Off-specular Reflectivity Research Articles

Off-specular reflection from flat interfaces with density or compositional fluctuations

The reflection or scattering from a flat interface with density or compositional fluctuations has been investigated. An integral equation to relate the scattered intensities and the interface structure was proposed using a two-potential approach. The reflection geometry was taken into consideration explicitly in this derivation. This integral equation was applied to relate the off-specular scattering intensities to the interface structure in neutron or x-ray reflectivity measurements. Some numerical calculations based on model interfaces with certain structural features are conducted; and the results demonstrate the possibility of using the information from off-specular scattering to narrow the selections among the many model potentials or interface structures allowed by the specular reflectivity results.

The Use of a Conventional Powder Diffractometer for Thin-Film Thickness Determination From Reflectivity DATA

AbstractPrecise thin-film thicknesses have been obtained from X-ray specular and off-specular reflectivity data collected with a conventional powder diffractometer. An analysis of the specular reflectivity curve for a 565.9-Å thick pt film showed the results agreed with those determined previously from high-resolution reflectometer data to within 6.6 Å or 1.2%. An analysis of the off-specular reflectivity curves which have well-defined interference fringes showed that the results were insensitive to the surface alignment. Values of Pt thickness for the off-specular reflectivity curves agreed with that of the specular reflectivity curve to within 6.2 Å or 1.1%. The insensitivity in film-surface misalignment makes conventional powder diffractometer attractive for film-thickness determination and opens this techniques to many laboratories.

Dehydrogenation of C2H4absorbed on Si(111)7 × 7 surfaces

Using HREELS it has been shown that C2H4 associatively adsorbs on Si(111)7 × 7 at room temperature. From a comparison of data obtained for specular reflection with those obtained for specular reflection with those obtained for off-specular reflection it is assumed that the molecule absorbs in a flat-lying position. Thermal processing leads to dehydrogenation with the hydrogen occupying free on-top sites above 180 degrees C. Above 390 degrees C hydrogen desorbs. Annealing to temperatures above 490 degrees C leaves behind only carbon on the surface in an adsorbed configuration, this changes into a carbide-like configuration after annealing to higher temperatures.

Theoretical Polarization of Off-Specular Reflection Peaks

Theoretical Polarization of Off-Specular Reflection Peaks

Theory for Off-Specular Reflection From Roughened Surfaces*

The directional distribution of radiant flux reflected from roughened surfaces is analyzed on the basis of geometrical optics. The analytical model assumes that the surface consists of small, randomly disposed, mirror-like facets. Specular reflection from these facets plus a diffuse component due to multiple reflections and/or internal scattering are postulated as the basic mechanisms of the reflection process. The effects of shadowing and masking of facets by adjacent facets are included in the analysis. The angular distributions of reflected flux predicted by the analysis are in very good agreement with experiment for both metallic and nonmetallic surfaces. Moreover, the analysis successfully predicts the off-specular maxima in the reflection distribution which are observed experimentally and which emerge as the incidence angle increases. The model thus affords a rational explanation for the off-specular peak phenomenon in terms of mutual masking and shadowing of mirror-like, specularly reflecting surface facets.