Mode Conversion Trimming in Asymmetric Directional Couplers Enabled by Silicon Ion Implantation.

An on-chip asymmetric directional coupler (DC) can convert fundamental modes to higher-order modes and is one of the core components of mode-division multiplexing (MDM) technology. In this study, we propose that waveguides of the asymmetric DC can be trimmed by silicon ion implantation to tune the effective refractive index and facilitate mode conversion into higher-order modes. Through this method of tuning, transmission changes of up to 18 dB have been realized with one ion implantation step. In addition, adjusting the position of the ion implantation on the waveguide can provide a further degree of control over the transmission into the resulting mode. The results of this work present a promising new route for the development of high-efficiency, low-loss mode converters for integrated photonic platforms, and aim to facilitate the application of MDM technology in emerging photonic neuromorphic computing.

Development and optimization of a systematic approach to identifying lead service lines: One community's success.

Lead service lines (LSLs), when present, are the largest source of lead in drinking water, and their removal is necessary to reduce public exposure to lead from drinking water. Unfortunately, the composition of many service lines (SLs) is uncertain. The town of Bennington, Vermont, for example, has unreliable SL records, making it challenging to build an inventory and conduct an LSL replacement program. In 2017, Bennington commenced a project to identify SL materials and replace all LSLs. 159 control homes, consisting of 99 LSL and 60 non-LSL sites, were chosen for record reviews, visual SL observations, fully flushed (FF) and sequential profile water sampling, and test excavations to evaluate method accuracies. Of the 159 control homes, records for 90 % of the 99 known LSL homes were accurate. Whereas 3 % of the 60 non-lead SL homes' records accurately identified SL material. Fully flushed and sequential profile samples (SPSs) were 73 % and 95 % accurate for identifying LSLs and 95 % and 83 % accurate for identifying non-LSLs, respectively. Results were 100 % accurate when visual observations, FF samples, and test excavation were used in a stepwise approach. A stepwise approach consisting of visual SL observations, FF samples, and SPSs achieved a 98 % accuracy at identifying LSLs and a 67 % cost reduction compared to performing test excavations at each home. Findings from this control group study are critical for state, tribal, and local officials to inform their decisions about the selected approach to identify unknown SLs.

A one-step, tunable method of selective reactive sputter deposition as a wrinkling approach for silver/polydimethylsiloxane for electrically conductive pliable surfaces.

The wrinkle period and morphology of a metal thin film on an elastic substrate is typically controlled by modifying the substrate before carrying out additional metal deposition steps. Herein, we show that a simultaneously selective and reactive sputtering plasma that modifies the surface of a polydimethylsiloxane (PDMS) substrate while not reacting with the metal during the deposition process decreases the wrinkle wavelength and induces additional wrinkling components and features such as ripples or folds. The selective reaction of the nitrogen plasma with PDMS functionalizes the siloxane surface into silicon oxynitride. This hardens the immediate surface of PDMS, with a quadratic increase in the Young's modulus as a function of the sputtering flow ratio. The increase in the critical strain mismatch and the corresponding presence of folds in the nitrogen-modified wrinkled silver film form a suitable plasmonic platform for surface-enhanced Raman spectroscopy (SERS), yielding an enhancement factor of 4.8 × 105 for detecting lipids. This enhancement is linked to the emergence of electromagnetic hotspots from surface plasmon polariton coupling between the folds/wrinkles, which in turn enables the detection of low concentrations of organics using SERS. Furthermore, when strained, the nitrogen-modified wrinkles enhance electrical conductivity by a factor of 12 compared with unmodified films. Finally, the optical properties of the substrate can be tuned by altering the N2 content. The simple addition of nonreactive nitrogen to silver sputtering enables simultaneous PDMS hardening and growth of the silver film and together provide a new avenue for tuning wrinkling parameters and enhancing the electrical conductivity of pliable surfaces.

Rechargeable Aqueous Electrochromic Batteries Utilizing Ti-Substituted Tungsten Molybdenum Oxide Based Zn2+ Ion Intercalation Cathodes.

Batteries are used in every facet of human lives. Desirable battery architectures demand high capacity, rechargeability, rapid charging speed, and cycling stability, all within an environmentally friendly platform. Many applications are limited by opaque batteries; thus, new functionalities can be unlocked by introducing transparent battery architectures. This can be achieved by incorporating electrochromic and energy storage functions. Transparent electrochromic batteries enable new applications, including variable optical attenuators, optical switches, addressable displays, touch screen devices, and most importantly smart windows for energy-efficient buildings. However, this technology is in the incipient state due to limited electrochromic materials having satisfactory optical contrast and capacity. As such, triggering electrochromism via Zn2+ intercalation is advantageous: Zn is abundant, safe, easily processed in aqueous electrolytes and provides two electrons during redox reactions. Here, enhanced Zn2+ intercalation is demonstrated in Ti-substituted tungsten molybdenum oxide, yielding improved capacity and electrochromic performance. This technique is employed to engineer cathodes exhibiting an areal capacity of 260 mAh m-2 and high optical contrast (76%), utilized in the fabrication of aqueous Zn-ion electrochromic batteries. Remarkably, these batteries can be charged by external voltages and self-recharged by spontaneously extracting Zn2+ , providing a new technology for practical electrochromic devices.

Solution-Processed Interfacial PEDOT:PSS Assembly into Porous Tungsten Molybdenum Oxide Nanocomposite Films for Electrochromic Applications.

Electrochromic devices (ECDs) have received increased attention for applications including optoelectronics, smart windows, and low-emission displays. However, it has been recognized that the ECDs with transition-metal oxide (TMO) electrodes possess a high charge transport barrier because of their poor electrical conductivity, which limits their electrochromic performance. In this work, we addressed this limitation by utilizing a conjugated polymer to fabricate an organic-inorganic nanocomposite film that decreases the charge transport barrier of typical TMO electrodes. Using a conventional spray-layer-by-layer (spray-LbL) deposition technique, we demonstrate an electrochromic film composed of porous layers of tungsten molybdenum oxide (W0.71Mo0.29O3) nanorods permeated with an interconnected conductive layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The introduction of PEDOT:PSS is shown to significantly reduce the charge transport barrier, allowing the nanocomposite W0.71Mo0.29O3/PEDOT:PSS electrode to exhibit significantly improved electrochromic switching kinetics compared with the deposited W0.71Mo0.29O3 films. Furthermore, the optical contrast of the nanocomposite electrode was observed to be superior to both pure PEDOT:PSS and W0.71Mo0.29O3 electrodes, with a performance that exceeded the linearly predicted contrast of combining the pure films by 23%. The enhanced performance of the PEDOT:PSS-intercalated porous W0.71Mo0.29O3 nanocomposite electrodes and the facile synthesis through a spray-LbL method demonstrate a viable strategy for preparing fast assembling high-performance nanocomposite electrodes for a wide variety of electrochemical devices.