Raman line scanning

In this example a polymer laminate film (for packaging) was examined, which was composed of nine layers (see Table 2), by both FTIR imaging and Raman line scan. For the IR measurements thin sections (5 pm) were cut. The central ethylene/vinyl acetate (EVA) copolymer layer is very soft, and holes can be seen in the visible image (Figure 12). 

A simple line scan with Raman microscopy, however, clearly showed the LLDPE-MAH layer as a ca. 5-p.m broad plateau from the evaluation of three different Raman band intensities (Figure 14). In this case a simple Raman line scan obviously is the better choice for a determination of the LLDPE-MAH layer thickness, superior even to IR-ATR imaging. We used three Raman bands... 

Figure 14 (a) Raman spectra of the individual layers 1, LLDPE-MAH 2, COPA 3, EVA (abscissa wavenumber (cm ), ordinate intensity in arbitrary units), (b) Raman line scan of polymer laminate using three different Raman bands (abscissa position in pm, ordinate intensity in arbitrary units). 

Fig. 64. Raman line scans across the groove in Si showing the increase in residual compressive stress with the depth of cut.

For the detection of weak Raman lines, high laser power, high signal amplification, long pen period, and very slow scanning speed should be... 

By calculating an average Raman spectrum from a line scan over the long axis of yeast cells a differentiation of single yeast cells on a species and strain level can be performed [110, 111]. The application of Raman spectroscopy in combination with a supervised classification method allows for the identification of single yeast cells in a large data set [69]. 

Here, T is the observed line width (Av << F), 7d is the peak-to-valley intensity in the difference spectrum, and To is the peak height of the Raman line. Although this equation is for Lorentzian-shaped bands, the results are approximately the same for Gaussian-shaped bands (the constant 0.385 becomes 0.350). In the case of carbon disulfide-benzene mixtures, the smallest shift observed was -0.06 cm-1, and the associated error was 0.02 cm-1 (77). A convenient rotating system that can be used for (1) difference spectroscopy, (2) normal rotating sample techniques (solid and solution), and (3) automatic scanning of the depolarization ratios as a function of the wave number has been designed (45). 

Fig. 3.5-10 c shows another sample arrangement which makes use of a fiber-optical connection from the laser to the sample and back to the spectrometer. It is specially designed for the scanning of surface layers, e.g., of precious prints or paintings. The half spheric concave mirror reflects the portion of exciting radiation and Raman radiation back to the sample which has been. scattered by the sample and is not collected by the optical fiber. Thus the mirror as a component of a multiple reflection system enhances the observed intensity of the Raman lines by a factor of 2 to 8, depending on the properties of the sample. 

Sample arrangements for Raman spectroscopy 143 Micro and 2D scanning arrangements 148 The radiant power of Raman lines 151... 

FIGURE 12.17 Spectral in-line scan (2 pm step) of a composite cross section. Spectra were recorded from one NLM202 fiber to another, through the aluminosilicate + (Zr02 Ge02) tailored interface and the mullite matrix. (Reprinted from Colomban, R, Raman microspectrometry and imaging of ceramic fibers in CMCs and MMCs, 103, 517, 2000. With permission from The American Ceramic Society.)... 

Figure 11.17. Video and Raman image of an integrated circuit, obtained with line scanning and stage translation on a Dilor XY spectrometer. Area in white box was observed with a 28 x 28 spatial grid, and the Raman image was reconstructed from 28 CCD exposures. White regions in the Raman image correspond to higher Raman intensity in the 501 to 536 cm Raman shift range.

Figure 11.23. Raman images of a pharmaceutical tablet reconstructed from 28 line images obtained with mechanical line scanning in a Dilor XY spectrometer. Both images are of the same area on the tablet, but image A is derived from an acetamidophenol band, while image B is from an excipient band. False color intensity scale is shown to the right of both images. Individual spectra are shown in Figure 11.7. (See color plates.)...

Both optical and mechanical line scans generate large data sets when used to construct a two-dimensional Raman image, but computer power and storage is inexpensive in the post-PC world. An advantage of such large data sets is the retention of complete spectra for each spatial element, with often high spectral... 

The Raman lines for benzene, cyclohexane and chloroform in aqueous solution were measured for the saturated concentrations ( ca. O.OU, 0.001, and 0.1 mol respectively), and solutions of the same concentrations were used for other reference solvents. In solutions of such low cqncentrations, parallel component spectra could be observed with a single scan because of rather high Raman intensities, but perpendicular component spectra could be obtained with 100 or more accumulated... 

Fig. 6.2 Raman spectra from a line scan through the thickness of PVC film (A) a control sample, (B) a film degraded with triethylenediamine for 21 days [20]. The band at 1520 cm is due to C=C, from the dehydrochlorination of PVC. Its intensity as a function of depth can be analyzed to give degradation and diffusion kinetics. (From Bowden et ah [20] reproduced with permission.)...

For a comparison of the performance of a global imaging system to a system producing Raman maps created from a confocal line scan, the reader is referred to Ref. 76. 

Figure 7 Raman maps of a multiphase fluid inclusion within a quartz host produced by confocal line scanning. Left side, top water phase right side, top CO2 bottom nacholite or NaHCOg.

M Bowden, DJ Gardiner, G Rice, DL Gerrard. Line-scanned micro Raman spectroscopy using a cooled CCD imaging detector. J Raman Spectrosc 21 37-41, 1990. 

A variety of methods have been developed to image materials based on their Raman contrast. The methods can be classified broadly as source scanning approaches or as wide-field source illumination approaches and are diagrammed in Fig. 2, Figure 2A describes point-scan Raman imaging, whereas Fig. 2B shows line-scan imaging and Fig. 2C shows the wide-field approach. 

Figure 2 Strategies for collecting Raman images (A) point scan (B) line scan (C) wide field.

In addition, the spatial resolution parallel to the laser line is the convolution of the microscope magnification by the pixel size. As a result, submicron spatial resolution is achievable in one spatial dimension. In the dimension perpendicular to the laser line, the spatial resolution of the image continues to be limited by the width of the laser line on the sample convolved by the scanning precision of the instrument. Although line-scan imaging has not been as widely explored as point-scan imaging, it has been demonstrated in several applications [12-15] and line-scan Raman imaging systems are commercially available. 

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