Poly(dimethylsiloxane)-polyimide blends in the formation of thick polyimide films

Thick polyimide layers can be formed by using some unique properties of poly(dimethylsiloxane)-polyimide (PDMS/PMDA–ODA) blends followed by surface modification and deposition of a second layer of polyimide precursor chemicals. The method is based on the micro-phase separation characteristics of these blends to yield surfaces that have PDMS-like character. Upon modification with UV/ozone treatment, a surface that is essentially SiO _x and hydrophilic in nature is produced. This surface is amenable to reaction and deposition of a second polyimide layer from polyimide precursors. The thicker polyimide layer has enhanced adhesion between the original layer of the blend and the new polyimide layer and this approach finds extensive applications for products that require thick polymer layers. Changes in surface energy for various blend compositions were monitored by measurement of advancing contact angle with de-ionized water. Contact angle for unmodified polyimide films was on the order of 70° and it increased to about 104° after blending with PDMS and curing. UV/ozone treatment reduced the contact angle of the doped polyimide to less than 5°. X-ray photoelectron spectroscopy (XPS) and angle resolved XPS (ARXPS) measurements were used to monitor the chemical compositions of the various surfaces. High-resolution XPS spectra in the Si2p region confirm the transformation of O–Si–C bonds in PDMS to SiO _x , where x is about 2. Scanning electron microscopy (SEM) of some selected samples shows that the blends contain phase separation of the polymers at the surfaces of the samples. Atomic force microscopy (AFM) of siloxane-free polyimide, and PDMS/PMDA–ODA blends both prior to and after UV/ozone exposure, show that the films are essentially flat at short treatment times (less than 60 min). AFM also reveals the separation of PDMS into micro-domains at the cured film surface and throughout the layer below the surface of the blended films. Adhesion of a subsequently deposited polyimide layer to the modified polyimide surface was found to be greatly improved when compared to the adhesion obtained for deposition onto a pristine polyimide surface.     

Transformation of poly(dimethylsiloxane) into thin surface films of SiO x by UV/ozone treatment. Part II: segregation and modification of doped polymer blends

UV/ozone treatment of organic polymers having silicone additives to produce oxidized layers was achieved by doping a host polymer or prepolymer with a silicone additive, poly(dimethylsiloxane) (PDMS). The concentration of PDMS in the host polymer was low, typically in the range of 0.1–2.0% by weight. Host polymers were polyethylene, polyimide, and polyurethane. After film formation, the presence of PDMS was detected on the surface using X-ray photoelectron spectroscopy (XPS), consistent with wetting angle measurements that revealed a hydrophobic surface. The doped blend was then subjected to exposure in a UV/ozone environment such that a thin, stable barrier of SiO _x was formed at the surface of the film. Rate of film modification was monitored by XPS and measurement of advancing contact angle using deionized water. XPS measurements also showed some evidence of modified fragments of the host polymer near the surface. Significant segregation of PDMS and subsequent transformation to silicon oxides has been demonstrated to occur in these doped systems. The stability of the modified glassy surface formed by UV/ozone treatment of a commercially available epoxy formulation containing a silicone additive was shown to be superior to that obtained by other treatment techniques, e.g., oxygen plasma modification.     

Forming wrinkled stiff films on polymeric substrates at room temperature for stretchable interconnects applications

Periodically wrinkled stiff thin films on elastomeric substrates have been found extensive applications, such as in stretchable electronics. This paper presents a cost-effective and simple method to form wrinkled stiff SiO_x thin films on polydimethylsiloxane (PDMS) substrates at room temperature by ultraviolet/ozone (UV/O) radiation on pre-strained PDMS. Systemic studies have been conducted to understand the dependence of the wavy profile on the PDMS pre-strain, UV/O exposure time, and PDMS modulus. The mechanics analysis has been verified to be quantitatively or qualitatively accurate by experimental comparisons. The wrinkled SiO_x/PDMS system is stretchable and provides a wavy mold for stretchable electrodes. The constant electrical resistance during mechanical stretching shows the stretchability of this system.     

Effect of oxygen to argon ratio on the properties of thin SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films deposited by r.f. sputtering

Energy Dispersive X-ray and X-ray Photoelectron (XPS) spectroscopies show that SiO _x films deposited by reactive r.f. magnetron sputtering at partial pressure ratios R between oxygen and argon in a wide range (1–0.005) have compositions close to the stoichiometric one. For these films high temperature annealing at 1,000 °C shifts the band in the Fourier Transform-Infrared spectrum due to the Si–O–Si stretching vibration to values typical of stoichiometric SiO₂. Further decrease of R leads to splitting of the Si 2p XPS line indicating increase of the Si content and formation of a second phase in a SiO₂ matrix. The electrical properties of test MOS structures with SiO _x gate dielectric, regarding defect density in the oxide and at the SiO _x /c-Si interface, degrade with the decrease of R. High temperature annealing at 1,000 °C strongly improves the properties of all films regarding leakage current and properties of the interface.     

Composite SiOx/fluorocarbon plasma polymer films prepared by r.f. magnetron sputtering of SiO2 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 (SiO₂) 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/mm²) when the volume fraction ratio (filling factor) of SiO₂ 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.     

Ion beam synthesis of the diamond like carbon films for nanoimprint lithography applications

Ion beam deposited hydrogenated undoped as well as SiO_x (SiO_x + N₂, SiO_x + Ar) doped DLC thin films were deposited and evaluated as possible anti-adhesive layers for nanoimprint lithography. Film surface contact angle with water was investigated as a measure of the surface free energy and anti-sticking properties. Contact angle of the DLC films was independent of SiO_x doping and ion beam energy. Air-annealing resistance in terms of the contact angle with water of the synthesized diamond like carbon films was investigated. Optical transmittance spectra of the DLC films in UV-VIS range were measured to investigate it as possible anti-sticking layers for UV imprint lithography applications. DLC films with the most promising combination of the UV absorption and anti-sticking properties were revealed. Preliminary imprint tests with uncoated and thin DLC film coated hot imprint stamps were performed.     

The microstructure and wettability of the TiOx films synthesized by reactive DC magnetron sputtering

Different chemical state of titanium oxide films were deposited on commercially pure Ti (CP Ti) by reactive DC magnetron sputtering under different oxygen flow rates to examine a possibility of their applications to endovascular stents. The chemical composition and crystal structure of the obtained films were analyzed by XPS and XRD, respectively. In dependence on the deposition parameters employed, the obtained films demonstrated different mixture of anatase TiO₂, Ti₂O₃, TiO and Ti. The wettability of the films was measured by the water contact angle variation. By formation of titanium oxide film on CP Ti, contact angle was decreased. In order to modify and control the surface wettability, the resultant TiO_x films were etched subsequently by different plasma. The wettability was influenced by etched process according to the decreased contact angle values of etched TiO_x film. Furthermore, TiO_x films became highly hydrophilic by ultraviolet (UV) irradiation, and returned to the initial relatively hydrophobic state by visible-light (VIS) irradiation. The wettability of the TiO_x film was enabled to convert between hydrophilic and hydrophobic reversibly by alternative UV and VIS irradiation. By adjusting deposition parameter and further modification process, the wettability of the TiO_x films can be changed freely in the range of 0–90°.     

Magnetic and optical properties of MgAl2O4-(Ni0.5Zn0.5)Fe2O4 thin films prepared by pulsed laser deposition

Abstract

Thin films composed of MgAl₂O₄ and (Ni_0.5Zn_0.5)Fe₂O₄ ([MA(100-x)-NZFx] films) were grown on fused SiO₂ substrates by pulsed laser deposition. X-ray diffraction measurements revealed that the films were polycrystalline, and that their lattice constant varied linearly with composition, indicating the formation of a solid solution. The film with x=60 was paramagnetic and those with x ≥ 70 were ferromagnetic. The films had a transparency above 75% in the visible range, but the transparency decreased with the x value. The optical band gaps were 2.95, 2.55, 2.30 and 1.89 eV for x=20, 40, 60, 80 and 100, respectively. The Faraday rotation angle increased with x in the visible range, and the film with x=70 exhibited a value of 2000 degrees cm^-1 at 570 nm, which is comparable to the rotation angle of Y₃Fe₅O₁₂. Owing to their high transparency, which extends into the visible range, the [MA(100-x)-NZFx] films can be used in novel magneto-optical devices.     

Effect of impinging ion energy on the substrates during deposition of SiOx films by radiofrequency plasma enhanced chemical vapor deposition process

Radiofrequency (13.56 MHz) plasma enhanced chemical vapor deposition process is used for deposition of SiO_x films on bell metal substrates using Ar/hexamethyldisiloxane/O₂ glow discharge. The DC self-bias voltage developed on the substrates is observed to be varied from − 35 V to − 115 V depending on the RF power applied to the plasma. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. The deposited films are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, nano-scratch test and thermogravimetric analysis. The characterization results show strong dependency of the SiO_x films properties on the energy of the ions impinging on the substrates during deposition. Analysis of Raman spectra indicates an increase in vitreous silica content and reduction in defective Si-O-Si chemical structure in the deposited SiO_x films with increasing ion energy impinging on the substrates. The increase in inorganic (Si and O) content in the SiO_x films is further confirmed from XPS analysis. The growth of SiO_x films with more inorganic content and defect free chemical structure apparently contribute to the increase in their hardness and scratch resistance behavior. The films show higher thermal stability as the energy of the ions arriving at substrates increases with DC self-bias voltage. The possibility of using SiO_x films for surface protection of bell metal is also explored.     

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiO_x nanocomposite films have been fabricated by co-sputtering Au wires and SiO₂ target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiO_x films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiO_x films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiO_x films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiO_x NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.     

Gold catalysts for the abatement of environmentally harmful materials: Modeling the structure dependency

FeO_x, TiO₂ and CeO_x layers were deposited by pulsed laser deposition (PLD) technique onto Au films or Au nanoparticles supported on SiO₂/Si(100). The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and their reactivity was studied in catalytic CO oxidation. Comparison was made with reference samples of FeO_x/SiO₂/Si(100), TiO₂/SiO₂/Si(100), CeO_x/SiO₂/Si(100) and Au/SiO₂/Si(100) layers. The catalytic activity of the metal-oxide/Au/SiO₂/Si(100) samples must be attributed to active sites located on the metal-oxides overlayer modified by gold underneath, since no Au was exposed to the surface according to the XPS and SIMS. We found a promoting effect of gold on the catalytic activity of the FeO_x overlayer and an inhibiting effect of gold on the TiO₂ and CeO_x overlayers. These findings are discussed in terms of electronic interactions at the Au/metal oxide interface.     

Effect of oxygen pressure of SiOx buffer layer on the electrical properties of GZO film deposited on PET substrate

The present work was made to investigate the effect of oxygen pressure of SiO_x layer on the electrical properties of Ga-doped ZnO (GZO) films deposited on poly-ethylene telephthalate (PET) substrate by utilizing the pulsed-laser deposition at ambient temperature. For this purpose, the SiO_x buffer layers were deposited at various oxygen pressures ranging from 13.3 to 46.7 Pa. With increasing oxygen pressure during the deposition of SiO_x layer as a buffer, the electrical resistivity of GZO/SiO_x/PET films gradually decreased from 7.6 × 10^− 3 to 6.8 × 10^− 4 Ω·cm, due to the enhanced mobility of GZO films. It was mainly due to the grain size of GZO films related to the roughened surface of the SiO_x buffer layers. In addition, the average optical transmittance of GZO/SiO_x/PET films in a visible regime was estimated to be ~ 90% comparable to that of GZO deposited onto a glass substrate.     

Oxygen plasma treatment of SiOxCy(− H) films polymerized by atmospheric pressure dielectric barrier discharge using hexamethylcyclrotrisiloxane

The SiO₂-like layers were obtained by plasma-oxidation of the SiO_xC_y(− H) films deposited from hexamethylcyclotrisiloxane (HMCTSO) with helium and oxygen. The SiO₂-like layers were formed on as-deposited SiO_xC_y(− H) films within a second by oxidation using the He/O₂ atmospheric pressure dielectric barrier discharge (APDBD). The elemental ratio of oxygen to silicon in the layer was increased up to 1.95 which is closed to stoichiometry of SiO₂. The elemental composition and surface morphology were studied by means of x-ray photoelectron spectroscopy and atomic force microscopy. Wettability of the oxidized thin films was investigated by water droplet contact angle measurement. The contact angle of SiO_xC_y(− H) films are decreased from 63° to below 10° within a second by oxidation. Correlation between the elemental composition and the contact angle were discussed. The effects of oxidation duration and discharge generation voltage on the composition and surface morphology of the film were investigated.     

Fabrication of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> double layer thin films with self-cleaning and photocatalytic properties

Transparent antireflective SiO₂/TiO₂ double layer thin films were prepared using a sol–gel method and deposited on glass substrate by spin coating technique. Thin films were characterized using XRD, FE-SEM, AFM, UV–Vis spectroscopy and water contact angle measurements. XRD analysis reveals that the existence of pure anatase phase TiO₂ crystallites in the thin films. FE-SEM analysis confirms the homogeneous dispersion of TiO₂ on SiO₂ layer. Water contact angle on the thin films was measured by a contact angle analyzer under UV light irradiation. The photocatalytic performance of the TiO₂ and SiO₂/TiO₂ thin films was studied by the degradation of methylene blue under UV irradiation. The effect of an intermediate SiO₂ layer on the photocatalytic performance of TiO₂ thin films was examined. SiO₂/TiO₂ double layer thin films showed enhanced photocatalytic activity towards methylene blue dye.     

Surface modification of titanium thin film with chitosan via electrostatic self-assembly technique and its influence on osteoblast growth behavior

Chitosan (Chi) and poly (styrene sulfonate) (PSS) were employed to surface modify titanium thin film via electrostatic self-assembly (ESA) technique in order to improve its biocompatibility. The surface chemistry, wettability and surface topography of the coated films with different number of deposited layers were investigated by using X-ray photoelectron spectroscopy (XPS), water contact angle measurement and atomic force microscopy (AFM), respectively. The results indicated that a full surface coverage for the outmost layer was achieved at least after deposition of five layers, i.e., PEI/(PSS/Chi)₂ on the titanium films. The formed multi-layered structure of PEI(PSS/Chi) _x (x ≥ 2) on the titanium film was stable in air at room temperature and in phosphate buffered solution (PBS) for at least 3 weeks. Cell proliferation, cell viability, DNA synthesis as well as differentiation function (alkaline phosphatase) of osteoblasts on chitosan-modified titanium film (PEI/(PSS/Chi)₆) and control sample were investigated, respectively. Osteoblasts cultured on chitosan-modified titanium film displayed a higher proliferation tendency than that of control (p < 0.01). Cell viability, alkaline phosphatase as well as DNA synthesis measurements indicated that osteoblasts on chitosan-modified titanium films were greater (p < 0.01) than those for the control, respectively. These results suggest that surface modification of titanium film was successfully achieved via deposition of PEI/(PSS/Chi) _x layers, which is useful to enhance the biocompatibility of the titanium film.     

Surface energy modification of SiOxCyHz film using PECVD by controlling the plasma processes for OMCTS (Si4O4C8H24) precursor

SiO_x films produced from octamethylycyclodisiloxane (Si₄O₄C₈H₂₄, OMCTS) with oxygen carrier gas have a low contact angle. The surface energy of the SiO_x films can be changed by controlling the plasma process. SiO_xC_yH_z films were deposited on polycarbonate substrates by plasma enhanced chemical vapor deposition using OMCTS without oxygen carrier gas. The input power in the radio frequency plasma was changed to optimize the surface energy of the resulting SiO_xC_yH_z film. The plasma diagnostics, surface energy and surface morphology were characterized by optical emission spectrometry, contact angle measurements and atomic force microscopy, respectively. The chemical properties of the coatings were examined by Fourier transform infrared spectroscopy. The surface energy of the SiO_xC_yH_z films produced using a room temperature plasma process could be controlled by employing the appropriate intensity of excited neutrals, ionized atoms, molecules and energy (input rf power and bias), as well as the suitable dissociation of OMCTS.     

Effect of rapid thermal annealing time on Au/SiOx film prepared by hot wire assisted plasma enhanced chemical vapour deposition technique

In this study, nanocomposite material consisting of silicon suboxide (SiO_x) film embedded with gold nanoparticles (Au NPs) was synthesized using hybrid technique combining hot wire evaporation and plasma enhanced chemical vapour deposition (PECVD) method. As prepared Au/SiO_x films were rapid thermal annealed at constant temperature of 800 °C for different annealing times from 30 to 120 s. The use of tungsten filament for Au evaporation allowed the effective reduction of the silicon content. Depth profiling analysis confirmed the embedded in structure of Au/SiO_x film. FESEM, UV/VIS/NIR and PL spectroscopy were utilized to study the structural and optical properties of annealed Au/SiO_x film for different times. Embedded Au NPs diffused towards the surface of SiO_x film agglomerate and increased in size with an increase in annealing time. Localized surface plasmon resonance (LSPR) peak induced by Au NPs in SiO_x, which is dependent on annealing time, was clearly observed in optical spectra. Intensity and position of the PL peak located at 580 nm experienced a decrease and red-shift, as annealing time increased.     

Magnetic and optical properties of MgAl2O4-(Ni0.5Zn0.5)Fe2O4 thin films prepared by pulsed laser deposition

Thin films composed of MgAl₂O₄ and (Ni_0.5Zn_0.5)Fe₂O₄ ([MA(100-x)-NZFx] films) were grown on fused SiO₂ substrates by pulsed laser deposition. X-ray diffraction measurements revealed that the films were polycrystalline, and that their lattice constant varied linearly with composition, indicating the formation of a solid solution. The film with x=60 was paramagnetic and those with x ≥ 70 were ferromagnetic. The films had a transparency above 75% in the visible range, but the transparency decreased with the x value. The optical band gaps were 2.95, 2.55, 2.30 and 1.89 eV for x=20, 40, 60, 80 and 100, respectively. The Faraday rotation angle increased with x in the visible range, and the film with x=70 exhibited a value of 2000 degrees cm^-1 at 570 nm, which is comparable to the rotation angle of Y₃Fe₅O₁₂. Owing to their high transparency, which extends into the visible range, the [MA(100-x)-NZFx] films can be used in novel magneto-optical devices.     

Photo-induced superhydrophilicity of nanocomposite TiO2-SiO2 thin film

In this work, TiO₂ and TiO₂-SiO₂ thin films on glass substrates were prepared by the sol-gel dip coating process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the structural and chemical properties of the films. The super-hydrophilicity was assessed by water contact angle measurement. XRD measurements confirmed the presence of polycrystalline anatase and rutile phases in the films. The water contact angle measurements showed that addition of SiO₂ has a significant effect on the super-hydrophilicity of TiO₂ thin films, especially if they are stored in a dark place.     

Characterization of the Polarity Dependent Memory and Switching effect in sandwiches of metal/a-Si/ITO

The Polarity Dependent Memory and Switching effect (PDMS) has been observed in sandwiches of metal/a-Si/ITO layers and metal/a-Si/In. The film composition has been analysed by Auger Electron Spectroscopy and peak heights of the metals, Si and SiO_x have been measured as a function of film depth. No penetration of electrode material into the a-Si film was observed and the interfaces were abrupt even after many cycles of switching. A mechanism based on dendrite formation does not therefore operate in this type of PDMS. Traces of SiO_x have been found at the ITO/a-Si interface which are attributed to the presence of ITO or the deposition of In after exposure of a-Si to air. The SiO_x layer appears only in the OFF state and not in the ON state of the device. Hence a model based on voltage formation and destruction of an approximately 500 Å thick SiO_x layer at the a-Si/ITO interface is given.