Designing the next generation of electronics using neutron science
An international team are using neutron science to help develop the next generation of electronic devices. The researchers from the Institut Laue Langevin (ILL) and other institutions are experimenting with the design of semiconductors, which form an essential component of modern computer chips. They hope their studies could herald the future of electronics through the use of organic materials and bespoke designs.
“We’re on the brink of a revolution in the chemical design of organic semiconductors because of advances in computational chemistry and artificial intelligence,” explains Dr. Anne Guilbert from Imperial College London, who contributed to the studies.
Semiconductors are vital to microchips thanks to their ability to carry different amounts of electrical current depending on heat and light, or impurities introduced into their crystalline structure. Their inclusion in electronic devices, such as transistors, has led to the development of technologies as critical to modern life as TVs, smartphones, light-emitting diodes (LEDs) and solar cells.
Most semiconductors are made of inorganic materials, such as silicon in silicon microchips. However, organic semiconductors, which contain carbon, are now gaining in popularity due to their flexibility, stretchability, low toxicity and ease of production. As a result, a multinational group of researchers, including Dr. Mohamed Zbiri from ILL, wanted to better understand why two similar organic semiconductors might carry electricity differently – with the aim of creating more efficient and bespoke designs.
“The ultimate goal of this work was to understand why (two) molecules with very similar chemical structure would feature a marked difference in conducting electricity,” explains Professor Emanuele Orgiu from the University of Strasbourg and Institut National de la Recherche Scientifique in Québec, who led the study.
According to Dr. Guilbert, electronic conductivity occurs as a result of electrons ‘hopping’ between molecules. The amount of hopping depends on the distance between the molecules and their orientation. In a crystal, such as a semiconductor, the distance and orientation are fixed, and differences between electronic conductivity are instead due to molecular vibrations. These vibrations are due to long-distance interactions between molecules and vary depending on the chemistry of the material.
“On a very short timescale, [molecular vibrations] impact the distance and relative orientation of molecules, sometimes promoting and often inhibiting hopping,” says Dr. Guilbert. Depending on the arrangement of the crystals, vibrating may be easier in one direction than the other.
Dr. Zbiri and Dr. Guilbert used inelastic neutron scattering (INS) to examine how the atoms and molecules interacted in two organic semiconductors with similar crystal structures, but different chemistry. According to Dr. Zbiri, the length and time scales associated with neutron scattering match perfectly with the processes at atomic and molecular scales. “We can basically ‘see’ all the vibrational features and map them out entirely,” he explains. Subsequently, Dr. Guilbert used computer simulations and models to identify which vibrations might affect electronic conductivity.
Using INS, the team were able to separate the effects of lattice vibrations (within the crystal) from long-distance molecular vibrations. Moreover, they were able to understand how small differences in the chemistry of the two materials directly impacted their ability to conduct electricity, by ‘locking’ vibrations in one direction compared to another.
According to Dr. Guilbert, the results show that combining crystal design with an understanding of the internal molecular chemistry of semiconductors can be a powerful way to improve their design.
The researchers are now experimenting with tailoring the chemistry of organic semiconductors to new applications, such as biosensors. In a recent study, the team used INS to study a bespoke semiconductor that combined biological (ionic) signalling with electronic conductivity.
“We identified structural changes impacting the dynamics of the part of the molecules responsible for ionic conductivity without impacting the other molecular part responsible for electronic conductivity,” says Dr. Guilbert. The team now plan to continue this work and create design rules that can be used to develop a new generation of bioelectronic devices.
The studies were published in Advanced Materials and Chemical Physics Physical Chemistry.
Analysis of External and Internal Disorder to Understand Band‐Like Transport in n‐Type Organic Semiconductors. Marc-Antoine Stoeckel, Yoann Olivier, Marco Gobbi, Dmytro Dudenko, Vincent Lemaur, Mohamed Zbiri, Anne A Y Guilbert, Gabriele D’Avino, Fabiola Liscio, Andrea Migliori, Luca Ortolani, Nicola Demitri, Xin Jin, Young-Gyun Jeong, Andrea Liscio, Marco-Vittorio Nardi, Luca Pasquali, Luca Razzari, David Beljonne, Paolo Samorì, Emanuele Orgiu
Effect of substituting non-polar chains with polar chains on the structural dynamics of small organic molecule and polymer semiconductors. Anne A. Y. Guilbert, Zachary S. Parr, Theo Kreouzis, Duncan J. Woods, Reiner Sebastian Sprick, Isaac Abrahams, Christian B. Nielsen and Mohamed Zbiri