Spectroscopic analysis of electrically polarized polyacrylonitrile

Electrically polarized and unpolarized films of polyacrylonitrile (PAN) have been investigated by both infrared attenuated total reflection (ATR) and thermally stimulated discharge (TSD). ATR analysis of PAN films has been aimed at explaining the molecular origin of thermally stimulated currents, and consequently that of phenomena contributing to electrical polarization in this material. Preferred orientation of nitrile dipoles along the thickness direction (applied electric field direction) has been detected by ATR in both polarized and unpolarized films. It is suggested that dipolar alignment in unpolarized solvent-cast films could result from internal electric fields associated with space charges. The observed orientational anisotropy is found to disappear gradually as films (both polarized and unpolarized) are heated from ambient temperature to 100°C and rotational motion in the backbone is thermally activated. TSD currents observed in this thermal range are thus associated with randomization of molecular dipoles. TSD currents observed above 100°C are suggested to originate from drift of space charges, since both an isotropic orientation of dipoles and onset of considerable diffusion are detected by ATR in this temperature range. PAN films polarized by high-intensity electric fields (5 × 10⁵Vcm^?1, as opposed to 5 × 10⁴Vcm^?1) are found to retain orientational anisotropy above 100°C, and this is believed to be associated with a structural rearrangement induced by electrical polarization.     

Photo-Induced Hydrophilicity of TiO<Subscript>2</Subscript> Films Deposited on Stainless Steel via Sol-Gel Technique

The photo-induced hydrophilicity of TiO₂ films deposited on stainless steel substrates and silicon wafers using two different sol-gel routes has been investigated. The results indicate that crystalline titanium oxide films with excellent hydrophilic properties can be obtained on silicon wafer with both routes. XPS and XRD data reveal that films deposited on stainless steel exhibit crystallization features similar to those of films deposited on silicon wafers, and only differ by their oxidation degree owing to a TiO₂ reduction process associated to a diffusion of iron ions during deposition of the acidic sol and/or high temperature post-treatment. Consequently, hydrophilic properties of films deposited on stainless steel are inhibited. The deposition of a SiO_x barrier layer at the film/substrate interface allows preventing such a detrimental substrate influence. A low temperature deposition route of the TiO₂ film associated to the presence of a barrier layer yields best results in preventing iron contamination of the films.     

MoS x Thin Films by Thermolysis of a Single-Source Precursor

Thin films of MoS _x have been prepared on silicon substrates by spin coating and thermolysis of 0.5 M solutions of alkyldiammonium tetrathiomolybdates in 1,2-ethanediamine (EDA) and 1,2-propanediamine (12PDA). The films have been heat treated in air at temperatures between 80 and 250°C and under N₂ atmosphere at temperatures between 300 and 800°C. X-ray diffraction shows a restricted crystallisation and amorphous residues in both kind of films. EDA-based films exhibit a high tendency to crystallise whereas 12PDA-based films form associated structures with the solvent preventing precursor crystallisation. An insight into the processes occurring in film formation is gained by infrared spectroscopy which indicates a beginning of the decomposition of the 12PDA-based film at temperatures as low as 80°C with incorporation of the diamine solvent. In contrast, the EDA-based films show first signs of a decomposition at 150°C. The decomposition of the intermediate MoS₃ in both cases starts between 250 and 300°C. By means of SNMS depth profiles carbon contents up to 21 and 32 atom-% were found in EDA- and 12PDA-based films, respectively. The films show a significant deficit of sulphur which is compensated by the carbon. Near the surface of the coatings a loss of carbon is observed.     

Effect of Deposition Temperature on Structural and Optical Properties of Chemically Sprayed ZnS Thin Films

Zinc sulfide (ZnS) thin films have been successfully deposited via spray pyrolysis using an aqueous solution of thiourea and zinc acetate onto glass substrate. The effect of varying substrate temperature (150, 200,250 and 300 °C) on structure and optical properties is presented. The films have been characterized by X- ray diffraction (XRD), UV-Vis-NIR spectrometry, photoluminescence (PL) spectroscopy and field emission scanning electron microscopy (FESEM). All the deposited ZnS films exhibit a cubic structure, while crystallinity and morphology are found to depend on spray temperature. PL analysis indicates the presence of violet and green emissions arising from Zn and S vacancies. The value of bandgap of ZnS films is found to decrease slightly with increasing substrate temperature; varying in the range 3.52–3.25 eV, most probably associated with the formation of Zn(S,O) solid solution.     

Structure of Glancing Incidence Deposited TiO2 Thin Films as Revealed by Grazing Incidence Small‐Angle X‐ray Scattering

For the first time, grazing incidence small‐angle X‐ray scattering (GISAXS) analysis is used to characterize the morphology of TiO₂ thin films grown by glancing angle physical vapor deposition (GLAD). According to cross‐section scanning electron microscopy (SEM) images, the films consist of near isotilted TiO₂ columns of different length and width depending on film thickness. The obtained GISAXS patterns show a characteristic asymmetry with respect to the incidence plane, which is associated with the tilted geometry of the TiO₂ columns. The patterns also show the existence of two populations of columns in these GLAD‐TiO₂ films. The population of the thinnest columns appears related to the first grown layer and is common for all the films investigated, while the second population of columns grows with the thickness of the films and has been related to wider columns formed by shadowing at the expense of the initially formed columns.     

In plane and out of plane anisotropy in Langmuir-Blodgett films of discogenic molecules

Abstract

Langmuir-Blodgett films of a discotic mesogenic pyrylium tetrafluoroborate salt (1) have been investigated from the point of view of their in-plane anisotropy, i.e. considering the average molecular orientation with respect to the dipping direction. The molecules are found to stand on edge with their flat polycyclic core more or less perpendicular to the dipping direction. Mixing 1 with N(C₄H₉)₄ ⁺ TCNQ^? in the spreading solvent leads to a different behaviour of the monolayer at the air-water interface, involving the formation of the Pyrylium-TCNQ salt. In contrast to the films of pure 1, these films do not exhibit any in-plane anisotropy after deposition on a solid substrate. The temperature dependance of the molecular anisotropy of both films has also been investigated. The results are presented and discussed in the framework of their mesomorphic properties together with the influence of the anion associated with Pyrylium.     

Influence of current density on the distribution of tungsten tracer in porous anodic alumina films

Porous anodic alumina films have been much studied recently due to interest in the application of the self‐ordered porosity in nanotechnological systems. Experimental investigations have identified anodising regimes that generate pores with a relatively high degree of long‐range order. However, the growth mechanism of the films, and its relation to the ordering of pores, is only partially understood. In the present work, the growth processes are studied over a range of current densities for films formed in oxalic acid. The films are formed on sputtering‐deposited substrates containing tungsten nanolayers that provide W⁶⁺ tracer species in the films. The distributions of tracer species are observed by scanning and transmission electron microscopes and the amounts of tracer species quantified by Rutherford backscattering spectroscopy. It is shown that the tungsten tracer remains within an inner region of the cells, with a tungsten‐free region being present next to the pore walls during the growth of the anodic films. Further, the thickness of the anodic film relative to that of oxidised metal increases with increasing current density, which is associated with an increase in the efficiency of film formation. This behaviour is consistent with the formation of pores by flow of film material in the barrier layer to the pore wall regions. Copyright © 2010 John Wiley & Sons, Ltd.     

SnO2 thin films doped indium prepared by the sol–gel method: structure, electrical and photoluminescence properties

This paper reports on the preparation, characterization, electrical and optical properties of tin oxide (SnO₂) thin films doped indium prepared by the sol–gel method and deposited on glass substrates with dip coating technique. X-ray diffraction patterns showed an increase in the crystallinity of the films with increase in annealing temperatures. Atomic force microscopy analyses revealed an increase of grain growth with raise in annealing temperature. The film surface revealed positive skewness and kurtosis values less than 3 which make them favorable for OLEDs applications. The lowest resistivity (about 10^?7) was obtained for the ITO films annealed at 500 °C. These films acquire n-type conductivity due to the non-stoichiometric in the films like (interstitial tin atoms) and also due to low indium doping concentration. The optical properties of the films have been studied from transmission spectra. An average transmittance of >80 % in ultraviolet–visible region was observed for all the films. Optical band gap energy (E _gap) of ITO films was found to vary in the range of 3.69–3.81 eV with the increase in annealing temperature. This slight shift of E _gap to higher photon energies could be related to the crystalline nature of the films associated with the decrease in the defect concentration caused by annealing. Photoluminescence spectra of the films exhibited an increase in the emission intensity with increase in annealing temperature. The high temperature annealing would be expected to decrease the density of defects, improve the crystal orientation and reduce the traps for non-radiative transition and also increase the oxidation processes.     

The structure of electron beam-modified cellulose triacetate

The structure, relaxation, and surface properties of cellulose triacetate (CTA) fibers and films modified by electron-beam irradiation in the absorbed dose range of D = 0−1000 kGy have been studied. The relation of the glass transition and melting temperatures of the irradiated CTA samples with the local density and the fractal dimensionality of the macrochain has been revealed. It has been shown that the radiation-chemical processes associated with the rupture of acetal bonds and the hydrolysis of CTA acetate groups predetermine the change in the structural and relaxation characteristics of the irradiated samples, as well as a nonmonotonic form of the dependence of the density and the surface energy of the films upon the absorbed dose near the threshold value of D = 75 kGy.     

Synthesis,Characterization and Electrochemical Polymerization of a Ru2+ Functionalized Pyrrole Monomer

A ruthenium(II) functionalized pyrrole, Ruthenium‐bis‐N,N′‐(2,2′‐bipyridyl)‐N‐(pyridine‐4‐ylmethyl‐(8‐pyrrole‐1‐yl‐octyl)amine)chloride, 1 , has been synthesized and characterized by spectroscopic (UV/vis, ¹H NMR) techniques and cyclic voltammetry. In solution 1 gave a redox couple associated with the Ru^3+/2+ redox system and an irreversible wave associated with the oxidation of the covalently linked pyrrole moiety. What is believed to be homopolymerization, redox active surface films of 1 have been prepared by electrooxidation of the monomeric solution. The resulting polymeric film exhibited clear redox activity associated with the incorporated Ru²⁺ redox centre, which is covalently linked ruthenium centre to the pyrrole moiety in 1. The effect of surface coverage upon the electrochemical behavior of the deposited films has been undertaken. Preliminary investigations into the homogeneous charge transport dynamics of the polymeric film deposited onto platinum microelectrodes has been undertaken. Copolymerization with 3‐methylthiophene was carried out and a clear ruthenium response was seen. Films were formed by both cyclic voltammetry and chronocoulometry and studied. Various ratios were attempted but the ideal was found to be 52 : 5 mmol (3‐methylthiophene: 1 ).     

Application of positron annihilation technique to reverse osmosis membrane materials

Positron annihilation lifetime spectroscopy has been adopted as a new approach for studying vacancies of reverse osmosis membrane materials composed of cellulose acetate films and aromatic polyamide resins. The intensity of the ortho-positronium (o-Ps) lifetime increased with the amount of vacancies determined using N₂ isotherm at −195°C. Changes of vacancy profiles induced by heat treatment in the cellulose acetate films were detected using o-Ps. It was found that the positron annihilation technique is applicable to the study of vacancy profiles associated with salt selectivity in typical reverse osmosis membranes.     

Effect of diphenyldiethoxysilane on the self-organized formation of nanocrystalline layered organosilicates in organic–inorganic hybrid films

Hybrid organic–inorganic films containing layered organosilicate nanocrystals have been obtained through self-organization from aqueous precursor sols containing 3-glycidoxypropyltrimethoxysilane. Diethoxydiphenylsilane has been added, in different amounts, to the precursor sol containing 3-glycidoxypropyltrimethoxysilane to prepare hybrid films with the ordered nanostructures. The effect of aging time of the precursor sol has been studied preparing different samples from sols aged up to 8 days; the formation of crystalline layered films has been observed in the samples obtained from sols of higher aging time. The hybrid films have been characterized by gracing incidence X-ray diffraction, Raman and Fourier transform infrared spectroscopy, transmission electron microscopy and UV–Vis spectroscopy. The change of the surface contact angle as a function of sol aging time and composition has been also measured. The capability of the films to be used in devices through lithographic techniques has been tested by writing the films with direct exposition to deep X-ray lithography and soft lithography with micromolds; patterns of different geometries with a thickness up to 100 μm have been obtained.     

Unusual photo-induced behaviour in a side chain liquid crystalline azo-polyester

An unusual behaviour has been observed in the photo-induced response of an azobenzene side chain liquid crystalline polyester (P6d4). Room temperature irradiation with linearly polarised 488 nm light does not induce any birefringence (Δn) in films of this polymer that have been quenched from the isotropic state. However, using the same irradiation conditions Δn is induced in quenched films that have been kept in darkness for a few minutes. Besides, no photo-induced Δn is observed in films irradiated with 488 nm light that have been previously irradiated with UV light. In this case, Δn can be recorded if the UV irradiated films have been kept in darkness for several hours. In another set of experiments performed with the P6d4 polymer, irradiation with high intensity linearly polarised 488 nm light induces an initial increase of Δn and then it goes back to zero. Subsequent irradiation with linearly polarised 633 nm light induces an orientation of the azobenzene chromophores perpendicular to the polarisation of the 488 nm light and independent of the 633 nm light polarisation direction. These results are very different from those obtained in other side chain polyesters which only differ from P6d4 in the end substituent. The anomalous behaviour of P6d4 is discussed in terms of a supercooling effect of the isotropic phase, the trans to cis back isomerization, the trans aggregation kinetics and a memory effect associated with the main chain orientation.     

Low Temperature Sol-Gel Preparation of Nanocrystalline TiO2 Thin Films

TiO₂ nanocrystalline thin films with varying degree of porosity have been prepared using a low temperature method. TiO₂ films of the anatase form have been obtained by using a polyethylene glycol (PEG) modified sol-gel method. Densification and crystallization of the films was found to result from the thermal treatment of the dip coated films in boiling water. The films have been characterized by Raman, XRD, FTIR, AFM and optical methods. Highly transparent films with transmission in excess of 85% and porosity as high as 58% are formed predominantly of anatase crystallites of dimensions of the order of 5 nm. Initial results on lithium intercalation into these films resulting in an efficient optical modulation in the visible and near infrared regions demonstrate a good potential of these films for electrochromic applications.     

Photolabile carboxylic acid protected terpolymers for surface patterning. Part 2: Photocleavage and film patterning

The surface properties of films made of p-methoxyphenacyl derivative terpolymers, associated with photocleavage by UV irradiation, and their optical patterning are investigated. The deprotection reaction has been monitored by UV and FTIR spectroscopy, contact angle measurements, and X-ray photoelectron spectroscopy, revealing the photoremoval of the protecting p-methoxyphenacyl group in high yields under mild conditions. Parallel and serial patterning of the films has been performed by selective irradiation through optical masks and by laser irradiation via fiber tips of a scanning near-field optical microscope, respectively. By irradiation of photolabile protected functional groups, free carboxylic groups become exposed to the surface with which fluorescent dyes and proteins can be associated specifically.     

Don't forget Langmuir-Blodgett films

Langmuir-Blodgett (LB) films have been investigated, extensively, over the past 70 years. Despite considerable efforts aimed at exploiting their nonlinear optical, piezoelectric, pyroelectric, semiconducting, sensing and barrier properties, problems associated with film quality and stability have hampered their practical development. This feature article highlights one recent advance in the LB area (i.e., the ionic cross-linking of LB films or "gluing"), which has resulted in single bilayer membranes possessing extraordinary quality and stability. The gluing of LB films provides new opportunities for an old technology that has been waning in recent years.     

THE ROLE OF HYDRATION IN THE PHOTOTRANSFORMATION OF PHYTOCHROME

Abstract— Changes in the visible absorption spectrum and in phototransformation of phytochrome have been found to be associated with dehydration and rehydration. These spectral properties explain the previously reported rapid appearance of phytochrome in imbibing seeds. No evidence was found for the orientation of the phytochrome chromophore in gelatin films or in preparations subjected to a shearing force.     

有机HTDIOO分子LB膜结构的AFM研究

利用原子力显微镜（ＡＦＭ）对有机分子ＨＴＤＩＯＯ单层和多层ＬＢ膜结构进行了观察。实验结果表明，针尖与ＬＢ膜表面分子间的相互作用力会对成像的膜结构有影响。当悬臂针尖与ＬＢ膜表面分子的相互作用力较大时，针尖会扰动ＨＴＤＩＯＯ分子在单层ＬＢ膜中的有序排列。ＨＴＤＩＯＯ单层ＬＢ膜具有有序结构；而在多层ＬＢ膜中，ＨＴＤＩＯＯ分子则聚集在一起形成了一定的畴结构。     

Chiral nematic assemblies of silver nanoparticles in mesoporous silica thin films

Silver nanoparticles (NPs) have been synthesized inside mesoporous silica films with chiral nematic structure. Circular dichroism measurements of the silver NP-loaded silica films show NP-based optical activity in the vicinity of the surface plasmon resonance. These materials, with an optical response associated with the chiral assembly of metal NPs, may be useful for developing new sensors.     

Surface enhanced Raman spectroscopic characterization of molecular structures in diamond-like carbon films

Vibrational bands associated with the out of plane bending modes of CH groups attached to various aromatic ring structures have been identified in surface enhanced Raman spectra of diamond-like amorphous carbon films deposited by femtosecond laser ablation of graphite. The appearance of enhanced modes associated with specific ring structures is assigned to solo-, duo-, trio- and quartet-CH groups and to pendant rings. Analysis of these bands provides insight into the nature of the molecular ring components of fs-DLC films. The resulting composition consists of polycyclic aromatic carbon (PAH)-like ring molecules and polyyne chains stabilized in a sp³-bonded network.