Optical characterization techniques

For applied work, an optical characterization technique should be as simple, rapid, and informative as possible. Other valuable aspects are the ability to perform measurements in a contactless manner at (or even above) room temperature. Modulation Spectroscopy is one of the most usehil techniques for studying the optical proponents of the bulk (semiconductors or metals) and surface (semiconductors) of technologically important materials. It is relatively simple, inexpensive, compact, and easy to use. Although photoluminescence is the most widely used technique for characterizing bulk and thin-film semiconductors. Modulation Spectroscopy is gainii in popularity as new applications are found and the database is increased. There are about 100 laboratories (university, industry, and government) around the world that use Modulation Spectroscopy for semiconductor characterization. 

In this paper it has been attempted to provide an introductory overview of some of the various nonlinear optical characterization techniques that chemists are likely to encounter in studies of bulk materials and molecular structure-property relationships. It has also been attempted to provide a relatively more detailed coverage on one topic to provide some insight into the connection between the macroscopic quantities measured and the nonlinear polarization of molecules. It is hoped that chemists will find this tutorial useful in their efforts to conduct fruitful research on nonlinear optical materials. 

Reflectance-based optical characterization techniques offer the advantages of high energy resolution and sensitivity to both macrostructural and microstructural effects while nondestructively providing real-time information with the sample in any transparent ambient. Experimental and analytical methods are discussed, and examples are given to illustrate representative applications to problems of current interest in semiconductor technology. 

This paper is intended to give a brief overview of reflectance-based optical characterization techniques and their applications to determining sample properties. The next section deals with general principles, and includes comments about Instrumentation and analytic methods. The rest of the paper consists of representative examples. Other applications can be found in several recent reviews and symposium proceedings (1-5). Length limitations preclude extensive discussions references should be consulted for further details. 

Real Time Applications. Optical characterization techniques can provide unique information in real-time applications involving deposition or etching. Line-of-slght access to the sample by both Incident and reflected beams is required. The use of reflectance techniques to monitor material removal, e.g., in plasma reactors, is well known (28 1 the examples selected here will Illustrate less well explored possibilities in deposition. 

The above examples are representative of the present capabilities of reflectance-based optical characterization techniques. Other applications can be found in the general references given in the introductory paragraphs. Ir reflectance has not been discussed, not from lack of examples (31. 32), but because the major fraction of reflectance characterization has been done in the v-uv. Additional progress and new applications can be expressed in all areas. 

Optical characterization techniques are usually non-destructive, fast, and of simple implementation, most requiring very little sample preparation. These techniques explore the change on intensity, energy, phase, direction, or polarization of the light wave after interaction with the object being studied. Many of them can be performed at room temperature and atmosphere, dispensing the use of complex vacuum chambers. That, allied to the fact that the optical properties of a material... 

Since the allowed modes of vibration of a sohd or molecule are intimately linked to its structure and chemical composition, inelastic light scattering can be efficiently used as a structural characterization method or as a substance detection and identification tool. Below we will review the Raman scattering and its use as an optical characterization technique in more detail. 

The main limitations of the technique are that being an optical characterization technique, it cannot be used to study interfaces buried in opaque materials, i.e. with no hght access. It requires relatively flat surfaces and parallel interfaces with a non-zero specular reflectance to gather information about those interfaces. It is an indirect technique in the sense that it requires a physical model to be fitted to the experimental data to enable us to obtain physical properties of samples. Due to this fact it also requires some previous knowledge about the sample to avoid time-consuming analysis. 

Raman spectroscopy is one of the most versatile and powerful optical characterization techniques. It has applications which range from materials structural and chemical characterization [45] to medical diagnostics [46], to applications in the... 

X-ray analysis methods (including diffraction and reflectometry) described in Chap. 1 are the most widely used tools for the identification of crystalline properties of materials, in addition to materials strain, texture, stress, density, and surface roughness—properties that are key parameters for various industrial applications. Chapter 2 covers a wide range of optical characterization techniques with focus on ellipsometry, Raman scattering, Fourier transform infrared spectroscopy, and spectrophotometry. Those methods, covering a wide range of photon energy and laser... 

Ellipsometry is a high-precision optical characterization technique, the potential of which has not yet been sufficiently exploited in polymer science. It is a rapid and nondestructive experimental method for the analysis of surfaces and thin films. Besides the determination of film thickness with high sensitivity ( 0.1 nm), optical parameters related to material properties can also be evaluated [1]. The facts that ellipsometric measurements can be performed under any ambient conditions, and require no special sample preparation procedures, provide a definite advantage over other surface science techniques [2—4]. 

V. (2009) Second-Order Nonlinear Optical Characterizations Techniques An Introduction, CRC Press, New York. 

B.M. Nebeker, G.W. Starr, E.D. Hirleman, Light scattering from patterned surfaces and particles on surfaces. In Optical Characterization Techniques for high Performance Microelectronic Device Manufacturing II, ed. by J.K. Lowell, R.T. Chen, J.P. Mathur (Proc. SPIE 2638, 1995) pp. 274-284... 

Specific applications of DIRLD spectroscopy are presented for several polymer systems to demonstrate the types of information obtainable from this powerful rheo-optical characterization technique. A DIRLD study of atactic polystyrene revealed the existence of highly localized motion of various molecular constituents induced by a macroscopic dynamic strain.It was discovered the rate of reorientational motion of the polystyrene backbone differs considerably from that of the phenyl side groups. The reorientation direction of the phenyl side groups changes dramatically as the temperature of the system is raised above the glass transition temperature. This result may be interpreted as the onset of a new submolecular... 

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