Plasma Polymerized Fluorocarbon Films Research Articles

Thermal reflow of plasma-polymerized fluorocarbon for nanochannels and particle encapsulation

Thermal reflow is an important property for thermoplastic polymers, which has been studied extensively especially for photoresists and electron beam resists in semiconductor industries. While the surface smoothening effect is beneficial to reduce the roughness of micro- and nanostructures, the drastic morphology change has been tested to be efficient to fabricate optical devices like microlens arrays. Plasma-polymerized fluorocarbon (PPFC) is a feasible polymer material, which can be achieved conveniently with standard plasma etching systems, however, there have been limited studies regarding its properties and applications apart from its usage as a passivation layer during reactive ion etching. In this study, the thermal reflow behavior of PPFC on various substrates will be presented, including planar surfaces, gratings and trenches. Importantly, the formation of buried micro- and nanochannels has been demonstrated, when PPFC is heated above its glass transition temperature on trench structures. This encapsulation dynamics is analyzed with regard to various parameters like temperature and duration of thermal treatment, trench widths and initial thickness of PPFC film. As a proof of concept, silicon nanorods have been encapsulated in the microchannels by the reflowed PPFC. The results have demonstrated strong potentials of PPFC for applications like micro- and nanofluidics, microcontainers and drug delivery. Because of its good chemical stability and biocompatibility, PPFC can also be expected to be used for various biological devices like brain-machine interfaces, neural probes, epidermal devices and biological implants.

Nanostructured Plasma Polymerized Fluorocarbon Films for Drop Coating Deposition Raman Spectroscopy (DCDRS) of Liposomes.

Raman spectroscopy is one of the most used biodetection techniques. However, its usability is hampered in the case of low concentrated substances because of the weak intensity of the Raman signal. To overcome this limitation, the use of drop coating deposition Raman spectroscopy (DCDRS), in which the liquid samples are allowed to dry into well-defined patterns where the non-volatile solutes are highly concentrated, is appropriate. This significantly improves the Raman sensitivity when compared to the conventional Raman signal from solution/suspension. As DCDRS performance strongly depends on the wetting properties of substrates, we demonstrate here that the smooth hydrophobic plasma polymerized fluorocarbon films prepared by magnetron sputtering (contact angle 108°) are well-suited for the DCDRS detection of liposomes. Furthermore, it was proved that even better improvement of the Raman signal might be achieved if the plasma polymer surfaces are roughened. In this case, 100% higher intensities of Raman signal are observed in comparison with smooth fluorocarbon films. As it is shown, this effect, which has no influence on the profile of Raman spectra, is connected with the increased hydrophobicity of nanostructured fluorocarbon films. This results in the formation of dried liposomal deposits with smaller diameters and higher preconcentration of liposomes.

Deposition of fluorocarbon film with 1,1,1,2-tetrafluoroethane pulsed plasma polymerization

The fluorocarbon films were synthesized by radio frequency pulsed 1, 1, 1, 2-tetrafluoroethane plasma polymerization using various duty cycles. The deposition rates and water contact angles were examined for radio frequency pulsed plasma polymerized fluorocarbon films. The film surface properties were also determined by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. For varying duty cycle from 100% to 10% in pulsed plasma process, the plasma polymerized film drastically changed the surface property. Specifically, it has been observed that modulated plasmas with the proper duty cycle of 10% lead to the formation of the super-hydrophobic film by static water contact angle value of 150°. The surface properties of fluorocarbon films were determined as the Cassie state. In the transmittance, UV–VIS transmission spectra showed that these radio frequency pulsed plasma polymerized coatings were transparent in visible light region. By adjusting duty cycles in relation to radio frequency pulsed plasma polymerization, the hydrophobicity of the resulting thin fluorocarbon films could be tuned.

Simple Fabrication of Antireflective Silicon Subwavelength Structure with Self-Cleaning Properties

A subwavelength structure (SWS) was formed via a simple chemical wet etching using a gold (Au) catalyst. Single nano-sized Au particles were fabricated by metallic self-aggregation. The deposition and thermal annealing of the thin metallic film were carried out. Thermal annealing of a thin metallic film enables the creation of metal nano particles by isolating them from each other by means of the self-aggregation of the metal. After annealing, the samples were soaked in an aqueous etching solution of hydrofluoric acid and hydrogen peroxide. When silicon (Si) was etched for 2 minutes using the Au nano particles, the reflectance was decreased almost 0% over the entire wavelength range from 300 to 1300 nm due to its deep and steeply double tapered structure. When given varying incident angle degrees from 30 degrees to 60 degrees, the reflectance was also maintained at less than 3%. Following this, the etched silicon was treated with a plasma-polymerized fluorocarbon (PPFC) film of about 5 nm using an ICP reactor for surface modification. The result of this surface treatment, the contact angle increased significantly from 27.5 degrees to 139.3 degrees. The surface modification was successful and maintained almost 0% reflectance because of the thin film deposition.

Performance enhancement in organic photovoltaic devices using plasma-polymerized fluorocarbon-modified Ag nanoparticles

In this work, Ag nanoparticles were modified by an ultra-thin plasma-polymerized fluorocarbon film (CF X) to form a composite CF X-modified Ag nanoparticles/indium tin oxide (ITO) anode for application in organic photovoltaic (OPV) devices. A CF X-modified Ag nanoparticles/ITO anode exhibited a superior surface work function of 5.4 eV suited for application in OPV devices. The performance of zinc phthalocyanine:fullerene-based OPV devices showed a significant improvement when the structural identical cells are made with the CF X-modified Ag nanoparticles/ITO. This work yielded a promising power conversion efficiency of 3.5 ± 0.1%, notably higher than that with a bare ITO anode (2.7 ± 0.1%).

High performance optoelectronic device based on semitransparent organic photovoltaic cell integrated with organic light-emitting diode

A high performance organic optoelectronic device that integrates a front semitransparent organic photovoltaic (OPV) cell and a microcavity organic light-emitting diode (MOLED) connected with a 0.3-nm-thick plasma-polymerized fluorocarbon film (CF X )-modified ultra-thin silver interlayer (Ag/CF X ) has been reported. Through proper selection of the active materials, and optimal design of the device structure, the semitransparent OPV cell in the integrated device achieves power conversion efficiency of 88% of the discrete control OPV device. Here we show that the integrated device possesses a high power conversion efficiency of 3.30% measured under air mass 1.5 global irradiation and a high luminous efficiency of 11.5 cd/A operated at 4.5 V. The performance of devices holds great potential for application in organic sensors possessing both high power conversion efficiency and high luminous efficiency.

Deposition of nanostructured fluorocarbon plasma polymer films by RF magnetron sputtering of polytetrafluoroethylene

The RF magnetron sputtering of polytetrafluoroethylene target is studied with the aim to find out conditions leading to the deposition of super-hydrophobic thin films. It is shown that such coatings can be prepared at elevated pressures and a longer distance between the sputtered target and the substrate. This is explained by an increase in the density of longer C xF y molecules that reach the substrate and a lower flux of ions and CF 2 radicals on the surface of growing film under such deposition conditions, as observed by optical emission spectroscopy and mass spectrometry. Such changes in plasma composition result in a deposition of rough films having F/ C ratio close to 2 as observed by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. These findings clearly distinguish our results from the previous investigations of polytetrafluoroethylene sputtering performed at shorter distances from the target, where either low F/ C ratio or low roughness of the deposited films did not allow reaching super-hydrophobic character of the coatings.

Control of the Electrical and Optical Properties of Plasma Polymerized Fluorocarbon Films

not Available.

Enhanced electrical properties of pentacene-based organic thin-film transistors by modifying the gate insulator surface

A reliable surface treatment for the pentacene/gate dielectric interface was developed to enhance the electrical transport properties of organic thin-film transistors (OTFTs). Plasma-polymerized fluorocarbon (CFx) film was deposited onto the SiO 2 gate dielectric prior to pentacene deposition, resulting in a dramatic increase of the field-effect mobility from 0.015 cm 2/(V s) to 0.22 cm 2/(V s), and a threshold voltage reduction from −14.0 V to −9.9 V. The observed carrier mobility increase by a factor of 10 in the resulting OTFTs is associated with various growth behaviors of polycrystalline pentacene thin films on different substrates, where a pronounced morphological change occurs in the first few molecular layers but the similar morphologies in the upper layers. The accompanying threshold voltage variation suggests that hole accumulation in the conduction channel-induced weak charge transfer between pentacene and CFx.

Growth of Fluorocarbon Films by Low-Pressure Dielectric Barrier Discharge

Plasma polymerized fluorocarbon (FC) films have been deposited on silicon substrates from dielectric barrier discharge (DBD) plasma of C4F8 at room temperature under a pressure of 25∼125 Pa. The effects of the discharge pressure and frequency of power supply on the films have been systematically investigated. FC films with a less cross linked structure may be formed at a relatively high pressure. Increase in the frequency of power supply leads to a significant increase in the deposition rate. Static contact angle measurements show that deposited FC films have a stable, hydrophobic surface property. All deposited films show smooth surfaces with an atomic surface roughness. The relationship between plasma parameters and the properties of the deposited FC films are discussed.

Comparing the growth of PVD silver nanoparticles on ultra thin fluorocarbon plasmapolymer films and self-assembled fluoroalkyl silane monolayers

Adsorbed silver nanoparticles were prepared by means of electron beam evaporation ofsilver on ultra thin Si-supported heptadecafluoro-1-decene plasma polymer films andself-assembled heptadecafluorodecyl-trimethoxysilane monolayers. The morphology of thesilver nanoparticles, characterized by their size, size distribution, shape and interparticleseparation, was observed to depend on the type, chemical composition and surface energyof the sub-layer as well as the amount of silver deposited. Field emission-scanning electronmicroscopy was used to study the change in the morphology of the silver nanoparticles as afunction of the preparation parameters. The silver nanoparticles on the ultra thin plasmapolymer films demonstrated a much smaller and narrower size distribution due to thecross-linking within the film, which more effectively hinders the penetration of silverthrough the film in comparison to the self-assembled monolayers. Moreover, the opticalproperties of the resulting silver nanoparticles on the ultra thin fluorocarbon plasmapolymers and their correlation to size and size distribution were investigatedby spectroscopic ellipsometry in the wavelength range between 300 and 800 nm.

Influence of Fluorocarbon Plasma Polymer Films on the Growth of Primary Human Fibroblasts

AbstractSummary: Pulsed radio‐frequency plasmas containing a mixture of fluorocarbon, argon, and water vapor have been applied to multichamber slides in order to study the biocompatibility in accordance with ISO 10993‐5. According to this standard, the biocompatibility and/or in vitro toxicity of new developed materials is tested with fibroblast cultures. This study deals with the examination of adhesion, proliferation, and cell death of human primary fibroblasts on surfaces gradually coated with fluorocarbon polymer. Besides surface energy, chemical effects as there are chemical functions and the chemical composition of the surface, play an important role in the interaction of human fibroblasts with surfaces. Thus, the data obtained from cell cultivation are correlated to the surface properties as obtained from contact angle measurements and X‐ray photoelectron spectroscopy.Microscope images reveal the influence of fluorocarbon polymer coatings: The untreated reference surface and the surface treated in a pulsed discharge at 33% duty cycle influence the cell proliferation differently.magnified imageMicroscope images reveal the influence of fluorocarbon polymer coatings: The untreated reference surface and the surface treated in a pulsed discharge at 33% duty cycle influence the cell proliferation differently.

Sorption and desorption behaviors of hexadecane vapors in plasma deposited fluorocarbon films using a quartz crystal microbalance

Fluorocarbon films can provide barrier properties such as hydrophobicity and oleophobicity to paper- and cellulose-based materials. While qualitative methods such as “oil kit tests” provide information on grease barrier properties, they do not quantify the extent of grease barrier properties. In this study, we report the sorption and desorption behaviors of a grease surrogate (hexadecane) vapor in plasma polymerized fluorocarbon films deposited from pentafluoroethane. Three different film thicknesses (0.5, 0.75, and 1μm) were exposed to varying concentrations of hexadecane vapor and uptake evaluated using a quartz crystal microbalance. The amount of hexadecane sorbed in the fluorocarbon film increased with hexadecane concentration until film saturation occurred, at which point the mass of hexadecane sorbed no longer increased with concentration. While the amount of hexadecane sorbed for a given hexadecane concentration increased with film thickness, the wt % of hexadecane sorbed into the fluorocarbon film was essentially independent of the film thickness reaching ∼0.6% of the maximum hexadecane concentration studied for all film thicknesses. These results indicate that fluorocarbon films have low affinity for hexadecane vapor. Transient sorption and desorption studies were also conducted using hexadecane vapor; both processes followed dual-mode sorption behavior. Diffusivities of hexadecane as determined from sorption and desorption were ∼10−13cm2∕s.

Spectroellipsometric analysis of CHF3 plasma-polymerized fluorocarbon films

Optical and morphological properties of fluorocarbon films (CFx) deposited on Si substrates from CHF3 in a reactive ion etcher were studied by spectroscopic ellipsometry (SE). The study has led for 0.3–1.5μm thick films to a thickness-independent, roughnessless, apparently nongraded two-layer model that requires the Cauchy dispersion and the Gaussian absorption for the film refractive index and extinction coefficient, and to an interface mixture of CFx, Si, and voids. The Si native oxide removal was ascertained from films formed on SiO2-sputtered Si substrate. The sample SE results were further verified by x-ray diffraction, atomic force microscopy, Fourier transform infrared, x-ray photoelectron and Auger electron spectroscopies, and capacitance studies. The film microstructure may thus be considered isotropic and homogeneous resulting from a random addition of CFx fragments including cross-links along the film depth. The films have low-dielectric constant(k≈2.2) quality index of 1.38(615nm) and are noticeably absorbent in UV while exhibiting strong transparency in visible. These films growing at a rate of 0.033μm∕min have 2%–3% thickness nonuniformity. The SE model decision making steps are described and the degree of confidence on the SE results are discussed with the support of literature results and those from and the above studies.

Composite SiO x/fluorocarbon plasma polymer films prepared by r.f. magnetron sputtering of SiO 2 and PTFE

Composite films SiO x /fluorocarbon plasma polymers were prepared by r.f. sputtering from two balanced magnetrons equipped with polytetrafluoroethylene (PTFE) and silica (SiO 2) targets. Argon was used as the working gas. The obtained films were characterised by means of XPS, RBS, FTIR, AFM, TEM, microhardness and static contact angle measurements. The obtained SiO x /fluorocarbon plasma polymer films reveal different wettability (static contact angle of water ranges from 68° to 40°) and hardness (ranges from 720 to 3200 N/mm 2) when the volume fraction ratio (filling factor) of SiO 2 changes from 0.01 to 0.7. The concentration of elements determined by RBS/ERDA varies strongly over this range of filling factors. The heterogeneous structure of the composite films is indicated by TEM at high SiO x contents.

Photoemission and vibrational studies of metal/organic interfaces modified by plasma-polymerized fluorocarbon films

Photoemission and vibrational studies of metal/organic interfaces modified by plasma-polymerized fluorocarbon films

Surface modification of paper and cellulose by plasma-assisted deposition of fluorocarbon films

Plasma polymerized fluorocarbon films have been deposited on paper and regenerated cellulose surfaces to enhance their barrier properties and to achieve hydrophobic surfaces. The primary monomers used for plasma polymerization were pentafluoroethane (CF 3CHF 2) and octafluorocyclobutane (C 4F 8). The equilibrium moisture uptake of films deposited from either precursor was less than 0.14 wt.%. Although water vapor uptake of the fluorocarbon films is low, moisture diffusivity through the films is high; that is, moisture penetrates the films but is not chemically bonded. Quartz crystal microbalance (QCM) studies demonstrate that the absorption of water vapor is a bulk phenomenon in which the moisture penetrates into the film. Transient moisture absorption studies were conducted using the QCM to evaluate the rate of moisture uptake and diffusivity. Although the films allow water vapor diffusion, the films are hydrophobic and are not “wetted” when liquid water contacts these layers. Contact angle studies reveal that a minimum fluorocarbon film thickness of about 70 nm on paper is required to completely cover surface and near-surface fibers, thereby providing the paper with long term hydrophobic character. The films also impart the paper with an improved barrier to lipophilic material.

Fabrication and surface treatment of silicon mold for polymer microarray

We present the results of our development of deep silicon etching process and surface treatment method for 40∼50 μm deep silicon mold. Silicon mold was fabricated with conventional photolithography and deep silicon etching. A ‘modified Bosch process’ was developed for positively tapered sidewall profile that will allow the release of the mold from a polymer substrate after UV embossing without breakage of the silicon mold. Deeply etched silicon shows high etch rate (>1.2 μm/min) and positively tapered sidewall slope (∼85°). In this paper, silicon mold was treated with plasma-polymerized fluorocarbon (PPFC) film using ICP reactor for easier release and better integrity of molded structure. These PPFC films were characterized by deposition rate, surface roughness, and contact angle with various deposition conditions. PPFC film deposited with ICP reactor showed high deposition rate (∼80 nm/min) and smooth roughness (∼1.5 nm). The result of contact angle measurement confirmed that silicon mold treated with PPFC film has strong hydrophobicity ( θ c>108°). Finally, polymer microarray was successfully replicated from silicon mold. To find that the replication has been performed successfully, the released polymer microarray was also examined with SEM and surface profiler.

Plasma polymer films rf sputtered from PTFE under various argon pressures

Fluorocarbon plasma polymer films were prepared by radio-frequency (rf) sputtering of polytetrafluoroethylene (PTFE). Their wettability decreased with the increase in pressure of argon working gas. The films deposited at 70 Pa were found to be superhydrophobic plasma polymers with a static contact angle 146° for water. Sputtered fluorocarbon plasma polymer films were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy. The paper shows that the surface composition and chemical structure of the films vary with altering the argon gas pressure.

Photoemission and vibrational studies of metal/organic interfaces modified by plasma-polymerized fluorocarbon films

While gold and silver have high work functions, they are known to form relatively poor hole injecting contacts with organic semiconductors. We have found that inserting an ultrathin layer of plasma-polymerized fluorocarbon (CF x ) between the metal and organic materials can substantially improve the hole injection. The working mechanism of the CF x interlayer was investigated with ultraviolet and x-ray photoemission spectroscopy and high resolution electron energy loss spectroscopy. The hole injection enhancement was caused by the reduced hole injection barrier, attributed to an interfacial electric field induced by the partial charge transfer from the metal to the CF x layer. Stability of the dipolar interface upon exposure to air was also demonstrated.