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In this study, we investigate the changes in the crystalline structure of MBE-deposited SrTiO3 layers on Si with different deviations from Sr/Ti stoichiometry as deposited but also after annealing at high temperatures (>600 °C). We show that as-grown 15 nm thick non-stochiometric SrTiO3 layers present surprisingly lower FWHM values of the (002) omega diffraction peak compared to fully stoichiometric layers of similar thickness. This can misleadingly point to superior crystalline quality of such non-stochiometric layers. However, thermal post-deposition anneals of these layers at temperatures up to 850 °C in oxygen show strong detrimental effects on the crystalline structure, surface and interface with the Si (001) substrate. On the contrary, the post-deposition anneals applied to the stoichiometric samples strongly improve the physical, optical and electrical properties of the epitaxial SrTiO3 thin films. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of high-quality thin films of the topological semimetal (Bi2)5(Bi2Se3)7. Cryogenic magnetotransport experiments reveal strong metallic character and spin--orbit coupling in the films. By studying the temperature dependence of the electrical resistance of the topological semimetal, we observe a pronounced Kondo effect, which points toward the presence of magnetic scatterers. With the aid of density functional theory calculations, we identify Bi vacancies as intrinsic magnetic scatterers in this topological semimetal. [ABSTRACT FROM AUTHOR]

Barium titanate (BaTiO3 or BTO) is a perovskite structure material with interesting intrinsic properties, such as spontaneous ferroelectricity or electro-optical behavior, which strongly depend on thin film crystallinity. For such functional oxide systems, the pulsed-laser deposition (PLD) approach is one promising growth technique due to its precise stoichiometry control of the metals composing the perovskite crystal and higher oxygen environment compared to the classically used molecular beam epitaxy (MBE) approach. In this article, we demonstrate a BTO epitaxial layer by PLD onto an Si(001) substrate thanks to a thin pseudomorphic SrTiO3 buffer layer grown by MBE. In our study, the various investigated PLD parameters show strong impacts on the BTO polarization orientation. Hence, adjusting the growth conditions allows control of the polarization orientation, which is crucial for both electronic and optical applications. In addition, lattice parameter changes of BTO layers are investigated using x-ray diffraction and cross-sectional transmission electron microscopy, which evidenced a correlation between mismatch relaxation and oxygen growth pressure. Finally, with the analysis of BTO C–V curves, the polarization direction transition is demonstrated electrically. [ABSTRACT FROM AUTHOR]

In this work, we present a systematic study of the effect of the stoichiometry of BaTiO3 (BTO) films grown on the Ge(001) substrate by molecular-beam-epitaxy using different characterization methods relying on beam diffraction, including reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and selected-area electron diffraction in transmission electron microscopy. Surprisingly, over a wide range of [Ba]/[Ti] ratios, as measured by the Rutherford backscattering spectrometry, all the BTO layers exhibit the same epitaxial relationship h100iBTO(001)// 〈110〉Ge(001) with the substrate, describing a 45° lattice rotation of the BTO lattice with respect to the Ge lattice. However, varying the [Ba]/[Ti] ratio does change the diffraction behavior. From RHEED patterns, we can derive that excessive [Ba] and [Ti] generate twinning planes and a rougher surface in the non-stoichiometric BTO layers. XRD allows us to follow the evolution of the lattice constants as a function of the [Ba]/[Ti] ratio, providing an option for tuning the tetragonality of the BTO layer. In addition, we found that the intensity ratio of the 3 lowest-order Bragg peaks I(001)/ I(002), I(101)/I(002), and I(111)/I(002) derived from ω-2θ scans characteristically depend on the BTO stoichiometry. To explain the relation between observed diffraction patterns and the stoichiometry of the BTO films, we propose a model based on diffraction theory explaining how excess [Ba] or [Ti] in the layer influences the diffraction response. [ABSTRACT FROM AUTHOR]