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Lee, Dongbok,Kang, Dongmin,Kwon, Min-Ho,Jun, Hyun-Goo,Kim, Ki-Bum,Lyeo, Ho-Ki,Lee, Hyun-Suk,Cheong, Byung-ki Elsevier 2010 CURRENT APPLIED PHYSICS Vol.10 No.1
<P><B>Abstract</B></P><P>The dynamics of the melt-quenched amorphization in TiO<I><SUB>x</SUB></I> mixed Ge<SUB>2</SUB>Sb<SUB>2</SUB>Te<SUB>5</SUB> films were studied using real-time reflectivity measurements with a nanosecond laser pulse and various amounts of TiO<I><SUB>x</SUB></I>. It was observed that the laser-power required for amorphization was significantly reduced by 27% when 9.1mol% of TiO<I><SUB>x</SUB></I> was incorporated with Ge<SUB>2</SUB>Sb<SUB>2</SUB>Te<SUB>5</SUB>. The lowering of the thermal conductivity of the films, due to the increase in the number of interface between the Ge<SUB>2</SUB>Sb<SUB>2</SUB>Te<SUB>5</SUB> and TiO<I><SUB>x</SUB></I> phases, led to an increase in the thermal efficiency. Such enhanced thermal efficiency is of great technological importance in phase change storage applications.</P>
Ryu, Seung Wook,Lyeo, Ho-Ki,Lee, Jong Ho,Ahn, Young Bae,Kim, Gun Hwan,Kim, Choon Hwan,Kim, Soo Gil,Lee, Se-Ho,Kim, Ka Young,Kim, Jong Hyeop,Kim, Won,Hwang, Cheol Seong,Kim, Hyeong Joon IOP Pub 2011 Nanotechnology Vol.22 No.25
<P>This study examined the various physical, structural and electrical properties of SiO<SUB>2</SUB> doped Ge<SUB>2</SUB>Sb<SUB>2</SUB>Te<SUB>5</SUB> (SGST) films for phase change random access memory applications. Interestingly, SGST had a layered structure (LS) resulting from the inhomogeneous distribution of SiO<SUB>2</SUB> after annealing. The physical parameters able to affect the reset current of phase change memory (<I>I</I><SUB>res</SUB>) were predicted from the Joule heating and heat conservation equations. When SiO<SUB>2</SUB> was doped into GST, thermal conductivity largely decreased by ∼ 55%. The influence of SiO<SUB>2</SUB>-doping on <I>I</I><SUB>res</SUB> was examined using the test phase change memory cell. <I>I</I><SUB>res</SUB> was reduced by ∼ 45%. An electro-thermal simulation showed that the reduced thermal conductivity contributes to the improvement of cell efficiency as well as the reduction of <I>I</I><SUB>res</SUB>, while the increased dynamic resistance contributes only to the latter. The formation and presence of the LS thermal conductivity in the set state test cell after repeated switching was confirmed. </P>
Kang, Stephen Dongmin,Lim, Seong Chu,Lee, Eui-Sup,Cho, Young Woo,Kim, Yong-Hyun,Lyeo, Ho-Ki,Lee, Young Hee American Chemical Society 2012 ACS NANO Vol.6 No.5
<P>Thermal transport at carbon nanotube (CNT) interfaces was investigated by characterizing the interfacial thermal conductance between metallic or semiconducting CNTs and three different surfactants. We thereby resolved a difference between metallic and semiconducting CNTs. CNT portions separated by their electronic type were prepared in aqueous suspensions. After slightly heating the CNTs dispersed in the suspension, we obtained cooling curves by monitoring the transient changes in absorption, and from these cooling curves, we extracted the interfacial thermal conductance by modeling the thermal system. We found that the semiconducting CNTs unexpectedly exhibited a higher conductance of 11.5 MW/m<SUP>2</SUP>·K than that of metallic CNTs (9 MW/m<SUP>2</SUP>·K). Meanwhile, the type of surfactants hardly influenced the heat transport at the interface. The surfactant dependence is understood in terms of the coupling between the low-frequency vibrational modes of the CNTs and the surfactants. Explanations for the electronic-type dependency are considered based on the defect density in CNTs and the packing density of surfactants.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-5/nn2049762/production/images/medium/nn-2011-049762_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn2049762'>ACS Electronic Supporting Info</A></P>
Thermoelectric imaging of structural disorder in epitaxial graphene
Cho, Sanghee,Kang, Stephen Dongmin,Kim, Wondong,Lee, Eui-Sup,Woo, Sung-Jae,Kong, Ki-Jeong,Kim, Ilyou,Kim, Hyeong-Do,Zhang, Tong,Stroscio, Joseph A.,Kim, Yong-Hyun,Lyeo, Ho-Ki Nature Publishing Group, a division of Macmillan P 2013 Nature materials Vol.12 No.10
Heat is a familiar form of energy transported from a hot side to a colder side of an object, but not a notion associated with microscopic measurements of electronic properties. A temperature difference within a material causes charge carriers, electrons or holes to diffuse along the temperature gradient inducing a thermoelectric voltage. Here we show that local thermoelectric measurements can yield high-sensitivity imaging of structural disorder on the atomic and nanometre scales. The thermopower measurement acts to amplify the variations in the local density of states at the Fermi level, giving high differential contrast in thermoelectric signals. Using this imaging technique, we uncovered point defects in the first layer of epitaxial graphene, which generate soliton-like domain-wall line patterns separating regions of the different interlayer stacking of the second graphene layer.