Ultrathin Pyroelectric Photodetector with Integrated Polarization-Sensing Metasurface.

An abundance of metallic metasurfaces have been realized with miniscule, intricate features capable of tailored scattering, reflection, and absorption; however, high losses through heat limit their use in optoelectronics. Here, codesign of a detector and a polarization-sensing metasurface overcomes this challenge by utilizing the heat generation for integrated pyroelectric detection of the incoming light polarization. Using a nanogap metasurface with asymmetric metallic elements, polarization-sensitive photodetection exhibits high extinction ratios up to 19 for orthogonally polarized light and allows extraction of Stokes parameters with <12% deviation from theoretical values. This polarization-sensitive photodetector is ultrathin, consisting of active layers of only 290 nm, and exhibits fast response times of ∼2 ns. The structure is fully integrated, requiring no external cameras, detectors, or power sources, and points toward the creation of layered, multifunctional devices that utilize exotic metasurface properties for novel and compact sensing and imaging.

Shortwave Infrared Photodetection with oCVD Polythiophene.

Shortwave infrared (SWIR, λ = 1-3 µm) photodetectors typically use compound semiconductors that are fabricated using high-temperature epitaxial growth and require active cooling. New technologies that overcome these constraints are the focus of intensive current research. Herein, oxidative chemical vapor deposition (oCVD) is used for the first time to create a room temperature, vapor-phase deposited SWIR photoconductive detector with a unique tangled wire film morphology that detects nW-level photons emitted from a 500 °C cavity blackbody radiator-a rarity for polymer systems. A new, window-based process that greatly simplifies device fabrication is used to construct doped polythiophene-based SWIR sensors. The detectors feature an 8.97 kΩ dark resistance and are limited by 1/f noise. They feature an external quantum efficiency (gain-external quantum efficiency) product of 395% and have a measured specific detectivity (D*) of 106 Jones, with the potential to reach D* = 1010 Jones after 1/f noise is minimized. Still, the measured D* is only a factor of 102 lower than a typical microbolometer and after optimization, the newly described oCVD polymer-based IR detectors will be in a category competitive with commercially available, room temperature lead salt photoconductors and within reach of room temperature photodiodes.

The Role of Nanoscale Seed Layers on the Enhanced Performance of Niobium doped TiO2 Thin Films on Glass.

Transparent conducting oxide (TCO) coatings with decreased cost and greater process or performance versatility are needed for a variety of optoelectronic applications. Among potential new TCO candidates, doped titanium dioxide is receiving particular interest. In this study, niobium-doped titania bilayer structures consisting of a nanoscale seed layer (deposited by atomic layer deposition or RF magnetron sputtering) followed by a thick bulk-like layer were grown directly on glass in order to examine the effects of the seed layer processing on the subsequent crystallization and electrical properties of these heterostructures. Observations from Raman spectroscopy suggest that higher oxygen content in the seed layer suppresses the formation of detrimental titania polymorph phases, found in films produced by annealing directly after synthesis without any exposure to oxygen. Furthermore, our results indicate that the generation of excellent Nb:TiO2 conductors on glass (without breaking vacuum) only occurs within a narrow processing range and that the sequential deposition of oxygen-poor layers on oxygen-rich layers is a critical step towards achieving films with low resistivity.

Readily processed protonic ceramic fuel cells with high performance at low temperatures.

Because of the generally lower activation energy associated with proton conduction in oxides compared to oxygen ion conduction, protonic ceramic fuel cells (PCFCs) should be able to operate at lower temperatures than solid oxide fuel cells (250° to 550°C versus ≥600°C) on hydrogen and hydrocarbon fuels if fabrication challenges and suitable cathodes can be developed. We fabricated the complete sandwich structure of PCFCs directly from raw precursor oxides with only one moderate-temperature processing step through the use of sintering agents such as copper oxide. We also developed a proton-, oxygen-ion-, and electron-hole-conducting PCFC-compatible cathode material, BaCo(0.4)Fe(0.4)Zr(0.1)Y(0.1)O(3-δ) (BCFZY0.1), that greatly improved oxygen reduction reaction kinetics at intermediate to low temperatures. We demonstrated high performance from five different types of PCFC button cells without degradation after 1400 hours. Power densities as high as 455 milliwatts per square centimeter at 500°C on H2 and 142 milliwatts per square centimeter on CH4 were achieved, and operation was possible even at 350°C.

Assessing the purity of metal-organic frameworks using photoluminescence: MOF-5, ZnO quantum dots, and framework decomposition.

Photoluminescence (PL) spectroscopy was used to characterize nanoscale ZnO impurities, amine-donor charge-transfer exciplexes, and framework decomposition in samples of MOF-5 prepared by various methods. The combined results cast doubt on previous reports describing MOF-5 as a semiconductor and demonstrate that PL as a tool for characterizing MOF purity possesses advantages such as simplicity, speed, and sensitivity over currently employed powder XRD MOF characterization methods.