Pham V. Huong

Structural studies of diamond films and ultrahard materials by Raman and micro-Raman spectroscopies

Abstract Correlations between phonon Raman spectra and structure were established and illustrated with natural diamond, graphite, carbon, novel brilliants and novel ultrahard substances. Diamond-like film is characterized by a Raman band at 1540 ± 20 cm −1 which differs from those of graphite and amorphous carbon. A new structure named “bridged graphite” or “diamite”, with interlayer bonds is proposed for diamond-like material. A mechanism for the destruction of ultrahard coatings is also suggested.

Structure and orientation of a superconducting Y-Ba-Cu-O thin film on zirconia substrate. A study by micro-Raman spectroscopy

Abstract A thin film of YBa2Cu3Ox deposited on Zirconia (100) substrate, and transiting at 92 K was examined by micro-Raman spectroscopy. The layer is revealed to be an aggregation of two types of micro-crystals: one of them is oriented with the c axis nearly perpendicular to the surface and having often truncatures which give them the appearance of nearly square pyramids, and the others with the c axis parallel to the surface. The oxygen content is evaluated to be x = 6.97, therefore the formula of the superconducting material could be YBa2Cu3O7. This oxygen amount is relatively homogeneous at various areas on the surface even where the distribution of the crystal aggregate is not homogeneous. After six months, a lost of oxygen, down to x = 6.8 in the same sample is recorded. These micro-crystals appear to grow on a continuous ground which was identified as a green phase, Y2BaCuO5 resulting from the interaction at the interface between YBa2Cu3O7 and the substrate dopped itself with Y2O3.

Structure of liquid hydrogen fluoride studied by infrared and Raman spectroscopy

Infrared and Raman spectra of hydrogen fluoride, deuterium fluoride, and their isotopic mixtures at various temperatures from 293 to 77 K have been recorded and analyzed in comparison with calculated data obtained from the classical G.F. matrix method applied to hypothetical structures chosen a priori. The best fit lead to the most probable structure of HF at 293 K which is a zig–zag chain with six or seven molecules having an angle of 42° with the average axis. At a lower temperature (190 K), just before solidification, the chains become longer, n=8 with an angle θ≂35 °. These structures fit well with the high dielectric constant of liquid hydrogen fluoride and lead to a calculated Kirkwood factor g1=3.65 at 293 K and g1=5.36 at 190 K which are in perfect agreement with known experimental values.

Characterization of Materials by Micro-Raman Spectroscopy

Abstract When illuminating a sample with a laser through an optical microscope, before collecting the scattered light in the monochromator of a Raman spectrometer, micro-Raman spectra can be recorded from a surface area as small as 1 μm 2 . Thus the individual components of a heterogeneous sample of micrometre size can be selectively investigated. Vibrations and phonons observed in Raman spectra are directly connected with the structure and dynamics of the solids. Thus many useful correlations can be deduced. Raman polarization is also helpful in the determination of the orientations of solids and layers. Step-etched and bevelled samples of layers on substrates studied by micro-Raman spectroscopy can reveal local structural changes and new chemical bonds at the interfaces as well as the regularity of epitaxial layers as a function of their thickness. These and other advantages due to recent advances in micro-Raman technology will be illustrated by examples of new semiconductor and superconductor materials.

NEW POSSIBILITIES OF RAMAN MICRO-SPECTROSCOPY

Abstract The principle of Raman micro-spectroscopy with a spatial resolution better than 1 μm2 is given and accessories are described for improving the technique. Wide fields of application are presented including in particular studies of heterogenous samples like composite materials, drugs, inclusion complexes, contaminants, pictural pigments in paintings and illuminations. Inhomogeneities and gradients on the surfaces or in the bulk of new semiconductors and superconductors as well as structural modifications at the interfaces are also analyzed. Finally, examples are given concerning biomaterials and living objects, in particular the blue particles found in cancer tumours.

Evidence by Raman spectroscopy and x‐ray diffraction of a strong influence of H2O traces on the metalorganic vapor phase epitaxy of GaAs on Si

The metalorganic vapor phase epitaxy of GaAs on Si is shown to be strongly sensitive to the residual water vapor content in the growth reactor atmosphere. This finding is evidenced both by Raman spectroscopy and double‐crystal x‐ray diffraction. For the growth of good crystalline quality GaAs on Si, the upper hygrometric level limit is found around 0.5 ppm by volume.

Vibrational Spectra of Fluoronium Ions, FH2+, FD2+, and FHD+

The first direct observation of fluoronium ions, FH2+, FD2+, and FHD+, is reported. The method of production of the fluoronium salts is described, and their infrared spectra are analyzed. The structure of the fluoronium ions is shown to be angular. The force constants have been evaluated. In the presence of liquid hydrogen fluoride, the fluoronium ions are strongly solvated by hydrogen bonds in the form (HF)nH+.

Microstructure of high temperature superconductor thin films as studied by micro-Raman spectroscopy

Abstract Based on correlations established between Raman spectra and structure and on high anisotropy in Raman polarization of superconducting materials, the micro-structure and orientation of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O thin films deposited on various substrates were determined for both surfaces having grains or without grain. A relationship, established between the Cu 2 -O 1 vibrational frequency v H (467–503 cm -1 ) and the oxygen content x in YBa 2 Cu 3 O x : x = 0.025 v H − 5.57 facilitated a rapid evaluation of the oxygen content of any surface, by this non destructive technique. With step-etched surfaces, the micro-structure and epitaxial quality can be observed in function of the thickness of the deposit. Finally, with bevelled samples, micro-Raman spectroscopic technique also allows to illuminate a bilayer from the substrate to the interface then to the ourter surface and can eventually show structural modifications or the appearance of new chemicals due to the interaction between the superconducting layer and the substrate.

Drug analysis by Raman and micro-Raman spectroscopy☆

The technique of Raman spectroscopy, resonance Raman spectroscopy and micro-Raman spectroscopy is described for application to drug analysis and investigation. Possibilities and limits are mentioned for qualitative and quantitative analyses as well as for studies of structure and interactions. Some principal interaction modes, such as hydrogen bonding, proton transfer, charge transfer and ion-molecule attraction, are shown to explain drug reactivity. Illustrations are given based on several drug families, in particular vitamins, anti-depressants, cardio-active and anticancer drugs.

Diamond and diamond simulants as studied by micro-Raman spectroscopy

The ability of Raman and micro-Raman spectroscopies in the characterization and structural studies of diamond and novel diamond materials and films is presented. Correlations between Raman spectra and structure have been established and illustrated with natural diamond, graphite, carbon, novel brilliants and artificial ultrahard substances. Diamond-like films are well individualized and characterized by a Raman band at 1540±20 cm−1 which differs from those of graphite and amorphous carbon. A new structure, named “diamite” or “bridged graphite” having interlayer bonds is proposed for diamond-like material. A mechanism of destruction of ultrahard coatings is also suggested.