Raman microscopy is a useful technique for imaging biological samples because it can provide chemical information about specific molecules — such as proteins — that take part in the body’s processes. However, the Raman light that comes from biological samples is very weak, so the signal can often get swamped by the background noise, leading to poor images.

The researchers have developed a microscope that can maintain the temperature of previously frozen samples during the acquisition. This has allowed them to produce images that are up to eight times brighter than those previously achieved with Raman microscopy.

“One of the main reasons for blurry images is the motion of the things you’re trying to look at,” explains lead author of the study, Kenta Mizushima. “By imaging frozen samples that were unable to move, we could use longer exposure times without damaging the samples. This led to high signals compared with the background, high resolution, and larger fields of view.” The technique uses no stains and doesn’t require any chemicals to fix the cells in position, so can provide a highly representative view of processes and cell behavior.

The team was also able to confirm that the freezing process conserved the physicochemical states of different proteins. This gives the cryofixing approach a distinct advantage of achieving what the chemical fixing methods cannot.

“Raman microscopy adds a complementary option to the imaging toolbox,” says senior author Katsumasa Fujita. “The fact that it not only provides cell images, but also information about the distribution and particular chemical states of molecules, is very useful when we are continually striving to achieve the most detailed possible understanding.”

The new technique can be combined with other microscopy techniques for detailed analysis of biological samples and is expected to contribute to a wide range of areas in the biological sciences including medicine and pharmaceutics.

Conducted under the supervision of Prof. KWOK Hoi-Sing, Founding Director of the State Key Laboratory of Advanced Displays and Optoelectronics Technologies at HKUST, the study was a collaborative effort with the Southern University of Science and Technology, and the Suzhou Institute of Nanotechnology of the Chinese Academy of Sciences.

A lithography machine is crucial equipment for semiconductor manufacturing, applying short-wavelength ultraviolet light to make integrated circuit chips with various layouts. However, traditional mercury lamps and deep ultraviolet LED light sources have shortcomings such as large device size, low resolution, high energy consumption, low light efficiency, and insufficient optical power density.

To overcome these challenges, the research team built a maskless lithography prototype platform and used it to fabricate the first microLED device by using deep UV microLED with maskless exposure, improving optical extraction efficiency, heat distribution performance, and epitaxial stress relief during the production process.

Prof. KWOK highlighted, “The team achieved key breakthroughs for the first microLED device including high power, high light efficiency, high-resolution pattern display, improved screen performance and fast exposure ability. This deep-UV microLED display chip integrates the ultraviolet light source with the pattern on the mask. It provides sufficient irradiation dose for photoresist exposure in a short time, creating a new path for semiconductor manufacturing.”

“In recent years, the low-cost and high-precision maskless lithography technology of traditional lithography machines has become an R&D hotspot because of its ability to adjust the exposure pattern, provide more diverse customization options, and save the cost of preparing lithography masks. Photoresist-sensitive short-wavelength microLED technology is therefore critical to the independent development of semiconductor equipment,” Prof. KWOK explained.

“Compared with other representative works, our innovation features smaller device size, lower driving voltage, higher external quantum efficiency, higher optical power density, larger array size, and higher display resolution. These key performance enhancements make the study a global leader in all metrics,” Dr. FENG Feng, postdoctoral research fellow at HKUST’s Department of Electronic and Computer Engineering (ECE), concluded.

Their paper, titled “High-Power AlGaN Deep-Ultraviolet Micro-Light-Emitting Diode Displays for Maskless Photolithography,” has been published in the top journal Nature Photonics. It has since earned wide recognition in the industry and was named by the 10th International Forum on Wide Bandgap Semiconductors (IFWS) as one of the top ten advances in China’s third-generation semiconductor technology in 2024.

Looking forward, the team plans to continue enhancing the performance of AlGaN deep ultraviolet microLEDs, improve the prototype, and develop 2k to 8k high-resolution deep ultraviolet microLED display screens.

Dr. FENG is the first author, while Prof. LIU Zhaojun, Adjunct Associate Professor of HKUST’s ECE Department, who concurrently serves as an Associate Professor at Southern University of Science and Technology, is the corresponding author. Team members also include ECE postdoctoral research fellow Dr. LIU Yibo, PhD graduate Dr. ZHANG Ke, and collaborators from other institutions.

Currently, radar systems for automotive and aerospace applications require resolution-enhancement technologies to improve object recognition precision. Achieving this typically involves increasing bandwidth or utilizing ultra-high-resolution algorithms with significant complexity. However, it results in higher costs and increased system complexity.

The research team discovered that additional information embedded in the envelope of radar signals could be used. On that basis, they developed a new algorithm that analyzes the contour features of received signals. This innovative technology improves target differentiation without bandwidth expansion, achieving nearly double the resolution through signal processing on existing radar hardware. In addition, it enables the precise identification of objects both inside and outside the vehicle.

Dr. Bongseok Kim of the DGIST Automotive Technology Division stated, “I am delighted that our work has been published in the IEEE Sensors Journal … We will continue to enhance this technology through follow-up research to enable its practical application in autonomous vehicles and industrial environments.”

Meanwhile, this research was conducted with the support of DGIST’s general project (D-PIC 4.0) and the National Research Foundation of Korea’s Basic Research Support Program. The research results (first author: Dr. Bongseok Kim, DGIST; corresponding author:Dr. Sangdong Kim, DGIST) were published in the IEEE Sensors Journal in December.

The research team designed the electrodes using a nickel-based carbonate and hydroxide composite material and maximized the conductivity and stability of the electrodes by adding transition metal ions such as Mn, Co, Cu, Fe, and Zn. This technology has greatly improved the performance of energy storage devices, demonstrating significant advancements in energy density, power density, and charge and discharge stability.

Particularly, the energy density achieved in this study is 35.5 Wh kg⁻¹, which is significantly higher than the energy storage per unit weight in previous studies (5-20 Wh kg⁻¹). The power density is 2555.6 W kg⁻¹, significantly exceeding the values from previous studies (- 1000 W kg⁻¹), demonstrating the ability to release higher power rapidly, enabling immediate energy supply even for high-power devices. Additionally, the performance showed minimal degradation during repeated charge and discharge cycles, confirming the long-term usability of the device.

Furthermore, the research team developed an energy storage device that combines silicon solar cells with supercapacitors, creating a system capable of storing solar energy and utilizing it in real time. This system achieved an energy storage efficiency of 63% and an overall efficiency of 5.17%, effectively validating the potential for commercializing the self-charging energy storage device.

Jeongmin Kim, Senior Researcher at the Nanotechnology Division of DGIST, states, “This study is a significant achievement, as it marks the development of Korea’s first self-charging energy storage device combining supercapacitors with solar cells. By utilizing transition metal-based composite materials, we have overcome the limitations of energy storage devices and presented a sustainable energy solution.” Damin Lee, a researcher at the RLRC of Kyungpook National University, stated, “We will continue to conduct follow-up research to further improve the efficiency of the self-charging device and enhance its potential for commercialization.”

This research was conducted with support from DGIST’s Institutional Core Projects, the Early Career Researcher Projects, and the Kyungpook National University’s Regional Leading Research Center for Carbon-Neutral Intelligent Energy System. The research findings were published in the journal Energy in December.

Conventional solid polymer electrolyte batteries perform poorly due to structural limitations which hinder an optimal electrode contact. This could not eliminate the issue of “dendrites” either, where lithium grows in tree-like structures during repeated charging and discharging cycles. Dendrites are a critical issue, as an irregular lithium growth can disrupt battery connections, potentially causing fires and explosions.

The research team, therefore, developed a triple-layer structure for the electrolyte to address such issues. Each layer serves a distinct function, significantly enhancing the battery’s safety and efficiency. This electrolyte incorporates “decabromodiphenyl ethane (DBDPE)” to prevent fires, “zeolite” to enhance the electrolyte’s strength, and a high concentration of a lithium salt, “lithium bis (trifluoromethanesulfonyl) imide) (LiTFSI),” to facilitate a rapid movement of lithium ions.

The triple-layer solid electrolyte features a robust middle layer that boosts the battery’s mechanical strength, while its soft outer surface ensures an excellent electrode contact, facilitating an easy movement of lithium ions. This enables a faster movement of lithium ions, enhancing energy transfer rates and preventing dendrite formation effectively.

The experiment showed that the battery developed by the research team retained about 87.9% of its performance after 1,000 charging and discharging cycles, demonstrating a notable improvement in durability compared with traditional batteries, which typically maintain 70-80% of their performance. It can also extinguish itself in a fire, thus significantly reducing the fire risk. This battery is expected to be applicable across various sectors, ranging from small devices like smartphones and wearables to electric vehicles and large-scale energy storage systems.

Dr. Kim stated, “This research is anticipated to make a significant contribution to the commercialization of lithium metal batteries using [solid polymer] electrolytes, while providing enhanced stability and efficiency [to] energy storage devices.”

This study was supported by the Future Materials Discovery Project (led by Professor Lee Jung-ho of Hanyang University) and the Mid-Career Researcher Program (led by Dr. Kim Jae-hyun) of the National Research Foundation of Korea. The findings were published as the cover article in an international academic journal, Small, published by Wiley.