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    High Performance, Biocompatible Dielectric Thin‐Film Optical Filters Integrated with Flexible Substrates and Microscale Optoelectronic Devices
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    Abstract:
    Abstract Miniaturized, wearable, and implantable optoelectronic devices and systems provide incomparable opportunities for applications in biomedical fields. Optical filters with wavelength selective reflective/transmissive responses that can be integrated onto these biointegrated platforms are critically important for high performance operation. Here, high quality, dielectric thin‐film optical filters on unconventional substrates via transfer printing are reported. Designed filters formed on flexible substrates exhibit highly spectral selective transmission and reflection, with the maximum optical density at stop band reaching 6. Additionally, freestanding filter membranes are combined with microscale optoelectronic devices, achieving enhanced emission intensity for light‐emitting diodes and spectral sensitivity for photovoltaic detectors. Finally, their in vitro cytotoxicity is evaluated within cell culture, and in vivo biocompatibility is supported in living animals. The presented results offer viable routes to high performance optical components for advanced biointegrated optoelectronic systems.
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    Microscale chemistry
    Gold and platinum nanocapacitors have been fabricated using a magnetron sputtering technique. TiO 2 is used as a dielectric material to separate the metal layers which act as the parallel plates for the capacitors. The thickness for metal films and TiO 2 layer is 80 nm and 400 nm, respectively. Capacitance of the nanocapacitors has been measured and dielectric constant of TiO 2 calculated. Both capacitance and dielectric constant are observed to have strong frequency dependence.
    High-κ dielectric
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    Abstract Sol-gel derived PLZT, including PbTiO3, PbLaTiO3 28, PLZT 9/65/35 and PZT 53/47 films were prepared on platinized substrates. The dielectric and ferroelectric properties of the films were measured at 260K -580K. The values of polarization, coercive field dielectric constant and dissipation factor in these films typically increased with increasing temperature. The changes in dielectric properties of the films with temperature were not sharp unlike the transitions in single crystals or bulk ceramics. The pyroelectric coefficients, on the other hand, decreased monotonically with increasing temperature in all these films.
    Dissipation factor
    Dielectric loss
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    In this work, 0-3 lead zirconate titanate (PZT) was mixed with normal Portland cement to produce 0-3 connectivity composites. The effect of temperature on the dielectric properties such as the dielectric constant and dielectric loss was determined. It was found that with increasing PZT content the Tc increases where the optimum dielectric constant was observed and that at the temperature up to 100°C there is a significant change in the dielectric properties in PZT-cement composites. This is due to the loss of water molecules at up to 100°C. At above 100°C, the dielectric properties of the composites were found to have a similar behavior to that of PZT ceramic with Tc being ≈420°C.
    Lead zirconate titanate
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    Abstract The impregnation of a glass woven fabric with an amorphous polyethylene terephthalate copolymer (PET‐ g ) matrix was investigated using a finite element (FE) model for interbundle and intrabundle flow of the matrix. Micrographs of samples obtained by film stacking of PET‐ g to impregnate the glass fabric have confirmed the occurrence of interbundle and intrabundle flow, taking place as separate steps. On the basis of this evidence, two different mechanisms for the fiber impregnation were postulated. The first flow process is associated with a macroscale interbundle impregnation, whereas the second is associated with microscale intrabundle impregnation. Two different FE models were developed to simulate the microscopic and macroscopic flow of the matrix, considering a large number of different random fiber arrangements. Both models could account for the non‐Newtonian rheological behavior of the thermoplastic matrix. The microscale impregnation of fibers was simulated by using randomly spaced and nonoverlapping unidirectional filaments. The effect of the number of filaments and the number of random distributions necessary to achieve an adequate accuracy of the method was assessed. The results obtained from the simulation showed that at low pressures, the polymer melt exhibits Newtonian behavior, which makes it possible to predict the tow permeability by the Darcy law. A more difficult situation arises at high pressures because of the non‐Newtonian behavior of the melt. This requires the introduction of a value for the permeability that is also dependent on the rheological properties of the melt. The same non‐Newtonian behavior of the matrix was observed for macroscale impregnation of bundles. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:122–130, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/adv.20179
    Microscale chemistry
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    A method for forming efficient, ultrathin GaN light-emitting diodes (LEDs) and for their assembly onto foreign substances is reported. The LEDs have lateral dimensions ranging from ∼1 mm × 1 mm to ∼25 μm × 25 μm. Quantitative experimental and theoretical studies show the benefits of small device geometry on thermal management, for both continuous and pulsed-mode operation, the latter of which suggests the potential use of these technologies in bio-integrated contexts. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
    Microscale chemistry
    Wide-bandgap semiconductor
    Citations (207)