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Monitoring the Evaporation of Fluids from Fiber-Optic Micro-Cell Cavities

Fiber-optic sensors provide remote access, are readily embedded within structures, and can operate in harsh environments. Nevertheless, fiber-optic sensing of liquids has been largely restricted to measurements of refractive index and absorption spectroscopy. The temporal dynamics of fluid evaporation have potential applications in monitoring the quality of water, identification of fuel dilutions, mobile point-of-care diagnostics, climatography and more. In this work, the fiber-optic monitoring of fluids evaporation is proposed and demonstrated. Sub-nano-liter volumes of a liquid are applied to inline fiber-optic micro-cavities. As the liquid evaporates, light is refracted out of the cavity at the receding index boundary between the fluid and the ambient surroundings. A sharp transient attenuation in the transmission of light through the cavity, by as much as 50 dB and on a sub-second time scale, is observed. Numerical models for the transmission dynamics in terms of ray-tracing and wavefront propagation are provided. Experiments show that the temporal transmission profile can distinguish between different liquids.

Self-assembled monolayer assisted bonding of Si and InP

A versatile procedure for the low-temperature bonding of silicon and indium-phosphide to silicon is proposed and demonstrated. The procedure relies on the deposition and functionalization of self-assembled, single molecular layers on the surface of one substrate, and the subsequent attachment of the monolayer to the surface of the other substrate with or without its own monolayer coating. The process is applicable to the fabrication of hybrid-silicon, active photonic devices.

Protective molecular passivation of black phosphorus

Black phosphorus is a fascinating layered material, with extraordinary anisotropic mechanical, optical and electronic properties. However, the sensitivity of black phosphorus to oxygen and moisture poses significant challenges for technological applications of this unique material. Here, we report a viable solution that overcomes degradation of few-layer black phosphorus by passivating the surface with self-assembled monolayers of octadecyltrichlorosilane that provide long-term stability in ambient conditions. Importantly, we show that this treatment does not cause any undesired carrier doping of the bulk channel material, thanks to the emergent hierarchical interface structure. Our approach is compatible with conventional electronic materials processing technologies thus providing an immediate route toward practical applications in black phosphorus devices.Making black phosphorus airtightBlack phosphorus is a leading contender among new semiconductors for nanoscale optoelectronics, but its use is impeded by rapid degradation in air. A team of Israeli and US scientists, led by Doron Naveh from Bar Ilan University, has devised an inexpensive and scalable approach for long-term stabilization of black phosphorus, bringing it one step closer to real-world applications. By treating black phosphorus with octadecyltrichlorosilane (OTS), a chemical commonly used in semiconductor processing, Naveh and coworkers were able to produce self-assembled polymer coatings that protect black phosphorus from oxygen and moisture. Importantly, this chemical treatment does not alter the overall electronic properties of black phosphorus nor does it complicate subsequent device fabrication. With this advance, researchers can now stabilize and study black phosphorus devices with relative ease under normal operating conditions.

Monitoring and analysis of pendant droplets evaporation using bare and monolayer-coated optical fiber facets

The monitoring of sub nano-liter pendant liquid droplets, during their evaporation from the cleaved facet of a standard optical fiber, is proposed and demonstrated. The combined reflections of incident light from the two boundaries, between fiber and liquid and between liquid and air, give rise to interference fringes as the fluid evaporates. The analysis of the fringe pattern allows for the reconstruction of the instantaneous size and evaporation rate of the droplets. These, in turn, provide information regarding the properties of the liquid itself, and the surface to which it is applied. The sensor readout is validated against direct video observation of evaporating droplets. Several examples illustrate the potential of the proposed sensor. Evaporation dynamics measurements identify the ethanol contents in binary ethanol-water mixtures with 2% certainty. The evaporation dynamics are modified by the application of a hydrophobic self-assembled monolayer coating to the tip of the fiber. Ten different organic solvents are accurately classified by clustering analysis of their evaporation data, collected using bare and coated fibers. Potential applications of the sensors could include quality control of water, beverages and oils, recognition of flexible fuel blends and fuel dilutions, mobile point-of-care diagnostics, and laboratory analysis of surface treatments.

Fiber Optic Monitoring of Fluid Evaporation

Fiber-optic monitoring of fluids evaporation is demonstrated. Solvents are recognized based on their volatility. Measurements of water evaporation from a standard fiber before and after hydrophobic nanometric coating agree with conventional methods.

Voltage-Induced Phase Shift in a Hybrid LiNbO3-on-Silicon Mach-Zehnder Interferometer

A hybrid Mach-Zehnder interferometer with directly bonded LiNbO3 on silicon-on-insulator waveguides is designed and demonstrated. The transfer function of the device shows a pi phase shift subject to an external field of 0.5 V/micro-meter

Low temperature wafer bonding of silicon to InP and silicon to LiNbO 3 using self-assembled monolayers

Procedures for wafer bonding between silicon and InP and between silicon and LiNbO3 at temperatures below 120 °C are reported. The bonding is based on the deposition of functionalized, organic self assembled monolayers.

Erratum: Protective molecular passivation of black phosphorus

A correction to this article has been published and is linked from the HTML version of this article.

Analysis of organic solvents and liquid mixtures using a fiber-tip evaporation sensor

The instantaneous size and rate of evaporation of pendant liquid droplets placed on the cleaved facet of a standard fiber are reconstructed based on reflected optical power. Using the evaporation dynamics, the relative contents of ethanol in ethanol-water binary mixtures are assessed with 1% precision and different blends of methanol in gasoline are properly recognized. The latter application, in particular, is significant for the use of alternative fuels in the automotive sector. Also, ten organic solvents are identified based on their evaporation from a fiber facet coated with a hydrophobic, selfassembled monolayer.

Wafer bonding techniques for hybrid silicon photonic devices based on surface modifications

The low-temperature bonding of lithium-niobate to silicon and of indium-phosphide to silicon is reported. The bonding technique is based on modifications to the surfaces of the substrates to-be-bonded, through the deposition of self-assembled, single layers of organic molecules. Chemical functionalization of the monolayers promotes the subsequent formation of bonds across the interface between the two substrates. The technique could be applicable to the fabrication of hybrid-silicon active photonic devices such as light sources, amplifiers and modulators, which are more difficult to implement solely in the silicon materials platform. Compared with direct molecular bonding methods that are currently being used in the fabrication of such devices, monolayers-assisted bonding provides numerous potential advantages: the functional groups at the monolayers termini can be chosen and adjusted to accommodate specific substrates; the process is carried out at a relatively low temperature of 120-150 °C; the outgassing of by-products may be avoided; lastly, while the bonding interface is only a few nm-thin and does not disrupt optical coupling, it may nevertheless provide a relaxation of the substrate flatness and micro-roughness requirements.