Mechanisms for the SAR Imaging of the Ocean

We perform a comparative analysis of two mechanisms for the formation of a synthetic aperture radar (SAR) image of the ocean, which are related to orbital velocities on the surface. It is shown that the mechanism of fluctuations of the effective density of scatterers, which is commonly accepted at present as the physical basis for the SAR diagnostics of roughness, actually works only in the case of a sufficiently flat swell. In the presence of wind roughness, the dominant role is played by another mechanism, namely, fluctuations of the number of surface elements whose images are randomly shifted and superimposed in the image plane due to orbital velocities. In the case of a developed wind roughness propagated in the azimuthal direction, the power contributions of two above-mentioned mechanisms to the SAR imaging of the ocean differ by about two orders of magnitude.     

Oleophobic properties of the step-and-terrace sapphire surface

Crystallography Reports - Sapphire is widely used in production of optical windows for various devices due to its mechanical and optical properties. However, during operation the surface can be...     

Catalytic epitaxy of ZnO whiskers via the vapor–crystal mechanism

A model of oriented growth of (0001) ZnO whiskers on sapphire substrates via the vapor–crystal mechanism using the catalytic properties of gold islands is proposed. The morphological transition from the primary pyramidal ZnO structures to hexagonal ZnO whiskers is described in terms of the minimization of the free energy density of three-dimensional heteroepitaxial islands.     

Effect of the Morphology of an Ensemble of ZnO Microrods on the Optical and Luminescence Properties

JETP Letters - From measurements of the oscillatory magnetoresistance in weak perpendicular magnetic fields, we found that the quantum oscillations in two-dimensional electron systems in Si-MOS...     

X-Ray Luminescence of ZnO Tetrapods Grown in the Presence of Copper and Gold Admixtures in Initial Charge

Optics and Spectroscopy - We investigated the morphology and luminescent properties of ZnO tetrapod powders with copper and gold admixtures, obtained by carbothermal pyrolysis. A broad band in the...     

Mass-spectrometric study of tellurium-film condensation and evaporation on sapphire

The processes of the condensation and evaporation of a tellurium film produced by a molecular beam of Te₂ on a sapphire surface are studied. It is experimentally shown that the desorption of tellurium from a surface upon growth under nonequilibrium conditions exceeds the equilibrium thermal desorption. If the beam intensity is less than the equilibrium value, then desorption is also lower than the equilibrium value. A model of this process with allowance for the transient states of tellurium in the adsorption layer is proposed. Within this model equilibrium and Langmuir beams are expressed in terms of the process parameters. The reflection coefficient of the beam is also a function of the process characteristics. The experimental data make it possible to estimate some of the basic parameters of the process, including the coverage and desorption rate in the adsorption layer. Taking these results into account is important for manufacturing perfect films not only of Te, but also of CdTe.     

Manifestation of the Sapphire Crystal Structure in the Surface Nanopattern and Its Application in the Nitride Film Growth

The “quenching” technique was used to investigate the initial stage of the formation of a terracestep nanostructure on the R-cut surface of sapphire crystal upon high-temperature annealing in air. The morphological features of the formation of A- and R-sapphire planes are experimentally shown in dependence on the misorientation direction and qualitatively interpreted with allowance for the surface energy density for the main sapphire faces. The possibilities of forming AlN layers on the R-sapphire surface with a terrace-step nanostructure under thermochemical effect and high-temperature substrate annealing in a mixture of nitrogen and reducing gases are considered.     

Scanning tunneling microscopy of the atomically smooth (001) surface of vanadium pentoxide V<Subscript>2</Subscript>O<Subscript>5</Subscript> crystals

The (001) cleavage surface of vanadium pentoxide (V₂O₅) crystal has been studied by scanning tunneling spectroscopy (STM). It is shown that the surface is not reconstructed; the STM image allows geometric lattice parameters to be determined with high accuracy. The nanostructure formed on the (001) cleavage surface of crystal consists of atomically smooth steps with a height multiple of unit-cell parameter с = 4.37 Å. The V₂O₅ crystal cleavages can be used as references in calibration of a scanning tunneling microscope under atmospheric conditions both along the (х, y) surface and normally to the sample surface (along the z axis). It is found that the terrace surface is not perfectly atomically smooth; its roughness is estimated to be ~0.5 Å. This circumstance may introduce an additional error into the microscope calibration along the z coordinate.     

Epitaxy of CdTe on sapphire substrates with titanium buffer layers

The formation of a developed electrical relief on the sapphire substrate surface is investigated. A technique is proposed for introducing Ti⁴⁺ impurity atoms into the sapphire crystal lattice by depositing titanium layers with a thickness of about 5 nm and their annealing in air (oxidizing atmosphere) to a temperature of 1400°C. It is shown that this preliminary treatment of the sapphire substrate surface results in epitaxial growth of (111) СdTe films parallel to the sapphire (0001) plane at a temperature of 350°C.