Plasmonic-resonant bowtie antenna for carbon nanotube photodetectors

The design of bowtie antennas for carbon nanotube (CNT) photodetectors has been investigated. CNT photodetectors have shown outstanding performance by using CNT as sensing element. However, detection wavelength is much larger than the diameter of the CNT, resulting in small fill factor. Bowtie antenna can confine light into a subwavelength volume based on plasmonic resonance, thus integrating a bowtie antenna to CNT photodetectors can highly improve photoresponse of the detectors. The electric field enhancement of bowtie antennas was calculated using the device geometry by considering fabrication difficulties and photodetector structure. It is shown that the electric field intensity enhancement increased exponentially with distance reduction between the CNT photodetector to the antenna. A redshift of the peak resonance wavelength is predicted due to the increase of tip angles of the bowtie antennas. Experimental results showed that photocurrent enhancement agreed well with theoretical calculations. Bowtie antennas may find wide applications in nanoscale photonic sensors. Copyright © 2012 Hongzhi Chen et al.Link_to_subscribed_fulltex

Recent Progress in the Preparation Technologies for Micro Metal Coils

The recent development of micro-fabrication technologies has provided new methods for researchers to design and fabricate micro metal coils, which will allow the coils to be smaller, lighter, and have higher performance than traditional coils. As functional components of electromagnetic equipment, micro metal coils are widely used in micro-transformers, solenoid valves, relays, electromagnetic energy collection systems, and flexible wearable devices. Due to the high integration of components and the requirements of miniaturization, the preparation of micro metal coils has received increasing levels of attention. This paper discusses the typical structural types of micro metal coils, which are mainly divided into planar coils and three-dimensional coils, and the characteristics of the different structures of coils. The specific preparation materials are also summarized, which provides a reference for the preparation process of micro metal coils, including the macro-fabrication method, MEMS (Micro-Electro-Mechanical System) processing technology, the printing process, and other manufacturing technologies. Finally, perspectives on the remaining challenges and open opportunities are provided to help with future research, the development of the Internet of Things (IoTs), and engineering applications

Nanopteron solution of the Korteweg-de Vries equation

The nanopteron, which is a permanent but weakly nonlocal soliton, has been an interesting topic in numerical studies for many decades. However, the analytical solution of such a special soliton is rarely considered. In this letter, we study the explicit nanopteron solution of the Korteweg-de Vries (KdV) equation. Starting from the soliton-cnoidal wave solution of the KdV equation, the nanopteron structure is shown to exist. It is found that for the suitable choice of the wave parameters, the soliton core of the soliton-cnoidal wave trends to be a classical soliton of the KdV equation and the surrounded cnoidal periodic wave appears as small amplitude sinusoidal variations on both sides of the main core. Some interesting features of the wave propagation are revealed. In addition to the elastic interaction, it is surprising that the phase shift of the cnoidal periodic wave after the interaction with the soliton core is always half its wavelength, and this conclusion is universal to soliton-cnoidal wave interactions

Diterpenoid Tanshinones and Phenolic Acids from Cultured Hairy Roots of Salvia miltiorrhiza Bunge and Their Antimicrobial Activities

Four diterpenoid tanshinones and three phenolic acids were isolated from the crude ethanol extract of the cultured hairy roots of Salvia miltiorrhiza Bunge by bioassay-guided fractionation. By means of physicochemical and spectrometric analysis, they were identified as tanshinone ΙΙA (1), tanshinone Ι (2), cryptotanshinone (3), dihydrotanshinone Ι (4), rosmarinic acid (5), caffeic acid (6), and danshensu (7). These compounds were evaluated to show a broad antimicrobial spectrum of activity on test microorganisms including eight bacterial and one fungal species. Among the four tanshinones, cryptotanshinone (3) and dihydrotanshinone Ι (4) exhibited stronger antimicrobial activity than tanshinone ΙΙA (1) and tanshinone Ι (2). The results indicated that the major portion of the antimicrobial activity was due to the presence of tanshinones and phenolic acids in S. miltiorrhiza hairy roots, which could be used as the materials for producing antimicrobial agents for use in agricultural practice in the future

Recent Progress in the Preparation Technologies for Micro Metal Coils

The recent development of micro-fabrication technologies has provided new methods for researchers to design and fabricate micro metal coils, which will allow the coils to be smaller, lighter, and have higher performance than traditional coils. As functional components of electromagnetic equipment, micro metal coils are widely used in micro-transformers, solenoid valves, relays, electromagnetic energy collection systems, and flexible wearable devices. Due to the high integration of components and the requirements of miniaturization, the preparation of micro metal coils has received increasing levels of attention. This paper discusses the typical structural types of micro metal coils, which are mainly divided into planar coils and three-dimensional coils, and the characteristics of the different structures of coils. The specific preparation materials are also summarized, which provides a reference for the preparation process of micro metal coils, including the macro-fabrication method, MEMS (Micro-Electro-Mechanical System) processing technology, the printing process, and other manufacturing technologies. Finally, perspectives on the remaining challenges and open opportunities are provided to help with future research, the development of the Internet of Things (IoTs), and engineering applications

Photonic crystal with a HfO 2 defect to improve performance of carbon nanotube based photodetectors

It has been demonstrated that carbon nanotube (CNT) acts as a promising functional material to effectively detect infrared signals due to the unique properties arose from its novel geometry. However, the performance of CNT based photodetectors is limited by low fill factor owing to their small photon absorption area. In order to address this problem, a photonic cavity, using photonic crystal with a point defect made of HfO 2, was fabricated on top of the CNT photodetectors in order to enhance the local photon density. By drilling holes, with size of the scale of light wavelengths, in the parylene slab, the periodic change of reflective index forms photonic crystal. Replacing one of the holes with HfO 2 as a point defect, most of the light will be trapped in this defect. A photonic crystal was designed to concentrate the infrared light with 1064 nm wavelength, and 91 % of the light can be confined into the HfO 2 defect. The fabrication process of this photonic crystal is introduced, and photocurrents of a CNT based photodetector are compared under the circumstance of without and with photonic crystal. It is found that the photocurrent is enhanced about 4 times after the fabrication of photonic cavity. © 2011 IEEE.Link_to_subscribed_fulltex

Photonic crystal wave guide for non-cryogenic cooled carbon nanotube based middle wave infrared sensors

We report high sensitivity carbon nanotube (CNT) based middle wave infrared (MWIR) sensors with a two-dimensional photonic crystal waveguide. MWIR sensors are of great importance in a variety of current military applications including ballistic missile defense, surveillance and target detection. Unlike other existing MWIR sensing materials, CNTs exhibit low noise level and can be used as new nano sensing materials for MWIR detection where cryogenic cooling is not required. However, the quantum efficiency of the CNT based infrared sensor is still limited by the small sensing area and low incoming electric field. Here, a photonic nanostructure is used as a resonant cavity for boosting the electric field intensity at the position of the CNT sensing element. A two-dimensional photonic crystal with periodic holes in a polymer thin film is fabricated and a resonant cavity is formed by removing holes from the array of the photonic crystal. Based on the design of the photonic crystal topologies, we theoretically study the electric field distribution to predict the resonant behavior of the structure. Numerical simulations reveal the field is enhanced and almost fully confined to the defect region of the photonic crystal. To verify the electric field enhancement effect, experiments are also performed to measure the photocurrent response of the sensor with and without the photonic crystal resonant cavity. Experimental results show that the photocurrent increases ~3 times after adding the photonic crystal resonant cavity. © 2010 Copyright SPIE - The International Society for Optical Engineering.Link_to_subscribed_fulltex