New Optical Nanoscopy Reveals Ultrafast Dynamics in Nanomaterials

July 25, 2024

(Nanowerk News) Scientists at the University of California, Berkeley, have developed cutting-edge nano-scale optical imaging techniques to provide unprecedented insight into the dynamics of ultrafast carriers in advanced materials. Two recent studies, published in Advanced materials (“Transient nanoscopy of exciton dynamics in two-dimensional transition metal dichalcogenides”) and ACS Photonics (“Non-scale imaging of phases and carrier dynamics in vanadium dioxide nanobeams in the near field”) represent a significant advance in understanding carrier behavior in two-dimensional and phase-change materials, which may have implications for next-generation electronic and optoelectronic devices.

A research team led by Prof. Costas P. Grigoropoulos, Dr. Jingang Li and graduate student Rundi Yang used a novel technique called near-field transient nanoscopy to study the behavior of materials at the nanoscale with high spatial and temporal resolution. This approach overcomes the limitations of traditional optical methods, allowing researchers to directly visualize and analyze phenomena that were previously difficult to observe. Schematic of near-field transient nanoscopy. (Graphic: Adapted from DOI:10.1002/adma.202311568, CC BY-NC-ND 4.0)

“Our technique allows us to study how charge carriers and excitons behave and interact at the nanoscale in different materials,” Li explains. “This is crucial for understanding and optimizing the performance of advanced devices based on these materials.”

In one study, the team focused on atomically thin transition metal dichalcogenides (TMDCs), materials known for their unique optical and electronic properties. They observed intricate details of exciton recombination and diffusion processes in monolayers and bilayers of MoS2revealing distinct dynamics near crystalline interfaces and in regions with nanoscale stresses.

Extending their research, the researchers also examined vanadium dioxide (VO2), a material known for its extraordinary phase change properties. Using advanced imaging techniques, they mapped the nanometric distribution of metallic and insulating phases in a bent VO2 nanobeams.

“We managed to directly visualize the coexistence of different phases in the VO2 in unprecedented detail,” Yang says. “This allows us to understand how deformation affects the electronic properties of the material at a fundamental level.”

Surprisingly, the team observed slower carrier recombination but faster diffusion in the VO metal phase.2 compared to the insulating phase. This discovery provides new insights into the behavior of the material during phase transitions, which could be crucial for the development of advanced switching and memory devices.

The studies also highlighted the influence of local material properties, such as strain and interfaces, on the exciton and carrier dynamics in TMDCs and VOs.2. Understanding this is key to engineering devices that can exploit these nano-scale effects to improve performance.

Prof. Grigoropoulos emphasizes the broader impact of this research: “These techniques open up new possibilities for studying a wide range of nanomaterials and nanodevices. We are excited about the potential applications in areas ranging from energy harvesting to quantum information processing.”

The combined results of these studies demonstrate the power of advanced nano-imaging techniques to unravel the complex physics of nanomaterials. As scientists refine these methods, we can expect further breakthroughs in our understanding of materials at the atomic scale, paving the way for innovative technologies that exploit the unique properties of nanomaterials.

These findings have important implications for the development of next-generation electronic and optoelectronic devices, including high-performance sensors, memory devices, and adaptive optical components. The ability to probe and manipulate material properties at such small scales promises to accelerate the development of more efficient and effective technologies across a wide range of applications.