Microstructure and dielectric properties of compositionally graded Ba1-xSrxTiO3 multilayer tunable capacitors

Li₂O/B₂O₃-added Ba_1-xSr_xTiO₃ (B_1-xS_xT) ceramics, where 0.2 ≤ x ≤ 0.35, were well densified at 920 °C with pure perovskite structure. The dielectric constant, tunability, and figure of merit (FOM) of B_1-xS_xT ceramics increased with x because of the decreasing Curie temperature (T_C). The specimen with x = 0.35, whose T_C was close to room temperature, exhibited a large tunability of 27.4 % and FOM of 110 at 10 kV/cm. A compositionally graded multilayer (CGML), which was sintered at 920 °C, was fabricated using B_1-xS_xT thick films to produce a temperature-stable tunable capacitor, and it evinced a dense microstructure and a continuous interface between the B_1-xS_xT thick film and the Ag electrode. This CGML capacitor showed a large tunability (51 %) and FOM (150) at 20 kV/cm. It also exhibited stable tunability (17–28 % at 10 kV/cm) at temperatures between 30–90 °C. Therefore, the B_1-xS_xT CGML capacitor is a suitable candidate for temperature-stable tunable capacitors.     

Theoretical and experimental study of the second-order polarizabilities of Schiff''s bases for nonlinear optical applications

A series of twenty-four Schiff's bases was synthesized and nonresonant static molecular second order polarizabilities (β) of these compounds were theoretically calculated and compared with experimental values. The computational method employed obtained: (a) values of polarization versus static electric fields using a semiempirical Hamiltonian; (b) all tensor elements of β by performing polynomial fits of the former data, within the finite-field approach. The experimental values were obtained using a modified electric field induced second harmonic generation (EFISH) experiment with 1,4-dioxane as the solvent. The measured quantities were the projection of β on μ (the permanent dipole moment), relative to MNA (2-methyl-4-nitroaniline). The correlation between the predicted static molecular quantities and their corresponding experimental values was 0.95 (based on a simple least-squares regression forced through the origin). A factor of 8.7 ± 0.3 was determined to be the adjustment parameter for Schiff's bases to account for the solvent and dispersion effects at the fundamental wavelength of 1064 nm.     

Backscatter Compensation in IFOG Based Inertial Measurement Units With Polymer Phase Modulators

Precision guidance in navigation systems requires highly accurate, compact, and low cost inertial measurement units (IMUs). The key active guided-wave component of the IMU is the phase modulator. In our approach, electro-optic polymers have been utilized in fabricating low loss phase modulators with low half-wave drive voltage using advanced hybrid waveguide fabrication processes and novel optical integration techniques. However, the interference between the primary wave and the backscatter waves generated by the phase modulator and/or the interference between the two counter-propagating backscatter waves at the detector of the IMU has been a major source of error in this approach. A novel technique was introduced in assessing the error caused by backscatter and an offset waveguide design was developed to suppress the interference of backscatter light. The novel design not only preserved the miniaturization, but also improved the insertion loss with the use of a shorter waveguide. The gyro level tests performed with the backscatter compensated modulators showed about 5 times improvement of the average bias uncertainty over gyros integrated with a standard symmetric phase modulator.     

Multi-month thermal aging of electro-optic polymer waveguides: Synthesis, fabrication, and relaxation modeling

The preparation of polyimides containing side-chain chromophores and the long-term aging performance of poled films are described. These materials were compared to guest-host polycarbonate films. Mach-Zehnder optical interferometers were fabricated from these polymers that contained CLD- and FTC-type chromophores. Changes in optical properties were monitored for months at four temperatures ranging from ambient to 110 °C. The isothermal relaxation data were modeled using both a stretched exponential equation and a power law in time equation. The temperature dependency of the time constants of these equations was modeled using a new activation-energy equation: ln(τ/τ_p) = E_R(1 + tanh[(T_c − T)/D])/2RT + E_p/RT where T_c is the central temperature of the transition zone, D is the breadth of the zone, and Es are the activation energies of rigid and pliable materials. Multi-year high-temperature stability of the poled guest-host and side-chain materials was predicted.     

Wafer‐Scale Single‐Crystalline Ferroelectric Perovskite Nanorod Arrays

1D ferroelectric nanostructures are promising for enhanced ferroelectric and piezoelectric performance on the nanoscale, however, their synthesis at the wafer scale using industrially compatible processes is challenging. In order to advance the nanostructure‐based electronics, it is imperative to develop a silicon‐compatible growth technique yielding high volumetric density and an ordered arrangement. Here, a major breakthrough is provided in addressing this need and ordered and close‐packed single crystalline ferroelectric nanorod arrays, of composition PbZr_0.52Ti_0.48O₃ (PZT), grown on commercial grade 3 in. silicon wafer are demonstrated. PZT nanorods exhibit enhanced piezoelectric and ferroelectric performance compared to thin films of similar dimensions. Sandwich structured architecture utilizing 1D PZT nanorod arrays and 2D reduced graphene oxide thin film electrodes is fabricated to provide electrical connection. Combined, these results offer a clear pathway toward integration of ferroelectric nanodevices with commercial silicon electronics.     

Design and Demonstration of Polarizing Polymer Waveguides Using Birefringent Polymers

TE-pass and TM-pass polarizing waveguides were fabricated by adjusting the birefringence properties of multi-layer stacks. The desired values of indices of refraction and birefringence were obtained by the proper selection and customization of core and cladding materials. The technique developed was used in the fabrication of waveguides in various design configurations such as etched ribs, backfilled trenches and photobleached channels. Both passive and active (electro-optic) core materials were successfully used in demonstrating the polarization extinction ratios as high as 61 dB. To our knowledge, this is the highest extinction ratio reported with polarizing polymer waveguides. In the case of electro-optic polymer waveguides, the designs were modified to enhance the electric field strength in the core without compromising the polarizing extinction ratios of the waveguides.     

Laser‐Induced Molybdenum Carbide–Graphene Composites for 3D Foldable Paper Electronics

Versatile and low‐cost manufacturing processes/materials are essential for the development of paper electronics. Here, a direct‐write laser patterning process is developed to make conductive molybdenum carbide–graphene (MCG) composites directly on paper substrates. The hierarchically porous MCG structures are converted from fibrous paper soaked with the gelatin‐mediated inks containing molybdenum ions. The resulting Mo₃C₂ and graphene composites are mechanically stable and electrochemically active for various potential applications, such as electrochemical ion detectors and gas sensors, energy harvesters, and supercapacitors. Experimentally, the electrical conductivity of the composite is resilient to mechanical deformation with less than 5% degradation after 750 cycles of 180° repeated folding tests. As such, the direct laser conversion of MCGs on papers can be applicable for paper‐based electronics, including the 3D origami folding structures.     

Fullerene Polymer Complex Inducing Dipole Electric Field for Stable Perovskite Solar Cells

Lead halide perovskite solar cells (PSCs) have demonstrated great potential for realizing low‐cost and easily fabricated photovoltaics. At this juncture, power conversion efficiency and long‐term stability are two important factors limiting their transition. PSCs exhibit rapid environmental degradation since the perovskite layer is very sensitive to factors such as humidity, temperature, and ultraviolet light. Here, a novel successful approach is demonstrated that simultaneously improves the efficiency and stability of PSCs. This approach relies on incorporation of a dual‐functional polymethyl methacrylate (PMMA)–fullerene complex into the perovskite layer. The fullerene within perovskite layer forms a localized dipole‐like electric field that favors electron–hole separation, resulting in significant improvement in current density and fill factor with conversion efficiency reaching 18.4%. The molecular‐scale coating of hydrophobic PMMA on the perovskite grain boundary effectively blocks moisture penetration into the perovskite, thereby, significantly improving the stability against moisture, heat, and light. The PSCs with PMMA–fullerene complex showed no photovoltaic performance degradation for 250 d and exhibited 60 times higher stability compared to the state‐of‐the‐art devices under continuous 1 sun illumination in ambient air.