Heterostructures of two-dimensional materials have unique properties. Amongst them, lateral heterostructures, which could be used to make electronic devices, are difficult to synthesize. To deal with this, researchers used a brand new transmetallation technique to fabricate heterostructures with in-plane heterojunctions using Zn3BHT coordination nanosheet. This easy and powerful method enables the fabrication of ultrathin electronic devices for ultralarge-scale integrated circuits, marking a major step forward for 2D materials research.
Electronically conducting two-dimensional (2D) materials are currently hot topics of research in each physics and chemistry owing to their unique properties which have the potential to open up latest avenues in science and technology. Furthermore, the mixture of various 2D materials, called heterostructures, expands the range of their electrical, photochemical, and magnetic properties. This will result in modern electronic devices not achievable with a single material alone.
Heterostructures could be fabricated in two ways: vertically, with materials stacked on top of one another, or laterally, where materials are stacked side-by-side on the identical plane. Lateral arrangements offer a special advantage, confining charge carriers to a single plane and paving the way in which for exceptional “in-plane” electronic devices. Nonetheless, the development of lateral junctions is difficult.
On this regard, conducting 2D materials made using organic materials, called “coordination nanosheets,” are promising. They could be created by combining metals and ligands, starting from those with metallic properties reminiscent of graphene and semiconducting properties reminiscent of transition metal dichalcogenides to those possessing insulating properties reminiscent of boron nitride. These nanosheets enable a novel method called transmetallation. This enables the synthesis of lateral heterostructures with “heterojunctions,” which can’t be achieved through direct response. Heterojunctions are interfaces between two materials which have distinct electronic properties and subsequently can function electronic devices. Moreover, by utilizing heterojunctions of coordinated nanosheets, latest electronic properties which were difficult to get with conventional 2D materials could be created. Despite these benefits, the research on transmetallation as a way to fabricate heterostructures remains to be limited.
To deal with this information gap, a team of researchers from Japan, led by Professor Hiroshi Nishihara from the Research Institute for Science and Technology at Tokyo University of Science (TUS), Japan, used sequential transmetallation to synthesize lateral heterojunctions of Zn3BHT coordination nanosheets. The team included Dr. Choon Meng Tan, Assistant Professor Naoya Fukui, Assistant Professor Kenji Takada, and Assistant Professor Hiroaki Maeda, also from TUS. The study, a joint research effort by TUS, the University of Cambridge, the National Institute for Materials Science (NIMS), Kyoto Institute of Technology, and the Japan Synchrotron Radiation Research Institute (JASRI), was published within the journal Angewandte Chemie International Edition on January 05, 2024.
The team first fabricated and characterised the Zn3BHT coordination nanosheet. Next, they investigated the transmetallation of Zn3BHT with copper and iron. Prof. Nishihara explains: “Via sequential and spatially limited immersion of the nanosheet into aqueous copper and iron ion solutions under mild conditions, we easily fabricated heterostructures with in-plane heterojunctions of transmetallated iron and copper nanosheets.”
This method is an answer process at room temperature and atmospheric pressure, from the fabrication of coordinated nanosheets to the fabrication of in-plane heterojunctions. This process is totally different from the high-temperature, vacuum, gas-phase processing process that’s utilized in lithography technology for silicon semiconductors. It is an easy and cheap process that doesn’t require large equipment. The challenge is tips on how to create highly crystalline thin movies which can be freed from impurities. If clean rooms and highly purified reagents can be found, commercially viable manufacturing techniques will soon be achieved.
The resulting seamless heterojunction obtained by the researchers demonstrated rectifying behavior common in electronic circuits. Testing the characteristics of the diode revealed the flexibility of the Zn3BHT coordination nanosheet. These characteristics could be modified easily with none special equipment. Furthermore, this material also enables the fabrication of an integrated circuit from only a single coordination sheet, with none patchworking from different materials. Prof. Nishihara highlights the importance of this system: “Ultrathin (nanometer-thick) rectifying elements obtained from our method can be quite useful for the fabrication of ultralarge-scale integrated circuits. Concurrently, the unique physical properties of monoatomic layer movies with in-plane heterojunctions can result in the event of recent elements.”
Moreover, through the use of this transmetallation response, it is feasible to create junctions with various electronic properties, reminiscent of p-n, MIM (metal-insulator-metal) and MIS (metal-insulator-semiconductor) junctions. The power to bond single-layer topological insulators may also enable latest electronic devices reminiscent of electron splitters and multilevel devices which have only been theoretically predicted.
Overall, this study presents an easy yet powerful technique for crafting lateral heterostructures, marking a major step in 2D materials research.
