P. Dhamelincourt

Characteristics of Raman Microscopy

Publisher Summary This chapter focuses on those characteristics which differentiate Raman microspectroscopy from the more conventional techniques. The important characteristics of Raman microscopy are directly related to two fundamental optical considerations: (1) the focusing of the incident laser excitation on the sample and (2) the collection of the scattered light. The chapter analyzes the specific problem of coupling a microscope to a Raman spectrometer. The confocal effect is described, as it the basis of recent advances in Raman instrumentation, including imaging techniques. The total Raman intensity depends on the solid angle Ω in which the scattered light is collected. In the backscattering configuration Ω describes approximately the cones of both the incident and scattered light. The optimum use of the Raman light flux o collected from a sample requires it to be transmitted from sample to detector via the successive apertures of the instrument. The invariance conditions of the optical extent can be fulfilled with the use of coupling optics which result in good matching between all of the apertures along the entire light path, from microscope to the spectrometer detector.

The infrared and Raman spectra of ethylammonium hexafluorosilicate [C2H5NH3]2SiF6

The X-rays powder diffraction pattern of [C2H5NH3]2SiF6 was obtained and indexed on the basis of a hexagonal unit cell. The vibrational spectra (IR and Raman) of this compound were recorded and discussed in relation to the above-mentioned crystal structure. The vibrational spectra of the cations indicate that they are disordered and hydrogen bonded to the anions. On the opposite, the Raman spectrum of the anions could be interpreted in terms of ordered groups. The combination bands observed in the 2300-1800 cm(-1) spectral region in the IR spectrum indicate that this compound may contain C-NH3 groups.

Raman characterization of Mg+ ion-implanted GaN

Mg+ ions were implanted at room temperature in n-type hexagonal GaN for the device isolation purposes. The implantation dose varied from 7.5 × 1012 to 1016 ions cm−2. We performed resonance Raman spectroscopy and DC electrical measurements in order to monitor the structural and electrical changes of non-annealed and annealed implanted GaN samples. Annealing was carried out at 900 °C for 30 s, these conditions being used to achieve good Ohmic contacts. The aim was to determine, on the one hand, the influence of ion doses on the device isolation and, on the other, to establish the order of the technological steps which should be made between ion implantation and Ohmic contact annealing. On increasing the implantation dose from 7.5 × 1012 to 2 × 1014 ions cm−2, an increase in the electrical isolation and a decrease in the photoluminescence (PL) were observed. For the highest dose, the implanted layer became conductive owing to a hopping mechanism and only the first-order phonon lines remained observable. After annealing, the implanted samples became conductive and the PL reappeared or increased compared with the non-annealed samples at same implantation doses, except for the sample implanted at the highest dose, which became insulating. Then, it is possible to achieve device electrical isolation by using a lower ion dose without thermal annealing or using a higher ion dose with thermal annealing.

Polysulphides in dimethylformamide: a micro‐Raman spectroelectrochemical study

The reduction of sulphur and the redox properties of polysulphide anions in dimethylformamide (DMF) were studied by time-resolved spectroelectrochemistry, coupling cyclic voltammetry with micro-Raman spectrometry. The measurement system allows one to record several spectra in real time during the potential scan of the working electrode. The data obtained under thin-layer conditions, at room temperature, were compared with those obtained by cyclic voltammetry and by visible time-resolved spectrophotometry. The variations of the Raman (535 cm-1) and visible (610 nm) characteristics of the radical anion S3- during the potential scan for S8–DMF and Li2S6–DMF solutions are presented and these results are discussed.

Infrared and Dielectric Studies of [(C2H5)4N]2SiF6

The infrared spectrum of [(C2H5)4N]2SiF6 was recorded and discussed in relation to its crystal structure. This spectrum indicates that cations and anions are distorted and are not hydrogen bonded. Two structural phase transitions were observed in the tetraethylammonium compound [(C2H5)4N]2SiF6 by means of dielectric measurements. High-frequency dielectric dispersion phenomena in this compound were also analysed. The evolution of the dielectric constant with the temperature indicates the presence of two phase transitions, at high temperatures, which are of order-disorder character.

Use of spectroscopic techniques for the study of natural and synthetic gems: Application to rubies

Spectroscopic techniques were applied to the study of natural and synthetic gems, especially rubies, It is shown that among the spectroscopic techniques available, micro-Raman spectroscopy is the easiest to use and the most efficient Moreover, this technique can be applied to mounted gems without removing them from the setting. However, complementary methods such as micro-Fourier transform infrared, micro-fluorescence, electron probe and MMR spectroscopy, were used in order to characterize the gems more thoroughly in order to differentiate between natural and synthetic specimens

Structure and vibrational study of the trimethylammonium hexafluorosilicate [(CH3)3NH]2SiF6 compound

The X-ray powder diffraction pattern of [(CH(3))(3)NH](2)SiF(6) was obtained and indexed on the basis of a centred cubic unit cell with the P4(1)32 as the likely space group. The Infrared and Raman spectra of this compound have been recorded at room temperature and discussed in relation to the crystal structure. In this salt, the bands corresponding to the cation vibrational modes show that the symmetry of these cations is distorted from the free C(3v) one and that they are strongly hydrogen-bonded to the respective anions. However, the spectra of the anions can be interpreted in term of ordered groups as indicated by the splitting of the bands corresponding to some degenerate vibrational modes. The harmonic frequencies, corresponding to the (CH(3))(3)NH-SiF(6)-NH(CH(3))(3) optimised geometry, were calculated using the SCF semi-empirical MNDO-PM3 method.

Raman characterization of GaN synthesized by N implantation in GaAs substrate

GaN material was synthesized by implantation of N ion into a GaAs (001) semi-insulating substrate. After implantation, different annealing treatments were applied and the results were investigated using UV Raman spectroscopy. More particularly, temperature and time treatments ranging between 500 and 950 °C and 1 and 20 min, respectively, were studied. The results of these studies showed that, by using appropriate annealing conditions, a high-quality GaN crystalline layer can be obtained on GaAs substrates. Copyright

Vibrational study of tin‐containing siloxane ring compounds

By a condensation reaction of (t-Bu)2Si(OH)2 (L) with tin tetrachloride (SnCl4), two different compounds were obtained: a condensation product between two molecules of L and a tin-containing siloxane bicycloheptane ring compound formed by a subsequent reaction between partially hydrolysed SnCl4 and L. The latter was identified by x-ray diffraction. The Raman spectra of both isolated compounds were recorded and confirmed the structure obtained for the ring compound.

Application to Materials Science

Publisher Summary This chapter focuses on the applications of Raman microspectroscopy to materials science. Chemical compositions, molecular configurations and conformations in polymers are identified through their vibrational frequencies. This information can be obtained by the Fourier transform (FT)–infrared(IR) techniques and more recently with the use of FT-Raman accessories proposed by IR instrument manufacturers. However, Raman microscopy remains a unique, invaluable tool for the analysis of polymers at the microvolume level. Thus, the nature of defects or inhomogeneities can be readily identified. In the same way, investigation of polymer morphology and quantitative measurements of localized molecular symmetry in oriented polymers are possible from Raman polarization measurements. The chapter also discusses microelectronics and semiconductors. The Raman microprobe provides a powerful technique for the investigation of semiconductor materials and the analysis of problems in microelectronic devices. This method is a non-destructive one which is important for the characterization of semiconductors with composite structures, ceramics consisting of grains, and heterogeneous and device structures. A Raman microprobe measurement is not limited to the study of a local point in bulk materials and small particles. Recent developments in Raman technology have enabled one- or two-dimensional images to be obtained.