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We report here the first observation of surface-enhanced infrared spectroscopy on platinized platinum surfaces, as well as a thorough explanation of the resulting spectra. Smooth platinum electrodes were electrochemically platinized to produce regular metal island surfaces that led to enhanced absorption of the infrared spectrum of adsorbed carbon monoxide. The infrared spectrum of CO adsorbed from an aqueous electrolyte onto the electrode surface was measured in situ by external reflection spectrometry. The amount of adsorbed CO was estimated from the difference spectrum before and after the CO was oxidized to CO 2 by finding the ratio of the absorbance of adsorbed CO prior to oxidation to the absorbance of dissolved carbon dioxide formed when the adsorbed CO was oxidized. By varying the platinization conditions, platinized Pt surfaces that yielded IR band enhancements of up to 20 times that of CO adsorbed on smooth Pt electrodes were prepared. When CO was adsorbed on a smooth Pt electrode, the shape of the band due to the CO stretching mode was quite symmetrical. As the degree of platinization was increased, the band became asymmetrical, then bipolar, and finally appeared as a reflection maximum. This behavior was simulated using the Bergman representation of effective dielectric function.

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This work reports growth of α-(AlxGa1-x)2O3 single crystals with high incorporation of Al by a Mist Chemical Vapor Deposition two-chamber system, which was rationally designed to avoid side-reactions between different precursors during solution preparation for multi-component thin film growth. Multiple acceleration voltages were used in Energy Dispersive X-ray measurements to reliably obtain the Al composition x of the films. As a result, Vegard's law for lattice constants was verified and found to be valid in the α-(AlxGa1-x)2O3 system. However, Vegard's law for optical bandgaps, derived from different models, required an additional term to account for the bowing effect. At x = 0.71, the gaps were 7.74, 7.03, 7.26, and 7.34 eV as derived from the Tauc plots for the direct bandgap, indirect bandgap, Tauc-Lorentz model, and O'Leary-Johnson-Lim model, respectively. The two-chamber system provides reliable and effective control of the Al content in α-(AlxGa1-x)2O3 alloys and heterostructures.

Porosity superlattices have been investigated by transmission electron microscopy, photoluminescence and reflectance spectroscopy. The superlattices were formed on p-type doped Si using two different techniques. Firstly, for homogeneously doped substrates we have periodically varied the formation current density and thereby the porosity. Secondly, the current density was kept constant while etching was performed on periodically doped Si layers. For the first type of superlattices the layer thicknesses were determined by transmission electron microscopy. The results are in good agreement with the values calculated from the etching rate and time. For both types of superlattices, reflectance and photoluminescence spectra show strong modulation due to the periodicity of the superlattice.

SummaryFor the optical analysis of heterogeneous materials the microtopology ofthe samples plays an important role. In the long wavelength limit (i.e. light wavelengths much larger than the typical size of the inhomogeneities) effective medium theories give the desired connection between the component properties and the average 'effective' optical behaviour. On the basis ofthe general Bergman representation for effective dielectric functions we discuss simple and advanced effective medium concepts and show how they can successfully be used in optical spectroscopy. IntroductionMost of the knowledge about solid state physics has been obtained preparing and studying very pure materials. In orderto find rules anddevelop theoretical models the systems studied had to be as simple as possible, in theory as well as in experiments. Therefor an important basic step for many conceptual breakthroughs has been the preparation of large single-crystalline samples--minimizing discrepancies between theoretical simplifications and experimental conditions. By now the understandingofmany solid state phenomena observed in pure singlecrystalline systems is quite complete and is the basis ofnumerous technical applications,the most prominent and important one being semiconductorelectronics. In many cases,on the otherhand, what is needed for an application is not exactly what is found in clean samples--then a change ofthe 'pure material properties' is demanded.Consequently semiconductorphysics has learned to handle 'dirty' materials with the desired deviations obtained by doping pure materials on an atomic scale with impurities.Besides this 'shifting' of a bulk property by disturbing a pure material one can also get new materials fortechnical applications by mixing different constituents abovethe

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A new analytical technique is presented for the simultaneous evaluation of molecular orientation and optical parameters in organic ultrathin films on a dielectric substrate by integration of oscillators-model simulation analysis and infrared external-reflection (ER) spectroscopy. The surface-normal and -tangential components of vibrational TO and LO modes in the film were independently represented by two dielectric dispersion functions with the use of Kim's oscillators models. The reflection absorbance of each band in the ER spectra was analyzed by use of the two functions on the assumption of the anisotropic optical system. Two p-polarization infrared ER spectra observed at two angles of incidence were subjected to an optimization calculation, so that the parameters in the two functions were simultaneously converged. The converged results yielded refractive-index dispersions and orientation angles at the same time. As an example study, the molecular structure in a 5-monolayer cadmium stearate Langmuir−Blodgett (LB) film has been analyzed with the new technique. The evaluated optical parameters were consistent with other experimental results. The new technique has also revealed the fine molecular orientation around the α-carbon atom, which has not been shown experimentally thus far. The new method proved to enable us to discuss fine properties in thin condensed matter without using library values of optical parameters.