Insulator-on-Conductor Fouling Amplifies Aqueous Electrolysis Rates.

The chemical industry is a major consumer of fossil fuels. Several chemical reactions of practical value proceed with the gain or loss of electrons, opening a path to integrate renewable electricity into chemical manufacturing. However, most organic molecules have low aqueous solubility, causing green and cheap electricity-driven reactions to suffer from intrinsically low reaction rates in industry's solvent of choice: water. Here, we show that a strategic, partial electrode fouling with hydrophobic insulators (oils and plastics) offsets kinetic limitations caused by poor reactant solubility, opening a new path for the direct integration of renewable electricity into the production of commodity chemicals. Through electrochemiluminescence microscopy, we reveal for the oxidation of organic reactants up to 6-fold reaction rate increase at the "fouled" oil-electrolyte-electrode interface relative to clean electrolyte-electrode areas. Analogously, electrodes partially masked (fouled) with plastic patterns, deposited either photolithographically (photoresists) or manually (inexpensive household glues and sealants), outperform clean electrodes. The effect is not limited to reactants of limited water solubility, and, for example, net gold electrodeposition rates are up to 22% larger at fouled than clean electrodes. In a system involving a surface-active reactant, rate augmentation is driven by the synergy between insulator-confined reactant enrichment and insulator-induced current crowding, whereas only the latter and possibly localized decrease in iR drop near the insulator are relevant in a system composed of non-surface-active species. Our counterintuitive electrode design enhances electrolysis rates despite the diminished area of intimate electrolyte-electrode contact and introduces a new path for upscaling aqueous electrochemical processes.

Atomic force microscopy with integrated on-chip interferometric readout.

The most common readout technique used in atomic force microscopy (AFM) is based on optical beam deflection (OBD), which relies on monitoring deflection of the cantilever probe by measuring the position of the laser beam reflected from the free end of the AFM cantilever. Although systems using the OBD readout can achieve subnanometre displacement resolution and video rate imaging speeds, its main limitation is size, which is difficult to minimise, thus limiting multiprobe imaging capability. Currently, system miniaturisation has been accommodated by adopting on-chip electrical readout solutions, often at the expense of measurement sensitivity. To date, no cost-effective AFM readout solution exists without sacrificing either measurement sensitivity, system miniaturisation, or multiprobe array scalability. In this paper we present an AFM probe with integrated on-chip optical interferometric readout based on silicon photonics. Our AFM probe combines the advantages of subnanometre resolution of optical readouts with on-chip miniaturisation. The adopted approach determines deflection of the cantilever using an integrated on-chip photonics waveguide by monitoring the separation between the sensing cantilever and an interrogating grating. The implemented methodology provides ultimate interferometric resolution and sensitivity, on-chip miniaturisation, and array scalability, which makes possible ultrafast multiprobe-array AFM imaging. Using a Digital Instruments D3000 AFM retrofitted with our cantilever probe and integrated readout, we report sub-nanometre AFM topography images obtained on reference samples. We demonstrate RMS static AFM noise level of 19 pm, outperforming the operation of this system in its standard, optical beam deflection configuration (51 pm). The noise spectrum measurements of our probe indicate that the integrated readout is shot noise limited, achieving a deflection noise density (DND) of 36fm/Hz.

Ultrathin tunable terahertz absorber based on MEMS-driven metamaterial.

The realization of high-performance tunable absorbers for terahertz frequencies is crucial for advancing applications such as single-pixel imaging and spectroscopy. Based on the strong position sensitivity of metamaterials' electromagnetic response, we combine meta-atoms that support strongly localized modes with suspended flat membranes that can be driven electrostatically. This design maximizes the tunability range for small mechanical displacements of the membranes. We employ a micro-electro-mechanical system technology and successfully fabricate the devices. Our prototype devices are among the best-performing tunable THz absorbers demonstrated to date, with an ultrathin device thickness (~1/50 of the working wavelength), absorption varying between 60% and 80% in the initial state when the membranes remain suspended, and fast switching speed (~27 µs). The absorption is tuned by an applied voltage, with the most marked results achieved when the structure reaches the snap-down state. In this case, the resonance shifts by >200% of the linewidth (14% of the initial resonance frequency), and the absolute absorption modulation measured at the initial resonance can reach 65%. The demonstrated approach can be further optimized and extended to benefit numerous applications in THz technology.

On-chip read-out of picomechanical motion under ambient conditions.

Monitoring the nanomechanical movement of suspended cantilever structures has found use in applications ranging from biological/chemical sensing to atomic force microscopy. Interrogating these sensors relies on the ability to accurately determine the sub-nanometre movements of the cantilever. Here we investigate a technique based on the combination of integrated silicon photonics and microelectromechanical systems (MEMS) to create an optically resonant microcavity and demonstrate its use for monitoring of the position of cantilevers on the picometer scale under ambient conditions with dynamic range extending over several microns. The technique is interferometric, and we show it to be sufficiently sensitive to measure both the first and second modes of cantilever Brownian motion. We anticipate that application of this technique will provide a physically robust, picometer precision, integrated cantilever movement read-out technology which can take cantilever sensors from laboratory controlled environments into real world conditions, allowing everyday applications.

Uniform dispersion of lanthanum hexaboride nanoparticles in a silica thin film: synthesis and optical properties.

Silica thin films containing uniformly dispersed lanthanum hexaboride (LaB6) nanoparticles have been prepared by spin-coating a sol-gel silica solution containing cetyltrimethyl ammonium bromide (CTAB)-stabilized LaB6 nanoparticles onto a glass substrate followed by a standard heat treatment. The production of this thin film involved three steps: (i) a CTAB-stabilized LaB6 nanoparticle dispersion was prepared in water and then dried, (ii) the dried nanoparticles were redispersed in a small amount of water and mixed with tetraethoxyorthosilane (TEOS), ethanol, and a little acid to initiate the sol-gel reaction, and (iii) this reaction mixture was spun to produce a thin film and then was annealed. A range of techniques such as zeta potential, laser sizing, energy-filtered transmission electron microscopy (EFTEM), scanning TEM (STEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectrum (EDS) were employed to characterize the particle's size, elemental composition, and stability and the optical properties of silica thin films with LaB6 nanoparticles. On the basis of the optical transmittance and reflectance spectra of an annealed silica thin film with LaB6 nanoparticles, the annealed thin films clearly showed positive absorption of radiation in the near infrared (NIR) region meeting a main objective of this study. A potential optical micro-electromechanical sensing system in the NIR range can be realized on the basis of this silica thin film with LaB6 nanoparticles.