PMMA: A key macromolecular component for dielectric low-κ hybrid inorganic-organic polymer films

Inorganic-organic composite and hybrid films find widespread applications for the development of functional materials. Polymer matrices with embedded inorganic fillers, nanoparticles or clusters are particularly appealing for optical, electronic, dielectric and magnetic applications. In particular, the development of hybrid layers with tailored dielectric properties represents a key issue in many technological fields.In this framework, poly(methyl methacrylate) (PMMA), due to its outstanding chemico-physical properties, represents a particularly suitable polymer component for the embedding of both microscopic and nanoscopic functional inorganic fillers. The wide use of such a matrix has to be traced back to the favourable combination of chemical and physical properties and easy processing. In this review, the main features and properties of PMMA, with a particular focus on dielectric ones, are firstly briefly described. Selected examples to illustrate the state-of-the art of its corresponding use as dielectric matrix are given and several examples are provided and surveyed.Finally, three case studies concerning PMMA-based hybrid films, produced for very different application fields, are described and discussed. The first example deals with the entrapment of micrometric zinc sulphide powders in PMMA, which acts as a host matrix for the electroluminescent particles in thick film-based Alternate Current Powder Electroluminescent Lamps (ACPELs). The second example describes the preparation of low-κ inorganic-organic hybrid dielectric films based on a PMMA-polyvinylchloride(PVC) blend and a hydrophobic silica powder functionalised on the surface with trimethylsiloxane groups (m-SiO₂). The composition of the investigated materials is [(PMMA)_x(PVC)_y]/(m-SiO₂)_z with z ranging from 0 to 38.3 wt% and x = y = (100 − z)/2. The third case concerns the use of PMMA as a matrix to embed zirconium oxoclusters through the formation of covalent bonds. The obtained material, characterised by a dielectric constant value remarkably lower (1.93 at 1 kHz and 25 °C) than in pristine PMMA (3.0 at 1 kHz and 25 °C), appears as very appealing for the development of microelectronic devices based on low dielectric constant polymer films such as, for instance, field-effect transistor (FET).These three cases are paradigms of three different approaches to composite and hybrid materials based on the embedding of particles in PMMA polymer matrix.     

Supersonic molecular beam growth of thin films of organic materials: A novel approach to controlling the structure,morphology, and functional properties

Thin films of semiconducting molecular materials can be grown with a seeded supersonic molecular beam epitaxy (SuMBE), which provides unprecedented control over structural, morphological, and, therefore, functional properties. This novel technique of deposition takes full advantage of its ability to regulate the initial state of the molecular precursors in the beams and, in particular, the kinetic energy, to control the morphology, structure, and functional properties of growing films. This article reviews the state of the art of SuMBE, discussing the basic aspects of the technique and the major achievements so far. The major results obtained with respect to growth on dielectrics and metal substrates of films of oligothiophenes and pentacene and with respect to the codeposition of phthalocyanines and fullerenes are discussed and compared with the state of the art of more conventional organic molecular beam deposition. The potential impact of SuMBE in the field of π‐conjugated materials and devices is also examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2501–2521, 2003     

Light‐emitting diodes and lasers based on polymer films doped with small organic molecules and rare‐earth complexes

We investigated the lasing properties of optically pumped polymer films. Amplified spontaneous emission (ASE) around 400 nm was observed in polymer films of polystyrene (PS) and poly(N‐vinylcarbazole) (PVK) doped up to 20% with the hole‐transporting organic molecule N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine (TPD). Thus, TPD‐based films are candidates for blue‐emitting organic diode lasers. Films containing several semiconducting organic molecules and polymers and rare‐earth complexes were also investigated. Energy transfer was observed in PVK films doped with various europium and samarium complexes. PS films containing the electron‐transporting organic molecule 2‐(4‐biphenylyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole and small amounts of TPD also showed energy transfer to the europium complexes, but not to the samarium ones. None of these films demonstrated ASE; therefore, they are not appropriate for lasing purposes. However, because rare‐earth ions have very sharp emission spectra, these materials are candidates for very monochromatic light‐emitting diodes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2706–2714, 2003     

Thioether moiety functionalization of mesoporous silica films for the encapsulation of highly dispersed gold nanoparticles

Highly dispersed gold nanoparticles within mesoporous thin films (MTFs) have been synthesized through a newly developed controllable strategy, in which (1,4)-bis(triethoxysilyl)propane tetrasufide (BPTS) organosiloxane coupling agent was co-assembled with tetraethyl orthosilicate (TEOS) to form organic groups functionalized mesoporous composite films followed with oxidization, ion-exchange with Au(en)₂Cl₃ (en: 1,2-ethanediamine) compound and calcination under hydrogen/nitrogen mixing atmosphere. Small-angle X-ray diffraction (XRD) characterization indicated that up to 10 mol% of BPTS could be incorporated into mesoporous hybrid films, and that would not breakup the structural integrity and long-range periodicity. The loaded gold nanoparticles were uniformly distributed due to the molecular level homogenous mixing of the BPTS precursor with TEOS, and its concentration could be controlled via the original ratio of BPTS to TEOS. The nanoparticles had a narrow size distribution with diameters in the size range of 3-7 nm through transmission electron microscopy (TEM) observation and underwent a slight size increase with the higher gold load level. An overall increase in the absorption intensity, a red shift of absorption peak, together with a comparatively narrower bandwidth could be observed at higher gold concentration within composite films from UV-vis spectra. Wide-angle XRD, TEM, X-ray photoelectron spectroscopy (XPS) and UV-vis spectra characterizations all agreed on the fact that the gold loading level could be controlled by the amount of BPTS in the starting sol for preparing MTFs.     

Ultraweak spectrally resolved thermoluminescence in polymers

Spectrally resolved thermoluminescence (TL) measurements provide a lot of information concerning trapping and recombination states in various dielectric materials. As long-lived luminescence is typically weak, this technique requires a very sensitive apparatus. This paper describes the measurement system that is used for studying spectrally resolved TL and phosphorescence decay in polymers. Exemplary investigations are presented for poly(N-vinylcarbazole) (PVK) thin films. The obtained spectra clearly indicate the influence of solvents (dioxane, chlorobenzene) and excitation wavelengths on TL in PVK samples.     

Speciation measurements of uranium in alkaline waters using diffusive gradients in thin films technique

This work investigated the application of diffusive gradients in thin films technique (DGT) to uranium speciation measurements in natural water. Two binding phases were examined, a commercially available affinity membrane, Whatman DE 81 (DE 81), with amino binding functional groups and the conventionally used Chelex 100 beads imbedded polyacrylamide hydrogel (Chelex) with iminodiacetate functional groups. The DGT devices assembled with the binding phases of DE 81 (DE 81 DGT) and Chelex gel (Chelex DGT) were tested both in synthetic river water solutions and in local river water. DE 81 DGT and Chelex DGT measured 80% and 75% of the total uranium in synthetic river water solution, respectively, and measured 73% and 60% of the total uranium in St. Lawrence River, Canada, respectively. The binding properties of the DE 81 membrane and Chelex gel for uranium, and the diffusion of uranyl complexes in the polyacrylamide gel (PAM) were also studied.     

Propargyl Amine Synthesis Catalysed by Gold and Copper Thin Films by Using Microwave‐Assisted Continuous‐Flow Organic Synthesis (MACOS)

An effective multi‐component reaction (MCR) protocol has been developed for the construction of propargyl amines from aldehydes, amines and terminal alkynes by using microwave‐assisted continuous‐flow organic synthesis (MACOS). The process is catalysed by thin films of either copper or gold that achieve temperatures in excess of 900 °C when irradiated with low levels of microwave power. The process works equally well for premixed solutions of the three starting materials, or as three separate streams, which improves the combinatorial efficiency of the method. The process tolerates a wide variety of functional groups and heterocycles, and conversion over these diverse substrates ranges from 70–90 %.     

Chemical vapor deposition and electric characterization of perovskite oxides LaMO3 (M=Co, Fe, Cr and Mn) thin films

Oxides with a perovskite structure are important functional materials often used for the development of modern devices. In view of extending their applicability, it is necessary to efficiently control their growth as thin films using technologically relevant synthesis methods. Pulsed spray evaporation CVD was used to grow several perovskite-type oxides on planar silicon substrates at temperatures ranging from 500 to 700 °C. The optimization of the process control parameters allows the attainment of the perovskite structure as a single phase. The electrical characterization using the temperature-dependent conductivity and thermopower indicates the p-type conduction of the grown films and shows a decreasing concentration of the charge carrier, mobility and band gap energy in the sequence LaCoO₃>LaMnO₃>LaCrO₃>LaFeO₃. The investigation of the electric properties of the obtained perovskite thin films shows the versatility of CVD as a method for the development of innovative devices.     

Synthesis and properties of photosensitive polyimide-nanocrystalline titania optical thin films

In this study, synthesis, morphology, and properties of high refractive index photosensitive polyimide-nanocrystalline titania hybrid materials are reported. A soluble polyimide grafted with carboxylic acid or methacrylate groups (P1) was first synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,5-diaminobenzoic acid (DABA), 4-aminobenzoic acid (4ABA), and 2-hydroxyethyl methacrylate (2HEMA). The residual carboxylic acid groups could undergo an esterification reaction with titanium butoxide to provide an organic-inorganic bonding. On the other hand, the grafted methacrylate groups rendered photosensitive property for photopatterning. A homogeneous hybrid solution was obtained through the formulation on different mole ratios of titanium butoxide/carboxylic acid, water/acid content in a mixed solvent. It was followed by spin-coating, photocuring and post-baking. The titania domain size in the hybrid materials analyzed by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) was around 4-7 nm. The prepared optically transparent films had tunable refractive index (1.583 < n < 2.029), relatively good surface planarity and high thermal stability. A fine pattern with a line width of 50 μm was produced by direct lithographic process on the hybrid films. The present study demonstrates a novel approach for preparing high refractive index hybrid photosensitive materials with patternability.     

Evaluation of the initial growth of electroless deposited Co(W,P) diffusion barrier thin film for Cu metallization

The formation mechanism of electroless deposited Co(W,P) films is investigated. Co(W,P) films, containing 88-90 at% of Co and 10-12 at% of W and P, are deposited directly onto p-type Si(100) substrate via Pd wet activation. Co(W,P) initially nucleates around Pd activation sites and this is followed by a strong lateral growth. Uniform Co(W,P) thin films can be obtained after 2 min deposition. Fast immersion measurement shows that the mixed potential of Co(W,P) is −0.78 V versus Ag/AgCl electrode. XRD examination shows that the Pd layer has a domination of (111) texture and the principle microstructure of the as-deposited Co(W,P) film is the hcp phase of nano-sized ε-Co. The inelastic mean free path of diffused Cu in Co(W,P) is determined to be 7.37 Å which is significantly smaller than that (9.9 Å) in pure Co, indicating that Co(W,P) is a very effective barrier layer.     

Application of diffusive gradient in thin films technique (DGT) to measurement of mercury in aquatic systems

The diffusive gradient in thin films (DGT) technique was investigated and used to measure mercury concentration in river water. Mercury ions are covalently bound to amide nitrogen groups of commonly used polyacrylamide, which makes this gel unsuitable as a diffusive medium. In contrast, agarose gel was found as the diffusive gel for mercury measurements. Basic performance tests of agarose DGT verified the applicability of Fick's first law for DGT measurements. Two selective resins, Chelex-100 with iminodiacetic groups and Spheron-Thiol with thiol groups were used. The measured diffusion coefficient in agarose gel was close to that in water. The concentration of mercury in Svitava river measured by DGT with Speron-Thiol resin gel was higher (0.0116 ± 0.0009 μg l⁻¹) than those obtained by Chelex-100 (0.0042 ± 0.0005 μg l⁻¹). Different capture efficiencies of two adsorbents enable to estimate fractions of mercury bonded in different complexes in the river water. The concentrations of mercury found by DGT both Chelex-100 and Speron-Thiol resin gels are much lower than that measured directly in the river water (0.088 ± 0.012 μg l⁻¹). This difference indicates that DGT concerns inorganic ions and labile species only, and that it is not able to include inert organic species and colloids.     

Sampling 4-chlorophenol in water by DGT technique with molecularly imprinted polymer as binding agent and nylon membrane as diffusive layer

For the first time, a diffusive gradients in thin films (DGT) device using molecularly imprinted polymer (MIP) as the binding agent and nylon membrane (NM) as the diffusive layer (NM-MIP-DGT) has been developed for sampling 4-chlorophenol (4-CP) in water. The MIP was prepared by precipitation polymerization with methacrylic acid as monomer and ethyleneglycoldimethacrylate as cross-linker. The diffusion coefficient of 4-CP through NM was obtained to be 0.788 ± 0.040 μ cm² s⁻¹ by diffusion cell method. The ratio was 1.01 ± 0.05 (mean ± standard deviation) for the concentration of 4-CP sampled by NM-MIP-DGT and analyzed by HPLC method to the total concentration of 4-CP in the synthetic solution where free 4-CP species dominated. The results showed that NM-MIP-DGT could sample 4-CP in synthetic solution accurately. The performance of NM-MIP-DGT for sampling 4-CP was independent of pH in the range of 3–7 and ionic strength in the range of 0.0001–0.1 mol L⁻¹ NaCl solution. The concentration of free form of 4-CP sampled by NM-MIP-DGT decreased with the increasing concentration of dissolved organic carbon in different water samples due to the electrostatic interaction of natural organic compounds with 4-CP. 1.8 mg L⁻¹ of the free form of 4-CP was determined by HPLC which was sampled by NM-MIP-DGT in an intermediate untreated industrial effluent. The NM-MIP-DGT can be a potential passive tool for sampling the free form of 4-CP in water.     

Tailored interfaces for biosensors and cell-surface interaction studies via activation and derivatization of polystyrene-block-poly(tert-butyl acrylate) thin films

Thin spin-coated films of polystyrene-block-poly(tert-butyl acrylate) (PS₆₉₀-b-PtBA₁₂₁₀) on various substrates are introduced as versatile, robust reactive platform for the immobilization of (bio)molecules for the fabrication of tailored biointerfaces. The films are characterized by high stability and (bio)reactivity due to the presence of a glassy PS and a reactive PtBA block, respectively. The selective deprotection of the tert-butyl-ester groups in the PtBA skin layer by hydrolysis under acidic conditions, the activation with N-hydroxysuccinimide and the subsequent derivatization with amino functionalized (bio)molecules were investigated. Based on contact angle, FTIR spectroscopy and XPS, fluorescence microscopy and AFM data, it was shown that the (bio)molecules were coupled covalently to the polymer films and that high molecular coverages up to ∼2.4 poly(ethylene glycol) (PEG) molecules per nm² (M_n = 500 g/mol) were obtained. Organic dyes, polyamidoamine dendrimers, polypeptides, proteins and amino end-functionalized DNA were efficiently and homogeneously immobilized on the PS-PtBA platforms. Grafting of ω-amino functionalized PEG afforded surfaces with substantially reduced non-specific adsorption of proteins and DNA. Owing to the glassy nature of PS and the covalent amide linkages, the derivatized films showed excellent stability under a broad range of processing conditions. Finally, the viability of PS₆₉₀-b-PtBA₁₂₁₀ platforms as versatile biointerfaces was demonstrated in DNA hybridization experiments, as well as cell-surface interaction studies using pancreatic cancer and K562 cells.     

Response mechanism of novel polyaniline composite conductimetric pH sensors and the effects of polymer binder, surfactant and film thickness on sensor sensitivity

This paper reports on investigations into the response mechanism of novel polyaniline composition conductimetric pH sensors and the effects of polymer binder, surfactant and film thickness on this response. It was revealed through X-ray photoelectron spectroscopy, focussed ion beam milling and impedance spectroscopy that the response mechanism was due to the deprotonation of the polymer backbone nitrogen atoms located on the uppermost surface level of the functional material particles. The equivalent circuits for the sensing layer were modelled using the Cole-Cole model for a range of pH environments. The optimum sensing layer composition was determined to contain less than 50 wt.% polymer binder with 5 wt.% surfactant. This composition was determined by examining the effects of both binder and surfactant on the electrical characteristics and sensor response of the composite films. The thickness of the sensing layer was found to have no discernable response on the sensing characteristics of the conductimetric pH sensors.     

MOCVD生长铁电氧化物薄膜MO源研究进展

高性能铁电氧化物薄膜是当今功能材料的研究热点之一.随着新型MO源的不断研究与开发,利用MOCVD技术制备高质量铁电薄膜材料得到了快速的发展.本文在分析金属醇盐和金属β-二酮化合物等MO源的结构与其物性依赖关系基础上,分类综述了近年来在用于MOCVD方法生长铁电氧化物薄膜的新型MO源研究和开发方面的发展动态与趋势,为MOCVD方法制备铁电薄膜材料MO源的选择提供有用的参考与借鉴.     

Optimization of the synthesis and characterizations of chemical bath deposited Cu2S thin films

Semiconducting copper sulphide (Cu₂S) thin films have been deposited on various substrates (SnO₂:F/glass, glass) by the simple and economical chemical bath deposition technique. The depositions were carried out during a deposition time of about 32.5 min in the pH range of 9.4 to 11. The synthesized Cu₂S thin films were characterized using various techniques without any annealing treatment. X-ray diffraction study shows that Cu₂S films exhibit the best crystallinity for pH = 10.2. For this pH value, Auger electron spectroscopy investigations show that Cu₂S thin films grown on an SnO₂/glass substrate exhibit stochiometric composition with [Cu]/[S] concentrations ratio equal to 2.02. Using the Kelvin method, the work function difference (Ф_material– Ф_probe) for the Cu₂S films deposited on SnO₂/glass substrates at the optimum pH value was found to be equal to 145 meV. Hall measurements confirm the p-type electrical conductivity of the obtained films. The electrical resistivity was of the order of 3.85 × 10⁻⁴ Ω-cm. The transmission and reflection coefficients vary in the range of [35–60] % and [5–15] % respectively, in the visible range, and the band gap energy is about 2.37 eV.     

Functionalized mesoporous materials for adsorption and release of different drug molecules: A comparative study

The adsorption capacity and release properties of mesoporous materials for drug molecules can be improved by functionalizing their surfaces with judiciously chosen organic groups. Functionalized ordered mesoporous materials containing various types of organic groups via a co-condensation synthetic method from 15% organosilane and by post-grafting organosilanes onto a pre-made mesoporous silica were synthesized. Comparative studies of their adsorption and release properties for various model drug molecules were then conducted. Functional groups including 3-aminopropyl, 3-mercaptopropyl, vinyl, and secondary amine groups were used to functionalize the mesoporous materials while rhodamine 6G and ibuprofen were utilized to investigate the materials’ relative adsorption and release properties. The self-assembly of the mesoporous materials was carried out in the presence of cetyltrimethylammonium bromide (CTAB) surfactant, which produced MCM-41 type materials with pore diameters of ∼2.7-3.3 nm and moderate to high surface areas up to ∼1000 m²/g. The different functional groups introduced into the materials dictated their adsorption capacity and release properties. While mercaptopropyl and vinyl functionalized samples showed high adsorption capacity for rhodamine 6G, amine functionalized samples exhibited higher adsorption capacity for ibuprofen. While the diffusional release of ibuprofen was fitted on the Fickian diffusion model, the release of rhodamine 6G followed Super Case-II transport model.     

An evaluation of ferrihydrite- and Metsorb™-DGT techniques for measuring oxyanion species (As,Se, V,P): Effective capacity,competition and diffusion coefficients

This study investigated several knowledge gaps with respect to the diffusive gradients in thin films (DGT) technique for measurement of oxyanions (As(III), As(V), Se(IV), Se(VI), PO₄³⁻, and V(V)) using the ferrihydrite and Metsorb™ binding layers. Elution efficiencies for each binding layer were higher with 1:20 dilutions, as analytical interferences for ICP-MS were minimised. Diffusion coefficients measured by diffusion cell and by DGT time-series experiments were found to agree well and generally agreed with previously reported values, although a range of diffusion coefficients have been reported for inorganic As and Se species. The relative binding affinity for both ferrihydrite and Metsorb™ was PO₄³⁻ ≈ As(V) > V(V) ≈ As(III) > Se(IV) ? Se(VI) and effective binding capacities were measured in single ion solutions, and spiked synthetic freshwater and seawater, advising practical decisions about DGT monitoring. Under the conditions tested the performance of both ferrihydrite and Metsorb™ binding layers was directly comparable for As(V), As(III) Se(IV), V(V) and PO₄³⁻ over a deployment spanning ≤2 days for both freshwater and seawater. In order to return quantitative data for several analytes we recommend that the DGT method using either ferrihydrite or Metsorb™ be deployed for a maximum of 2 days in marine waters likely to contain high levels of the most strongly adsorbing oxyanions contaminants. The high pH, the competitive ions present in seawater and the identity of co-adsorbing ions affect the capacity of each binding layer for the analytes of interest. In freshwaters, longer deployment times can be considered but the concentration and identity of co-adsorbing ions may impact on quantitative uptake of Se(IV). This study found ferrihydrite-DGT outperformed Metsorb-DGT while previous studies have found the opposite, with variation in binding materials masses used being a likely reason. Clearly, preparation of both binding layers should always be optimised to produce the highest capacity possible, especially for seawater deployments.     

表面活性剂胶束实现疏水分子在聚合物微凝胶层层组装膜中的高效负载

基于层层组装技术制备了聚烯丙基胺-葡聚糖微凝胶(记作PAH-D)/透明质酸钠(HA)膜, 将包覆有芘分子的十二烷基硫酸钠(SDS)表面活性剂胶束基于静电作用力负载到PAH-D/HA微凝胶膜中, 实现了疏水分子芘在微凝胶膜中的高效负载. 紫外-可见吸收光谱和荧光光谱证实了SDS胶束包覆的芘分子被稳定地负载在PAH-D微凝胶膜中. 透过光谱表明负载有芘分子的(PAH-D/HA)*10微凝胶膜在可见光区仍保持良好光学透过性. 芘在膜中的负载量可以通过改变PAH-D/HA微凝胶膜的沉积周期数和SDS胶束中包覆芘分子的浓度而实现调控. 具有光致变色性质的螺吡喃分子同样可以借助SDS胶束负载到PAH-D/HA微凝胶膜中, 制备具有光致变色性质的层层组装膜. 本工作为疏水有机分子在层层组装聚合物膜中的高效负载提供了一种简便、易行的方法.     

Characterisation and ac-electrical investigation of sublimated bis(dimethylglyoximato)palladium(II) thin films

Thin films of bis(dimethylglyoximato)palladium(II) complex of polycrystalline structure were prepared by sublimation in a vacuum at 140 °C, on glass and p-Si substrates. The films were characterised by spectral optical absorption, energy dispersion X-ray fluorescence (EDXRF), and X-ray diffraction (XRD) methods. After characterisation, metal-insulator (complex)-semiconductor MIS devices were fabricated to measure the frequency dependence of ac-conductivity in a range of 5-100 kHz. Data of ac-measurements follow the correlated barrier-hopping CBH model, from which one of the fundamental absorption peaks, the minimum hopping distance, and other parameters of the CBH model were determined, connecting and relating the optical, structural, and electrical measurements. The dielectric properties of the complex were studied through Debye model, from which the relaxation time for the dipoles (2.45 × 10⁻⁶ s) and the molecular dipole moment (3.63 × 10⁻³⁰ C m ) were determined.