6533b7d8fe1ef96bd126aee7
RESEARCH PRODUCT
High-Pressure Softening of the Out-of-Plane A2u(Transverse-Optic) Mode of Hexagonal Boron Nitride Induced by Dynamical Buckling
Takashi TaniguchiLluís ArtúsKanji WatanabeGuillaume CassaboisRamón CuscóAlfredo SeguraBernard Gilsubject
Materials sciencePhononReflectionAstrophysics::Cosmology and Extragalactic Astrophysics02 engineering and technologyNitride010402 general chemistry01 natural sciencesNitridesCondensed Matter::Materials Sciencechemistry.chemical_compoundCondensed Matter::SuperconductivityPhysical and Theoretical ChemistryAbsorption (electromagnetic radiation)AnisotropySofteningAstrophysics::Galaxy AstrophysicsCondensed matter physics021001 nanoscience & nanotechnology0104 chemical sciencesSurfaces Coatings and FilmsElectronic Optical and Magnetic MaterialsBoron nitrideTransverse planeGeneral EnergychemistryBucklingBoron nitride[PHYS.COND.CM-GEN]Physics [physics]/Condensed Matter [cond-mat]/Other [cond-mat.other][PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci]CalculationsIII-V semiconductorsPhononsSingle crystalsAstrophysics::Earth and Planetary Astrophysics0210 nano-technologydescription
We investigate the highly anisotropic behavior of the in-plane and out-of-plane infrared-active phonons of hexagonal boron nitride by means of infrared reflectivity and absorption measurements under high pressure. Infrared reflectivity spectra at normal incidence on high-quality single crystals show strict fulfillment of selection rules and an unusually long E1u[transverse-optic (TO)] phonon lifetime. Accurate values of the dielectric constants at ambient pressure ϵ0= 6.96, ϵ∞= 4.95, ϵ 0= 3.37, and ϵ∞ = 2.84 have been determined from fits to the reflectivity spectra. The out-of-plane A2u phonon reflectivity band is revealed in measurements on an inclined facet, and absorption measurements at an incidence angle of 30° allow us to observe both the transverse- and longitudinal-optic A2u modes. Pressure coefficients and Grüneisen parameters for all infrared-active modes are determined and compared with ab initio calculations. While Grüneisen parameters are generally small in this layered crystal, the A2u(TO) displays an exceptionally large and negative Grüneisen parameter that results in widening of the type I hyperbolic region with increasing pressure. Softening of the A2u(TO) mode is induced by dynamical buckling of the flat honeycomb layers. © 2019 American Chemical Society.
| year | journal | country | edition | language |
|---|---|---|---|---|
| 2019-07-24 |