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UV-visible spectroscopic ellipsometry was used to study the thickness and composition of the oxidized zone in Fe- and Ni-based alloys as a function of oxygen partial pressure. In the case of AISI 304 stainless steel, the weathered thickness increases with oxygen partial pressure, whereas in the case of Inconel 600, it appears to be independent of oxygen pressure. This trend is confirmed by the AFM measurements. For both materials studied, the oxygen-modified zone consists of two layers as confirmed by glow discharge optical emission spectrometry (GDOES) measurements. The thicknesses of these two layers vary differently on either side of an oxygen partial pressure of 0.1 Torr. In the case of AISI 304 stainless steel, the thickness of the Fe-rich outer layer decreases in favor of the Cr-rich inner layer. In the case of Inconel 600, the trend is reversed. The Ni-rich outer layer increases significantly above this critical pressure, while the Cr-rich inner layer decreases slightly. The composition of each layer in the oxidized zone is discussed in terms of its dielectric function in relation to reference material. The use of UV-visible ellipsometry as a non-destructive tool to study the structure and composition of the oxide bilayer of absorbing systems such as the alloys under investigation is a first. [ABSTRACT FROM AUTHOR]

ZnO thin films have been prepared by sol gel and deposited by spin coating. The dielectric function has been determined by spectroscopic ellipsometry. Ellipsometric spectra are inverted by a direct numerical method without using the standard fitting procedures. The obtained dielectric function presents a broad excitonic effect. The dielectric function is studied using Elliot excitonic theory including exciton plus band-to-band Coulomb interactions with standard Lorentzian broadening. A modification of this model dielectric function with independent bound and unbound exciton contributions is empirically proposed to improve modelling of the band gap excitonic peak. [ABSTRACT FROM AUTHOR]

A method is proposed to extract refractive index, extinction coefficient, and thickness of an unknown layer inside a multilayer sample from spectroscopic ellipsometry measurement. The method is a combination of improved standard and new wavelength-by-wavelength (point-by-point) approaches, treating each point of the spectrum sequentially but considering spectral physical constraints on the extracted optical parameters. The inversion is performed first by extracting thickness in the range of transparency, then by extracting refractive index and extinction coefficient over the whole spectral range, and finally by applying a regularization to enforce Kramers–Kronig consistency between refractive index and extinction coefficient, while optimizing the sample structure parameters (thicknesses). The layer needs to be transparent over one part of the considered spectrum, which is the case of most semiconductors, but no other assumption is necessary about its optical constants. Efficiency of the method is illustrated through the typical example of a zinc oxide (ZnO) layer. This method should be helpful in many practical cases of ellipsometry data interpretation. [ABSTRACT FROM AUTHOR]

We propose an investigation of nano-granular ZnO very thin layers ( < 100 nm ) , which morphologies are varied by changing the annealing temperature between 300 and 650° C. A detailed investigation of the optical properties is performed by coupling emission obtained from photoluminescence and dielectric function obtained from spectroscopic ellipsometry. The dielectric function shows a strong excitonic behavior increasing with annealing temperature. The UV emission is optimal at 450° C and the defect related visible bands gradually increase with annealing temperature. A particular attention is paid on i) the blueshift between emission and absorption UV onsets which is analyzed using contribution such as phonon replicas, carriers, bandgap renormalization, band filling and non-parabolicity; ii) the correlated evolution of absorption and emission intensities which is analyzed in terms of simultaneous curing of morphological defects and activation of intrinsic defects with temperature. [ABSTRACT FROM AUTHOR]

An original method of ellipsometric data inversion is proposed based on the use of constrained splines. The imaginary part of the dielectric function is represented by a series of splines, constructed with particular constraints on slopes at the node boundaries to avoid well-know oscillations of natural splines. The nodes are used as fit parameters. The real part is calculated using Kramers–Kronig relations. The inversion can be performed in successive inversion steps with increasing resolution. This method is used to characterize thin zinc oxide layers obtained by a sol–gel and spin-coating process, with a particular recipe yielding very thin layers presenting nano-porosity. Such layers have particular optical properties correlated with thickness, morphological and structural properties. The use of the constrained spline method is particularly efficient for such materials which may not be easily represented by standard dielectric function models. [ABSTRACT FROM AUTHOR]

Thin nano-granular ZnO layers were prepared using a sol–gel synthesis and spin-coating deposition process with a thickness ranging between 20 and 120 nm. The complex dielectric function ( ϵ ) of the ZnO film was determined from spectroscopic ellipsometry measurements. Up to a critical thickness close to 60 nm, the magnitude of both the real and the imaginary parts of ϵ rapidly increases and then slowly tends to values closer to the bulk ZnO material. This trend suggests a drastic change in the film porosity at both sides of this critical thickness, due to the pre-heating and post-crystallization processes, as confirmed by additional characterization of the structure and the morphology of the ZnO films. [ABSTRACT FROM AUTHOR]