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RISS 인기검색어
- 검색키워드
- 저자 : Bazylewski, P.F. (검색결과 5 건)
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Bazylewski, Paul F.,Kim, Kyung Hwan,Forrest, Jay L.,Tada, Hirokazu,Choi, Dong Hoon,Chang, Gap Soo Elsevier 2011 Chemical physics letters Vol.508 No.1
<P><B>Graphical abstract</B></P><P><ce:figure id='f0025'></ce:figure></P><P><B>Highlights</B></P><P>► Verification of energy symmetry breaking of C<SUB>60</SUB> π-orbitals due to side chain. ► Angle-dependent π<SUP>∗</SUP> feature revealing asymmetrical orbital distribution of PCBM. ► The presence of partially lifted LUMO degeneracy around the attachment point. ► Ordered molecular stacking structures determined from X-ray polarization dependence.</P> <P><B>Abstract</B></P><P>The electronic structure and molecular stacking arrangement of [6,6]-phenyl-C<SUB>61</SUB>-butyric acid methyl ester (PCBM) was studied using a combination of near-edge X-ray absorption fine structure measurements and density functional theory calculations. Measurements show that the side chain lifts the energy degeneracy of the C60 molecular orbitals around the chain attachment. This breaks the orbital symmetry of the LUMO of the C60 backbone which is observed through polarization dependence of C 1s→π<SUP>∗</SUP> transitions. This dependence is analyzed to determine the bulk crystal structure of PCBM. X-ray emission and absorption measurements indicate the band gap energy of PCBM to be 1.87eV.</P>
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Self-Ordering Properties of Functionalized Acenes for Annealing-Free Organic Thin Film Transistors
Bazylewski, Paul,Kim, Kyung Hwan,Choi, Dong Hoon,Chang, Gap Soo American Chemical Society 2013 The journal of physical chemistry. B, Condensed ma Vol.117 No.36
<P>Presented here is a study of the molecular self-ordering properties of four bis(phenylethynyl) anthracene based organic semiconductors related to their electronic structure employing X-ray spectroscopy techniques and density functional theory (DFT) calculations. The local molecular order through polarization dependence of C 1<I>s</I> → π* transitions revealed ordered π-stacking nearly perpendicular to the substrate due to van der Waals interactions between alkyl groups. DFT calculations were used to deconvolute the measured electronic structure and examine effects of small changes in molecular geometry in relation to measured charge carrier mobility in top contact field effect transistors. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are found to be conjugated from the anthracene core across the bridging ethynyl groups to the thiophene and phenyl end groups. The inclusion of ethynyl bridges connecting the thiophenes has a twofold effect of both reducing the rotational freedom of this functional group and increasing HOMO/LUMO conjugation across the molecules. These features help create a more rigid upright structure for HB-ant-THT with better molecular orbital conjugation and subsequent higher mobility. With this understanding of how different functional groups interact with an acene core, future synthesis of new materials may be directed toward annealing-free organic semiconducting materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2013/jpcbfk.2013.117.issue-36/jp405828d/production/images/medium/jp-2013-05828d_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp405828d'>ACS Electronic Supporting Info</A></P>
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Atomic and electronic structure of a copper/graphene interface as prepared and 1.5 years after
Boukhvalov, D.W.,Bazylewski, P.F.,Kukharenko, A.I.,Zhidkov, I.S.,Ponosov, Yu. S.,Kurmaev, E.Z.,Cholakh, S.O.,Lee, Y.H.,Chang, G.S. Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.426 No.-
<P><B>Abstract</B></P> <P>We report the results of X-ray spectroscopy and Raman measurements of as-prepared graphene on a high quality copper surface and the same materials after 1.5 years under different conditions (ambient and low humidity). The obtained results were compared with density functional theory calculations of the formation energies and electronic structures of various structural defects in graphene/Cu interfaces. For evaluation of the stability of the carbon cover, we propose a two-step model. The first step is oxidation of the graphene, and the second is perforation of graphene with the removal of carbon atoms as part of the carbon dioxide molecule. Results of the modeling and experimental measurements provide evidence that graphene grown on high-quality copper substrate becomes robust and stable in time (1.5 years). However, the stability of this interface depends on the quality of the graphene and the number of native defects in the graphene and substrate. The effect of the presence of a metallic substrate with defects on the stability and electronic structure of graphene is also discussed</P> <P><B>Highlights</B></P> <P> <UL> <LI> Proposed model of step by step perforation of graphene on metals during process of oxidation. </LI> <LI> Modeling and measurements demonstrate important role of substrate quality for protective properties of graphene. </LI> <LI> Effect of imperfectness of carbon sheet and substrate to electronic structure of graphene are shown. </LI> <LI> Key conditions for long-term anti-corrosion protection are discussed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Reduction of conductivity and ferromagnetism induced by Ag doping in ZnO:Co
Bieber, H.,Colis, S.,Schmerber, G.,Pierron-Bohnes, V.,Boukhvalov, D.W.,Kurmaev, E.Z.,Finkelstein, L.D.,Bazylewski, P.,Moewes, A.,Chang, G.S.,Dinia, A. Elsevier 2013 THIN SOLID FILMS - Vol.545 No.-
<P><B>Abstract</B></P> <P>Cobalt and silver co-doping has been undertaken in ZnO thin films grown by pulsed laser deposition in order to investigate the ferromagnetic properties in ZnO-based diluted magnetic materials and to understand the eventual relation between ferromagnetism and charge carriers. Hall transport measurements reveal that Ag doping up to 5% leads to a progressive compensation of the native <I>n</I>-type carriers. The magnetization curves show ferromagnetic contributions for all samples at both 5K and room temperature, decreasing with increasing the Ag concentration. First principles modeling of the possible configurations of Co–Ag defects suggests the formation of nano-clusters around interstitial Co impurity as the origin of the ferromagnetism. The Ag co-doping results in a decrease of the total spin of these clusters and of the Curie temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We fabricate ZnO:Co films co-doped by Ag. </LI> <LI> Reduction of the number of charge carriers in co-doped samples is observed. </LI> <LI> Decrease of magnetic moment per Co in Ag-rich samples is observed. </LI> <LI> Theoretical calculations support suppression of ferromagnetism in Ag-doped ZnO:Co. </LI> </UL> </P>
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