Search results for "Phonon"
showing 10 items of 466 documents
Structural, Optical, and Dielectric Investigations of the Relaxor PLZT 9,75/65/35 Ceramics Irradiated by High-Current Pulsed Electron Beam
2003
A comprehensive study of high-current pulsed electron irradiation effects on the structural, optical and dielectric properties of relaxor (Pb (1-x )La x )(Zr 0.65 Ti 0.35 ) 1-x/4 O 3 ceramics with x = 9,75 at.% has been performed for the first time. The electron beam had the following parameters: energy E = 250 keV, current density I = 1000 A/cm 2 , pulse duration τ = 300 ns, beam density -10 15 electrons/cm 2 per pulse. Infrared reflectivity spectra in the region of 100 ÷ 2000 cm -1 were obtained in virgin, irradiated by 1500 pulses and annealed up to 500°C ceramics. The reconstruction of perovskite ABO 3 structure in irradiated samples has been studied by combined use of X-ray diffraction…
Minimizing coherent thermal conductance by controlling the periodicity of two-dimensional phononic crystals
2019
Periodic hole array phononic crystals (PnC) can strongly modify the phonon dispersion relations, and have been shown to influence thermal conductance coherently, especially at low temperatures where scattering is suppressed. One very important parameter influencing this effect is the period of the structure. Here, we measured the sub-Kelvin thermal conductance of nanofabricated PnCs with identical hole filling factors, but three different periodicities, 4, 8, and 16 $\mu$m, using superconducting tunnel junction thermometry. We found that all the measured samples can suppress thermal conductance by an order of magnitude, and have a lower thermal conductance than the previously measured small…
12C + 12C large angle elastic scattering at 240 MeV
2010
Abstract The measurement of the differential cross sections of the 12C + 12C and the 13C + 12C elastic scattering are carried out at the 12C energy 240 MeV and the 13C energy 250 MeV to solve some interpretation problem of the 12C + 12C scattering data. Is it possible that the 1st Airy minimum in 12C + 12C scattering data is missing? Our analysis shows that the positions of the 1st Airy minima obtained in former measurements are confirmed.
Electron-phonon heat transport in arrays of Al islands with submicrometer-sized tunnel junctions.
1996
We present experimental evidence of the effect of electrode volume and its shape on thermalization of small metallic islands for single electron tunneling. We have investigated the power law and the magnitude of the thermal transport and found that it obeys the common ${T}^{5}$ law for electron-phonon coupling only for the smallest islands studied, and in other cases considered, with cooling fins attached to the islands, the coupling per unit volume is weaker and it rather follows a law $\ensuremath{\propto}{T}^{p}$, where $pl5$. We attribute this to local hot electrons adjacent to the tunnel junctions.
Design for a high resolution electron energy loss microscope.
2019
International audience; An electron optical column has been designed for High Resolution Electron Energy Loss Microscopy (HREELM). The column is composed of electron lenses and a beam separator that are placed between an electron source based on a laser excited cesium atom beam and a time-of-flight (ToF) spectrometer or a hemispherical analyzer (HSA). The instrument will be able to perform full field low energy electron imaging of surfaces with sub-micron spatial resolution and meV energy resolution necessary for the analysis of local vibrational spectra. Thus, noncontact, real space mapping of microscopic variations in vibrational levels will be made possible. A second imaging mode will al…
Single Molecule Studies of a Ladder Type Conjugated Polymer: Vibronic Spectra, Line Widths, and Energy Transfer
2014
Confocal fluorescence microscopy and spectroscopy are employed to investigate single poly(ladder-type pentaphenylene) (LPPentP) molecules dispersed in thin poly(methyl methacrylate) (PMMA) films at 1.2 K. Emission spectra of single chains show single as well as multi-chromophore emission indicating variegated communication along the chains. The vibronic structure in the emission spectra resembles the one found for other ladder-type polymers. Purely electronic zero-phonon lines in emission are substantially broadened, most probably due to fast spectral diffusion. By surmounting the limitations of emission spectroscopy, nonemitting donor chromophores, which transfer their excitation energy in…
Engineering thermal conductance using a two-dimensional phononic crystal
2014
Controlling thermal transport has become relevant in recent years. Traditionally, this control has been achieved by tuning the scattering of phonons by including various types of scattering centres in the material (nanoparticles, impurities, etc). Here we take another approach and demonstrate that one can also use coherent band structure effects to control phonon thermal conductance, with the help of periodically nanostructured phononic crystals. We perform the experiments at low temperatures below 1 K, which not only leads to negligible bulk phonon scattering, but also increases the wavelength of the dominant thermal phonons by more than two orders of magnitude compared to room temperature…
Pressure effects on the vibrational properties of alpha-Bi2O3: an experimental and theoretical study
2014
We report an experimental and theoretical high-pressure study of the vibrational properties of synthetic monoclinic bismuth oxide (alpha-Bi2O3), also known as mineral bismite. The comparison of Raman scattering measurements and theoretical lattice-dynamics ab initio calculations is key to understanding the complex vibrational properties of bismite. On one hand, calculations help in the symmetry assignment of phonons and to discover the phonon interactions taking place in this low-symmetry compound, which shows considerable phonon anticrossings; and, on the other hand, measurements help to validate the accuracy of first-principles calculations relating to this compound. We have also studied …
Elastic properties of CsCN
1983
The temperature dependence of the elastic constants of CsCN exhibiting the CsCl structure was measured with ultrasonic and neutron techniques. The room temperature values were found to bec11=18.8,c12=10.7 andc44=2.95 1010 dyn/cm2. The sound waves inT2g andEg symmetries exhibit anomalous temperature effects which are similar but definitively weaker than those in the NaCl type cyanides. In addition we measured the acoustic phonon dispersion along [100] and [110]. These results are compared with recent molecular dynamics calculations.
The Effects of the Electron-Phonon Interaction on the Vibrational Anomalies and Polymorphism in Titanium
1997
AbstractWe apply the frozen phonon and molecular dynamics methods within the semiempirical orthogonal tight-binding framework to study the anomalous behaviour of the (0001) optical longitudinal (LO) and transverse (TO) phonons in the low temperature hep phase of Ti, and the ⅔[111]L and ½[110]T1 phonons in the high temperature bec phase. We demonstrate that, in agreement with previous findings in Zr, the anomalous thermal frequency shifts in hep Ti are related to the strong coupling of the electron density of states (DOS) to the particular lattice distortions. The distortions along the bec ⅔[111]L and ½[110]T1 phonons also significantly affect the DOS, resulting in the instability of these m…