Chang-Wook Lee

Spinel LiMn2O4/reduced graphene oxide hybrid for high rate lithium ion batteries

A well-crystallized and nano-sized spinel LiMn2O4/reduced graphene oxide hybrid cathode material for high rate lithium-ion batteries has been successfully synthesized via a microwave-assisted hydrothermal method at 200 °C for 30 min without any post heat-treatment. The nano-sized LiMn2O4 particles were evenly dispersed on the reduced graphene oxide template without agglomeration, which allows the inherent high active surface area of individual LiMn2O4 nanoparticles in the hybrid. These unique structural and morphological properties of LiMn2O4 on the highly conductive reduced graphene oxide sheets in the hybrid enable achieving the high specific capacity, an excellent high rate capability and stable cycling performance. An analysis of the cyclic voltammogram data revealed that a large surface charge storage contribution of the LiMn2O4/reduced graphene oxide hybrid plays an important role in achieving faster charge/discharge.

Mesoporous nickel/carbon nanotube hybrid material prepared by electroless deposition

A mesoporous nickel/carbon nanotube (Ni/CNT) hybrid material was synthesized by electroless deposition in the presence of lyotropic liquid crystal (LLC) of the nonionic surfactant Brij 56 through the heterogeneous nucleation and growth of mesoporous Ni on the outer surface of the CNT template. The Brunauer–Emmett–Teller (BET) surface area of the hybrid material was 112.8 m2 g−1 with a total pore volume of 0.356 cm3 g−1. Its electrochemical properties were studied by cyclic voltammetry (CV), which revealed it to be a promising candidate for electrochemical energy storage applications.

A two-dimensional highly ordered mesoporous carbon/graphene nanocomposite for electrochemical double layer capacitors: effects of electrical and ionic conduction pathways

A two-dimensional highly ordered mesoporous carbon/graphene nanocomposite (MCG) was synthesized by replicating a KIT-6/graphene nanocomposite. The MCG exhibited a high Brunauer–Emmett–Teller surface area of 1179 m2 g−1 and a large total pore volume of 0.94 cm3 g−1. On account of its large surface area and high electrical conductivity with 2D morphology, MCG showed a very high specific capacitance of 276 F g−1 at 1 A g−1 and maintained 86% of initial capacitance at 100 A g−1 in 1.0 M TEABF4/AN.

High‐Surface‐Area Nitrogen‐Doped Reduced Graphene Oxide for Electric Double‐Layer Capacitors

A two-step method consisting of solid-state microwave irradiation and heat treatment under NH3 gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007 m(2)  g(-1) ), high electrical conductivity (1532 S m(-1) ), and low oxygen content (1.5 wt %) for electrical double-layer capacitor applications. The specific capacitance of N-RGO was 291 F g(-1) at a current density of 1 A g(-1) , and a capacitance of 261 F g(-1) was retained at 50 A g(-1) , which indicated a very good rate capability. N-RGO also showed excellent cycling stability and preserved 96 % of the initial specific capacitance after 100 000 cycles. Near-edge X-ray absorption fine-structure spectroscopy results provided evidenced for the recovery of π conjugation in the carbon networks with the removal of oxygenated groups and revealed chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content.

A New Fuse Architecture and a New Post-Share Redundancy Scheme for Yield Enhancement in 3-D-Stacked Memories

3-D-stacked memory using through-silicon-vias (TSVs) has emerged as a good alternative for overcoming the limitation of 2-D memory technology. Among many issues with 3-D-stacked memory, yield is one of the major challenges for mass production. This paper proposes a new fuse architecture and redundancy scheme to improve the yield of 3-D-stacked memories. The new fuse architecture is developed based on the fact that the unused redundancies in prebond repair cause the inefficiency. Therefore, the new fuse architecture provides a way to share redundancies in prebond and postbond repairs. There are two kinds of operation modes. One is an enable mode for collecting the used redundancy information. The other is a mask mode for obtaining faulty redundancy information using a short test algorithm. Using the new fuse architecture, a new redundancy scheme called the post-share scheme is developed to achieve optimal yield. The post-share scheme allocates the fixed number of spare rows and columns for each repair just like other schemes. However, only allocated redundancies are used in prebond repair, while both the redundancies allocated for postbond repair and unused redundancies in prebond repair can be used for postbond repair. Experimental results show that the post-share redundancy scheme significantly increases the final yield of 3-D-stacked memories and the increase of area overhead is small.

Deformation of the Augustine Volcano, Alaska, 1992–2005, measured by ERS and ENVISAT SAR interferometry

The Augustine Volcano is a conical-shaped, active stratovolcano located on an island of the same name in Cook Inlet, about 290 km southwest of Anchorage, Alaska. Augustine has experienced seven significant explosive eruptions—in 1812, 1883, 1908, 1935, 1963, 1976, 1986, and in January 2006. To measure the ground surface deformation of the Augustine Volcano before the 2006 eruption, we applied satellite radar interferometry using Synthetic Aperture Radar (SAR) images from three descending and three ascending satellite tracks acquired by European Remote Sensing Satellite (ERS) 1 and 2 and the Environment Satellite (ENVISAT). Multiple interferograms were stacked to reduce artifacts caused by atmospheric conditions, and we used a singular value decomposition method to retrieve the temporal deformation history from several points on the island. Interferograms during 1992 and 2005 show a subsidence of about 1–3 cm/year, caused by the contraction of pyroclastic flow deposits from the 1986 eruption. Subsidence has decreased exponentially with time. Multiple interferograms between 1992 and 2005 show no significant inflation around the volcano before the 2006 eruption. The lack of a pre-eruption deformation signal suggests that the deformation signal from 1992 to August 2005 must have been very small and may have been obscured by atmospheric delay artifacts.

Soft templated mesoporous manganese oxide/carbon nanotube composites via interfacial surfactant assembly

A mesoporous manganese oxide/carbon nanotube (CNT) composite was successfully synthesized using cetyltrimethylammonium bromide as a protection layer to prevent the direct contact between CNT and MnO4− ions, a linking agent to interact with MnO4− ions and a structure-directing agent for the formation of mesoporous oxide. The observed improvement in electrochemical utilization of MnO2 was due to the synergetic effect of the mesoporous structure and CNTs, which enhanced the overall electronic and ionic conductivities.

A Die Selection and Matching Method with Two Stages for Yield Enhancement of 3-D Memories

Three-dimensional (3-D) memories using through-silicon-vias (TSVs) as vertical buses across memory layers has regarded as one of 3-D integrated circuits (ICs) technology. The memory dies to stack together in a 3-D memory are selected by a die selection method. In order to improve yield of 3-D memories, redundancy sharing between inter-die using TSVs is an effective strategy. With the redundancy sharing strategy, the bad memory dies can become good 3-D memories through matching the good memory dies. To support die selection and matching efficiently, a novel redundancy analysis (RA) algorithm, which considers various repair solutions, is proposed. Because the repair solutions can be various, the proposed die selection and matching is performed with two stages; general die selection and matching method in the first stage and re-matched remained memory dies, after the first stage, applying other repair solutions in the second stage. Thus, the proposed die selection and matching algorithm using the proposed RA algorithm can improve yield of 3-D memories. The experimental results show that the proposed die selection and matching method can achieve higher yield of 3-D memories than that of the previous state-of-the-art the die selection and matching methods.

Analysis of the relationships between topographic factors and landslide occurrence and their application to landslide susceptibility mapping: a case study of Mingchukur, Uzbekistan

This paper uses a probability-based approach to study the spatial relationships between landslides and their causative factors in the Mingchukur area, Bostanlik districts of Tashkent, Uzbekistan. The approach is based on digital databases and incorporates methods including probability analysis, spatial pattern analysis, and interactive mapping. First, an object-oriented conceptual model for describing landslide events is proposed, and a combined database of landslides and environmental factors is constructed by integrating various databases within a unifying conceptual framework. The frequency ratio probability model and landslide occurrence data are linked for interactive, spatial evaluation of the relationships between landslides and their causative factors. In total, 15 factors were analyzed, divided into topography, hydrology, and geology categories. All analyzed factors were also divided into numerical and categorical types. Numerical factors are continuous and were evaluated according to their R2 values. A landslide susceptibility map was constructed based on conditioning factors and landslide occurrence data using the frequency ratio model. Finally, the map was validated and the accuracy showed the satisfactory value of 83.3%.

Analysis of the relationship between volcanic eruption and surface deformation in volcanoes of the Alaskan Aleutian Islands using SAR interferometry

The Alaskan Aleutian Islands form one of the world’s largest volcanic island chains. The islands are exposed to both direct and indirect damage from continuous volcanic eruptions. Surface deformation is mostly observed before volcanic eruption, but with some volcanoes, such as Ontake Volcano, deformations cannot be detected. In this study, we analyzed volcanic eruptions in the Alaskan Aleutian Islands, which is a region of frequent volcanic eruptions. Based on our results, we predicted the type of eruption that would occur on Baekdusan Volcano according to the presence or absence of surface deformation. For this purpose, 10 sites were selected from areas where recent volcanic activity had occurred in the Aleutian Islands. Additionally, Advanced Land Observing Satellite Phased Array-type L-band Synthetic Aperture Radar (ALOS-PALSAR) and European Remote Sensing (ERS)-1/2 satellite data were obtained from 10 experimental sites. Based on the radar satellite data, the volcanic surface deformations were identified, and the characteristics of the volcanic eruption were quantitatively calculated by determining the presence of surface deformation. The results of this study should facilitate the process of correlation between volcanic eruption and surface deformation.