| Autor: |
Yao CH; Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States., Gao H; Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States., Ping L; Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States., Gulo DP; Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan., Liu HL; Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan., Tuan Hung N; Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan., Saito R; Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan.; Department of Physics, Tohoku University, Sendai 980-8578, Japan., Ling X; Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States.; Division of Materials Science and Engineering, Boston University, Boston, Massachusetts 02215, United States.; Photonics Center, Boston University, Boston, Massachusetts 02215, United States. |
| Abstrakt: |
Resonant Raman spectra of a two-dimensional (2D) non-van der Waals (vdW) material, molybdenum nitride (Mo 5 N 6 ), are measured across varying thicknesses, ranging from a few to tens of nanometers. Fifteen distinct Raman peaks are observed experimentally, and their assignments are made using first-principles calculations for the most stable AABB-stacking structure of Mo 5 N 6 . The assignments are further supported by angular-dependent Raman measurements for all peaks, except the most intense one at 215 cm -1 . Calculations reveal that the 215 cm -1 peak does not appear for three-dimensional molybdenum nitrides and is not a first-order Raman-active mode. We further investigated the origin of the 215 cm -1 peak and assigned it as a defect-induced double-resonance peak. Moreover, thickness-dependent Raman measurements reveal that both the 215 and 540 cm -1 peaks─assigned to out-of-plane and in-plane modes, respectively─blue shift as thickness increases, reaching a plateau around 20 nm. This thickness-dependent Raman shift over a wide thickness range is nontrivial compared to other common vdW 2D materials and is attributed to the much stronger stacking interaction between the constituent layers in non-vdW materials. This finding highlights Raman spectroscopy as a valuable tool for characterizing the thickness of 2D non-vdW materials. |
