Papers by Keyword: Raman Spectroscopy

Abstract: This paper aims to report the influence of water vapor on thermal oxide scale grown on incoloy800HT at 850°C. Alloy was prepared in coupons with a surface finishing up to 1200 SiC abrasive paper. Oxidization was performed in tubular furnace at 850°C during 50 hours. The oxidizing gases were varied as a dry oxygen gas and a wet oxygen gas. Thermal oxide morphology was characterized by scanning electron microscopy (SEM). Oxide phases were identified by X-ray diffraction (XRD) and Raman spectroscopy techniques. The oxide multilayers were revealed in all the oxidized samples. Oxide spallation was obviously detected on the samples oxidized under a dry oxygen gas, whereas, the spallation was not detected on the samples oxidized under a wet oxygen gas. Moreover, by water vapor mixing gas, the alloy surface presented a finer oxide. XRD and Raman spectroscopy provided the coincident oxide identification results. The corundum oxide of (Fe,Cr)₂O₃ and the spinel oxide of (Fe,Cr)₃O₄ were identified as a typical thermal oxide, however, the oxides were different in stoichiometry. The existence of water vapor promoted a Cr₂O₃ corundum oxide, whereas, a Fe₃O₄ spinel oxide was hindered from the outer oxide layer. Hence, water vapor not only clearly influenced on oxide scale morphology but also affected on stoichiometry of (Fe,Cr)₂O₃ and (Fe,Cr)₃O₄ solid solution.

Abstract: In this study, We demonstrate mono and few layers MoS₂ samples on the SiO₂(270nm)/Si substrate from bulk MoS₂ crystal by micromechanical exfoliation technique. We have systematically studied Atomic Force Microscopy, Raman and PL properties of mono and few layer MoS₂ on the SiO₂(270nm)/Si substrate. First, we find that the number of layer values dependent the Raman and PL emission. First, Raman intensity area ratio of the MoS₂ E¹_2g, A_1g and 2LA modes to that area of the Si substrate increased linear with increasing number of layers MoS₂. Second, Normalized PL intensity area of the (A) peak decreased linear with increasing number of layers MoS₂. The value of those graphs is a method to understand the number of layers the exfoliated MoS₂.

Abstract: Natural ferrite oxide nanoparticles (NPs) embed with tellurite glasses ((89-x) TeO₂-10ZnO-1Er₂O₃-(x)Fe₃O₄, (x = 0 – 0.8 mol %)) were prepared by conventional melt quenching method to study the influence of the Fe₃O₄ NPs concentration on the stuctural properties of the glass. Studies on these glassy materials characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and RAMAN spectroscopic measurements are presented. It is observed that the amorphous nature of the glass is confirmed by x-ray diffraction. The FTIR studies support the formation of Te-O-Fe linkages. The FTIR spectra reveal modification in network structures evidenced from vibrational wave-number shifts of TeO₄ and TeO₃ structural units. Raman spectroscopy have been manipulated to observe the structural modification of [TeO₄] trigonal bipyramidal structural unit.

Abstract: In the present study, the Raman spectra of diamond-like amorphous (a-C) and hydrogenated amorphous (a-C:H) carbon films on silicon obtained using the ion-beam methods and the pulse cathodic arc deposition technique were investigated with the aim of elucidating the relation between the hardness and structure of the films. The hardness of the samples used in the present study was 19 – 45 GPa. Hydrogenated carbon films were synthesized using END–Hall ion sources and a linear anode layer ion source (LIS) on single-crystal silicon substrates. The gas precursors were CH₄ and C₃H₈, and the rate of the gas flow fed into the ion source was 4.4 to 10 sccm. The ion energies ranged from 150 to 600 eV. a-C films were deposited onto Si substrates using the pulse cathodic arc deposition technique. The films obtained by the pulse arc technique contained elements with an ordered structure. In the films synthesized using low- (150 eV) and high-energy (600 eV) ions beams, an amorphous phase was the major phase. The significant blurriness of the diffraction rings in the electron diffraction patterns due to a large film thickness (180 – 250 nm) did not allow distinctly observing the signals from the elements with an ordered structure against the background of an amorphous phase.

Abstract: Zircon samples from Ubon Ratchathani, Thailand; Rattanakiri, Cambodia and Dak Nong, Vietnam change their color from light brown and reddish-brown to blue color after thermal enhancement at 1000 ^๐C in reducing condition for 60 min. The high temperature is one of the factors for the zircon structure to recrystallize. The objective of this study is to describe the crystal structure of zircon samples before and after thermal enhancement. Zircon is a metamict mineral whose structure is destroyed by some trace elements. There are radioactive elements such as U and Th in the zircon structure. In this study, Raman spectroscopy was used to analyze the molecular vibration in zircon structure before and after thermal enhancement. As a result, the Raman spectra of zircon samples after thermal enhancement show the Raman shift at peak position of V₃(SiO₄) stretching around 1008cm^-1 to higher wavenumber concerning to the full width at half maximum (FWHM) values calculated by PyMCA software. The results could be summarized that the metamict zircon will be recrystallized to the crystalline zircon after thermal enhancement. The advantage of this study is about the identification of zircon before and after thermal enhancement.

Abstract: Epitaxial graphene on semiinsulating silicon carbide was grown using a high temperature method at atmospheric pressure in argon atmosphere. The temperature dependence of the layer quality was analysed using Raman and infrared spectroscopy. It is demonstrated that infrared spectroscopy can be used as a versatile tool to access the layer count and the quality of the epitaxial grown graphene on silicon carbide. The results obtained by infrared spectroscopy correlate with the Raman measurements.

Abstract: The relationship between structure and refractive index for SiO₂-B₂O₃- Ta₂O₅-ZrO₂-Na₂O system glasses was investigated via Raman spectrum and V-block technology. The results showed that refractive index of the borosilicate glasses is mainly influenced by network structure such as planar [BO₃] triangle, [BO₄] tetrahedron and [SiO₄] tetrahedron. Refractive index decreases from 1.629 to 1.616 when B₂O₃ content increases from 15 mol% to 50 mol%. Na₂O component has a strong preference to provide non-bridging oxygen (NBO) atoms, which not only promotes the conversion of [BO₃] to [BO₄] unit but also depolymerizes the network structure. The refractive index has the highest value, =1.6264, when Na₂O content reaches to 28 mol%. Both ZrO₂ and Ta₂O₅ can promote structure formation of borosilicate glasses and make higher connection degree. However, the refractive index increasing with Ta₂O₅ addition is quicker than that with ZrO₂ addition.

Abstract: Nanocrystalline NiO has been prepared successfully by chemical precipitation route using nickel nitrate hexahydrate (Ni (NO₃)_{2 ·}6H₂O) and sodium hydroxide (NaOH) aqueous solution at a temperature of 60 ̊C. Their compositional, structural, morphological, thermal and optical properties were studied using energy dispersive analysis of X-rays (EDAX), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence (PL) spectroscopy and Raman spectroscopy. From XRD pattern we confirmed the face centered cubic (fcc) structure of the synthesized NiO nanoparticles. The selected area electron diffraction (SAED) pattern indicated the same crystalline planes as seen in XRD pattern. TGA indicates good thermal stability of synthesized NiO nanoparticles and the optical absorption spectrum of NiO nanoparticles shows the strong absorption edge at 235nm (4.10eV). PL spectra of NiO nanoparticles shows two wide emission peaks at 420nm (2.95eV) and 440nm (2.82eV) and a strong–broad peak at 460nm (2.70eV) in violet emission band whereas the Raman peak observed at 518cm^-1 shows the Ni-O stretching mode of vibration.

Abstract: Porous silicon (PS) was formed by using an electrochemical pulse etching (PC) and conventional direct current (DC) etching techniques. The study aims to compare the effect of crystal orientations (n-type (100) and n-type (111)) on the formation of the PS under various conditions. For DC etching technique, the silicon wafers were etched in Hydrofluoric (HF) based solution with a current density of J=10 mA/cm² for 30 minutes. While for the PC process, an electroless chemical etching with a different delay time (T_d) of 0 min and 2 min were imposed before PC process starts. After that, the pulse current of J=10 mA/cm² with the cycle time (T) of 10 ms and pause time (T_off) of 4ms were supplied in 30 min etching time in HF based electrolyte. Three samples from n-type (100) are DC1, PC1 and PC2 while the three samples from n-type (111) are DC2, PC3, and PC4 respectively. Field Emission Scanning Electron Microscopy (FESEM) images showed that the samples from n-type (100) produce more uniform circular structures and dense compared to n-type (111). The introduction of 2 minutes delay during PC process resulted in better structural of PS formation and also the optical properties shown by the Raman and Photoluminescence (PL) spectroscopies. For PL observation, the as grown Si shows no emission at the visible spectrum while all the PS samples (DC and PC techniques) exhibited significant broad spectrum between 500 nm to 900 nm respectively. It can be seen that the uniform circular pore of n-type (100) enhanced the PL emission indicated by the higher PL intensity (PC1 and PC2) compared to PC3 and PC4 from n-type (111). Raman spectroscopy showed that an improvement in the crystalline quality of PS in PC technique compared to DC indicated by the reduction of full width at half maximum (FWHM).

Abstract: The Raman spectra of boron-doped single-crystalline diamond were measured at excitation wavelengths between 364.0 and 1064.0 nm and found that the first-order Raman band at 1332 cm^-1 shifts to the low-frequency side, broadens, and develops a derivative-like lineshape as the boron concentration increases. The derivative-like lineshape can be explained by Fano interference. Furthermore, I found that the asymmetric lineshape changes between excitation wavelengths of 514.5 and 785.0 nm. From a comparison of the normalized relative Raman intensity as a function of the excitation energy and the density of states (DOS) in the valence band in the B-doped diamond calculated previously by the coherent potential approximation, the abnormal change in the Raman lineshape is attributed to a change in the DOS in the valence band at approximately 2.0 eV. Raman spectroscopy provides us with extensive information on carrier concentrations, and electronic band structures of B-doped diamond.