Spatial resolution Raman spectroscopy

Laser Raman diagnostic teclmiques offer remote, nonintnisive, nonperturbing measurements with high spatial and temporal resolution [158], This is particularly advantageous in the area of combustion chemistry. Physical probes for temperature and concentration measurements can be debatable in many combustion systems, such as furnaces, internal combustors etc., since they may disturb the medium or, even worse, not withstand the hostile enviromnents [159]. Laser Raman techniques are employed since two of the dominant molecules associated with air-fed combustion are O2 and N2. Flomonuclear diatomic molecules unable to have a nuclear coordinate-dependent dipole moment caimot be diagnosed by infrared spectroscopy. Other combustion species include CFl, CO2, FI2O and FI2 [160]. These molecules are probed by Raman spectroscopy to detenuine the temperature profile and species concentration m various combustion processes. 

Sample preparation is straightforward for a scattering process such as Raman spectroscopy. Sample containers can be of glass or quartz, which are weak Raman scatterers, and aqueous solutions pose no problems. Raman microprobes have a spatial resolution of - 1 //m, much better than the diffraction limit imposed on ir microscopes (213). Eiber-optic probes can be used in process monitoring (214). 

The combination of atomic force microscopy (AFM) and Raman spectroscopy is another approach to attain high spatial resolution. AFM also employs a sharp tip close to a sample surface. When the tip is made of metal and light is irradiated onto the tip and surface, Raman scattering is largely enhanced. In this way, a spatial resolution of 15 nm is achieved [2]. 

In summary, recent progress and future prospects in the research field of fiuorescence and Raman spectroscopy combined with STM in order to achieve high spatial resolution spectroscopy have been reviewed. In the near future, single (sub-) molecule STM spectroscopy is expected to be applied to the nano-world of science and engineering. 

In 1994, we proposed that a metallic needle having a nano-tip at its apex be employed as a nano-light-source for microscopy attaining nanometric spatial resolution [2]. Later, we expanded the technique to Raman spectroscopy for molecular nano-identification, nano-analysis and nano-imaging. In this chapter, we give a brief introduction to local plasmons and microscopy using a metallic nano-needle to produce the local plasmons. Then, we describe the microscope that we built and... 

A nano-light-source generated on the metallic nano-tip induces a variety of optical phenomena in a nano-volume. Hence, nano-analysis, nano-identification and nanoimaging are achieved by combining the near-field technique with many kinds of spectroscopy. The use of a metallic nano-tip applied to nanoscale spectroscopy, for example, Raman spectroscopy [9], two-photon fluorescence spectroscopy [13] and infrared absorption spectroscopy [14], was reported in 1999. We have incorporated Raman spectroscopy with tip-enhanced near-field microscopy for the direct observation of molecules. In this section, we will give a brief introduction to Raman spectroscopy and demonstrate our experimental nano-Raman spectroscopy and imaging results. Furthermore, we will describe the improvement of spatial resolution... 

Similarly, the first-order expansion of the p° and a of Eq. (5.1) is, respectively, responsible for IR absorption and Raman scattering. According to the parity, one can easily understand that selection mles for hyper-Raman scattering are rather similar to those for IR [17,18]. Moreover, some of the silent modes, which are IR- and Raman-inactive vibrational modes, can be allowed in hyper-Raman scattering because of the nonlinearity. Incidentally, hyper-Raman-active modes and Raman-active modes are mutually exclusive in centrosymmetric molecules. Similar to Raman spectroscopy, hyper-Raman spectroscopy is feasible by visible excitation. Therefore, hyper-Raman spectroscopy can, in principle, be used as an alternative for IR spectroscopy, especially in IR-opaque media such as an aqueous solution [103]. Moreover, its spatial resolution, caused by the diffraction limit, is expected to be much better than IR microscopy. 

In ocular applications, Raman spectroscopy can quickly and objectively assess composite lutein and zeaxanthin concentrations of macular pigment using spatially averaged, integral measurements or images that quantify and map the complete MP distribution with high spatial resolution. Importantly, both variants can be validated with HPLC methods in excised human eyecups and in animal models. 

In transmission mode a spatial resolution of about 15-20 pm can be achieved with infrared microscopes [32]. This is generally sufficient to properly identify such as small impurities, inclusions, gels or single components of multilaminate foils. Similar to Raman spectroscopy, line profiles or maps over larger sample areas can be performed. 

Several groups have used Raman spectroscopy in combination with OCT, which is a rapid, high spatial resolution technique. OCT is used to identify suspicious areas of tissue and single-point Raman spectroscopy is used to confirm presence or absence of disease. Application to dental caries is discussed in Chap. 15. A very recent development is an integrated Raman/OCT probe [34], which is shown in Fig. 5.6. Using biopsied breast tissue, the instrument... 

Raman spectroscopy Raman spectra from small SWNT pieces with typical dimensions of 100 pm were recorded in the back-scattering geometry using two different micro-Raman setups comprised of a triple monochromator DILOR XY and a CCD detector system, cooled either to liquid nitrogen temperature or -100°C. The 488 or 514.5 nm line of an Ar+ laser, as well as the 647.1 nm line of a Kr+ laser, were used for excitation, while the beam intensity on the sample was =0.5 mW. The laser line was focused on the sample by means of a lOOx objective with a spatial resolution of 1 pm. 

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