Tunable 3D Nanoresonators for Gas‐Sensing Applications

The detection of gas species with high sensitivity is a significant task for fundamental sciences as well as for industrial applications. Similarly, the ongoing trend for device miniaturization brings new challenges for advanced fabrication including on‐demand functionality tuning. Following this motivation, here the additive, direct‐write fabrication of freestanding 3D nanoarchitectures is introduced, which can be brought into mechanical resonance via electric AC fields. Specifically, this study focuses on the 3D nanostructure synthesis, the subsequent determination of Young's modulus, and demonstrates a postgrowth procedure, which can precisely tune the material modulus. As‐fabricated resonators reveal a Young's modulus of 9–13 GPa, which can be increased by a factor greater than 5. Next, the electric readout of the resonance behavior is demonstrated via electric current measurement as an essential element for the resonance sensor applications. Finally, the implications of gas‐physisorption and gas‐chemisorption on the resonance frequencies are studied, representing a proof‐of‐principle for sensing applications by the here presented approach.     

Highly Improved Sb2S3 Sensitized‐Inorganic–Organic Heterojunction Solar Cells and Quantification of Traps by Deep‐Level Transient Spectroscopy

The light‐harvesting Sb₂S₃ surface on mesoporous‐TiO₂ in inorganic–organic heterojunction solar cells is sulfurized with thioacetamide (TA). The photovoltaic performances are compared before and after TA treatment, and the state of the Sb₂S₃ is investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, and deep‐level transient spectroscopy (DLTS). Although there are no differences in crystallinity and composition, the TA‐treated solar cells exhibit significantly enhanced performance compared to pristine Sb₂S₃‐sensitized solar cells. From DLTS analysis, the performance enhancement is mainly attributed to the extinction of trap sites, which are present at a density of (2–5) × 10¹⁴ cm^?3 in Sb₂S₃, by TA treatment. Through such a simple treatment, the cell records an overall power conversion efficiency (PCE) of 7.5% through a metal mask under simulated illumination (AM 1.5G, 100 mW cm^–2) with a very high open circuit voltage of 711.0 mV. This PCE is, thus far, the highest reported for fully solid‐state chalcogenide‐sensitized solar cells.     

Improving Radio Frequency Transmission Properties of Graphene via Carrier Concentration Control toward High Frequency Transmission Line Applications

Graphene has been gradually studied as a high‐frequency transmission line material owing to high carrier mobility with frequency independence up to a few THz. However, the graphene‐based transmission lines have poor conductivity due to their low carrier concentration. Here, it is observed that the radio frequency (RF) transmission performance could be severely hampered by the defect‐induced scattering, even though the carrier concentration is increased. As a possible solution, the deposition of the amorphous carbon on the graphene is studied in the high‐frequency region up to 110 GHz. The DC resistance is reduced by as much as 60%, and the RF transmission property is also enhanced by 3 dB. Also, the amorphous carbon covered graphene shows stable performance under a harsh environment. These results prove that the carrier concentration control is an effective and a facile method to improve the transmission performance of graphene. It opens up the possibilities of using graphene as interconnects in the ultrahigh‐frequency region.     

Design of Scannable Non‐uniform Planar Array Structure for Maximum Side‐Lobe Reduction

In this letter, we propose a novel design scheme for an optimal non‐uniform planar array geometry in view of maximum side‐lobe reduction. This is implemented by a thinned array using a genetic algorithm. We show that the proposed method can maintain a low side‐lobe level without pattern distortion during beam steering.     

An Analog Front‐End Circuit for ISO/IEC 14443‐Compatible RFID Interrogators

An analog front‐end circuit for ISO/IEC 14443‐compatible radio frequency identification (RFID) interrogators was designed and fabricated by using a 0.25 µm double‐poly CMOS process. The fabricated chip was operated using a 3.3 Volt single‐voltage supply. The results of this work could be provided as reusable IPs in the form of hard or firm IPs for designing single‐chip ISO/IEC 14443‐compatible RFID interrogators.     

Temperature Distribution of a Low Temperature Heat Pipe with Multiple Heaters for Electronic Cooling

A numerical study has been performed to predict the characteristics on the transient operation of the heat pipe with multiple heaters for electronic cooling. The model of the heat pipe was composed of the evaporator section with four heaters, insulated transport section, and the condensor section with a conductor which is cooled with uniform heat flux condition to surrounding. The governing equations and the boundary conditions were solved by the generalized PHOENICS computational code employing the finite volume method. Two test cases are investigated in present study; Case 1 indicates that the 1st and 2nd heaters among four heating sources are heated off, while the 3rd and 4th heaters are heated on. Case 2 is the inverse situation switched from heating location of Case 1. The results show that the transient time to reach the steady state is shorter for Case 1 than for Case 2. Especially, the temperature difference of the heater during switching operation is relatively small compared to the maximum all- owable operating temperature difference in electronic system. Hence, it is predicted that the heat pipe in present study operates with thermally good reliability even for switching the heaters.     

Still image coding based on vector quantization and fractalapproximation

In this paper, we propose a coding algorithm for still images using vector quantization (VQ) and fractal approximation, in which low-frequency components of an input image are approximated by VQ, and its residual is coded by fractal mapping. The conventional fractal coding algorithms indirectly used the gray patterns of an original image with contraction mapping, whereas the proposed fractal coding method employs an approximated and then decimated image as a domain pool and uses its gray patterns. Thus, the proposed algorithm utilizes fractal approximation without the constraint of contraction mapping. For approximation of an original image, we employ the discrete cosine transform (DCT) rather than conventional polynomial-based transforms. In addition, for variable blocksize segmentation, we use the fractal dimension of a block that represents the roughness of the gray surface of a region. Computer simulations with several test images show that the proposed method shows better performance than the conventional fractal coding methods for encoding still pictures.     

Enhancement of the photoelectric performance of dye-sensitized solar cells by using a CaCO3-coated TiO2 nanoparticle film as an electrode

Core-shell-type nanoparticles with TiO₂ cores and CaCO₃ shells were applied as the electrode of dye-sensitized solar cells. The performance of the cell was significantly improved (as high as 26.7%) compared to the case when un-coated TiO₂ particle film was used as electrode. The improved energy conversion efficiency has been ascribed to (i) enhanced dye adsorption due to the high isoelectric point of the overlayer, and (ii) the prevention of the back electron transfer by the insulating nature of the overlayer.