Papers by Keyword: Raman Spectroscopy

Abstract: Er³⁺ doped CaMoO₄(CaMoO₄:Er³⁺) and Er³⁺/Yb³⁺ co-doped CaMoO₄ (CaMoO₄:Er³⁺/Yb³⁺) particles was successfully synthesized by a cyclic microwave-assisted metathetic (MAM) method, followed by heat-treatment. Well-crystallized UC CaMoO₄:Er³⁺/Yb³⁺ particles formed after heat-treatment at 600°C for 3 h showed a fine and homogeneous morphology with particle sizes of 1-3 μm. At excitation at 980 nm, CaMoO₄:Er³⁺/Yb³⁺ particles exhibited a strong 525-nm emission band and a weak 550-nm emission band in the green region, and a weak 655-nm emission band in the red region. The UC intensities of CaMoO₄:Er³⁺/Yb³⁺ particles were much higher than that of the CaMoO₄:Er³⁺ particles. The Raman spectra of CaMoO₄:Er³⁺ and CaMoO₄:Er³⁺/Yb³⁺ particles indicated the appearance of additional strong peaks in comparision with that of pure CaMoO₄.

Abstract: Two different silver colloids were produced by the reduction of AgNO₃ using sodium citrate (SCAg colloid) or hydroxylamine hydrochloride (HHAg colloid) as reductant. A comparative study was made on SERS spectra (λexc=514.5 nm) of the calf thymus DNA on the two silver colloids in solution of 0.06mol/L NaCl, pH7.0. With the SCAg colloid, the bands at 732, 915, 1340, and 1448 cm^-1 for adenine, and 800, 1180, 1590, 1625 and 1651 cm^-1 for thymidine are dramatically enhanced. It shows that the DNA molecules can be oriented relatively perpendicularly to the SCAg colloidal surface via the N6H₂, N7 of adenine and C2=O of thymine residues. While with the HHAg colloid, most of the in-plane modes of the bases are poorly enhanced, except for some weak bands or shoulders assigned to cytosine and guanine. Thus the DNA molecules is supposed to be adsorbed on the HHAg colloid surface in a tilted mode.

Abstract: In this study, we study the physical property and antibacterial bioactivity of ZnO nanopowder towards Staphylococcus Aureus. Transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), FTIR, Raman spectroscopy and UV-Vis were used to characterize the ZnO nanopowder. The major morphology consists of nanorods which have length 70-200 nm and width 30-120 nm. FTIR spectra performed a well-synthesis of ZnO that has Zn-O stretching bond (482 cm^-1). UV-Vis absorption spectra showed an intense UV absorption at 387 nm, corresponding to optical bandgap 3.24 eV. Raman spectroscopy exhibited a prominent peak in E₂^high mode located at 435 cm^-1. The antibacterial response of ZnO was performed toward Staphylococcus aureus. Higher concentration of ZnO had caused higher inhibition of the bacteria. Besides, the increment of capability of ZnO towards the bacteria was observed under UV radiation. It was believed that the irradiation had induced oxygen to be released from the surface of the ZnO and caused the increasing of reactive oxygen species, which enhance the bacteria inhibition.

Abstract: The stress and lattice constants in zinc oxide (ZnO) nanoparticles play a major role in determining the distortions that occur in the crystal during the preparation of the sample as a result of exposure to several factors, such as external strain, temperature, pressing, and structural defects (oxygen vacancies and zinc/oxygen interstitials). 20 nm zinc oxide nanoparticles were used to make high-density ZnO discs doped with Bi₂O₃ and Mn₂O₃ via uniaxial pressing at 4 ton/cm² and sintering at 1200 °C for 1 h. Structural, elemental, and optical characterizations were then performed on the samples using various techniques. High-oxygen thermal annealing significantly affected the varistor, particularly in enhancing the growth of the grain even at a low annealing temperature (400 °C). The strong solid-state reaction during annealing may be attributed to the high surface area of the 20 nm ZnO nanoparticles that exhibited a strong surface reaction even at low annealing temperatures. The annealing treatment also improved the grain crystallinity, as shown by the transition of the intrinsic compressive stress to tensile stress based on the XRD lattice constant and full-width at half-maximum data. Therefore, high-oxygen thermal annealing can be used as a new technique in controlling the stress in ZnO nanoparticle-Bi₂O₃-Mn₂O₃ based varistors with improved structural and optical properties.

Abstract: The morphology and structure of nanocrystalline diamond films as well as the plasma chemistry were studied by altering the plasma impedance. These impedances related to electron density were altered via the matching system. Two films were grown by the microwave plasma under different values of the plasma impedance, resulting in low and high electron densities in the plasma. By the use of measurements of plasma impedance and optical emission, the lowering of an inductive component of the impedance, indicating an increasing electron density, encouraged H-radical concentration present in the plasma. As the plasma was changed to the high electron density, Raman spectra of the films showed the sp³ Raman peak shifted from 1325 to 1328.5 cm^-1 with narrower broadening. This behavior arose from an increase in grain size, corresponding to images from a field emission scanning electron microscope. Raman spectra of G-peak position and white light reflectometry showed a reduction in sp² carbon content of the film. The G-peak shifted from 1564 to 1541 cm^-1 and refractive index increased from 1.84 to 2.16. The formation of the films related to the concentrations of H and CH₃ radicals. The plasma impedance affected the radical concentrations.

Abstract: This paper presents an experimental study on the tensile mechanical properties of carbon nanotube (CNT) fibers by in situ Raman spectroscopy. The comprehensive spectral information, such as Raman shift, width and intensity, are recorded during the whole loading–unloading–reloading procedures of CNT fibers. Based on the experimental results, the elastic-plastic deformation evolution of CNT fibers are analyzed at multi-scale levels. It is found that the elastic deformation of the fiber is mainly attributable to the elastic stretching of the CNTs inside the bundles. And the plastic deformation is caused mainly by the slippages at the interfaces among CNTs inside the bundles. Meanwhile, the CNTs deform elastically during the whole loading–unloading–reloading procedures.

Abstract: Microfibrillated cellulose (MFC) was successfully prepared from lyocell fibers using combined homogenization and sonication treatments. MFC fibrils with a mean diameter of ~365 nm were observed, after the lyocell fibers with diameters of ~10 μm were mechanically treated for 60 min. Poly (vinyl alcohol) (PVA) composites reinforced with MFC were then fabricated using a solvent casting method. Physical and mechanical properties of the MFC reinforced PVA composites were investigated. An increase of ~13 and ~34 % of tensile strength and Youngs modulus was observed for the 3 wt% MFC reinforced composites, compared to those of the pure PVA. Raman spectroscopy was also employed to study the deformation micromechanics of the MFC reinforced PVA composites. The position of the Raman peak initially located at 1095 cm^-1, corresponding to the C-O ring stretching and C-O-C glycosidic bond stretching modes, was recorded. During tensile deformation, this peak was observed to shift towards a lower wavenumber position, indicating stress-transfer between the resin and the fibrils.

Abstract: In order to investigate the evidence for the formation of Sr²⁺-Zr⁴⁺ defect complexes in high-k Sr and Zr co-doped BaTiO₃ ceramics, BaTiO₃, (Ba_0.85Sr_0.15)TiO₃, Ba (Ti_0.8Zr_0.2)O₃, and (Ba_0.85Sr_0.15)(Ti_0.8Zr_0.2)O₃ (BS15TZ20) ceramics were prepared using a mixed oxide method. The Y5V-type BS15TZ20 shows a high-k diffuse phase transition behavior (ε ́_m = 8000) and its Curie peak occurs near room temperature. The evolution in crystal structure and in dielectric property for the four samples gives four evidences for the formation of Sr²⁺-Zr⁴⁺ defect complexes in BS15TZ20. The splitting of the 720 cm^-1 Raman band does not relate to Sr²⁺-Zr⁴⁺ defect complexes, but to a multiphonon (A₁ (TO₂) + A₁ (TO₃)).

Abstract: Through ten years physical investigation on the geometrically frustrated coordination compound series basic (hydroxyl and deuteroxyl) transition-metal halides M₂(OH/D)₃X (M=Mn, Fe, Co, Ni and Cu; X=Cl, Br and I), we have determined the existence of four crystal structures, whose space groups belong to Nos. 11, 14, 62 and 166, respectively, in this series till now. After studying their Raman spectra, we firmly believe that a nonnegligible hydrogen bond (H-bond) exists in every material. Considering carefully their local lattice environments of the basic groups, we find a new kind, to the best of our knowledge, of H-bond [(OH)₃···M] and nominate it as the trimeric H-bond, and further confirm three types of symmetric structures, which have totally four subtypes of trimeric H-bonds so far. More two subtypes are predicted to exist in nature. This result may provide a new interesting subject for quantum chemists and material physicists.

Abstract: The low temperature (T) Raman spectroscopic study on the geometrically frustrated clinoatacamite γ-Cu₂(OH)₃Cl is reported. By measuring the T-dependent spectral profiles and representative modes, we have obtained auxiliary evidence of successive magnetic transitions near T_c1 =18.1 K and T_c2 =6.4 K determined accurately by the magnetic experiments in the Raman band frequencies and peak widths of the representative modes for magnetic research conclusions and observed a pronounced Raman spectroscopy background featuring a broad continuum at all Ts. A quantitative analysis reveals spin fluctuations on a picosecond time scale in the intermediate phase.