Rectification and negative differential resistance via orbital level pinning

Abstract

A donor-acceptor system, 4-thiophenyl-azafulleroid (4TPA-C60), is investigated at the point of HOMO/LUMO resonance and beyond to understand how negative differential resistance (NDR) features may be observed in such systems. Our previous investigation showed that charge transfer between the occupied and unoccupied states at resonance hindered crossing of the HOMO and LUMO levels, thus preventing the formation of an NDR feature. In this work, it is shown that the negative differential resistance feature of 4TPA-C60 can be tailored based on the couplings at the metal/molecule interface. Ab initio calculations show that limited charge extraction from atomically sharp contacts results in a HOMO-LUMO pinning effect which delays the onset of the NDR feature. Subsequent unpinning of the states can only occur when additional charge extraction channels enter the bias window, highlighting an important role which non-frontier states play in charge transport. The proposed charge transfer mechanism is then exploited by introducing a fluorine atom into the C60 cage to tune the energies of the acceptor, and narrow the width of the current peak. These findings not only demonstrate the importance of the metal/molecule interface in the design of molecular electronic architectures but also serve to inform future design of molecular diodes and RTDs.

Unveiling the dual role of chemically synthesized copper doped zinc oxide for resistive switching applications

“…For this region, the most probable cause for the transport could be the non-frontier states, which provide channels and the charge can be transported across the interface of metal/TMO. 41,42 Moreover, the trapped electrons can be swept out from their trapping centres and are stimulated toward the anodic side, colliding with various scattering centres within the ZnO. Finally, the thermionic emission comes into play when the voltage was reduced from −2.20 to 0 V, which is shown in Fig.…”

A Chemically Soldered Polyoxometalate Single‐Molecule Transistor

“…Data is then sliced and processed using the automated algorithms described in the Supporting Information to produce the 2D density maps presented in Figure c,d. The I / V characteristics show a good ohmic behaviour up to relatively high biases (≈0.7 V, see the Supporting Information for linear‐scale plots) with no evident asymmetry or rectification arising from the presence of a molecular orbital with an energy sufficiently close to the Fermi levels of the gold electrodes under the two‐terminal conditions employed. This further confirms off‐resonant tunnelling as the charge‐transport mechanism, and this would also account for the observed relatively low conductance.…”

Why Asymmetric Molecular Coupling to Electrodes Cannot Be at Work in Real Molecular Rectifiers

“…Current rectification (RR ≡ I(V )/|I(−V )| = 1) using single molecule devices, a topic pioneered by Aviram and Ratner, 1 continues to represent a major topic of molecular electronics. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The present work is motivated by a confusion that persists on the physical origin of this phenomenon. It is generated by the fact that electrodes used to fabricate molecular junctions (planar substrate s and more or less sharp tip t) have often shapes different of each other.…”