Ultrastretchable Conductor Fabricated on Skin‐Like Hydrogel–Elastomer Hybrid Substrates for Skin Electronics

Printing technology can be used for manufacturing stretchable electrodes, which represent essential parts of wearable devices requiring relatively high degrees of stretchability and conductivity. In this work, a strategy for fabricating printable and highly stretchable conductors are proposed by transferring printed Ag ink onto stretchable substrates comprising Ecoflex elastomer and tough hydrogel layers using a water‐soluble tape. The elastic modulus of the produced hybrid film is close to that of the hydrogel layer, since the thickness of Ecoflex elastomer film coated on hydrogel is very thin (30 µm). Moreover, the fabricated conductor on hybrid film is stretched up to 1780% strain. The described transfer method is simpler than other techniques utilizing elastomer stamps or sacrificial layers and enables application of printable electronics to the substrates with low elastic moduli (such as hydrogels). The integration of printed electronics with skin‐like low‐modulus substrates can be applied to make wearable devices more comfortable for human skin.     

Ruthenium Nanoparticles on Cobalt‐Doped 1T′ Phase MoS2 Nanosheets for Overall Water Splitting

2D MoS₂ nanostructures have recently attracted considerable attention because of their outstanding electrocatalytic properties. The synthesis of unique Co–Ru–MoS₂ hybrid nanosheets with excellent catalytic activity toward overall water splitting in alkaline solution is reported. 1T′ phase MoS₂ nanosheets are doped homogeneously with Co atoms and decorated with Ru nanoparticles. The catalytic performance of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is characterized by low overpotentials of 52 and 308 mV at 10 mA cm^?2 and Tafel slopes of 55 and 50 mV decade^?1 in 1.0 m KOH, respectively. Analysis of X‐ray photoelectron and absorption spectra of the catalysts show that the MoS₂ well retained its metallic 1T′ phase, which guarantees good electrical conductivity during the reaction. The Gibbs free energy calculation for the reaction pathway in alkaline electrolyte confirms that the Ru nanoparticles on the Co‐doped MoS₂ greatly enhance the HER activity. Water adsorption and dissociation take place favorably on the Ru, and the doped Co further catalyzes HER by making the reaction intermediates more favorable. The high OER performance is attributed to the catalytically active RuO₂ nanoparticles that are produced via oxidation of Ru nanoparticles.     

Lensed fiber probes designed as an alternative to bulk probes in optical coherence tomography

We demonstrate a compact all-fiber sampling probe for an optical coherence tomography (OCT) system. By forming a focusing lens directly on the tip of an optical fiber, a compact sampling probe could be implemented. To simultaneously achieve a sufficiently long working distance and a good lateral resolution, we employed a large-mode area photonic crystal fiber (PCF) and a coreless silica fiber (CSF) of the same diameters. A working distance of up to 1270 microm, a 3 dB distance range of 2210 microm, and a transverse resolution of 14.2 microm were achieved with the implemented PCF lensed fiber; these values are comparable to those obtainable with a conventional objective lens having an NA of 0.25 (10 x). The performance of the OCT system equipped with the proposed PCF lensed fiber is presented by showing the OCT images of a rat finger as a biological sample and a pearl as an in-depth sample.     

16‐QAM‐Based Highly Spectral‐Efficient E‐band Communication System with Bit Rate up to 10 Gbps

This paper presents a novel 16‐quadrature‐amplitude‐modulation (QAM) E‐band communication system. The system can deliver 10 Gbps through eight channels with a bandwidth of 5 GHz (71‐76 GHz/81‐86 GHz). Each channel occupies 390 MHz and delivers 1.25 Gbps using a 16‐QAM. Thus, this system can achieve a bandwidth efficiency of 3.2 bit/s/Hz. To implement the system, a driver amplifier and an RF up‐/down‐conversion mixer are implemented using a 0.1 µm gallium arsenide pseudomorphic high‐electron‐mobility transistor (GaAs pHEMT) process. A single‐IF architecture is chosen for the RF receiver. In the digital modem, 24 square root raised cosine filters and four (255, 239) Reed‐Solomon forward error correction codecs are used in parallel. The modem can compensate for a carrier‐frequency offset of up to 50 ppm and a symbol rate offset of up to 1 ppm. Experiment results show that the system can achieve a bit error rate of 10^?5 at a signal‐to‐noise ratio of about 21.5 dB.     

Towards Efficient Integrated Perovskite/Organic Bulk Heterojunction Solar Cells: Interfacial Energetic Requirement to Reduce Charge Carrier Recombination Losses

Integrated perovskite/organic bulk heterojunction (BHJ) solar cells have the potential to enhance the efficiency of perovskite solar cells by a simple one‐step deposition of an organic BHJ blend photoactive layer on top of the perovskite absorber. It is found that inverted structure integrated solar cells show significantly increased short‐circuit current (J_sc) gained from the complementary absorption of the organic BHJ layer compared to the reference perovskite‐only devices. However, this increase in J_sc is not directly reflected as an increase in power conversion efficiency of the devices due to a loss of fill factor. Herein, the origin of this efficiency loss is investigated. It is found that a significant energetic barrier (≈250 meV) exists at the perovskite/organic BHJ interface. This interfacial barrier prevents efficient transport of photogenerated charge carriers (holes) from the BHJ layer to the perovskite layer, leading to charge accumulation at the perovskite/BHJ interface. Such accumulation is found to cause undesirable recombination of charge carriers, lowering surface photovoltage of the photoactive layers and device efficiency via fill factor loss. The results highlight a critical role of the interfacial energetics in such integrated cells and provide useful guidelines for photoactive materials (both perovskite and organic semiconductors) required for high‐performance devices.     

Forecasting demand for low earth orbit mobile satellite service in Korea

Forecasting a new service diffusion process is critical in designing marketing strategies and analyzing the costs and benefits for service providers. It is very difficult, however, in cases that data are not available. We suggest the combination of analogy and survey to forecast the demand for Low Earth Orbit (LEO) mobile satellite service in Korea. First, we analyze the diffusion of existing mobile phone service, which is similar to LEO service. The diffusion parameters for mobile phone service are then used in a model for LEO service. A survey was made on two hundred fifty‐five subscribers of existing mobile phone service in Korea. We estimate the potential market size of LEO service by applying the logit model to the survey data. Then, we forecast the annual demand for LEO service in Korea from 1998 to 2005. We also derive the price elasticity of market potential of LEO service. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optimization of lead- and cadmium-free front contact silver paste formulation to achieve high fill factors for industrial screen-printed Si solar cells

Screen-printed n⁺–p–p⁺ solar cells were fabricated on Cz single crystalline Si material, with a 45 Ω/sq emitter and PECVD SiNx antireflective coating with a thickness of 700 Å, using different Ag pastes and commercial leaded reference paste (CN33-462, Ferro Corp.). Ag and Al contacts were co-fired using a mass-production line equipped with mesh belt conveyer furnace systems (Centrotherm thermal solution GmbH & Co. KG). The average results for single crystalline Si solar cells (156 cm²) are: I_sc=5.043 A, V_oc=0.621 V, R_s=0.0087 Ω, R_sh=15.3 Ω, FF=0.773, and E_ff=16.45%. R_sh and fill factor values of fabricated cells were slightly higher when compared with the commercial leaded Ag paste, although cells were fabricated by metallizing the lead-free silver pastes. For the lead-free Ag paste used in this study, the line pattern continuity is retained with improved edge definition in sharp contrast to that of reference Ag paste. Average value of R_s was also equivalent approximately to that of the leaded Ag paste.