Nagoya University-led researchers have created "plumbene", a 2D-honeycomb sheet of lead atoms. Plumbene has the largest spin-orbit interaction of any Group 14 elemental 2D material, potentially making it a robust 2D topological insulator in which the Quantum Spin Hall Effect might occur even above room temperature. As a surprising by-product, the research group also observed a nanoscale palladium-lead bubble structure in the palladium substrate that is reminiscent of a Weaire-Phelan structure (which partitions space into cells of equal volume with the least total surface area of the walls between them, solving the "Kelvin Problem"). The Weaire-Phelan structure was the inspiration for the design of the Beijing National Aquatics Centre ("Water Cube") of the 2008 Olympics in Beijing.
Two-dimensional materials made of Group 14 elements (Fig. 1 (a)), graphene's cousins, have attracted enormous interest in recent years (Fig. 1 (b)) because of their unique potential as useful topological insulators.
In particular, the up-to-now purely theoretical possibility of a lead-based 2D honeycomb material, called plumbene, has generated much attention because it has the largest spin-orbit interaction, due to lead's orbital electron structure and therefore the largest energy band gap (Fig. 2), potentially making it a robust 2D topological insulator in which the Quantum Spin Hall Effect might occur even above room temperature.
Now, Nagoya University-led researchers have created plumbene by annealing an ultrathin lead (Pb) film on palladium Pd(111). The resulting surface material has the signature honeycomb structure of a 2D monolayer, as revealed by scanning tunneling microscopy (Fig.3).
Surprisingly, beneath the plumbene, a palladium-lead (Pd-Pb) alloy thin film forms with a bubble structure (Fig. 4 (a)) reminiscent of a Weaire-Phelan structure (which partitions space into cells of equal volume with the least total surface area of the walls between them, solving the "Kelvin Problem"). The Weaire-Phelan structure was the inspiration for the design of the Beijing National Aquatics Centre ("Water Cube") of the 2008 Olympics in Beijing (Fig. 4 (b)).
Group leader Professor Junji Yuhara jokingly recalls that the case of the Beijing Water Cube and the Weaire-Phelan structure is not the first time that architects and materials scientists have inspired each other. "Architect Buckminster Fuller designed the geodesic sphere for the World Expo 1967 in Montreal, and later the Buckminster Fullerene, C60, was named after him."
According to Professor Yuhara, "Both plumbene and the 'nano water cube' are a beautiful addition to the Nano Nature World. The buildings of the 2020 Tokyo Olympics, the 2024 Paris Olympics, Expo 2020 Dubai, Expo 2023 Buenos Aires, Expo 2025 Osaka, and so on may also be placed in the spotlight again as future new materials," he says.
"The advent of plumbene", remarks Professor Yuhara, "has been long awaited, and comes after the creation of silicene in 2012, germanene in 2014 and stanene in 2015. It will certainly launch a rush for applications."
"Graphene's Latest Cousin: Plumbene Epitaxial Growth on a 'Nano WaterCube'." This paper recently appeared in Advanced Materials and can be accessed at https://doi.org/10.1002/adma.201901017
Junji Yuhara, Bangjie He, Noriaki Matsunami, Masashi Nakatake and Guy Le Lay.
Professor John Wojdylo, john.wojdylo+at+s.phys.nagoya-u.ac.jp
About Nagoya University
Nagoya University has a history of about 150 years, with its roots in a temporary medical school and hospital established in 1871, and was formally instituted as the last Imperial University of Japan in 1939. Although modest in size compared to the largest universities in Japan, Nagoya University has been pursuing excellence since its founding. Six of the 13 Japanese Nobel Prize-winners since 2000 did all or part of their Nobel Prize-winning work at Nagoya University: four in physics - Maskawa and Kobayashi in 2008, and Akasaki and Amano in 2014 - and two in Chemistry - Noyori in 2001 and Shimomura in 2008. In mathematics, Mori did his Fields Medal-winning work at Nagoya University. A number of other important discoveries have been made at Nagoya University, including the Okazaki DNA Fragments by Reiji and Tsuneko Okazaki in the 1960s; and depletion forces by Asakura and Oosawa in 1954.
In addition, Nagoya University currently engages in research and educational programs aimed at helping developing countries in Africa and Asia improve food security, nutrition and environmental conservation. For example, Nagoya University researchers have potentially solved the striga (witchweed) problem, which causes $13 billion damage annually in Africa to food crops like maize and sorghum. Field tests are now underway in Kenya. In Asia, local farmers are being trained by Nagoya University researchers in growing food crops more sustainably. And new rice varieties have been developed at Nagoya University that can feed more people and thereby reduce food scarcity in developing countries. Many other such programs are currently being undertaken by Nagoya University researchers.
Nagoya is Japan's fourth-largest city with 2.2 million residents and third-largest metropolitan area after the Tokyo and Osaka urban areas. Nagoya's surrounding Aichi Prefecture has led Japan in industrial output since 1977. Greater Nagoya produces 51.7% of Japan's total automobile output and 45% of the country's auto parts. This represents 8.2% of global automobile production. The Greater Nagoya Area produces 27% of Japan's manufacturing output (versus 11% in Greater Tokyo and 10.2% in Greater Osaka) and 24% of Japan's exports. The Greater Nagoya area is the hub of Japanese manufacturing industries, producing over 40% of major manufacturing categories such as automobiles, automobile parts, machine tools and aircraft parts. Nagoya Port is Japan's largest in terms of import and export tonnage and in terms of export value. The Greater Nagoya GDP is $US461 billion: as a country it would be 22nd in the world, below Poland and above Belgium (Japanese Cabinet figures, 2015).