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The measured optical and transport properties of singlecrystal SrTiO3have been determined as a function of oxidation and reduction using spectroscopic ellipsometry, Hall and resistivity measurements. A decrease in the valence to conduction band transitions across the band gap, from O 2p to Ti 3d states, is observed by decreases in both the index of refraction and the extinction coefficient at the region of the band gap energy, in the ultraviolet region. This supports the model that oxygen nonstoichiometry depletes the O 2p densities of states in the top of the upper valence band, in agreement with previous photoemission studies. The degree of reduction decreases the band gap energy, calculated from the optical absorption coefficient spectra. The direct gap energy varies from 3.88 to 3.58 eV, and the indirect band gap energy ranging from 3.77 to 3.0 eV with increasing reduction. The resistivities of the samples decrease with increased reduction, yet free carrier densities are also found to decrease, suggesting an increase in electron mobility with reduction.

This scattering of light by small particles embedded in a continuous transparent medium is influenced not only by the bulk optical properties of the particles and the medium but also by the size, shape, and spatial arrangement of the particles—that is, by the microstructure. If the particles are close together, as in agglomerated coatings or stereolithographic suspensions, interactions between the radiation fields of adjacent particles can lead to variations in the magnitude and spatial arrangement of the scattered light in the near and the far field, which can affect the color and hiding power of a coating, the cure depth and homogeneity in stereolithography, and the threshold intensity for stimulated emission in random lasers. Our calculations of the near- and the far-field scattering distribution for 200-nm TiO_2 spheres in pairs of various orientations and in an ordered array of five particles show that, depending on the orientation of the particles with respect to the incident light, these interactions can either increase or decrease the scattering efficiency, the isotropy of the scattering, and the magnitude of the electric field strength within the matrix and the particles. In the mid-visible range, two particles in line increase the backscattering fraction by 28% and the scattering strength by 38% over that of a single particle, whereas if the particles are in the diagonal configuration the backscattering fraction and scattering strength are actually reduced by addition of the second particle. At shorter or longer wavelengths the backscattering fraction is reduced regardless of the location of the second particle, by as much as 60% when five particles are arranged in the zigzag configuration. These results are surprising in that it is generally assumed that multiple scattering enhances backscattering. Simple models of multiple scattering or scattering of two particles as a single, larger particle are inadequate to explain these results.

Although the velocity gradient, [image omitted] is a parameter common to almost all the phenomenlogicaltheories of turbulence and turbulent mixing, relatively few accurateevaluations of this factor have been made (3). Most experimental values of thevelocity gradient in turbulent flow have been determined indirectly by firstobtaining an experimental velocity profile and then graphically differentiating thisprofile. Thus, [image omitted] reflects errors made in measuring the velocity profile and errorsmade in obtaining the derivative of this profile by graphical techniques. Hence, theaccuracy of [image omitted] and the subsequent mixing length and transfer coefficient calculationscould be improved if an experimental method of obtaining [image omitted] directly in fully-developed,two-dimensional, turbulent boundary layer flow were available. The devicewas calibrated in a rectangular duct, and the results clearly demonstrate the validityof the design and the feasibility of measuring [image omitted] directly and accurately.

With the advent of computerized data acquisition in spectroscopy, it has become possible to acquire large quantities of data with relative ease. Without a convenient method for archiving and accessing the data at a later date, a number of the capabilities inherent in these systems are unrealized. We have developed a generalized archival system which automatically archives all raw data and generates a rapidly searchable database of text information and spectral data for all spectroscopic results covering the spectral regions from 30 nm to 1000 µun (3.3 × 105to 10 cm−1). The system executes on a local area network (LAN) of personal computers and consists of a customized file-naming and comment convention that organizes data by research notebooks, an integrated data backup routine, and a spectral database system. The data backup and spectral database consist of two programs: (1) a DOS level copy routine to back up the system and data to an optical write once/read many (WORM) drive, and (2) a spectral database program written in the Lab Calc spectroscopy environment. Stored with each spectral library entry are searchable text fields of character data parsed from a standardized comment line which is entered prior to data acquisition. This system is used consistently with three different spectrophotometers, allowing all results to be treated equivalently for further numerical analysis.

The band structures of SrTiO3 BaTio3 and KNbO3 in the cubic perovsikte structure are calculated using the first-prinicipals selfconsistent orthogonalized linear combination of atomic orbitals method. In all three crystals, indirect band gaps of about 3 eV are obtained. The top of the valence band is at R and the minimum in the conduction band is at Γ. Effective charge calculation and the charg. 1 density maps reveal the highly ionic nature of the crystal bonding in these ferroelectric crystals. The optical conductivities and the frequency dependent dielectric functions up to 20 eV in all three crystals are also evaluated using the energy eigenvalues and wave functions obtained from the band calculation. The calculated spectra are found to be in good agreement with the existing experimental measurements.

The local electronic structure of ceramic materials can be determined from valence electron energy loss (Veel) spectra via the dielectric function. The quality of the data is comparable to vacuum ultraviolet spectroscopy with the added benefit of high spatial resolution. We have built and implemented a system for spectrum imaging which not only allows automatic data acquisition but also analysis of the full data set. The system consists of a Gatan PEELS and a Gatan Digiscan fitted to a VG HB501 UX STEM and home-built hardware additions. The hardware extensions allow to acquire 1, 2, 3, 4 or 8 spectra for each pixel and in the case of 2 spectra/pixel to vary the exposure time of the specimen to the primary electron beam by controlling the beam blanker (Fig. 1). The first spectrum (2 to 20 ms) contains an unsaturated zero loss peak and the second spectrum (0.05 to 100 s) at the same position the plasmon peak near to but below saturation (Fig. 2).

Review: (discussion of the investigation methods (i.e.

It is demonstrated that Al(OH)3and Al2O3prepared from commercial, productiongrade AlEt3contain significantly lower amounts of metal ion impurities (Th and U below the detection limits of 1‐9 ppb, Fe: ∼ 1 ppm) Si: 1‐3 ppm) than Al oxides prepared from mineral sources.