Effect of dye dopants in poly(methylphenyl silane) light-emitting devices

To investigate the inter-molecular energy transfer between polysilane and dye dopants, poly(methylphenylsilane)(PMPS) was used as a host material and perylene as the blue dopant. The structure of the devices is indium–tin oxide (ITO)/PEDOT:PSS(30 nm)/PMPS:perylene(dye dopant 0.1–1.0 mol%)(60 nm)/Alq₃(20 nm)/LiF(0.5 nm)/Al(100 nm). Poly(3,4-ethylenedioxythiophene) (PEDOT):poly(4-styrenesulfonate) (PSS) is used as a buffer layer, tris(8-hydroxyquinoline)aluminum (Alq₃) as hole transporting layer, LiF as hole injection layer. The device shows a luminance 810 cd/m² at current density of 28 mA/cm², luminous efficiency of 0.14 lm/W. The external quantum efficiency (EQE) is about 0.5% and EQE increased up to 0.52% by doping with single wall carbon nanotubes (SWNT) into the emissive layer. We found an efficient inter-molecular energy transfer from polysilane to dye dopants. Furthermore, using the polysilane and energy-matched dye dopants enable to fabricate the electroluminescence devices through wet processes.     

The influence of the substrate temperature on the preparation of DNA films for studies under vacuum conditions

Experiments were carried out to determine the dependence of the physical form of supercoiled DNA films on the initial temperature of the substrate. Such films are often used in irradiation experiments involving low energy particles, like electrons or photons. In order to obtain absolute values for cross sections for such experiments, the spatial distribution of the sample in the film has to be well estimated. These investigations aim to correlate the size and form of a DNA film with the initial temperature of the substrate, on which the liquid sample is deposited prior to evacuation. From our previous studies we concluded that the presence of agents preventing DNA structural water evaporation is required in order to preserve the supercoiled plasmid DNA form under vacuum conditions. Therefore, we examined the temperature dependence on films prepared from plasmid suspended in solutions containing magnesium hydroxide, Tris-Cl buffer and various concentrations of sodium hydroxide. To visualise the films we used a conventional light microscope with a CCD camera and a scanning electron microscope. The results revealed a significant influence of the temperature of the substrate on both the area of the substrate covered by the film as well as on the spatial distribution of DNA molecules. An increase in the amount of sodium hydroxide that stabilises supercoiled DNA under vacuum increases DNA aggregation. After these investigations we conclude that the best temperature of the substrate to produce uniform and thin films should be between –5 °C and -10 °C for substrates which are not atomically flat and above 0 °C for atomically flat substrates.     

The influence of UV-irradiation and support type on surface properties of poly(methyl methacrylate) thin films

Thin poly(methyl methacrylate) (PMMA) films were prepared by a solution casting on different supports (glass and aluminium plates with different gloss). UV-irradiation (λ = 254 nm) was used for polymer modification. Surface properties of PMMA were studied by contact angle measurements, attenuated total reflection infrared spectroscopy and optical microscopy. It was found that support type has no influence on surface properties of virgin PMMA, however, the changes in these properties were observed during UV modification of polymer film. The most efficient photochemical reactions appeared in sample placed on the rough Al, whereas the smallest effect was observed in polymer on the glass.     

The influence of boron concentrations on structural properties in disorder silicon films

In this work we present a detailed structural of a series of B-doped hydrogenated microcrystalline silicon (μc-Si:H) films deposited by plasma-enhanced chemical vapor deposition (PECVD) and B-doped polycrystalline silicon (poly-Si) films produced by step-by-step laser crystallization process from amorphous silicon. The influence of doping on the structural properties and structural changes during the sequential crystallization processes were monitored by Raman spectroscopy. Unlike μc-Si:H films, that consist of a two-phase mixture of amorphous and ordered Si, partially crystallized sample shows a stratified structure with polycrystalline silicon layer at the top of an amorphous layer. With increasing doping concentration the LO-TO phonon line in poly-Si shift to smaller wave numbers and broadens asymmetrically. The results are discussed in terms of resonant interaction between optical phonons and direct intraband transitions known as a Fano resonance. In μc-Si:H films, on the other hand, the Fano effect is not observed. The increase of doping in μc-Si:H films suppressed the crystalline volume fraction, which leads to an amorphization in the film structure. The structural variation in both μc-Si:H and poly-Si films leads to a change in hydrogen bonding configuration.     

The photovoltaic effect in poly(alkylthiophene) films on a silicon substrate

A study of photovoltage was made for a series of sandwich structures on the basis of poly(3-dode-cylthiophene) films having characteristic thicknesses 100 and 500 nm and being deposited on n-Si and p-Si substrates from a solution. Semitransparent Al and Au electrodes were obtained on the surfaces of these films by thermal evaporation. A clear photoresponse was obtained in films on an n-Si substrate. Two distinct spectral components of the photovoltage were observed in the 1.3-to 3.6-eV (900–300 nm) energy range for incident quanta. The first component corresponds to the absorption edge of the Si substrate (1.4–1.6 eV). The other corresponds to the π-π* absorption of the polythiophene films (1.7–2.1 eV). The dependences of the photovoltage upon radiation intensity are different for these two spectral components. The relaxation time of the photoresponse for the second component, corresponding to the absorption in the film, is 10–20 min. This is 3–4 orders of magnitude higher than the relaxation time for the first component. A model of the potential barrier at the polythiophene/n-Si interface, allowing one to explain the main experimental results, is proposed. This barrier is formed as a result of the chemical interaction of the polythiophene molecules with the substrate.     

Thermochromic transitions in poly(di-n-hexylsilane) films

The spectra of absorption (77–398 K) and luminescence (5 K) of poly(di-n-hexylsilane) films are studied in relation to the heating of the films above the phase transition temperature. Two new absorption bands in the region of the band of the gauche conformation are found. The position and intensity of these bands depend on the annealing temperature, annealing regime, and sample thickness. These bands are assumed to be associated with the appearance of a liquid crystalline phase in the polymer, which is determined by intermolecular interactions between neighboring polymer chains. The appearance of the liquid crystalline phase in the heat-treated polymer films is confirmed by the increase in their birefringence in comparison with the birefringence of the initial films and by the observation of a stable orientation of an E 7 nematic liquid crystal applied to the surface of an annealed sample. In addition, the absorption spectra of the films cooled after the annealing exhibit many new bands in comparison with the spectra of the initial samples. These bands are associated with the appearance in the polymer of defect states and longer segments as a result of orientation of polymer chains. The appearance of longer segments is consistent with the observation of a long-wavelength band in the luminescence spectra of the annealed samples.     

Manganese doping influence on the plasmon energy of nickel films

Manganese doping in nickel films capped with copper have been prepared by evaporation in vacuum. The films are composed of grains with an average diameter of ~ 20 nm from scanning electron microscope scans. Optical absorption is measured over a wavelength range of 190–450 nm. Two plasmon peaks are observed at 3.30 eV and 4.45 eV for a range of concentrations of films. The 4.45 eV peak is a bulk plasmon peak that is enhanced by increasing the manganese in nickel. The 3.30 eV peak is a surface plasmon peak that increases in width or strength of plasmon resonance with increasing concentration of manganese. This may be a combination effect of charge carrier concentration and dielectric screening from the reformed electronic band structure caused by manganese doping. By adding manganese into nickel, the ferromagnetic order is further destroyed as a transition into a spin glass occurs. This spin glass behavior is seen in a coercivity measurement at 4 K where the coercivity drops precipitously as the doping concentration increases.     

Near-field time-resolved fluorescence studies of poly(phenylmethyl silane) with subwavelength resolution

We present an example of the first time-correlated single-photon counting (TCSPC) near-field optical measurement. The aperture size of our prepared aluminun-coated fiber-optic probe was approximately 50 nm, which represents a spatial resolution of _ex/7 for our UV measurements. Near-field fluorescence decays of poly(phenylmethyl silane) in solid thin films excited in the range 325–360 nm were obtained and the steady-state excitation spectra compared with the excitation spectral information obtained in the far field. Fluorescence decays showed single exponential lifetimes ranging from 45 to 277 ps, which was dependent on the excitation wavelength and the selected near-field tip. The proximity of the metal-coated tip to the sample may be the reason for the modulation in fluorescence lifetime.     

Collagen fibril formation in poly(vinyl alcohol) and poly(vinyl pyrrolidone) films

The formation of collagen fibrils in poly(vinyl alcohol) (PVA) and in poly(vinyl pyrrolidone) (PVP) was investigated using Atomic Force Microscopy (AFM). The water solutions of PVA and PVP containing 1%, 3% and 5% of collagen were cast onto glass plate. After slow solvent evaporation thin polymeric films were obtained. AFM images showed the fibril formation in both, PVA and PVP films containing collagen. The amount of collagen in PVA and PVP matrix has an important effect on the structure and size of collagen fibril formed. The diameter of collagen fibrils in PVA films is bigger than the diameter of collagen fibrils formed in PVP films.     

The influence of crystal orientation on the electron energy loss spectrum of monocrystalline silver films

In electron energy loss measurements (50 keV) on monocrystalline silver films in transmission the intensity of the 3.8 eV volume plasma loss is found to be dependent on the crystal orientation. If the crystal is tilted relatively to the electron beam by an angle α the elastic intensity I_el in the primary direction oscillates by 10%, the intensity of the volume plasmon however varies much stronger similar to I_el; it can become even zero at certain angles α. The intensity of the surface loss is nearly proportional to the elastic intensity. An explanation of this phenomenon is missing. Presumably it must lie in the dynamic theory of electron diffraction.     

Current-voltage characteristics of poly(diphenylenephthalide) thin films

Charge transfer near the threshold of polymer film transition (induced by a low uniaxial pressure) to the high-conductivity state is studied in an attempt to tackle the question of how the energy band structure of a wide-gap organic insulator varies near this threshold. The I-V characteristics of poly(diphenylenephthalide) films of various thickness versus uniaxial pressure are analyzed. The results obtained are treated within the model of space-charge-limited injection currents. The parameters of the injection model, such as the equilibrium concentration of electrons, electron mobility, the occupation of traps, etc., are estimated. It is concluded that deep traps due to an excess charge may appear in the energy gap of the polymer near the imref. This probably causes a narrow subband to arise, and charge transfer via this subband increases the charge carrier mobility and, hence, conductivity.     

Environmentally friendly films based on poly(3-hydroxybutyrate) and poly(lactic acid): A review

A review of data on the thermo, photo-, and biodegradation of compositions of synthetic polymers with poly-3-hydroxybutyrate and poly(lactic acid) is presented. The influence of these polymers on the thermal, microstructural, and rheological properties of mixtures is examined. The destruction of pure biopolymers, as well as compositions thereof with polyethylene, poly-(3-hydroxybutyrate-co-3-hydroxyvalerate), and polycaprolactone is studied.     

Charge carrier energy disorder in polar amorphous organic thin films

We report Monte Carlo calculations of the charge carrier energy level disorder in polar amorphous organic solids arising from electrostatic interactions between polarizable molecular charge distributions. In contrast with previous reports in which the discrete molecular polarizibilities are modeled as a dielectric continuum having dielectric constant epsilon, our calculations take account of the molecular-scale polarization inhomogeneity. We find that the previously reported 1/epsilon scaling rule underestimates the charge carrier energy level disorder by more than a factor of 2 for typical values of epsilon. Such an underestimation strongly impacts the analysis of charge carrier transport in polar amorphous organic thin films, due to the strong dependence of the charge carrier mobility on the energy disorder.     

Preparation of superhydrophobic membranes by electrospinning of fluorinated silane functionalized poly(vinylidene fluoride)

Fluorinated silane functionalized poly(vinylidene fluoride) (PVDF) is synthesized by graft polymerization of 3-trimethoxylpropyl methylacrylate with PVDF followed by coupling of fluorinated silanes. Flat membrane prepared using this functionalized PVDF has a water contact angle of 140°. Superhydrophobic PVDF membrane with a contact angle larger than 150° is prepared by the electrospinning of the fluorinated silane functionalized PVDF. The morphologies of the membranes are characterized using scanning electron microscopy. The surface composition of the membranes is analyzed using FTIR and the contact angles and water drops on the surface of the membrane are measured using video microscopy.     

Influence of preparation conditions on the dispersion parameters of sprayed iron oxide thin films

Iron oxide thin films were prepared by spray pyrolysis technique (SPT) at various substrate temperatures (T_sub) and different deposition time. X-ray diffraction (XRD) analysis showed that, at T_sub ≥ 350 °C, a single phase of α-Fe₂O₃ film is formed which has the rhombohedral structure. Moreover, the crystallinity was improved by increasing T_sub. The effect of T_sub as well as deposition time on the optical dispersion of these films has been investigated. The optical transmittance and reflectance measurements were performed by using spectrophotometer in the wavelength range from 300 to 2500 nm. The refractive index was determined by using Murmann's exact equation. It was observed that, the refractive index increased with increasing in both the T_sub and film thickness. The optical dispersion parameters have been evaluated and analyzed by using Wemple-Didomenico equation. The obtained results showed that, the dielectric properties have weak dependencies of growth temperature and film thickness. At T_sub ≥ 350 °C, the average values of oscillator energy, E_o and dispersion energy, E_d were found to be 5.96 and 34.08 eV. While at different thickness, the average values of dispersion energies were found to be 3.93 and 17.08 eV. Also, the average values of oscillator strength S_o and single resonant frequency ω_o were estimated 10.78 × 10¹³ m⁻² and 5.99 × 10¹⁵ Hz, while at different thickness were evaluating 4.81 × 10¹³ m⁻² and 6.11 × 10¹⁵ Hz. Furthermore, the optical parameters such as wavelength of single oscillator λ_o, plasma frequency ω_p, and dielectric constant ? have been evaluated. The carrier concentration N_opt by using Drud's theory was obtained the range of 5.07 × 10²⁵ m⁻³ to 1.04 × 10²⁶ m⁻³.     

Electrical properties of poly(2-vinylpyridine)-iodine films

The d.c. electrical conductivity of thick films of poly(2-vinylpyridine)-iodine is measured as a function of iodine concentration and temperature. The results are interpreted in terms of electronic hopping between ionic centers dispersed at random in the polymer.     

Thickness dependence of the dynamics in thin films of isotactic poly (methylmethacrylate)

The film thickness dependence of both the glass transition temperature (T(g)) and the 1 kHz alpha relaxation were studied for thin films of isotactic Poly (methylmethacrylate) (i-PMMA) supported on aluminium substrates. Films in the thickness range 7-200 nm were studied. The ellipsometrically determined T(g) was found to show reductions for films thinner than 60 nm, with the largest observed reduction being 12 K for a 7 nm thick film. Measurements of the T(g) were also performed on i-PMMA films supported on silicon substrates. Dielectric studies of the temperature dependent 1 kHz alpha relaxation peak, showed that the position (T(alpha)) and shape of the peak have no film thickness dependence. This was shown to hold for films with one free surface and films with a 30 nm thermally evaporated capping layer. Capping the films was shown to have no effect on the thickness dependence of either T(g) or T(alpha). The implications of these results are discussed further and the different film thickness dependencies of T(g) and T(alpha) are discussed. This is done within the framework of the Vogel-Fulcher-Tamann (VFT) theory of glass forming materials and also in the context of the existence of a dynamic correlation length xi.     

Thickness dependence of the dynamics in thin films of isotactic poly (methylmethacrylate)

The European Physical Journal E - The film thickness dependence of both the glass transition temperature (T g ) and the 1 kHz alpha relaxation were studied for thin films of isotactic Poly...     

Effect of pyrene and acetophenone on photostability of poly(methylphenylsilane) films

We have used investigations of low-temperature photoluminescence and thermally stimulated luminescence to study the effect of acetophenone and pyrene dopants on the photochemical stability of poly(methylphenylsilane) (PMPS) films. We have established that pure PMPS films and acetophenone-doped PMPS films degrade on exposure to UV radiation due to breaking of Si-Si bonds followed by formation of crosslinks between the macromolecules. At the same time, pyrene inhibits degradation of PMPS to a significant extent. This proves that photoinduced breaking of the Si-Si bond can occur upon excitation of the macromolecule to the first triplet T₁(σσ*) state, since acetophenone sensitizes while pyrene quenches the intrinsic phosphorescence of PMPS. So the photochemical stability of PMPS can be improved by introducing a dopant which quenches triplet excitations of the macromolecule. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 315–320, May–June, 2007.