Search results for "RAMAN"
showing 10 items of 1328 documents
Breaking Bonds and Forming Nanographene Diradicals with Pressure.
2017
New anthanthrone-based polycyclic scaffolds possessing peripheral crowed quinodimethanes have been prepared. While the compounds adopt a closed-shell butterfly shaped structure in the ground state, a concave-to-convex fluxional dynamic inversion is accessible with a low energy barrier through an open-shell diradicaloid transition-state. Mainly driven by the release of strainattributed to the steric hindrance at the peri position of the anthanthrone core, a low-lying open-shell diradical is accessible through planarization of the core, which can be achieved by thermal excitation in solution. Alternatively, planarization can be achieved by application of mild pressure in the solid state, in w…
Multiscale Investigation of the Structural, Electrical and Photoluminescence Properties of MoS2 Obtained by MoO3 Sulfurization
2022
In this paper, we report a multiscale investigation of the compositional, morphological, structural, electrical, and optical emission properties of 2H-MoS2 obtained by sulfurization at 800 °C of very thin MoO3 films (with thickness ranging from ~2.8 nm to ~4.2 nm) on a SiO2/Si substrate. XPS analyses confirmed that the sulfurization was very effective in the reduction of the oxide to MoS2, with only a small percentage of residual MoO3 present in the final film. High-resolution TEM/STEM analyses revealed the formation of few (i.e., 2–3 layers) of MoS2 nearly aligned with the SiO2 surface in the case of the thinnest (~2.8 nm) MoO3 film, whereas multilayers of MoS2 partially standing up with r…
Micrometer-size crystalline monolayer MoS2 domains obtained by sulfurization of molybdenum oxide ultrathin films
2023
In this work, the formation of micrometer-size crystalline monolayer (1L) MoS2 flakes with triangular shape and a central multilayer core is obtained by the sulfurization at 800 °C of pre-deposited ultrathin MoOx films (1.2–1.8 nm) on c-sapphire substrates. The thickness uniformity, crystalline quality, doping and strain distribution in the MoS2 flakes as a function of the initial MoOx thickness was evaluated by micro-Raman (μR) mapping. The excellent crystalline quality of the triangular 1L-MoS2 flakes was confirmed by micro-photoluminescence (μPL) maps, showing a very intense peak at ∼1.85 eV, that decreases in the central part, as expected for multilayers MoS2. A biaxial strain of ∼0.38–…
Structure of nanoporous carbon materials for supercapacitors
2012
Activated carbons with highly developed porous structure and nanosized pores (8 - 11 A) were prepared from alder wood using thermochemical activation method with sodium hydroxide. Properties of the obtained activated carbons were examined by benzene and nitrogen sorption, X-Ray diffraction and Raman spectroscopy. Tests of activated carbons as electrodes in supercapacitors were performed as well. It was found that specific surface area of above mentioned activated carbons was 1800 m 2 /g (Dubinin - Radushkevich). Raman spectroscopy demonstrated the presence of ordered and disordered structures of graphite origin. The performance of activated carbons as electrodes in supercapacitors have show…
Possible superlattice formation in high-temperature treated carbonaceous MgB2 at elevated pressure
2003
We report indications of a phase transition in carbonaceous MgB2 above 9 GPa at 300 K after stress relaxation by laser heating. The transition was detected using Raman spectroscopy and X-ray diffraction. The observed changes are consistent with a second-order structural transition involving a doubling of the unit cell along c and a reduction of the boron site symmetry. Moreover, the Raman spectra suggest a reduction in electron-phonon coupling in the slightly modified MgB2 structure consistent with the previously proposed topological transition in MgB2. However, further attributes including deviatoric stress, lattice defects, and compositional variation may play an important role in the obs…
Investigation of the epitaxy of thin YBa2Cu3O7-delta films
1990
Abstract The degree of epitaxy of thin sputtered and laser ablated films have been investigated by Raman spectroscopy. Using the selection rules for Raman scattering for the different phonons in YBa 2 Cu 3 O 7−δ the superconducting films on SrTiO 3 and MgO are found to be epitaxially grown with the c -axis perpendicular to the substrate. On ZrO 2 the films also grow with their c -axis perpendicular to the substrate, but with randomly oriented a / b -directions in the plane of the film.
Raman scattering studies of ultrathin-layer YBa2Cu3O7/PrBa2Cu3O7 superlattices
1994
We present Raman scattering studies ofc-oriented ultrathin-layer superconducting (YBa2Cu3O7) m /(PrBa2Cu3O7) n superlattices. For the superlattice with (m=2,n=1) sequence, Raman spectra reveal a new line in the spectral region around 320 cm−1. It is interpreted as a mode representing a combination of IR optical phonons of the Y-sublayers with an admixture of aB1g type Raman active vibration in the Pr sublayers. This new line, which is similar to those from the interior of the Brillouin zone of the original lattice, does not exhibit superconductivity-induced self-energy effects, although its counterpart in the pure substance does. No additional line is found in the (m=1,n=2) superlattice in …
EFFECT OF LOW-FREQUENCY NOISE ON ADIABATIC PASSAGE IN A SUPERCONDUCTING NANOCIRCUIT
2011
Recent experiments have demonstrated coherent phenomena in three-level systems based on superconducting nanocircuits. This opens the possibility to detect Stimulated Raman Adiabatic Passage (STIRAP) in artificial atoms. Low-fequency noise (often 1/f) is one of the main sources of decoherence in these systems, and we study its effect on the transfer efficiency. We propose a way to analyze low frequency fluctuations in terms of fictitious correlated fluctuations of external parameters. We discuss a specific implementation, namely the Quantronium setup of a Cooper-pair box, showing that optimizing the trade-off between efficient coupling and protection against noise may allow us to observe co…
Intensity of theB1gphonon Raman scattering inYBa2Cu3O7: Comparison of normal and superconducting states
1995
We compare theoretically the intensity of the ${\mathit{B}}_{1\mathit{g}}$ phonon Raman scattering in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ above and below the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$. Our analysis shows that a considerable enhancement of the scattering intensity in the superconducting state that is observed experimentally can be caused by an extension of the number of intermediate electronic states near the Fermi surface that participate in the Raman process.
High-pressure Raman study of theN2stretching vibration in argon-nitrogen mixtures at room temperature
1996
We present room-temperature Raman investigations of the nitrogen molecule stretching vibration in ${\mathrm{Ar}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$(${\mathrm{N}}_{2}$${)}_{\mathit{x}}$ from x=1 to x=0.59 in the pressure range 1\ensuremath{\le}p\ensuremath{\le}31 GPa. Ar substitution leads to an inhomogeneous broadening of the vibrational signal. The \ensuremath{\beta}-\ensuremath{\delta} phase transition of pure ${\mathrm{N}}_{2}$ is shifted to higher pressures for x=0.75. The substituted Ar atoms preferentially occupy the 2a sites of the cubic elementary cell of the orientationally disordered \ensuremath{\delta} phase. This interpretation of the experimental data is supported by our mod…