Search results for "Espectroscòpia Raman"
showing 10 items of 16 documents
Influence of krypton atoms on the structure of amorphous hydrogenated carbon deposited by plasma enhanced chemical vapor deposition
2010
Hydrogenated amorphous carbon (a-C:H) films were prepared by plasma enhanced chemical vapor deposition using methane (CH4 ) plus krypton (Kr) mixed atmosphere. The depositions were performed as function of the bias voltage and krypton partial pressure. The goal of this work was to study the influence of krypton gas on the physical properties of a-C:H films deposited on the cathode electrode. Krypton concentration up to 1.6 at. %, determined by Rutherford Back-Scattering, was obtained at high Kr partial pressure and bias of -120 V. The structure of the films was analyzed by means of optical transmission spectroscopy, multi-wavelength Raman scattering and Fourier Transform Infrared spectrosco…
Ambient-temperature high-pressure-induced ferroelectric phase transition in CaMnTi2O6
2017
Physical review / B 96(9), 094101 (2017). doi:10.1103/PhysRevB.96.094101
Snapshots of a solid-state transformation: Coexistence of three phases trapped in one crystal
2016
Crystal-to-crystal transformations have been crucial in the understanding of solid-state processes, since these may be studied in detail by means of single crystal X-ray diffraction (SCXRD) techniques. The description of the mechanisms and potential intermediates of those processes remains very challenging. In fact, solid-state transient states have rarely been observed, at least to a sufficient level of detail. We have investigated the process of guest extrusion from the non-porous molecular material [Fe(bpp)(HL)](ClO)·1.5CHO (bpp = 2,6-bis(pyrazol-3-yl)pyridine; HL = 2,6-bis(5-(2-methoxyphenyl)-pyrazol-3-yl)pyridine; CHO = acetone), which occurs through ordered diffusion of acetone in a c…
Unraveling the strain state of GaN down to single nanowires
2016
International audience; GaN nanowires (NWs) grown by molecular beam epitaxy are usually assumed free of strain in spite of different individual luminescence signatures. To ascertain this usual assumption, the c/a of a GaN NW assembly has been characterized using both X-ray diffraction and Raman spectroscopy, with scaling the measurement down to the single NW. Free-standing single NWs have been observed free of strain-defined as [c/a = (c/a)(o)]/(c/a)(o)-within the experimental accuracy amounting to 1.25 x 10(-4). However, in the general case, a significant portion of the NWs is coalesced, generating an average tensile strain that can be partly released by detaching the NWs from their substr…
Quantifying the Covalent Functionalization of Black Phosphorus
2020
Abstract A straightforward quantification method to consistently determine the overall functionalization degree of covalently modified two‐dimensional (2D) black phosphorus (BP) by Raman spectroscopy has been carried out. Indeed, the successful reductive methylation of the BP lattice using sodium intercalation compounds and exhibiting different functionalization degrees has been demonstrated by 31P‐magic angle spinning (MAS) NMR spectroscopy. Furthermore, the correlation of 31P‐MAS NMR spectroscopy and statistical Raman spectroscopy (SRS) revealed the first method to determine the functionalization degree of BP solely by evaluating the intensities of distinct peaks in the Raman spectra of t…
Lattice Opening upon Bulk Reductive Covalent Functionalization of Black Phosphorus
2019
The chemical bulk reductive covalent functionalization of thin-layer black phosphorus (BP) using BP intercalation compounds has been developed. Through effective reductive activation, covalent functionalization of the charged BP by reaction with organic alkyl halides is achieved. Functionalization was extensively demonstrated by means of several spectroscopic techniques and DFT calculations; the products showed higher functionalization degrees than those obtained by neutral routes.
Raman Spectra of ZrS2 and ZrSe2 from Bulk to Atomically Thin Layers
2016
In the race towards two-dimensional electronic and optoelectronic devices, semiconducting transition metal dichalcogenides (TMDCs) from group VIB have been intensively studied in recent years due to the indirect to direct band-gap transition from bulk to the monolayer. However, new materials still need to be explored. For example, semiconducting TMDCs from group IVB have been predicted to have larger mobilities than their counterparts from group VIB in the monolayer limit. In this work we report the mechanical exfoliation of ZrX2 (X = S, Se) from bulk down to the monolayer and we study the dimensionality dependence of the Raman spectra in ambient conditions. We observe Raman signal from bul…
Polarized and resonant Raman spectroscopy on single InAs nanowires
2011
We report polarized Raman scattering and resonant Raman scattering studies on single InAs nanowires. Polarized Raman experiments show that the highest scattering intensity is obtained when both the incident and analyzed light polarizations are perpendicular to the nanowire axis. InAs wurtzite optical modes are observed. The obtained wurtzite modes are consistent with the selection rules and also with the results of calculations using an extended rigid-ion model. Additional resonant Raman scattering experiments reveal a redshifted E1 transition for InAs nanowires compared to the bulk zinc-blende InAs transition due to the dominance of the wurtzite phase in the nanowires. Ab initio calculatio…
Phonon-plasmon coupling in Si doped GaN nanowires
2016
Abstract The vibrational properties of silicon doped GaN nanowires with diameters comprised between 40 and 100 nm are studied by Raman spectroscopy through excitation with two different wavelengths: 532 and 405 nm. Excitation at 532 nm does not allow the observation of the coupled phonon–plasmon upper mode for the intentionally doped samples. Yet, excitation at 405 nm results in the appearance of a narrow peak at frequencies close to that of the uncoupled A 1 (LO) mode for all samples. This behavior points to phonon–plasmon scattering mediated by large phonon wave-vector in these thin and highly doped nanowires.
WS2 2D Semiconductor Down to Monolayers by Pulsed-Laser Deposition for Large-Scale Integration in Electronics and Spintronics Circuits
2020
International audience; We report on the achievement of a large-scale tungsten disulfide (WS2) 2D semiconducting platform derived by pulsed-laser deposition (PLD) on both insulating substrates (SrTiO3), as required for in-plane semiconductor circuit definition, and ferromagnetic spin sources (Ni), as required for spintronics applications. We show thickness and phase control, with highly homogeneous wafer-scale monolayers observed under certain conditions, as demonstrated by X-ray photoelectron spectroscopy and Raman spectroscopy mappings. Interestingly, growth appears to be dependent on the substrate selection, with a dramatically increased growth rate on Ni substrates. We show that this 2D…