Raman spectroscopy sheds light on vibrational tuning in black phosphorus nanostructures

Controlling vibrational properties is a key step in designing low-dimensional materials for advanced applications and devices. In a new study published in Nano Research on June 24, 2025, scientists demonstrate how nanoscale confinement, edge effects, and structural disorder in nanostructures—such as phosphorene nanoribbons (PNRs)—can be harnessed to engineer the phonon dispersion of black phosphorus (BP), a 2D semiconductor with promising electronic, optoelectronic, and thermoelectric properties.

Using an electrochemical intercalation method developed by the team, researchers synthesized two types of nanostructured BP: one intercalated with sodium ions and another with lithium. Sodium intercalation produced tightly aligned bundles of sub-10 nm-wide PNRs separated by amorphous channels, while lithium intercalation yielded short, irregular segments embedded in a more disordered matrix.

The nanostructures were characterized using angle-resolved polarized Raman spectroscopy (ARPRS), a powerful technique that probes the symmetry and orientation of vibrational modes in materials. ARPRS revealed stark contrasts between the two systems: sodium-intercalated samples displayed strongly anisotropic Raman signatures, while lithium-intercalated samples exhibited weaker anisotropy and more isotropic features—consistent with greater disorder.

Notably, six additional Raman peaks (P1–P6) were observed in both intercalated materials, attributed to vibrations originating from the amorphous regions. These peaks showed little angular dependence, reinforcing their connection to structural disorder.

To interpret the results, the team performed first-principles-based vibrational density of states (FDOS) simulations. The modeling confirmed that phonon confinement, band folding, and mode mixing—driven by nanoribbon geometry and edge effects—underlie the observed behavior.

“Our work demonstrates that the vibrational properties of black phosphorus can be tuned by tailoring its nanoscale morphology,” said Jasinski, one of the lead authors and theme leader at the Conn Center for Renewable Energy Research in the J.B. Speed School of Engineering the University of Louisville. “By combining ARPRS with vibrational modeling, we gain new insight into how nanostructure—down to edge configuration and ribbon width—affects phonon dispersions.”

This collaborative research was conducted at the University of Louisville by a multidisciplinary team led by Jasinski, with key contributions from several researchers in the Department of Physics and Astronomy—most notably Professors Sumanasekera and Yu, graduate student and first author Karki, and Dr. Irziqat, who helped develop the ARPRS capability used in the Raman measurements—as well as Professors Wang and Narayanan from the Department of Mechanical Engineering.

This research marks one of the first studies to use ARPRS to explore nanoribbon structures, offering a valuable platform for probing and engineering vibrational modes in low-dimensional materials.

The findings highlight a promising strategy for phonon engineering and the design of materials with optimized heat and charge transport properties—relevant for applications in thermoelectrics, thermal management, and quantum materials, where precise control of phonons is critical.

Looking ahead, the team plans to explore how alloying, edge functionalization, and size control can further refine the vibrational and electronic properties of phosphorene-based nanostructures.

This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award # DE-SC0024131.

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.