Ellipsometry standard

D. D. Eley, ed., Adhesion, The Clarendon Press, Oxford, 1961. E. Passaglia, R. R. Stromberg, and J. Kruger, eds., Ellipsometry in the Measurement of Surfaces and Thin Films, National Bureau of Standards Miscellaneous Publication 256, Washington, DC, 1964. 

Infrared ellipsometry is typically performed in the mid-infrared range of 400 to 5000 cm , but also in the near- and far-infrared. The resonances of molecular vibrations or phonons in the solid state generate typical features in the tanT and A spectra in the form of relative minima or maxima and dispersion-like structures. For the isotropic bulk calculation of optical constants - refractive index n and extinction coefficient k - is straightforward. For all other applications (thin films and anisotropic materials) iteration procedures are used. In ellipsometry only angles are measured. The results are also absolute values, obtained without the use of a standard. 

De Souza et al. (1997) used spectroscopic ellipsometry to study the oxidation of nickel in 1 M NaOH. Bare nickel electrodes were prepared by a series of mechanical polishing followed by etching in dilute HCl. The electrode was then transferred to the spectroelectrochemical cell and was cathodicaUy polarized at 1.0 V vs. Hg/HgO for 5 minutes. The electrode potential was then swept to 0.9 V. Ellipsometry data were recorded at several potentials during the first anodic and cathodic sweep. Figure 27.30 shows a voltammogram for Ni in l.OM NaOH. The potentials at which data were recorded are shown. Optical data were obtained for various standard materials, such as NiO, a -Ni(OH)2, p-Ni(OH)2, p-NiOOH, and y-NiOOH. 

Values are mean values with the standard deviation shown in parentheses n=7 in each case, a ESCA measurements on silicon substrates, b Sessile drop measurements on glass slides, c Ellipsometry measurements on silicon substrates, d First receding contact angle. 

The uniformity of such an OVPD film of Alq3 is shown in Fig. 9.6. Analysis by variable angle spectroscopic ellipsometry (VASE) confirmed the surface was smooth across the entire substrate area with thickness deviation of +1.7%, a standard deviation, a, of 1.0% only. Atomic force microscopic analysis of such a typical film revealed RMS values to be 6 A, i.e. thickness differences in the range of a single monolayer only, irrespective of deposition rate [20-22]. 

The main experimental technique applied in this chapter is SE. Several textbooks were written on SE [73,114-118], Therefore, only some basic concepts are described. SE examines the relative phase change of a polarized light beam upon reflection (or transmission) at a sample surface. In Fig. 3.4 the setup of an ellipsometry experiment is shown. Upon model analysis of the experimental data, the DFs and thicknesses of the sample constituents can be extracted. Two different experimental approaches have to be distinguished, standard and generalized ellipsometry. 

With ellipsometry the polarization state of reflected radiation rather than just its intensity, is experimentally determined. Ellipsometry is not so much another experimental technique but a more thorough variety of the traditional ones, whether external or internal reflection. Two results per resolution element, namely the ellipsometric parameters (cf. Eq. 6.4-17) and A, are derived independently from the measurements. These can further be evaluated for the two optical functions of the medium behind the reflecting surface or other two data of a more complex sample. In any case there is no information necessary from other spectral ranges as it is for Kramers-Kronig relations. In comparison to the conventional reflection experiment, ellipsometry grants more information with a more reliable basis, e.g. since no standards are needed. 

Basically, ellipsometry is a relatively slow but accurate technique because in 12.5.4) the phase d and modulus yf must be simultaneously measured. However, the procedure can be made substantially more rapid by using fast modulators of the poleirizatlon plane in so-called Pockels cells. After standardization, elllpso-metiy can also be very conveniently employed to follow changes in adsorption. 

Deposition of a monolayer film of 3S at 20 mN/m surface pressure on a silicon wafer was achieved by z-type with transfer efficiency consistently in the range of about 0.5-0.6 (Figure 2). Such low transfer may imply that the hyperbranched polymer can be squeezed under compression, through either conformational change or intercalation. The overcompression could be relieved by transfer onto a solid substrate where the molecule occupies an area larger than on the water/air interface. The thickness of the deposited monolayer measured by ellipsometry was about 32A for the first few layers, but this number declined slowly as the number of depositions increased. The homogeneity of the film, judged from the standard deviation of the film thickness, also deteriorated. The... 

Ellipsometry in the Measurement of Surfaces and Thin Films, U.S. Dept, of Commerce, National Bureau of Standards Miscellaneous Publication 256, 1963. 

EUipsometiy is an optical reflection measurement using polarized light (Fig. 14). Ellipsometiy can provide the information about thickness, refiacthre index, and overall morpholt of thin films, surfaces, and multi-layers. The technique has been known for almost a century and has many standard applications. It is mainly used in semiconductor research and fiibrication to determine properties of layer stacks of thin films and the interlaces between the layers. However, ellipsometry is also becoming an important tool for research in other disciplines such as biology and medicine. 

Figure 12 shows typical variable angle measiuements made in a standard XPS instrmnent (39) using Mg K-o x-rays to excite the Si 2p spectrum. The silicon dioxide layer thickness was approximately 9 A as measured by ellipsometry. Ib curve fit the data, a third intermediate silicon oxidation state (SiO) was included. The amplitude of this and the main Si 2p peaks due to SiOx and the substrate were obtained as a function of sampled depth (variable angle) to obtain the inter ce thickness. Ishizaka and Iwata (39) estimated the interface transition region to be 2 to 3 A thick SiO from these data. 

Fig. tr.1-157 ZnS, cubic. Dielectric-function spectrum e E), measured by spectroscopic ellipsometry at 300 K after chemomechanical polishing of the sample (circles). The solid lines show values calculated from a model dielectric function for interband critical points. The dashed lines represent the best-fit standard critical-point lineshapes [1.132]... 

In the case of PFAND (Figure 5), the dependence of surface coverage on assembly time as well as on solution concentration, with standard deviations below 10%, is clearly visible. While for a concentration of 7 fiM the layer thickness shows no time dependence, values of concentration in the range of 44-440 /tM were found to be suitable for the fabrication of gradients by the method used in this study. A value of 220 /tM was chosen as the standard concentration. XPS data confirm the (logarithmic) trend observed by ellipsometry for the N/Ti and F/Ti ratios... 

Various techniques have been used for the study of precursor films (interferometry, scanning electron microscopy and even timneling microscopy).35 However, the standard technique is ellipsometry which allows to measure thicknesses in the A range with a spatial resolution between 0.5 mm (usual) and 20 pm.35 Spectroscopic ellipsometry is also... 

Monolayers of PDA were prepared by spreading a solution of PDA in petroleum ether or hexane on a thoroughly cleaned water surface (pH = 2)in a glass trough with paraffin coated edges. The surface density of molecules was controlled by a movable Teflon barrier and the surface tension was measured by a Wilhelmy plate. For the ellipsometry measurements we used a weak He-Ne laser at 632.8 nm. The phase shift was measured by a standard high resolution ellipsometry technique.5 The accuracy in (j> was 10 4 rad. 

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