A Study on the Size Effect Via Spectrophotometry and Impedence Measurements

The optical and dielectric properties of polycarbonate films have been studied as a function of sample thickness. The observed optical energy gaps were determined from the absorption spectra. The dielectric constant was determined from impedance data collected in the frequency range of 30 Hz–40 kHz. Four polycarbonate thin sheets of different thickness (0.17, 0.25, 0.30, and 0.55 mm) were used to assess the size effect on the physical behavior of this material. It was found that the measured properties as optical energy gap, dielectric constant, refractive index, and glass transition temperature are nearly independent of the specimen thickness. In general, it can be seen that the processing conditions of the glassy polymer sheets are quite identical and not producing structural changes leading to detectable size effect.     

Multiwavelength interferometry and competing optical methods for the thermal probing of thin polymeric films

Multiple‐wavelength interferometry (MWI), a new optical method for the thermal probing of thin polymer films, is introduced and explored. MWI is compared with two standard optical methods, single‐wavelength interferometry and spectroscopic ellipsometry, with regard to the detection of the glass transition temperature (T_g) of thin supported polymer films. Poly(methyl methacrylate) films are deposited by spin coating on Si and SiO₂ substrates. MWI is also applied to the study of the effect of film thickness (25–600 nm) and polymer molecular weight (1.5 × 10⁴ to 10⁶) on T_g, the effect of film thickness on the coefficients of thermal expansion both below and above T_g, and the effect of deep UV exposure time on the thermal properties (glass transition and degradation temperatures) of the films. This further exploration of the MWI method provides substantial insights about intricate issues pertinent to the thermal behavior of thin polymer films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4764–4774, 2006     

Synthesis of TiO2 porous thin films by polyethylene glycol templating and chemistry of the process

Titanium dioxide porous films have been deposited on glass slides by sol–gel technology. Tetrabutylorthotitanate and polyethylene glycol were used as a precursor and template, respectively. The chemical mechanism is discussed in relation to the sol–gel transition, which provides a possible theoretic explanation to the formation of TiO₂ porous films. The morphology of porous TiO₂ thin films strongly depends on the amount of water, the types of solvents and complexing agents, and the concentration and molecular weight of the template. It was shown that the diameter of pores is tunable in the range of 10–500 nm and the maximum of BET specific area of the films is 72 m²/g.     

Compared properties of aromatic polyisophthalamides containing 5‐(4‐acetoxy‐benzamido) pendent groups

A series of aromatic polyamides containing 5‐(4‐acetoxy‐benzamido) pendent groups have been synthesized and their properties have been characterized and compared with those of related polyamides. The polyamides have weight‐ and number‐average molecular weights in the range of 36,680–65,700 and 12,685–35,490, respectively, and polydispersities in the range of 1.82–3.66. These polymers show good thermal stability comparable to traditional aromatic polyisophthalamides, with initial decomposition temperature between 270–320°C and glass transition temperature in the range of 230–270°C. Compared with related polyisophthalamides without any pendent groups, the present polymers show better solubility in certain solvents such as N‐methylpyrrolidinone and dimethylacetamide and can be cast from solutions into thin transparent flexible films having dielectric constants in the range of 3.42–4.27. The polymer films display remarkable hydrophilicity, which makes them potential candidates for use as advanced materials in humidity sensors. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 650–657, 2001     

Effects of potassium incorporation on the structural,optical, vibrational and electrical properties of NiO sprayed thin films for p-type optical windows

Nickel oxide thin films were deposited on glass substrates by a simple mini spray technique at 460 °C. Alternatively, some of the obtained films were doped with potassium at the molar rates of: 1, 2 and 3% (K). In addition to the classical structural investigations including XRD, the opto-thermal studies, Raman spectroscopy and photoluminescence measurements were investigated.First, structural study by means of X-ray diffraction shows that all K-doped NiO thin films crystallized in cubic space group with some noticeable changes in terms of [K]/[Ni] ratio. In the same line, Raman spectroscopy reveals the principal NiO vibration’s mode with the shift related to K incorporation in NiO matrix. Second, some optical parameters, such as optical band gap, Urbach energy, refractive indices extinction coefficients and dielectric constant were studied in terms of K doping level. For all NiO:K prepared thin films, PL measurements show three large bands located at 405, 420, 485 and 529 nm.Furthermore, electrical properties were performed using impedance spectroscopy technique in the frequency range 5 Hz–13 MHz at various temperatures. DC conductivity is thermally activated showing a semiconductor behavior of NiO:K sprayed thin films. This study shows that the electrical conductivity is thermally activated. The calculated values of the activation energy show semiconductor behavior of such films.On the other hand AC conductivity is investigated through Jonscher law. The imaginary part of the complex impedance has a maximum whose relaxation frequency increases with temperature according to Arrhenius law.     

Structural relaxation and dynamic fragility of freely standing polymer films

In addition to a tremendous reduction in the glass transition temperature, dielectric spectra of freely standing films reveal two other intriguing features: a temperature dependent asymmetric broadening of the structural relaxation peak towards lower temperatures and a reduction of the dynamic fragility down to the monomer limit. We verified that this experimental evidence is a manifestation of a gradient of glass transition temperatures across the film thickness induced by an enhanced molecular mobility at the two free surfaces of the membrane. As a direct implication of the peculiar features just described, the properties of freely suspended membranes neither correspond to those in bulk nor to a simplified scenario where the structural relaxation peak is merely shifted towards lower temperatures.     

Substrate temperature-dependent physical properties of nanocrystalline zirconium titanate thin films

Nanocrystalline zirconium titanate thin films were deposited by direct current magnetron reactive sputtering on to glass substrates at room temperature and at different substrate temperatures of 423, 473, 523, and 573 K under high vacuum conditions. The deposited films have been characterized to study the physical properties of the films as a function of substrate temperature. Though the film exhibited amorphous characteristics at room temperature the higher temperatures resulted in the evolution of crystallites in the films. The crystallinity increased with temperature from 423 K onwards and the film deposited at 523 K exhibited a high crystallite size of 22 nm. The SEM images of the films revealed the improvement in the crystallinity from 423 to 523 K with dense columnar structure normal to the substrate. Further higher treatment deteriorated the film properties. The films showed a good transmittance of above 80%. A high optical transmittance of 91% and a high packing density of 96% have been observed for the film deposited at 523 K. The thickness of the films remained consistent at ~230 nm (±6 nm). It is noticed that an increase in the substrate temperature enhanced the structural, optical, and electrical properties of the films up to 523 K.     

Thermal and electrical behaviour of some hybrid polyimide films containing barium and titanium oxides

Aromatic polyimides are high‐performance polymers used in applications demanding service at enhanced temperature while maintaining their structural integrity and excellent combination of chemical, physical and mechanical properties. The incorporation of various metallic additives into a polyimide matrix improves its properties, leading to materials required by specific applications. Hybrid polyimide films containing barium and titanium oxides having thicknesses in the range of tens of micrometres were prepared. These films were obtained using the sol–gel technique starting from a poly(amic acid) and a soluble precursor of metal oxides. They exhibited good thermal stability having an initial decomposition temperature above 460 °C, and a glass transition temperature in the range 217–238 °C. Two subglass transitions, γ and β, were evident from dynamic mechanical analysis and dielectric spectroscopy. A study of the thermal and electrical behaviour of some hybrid polyimide films containing barium and titanium oxides is presented. On increasing the concentration of metal oxides, an increase of dielectric constant and a decrease of thermal stability of the hybrid films were observed. The presence of metal oxides shifted the glass transition temperature and the temperature of the β transition to higher values. Copyright © 2009 Society of Chemical Industry     

Effect of substrate temperature on the physical properties of co-evaporated Sn2S3 thin films

We report the deposition of tin sulfide (Sn₂S₃) thin films by co-evaporation technique at different substrate temperatures. The influence of substrate temperature on the structural and optical properties of the thin films is investigated. X- ray diffraction (XRD) analysis and Micro-Raman studies confirm the formation of Sn₂S₃ phase. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to examine the surface morphology. The transmission spectra of the deposited Sn₂S₃ thin films have been recorded in the wavelength range of 200–3000 nm using UV–vis-NIR spectrometer. Film thickness (d) and optical constants such as refractive index (n), extinction coefficient (k), real (ε₁) and imaginary (ε₂) parts of the dielectric constants of thin films are estimated from the optical transmittance. The optical band gaps of the deposited films at different substrate temperatures are in the range of 1.46–1.64 eV. Hall effect measurements confirm the n-type nature of the as-prepared Sn₂S₃ thin films.     

Synthesis and characterization of new fluorinated aromatic polyesters containing trifluoromethylphenoxy pendant groups

A series of novel fluorinated aromatic polyesters containing trifluoromethylphenoxy pendant groups was synthesized by interfacial polycondensation of 2‐(4‐trifluoromethylphenoxy)terephthalyl chloride with various bisphenols in dichloromethane. The polyesters obtained in good yields had weight‐average molecular weights of 70,600–29,800 g/mol, polydispersities of 1.81–2.08, and were all amorphous. All polyesters were easily soluble in organic solvents such as N,N‐dimethylformamide, tetrahydrofuran, o‐chlorophenol, pyridine, and dichloromethane. These fluorinated polyesters showed glass transition temperature of 133–210°C, and good thermal stability with almost no weight loss up to 378°C, the 10% weight loss temperature of 472–523°C as well as char yield of 32–63% at 600°C in nitrogen. These polyester films cast from chloroform solutions exhibited tensile strengths ranging from 102 to 126 MPa, elongation at break from 6.3% to 11.7%, and tensile moduli from 2.1 to 3.3 GPa. The resulting polyester films also displayed low dielectric constants between 2.18 and 2.49 (1 MHz), high transparency with an ultraviolet‐visible absorption cut‐off wavelengths in the 332–355 nm range, and excellent electric strengths (50.4–65.6 kV/mm) and volume resistivity (2.51–6.03 × 10¹⁶ Ω cm). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Measurements of the surface resistance and conductivity of thin conductive films at frequency about 1 GHz employing dielectric resonator technique

A dielectric resonator technique has been developed for measurements of conductivity and surface resistance of thin metal films deposited on a dielectric substrate. This technique allows for measurements of films having surface resistances that are smaller than 5 Ω without requiring the need to perform measurements of the substrate thickness. The uncertainty of the surface resistance measurements is about 2–3% for both thin films and bulk materials. The accuracy of the conductivity measurements of the thin films is similar to the accuracy of the measurements of their thickness. Several samples have been measured having thicknesses that range from 66 nm to 50 μm.     

Mechanical and Electrical Properties of SomeSilicon-Containing Poly(Amide-Imide)s

Aromatic silicon-containing poly(amide-imide)s have been prepared by low temperature solution polycondensation reaction of various aromatic diamines having ether bridges between phenylene rings with a diacid chloride, namely bis[N-(4-chlorocarbonylphenyl) phthalimidyl]dimethylsilane. These polymers were easily soluble in polar amidic solvents such as N-methylpyrrolidone,N,N-dimethylacetamide, and N,N-dimethylformamide and can be cast from solutions into thin, flexible films. They showed good thermal stability, with initial decomposition temperature being above 410°C and glass transition temperature in the range of 263–285°C. The polymer films exhibited good mechanical properties with tensile strengths in the range of 78–109 MPa, tensile modulus in the range of 1.44–1.76 GPa, and elongation at break values ranging from 11% to 24%. Electrical insulating properties of two polymer films were evaluated on the basis of dielectric constant and dielectric loss and their variation with frequency and temperature.     

Physical and relaxation properties of flame-sprayed ethylene-methacrylic acid copolymer

A range of physical and chemical properties of flame-sprayed ethylenemethacrylic acid copolymer (EMAA) were assessed, following different processing conditions. Coatings were produced at a range of specific temperatures by varying the propane flow rate and gun traverse rate. The flame spraying process oxidizes the EMAA copolymer during processing, the extent of oxidation increasing with greater deposition temperatures. Coatings were scanned using dielectric relaxation spectroscopy at a frequency range from 10² to 10⁶ Hz over a temperature interval of -20 to 85°C. The glass transition temperature (usually denoted as the β′ relaxation in this system), is attributed to the microBrownian motion of long chain segments in the amorphous phase and is found to decrease with increasing deposit temperature. The oxidation process appears to reduce the position of the β relaxation due to chain scission. The molecular weight for the EMAA powder was reduced from 22,693 g/mol to 9302 g/mol when deposited at 271°C as shown by gel permeation chromatography. Despite the decrease in chain length, the activation energies for β′ relaxation increased with increasing coating temperatures. This is attributed to the increased polarity of the oxidized coatings resulting in greater intermolecular association, which outweighs the decreased chain length.     

New poly(arylene ether)s containing phthalimidine group in the main chain

Five new poly(arylene ether)s containing phthalimidine group in the main chain and pendent trifluoromethyl group have been prepared by the reaction of 4,4′‐(bis‐4‐fluoro‐3‐trifluoromethylphenyl)benzene (BTF) with bisphenols. Different molar ratios of N‐phenyl‐3,3‐bis(4‐hydroxyphenyl)phthalimidine (PA) and 4,4′‐isopropylidenediphenol (BPA) have been used to generate different copolymers. The polymers obtained by step growth polymerization exhibited weight‐average molecular weight upto 134,000 g/mol with a polydispersity index of 2.1–2.4. The homopolymer from BTF and PA showed very high glass transition temperature of 258°C and outstanding thermal stability upto 536°C for 5% weight loss under nitrogen. The polymers were soluble in a wide range of organic solvents. Transparent thin films of these polymers exhibited tensile strengths upto 65 MPa and elongation at break upto 45% depending on the exact repeat unit structures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and electrical properties of copoly(1,3,4‐oxadiazole‐ethers) containing fluorene groups

A series of aromatic copolyethers containing 1,3,4‐oxadiazole rings and fluorene groups was prepared by nucleophilic substitution polymerization technique of 9,9‐bis(4‐hydroxyphenyl)fluorene, 1 , or of different amounts of 1 and an aromatic bisphenol, such as 4,4′‐isopropylidenediphenol or phenolphthalein, with 2,5‐bis(p‐fluorophenyl)‐1,3,4‐oxadiazole. The polymers were easily soluble in polar solvents like N‐methylpyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide, and chloroform and can be cast from solutions into thin flexible films. They showed high thermal stability, with decomposition temperature being above 425°C. The polymers exhibited a glass‐transition temperature in the range of 195–295°C, with a reasonable interval between glass‐transition and decomposition temperature. Electrical insulating properties of some polymer films were evaluated on the basis of dielectric constant and dielectric loss and their variation with frequency and temperature. The values of the dielectric constant at 10 kHz and 20°C were in the range of 3.16–3.25. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication and Dielectric Properties of Ba0.63Sr0.37TiO3 Thin Films on SiC Substrates

Ba_0.63Sr_0.37TiO₃ (BST) films were first deposited on SiC substrates with LNO bottom electrodes by magnetron sputtering. The BST/LNO/SiC thin films exhibit high dielectric tunability and low dielectric loss while maintaining excellent temperature coefficient of dielectric constant in the temperature range between 250 and 350 K. We also investigated the effect of film thickness on the dielectric properties. BST(430 nm)/LNO/SiC film has higher tunability (68.09% @700 kV/cm), lower loss tangent (tanδ = 0.00987) and quite a bit higher figure of merit (FOM = 68.99) as compared with that of BST(300 nm)/LNO/SiC film. Our results demonstrate that combining ferroelectric BST films with SiC substrates is very promising for the development of tunable devices over a large temperature range.     

Preparation and tunability properties of Ba(ZrxTi1−x)O3 thin films grown by a sol–gel process

Ba(Zr_xTi_1−x)O₃ (BZT) thin films were deposited via sol–gel process on LaNiO₃, as buffer layer, and Pt-coated silicon substrates. The BZT films were perovskite phase and showed a (1 0 0) preferred orientation dependent upon zirconium content. The grain size decreased and the microstructure became dense with increasing zirconium content. The addition of Zr to the BaTiO₃ lattice decreased the grain size of the crystallized films. The temperature dependent dielectric constant revealed that the thin films have relaxor behavior and diffuse phase transition characteristics that depend on the substitution of Zr for Ti in BaTiO₃. The dependence of electrical properties on film thickness has been studied, with the emphasis placed on dielectric nonlinear characteristics. Ba(Zr_0.35Ti₆₅)O₃ thin films with weak temperature dependence of tunability in the temperature range from 0 to 130 °C could be attractive materials for situations in which precise control of temperature would be either impossible or too expensive.     

Pulsed laser deposition BTS thin films: The role of substrate temperature

BaSn_0.15Ti_0.85O₃ (BTS) thin films were deposited on Pt/Ti/SiO₂/Si(1 0 0) substrate by pulsed laser deposition and the effects of substrate temperature on their structure, dielectric properties and leakage current density were investigated. The results indicate that the substrate temperature has a significant effect on the structural and dielectric properties of the BTS thin films which exhibit a polycrystalline perovskite structure if the substrate temperature ranges within 550–750 °C. The dielectric constant and loss tangent of the BTS thin films deposited at 650 °C are 341 and 0.009 at 1 MHz, respectively, the tunability is 72.1% at a dc bias field of 400 kV/cm, while the largest figure of merit (FOM) is 81.1. The effect of the substrate temperature on the leakage current of the BTS thin films is discussed.     

Properties of Liquid-Phase Deposited Silica Films for Low-k Dielectric Applications

Both the electrical and mechanical properties of silica thin films deposited by liquid phase deposition (LPD) have been evaluated in this study. Silica thin films have been prepared on glass surface by immersing it in a supersaturated Hexafluorosilicic acid (H₂SiF₆)-based solution at a low temperature of 50°C. The as-deposited LPD silica films exhibit a low dielectric constant ( k ) that varies from 1.7 to 2.7 depending on the film morphology and fluorine content of the film. Young's modulus of these films was measured in the range of 18.9–24.5 GPa by a nanoindentation technique. The combination of extremely low k and fairly high modulus made this low-temperature-processed LPD silica films a very promising candidate for an interlayer dielectric film for the next-generation semiconductor devices.     

Preparation of polymer latex films by a flash casting technique

Conventional film casting methods have proved unsuitable for the preparation of thin (10–100 μ) films from surfactant-free polymer latices. A flash casting technique has been devised and successfully employed to cast films from a wide range of surfactant-free homopolymer, copolymer and core-shell polymer latices. Essentially, the method involves spraying the latex at a specially designed hotplate, the surface of which is coated with a thin layer of PTFE. The hotplate is maintained at a temperature between 393 and 473 K. When sufficient thickness of film has been built up, the hotplate is switched off and allowed to cool to the temperature at which the film is to be removed. For homogeneous latex films, the optimum temperature range for removal lies in the region of the glass transition temperature of the polymer concerned. Where this is below ambient, the appropriate cooling mixture is placed in a slush bath, situated to the rear of the hotplate, thereby cooling the hotplate to the correct temperature. The film is removed by gently peeling it from the surface. The surfaces of the films appeared smooth to the naked eye, but the sprayed surfaces of freshly prepared poly(n-butyl methacrylate) films were rough when examined by scanning electron microscopy. The surfaces smoothed out on ageing, resembling those of solvent-cast films after one months storage.