Papers by Keyword: Raman

Abstract: CuO/TiO₂ nanocomposites were synthesized using an economical drop-casting method and subsequently irradiated with high-energy C⁺ ions at fluence levels of 1 × 10¹⁴, 1 × 10¹⁵, 1 × 10¹⁶, and 1 × 10¹⁷ ions cm⁻². While ion irradiation of metal oxide materials is well established, the systematic investigation of C⁺ ion effects on the structural and optical properties of CuO/TiO₂ nanocomposites under these specific fluence conditions has been limited. This study therefore contributes new insight into how controlled C⁺ irradiation can tailor the behavior of this composite. These un-irradiated and irradiated nanocomposites were characterized using various techniques such as Energy Dispersive X-Ray Spectroscopy (EDX), Raman Spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Photoluminescence (PL) Spectroscopy and Diffuse Reflectance Spectroscopy (DRS) to analyze structural, morphological and optical properties of these nanocomposites. The Raman and EDX analysis confirmed the formation of pure CuO/TiO₂ nanocomposites. The SEM results represent the spherical morphology of these nanocomposites in aggregated form. PL spectra’s depicted the pure and C⁺ ions irradiated nanocomposites were the same before and after C⁺ irradiation in the Photoluminescence emission. DRS results indicated that band gap energy was decreased as the fluence rate of C⁺ ions increased up to 1 × 10¹⁷ ions cm^-2.

Abstract: In this paper, we report on the growth of highly uniform MoS₂ films, mostly consisting of monolayers, on SiC surfaces with different doping levels (n- SiC epitaxy, ~10¹⁶ cm^-3, and n⁺ SiC substrate, ~10¹⁹ cm^-3) by sulfurization of a pre-deposited ultra-thin MoO_x films. MoS₂ layers are lowly strained (~0.12% tensile strain) and highly p-type doped (<N_h>≈4×10¹⁹ cm⁻³), due to MoO₃ residues still present after the sulfurization process. Nanoscale resolution I-V analyses by conductive atomic force microscopy (C-AFM) show a strongly rectifying behavior for MoS₂ junction with n^- SiC, whereas the p⁺ MoS₂/n⁺ SiC junction exhibits an enhanced reverse current and a negative differential behavior under forward bias. This latter observation, indicating the occurrence of band-to-band-tunneling from the occupied states of n⁺ SiC conduction band to the empty states of p⁺ MoS₂ valence band, is a confirmation of the very sharp hetero-interface between the two materials. These results pave the way to the fabrication of ultra-fast switching Esaki diodes on 4H-SiC.

Abstract: In this paper the stress field distribution in 3C-SiC (111) resonators has been studied by micro-Raman measurements and COMSOL simulations. The measurements show that the asymmetry of the anchor points configuration produce an asymmetry in the stress filed distribution. This behavior has been confirmed also by the simulations. Furthermore, from the simulations the importance of the reduction of the under etching of the anchor points of the resonators has also been observed. In fact the reduction of this under etch produces a decrease of the stress in the double clamped beams, a small reduction of the resonance frequency, and a large reduction of the Q-factor and then of the oscillation frequency stability of the resonators in closed-loop operation.

Abstract: Due to high growth temperatures during the physical vapor transport (PVT) it is still almost impossible to gain proper insight into the actual growth conditions. Therefore, computer tomography (CT) is used as an in-situ monitoring during the crystal growth process. With the help of this technique, it is possible to observe the nucleation centers during the initial stage of growth (CT after 0h) of a 4H-SiC single crystal. These growth islands are likely built before the actual growth conditions are reached. Raman investigations of the area around a growth island located directly on the interface between seed and grown crystal is used to support this assumption. In addition, optical analysis after KOH etching were made to reveal the defects around the growth island. The island exhibits a rough doping concentration in comparison to the surrounding grown crystal.

Abstract: In this study, a catalyst based on Montmorillonite clay was implemented for carbon nanotubes (CNTs) synthesizing. The kaolinite clay was used as a supporting material for iron-cobalt bimetallic catalytic nanoparticles. The CNTs have been synthesized by using atmospheric chemical vapor deposition (APCVD). To assess the quality of preparation both the catalyst and CNTs have been characterized by different techniques. The chemical bonding and interactions were verified by FT-IR. The general overview of microstructure was examined using SEM, while, the detailed structure and morphology were examined by HR-TEM, in addition to thermal analysis (DTA); surface area (BET); X-ray fluorescence (XRF), Raman spectroscopy, and XRD analysis. The results revealed that; Fe₂O₃ and Co₃O₄ NPs were uniformly assembled on the clay nanoplatelets. The specific BET surface area of the clay and catalyst was determined to be 46.12 and 57.06 m²/g respectively. Also, from XRD, the peaks at 26° and 42.7° confirm the presence of CNTs. The FTIR absorption bands, D, G, and G^\ bands from the Raman spectrum confirm the hexagonal structure of the CNTs. The obtained results prove the high quality of CNTs preparation.

Abstract: The layers of Al and Co are deposited successively on SiO₂ substrates using magnetron sputtering technique. Thereafter, annealing is provided at 1100°C in 2-195 minutes in the muffle furnace. The color of the layers is changed gradually from brown at 2 minutes to blue at 195 minutes. The change of the structure during annealing is seen from the Raman spectra. The line at 188 cm^-1 shifts to 203 cm^-1, which shows the substitution of the Co³⁺ with less massive Al³⁺ ions during the formation of CoAl₂O₄. The most intensive peak at 505 cm^-1 disappears after the process is finished in 60 minutes. the annealing is provided in the Ar+O₂ atmosphere with 5% and 0.07% of oxygen in the temperature range from 850 to 1100 °C. The film with the layered structure is obtained at the low oxygen conditions.

Abstract: In this work, we investigate, by μ-Raman spectroscopy the distribution of stress field on a micro-machined structures. They were realized on a 3C-SiC substrate, grown on a Silicon On Insulator (SOI) wafer, after lithography and etching processes. Various structures, such as strain gauge, single and double clamped beams, were analyzed, showing different stress distributions. All the structures show an intense variation of stress close to the undercut region.

Abstract: This paper discusses a novel annealing technique for 4H-SiC implants which involves the use of pulsed XeCl laser (l=308 nm). In particular, an absorbing graphitic coating is used to protect the sample from surface atoms desorption or phase separation. Both conventional furnace annealing and laser annealing on P and Al implants, commonly employed for source and body in metal-oxide-semiconductor field-effect transistors (MOSFETs), were examined through Transmission Electron Microscopy (TEM), u-Raman spectroscopy and Scanning Electron Microscopy (SEM). It is shown that the implant activated through traditional thermal annealing at 1650 °C for 30 min has a large network of dislocation loops, while they do not appear to be present in the laser annealed implant. Through Raman spectroscopy and SEM investigations both the crystalline quality of the laser annealed sample and the integrity of the surface were attested.

Abstract: This paper studies the electrical efficiency of carbon nanotubes (CNT) with nanosized diameter inserted into palm-based oil at various concentrations (0, 0.0125, 0.025, 0.0375, 0.05, 0.125, 0.25 and 0.5 g/L). Dispersion methods, including sonication and drying process were systematically applied for producing stable CNT nanofluids. Several parameters such as electrical properties (AC breakdown voltage) and dielectric properties (dissipation factor, relative permittivity and resistivity) were measured accordingly based on IEC 60156 and IEC 60247 international standards. The test results reveal that the higher concentration of CNTs dispersed in palm oil, the lower AC breakdown voltages produced. At 0.5 g/L concentration, the average of 50 breakdown was 22.30 kV, which is 72.33% decrement compared to palm oil without any nanofiller. Besides, the permittivity and resistivity of CNT nanofluids decrease as concentrations increased, while dissipation factor increases along with CNT concentrations. In order to further support this indication, Raman analysis is measured to relate the behavior of AC breakdown voltages and chemical structure of CNT nanofluids. Based on the Raman spectra at 2800-3200 cm^-1 region, it is shown that the value of total unsaturated fatty acid and total fatty acid decreased as concentrations of CNT increased. This occurrence directly influences the degradation performance of AC breakdown voltages.

Abstract: Novel electronic nanomaterial, the carbon nanotube (CNT) has emerged in many sensor applications as such its state dispersion has considerable importance to ensure the sustainability of its electronic properties. In this paper, we reported a state of art conductivity mapping on nanostructure surface of single walled carbon nanotubes (SWCNT) and poly(3-hexylthiophene-2,5-diyl), (P3HT) as potential sensing film. This composite is proposed to give selective analyte anchoring across the film as well as improved carrier mobility. The easy solution processing method was chosen to produce non-covalently wrapped conducting polymer onto the surface of SWCNT. We successfully observed high resolution images of the SWCNT walls that indicated increase of the thickness due to polymer wrapping. The image obtained from conductivity atomic force microscopy (CAFM) show the film’s electrical distribution that correlated with the observed nanostructure of film. Supporting optical characteristics of the nanocomposite obtained from UV-Vis spectroscopy and Raman spectroscopy discussed the morphology of the polymer wrapping and the state of dispersion of the polymer and the nanotubes. It is hypothesized the filament structures made by P3HT/SWCNT can give better sensing performance due to modification of π-π electronic band of SWCNT.