V. I. Sakharov

Improved cationic stoichiometry and insulating behavior at the interface of LaAlO3/SrTiO3 formed at high oxygen pressure during pulsed-laser deposition

Medium-energy ion spectroscopy, MEIS, and scanning transmission electron microscopy, STEM, were used to correlate the atomic structure of LaAlO3/SrTiO3 interfaces with their electrical properties. Interfaces were prepared at high (5x10(-2) mbar) and low (10(-4) mbar) oxygen pressure by pulsed-laser deposition. The high-oxygen-pressure heterostructures were insulating for all thicknesses while the low-oxygen-pressure ones became metallic for thicknesses above 4 unit cells. MEIS data show enhancement of the Sr surface peak and suppression of the La one in interfaces prepared at low oxygen pressure, which is interpreted as a La-Sr intermixing. The effect was considerably smaller in high-oxygen-pressure samples. Analysis of high-angle annular-dark-field STEM images of the LAO films also indicates intermixing between La and Sr in low-oxygen-pressure samples, supporting MEIS data. Our results reveal the important role of oxygen pressure on the formation of the interface electron gas. Copyright (C) EPLA, 2011

Optimized transport properties of LaAlO3/SrTiO3 heterointerfaces by variation of pulsed laser fluence

We show the influence of pulsed laser deposition fluence on the transport properties of the LaAlO(3)/SrTiO(3) (LAO/STO) heterointerface. Structural characterization by x-ray diffraction and medium energy ion spectrometry enables us to deduce that the electronic behaviour is extremely sensitive to the stoichiometry of the LAO layer as well as the structural quality of the STO surface. An optimum balance of these two quantities is demonstrated for an intermediate laser fluence.

Dislocation-related luminescence in single-crystal silicon subjected to silicon ion implantation and subsequent annealing

Implantation of silicon ions with an energy of 100 keV at a dose of 1 × 1017 cm−2 into n-type floatzone Si does not lead to the formation of an amorphous layer. Subsequent annealing in a chlorine-containing atmosphere at 1100°C gives rise to dislocation-related luminescence. The intensity of the dominant D1 line peaked at a wavelength of ∼1.54 μm grows as the annealing time is increased from 15 to 60 min.

Light-induced transformation of C60 films in the presence and absence of oxygen

The composition and structure of C60 fullerite films prepared by discrete evaporation in quasiclosed volume, as well as their changes induced by laser irradiation, have been studied by ellipsometry and Rutherford backscattering. The starting film has a 150-Å thick stable top layer and a carbon to oxygen ratio of 10:1. Exposure of a film both to vacuum and to air results in formation of an insoluble photo-transformed phase, but in the second case the change in the refractive index implies the appearance of compounds with oxygen. The material does not undergo complete polymerization, although all structural changes cease at an irradiation dose of 104 photons per fullerene molecule. Treatment of the polymerized phase with organic solvents produces a porous structure, with the voids totaling 48% in the case of exposure in vacuum, and 30% when exposed in air.

Investigation of the initial stages of the growth of barium strontium titanate ferroelectric films by medium-energy ion scattering

The initial stages of the growth of barium strontium titanate (BaSrTiO3) ferroelectric films deposited on single-crystal sapphire substrates have been studied using medium-energy ion scattering. It has been found that, depending on the variation in the deposition temperature, the mechanisms of formation of the ferroelectric film change as a result of the change in the mechanism of mass transfer of the deposited atoms. It has been shown that the minimum thickness of the continuous ferroelectric film on sapphire is of the order of 6 nm.

Composition and porosity of multicomponent structures: porous silicon as a three-component system

It is shown for the system porous silicon (por-Si)-silicon (Si) that effective nondestructive investigation of the interfacial morphology of layered semiconductor systems and of the composition of multicomponent layers by ellipsometry and Rutherford backscattering is possible. Both methods were used to determine the percentage composition of the main components of por-Si: crystal silicon, silicon oxide, and voids (porosity). It is shown that por-Si obtained by pulse-anodization contains a substantial quantity of silicon oxide. It is also shown that spectral ellipsometry can be used to determine the specific ratio of individual layers or components of multilayer and multicomponent systems (provided that the spectral dispersion of the optical constants of these components is known).

Atomic rearrangements at the TiO2-terminated (001)SrTiO3 surface and growth of thin LaMnO3 films

SrTiO3 is commonly used as a substrate for growth of various oxide films. Different reconstructions at the SrTiO3 surface have been claimed. A question is whether these survive subsequent depositions of thin films and influence film properties. Medium energy ion scattering (MEIS) was used to probe structure and composition of the surface layer of a TiO2-terminated (001) SrTiO3 single-crystal substrate and 1-4 unit cell (u.c.) thick LaMnO3 epilayers. Aligned spectra indicate enrichment of Ti at the surface and a TiO2 double-layer (DL) configuration. The DL arrangement survives pulsed-laser deposition of LaMnO3 in a background of high oxygen pressure (5 x 10(-2) mbar) while it is destroyed at lower oxygen pressure (10(-4) mbar). Simulations of random MEIS spectra indicate substantial interdiffusion and La doping of the substrate surface but all interfaces are nevertheless insulating.

Aerosol Deposition of Detonation Nanodiamonds Used as Nucleation Centers for the Growth of Nanocrystalline Diamond Films and Isolated Particles

The aerosol deposition of detonation nanodiamonds (DNDs) on a silicon substrate is comprehensively studied, and the possibility of subsequent growth of nanocrystalline diamond films and isolated particles on substrates coated with DNDs is demonstrated. It is shown that a change in the deposition time and the weight concentration of DNDs in a suspension in the range 0.001–1% results in a change in the shape of DND agglomerates and their number per unit substrate surface area Ns from 108 to 1011 cm−2. Submicron isolated diamond particles are grown on a substrate coated with DND agglomerates at Ns ≈ 108 cm−2 using microwave plasma-enhanced chemical vapor deposition. At Ns ≈ 1010 cm−2, thin (∼100 nm) nanodiamond films with a root-mean-square surface roughness less than 15 nm are grown.

Component composition and strain of barium-strontium titanate ferroelectric films

The effect of the ratios of the cationic components and internal strains on the critical temperature Tc and the dielectric characteristics of BSTO ferroelectric films grown on α-Al2O3 [1012] and LaAlO3 substrates were investigated. Ion backscattering diagnostics revealed a barium deficiency in the surface layer of the films and showed that the films differ in structural quality.

Effect of annealing on the optical and structural properties of GaN:Er

The effect of annealing on the optical and structural properties of gallium nitride layers grown by metalorganic chemical vapor deposition and implanted with 0.8 to 2.0-MeV erbium ions at doses of (1−4)×1014 cm−2 is investigated. Additional implantation of 0.11 to 0.28-MeV oxygen ions at doses of (1−4)×1015 cm−2 is performed on some samples. Measurements of the Rutherford backscattering of protons show that amorphization of the gallium nitride layers does not occur at the erbium implantation doses investigated. The formation of erbium-related luminescence centers which emit at 1.54 µm ends before the defect structure of the implanted layers is restored during a postimplantation anneal in the temperature range 700–1300 °C.