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PubMed2004

Investigation of transition States in bulk and freestanding film polymer glasses.

We have performed transition state searches on the potential energy landscape for bulk and freestanding film polymer glasses and identified connected minima. An analysis of the displacements between minima shows that the sites that undergo the greatest displacement are highly localized in space for both the bulk and the thin-film systems studied. In the case of the thin film, the clusters originate at the surface and penetrate into the center of the film thereby coupling the relaxation in the center of the film to the mobile surface layer. Furthermore, the energy barriers between minima are lower in the thin film than in the bulk system. These findings can rationalize the experimentally observed depression of the glass transition temperature in freestanding polymer films.

Journal Article↗
PubMed2005

Band structure and oscillatory electron-phonon coupling of Pb thin films determined by atomic-layer-resolved quantum-well states.

Using a low temperature growth method, we have prepared atomically flat Pb thin films over a wide range of film thickness on a Si-(111)-7 x 7 surface. The Pb film morphology and electronic structure are investigated in situ by scanning tunneling microscopy and angle-resolved photoemission spectroscopy. Well-defined and atomic-layer-resolved quantum-well states of the Pb films are used to determine the band structure and the electron-phonon coupling constant (lambda) of the films. We found an oscillatory behavior of lambda with an oscillation periodicity of two atomic layers. Almost all essential features in the Pb/Si(111) system, such as the growth mode, the oscillatory film stability, and the 9 monolayer envelope beating pattern, can be explained by our results in terms of the electron confinement in Pb films.

Journal Article↗
PubMed2005

Surface acoustic wave properties of proton-exchanged LiNbO3 waveguides with SiO2 film.

Surface acoustic wave (SAW) properties of proton-exchanged (PE) z-cut lithium niobate (LiNbO3) waveguides with silicon dioxide (SiO2) film layers were investigated using octanoic acid. The distribution of hydrogen measured by secondary ion mass spectrometry (SIMS) showed a step-like profile, which was assumed to be equal to the waveguide depth (d). The SiO2 film was deposited on z-cut LiNbO3 waveguide by radio frequency (rf) magnetron sputtering. We investigated the important parameters for the design of SAW devices such as phase velocity (Vp), insertion loss (IL) and temperature coefficient of frequency (TCF) by a network analyzer using thin-film aluminum interdigital transducer electrodes on the upper SiO2 film surface. The experimental results showed that the Vp of SAW decreased slightly with the increase of h/lambda, where h was the thickness of SiO2 films and lambda was the wavelength. The IL of SAW increased with increased h/lambda. The TCF of SAW calculated from the frequency change of the output of SAW delay line showed an evident decrease with the increase of h/lambda. The TCF for PE z-cut LiNbO3 was measured to be about -54.72 ppm/degreees C at h/lambda = 0.08. It revealed that the SiO2 films could compensate and improve the temperature stability as compared with the TCF of SAW on PE samples without SiO2 film.

Letter↗
PubMed2005

Fabrication and characterization of piezoelectric micromachined ultrasonic transducers with thick composite PZT films.

Ferroelectric microelectromechanical systems (MEMS) has been a growing area of research in past decades, in which ferroelectric films are combined with silicon technology for a variety of applications, such as piezo-electric micromachined ultrasonic transducers (pMUTs), which represent a new approach to ultrasound detection and generation. For ultrasound-radiating applications, thicker PZT films are preferred because generative force and response speed of the diaphragm-type transducers increase with increasing film thickness. However, integration of 4- to 20-microm thick PZT films on silicon wafer, either the deposition or the patterning, is still a bottleneck in the micromachining process. This paper reports on a diaphragm-type pMUT. A composite coating technique based on chemical solution deposition and high-energy ball milled powder has been used to fabricate thick PZT films. Micromachining of the pMUTs using such thick films has been investigated. The fabricated pMUT with crack-free PZT films up to 7-microm thick was evaluated as an ultrasonic transmitter. The generated sound pressure level of up to 120 dB indicates that the fabricated pMUT has very good ultrasound-radiating performance and, therefore, can be used to compose pMUT arrays for generating ultrasound beam with high directivity in numerous applications. The pMUT arrays also have been demonstrated.

Computer-Aided Design↗
PubMed2006

Paraelectric thin films by nanoscale engineering of epitaxy and planar anisotropy for microwave phase shifter applications.

Epitaxial and (110) oriented paraelectric thin films of Ba0.60Sro.40TiO3 were grown on (100) oriented NdGaO3 orthorhombic substrates, and the nonlinear dielectric properties were studied at 10 GHz along selected in-plane crystallographic directions in the film thickness range of 25-1200 nm. The measured dielectric properties show strong residual strain and in-plane directional dependence. For instance, the in-plane relative permittivity is found to vary from as much as 500 to 150 along [110] and [001], respectively, in the 600 nm film. Tunability was found to vary from as much as 54% to 20% in all films and directions. In a given film, the best tunability is observed along the compressed axis in a mixed strain state, 54% along [110] in the 600 nm film. It is shown that, by nanoscale manipulation of epitaxy and planar anisotropy, the return loss and phase shift in a paraelectric can be tuned over a rather wide range. The approach presented herein opens avenues for obtaining various degrees of phase shift on the same film, enabling one with an additional degree of freedom in device design and fabrication as well as multifunctionality.

Anisotropy↗
PubMed2007

Micromachined thin film plate acoustic resonators utilizing the lowest order symmetric lamb wave mode.

Thin film integrated circuits compatible resonant structures using the lowest order symmetric Lamb wave propagating in thin aluminum nitride (AlN) film membranes have been studied. The 2-microm thick, highly coriented AlN piezoelectric films have been grown on silicon by pulsed, direct-current magnetron reactive sputter deposition. The films were deposited at room temperature and had typical full-width, half-maximum value of the rocking curve of about 2 degrees. Thin film plate acoustic resonators were designed and micromachined using low resolution photolithography and deep silicon etching. Plate waves, having a 12-microm wavelength, were excited by means of both interdigital (IDT) and longitudinal wave transducers using lateral field excitation (LW-LFE), and reflected by periodical aluminum-strip gratings deposited on top of the membrane. The existence of a frequency stopband and strong grating reflectivity have been theoretically predicted and experimentally observed. One-port resonator designs having varying cavity lengths and transducer topology were fabricated and characterized. A quality factor exceeding 3000 has been demonstrated at frequencies of about 885 MHz. The IDT based film plate acoustic resonators (FPAR) technology proved to be preferable when lower costs and higher Qs are pursued. The LW-LFE-based FPAR technology offers higher excitation efficiency at costs comparable to that of the thin film bulk acoustic wave resonator (FBAR) technology.

Acoustics↗
PubMed1983

The thin-film adsorber hemoperfusion device: detailed mass transfer and flow characteristics.

Further testing and evaluation of the thin-film adsorber (TFA) type of hemoperfusion device is reported here to complement an earlier paper describing the development of these devices and clearance tests performed with them. The present paper describes the results of pressure drop tests, flow uniformity tests, and detailed studies of the mass transfer characteristics of the components of the TFA units. The TFA units consist of powdered activated charcoal embedded in thin films of cellulose nitrate. These films are sprinkled with small particles of granular charcoal and then wound into spools, which are then placed in a plastic housing. The use of powdered charcoal exploits the enormous rate-of-uptake advantage of powdered charcoal over the granular sorbents used in other hemoperfusion devices. The present tests showed that the pressure drops in the TFA devices are intrinsically low, but that their priming volumes are only marginally acceptable. Significant flow nonuniformities also exist. Despite this, the overall mass transfer resistance values for the TFA devices are lower than those for available commercial hemoperfusion units. Measurements of diffusion coefficients in the carbon and in the carbon-loaded polymer film showed that in the carbon-loaded film, the slowest diffusion step involves the carbon particles themselves. Other tests disclosed that the liquid external to the film (i.e., in the flow spaces) offers even greater mass transfer resistance than does the carbon-loaded film. Further evaluations of the TFA type of device are suggested, particularly concerning its thrombogenic properties.

Adsorption↗
PubMed2005

Photoelectric dye-coupled polyethylene film as a prototype of retinal prostheses.

Photoelectric dyes, which absorb light and convert photon energy to electric potentials, have been previously shown to stimulate retinal neurons in culture. In this study, a photoelectric dye was coupled to a polyethylene film surface and tested in vitro using retinal tissues from chick embryos at the 12-day embryonic stage, at which time outer segments of retinal photoreceptor cells have not yet developed. Carboxyl moieties were introduced to a polyethylene film surface by fuming nitric acid, and then a photoelectric dye, 2-[2-[4-(dibutylamino)phenyl]ethenyl]-3-carboxymethylbenzothiazolium bromide, was coupled to the film through amide linkage. Intracellular calcium elevation was observed with Fluo-4 in retinal tissues placed on the dye-coupled polyethylene film, in contrast to retinal tissues which had no contact with the film. The response was inhibited by calcicludine, a voltage-gated calcium channel blocker, and also by extracellular calcium depletion. The photoelectric dye, coupled to the polyethylene film surface, absorbed light under a dissecting microscope and stimulated neurons in retinal tissues, showing that the dye-coupled film could be used as a prototype of retinal prostheses.

Aniline Compounds↗
PubMed1995

Effect of dynamic loading methods on cement film thickness in vitro.

PURPOSE: Reduced cement flm thicknesses can improve crown seating and decrease marginal discrepancies. Improved marginal adaptation has the potential to reduce plaque accumulation, periodontal disease, and cement dissolution. Studies have indicated that dynamic seating methods can reduce seating discrepancies associated with zinc phosphate and resin cements. However, other types of cements and other dynamic techniques have not yet been studied or compared, nor has the mechanism for improved seating been fully explained. Therefore, the purpose of this study was to investigate the effect of a variety of loading methods on the film thicknesses of current types of crown and fixed partial denture cements compressed between glass plates. MATERIALS AND METHODS: This study investigated the effect of three dynamic loading methods on film thickness of six representative fixed prosthodontic cements. These included zinc phosphate, resin-modified glass ionomer, encapsulated glass ionomer, adhesive composite resin, composite resin, and polycarboxylate. The method was derived from American Dental Association specifications for cement film thickness. In control groups, the cements were placed between two glass glass plates and statically loaded with a 15-kg weight. The test groups were initially similarly loaded, and then for 30 seconds further subjected to simulated repeated patient opening and closing, vibrations from an electromallet, or an ultrasonic device. RESULTS: Mean film thicknesses ranged from 7.4 micrometers for polycarboxylate / ultrasound up to 40.3 micrometers for composite resin / static. Two-way analysis of variance revealed that the effects of material type and cementation method and their interaction all significantly affected film thickness (P < .0001). Multiple range analysis showed that dynamic methods were generally superior to static loading and that the ultrasonic method was the best overall. CONCLUSIONS: The different dynamic loading methods all significantly decreased cement film thicknesses between glass plates. The ultrasonic method was the most effective. The type of cement used also influenced film thickness. Composite resins were more affected than other materials.

Analysis of Variance↗
PubMed2005

Effect of resin hydrophilicity on water-vapour permeability of dental adhesive films.

This study examined the water-vapour permeability of thin polymerized resin films fabricated from five co-monomer blends of increasing degrees of hydrophilicity, as measured by their Hoy's solubility parameters. Neat resin films were prepared from five experimental light-curable resins (n = 10). Each film was mounted in a Fisher permeability cup with 8 g of water placed inside the cup. The experiments were conducted in a modified twin-outlet desiccator connected to a vacuum pump in one outlet to permit a continuous airflow to encourage water evaporation. Weight losses by water evaporation were measured at 3, 6, 9, 24, 30, and 48 h by using an analytical balance. Additional resin films were examined by using transmission electron microscopy (TEM) after immersion in ammoniacal silver nitrate. A significant correlation was observed between the cumulative water loss at 48 h and the Hoy's total cohesive energy density (delta(t)). Transmission electron microscopy revealed silver-filled channels along film peripheries and silver grains of decreasing dimensions toward the film centres in co-monomer blends 3, 4, and 5 of increasing hydrophilicity. Hydrophilic dentin adhesives polymerized in thin films are prone to water loss by evaporation. This probably accounts for the water droplets seen on the surface of vital-bonded dentin after the application of simplified dentin adhesives.

Dentin-Bonding Agents↗
PubMed1983

Analysis of the permeation and mechanical characteristics of some aqueous-based film coating systems.

The moisture permeability and mechanical properties of some aqueous-based free films have been evaluated using sorption-desorption and stress-strain techniques, respectively. These properties for blends of two film-formers--hydroxypropyl methylcellulose and polyvinyl alcohol--have been compared with those of hydroxypropyl methylcellulose films plasticized with polyethylene glycols. The polyethylene glycols generally increased the moisture permeability of hydroxypropyl methylcellulose films while polyvinyl alcohol decreased it. Both polyvinyl alcohol and the polyethylene glycols lowered tensile strength at break and Young's modulus but the effects of the polyethylene glycols were more pronounced. These results are discussed in terms of structural interactions between film components. All film systems evaluated, except that containing hydroxypropyl methylcellulose alone, exhibited a degree of anisotropy, a phenomenon with potentially adverse consequences in tablet film coating.

Chemistry, Pharmaceutical↗
PubMed1984

The opacity of tablet film coatings.

The opacity of tablet film coatings containing a variety of pigments and fillers has been assessed using a contrast ratio defined as the ratio of the measured reflectance of the incident light when the film is placed on a black substrate to the measured reflectance of the incident light when the film is placed on a white substrate. Films pigmented with calcium carbonate, calcium sulphate or talc had very low contrast ratios and only the inclusion of titanium dioxide imparted opacity. Films pigmented with the coloured lake pigments had contrast ratios dependent on both the parent dye and the dye concentration with the contrast ratios decreasing blue greater than red greater than orange greater than yellow. Films pigmented with the synthetic iron oxides all had very high contrast ratios. The results are consistent with the known theories of light scattering and absorption and illustrate the potential of this accurate, rapid and simple technique in the optimization of film formulations during product development.

Chemistry, Pharmaceutical↗
PubMed1985

Stress crack resistance of some pigmented and unpigmented tablet film coating systems.

Stress crack resistance parameters--tensile strength: Young's modulus ratio, relative surface energy, and toughness index--have been examined for unpigmented free films of hydroxypropyl methylcellulose containing polyvinyl alcohol, and polyethylene glycols 400 and 1000, as well as similar film systems pigmented with either talc or titanium dioxide. Incorporation of either polyvinyl alcohol or polyethylene glycols 400 and 1000 in hydroxypropyl methylcellulose film coatings eliminated the incidence of edge splitting in the coated tablets. Increase in pigment concentration generally led to a decrease in the crack resistance of pigmented films. There was a relation between the stress crack resistance of pigmented free films and the incidence of edge splitting of corresponding film coatings applied to aspirin tablets--generally, the higher the crack resistance the lower the incidence of edge splitting. A similar relationship applied to the unpigmented films only when the tensile strength: Young's modulus ratio was considered.

Aspirin↗
PubMed2005

Performance comparison of an active matrix flat panel imager, computed radiography system, and a screen-film system at four standard radiation qualities.

Four standard radiation qualities (from RQA 3 to RQA 9) were used to compare the imaging performance of a computed radiography (CR) system (general purpose and high resolution phosphor plates of a Kodak CR 9000 system), a selenium-based direct flat panel detector (Kodak Direct View DR 9000), and a conventional screen-film system (Kodak T-MAT L/RA film with a 3M Trimax Regular screen of speed 400) in conventional radiography. Reference exposure levels were chosen according to the manufacturer's recommendations to be representative of clinical practice (exposure index of 1700 for digital systems and a film optical density of 1.4). With the exception of the RQA 3 beam quality, the exposure levels needed to produce a mean digital signal of 1700 were higher than those needed to obtain a mean film optical density of 1.4. In spite of intense developments in the field of digital detectors, screen-film systems are still very efficient detectors for most of the beam qualities used in radiology. An important outcome of this study is the behavior of the detective quantum efficiency of the digital radiography (DR) system as a function of beam energy. The practice of users to increase beam energy when switching from a screen-film system to a CR system, in order to improve the compromise between patient dose and image quality, might not be appropriate when switching from screen-film to selenium-based DR systems.

Radiographic Image Enhancement↗
PubMed1992

Resonance-enhanced x-rays in thin films: a structure probe for membranes and surface layers.

An x-ray resonance effect in an organic thin film on an x-ray reflecting mirror is reported. The resonance effect is the result of interference between reflected and refracted x-rays at the air-organic thin film interface and occurs at incident angles slightly above the critical angle of the film. In excellent agreement with theory, the primary resonant x-ray electric field that is confined in the organic thin film is approximately 20 times as intense as the electric field of the incident beam when measured at a position close to the center of the film. Resonance-enhanced x-rays can be used to characterize the internal structure of Langmuir-Blodgett thin film membranes. This effect may also find use in x-ray-based thin film devices and in the structural analysis of adlayers and surfaces that have thus far proved difficult, if not impossible, to study because of sensitivity limitations.

Electron Probe Microanalysis↗
PubMed1996

Structure in Thin and Ultrathin Spin-Cast Polymer Films

The molecular organization in ultrathin polymer films (thicknesses less than 1000 angstroms) and thin polymer films (thicknesses between 1000 and 10,000 angstroms) may differ substantially from that of bulk polymers, which can lead to important differences in resulting thermophysical properties. Such constrained geometry films have been fabricated from amorphous poly(3-methyl-4-hydroxy styrene) (PMHS) and semicrystalline poly(di-n-hexyl silane) (PD6S) by means of spin-casting. The residual solvent content is substantially greater in ultrathin PMHS films, which suggests a higher glass transition temperature that results from a stronger hydrogen-bonded network as compared with that in thicker films. Crystallization of PD6S is substantially hindered in ultrathin films, in which a critical thickness of 150 angstroms is needed for crystalline morphology to exist and in which the rate of crystallization is initially slow but increases rapidly as the film approaches 500 angstroms in thickness.

Journal Article↗
PubMed2004

Multilayer polyelectrolyte films functionalized by insertion of defensin: a new approach to protection of implants from bacterial colonization.

Infection of implanted materials by bacteria constitutes one of the most serious complications following prosthetic surgery. In the present study, we developed a new strategy based on the insertion of an antimicrobial peptide (defensin from Anopheles gambiae mosquitoes) into polyelectrolyte multilayer films built by the alternate deposition of polyanions and polycations. Quartz crystal microbalance and streaming potential measurements were used to follow step by step the construction of the multilayer films and embedding of the defensin within the films. Antimicrobial assays were performed with two strains: Micrococcus luteus (a gram-positive bacterium) and Escherichia coli D22 (a gram-negative bacterium). The inhibition of E. coli D22 growth at the surface of defensin-functionalized films was found to be 98% when 10 antimicrobial peptide layers were inserted in the film architecture. Noticeably, the biofunctionalization could be achieved only when positively charged poly(l-lysine) was the outermost layer of the film. On the basis of the results of bacterial adhesion experiments observed by confocal or electron microscopy, these observations could result from the close interaction of the bacteria with the positively charged ends of the films, which allows defensin to interact with the bacterial membrane structure. These results open new possibilities for the use of such easily built and functionalized architectures onto any type of implantable biomaterial. The modified surfaces are active against microbial infection and represent a novel means of local host protection.

Adsorption↗
PubMed1986

Growth characteristics of selected fungi on polyvinyl chloride film.

The objective of this study was to determine if plasticized polyvinyl chloride film would support the growth of any of nine species of fungi. The film was suspended in distilled water with no nutrients or with glucose or ammonium sulfate. Spores of each of the test species were inoculated into the suspension medium, and the mixture was incubated at 30 degrees C for up to 18 weeks. Most species were found to be capable of utilizing the film for carbon or nitrogen when the other nutrient was supplied. Only two species, Aspergillus fischeri and Paecilomyces sp., were found to be capable of utilizing components of the film without added nutrients. Components of the polyvinyl chloride film were then incorporated into mineral salts medium to determine if these components could serve as carbon sources in the presence of ammonium nitrate. The only component found to be utilized by all the fungi as a carbon source was epoxidized oil, a plasticizer-stabilizer. Calcium-zinc stearate was an available carbon source for all except the Penicillium and Verticillium strains. The only other component utilized was a stearamide, which was metabolized solely by the Aspergillus sp. Only the stearamide contained enough nitrogen to serve as a primary source in the film. The compound, however, did not support growth of fungi in the presence of glucose. It was theorized that either the nitrogen of the stearamide was more readily available to the fungi in the whole film due to the presence of trace nutrients or the nitrogen was supplied by exogenous sources.

Aspergillus↗