Ultrathin Plasma Research Articles

Development of Wafer-Type Plasma Monitoring Sensor with Automated Robot Arm Transfer Capability for Two-Dimensional In Situ Processing Plasma Diagnosis.

In this work, we propose our newly developed wafer-type plasma monitoring sensor based on a floating-type double probe method that can be useful for two-dimensional (2D) in situ plasma diagnosis within a semiconductor processing chamber. A key achievement of this work is the first realization of an ultra-thin plasma monitoring sensor with a system thickness of ~1.4 mm, which supports a fully automated robot arm transfer capability for in situ plasma diagnosis. To the best of our knowledge, it is the thinnest accomplishment among all wafer-type plasma monitoring sensors. Our proposed sensor is assembled with two Si wafers and SiO2-based probes; accordingly, it makes it possible to monitor the actual dynamics of processing plasmas under electrostatic chucking (ESC) conditions. Also, it allows for the prevention of chamber contamination issues after continuously exposing the radio frequency (RF) to various processing gases. Using a test-bed chamber, we successfully demonstrated the feasibility and system performance of the proposed sensor, including robot arm transfer capability, vacuum and thermal stress durability, and data integrity and reproducibility. Consequently, compared with the conventional plasma diagnostic tools, we expect that our proposed sensor will be highly beneficial for tool-to-tool matching (TTTM) and/or for studying various plasma-related items by more accurately providing the parameters of processing plasmas, further saving both time and manpower resources required for preventive maintenance (PM) routines as well.

SILVER-COATED CUSTOM COMPONENTS FOR ACETABULAR AND HEMIPELVIS RECONSTRUCTION MITIGATE INFECTION RISK WITHOUT COMPROMISING BONE ONGROWTH

Complex acetabular reconstruction for oncology and bone loss are challenging for surgeons due to their often hostile biological and mechanical environments. Titrating concentrations of silver ions on implants and alternative modes of delivery allow surgeons to exploit anti-infective properties without compromising bone on growth and thus providing a long-term stable fixation. We present a case series of 12 custom acetabular tri-flange and custom hemipelvis reconstructions (Ossis, Christchurch, New Zealand), with an ultrathin plasma coating of silver particles embedded between layers of siloxane (BioGate HyProtect™, Nuremberg, Germany).At the time of reporting no implant has been revised and no patient has required a hospital admission or debridement for a deep surgical site infection. Routine follow up x-rays were reviewed and found 2 cases with loosening, both at their respective anterior fixation. Radiographs of both cases show remodelling at the ilium indicative of stable fixation posteriorly. Both patients remain asymptomatic. 3 patients were readmitted for dislocations, 1 of whom had 5 dislocations within 3 weeks post-operatively and was immobilised in an abduction brace to address a lack of muscle tone and has not had a revision of their components.Utilising navigation with meticulous implant design and construction; augmented with an ultrathin plasma coating of silver particles embedded between layers of siloxane with controlled and long-term generation of silver ion diffusion has led to outstanding outcomes in this series of 12 custom acetabular and hemipelvis reconstructions. No patients were revised for infection and no patients show signs of failure of bone on growth and incorporation. Hip instability remains a problem in these challenging mechanical environments and we continue to reassess our approach to this multifaceted problem.

Enhanced corrosion resistance of epoxy-films on ultra-thin SiOx PECVD film coated laser surface melted Al-alloys

The influence of ultra-thin SiOx plasma deposited films on the corrosion resistance of adhesive films on a laser surface melted 7075 aluminium alloy was investigated by means of complementary techniques in comparison to the just laser surface melted state. Laser surface melting (LSM) was performed using a continuous wave mode at a wavelength of 1064 nm. Ultra-thin plasma polymer films were deposited from a mixture of hexamethyldisilane (HMDSO), oxygen, and argon by means of an audio-frequency glow discharge. The surface morphology and surface chemistry compositions were investigated by employing field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), diffuse reflection infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy. The corrosion resistance of plasma polymer coated LSM Al-7075 alloy was studied using linear sweep voltammetry and electrochemical impedance spectroscopy in a chloride-containing electrolyte. The electrochemical studies showed an improved corrosion resistance for plasma film-coated alloys compared to the just laser surface melted state. To study the corresponding surface adhesive properties, the samples were coated with an epoxy amine adhesive. 90°-peel test under humid conditions confirmed the improvement of interfacial wet-adhesion corrosion tests showed a strong improvement of the delamination resistance of adhesives caused by the ultra-thin interfacial SiOx-films.

Ultrathin Plasma Polymer Passivation of Perovskite Solar Cells for Improved Stability and Reproducibility

AbstractDespite the youthfulness of hybrid halide perovskite solar cells, their efficiencies are currently comparable to commercial silicon and have surpassed quantum‐dots solar cells. Yet, the scalability of these devices is a challenge due to their low reproducibility and stability under environmental conditions. However, the techniques reported to date to tackle such issues recurrently involve the use of solvent methods that would further complicate their transfer to industry. Herein a reliable alternative relaying in the implementation of an ultrathin plasma polymer as a passivation interface between the electron transport layer and the hybrid perovskite layer is presented. Such a nanoengineered interface provides solar devices with increased long‐term stability under ambient conditions. Thus, without involving any additional encapsulation step, the cells retain more than 80% of their efficiency after being exposed to the ambient atmosphere for more than 1000 h. Moreover, this plasma polymer passivation strategy significantly improves the coverage of the mesoporous scaffold by the perovskite layer, providing the solar cells with enhanced performance, with a champion efficiency of 19.2%, a remarkable value for Li‐free standard mesoporous n‐i‐p architectures, as well as significantly improved reproducibility.

Effect of laser pulse group velocity on ion acceleration from transversely expanded plasma foil in radiation pressure dominant regime

We have analytically and numerically analysed the interaction of an ultra-intense laser pulse with ultra thin dense plasma foil in the radiation pressure dominant (RPD) regime taking into account the group velocity of the laser and the transverse expansion of the target. The group velocity decreases and the transverse expansion increases the ion energy. As the group velocity reduces the transverse expansion due to the early termination of the acceleration process, its effect dominates the transparency.

Low frequency vibrations observed on assemblies of vertical multiwall carbon nanotubes by Brillouin light scattering: determination of the Young modulus

Assemblies of vertical multiwall carbon nanotubes, (VCNTs), have been synthesized by coupling dewetting of cobalt or nickel ultrathin layers and plasma enhanced chemical vapor deposition. Electronic microscopies revealed well defined micrometer length nanotubes with inner radius of 3–4 nm and outer radius of 8–9 nm. Similar structural qualities have been revealed by Raman measurements. Dynamic behaviour of these VCNTs assemblies have been studied by means of Brillouin light scattering technique. The measured inelastic light scattering from VCNTs is attributed to bending vibrations of the nanotubes. The observed frequencies on both assemblies, considered as dense effective media, are compatible with an effective Young modulus of 850 GPa.

A novel metal/dielectric combined grating structure incorporating optically thin plasma metals with the properties of controllably polarization and spectral filtering

A novel metal/dielectric hybrid grating structure incorporating ultrathin plasma metals and intercross-cascaded dielectric gratings is proposed, characterized by owning the capacities of freely design of resonance and flexibly controls of filtering and polarization, for TE- and TM-polarized lights. Its distinctive resonant behaviors in reflection and transmission and controllable trimming ability in coloration and spectrum are systematically studied as well as origins of the resonances. Several specific grating structures are designed and optimized for color security and transparent display, and their characteristics of peak-splitting, resonance, filtering and polarization for coloration also discussed. By virtue of the structure, respectively manipulation and control for resonant spectra including locations of peak-valley, line-shapes and band-widths for TE- and TM-lights can be realized as well as simultaneously combined modulation for both polarizations. Better prospect of application exists in various fields for the structure including color decoration, optical and color security, transparent display and color imaging, etc.

Enhancing Moisture and Water Resistance in Perovskite Solar Cells by Encapsulation with Ultrathin Plasma Polymers

A compromise between high power conversion efficiency and long-term stability of hybrid organic-inorganic metal halide perovskite solar cells is necessary for their outdoor photovoltaic application and commercialization. Herein, a method to improve the stability of perovskite solar cells under water and moisture exposure consisting of the encapsulation of the cell with an ultrathin plasma polymer is reported. The deposition of the polymer is carried out at room temperature by the remote plasma vacuum deposition of adamantane powder. This encapsulation method does not affect the photovoltaic performance of the tested devices and is virtually compatible with any device configuration independent of the chemical composition. After 30 days under ambient conditions with a relative humidity (RH) in the range of 35-60%, the absorbance of encapsulated perovskite films remains practically unaltered. The deterioration in the photovoltaic performance of the corresponding encapsulated devices also becomes significantly delayed with respect to devices without encapsulation when vented continuously with very humid air (RH > 85%). More impressively, when encapsulated solar devices were immersed in liquid water, the photovoltaic performance was not affected at least within the first 60 s. In fact, it has been possible to measure the power conversion efficiency of encapsulated devices under operation in water. The proposed method opens up a new promising strategy to develop stable photovoltaic and photocatalytic perovskite devices.

Thermal Conductivity of Nanocomposites Based in High Density Polyethylene and Surface Modified Hexagonal Boron Nitride via Cold Ethylene Plasma

Hexagonal boron nitride nanoparticles (hBN) were surface modified by treatment with cold ethylene plasma. During this treatment, an ultrathin plasma polymerized polyethylene layer is deposited on the surface of the hBN nanoparticles. Before and after the plasma treatment, the nanoparticles were characterized by infra-red spectroscopy, thermogravimetric analysis, transmission electron microscopy (TEM) and X-ray diffraction. Untreated and plasma treated nanoparticles were incorporated via melt mixing into high density polyethylene (HDPE), at different concentrations. Dispersion of hBN within the polymer and the polymer-particle interaction were studied by TEM. Thermal conductivity of the prepared nanocomposites was determined by modulated differential scanning calorimetry. In general, the thermal conductivity of all HDPE–hBN prepared nanocomposites was higher than that of pure HDPE. However, the higher conductivity values, 97 and 114% higher than that of pure HDPE, were obtained in plasma treated samples (treated at 100 W for 5 min) with 8 and 15 wt% loading of hBN.

Promotion of Adhesion of Green Flame Retardant Coatings onto Polyolefins by Depositing Ultra-Thin Plasma Polymer Films: A Critical Review

Various methods have been used for introducing fire retardant additives into polymers. Deposition of thick fire retardant coatings directly onto polymer substrates is an alternative technique. An important advantage of the coating technique is the preservation of the physical and chemical integrity of the polymer material. Moreover, the fire retardancy of the polymer materials can be achieved following their production. Suitable coating materials are inorganics, intumescent, char-forming, oxygen-diluting, and cooling or radical quenching layers. The most important problem is to achieve sufficient coating thickness to withstand the direct attack of flame and to protect the polymer bulk from pyrolysis, otherwise blistering of coating, caused by emitted pyrolysis gases, is often observed. To avoid blistering of coating, the adhesion between polyolefin substrate and fire retardant coating has to be extraordinarily high. In order to achieve such a high level of adhesion, the polymer surface has to be modified with adhesion-promoting functional groups. The deposition of thin plasma polymers as adhesion-promoting layers with NH2, OH or COOH groups has been the most suited method. These functional groups are able to form covalent bonds and other interactions between the fire-resistant coating and the plasma-modified polyolefin substrate. Additionally, the plasma polymer counteracts the strong mechanical stresses in the laminate on exposure to high temperatures by its flexibility. The thick fire retardant coatings were chosen based on green ecological aspects to avoid flame-initiated emission of toxic or corrosive gases and remains of toxic char.

Formation of Low-Resistivity Metal/Germanium Contact with Ultra-Thin Interlayer and Plasma Oxidation for n-Channel Germanium FET

In this work, the plasma oxidation process is introduced into the metal–interlayer–semiconductor (M–I–S) structure to reduce the contact resistance of the metal/n-type germanium (n-Ge) contact. The GeOx layer formed by the plasma oxidation process acts as a good passivation layer between TiO2 and Ge, and also an additional metal induced gap states (MIGS) blocking layer. From these effects of the GeOx layer, the M–I–S structure with multi-layered interlayer stack, TiO2/GeOx, shows approximately four orders of magnitude of the reverse current density improvement from the M–S contact. This technique can be a solution of the severe Fermi-level pinning (FLP) and the high contact resistance in source/drain (S/D) regions of the n-channel germanium field-effect transistor (FET).

Formation of Low-Resistivity Metal/Germanium Contact with Ultra-Thin Interlayer and Plasma Oxidation for n-Channel Germanium FET

Germanium (Ge) has emerged as a new channel material substituting traditional silicon (Si) in CMOS technology due to its high carrier mobility and process compatibility with Si. However, n-channel Ge MOSFET has not exhibited high performance because of some bottlenecks. High source/drain (S/D) contact resistance resulted from Fermi-level pinning (FLP) between the metal and Ge is the most serious obstacle for the development of Ge n-MOSFET. The metal/n-Ge contact has very large Schottky barrier height, approximately 0.55eV, regardless of metal work function because the Fermi-level on the metal side is strongly pinned to the edge of the valence band of Ge. Metal-induced gap states (MIGS) are the main cause of Fermi-level pinning, however, effect of interface states at the Ge surface on FLP is turned out to be not small by previous researches [1, 2]. Therefore, it is important to reduce both MIGS and interface states in order to alleviate FLP and form low-resistance Ge S/D contact. In this work, moderately-doped n-Ge wafer (N d = 1×1017 cm–3) was used as a substrate. In order to alleviate FLP of metal/n-Ge contact, 1.5 nm-thick ultra-thin TiO2 layer is inserted between the metal and n-Ge to block MIGS penetration into the energy gap of Ge, and plasma oxidation process is introduced before and after TiO2 deposition, respectively, to passivate Ge surface and reduce interface states [3]. Two approaches of plasma oxidation are applied; pre-oxidation and post-oxidation. The plasma oxidation process was carried out using ICP-RIE system. For pre-oxidation process, Ge substrate was oxidized prior to the TiO2 deposition with source power of 500 W, no bias power, gas flow of O2 40 sccm/Ar 5 sccm, pressure of 10 mTorr, and process time of 70 sec. For post-oxidation process, Ge substrate was oxidized after the TiO2 deposition with bias power of 50 W and process time of 30 sec with other plasma conditions not changed. The TiO2interlayer was deposited using atomic layer deposition (ALD) system at process temperature of 250 °C. As a result, a back-to-back reverse current density of Ti/TiO2/GeOx/n-Ge structure is improved compared to that of Ti/TiO2/n-Ge structure for both pre-oxidation and post-oxidation as shown in Fig. 1, which means Fermi-level on the metal side was more unpinned due to the GeOx passivation layer. It exhibits 4 orders of magnitude of reverse current improvement than the Ti/n-Ge structure does. Besides, the TiO2/GeOx stack shows better electrical properties than single TiO2 does when they have the same total thickness, approximately 2.1 nm (not shown here). It means an increase of single interlayer thickness in metal-interlayer-semiconductor (M-I-S) structure cannot be the best solution for FLP, and multi-layered structure should be introduced to reduce both MIGS and interface states. The Ti/TiO2/pre-GeOx/n-Ge shows slightly better performance than the Ti/TiO2/post-GeOx/n-Ge does. This is because the amount of GeOx formed by post-plasma oxidation process is smaller than that formed by pre-oxidation process due to the presence of TiO2 interlayer as shown in Fig. 2. Thicker GeOx can block MIGS more resulting in slight increase of reverse current density, however, GeOx layer formed by post-oxidation process has more GeO2-like characteristics which can passivate Ge surface better. For this reason, the Ti/TiO2/post-GeOx/n-Ge structure exhibits more ohmic-like (i.e., more linear) I–V characteristics, and post-oxidation process is considered to have more potential to plasma passivation process for the M-I-S structure. In conclusion, we successfully demonstrate the effect of pre- and post-oxidation process on Ge M-I-S structure. The GeOx layer formed by plasma oxidation between the metal and the TiO2 interlayer can reduce interface state density resulting in additional Fermi-level unpinning. Therefore, this plasma oxidation process with M-I-S structure can be a key technology to overcome the bottleneck of Ge n-channel MOSFET development by alleviating FLP effectively and reducing S/D contact resistance. [1] G.-S. Kim et al., IEEE Electron Device Lett., 36, 8 (2015) [2] J.-R. Wu et al., Appl. Phys. Lett., 99, 25 (2011) [3] J. Kang et al., Opt. Express, 23, 13 (2015) Figure 1

Ultra-Thin Plasma Polymer Films as a Novel Class of Adhesion Promoters: A Critical Review

Several reaction mechanisms have been proposed for formation of plasma polymers, such as monomer fragmentation followed by poly-recombination into randomly structured and crosslinked films; fragmentation, accompanied by the formation of acetylene or other film-forming intermediates and deposition of polystyrene-like material; plasma-initiation of radical chain-growth polymerization; and ion-molecule reactions, as well as ionic chain-growth polymerization. The bulk structure of plasma polymers was found to be more or less randomly formed, far from that of classic polymers. Nevertheless, the retention of functional groups in the plasma polymer is higher than the retention of monomer structure in repeat units of polymer backbones. Such functional groups bearing plasma polymers were found to be suitable as adhesion promoting layers in polymer composites. These functional groups are essential for covalent bonding to substrate and coating. Additional introduction of aliphatic spacers could flexibilize the interface between plasma polymer covered substrate and coating. Thus, maximum adhesion in composites and laminates was produced. Several examples are given where plasma polymers alone or linked with spacers have been shown to be effective as adhesion promoter.

Plasma-Activated Electrospun Polylactide Fiber Meshes as Matrices for Tissue Engineering

Poly (L-lactide-co-D/L-lactide)-based fiber meshes resembling structural features of the native extracellular matrix have been prepared by electrospinning. Subsequent coating of the electrospun fibers with an ultrathin plasma polymerized allylamine (PPAAm) layer changed the hydrophobic nature of the polylactide surface into a hydrophilic polymer network and provided positively charged amino groups on the fiber surface able to interact with negatively charged pericellular matrix components. Cell experiments in vitro using different types of human epithelial cells (gingiva, uroepithel) revealed that the PPAAm-activated surfaces promoted the occupancy of the meshes by cells accompanied by improved initial cell spreading. An in vivo study in a rat intramuscular implantation model demonstrated that the local inflammatory tissue response did not differ between PPAAm-coated and untreated polylactide meshes.

Numerical investigation on high power microwave flashover and breakdown on inner and outer surface of output-window by EM-fluid simulation

In this paper, an electromagnetic-field FDTD method coupled with plasma fluid model is put forward to investigate the different physical phenomena of high power microwave (HPM) flashover and breakdown on inner and outer surface of output-window. Based on the above theoretical models, a one-dimensional (1D) electromagnetic field and plasma interaction code is programmed by authors. By using the code, the HPM flashover and breakdown on inner and outer surface of output-window are simulated. The numerical results could be concluded as follows. For flashover and breakdown on outer surface, output microwave pulse is shortened without cut-off; there is a standing-wave distribution of electric field RMS (Root-Mean-Square) value before the window with fixed-positions of wave nodes and antinodes; there is a ultra-high-density (～1021 m-3) and ultra-thin (～mm) plasma shell with slow diffusion, microwave could penetrate the plasma-shell partly; the shortening of output microwave is caused by plasma absorption mostly. The output pulse of microwave could be lengthened by reducing the initial density or depth of plasmas; the other way is to shorten incident microwave pulse or reduce the value of incident microwave power. For flashover and breakdown on inner surface, there is also a standing-wave distribution of electric field RMS value before the window but the positions of wave nodes and antinodes vary with time; the plasma region moves toward the microwave source; with strong-outgassing, output microwave pulse is shortened without cut-off, there are “thread-like” ultra-high-density (～ 1021 m-3) and ultra-thin (～mm) plasma regions with slow diffusion, the distance between two “thread-like” regions is about a quarter of microwave wavelength, the shortening of output microwave is caused by plasma absorption mostly; with weak-outgassing and low electric field value, the output pulse of microwave is lengthened but cut-off finally, there are “belt-like” high-density (～ 1018 m-3) and thin (mm-cm) plasma regions with fast diffusion, the distance between two “belt-like” region is about a quarter of microwave wavelength, the shortening of output microwave is caused by plasma absorption mostly; with weak-outgassing and high electric field value, output pulse of microwave is cut-off quickly, “block-like” diffuse ultra-high-density (～1021 m-3) and deep (～ cm) plasma regions are formed with very fast diffusion, and the shortening of output microwave is caused by plasma reflection mostly.

Combined in situ FTIR-spectroscopic and electrochemical analysis of nanopores in ultra-thin SiOx-like plasma polymer barrier films

Plasma polymerized SiOx barrier films were investigated by means of in situ spectroscopic and electrochemical methods to correlate the process parameters such as applied substrate bias with the resulting barrier properties. SiOx layers with various hexamethyldisiloxane/oxygen ratio were deposited with and without applied substrate bias. The resulting film morphologies were characterized by means of atomic force microscopy, and the presence of nanopores was analysed by cyclic voltammetry. In order to compare the film density and the presence of nanopore structure, evaluation of interfacial hydroxyl groups was performed by means of discrete polarization modulation Fourier transform infrared reflection-absorption spectroscopy in atmospheres with controlled partial pressures of H2O or D2O. It could be shown that the electrochemical and in situ spectroscopic approach allows for the analysis of nanopores and that a clear correlation of process parameters and film structure can be established.

An ultra-thin Shadow Mask Plasma Display Panel

An ultra-thin (260μm) Shadow Mask Plasma Display Panel (ultra-thin SMPDP) which meets the demands of further reducing the thickness and weight of display panels has been developed. This device is also an important candidate for semi-flexible and/or semi-transparent display. Its discharge performance has been investigated based on the fluid model. The result shows that the discharge efficiency is improved by about 20% thanks to the low relative permittivity of the ultra-thin glass foil. Both firing and sustaining voltage of the ultra-thin SMPDP will increase about 15V if a 30μm ultra-thin glass is used. Considering the influence of the thickness of ultra-thin glass foil on the driving voltage, 50μm is chosen as the optimal thickness for the ultra-thin SMPDP. In addition, a 5cm×5cm tubeless panel has been made using an in-vacuum sealing technique. Moreover, the driving voltage and discharge process of the panel have also been measured. It has been found that the discharge is confined in the center of the cell, where the electric field is weaker during each sustain period. Theoretically, this will further increase the discharge efficiency. However, the measured difference between firing voltage and sustain voltage is relatively small compared with the simulation, indicating a loss of wall-voltage.

Effects of the post nitridation anneal temperature on performances of the nano MOSFET with ultra-thin (

A post nitridation annealing (PNA) is used to improve performances of the metal oxide semiconductor field effect transistor (MOSFETs) with nano scale channel and pulsed radio frequency decoupled plasma nitrided ultra-thin (<50Å) gate dielectric. Effects of the PNA temperature on the gate leakage and the device performances are investigated in details. For a n-type MOSFET, as the PNA temperature rises from 1000 to 1050°C, the saturation current and gate leakage are increased and reduced 7.9% and 3.81%, respectively. For a p-type MOSFET, the improvement is more significant i.e., 16.7% and 4.31% in saturation current increase and gate leakage reduction, respectively. The significant improvements in performance are attributed to the higher PNA temperature caused Si/SiON interface improvement and increase of EOT. Most of all, the high temperature PNA does not degrade the gate oxide integrity.

Plasma polymerized allylamine films deposited on 316L stainless steel for cardiovascular stent coatings

Coronary stents are metallic (316L stainless steel) medical devices used during balloon angioplasty to scaffold diseased arteries and prevent their reblockage. To reduce the restenosis rate, bare metal stent coating is a promising solution. The coating can protect the metallic surface of the stent from corrosion attack caused by the biological environment. In addition, according to Food and Drug Administration (FDA) the coating properties must be guaranteed even after stent expansion. The aim of this study was to develop a dry process to coat the metallic surface from the biological environment by depositing an ultra-thin, stable, cohesive and adhesive plasma polymerized allylamine (CH2=CH―CH2―NH2) coating with high selectivity towards primary amine groups. Plasma polymerized allylamine (PPAA) coatings were deposited on electropolished 316L stainless steel (316L SS) samples using a low pressure plasma reactor (70kHz). XPS (X-Ray Photoemission Spectroscopy) and FTIR-ATR (Fourier Transform Infrared-Attenuated Total Reflectance) spectroscopy measurements were used to investigate the chemical composition of the coatings. A chemical derivatization technique was employed in order to quantify the amine retention rate of the deposited films. Morphology of the films was evaluated by FE-SEM (Field Effect-Scanning Electron Microscopy) imaging. Furthermore, special attention was devoted to study the stability of the coating and its adhesion properties after plastic deformation up to 25%. The effect of the power discharge and treatment time on these properties was also investigated. Our results showed that coatings present the required adhesion and cohesion properties to be stable upon deionised (D.I.) water immersion and to resist to a stent expansion.

Variations in cross-link density with deposition pressure in ultrathin plasma polymerized benzene and octafluorocyclobutane films

Neutron reflectometry (NR) measurements of ultrathin films from octafluorocyclobutane (OFCB) and benzene (B) precursors deposited using Plasma Enhanced Chemical Vapor Deposition (PECVD) at two pressures (0.6 and 0.05 torr) reveal that under both deposition conditions there are a 7 nm-thick surface layer and an approximately 1 nm-thick transition layer next to the substrate which have structures different than those in the middle of the film. NR measurements of films swollen with solvent reveal that the density of cross-linking next to the substrate is lower than that in the middle of the film or the region adjacent to the surface of the film for both precursors. Variations in the cross-link density with processing pressure are much stronger for PP-B films than for PP-OFCB films.