Team develops 1nm thin films inspired by interstitial metal alloys to withstand high voltage
Concept of metal alloy applied to organic monolayers, lowering the possibility of short circuits even under high voltage

The research team led by Professor Yoon Hyo-jae of the Department of Chemistry under the College of Science applied the concept of metal alloys to organic nanomaterials, opening up new possibilities for the development of electronic devices using organic molecules. The study was published in the international journal Nano Letters on April 2.

Semiconductor technology capable of processing astronomical amounts of data at once is essential for supporting the emerging trends of the fourth industrial revolution, such as IoT, artificial intelligence, smart devices, and self-driving cars. Thanks to the efforts of global semiconductor companies over the past few decades, semiconductor process technology has developed to such an extent that it creates units at the tens of nanometer scale.

Molecules, about 1 nm in size, may be the solution to achieving high integration density in semiconductor devices. Extensive studies have been conducted over the past 40 years, but many issues, such as durability and stability, still need addressing before commercialization. When 1nm-thick thin films are formed on electrode surfaces, the resulting structural defects cause the monolayers to deteriorate under high voltage. Consequently, molecular electronics research has been limited to low voltage, with high voltage experiments failing due to the formation of short circuits.

The concept of alloys has been known since ancient times. Alloys are obtained by combining a metal element with other elements, and they exhibit properties different from their constituents. They are usually made to improve on the strength and hardness of pure metals. Today, most metallic materials exist in the form of alloys.

Professor Yoon Hyo-jae’s team examined cases of alloys improving the durability of metallic materials. They aimed to solve the low-voltage operation issue of molecular-scale electronic devices by enhancing the ability of organic monolayers to withstand voltages based on the alloy concept. The principle behind the formation of interstitial alloys is that small atoms fill the voids between large atoms when two metals are combined. This project introduced a similar concept to organic monolayers. The team demonstrated for the first time in the world that interstitially mixed self-assembled monolayers (imSAMs) can be obtained through Repeated Surface Exchange of Molecules (ReSEM), which involves diluting a matrix molecule with a reinforcement molecule. The new approach was enabled by electrochemical and spectroscopic surface analysis, and molecular dynamics simulations performed by Professor Chang Rak-woo’s team at the Department of Chemistry of the University of Seoul.

Molecular electronics has established that pure thin films have high breakdown voltages that may affect the performance of the devices they are integrated into. The team’s study, however, proved that imSAMs have significantly enhanced electrical stability compared to pure SAMs comprised of only matrix molecules. The findings provide new, unprecedented insights into the properties of molecular-scale electronic devices at high voltage.

Supported by the National Research Foundation of Korea (Individual Basic Research Project and Key Research Institute Support Project, Next-Generation Intelligent Semiconductor Technology Development Project) and Korea Institute of Science and Technology Information, the study was published online in Nano Letters, a leading journal in nanoscience published by the American Chemical Society on April 2.
- Authors: Kong Gyu-don (first author, Korea University), Song Hyun-sun (co-first author, Korea University), Yoon Seung-min (co-author, Kwangwoon University), Chang Rak-woo (co-corresponding author, University of Seoul), Yoon Hyo-jae (corresponding author, Korea University)
- Title of paper: Interstitially Mixed Self-Assembled Monolayers Enhance Electrical Stability of Molecular Junctions
- Journal: Nano Letters (Published online on April 2, 2021; https://pubs.acs.org/doi/10.1021/acs.nanolett.1c00406) https://pubs.acs.org/doi/10.1021/acs.nanolett.1c00406)

▲ Overview of research. span>

(A) Schematic illustrating formation of the proposed ReSEM method.

(B) The matrix and reinforcement molecules used in the study.

(C) The structure of imSAM obtained by ReSEM, and the resulting enhanced breakdown voltage compared to that of a pure SAM comprised of only matrix molecules.