Correlation of Kondo effect and molecular conformation of the acceptor molecule in the TTF-TCNE charge transfer complex

A Kondo resonance has been observed on purely organic molecules in several combinations of charge transfer complexes on a metal surface. It has been regarded as a fingerprint of the transfer of one electron from the donor to the extended π orbital of the acceptor's LUMO. Here, we investigate the stoichiometric checkerboard structure of tetrathiafulvalene (TTF) and tetracyanoethylene (TCNE) on a Au(1 1 1) surface using scanning tunneling and atomic force microscopy at 4.8 K. We find a bistable state of the TCNE molecules with distinct structural and electronic properties. The two states represent different conformations of the TCNE within the structure. One of them exhibits a Kondo resonance, whereas the other one does not, despite of both TCNE types being singly charged

Wie in der Lehrerbildung Wissenschaft marginalisiert und zur Akzeptanzbeschaffung umfunktioniert wird

Der Autor kritisiert die Ausrichtung der Lehrerbildung an den Universitäten. Er zeigt auf, welches Verständnis von Theorie und Praxis sowie deren Beziehung zueinander in der Lehrerbildung vorherrscht und wie dies einer akademischen Lehrerbildung im Medien der Wissenschaft entgegensteht. (DIPF/Orig.

GLOBALIZAÇÃO NA NOVA ORDEM ECONÔMICA INTERNACIONAL

O artigo propõe analisar a “nova ordem econômica mundial” formalizada em 1974 pela Assembleia Geral das Nações Unidas, instrumentalizada através de um conjunto de Declarações, Planos de Ação e Carta de Direitos e Deveres dos Estados em contraponto com a globalização enquanto fenômeno irreversível do capitalismo contemporâneo e os impactos nas relações internacionais e na efetivação de direitos humanos. Atendendo a metodologia qualitativa a pesquisa teórica denota a intrínseca relação entre a efetividade dos direitos humanos e a distribuição de riquezas e as políticas transnacionais relacionadas ao crescimento econômico

Quantum tunneling in real space: Tautomerization of single porphycene molecules on the (111) surface of Cu, Ag, and Au

Tautomerization in single porphycene molecules is investigated on Cu(111), Ag(111), and Au(111) surfaces by a combination of low-temperature scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. It is revealed that the trans configuration is the thermodynamically stable form of porphycene on Cu(111) and Ag(111), whereas the cis configuration occurs as a meta-stable form. The trans → cis or cis → trans conversion on Cu(111) can be induced in an unidirectional fashion by injecting tunneling electrons from the STM tip or heating the surface, respectively. We find that the cis → cis tautomerization on Cu(111) occurs spontaneously via tunneling, verified by the negligible temperature dependence of the tautomerization rate below ∼23 K. Van der Waals corrected DFT calculations are used to characterize the adsorption structures of porphycene and to map the potential energy surface of the tautomerization on Cu(111). The calculated barriers are too high to be thermally overcome at cryogenic temperatures used in the experiment and zero-point energy corrections do not change this picture, leaving tunneling as the most likely mechanism. On Ag(111), the reversible trans → cis conversion occurs spontaneously at 5 K and the cis → cis tautomerization rate is much higher than on Cu(111), indicating a significantly smaller tautomerization barrier on Ag(111) due to the weaker interaction between porphycene and the surface compared to Cu(111). Additionally, the STM experiments and DFT calculations reveal that tautomerization on Cu(111) and Ag(111) occurs with migration of porphycene along the surface; thus, the translational motion couples with the tautomerization coordinate. On the other hand, the trans and cis configurations are not discernible in the STM image and no tautomerization is observed for porphycene on Au(111). The weak interaction of porphycene with Au(111) is closest to the gas-phase limit and therefore the absence of trans and cis configurations in the STM images is explained either by the rapid tautomerization rate or the similar character of the molecular frontier orbitals of the trans and cis configurations

Mechanochemistry Induced Using Force Exerted by a Functionalized Microscope Tip

Atomic-scale mechanochemistry is realized from force exerted by a C-60-functionalized scanning tunneling microscope tip. Two conformers of tin phthalocyanine can be prepared on coinage-metal surfaces. A transition between these conformers is induced on Cu(111) and Ag(100). Density-functional calculations reveal details of this reaction. Because of the large energy barrier of the reaction and the strong interaction of SnPc with Cu(111), the process cannot be achieved by electrical means.National Natural Science Foundation of China [21522301, 21373020, 21403008, 61321001, 21433011, 11304107, 61371015]; Ministry of Science and Technology [2014CB239302, 2013CB933404, 2017YFA0205003]; Deutsche Forschungsgemeinschaft [Sonderforschungsbereich 677]SCI(E)ARTICLE3911769-117735