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.     

Symbiotic Dynamic Memory Balancing for Virtual Machines in Smart TV Systems

Smart TV is expected to bring cloud services based on virtualization technologies to the home environment with hardware and software support. Although most physical resources can be shared among virtual machines (VMs) using a time sharing approach, allocating the proper amount of memory to VMs is still challenging. In this paper, we propose a novel mechanism to dynamically balance the memory allocation among VMs in virtualized Smart TV systems. In contrast to previous studies, where a virtual machine monitor (VMM) is solely responsible for estimating the working set size, our mechanism is symbiotic. Each VM periodically reports its memory usage pattern to the VMM. The VMM then predicts the future memory demand of each VM and rebalances the memory allocation among the VMs when necessary. Experimental results show that our mechanism improves performance by up to 18.28 times and reduces expensive memory swapping by up to 99.73% with negligible overheads (0.05% on average).     

Impedance-matching arrangement for microwave transponder operating over plurality of bent installations of antenna

An impedance-matching arrangement is considered for an essentially flexible RFID transponder that can operate over a plurality of its bent installations. The novel structure matches the actual complex impedance of the transponder's application-specific integrated circuit to the input impedance of the antenna over different forms of mechanical deformation and thereby improves overall performances of the passive identification system.     

Low-noise amplifier design for ultrawideband radio

A new theoretical approach for designing a low-noise amplifier (LNA) for the ultra-wideband (UWB) radio is presented. Unlike narrow-band systems, the use of the noise figure (NF) performance metric becomes problematic in UWB systems because of the difficulty in defining the signal-to-noise ratio (SNR). By defining the SNR as the matched filter bound (MFB), the NF measures the degree of degradation caused by the LNA in the achievable receiver performance after the digital decoding process. The optimum noise matching network that minimizes the NF as defined above has been solved. When the narrow-band LNA assumption is made, the proposed optimum matching network simplifies to the published optimum narrow-band matching network, and the corresponding NF value also becomes equivalent. Since realizing the optimum matching network is in general difficult, an approach for designing a practical but suboptimum matching network is also presented.     

Enhanced Optical Properties and Stability of CsPbBr3 Nanocrystals Through Nickel Doping

To improve the quantum efficiency and stability of perovskite quantum dots, the structural and optical properties are optimized by varying the concentration of Ni doping in CsPbBr₃ perovskite nanocrystals (PNCs). As Ni doping is gradually added, a blue shift is observed at the photoluminescence (PL) spectra. Ni-doped PNCs exhibit stronger light emission, higher quantum efficiency, and longer lifetimes than undoped PNCs. The doped divalent element acts as a defect in the perovskite structure, reducing the recombination rate of electrons and holes. A stability test is used to assess the susceptibility of the perovskite to light and moisture. For ultra-violet light irradiation, the PL intensity of undoped PNCs decreases by 70%, whereas that of Ni-doped PNCs decreases by 18%. In the water addition experiment, the PL intensity of Ni-doped PNCs is three times that of undoped PNCs. For CsPbBr₃ and Ni:CsPbBr₃ PNCs, a light emitting diode is fabricated by spin-coating. The efficiency of Ni:CsPbBr₃ exceeds that of CsPbBr₃ PNCs, and the results significantly differ based on the ratio. A maximum luminance of 833 cd m^–2 is obtained at optimum efficiency (0.3 cd A^–1). Therefore, Ni-doped PNCs are expected to contribute to future performance improvements in display devices.     

Retina-Inspired Structurally Tunable Synaptic Perovskite Nanocones

Artificial photonic synapses with morphologically controlled photoreception, allowing for area-dependent tunable light reception as well as information storage and learning, have potential for application in emerging photo-interactive neuro-computing technologies. Herein, an artificially intelligent (AI) photonic synapse with area-density-tunable perovskite nano-cone arrays templated in a self-assembled block copolymer (BCP) is presented, which is based on a field effect transistor with a floating gate of photoreceptive perovskite crystal arrays preferentially synthesized in a micro-phase-segregated BCP film. These arrays are capable of electric charge (de)trapping and photo-excited charge generation, and they exhibit versatile synaptic functions of the nervous system, including paired-pulse facilitation and long-term potentiation, with excellent reliability. The area-density variable perovskite floating gate developed by off-centered spin coating process allows for emulating the human retina with a position-dependent spatial distribution of cones. 60 × 12 arrays of the developed synapse devices exhibit position-dependent dual functions of receptor and synapse. They are AI and exhibit a pattern recognition accuracy up to ≈90% when examined using the Modified National Institute of Standards and Technology handwritten digit pattern recognition test.     

Energy‐efficient power control for uplink spectrum‐sharing heterogeneous networks

This article considers energy‐efficient power control schemes for interference management in uplink spectrum‐sharing heterogeneous networks that maximize the energy efficiency of users, protect the macro base station, and support users with QoS consideration. In the first scenario, we define the objective function as the weighted sum of the energy efficiencies and develop an efficient global optimization algorithm with global linear and local quadratic rate of convergence to solve the considered problem. To ensure fairness among individual user equipments (UEs) in terms of energy efficiency, we consider the max‐min problem, where the objective is defined as the weighted minimum of the energy efficiencies, and a fractional programming theory and the dual decomposition method are jointly used to solve the problem and investigate an iterative algorithm. As by‐products, we further discuss the global energy efficiency problem and consider near‐optimal schemes. Numerical examples are provided to demonstrate significant improvements of the proposed algorithms over existing interference management schemes.     

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.