Thin films optical characterization

Buso, D., Pacifico, J., Martucci, A., and Mulvaney, P. (2007) Gold-nanoparticle-doped Ti02 semiconductor thin films optical characterization. Adv. Funct Mater., 17, 347-354. 

Commonly used spectroscopic or analytical techniques for characterizing surfaces and coating layers on porous silicon are Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, energy dispersive X-ray spectrometry, fluorescence spectroscopy, UV-Vis absorption/reflectance spectroscopy, thin film optical interference spectroscopy, impedance spectroscopy, optical microscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, ellipsometry, nitrogen adsorption/desorp-tion analysis, and water contact angle. 

The optical, morphological and hydrophilic properties of the thin films were characterized by UV-Vis spectrophotometer, atomic force microscope (AFM) and water contact angle technique, respectively whereas the crystalline form, the specific surface area and the chemical state/composition were determined by X-ray diffraction, BET nitrogen sorption analysis and X-r photoelectron spectroscopy (XPS), respectively. 

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. 

Absorption. Absorption, the attenuation of a beam through a transparent medium, can be characterized by an absorption coefficient. For thin films, such as those of optical oxides, absorption is very small and can usually be ignored. In metallic or semiconductor coatings however, absorption is a major factor. 

The potentiostatic electrodeposition of iron selenide thin films has been reported recently in aqueous baths of ferric chloride (FeCb) and Se02 onto stainless steel and fluorine-doped TO-glass substrates [193], The films were characterized as polycrystalline and rich in iron, containing in particular a monoclinic FesSea phase. Optical absorption studies showed the presence of direct transition with band gap energy of 1.23 eV. 

K. Vedam (guest editor). Physics of Thin Films. Advances in Research and Development, Optical Characterization of Real Surfaces and Films, Volume 19,... 

Ousi-Benomar, W. Xue, S. S. I. cssard, R. A. Singh, A. Wu, Z. L. Kuo, P. K. 1994. Structural and optical characterization of BaTi03 thin films prepared by metal-organic deposition from barium 2-ethylhexanoate and titanium dimethoxy dineodecanoate. J. Mat. Res. 9 970-979. 

Nonlinear optical techniques are extremely useful in characterizing the chiral properties of materials, as is pointed out by Verbiest and Persoons in Chapter 9. These authors give an in-depth discussion of this tool, both from an experimental and theoretical point of view, paying special attention to the characterization of chiral surfaces and thin films. In the second part of their contribution they highlight the role chiral materials can play in the field of nonlinear optics and photonics, which opens the way for a variety of applications. 

The sensing methods summarized thus far are intended for absorption detection of molecules in the ambient, but molecules (or indeed thin films) on the microresonator surface can also be detected. In particular, if the surface is covered to such an extent that the optical energy absorbed heats the microresonator, the resulting thermal bistability in the frequency-scan response can be used to determine the absorption and/or thickness of the thin-film coating. This and surface characterization by measurement of the thermal accommodation coefficient were described in Sect. 5.5. These methods offer quite precise measurement, provided that certain reasonable and easily implemented assumptions are satisfied. 

The covalent chemistry of fullerenes has developed very rapidly in the past decade in an effort to modify fuUerene properties for a number of applications such as photovoltaic cells, infrared detectors, optical limiting devices, chemical gas sensors, three-dimensional electroactive polymers, and molecular wires [8, 25, 26, 80-82]. Systematic studies of the redox properties of Cgo derivatives have played a crucial role in the characterization of their unique electronic properties, which lie at the center of these potential applications. Furthermore, electrochemical techniques have been used to synthesize and separate new fullerene derivatives and their isomers as well as to prepare fullerene containing thin films and polymers. In this section, to facilitate discussion of their redox properties, Cgo derivatives have been classified in three groups on the basis of the type of attachment of the addend to the fullerene. In group one, the addends are attached via single bonds to the Cgo surface as shown in Fig. 6(a) and are referred to as singly bonded functionalized derivatives. The group includes... 

Semiconducting thin films of CdSe were electrochemically deposited on Ti substrates [186,187]. The film electrodes were characterized with photoelectrochemical imaging, optical microscopy, and scanning electron microscopy (SEM)/energy-dispersive X-ray analysis. 

A very common and useful approach to studying the plasma polymerization process is the careful characterization of the polymer films produced. A specific property of the films is then measured as a function of one or more of the plasma parameters and mechanistic explanations are then derived from such a study. Some of the properties of plasma-polymerized thin films which have been measured include electrical conductivity, tunneling phenomena and photoconductivity, capacitance, optical constants, structure (IR absorption and ESCA), surface tension, free radical density (ESR), surface topography and reverse osmosis characteristics. So far relatively few of these measurements were made with the objective of determining mechanisms of plasma polymerization. The motivation in most instances was a specific application of the thin films. Considerable emphasis on correlations between mass spectroscopy in polymerizing plasmas and ESCA on polymer films with plasma polymerization mechanisms will be given later in this chapter based on recent work done in this laboratory. 

Despite the fact that optical applications require thin films of poly(3-alkylthiophene)s, the photochemistry of these materials has been characterized in solution but only scarcely in the solid state. The UV/Vis spectra of these films of poly(3-butylthiophene) show an absorption band in the visible range corresponding to a n—n transition whose energy depends on 7r-electron delocalization. 

Wang, X., Masumoto, H., Someno, Y., Hirai, T., (1998), Optical characterization of Si02-Ti02 thin films with graded refractive index profiles , J Japan Inst. Met, 62(11), 1069-1074. 

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