Ellipsometry sensitivity

The Fresnel equations predict that reflexion changes the polarization of light, measurement of which fonns the basis of ellipsometry [128]. Although more sensitive than SAR, it is not possible to solve the equations linking the measured parameters with n and d. in closed fonn, and hence they cannot be solved unambiguously, although their product yielding v (equation C2.14.48) appears to be robust. 

The most recently introduced optical teclmique is based on the retardation of light guided in an optical waveguide when biomolecules of a polarizability different from that of the solvent they displace are adsorbed at the waveguide surface (optical waveguide lightmode spectroscopy, OWLS) [H]. It is even more sensitive than ellipsometry, and the mode... 

Ellipsometry can be sensitive to layers of matter only one atom thick. For example, oxidation of freshly cleaved single-crystal graphite can be monitored from the first monolayer and up. The best thicknesses for the ellipsometric study of thin films are between about 1 nm and 1000 nm. Although the spectra become complicated, films thicker than even 1 pm can be studied. Flat planar materials are optimum, but surface and interfacial roughness can be quantitatively determined if the roughness scale is smaller than about 100 nm. Thus ellipsometry is ideal for the investigation of interfacial surfaces in optical coatings and semiconductor struc-... 

G. H. Bu-Abbud, N. M. Bashara, and J. A. Woollam. Thin Solid Films. 138,27, 1986. Description of Marquardt algorithm and parameter sensitivity correlation in ellipsometry. 

Ellipsometry is a method of measuring the film thickness, refractive index, and extinction coefficient of single films, layer stacks, and substrate materials with very high sensitivity. Rough surfaces, interfaces, material gradients and mixtures of different materials can be analyzed. 

Ellipsometry in the vacuum UV (< 190 nm) enables the analysis of materials for the next generation lithography (photoresist, AR coatings) at the latest exposure wavelengths (157 nm and 193 nm). The short wavelengths increase the sensitivity of ellipsometric measurements of ultra thin films (<10 nm). New prospects are expected for the analysis of thin metallic and dielectric layers. 

Ellipsometry is concerned with the measurement of the changes in polarisation state, as well as light intensity, on reflection since these parameters are highly sensitive probes of the thickness and refractive index, rtf, of a surface film. A full treatment of the principles involved in ellipsometric measurements can be found in any one of several excellent reviews (see references). 

The measurement of 4 and A gives rP/rs via equation (2.74), for the coated electrode system, with both of these parameters highly sensitive to the properties of the film. However, whereas a knowledge of A and 4 allowed the direct calculations of the optical properties of an uncoated metal via equations (2.80) and (2.81), these equations no longer apply in the case of a coated substrate. At this point, the central problem in ellipsometry is encountered. To characterise the film completely, three parameters are required n, k and L, However, the above discussion includes only the determination of two parameters, a. and c, giving 4 and A. One of two approaches is commonly employed to solve the equations to give /i, k and L. 

When cells are suspended in a biological fluid or culture medium, both serum proteins and cells interact with the surface substrate. Serum protein adsorption behavior on SAMs has been examined with various analytical methods, including SPR [58-61], ellipsometry [13, 62, 63], and quartz QCM [64—66]. These methods allow in situ, highly sensitive detection of protein adsorption without any fluorescence or radioisotope labeling. SPR and QCM are compatible with SAMs that comprise alkanethiols. In our laboratory, we employed SPR to monitor protein adsorption on SAMs. 

Until quite recently the very initial stages of metal deposition were difficult to characterize in detail by structure- and morphology-sensitive techniques. As a consequence and for practical purposes - multilayers were more useful for applications than monolayers - the main interest was focussed onto thick deposits. Optical and electron microscopy, ellipsometry and specular or diffuse reflectance spectroscopy were the classic tools, by which the emerging shape of the deposit was monitored [4-7],... 

Spectroscopic ellipsometry is a non-destructive, interface sensitive, in situ technique for interface characterization. Time resolved ellipsometric spectroscopy was used to determine the mechanism of electrochemical deposition of photoresists on copper electrodes under potentiostatic, anodic conditions. Nucleation of photoresist deposition occurs randomly. During the early stages of nucleation the semi-spherical particles are separated by about 100 A. The deposits tend to grow like "pillars" up to 50 A. Further growth of the "pillars" lead to coalescence of the photopolymer deposits. 

Time resolved ellipsometry is a surface sensitive technique that can be used to study the kinetics and mechanism of electrochemical deposition of photopolymer films. 

A variety of surface-sensitive spectroscopic and microscopic methods were critical in the investigation of these systems. In the work by Advincula et al, the composition, thickness, physical and thermal properties, and morphology of the tethered polymer brushes were carefully analyzed [72]. A variety of surface-sensitive techniques such as ellipsometry, contact angle measurements, AFM, quartz crystal microbalance (QCM), FT-IR grazing incidence... 

How Can Ellipsometry Be So Sensitive Some students who approach ellipsometry for the first time find the extraordinary sensitivity of ellipsometry in measuring thickness difficult to believe. Thus, their first thought is that the minimum size of an object that disturbs a beam of electromagnetic radiation is that of the wavelength in the incident light. If the disturbing entity, a film, say, is less than X in thickness (about 500 nm), it will not be seen except by some form of... 

Apart from optical microscopy, there are some other optical techniques which are truly surface sensitive and have found widespread use. Examples are ellipsometry (see Section 9.4.1), total internal reflection fluorescence (TIRF) [316], and surface plasmon resonance techniques [348],... 

Another interesting and different type of catalysis is involved in the catalyzed reconstruction of an indium oxide overlayer on indium. This study was alluded to earlier in the discussion of acetate ion species formed on indium oxide by chemisorption from several torr of acetic acid gas. At low partial pressures of acetic acid (<< 0.1 torr) the reversible adsorption of acetic acid catalyzes the reconstruction of a thin ( 10-15A), porous indium oxide overlayer to a defect-free (no pin holes) film as judged by pinhole sensitive tunnel junction measurements. Some clues as to the mechanism were obtained from IR plus Auger and electron loss spectroscopy as well as ellipsometry measurements. The overall process is shown in Fig. 8. This is an example where processes in the substrate themselves can be usefully catalyzed. 

The excitation of an SEW using a single prism is seen as a dip in the reflectivity from the prism base (see Fig. 8) when the angle of incidence satisfies Eq. (8). The location in angle of the minimum in reflectivity, the depth of the minimum and its width are very sensitive to the presence of an overlayer on the metal substrate. Pockrand, et al.— have pointed out that this technique is considerably more sensitive than ellipsometry for measuring the optical properties of thin films. They also discuss the problems due to the fact that the dye films are really anistropic. 

The reason for the increased sensitivity over ellipsometry is that the position of the reflectivity minima is extremely sensitive to the presence of attached molecules. A particularly... 

The technique can also be used for multilayered structures. The corresponding equations are then more complicated and are usually applied to inorganic semiconductors [36-38] due to their better defined interfaces and geometry compared with organic semiconductors. In the case of transparent media (k = 0), the ellipsometric equations can be used to determine both n and the thickness of the film with sensitivity below 1 A. This is much better than can be achieved by methods based on 7Z and T, thus reducing the uncertainty in the n determination. Several examples of ellipsometry applied to CPs are reported in the literature [32,43,44],... 

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... 

Adsorption of polymers on inorganic substrates has been subject of numerous investigations because of the simple procedure for application [12-15], In this work the influence of the amino group content and pH of the PVFA-co-PVAm solution on the amount of adsorbed polymer on various metal surfaces has been studied. Metal substrate samples of different size and shape (particles, sheets) have been used which limits the application of special surface sensitive methods such as ellipsometry. 

All sensitive layers were prepared from solutions of Makrolon in mixtures of chloroform and dichlorobenzene by a spin-coating process. By adjustment of the rotation speed and time the thickness of the layers were varied between 35 nm and 455 nm. Layer thicknesses and refractive indices were determined by spectral ellipsometry. Furthermore the polymer thicknesses were verified by a surface profilometer (Alpha Step 500, Tencor Instruments, Mountain View, USA). 

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