TY - JOUR
T1 - Combined Impact of Denticity and Orientation on Molecular-Scale Charge Transport
AU - Yasini, Parisa
AU - Shepard, Stuart
AU - Albrecht, Tim
AU - Smeu, Manuel
AU - Borguet, Eric
N1 - Funding Information:
This work was supported by funding from National Science Foundation (CHE-1508567). S.S. and M.S. were supported by funding from Binghamton University. NEGF-DFT calculations were performed on the Spiedie HPC cluster at Binghamton University and the Extreme Science and Engineering Discovery Environment (XSEDE, supported by NSF Grant ACI-1053575). T.A. would like to thank the EPSRC (EP/N032977) for support.
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/4/30
Y1 - 2020/4/30
N2 - Reducing the dimensions of electronic devices to the nanoscale is an important objective with significant scientific and technical challenges. In molecule-based approaches, the orientation of the molecule and coordination to electrodes (denticity) can dramatically affect the electrical properties of the junction. Typically, higher conductance is associated with shorter transport distances and stronger molecule-electrode coupling; however, this is not always the case, as highlighted in this study. We focused on 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) molecules and have used the scanning tunneling microscopy break junction (STM-BJ) method to measure the electrical conductance of single molecules bridged between gold electrodes with different molecular orientations and with varying denticities. In conjunction with the experiments, density functional theory (DFT) and nonequilibrium Green's function (NEGF) calculations were performed to determine the conductance of four distinct molecular configurations. The calculated conductances show how different configurations and denticities influence the molecular orbital offsets with respect to the Fermi level and provide assignments for the experimental results. Surprisingly, lower denticity results in higher conductance, with the highest predicted molecular conductance being 0.6 G0, which is explained by the influence of molecule-electrode coupling on the energy of molecular orbitals relative to the Fermi level. These results highlight the importance of molecular geometry and binding configuration of the molecule to the electrode. Consequently, our findings have profound ramifications for applications in which orbital alignment is critical to the efficiency of charge transport, such as in dye sensitized solar cells, molecular switches, and sensors.
AB - Reducing the dimensions of electronic devices to the nanoscale is an important objective with significant scientific and technical challenges. In molecule-based approaches, the orientation of the molecule and coordination to electrodes (denticity) can dramatically affect the electrical properties of the junction. Typically, higher conductance is associated with shorter transport distances and stronger molecule-electrode coupling; however, this is not always the case, as highlighted in this study. We focused on 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) molecules and have used the scanning tunneling microscopy break junction (STM-BJ) method to measure the electrical conductance of single molecules bridged between gold electrodes with different molecular orientations and with varying denticities. In conjunction with the experiments, density functional theory (DFT) and nonequilibrium Green's function (NEGF) calculations were performed to determine the conductance of four distinct molecular configurations. The calculated conductances show how different configurations and denticities influence the molecular orbital offsets with respect to the Fermi level and provide assignments for the experimental results. Surprisingly, lower denticity results in higher conductance, with the highest predicted molecular conductance being 0.6 G0, which is explained by the influence of molecule-electrode coupling on the energy of molecular orbitals relative to the Fermi level. These results highlight the importance of molecular geometry and binding configuration of the molecule to the electrode. Consequently, our findings have profound ramifications for applications in which orbital alignment is critical to the efficiency of charge transport, such as in dye sensitized solar cells, molecular switches, and sensors.
UR - http://www.scopus.com/inward/record.url?scp=85084078013&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.9b10566
DO - 10.1021/acs.jpcc.9b10566
M3 - Article
AN - SCOPUS:85084078013
SN - 1932-7447
VL - 124
SP - 9460
EP - 9469
JO - The Journal of physical chemistry C
JF - The Journal of physical chemistry C
IS - 17
ER -