Optical Reflectance Technique Research Articles

Bismuth titanate-ferroelastic distortion and domain studies

Abstract The monoclinic shear distortion in single-crystal bismuth titanate has been measured directly by an optical-reflection technique. The shear angle is ∼1.45 min at room temperature and has a negative temperature coefficient. The shear distortions at domain walls were measured in an interference microscope. These and other electrical-mechanical measurements indicate that ferroelectric-ferroelastic coupling in bismuth titanate is relatively small.

The roughness of cleaved semiconductor surfaces

A surface must be clean and atomically flat to enable a unique and simple interpretation of results. In many fundamental studies clean surfaces are used, whereas flatness is checked only qualitatively or simply assumed to be present. Therefore in the present investigation cleaved surfaces of Si and Ge have been studied systematically with respect to deviations from the flat surface. By using LEED, electron microscopy and a novel optical reflection technique several parameters have been determined: angles of inclination, the average angle, atomic step height, orientation and arrangement of steps, and average edge atom density. A description of the shape of a cleaved surface is given by a combination of various results. Since about 1–5 % of all surface atoms are in edge position, those atoms may be very important with respect to electronic and photoelectric properties.

Interaction of erythrocyte apoprotein with bimolecular lipid membranes

Summary Conductance and optical reflectance techniques have been used to study the interaction of erythrocyte apoprotein with erythrocyte lipid bilayers. It is found that addition of apoprotein increases the conductance and reduces the stability of the bilayer. Reflectance measurements demonstrate that the apoprotein forms a surface layer on the lipid membrane; the thickness of this layer is estimated to be about 13A. This finding, together with infra red data, indicates that the protein is extended over the membrane surface rather than in a compact globular form.

Multiband-Moments Model for the Conductivities of Chromium

Klemens' s moment integral formulation of the transport coefficients has been expressed in multiband form. A two-band moments model consisting of a standard and a nonstandard band has been adduced to explain the anomalies in the electrical and thermal conductivities of chromium $\ensuremath{\sigma}$ and $k$, respectively, in the vicinity of the N\'eel temperature as if they were mostly the result of the changes in the band structure that occur during the antiferromagnetic transformation. It can be seen that the behavior of the Lorenz number $L=\frac{k}{\ensuremath{\sigma}T}$ clearly indicates that a BCS-type gap has opened over a portion of the Fermi surface during this transformation. The zero-temperature-gap ratio is $2{\mathit{\ensuremath{\Delta}}}_{0}=5.2$, a value that is in excellent agreement with the value ($2{\mathit{\ensuremath{\Delta}}}_{0}=5.1$) found experimentally by Barker et al. using optical reflectivity techniques. The ratio $R$ of the antiferromagnetic and paramagnetic Fermi surfaces is 0.51, a value in very good agreement with the theoretical prediction of Asano and Yamashita. It is possible to show that a recently observed minimum in the thermal resistivity near the N\'eel temperature can occur even in the case of elastic scattering.

Reflectance and ellipsometry of metal/electrolyte interfaces

The improving sensitivity and increasing use of optical reflection techniques in the study of metals and semiconductors in contact with electrolytes, makes it timely to review the interpretation of such measurements. The surface charge on the conductor, the layer of solvent molecules forming the compact layer, the adsorption of ions on the electrode as well as the distribution of ions in the diffuse layer, are all features of the electrical double layer which can contribute to optical measurements. Models of these features are described which facilitate computation of their optical effects, and specimen results are presented. The fact that all of these features may make comparable contributions to optical measurements is illustrated for the system mercury + aqueous sodium fluoride, and the predicted contributions are compared with experimental results.

Interdiffusion between Films of Gold and Silver

A knowledge of diffusion rates in thin films is often necessary in order to predict the useful operating temperature range of thin film components. The few reported measurements available generally indicate that film diffusion rates at low temperatures (25°–300 °C) are substantially higher than would be inferred from extrapolations of bulk diffusion data to these temperatures. This is not surprising since high defect densities are common in films, and defects are known to act as high diffusivity paths. In this paper, measurements of diffusion rates are reported for films containing a range of defect densities. Films were prepared by evaporation and getter sputtering onto glass substrates. For each set of preparation conditions, films were characterized in terms of topography and defect density, by electron microscopy techniques. Diffusion rate measurements on Au/Ag thin film couples were made by an optical reflectivity technique. Values of the diffusion coefficient for evaporated films typically lay in th...

Navier-Stokes Calculations of Argon Shock Wave Structure

The classical Navier-Stokes theory was used to calculate profiles of plane shock waves in argon. The viscosity-temperature relationship employed in the calculation was based on a Lennard-Jones 6–12 intermolecular potential function for which the parameters were derived from experimental viscosity measurements up to 1100°K. With this viscosity function, the maximum-slope shock thicknesses obtained were smaller than previously calculated assuming viscosity proportional to T0.816. Also it was found that the maximum-slope thickness based on the density profile was less than that based on the velocity profile. The density profile thicknesses calculated with the Lennard-Jones viscosity function were the same order of magnitude as, but not in quantitative agreement with experimental density thicknesses obtained with the optical reflectivity technique. It was found that Navier-Stokes profiles become asymmetric as the shock strength is increased. However, the calculated asymmetry would have a negligible effect on thickness measurements by the optical reflectivity method.

Structure of Detonation Waves in Gases

The optical reflectivity technique has been used to study the structure of detonation waves in H2:3O2 at initial pressures of 20 to 40 psia. The detonation fronts were found to be comparable to those of normal shock waves in their thickness and planarity. The density change across the front appears to be less than the theoretical value, suggesting that rotational relaxation of oxygen (and hydrogen) in the front may not be complete. Experiments on shock waves in oxygen at M=3.0, where the final temperature is 872°K, confirm the rotational heat capacity lag and suggest that rotational relaxation is much slower at high temperatures than at room temperature.