Basics of Optical Spectroscopy

The book starts with a short introduction to the fundamentals of optical spectroscopy, (Chapter 1) describing the basic standard equipment needed to measure optical spectra and the main optical magnitudes (the absorption coefficient, transmittance, reflectance, and luminescence efficiency) that can be measured with this equipment. The next two chapters (Chapters 2 and 3) are devoted to the main characteristics and the basic working principles of the general instrumentation used in optical spectroscopy. These include the light sources (lamp and lasers) used to excite the crystals, as well as the instrumentation used to detect and analyze the reflected, transmitted, scattered, or emitted light. 

A basic limitation existing today in a number of areas of optical spectroscopy is the lack of a viable, compact, rugged, easily operated, sensitive device capable of simultaneously monitoring any or all portions of a reasonably wide spectral region with sufficient resolution. 

The spectra measured by any method of optical spectroscopy may be subject to qualitative (what is it ) or quantitative (how much is it ) evaluation. We assume here that the basic rules described in other chapters for the overall analytical process are obeyed, in particular for sample selection and sample preparation. Errors during sample preparation or simply due to an incorrect positioning of the specimen in the optical beam can never be corrected for in the measured spectra. Restricted quality in the experimental spectra will lead to errors either in qualitative evaluation (e.g. iU-defined results in spectral search) or in quantitative evaluation (e.g. erroneous determination of concentration). 

It should be noted that because the material is presented in such a manner, this monograph may serve as a handbook. It includes the theoretical foundations for the interaction of IR radiation with thin films, as well as the optimum conditions of measuring spectra of various systems, which are analyzed by computer experiments and illustrated by specific examples. Complementary to this, the basic literature devoted to the application of IR spectroscopy in the investigation of nanolayers of solids and interfaces is presented, and the necessary reference material for the interpretation of spectra is tabulated. Thus this book will be extremely useful for any laboratory employing IR spectroscopy, and for each industrial firm involved in the production of thin-film structures, as well as by final-year and postgraduate students specializing in the fields of optics, spectroscopy, or semiconductor technology. 

For the purposes of basic understanding of this branch of optical spectroscopy, molecules can be visualized as a set of weights (the atoms) joined together by springs (the chemical bonds). The atoms can vibrate toward and away from each other, or they may bend at various angles to each other as... 

The principle of optical spectroscopy involves the measurement of the amount of light (radiation) that is absorbed by the sample when the radiation interacts with the sample. The most basic method involves the determination of the fraction of the radiation that is actually transmitted through a sample. The aspects of the measurement, and their relationship to the actual absorption of radiation are illustrated in Fig. 56. In this example, 7o is the power of the incident radiation from the infrared light source, and I is the actual amount of radiation transmitted through the sample. The fundamental relationships are provided with Fig. 56, and these form the basis of a fundamental expression that is used to correlate the analytical spectrum with the amount(s) of material(s) present in a sample. This fundamental expression is a simple rendering of the Beer-Lambert-Bouguer law, which is used in one form or another in the quantitative determination of material composition. 

It is assumed that the reader has a basic knowledge of optical spectroscopy and the molecular theory of chemistry. Infrared (IR) spectroscopy is... 

In this chapter, we introduce some of the most common spectroscopies and methods available for the characterization of heterogeneous catalysts [3-13], These techniques can be broadly grouped according to the nature of the probes employed for excitation, including photons, electrons, ions, and neutrons, or, alternatively, according to the type of information they provide. Here we have chosen to group the main catalyst characterization techniques by using a combination of both criteria into structural, thermal, optical, and surface-sensitive techniques. We also focus on the characterization of real catalysts, and toward the end make brief reference to studies with model systems. Only the basics of each technique and a few examples of applications to catalyst characterization are provided, but more specialized references are included for those interested in a more in-depth discussion. 

The interpretation of optical spectra of solids is even more complicated than for atomic and molecular systems, as it requires a previous understanding of their atomic and electronic structure. Unlike liquids and gases, the basic units of solids (atoms or ions) are periodically arranged in long (crystals) or short (glasses) order. This aspect confers particular characteristics to the spectroscopic techniques used to analyze solids, and gives rise to solid state spectroscopy. This new branch of the spectroscopy has led to the appearance of new spectroscopic techniques, which are increasing day by day. 

It is not the purpose of the present chapter to deal with all of the aspects related to this impressive capability. Rather, we will try to give some basic concepts, so that a nonspecialist in group theory is able to calibrate its potentiality and to apply it to simple problems in optical spectroscopy. 

This book treats the most basic aspects to be initiated into the field of the optical spectroscopy of solids, so that a student with some background in quantum physics, optics, and solid state physics may be able to interpret simple optical spectra (absorption, reflectivity, emission, scattering, etc.) and learn about the main basic instrumentation used in this field. 

The measurement of vibrational optical activity requires the optimization of signal quality, since the experimental intensities are between three and six orders of magnitude smaller than the parent IR absorption or Raman scattering intensities. To date all successful measurements have employed the principles of modulation spectroscopy so as to overcome short-term instabilities and noise and thereby to measure VOA intensities accurately. In this approach, the polarization of the incident radiation is modulated between left and tight circular states and the difference intensity, averaged over many modulation cycles, is retained. In spite of this common basis, there are major differences in measurement technique and instrumentation between VCD and ROA consequently, the basic experimental methodology of these two techniques will be described separately. 

Figure 1.2 shows the basic instrumentation for atomic mass spectrometry. The component where the ions are produced and sampled from is the ion source. Unlike optical spectroscopy, the ion sampling interface is in intimate contact with the ion source because the ions must be extracted into the vacuum conditions of the mass spectrometer. The ions are separated with respect to mass by the mass analyser, usually a quadrupole, and literally counted by means of an electron multiplier detector. The ion signal for each... 

Spectroscopy has become a powerful tool for the determination of polymer structures. The major part of the book is devoted to techniques that are the most frequently used for analysis of rubbery materials, i.e., various methods of nuclear magnetic resonance (NMR) and optical spectroscopy. One chapter is devoted to (multi) hyphenated thermograviometric analysis (TGA) techniques, i.e., TGA combined with Fourier transform infrared spectroscopy (FT-IR), mass spectroscopy, gas chromatography, differential scanning calorimetry and differential thermal analysis. There are already many excellent textbooks on the basic principles of these methods. Therefore, the main objective of the present book is to discuss a wide range of applications of the spectroscopic techniques for the analysis of rubbery materials. The contents of this book are of interest to chemists, physicists, material scientists and technologists who seek a better understanding of rubbery materials. 

A chemical sensor is a device that transforms chemical information into an analytically useful signal. Chemical sensors contain two basic functional units a receptor part and a transducer part. The receptor part is usually a sensitive layer, therefore a well founded knowledge about the mechanism of interaction of the analytes of interest and the selected sensitive layer has to be achieved. Various optical methods have been exploited in chemical sensors to transform the spectral information into useful signals which can be interpreted as chemical information about the analytes [1]. These are either reflectometric or refractometric methods. Optical sensors based on reflectometry are reflectometric interference spectroscopy (RIfS) [2] and ellipsometry [3,4], Evanescent field techniques, which are sensitive to changes in the refractive index, open a wide variety of optical detection principles [5] such as surface plasmon resonance spectroscopy (SPR) [6—8], Mach-Zehnder interferometer [9], Young interferometer [10], grating coupler [11] or resonant mirror [12] devices. All these optical... 

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