Concentration dependence of photoluminescence properties in poly[(2-methoxy,5-octoxy)1,4-phenylenevinylene] thin films

Photoluminescence and selective excitation photoluminescence measurements at room temperature have been performed on poly[(2-methoxy,5-octoxy) 1,4-phenylenevinylene] (MO-PPV) thin films, which are prepared from MO-PPV chloroform solutions of different concentrations. The position of the S0→S1 absorption peak shows red-shift and broadened relative to that in an MO-PPV solution form due to the solidification effect, while no relative shifts between the absorption spectra of these film samples are observed. A long wavelength emission component near 630 nm has been identified as S2→S0 vibronic transition through the Gaussian decomposition method and confirmed by below-gap PL and selective-excitation PL experiments. This second vibronic component cannot be observed in the spectra of thick films. The PL efficiency of MO-PPV thin film is also investigated through comparison with that of an MEH-PPV thin film and explained by the side substituent effect.     

An investigation of the proton conductivities of hydrated poly(vinyl alcohol)/boric acid complex electrolytes

Proton-conducting polymer complex electrolytes were prepared by incorporation of boric acid, H₃BO₃ into poly(vinylalcohol), PVA, to form hydrated PVAxH₃BO₃ where x denotes the number of moles of boric acid per polymer repeat unit. The dried materials were characterized via Fourier transform infrared spectroscopy, thermogravimetry, and X-ray diffraction. The proton conductivity of the hydrated complex electrolytes was measured by AC impedance spectroscopy. PVA2H₃BO₃ with RH ∼25% was found to be optimum composition that exhibited proton conductivity of 1.3 × 10⁻³ S/cm at 80 °C.     

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.     

Glass transition and dynamics of single and stacked thin films of poly(2-chlorostyrene)

The glass transition temperature and the dynamics of the α-process have been investigated using dielectric relaxation spectroscopy for single and stacked thin films of poly(2-chlorostyrene) (P2CS). The stacked film consists of 10 layers of single thin films with thickness of 12 nm or 18 nm. The glass transition temperature T _g of the single thin films of P2CS is found to decrease with decreasing film thickness in a similar way as observed for polystyrene thin films. The magnitude of the depression of T _g for the stacked thin films is larger than that of the single thin films with corresponding thickness. The depression of the temperature at which the dielectric loss shows a peak due to the α-process at a given frequency, T _α, is larger than that of the single thin films, although the magnitude is smaller than that of T _g . Annealing at a high temperature could cause the T _g and T _α of the stacked thin films to approach the values of the bulk system.     

Co与Cu掺杂ZnO薄膜的制备与光致发光研究

采用溶胶-凝胶旋涂法在玻璃衬底上制备了Co, Cu单掺杂及Co,Cu共掺杂ZnO薄膜.用金相显微镜观察了Co与Cu掺杂对ZnO薄膜形貌的影响.X射线衍射（XRD）研究揭示所有ZnO薄膜样品都存在（002）择优取向,在Cu单掺的ZnO薄膜中晶粒尺寸最大.对所有样品的室温光致发光测量都观察到较强的蓝光双峰发射和较弱的绿光发射,其中长波长的蓝光峰和绿光峰都能够通过掺杂进行控制.对不同掺杂源的ZnO薄膜发光性能进行了分析,认为蓝光峰来源于电子由导带底到锌空位能级的跃迁及锌填隙到价带顶的跃迁,绿光峰是由于掺杂造成的 关键词： ZnO薄膜 溶胶-凝胶 Co Cu掺杂 光致发光     

Characterization of bioactive RGD peptide immobilized onto poly(acrylic acid) thin films by plasma polymerization

Plasma surface modification can be used to improve the surface properties of commercial pure Ti by creating functional groups to produce bioactive materials with different surface topography. In this study, a titanium surface was modified with acrylic acid (AA) using a plasma treatment and immobilized with bioactive arginine-glycine-aspartic acid (RGD) peptide, which may accelerate the tissue integration of bone implants. Both terminals containing the -NH₂ of RGD peptide sequence and -COOH of poly(acrylic acid) (PAA) thin film were combined with a covalent bond in the presence of 1-ethyl-3-3-dimethylaminopropyl carbodiimide (EDC). The chemical structure and morphology of AA film and RGD immobilized surface were investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), atomic force microscopy (AFM), and scanning electron microscopy (SEM). All chemical analysis showed full coverage of the Ti substrate with the PAA thin film containing COOH groups and the RGD peptide. The MC3T3-E1 cells were cultured on each specimen, and the cell alkaline phosphatase (ALP) activity were examined. The surface-immobilized RGD peptide has a significantly increased the ALP activity of MC3T3-E1 cells. These results suggest that the RGD peptide immobilization on the titanium surface has an effect on osteoblastic differentiation of MC3T3-E1 cells and potential use in osteo-conductive bone implants.     

Synthesis and properties of In2(Se1-xTex)3 thin films: a new semiconductor compound

In₂(Se_1-xTe_x)₃ polycrystalline films were prepared by a dual-source thermal evaporation technique. The depositions onto glass and SnO₂-coated glass substrates were carried out in a vacuum chamber and followed by an annealing in neutral ambient (Ar or N₂). The structural, morphological and compositional studies of the films were made by X-ray diffraction, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, Raman scattering and optical transmission. Optimum conditions are investigated for the formation of the ternary compound In₂(Se_1-xTe_x)₃ in order to tune the band gap by changing the Te concentration. The film properties as a function of Te amount are discussed. It is shown that single-phase, textured and homogeneous layers of In₂(Se_1-xTe_x)₃ can be grown with x≤0.2 at optimal deposition and heat treatment conditions. For x≅0.17 these films showed an energy band gap of about 1.45 eV and an electrical conductivity at room temperature six orders of magnitude higher than that of the binary γ-In₂Se₃ thin films. Received: 9 July 1999 / Accepted: 25 November 1999 / Published online: 13 July 2000     

Efficient fabrication of transparent antimicrobial poly(vinyl alcohol) thin films

We have explored in situ synthesis of Ag nanoparticles in transparent PVA films in view of increasing areas of application of those films. The two-step procedure consists of ion incorporation in the matrix and subsequent thermal reduction. Smooth and transparent PVA films containing Ag nanoparticles of 5–20 nm were fabricated by this approach. The optical property of the films and the size of metal nanoparticles could be controlled by changing the reaction conditions. By increasing heating temperature, the absorbance and wavelength of surface plasmon resonance (SPR) of the composite film increased, and nanoparticles with larger particle sizes and broader size distributions were obtained. In the temperature range of 130–170 °C, the wavelength of SPR increased with increasing the AgNO₃ concentration. At 190 °C, however, the wavelenght of SPR blue-shifted initially when the AgNO₃ concentration increased from 10 to 80 mmol/L, and red-shifted thereafter. The composite films showed excellent antimicrobial performance toward bacteria such as Escherchia coli. Such hybrids afford very effective and environment-friendly antimicrobial surface coatings.     

Molecular dynamics in thin films of isotactic poly(methyl methacrylate)

The molecular dynamics in thin films (18 nm-137 nm) of isotactic poly(methyl methacrylate) (i-PMMA) of two molecular weights embedded between aluminium electrodes are measured by means of dielectric spectroscopy in the frequency range from 50 mHz to 10 MHz at temperatures between 273 K and 392 K. The observed dynamics is characterized by two relaxation processes: the dynamic glass transition (α-relaxation) and a (local) secondary β-relaxation. While the latter does not depend on the dimensions of the sample, the dynamic glass transition becomes faster (≤2 decades) with decreasing film thickness. This results in a shift of the glass transition temperature T _g to lower values compared to the bulk. With decreasing film thickness a broadening of the relaxation time distribution and a decrease of the dielectric strength is observed for the α-relaxation. This enables to deduce a model based on immobilized boundary layers and on a region displaying a dynamics faster than in the bulk. Additionally, T _g was determined by temperature-dependent ellipsometric measurements of the thickness of films prepared on silica. These measurements yield a gradual increase of T _g with decreasing film thickness. The findings concerning the different thickness dependences of T _g are explained by changes of the interaction between the polymer and the substrates. A quantitative analysis of the T _g shifts incorporates recently developed models to describe the glass transition in thin polymer films. Received 12 August 2001 and Received in final form 16 November 2001     

Electrical characteristics of poly(methylsilsesquioxane) thin films for non-volatile memory

In this communication the electrical characteristics of poly(methylsilsesquioxane) (PMSSQ) thin films and the possibility of charge storage in the Au nanoparticle embedded PMSSQ film base memory element have been studied. PMSSQ films were sandwiched between Al and Si electrodes to fabricate metal-polymer-semiconductor (MPS) structures. The conduction mechanism in PMSSQ films has been investigated. The charge transport mechanism appears to be space charge limited current (SCLC) at the higher-voltage region. Various electrical parameters such as reverse saturation current, barrier height, ideality factor, rectification ratio, shunt and series resistance and charge carrier mobility in PMSSQ have been determined. C-V analysis is performed to confirm the memory effect for Au nanoparticles embedded MPS structures. A definite clockwise hysteresis is observed which indicates the possibility of charge storage in the Au nanoparticles embedded PMSSQ film.     

Properties of nano-ZnO/poly(vinyl alcohol)/poly(ethylene oxide) composite thin films

A series of poly(vinyl alcohol)/nano-ZnO composites were prepared by dispersing nano-ZnO in aqueous solutions containing mixtures of the biodegradable polymers poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO), and composite thin films were prepared by casting. The introduction of nano-ZnO into PVA/PEO mixed solutions significantly decreased the resistivity of the solutions. Ultraviolet absorption, thermal behaviour and visco-elastic properties of the thin films were determined as a function of nano-ZnO content up to 15 wt%. Optimum film properties were obtained with 1 wt% nano-ZnO, higher proportions of nano-ZnO resulting in agglomeration of ZnO particles and deterioration in film properties. The Forouhi and Bloomer model was used for the modelling of ZnO thin films.     

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...     

Crystallization kinetics and crystal morphology in thin poly(ethylene oxide) films

We present a detailed study of the kinetics of crystallization for thin films of poly(ethylene oxide) (PEO). Measurements of the growth rate have been carried out using optical-microscopy techniques on films of monodisperse PEO. Films with thicknesses from 13 nm to ~2 m were crystallized isothermally at temperatures ~20°C below the melting point. A remarkable non-monotonic slowing-down of the crystal growth is observed for films with thickness less than ~400 nm. The changes in the growth rate from bulk-like values is significant and corresponds to a factor of 40 decrease for the thinnest films studied. The morphologies of isothermally crystallized samples are studied using atomic-force microscopy. We find that a morphology, similar to diffusion-controlled growth (dendritic growth and densely branched growth), is observed for films with h < 150 nm. In addition, changes in the morphology occur for thicknesses consistent with changes in the growth rate as a function of film thickness.     

Hall mobility and characteristics of gas-phase polymerized poly(3-iodothiophene) thin films

The semi-conductive poly(3-iodothiophene)(P3IT) films were fabricated by gas-phase polymerization through a chemical vapor deposition process. The P3IT nanoscale films have a high crystalline morphologies, and possessed a high Hall mobility up to 10 cm²/Vs. The degree of crystalline and the mobility values measured through Scanning Electron Microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy with structural analysis. These conductive thin films, possessing polycrystalline structures, have a very high mobility and are capable of being applied to organic electronic layers for electrical devices such as the thin film transistors and organic photovoltaic cells.     

Nanocrystalline versus microcrystalline Li(2)O:B(2)O3 composites: anomalous ionic conductivities and percolation theory

We study ionic transport in nano- and microcrystalline (1-x)Li(2)O:xB(2)O3 composites using standard impedance spectroscopy. In the nanocrystalline samples (average grain size of about 20 nm), the ionic conductivity sigma(dc) increases with increasing content x of B2O3 up to a maximum at x approximately 0.5. Above x approximately 0.92, sigma(dc) vanishes. By contrast, in the microcrystalline samples (grain size about 10 &mgr;m), sigma(dc) decreases monotonically with x and vanishes above x approximately 0. 55. We can explain this strikingly different behavior by a percolation model that assumes an enhanced conductivity at the interfaces between insulating and conducting phases in both materials and explicitly takes into account the different grain sizes.     

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.     

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.