Unlocking Klockmannite: Formation of Colloidal Quasi‐2D CuSe Nanocrystals and Photo‐Physical Properties Arising From Crystal Anisotropy

Why It Matters

The ability to synthesize anisotropic CuSe nanocrystals without surfactants unlocks scalable production of NIR‑active plasmonic materials, accelerating their adoption in photonic, sensing, and ultrafast optoelectronic applications.

Key Takeaways

• Thiol-free hot injection yields quasi‑2D CuSe nanocrystals
• Shape control achieved via temperature and precursor tuning
• Triangular nanoplatelets exhibit strong NIR plasmonic absorption
• Optical anisotropy leads to hyperbolic regime in NIR
• Ultrafast studies reveal hot‑hole cooling and coherent phonons

Pulse Analysis

The newly reported thiol‑free hot‑injection method marks a departure from ligand‑heavy protocols that dominate colloidal nanocrystal synthesis. By simply adjusting injection temperature and precursor concentrations, researchers produced quasi‑2D klockmannite CuSe nanosheets spanning 200 nm to several micrometers, as well as monocrystalline triangular nanoplatelets only 12–25 nm across. This level of shape precision without additional surfactants simplifies scale‑up and reduces surface contamination, addressing a long‑standing bottleneck for integrating copper selenide into optoelectronic platforms. The approach also showcases the broader potential of temperature‑driven anisotropic growth in layered chalcogenides.

The anisotropic crystal structure of klockmannite CuSe imparts pronounced optical directionality, which the authors quantified using complex‑scaled discrete dipole approximation. Calculations reveal a hyperbolic regime in the near‑infrared, where propagating and evanescent fields coexist, dramatically enhancing plasmonic absorption in the triangular nanoplatelets. Such hyperbolic behavior is rare in colloidal systems and opens pathways for sub‑diffraction imaging, ultrafast modulators, and NIR sensing. Moreover, the strong, tunable NIR plasmon resonance aligns with the spectral window of telecommunications and biomedical diagnostics, positioning these nanocrystals as versatile photonic building blocks.

Beyond static optical properties, the study probes ultrafast carrier dynamics in the klockmannite phase. Transient absorption measurements capture rapid hot‑hole cooling, subsequent trapping, and the generation of coherent phonons within picoseconds, underscoring the material’s capacity for swift energy dissipation. These dynamics are crucial for applications such as photodetectors, where fast response times dictate performance, and for plasmon‑driven catalysis, where hot carriers drive chemical transformations. The combined insights into synthesis, anisotropic optics, and femtosecond photophysics lay a foundation for engineering CuSe nanocrystals tailored to next‑generation optoelectronic and photonic devices.