Search

Raman instrumentation design has improved radically in efficiency and ease of use over the past 15 years. New technologies made this possible with introduction of the first commercial high-efficiency (high speed) Raman systems incorporating low power lasers. Systems were introduced for the first time on production and process lines. Higher efficiency systems have continued to evolve, as a result of novel engineering solutions. Raman-near field optical systems and Raman-SEM (scanning electron microscopy) combinations have created a new area of nanoscale spectroscopic measurements. New application areas are: (a) semiconductor processing; (b) pharmaceutical drug processing; (c) gemology; (d) narcotic and explosives forensic detection; (e) coatings on computer hard disks and read heads; (f) endoscopic and Raman detection of oesophageal and other types of cancer. Comparisons are made with competing optical and alternative instrumentation techniques for general Raman work and the applications.

Raman scattering properties from various GaN thin films grown on sapphire by metalorganic chemical vapor deposition were studied. Visible micro-Raman measurements show different mode behaviors with different laser incidence configurations. Raman lineshape analyses through two sets of equations led to the monitoring of the sample quality and stress and the optical determination of electrical properties of GaN films. An approximate 3 cm−1 shift in the E1(LO) mode wavenumber is observed across the GaN film from the sapphire/GaN interface to the GaN surface, indicating the spatial variation of strains along the film growth direction within a few microns thickness range. Combined Raman and PL spectra were obtained under UV excitation, and interesting high-order resonance Raman features were observed using a sensitive UV–Raman–photoluminescence microscope. A new way to characterize p-type GaN is introduced. Copyright © 2001 John Wiley & Sons, Ltd.

Confocal Raman microspectroscopy has previously used pinholes placed at the back focal plane of the microscope to provide depth resolution along the optical axis. The process of optimizing the pinhole alignment can often be difficult and time-consuming. We demonstrate a different approach to setting up a confocal Raman microscope using a stigmatic spectrograph and a CCD detector. This arrangement is easy to use and provides a depth resolution of ∼2 μm.

Raman spectroscopy is steadily growing in importance in the industrial analytical laboratory. The nature of the equipment, its ease of use and its cost are making the method more acceptable to non-experts. This paper illustrates the capabilities of a recent commercialized Raman system which fulfils the criteria of ease of use, speed and low cost. The system is designed for Raman microscopy and uses a single spectrograph and CCD detector. The combination provides confocal microscopy, high throughput and optimum sensitivity, to the extent that it only requires the use of a low-powered laser to provide high-quality spectral data. The additional feature of direct Raman imaging is seen as being beneficial in the industrial environment in that it provides spatial information over large surface areas quickly and without the need for excessive amounts of data processing. The performance of the instrument is illustrated with applications taken from the industrial environment.

Fourier transform Raman spectroscopy has been carried out remote from the instrumentation using fibre-optic probes. The quality of the data is good; the measured signal-to-noise ratios from spectra obtained using a conventional sampling arrangement are better only by a factor of ca. 5. The choice of fibre-optic material and grade is crucial to the success of this work. Two different fibres have been tested and compared. Technical improvements are discussed.

The fourier transform (FT) Raman method, the main technique for overcoming background fluorescence in Raman spectroscopy, was applied to small samples which proved difficult to study using visible laser Raman methods. Various examples are given and the minimum sample size for FT-Raman spectroscopy has been shown to be in the microgram range.

In situ Raman spectroscopic studies of the electrochemical reduction of carbon dioxide at lead-impregnated PTFE-bonded carbon gas diffusion electrodes are reported. Polarization of the electrode surface resulted in the appearance of two weak bands at 2824 and 2915 cm−1. These do not correspond to the wavenumber shifts expected for free formic acid, but they are thought to arise from the presence of a ‘free’ formate ion and the formic acid perturbed at the electrode surface, respectively. Spectral changes observed at lower wavenumber shifts on polarization of the electrodes are interpreted in terms of the reduction of lead oxide to lead.

The full resonance Raman spectra of cobalt(II) and cobalt(I) phthalocyanine are presented. By comparison with the Raman spectra of similar compounds, it has been possible to assign many of the bands. The resonance Raman spectrum of cobalt(II) phthalocyanine was replaced by that of cobalt(I) phthalocyanine when a PTFE-bonded carbon gas diffusion electrode impregnated with a small amount of cobalt(II) phthalocyanine was maintained at a potential of −1.80 V, the gas side of the electrode being exposed to a carbon dioxide atmosphere. These results indicate that cobalt(I) phthalocyanine is a reactive intermediate in the electrochemical reduction of carbon dioxide to carbon monoxide at cobalt(II) phthalocyanine-impregnated electrodes.

Polyacetylene prepared by the Durham precursor route can be obtained in a range of forms. Unstretched films show little crystallinity and short conjugation sequences, whereas films that are stretched during the transformation reaction can be highly-oriented, exhibiting a high degree of crystallinity, and showing evidence, from Raman, ESR and conductivity experiments for longer conjugation lengths. We review here our work on the transformation and isomerisation reactions,and on the electronic properties of the Durham-route materials. We present measurements of the anisotropy of the photoconductivity and photo-induced absorption (at 0.45 eV) in oriented films. Both phenomena are more strongly excited when the E vector of the band-gap illumination is perpendicular to the chain direction, indicating the importance of interchain electronic transitions.

The free-radical cations of benzidine, [2H4]benzidine and N,N,N′,N′-tetramethylbenzidine have been formed by u.v. photolysis of the neutral parent compounds trapped in clear glassy ethanol matrices at 77 K. The radicals all have intense visible absorption bands which facilitate excitation of their resonance Raman spectra. These Raman spectra have been assigned and interpreted in terms of structural changes from the corresponding parents.