Optical measurement methods, chemical

Lehaitre et al. [23] have described a fibre-optic spectrophotometric method for the in situ measurement of biological and chemical species. This instrument can measure phytoplanktonic species, and the potential for chemical measurement such as dissolved carbon dioxide is analysed. 

However, atom motions cannot be unambiguously imaged by time-resolved optical spectroscopic methods as they do not directly measure the structural dynamics but instead characterize energetic properties. Consequently, novel methods that enable the direct measurement of molecular motions during chemical processes are needed. Furthermore, chemical reactions often occur in solution and, consequently, it is desirable that such methods are applicable to chemical processes in the liquid phase. 

It is hard to And better monitoring tools than optical spectroscopy methods when high spatial and temporal resolution is required in addition to noninvasiveness. Traditionally, absorption, light scattering, chemiluminescence, and fluorescence measurements are used for this purpose (Janasek et al. 2006). Those are well-established techniques that establish a simple way of obtaining useful information. However, absorption and scattering measurements provide very little information about the chemical composition. Fluorescence spectroscopy provides more information but is... 

A common method for on-line monitoring of chemical compositions is the use of FIA. This approach is in essence a miniaturised wet chemical laboratory analysis. The approach was developed in the 1970s to adapt existing measurement methods to the task of rapid measurements. Typically, small pumps, tubes and mixing chambers combine to produce a flowing solution that is subjected to analysis by optical or electrochemical means using essentially the same reagents as in a normal-scale analytical determination. The key to sensitivity with these systems is to prevent dispersion in the stream. There are opportunities for imprinted polymers in both the sample purification and the detection of analytes. 

Chemical methods can also be applied for the measurement of the interior temperature of microsystems. A fluorescent molecular thermometer using temperature-induced phase transitions seems to be quite attractive,but it needs a transparent window on the wall of the microchannel for the optical measurement. However, this may change the heat transfer ability of the wall. 

A tunable pulsed laser Raman spectrometer for time resolved Raman studies of radiation-chemical processes is described. This apparatus utilizes the state of art optical multichannel detection and a-nalysis techniques for data acquisition and electron pulse radiolysis for initiating the reactions. By using this technique the resonance Raman spectra of intermediates with absorption spectra in the 248-900 nm region, and mean lifetimes > 30 ns can be examined. This apparatus can be used to time resolve the vibrational spectral o-verlap between transients absorbing in the same region, and to follow their decay kinetics by monitoring the well resolved Raman peaks. For kinetic measurements at millisecond time scale, the Raman technique is preferable over optical absorption method where low frequency noise is quite bothersome. A time resolved Raman study of the pulse radiolytic oxidation of aqueous tetrafluoro-hydroquinone and p-methoxyphenol is briefly discussed. 

Semiconductor materials have had to meet progressively more stringent requirements as the density and performance of semiconductor devices has increased. This trend will continue. The purity of the matoial, the dimensions of the devices, and the electrical properties require higher precision in their measurement and the ability to determine the device parameters to a resolution and sensitivity that pushes measurement techniques to their very limit. Semiconductor measurements cover a broad range of techniques and disciplines. After a brief listing of optical and physicall chemical characterization methods we give in this chapter a discussion of the general trend in electrical characterization and present a few examples of the charactmzation techniques used today. 

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