently, long-range surface plasmon resonance (LRSPR) sensor has attracted a great deal of attention as a potentially non-destructive and label-free technique for cellular studies in real time. Thus, much effort has been placed on the fabrication and optimization of multilayered structure required for the excitation of LRSPR. In this work, a detailed study about the influence of both plasma polymerized dielectric buffer layer (DBL) and thin gold film on the excitation of LRSPR was performed. The DBLs of different thicknesses were deposited directly onto SF11 glass slides by radio frequency plasma polymerization (pp) of perfluorooctyl ethylene (PFOE). Thereafter, Au films of different thicknesses were thermally evaporated onto the ppPFOE layers. Atomic force microscopy (AFM) results suggest that the resulting SF11/ppPFOE/Au structure has a smooth surface regardless of Au film’s thickness. LRSPR measurements indicate that the excitation of LRSPR relies not only on the thickness of the ppPFOE buffer layer, but also on the thickness and optical property of thin Au film. Theoretical simulation based on Fresnel’s equation allows for the determination of both the thickness and optical constant of each layer supporting the LRSPR, and also enables us to predict the optimum combination of ppPFOE and Au film in a LRSPR sensor. The performance of various LRSPR sensors to monitor the bulk refractive index variation has also been investigated.

Response of Plasma-Polymerized Hexamethyldisiloxane Films to Aqueous Environments.

Thin plasma polymer films were deposited in hexamethyldisiloxane (HMDSO) and HMDSO/O2 low-pressure discharges and their chemical structures analyzed using infrared (IR) spectroscopy and neutron reflectometry (NR). The (plasma-polymerized) ppHMDSO film exhibits hydrophobic, poly(dimethylsiloxane)-like properties, while the retention of carbon groups is reduced by O2 addition, yielding a more inorganic, hydrophilic ppSiOx film. Both films show a minor (vertical) density gradient perpendicular to the substrate, where the exposed film surface seems to be more oxidized, indicating oxidative aging reactions upon contact with air. The hydration and water uptake abilities of the films in aqueous environments were investigated in humid environments using ellipsometry, NR in D2O, and multiple transmission-reflection IR measurements after equilibration of the films in water.

Thin films growth by PIIID technique from hexamethyldisilazane/argon mixture

Abstract Plasma polymer thin films are pinhole-free and have also a high cross-linked structure. These kinds of films are insoluble in mild acids and bases and present good adhesion on different materials. These features make the films relevant for industrial applications and are used in different fields such as electronics, mechanics, biomedics, electrics, protective coatings and others. The plasma polymer hexamethyldisilazane/argon films (ppHMDSN/Ar) were deposited on substrates which were placed between two stainless steel parallel plate electrodes fed by a radio-frequency source operated at 13.56 MHz and 50 W at a total pressure (HMDSN and argon) of 80 mTorr. The negative bias of 10 kV and 10 Hz pulse were used for ion implantation. The structural characterization of the films was done by FTIR spectroscopy. The contact angle for water was of approximately 98° and the surface energy of 30 mJ/m2 which represents a hydrophobic surface, measured by goniometric method. The refractive index of these materials presents values from 1.56 to 1.64 measured by ultraviolet–visible technique. The thickness of the samples was measured by profilometry and showed values from 96 to 210 nm for different deposition conditions resulting in deposition rates from 4.8 to 10.5 nm/min. Hardness values ranging from 0.9 to 2.6 GPa were found for the films measured by nanoindentation technique.

Electrical conduction mechanism in plasma polymerized 2‐(diethylamino)ethyl methacrylate thin films

Thin films of different thicknesses were prepared through glow discharge of 2‐(diethylamino)ethyl methacrylate (DEAEMA) using a capacitively coupled reactor. Current density–voltage (J–V) characteristics for plasma polymerized (PP) DEAEMA thin films of thicknesses 100, 200, 250, and 300 nm in aluminum/PPDEAEMA/aluminum sandwich configuration were studied over the temperature range from 298 to 423 K. J–V curves reveal that in the low‐voltage region, the conduction current obeys Ohm's law while in the high‐voltage region the behavior attributed to be space charge‐limited conduction in PPDEAEMA thin films. The carrier mobility was calculated to be about 6.80 × 10−19 to 2.38 × 10−18 m−2 V−1s−1 for various thicknesses. The free carrier density was found to be about 1.78 × 1023 to 2.04 × 1023 m−3, and the trap density was found to be about 6.93 × 1023 to 15.9 × 1023 m−3 for different thicknesses. The activation energies were estimated to be about 0.005–0.016 eV for 2 and 30 V of PPDEAEMA thin films of different thicknesses. The low‐activation energies indicate that the thermally activated hopping conduction is operative in PPDEAEMA thin films. POLYM. ENG. SCI., 55:2729–2734, 2015. © 2015 Society of Plastics Engineers