Surface Of Strontium Titanate Research Articles

Formation of quasi-ordered structures on the surface of strontium titanate in a plasma field

The X-ray diffraction and X-ray spectroscopic properties of strontium titanate single crystals and their surface exposed to plasma have been investigated. Both undoped SrTiO3 crystals and crystals containing impurity ions of the iron or lanthanum groups have been analyzed. Data on the plasma-induced formation of ordered crystallites on the sample surface were obtained by electron and atomic force microscopy. The crystallites are from 10−7 to 10−9 m in size and their hypothetical orientation [321] is independent of the sample orientation and irradiation dose.

Sorption of uranium(VI) onto strontium titanate in KNO3 medium

The sorption of uranium(VI) on the perovskite structure of strontium titanate in a 0.5M KNO3 solution is studied. SrTiO3 commercial material was characterized by XRD showing a tausonite face, with a specific area of 2.42 m 2. g –1 . The electrical surface characterization of the compound was performed by mass and potentiometric titrations. pHpzc in water was 8.5±0.3 and 9.1±0.2 in 0.5M KNO3 solution, showing a positively charged surface. FITEQL 4.0 program was used to calculate the sorption curves and the surface acidity constants by the constant capacitance model obtaining: log K1 = 8.67 and log K2 = –9.43. The sorption edge was fitted with two different uranium(VI) species sorbed, corresponding to bidentate complexes of UO2 and UO2(OH)2H2O on the surface of strontium titanate.

RHEED study of stepped (0 0 1) surface of strontium titanate

Low-temperature RHEED technique was employed to study the structure of the regular-stepped (0 0 1) surface of strontium titanate with a miscut angle of 7° between crystallographic planes and real surfaces. Specific diffraction images resulting from miscut demonstrate an additional periodicity with a characteristic length equal to the width of terraces. A histogram method was applied in order to obtain a complete set of characteristic lattice parameters at the surface. A relaxation parallel to the surface was found to be different along and across steps. Surface lattice parameters exhibit several anomalies as a function of temperature, which are interpreted as surface phase transitions promoted by a surface anisotropy which removes the three-fold degeneracy of titanium-centered oxygen octahedra rotations around [0 0 1] axes.

Epitaxial Growth Mechanism of Chemical-Vapor-Deposited Anatase on Strontium Titanate Substrate

Titanium dioxide films were chemically prepared on (001) single-crystal strontium titanate, SrTiO3, using a vapor deposition apparatus operating under atmospheric pressure with titanium tetra-isopropoxide. At a substrate temperature of 400°C, titanium dioxide grew epitaxially with lateral growth of steps, as well as multinucleation was observed during the initial growth process, i.e., the so-called Stranski-Krastanov growth. As a result, the surface of strontium titanate was completely covered by titanium dioxide steps with an average lateral growth rate of 100nm/s, followed by multinucleation growth. The nuclei developed in a number of highly oriented crystallites having well defined facets. X-ray diffractometry and transmission electron microscopy revealed that these crystallites consisted of ‹001›-oriented anatase-type structure.

Atomic-Force Microscopy of Gold Nanocrystallites on Smooth and Stepped Strontium Titanate Surfaces

ABSTRACTWe have studied the nucleation and growth of Au nanocrystallites with dimensions of tens of nanometers on strontium titanate surfaces using an atomic force microscope. Strontium titanate ablated from a pressed pellet target by a KrF laser was deposited on both planar and offcut strontium titanate substrates. In a separate step, submonolayer quantities of gold were deposited, also by pulsed laser deposition, on the strontium titanate. The surfaces were then scanned by an atomic-force microscope to determine the effects of surface defects (such as steps and kinks on offcut surfaces), substrate temperature, and gold ablation yield on the nucleation, growth and size distribution of the nanocrystallites. The competition between diffusion and nucleation on planar vs stepped surfaces was particularly apparent in the AFM images. These results suggest several ways in which lateral decoration of the strontium titanate by the gold nanocrystallites can be achieved, an important step toward designer nonlinear photonic materials.

Surface spectroscopy studies of the SrTiO3(100) surface and the platinum-SrTiO3(100) interface

Auger-electron spectroscopy (AES), low-energy-electron diffraction (LEED), electron-energy-loss spectroscopy (ELS), and ultraviolet-photoelectron spectroscopy (UPS) were used to characterize the composition, structure, and electronic properties of the strontium-titanate (100) surface and the platinum---strontium-titanate interface. The strontium 65-eV Auger signal on the clean strontium-titanate surface decreases abruptly as the temperature is raised beyond 240\ifmmode^\circ\else\textdegree\fi{}C. Partial ordering occurs when platinum is deposited on the strontium-titanate (100) surface as evidenced by LEED. Platinum appears to remove surface ${\mathrm{Ti}}^{3+}$ by electron transfer from SrTi${\mathrm{O}}_{3}$ to platinum. These results are discussed in light of the findings in photoelectrolysis and other photocatalytic studies using SrTi${\mathrm{O}}_{3}$.

The photoassisted reaction of gaseous water and carbon dioxide adsorbed on the SrTiO 3 (111) crystal face to form methane

The photosynthetic reaction of gas phase water and carbon dioxide molecules adsorbed onto strontium titanate surfaces that are in contact with platinum foils is reported. The dominant reaction product detected at 15 torr partial pressures of the reactant gases is methane. The reaction takes place without any externally applied potential (between the foil and SrTiO 2) and in the absence of liquid electrolyte, when the clean, reduced SrTiO 3 (111) crystal face in illuminated with light of energy greater than the band gap. A thermal process, which produces methane, when the SrTiO 3P̄t sandwich is healed in CO 2 and water, is also observed. The photo and thermal processes are easily distinguished by the use of filters.

Surface barrier energies on strontium titanate

The metal-semiconductor surface-barrier systems consisting of the metals gold, palladium, copper, or indium on chemically prepared or cleaved strontium titanate surfaces have been investigated in detail. Surface-barrier energies have been studied by photoresponse, forward current versus voltage, and thermal activation energy techniques yielding values in excellent agreement with each other. Forward current-voltage characteristics were in quantitative agreement with simple diode thermionic theory as modified by the inclusion of image force lowering. The reverse current-voltage characteristic of these stable barriers also is in agreement with that expected from thermionic theory including simple image force lowering over a bias range from −0.1 to −4 V.