Lattice dynamics is one of the most fundamental properties of two-dimensional (2D) crystals, which provides the foundation for mechanical and elastic properties, heat transport, charge carrier dynamics, phonon-assisted optical excitation, and other phenomena. Researchers will be eager to collect trustworthy data on the phonon dispersion relationship of 2D materials in this setting. Alfa Chemistry provides a professional 2D material phonon dispersion measurement service to its customers, which aids in the understanding of crystalline materials' mechanical and optical characteristics. Please get in touch with us right away so we can assist you with your 2D material testing!
Learn About Phononics and Phonon Dispersion
All physical processes in solids are influenced by phonons, which are quanta of lattice vibrations. They alter the optical characteristics of 2D crystalline materials by limiting electron mobility around room temperature (RT). In insulators and semiconductors, phonons are the primary heat transporters. Acoustic waves are created by long-wavelength phonons. Phonons, like electrons, are distinguished by their dispersion ω (q). The phonon dispersion relation (PDR) is the dependence of the phonon frequency ω on its wave vector q.
Fig 1. Predicted phonon dispersion curves. (A) C-Diamond and (B) Graphene calculated with the MMP potential. (Monteverde U, et al. 2015)
There are two types of phonons in graphene: transverse and longitudinal acoustic and optical branches generated by lattice vibrations in the plane of the sheet, and bending phonons generated by lattice vibrations outside the plane of the layer. Graphene's phonons can reveal information about the material's elastic characteristics. The in-plane stiffness and shear modulus of 2D materials may be calculated using the acoustic velocities of the transverse and longitudinal acoustic branches. Optical phonons are used to determine the number of atomic planes in the few layers by Raman spectroscopy. The remarkable thermal characteristics of two-dimensional (2D) materials are due to the uniqueness of phonon transport, which may be changed more dramatically than in bulk crystals.
Our Measurement Techniques
Alfa Chemistry frequently uses inelastic neutron scattering (INS) or inelastic X-ray scattering to determine the dispersion relation (energy vs. momentum) of phonons (IXS). In these experiments, neutrons or X-ray photons lose/gain energy and momentum when scattering quanta of lattice vibrations, which are used to map the discrete energy and momentum values of phonons in a given solid. We also utilize nanostructure Raman scattering (RS) to monitor high-frequency optical phonons. In addition, methods such as electron energy loss spectroscopy and Brillouin scattering may be used to directly quantify phonons in materials.
Among these, High-Resolution Electron Energy Loss Spectroscopy (HREELS) is a powerful tool used by Alfa Chemistry to study surface phonon dispersion, surface structure and monitor epitaxial growth in 2D materials. High surface sensitivity, great resolution in the energy and momentum domains, and large energy and momentum windows are among HREELS' key features.
Fig 2. HREEL spectra for monolayer graphene/Pt(111) as a function of the scattering angle. The incidence angle is 80.0° and the impinging energy is 20 eV. (Politano A, et al. 2012)
- Example One: Alfa Chemistry evaluated Young's modulus and Poisson's ratio of quasi-independent graphene samples produced on metal substrates using phonon dispersion techniques, which gives a unique chance to quantify ripple-free and quasi-independent graphene sheets.
- Example Two: Alfa Chemistry used time-of-flight inelastic neutron scattering to evaluate the phonon dispersion of YBa2Cu3O6.15 and YBa2Cu3O6.95.
References
- Monteverde U, et al. (2015). "Under Pressure: Control of Strain, Phonons and Bandgap Opening in Rippled Graphene." Carbon. 91: 266-274.
- Politano A, et al. (2012). "Elastic Properties of A Macroscopic Graphene Sample from Phonon Dispersion Measurements." Carbon. 50: 4903-4910.
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