Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEffect of isotope disorder on the Raman spectra of cubic boron arsenide
105
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Boron arsenide (c-BAs) is at the forefront of research on ultrahigh thermal conductivity materials. We present a Raman scattering study of isotopically tailored cubic boron arsenide single crystals for 11 isotopic compositions spanning the range from nearly pure c-$^{10}$BAs to nearly pure c-$^{11}$BAs. Our results provide insights on the effects of strong mass disorder on optical phonons and the appearance of two-mode behavior in the Raman spectra of mixed crystals. Strong isotope disorder also relaxes the one-phonon Raman selection rules, resulting in disorder-activated Raman scattering by acoustic phonons.
rate research
Read More
The ultrahigh thermal conductivity of boron arsenide makes it a promising material for next-generation electronics and optoelectronics. In this work, we report measured optical properties of cubic boron arsenide crystals including the complex dielectric function, refractive index, and absorption coefficient in the ultraviolet, visible, and near-infrared wavelength range. The data were collected at room temperature using spectroscopic ellipsometry as well as transmission and reflection spectroscopy. We further calculate the optical response using density functional and many-body perturbation theory, considering quasiparticle and excitonic corrections. The computed values for the direct and indirect band gaps (4.25 eV and 2.07 eV) agree well with the measured results (4.12 eV and 2.02 eV). Our findings contribute to the effort of using boron arsenide in novel electronic and optoelectronic applications that take advantage of its demonstrated ultrahigh thermal conductivity and predicted high ambipolar carrier mobility.
Recent measurements of an unusual high thermal conductivity of around 1000 W m-1 K-1 at room temperature in cubic boron arsenide (BAs) confirm predictions from theory and suggest potential applications of this semiconductor compound for thermal management applications. Knowledge of the thermal expansion coefficient and Gruneisen parameter of a material contributes both to the fundamental understanding of its lattice anharmonicity and to assessing its utility as a thermal-management material. However, previous theoretical calculations of the thermal expansion coefficient and Gruneisen parameter of BAs yield inconsistent results. Here we report the linear thermal expansion coefficient of BAs obtained from the X-ray diffraction measurements from 300 K to 773 K. The measurement results are in good agreement with our ab initio calculations that account for atomic interactions up to fifth nearest neighbours. With the measured thermal expansion coefficient and specific heat, a Gruneisen parameter of BAs of 0.84 +/- 0.09 is obtained at 300 K, in excellent agreement with the value of 0.82 calculated from first principles and much lower than prior theoretical results. Our results confirm that BAs exhibits a better thermal expansion coefficient match with commonly used semiconductors than other high-thermal conductivity materials such as diamond and cubic boron nitride.
Boron carbide, a lightweight, high temperature material, has various applications as a structural material and as a neutron absorber. The large solubility range of carbon in boron, between $approx$ 9% and 20%, stems from the thermodynamical stability of three icosahedral phases at low temperature, with respective carbon atomic concentrations: 8.7% (B$_{10.5}$C, named OPO$_1$), 13.0 % (B$_{6.7}$C, named OPO$_2$), whose theoretical Raman spectra are still unknown, and 20% (B$_4$C), from which the nature of some of the Raman peaks are still debated. We report theoretical and experimental results of the first order, non-resonant, Raman spectrum of boron carbide. Density functional perturbation theory enables us to obtain the Raman spectra of the OPO$_1$ and OPO$_2$ phases, which are perfectly ordered structures with a complex crystalline motif of 414 atoms, due to charge compensation effects. Moreover, for the carbon-rich B$_4$C, with a simpler 15-atom unit cell, we study the influence of the low energy point defects and of their concentrations on the Raman spectrum, in connection with experiments, thus providing insights into the sensitivity of experime ntal spectra to sample preparation, experimental conditions and setup. In particular, this enables us to propose a new structure at 19.2% atomic carbon concentration, B$_{4.2}$C, that lies very close to the convex hull of boron carbide, on the carbon-rich side. This new phase, derived from what we name the 3+1 defect complex, helps in reconciling the experimentally observed Raman spectrum with the theory around 1000 cm$^{-1}$. Finally, we predict the intensity variations induced by the experimental geometry and quantitavely assess the localisation of bulk and defect vibrational modes and their character, with an analysis of chain and icosahedral modes.
The 300 K equation of state of cubic (zinc-blende) boron phosphide BP has been studied by in situ single-crystal X-ray diffraction with synchrotron radiation up to 55 GPa. The measurements have been performed under quasi-hydrostatic conditions using a Ne pressure medium in a diamond anvil cell. A fit of the experimental p-V data to the Vinet equation of state yields the bulk modulus B0 of 179(1) GPa with its pressure derivative of 3.3(1). These values are in a good agreement with previous elastic measurements, as well as with semiempirical estimations.
The three dimensional distribution of the X-ray diffuse scattering intensity of BaTiO$_3$ has been recorded in a synchrotron experiment and simultaneously computed using molecular dynamics simulations of a shell-model. Together these have allowed the details of the disorder in paraelectric BaTiO$_3$ to be clarified. The narrow sheets of diffuse scattering, related to the famous anisotropic longitudinal correlations of Ti ions, are shown to be caused entirely by the overdamped anharmonic soft phonon branch. This finding demonstrates that the occurrence of narrow sheets of diffuse scattering agrees with a displacive picture of the cubic phase of this textbook ferroelectric material.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
