Raman microspectroscopy can be used effectively to study very small samples or to study small areas within a transparent sample. With the application of the technique of confocal microscopy to a Raman microscope, the depth resolution of the instrument can be enhanced considerably. Confocal microscopy uses a pinhole, placed in the back image plane of the microscope objective, to block light from outside the focal plane. In this way the signal from the small volume element one wants to study can be better separated from the signals arising from the surrounding material. In this paper we show that the performance of the confocal Raman microscope can be described satisfactorily by geometrical optics. Furthermore, we have performed measurements to determine the depth resolution of our system for different combinations of objectives and pinholes. Finally, we report on the applications of this technique to different polymer systems, such as multilayer foils, fibers, and fiber composites.

The original work of Strobl and Hagedorn suggesting the presence of a third intermediate phase in semicrystalline polyethylene was revisited. The current study, involving the collection of Raman spectroscopic data on a set of 16 polyethylene samples recorded on two different types of instruments in two different laboratories and employing two different methods of curve fitting to both sets of experimental data, has revealed that the claims in the original paper cannot be asserted. The most important reason leading to this conclusion is a problem in correctly describing the complicated overlapping spectral structure in the 1000-1200 and 1400-1500 cm-l spectral ranges. It is noted that the contribution of the melt in the 1000-1150 cm-l range cannot be described by a single line centered around 1080 cm-l. The present results indicate that the quantification of a third, intermediate, phase in polyethylene is not possible when based on standard Raman spectra.

Surface-enhanced Raman spectroscopy (SERS) is evaluated as a quantitative analytical tool for low concentrations of melamine and melamine derivatives in solution. Substantial variations in absolute and relative intensities of SERS bands were encountered using silver sols, which cannot be controlled. Alternatively, it was shown that SERS using a roughened silver electrode, while conditioning the applied potential, permits the acquisition of Raman spectra from electrode spots down to 1 µm in size, and the results of multiple measurements using a hard cathodic cleaning step in between each adsorption experiment gave a relative standard deviation of 15%. The high enhancement factor of the electrode micro-Raman scattering intensity creates a new trace analytical technique for obtaining high-resolution spectra of melamine from dilute aqueous solution (detection limit ∼ 10 -7 mol L -1 ) in the opto-electrochemical cell. As an alternative for the hard cathodic cleaning step, we demonstrated that the cationic surfactant molecule cetylpyridinium chloride is able to remove preadsorbed melamine within a few seconds. The surfactant molecules can subsequently be removed from the surface by switching to a negative applied potential. This procedure results in a relative standard deviation of 10%. The effects of electrode potential on the observed SERS spectra are consistent with current 'SERS surface selection rules'. The electrode potential and the surface concentration of the chloride counterions strongly affect the intensity of the out-of-plane modes in the adsorbed state. However, additional experiments using various excitation lines showed that an alternative theory, surface complex formation combined with charge transfer resonance Raman processes with Herzberg-Teller contributions, plays an important role.

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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.