Papers by Keyword: Raman Spectroscopy

Abstract: The influence of the chemical composition of the substrate material on the chemical and phase composition of the formed coating was investigated. A number of experiments aimed at studying the interaction of titanium alloys with ultrashort laser pulses in different reaction media was carried out. A new method for the formation of titanium carbide under the action of ultrashort laser pulses on the surface of a titanium sample in a liquid hydrocarbon and liquid nitrogen medium is described. The description of the experiment is presented. The treated surface was investigated using a scanning electron microscope. Raman spectra from the surface of treated titanium alloys under different exposure conditions are obtained.

Abstract: In this paper, the influence of immersion time on the structural and optical properties of SnO2 thin films was investigated. A series of samples was deposited by Sol-Gel dip coating method onto glass substrates. The number of layers was fixed at 03, but the immersion time was varied between 01 to 10 minutes. The samples [(3 layers) - SnO2 / glass] were submitted to thermal treatments in air at 500°C during 2h. The specimens are characterized by Raman spectroscopy and UV-Visible spectroscopy. Raman spectroscopy show that the thin films of SnO2 obtained at 06 and 10 minutes of immersion time, are crystallizes in rutile phase. The obtained results of optical analysis showed that the SnO2 thin films are transparent (77-85%) in the visible region and the values of the optical band gap varied from 3.81eV and 3.86 eV.

Abstract: The effect of the formation and heat treatment modes of silicon-carbon coatings deposited by ion-beam sputtering of silicon carbide on their morphology, chemical and phase composition is determined. It has been established that an increase in the power of the ion source from 432 W to 738 W leads to a decrease in the sp³/sp² phase ratio by 1.7 times and an increase in the ratio of Si-C/Si-O bonds by 1.9 times. It is shown that doping of carbon coatings with silicon carbide increases their heat resistance.

Abstract: The electrochemical properties of the nitrogen-enriched carbons obtained by plant raw treatment as electrode material for supercapacitors were investigated by electrochemical impedance spectroscopy, cycling voltammetry and galvanostatic charge-discharge cycling in KOH aqueous electrolyte. The effect of activation agent (NaOH) concentration and carbonization temperature were analyzed. The separation of double layer and redox capacitance components was done. The dominating role of microporosity for capacitive properties was demonstrated. The capacitance of model capacitors based on carbons obtained at different modes was calculated from both from cycling voltammetry and galvanostatic charge-discharge data. The maximal values of specific capacitance of carbon materials carbonized at 600°C and 900°C are about 100 and 120 F/g, respectively.

Abstract: Raman spectroscopy and sheet resistance measurements were used to study the preparation processes of low-resistance p-type 4H-SiC by Al ion implantation with ion doses of 2.45×10¹² - 9.0×10¹⁴ cm^-2 and annealing treatment with temperatures of 1700 - 1900 °C. Greatly different from the LOPC (longitudinal optical phonon-plasmon coupled) Raman mode found from the sample of doping 4H-SiC during epitaxial growth, no significant influence on the surface concentration could be found for the longitudinal optical (LO) mode of Al-implanted 4H-SiC samples. When the Al surface concentration is larger than around 10¹⁸ cm^-3, it was found that the intensity of the LO+ Raman peak (~ 980 - 1000 cm^-1) increases and its full width at half maximum (FWHM) drops with the increase of surface concentration after annealing treatment. Moreover, for surface concentrations above 10¹⁸ cm^-3, the LO+ Raman peak showed a left shift towards the LO peak, which could be related to the increase of free carrier concentration in the Al-implanted 4H-SiC samples. After higher annealing temperatures of 1800 °C and 1900 °C, the crystallinity of Al-implanted 4H-SiC was found to be improved compared to annealing at 1700 °C for surface concentrations larger than 10¹⁸ cm^-3, which is consistent with the results of sheet resistance measurements.

Abstract: Hybrid laminates consisting of fibre-reinforced thermoplastic films and metallic thin sheets are successively replacing thermoset based systems due to their obvious advantages of higher formability and aptitude for mass production. In order to monitor the material under operating conditions, hybrid laminates need to be equipped with smart sensor units. Artifact-free integration of commercial strain gauges into hybrid laminates is almost impossible. Therefore, a new thin film strain sensor based on a PVD sputtering process was developed.The aim of this work was to evaluate the influence of the layer thickness as well as the elevated temperature during the sputtering process on the electrical performance of Ni-C strain sensors. The Ni-C films with different layer thickness and different sputtering temperatures manufactured by means of a magnetron sputtering process were investigated for the sheet resistance and the change of temperature coefficients of resistance. In addition, Raman spectroscopy was utilized to investigate the phase development with regard to different sputtering temperatures. It can be seen that the gauge factor gets doubled while optimizing the layer thickness. When the sputtering temperature was increased, the graphitic phase formation was preferred and the impurities were reduced. These results are discussed in this paper and appropriate solution concepts are provided.

Abstract: Double rare-earth (La; Sm/Gd) substituted Aurivillius family of Bismuth Layered Structured Ferroelectrics (BLSF) namely Bi_2.6Sm_0.2La_0.2TiNbO₉ (BSLT; sample-A), Bi_2.6Gd_0.2La_0.2TiNbO₉ (BGLT; sample-B), single phase ceramics were prepared by solid state route. In addition, intergrowth (x BSLT - (1-x) BGLT, where x=0.49; sample-C) and solid solution (BSLT_­x - BGLT_y; where x + y=0.4; sample-D) materials were prepared. Dielectric, ferroelectric and Raman spectroscopic properties were studied on the said above materials. The X-ray diffraction analysis and Raman spectra revealed well-formation of stable structure. Though, the sample-C and sample-D have lower coercive field, compared to the sample-A and sample-B, but they exhibited sharp hysterisis loop. Therefore the instrinsic defects of sample-D inhabits more sensitivity towards the ferroelectric behaviour. The results were corroborated to the impedance and dielectrical data. The results were consistent with the SEM micrographs and complex impedance plots. An attempt is made to understand the effect of rare-earth ions on A-site of layered-pervoskite structure, defined as: (Bi₂O₂)²⁺(A_n-1B_nO_3n+1)^2-.The term n represents number of pervoskite blocks interleaved with the bismuth oxide layers.

Abstract: A promising two-dimensional material for applications in optoelectronic and photonics, MoS₂ is in focus since last decade. Its optical, structural and electronic properties are of practical importance along with its exciton dynamics. MoS₂ thin films were synthesized with Chemical Vapour Deposition (CVD) technique on Si/SiO₂ substrates. The thickness dependent regularities were controlled and examined to quantitatively control the film quality with thickness variation. Various characterization techniques were employed to investigate structural and morphological changes induced systematically to reveal the van der waal stacked layers of MoS₂ material. The In-plane characteristic mode E¹_2g and out of plane A_1g vibrational modes were detected in different configurations of film’s structure. Optical absorption spectra gave us information on photon energy with the absorbance; extrapolation of this curve gave optical bandgap (E_g) in the form of Tauc plot. These energies can be associated to interband electronic transitions in the Brillouin zone. The intrinsic excitonic response as a consequence of layer stacking and velly indexing can be attributed to this change in bandgap from 1.68 to 1.91 eV. Surface morphology of the as-grown films also provides better understanding of MoS₂ material with root mean square (RMS) roughness in the range of 1.32 to 3.85 nm.

Abstract: The hydrolytic lignin (HL) derivatives have been prepared via its physical activation (high-temperature annealing in vacuum) followed by chemical modification (fluorination). It was found that the graphitized product of thermal activation up to 1000 °C at a low temperature gain rate of < 2 °C/min under high vacuum shows an enhanced specific surface area (215 m²/g), that makes it potentially useful as sorbent, catalytic substrate, or electrode material. It was revealed from the experimental data the manufactured graphitized material consists of nanometric structural blocks, possibly nanographites and/or few-layer nanographenes. The edges of graphenes in agglomerates in activated hydrolytic lignin (AHL) have armchair and zigzag shapes. The nontrivial electronic structure of the zigzag edges, along with the electronic conductivity and the ability of AHL to absorb oxygen, can cause an increase in the energy intensity of lithium battery (LB) manufactured using AHL.The carbon-fluorine bond of semi-ionic type was detected in HL and AHL fluorinated in the temperature range of synthesize 60 – 300 oC. The fluorinated forms of both HL and its thermally activated product show increased values of operating voltage due to the participation of fluorine bound to carbon in the electrochemical process.

Abstract: Graphene has been employed as electrode materials in various electrochemical biosensors due to its excellent electrical, mechanical, thermal and optical properties. In the present study, Chemical Vapor Deposited (CVD) and epitaxial graphene on SiC were examined as material for electrochemical biosensing application. The surface of both types of graphene were characterized using Raman spectroscopy as well as with Scanning Electron Microscopy (SEM). As the key point for the comparison, the impedance spectroscopy measurements of different graphene films using deionized water and saline 0.9% NaCl solution were performed as well. The method of impedance measurements applied to graphene films expands the range of possibilities for using this material as sensitive biosensors. Based on the comparative tests results, it is possible to draw the first simple conclusions about the advantages of CVD or epitaxial graphene. Based on the results of impedance spectroscopy, it is possible to draw a simple conclusion – single layer graphene has the higher sensitivity.