Polysaccharide surface engineering of poly(D, L-lactic acid) via electrostatic self-assembly technique and its effects on osteoblast growth behaviours

The objective of this study was to surface modify the poly (D, L-lactic acid) (PDLLA) films and assess the effects of the modified surfaces on the functions of osteoblasts cultured in vitro. A layer-by-layer (LBL) self assembly technique, was used leading to the formation of multilayers on the PDLLA film surfaces. Chitosan (Chi) and poly (styrene sulfonate, sodium salt) (PSS) were utilized as polycation and polyanion in this study, respectively. The layer structure was investigated by using X-ray photoelectron spectroscopy (XPS) and water contact angle measurement, respectively. XPS analysis displayed the presence of chitosan on PDLLA surface. A full coverage of coating with PSS/Chi layers was achieved on the PDLLA surface only after the deposition layers of PEI/(PSS/Chi)₂. These results showed that PDLLA films could be modified with PSS/Chi pairs which may affect the biocompatibility of the modified PDLLA films. To confirm this hypothesis, cell proliferation, cell viability as well as alkaline phosphtase activity of osteoblasts on layer-by-layer modified PDLLA films as well as control samples were investigated in vitro. The proliferation of osteoblasts on modified PDLLA films was found to be greater than that on control (p < 0.05 and p < 0.01) after 1, 4 and 7 days culture, respectively. Cell viability measurement showed that the PSS/Chi modified PDLLA films have higher cell viability (p < 0.01) than control. Osteoblast differentiation function (ALP) on LBL-modified PDLLA film was found significantly higher (p < 0.01) than that of virgin PDLLA films. These data suggests that PSS/Chi pair was successfully employed to surface modify PDLLA film via a layer-by-layer technique, and enhanced its cell biocompatibility.     

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.     

Influence of the energy density on the structure and morphology of polycrystalline silicon films treated with electron beam

Microstructures of electron beam remelted polycrystalline silicon films (20 μm thickness) deposited on a borosilicate glass solar cell absorber with a tungsten inter layer were investigated. It was found that WSi₂ compound was formed in both the tungsten/silicon interface and the grain boundaries of the silicon. The wetting and adhesion between the silicon melt and substrate were enhanced by the formation of WSi₂ compound. The electrical properties of the solar absorber were deteriorated by the tungstendisilicide interlayer. Because of the fast melting and cooling of the silicon film, the silicon film was solidified in a non-equilibrium manner due to the fast cooling rate during the EB remelting. Microstructural analysis indicated that the surface morphology of the film was affected by the EB energy density used in the remelting process. The capping layer became smooth and continuous and the number of pinholes was reduced when the EB energy density was increased. The deposited films exhibited large voids in the outmost surface layer and more WSi₂/Si eutectic crystallites in silicon layer and the WSi₂ layer became thicker if the EB energy density was too high.     

Layer-by-layer assembly of poly(p-xylyleneviologen)–DNA multilayers and their electrochemical properties

Multilayers of poly(p-xylyleneviologen) (PXV) and calf thymus DNA were constructed on the gold surface by layer-by-layer (LBL) method. The assembly process was examined by quartz crystal microbalance (QCM) measurements. According to the frequency change, the average mass increase was estimated to be about 97 and 110 ng/cm² for each assembly of PXV and DNA layer, respectively. Cyclic voltammograms of the multilayer modified gold electrodes showed a couple of redox peaks, the potentials of which were closely dependent on the layer numbers and nature of the outmost layer. The alternatively assembled DNA layers could hinder formation of π-complex dimer of viologen groups due to the strong interlayer electrostatic interaction. The charge transfer process was discussed by the chronocoulometry method. The assembled PXV–DNA multilayers showed high long-term stability at ambient conditions and in electrolyte solution.     

Roughness-enhanced thermal-responsive surfaces by surface-initiated polymerization of polymer on ordered ZnO pore-array films

The correlation between stimuli-responsive wettability switching and surface morphology of poly(N-isopropylacrylamide) (PNIPAm)-modified ZnO pore-array surface is studied. PNIPAm is grafted to the ZnO pore-array surface by surface-initiated polymerization. The effects of thickness of the PNIPAm layer and surface morphology on the thermally responsive switching behavior of the PNIPAm-modified films were studied considering the influences 3D capillary effect (Wenzel's model) and air trapping effect (Cassie's model). The air trapping effect can be controlled by the pore size, amount of grafted PNIPAm polymer, and shape of the pore edge. The surface roughness and expanded pore edge with mushroom-like texture of S2 film amplify the thermally responsive wettability switching between hydrophilicity and hydrophobicity. When the pore structure is completely filled, the switching properties get lower. The thermally responsive switching behavior is enhanced with increasing molecular chain length of the PNIPAm. By controlling the ZnO pore-array structure and the amount of grafted PNIPAm layer, the S2 film shows excellent reversibility for more than 3 cycles and a quick transformation between hydrophilicity and hydrophobicity.     

The thickness effect of Bi3.25La0.75Ti3O12 buffer layer in PbZr0.58Ti0.42O3/Bi3.25La0.75Ti3O12 (PZT/BLT) multilayered ferroelectric thin films

A series of PbZr_0.58Ti_0.42O₃ (PZT) thin films with various Bi_3.25La_0.75Ti₃O₁₂ (BLT) buffer layer thicknesses were deposited on Pt/TiO₂/SiO₂/p-Si(100) substrates by RF magnetron sputtering. The X-ray diffraction measurements of PZT film and PZT/BLT multilayered films illustrate that the pure PZT film shows (111) preferential orientation, and the PZT/BLT films show (110) preferential orientation with increasing thickness of the BLT layer. There are no obvious diffraction peaks for the BLT buffer layer in the multilayered films, for interaction effect between the bottom BLT and top PZT films during annealing at the same time. From the surface images of field-emission scanning electron microscope, there are the maximum number of largest-size grains in PZT/BLT(30 nm) film among all the samples. The growth direction and grain size have significant effects on ferroelectric properties of the multilayered films. The fatigue characteristics of PZT and PZT/BLT films suggest that 30-nm-thick BLT is just an effective buffer layer enough to alleviate the accumulation of oxygen vacancies near the PZT/BLT interface. The comparison of these results with that of PZT/Pt/TiO₂/SiO₂/p-Si(100) basic structured film suggests that the buffer layer with an appropriate thickness can improve the ferroelectric properties of multilayered films greatly.     

Photopatterning of heterostructured polymer Langmuir-Blodgett films

Heterostructured polymer Langmuir-Blodgett (LB) film prepared by using poly(N-dodecylacrylamide-co-t-butyl 4-vinylphenyl carbonate) (p(DDA-tBVPC53)) and poly(N-neopentyl methacrylamide-co-9-anthrylmethyl methacrylate) (p(nPMA-AMMA10)) polymer LB films which can act as photogenerator layers were investigated. Patterns with a resolution of 0.75 μm were obtained on heterostructured polymer LB films composed of 4 layers of p(nPMA-AMMA10) LB film (top layers) and 40 layers of p(DDA-tBVPC53) LB film (under layers) on a silicon wafer by deep UV irradiation followed by development with 1% tetramethylammonium hydroxide aqueous solution. The sensitivity of the heterostructured polymer LB films was improved without loss of the resolution compared with p(DDA-tBVPC53) LB film. The etch resistance of the heterostructured polymer LB films was sufficiently good to allow patterning of a copper film suitable for photomask fabrication.     

Crystallographic properties of four-fold grain K3Li2Nb5O15 thin films

The structural properties of a potassium lithium niobate (KLN; K₃Li₂Nb₅O₁₅) thin film deposited by rf-magnetron sputtering on a Pt/Ti/SiO₂/Si(100) substrate were investigated. The crystalline structures of the Pt under layer and KLN thin films were examined using θ-2θ, θ-rocking, and mesh scan X-ray diffraction (XRD). The XRD results revealed that the Pt under layer was a strong (111) direction orientated poly crystal. Unlike the Pt under layer film, the KLN(001) peak was found to consist of two separate peaks, one with a broad full width half maximum (FWHM) and the other with a narrow FWHM, indicating that the KLN film had a single crystalline structure. The surface and cross-section morphology were investigated using a scanning electron microscope (SEM). Accordingly, from the results of the SEM and XRD experiments, it was concluded that the KLN film was composed of small single crystals, which had a four-fold symmetry morphology with a c-axis normal to the substrate.     

Electroluminescent characteristics of spin-assembled multilayer films with confined layer structure

Multilayer films composed of poly(p-phenylene vinylene) (PPV) as the semiconducting polymer and poly(methacrylic acid) (PMAA) as the insulating polymer were fabricated by spin-assembly method. These films, comprising a confined layer structure, showed that the water contact angles are periodically and distinctly oscillated when the top surface layer is alternated between PPV precursor and PMAA. The turn-on voltage of the multilayer electroluminescent (EL) devices increased from 2.6 V to 9.8 V as the thickness of the PMAA layer inserted between neighboring PPV layers was increased from 0 (i.e., PPV single layer film) to 2.0 nm. Furthermore, the emission peaks in the photoluminescent and EL spectra of these devices were strongly blue-shifted due to excitons formed at the confined PPV layers. Particularly when inserting about 1.0 nm thick PMAA layers, which possibly induced a tunneling effect on the charge carriers (i.e., holes and electrons), these multilayer films decreased the mobility of the hole carriers in the PPV layers with strong hole transporting characteristics, and therefore increased the recombination probability in the emitting layer with confined geometry. As a result, the device efficiency was significantly improved in comparison with that of a PPV single layer device without PMAA layer and with that of devices with relatively thick PMAA layers of 1.4 or 2.0 nm.     

Evolution of morphology of surface during film growth of polycrystalline silicon with hemispherical grains

Evolution of surface morphology during film growth of polycrystalline silicon with hemispherical grains (HSG-Si films) is studied using scaling analysis of surface images obtained by atomic-force microscopy. It has been found from the height-height correlation functions that roughness exponent α = 0.92 ± 0.03 and does not depend on the thickness of a film. The dependences of interface width W(t), correlation length ξ(t) and wavelength λ(t) on deposition time, as well as the scaling coefficients β, 1/z, and p, are found.     

Influence of additives on the morphological,phase and chemical characteristics of gas sensitive SnO2 sprayed films

The morphology, and also the chemical and phase composition of sprayed SnO₂ films doped with Cu, Zr, Fe and P have been investigated. It was found that in general, the film morphology was characterized by a fine grained basic layer with a few large crystallites located on the surface. All the doping elements decreased the grain size in the basic layer. For Fe, Zr and P the grain size depended on the doping level in the spray solution. It was established that the dopant: Sn ratio in the films was much lower than that in the spray solution. The doping element was preferentially accomodated in the large crystallites with only a small quantity of the dopant being introduced into the basic layer. The gas sensing properties of the films have are discussed on the basis of these results.     

Temperature effect on structure and surface morphology of indium tin oxide films deposited by reactive ion-beam sputtering

Indium tin oxide (ITO) films were deposited by reactive ion-beam sputtering. The relationship among the surface morphology, the resistivity ρ of the films, the substrate temperature T_S and the film thickness t_F was investigated. The heat power from the ion source during the sputtering was 265 W. T_S increased from 30 to 145 °C with an increase of t_F. The films thinner than 187 nm at T_S lower than 120 °C were amorphous, the film surface was as smooth as the substrate. The films deposited at T_S in the range between 135 and 145 °C were polycrystalline. So, the films thicker than 375 nm were in a multilayer structure of a polycrystalline layer on an amorphous layer. The surface of the polycrystalline films became rough. ρ of the films suddenly decreased at t_F of 375 nm, where the structure of the films changed. Next, the amorphous films with t_F of 39 nm were annealed in the atmosphere. The film structure changed to a polycrystalline structure at annealing temperature T_A of 350 °C. However, the surface roughness of all the films was almost same. As a result, the substrate temperature during the sputtering was important for the deposition of the films with a very smooth surface.     

Surface morphology and thickness of a multilayer film composed of strong and weak polyelectrolytes: Effect of the number of adsorbed layers, concentration and type of salts

Self-assembled multilayered films were prepared by alternate deposition of a strong cationic polyelectrolyte, poly(trimethylammonium ethyl methacrylate chloride) and a pH-dependant anionic polyelectrolyte, poly(acrylic acid). The layer-by-layer adsorption was followed in-situ by optical fixed-angle reflectometry and after drying by ellipsometry. A recently developed “substrate thickness method” was applied to calculate the adsorbed amount of polymer from the reflectometric signal. Surface film morphology was imaged before and after drying with atomic force microscopy (AFM). Influence of the number of adsorbed layers, concentration and type of salts on the multilayer growth was examined. The number of adsorbed layers produced a specific effect on the reflectometric signal which is linked to the refractive index of the film. Adjustment of the adsorbed amount of polyelectrolytes was done by changing sodium chloride salt concentration within a range of 10^− 3 to 10^− 1 M. AFM observations showed a significant evolution in surface morphology and a maximum of surface roughness for films built-up at 10^− 2 M. Experiments were then carried out at 10^− 3 M in either barium chloride or zinc chloride salts. In the presence of Ba²⁺ and Zn²⁺ ions, adsorption of 5 bilayers is completely modified and the surface morphology was smoother than the multilayers obtained using sodium chloride salt.     

Photoelectrochemical and in situ atomic force microscopy studies of films derived from o-methoxyaniline solution on gallium arsenide (100) photoelectrode

Organic films derived from o-methoxyaniline water solution were deposited on GaAs electrodes in an adsorption process. The photoelectrochemical behavior of the modified electrodes was examined by potentiodynamic and potentiostatic methods. The film morphology dependencies on the monomer concentration in the bulk of solution, electrode potential and oxidation time were monitored by in situ atomic force microscopy. The monitored morphology changes were correlated with the changes in the photocurrent. The differences in the onset potentials and photocurrent magnitude were explained in terms of the formation of a continuous organic film and on the basis of the p-n junction creation at the GaAs/organic film interface. It is suggested that the organic film mediates transfer of the photocharge to the solution. Based on morphological changes in the deposited film and the spectrophotometric data, the formation of the leucoemeraldine, a reduced form of poly (o-methoxyaniline) is proposed.     

Effect of chain conformation on micro-mechanical behaviour of MEH–PPV thin film

The morphology, photoluminescent properties and micro-mechanical character of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH–PPV) thin films prepared from toluene (T film) and chloroform (C film) were studied by transmission electron microscopy (TEM), absorption, photoluminescence spectrophotometry and nanoindentation test. The morphological feature of worm-like entities which appeared in T film was ~10–20 nm in length and 3–5 nm in width. The C film displayed the continuous cotton fibre-shaped morphology. In contrast with C film, the band-edge absorption and maximum emission for T film shifted to the longer wavelength. An analysis from TEM photograph, absorption and photoluminescence spectra indicated that different chain conformation presented in these two kinds of films. The nanoindentation test showed that the elastic modulus and indentation hardness of T film under the same experimental parameter (load: 50–200 μN, loading rate: 20 μN/s and holding time: 20 s) decreased by 33·3 ± 0·3 and 8·9 ± 0·5%, respectively comparing with C film. In addition, critical bending radius of these two films based on the flexible base was also evaluated from the obtained experimental results.     

Characterization of spray-coating methods for conjugated polymer blend thin films

We examine the characteristics and functionality of conjugated polymer thin films, based on blends of poly(9,9-dioctylfluorene-2,7-diyl-co-bis-N,NN′-(4-butylphenyl)-bis-N,N′-phenyl-1,4-phenylenediamine) (PFB) and poly(9,9-dioctylfluorene-2,7-diyl-co-benzothiadiazole) (F8BT), using a spray-coating deposition technique suitable for large areas. The morphological properties of these blend films are studied in detail by atomic force microscopy (AFM) methods, showing that favourable results, in terms of layer deposition rate and uniformity, can be achieved using a 5:1 blend of o-dichlorobenzene and chlorobenzene as the solvent medium. A photoluminescence quenching efficiency of above 80 % is also observed in such blend films. As a feasibility study, prototypical photovoltaic devices exhibit open circuit voltages of up to 1.0 V under testing, and solar power conversion efficiencies in the 0.1–1 % order of magnitude; metrics which are comparable with those reported for spin-coated cells of the same active blend and device architecture.     

Electrochemical investigation and characterization of thin-film porosity

In thin-film applications it is necessary to control film properties such as homogeneity and porosity to obtain high-quality coatings. Electrochemistry can be a very helpful tool since it can provide information about processes taking place at the interface between substrate and coating. Different thin carbon-based coatings were deposited via physical vapour deposition methods and vapour phase polymerization on pure iron substrates: fullerene films, which were modified by an ion bombardment and thin films of poly(p-xylylene), which is a very good insulating polymer. The film porosity and stability of the film/substrate system against aqueous corrosion were investigated and compared using cyclic voltammetry. The dependence of porosity and film stability on various deposition process parameters such as film thickness and plasma conditions was measured via the dissolution current density and the open circuit potential shift of the substrate material. It could be shown that the two measurements, current density I_crit. and open circuit potential E_ocp. can provide useful complementary information about film porosity that can lead to a better understanding of the coatings properties and the deposition process as well.     

Enhanced magnetic properties of chemical solution deposited BiFeO3 thin film with ZnO buffer layer

Magnetic properties of BiFeO₃ films deposited on Si substrates with and without ZnO buffer layer have been studied in this work. We adopted the chemical solution deposition method for the deposition of BiFeO₃ as well as ZnO films. The x-ray diffraction measurements on the deposited films confirm the formation of crystalline phase of BiFeO₃ and ZnO films, while our electron microscopy measurements help to understand the morphology of few micrometers thick films. It is found that the deposited ZnO film exhibit a hexagonal particulate surface morphology, whereas BiFeO₃ film fully covers the ZnO surface. Our magnetic measurements reveal that the magnetization of BiFeO₃ has increased by more than ten times in BiFeO₃/ZnO/Si film compared to BiFeO₃/Si film, indicating the major role played by ZnO buffer layer in enhancing the magnetic properties of BiFeO₃, a technologically important multiferroic material.     

Ellipsometric determination of optical properties of carbazole-containing poly(l-glutamate) thin films prepared from different solvents

In this study, the refractive indices (n) and thicknesses of carbazole-containing hole-transport materials such as poly(γ-carbazolylethyl l-glutamate) (PCELG) and poly(N-vinyl carbazole) (PVCz) films were determined by carrying out ellipsometric measurements. The thicknesses of PCELG and PVCz films determined by ellipsometric analysis were in good agreement with those determined by surface profilometry. The dependence of the refractive indices of the PCELG films on film thickness was classified into two types on the basis of the solvent from which the films were prepared: the refractive indices either increased with increasing film thickness, as in the case of PCELG films prepared from 1,2-dichloroethane (DCE) and monochlorobenzene (?-Cl), or were independent of the film thickness, as in the case of films prepared from 1,1,2,2-tetrachloroethane (TCE). A comparison of these results with the structures of the polymers, as determined by ¹H NMR, reveals that the two types of dependences of the refractive indices of the PCELG thin film on the film thickness can be attributed to the two types of aggregation structures and/or orientational characteristics corresponding to the helical conformation of the polymer. In contrast, the refractive indices of PVCz films are governed mainly by the film thickness. Finally, we would like to emphasize that the combination of ellipsometry and other techniques such as NMR and surface profilometry provide information not only on the film thickness and refractive index but also on the aggregation structure in thin films with thicknesses on the order of 50 nm.     

Nanostructure and mechanical properties of aromatic polyamide and reactive organoclay nanocomposites

Aromatic polyamide/organoclay nanocomposites were synthesized using the solution blending technique. Treatment of montmorillonite clay with p-phenylenediamine produced reactive organophilic clay for good compatibility with the matrix. Polyamide chains were prepared by condensing a mixture of 1,4-phenylenediamine and 4-4′-oxydianiline with isophthaloyl chloride under anhydrous conditions. These chains were end capped with carbonyl chloride using 1% extra acid chloride near the end of reaction to develop the interactions with organoclay. The dispersion and structure–property relationship were monitored using FTIR, XRD, FE-SEM, TEM, DSC and tensile testing of the thin films. The structural investigations confirmed the formation of delaminated and disordered intercalated morphology with nanoclay loadings. This morphology of the nanocomposites resulted in their enhanced mechanical properties. The tensile behavior and glass transition temperature significantly augmented with increasing organoclay content showing a greater interaction between the two disparate phases.