Search results for "RAMAN"

Raman signal reveals the rhombohedral crystallographic structure in ultra-thin layers of bismuth thermally evaporated on amorphous substrate

2021

Under the challenge of growing a single bilayer of Bi oriented in the (111) crystallographic direction over amorphous substrates, we have studied different thicknesses of Bi thermally evaporated onto silicon oxide in order to shed light on the dominant atomic structures and their oxidation. We have employed atomic force microscope, X-ray diffraction, and scanning electron microscope approaches to demonstrate that Bi is crystalline and oriented in the (111) direction for thicknesses over 20 nm. Surprisingly, Raman spectroscopy indicates that the rhombohedral structure is preserved even for ultra-thin layers of Bi, down to $\sim 5$ nm. Moreover, the signals also reveal that bismuth films expo…

2020

Abstract. Residual pressure can be preserved in mineral inclusions, e.g. quartz-in-garnet, after exhumation due to differential expansion between inclusion and host crystals. Raman spectroscopy has been applied to infer the residual pressure and provides information on the entrapment temperature and pressure conditions. However, the amount of residual pressure relaxation cannot be directly measured. An underestimation or overestimation of residual pressure may lead to significant errors between calculated and actual entrapment pressure. This study focuses on three mechanisms responsible for the residual pressure modification: (1) viscous creep; (2) plastic yield; (3) proximity of inclusion …

Phonon Softening and Electron-Phonon Interaction in YBa2Cu3O7−δ

1993

We report on the Raman scattering investigation of the 335 cm−1 phonon of Ag (pseudo-B1g) symmetry in thin YBa2Cu3O7−δfilms on various substrates. The experiments yield values for the phonon softening below Tc, which differ from sample to sample. We find a linear relation between the softening and the inverse asymmetry parameter of the phonon Fano-like lineshape, when these parameters, obtained from different samples, are compared with each other. In contrast to this, the onset temperatures for the softening are the same for these samples.

The effect of wear on the tetragonal-to-monoclinic transformation and the residual stress distribution in zirconia-toughened alumina cutting tools

1998

Abstract Zirconia-toughened alumina cutting tools have been examined after machining an AISI 1040 steel. The Raman spectrum of zirconia and the fluorescence spectrum from alumina have been used to determine the extent of the tetragonal-to-monoclinic (t-m) transformation and the residual stresses in and around the worn-out crater, respectively. Although about 15% vol. m-zirconia is present even in a brand new cutting tool, it was shown that the crater region undergoes the t-m transformation up to 40% vol. In both cases, the transformed zone is concentrated near the surface. The residual stresses in alumina are slightly compressive in the new cutting tool and away from the crater region, but …

Transverse chemical interface detection with coherent anti-Stokes Raman scattering microscopy

2011

International audience; Transverse "chemical" interfaces are revealed with a conventional two beam narrowband coherent anti-Stokes Raman scattering microscopy setup in a collinear configuration. The exciting "pump" and "Stokes" beams are focused on the sample in two opposite directions. The subtraction of the two generated anti-Stokes signals gives rise to a signal that is directly proportional to the pure Raman spectrum of the resonant medium. This property is used to highlight an interface between glass and N,N-dimethylformamide (DMF) and recover the pure Raman spectrum of DMF around its 1408 cm−1 vibrational band.

Strong enhancement of the Breit-Wigner-Fano Raman line in carbon nanotube bundles caused by plasmon band formation

2002

We investigate the origin of the Breit-Wigner-Fano line in the Raman spectra of individual single-walled carbon nanotubes and their bundles. Using confocal Raman microscopy and atomic-force microscopy we found that the Breit-Wigner-Fano line intensity increases strongly with the bundle thickness. We confirmed this result by Raman investigations of partially decomposed bundles, which were additionally investigated by transmission electron microscopy. Our random-phase approximation based theory, which identifies the Breit-Wigner-Fano line as an excited band of plasmon-phonon modes, is fully consistent with the experimental results.

Non radiative recombination centers in ZnO nanorods

2013

ABSTRACTNowadays, the nature of the non radiative recombination centres in ZnO is a matter of controversy; they have been related to extended defects, zinc vacancy complexes, and surface defects, among other possible candidates. We present herein the optical characterization of catalyst free ZnO nanorods grown by atmospheric MOCVD by microRaman and cathodoluminescence spectroscopies. The correlation between the defect related Raman modes and the cathodoluminescence emission along the nanorods permits to establish a relation between the non radiative recombination centers and the defects responsible for the local Raman modes, which have been related to Zn interstitial complexes.

Fourth order cascaded Raman shift in As38Se62 chalcogenide suspended core fiber pumped at 1.995 μm

2011

Fourth order cascaded Raman wavelength shift is demonstrated in As 38 Se 62 suspended core fiber using 1995 nm nanosecond source. The measured Raman gain coefficient is∼2×10−11 m/W at 1995 nm. The Raman peaks are reproduced by numerical simulations.

Modulational instability processes in optical isotropic fibers under dual-frequency pumping

2001

Experiments are presented showing that under dual-frequency, circular polarization pumping, a host modulational instability processes can be generated in a single isotropic fiber, by carefully tuning the frequency spacing between the pumps.

2021

Gold-assisted mechanical exfoliation currently represents a promising method to separate ultralarge (centimeter scale) transition metal dichalcogenide (TMD) monolayers (1L) with excellent electronic and optical properties from the parent van der Waals (vdW) crystals. The strong interaction between Au and chalcogen atoms is key to achieving this nearly perfect 1L exfoliation yield. On the other hand, it may significantly affect the doping and strain of 1L TMDs in contact with Au. In this paper, we systematically investigated the morphology, strain, doping, and electrical properties of large area 1L MoS2 exfoliated on ultraflat Au films (0.16-0.21 nm roughness) and finally transferred to an i…