Thermal micro‐Raman spectroscopic study of polymorphic transformation of famotidine under different compression pressures

The objective of this study was to investigate the effect of pressure and/or temperature on the polymorphic transformation of famotidine from form B to form A by using a thermal confocal Raman microspectroscopy. A compact with a wide transparent zone in the center and an opaque zone surrounding it was prepared by compressing a conical mass of famotidine form B. Two unique Raman peaks at 2897 and 2920 cm⁻¹ for famotidine forms B and A, respectively, were used as markers. The result indicates that the opaque zone in each compact was composed of famotidine from B, and it did not undergo any polymorphic transformation by preparing with higher compression pressure and/or by heating. The Raman peak intensity ratio of the 2920 cm⁻¹ and 2897 cm⁻¹ bands markedly increased starting from 120 °C for the transparent zone prepared by compressing with 19.61 × 10⁴ kPa pressure, but increased from 100 °C with 49.03 × 10⁴ kPa pressure, indicating the occurrence of thermally induced polymorphic transformation of famotidine from form B to form A. However, the transparent zone prepared by 9.81 × 10⁴ kPa compression pressure retained the same Raman spectrum as that of the famotidine form B, revealing that the thermally induced polymorphic transformation of famotidine was dependent on the pressure applied. There was no polymorphic transformation of famotidine in the transparent zone when it was prepared by a higher compression pressure at a lower temperature or by a lower pressure at a higher temperature. The combined effect of compression and temperature was found to accelerate the polymorphic transformation from form B to form A in the transparent zone of famotidine. Copyright © 2006 John Wiley & Sons, Ltd.     

Fast piezoresistive sensor and UV photodetector based on Mn‐doped ZnO nanorods

A low cost hydrothermal synthesis method to synthesize Mn‐doped ZnO nanorods (NRs) with controllable morphology and structure has been developed. Ammonia is used to tailor the ammonium hydroxide concentration, which provides a source of OH^– for hydrolysis and precipitation during the growth instead of HMT. The morphological, chemical composition, structural, and electronic structure studies of the Mn‐doped ZnO NRs show that the Mn‐doped ZnO NRs have a hexagonal wurtzite ZnO structure along the c‐axis and the Mn ions replace the Zn sites in the ZnO NRs matrix without any secondary phase of metallic manganese element and manganese oxides observed. The fabricated PEDOT:PSS/Zn_0.85Mn_0.15O Schottky diode based piezoresistive sensor and UV photodetector shows that the piezoresistive sensor has pressure sensitivity of 0.00617 kPa^–1 for the pressure range from 1 kPa to 20 kP and 0.000180 kPa^–1for the pressure range from 20 kPa to 320 kPa with relatively fast response time of 0.03 s and the UV photodetector has both relatively high responsivity and fast response time of 0.065 A/W and 2.75 s, respectively. The fabricated Schottky diode can be utilized as a very useful human‐friendly interactive electronic device for mass/force sensor or UV photodetector in everyday living life. This developed device is very promising for small‐size, low‐cost and easy‐to‐customize application‐specific requirements. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

A Facile Strategy for Low Young's Modulus PDMS Microbeads Enhanced Flexible Capacitive Pressure Sensors

Flexible pressure sensors are widely demanded in human care systems. A simple and effective strategy for sensor fabrication can markedly promote its application. Herein, a facile strategy is employed to prepare a flexible capacitive pressure sensor with a polydimethylsiloxane microbeads-modified dielectric layer. Owing to the microbeads structure, the proposed sensor achieves a sensitivity of 0.048 kPa⁻¹ in the range of 0–10 kPa with a wide dynamic range (up to 100 kPa). The sensitivity is nine times higher than that of the planar structure. Moreover, the microbeads structured sensor obtains a low limit of detection (0.2 kPa), fast response time (120 ms), and good stability (variation lower than 3.30% after 1000 loading/unloading cycles at 20 kPa). The finite-elemental analysis reveals that the microbeads structure is critical to enhance the performance of sensors. Finally, the pressure sensor is successfully applied to detect touch signal, joints movement, and breathing, exhibiting its promising prospects as smart wearable devices. Furthermore, the strategy may provide a new idea for the microstructural design of capacitive pressure sensors.     

Highly flexible,transparent, conductive and antibacterial films made of spin-coated silver nanowires and a protective ZnO layer

We prepared highly flexible, transparent, conductive and antibacterial film by spin coating a silver nanowire suspension on a poly (ethylene terephthalate) (PET) substrate. The ZnO layer covered the conductive silver nanowire (AgNW) network to protect the metal nanowires from oxidization and enhance both wire-to-wire adhesion and wire-to-substrate adhesion. It is found that the number of AgNW coatings correlates with both the sheet resistance (R_s) and the transmittance of the AgNW/ZnO composite films. An excellent 92% optical transmittance in the visible range and a surface sheet resistance of only 9 Ω sq⁻¹ has been achieved, respectively. Even after bending 1000 times (5 mm bending radius), we found no significant change in the sheet resistance or optical transmittance. The real-time sheet resistance measured as a function of bending radius also remains stable even at the smallest measured bending radius (1 mm). The AgNW/ZnO composite films also show antibacterial effects which could be useful for the fabrication of wearable electronic devices.     

Biomimetic-inspired highly sensitive flexible capacitive pressure sensor with high-aspect-ratio microstructures

The high sensitivity flexible capacitive pressure sensor (FCPS) manufactured in a fast and efficient way has friendly man-machine interaction function. In this paper, a high-sensitivity FCPS is developed by using a two-step template method to reproduce biomimetic microtower polydimethylsiloxane (PDMS) from the lotus leaf surface. The capacitive sensor is composed of a PDMS dielectric layer and the Cu nanowire electrodes sandwiching in the middle, with a high sensitivity of ~1.207 kPa⁻¹, a low detection limit of less than 0.02 kPa and a fast response time of 61.6 ms. Particularly, the sensing performance can be kept basically unchanged when bent at a 5 mm radius. Moreover, the FCPS can withstand 4000 repeated tests and maintain stable performance, and the sensitivity is almost the same in the process of loading and unloading, suggesting the high robustness. These results demonstrates the FCPSs have potential applications in electronic wearables, human health monitoring and uneven surface applications.     

基于银纳米线电极-rGO敏感材料的柔性NO2气体传感器

使用银纳米线作为材料制备柔性叉指电极,用还原氧化石墨烯(reduced graphene oxide, rGO)作为气体敏感材料制备出柔性气体传感器,并研究其对二氧化氮气体的响应特性以及柔韧性能.实验结果表明,制备的以银纳米线作为电极的r GO气体传感器可以实现室温下对浓度为5-50 ppm (1 ppm=10^–6)的NO2气体的检测,对50 ppm的NO2的响应能够达到1.19,传感器的重复性较好,恢复率能够保持在76%以上,传感器的灵敏度是0.00281 ppm^-1,对浓度为5 ppm的NO2气体的响应时间是990 s,恢复时间是1566 s.此外,传感器在0°-45°的弯曲角度下仍表现出优异的电学特性与气体传感性能,所制备的器件具有相对稳定的导电性和较好的弯曲耐受性.     

Direct-write pulsed laser processed silver nanowire networks for transparent conducting electrodes

Metal nanowire networks are promising alternatives for transparent conducting layers in flexible electronics. However, the inverse relationship between transparency and conductivity limits their viability in many critical applications. In this work, we demonstrate a direct-write refining technique in which a solution-processed nanowire network, deposited by spin coating, is exposed to monochromatic UV pulsed laser processing near a plasmonic resonance. Our results exhibit a 75?% reduction in surface resistance along with marginal improvements in optical transparency. The local nature of the laser technique enables direct-write or large area processing on a variety of substrates including flexible, and organic materials.     

基于石墨烯/石墨烯卷轴复合薄膜高灵敏度柔性压力传感器

一维导电材料例如纳米线，大量应用于柔性压力传感器中. 但是一维材料和基底之间接触时相互作用力较弱，使得传感器灵敏度、响应时间、和循环寿命等性能指标有待进一步提高. 针对这些问题，设计了石墨烯/石墨烯卷轴多分子层复合薄膜作为传感器导电层. 石墨烯卷轴具有一维结构，而石墨烯的二维结构可以牢固地固定卷轴，以确保高导电性复合薄膜与基底之间的粘附性，同时整体结构的导电通道得到了增加. 由于一维和二维结构的协同效应，实现了应变灵敏度系数3.5 kPa^-1、 响应时间小于50 ms、能够稳定工作1000次以上的压阻传感器.     

Where science fiction meets reality? With oxide semiconductors!

Transparent electronics is today one of the most advanced topics for a wide range of device applications, where the key components are wide band gap semiconductors, where oxides of different origin play an important role, not only as passive components but also as active components similar to what we observe in conventional semiconductors. As passive components they include the use of these materials as dielectrics for a wide range of electronic devices and also as transparent electrical conductors for use in several optoelectronic applications, such as liquid crystal displays, organic light emitting diodes, solar cells, optical sensors etc. As active materials, they exploit the use of truly electronic semiconductors where the main emphasis is being put on transparent thin film transistors, light emitting diodes, lasers, ultraviolet sensors and integrated circuits among others.

     

Fabrication of substrate-free double-side emitting flexible device based on silver nanowire-polymer composite electrode

Flexible light emitting diodes are a promising component for future electronic devices, but require a simple structure and fast fabrication method. Organic light emitting diodes are a viable option as they are lightweight, thin, and flexible. However, they currently have costly fabrication procedures, complicated structures, and are sensitive to water and oxygen, which hinder widespread application. Here, we present a novel approach to fabricate flexible light emitting devices by employing Ag nanowire/polymer composite electrodes and ZnS phosphor particles. The composite electrode was fabricated using inverted layer processing, and used as both a bottom electrode and a dielectric layer. The high mechanical stability of the composite allowed the device to be free standing and mechanically flexible, eliminating the need for any additional support. Using Ag nanowires in both the top and bottom electrodes made a double-sided light emitting device that could be applied to wearable lightings or flexible digital signages.