TY - JOUR

T1 - Molecular heterojunctions of oligo(phenylene ethynylene)s with linear to cruciform framework

AU - Wei, Zhongming

AU - Hansen, Tim

AU - Santella, Marco

AU - Wang, Xintai

AU - Parker, Christian Richard

AU - Jiang, Xingbin

AU - Li, Tao

AU - Glyvradal, Magni

AU - Jennum, Karsten Stein

AU - Glibstrup, Emil

AU - Bovet, Nicolas Emile

AU - Wang, Xiaowei

AU - Hu, Wenping

AU - Solomon, Gemma C.

AU - Nielsen, Mogens Brøndsted

AU - Qiu, Xiaohui

AU - Bjørnholm, Thomas

AU - Nørgaard, Kasper

AU - Laursen, Bo Wegge

PY - 2015

Y1 - 2015

N2 - Electrical transport properties of molecular junctions are fundamentally affected by the energy alignment between molecular frontier orbitals (highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO)) and Fermi level (or work function) of electrode metals. Dithiafulvene (DTF) is used as substituent group to the oligo(phenylene ethynylene) (OPE) molecular wires and different molecular structures based on OPE3 backbone (with linear to cruciform framework) are achieved, with viable molecular orbitals and HOMO-LUMO energy gaps. OPE3, OPE3-DTF, and OPE3-tetrathiafulvalene (TTF) can form good self-assembled monolayers (SAMs) on Au substrates. Molecular heterojunctions based on these SAMs are investigated using conducting probe-atomic force microscopy with different tips (Ag, Au, and Pt) and Fermi levels. The calibrated conductance values follow the sequence OPE3-TTF > OPE3-DTF > OPE3 irrespective of the tip metal. Rectification properties (or diode behavior) are observed in case of the Ag tip for which the work function is furthest from the HOMO levels of the OPE3s. Quantum chemical calculations of the transmission qualitatively agree with the experimental data and reproduce the substituent effect of DTF. Zero-bias conductance, and symmetric or asymmetric couplings to the electrodes are investigated. The results indicate that improved fidelity of molecular transport measurements may be achieved by systematic studies of homologues series of molecular wires applying several different metal electrodes.

AB - Electrical transport properties of molecular junctions are fundamentally affected by the energy alignment between molecular frontier orbitals (highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO)) and Fermi level (or work function) of electrode metals. Dithiafulvene (DTF) is used as substituent group to the oligo(phenylene ethynylene) (OPE) molecular wires and different molecular structures based on OPE3 backbone (with linear to cruciform framework) are achieved, with viable molecular orbitals and HOMO-LUMO energy gaps. OPE3, OPE3-DTF, and OPE3-tetrathiafulvalene (TTF) can form good self-assembled monolayers (SAMs) on Au substrates. Molecular heterojunctions based on these SAMs are investigated using conducting probe-atomic force microscopy with different tips (Ag, Au, and Pt) and Fermi levels. The calibrated conductance values follow the sequence OPE3-TTF > OPE3-DTF > OPE3 irrespective of the tip metal. Rectification properties (or diode behavior) are observed in case of the Ag tip for which the work function is furthest from the HOMO levels of the OPE3s. Quantum chemical calculations of the transmission qualitatively agree with the experimental data and reproduce the substituent effect of DTF. Zero-bias conductance, and symmetric or asymmetric couplings to the electrodes are investigated. The results indicate that improved fidelity of molecular transport measurements may be achieved by systematic studies of homologues series of molecular wires applying several different metal electrodes.

KW - Atomic force microscopy

KW - Cruciform

KW - Dithiofulvalene

KW - Molecular electronics

KW - Oligo(phenylene ethynylene)

U2 - 10.1002/adfm.201404388

DO - 10.1002/adfm.201404388

M3 - Journal article

VL - 25

SP - 1700

EP - 1708

JO - Advanced Materials for Optics and Electronics

JF - Advanced Materials for Optics and Electronics

SN - 1057-9257

IS - 11

ER -