Research Bits: June 18

Gallium nitride can take the heat; liquid metal logic; ultra-thin lens.


Gallium nitride can take the heat

Researchers from Massachusetts Institute of Technology (MIT), the UAE’s Technology Innovation Institute, Ohio State University, Rice University, and Bangladesh University of Engineering and Technology investigated the performance of ohmic contacts in a gallium nitride (GaN) device at extremely high temperatures, such as those that would be required for devices that could operate on the surface of Venus or in other extreme situations like geothermal energy extraction or jet engine monitoring.

Temperatures of 500 degrees Celsius didn’t cause significant degradation to the gallium nitride material or contacts, which remained structurally intact even when held at that temperature for 48 hours. After that, the material did start to degrade, but the team is working to improve long-term performance.

In a release, John Niroula, an electrical engineering and computer science graduate student at MIT, explained why the team initially used gallium nitride transfer length method structures, which are composed of a series of resistors, in the experiments. “Transistors are the heart of most modern electronics, but we didn’t want to jump straight to making a gallium nitride transistor because so much could go wrong. We first wanted to make sure the material and contacts could survive, and figure out how much they change as you increase the temperature. We’ll design our transistor from these basic material building blocks.” [1]

Liquid metal logic

Researchers from the Hong Kong University of Science and Technology (HKUST) and Xiamen University developed a liquid metal-based electronic logic device that exhibits memory and counting properties and is capable of responding to various stimulus sequences without the need for additional electronic components in a way that mimics the prey-capture mechanism of Venus flytraps.

The liquid metal-based logic module (LLM) is based on the extension/contraction deformation of liquid metal wires in sodium hydroxide solution. Controlling the length of the liquid metal wires based on electrochemical effects regulates cathode output according to the stimuli applied to the anode and gate. The LLM itself can memorize the duration and interval of electrical stimuli, calculate the accumulation of signals from multiple stimuli, and exhibit significant logical functions similar to those of Venus flytraps.

The team used the LLM along with a switch-based sensory hair, and soft electric actuator-based petal to construct an artificial Venus flytrap system, which they said demonstrated potential applications of the LLM for functional circuit integration, filtering, and artificial neural networks. [2]

Ultra-thin lens

Physicists from the University of Amsterdam and Stanford University created a flat lens that is only three atoms, or 0.6 nanometers, thick. Made of concentric rings of tungsten disulphide (WS2), the lens focuses light using diffraction. The size and distance between the rings determines the lens’s focal length. In this case, the team’s device focuses red light 1 mm from the lens.

Quantum effects within WS2 enable the material to efficiently absorb and re-emit light at specific wavelengths. “First, WS2 absorbs light by sending an electron to a higher energy level. Due to the ultra-thin structure of the material, the negatively charged electron and the positively charged ‘hole’ it leaves behind in the atomic lattice stay bound together by the electrostatic attraction between them, forming what is known as an ‘exciton’. These excitons quickly disappear again by the electron and hole merging together and sending out light. This re-emitted light contributes to the lens’s efficiency,” the researchers explain in a statement.

While some of the light passing through the lens makes a bright focal point, most of it passes through unaffected, which is ideal for certain applications, said Jorik van de Groep of the University of Amsterdam, in a statement. “The lens can be used in applications where the view through the lens should not be disturbed, but a small part of the light can be tapped to collect information. This makes it perfect for wearable glasses such as for augmented reality.”

The team next plans to design and test more complex and multifunctional optical coatings whose function can be adjusted electrically. [3]


[1] John Niroula, Qingyun Xie, Nitul S. Rajput, Patrick K. Darmawi-Iskandar, Sheikh Ifatur Rahman, Shisong Luo, Rafid Hassan Palash, Bejoy Sikder, Mengyang Yuan, Pradyot Yadav, Gillian K. Micale, Nadim Chowdhury, Yuji Zhao, Siddharth Rajan, Tomás Palacios. High temperature stability of regrown and alloyed Ohmic contacts to AlGaN/GaN heterostructure up to 500 °C. Appl. Phys. Lett. 13 May 2024; 124 (20): 202103.

[2] Yang, Y., Shen, Y. A liquid metal-based module emulating the intelligent preying logic of flytrap. Nat Commun 15, 3398 (2024).

[3] Ludovica Guarneri, Qitong Li, Thomas Bauer, Jung-Hwan Song, Ashley P. Saunders, Fang Liu, Mark L. Brongersma, and Jorik van de Groep. Temperature-Dependent Excitonic Light Manipulation with Atomically Thin Optical Elements. Nano Letters 2024 24 (21), 6240-6246

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