Phonon transition across an isotopic interface

Abstract

Natural materials usually consist of isotopic mixtures, for which different isotopic ratios can lead to distinct material properties such as thermal conductivity and nucleation process. However, the knowledge of isotopic interface remains largely unexplored mainly due to the challenges in isotopic identification and property measurement at an atomic scale. Here, by using monochromated electron energy-loss spectroscopy in a scanning transmission electron microscope, we reveal momentum-transfer-dependent lattice vibration behavior at an artificial h-10BN/h-11BN heterostructure with sub-unit-cell resolution. We find the vibrational energy changes across the isotopic interface gradually, featuring a wide transition regime, which suggests strong delocalization of the out-of-plane optical phonons at the interface. In addition, we identify phonons near the Brillouin zone center have a transition regime ~3.34 nm (10 atomic layers), whereas phonons at the Brillouin zone boundary transition in ~1.66 nm (5 atomic layers). We propose that the isotope-induced charge effect at the interface accounts for the distinct delocalization behavior. Moreover, intra-atomic layer variation of vibration energy is also sensitive to the momentum transfer, thus at the interface it depends on both of momentum transfer and mass change. The revealed lattice vibration behavior at an isotopic interface provides new insights to understand the isotopic effects on properties in natural materials.

References in corpus (13)

• Van der Waals heterostructures
• Evolution of graphene growth on Cu and Ni studied by carbon isotope labeling
• Ultra-low-loss Polaritons in Isotopically Pure Materials: A New Approach
• Measuring phonon dispersion at an interface
• Experimental Observation of Localized Interfacial Phonon Modes
• Vibrational Spectroscopy at Atomic Resolution with Electron Impact Scattering
• Negative refraction in hyperbolic hetero-bicrystals
• Understanding the image contrast of material boundaries in IR nanoscopy reaching 5 nm spatial resolution
• Outstanding Thermal Conductivity of Single Atomic Layer Isotope-Modified Boron Nitride
• Imaging of isotope diffusion using atomic-scale vibrational spectroscopy
• Isotope effect in superconducting lanthanum hydride under high compression
• On the isotope effect in compressed superconducting H${}_{\text{3}}$S and D${}_{\text{3}}$S
• Atomic-Scale Vibrational Mapping and Isotope Identification with Electron Beams

Cited by in corpus (1)

• Origin of interlayer exciton-phonon coupling in 2D heterostructures