Research Bits: October 17

High-entropy multielement ink semiconductors; stretchable miniature antennas; silicon photonics for quantum simulators.


High-entropy multielement ink semiconductors

Researchers from Lawrence Berkeley National Laboratory and UC Berkeley developed a high-entropy semiconducting material called ‘multielement ink’ that can be processed at low-temperature or room temperature.

“The traditional way of making semiconductor devices is energy-intensive and one of the major sources of carbon emissions,” said Peidong Yang, a faculty senior scientist in Berkeley Lab’s Materials Sciences Division and professor of chemistry and materials science and engineering at UC Berkeley. “Our new method of making semiconductors could pave the way for a more sustainable semiconductor industry.”

The method makes use of two unique families of semiconducting materials: hard alloys made of high-entropy semiconductors, which are made of five or more different chemical elements that self-assemble in near-equal proportions into a single system, and a soft, flexible material made of crystalline halide perovskites.

While conventional high-entropy alloy materials require far less energy than silicon to process for manufacturing, they still require temperatures of over 1,000 degrees C (over 1,832 degrees F).

However, the ionic bonding nature of halide perovskites enables them to be processed from solution at lower temperatures. The team was able to synthesize high-entropy halide persovskite single crystals within hours of mixing a solution and precipitating under room temperature or low-temperature conditions (80 degrees C or 176 degrees F). The resulting octahedral and cuboctahedral crystals are high-entropy halide perovskite single crystals: one set made of five elements (SnTeReIrPt or ZrSnTeHfPt), and another set made of six elements (SnTeReOsIrPt or ZrSnTeHfRePt). The crystals are approximately 30 – 100 micrometers in diameter.

“Intuitively, making these semiconductors is like stacking octahedral-shaped molecular ‘LEGOs’ into larger octahedral single crystals,” said Yang. “Imagining each of these individual molecular LEGOs will emit at different wavelengths, one can in principle design a semiconductor material that would emit an arbitrary color by selecting different molecular octahedral LEGOs.”

Yang said that the multielement ink has a number of potential applications, particularly as a color-tunable LED or other solid-state lighting device, or as a thermoelectric for waste heat recovery. In addition, the material could potentially serve as a programmable component in an optical computing device that uses light to transfer or store data.

Folgueras, M.C., Jiang, Y., Jin, J. et al. High-entropy halide perovskite single crystals stabilized by mild chemistry. Nature 621, 282–288 (2023).

Stretchable miniature antennas

Researchers from Xi’an Jiaotong University created tiny stretchable antennas from a hydrogel and liquid metal that could be used in wearable and flexible wireless electronic devices to provide a link between the device and external systems.

“Using our new fabrication approach, we demonstrated that the length of a liquid metal antenna can be cut in half,” said Tao Chen from Xi’an Jiaotong University in China. “This may help downsize wearable devices used for health monitoring, human activity monitoring, wearable computing and other applications, making them more compact and comfortable.”

The technique involves injecting eutectic gallium-indium, a metal alloy that is a liquid at room temperature, into a microchannel created with a single-step femtosecond-laser ablation process. They used this method to create an antenna measuring 24 mm x 0.6 mm x 0.2 mm embedded into a 70 mm x 12 mm x 7 mm hydrogel slab.

To demonstrate the new fabrication approach, the researchers prepared stretchable dipole antennas and measured their reflection coefficients at different frequencies. These experiments showed that the pure hydrogel reflects almost all the incident electromagnetic wave energy, while the liquid metal dipole antenna embedded in hydrogel radiates most of the incident electromagnetic wave effectively into free space, with less than 10% reflected at the resonance frequency. They also showed that by varying the applied strain from 0 to 48%, the resonant frequency of the antenna can be tuned from 770.3 MHz to 927.0 MHz.

“Stretchable and flexible antennas could be useful for wearable medical devices that monitor temperature, blood pressure and blood oxygen, for example,” said Chen. “Separate mobile devices could connect to a larger control unit via the flexible antennas — which would transfer data and other communications — forming a wireless body-area network. Since the resonance frequencies of the flexible antennas vary with applied strain, they could potentially also be used as a wearable motion sensor.”

The researchers are working to improve the sealing technique used on the laser-induced microchannels to increase the strength of the flexible stretchable antenna and the threshold strain of liquid metal leaking. They also plan to explore how the approach could be applied for developing fully flexible multidimensional strain and pressure sensors with complicated 2D or 3D structures.

P. Zhao, T. Chen, J. Si, H. Shi, X. Hou, “Fabrication of flexible stretchable hydrogel-based antenna using femtosecond laser for miniaturization,” Opt. Express, 31, 20, 32704-32716 (2023).

Silicon photonics for quantum simulators

Researchers from the University of Washington developed a silicon photonic chip that could act as the foundation for building a quantum simulator.

“The fabrication process that we have for this chip can directly latch onto the already well-matured silicon fabrication that we do for transistors and other computer chips,” said Abhi Saxena of the National Institute of Standards and Technology. “Whereas for other quantum simulator platforms that’s not feasible, even though many of them have already demonstrated prototypical devices.”

The chip uses a photonic coupled cavity array, a pseudo-atomic lattice made up of eight photonic resonators, where photons can be confined, raised and lowered in energy, and moved around in a controlled manner, essentially forming circuits. The team also created a mathematical algorithm that allowed them to characterize the chip in detail, using only information available on the boundaries of the chip, and designed a new kind of architecture for heating and independently controlling each cavity in the array, which let the team program the device.

“We are demonstrating everything on a chip, and we have shown scalability, measurability and programmability — solving three of the four major obstacles to using a silicon photonic chip as a platform for a quantum simulator,” said Arka Majumdar, an ECE and physics associate professor at UW. “Our solution is a small size, it is not misalignment-prone, and we can program it.”

The team is currently exploring ways to create nonlinearity and optimize it for standard chip foundries.

Saxena, A., Manna, A., Trivedi, R. et al. Realizing tight-binding Hamiltonians using site-controlled coupled cavity arrays. Nat Commun 14, 5260 (2023).

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