Junções moleculares: O impacto dos eletrodos e dos grupos ancoradores nas propriedades estruturais, eletrônicas e de transporte
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2019-03-26
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Universidade Federal de Goiás
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In this Thesis we performed atomistic first-principles calculations aiming to investigate the structural,
electronic, and transport properties of single-molecule junctions formed by electrodes of gold (Au), silver
(Ag), or copper (Cu), and 1,4-benzenediamine or 1,4- benzeneaminethiol (only to gold electrodes)
molecules. Such molecules were studied under two conditions: (i) with the hydrogen atoms linked to the
anchoring groups (BDAH 4 and BATH 3 ), and (ii) without the hydrogen atoms linked in the anchoring
groups (BDA and BAT). This work shows that intensity of the interaction of the molecule BDAH 4 with the
electrodes of Au, Ag, and Cu follows the trend: Cu > Au > Ag. For the electronic transport properties, it is
observed that the transmittance, at the Fermi level, of the junctions containing the molecule BDAH 4 occur
due to the HOMO of this molecule and, in addition, the transmission coefficients follow the order: T(E F ) Au
= 2,54 × 10 −2 > T (E F ) Cu = 1,97 × 10 −2 > T(E F ) Ag = 1,96 × 10 −2 , which is in good agreement with the work
function of the metallic electrodes. For the junctions with the molecule BDA, the same tendency, for the
intensity of the interaction, that the junctions containing the molecule BDAH 4 is obtained (Cu > Au > Ag).
On the other hand, a significant increasing in the intensity of the interaction with the Au, Ag, and Cu
electrodes, can also be seen, with respect to the junctions containing the molecule BDAH 4 . In addition,
there is an increasing in the mechanical stretching of these junctions. The length of the elongations is in
agreement with the reorganization capacity of the atoms that compose the electrodes. On the absence of the
hydrogen atoms in the anchoring groups, the molecule BDA becomes spin-dependent, and when it is
coupled to the metallic electrodes this spin-dependence vary with mechanical stretching of the junctions.
Thus, the spin-resolved transmittances of these junctions are dependent upon the stretching of the junction.
It is also verified that the Au/BATH 3 /Au junction exhibit mechanical and electronic transport properties
similar to the Au/BDAH 4 /Au junction, since the rupture of the junction occurred between an atom of the tip
and the nitrogen atom. However, for the Au/BAT/Au junction the rupture occurs between the atom of the
tip of the electrode and the sulfur atom. It was verified that this occurs due to the intensity of the interaction
between the electrode atoms and sulfur (1,09 eV) to be smaller than the interaction of the nitrogen (1,28
eV). Finally, by analyzing the DFT-NEGF calculated I × V curves, for the junctions Au, Ag,
Cu/BDAH 4 ,BDA/Cu, Ag, Au and Au/BATH 3 ,BAT/Au, we verified an ohmic behavior, with a weak
rectification performance.
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SILVA, C. E. Junções moleculares: o impacto dos eletrodos e dos grupos ancoradores nas propriedades estruturais, eletrônicas e de transporte. 2019. 170 f. Tese (Doutorado em Fisica) - Universidade Federal de Goiás, Goiânia, 2019.