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Register a new userRayleigh-Brillouin scattering in binary mixtures of disparate-mass constituents: SF$_6-$He, SF$_6-$D$_2$ and SF$_6-$H$_2$
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The spectral distribution of light scattered by microscopic thermal fluctuations in binary mixture gases was investigated experimentally and theoretically. Measurements of Rayleigh-Brillouin spectral profiles were performed at a wavelength of 532 nm and at room temperature, for mixtures of SF$_6-$He, SF$_6-$D$_2$ and SF$_6-$H$_2$. In these measurements, the pressure of the gases with heavy molecular mass (SF$_6$) is set at 1 bar, while the pressure of the lighter collision partner was varied. In view of the large polarizability of SF$_6$ and the very small polarizabilities of He, H$_2$ and D$_2$, under the chosen pressure conditions these low mass species act as spectators and do not contribute to the light scattering spectrum, while they influence the motion and relaxation of the heavy SF$_6$ molecules. A generalized hydrodynamic model was developed that should be applicable for the particular case of molecules with heavy and light disparate masses, as is the case for the heavy SF$_6$ molecule, and the lighter collision partners. Based on the kinetic theory of gases, our model replaces the classical Navier-Stokes-Fourier relations with constitutive equations having an exponential memory kernel. The energy exchange between translational and internal modes of motion is included and quantified with a single parameter $z$ that characterizes the ratio between the mean elastic and inelastic molecular collision frequencies. The model is compared with the experimental Rayleigh-Brillouin scattering data, where the value of the parameter $z$ is determined in a least-squares procedure. Where very good agreement is found between experiment and the generalized hydrodynamic model, the computations in the framework of classical hydrodynamics strongly deviate. Only in the hydrodynamic regime both models are shown to converge.
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Here we report the fabrication of stable, shallow (< 5 nm) nitrogen-vacancy (NV) centers in diamond by nitrogen delta doping at the last stage of the chemical vapor deposition (CVD) growth process. The NVs are stabilized after treating the diamond in $SF_6$ plasma, otherwise the color centers are not observed, suggesting a strong influence from the surface. X-Ray photoelectron spectroscopy measurements show the presence of only fluorine atoms on the surface, in contrast to previous studies, and suggests very good surface coverage. We managed to detect hydrogen nuclear magnetic resonance signal from protons in the immersion oil, revealing a depth of the NVs of about 5 nm
Electronic spectra of C$_6$H are measured in the $18,950-21,100$ cm$^{-1}$ domain using cavity ring-down spectroscopy of a supersonically expanding hydrocarbon plasma. In total, 19 (sub)bands of C$_6$H are presented, all probing the vibrational manifold of the B$^2Pi$ electronically excited state. The assignments are guided by electronic spectra available from matrix isolation work, isotopic substitution experiments (yielding also spectra for $^{13}$C$_6$H and C$_6$D), predictions from ab initio calculations as well as rotational fitting and vibrational contour simulations using the available ground state parameters as obtained from microwave experiments. Besides the $0_0^0$ origin band, three non-degenerate stretching vibrations along the linear backbone of the C$_6$H molecule are assigned: the $ u_6$ mode associated with the C-C bond vibration and the $ u_4$ and $ u_3$ modes associated with C$equiv$C triple bonds. For the two lowest $ u_{11}$ and $ u_{10}$ bending modes, a Renner-Teller analysis is performed identifying the $mu^2Sigma$($ u_{11}$) and both $mu^2Sigma$($ u_{10}$) and $kappa^2Sigma$($ u_{10}$) components. In addition, two higher lying bending modes are observed, which are tentatively assigned as $mu^2Sigma$($ u_9$) and $mu^2Sigma$($ u_8$) levels. In the excitation region below the first non-degenerate vibration ($ u_6$), some $^2Pi-^{2}Pi$ transitions are observed that are assigned as even combination modes of low-lying bending vibrations. The same holds for a $^2Pi-^{2}Pi$ transition found above the $ u_6$ level. From these spectroscopic data and the vibronic analysis a comprehensive energy level diagram for the B$^2Pi$ state of C$_6$H is derived and presented.
The topological property of SrRu$_2$O$_6$ and isostructural CaOs$_2$O$_6$ under various strain conditions is investigated using density functional theory. Based on an analysis of parity eigenvalues, we anticipate that a three-dimensional strong topological insulating state should be realized when band inversion is induced at the A point in the hexagonal Brillouin zone. For SrRu$_2$O$_6$, such a transition requires rather unrealistic tuning, where only the $c$ axis is reduced while other structural parameters are unchanged. However, given the larger spin-orbit coupling and smaller lattice constants in CaOs$_2$O$_6$, the desired topological transition does occur under uniform compressive strain. Our study paves a way to realize a topological insulating state in a complex oxide, which has not been experimentally demonstrated so far.
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