We are interested in studying quantum physics in hybrid low-dimensional materials. We fabricate artificial low-dimensional materials with new physical properties and functionalities through multiple technologies, such as twistronics and straintronics.

——  Join Our Team! —— 

We are looking for motivated undergraduate and graduate students to join our research group. If you're passionate about what we do, eager to learn, and excited to contribute to cutting-edge research, we’d love to hear from you!

How to Reverse the Energy of Photons?

Light plays a crucial role in our daily lives, with different applications requiring various energy levels. For example, ultraviolet light is commonly used for sterilization, visible light brightens our world and is efficiently converted into electrical energy by solar cells. Infrared light, however, with its lower energy, is not as easily utilized. Furthermore, when light interacts with matter, it typically loses energy, resulting in lower-energy light and heat. By converting these low-energy photons into high-energy photons, a process known as "photon upconversion," we can significantly enhance the efficiency of light usage.

Magicians of Light: Dark Excitons to the Rescue!

Our team utilized "upconversion photoluminescence spectroscopy" to observe photon upconversion in common two-dimensional semiconductor materials like MoS2, MoSe2, WS2, and WSe2 under normal indoor lighting conditions. For instance, these atomic-scale materials can absorb low-energy red light and emit higher-energy near-ultraviolet light. Furthermore, in collaboration with theoretical physics teams from NYCU and TKU, we revealed that the key mechanism behind photon upconversion is "dark exciton-dark exciton annihilation," where two dark excitons with opposite momenta interact, transform into a higher-energy bright exciton, and release light energy (Figure 1). These two-dimensional semiconductor materials can adjust the upconversion range from green to ultraviolet light, allowing for the tuning of the spectral range according to different application needs (Figure 2). 

Exciting Discovery with a New Kind of Thin Material!

In our recent cool project with Dr. Wei-Hua Wang and Dr. Yang-hao Chan at the Institute of Atomic and Molecular Sciences in Academia Sinica, we've made a groundbreaking discovery and shared it in a science journal for 2D materials!

We worked with a super thin material called indium selenide (InSe). For the first time ever, we saw this thin layer glow brightly under certain conditions, which is a big deal because it shows us something new about how light interacts with materials.

What's really interesting is that this glow comes from something called "dark excitons." Usually, these excitons are like hidden sparks that don't give off light, making them really hard to see. But in our experiment, we found a way to make these hidden sparks shine brightly, thanks to the help of tiny vibrations called acoustic phonons and the strong interaction of exciton to these phonons. We also looked closely at how these dark excitons behave and move around in the thin layer, which helps us understand more about this fascinating material.

Our recent work, collaborating with Prof. Shun-Jen Cheng's groups in NYCU Electrophysics, "The Key Role of Non-Local Screening in the Environment-Insensitive Exciton Fine Structures of Transition-Metal Dichalcogenide Monolayers" has been published in Nanomaterials. By combining experimental measurements of binding energies under different dielectric conditions with a theoretical model of non-local screening, we provide insights into the robustness of the binding energy of dark excitons in 2D materials. This finding has significant implications for understanding the behavior of dark excitons in these materials, particularly highlighting the importance of considering non-local screening effects when studying exciton fine structures.

Our recent work "P-Type Ohmic Contact to Monolayer WSe2 Field-Effect Transistors Using High-Electron Affinity Amorphous MoO3" has been published in ACS Applied Electronic Materials. In this work, we deposit MoO3 interfacing to WSe2. The surface charge transfer technique to realize Ohmic contacts to monolayer WSe2. Our results enable the study of interesting hole transport in 2D materials in the future.

Our recent work "Phase Modulation of Self-Gating in Ionic Liquid-Functionalized InSe Field-Effect Transistors" has been published in Nano Letters. In this work, we revealed strong intersystem Coulomb interactions at the InSe/liquid interface. We found the electron transport in InSe is significantly affected by the phase of the ionic liquid through capacitive coupling. Our results provide insight into developing liquid/2D material hybrid devices.