91 research outputs found
Dynamic mechanical analysis and morphology of petroleum-based and bio-epoxy foams with wood filler
Current challenges highlight the need for polymer research using renewable natural sources as a substitute for
petroleum-based polymers. In this study, consequently, the fabrication of green polyurethane (PU) foams and its composites
is to be demonstrated dependent on synthesis in the laboratory scale of hydroxylated bio-epoxy (B) and petroleum-based
synthetic-epoxy (E), crosslinker and wood fillers. Polyurethane foams were modified with two type of wood fiber fillers,
powder (P) and flakes (L) with specific percentage ratios of 0, 5, 10, 15 and 20 %wt. Bio-epoxy (B) and synthetic-epoxy
(E) foam and its composite were exposed to UV irradiation for a period of 2000 hours and 4000 hours by UV
Whetherometer apparatus. The morphology structure and viscoelastic properties such as storage modulus, E', damping
behavior, ta
Tuning a Schottky barrier in a photoexcited topological insulator with transient Dirac cone electron-hole asymmetry
The advent of Dirac materials has made it possible to realize two dimensional
gases of relativistic fermions with unprecedented transport properties in
condensed matter. Their photoconductive control with ultrafast light pulses is
opening new perspectives for the transmission of current and information. Here
we show that the interplay of surface and bulk transient carrier dynamics in a
photoexcited topological insulator can control an essential parameter for
photoconductivity - the balance between excess electrons and holes in the Dirac
cone. This can result in a strongly out of equilibrium gas of hot relativistic
fermions, characterized by a surprisingly long lifetime of more than 50 ps, and
a simultaneous transient shift of chemical potential by as much as 100 meV. The
unique properties of this transient Dirac cone make it possible to tune with
ultrafast light pulses a relativistic nanoscale Schottky barrier, in a way that
is impossible with conventional optoelectronic materials.Comment: Nature Communications, in press (12 pages, 6 figures
Ultrafast surface carrier dynamics in the topological insulator Bi2Te3
We discuss the ultrafast evolution of the surface electronic structure of the
topological insulator BiTe following a femtosecond laser excitation.
Using time and angle resolved photoelectron spectroscopy, we provide a direct
real-time visualisation of the transient carrier population of both the surface
states and the bulk conduction band. We find that the thermalization of the
surface states is initially determined by interband scattering from the bulk
conduction band, lasting for about 0.5 ps; subsequently, few ps are necessary
for the Dirac cone non-equilibrium electrons to recover a Fermi-Dirac
distribution, while their relaxation extends over more than 10 ps. The surface
sensitivity of our measurements makes it possible to estimate the range of the
bulk-surface interband scattering channel, indicating that the process is
effective over a distance of 5 nm or less. This establishes a correlation
between the nanoscale thickness of the bulk charge reservoir and the evolution
of the ultrafast carrier dynamics in the surface Dirac cone
Stacking, correlations and electronic dispersion in the photoexcited state of 1T-TaS<sub>2</sub>
Here we perform angle and time-resolved photoelectron spectroscopy on the commensurate Charge Density Wave phase of 1T-TaS2. Data with different probe pulse polarization are employed to map the dispersion of electronic states below or above the chemical potential. The experimental results are compared to Density-Functional Theory calculations with a self-consistent evaluation of the coulomb repulsion. Both out-of-plane dimerization and electronic correlations must be included in order to obtain good agreement with the experimental data. Upon Photoexcitation, the fluctuations of CDW order erase the band dispersion near to the chemical potential and halve the charge gap size. This transient phase sets within half a period of the coherent lattice motion and is likely favored by strong electronic correlations
Valence band electronic structure of V2O3: identification of V and O bands
We present a comprehensive study of the photon energy dependence of the
valence band photoemission yield in the prototype Mott-Hubbard oxide V2O3. The
analysis of our experimental results, covering an extended photon energy range
(20-6000 eV) and combined with GW calculations, allow us to identify the nature
of the orbitals contributing to the total spectral weight at different binding
energies, and in particular to locate the V 4s at about 8 eV binding energy.
From this comparative analysis we can conclude that the intensity of the
quasiparticle photoemission peak, observed close to the Fermi level in the
paramagnetic metallic phase upon increasing photon energy, does not have a
significant correlation with the intensity variation of the O 2p and V 3d
yield, thus confirming that bulk sensitivity is an essential requirement for
the detection of this coherent low energy excitation
Reply to: Ultrafast evolution and transient phases of a prototype out-of-equilibrium Mott-Hubbard material
International audienceReplying to D. Moreno-Mencía et al. Nature Communicationshttps://doi.org/10.1038/s41467-019-11743-3 (2019)
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