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Abstract: We report on the initial growth mechanisms of Ge on LaAlO3(001), a crystalline oxide with a high dielectric constant (high-κ material). Chemical and structural properties were investigated in situ, through X-ray photoelectron spectroscopy and reflection high-energy electron diffraction, and ex situ by using high-resolution transmission electron microscopy. Ge was deposited by molecular beam epitaxy at 600°C on a c(2×2) reconstructed LaAlO3(001) surface. At this temperature, a Volmer–Weber growth mode is observed due to a lower LaAlO3(001) surface free energy. It is characterized by the immediate formation of crystalline nano-islands. The Ge islands are relaxed and present an abrupt interface with the substrate. Some of them exhibit a preferential relationship in their heteroepitaxy, where the Ge(001) planes are parallel to the LaAlO3(001) ones, but rotated by 45° in the [001] direction. An additional rotation of 6° with respect to the growth axis is also observed, which compensates partially for the strain produced by the high lattice parameter mismatch (∼5%) between the semiconductor and the oxide. [Copyright &y& Elsevier]

Abstract: Chemical and structural characterizations of the LaAlO3(110) surface was investigated by XPS, XPD, LEED and RHEED. The atomic structure of this ternary alloy, can be viewed as a superposition of LaO and AlO2 planes in the [001] direction. For clean substrates, a c(4×2) surface reconstruction was pointed out by RHEED and LEED. Polar X-ray photoelectron diffraction investigations made in the [−110] azimuthal direction, for La3d, O1s and Al2score levels reveal well structured diagrams reflecting the atomic distribution of the two kinds of parallel planes in the [−110] direction and perpendicular to the (110) surface. The main crystallographic directions give strong forward-scattering peaks at 0°, 35° and 54.7° corresponding to the [110], [111] and [112] directions respectively. [Copyright &y& Elsevier]

Abstract: We report on the growth of Si on c(2×2) reconstructed LaAlO3(001) surfaces at high substrate temperature (700°C) by molecular beam epitaxy. An initial Volmer–Weber mode is evidenced using reflection high energy electron diffraction (RHEED), X-ray photoelectron diffraction (XPD) and atomic force microscopy. After the deposition of a few monolayers, the islands coalesce. Using X-ray photoelectron spectroscopy, we demonstrate that Si islands exhibit an abrupt interface with the LaAlO3 substrate without formation of silicate or silica. Finally, combined RHEED and XPD measurements show the epitaxial growth of Si with a unique Si(001)//LaAlO3(001) and Si<100>//LAO<110> relationship. [Copyright &y& Elsevier]

We report here on the atomic migration and associated nucleation mechanisms of Si nanocrystals on LaAlO3(001) surface, a high-κ crystalline oxide. Chemical and structural properties were investigated using X-ray photoelectron spectroscopy, X-ray photoelectron diffraction (XPD), reflection high-energy electron diffraction (RHEED), and ex situ with atomic force microscopy. The Si deposition was achieved by molecular beam epitaxy at room temperature. The morphological and chemical properties were followed as a function of isochronal post-growth annealing at increasing temperatures up to 800°C by 100°C steps. Up to 500°C the Si layer remains amorphous without any interdiffusion and interfacial alloy formation. Above 500°C Si nanocrystals nucleate on the surface by transformation of the amorphous Si layer into Si crystalline islands. Two kinds of annealing treatments were performed (direct current and electronic bombardment), leading to a better crystal quality (without stacking faults or twins) for a direct current heating process. Finally, a preferential epitaxial relationship between LaAlO3 and the Si islands was deduced by RHEED and confirmed by XPD: Si(001) planes are parallel to the LaAlO3(001) surface and rotated by 45° around the [001] growth axis. [ABSTRACT FROM AUTHOR]