Raman Result Research Articles

Effect of rare earth doping on the electromagnetic response of hard ferrites SrFe12O19 for potential application in high-frequency devices

This work explores the synthesis, characterization, and potential application of rare earth doping on hard ferrites, focusing on their unique electromagnetic properties for potential applications in radio frequency (RF) devices. This study investigates the influence of rare earth (Sm+3) doping on structural and dielectric properties of strontium ferrite. Samarium doped strontium ferrite with composition Sr1-xSmxFe12O19(x = 0.0,0.1,0.2,0.3) is prepared using the sol-gel auto combustion technique. The prepared samples' crystal structural and morphological properties were studied using an X-ray diffractometer (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and RAMAN spectroscopy. XRD patterns of rare earth substituted strontium ferrite confirmed the formation of a hexagonal phase together with an impurity phase of Fe2O3 for x = 0.3. FTIR analysis establishes metal and Oxygen (M-O) stretching vibrations in Sr1-xSmxFe12O19 due to various interstitial sites in its structure. The Raman result shows the presence of four Raman active modes in prepared powders. Meanwhile, the broadening of Raman peaks with Sm2+ doping is also observed. Electromagnetic properties were obtained in the frequency region 2–18 GHz. An increasing tendency is observed in the real part of permittivity and permeability of all doped samples in the frequency region 2–18 GHz. The reflection loss was observed for sample x = 0.2 with the maximum value of > -40 dB at 18 GHz, and the adequate absorption bandwidth is 10 GHz from 8 GHz to above 18 GHz. On the basis of these results, among all prepared samples, Sr0.8Sm0.2 Fe12O19 is found to be the most suitable candidate for microwave absorbers.

Fabrication and structural modification of graphene oxide-tetraethyl orthosilicate solution via liquid-phase pulsed laser ablation

Liquid-phase pulsed laser ablation (LP-PLA) is a physical deposition technique to fabricate micro- and nanoscale particles of polymer, glass, and ceramic materials. In this work, graphene oxide (GO) that was immersed in tetraethyl orthosilicate (TEOS) and ethanol was used to fabricate the graphene-silicone polymer using the LP-PLA technique. The GO-TEOS solution was ablated with different fluences of the laser. The ablated GO-TEOS solution was characterized by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive x-ray, and ultraviolet-visible (UV-Vis) spectroscopy to study the graphene-silicone polymer properties. The FTIR result shows that the laser ablation has provided sufficient laser energy to create or break the chemical species of GO and TEOS compounds as observed on Si–O and C–O bonds. The Raman result shows the changes in the intensity in the D band, which suggests that the carbon atom of the GO has been functionalized with other compounds. Several large flakes were observed in the SEM images, representing the silicon polymer with the GO aggregation. The particle size in the range of 3–8 and 66–110 μm was formed due to the presence of uniformly sized nanoparticles of the GO-TEOS mixture and aggregation of the GO-TEOS nanoparticles into clusters. The zeta potential results indicated that the stability of the GO-TEOS mixture decreases after laser ablation. The UV-Vis result shows a broad absorption band with center at 492 and 532 nm with increasing absorbance at low fluence then saturated and decreased at maximum laser fluence. From the results above, several chemical interactions between GO and TEOS were observed, and the data suggested the laser fluence as the major source to cause both photothermal and photochemical reactions on the samples. In short, laser ablations provide sufficient energy to induce chemical bonding, which further allows structural modification of materials.

Effect of Growth Temperature on Crystallization of Ge1−xSnx Films by Magnetron Sputtering

Ge1−xSnx film with Sn content (at%) as high as 13% was grown on Si (100) substrate with Ge buffer layer by magnetron sputtering epitaxy. According to the analysis of HRXRD and Raman spectrum, the quality of the Ge1−xSnx crystal was strongly dependent on the growth temperature. Among them, the GeSn (400) diffraction peak of the Ge1−xSnx film grown at 240 °C was the lowest, which is consistent with the Raman result. According to the transmission electron microscope image, some dislocations appeared at the interface between the Ge buffer layer and the Si substrate due to the large lattice mismatch, but a highly ordered atomic arrangement was observed at the interface between the Ge buffer layer and the Ge1−xSnx layer. The Ge1−xSnx film prepared by magnetron sputtering is expected to be a cost-effective fabrication method for Si-based infrared devices.

Synthesis and characterization of CeAlO3via solid state method

To obtain the efficient synthesis of CeAlO3, CeAlO3 was synthesized via the solid-state method under low oxygen partial pressure and the presence of excess carbon. The morphology and structure of the products were investigated by XRD, SEM-EDS, Raman spectroscopy, and TEM. Results showed that the CeAlO3 product with high purity could be obtained by the current method. The color of the synthesized CeAlO3 product was green and the space group of the synthesized CeAlO3 structure was P4/mmm in the current study. Raman result indicated the CeAlO3 had three Raman active modes at about 156 ​cm-1, 173 ​cm-1, and 496 ​cm-1. The CeAlO3 nucleated at the contact surface between the formed Ce2O3 and Al2O3 by rapid surface diffusion. When the CeAlO3 formation by the reaction, the lattice diffusion promoted further the formation and compositional homogeneity of CeAlO3.

Structural and magnetic properties of MgFe2O4 nanopowder synthesized via co-precipitation route

Mg ferrite was successfully synthesized by adopting a simple co-precipitation route. A physical property of Mg ferrite has been investigated employing XRD, FTIR, SEM, EDS, AFM and Raman spectroscopic techniques. The XRD results indicated the formation of single phase spinel ferrite with crystalline size of 36 nm. FTIR results confrmed ferrite tetrahedral (580 cm−1) and octahedral sites (430 cm−1) metal oxygen vibrations. The Raman result revealed the well defined Raman active modes of synthesized sample. Scanning electron microscopic (SEM) studies revealed nano crystalline nature of the sample. An elemental composition of the sample was studied by energy dispersive spectroscopy (EDS). Crystallite size, X-ray density, hopping length, and magnetic properties of the product are also reported. AFM provides surface roughness. The magnetic hysteresis curves clearly indicate the soft nature of the prepared nanoferrite. The Raman spectra shows five Raman active modes (A1g + Eg + 3F2g) which are expected in the spinel structure and Raman spectra has a very good agreement with reported data. Various magnetic parameters such as saturation magnetization (Ms), and remanence (Mr) and coerciviy (Hc) are obtained from the hysteresis loops.

Activated Carbon by KOH and NaOH Activation: Preparation and Electrochemical Performance in K2SO4 and Na2SO4 Electrolytes

Activated carbons were successfully prepared from rice husk (RH) by chemical activation using KOH (RH-K4) or NaOH (RH-N3) as activating agents and characterized by means of SEM, EDX, FTIR, Raman, Boehm titration, and TGA methods. The as-prepared activated carbon samples are composed of spherical particles with lots of cracks and crevices as showed in SEM images. They have numerous surface functional groups which proofed by FTIR and Boehm titration. Raman result revealed that the crystalline size along basal plane (La) of RH-K4 and RH-N3 are 3.27 and 3.46 nm, respectively, which demonstrated the higher disorder degree of RH-K4 compared to RH-N3. Cyclic voltammetry and charge-discharge tests exhibit the electric double layer capacitor characteristic of the electrodes. RH-K4 shows a better performance at low scan rate and current density, whereas RH-N3 is superior at high scan rate and current density. At all experimental conditions studied, the as-prepared electrodes behave better in K2SO4 electrolyte than in Na2SO4 electrolyte.

One-step rapid preparation of CNTs using the spark plasma–assisted pyrolysis of melamine and its photoluminescence properties

In this study, carbon nanotubes (CNTs) were successfully fabricated using a novel spark plasma–assisted pyrolysis (SPAP) method at 700–900 °C. The existence of CNTs was confirmed in all samples, the diameter of the CNTs is approximately 40–50 nm. The CNTs fabricated at 750 °C presented a helical shape, which is different from the CNTs fabricated at other temperatures which presented a bending shape. The defects of CNTs, such as bending and abnormal layer spacing, are explained through the TEM observations. The sharp diffraction peak from the XRD result and the ID/IG ratio (a minimum of 0.772) from the Raman result revealed that the CNTs prepared at higher temperature possess better crystallinity. The photoluminescence results show that the CNTs produced exhibited strong emission peaks, and the intensity of photoluminescence could be enhanced by increasing the preparation temperature. The highlighted technique is capable of achieving the preparation of CNTs quickly, safely, and inexpensively. This technique has provided a new possibility for other materials of preparation such as boron nitride nanotubes.

Pharmaceutical Cocrystal Formation of Pyrazinamide with 3-Hydroxybenzoic Acid: A Terahertz and Raman Vibrational Spectroscopies Study.

Vibrational modes of pyrazinamide (PZA), 3-hydroxybenzoic acid (3-hBA), and their cocrystal were characterized using terahertz time-domain (THz-TDS) and Raman vibrational spectroscopic techniques. In experimental THz spectra, the cocrystal has characteristic absorption bands at around 0.81, 1.47, and 1.61 THz, respectively, meanwhile the raw materials are absolutely different in this region. Raman spectra also show similar results about differences between the cocrystal and corresponding starting parent materials. Density functional theory (DFT) was used to simulate both optimized structures and vibrational modes of the cocrystal formed between PZA and 3-hBA. The vibrational modes of such cocrystal are assigned through comparing the simulation DFT frequency results with experimental vibrational spectra. The calculation of the theoretical THz spectrum shows that the hydrogen bonding effect established between H11–N12–H13 and the carboxyl group -COOH makes contributions to the formation of absorption peaks in 0.49, 0.62, 0.83, and 1.61 THz, which agrees pretty well with experimental results. The theoretical Raman result also matches well with experimental observations. The results provide a fundamental benchmark for the study of pharmaceutical cocrystal formation and also inter-molecular hydrogen bonding interactions between active pharmaceutical ingredients and various cocrystal coformers based on Raman and terahertz vibrational spectroscopic techniques combined with theoretical simulations.

Crystal structures, dielectric properties, and phase transition in hybrid improper ferroelectric Sr3Sn2O7-based ceramics

Hybrid improper ferroelectricity is induced by the coupling of oxygen octahedral rotation and tilt, and it may provide a promising way to develop new room-temperature single-phase multiferroic materials with a strong magnetoelectric effect. Though ferroelectric polarizations are confirmed by the electric hysteresis loops at room temperature, the ferroelectric-paraelectric phase transition has not been well understood. In the present work, the crystal structures, dielectric properties, and phase transition behaviors of Ruddlesden-Popper Sr3–xCaxSn2O7 ceramics are thoroughly determined. Ferroelectricity is confirmed through the polarization-electric field hysteresis loops at room temperature, and the Curie temperature is identified by the variable-temperature differential scanning calorimetric analysis and dielectric characterization. The polarizations and Curie temperatures of the present ceramics increase with increasing the calcium content. An improper ferroelectric transition is experimentally evidenced by a small dielectric constant and a step variation of dielectric constant around the Curie temperature, and the thermal hysteresis of dielectric constant confirms the first order transition nature. Moreover, the fitting result of Landau phase transition theory also suggests the first-order improper ferroelectric transition nature. The variable-temperature Raman result implies a tetragonal paraelectric phase above TC. The present work confidently confirms the first-order hybrid improper ferroelectric transitions in the present ceramics, and ferroelectric properties can be readily tuned by substituting the cations at the A-site.

Selective Hydrogenation of Acetylene Over Gold Nanoparticles Supported on CeO2 Pretreated Under Different Atmospheres

Supported gold catalysts are highly efficient for selective hydrogenation of acetylene. It has been shown that reducible materials such as ceria may influence the catalytic performance due to its unique charge shift between reduced and oxidized state. However, its role in catalytic performance remains fiercely debated. In this paper, differently morphological CeO2 supported Au catalysts were prepared with pretreatment under air and H2 atmospheres respectively, and evaluated for selective hydrogenation of acetylene. No matter with rod (abbreviated as R) or polyhedral (abbreviated as P) shape, the catalysts of Au/CeO2 reduced in air exhibits better catalytic performance than that in H2 atmosphere. The Au/CeO2 (R)-air catalyst shows the best performance. The C2H2 conversion is about three times of that over the catalyst of Au/CeO2 (R)-H2 at 300 °C. The Raman result and XPS analysis clearly showed a dependence of catalytic activity on the oxygen vacancy concentration of catalysts, revealing the correlation between its defect features and pretreatment atmosphere. Our report not only deepens the knowledge of catalytic performance affected by defect features of catalyst but also provides a possibility for the efficient heterogeneous gold/ceria catalysts by controlling the pretreatment atmosphere.

Synthesis and Characterization of Carbon Material Obtained from Coconut Coir Dust by Hydrothermal and Pyrolytic Processes

Since 2004, graphene has risen in popularity owing to its superior properties. However, limits to the scale of production methods have rendered graphene a costly material. Moreover, existing production methods require chemicals that are detrimental to the environment. This study uses Coconut Coir Dust (CCD) as a carbon precursor and an intermediate product in the manufacturing of graphene. Firstly, CCD sieved into a 100 mesh was carbonized using a hydrothermal method at temperatures of 235oC, 250oC, and 265oC, for 4 hours. Following this, the resulting solid residue was pyrolyzed at 1000oC for 2 hours under the protection of nitrogen (N2). The hydrothermal solid residue was labelled CHT (hydrothermal temperature) and the pyrolysis product was named as SP (hydrothermal temperature). Both samples were characterized using SEM, XRD and EDS. In addition, Raman characterization was conducted for SP samples. At the end of the process (SP), the XRD pattern showed two broad peaks centered around 2θ ~24o and 44o corresponding to a (002) and (100) graphite plane. This pattern is similar to that of reduced-graphene oxide. SEM images showed a sheet-like microstructure is caused by undegraded lignin. A perforated and corrugated sheet formed after pyrolysis, which subsequently confirms the formation of reduced graphene oxide. Furthermore, the Raman result indicates that higher hydrothermal temperatures lead to an increasing integrated ID/IG ratio. The ratios were 1.62, 1.71 and 1.77, for SP 235, SP 250, and SP 265, respectively. Research results conclude that the carbonaceous material formed through hydrothermal and pyrolytic processes contained a mixture of an amorphous carbon form and a graphene-like cluster. Results additionally show a similar structure with reduced graphene oxide.

Quinoline Hydrodenitrogenation over NiW/Al-MCM-41 Catalysts with Different Al Contents

Al-MCM-41 materials were prepared with different Al contents and used as supports for NiW catalysts. The supports and catalysts were characterized by XRD, N2 adsorption-desorption, XPS, Raman, H2-TPR techniques. The XPS result showed that the Al added to MCM-41 promoted the dispersion of W and Ni species. The Raman result showed that the Al added to MCM-41 favored the formation of the suitable W species. The H2-TPR result showed that the Al added to MCM-41 can reduce the reduction temperature of W species on the catalysts. The hydrodenitrogenation (HDN) results showed that the HDN activity followed the order of NiW/Al-2 > NiW/Al-1 > NiW/Al-4 > NiW. Moreover, this tendency was also valid for the ratio of propylcyclohexane/propylbenzene (PCH/PB). The high HDN activity and PCH/PB ratio of NiW/Al-2 are due to the well dispersion of the W and Ni species, the suitable W species and the low reduction temperature of W species.

Pressure-induced polymorphism in hypervalent CsI3

We report the results of ambient temperature high-pressure synchrotron-based x-ray diffraction, Raman, and electrical resistance study of $\mathrm{Cs}{\mathrm{I}}_{3}$ up to 29, 25, and 8 GPa, respectively, and confirm three-phase transitions under quasihydrostatic conditions. The ambient orthorhombic (space group (SG): Pnma) phase of $\mathrm{Cs}{\mathrm{I}}_{3}$ is stable up to a pressure of $\ensuremath{\sim}1.3\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, above which a phase transition to a trigonal ($\mathrm{SG}:P\text{\ensuremath{-}}3c1$) phase is observed. The stability region of the trigonal phase has been found to be up to 22.6 GPa, above which the trigonal phase transforms to a cubic ($\mathrm{SG}:Pm\text{\ensuremath{-}}3n$) phase which remains stable until the maximum pressure of 29 GPa achieved in this study. A third-order Birch-Murnaghan equation of state fit to the pressure volume ($P\text{\ensuremath{-}}V$) data yields a bulk modulus of 17.7(9) GPa for the trigonal phase. Raman spectroscopic measurements however indicate three-phase transitions at $\ensuremath{\sim}1.3,\phantom{\rule{0.16em}{0ex}}4.0$, and 22.6 GPa, respectively. The electrical resistance measured in the low-pressure region up to 8 GPa indicates an electronic transition at around 4 GPa confirming the Raman result observed at 4.0 GPa. The $P\text{\ensuremath{-}}V$ data when transformed to the universal equation of state (UEOS) show a deviation from linearity around 4.0 GPa confirming the electronic transition. The present study has thus revealed a three-phase structural sequence in alkali trihalides, viz., orthorhombic (SG: Pnma) to trigonal ($\mathrm{SG}:P\text{\ensuremath{-}}3c1$) to a cubic ($\mathrm{SG}:Pm\text{\ensuremath{-}}3n$) phase.

Investigation of Ti2AlC formation mechanism through carbon and TiAl diffusional reaction

Ti2AlC formation mechanism with carbon and TiAl alloy as reactants at 1000–1200°C have been investigated through Raman spectrometer and transmission electron microscope (TEM). Reaction products TiCx and Ti2AlC are confirmed. Full width at half height (FWHH) of Ti2AlC Raman peak is used to characterize crystallinity, which indicates better perfection of Ti2AlC grains near TiAl area and with higher reaction temperature. Variations of TiCx microstructure, especially stacking faults(SF) and nanotwins, are observed by TEM along reaction layer. Ti2AlC lattice uniformity of different reaction temperature is also confirmed by TEM, which is consistent with Raman result. TiCx is believed first formed through reaction between TiAl and C. With help of carbon vacancy, Al-doped TiCx SF and nanotwin can be formed under hot pressing, which becomes the basal frame of Ti2AlC.

Solid-state cocrystal formation between acyclovir and fumaric acid: Terahertz and Raman vibrational spectroscopic studies

The vibrational spectra of solid-state acyclovir, fumaric acid and their cocrystal have been investigated by using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. In experimental THz spectra, the cocrystal has absorption peaks in 0.65, 0.94 and 1.10THz respectively, while the raw materials are absolutely different in this region. Raman spectra also show similar results about differences between the cocrystal and raw materials. Density functional theory (DFT) was performed to simulate vibrational modes of different theoretical forms between acyclovir and fumaric acid. The calculation of theoretical THz spectra shows that O8C7N1H27 and the carboxyl group COOH establish a dimer theoretical cocrystal form by the hydrogen bonding effect, which makes contributions to the formation of absorption peaks in 0.70, 1.01 and 1.34THz, and agrees well with experimental observations. The theoretical Raman result also indicates that this dimer form matches with experimental results. The characteristic bands of the cocrystal between acyclovir and fumaric acid are also assigned based on the simulation results from the DFT calculation.

An experimental and theoretical study on soft chemically grown CuS thin film for photosensor application

Herein we report, the photosensitivity of in-situ chemical bath deposition (CBD) grown CuS thin film for the first time, also comparatively very short deposition time of 40min and much lower bath temperature i.e. 45°C are reported. The structural, surface topographical, optical, electronic and electrical properties of as-grown CuS thin film have been investigated. The XRD analysis revealed the formation of Orthorhombic (Covellite) structure with preferential growth along [113] direction having ~14nm average crystallite size. Raman spectrum indicating a sharp peak at 474cm−1 confirms the formation of CuS covellite structure. Polycrystalline nature of the film has been confirmed from the concentric ring pattern obtained from TEM–SAED and AFM revealed the rough surface topography with RMS roughness of ~27nm. The bond lengths of Cu(1)-S(1) and S(1)-S(1) were obtained from the DFT calculations based on GGA approximation, suggest S-S bond is much stronger as compared to Cu-S bond; these results are in good agreement with the Raman result. The film shows higher absorbance in the visible region with a band gap of 2.2eV. The electrical properties show a drastic increase in current after light illumination of 50 W which increases with increasing light intensity and tends to attain a saturation state around 200 W. The highest photosensitivity of ~66% has been calculated for 200 W with fast response time of ~34s and a complete recovery. These results represent CuS thin films promising candidature for photosensor application.

Structural investigation of the cocrystal formed between 5-fluorocytosine and fumaric acid based on vibrational spectroscopic technique

The vibrational spectra of 5-fluorocytosine, fumaric acid and their cocrystal were measured using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. Experimental THz results show that the cocrystal has distinct fingerprint spectra in terahertz region. The absorption peaks observed in the terahertz spectra of the cocrystal were at 0.61 and 0.91THz. These are quite different from corresponding raw starting materials. Raman spectra also show similar results about differences between the cocrystal and corresponding raw starting materials. Density functional theory (DFT) was used to simulate the structure of the possible salt form and the cocrystal form between 5-fluorocytosine and fumaric acid. The theoretical terahertz result shows that the cocrystal form has absorption at 0.62 and 0.87THz, which is in agreement with the experimental result. The theoretical Raman result also indicates that the cocrystal form has more possibilities than the salt form. So, it is more reasonable that the structure between 5-fluorocytosine and fumaric acid could be the corresponding cocrystal form. The characteristic bands of the cocrystal between 5-fluorocytosine and fumaric acid are also assigned based on the simulation results from the DFT calculation.

Morphology Control of Zinc Oxide Nanostructure on Single Layer Graphene.

Various morphologies of zinc oxide (ZnO) nanostructures on single layer graphene were synthesized by electrodeposition method. The current density was utilized to control the morphology of the ZnO. The Scanning Electron Microscope (SEM) was used to examine the surface morphology of the samples. SEM analysis shows morphology changes to nanorod, flower, and flakes with increase in the current density from 0.1, 0.2, and 0.3 mA/cm(-1) respectively. The XRD, XPS, and Raman spectroscopy were adopted to characterize the ZnO nanostructure and to understand the formation of various morphologies. The Raman result clearly shows extra modes due to for flakes structure caused by c-axis orientation along the substrate direction. Further, XPS data also supports formation of ZnO without any other intermediate compound such as Zn(OH)2. The formation of various morphologies was correlated to the formation different ratio of Zn2+ and OH- ions and the change in growth direction due to various current densities.

Effect of pH and Temperature on Physical Properties of Zinc Aluminate Based Nanostructure Synthesized via Co-Precipitation Method

Zinc aluminate (ZnAl2O4) nanopowders were synthesized by co-precipitation method using zinc chloride and aluminum chloride as starting precursors. The crucial preparation factors including pH and calcination temperature were varied and their influence on relevant physical properties of the product is investigated. Structural properties of as-synthesized nanoparticles were investigated by X-ray diffraction, scanning electron microscope and Raman spectroscopy. XRD results suggested that ZnAl2O4 in spinel structure with high crystallinity could be obtained by this process after calcination beyond specific temperature. Meanwhile, SEM images revealed that surface morphologies and structure of ZnAl2O4 were in spherical structure with average size of few hundred nanometer range at high pH condition. Raman result indicated the correlated chemical bonding relating to the formation of ZnAl2O4 structure.

Characterization and effect of calcination temperature on structural properties of spinel zinc aluminate synthesized via Co‐precipitation process

AbstractZinc aluminate (ZnAl2O4) nanopowders were synthesized by co‐precipitation method using zinc chloride and aluminum chloride as starting precursors. The calcination temperature which was a crucial preparation factor was varied and its influence on relevant physical properties of the product was investigated. Structural properties of synthesized nanoparticles were investigated by X‐ray diffraction, X‐ray absorption spectroscopy, scanning electron microscope, and Raman spectroscopy. The results suggest that that ZnAl2O4 in spinel structure with high crystallinity can be obtained after calcination beyond specific temperature affirmed by XRD results. Raman result indicates the correlated chemical bonding relating to the formation of ZnAl2O4 structure. Meanwhile, the Zn K‐edge X‐ray absorption near‐edge structure (XANES) spectra of these samples with different calcination temperature obtained from the synchrotron X‐ray absorption spectroscopy measurement show the existence of accurate oxidation state for zinc ion (Zn2+) in the spinel crystal structure. Moreover, it is revealed that the calcination temperature has significant effect on the local environment of the zinc absorbing atoms through the interesting change of white line appearance. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)