#heterostructures

Scientists shed light on how the magnetic properties of 2D interlayers can enhance spin accumulation effects in thermoelectric heterostructures.

Spin thermoelectric materials are an area of active research because of their potential applications in thermal energy harvesters. However, the physics underlying the effects of interlayers in these materials on spin transport phenomena are unclear. In a recent study, scientists from Chung-Ang University, Korea, shed light on this topic using a newly developed platform to measure the spin Seebeck effect. Their findings pave the way to large-area thermoelectric materials with enhanced properties.

Thermoelectric materials, which can generate an electric voltage in the presence of a temperature difference, are currently an area of intense research; thermoelectric energy harvesting technology is among our best shots at greatly reducing the use of fossil fuels and helping prevent a worldwide energy crisis. However, there are various types of thermoelectric mechanisms, some of which are less understood despite recent efforts. A recent study from scientists in Korea aims to fill one such gap in knowledge. Read on to understand how!

In a paper published today in “Science Advances,” Jing Shi, a professor of physics and astronomy at the University of California, Riverside, and colleagues at Massachusetts Institute of Technology (MIT), and Arizona State University report they have created a TI film just 25 atoms thick that adheres to an insulating magnetic film, creating a “heterostructure.” This heterostructure makes TI surfaces magnetic at room temperatures and higher, to above 400 Kelvin or more than 720 degrees Fahrenheit.

The surfaces of TI are only a few atoms thick and need little power to conduct electricity. If TI surfaces are made magnetic, current only flows along the edges of the devices, requiring even less energy. Thanks to this so-called quantum anomalous Hall effect, or QAHE, a TI device could be tiny and its batteries long lasting, Shi said.

Engineers love QAHE because it makes devices very robust, that is, hearty enough to stand up against defects or errors, so that a faulty application, for instance, doesn’t crash an entire operating system.

A team of scientists have “velcroed” 2D structures of MoS₂ and graphene using a covalent connection for the first time. The 2D-2D structures were used to build robust field effect transistors with controlled electronic communication, interface chemical nature and interlayer distance.

The most widespread method for the synthesis of 2D-2D heterostructures is the direct growth of materials on top of each other. 2D structures are atomically thin layered materials that can be stacked to build functional heterostructures. In such structures built by atomic deposition, 2D layers are weakly bonded by van der Waals interactions and can be taken apart in some solvents or thermal processes. The lack of control over the interface of the two materials in terms of electronic communication, chemical nature or interlayer distance thus impedes the construction of robust multi-purpose devices.

A team of researchers at Universidad Autónoma de Madrid and IMDEA Nanociencia (Spain) have connected covalently for the first time layers of 2D materials: MoS₂andgraphene. The team has used the tools of synthetic chemistry to “sew” several flakes of MoS₂ to single-layer graphene devices, using a bifunctional molecule with two anchor points. The results, published now in Nature Chemistry, show that the final electronic properties of the heterostructure are dominated by the molecular interface.