Control of the Morphology and Structural Development of Solution‐Processed Functionalized Acenes for High‐Performance Organic Transistors

Solution‐processable functionalized acenes have received special attention as promising organic semiconductors in recent years because of their superior intermolecular interactions and solution‐processability, and provide useful benchmarks for organic field‐effect transistors (OFETs). Charge‐carrier transport in organic semiconductor thin films is governed by their morphologies and molecular orientation, so self‐assembly of these functionalized acenes during solution processing is an important challenge. This article discusses the charge‐carrier transport characteristics of solution‐processed functionalized acene transistors and, in particular, focuses on the fine control of the films' morphologies and structural evolution during film‐deposition processes such as inkjet printing and post‐deposition annealing. We discuss strategies for controlling morphologies and crystalline microstructure of soluble acenes with a view to fabricating high‐performance OFETs.     

Simple and effective neural coreference resolution for Korean language

We propose an end-to-end neural coreference resolution for the Korean language that uses an attention mechanism to point to the same entity. Because Korean is a head-final language, we focused on a method that uses a pointer network based on the head. The key idea is to consider all nouns in the document as candidates based on the head-final characteristics of the Korean language and learn distributions over the referenced entity positions for each noun. Given the recent success of applications using bidirectional encoder representation from transformer (BERT) in natural language-processing tasks, we employed BERT in the proposed model to create word representations based on contextual information. The experimental results indicated that the proposed model achieved state-of-the-art performance in Korean language coreference resolution.     

Facile Fabrication of SWCNT/SnO2 Nanowire Heterojunction Devices on Flexible Polyimide Substrate

We report on the fabrication and electronic properties of single‐walled carbon nanotube (SWCNT)/tin oxide nanowire (SnO₂ NW) heterojunction device arrays on flexible polyimide (PI) substrates. Hetero‐NW junctions consisting of crossed SnO₂ NWs and SWCNTs were fabricated by sliding transfer of SnO₂ NWs onto the SWCNT channels on PI substrate. Individual SWCNTs and SnO₂ NWs field effect transistors showed p‐ and n‐type transfer properties with current on/off ratios of 7.0 × 10⁵ and 2.7 × 10⁶, respectively. The heterojunction diode showed a rectifying behavior with a rectification ratio of higher than 10³ at ±1 V and the analysis with an equivalent circuit model of serially connected diode and resistor estimated an ideality factor of 1.5 and the resistance of 20 MΩ. The rectification of AC input signal was clearly demonstrated by fabricating a full‐wave bridge circuit of heterojunctions. In addition, the heterojunctions showed a high UV photosensitivity of ～10⁴ under reverse bias, suggesting their implicit applications in UV sensors.     

Characterization of Ge<Subscript>22</Subscript>Sb<Subscript>22</Subscript>Te<Subscript>56</Subscript> and Sb-Excess Ge<Subscript>15</Subscript>Sb<Subscript>47</Subscript>Te<Subscript>38</Subscript> Chalcogenide Thin Films for Phase-Change Memory Applications

A phase-change memory device that utilizes an antimony (Sb)-excess Ge₁₅Sb₄₇Te₃₈ chalcogenide thin film was fabricated and its electrical properties were measured and compared with a similar device that uses Ge₂₂Sb₂₂Te₅₆. The resulting electrical characteristics exhibited I _reset values of 14 mA for Ge₂₂Sb₂₂Te₅₆ and 10.6 mA for Ge₁₅Sb₄₇Te₃₈. Also, the set operation time (t _set) for the device using Ge₁₅Sb₄₇Te₃₈ films was 140 ns, which was more than twice as fast as the Ge₂₂Sb₂₂Te₅₆ device. The relationship between the microstructure and the improved electrical performance of the device was examined by means of transmission electron microscopy (TEM).     

Design and Performance Analysis of Electronic Seal Protection Systems Based on AES

A very promising application of active RFID systems is the electronic seal, an electronic device to guarantee the authenticity and integrity of freight containers. To provide freight containers with a high level of tamper resistance, the security of electronic seals must be ensured. In this paper, we present the design and implementation of an electronic seal protection system. First, we propose the eSeal Protection Protocol (ePP). Next, we implement and evaluate various cryptographic primitives as building blocks for our protocol. Our experimental results show that AES‐CBC‐MAC achieves the best performance among various schemes for message authentication and session key derivation. Finally, we implement a new electronic seal system equipped with ePP, and evaluate its performance using a real‐world platform. Our evaluation shows that ePP guarantees a sufficient performance over an ARM9‐based interrogator.     

Enhanced Performance of Fullerene n‐Channel Field‐Effect Transistors with Titanium Sub‐Oxide Injection Layer

Enhanced performance of n‐channel organic field‐effect transistors (OFETs) is demonstrated by introducing a titanium sub‐oxide (TiO_x) injection layer. The n‐channel OFETs utilize [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PC₆₁BM) or [6,6]‐phenyl‐C₇₁ butyric acid methyl ester (PC₇₁BM) as the semiconductor in the channel. With the TiO_x injection layer, the electron mobilities of PC₆₁BM and PC₇₁BM FET using Al as source/drain electrodes are comparable to those obtained from OFETs using Ca as the source/drain electrodes. Direct measurement of contact resistance (R_c) shows significantly decreased R_c values for FETs with the TiO_x layer. Ultraviolet photoelectron spectroscopy (UPS) studies demonstrate that the TiO_x layer reduces the electron injection barrier because of the relatively strong interfacial dipole of TiO_x. In addition to functioning as an electron injection layer that eliminates the contact resistance, the TiO_x layer acts as a passivation layer that prevents penetration of O₂ and H₂O; devices with the TiO_x injection layer exhibit a significant improvement in lifetime when exposed to air.     

Combined First‐Principle Calculations and Experimental Study on Multi‐Component Olivine Cathode for Lithium Rechargeable Batteries

The electrochemical properties and phase stability of the multi‐component olivine compound LiMn_1/3Fe_1/3Co_1/3PO₄ are studied experimentally and with first‐principles calculation. The formation of a solid solution between LiMnPO₄, LiFePO₄, and LiCoPO₄ at this composition is confirmed by XRD patterns and the calculated energy. The experimental and first‐principle results indicate that there are three distinct regions in the electrochemical profile at quasi‐open‐circuit potentials of ～3.5 V, ～4.1 V, and ～4.7 V, which are attributed to Fe³⁺/Fe²⁺, Mn³⁺/Mn²⁺, and Co³⁺/Co²⁺ redox couples, respectively. However, exceptionally large polarization is observed only for the region near 4.1 V of Mn³⁺/Mn²⁺ redox couples, implying an intrinsic charge transfer problem. An ex situ XRD study reveals that the reversible one‐phase reaction of Li extraction/insertion mechanism prevails, unexpectedly, for all lithium compositions of Li_xMn_1/3Fe_1/3Co_1/3PO₄ (0 ≤ x ≤ 1) at room temperature. This is the first demonstration that the well‐ordered, non‐nanocrystalline (less than 1% Li–M disorder and a few hundred nanometer size particle) olivine electrode can be operated solely in a one‐phase mode.     

Enhanced privacy and authentication for the global system for mobile communications

The Global System for Mobile Communications (GSM) is widely recognized as the modern digital mobile network architecture. Increasing market demands point toward the relevancy of securityrelated issues in communications. The security requirements of mobile communications for the mobile users include: (1) the authentication of the mobile user and Visitor Location Register/Home Location Register; (2) the data confidentiality between mobile station and Visitor Location Register, and the data confidentiality between Visitor Location Register and Visitor Location Register/Home Location Register (VLR/HLR); (3) the location privacy of mobile user. However, GSM does not provide enough security functions to meet these requirements. We propose three improved methods to enhance the security, to reduce the storage space, to eliminate the sensitive information stored in VLR, and consequently to improve the performance of the system. Proposed methods include an improved authentication protocol for the mobile station, a data confidentiality protocol, and a location privacy protocol. The merit of the proposed methods is to improve but not to alter the existing architecture of the system. Furthermore, this study also performs computational and capacity analyses to evaluate the original GSM system and proposed approaches on a comparative basis.     

Visible Korean human: improved serially sectioned images of the entire body

The data from the Visible Human Project (VHP) and the Chinese Visible Human (CVH), which are the serially sectioned images of the entire cadaver, are being used to produce three-dimensional (3-D) images and software. The purpose of our research, the Visible Korean Human (VKH), is to produce an enhanced version of the serially sectioned images of an entire cadaver that can be used to upgrade the 3-D images and software. These improvements are achieved without drastically changing the methods developed for the VHP and CVH; thus, a complementary solution was found. A Korean male cadaver was chosen without anything perfused into the cadaver; the entire body was magnetic resonance (MR) and computed tomography (CT) scanned at 1.0-mm intervals to produce MR and CT images. After scanning, entire body of the cadaver was embedded and serially sectioned at 0.2-mm intervals; each sectioned surface was inputted into a personal computer to produce anatomical images (pixel size: 0.2 mm) without any missing images. Eleven anatomical organs in the anatomical images were segmented to produce segmented images. The anatomical and segmented images were stacked and reconstructed to produce 3-D images. The VKH is an ongoing research; we will produce a female version of the VKH and provide more detailed segmented images. The data from the VHP, CVH, and VKH will provide valuable resources to the medical image library of 3-D images and software in the field of medical education and clinical trials.     

Liver‐Specific and Echogenic Hyaluronic Acid Nanoparticles Facilitating Liver Cancer Discrimination

With the increasing demand for instant real‐time ultrasound (US) imaging of a specific organ, target‐specific and long‐circulating ultrasound contrast agents are of special interest. A new species of echogenic hyaluronic acid nanoparticles is presented as an ultralong‐acting, liver‐specific, US contrast agent that is distinct from conventional gas‐filled microbubbles. Using an oil‐in‐water (O/W) emulsification method, bioinert and hydrophobic perfluoropentane (PFP) is encapsulated as an ultrasound gas precursor into hyaluronic acid nanoparticles (HANPs) using hydrophobic interactions. HANPs are formulated by self‐assembly, with amphiphilic hyaluronic acid‐5β‐cholanic acid (HA‐CA) conjugating in aqueous conditions. The resulting echogenic PFP‐encapsulated HANPs (Echo‐NPs) show solid nanostructures, differentiated from core‐empty conventional microbubbles, and exhibiting outstanding physical properties as an ultrasound contrast agent. They are more stable and robust echogenic solid bodies with an in vivo favorable hydrodynamic size and because PFPs vaporize gradually, their expansion process is very slow in body conditions. After several systemic circulations, echo‐NPs generated intense and ultralong echo signals for US imaging at the target site. The echogenic properties of Echo‐NPs show a significantly increased half‐life and echo persistence, compared with conventional microbubbles. The results clearly show that echo‐NPs outperform conventional microbubbles in terms of both physical and echogenic in vitro and in vivo properties.