Phase-separated polydimethylsiloxane as a dielectric surface treatment layer for organic field effect transistors

We suggest a novel method for treating the surfaces of dielectric layers in organic field effect transistors (OFETs). In this method, a blend of poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) and dimethylsiloxane (DMS) with a curing agent is spin coated onto the surface of a dielectric substrate, silicon oxide (SiO₂), and then thermally cured. X-ray photoelectron spectroscopy, contact angle measurements, and morphology analysis were used to show that the hydrophilic DMS layer is preferentially adsorbed on the SiO₂ substrate during the spin coating process. After thermal curing, the bottom DMS layer becomes a hydrophobic PDMS layer. This bottom PDMS layer becomes thinner during curing due to the upward motion of the hydrophobic PDMS molecules. The FET mobility of the cured system was 10^?2 cm²/Vs, which is similar to that of polymeric semiconductors on octadecyltrichlorosilane treated SiO₂ dielectric layers. We also discuss the possibility of using this blend method to increase the air-stability of polymeric semiconductors.     

Determination of the interface energy level alignment of a doped organic hetero-junction using capacitance–voltage measurements

A simple method based on capacitance–voltage (C–V) measurements is reported to determine the interface energy level alignment at the junction of 15 mol% Cs₂CO₃ doped 4,7-diphenyl-1,10-phenanthroline (BPhen) and 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN) fabricated under high vacuum. The junction properties, such as the depletion layer thickness, built-in potentials and vacuum level shift were calculated with simple Mott–Schottky and Poisson’s equations with the boundary condition of a continuous electric flux density using the information from the C–V data. The interface energy level alignment determined by this method is well matched with the one determined using the in situ ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS) experiments performed under ultra-high vacuum. This method can be applied to other semiconductor junctions such as the organic p–n homojunctions and heterojunctions with known energy levels, as long as the metal/semiconductor contact is Ohmic without referring to the photoemission spectroscopies. Moreover, the energy level alignment determined by the C–V measurement gives a more realistic result since the films for the measurements are formed under high vacuum which is a normal device fabrication environment rather than under ultra high vacuum.     

Organic Phenolic Configurationally Locked Polyene Single Crystals for Electro‐optic and Terahertz Wave Applications

We investigate a configurationally locked polyene (CLP) crystal 2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor. The OH1 crystals with orthorhombic space group Pna2₁ (point group mm2) exhibit large second‐order nonlinear optical figures of merit, high thermal stability and very favorable crystal growth characteristics. Higher solubility in methanol and a larger temperature difference between the melting temperature and the decomposition temperature of OH1 compared to analogous CLP crystals, are of advantage for solution and melt crystal growth, respectively. Acentric bulk OH1 crystals of large sizes with side lengths of up to 1 cm with excellent optical quality have been successfully grown from methanol solution. The microscopic and macroscopic nonlinearities of the OH1 crystals are investigated theoretically and experimentally. The OH1 crystals exhibit a large macroscopic nonlinearity with four times larger powder second harmonic generation efficiency than that of analogous CLP crystals containing dimethylamino electron donor. A very high potential of OH1 crystals for broadband THz wave emitters in the full frequency range of 0.1–3 THz by optical rectification of 160 fs pulses has been demonstrated.     

Enhanced carrier confinement in AlInGaN-InGaN quantum wells in near ultraviolet light-emitting diodes

To increase carrier confinement, the GaN barrier layer was substituted with an AlInGaN quaternary barrier layer which was lattice-matched to GaN in the GaN-InGaN multiple quantum wells (MQWs). Photoluminescence (PL) and high-resolution X-ray diffraction measurements showed that the AlInGaN barrier layer has a higher bandgap energy than the originally used GaN barrier layer. The PL intensity of the five periods of AlInGaN-InGaN MQWs was increased by three times compared to that of InGaN-GaN MQWs. The electroluminescence (EL) emission peak of AlInGaN-InGaN MQWs ultraviolet light-emitting diode (UV LED) was blue-shifted, compared to a GaN-InGaN MQWs UV LED and the integrated EL intensity of the AlInGaN-InGaN MQWs UV LED increased linearly up to 100 mA. These results indicated that the AlInGaN-InGaN MQWs UV LED has a stronger carrier confinement than a GaN-InGaN MQWs UV LED due to the larger barrier height of the AlInGaN barrier layer compared to a GaN barrier layer.     

High‐Performance Micro‐Solid Oxide Fuel Cells Fabricated on Nanoporous Anodic Aluminum Oxide Templates

Micro‐solid oxide fuel cells (μ‐SOFCs) are fabricated on nanoporous anodic aluminum oxide (AAO) templates with a cell structure composed of a 600‐nm‐thick AAO free‐standing membrane embedded on a Si substrate, sputter‐deposited Pt electrodes (cathode and anode) and an yttria‐stabilized zirconia (YSZ) electrolyte deposited by pulsed laser deposition (PLD). Initially, the open circuit voltages (OCVs) of the AAO‐supported μ‐SOFCs are in the range of 0.05 V to 0.78 V, which is much lower than the ideal value, depending on the average pore size of the AAO template and the thickness of the YSZ electrolyte. Transmission electron microscopy (TEM) analysis reveals the formation of pinholes in the electrolyte layer that originate from the porous nature of the underlying AAO membrane. In order to clog these pinholes, a 20‐nm thick Al₂O₃ layer is deposited by atomic layer deposition (ALD) on top of the 300‐nm thick YSZ layer and another 600‐nm thick YSZ layer is deposited after removing the top intermittent Al₂O₃ layer. Fuel cell devices fabricated in this way manifest OCVs of 1.02 V, and a maximum power density of 350 mW cm^?2 at 500 °C.     

Application of Plasma-Doping (PLAD) Technique to Reduce Dark Current of CMOS Image Sensors

Plasma doping (PLAD) was applied to reduce the dark current of CMOS image sensor (CIS), for the first time. PLAD was employed around shallow trench isolation (STI) to screen the defective sidewalls and edges of STI from the depletion region of photodiode. This technique can provide not only shallow but also conformal doping around the STI, making it a suitable doping technique for pinning purposes for CISs with sub-2-mum pixel pitch. The measured results show that temporal noise and dark signal deviation as well as dark level decrease     

Bidirectional SCM Transmission Using a Noise-Suppressed Fabry–Pérot Laser Diode and a Reflective Semiconductor Optical Amplifier in a WDM/SCM-PON Link

We have proposed and experimentally demonstrated a bidirectional hybrid wavelength-division-multiplexed/subcarrier-multiplexed (SCM)-passive optical network based on a noise-suppressed Fabry-Peacuterot laser diode (FP-LD) and a reflective semiconductor optical amplifier (RSOA). For downlink data transmission, an FP-LD with multiple wavelength characteristics was used, and the mode partition noise of the FP-LD was reduced using a gain-saturated SOA with high-pass filter characteristics. For uplink data transmission, the downlink optical source was reused and remodulated by an SCM method, using an RSOA. A bidirectional SCM link with radio frequencies (RFs) of 2.4 GHz in the downlink and 1.0 GHz in the uplink was implemented. To confirm the validity of the proposed configuration, a 16-quadrature amplitude modulation transmission experiment was performed on a 10-km bidirectional optical access link. The transmission performance was investigated by means of the error vector magnitude and RF spectrum     

Strong Diffie-Hellman-DSA Key Exchange

To provide authentication to the Diffie-Hellman key exchange, a few integrated key exchange schemes which provide authentication using the DSA signature have been proposed in the literature. In this letter we point out that all of the previous Diffie-Hellman-DSA schemes do not provide security against session state reveal attacks. We also suggest a strong Diffie-Hellman-DSA scheme providing security against session state reveal attacks as well as forward secrecy and key independence     

Chiroptical‐Conjugated Polymer/Chiral Small Molecule Hybrid Thin Films for Circularly Polarized Light‐Detecting Heterojunction Devices

Herein, a simple and facile strategy is described to obtain chiroptically active semiconductor thin films by blending of poly(3‐alkylthiophene)s, which are conventional achiral polymer semiconductors, and 1,1′‐binaphthyl (BN), a versatile chiral molecule. As expected, the intermolecular interaction between the two materials is important to extend the chirality of the binaphthyl molecules to the hybrid films. The controlled phase separation and crystallization of poly[3‐(6‐carboxyhexyl)thiophene‐2,5‐diyl] (P3CT) and binaphthyl hybrid films result in unique heterojunction bilayer thin‐film structures that consisted of BN microcrystals at the top and a P3CT/BN mixed layer at the bottom. Such heterojunction bilayer films exhibit significantly amplified chiroptical response with weak broadened tails, which is due to the enhanced crystallization of the chiral BN molecules and formation of heteroaggregates in the hybrid films. Based on the characterization of crystalline structure and photoluminescence analysis, it is found that new electronic energy states are formed in the conduction band region of P3CTs in the P3CT/BN heteroaggregates, which contribute to chirality transfer from BN to the hybrid films. As a proof of concept, a photodiode capable of distinguishably sensing the left‐ and right‐handed circularly polarized light is successfully fabricated by using the hybrid films with the heterojunction bilayer structure.     

Power controlled H-ARQ in cdma2000 1/spl times/EV-DV

The newly applied H-ARQ technique in the reverse link of a cdma2000/spl reg/ 1/spl times/EV-DV system is shown to be similar in nature to the fast power control technique such that the two techniques both reduce interference to other users. In order to balance the H-ARQ gain and packet delay time, four modes of operation are defined: normal, reduction, boost, and boost reduction. The four modes are defined according to the way the channel gain is set for the H-ARQ operation. Simulation results show that the reduction modes have better performance in terms of both PER and packet delay time. It is also shown that the boost modes have lower PER and packet delay time than the non-boost modes, but at the expense of more energy.