Multilayer thin-film based nanophotonic windows: static versus electrotunable design

To meet the global energy demand, rapid growth in fossil fuel consumption has significantly contributed to global warming. Judicious utilization of renewable energy resources could help to combat this global challenge. Here, we present a comparative study on the designs of static and electro-tunable ‘smart’ windows that could help to reduce the energy need of typical airconditioning systems deployed in buildings and motor vehicles. Our design comprises insulator–metal–insulator multi-layered thin-films deposited over a silica glass substrate to filter visible and infrared solar radiation selectively. For static windows, we optimize our design to operate in diverse climatic conditions by choosing different combinations and thicknesses of metal and insulator layers. Whereas for electro-tunable windows, we use an electro–optic polymer as the insulator layers to dynamically control portions of transmitted solar radiation over a voltage range of −12 V to +12 V. Through size-dependence analysis, we could safely assume that the performance of smart windows is less likely to degrade during experimental realization. Our designs are lithography-free, large-area compatible, polarization-independent, angle-insensitive, and robust to fabrication imperfections. The analytical results show a near-perfect match with the simulation findings. The theoretically calculated figure of merit indicates that our proposed smart windows can outperform industry-standard commercial windows.

Poly(4-vinylphenol-co-methyl methacrylate)/Hafnium Oxide Nanocomposite Gate Insulators for Organic Thin-Film Transistors

We fabricate 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pn) thin-film transistors (TFTs) with nanocomposite insulators. The insulator layers consist of both poly(4-vinylphenol-co-methyl methacrylate) and high-dielectric constant hafnium oxide (HfO2) nanoparticles. The HfO2 nanoparticles are ball-milled for sufficient dispersion in a nanocomposite solution to enable solution process methods to be used in preparing the insulator layers. The nanocomposite insulators demonstrate high capacitances and improve the performance of TIPS-Pn TFTs. Nonetheless, particle aggregates are produced in the nanocomposites solution with high HfO2 concentrations, generating detrimental effects on the dielectric properties and the TFT performance. Our experimental result implies that the optimum concentration of HfO2 nanoparticles in a mixed solution will find to be ~11.5 wt%.

Increase in Critical Current Density for Increasing Applied Magnetic Field in a High-Temperature Superconducting Superlattice

In the present work, a superlattice structure comprising superconducting and insulator layers is studied. Here, if a magnetic field is applied parallel to the layers, the lack of a pinning center leads to a novel transition; in particular, as the applied magnetic field is reduced, the stationary wave surrounding the magnetic flux quantum in the superconducting layer eventually collides with the superconducting–insulating interfaces on both sides because its radius becomes larger than the width of the superconducting layer. At this instant, the stationary wave will collapse, and a transition will occur: the magnetic quanta are collapsed and thus the uniform magnetic field distribution is achieved, which corresponds to the transition from the superconducting state to the normal state over critical current. Considering a one-dimensional model of the structure, a critical current density equation is derived that indicates an increase in the critical current density for increased applied magnetic field. Subsequently, the same calculation was conducted after changing the direction of the magnetic field component, and the combination of these two calculations expresses the anisotropic property of the structure. The phenomenon is also predicted for anisotropic critical current density. This phenomenon is an important discovery that helps manufacture high-temperature superconducting tape as well as large high-temperature superconducting coils.