Papers by Keyword: Raman Spectroscopy

Abstract: SiC sputtered and e-beam evaporated layers have been deposited on 4H-SiC substrates. High temperature annealing with two plateaus at 1400°C and 1700°C is performed to recrystallize the layers. The crystallinity was investigated by Raman spectroscopy with laser lines of 785, 405 and 325nm. To determine the electrical conductivity of the layers, electrical measurements are made. Only the electron beam evaporated layers presents a recrystallization close to homoepitaxial quality but, contrary to sputtered layers, they don’t have an electrical conductivity.

Abstract: Mg/Al bilayer thin films were successfully deposited by using D.C. magnetron sputtering technique. To study the effect of hydrogenation on structural, optical and electrical properties of Mg/Al thin films, the hydrogenation of the annealed thin films was done under different hydrogen pressure (15, 30 & 30psi). The structural properties of the films were investigated by Raman spectroscopy and decrease in intensity of Raman peaks with increasing hydrogen pressure was observed; this typically confirms the existence of hydrogen in Mg/Al thin films. The thin film is of semiconducting nature and it was found that the electrical conductivity of the film decreases with increasing hydrogen pressure applied. In the hydriding kinetics of the films, it was seen that the resistivity increased along with hydrogen absorption time. Eventually, it attains the equilibrium stage indicating the hydrogen absorption in the thin films. The rate of absorption of hydrogen increases with the pressure of hydrogen over different time ranges and decreases with the absorption of hydrogen over time.

Abstract: Carbon nanotube yarns (CNTYs) are twisted hierarchical fibers which exhibit a strong property-structure relationship. Understanding of the property-structure relationship of CNTYs will allow their use in structural and energy dissipation (damping) applications. For this reason, the morphology and structure of dry-spun CNTYs are characterized by means of Raman spectroscopy mapping, atomic force microscopy, and scanning electron microscopy and correlated to their quasi-static and dynamic mechanical properties. The continuous CNTYs present some degree of structural variability, which explains the variability measured in their dynamic mechanical response. Under tension, 42.3 μm diameter (0.71 porosity) CNTYs reach specific strengths of ~0.8 N/tex and ultimate strains ranging from 4% to 7%. Mechanical hysteresis tests under incremental cyclic strain show that the CNTYs exhibits high energy dissipation, which concur with dynamic mechanical analysis (DMA). DMA shows that CNTYs are unconventional materials with high specific stiffness (per unit weight) as well as a very high damping ratio. The damping ratio increases with temperature and reach ~0.6 at 60 °C. The mechanical response of the CNTYs under tension can be explained mainly from changes in the hierarchical structural conformation of the yarn, rather than from changes in the carbon nanotube bond distance or inherent material properties.

Abstract: A non-destructive technique for the characterization of the doped regions inside wide bandgap (WBG) semiconductor structures of power devices is presented. It consists in local measurements of the surface potential by Kelvin Probe Force Microscopy (KPFM) coupled to micro-Raman spectroscopy. The combined experiments allow to visualize the space charge extent of the doped region using the near-field mapping and to estimate its dopant concentration using the Raman spectroscopy. The technique has been successfully applied for the characterization of a WBG SiC (silicon carbide) device.

Abstract: The characteristics of sputtered amorphous diamond-like carbon-containing copper (DLC: Cu films) films deposited on Si (100) substrates and Si (111) in argon gas-filled chamber using carbon target under different substrates deposition time, and RF power. The samples were deposited by RF magnetron sputtering and analyzed using Raman spectroscopy and X-ray reflectivity (XRR) methods. Different parameters of depositions were used to study the structure, thickness, roughness, and density of the samples. The Cu preliminary layer act as a catalyst to growth the DLC thin-film analyzed using XRR analysis to measure thickness, roughness, and density of the thin films. The film structures of the samples were analyzed using Raman spectroscopy with a 532nm laser source. Gaussian peak shapes were used in Raman spectrum fitting to analyzed to measure the D band and G band for both samples. The Films thickness, roughness, and mass density were studied by XRR techniques using XRD to acquire the multilayer structure of thin films grown by magnetron sputtering.

Abstract: Polyaniline (PANI) thin films were successfully prepared from an aqueous electrolyte bath containing aniline and sulphuric acid (H₂SO₄) using electrodeposition method. The present study demonstrates that the properties of PANI thin film depends on the variation of pH and aniline concentration in prepared precursor. The optical and structural of PANI thin films were characterized using UV-Visible spectrometer (UV-Vis), X-ray diffraction spectrometer (XRD), Fourier Transform Infra-Red spectrometer (FTIR) and Raman spectrometer. PANI layer grown at pH 2.00 displayed green colour layer which denoted as emeraldine base (half oxidized state of PANI) while at pH 3.80 the colour of PANI layer was yellow representing the leucoemeraldine base (fully reduced state of PANI). Result obtained from FTIR confirmed the footprint of PANI and Raman spectrometer confirmed the half oxidized emeraldine base of PANI. Optical analysis using UV-Vis demonstrated the smallest energy band gap, E_g of PANI is 3.54 eV for sample with 0.50 M aniline concentration and pH 2.00. The trend shows that the bandgap of PANI is increased as the pH increased from 2.00 to 3.80. XRD result showed that all the deposited PANI layers were amorphous. Full characterization of this material is providing some information on PANI behavior due to pH and concentration in the prepared precursor.

Abstract: One of the challenges in fabricating organic semiconductor thin film is to produce bettermolecular ordering that compromise its electronic properties. Molecular ordering of amorphous thin film can be improved in many ways. Here, high molecular weight polylactic acid (PLA) is introduced as binding matrix to promote 3'''-didodecyl-2,2':5',2'':5'',2'''-quaterthiophene (4T) film’s homogeinity across indium tin oxide (ITO) surface. Molecular ordering of the spin coated biodegradable PLA and 4T blend film processed at ambient atmosphere was studied using two vibrational spectroscopy methods. The complementary analysis of infrared absorption spectrum and Raman spectrum had identified several vibrational modes contributed by thiophene rings and alkyl functional groups. The Raman analysis implied there is a slight change of thiophene ringsʼ molecular orientation due to compressive stress after introduction of polymer. Microscopic characteristics of oligothiophenes especially at the π-π conjugated backbones contained crucial information in order to exploit the oligothiophene as flexible electronics devices.

Abstract: Sodium-ion batteries (SIBs) as low-cost alternatives to expensive lithium-ion batteries become a hot R&D topic in the recent days due to the natural abundancy of sodium in the Earth’s crust and also in the oceans. As far as solid electrolytes for SIBs are concerned, larger size of Na⁺ ions compared to that of Li⁺ ions hinders the ionic mobility resulting to insufficient ionic conductivity for practical applications. Development of quasi-solid state gel-polymer electrolytes (GPEs) would be a feasible solution to overcome this challenge. In this work, we developed Poly (methyl methacrylate) (PMMA) based GPEs with six different compositions dissolved in EC:PC (ethylene carbonate and propylene carbonate, 1:1 wt%) mixture. Among six different GPE samples investigated by Electrochemical Impedance Spectroscopic and Raman Spectroscopic techniques, the best ambient temperature ionic conductivity of 4.2 mS cm^-1 was obtained for 9PMMA:9NaPF₆:41EC:41PC (wt%). Variation of ionic conductivity with inverse temperature showed Arrhenius behavior with almost constant activation energies. The best conducting GPE showed an activation energy of 0.14 eV. In the Raman spectra, very sharp crystalline peaks (400-850 cm^-1 wave number range) of NaPF₆ disappear in the gel state of the electrolytes confirming the non-crystalline nature of the GPEs. Boson modes remain almost constant in intensity for all the six different compositions. The best conducting GPE seems to be highly suitable for practical applications in SIBs as it has sufficient ambient temperature ionic conductivity.

Abstract: Graphene as a wonder material has received great attention and importance due to its fascinating properties. Here in this study, we also demonstrate a simple two step process to prepare graphene sheets (GSs) from the electrochemical exfoliated graphene oxide (EE-GO) followed by microwave irradiation reduction. The properties and structure of the resulted product samples were studied by Ultraviolet spectroscopy (UV), Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy-dispersive X-ray (EDX or EDS), Raman spectroscopy and Atomic force microscopy (AFM) for validation of their distinguishing characteristics. UV spectra of microwave irradiation reduced graphene oxide (MI-RGO) and EE-GO exhibited an intense and sharp absorption peak concentrated at wavelengths of 236 and 266nm, respectively. The elimination of oxygen functionalities present in the EE-GO plane was illustrated by FTIR as a result of microwave irradiation treatment. The relative layer structures of MI-RGO and EE-GO were confirmed by XRD. Similarly, the Raman spectra revealed the difference in between the EE-GO and MI-RGO characteristic reflection bands. The thin, crumpled and curved type morphology of the obtained graphene sheets (GSs) was also displayed by SEM while the composition of a few layer graphene sheets with atomic mass percents of carbon (75%) and oxygen (25%) was established by EDX. The Synthesis procedure is simple, rapid and eco-friendly with high yield.

Abstract: Vanadium oxide thin films were deposited on glass substrates by O₂ reactive-RF magnetron sputtering from a vanadium (V) target without substrate-heating. The percentages of O₂ gas were 10%, 7.5%, 6.0%, 5.0% and 2.5%. The total gas flow rate (O₂/Ar) was kept at 25 sccm. As-deposited films were experienced post-annealing process at different temperatures and times. The crystallinity and chemical bonding states of films were examined by X-ray diffraction and Raman spectroscopy. The condition in annealing to active crystallinity depended on an earlier composition of the films. As O₂-gas percentages were 10% and 7.5%, after annealing, the as-deposited V_xO_y films were transformed into crystalline V₂O₅ films. With decreasing in O₂ percentage to 5.0% and 2.5%, the films were transformed into V₂O₃ and VO films, respectively. The films deposited with 6.0% O₂ were crystallized to VO₂ with phase B after annealing with 500 °C 15 h. By applying a longer time to 30 h at the high temperature 500 °C in annealing, VO₂ films revealed only phase M formation.