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Infrared analyses of clay mineral samples are usually performed by transmission techniques. While transmission measurements are easy and inexpensive, the sample preparation plays a critical role in the quality of the data. Alternatively, attenuated total reflection (ATR) provides a powerful and often simpler analysis method. However, the ATR spectra reveal significant differences when compared to transmission spectra sometimes leading to confusion in the interpretations. Indeed, optical effects play a prominent role in the ATR spectral profile and their identification is mandatory for obtaining quantitative information regarding molecular/particle orientation or film thickness. The objective of the present study was to perform exact spectral simulations of montmorillonite films by making use of optical theory, including the determination of the anisotropic optical constants from the experimental reflectance spectra by Kramers-Kronig (KK) transformation. This methodology was used: (1) to choose the appropriate optical conditions for advanced and reliable characterization of clay minerals; (2) to extract quantitative information such as the estimation of the film thickness; and (3) to discriminate optical phenomena (optical interferences) from chemical/structural features of the sample.
The a-, σ- and π-spectra of quartz in the IR regions were measured under FTIR spectroscopy, and overtone and combination modes perpendicular to the c-axis of quartz were confirmed to be electric vector active by the coincidence of the a-spectrum with the σ-spectrum among the three kinds of spectra. Absorption coefficients of overtone and combination modes intrinsic to the a- σ-, and п-spectra of quartz were measured. The thickness of quartz thin sections can be determined by applying the absorption coefficients obtained from the α- and σ-spectra to the polarized IR absorption spectra measured under E ⊥ the c-axis.
A new approach for measurement of local thickness and characterization of grain boundaries is presented. The method is embodied in a software tool that helps to find and set sample orientations useful for high-resolution transmission electron microscopic (HRTEM) examination of grain boundaries in polycrystalline thin films. The novelty is the simultaneous treatment of the two neighboring grains and orienting both grains and the boundary plane simultaneously. The same metric matrix-based formalism is used for all crystal systems. Input into the software tool includes orientation data for the grains in question, which is determined automatically for a large number of grains by the commercial ASTAR program. Grain boundaries suitable for HRTEM examination are automatically identified by our software tool. Individual boundaries are selected manually for detailed HRTEM examination from the automatically identified set. Goniometer settings needed to observe the selected boundary in HRTEM are advised by the software. Operation is demonstrated on examples from cubic and hexagonal crystal systems.
An accurate determination of specimen thickness is essential for quantitative analytical electron microscopy. Here we demonstrate that a position-averaged incoherent bright-field signal recorded on an absolute scale can be used to determine the thickness of on-axis crystals with a precision of ±1.6 nm. This method measures both the crystalline and the noncrystalline parts (surface amorphous layers) of the sample. However, it avoids the systematic error resulting from surface plasmon contributions to the inelastic mean-free-path thickness estimated by electron energy loss spectroscopy.
The structure of a chemical-vapor-deposited (CVD) diamond thin film on a Mo substrate was studied using quasi-parallel X-ray and glancing incidence techniques. Conventional X-ray diffraction analysis revealed that the sample consists of a diamond thin film, a Mo2C transition layer, and Mo substrate. The Mo2C transition layer was formed by a chemical reaction between the diamond film and the Mo substrate during the CVD process. A method for layer-thickness determination of the thin film and the transition layer was developed. This method was based on a relationship between X-ray diffraction intensities from the transition layer or its substrate and a function of grazing incidence angles. Results of glancing incidence X-ray diffraction analysis showed that thicknesses of the diamond thin film and the Mo2C transition layer were determined successfully with high precision.
High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) images of electron-transparent samples show dominant atomic number (Z-) contrast with a high lateral resolution. HAADF STEM at low electron energies <30 keV is applied in this work for quantitative composition analyses of InGaAs quantum wells. To determine the local composition, normalized experimental image intensities are compared with results of Monte Carlo simulations. For verification of the technique, InGaAs/GaAs quantum-well structures with known In concentration are used. Transmission electron microscopy samples with known thickness are prepared by the focused-ion-beam technique. The method can be extended to other material systems and is particularly promising for the analysis of materials that are sensitive toward knock-on damage.
XFILM is a computer program for determining the thickness and composition of thin films on substrates and multilayers by electron probe microanalysis. In this study, we describe the X-ray emission model implemented in the latest version of XFILM and assess its reliability by comparing measured and calculated k-ratios from thin-film samples available in the literature. We present and discuss examples of applications of XFILM that illustrate the capabilities of the program.
High-resolution transmission electron microscopy (HR-TEM) has been
used as the ultimate method of thickness measurement for thin films.
The appearance of phase contrast interference patterns in HR-TEM images
has long been confused as the appearance of a crystal lattice by
nonspecialists. Relatively easy to interpret crystal lattice images are
now directly observed with the introduction of annular dark-field
detectors for scanning TEM (STEM). With the recent development of
reliable lattice image processing software that creates crystal
structure images from phase contrast data, HR-TEM can also provide
crystal lattice images. The resolution of both methods has been
steadily improved reaching now into the sub-Ångstrom region.
Improvements in electron lens and image analysis software are
increasing the spatial resolution of both methods. Optimum resolution
for STEM requires that the probe beam be highly localized. In STEM,
beam localization is enhanced by selection of the correct aperture.
When STEM measurement is done using a highly localized probe beam,
HR-TEM and STEM measurement of the thickness of silicon oxynitride
films agree within experimental error. In this article, the optimum
conditions for HR-TEM and STEM measurement are discussed along with a
method for repeatable film thickness determination. The impact of
sample thickness is also discussed. The key result in this article is
the proposal of a reproducible method for film thickness
determination.
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