“Nanodot” controls may tweak light for sharper displays and quantum computing

According to an international team led by researchers at Pennsylvania State University, it is possible that the newly achieved light is precisely controlled from very small sources, several nanometers embedded in two-dimensional (2D) materials, and several nanometers embedded in two-dimensional (2D) materials.

In a recent study published in ACS Photonics, scientists worked together to show how light emitted from a 2D material can be modulated by embedding a second 2D material, like a small island of several nanometers in size. The team described how nanodot confinement was achieved in two dimensions, demonstrating that by controlling the size of the nanodots, the color and frequency of emitted light can be changed.

“If there is an opportunity to provide localized light emissions from these materials associated with quantum technology and electronics, it is very exciting,” said Nasim Alem, an associate professor of materials science and engineering at Pennsylvania State and co-author of the study. “We assume that we’re getting light from the zero dimension point of the field, like a dot in space. Not only that, we can control it. We can control the frequency. We can also control the wavelength.”

The researchers buried nanodots made of 2D material called molybdenum gillenide in another 2D material, tungsten gillenide, and aimed a beam of electrons into the structure to emit light. This technique, called casoductoluminescence, allowed the team to study how individual nanodots of a material emit light at high resolution.

“Combining transmission microscopy and photodetection tools, a powerful microscope that uses electrons to image samples, allows you to see much more detailed details than other technologies,” says Ciphanendra Batzhu, who served as a leading doctoral student in the study before completing his PhD from Pennsylvania in 2023. “Electronics have small wavelengths, so the resolution is very high and they can detect light from small dots that are separate from other nearby dots.”

They discovered that large dots emit one type of glow, and small dots produce another type. The dots are very small, less than 10 nanometers wide, this is the size of 11 hydrogen atoms lined up, and operate in a unique way, trapping energy and emitting light at a higher frequency, corresponding to a higher wavelength.

According to Alem, this phenomenon is called quantum confinement. It occurs when a dot is contained in a space small enough to be quantized with energy. This means discrete properties that allow for new properties including new electronic capabilities and optical functions. In this case, the researchers confirmed that the nanodots restrict the basic particle pairs known as excitons at the interface of molybdenum-direnide and tungsten disslenide.

Excitons can transport energy, but not net charges. It may also affect semiconductors (chips that support smartphones, computers, etc.). Scientists can manipulate light that emits more effectively by precisely controlling the excitons of materials. He said this could lead to faster and safer quantum systems, as well as other customizable energy-saving devices, such as high-resolution screen displays.

“Think about how an OLED display works,” Bachu said. “Each pixel has control over the exact color and brightness of each. This will give you accurate colors in true blacks, like red, green, and blue on your screen. Improved this process will make your image sharper and more vibrant.”

Control arises from adjusting the bandgap of a semiconductor material, essentially the energy threshold electrons must cross to cross. Low-sized materials such as single layers of 2D tungsten diolenide can have a direct bandgap. This is more efficient at emitting light compared to the thick, indirect bandgap counterpart, Alem said.

However, photoluminescence efficiency and other electronic and optical properties also vary in families of related 2D materials (such as disulfide molybdenum, tungsten disulfide, molybdenum disulfide, tungsten diolenide, etc.).

“By mixing them, you can combine molybdenum jurenide and tungsten jilenide in a specific ratio, and fine-tune the band gap to emit light in a specific color,” Batchu said. “This process, called bandgap engineering, is possible due to the wide variety of materials in this family, making it an excellent platform for studying and creating these light sources.”

Researchers said they are currently planning to build on the work.

“This is just the tip of the iceberg,” Alem said. “By exploring the role of atomic structures, chemistry, and other factors in controlling light emission, while expanding the lessons learned in this study, we can move this study to the next level and develop practical applications.”