Transformation of Poly(dimethylsiloxane) into thin surface films of SiO x by UV/Ozone treatment. Part I: Factors affecting modification

UV/ozone treatment of poly(dimethylsiloxane) (PDMS) was used to produce thin surface films of SiO _x . Films of PDMS were applied by spin-coating onto gold-coated silicon wafers having (100) orientation. Characterization of the UV/ozone system was performed to map the spatial distribution of intensities of UV radiation. This mapping was used to ensure reproducible modification of films and to aid in the understanding of modification as measured by advancing contact angle using deionized water and x-ray photoelectron spectroscopy (XPS). Rutherford backscattering spectroscopy (RBS) was used to measure thickness of the PDMS films. Treatment reduced the wetting angle, in some cases from a value greater than 100° to a value less than 5°. High resolution XPS spectra were used to study the nature of the modified PDMS film and its relationship to the characteristics of the unmodified PDMS. High resolution XPS spectra in the Si 2p region show that O–Si–C bonds in the siloxane, observed prior to treatment, are converted to SiO _x , where x is between 1.6 and 2. Modified films also contain some oxidized carbon components. The time required to reduce the contact angle to a minimum value was greater for the thicker PDMS film samples. The effects of ozone alone (without UV) and UV radiation at 184.9 and 253.7 nm (without ozone) were also investigated. The results of UV/ozone treatment are compared to results achieved by means of plasma surface oxidation.     

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.     

Effect of UV/ozone treatment on interactions between ink-jet printed Cu patterns and polyimide substrates

In this study, we apply UV/ozone treatment to modify the surface properties of polyimide substrate and investigate the effects of UV/ozone treatment on surface properties of polyimide and the morphologies of ink-jet printed Cu patterns. Wettability of polyimide surface is enhanced by UV/ozone treatment as confirmed by contact angle analysis and XPS results. The change in wettability affected droplet sizes and morphologies of ink-jet-printed lines. The average droplet size increased from 26.8 μm on untreated polyimide to 42.5 μm after UV/ozone treatment. Furthermore, irregular patterns of coexisting beads and short lines were observed in untreated polyimide film, despite minimal overlap of dots. In contrast, patterns that were ink-jet printed on polyimide film that was modified by UV/ozone for 1 h showed continuous lines with straight edges.     

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°.     

The study on imidization degree of polyamic acid in solution and ordering degree of its polyimide film

Polyamic acid (PAA) based on pyromellitic dianhydride and 4,4′-oxydianiline (PMDA–ODA) can be chemically converted to copolyamic acid-imide (PA-I) which is a partially converted PAA at ambient temperature by treatment with a mixture of acetic anhydride and pyridine. A systematic investigation by rotation viscometer and FT-IR revealed that phase separation in PA-I solution occurred when imidization degree was about 26%. Imidization degree of PA-I solution could be controlled by using adequate acetic anhydride amount, initial PAA concentration and imidization time. PA-I solutions with different imidization degree were converted to corresponding polyimide films by thermal imidization. WAXD showed that as imidization degree in PA-I solution increased, the degree of morphologic ordering of final PI film was improved, while tensile strength and modulus increased and ultimate elongation reduced slightly.     

Influence of fabrication parameters on crystallization,microstructure, and surface composition of NbN thin films deposited by rf magnetron sputtering

In this work NbN thin films have been grown by magnetron rf sputtering of a δ-NbN (99.99%) target. In particular, the influence of certain fabrication parameters (substrate temperature, power supplied to the target or additional N₂ flux in the preparation chamber) on the crystallization, microstructure, and surface composition of the deposited films have been studied. The films have been characterized by X-ray diffraction (XRD) at grazing angle in the θ–2θ configuration, scanning electron microscopy (SEM), wavelength dispersive spectrometry (WDS), and X-ray photoelectron spectroscopy (XPS). XRD results show that films grown at a substrate temperature of 573 K and a power supply applied to the target of 300 W present the same crystalline structure of the target while films grown at these temperature and power supply conditions plus the additional presence of N₂ during fabrication, grow highly textured along the plane (200). SEM results indicate that the films present columnar growth and a high homogeneity. WDS analysis shows that films grown at 573 K and 300 W are stoichiometric. XPS shows a complex surface composition of the films most external 5 nm, indicating the presence of niobium nitride (NbN _x ), niobium oxy-nitride (NbN _x O _y ), and niobium oxide (Nb₂O₅).     

Surface modifications to improve Ti–porcelain bonding

Investigations of surface modifications on cast titanium surfaces and titanium-ceramic adhesion were performed. Cast pure titanium was subjected to surface modification by preoxidation and introduction of an intermediate layer of SnO _x by sol–gel process. Surfaces only sandblasted with alumina were used as controls. Specimen surfaces were characterized by XRD and SEM/EDS. The adhesion between the titanium and porcelain was evaluated by three-point flexure bond test. Failure of the titanium–porcelain with preoxidation treatment predominantly occurred at the titanium-oxide interface. Preoxidation treatment did not affect the fracture mode of the titanium–ceramic system and did not increase the bonding strength of Ti–porcelain. However, a thin and coherent SnO _x film with small spherical pores obtained at 300 °C served as an effective oxygen diffusion barrier and improved titanium–ceramic adhesion. The SnO _x film changed the fracture mode of the titanium–ceramic system and improved the mechanical and chemical bonding between porcelain and titanium, resulting in the increased bonding strength of titanium–porcelain.     

Structure and electrochemical hydrogen storage properties of Pd/Mg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Pd thin films prepared by pulsed laser deposition

Three-layered Pd/Mg_1−x Al _x /Pd (x = 0, 0.13, 0.21, 0.39) thin films were prepared by means of pulsed laser deposition. In the present Al concentration range, X-ray diffraction analyses showed that the Mg_1−x Al _x layer was constituted of a single phase Mg(Al) solid solution. The Mg(Al) grains are preferentially orientated along the c-axis and their size decreased (from 18.5 to 10.5 nm) as the Al content increased. Scanning electron microscopy and atomic force microscopy observations indicated that all the films exhibited a globular surface structure. However, the surface roughness of the films decreased as the Al concentration increased. Rutherford backscattering spectroscopy revealed that the Mg–Al layer density (porosity) was strongly dependent on the Al content. Successive hydriding charge/discharge cycles were performed on the different Pd/Mg_1−x Al_x/Pd films in alkaline media. The highest discharge capacity was obtained with the Pd/Mg_0.79Al_0.21/Pd film, namely ~85 μAh cm⁻² μm⁻¹ or 320 mAh g⁻¹, which corresponds to a H/M atomic ratio of ~0.48 in the Mg–Al layer.     

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.     

The effect of surface silanol groups on the deposition of apatite onto silica surfaces: a computer simulation study

Computer modelling techniques were employed to investigate the effect of surface silanol groups on the strength of adhesion of apatite thin films to silica surfaces. To this end, we have studied a series of silica surfaces with different silanol densities and calculated their interaction with apatite thin films. Our findings indicate that apatite does not attach strongly to surface hydroxy groups, but that apatite should deposit at dehydrated silica surfaces, especially when the surface silicon and oxygen species rearrange to form O–Si–O links. Any dangling silicon and oxygen bonds at the silica surfaces are saturated by coordination to oxygen and calcium atoms in the apatite layer, but the extra reactivity afforded by these under-coordinated surface species does not necessarily lead to more favourable substrate/film interactions. The lowest energy silica/apatite interfaces are those where an undistorted apatite layer can be deposited on a regular, stable substrate surface. Our simulations support the suggestion, that in vivo surface hydroxy groups are first condensed to form O–Si–O bridges before deposition and growth of apatite.     

Physical and electrical properties of polyimide/ceramic hybrid films prepared via non-hydrolytic sol–gel process

In this study, TiO₂ and SiO₂ were chosen as ceramic fillers in the 3,3′,4,4′-benzophenone tetracarboxylic dianhydride–4,4′-oxydianiline (BTDA–ODA) polyimide matrix. Physical properties of hybrids with up to 30 wt% SiO₂ and 7 wt% TiO₂ were evaluated and discussed. Nano-size ceramic particles were prepared by non-hydrolytic sol–gel (NHSG) process. SEM micrographs show that both films have nano-sized ceramic particles with a narrow size distribution. Thermal conductivities of the hybrids increase from 0.12 to 0.21 W/m-K, as the SiO₂ and TiO₂ in the hybrid increases from 0 to 30 and 7 wt%, respectively. Electrical surface resistivity slightly decreases with increasing ceramic filler content. Dielectric constant of the hybrid increases from 2.45 to 2.72 with the incorporation of the 7 wt% (5.4 vol%) TiO₂. Water absorption decreases considerably with increasing filler content. With 30 wt% (20.2 vol%) SiO₂ addition, the water absorption of the hybrid film reduces by 85% from that of pure polyimide.     

Polycrystalline Si1-x Ge x thin film deposition by rapid thermal chemical vapor deposition

Polycrystalline silicon germanium (poly-Si_1−xGe_x) thin films on a-Si film have been deposited by rapid thermal chemical vapor deposition (RTCVD) with SiH₄–GeH₄–H₂. Effect of GeH₄/SiH₄ and deposition temperature on stoichiometry (x), Si-Ge binding character, composition, hydrogen configuration, crystallinity, preferred orientation, grain size, and surface roughness of poly-Si_1−xGe_x films has been investigated. Poly-Si_1−xGe_x deposited on the substrate with amorphous silicon buffer layer on oxide shows better crystallinity and contains the less amount of oxygen than the one deposited directly on the oxide surface. At low temperature region, the Ge–H bond with the small amount of Si–H₂ bond is dominant but all hydrogen bonds are desorbed at high temperature. All films have polycrystalline phase and the grain size and (111) orientation increased with increasing deposition temperature in which Ge content also increases at the fixed gas flow rate of GeH₄ to total source gas. Poly-Si_1−xGe_x/Si thin film transistors (TFT) are fabricated and hydrogen during post-hydrogenation process preferentially is attached to Ge dangling bond and the TFT characteristics could be improved.     

Effect of Firing Temperature on the Structure and Properties of YBa2Cu3O7−x Films by TFA-MOD Method

YBa₂Cu₃O_7−x (YBCO) films were fabricated on LaAlO₃ (LAO) substrate under various firing temperatures (760–870 °C) in the crystallization process by metalorganic deposition (MOD) method using trifluoroacetates. The effect of firing temperature on the structure and properties of YBCO films was systematically investigated. According to the XRD and SEM images, the films fired at low temperature (760–800 °C) showed poor electrical performance due to rough surfaces and impurity phases. However, the films fired at 850 °C showed the highest critical temperature of 90 K and the highest J _c of 3.1 MA/cm² which attribute to the formation of a purer YBCO phase, fewer pores, and stronger biaxial texture.     

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.     

Improvement in physical properties and cytocompatibility of zein by incorporation of pea protein isolate

A series of protein-based biocomposites was prepared from glycerol-plasticized zein (ZE) and pea protein isolate (PPI) using a hot press and moulding process. The effects of PPI content (W _PPI) on the structure and properties of ZE/PPI films were investigated. With an increase in W _PPI from 0 to 100%, the elongation at break of the films increased from 2.4 to 62.6%, and the water contact angle decreased from 31.8° to 5.8°. Cell toxicity and cytocompatibility of ZE/PPI films were evaluated in vitro. The cell viability of L929 cells cultured in extracts from ZE/PPI films containing 10–30% PPI was higher than that from other films and the control group. The L929 cells expanded very well on the surfaces of films containing 10–30% PPI. Incorporation of 10–30% PPI into ZE improved flexibility, surface hydrophilicity, cytocompatibility and its potential as biomaterials in zein-based composites.     

Adhesion characteristics of Cu/Ni–Cr/polyimide flexible copper clad laminates according to Ni:Cr ratio and Cu electroplating layer thickness

The adhesion strength of Cu/Ni–Cr/polyimide flexible copper clad laminate (FCCL) was evaluated according to the composition ratio of the Ni–Cr layer and the thickness of the Cu electroplating layer, by using a 90° peel test. The changes in the morphology, chemical bond and adhesion property were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The peel strength of the FCCL increased with increasing Cr content and increasing Cu electroplating layer thickness. This increasing FCCL peel strength was attributed to a lower C–N bond and higher C–O and carbonyl (C=O) bonds in the polyimide surface compared to the FCCL with a lower adhesion strength. The adhesion property of the FCCLs was significantly affected by the Ni:Cr ratio.     

Effect of the titanium ion concentration on electrodeposition of nanostructured TiNi films

Electrodeposition of nanostructured titanium–nickel films was performed and the effect of the concentration of the titanium source on the film characteristics was investigated. Scanning electron microscopy indicated circular crystallites on the surface of the electrodeposited titanium–nickel film with a fairly uniform size distribution. XRD studies showed that the electrodeposited TiNi films contained TiNi with a preferred crystallographic orientation of [002]. Surface analysis using X-ray photoelectron spectroscopy (XPS) revealed that the electrodeposited titanium–nickel film contained elemental titanium and nickel, hydroxide of nickel, and oxides of titanium and nickel. As the titanium ion concentration was increased, the titanium content in the film was increased while the deposition rate and crystallite size of the film were decreased. A blue-shift in the UV/Vis peak was also observed with increasing titanium ion concentration.     

The mechanical behaviour of polyimide-copper laminates

The peel energies of flexible laminates consisting of polyimide films bonded to copper foil with a polymeric adhesive have been measured and the peel mechanisms investigated by conducting peel tests inside a scanning electron microscope. These laminates were prepared from polyimide films that had been subjected to either a “high-thermal history” or “low-thermal history” treatment during the production of the film. The laminates prepared from the “high-thermal history” polyimide films had higher recorded peel energies and the locus of failure during the peel test was mainly by cohesive fracture through the adhesive layer. The laminates prepared from the “low-thermal history” polyimide films tended to fail in a weak boundary layer of the polyimide film. The peel energies were lower and displayed a greater scatter. Thein situ peel tests have also identified various failure mechanisms which account for the different features observed on the peeled surfaces and the various types of peel energy traces which were recorded.     

Microstructural investigation of Bi–Sr–Ca–Cu–oxide thick films on alumina substrates

The microstructure of Bi–Sr–Ca–Cu–oxide (BSCCO) thick films on alumina substrates has been characterized using a combination of X-ray diffractometry, scanning electron microscopy, transmission electron microscopy of sections across the film/substrate interface and energy-dispersive X-ray spectrometry. A reaction layer formed between the BSCCO films and the alumina substrates. This chemical interaction is largely responsible for off-stoichiometry of the films and is more significant after partial melting of the films. A new phase with f c c structure, lattice parameter a = 2.45 nm and approximate composition Al₃Sr₂CaBi₂CuO _x has been identified as reaction product between BSCCO and Al₂O₃. This revised version was published online in November 2006 with corrections to the Cover Date.     

Microanalyses of chemically etched thin film alumina-ferrite interfaces

Thin films of aluminium oxide were deposited on ferrite (Ni _x Zn_1−x Fe₂O₄) substrates by r.f. sputtering. The sputtered alumina films were not easily etched by hot phosphoric acid unlike readily etchable films prepared by physical deposition techniques. Microanalytical characterization of unetched films, partially etched films and interfacial regions was conducted to identify the microscopic features responsible for reluctant film etchability. The post-etched films were categorized as easily, partially and un-etchable (EE, PE and U respectively) and were examined using optical microscopy, SEM, XRD, EDS, XPS, AES, and TEM/STEM. TEM examination of cross-sections of partially etchable films revealed a non-uniform crystalline phase at the film-substrate interface. Electron diffraction data identified the phase asη-alumina although AES and EDS results suggest that the interfacial phase also contained some iron. The occurrence and orientation of theη-alumina phase was shown to depend on the orientation of the grains of the ferrite substrate.