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Sungho Seo,Sanghyun Jin,Bongyoung Yoo 한국표면공학회 2010 한국표면공학회 학술발표회 초록집 Vol.2010 No.11
Nanotwinned copper, which has higher strength and relatively low resistivity compensation, is fabricated by pulsed electrodeposition. In order to identify the formation mechanism of nanotwinned copper, we suggest new critical factor, dissolution effect. Off-time and pH are changed to investigate the effects of Cu dissolution in electrolyte on the density of nanotwin. It is confirm that the dissolution of Cu during the nucleation is significantly important to determine the amount of nanotwin, and the rate of dissolution could be controlled by using reverse pulse deposition.
Seo, Sungho,Oh, Min-Wook,Jeong, Youngkeun,Yoo, Bongyoung Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.696 No.-
<P><B>Abstract</B></P> <P>A reduction in the grain size of p-type thermoelectric materials, which increases phonon scattering at grain boundaries, can increase the figure of merit (<I>ZT)</I> due to decreased lattice thermal conductivity. Small grains are often observed in samples sintered from small powders. In this study, we investigated the effect of a reduction in powder size in Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> alloys synthesized using a new hybrid method. Tellurium (Te) nanowires were chemically synthesized without an organic surfactant and Bi<SUB>0.25</SUB>Sb<SUB>0.75</SUB> powders were physically synthesized using a ball-milling method. The Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB> powders synthesized from the previously prepared Te nanowires and Bi<SUB>0.25</SUB>Sb<SUB>0.75</SUB> powder were thermally alloyed by a solid state reaction. The morphology of the Te was found to be important in determining the powder size of the alloyed Bi<SUB>0.5</SUB>Sb<SUB>1.5</SUB>Te<SUB>3</SUB>. Reduced thermal conductivity was associated with smaller grain size, which enhanced thermoelectric properties.</P> <P><B>Highlights</B></P> <P> <UL> <LI> BiSbTe powders were synthesized with a solid state reaction from Te nanowires. </LI> <LI> The particle and grain sizes were much smaller than ball milled BiSbTe powders'. </LI> <LI> Reduced κ was associated with smaller grain size, which enhanced ZT values. </LI> <LI> The morphology of Te was important in determining the alloyed powder size. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Seo, Sungho,Yoo, Bongyoung American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11
<P>As the aspect ratio of via-holes is increased, the difficulty in forming a conformal seed layer with sputtered Cu also increases, especially at the side-walls of the holes. Electroless deposition is a cost-effective, non-vacuum process; however, it requires the noble metal, Pd, during the activation process. In this study, we investigated the deposition of a continuous Cu lining in via-holes with an aspect ratio of 11 (5 mu m-width and 55 mu m-depth) using electrolessly deposited Ru as an activator instead of Pd on a Ta diffusion barrier layer. The electroless Ru deposition was successfully developed without an activation process. This was accomplished by increasing the hydrophilicity of the surface of the Ta barrier layer. The formed Ru layer can be utilized for the diffusion barrier as well as the activator. The bilayer barrier (Ru/Ta) may enhance the total diffusion barrier properties, allowing a reduction in the thickness of the Ta barrier layer while maintaining the same properties.</P>
Seo, Sungho,Jeong, Youngkeun,Oh, Min-Wook,Yoo, Bongyoung ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.706 No.-
<P><B>Abstract</B></P> <P>The combination technique of ball-milling and sintering is commonly employed to manufacture high performance thermoelectric materials. However, during ball-milling and sintering, it is hard to avoid inclusion of oxygen in the lattice, which results in degradation of the thermoelectric properties. In this study, hydrogen annealing was carried out at different temperatures to remove the dissolved oxygen. The reduced oxygen content was confirmed after hydrogen annealing, and the extent of the reduction was increased with annealing temperature. The carrier (holes) concentration was increased with the reduction of the oxygen content, which is attributed to the increased concentration of the antisite defects. Consequently, the electrical conductivity was considerably increased whereas the Seebeck coefficient was marginally decreased. The variation of the Seebeck coefficient was interpreted with complex electronic structure. As a result, the power factor and ZT were enhanced 27.0% and 18.2%, respectively, compared with the non-annealed sample.</P> <P><B>Highlights</B></P> <P> <UL> <LI> As H<SUB>2</SUB> annealing temperature increased, the number of carrier increased with O<SUB>2</SUB> reduction and antisites. </LI> <LI> The power factor of annealed samples was enhanced as 27.0%. </LI> <LI> The peak ZT enhanced as 18.2% in the 400 °C-annealed sample, compared with the unannealed one. </LI> <LI> The H<SUB>2</SUB> annealing of ball-milled powders is useful for thermoelectric materials processed by the milling-sintering technique. </LI> </UL> </P>
Nam, Sungho,Woo, Sungho,Seo, Jooyeok,Kim, Wook Hyun,Kim, Hwajeong,McNeill, Christopher R.,Shin, Tae Joo,Bradley, Donal D. C.,Kim, Youngkyoo American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.29
<P>The performance of solar cells with a polymer:polymer bulk heterojunction (BHJ) structure, consisting of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) donor and poly[[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)] (P(NDI2OD-T2)) acceptor polymers, was investigated as a function of cosolvent (p-xylene:chlorobenzene (pXL:CB)) composition ratio. A remarkable efficiency improvement (similar to 38%) was achieved by spin-coating the photoactive blend layer from pXL:CB = 80:20 (volume) rather than pXL alone, but the efficiency then decreased when the CB content increased further to pXL:CB = 60:40. The improved efficiency was correlated with a particular PTB7-Th:P(NDI2OD-T2) donor-acceptor blend nanostructure, evidenced by a fiber-like surface morphology, a red-shifted optical absorption, and enhanced PL quenching. Further device optimization for pXL:CB = 80:20 films yielded a power conversion efficiency of similar to 5.4%. However, these devices showed very poor stability (similar to 15 min for a 50% reduction in initial efficiency), owing specifically to degradation of the PTB7-Th donor-component. Replacing PTB7-Th with a more stable donor polymer will be essential for any application potential to be realized.</P>