The formation of a 1/2 monolayer (ML) of strontium (Sr) on Si(001) represents the most widely used and effective passivation procedure for the epitaxial growth of strontium titanate (SrTiO3) on Si with molecular beam epitaxy (MBE). In the present study we demonstrate experimentally the possibility of preparing such a buffer layer with the pulsed-laser deposition (PLD) technique. In situ analysis using reflection high-energy electron diffraction (RHEED) showed surface structure evolution from two-domain (2×1)+(1×2), exhibited by the bare silicon surface, to a (3×2)+(2×3) structure at 1/6 ML Sr coverage, which is then replaced by (1×2)+(2×1) structure at 1/4 ML and maintained up to 1/2 ML coverage. In addition, two different processes for the removal of native SiO2 layer were studied: thermal and Sr-induced deoxidation process. Annealing above 1100°C proved to be the most efficient in terms of carbon contamination. The results highlight the possibilities of using the PLD technique for the synthesis of an epitaxial SrTiO3 layer on Si, needed for the integration of different functional oxides with a Si platform.
COBISS.SI-ID: 28399143
The epitaxial growth of functional oxides on silicon substrates requires atomically defined surfaces, which are most effectively prepared using Sr-induced deoxidation. The manipulation of metallic Sr is nevertheless very delicate and requires alternative buffer materials. In the present study the applicability of the chemically much more stable SrO in the process of native-oxide removal and silicon-surface stabilization was investigated using the pulsed-laser deposition technique (PLD), while the as-derived surfaces were analyzed in situ using reflection highenergy electron diffraction and ex situ using X-ray photoelectron spectroscopy, X-ray reflectivity, and atomic force microscopy. After the deposition of the SrO over Si/SiO2, in a vacuum, different annealing conditions, with the temperature ranging up to 850 °C, were applied. Because the deposition took place in a vacuum, a multilayer composed of SrO, Sr-silicate, modified Si, and Si as a substrate was initially formed. During the subsequent annealing the topmost layer epitaxially orders in the form of islands, while a further increase in the annealing temperature induced rapid desorption and surface deoxidation, leading to a 2 × 1 Srreconstructed silicon surface. However, the process is accompanied by distinctive surface roughening, and therefore the experimental conditions must be carefully optimized to minimize the effect. The results of the study revealed, for the first time, an effective pathway for the preparation of a SrO-induced buffer layer on a silicon substrate using PLD, which can be subsequently utilized for the epitaxial growth of functional oxides.
COBISS.SI-ID: 28025383
The deoxidation and passivation of a silicon surface represents one of the most important steps in the successful integration of functional oxides with silicon. Due to its reactivity and dissimilar properties with respect to oxides, silicon surfaces are conditioned using various buffer systems. Despite the quality of the resulting surface, these Sr-based buffers have not been commercialized because of the reactivity of the metallic Sr. SrO has demonstrated properties that are competitive with metallic Sr, but a successful integration with silicon has not yet been proven. In the present study we have determined the optimal pulsedlaser deposition (PLD) conditions for the SrO-induced deoxidation of a silicon surface, which results in a 2 × 1 reconstructed surface. Additionally, the as-prepared surface is oxide-free and atomically flat. The results show that the amount of SrO plays the most critical role in the optimization of the whole process. Deposited in batch mode, the amount of SrO affects the morphologies of the surfaces, which change from a dimerized surface to SrO islands and a polycrystalline layer in the final stage. However, in the case of an insufficient amount of deposited SrO, pits are formed on the surface, drastically increasing its roughness. The successful optimization of the PLD conditions for the formation of a SrO buffer layer opens a new pathway for interfacing oxides with silicon.
COBISS.SI-ID: 29705255
The integration of epitaxial complex oxides with Si represents an invaluable opportunity for the creation of novel devices with logic and sensing capabilities, both implemented in the same chip. In this work, Pulsed Laser Deposition (PLD) is used to grow epitaxial ultra-thin (3–4 nm) SrTiO3 (STO) layers on Si(001), showcasing the possibilities of this technique for the growth of templates for the integration of complex oxides with Si. Our procedure involves the growth of a 1/2 monolayer (ML) of Sr buffer layer on the reconstructed Si(001) surface by PLD, the deposition of STO in inert Ar atmosphere, and latter oxidation and crystallization phases. The optimization of STO deposition, oxidation, and crystallization parameters proves to be essential for the improvement of the layer's quality. It has been found that the minimization of the thermal budget during the crystallization phase increases the interface sharpness, but a minimum temperature is needed for a proper densification of the STO layer. A coverage of 2 ML before every crystallization and oxidation phases was determined as the best balance between the critical thickness, minimization of the thermal budget, and a proper coverage of the buffer layer, which prevents its reactions with the Sr/Si surface. These results improve the general knowledge and understanding of metal oxide/silicon heterojunctions, and represent a solid stepping stone for the growth of high-quality thin STO templates on Si by PLD.
COBISS.SI-ID: 30486055
High-temperature reactions during the solid-state synthesis of samples from the (1-x)Na0.5Bi0.5TiO3–xSrTiO3 system were investigated. Due to the number of chemically different elements, the processing of these ceramics is delicate and requires several firing steps under specific conditions to obtain phase-pure samples. Sintering in an air atmosphere resulted in a macroscopically inhomogeneous microstructure, which is a consequence of incomplete reaction between different secondary phases. However, prolongation of the sintering time aggregated the pores in the sample, while at a higher firing temperature the sample’s secondary phase melted. As a result, the nominal composition was altered, leading to the formation of the Na2Ti6O13 secondary phase. Sintering under an increased oxygen pressure of 1 MPa limited the evaporation of the secondary phase. This allowed the completion of the reaction, forming a homogeneous and dense sample. The study provides a set of experimental conditions for the successful preparation of ceramics from the investigated system.
COBISS.SI-ID: 30961959