Metallic nanowire breakthrough from Tokyo

In recent years a great deal of research has gone into creating revolutionary nanomaterials capable of self-assembling into a wide range of dimensional structures at an atomic level.

Transition metal chalcogenide (TMC) nanofibers are structures consisting of transition metal atoms such as tungsten, compounded by an element from the oxygen family on the periodic table (like sulfur or tellurium), called chalcogenides.

They are known for their unique electrical and optical properties, attracting significant interest in recent years for their potential use in a variety of advanced technological applications such as electronics, optoelectronics, energy conversion, and storage.

This class of structures consisting of latticed bundles of TMC nanofibers held together by metallic atoms has garnered particular interest in the field of new materials. Depending on the metals used, TMC structures could be engineered into flexible superconductors for use as wiring in nanocircuitry that allows electronic devices to be made smarter, lighter, and faster with less material.

The metallic nature of TMC nanowires originates from robust hybridization, where the metal atoms form lattices as the backbone of the nanowire and are capped by chalcogen atoms at the edges.

TMCs are emerging candidates in green energy applications due to their stability and unique physical and chemical properties. Uses are being researched for lithium-ion batteries, solar cells, hydrogen production, and wastewater treatment by photocatalytic means.

From theory to practice

Fabrication of TMC nanowires started in the 1990s, but results were difficult to create in sufficient lengths for proper study or utilization.

This year a team of researchers from Tokyo Metropolitan University has successfully produced exceptionally long bundles of tungsten telluride nanofibers. These are then treated with vaporized indium under vacuum at 500 degrees Celsius (932 degrees Fahrenheit) in order to interlace the threads with atom-thin rows of the soft metal. The indium forms a bridging row that binds the fibers together, creating a unique nanostructure ideal for application as flexible nanowires.

Indium is a silvery-white metal often used as an integral part of touchscreens, flatscreen TVs, and solar photovoltaic panels, as it is highly conductive and bonds well with glass. Indium nitride, phosphide and antimonide are semiconductors used in transistors and microchips. Tellurium is a brittle semiconductor used in certain electrical devices and specialized alloys.

Having successfully produced large amounts of these threaded TMC bundles, the team, led by Assistant Professor Yusuke Nakanishi and Associate Professor Yasumitsu Miyata, have finally produced significant material results matching computer simulations, proving conclusively that individual bundles with well-ordered atomic structures can be fabricated to behave like conductive metal.

These results demonstrate the potential for strong, flexible nanoelectronics with numerous tailored properties not limited by shape or elemental composition, which can be fine-tuned during fabrication by alloying either the chalcogen or the transition-metal elements.

The expanding potential of numerous atomic layers and precisely tuned electronic functions presents a powerful material platform for creating novel, low-power, high-performance devices that are closer than ever to becoming a reality.