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Chung, Sung Yun,Kim, Sunyoung,Lee, Ju‐,Hyuck,Kim, Kyongjun,Kim, Sang‐,Woo,Kang, Chong‐,Yun,Yoon, Seok‐,Jin,Kim, Youn Sang WILEY‐VCH Verlag 2012 ADVANCED MATERIALS Vol.24 No.45
<P>An all‐solution‐processed flexible piezoelectric nanogenerator, composed of polycrystalline ZnO thin film and functional polymer layers such as P3HT/PCBM and PEDOT:PSS, generates energy through a mechanical rolling and muscle stretching system. On page 6022, Youn Sang Kim, Sang‐Woo Kim, and co‐workers show that this all‐solution‐processed nanogenerator is feasible as a piezoelectric patchable device and is promising for use in future energy harvesters such as wearable human patches and mobile electronics. </P>
Compact Coarse Approach Mechanism for a Scanning Probe Microscope
Kyongjun Kim,Yongho Seo,Duhwan Hwang,Junhong Kim 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2
We report a compact design for a coarse approach mechanism, the so-called `walker', for a low-temperature ultra-high-vacuum scanning probe microscope. We adapted the slip-stick principle with three actuators driven by the time sequential scheme suggested by Pan {\it et al.} The shear piezo-stack was replaced by three rectangular pieces of a piezoelectric (PZT) actuator to reduce the walker volume. Three slip-stick actuators were used rather than six actuators in the original design. By using polished sapphire and rough alumina plates, we implemented perfect sticking and a sliding interface. Our design minimizes usage of glue or epoxy, where attachment strength would be deteriorated by repeated temperature cycling. By using teflon material, we reduced the frictional force of sliding parts. Without a metallic spring, elastic motion was provided by the teflon material against the holding force. A moving velocity of 18 μm/s and a step distance of 0.3 μm were measured at room temperature. We report a compact design for a coarse approach mechanism, the so-called `walker', for a low-temperature ultra-high-vacuum scanning probe microscope. We adapted the slip-stick principle with three actuators driven by the time sequential scheme suggested by Pan {\it et al.} The shear piezo-stack was replaced by three rectangular pieces of a piezoelectric (PZT) actuator to reduce the walker volume. Three slip-stick actuators were used rather than six actuators in the original design. By using polished sapphire and rough alumina plates, we implemented perfect sticking and a sliding interface. Our design minimizes usage of glue or epoxy, where attachment strength would be deteriorated by repeated temperature cycling. By using teflon material, we reduced the frictional force of sliding parts. Without a metallic spring, elastic motion was provided by the teflon material against the holding force. A moving velocity of 18 μm/s and a step distance of 0.3 μm were measured at room temperature.
Kim, Kyongjun,Park, Siyun,Seon, Jong‐,Baek,Lim, Keon‐,Hee,Char, Kookheon,Shin, Kyusoon,Kim, Youn Sang WILEY‐VCH Verlag 2011 Advanced Functional Materials Vol.21 No.18
<P><B>Abstract</B></P><P>Flexible transparent thin‐film transistors (TTFTs) have emerged as next‐generation transistors because of their applicability in transparent electronic devices. In particular, the major driving force behind solution‐processed zinc oxide film research is its prospective use in printing for electronics. Since the patterning that prevents current leakage and crosstalk noise is essential to fabricate TTFTs, the need for sophisticated patterning methods is critical. In patterning solution‐processed ZnO thin films, several points require careful consideration. In general, as these thin films have a porous structure, conventional patterning based on photolithography causes loss of film performance. In addition, as controlling the drying process is very subtle and cumbersome, it is difficult to fabricate ZnO semiconductor films with robust fidelity through selective printing or patterning. Therefore, we have developed a simple selective patterning method using a substrate pre‐patterned through bond breakage of poly(methyl methacrylate) (PMMA), as well as a new developing method using a toluene–methanol mixture as a binary solvent mixture.</P>
Kim, Kyongjun,Park, Si Yun,Lim, Keon-Hee,Shin, ChaeHo,Myoung, Jae-Min,Kim, Youn Sang The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.43
<P>A transparent thin film transistor (TTFT), including zinc oxide (ZnO), has come into the spotlight as an innovative TFT that has the potential to drive the future of the information technology industry. Herein, we developed a new direct patterning method, drop-casting with a new developing method, through the combination of an aqueous ammonia–ZnO process with the doping of Na ions and surface engineering for high n-type semiconducting performance with good operational stability at low temperature. In particular, the effective decomposition and removal of the residual ammonia compounds using methanol have a successful effect on both intrinsic and Na doped ZnO precursor processes for TFTs and they showed the extensive possibility of ammonia based metal oxide precursor solutions. In this method, the Na doped ZnO TTFTs showed good operational stability even with the process of low temperature sintering. The mobility <I>μ</I> = 0.80 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> was obtained at 200 °C sintering and the mobility <I>μ</I> = 0.10 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> at 100 °C sintering. In addition, in ambient conditions, the patterned Na doped ZnO TTFT exhibited high electron mobility <I>μ</I> = 1.84 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> with excellent device operational stability and scant hysteresis with sintering at 300 °C. This method is not only simple as compared with photolithography and inkjet printing, but is also a sophisticated patterning process with good fidelity for solution-processed ZnO TFTs. Moreover, the proposed method can be extended to plastic substrates on a large scale because of the low temperature development process of the ammonia–ZnO precursor using methanol and continuous patterning at ambient conditions. We believe that this method can be adapted to the advanced process toward future printed transparent electronic devices.</P> <P>Graphic Abstract</P><P>Patterned aqueous solutions were formed by selective wettability control as a direct patterning method is used with a photoinduced transformation technique of poly(dimethylsiloxane) (PDMS). <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm33790h'> </P>
Park, Si Yun,Kim, Beom Joon,Kim, Kyongjun,Kang, Moon Sung,Lim, Keon‐,Hee,Lee, Tae Il,Myoung, Jae M.,Baik, Hong Koo,Cho, Jeong Ho,Kim, Youn Sang WILEY‐VCH Verlag 2012 ADVANCED MATERIALS Vol.24 No.6
<P><B>Transfer characteristics of ZnO thin‐film transistors</B> (TFTs) based on ZnO doped with various alkali metals. A new doping method is demonstrated by employing alkali metals to achieve high‐performance and solution‐processed ZnO TFTs with a low processing temperature (∼300 °C), which is applicable to flexible plastic substrates.</P>
Yoo, Kyongjun,Jeon, Byung-Gu,Chun, Sae Hwan,Patil, Deepak Rajaram,Lim, Yong-jun,Noh, Seung-hyun,Gil, Jihyo,Cheon, Jinwoo,Kim, Kee Hoon American Chemical Society 2016 NANO LETTERS Vol.16 No.12
<P>Bulk magnetite (Fe3O4), the loadstone used in magnetic compasses, has been known to exhibit magnetoelectric (ME) properties below similar to 10 K; however, corresponding ME effects in Fe3O4 nanoparticles have been enigmatic. We investigate quantitatively the ME coupling of spherical Fe3O4 nanoparticles with uniform diameters (d) from 3 to 15 nm embedded in an insulating host, using a sensitive ME susceptometer. The intrinsic ME susceptibility (MES) of the Fe3O4 nanoparticles is measured, exhibiting a maximum value of similar to 0.6 ps/m at 5 K for d = 15 nm. We found that the MES is reduced with reduced d but remains finite until d = nm, which is close to the critical thickness for observing the Verwey transition. Moreover, with reduced diameter the critical temperature below which the MES becomes conspicuous increased systematically from 9.8 K in the bulk to 19.7 K in the nanoparticles with d = 7 nm, reflecting the core-shell effect on the ME properties. These results point to a new pathway for investigating ME effect in various nanomaterials.</P>
Seong, Kieun,Kim, Kyongjun,Park, Si Yun,Kim, Youn Sang The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.27
<P>Chemical imprinting was conducted on ZnO semiconductor films <I>via</I> a chemical reaction at the contact regions between a micro-patterned PDMS stamp and ZnO films. In addition, we applied the chemical imprinting on Li doped ZnO thin films for high performance TFTs fabrication. The representative micro-patterned Li doped ZnO TFTs showed a field effect mobility of 4.2 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> after sintering at 300 °C.</P> <P>Graphic Abstract</P><P>We developed a new patterning method <I>via</I> chemical imprinting with an ammonia soaked PDMS stamp which is simple, cost-effective, carried out under ambient conditions, and has no residual layer. In addition, chemical imprinting was applied on Li doped ZnO thin films for high performance TFTs. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc38021a'> </P>