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감상규,김현정,허철구,최영찬,이민규 한국환경과학회 2003 한국환경과학회지 Vol.12 No.7
Butyltin compounds (BTs), namely tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT), were measured in surface sediments collected in 2001 inside Hallim Harbor where a lot of shipping occurs as one of major harbors of Jeju Island, in order to evaluate their distribution. BTs were detected in surface sediments of all stations and their concentrations were comparable to those in surface sediments of other sites of domestic and foreign countries. The main species among BTs was MBT, although there was a little difference with a survey site. No correlations were obtained between organic matter or particles size of surface sediments and total BTs, indicating that these factors did not affect on the distribution of BTs. It was estimated that more complex factors including BTs loads and surrounding sedimentary environments, affected on the distribution of BTs. The high correlations between BTs indicated that DBT and MBT were mainly degraded from TBT based on antifouling paints of vessel etc. and other sources, such as DBT and MBT, could be ignored. The butyltin degradation indexes ([DBT] + [MBT]/[TBT]) were in the range of 1.5~3.3 (mean 2.5), indicating that the parent compound, TBT, were inflowed into the surface sediments a long years ago and degraded.
Graphene Oxide Thin Films for Flexible Nonvolatile Memory Applications
Jeong, Hu Young,Kim, Jong Yun,Kim, Jeong Won,Hwang, Jin Ok,Kim, Ji-Eun,Lee, Jeong Yong,Yoon, Tae Hyun,Cho, Byung Jin,Kim, Sang Ouk,Ruoff, Rodney S.,Choi, Sung-Yool American Chemical Society 2010 Nano letters Vol.10 No.11
<P>There has been strong demand for novel nonvolatile memory technology for low-cost, large-area, and low-power flexible electronics applications. Resistive memories based on metal oxide thin films have been extensively studied for application as next-generation nonvolatile memory devices. However, although the metal oxide based resistive memories have several advantages, such as good scalability, low-power consumption, and fast switching speed, their application to large-area flexible substrates has been limited due to their material characteristics and necessity of a high-temperature fabrication process. As a promising nonvolatile memory technology for large-area flexible applications, we present a graphene oxide based memory that can be easily fabricated using a room temperature spin-casting method on flexible substrates and has reliable memory performance in terms of retention and endurance. The microscopic origin of the bipolar resistive switching behavior was elucidated and is attributed to rupture and formation of conducting filaments at the top amorphous interface layer formed between the graphene oxide film and the top Al metal electrode, via high-resolution transmission electron microscopy and in situ X-ray photoemission spectroscopy. This work provides an important step for developing understanding of the fundamental physics of bipolar resistive switching in graphene oxide films, for the application to future flexible electronics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2010/nalefd.2010.10.issue-11/nl101902k/production/images/medium/nl-2010-01902k_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl101902k'>ACS Electronic Supporting Info</A></P>
A low-temperature-grown TiO<sub>2</sub>-based device for the flexible stacked RRAM application
Jeong, Hu Young,Kim, Yong In,Lee, Jeong Yong,Choi, Sung-Yool IOP Pub 2010 Nanotechnology Vol.21 No.11
<P>Flexible TiO<SUB>2</SUB> crossbar memory device arrays were fabricated on plastic substrates using amorphous titanium oxide thin films grown by the low-temperature plasma-enhanced atomic layer deposition method. Al/ TiO<SUB>2</SUB> /Al memory cells on polyethersulfone (PES) showed an enhanced endurance property (up to 10<SUP>4</SUP> cycles) and low switching voltages compared to the cells on rigid substrates. The multi-stacked memory arrays were constructed by forming the additional Al/ TiO<SUB>2</SUB> /Al layer on the first memory device layer. Memory cells on each layer exhibited stable switching characteristics and mechanical robustness without interlayer cell-to-cell interference. </P>
Jeong, Hu Young,Kim, Jong Yun,Yoon, Tae Hyun,Choi, Sung-Yool Elsevier 2010 Current Applied Physics Vol.10 No.1
<P><B>Abstract</B></P><P>We investigated the reversible resistive switching of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) thin films sandwiched between Al electrodes. The <I>J</I>–<I>V</I> sweep curve showed a hysteretic behavior which depends on the polarity of the applied voltage bias. From the analysis of <I>I</I>–<I>V</I> curves, it was revealed that the charge transport through the junction was governed by the bulk space-charge-limited conduction (SCLC) model. Using transmission electron microscopy (TEM) analysis, it was confirmed that the initial high resistance state of PEDOT:PSS films is related with the segregation of PSS<SUP>−</SUP> chains induced by redox reaction between a Al metal electrode and PEDOT:PSS film. Positive space charges present on the top region of PEDOT:PSS films can be proposed as a possible trap centers of electron trapping and detrapping process.</P>
Interface‐Engineered Amorphous TiO<sub>2</sub>‐Based Resistive Memory Devices
Jeong, Hu Young,Lee, Jeong Yong,Choi, Sung‐,Yool WILEY‐VCH Verlag 2010 Advanced Functional Materials Vol.20 No.22
<P><B>Abstract</B></P><P>Crossbar‐type bipolar resistive memory devices based on low‐temperature amorphous TiO<SUB>2</SUB> (<I>a‐</I>TiO<SUB>2</SUB>) thin films are very promising devices for flexible nonvolatile memory applications. However, stable bipolar resistive switching from amorphous TiO<SUB>2</SUB> thin films has only been achieved for Al metal electrodes that can have severe problems like electromigration and breakdown in real applications and can be a limiting factor for novel applications like transparent electronics. Here, amorphous TiO<SUB>2</SUB>‐based resistive random access memory devices are presented that universally work for any configuration of metal electrodes via engineering the top and bottom interface domains. Both by inserting an ultrathin metal layer in the top interface region and by incorporating a thin blocking layer in the bottom interface, more enhanced resistance switching and superior endurance performance can be realized. Using high‐resolution transmission electron microscopy, point energy dispersive spectroscopy, and energy‐filtering transmission electron microscopy, it is demonstrated that the stable bipolar resistive switching in metal/<I>a‐</I>TiO<SUB>2</SUB>/metal RRAM devices is attributed to both interface domains: the top interface domain with mobile oxygen ions and the bottom interface domain for its protection against an electrical breakdown.</P>