Research Bits: August 1

Thinner, tougher heat flux sensors
Researchers from the Department of Physics at the University of Tokyo have designed a heat flux sensor that can measure heat flux — the amount of heat that passes through a material — using a manufacturable, flexible thin film with circuits etched in a way that increases the anomalous Nernst effect (ANE).

ANE turns heat into an electrical signal using magnetic material based on iron and gallium. The researchers chose to use the ANE instead of other magnetic-based heat-sensing effects because ANE requires less material to get a sufficient signal and is more durable than typical Seebeck effect sensors.

Fig 1:  By etching the circuits in a special alternating pattern, undesirable effects are reduced which would otherwise impede the circuits’ ability to produce usable data. Source: University of Tokyo ©2023 Tanaka et al. CC-BY-ND

The heat flux sensors can be printed on a roll with a base layer of a thin sheet of clear, strong and lightweight PET plastic, “with magnetic and electrode materials sputtered onto it in thin and consistent layers. We then etch our desired patterns into the resultant film, similar to how electronic circuits are made,” said Tomoya Higo, the project’s associate professor.

Hirokazu Tanaka, Tomoya Higo, Ryota Uesugi, Kazuto Yamagata, Yosuke Nakanishi, Hironobu Machinaga, Satoru Nakatsuji. “Roll-to-Roll Printing of Anomalous Nernst Thermopile for Direct Sensing of Perpendicular Heat Flux”, Advanced Materials, DOI: 10.1002/adma.202303416

From graphite to graphene
A team researchers from University of Washington, Osaka University, and the National Institute for Materials Science in Japan, discovered that graphite, a bulk, 3D material that has some physical properties similar to its 2D counterpart, graphene, can pick up unusual properties when it is stacked and twisted with graphene. The moiré pattern generated on the surface of graphite surprised the researchers when they saw that “the resulting properties were bleeding across the whole crystal,” said co-lead author Dacen Waters, a UW postdoctoral researcher in physics.

“The entire crystal takes on this 2D state,” said co-lead author Ellis Thompson, a UW doctoral student in physics. “This is a fundamentally new way to affect electron behavior in a bulk material.” The team thinks the twist angle between graphene and a bulk graphite crystal could be used to create 2D-3D hybrids of its sister materials, including tungsten ditelluride and zirconium pentatelluride. In general, the research may inspire re-engineering the properties of conventional bulk materials using a single 2D interface. And with 2D moiré’s use in quantum computing, a 3D version could have more uses to explore.

Waters, D., Thompson, E., Arreguin-Martinez, E. et al. Mixed-dimensional moiré systems of twisted graphitic thin films. Nature (2023). https://doi.org/10.1038/s41586-023-06290-3

4D metamaterials control energy waves
University of Missouri researchers created a synthetic 4D metamaterial that can control mechanical surface waves on the surface of a solid material. These energy waves are fundamental to how vibrations travel along the surface of solid materials. The breakthrough, called topological pumping, may one day be used in quantum mechanics and quantum computing by allowing for the development of higher dimension quantum-mechanical effects.

“Conventional materials are limited to only three dimensions with an X, Y and Z axis,” said Guoliang Huang, the Huber and Helen Croft Chair in Engineering at the University of Missouri in a press release. “But now we are building materials in the synthetic dimension, or 4D, which allows us to manipulate the energy wave path to go exactly where we want it to go as it travels from one corner of a material to another.”

The discovery breakthrough could be used in micro-electromechanical systems (MEMS), civil engineering, and defense. Protecting against the effects of earthquakes, because of their surface waves, is a possible use. “Most of the energy — 90% — from an earthquake happens along the surface of the Earth,” Huang said. “Therefore, by covering a pillow-like structure in this material and placing it on the Earth’s surface underneath a building, and it could potentially help keep the structure from collapsing during an earthquake.”

Shaoyun Wang, Zhou Hu, Qian Wu, Hui Chen, Emil Prodan, Rui Zhu, Guoliang Huang. Smart patterning for topological pumping of elastic surface waves. Science Advances, 2023; 9 (30) DOI: 10.1126/sciadv.adh4310