Molecular Engineering of the Polarity and Interactions of Molecular Electronic Switches

Abstract

We have investigated and learned to control switching of oligo(phenylene ethynylene)s embedded in amide-containing alkanethiol self-assembled monolayers on Au{111}. We demonstrate bias-dependent switching of the oligo(phenylene ethynylene)s as a function of the interaction between the dipole moment of the oligo(phenylene ethynylene)s and the electric field applied between the scanning tunneling microscope tip and the substrate. We are able to invert the polarity of the switches by altering their design-inverting their dipole moments. For appropriately designed switches and matrix molecules, the conductance states are stabilized by intermolecular hydrogen bonding. These results further support the hypothesis that conductance switching in these molecules is due to hybridization changes at the molecule-substrate bonds due to tilting of the switch molecules.

Nanogap Electrodes

“…There are mainly two approaches for wiring molecules between electrodes. One method is to make top-contact junctions, which includes scanning probe microscopy (scanning tunneling microscopy (STM) and conducting atomic force microscopy (AFM)), [11][12][13][14][15][16][17][18][19][20][21][22] cross wire junctions, [23][24][25] mercury drop electrodes [26,27] and thermally deposited metal films. [6] All devices manufactured by this kind of method can be categorized as 'prototype devices', which are very useful for fundamental investigations and have already provided many important results.…”

“…[6] All devices manufactured by this kind of method can be categorized as 'prototype devices', which are very useful for fundamental investigations and have already provided many important results. [4][5][6][7][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] However, these devices are far from practical applications, as we can not imagine a nanometer device carrying a huge scanning probe microscopy (SPM) system or other systems. The other way utilizes nanogap electrodes [28][29][30][31][32] to form metal/molecule/metal devices.…”

Design and control of electron transport properties of single molecules

“…Despite of these recent advances, it remains a great challenge to actively control the electron transport in a molecule and to systematically change its behavior from one type to another since this requires not only precise control of molecular structure, but also accurate activation of different electron tunneling processes. Controlling electron transport at the molecular level has important consequences for many applications, such as molecular electronics (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26), biosensors (27), and solar cells (28,29). For certain molecules, change of electron transport properties could take place due to their specific response to the change of molecular conformation or orientation (19)(20)(21)(22)(23)(24)(25), chemical reactions (26), and tautomerization (18).…”

“…Controlling electron transport at the molecular level has important consequences for many applications, such as molecular electronics (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26), biosensors (27), and solar cells (28,29). For certain molecules, change of electron transport properties could take place due to their specific response to the change of molecular conformation or orientation (19)(20)(21)(22)(23)(24)(25), chemical reactions (26), and tautomerization (18). The latter experiment (18) has attracted considerable attention owning to the facts that the switching process involved does not result in drastic molecular conformation changes as often occurring in mechanical molecular switches induced by cis-trans isomerization of azobenzene (23)(24)(25), making the process potentially more relevant to applications in memory devices.…”

Orbital resolution of molecules covalently attached to a clean semiconductor surface

“…The uniform orientation of all the 'clovers' suggests that their ring planes are tuned and directionally aligned by a lateral electric field. This field is likely to be induced by the non-axisymmetric potential distribution of the sharp STM tip after molecular modification because both lateral and vertical electric fields produced by STM tips are able to significantly change the tilt angle, orientation and location of adsorbed polar molecules [25][26][27] . The sizes of all the adsorbed features in the STM images are larger than our theoretical prediction, which might be ascribed to the limitation of the simulation method 8 because it does not consider the tip effect.…”