Research Bits: September 26

2D waveguides; layered nickelate non-volatile PCM; perovskite p-type transistors.


2D waveguides

Researchers from the University of Chicago found that a sheet of glass crystal just a few atoms thick could trap and carry light efficiently up to a centimeter.

In tests, the researchers found they could use extremely tiny prisms, lenses, and switches to guide the path of the light along a chip.

“We were utterly surprised by how powerful this super-thin crystal is; not only can it hold energy, but deliver it a thousand times further than anyone has seen in similar systems,” said Jiwoong Park, a professor and chair of chemistry at the University of Chicago. “The trapped light also behaved like it is traveling in a 2D space.”

Scientists at the University of Chicago found a glass crystal just a few atoms thick can trap and carry light—and could be used for applications. The material is visible as the thin line in the center of the plastic, held by study co-author Hanyu Hong. (Credit: Jean Lachat / University of Chicago)

The 2D optical waveguides were built using molybdenum disulfide glass crystal that was thinner than the photon itself, such that part of the photon sticks out of the crystal as it travels. This property would make it easier to build intricate devices with the glass crystals, as the light can be easily moved with lenses or prisms, the researchers noted.

The team sees possibilities in using it to build sensors to molecular detection and thin photonic circuits that can be stacked.

Myungjae Lee et al., Wafer-scale δ waveguides for integrated two-dimensional photonics. Science 381, 648-653 (2023)

Layered nickelate for non-volatile phase change memory

Scientists from Tohoku University and University of Tsukuba investigated using a layered nickelate to build non-volatile phase change memory devices.

Layered nickelates are a class of complex oxide materials composed of nickel ions. They exhibit a layered structure, where planes of nickel and oxygen atoms are interspersed with layers containing other elements, often alkaline-earth or rare-earth elements.

The team used a layered nickelate composed of layers of strontium, bismuth, and oxygen atoms in a ‘rock salt’ structural arrangement, interleaved with layers of molecules of strontium, nickel, and oxygen atoms in a perovskite structure. The material exhibited a thermally reentrant crystalline phase change, which occurs when a material undergoes a reversible transition between three crystalline phases upon heating and cooling.

“Basically, the material can switch back and forth between the three phases multiple times as it is heated and cooled,” said Tomoteru Fukumura, a professor in the Department of Chemistry of Tohoku University.

This team said that this enables the reversible switching of electrical resistivity at room temperature, allowing for the development of multi-level non-volatile phase change memory for everyday applications.

Matsumoto, K., Kawasoko, H., Nishibori, E., Fukumura, T., Thermally Reentrant Crystalline Phase Change in Perovskite-Derivative Nickelate Enabling Reversible Switching of Room-Temperature Electrical Resistivity. Adv. Sci. 2023, 2304978.

Perovskite p-type transistors

Researchers from Pohang University of Science and Technology (POSTECH), Chinese Academy of Sciences, and University of Electronic Science and Technology of China developed tin halide perovskite p-type transistors with high hole mobility and reduced defects.

They fabricated the p-type perovskite semiconductor layer using three distinct perovskite cation processes. The resulting transistors showed high hole mobility (70 cm2V-1s-1) and an on/off current ratio (108), which the researchers claim is the highest performance level of p-type perovskite transistors reported to date.

“If the performance of low-temperature process p-type semiconductors improves to be comparable to n-type semiconductors, we can create electronic circuits with faster performance and greatly enhance data processing speeds,” said Yong-Young Noh, a professor in the Department of Chemical Engineering at POSTECH. “I hold hopes for this research to find widespread application in the electrical and electronic engineering arena, harnessing the potential of semiconductors and transistors.”

Zhu, H., Yang, W., Reo, Y. et al. Tin perovskite transistors and complementary circuits based on A-site cation engineering. Nat Electron 6, 650–657 (2023).

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