Controlling Contact Configuration of Carboxylic Acid-Based Molecular Junctions Through Side Group.

In this paper, the contact configuration of single molecular junction is controlled through side group, which is explored by electrochemical jump-to-contact STM break junction. The conductance values of 2-methoxy-1,3-benzenedicarboxylic acid (2-M-1,3-BDC) is around 10 G, which is different from that of 5-methoxy-1,3-benzenedicarboxylic acid (5-M-1,3-BDC) with 10 G. Interestingly, the conductance value of 2-M-1,3-BDC is the same as that of 1,3-benzenedicarboxaldehyde (1,3-BDCA), while single molecular junctions of 5-M-1,3-BDC and 1,3-benzenedicarboxylic acid (1,3-BDC) give out similar conductance value.

Comparative Study of Single Molecular Junctions with -Phthalic Acid and -Phthalic Acid Binding to Different Metal Electrodes.

In this paper, single molecular junctions of -phthalic acid and -phthalic acid with Au electrodes were studied by STM break junction approach. Conductance values of 10 G and 10 G were found for -phthalic acid and -phthalic acid, respectively. The conductance order between -phthalic acid and -phthalic acid with Au is different from that with Cu, which can be contributed to the different coupling between molecules and electrodes; different through-space interaction is proposed for such phenomenon between Cu and Au electrodes.

Low Tunneling Decay of Iodine-Terminated Alkane Single-Molecule Junctions.

One key issue for the development of molecular electronic devices is to understand the electron transport of single-molecule junctions. In this work, we explore the electron transport of iodine-terminated alkane single molecular junctions using the scanning tunneling microscope-based break junction approach. The result shows that the conductance decreases exponentially with the increase of molecular length with a decay constant β = 0.

Conductance Measurement of Pyrazine Molecular Junction with Cu and Ag Electrodes.

We have measured the conductance of pyrazine molecular junction contacting with Cu and Ag electrodes by using an electrochemical jump-to-contact based scanning tunneling microscopy break junction (ECSTM-BJ). While conductance values of 10-2.8 and 10-3.

Comparative Study on Single-Molecule Junctions of Alkane- and Benzene-Based Molecules with Carboxylic Acid/Aldehyde as the Anchoring Groups.

We have measured the alkane and benzene-based molecules with aldehyde and carboxylic acid as anchoring groups by using the electrochemical jump-to-contact scanning tunneling microscopy break junction (ECSTM-BJ) approach. The results show that molecule with benzene backbone has better peak shape and intensity than those with alkane backbone. Typically, high junction formation probability for same anchoring group (aldehyde and carboxylic acid) with benzene backbone is found, which contributes to the stronger attractive interaction between Cu and molecules with benzene backbone.

Single-molecule conductance of dipyridines binding to Ag electrodes measured by electrochemical scanning tunneling microscopy break junction.

We have measured the conductance of three pyridyl-terminated molecules binding to Ag electrodes by using electrochemical jump-to-contact scanning tunneling microscopy break junction approach (ECSTM-BJ). Three molecules, including 4,4'-bipyridine (BPY), 1,2-di(pyridin-4-yl)ethene (BPY-EE), and 1,2-di(pyridin-4-yl)ethane (BPY-EA), contacting with Ag electrodes show three sets of conductance values, which follow the order of BPY > BPY-EE > BPY-EA. These values are smaller than those of molecules with Au electrodes, but larger than those of molecules with Cu electrodes.

Enhancing electron transport in molecular wires by insertion of a ferrocene center.

We have determined the conductance of alkane-linked ferrocene molecules with carboxylic acid anchoring groups using the STM break junction technique, and three sets of conductance values were found, i.e. high conductance (HC), medium conductance (MC) and low conductance (LC) values.

Conductance measurement of pyridyl-based single molecule junctions with Cu and Au contacts.

We studied the conductance of pyridyl-based single molecule junctions with Cu contacts by using an electrochemical jump-to-contact scanning tunneling microscopy break junction (ECSTM-BJ) approach. The single molecule junctions of 4,4'-bipyridine (BPY), 1,2-di(pyridin-4-yl)ethene (BPY-EE) and 1,2-di(pyridin-4-yl)ethane (BPY-EA) bridged with Cu clusters show three sets of conductance values. These values are smaller than the conductance values of single molecule junctions with Au electrodes measured by the traditional scanning tunneling microscopy break junction in acidic or neutral solutions, which can be attributed to the different electronic coupling efficiencies between molecules and electrodes.