The joint research findings by KU, DGIST and SNU published in Nano Letters
The correlational effects of the tilt configuration of single molecules (1 nm) and the intermolecular van der Waals interaction on the charge transport in the molecular junction were investigated.

▲ from left, Prof. Gunuk Wang from KU-KIST Graduate School of Converging Science and Technology, Yun Hee Jang from the Department of Energy Science and Engineering of DGIST, first author Jaeho Shin from Korea University

The research team, led by Prof. Gunuk Wang from KU-KIST Graduate School of Converging Science and Technology, used conductive atomic force microscopy and found that charge transport could be controlled by molecular-tilt configuration and intermolecular interactions. They worked with Yun Hee Jang from the Department of Energy Science and Engineering of DGIST, Chul-Ho Lee from KU-KIST Graduate School of Converging Science and Technology, and Takhee Lee from Seoul National University (SNU).

Performed with financial support from the National Research Foundation of Korea, the KU-KIST research fund, and the Korea University Future Research Grant, the findings of the research were published in Nano Letters (impact factor: 12.712) on June 15.

※ Title: Correlational Effects of the Molecular-Tilt Configuration and the Intermolecular van der Waals Interaction on the Charge Transport in the Molecular Junction
※ Author Information: Seven in total, namely Jaeho Shin (Korea University, first author), Gunuk Wang (Korea University, corresponding author), Yun Hee Jang (DGIST, corresponding author), Kyungyeol Gu (DGIST), Seunghoon Yang (Korea University), Chul-Ho Lee (Korea University), and Takhee Lee (Seoul National University)

In the field of molecular electronics, this research is recognized for investigating the correlational effects of the molecular-tilt configuration and the intermolecular van der Waals interaction on charge transport in molecular junctions.

The team used conductive atomic force microscopy, which can measure the electric properties of very tiny spaces, and effectively lowered the molecular tunneling barriers that electrons experience when passing through insulators using the molecular-tilt configuration. This was confirmed by the results which showed that the transition voltage from direct tunneling was lowered within a certain voltage range. Then, the team confirmed stronger interfacial coupling between graphene and molecules at higher tilt angles. This implies that asymmetry coupling can transform into a symmetrical structure depending on the tilt angles. In addition, they successfully observed that the repulsive van der Waals forces increased as the intermolecular distances decreased, and that this played a role in limiting the molecular-tilt angles, while the angles changed in tandem with the pressure of the probe tip.

[Terminology]

1. Molecular electronics
◯ First proposed as a theory in 1974, the field of molecular electronics has significantly advanced as a technique to utilize single molecules (1-2 nm) or molecular monolayers as low-cost, very-large-scale-integrated electronic components to replace or complement semiconductor materials. Various functional single molecules are manufactured or studied to function as diodes, memories or transistors. However, the fundamental mechanism of interactive charge transport between layers of single molecules and other molecules needs to be identified.

2. Graphene
◯ Graphene, known to have very high physical and chemical stability, is 0.2 nm thick and used for pencil lead. It can conduct 100 times more electricity than copper, and electrons can travel over 100 times faster in graphene than in silicon. Graphene is 200 times stronger than steel, and its thermal conductivity is more than two fold that of diamond. Furthermore, it is highly flexible, and is transparent since most light penetrates through it.

3. Van der Waals force
◯ Van der Waals forces are distance-dependent interactions that exist between atoms or molecules Unlike ionic or covalent bonds, these interactions are not induced by unequal sharing of electrons. At closer distances they are repulsive in nature but as the distance increases they become attractive.

4. Atomic force microscopy (AFM)
◯ AFM is a technique that forms an image by measuring the optical force between the probe tip and a sample surface.

[Figure Description]

[Figure 1] (a) Schematic diagram of a molecular junction using a conductive atomic force microscopy technique and molecular structures with various tip-loading forces

[Figure 2] Experimental results showing electrical characteristics of molecules (b) Representative current−voltage (I−V) characteristics according to different tip-loading values (c) Tunneling barrier heights by tip-loading force