Papers by Keyword: Raman

Abstract: ZnS nanocrystals were embedded in a KBr single crystal matrix using the Czochralski growth technique. The X-ray diffraction, FT-IR and optical spectroscopy revealed the incorporation of ZnS nanocrystals. A blue shift of the absorption edge of the obtained samples has been observed, indicating the quantum confinement effect. The optical band-gap is estimated to be about 4.67 eV. Two excitonic peaks appeared at 300.4 nm and 271 nm. The average nanocrystal size was derived from the optical spectra. Annealing led to a shift in the absorption edge towards longer wavelengths and an increasing of the emissions intensity. Raman lines of the nanoparticles are broader and frequency-shifted compared to those of the bulk crystals. These results show that KBr is a good matrix-host of ZnS nanocrystals, and that the elaborated samples can be used for important technological applications.

Abstract: The performance of graphene/polymer nanocomposites depends on many factors but the major factor is a nanoparticles dispersion and distribution into the host matrix. The present work investigates the effect of the dispersion of graphene oxide upon the structure-property relations in metallocene linear low density polyethylene (PE), homo polypropylene (PP), and blends thereof. These nanocomposites were prepared by solvent processing, where DMF and o-xylene were used as solvents for Graphene Oxide (GO) powder and the polymers respectively, before the two components were combined to form a well-mixed initial state. Characterization of the structure and crystallization of the nanocomposites was carried out by small- and wide-angle X-ray scattering and diffraction (SAXS and WAXD). The chemical structures were characterized by Fourier transform infrared spectroscopy (FTIR) and by Raman spectroscopy, and the latter used to calculate the ID/IG value for a pure GO samples. The thermal properties of the resulting nanocomposites were investigated by DSC and TGA in order to obtain Melting temperature ( ), crystallization temperature ( ) and degree of crystallinity ( ) as well as a range of degradation temperatures. The effect of GO on the mechanical properties was studied via the ultimate tensile strength and elastic modulus.

Abstract: Scandium aluminum nitride (ScxAl1-xN) is a promising material for sensor applications as it exhibits enhanced piezoelectric properties compared to pristine AlN while maintaining other advantageous properties like high thermal stability. Magnetoelectric sensors in particular are used to detect magnetic fields which leads to special requirements regarding the investigated ScAlN in order to achieve high sensor sensitivities. Co-sputtered ScAlN layers are investigated in this work using XRD, XPS, FTIR and Raman spectroscopy for scandium concentrations from 0 to 34 %. The impact of Sc incorporation regarding residual biaxial strain and bond softening is discussed on basis of the experimental results. The activity of the B1 and E2 modes found in the FTIR measurements is of special interest as the presumably oxygen related excitation is expected to influence the piezoelectric properties.

Abstract: This work describes the development of a new post-implant crystal recovery technique in 4H-SiC using XeCl (l=308 nm) multiple laser pulses in the ns regime. Characterization was carried out through micro-Raman spectroscopy, Photoluminescence (PL), Transmission Electron Microscopy (TEM) and outcomes were than compared with 1h thermally annealed at 1650-1770-1750 °C P implanted samples (source implant) and P and Al implanted samples for 30 minutes at 1650 °C (source and body implants). Experimental results demonstrate that laser annealing enables crystal recovery in the energy density range between 0.50 and 0.60 J/cm². Unlike the results obtained with thermal annealing where stress up to 172 Mpa and high carbon vacancies (V_c) concentration is recorded, laser annealing provides almost stress free samples and much less defective crystal avoiding intra-bandgap carrier recombination. Implant was almost preserved except for step-bouncing and surface oxidation phenomena leading to surface roughening. However, the results of this work gives way to laser annealing process practicability for lattice damage recovery and dopant activation.

Abstract: The defect structure of Mg implanted GaN substrate was evaluated by TEM observations, AFM surface observations and Raman scattering spectroscopic analysis. Mg ions were implanted at room temperature (RT) and 500 °C. TEM results showed that the defect distribution along depth scale is different between RT and 500 °C condition. The several peaks originated from ion implantation were found from Raman scattering spectra and the characteristics of the defects by implantation were discussed. The crystal quality of the sample implanted at 500 °C was found to be better than that of RT by comparing the FWHM of the E₂ peak.

Abstract: Microstructure damage and evolution in 4H-SiC under He-ion implantation and post-annealing have been investigated by the combination of fourier transform infrared spectrometer (FTIR), Raman scattering spectroscopy and high resolution X-ray diffractometer (HRXRD). After implantation, the 4H-SiC specimen exhibits a heavy damage and some amorphous state appear. With increasing annealing temperature, to some extent recovery in damaged lattices was observed, as a result of the peaks of Raman and HRXRD regain their intensities. However, the reverse annealing behavior in damaged peaks was displayed after annealed at 973K. This reverse annealing effect was revealed to be due to the formation and the growth of He bubbles above 973K.

Abstract: In this paper, evolution of optical and electrical properties of diamond-like carbon (DLC) films deposited by ECR-CVD system are reported. By varying the deposition different substrates bias (0, -55, -100 V) and volume amount of C₂H₂ from 40 to 55 cc onto substrate Si/TiN and quarts. The structure of the DLC films were analyzed from Raman spectroscopy. DLC films deposited bias at-100 V and C₂H₂ at 40 cc show excellent optical transmittance and high resistivity. As a result, I_D/I_G ratio corresponds to the optical transmittance and resistivity with I_D/I_G ratio decreased making the film like to the diamond. Most importantly, the transparency and resistivity properties of the DLC films can be tailored to approaching diamond by adjusting substrates bias and volume C₂H₂, is important to many applications, which is improve film properties.

Abstract: In this work, we have studied the crystal defectiveness and doping activation subsequent to ion implantation and post-annealing by using various techniques including photoluminescence (PL), Raman spectroscopy and transmission electron microscopy (TEM). The aim of this work was to test the effectiveness of double step annealing to reduce the density of point defects generated during the annealing of a P implanted 4H-SiC epitaxial layer. The outcome of this work evidences that neither the first 1 hour isochronal annealing at 1650 - 1700 - 1750 °C, nor the second one at 1500 °C for times between 4 hour and 14 hour were able to recover a satisfactory crystallinity of the sample and achieve dopant activations exceeding 1%.

Abstract: There is serious concern that fat-soluble phthalates such as di (2-ethylhexyl) phthalate, or DEPH. Phthalates are not chemically bonded to the PVC and will with time escape by evaporation or by extraction when in contact with liquids. Raman spectroscopy excited with a 785 nm laser can be used to determine the content of plasticizers in commercial flexible polyvinyl chloride (PVC) construction plastics. This method is very convenient for rapid non-destructive remote determination of phthalates, such as for quality control of production lines, quality control or at customs.

Abstract: In this study the curing of an epoxy resin consisted of a diglycidyl ether of bisphenolA (DGEBA) resin and an aromatic Polyamine hardener was monitored combining a Raman-spectrometer and shear rheometry (Rheo-Raman). The set-up allow to carry out curing experiments at various temperatures (100, 120, 140 and 160 °C) where rheological measurements were performed using an oscillation rheometer and a plate-plate geometry while simultaneously Raman spectra were recorded. Raman-spectroscopy allows the determination of the reaction turnover and therefore the degree of cross-linking. Combined with the rheological data obtained, e.g. the gel point and the vitrification point, one can get a better insight in the processes occurring and the influence of different measurement parameters on the obtained rheological properties. Thus, the reaction turnover has been investigated at significant stages of the curing process.