The Polarization-Resolved and Helicity-Resolved Raman Spectroscopy of the Twisted 1D/2D MoO₂ Mixed-Dimensional Homojunction

The anisotropic/anisotropic mixed-dimensional nanostructures, integrating two-dimensional (2D) materials with other low-dimensional counterparts, can generate a unique quantum phenomenon due to an additional degree of freedom enabling precise control over anisotropy and may provide a fascinating platform for advanced materials and innovative devices. Herein, we report the synthesis of an anisotropic/anisotropic 1D/2D mixed-dimensional homojunction, specifically a 1D/2D MoO₂ mixed-dimensional homojunction, composed of a 1D MoO₂ anisotropic nanowire and a 2D MoO₂ anisotropic nanoplate. This synthesis was achieved in a single step using the space-constrained rapid chemical vapor deposition (s-CVD) method. Four distinct types of the 1D/2D MoO₂ mixed-dimensional homojunctions were successfully synthesized, characterized by specific twisted angles of 0°, 41.5°, 90°, and 138.5° between the nanowire and nanoplate's long diagonal. Angle-resolved polarization Raman spectroscopy (ARPRS) confirms that both the MoO₂ nanowire and nanoplate exhibit strong in-plane anisotropy, with the 1D/2D MoO₂ mixed-dimensional homojunctions demonstrating significantly enhanced anisotropic properties. Furthermore, helicity-resolved Raman spectroscopy (HRRS), supported by theoretical calculations, reveals that the helicity of the 1D/2D MoO₂ mixed-dimensional homojunctions is conserved in A_g modes and reversed in B_1g modes. Notably, the chiral phonons in these structures are directly visualized through line-scan HRRS. These findings establish an interesting pathway for constructing anisotropic/anisotropic nanostructures by combining two or more anisotropic materials. The insights gained into chiral phonon modes and in-plane anisotropy may provide valuable guidance for the rational design of next-generation anisotropic and chiral optoelectronic devices.