High environmental compatibility photopolymers compared to PVA/AA based materials at zero spatial frequency limit

In holographic applications the direct parameters determination of photopolymers as optical recording media is a very difficult task due to the presence of two different phenomena: polymer formation and monomer diffusion. We propose a direct method based on zero spatial frequency recording, to eliminate the diffusion influence, and on interferometric techniques, both in transmission and in reflection, to obtain quantitative values of: shrinkage, polymerization rate, polymer refractive index and relation between polymerization and recording intensity. Recent investigations confirm the toxic potential of acrylamide. Starting from polyvinylalcohol/acrylamide photopolymer we have proposed different compositions of new competitive photopolymers with high environmental compatibility. We have studied the ways to optimize the optical behavior and the environmental compatibility. Parameters comparison with the polyvinylalcohol/acrylamide photopolymers shows significant differences.     

Optimization of holographic storage with modulated recording beams in a thick polyvinyl alcohol/acrylamide photopolymer

In a holographic photopolymer system, the storage properties were often limited due to the attenuation in depth of light during the recording step. To obtain smaller values of the depth attenuation profiles in 1 mm thick polyvinyl alcohol/acrylamide (PVA/acrylamide) photopolymers, we used a triangle prism, sitting one face tilted at 13.7 degrees to the axis within the focus of a lens, to modulate the distribution of recording beams. Doing this permitted larger refractive index modulation depth to be achieved, and larger dynamic range (M#=9.2) was obtained in the PVA/acrylamide photopolymers.     

Thermal wave interferometry for measuring the thermal diffusivity of thin slabs

Thermal wave interferometry applied to the evaluation of thermal diffusivity of freestanding coatings and single layers is herewith presented. Measurements on a set of eight different materials (oxides free copper, an aluminium alloy, Armco iron, AISI 316 stainless steel, Nimonic90 and IN738 nickel based alloys and Yttria partially stabilised Zirconia coatings) have been carried out. The corresponding thermal diffusivity values cover a very large range (about three order of magnitude). A comparison of 1D and 3D models has been done in order to optimise the main measurement parameters. Sample thickness, heating beam size and modulation frequency range have been selected in order to maximise the photothermal signal and its phase variation as a function of the frequency. Experimental results give evidence of a very good agreement between literature and experimental values for all samples confirming the capability of this technique for measuring the thermal diffusivity of thin slabs.     

Analysis of PVA/AA based photopolymers at the zero spatial frequency limit using interferometric methods

One of the problems associated with photopolymers as optical recording media is the thickness variation during the recording process. Different values of shrinkages or swelling are reported in the literature for photopolymers. Furthermore, these variations depend on the spatial frequencies of the gratings stored in the materials. Thickness variations can be measured using different methods: studying the deviation from the Bragg's angle for nonslanted gratings, using MicroXAM S/N 8038 interferometer, or by the thermomechanical analysis experiments. In a previous paper, we began the characterization of the properties of a polyvinyl alcohol/acrylamide based photopolymer at the lowest end of recorded spatial frequencies. In this work, we continue analyzing the thickness variations of these materials using a reflection interferometer. With this technique we are able to obtain the variations of the layers refractive index and, therefore, a direct estimation of the polymer refractive index.     

Wafer-scale fabrication of polymer-based microdevices via injection molding and photolithographic micropatterning protocols

Because of their broad applications in biomedical analysis, integrated, polymer-based microdevices incorporating micropatterned metallic and insulating layers are significant in contemporary research. In this study, micropatterns for temperature sensing and microelectrode sets for electroanalysis have been implemented on an injection-molded thin polymer membrane by employing conventional semiconductor processing techniques (i.e., standard photolithographic methods). Cyclic olefin copolymer (COC) is chosen as the polymer substrate because of its high chemical and thermal stability. A COC 5-in. wafer (1-mm thickness) is manufactured using an injection molding method, in which polymer membranes (approximately 130 microm thick and 3 mm x 6 mm in area) are implemented simultaneously in order to reduce local thermal mass around micropatterned heaters and temperature sensors. The highly polished surface (approximately 4 nm within 40 microm x 40 microm area) of the fabricated COC wafer as well as its good resistance to typical process chemicals makes it possible to use the standard photolithographic and etching protocols on the COC wafer. Gold micropatterns with a minimum 5-microm line width are fabricated for making microheaters, temperature sensors, and microelectrodes. An insulating layer of aluminum oxide (Al2O3) is prepared at a COC-endurable low temperature (approximately 120 degrees C) by using atomic layer deposition and micropatterning for the electrode contacts. The fabricated microdevice for heating and temperature sensing shows improved performance of thermal isolation, and microelectrodes display good electrochemical performances for electrochemical sensors. Thus, this novel 5-in. wafer-level microfabrication method is a simple and cost-effective protocol to prepare polymer substrate and demonstrates good potential for application to highly integrated and miniaturized biomedical devices.     

Experimental fatigue crack growth and crack-front shape analysis of asymmetric repaired aluminium panels with glass/epoxy composite patches

In this study, we investigate the experimental fatigue crack-growth behaviour of centrally cracked aluminium panels in mode-I condition which have been repaired with single-side composite patches. It shows that the crack growths non-uniformly from its initial location through the thickness of the single-side repaired panels. The propagated crack-front shapes are preformed for various repaired panels with different patch thicknesses. It is shown that there are considerable differences between the crack-front shapes obtained for thin repaired panels with various patch thicknesses. However, the crack-front shapes of thick repaired panels are not significantly changed with various patch thicknesses. Furthermore, effects of patch thickness on the crack growth life of the repaired panels are investigated for two typical thin and thick panel thicknesses. It shows that the crack growth life of thin panels may increase up to 236% using a 16 layers patch. However, for thick panels, the life may extended about 21–35% using a 4 layers patch, and implementing 8 and 16 layers patches has not a significant effect on the life extension with respect to the 4 layers patch life.     

Holographic scattering in SiO2 nanoparticle-dispersed photopolymer films

We describe an experimental study of holographic (coherent) scattering due to parasitic noise gratings recorded in SiO2 nanoparticle-dispersed photopolymer films. Dependences of film thickness and nanoparticle concentration on holographic scattering losses are evaluated. It is shown that the geometric feature of the holographic scattering pattern in the two-beam recording setup can be explained by the Ewald sphere construction. It is found that holographic scattering becomes noticeable when a film with nanoparticle concentrations higher than 10 vol.% is thicker than 100 microm. The significance of holographic scattering in the characterization of a volume grating recorded in a thick (>100 microm) nanoparticle-dispersed photopolymer film is also discussed.     

Optimization of a thick polyvinyl alcohol-acrylamide photopolymer for data storage using a combination of angular and peristrophic holographic multiplexing

The capability of polyvinyl alcohol-acrylamide photopolymer materials to obtain angularly multiplexed holographic gratings has been demonstrated [Appl. Phys. B 76, 851 (2003)]. A combination of two multiplexing methods--peristrophic and angular multiplexing--is used to record 60 holograms. An exposure schedule method is used to optimize the capability of the photopolymerizable holographic material and obtain holograms with a higher, more uniform diffraction efficiency. In addition, because of this exposure schedule method, the entire dynamic range (M#) of the material will be exploited, obtaining values of approximately M# approximately 9 in layers approximately 800 microm thick.     

Comparison of holographic photopolymer materials by use of analytic nonlocal diffusion models

The one-dimensional diffusion equation governing holographic grating formation in photopolymers, which includes both nonlocal material response and generalized dependence of the rate of polymerization on the illuminating intensity, has been previously solved under the two-harmonic expansion assumption. The resulting analytic expressions for the monomer and polymer concentrations have been derived and their ranges of validity tested in comparison with the more accurate numerical four-harmonic case. We used these analytic expressions to carry out a study of experimental results presented in the literature over a 30-year period. Automatic fitting of the data with these formulas allows material parameters, including the nonlocal chain-length variance sigma, to be estimated. In this way, (i) a quantitative comparison of different materials can be made, and (ii) a standard form of experimental result presentation is proposed to facilitate such a procedure.     

Étude électrique de couches minces de polymère obtenues dans une décharge luminescente I: Caractérisation électrique sous champ continu

The behaviour of thin polystyrene layers biased by a d.c. electric field has been studied. These thin polymer layers, obtained by glow discharge polymerisation of styrene, have thickness between 1000 and 10 000 Å.

The transient mode which appears when a step voltage is applied to a metal-polymer-metal (MPM) structure has been studied. Absorption and resorption currents are explained by the standard Cole and Cole formalism which is in good agreement with the experimental results.

The study of the permanent mode and its variation with the amplitude of the step voltage allows the polymer conduction mechanism to be analysed. Study of the conductivity variation with the polymer thickness and with its temperature shows that only the Poole-Frenkel effect can explain the experimental results, the depth of the corresponding potential well being 0.85 eV.     

Measurement of the thermal diffusivity of thin films on substrate by the photoacoustic method

Measurements of the thermal diffusivity of thin films on substrate have been performed by the photoacoustic method. In order to examine the method we have built a new apparatus and proposed (1) a system calibration procedure using optically and thermally thick reference samples and (2) a data analysis procedure based on the RG (Rosencwaig and Gersho) theory. As a result of using a transparent photoacoustic cell, the systematic errors which are caused by stray light have been reduced. With this apparatus, measurements have been performed on platinum, titanium, and stainless steel (SUS304) thin foils (thickness form 50 to 100 µm) with three different liquid backing materials (water, glycerol, and ethyl alcohol). The reproducibility was within ±7% regardless of film thickness and substrate materials.     

Multiplexed holographic data page storage on a polyvinyl alcohol/acrylamide photopolymer memory

Holographic data pages were multiplexed in different thickness layers of a polyvinyl alcohol/acrylamide photopolymer. This material is formed of acrylamide photopolymers, which are considered interesting materials for recording holographic memories. A liquid crystal device was used to modify the object beam and store the data pages. A peristrophic multiplexing method is used to store a large number of data pages in the same spot in the material. The bit error rate was calculated fitting the histograms of the images to determine what parameters improve the quality of the images.     

Self-developing, glycerin-containing, thick-layer bichromated gelatin as a medium for recording volume holograms

The synthesis of layers of glycerin-containing, self-developing bichromated gelatin between 100 and 500 μm thick is described and the holographic characteristics of this light-sensitive material are discussed. Experimental data obtained by measuring the diffraction efficiency of holograms of two plane waves recorded using a symmetric system for layers of different thickness and various ammonium bichromate concentrations showed that the optimum layers for hologram recording are around 200 μm thick and have an ammonium bichromate concentration of 2–2.5% by weight of dry gelatin. The sensitivity of these layers is 5–10 J/cm². Pis’ma Zh. Tekh. Fiz. 25, 64–69 (March 12, 1999)     

Nanoscale Probing of a Polymer‐Blend Thin Film with Tip‐Enhanced Raman Spectroscopy

Fundamental advances have been made in the spatially resolved chemical analysis of polymer thin films. Tip‐enhanced Raman spectroscopy (TERS) is used to investigate the surface composition of a mixed polyisoprene (PI) and polystyrene (PS) thin film. High‐quality TER spectra are collected from these nonresonant Raman‐active polymers. A wealth of structural information is obtained, some of which cannot be acquired with conventional analytical techniques. PI and PS are identified at the surface and subsurface, respectively. Differences in the band intensities suggest strongly that the polymer layers are not uniformly thick, and that nanopores are present under the film surface. The continuous PS subsurface layer and subsurface nanopores have hitherto not been identified. These data are obtained with nanometer spatial resolution. Confocal far‐field Raman spectroscopy and X‐ray photoelectron spectroscopy are employed to corroborate some of the results. With routine production of highly enhancing TERS tips expected in the near future, it is predicted that TERS will be of great use for the rigorous chemical analysis of polymer and other composite systems with nanometer spatial resolution.     

Thermal Effusivity Determination of Metallic Films of Nanometric Thickness by the Electrical Micropulse Method

The thermal effusivity of gold, aluminum, and copper thin films of nanometric thickness (20 nm to 200 nm) was investigated in terms of the films’ thickness. The metallic thin films were deposited onto glass substrates by thermal evaporation, and the thermal effusivity was estimated by using experimental parameters such as the specific heat, thermal conductivity, and thermal diffusivity values obtained at room conditions. The specific heat, thermal conductivity, and thermal diffusivity values of the metallic thin films are determined with a methodology based on the behavior of the thermal profiles of the films when electrical pulses of few microseconds are applied at room conditions. For all the investigated materials, the thermal effusivity decreases with decreased thickness. The thermal effusivity values estimated by the presented methodology are consistent with other reported values obtained under vacuum conditions and more elaborated methodologies.     

A Method for Measuring the Thermal Diffusivity of Intermediate Thickness Surface Absorbing Samples and Obtaining the Ratio of Anisotropy by the Converging Wave Flash Method

The converging thermal wave, flash technique for measuring thermal diffusivity is suitable for use on samples that are sufficiently thick or thin in comparison to the annular heat source, to be described by a three-dimensional or two-dimensional approximation of the heat conduction equation, and sufficiently absorbing to ensure generation of a heat source at the surface. However, samples of intermediate thickness, which lie between these regimes, cannot be analyzed. In this article, heat diffusion in the samples of varying thicknesses is modeled, and a semi-analytic expression is used to describe the dimensionality of any thickness, allowing the converging wave method to be extended to intermediate thickness samples. Applying the analysis to anisotropic samples, a method is proposed to find the anisotropy ratio of the in-plane to perpendicular-to-plane diffusivity using the converging wave method.     

Electrochemical quartz crystal impedance study of redox hydrogel mediators for amperometric enzyme electrodes

Quartz crystal impedance around the resonant frequency at 10 MHz of a composite quartz crystal resonator has been studied simultaneously with cyclic voltammetry. A modified quartz crystal with a redox hydrogel (poly(allylamine)-ferrocene cross-linked with glucose oxidase) and immersed in liquid electrolyte was used. Impedance parameters (R(f) and X(L)((f))) of the surface redox gel film were obtained by fitting the resonator transfer function |V(o)/V(i)| vs ω to a BVD equivalent circuit and analyzed with the multiple nonpiezoelectric layer model of Martin. Two limiting hydrogel layers of the same composition were studied while oxidizing and reducing the ferrocene/ferricenium moieties attached to the swollen polymer backbone: thin and thick redox hydrogel films. For the thin films, the Sauerbrey approximation was valid. The mass/thickness and film viscosity changes that resulted from the anion and water exchange were evaluated while redox switching the polymer on the assumption of negligible storage modulus G' and a density of 1. For thick gel layers, on the other hand, the penetration depth of the acoustic wave was far less than the film thickness, and a liquid-like behavior was apparent. Film storage modulus and film loss modulus were simultaneously evaluated with the cyclic voltammetry.     

Berührungslose Prüfung von Kunststoffen mittels photothermischer Wärmewellenanalyse

Remote Testing of Polymers with Photothermal Analysis of Thermal Waves After an introduction to thermal waves a comparison is made of photoacoustic detection methods (gas cell, piezoceramic) and photothermal detection arrangements (front surface and rear surface methods). Previously only photoacoustic methods have been applied to polymer related problems, while the advantages of photothermal measurements – remote and nondestructive evaluation – have been demonstrated on metals. The experimental part of this paper presents first steps to apply photothermal analysis of thermal waves to some problems of polymers: thickness measurement of thin layers; on-surface and subsurface defects; delamination of bonding and coating curing reactions; glass fibre content; orientation of fibres and molecules; aging processes. The present results indicate that the method can be used for nondestructive remote quality assurance of thin layers and foils. Further development is required to apply the method to nondestructive testing of thick walled components.     

Holographic edge-illuminated polymer Bragg gratings for dense wavelength division optical filters at 1550 nm

We discuss the use of holographic photopolymer materials for use as dense wavelength division multiplexing filters in the C-band of the optical communication spectrum. An edge-illuminated hologram configuration is described that effectively extends the grating length to achieve narrow band filters operating near 1550 nm in photopolymers that are 100-200-microm thick. This configuration enables the formation of apodized and cascaded filter systems. Rouard's method is used to examine the properties of both apodization and cascaded gratings and indicates the potential for narrow spectral bandwidths (< 0.2 nm) and high side-lobe suppression (<-- 30 dB). Initial experimental results with a commercially available photopolymer are provided that verify narrowband spectral-transmittance properties (< 0.6 nm) and the ability to apodize the index profile. The primary limitation of the design is the absorption of existing photopolymer materials. Optimizing the polymer chemistry for filter design at 1550 nm may solve this problem.     

Determination of Thermophysical Properties for Polymer Films using Conduction Analysis of Laser Heating

Determination of the thermophysical properties of thin film materials is important for modeling and optimizing laser microvia drilling of organic substrates in microelectronics applications. Techniques to measure the density, thermal conductivity, thermal diffusivity, thermal decomposition point, and specific ablation heat of thin polymer films are described. An experimental apparatus was set up for laser heating of the sample. To measure the thermal diffusivity, an analytic heat transfer model is developed. One-dimensional heat conduction is assumed due to the small thickness of the film compared to the radius of the laser beam. The value of thermal diffusivity is obtained by fitting the experimental data to the theory. The specific ablation heat is obtained by measuring the mass loss during laser ablation. The experimental apparatus and the property determination methodology can also be applied to thin samples of other materials.