Team led by Gunuk Wang and Chul-Ho Lee invents “diode with molecular monolayer”

Results published in world-renowned journal Nature Communications

▲ (From left) Jaeho Shin (first author, integrated master’s and doctoral degree program), Seunghoon Yang (integrated master’s and doctoral degree program), Chul-Ho Lee (corresponding author, professor), Gunuk Wang (corresponding author, professor)

A research team led by Professor Gunuk Wang and Professor Chul-Ho Lee of KU-KIST Graduate School of Converging Science and Technology fabricated a molecular diode (< 2nm) based on energy band engineering between organic molecular monolayers and 2D semiconductor materials.

Diodes can be used for various purposes such as switching, signal delivery and rectification. Theoretically proposed by Avriam & Ratner in 1974, molecular electronics relies on monomolecular materials (1–2 nm) to fabricate highly integrated, low cost, and low power electronic materials/devices. Given the new possibilities offered by silicon-based CMOS electronic devices at the monomolecular level (1–2 nm), extensive research has been conducted on molecular electronics to develop next-generation materials and devices.

* Molecular electronic device: An active research field that uses organic molecules as a key component of electronic devices. Involves very small molecules (smaller than a few nanometers, or a few millionths of a meter), supports self-assembly, and suitable for fabricating highly integrated devices at low cost.

Molecular diodes were typically implemented by fabricating specific molecules and adjusting their orbital energy levels to create differences in charge transport according to the direction of applied voltage. With existing methods, it is difficult to obtain a rectification ratio higher than 100. Past research has mainly focus on conceptual demonstrations of limited devices. This study, however, succeeded in implementing a new molecular diode with a rectification ratio as large as 10^4 based on energy band engineering between readily available organic monomolecular materials and 2D semiconductor materials.

* Energy level: Discrete values of energy that can be attributed to particles (electron, proton, neutron, etc.) subject to quantum mechanics.

The study was conducted by a team led by Professor Gunuk Wang (advisor to Jaeho Shin) and Professor Chul-Ho Lee (advisor to Seunghoon Yang) of KU-KIST Graduate School of Converging Science and Technology, with Professor Takhee Lee (Seoul National University) and Professor Tae-Wook Kim (Jeonbuk National University) as co-authors.

* Author information: Jaeho Shin (first author, integrated master’s and doctoral degree program at Korea University), Seunghoon Yang (first author, integrated master’s and doctoral degree program at Korea University), Yeonsik Jang (co-author, integrated master’s and doctoral degree program at Seoul National University), Jung Sun Eo (co-author, integrated master’s and doctoral degree program at Korea University), Tae-Wook Kim (co-author, professor of Jeonbuk National University), Takhee Lee (co-author, professor of Seoul National University), Chul-Ho Lee (corresponding author, professor of Korea University), Gunuk Wang (corresponding author, professor of Korea University)

The results were published in the world-renowned Nature Communications on March 16. The work was funded by the National Research Foundation of Korea (NRF-2019R1A2C2003704, 2017R1A5A1014862 (SRC Program: vdWMRC Center), National Creative Research Laboratory Program (grant no. 2012026372), KU-KIST School Research Fund, Korea TORAY Science Foundation, and Korea University Grant.

* Title of paper: Tunable rectification in a molecular heterojunction with two-dimensional semiconductors

* Nature Communications: Nature Communications is a peer-reviewed open access journal published by Nature Publishing Group since 2010. It covers the natural sciences, including physics, chemistry, earth sciences, medicine, and biology.

Fig. 1. (From left) Schematic of molecular heterojunction comprised of a molecular monolayer and 2D semiconductor materials as viewed under an atomic force microscope. Molecular species used in the experiment (OPT: Oligophenylene thiol & C: Alkanethiol), 2D semiconductor materials (Molybdenum disulfide (MoS2) & Tungsten diselenide (WSe2), and electrical properties of the molecular heterojunction.

Fig. 2. a. Changes in electrical properties with varying layers of 2D semiconductor materials. Increasing the number of MoS2 layers leads to a higher current at negative voltage, resulting in a smaller rectification ratio. b. Changes in electrical properties with increasing molecular length. Increasing the molecular length leads to a greater decrease in current at negative voltage than positive voltage, resulting in a larger rectification ratio. c. Contour plots of estimated rectification ratio as a function of molecular length and barrier height with different numbers of MoS2 layers.