Fabrication and Characterization of Benzocyclobutene Optical Waveguides by UV Pulsed-Laser Illumination

Buried-type benzocyclobutene (BCB) optical waveguides fabricated by UV pulsed-laser illumination are proposed and comprehensively characterized in this paper. The fabrication process is greatly simplified as compared to conventional dry-etched ridge-type BCB waveguides. The measured propagation loss at 1548 nm is as low as 0.6 dB/cm due to the buried waveguide structure. And the produced refractive index change is dependent upon the number of laser shots such that single-mode waveguides with different mode sizes can be tailored for efficient coupling. Furthermore, rigorous analyses of surface damage threshold, rms roughness, and chemical characteristics under different illumination conditions are presented to illustrate the design considerations and the chemical mechanism of the UV-induced BCB waveguides     

Kasami Code-Shift-Keying Modulation for Ultra-Wideband Communication Systems

Ultra-wideband (UWB) communication systems are generally applied to short-range wireless communications. In order to achieve higher rates or to support multiple access capabilities, direct sequence spread spectrum (DSSS) techniques have been introduced to UWB systems, and multiple pulses corresponding to a certain pseudo-noise (PN) code are transmitted to represent a symbol. In addition, the concept of M-ary code shift keying (M-CSK) was introduced into DSSS systems to achieve higher rates. In this work, we propose an M-CSK modulation technique based on the large set of Kasami sequences since it possesses good code properties, including a large code set size and low cross correlations. The modulation and demodulation schemes are developed, and the system performance in additive white Gaussian noise (AWGN) and UWB channels exposed to multiple user interference is investigated thoroughly. It was found that the Kasami M-CSK modulation is superior to other M-CSK modulation schemes in the bandwidth efficiency, and therefore a higher data rate can be achieved. Furthermore, based on our proposed demodulation scheme, the hardware complexity of receivers can be greatly reduced to O(M^1/3), and the implementation of receivers for a very large M becomes feasible.     

Morphological Stabilization by Supramolecular Perfluorophenyl‐C60 Interactions Leading to Efficient and Thermally Stable Organic Photovoltaics

A new PC₆₁BM‐based fullerene, [6,6]‐phenyl‐C₆₁ butyric acid pentafluorophenyl ester (PC₆₁BP^F) is designed and synthesized. This new n‐type material can replace PC₆₁BM to form a P3HT:PC₆₁BP^F binary blend or serve as an additive to form a P3HT:PC₆₁BM:PC₆₁BP^F ternary blend. Supramolecular attraction between the pentafluorophenyl group of PC₆₁BP^F and the C₆₀ cores of PC₆₁BP^F/PC₆₁BM can effectively suppress the PC₆₁BP^F/PC₆₁BM materials from severe aggregation. By doping only 8.3 wt% PC₆₁BP^F, device PC₆₁BP^F651 exhibits a PCE of 3.88% and decreases slightly to 3.68% after heating for 25 h, preserving 95% of its original value. When PC₆₁BP with non‐fluorinated phenyl group is used to substitute PC₆₁BP^F, the stabilizing ability disappears completely. The efficiencies of PC₆₁BP651 and PC₆₁BP321 devices significantly decay to 0.44% and 0.11%, respectively, after 25 h isothermal heating. Most significantly, this strategy is demonstrated to be effective for a blend system incorporating a low band‐gap polymer. By adding only 10 wt% PC₆₁BP^F, the PDTBCDTB: PC₇₁BM‐based device exhibits thermally stable morphology and device characteristics. These findings demonstrate that smart utilization of supramolecular interactions is an effective and practical strategy to control morphological evolution.     

Improved Light Extraction Efficiency in AlGaInP Light-Emitting Diodes by Applying a Periodic Texture on the Surface

In this letter, AlGaInP-GaP-based light-emitting diodes (LEDs) were fabricated with an Si substrate and an SiO₂-ITO-Ag omni-directional reflector using a metal-to-metal bonding technique. To enhance light extraction efficiency, a periodic texture was applied to the (Al_0.5Ga_0.5)_0.5In_0.5P surface layer of AlGaInP-Si LEDs by photolithography and a wet etching process. The exterior of the etched texture consists of a series of bowl-shaped recesses. With a 350-mA current injection, the typical output power of the AlGaInP-Si LEDs with and without the textured surface (LED-I and LED-II, respectively) were measured at approximately 118 and 81 mW, respectively, when the LED chips were bonded on the TO 46 without resin encapsulation. The enhancement of output power in LED-I can be attributed to a multitude of bowl-shaped notches on the surface, which resulted in a reduction of the reabsorption probability of the photons due to the fact that the photon path length in LED-I is shorter than in LED-II before the photons escape into the free space.     

Solution‐Processed High‐Performance Tetrathienothiophene‐Based Small Molecular Blends for Ambipolar Charge Transport

Four soluble dialkylated tetrathienoacene ( TTAR) ‐based small molecular semiconductors featuring the combination of a TTAR central core, π‐conjugated spacers comprising bithiophene ( bT ) or thiophene ( T ), and with/without cyanoacrylate ( CA ) end‐capping moieties are synthesized and characterized. The molecule DbT‐TTAR exhibits a promising hole mobility up to 0.36 cm² V^?1 s^?1 due to the enhanced crystallinity of the microribbon‐like films. Binary blends of the p‐type DbT‐TTAR and the n‐type dicyanomethylene substituted dithienothiophene‐quinoid ( DTTQ‐11 ) are investigated in terms of film morphology, microstructure, and organic field‐effect transistor (OFET) performance. The data indicate that as the DbT‐TTAR content in the blend film increases, the charge transport characteristics vary from unipolar (electron‐only) to ambipolar and then back to unipolar (hole‐only). With a 1:1 weight ratio of DbT‐TTAR DTTQ‐11 in the blend, well‐defined pathways for both charge carriers are achieved and resulted in ambipolar transport with high hole and electron mobilities of 0.83 and 0.37 cm² V^?1 s^?1, respectively. This study provides a viable way for tuning microstructure and charge carrier transport in small molecules and their blends to achieve high‐performance solution‐processable OFETs.     

Assembly of Nanoparticle Patterns with Single‐Particle Resolution Using DNA‐Mediated Charge Trapping Technique: Method and Applications

We report a unique approach for producing one‐dimensional gold‐nanoparticle patterns with single‐particle resolution in which the linewidth is only limited by the particle size. In this approach, a focused electron beam was first utilized to generate a positive charge layer on a SiO₂ surface. Biotinated DNA molecules attracted by these positive charges were subsequently used to grasp Au‐nanoparticles revealing the e‐beam exposure patterns. Due to repulsive force between Au colloidal particles, the particles in the single‐line patterns were orderly separated. We further show that the single‐line patterns hold potential in nano‐photonics and nano‐electronics. For the latter, we demonstrate that the line patterns can serve as a template for conductive nanowires of high or low resistance. While low resistance wires showed linear current–voltage characteristics with an extremely high maximum allowed current density, the high resistance wires exhibited charging effect with clear Coulomb oscillation behavior at low temperatures. This demonstrates that the technique is capable of producing interconnects as well as single‐electron‐transistors, and opens up possibilities for fabrication of integrated circuits.     

Fabrication of antireflection structures on TCO film for reflective liquid crystal display

The cholesteric liquid crystals display (ChLCD) is one kind of reflective liquid crystal display, the antireflective layer on its transparent conduction oxides (TCO) film is needed for good contrast and color performance. In this study, the finite difference time domain (FDTD) simulation and nanoimprinting fabrication of AR structures on the TCO film are developed. Finally, the reflectance of AR structures on TCO film is just half of the original film, and this result is useful for the reflective ChLCD product commercialized in the future.     

A new authenticated group key agreement in a mobile environment

A group key agreement protocol enables a group of communicating parties over an untrusted, open network to come up with a common secret key. It is designed to achieve secure group communication, which is an important research issue for mobile communication. In 2007, Tseng proposed a new group key agreement protocol to achieve secure group communication for a mobile environment. Its security is based on the decisional Diffie–Hellman assumption. It remedies the security weakness of the protocol of Nam et al. in which participants cannot confirm that their contributions were actually involved in the group key. Unfortunately, Tseng’s protocol is a nonauthenticated protocol that cannot ensure the validity of the transmitted messages. In this paper, the authors shall propose a new authenticated group key agreement to remedy it. It is based on bilinear pairings. We shall prove the security of the proposed protocol under the bilinear computational Diffie–Hellman assumption. It is also proven to a contributory group key agreement protocol.     

Toward Cloud-Based Parking Facility Management System： A Preliminary Study

An e-tag used on the freeway is a kind of passive sensors composed of sensors and radio-frequency identification (RFID) tags. The principle of the electronic toll collection system is that the sensor emits radio waves touching the e-tag within a certain range, the e-tag will respond to the radio waves by induction, and the sensor will read and write information of the vehicles. Although the RFID technology is popularly used in campus management systems, there is no e-tag technology application used in a campus parking system. In this paper, we use the e-tag technology on a campus parking management system based on the cloud-based construction. By this, it helps to achieve automated and standardized management of the campus parking system, enhance management efficiency, reduce the residence time of the vehicles at the entrances and exits, and improve the efficiency of vehicles parked at the same time.