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All Graphene-Based Thin Film Transistors on Flexible Plastic Substrates
Lee, Seoung-Ki,Jang, Ho Young,Jang, Sukjae,Choi, Euiyoung,Hong, Byung Hee,Lee, Jaichan,Park, Sungho,Ahn, Jong-Hyun American Chemical Society 2012 Nano letters Vol.12 No.7
<P>High-performance, flexible all graphene-based thin film transistor (TFT) was fabricated on plastic substrates using a graphene active layer, graphene oxide (GO) dielectrics, and graphene electrodes. The GO dielectrics exhibit a dielectric constant (3.1 at 77 K), low leakage current (17 mA/cm<SUP>2</SUP>), breakdown bias (1.5 × 10<SUP>6</SUP> V/cm), and good mechanical flexibility. Graphene-based TFTs showed a hole and electron mobility of 300 and 250 cm<SUP>2</SUP>/(V·s), respectively, at a drain bias of −0.1 V. Moreover, graphene TFTs on the plastic substrates exhibited remarkably good mechanical flexibility and optical transmittance. This method explores a significant step for the application of graphene toward flexible and stretchable electronics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-7/nl300948c/production/images/medium/nl-2012-00948c_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl300948c'>ACS Electronic Supporting Info</A></P>
Sharpened VO<sub>2</sub> Phase Transition via Controlled Release of Epitaxial Strain
Lee, Daesu,Lee, Jaeseong,Song, Kyung,Xue, Fei,Choi, Si-Young,Ma, Yanjun,Podkaminer, Jacob,Liu, Dong,Liu, Shih-Chia,Chung, Bongwook,Fan, Wenjuan,Cho, Sang June,Zhou, Weidong,Lee, Jaichan,Chen, Long-Qin American Chemical Society 2017 NANO LETTERS Vol.17 No.9
<P>Phase transitions in correlated materials can be manipulated at the nanoscale to yield emergent functional properties, promising new paradigms for nanoelectronics and nanophotonics. Vanadium dioxide (VO2), an archetypal correlated material, exhibits a metal insulator transition (MIT) above room temperature. At the thicknesses required for heterostructure applications, such as an optical modulator discussed here, the strain state of VO2 largely determines the MIT dynamics critical to the device performance. We develop an approach to control the MIT dynamics in epitaxial VO2 films by employing an intermediate template layer with large lattice mismatch to relieve the interfacial lattice constraints, contrary to conventional thin film epitaxy that favors lattice match between the substrate and the growing film. A combination of phase-field simulation, in situ real-time nanoscale imaging, and electrical measurements reveals robust undisturbed MIT dynamics even at preexisting structural domain boundaries and significantly sharpened MIT in the templated VO2 films. Utilizing the sharp MIT, we demonstrate a fast, electrically switchable optical waveguide. This study offers unconventional design principles for heteroepitaxial correlated materials, as well as novel insight into their nanoscale phase transitions.</P>
Electron–Lattice Coupling in Correlated Materials of Low Electron Occupancy
Eom, Kitae,Choi, Euiyoung,Yoon, Jonghyun,Choi, Minsu,Song, Kyung,Choi, Si-Young,Lee, Daesu,Lee, Jung-Woo,Eom, Chang-Beom,Lee, Jaichan American Chemical Society 2017 NANO LETTERS Vol.17 No.9
<P>In correlated materials including transition metal oxides, electronic properties and functionalities are modulated and enriched by couplings between the electron and lattice degrees of freedom. These couplings are controlled by external parameters such as chemical doping, pressure, magnetic and electric fields, and light irradiation. However, the electron-lattice coupling relies on orbital characters, i.e., symmetry and occupancy, of t(2g) and e(g) orbitals, so that a large electron-lattice coupling is limited to eg electron system, whereas t(2g) electron system exhibits an inherently weak coupling. Here, we design and demonstrate a strongly enhanced electron-lattice coupling in electron-doped SrTiO3, that is, the t(2g) electron system. In ultrathin films of electron-doped SrTiO3 [i.e., (La0.25Sr0.75)TiO3], we reveal the strong electron-lattice-orbital coupling, which is manifested by extremely increased tetragonality and the corresponding metal-to-insulator transition. Our findings open the way of an active tuning of the charge-lattice-orbital coupling to obtain new functionalities relevant to emerging nanoelectronic devices.</P>
Piezoelectrically Driven Self-Excited Microbridge VOCs Sensor
Shin, Sanghun,Lee, Nae-Eung,Park, Joon-Shik,Park, Hyo-Derk,Lee, Jaichan Taylor Francis 2006 Ferroelectrics Vol.338 No.1
<P>Piezoelectrically driven microbridge gas sensors have been fabricated by MEMS process. We have used the resonant frequency change of the microbridge transducer upon mass increase. The sol-gel derived Pb(Zr<SUB>0.52</SUB>,Ti<SUB>0.48</SUB>)O<SUB>3</SUB> (PZT) film capacitor as an actuating part was integrated into the thin SiN<SUB><I>x</I></SUB> bridge structure. The resonant frequency of the microbridge was in the range of 250 kHz to 260 kHz. The microbridge exhibited a mass sensitivity and gravimetric sensitivity factor of <I>ca</I>. 7.27 pg/Hz and 345 cm<SUP><I>2</I></SUP>/g, respectively. With the PMMA polymer sensing layer, the microbridge showed the gas sensitivity of 1.67 ppm/Hz for ethanol vapor.</P>
PIEZOELECTRICALLY DRIVEN MICROTRANSDUCER MASS SENSORS
SHIN, SANGHUN,LEE, NAE-EUNG,PARK, HYO-DERK,PARK, JOON-SHIK,LEE, JAICHAN Taylor Francis 2005 Integrated ferroelectrics Vol.76 No.1
<P>Various types of piezoelectrically driven microtransducers which have a similar physical dimension, i.e., microcantilever, microdiaphragm and microbridge, were fabricated by micro electromechanical system (MEMS) technique and are compared on the mass sensing behavior. The diol based sol-gel derived Pb(Zr 0.52 ,Ti 0.48 )O 3 (PZT) thin film capacitors were integrated for the piezoelectric actuation. We have used the resonant frequency change of microtransducer upon mass increase as a sensing mechanism. The resonant frequency of the microtransducer was measured by analysis of electrical signals from microtransducer such as impedance, capacitance, phase and dielectric loss. The fundamental resonant frequencies of the microcantilever, microbridge and microdiaphragm with similar dimension (∼⃒ 300 &mgr; m) were about 26 kHz, 260 kHz and 290 kHz, respectively. The mass sensitivities of bare microtransducers were measured by metallic thin film deposition and analysis of spectral responses from microtransducers. When various microtransducers are compared, the microcantilever exhibited the highest gravimetric sensitivity factor (Δ f /Δ m f 0 = 694.4 cm 2 /g), followed by the microbridge and microdiaphragm. However, the microbridge showed the highest mass sensitivity (Δ f /Δ m = 137.5 Hz/ng) among those transducers.</P>
Enhanced catalytic behavior of Ni alloys in steam methane reforming
Yoon, Yeongpil,Kim, Hanmi,Lee, Jaichan Elsevier 2017 Journal of Power Sources Vol.359 No.-
<P><B>Abstract</B></P> <P>The dissociation process of methane on Ni and Ni alloys are investigated by density functional theory (DFT) in terms of catalytic efficiency and carbon deposition. Examining the dissociation to CH<SUB>3</SUB>, CH<SUB>2</SUB>, CH, C, and H is not sufficient to properly predict the catalytic efficiency and carbon deposition, and further investigation of the CO gas-evolving reaction is required to completely understand methane dissociation in steam. The location of alloying element in Ni alloy needed be addressed from the results of <I>ab-inito</I> molecular dynamics (MD). The reaction pathway of methane dissociation associated with CO gas evolution is traced by performing first-principles calculations of the adsorption and activation energies of each dissociation step. During the dissociation process, two alternative reaction steps producing adsorbed C and H or adsorbed CO are critically important in determining coking inhibition as well as H<SUB>2</SUB> gas evolution (i.e., the catalytic efficiency). The theoretical calculations presented here suggest that alloying Ni with Ru is an effective way to reduce carbon deposition and enhance the catalytic efficiency of H<SUB>2</SUB> fueling in solid oxide fuel cells (SOFCs).</P> <P><B>Highlights</B></P> <P> <UL> <LI> DFT calculation was used to understand steam methane reforming on Ni alloys. </LI> <LI> CO gas-evolving reaction suppresses carbon deposition. </LI> <LI> CO gas-evolving reaction enhances the catalytic efficiency of H<SUB>2</SUB> generation. </LI> <LI> Ni-Ru alloy is an effective way to facilitate the CO gas-evolving reaction. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>