Periodic micro-structures in optical microfibers induced by Plateau-Rayleigh instability and its applications

Optically Programmable Plateau-Rayleigh Instability for High-Resolution and Scalable Morphology Manipulation of Silver Nanowires for Flexible Optoelectronics

The ability to engineer microscale and nanoscale morphology upon metal nanowires (NWs) has been essential to achieve new electronic and photonic functions. Here, this study reports an optically programmable Plateau-Rayleigh instability (PRI) to demonstrate a facile, scalable, and high-resolution morphology engineering of silver NWs (AgNWs) at temperatures <150 °C within 10 min. This has been accomplished by conjugating a photosensitive diphenyliodonium nitrate with AgNWs to modulate surface-atom diffusion. The conjugation is UV-decomposable and able to form a cladding of molten salt-like compounds, so that the PRI of the AgNWs can be optically programmed and triggered at a much lower temperature than the melting point of AgNWs. This PRI self-assembly technique can yield both various novel nanostructures from single NW and large-area microelectrodes from the NW network on various substrates, such as a nanoscale dot-dash chain and the microelectrode down to 5 μm in line width that is the highest resolution ever fabricated for the AgNW-based electrode. Finally, the patterned AgNWs as flexible transparent electrodes were demonstrated for a wearable CdS NW photodetector. This study provides a new paradigm for engineering metal micro-/nanostructures, which holds great potential in fabrication of various sophisticated devices.

Micro-/Nanofiber Optics: Merging Photonics and Material Science on Nanoscale for Advanced Sensing Technology

Micro-/nanofibers (MNFs) are optical fibers with diameters close to or below the wavelength of the guided light. These tiny fibers can offer engineerable waveguiding properties including optical confinement, fractional evanescent fields, and surface intensity, which is very attractive to optical sensing on the micro-/nano scale. In this review, we first introduce the basics of MNF optics and MNF optical sensors from physical and chemical to biological applications and review the progress and current status of this field. Then, we review and discuss hybrid MNF structures for advanced optical sensing by merging MNFs with functional structures including chemical indicators, quantum dots, dye molecules, plasmonic nanoparticles, 2-D materials, and optofluidic chips. Thirdly, we introduce the emerging trends in developing MNF-based advanced sensing technology for ultrasensitive, active, and wearable sensors and discuss the future prospects and challenges in this exciting research field. Finally, we end the review with a brief conclusion.

Novel temperature-independent microfiber sensor fabricated with the tapering-twisting-tapering technique

In this paper, a novel twist and refractive index microfiber sensor fabricated with the tapering-twisting-tapering technique has been proposed and demonstrated, for the first time to the best of our knowledge. Experimental results show that the interference intensity of the microfiber increases with the increment of pre-tapered length and the intervening twist number. The sensitivity of the microfiber sensor with respect to twist is found to be 2.817 dB/(rad/m) and the refractive index sensitivity of this microfiber sensor can reach to ∼809  nm/refractive index unit in the refractive index ranging from 1.30 to 1.33. Moreover, considering that its temperature sensitivity is 0.005 dB/°C, it will not suffer from the cross sensitivity to temperature.

Comprehensive Stability Improvement of Silver Nanowire Networks via Self-Assembled Mercapto Inhibitors

Instability of silver nanowire (AgNW) has been regarded as a major obstacle to its practical applications in optoelectrical devices as transparent electrodes. Physical barrier layers such as polymer, metal, and graphene have been generally employed to improve the stability of AgNW in previous study. Herein, we first report self-assembled organothiols as an inhibitor for AgNW to achieve an overall enhancement in antioxidation, antisulfidation, thermal stability, and anti-electromigration. The self-assembled monolayers (SAMs) of phenyl azoles, methoxy silane, and methyl alkane were formed on the surface of AgNW via Ag-S covalent bond as barrier layers which provided protective effects against corrosives (e.g., O₂, H₂S). In particular, the decoration of 2-mercaptobenzimidazole (MBI) offered the best resistance to H₂S and excellent stability under a high-temperature and high-humidity environment (85 °C and 85 RH %) for 4 months. Moreover, different SAMs exhibited a stabilizing or destabilizing effect on Plateau-Rayleigh instability of AgNW, which realized the tunability of degradation temperature of AgNWs, for example, increasing by ≥100 °C with MBI SAM or decreasing by ∼50 °C with octadecanethiol SAM compared with pristine AgNWs. Notably, the MBI-decorated AgNWs could survive at 400 °C which is by far the highest bearing temperature for solution-processed AgNW film. As a result, a transparent heater made of the MBI-AgNWs exhibited superior heating characteristics (higher working temperature and durability), as compared with the pristine AgNW-based heater. Our findings on the organothiols decoration not only provide a new paradigm in overall stability improvement of NW of noble metals but also show the potential in morphology controllability of metal NW.

Compact fiber biocompatible temperature sensor based on a hermetically-sealed liquid-filling structure

A compact and robust fiber temperature sensor based on a hermetically-sealed liquid-filling Fabry-Perot (FP) cavity was fabricated by low-cost but efficient processes, including fusion splicing, liquid injection, and fused tapering. Owing to the high thermal optical coefficient (TOC) of the ethanol, the optical path difference (OPD) in the FP cavity varied strongly with temperature, which consequently induced a drastic wavelength shift of the reflection spectrum. Meanwhile, the low freezing point of the ethanol caused the fiber sensor to have the ability of detecting the sub-zero temperatures. As a result, a linear sensitivity as high as 429 pm/°C was achieved in the range between -5 °C and 30 °C. In addition, our fiber temperature sensor also exhibited rapid response time, good repeatability, and stability. The biocompatible structure, low fabrication cost, and high performance of such a temperature sensor can provide it potential for biological applications.