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We study the oxidation mechanism of silicon in the presence of a thin HfO2layer. We performed a set of annealing in 18O2atmosphere on HfO2/SiO2/Si stacks observing the 18O distribution in the SiO2layer with time-of-flight secondary ion mass spectrometry (ToF-SIMS). The 18O distribution in HfO2/SiO2/Si stacks upon 18O2annealing suggests that what is responsible for SiO2growth is the molecular O2, whereas no contribution is found of the atomic oxygen to the oxidation. By studying the dependence of the oxidation velocity from oxygen partial pressure and annealing temperature, we demonstrate that the rate-determining step of the oxidation is the oxygen exchange at the HfO2/SiO2interface. When moisture is chemisorbed in HfO2films, the oxidation of the underlying silicon substrate becomes extremely fast and its kinetics can be described as a wet silicon oxidation process. The silicon oxidation during O2annealing of the atomic layer deposited HfO2/Si is fast in its early stage due to chemisorbed moisture and becomes slow after the first 10 s. [ABSTRACT FROM AUTHOR]

Properly tuning the Fermi level position in topological insulators is of vital importance to tailor their spin-polarized electronic transport and to improve the efficiency of any functional device based on them. Here, we report the full in situ metal organic chemical vapor deposition (MOCVD) and study of a highly crystalline Bi 2 Te 3 /Sb 2 Te 3 topological insulator heterostructure on top of large area (4″) Si(111) substrates. The bottom Sb 2 Te 3 layer serves as an ideal seed layer for the growth of highly crystalline Bi 2 Te 3 on top, also inducing a remarkable shift of the Fermi level to place it very close to the Dirac point, as visualized by angle-resolved photoemission spectroscopy. To exploit such ideal topologically protected surface states, we fabricate the simple spin-charge converter Si(111)/Sb 2 Te 3 /Bi 2 Te 3 /Au/Co/Au and probe the spin-charge conversion (SCC) by spin pumping ferromagnetic resonance. A large SCC is measured at room temperature and is interpreted within the inverse Edelstein effect, thus resulting in a conversion efficiency of λ IEEE ∼ 0.44 nm. Our results demonstrate the successful tuning of the surface Fermi level of Bi 2 Te 3 when grown on top of Sb 2 Te 3 with a full in situ MOCVD process, which is highly interesting in view of its future technology transfer.

Controlled insertion of electronic states within the band gap of semiconductor nanocrystals (NCs) is a powerful tool for tuning their physical properties. One compelling example is II-VI NCs incorporating heterovalent coinage metals in which hole capture produces acceptor-bound excitons. To date, the opposite donor-bound exciton scheme has not been realized because of the unavailability of suitable donor dopants. Here, we produce a model system for donor-bound excitons in CdSeS NCs engineered with sulfur vacancies ( V S ) that introduce a donor state below the conduction band (CB), resulting in long-lived intragap luminescence. V S -localized electrons are almost unaffected by trapping, and suppression of thermal quenching boosts the emission efficiency to 85%. Magneto-optical measurements indicate that the V S are not magnetically coupled to the NC bands and that the polarization properties are determined by the spin of the valence-band photohole, whose spin flip is massively slowed down due to suppressed exchange interaction with the donor-localized electron.

We show here the first colloidal synthesis of double perovskite Cs 2 AgInCl 6 nanocrystals (NCs) with a control over their size distribution. In our approach, metal carboxylate precursors and ligands (oleylamine and oleic acid) are dissolved in diphenyl ether and reacted at 105 °C with benzoyl chloride. The resulting Cs 2 AgInCl 6 NCs exhibit the expected double perovskite crystal structure, are stable under air, and show a broad spectrum white photoluminescence (PL) with quantum yield of ∼1.6 ± 1%. The optical properties of these NCs were improved by synthesizing Mn-doped Cs 2 AgInCl 6 NCs through the simple addition of Mn-acetate to the reaction mixture. The NC products were characterized by the same double perovskite crystal structure, and Mn doping levels up to 1.5%, as confirmed by elemental analyses. The effective incorporation of Mn ions inside Cs 2 AgInCl 6 NCs was also proved by means of electron spin resonance spectroscopy. A bright orange emission characterized our Mn-doped Cs 2 AgInCl 6 NCs with a PL quantum yield as high as ∼16 ± 4%.

Al:HfO2 is grown on III-V compound substrates by atomic layer deposition after an in situ trimethylaluminum-based preconditioning treatment of the III-V surface. After post-deposition rapid thermal annealing at 700 °C, the cubic/tetragonal crystalline phase is stabilized and the chemical composition of the stack is preserved. The observed structural evolution of Al:HfO2 on preconditioned III-V substrates shows that the in-diffusion of semiconductor species from the substrate through the oxide is inhibited. Al-induced stabilization of the Al:HfO2 crystal polymorphs up to 700 °C can be used as a permittivity booster methodology with possibly important implications in the stack scaling issues of high-mobility III-V based logic applications.

The localization of the donor electron wave function can be of key importance in various silicon applications, since for example it determines the interactions between neighboring donors. Interestingly, the physical confinement of the electrons in quasi-one-dimensional nanostructures, like silicon nanowires, noticeably affects this property. Using fully ab initio calculations, we show that the delocalization of the donor electron wave function along the axis of a nanowire is much greater in [011] oriented nanowires for phosphorus and selenium donors. We also demonstrate that its value can be controlled by applying a compressive or tensile uniaxial strain. Finally, we discuss the implications of these features from both an experimental and a theoretical point of view.

The self-assembly of Ge(1)Sb(2)Te(4) nanowires (NWs) for phase change memories application was achieved by metal organic chemical vapor deposition, catalyzed by Au nanoislands in a narrow range of temperatures and deposition pressures. In the optimized conditions of 400 °C, 50 mbar, the NWs are Ge(1)Sb(2)Te(4) single hexagonal crystals. Phase change memory switching was reversibly induced by nanosecond current pulses through metal-contacted NWs with threshold voltage of about 1.35 V., (© 2012 American Chemical Society)

We report a density functional study of the electronic properties and hyperfine structure of substitutional selenium in silicon nanowires using plane-wave pseudopotential techniques. We simulated hydrogen passivated [001] oriented nanowires with a diameter up to 2 nm, analyzing the effect of quantum confinement on the defect formation energy and on the hyperfine parameters as a function of the diameter and of the defect position. We show that substitutional Se in silicon has favorable configurations for positions near the surface with possible formation of chalcogen-hydrogen complexes. We also show that hyperfine interactions increase at small diameters, as long as the nanowire is large enough to prevent surface distortion which modifies the symmetry of the donor wave function. Moreover, surface effects lead to strong differences in the hyperfine parameters depending on the Se location inside the nanowire, allowing the identification of an impurity site on the basis of electron paramagnetic resonance spectra.