Surface modification of thin polystyrene films

 The sulfonation of polystyrene (PS) films with 50 and 96% sulfuric acid as a function of time is presented. In contrast to previous literature reports, we showed that the treatment of PS films even with dilute sulfuric acid yields sulfonated surfaces after reaction times of 30 s–1 h. The hydrophilicity of the modified PS increased considerably in comparison to the unreacted PS films. X-ray photoelectron spectroscopy yielded evidence for the sulfonation of PS at the surface. Unreacted spin-coated PS films were very smooth, while modified PS showed some clumps dispersed on a flat surface, as analyzed by atomic force microscopy. The surface morphology was identified as a phase-separated system composed of domains of unreacted PS and a matrix of sulfonated PS by fluorescence microscopy using the positively charged dye rhodamine B. The adsorption of the polycation diallyldimethylammonium chloride on the sulfonated PS surface could be detected. The thickness of the adsorbed polycation was 2.2 nm. Received: 3 November 1998 Accepted in revised form: 23 February 1999     

Nanostructured CuO/SrTiO3 bilayered thin films for photoelectrochemical water splitting

Bilayered thin films of CuO/SrTiO₃ with varying thickness of CuO were deposited by sol–gel spin-coating technique on indium tin oxide substrate and used as photoelectrode in the photoelectrochemical cell for water splitting reaction. Maximum photocurrent density of 1.85 mA/cm² at ?0.9 V/saturated calomel electrode was exhibited by 590-nm-thick CuO/SrTiO₃ bilayered photoelectrode, which is approximately eight times higher than that for CuO and 30 times higher than that for SrTiO₃. The bilayered system offered increased photocurrent density and enhanced photoconversion efficiency, attributed to improved conductivity, which ameliorate separation of the photo-generated carriers at the CuO/SrTiO₃ interface and higher value of flatband potential. Details about synthesis and various characterisations involving X-ray diffraction and scanning electron microscopy have been discussed. An energy band diagram has been proposed to dwell upon the mechanism of charge carrier transfer across the interface.     

Surface structural evolution in iron oxide thin films

Ordered iron oxide ultrathin films were fabricated on a single-crystal Mo(110) substrate under ultrahigh vacuum conditions by either depositing Fe in ambient oxygen or oxidizing preprepared Fe(110) films. The surface structure and electronic structure of the iron oxide films were investigated by various surface analytical techniques. The results indicate surface structural transformations from metastable FeO(111) and O-terminated Fe(2)O(3)(0001) to Fe(3)O(4)(111) films, respectively. The former depends strongly on the oxygen pressure and substrate temperature, and the latter relies mostly upon the annealing temperature. Our experimental observations are helpful in understanding the mechanisms of surface structural evolution in iron oxides. The model surfaces of Fe-oxide films, particularly O-terminated surfaces, can be used for further investigation in chemical reactions (e.g., in catalysis).     

Surface structure analysis of thin dewetted polymer blend films

The surface structure of thin polymer blend films of deuterated polystyrene (dPS) and polyparamethylstyrene (PpMS) after annealing above the glass transition temperature was investigated. With scanning force microscopy (SFM) the surface topography originated by a dewetting process is detected. The sample surface is covered with small droplets consisting of several polymer molecules. Utilizing grazing incidence small angle neutron scattering (GISANS) the topographical information as well as the in‐plane composition is probed. For thin confined blend films a substructure of the droplets resulting from an additional phase separation process at different length scales is detected.     

Surface plasmon fluorescence investigation of energy-transfer-controllable organic thin films

Thin functional organic films on a gold substrate were fabricated by adsorbing tetrakis(carboxyphenyl)porphyrin (TCPP) on a spacer layer, which was prepared by the layer-by-layer adsorption of a dendrimer and a linear polymer. The thickness and photoluminescence of the films were investigated by surface plasmon resonance and surface plasmon fluorescence techniques, respectively. TCPP adsorbed on the spacer layer in aqueous solutions of different ionic strengths resulted in a thick TCPP adlayer at high ionic strength and a shrunk spacer layer at low ionic strength. The fluorescence was quenched at high ionic strength but could be observed at low ionic strength. The effects are explained by the states of dye aggregation. This study shows the control of energy transfer from a metal surface to a dye layer by changing the dye adlayer. It can contribute to the development of molecular devices involving energy-transfer systems.     

Surface morphology of poly(cyano-p-xylylene) thin films

The surface morphology of poly(cyano-p-xylylene) thin films of different thicknesses (25–1500 nm or more than 5 μm) that were synthesized by vapor-deposition polymerization on the substrate surface in the temperature range from −22 to +35°C has been studied by atomic force microscopy. The surface topography is quantified through analysis of the height-height correlation function. The surface of all films is characterized by a similar granular morphology with a transverse size of granules of 50–500 nm. The surface morphology changes with the polymerization temperature (the substrate temperature) and the film thickness. The effect of film annealing on its surface morphology is considered. It has been established that annealing at 200°C leads to a change in the surface morphology of the films. Original Russian Text ? A.I. Buzin, D.S. Bartolome, K.A. Mailyan, A.V. Pebalk, S.N. Chvalun, 2006, published in Vysokomolekulyamye Soedineniya, Ser. A, 2006, Vol. 48, No. 9, pp. 1640–1646. This work was supported by the Russian Foundation for Basic Research (project nos. 03-03-32665 and 03-03-32634) and the Russian Science Support Foundation.     

Effect of pH on the properties of nanocrystalline CuO thin films deposited by sol-gel process

Nanocrystalline cupric oxide thin films were prepared using the sol-gel method. Three sols with different pH were performed in order to evaluate the pH effect on the morphology and optical properties of the films. XRD pattern confirmed the nanocrystalline monoclinic CuO phase formation. The influences of pH on surface morphology of films were investigated by scanning electron microscopy (SEM). It was observed that grains size increases by increasing the pH of the sol. UV-Vis spectrum measurement showed low transparency of the films in the visible region. Optical constants such as extinction coefficient, refractive index and optical band gap were evaluated from these spectra by using the Pointwise Unconstrained Minimization Approach (PUMA). The band gap of the films varies from 2.20 to 1.98 eV for various pH of sol.     

Surface forces measurements of spin-coated cellulose thin films with different crystallinity

A systematic study of the surface forces between a cellulose sphere and cellulose thin films of varying crystallinity has been conducted as a function of ionic strength and pH. Semicrystalline cellulose II surfaces and amorphous cellulose films were prepared by spin-coating of the precursor cellulose solutions onto oxidized silicon wafers before regeneration in water. Crystalline cellulose I surfaces were prepared by spin-coating wafers with aqueous suspensions of sulfate-stabilized cellulose I nanocrystals. These preparation methods produced thin, smooth films suitable for surface forces measurements. The interaction with the cellulose I was monotonically repulsive at pH 3.5, 5.8, and 8.5 and at 0.1, 1, and 10 mM ionic strengths. This was attributed to the presence of strongly ionizable sulfur-containing groups on the cellulose nanocrystal surfaces. The amorphous film typically showed a steric interaction up to 100 nm away from the interface that was independent of the solution conditions. A range of surface forces were successfully measured on the semicrystalline cellulose II films; attractive and repulsive regimes were observed, depending on pH and ionic strength, and were interpreted in terms of van der Waals and electrostatic interactions. Clearly, the forces acting near cellulose surfaces are very dependent on the way the cellulose surface has been prepared.     

Influence of nickel incorporation on structural,optical and electrical characteristics of SILAR synthesized CuO thin films

In this report, we have primarily studied the influence of nickel (Ni) incorporation on ac electrical conductivity, dielectric relaxation mechanism and impedance spectroscopy characteristics of copper oxide (CuO) thin films synthesized by successive ion layer adsorption and reaction (SILAR) technique. The materials has been characterized using X-ray diffraction and UV–VIS spectrophotometric measurements. Reduction in grain size in doped films up to a certain extent of doping (tentatively 6%) were confirmed from XRD analysis, beyond which there is a reverse tendency. Increase in band gap in doped films were observed up to 6% doping level which could be associated with enhanced carrier density in doped films. Impedance spectroscopy analysis confirmed enhancement of ac conductivity and dielectric constant for doped samples. The results are useful for capacitive application of the films. Beyond 6% doping level, AC conductivity and dielectric constant shows a reverse tendency indicating reduced density of charge carriers. Nyquist plot shows contribution of both grain and grain boundary towards total resistance and capacitance. Imaginary part of complex modulus and imaginary part of complex impedance was used to find the migration/activation energy to electrical conduction process. Nearly identical result was obtained from relaxation frequency/relaxation time approach suggesting hopping mechanism of charge carriers.

Open image in new window

     

Supramolecular chirality formation of bisazobenzene-substituted polydiacetylene LB films

In order to investigate the exact effect of stereoregular packing of head group in the side chain on the helical structure formation of polydiacetylene backbone, the larger size of bisazobenzene-substituted diacetylene monomer, 4-(4-nitrophenylazo) azobenzene-10, 12-pentacosadiynoate (BNADA) was synthesized successfully. Owing to overcrowded packing of bisazobenzene chromophores, the BNADA Langmuir-Blodgett (LB) films showed macroscopic supramolecular chirality, although BNADA molecules were achiral. Under circularly polarized UV light (CPUL) irradiation, supramolecular helix of bisazobenzene chromophores always maintained, due to the large size and lower photo-isomerization rate of bisazeobenzene chromophores. While for polydiacetylene backbone, the helical direction of the polymer chain should be decided by the competition of the effect of stereoregular packing of bisazobenzene chromophores and the interaction between the CPUL and the diacetylene dimer.     

Surface patterns induced by laser irradiation on thin polymer bilayer films

We report on the preparation of wavelike surface patterns with characteristic wavelengths on thin bilayers of poly(methyl methacrylate) on azobenzene liquid crystalline polymer films (LCP/PMMA) by irradiation of a single polarized pulsed laser beam. The formation of such patterns was influenced by the thickness of the upper layer and the laser fluence. We were also able to guide the wavelike pattern to have a specific orientation by placing an elastic polydimethylsiloxane (PDMS) mold on the surface of bilayer film prior to laser irradiation. Moreover, the property of the laser irradiation, that is, the selectivity through mask-projection systems, allowed us fabricating complicated micropatterns for novel microdevices.     

Growth and morphological studies of NiO/CuO/ZnO based nanostructured thin films for photovoltaic applications

At present, inorganic semiconducting materials are the most economical and viable source for the renewable energy industry. The present work deals with the morphological and optical characterization of copper oxide (CuO) and zinc oxide (ZnO) thin films fabricated by layer by layer deposition on nickel oxide (NiO) coated indium tin oxide (ITO) glass by solution processing methods, mainly chemical bath deposition (CBD) and hydrothermal deposition (HTD) processes at room temperature. As a whole, the above inorganic composite materials (NiO/CuO/ZnO) can be applied in photovoltaic cells. An attempt has been made to study structural, morphological and absorption characteristics of NiO/CuO/ZnO heterojunction using state of the art techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV spectroscopy. The energy band gaps of CuO and ZnO have also been calculated and discussed based on the UV spectroscopy measurements.     

Surface structure and photoluminescence properties of AZO thin films on polymer substrates

Al‐doped zinc oxide (AZO) thin films were deposited on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering method at room temperature. The effects of film thickness on the surface structure and the photoluminescence properties of the films were investigated by atomic force microscopy (AFM), secondary ion mass spectroscopy (SIMS) and room temperature photoluminescence (PL). AFM analysis showed that the surface of all films was extremely flat and uniform at nanoscale. Root mean square (RMS) value of the surface roughness which scanned the surface area of 3 µm by 3 µm and grain size increased with increasing the film thickness. Thus, the surface morphology of the films became rough because of the coarse grains. The depth profile of AZO layers was analyzed by SIMS. It was found that the thickness of the AZO layer is almost same with the desired film thickness. The PL intensity of the dominant peak decreased and shifted slightly towards the shorter wavelengths with increasing the film thickness. According to the relationships between luminescence intensity and crystalline characteristics, it was observed that the intensity of the peak decreased by the increased surface area of the grains. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface morphology and electrical properties of copper thin films prepared by MOCVD

Thin copper films have been grown in a vertical MOCVD (Metal-Organic Chemical Vapor Deposition) reactor using bis(2,2,6,6-tetramethyl-3,5-heptanedionato) copper(II), Cu(thd)₂, as precursor. Deposition has been carried out in a pure hydrogen atmosphere (pressure: 3, 20 mbar) at different substrate temperatures (350–750 ° C). The films have been investigated by profilometry, four-point resistivity measurements, ESCA, AES, XRD, AFM, and Normarsky microscopy. An unusual dependence of the film thickness with deposition time has been observed. Rapid growth occurred in the first minutes resulting in badly conducting films (thickness below 1000 Å). Good electrical resistivities have been obtained above 2000 Å. AFM has been used to gain information about the surface morphology of the films with different thicknesses. The grain size and surface roughness increased with increasing film thickness. Small grains grew in the beginning and the electrical properties have been governed by the highly Ohmic bridges between the individual grains.     

Surface and bulk ordering in thin films of a symmetrical diblock copolymer

Amphiphilic diblock copolymers have the ability to adapt their surface's molecular composition to the hydrophilicity of their environment. In the case of about equal volume fractions of the two polymer blocks, the bulk of these polymers is known to develop a laminar ordering. We report here our investigation of the relationship between bulk ordering and surface morphology/chemical composition in thin films of such an amphiphilic diblock copolymer. Upon annealing in vacuum, the expected lamella ordering in the bulk of the film is observed and we find the morphology of the film surface to be defined by the thickness of the as‐deposited film: If the as‐deposited thickness matches the height of a lamella stack, then the film exhibits a smooth surface. Otherwise, an incomplete lamella forms at the film surface. We show that the coverage of this incomplete layer can be quantified by X‐ray reflectivity. To establish the lamella ordering in the bulk, the film needs to be annealed above the glass temperature of the two blocks. Molecular segregation at the film surface, however, is already occurring at temperatures well below the glass temperature of the two blocks. This indicates that below the glass temperature of the blocks the bulk of the thin film is “frozen,” whereas the polymer chains composing the surface lamella have an increased mobility. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys., 2013 , 51, 1282–1287     

Surface chirality effects induced by magnetic fields

Symmetry breaking in magnetohydrodynamic vortices induces surface chirality on electrodeposit films.

1. Download : Download high-res image (104KB)
2. Download : Download full-size image

     

Photoinduced supramolecular chirality in amorphous azobenzene polymer films

Supramolecular chirality was optically induced in amorphous and achiral azobenzene polymer films by irradiation of a laser beam with elliptical polarization. The chirality resulted from helical orientation of azobenzene chromophores by a combined process of circular and linear polarization. The helix-handedness could be controlled by incident light-handedness.     

Surface plasmon resonance sensor for lysozyme based on molecularly imprinted thin films

Molecularly imprinted polymers (MIPs) selective for lysozyme were prepared on SPR sensor chips by radical co-polymerization with acrylic acid and N,N′-methylenebisacrylamide. Gold-coated SPR sensor chips were modified with N,N′-bis(acryloyl)cystamine, on which MIP thin films were covalently conjugated. The presence of NaCl during the polymerization and the re-binding tests affected the selectivity and the optimization of NaCl concentration in the pre-polymerization mixture and the re-binding buffer could enhance the selectivity in the target protein sensing. When the lysozyme-imprinted polymer thin films were prepared in the presence of 40 mM NaCl, the selectivity factor (target protein bound/reference protein bound) of MIP in the re-binding buffer containing 20 mM NaCl was 9.8, meanwhile, that of MIP in the re-binding buffer without NaCl was 1.2. A combination of SPR sensing technology with protein-imprinted thin films is a promising tool for the construction of selective protein sensors.     

Surface aggregation structure and surface mechanical properties of binary polymer blend thin films

During preparation of very thin polymer belnd films from a solution of polymers, the phase‐separated structures which are quite different from that observed for the bulk blend film was observed. From atomic force microscopic(AFM) observation, it is concluded that the surface undulation, which reflects the phase separated morphology of the blend system, is present. In the case of (polystyrene(PS)/poly(methyl methacrylate)(PMMA)) blend system, a large influence of end‐group chemistry on the surface morphology was observed. The phase identification of the (rubbery polymer/glassy polymer) binary blend thin films was successfully achieved by scanning vioscoelasticity microsopy(SVM).