The Fe/ZnO(0 0 0 1) interface: Formation and thermal stability

The room temperature growth mode and the interface reaction of Fe films on single crystalline ZnO(0 0 0 1) substrates prepared in ultra high vacuum (UHV) has been investigated by means of X-ray photoelectron and Auger electron spectroscopy (XPS, AES), low energy electron diffraction (LEED) and low energy ion scattering spectroscopy (LEIS). The results show that Fe grows in the pseudo layer-by-layer mode. At ambient temperature the deposited Fe film reduces the underlying ZnO single crystal resulting in FeO at the interface and metallic Zn, which partially diffuses into the remaining Fe overlayer. Annealing leads to a stepwise oxidation of the Fe to FeO (670 K) and Fe₂O₃ (820 K). The Fe₂O₃ mixes with the substrate resulting in two (1 1 1) oriented textures of a spinel phase found by electron backscatter diffraction analysis (EBSD). Fe-based spin-injection may play a vital role for ZnO-based spintronic devices.     

Effects and structures of the O/Cu surfactant layer in O-mediated film growth of Cu on Ru(0 0 0 1)

The O-mediated Cu-film growth on O-precovered Ru(0 0 0 1) is investigated by means of scanning tunneling microscopy for growth temperatures between 300 and 600 K. Cu-films on clean Ru(0 0 0 1) grow in a multilayer mode. For O precoverages (Θ) between 0.2 ML (monolayer) and the saturation coverage (Θ=0.5 ML), a layer-by-layer growth is observed at growth temperatures between 350 and 450 K. On Cu-islands, an O/Cu surfactant layer is formed, which floats on-top of the growing film and induces the layerwise Cu-film growth. The surface coverage of the O/Cu surfactant layer linearly rises with the O precoverage up to Θ≈0.4 ML, where it completely covers the surface. Two different types of the surfactant layer are identified, inducing different surfactant mechanisms. For Θ=0.1–0.4 ML, the O/Cu surfactant structure (A-type) displays some local order and induces inhomogeneous nucleation at the misfit-induced relaxation structure of the Cu-film. The layer-wise growth is explained by the concept of two mobilities, implying a large attempt frequency for adatom jumps over the interlayer diffusion barrier at the steps. For Θ = 0.4–0.5 ML, a disordered O/Cu surfactant layer is established (B-type), inducing homogeneous nucleation. The layer-wise Cu-film growth is attributed to a reduction of the effective interlayer diffusion barrier. Cu-film growth at 400 K on the ordered (3×2√3)O/Cu structure formed at temperatures around 520 K yields the conclusion that the O/Cu surfactant structures are composed of randomly arranged O–Cu–O strings and disrupted “Cu₂O(1 1 1)” fragments.     

Strain dependent growth of silicon on Ge/Si–C heterostructures

We report on structural investigations of strain dependent growth of Si on Ge/Si–C heterostructures. Very small islands of Ge were obtained by using a little C precoverage before the Ge deposition. These islands are visualized by scanning tunneling microscopy (STM) and the subsequent Si epitaxy is pursued. STM pictures taken upon some monolayers of Si epitaxy reveal an inhomogeneous growth mode, which leads to ditch like rings formed around the islands. Pictures of the following Si deposition suggest a strain dependent surface diffusion of Si until sufficient material has been deposited which then flattens the surface resulting in perfect epitaxial structures.     

Growth mode and interface structure of Ag on the HF-treated Si(111):H surface

A growth mode and interface structure analysis has been performed for Ag deposited at a high temperature of 300°C on the HF-treated Si(111):H surface by means of medium-energy ion scattering and elastic recoil detection analysis of hydrogen. The measurements show that Ag grows in the Volmer-Weber mode and that the Ag islands on the surface are epitaxial with respect to the substrate. The preferential azimuthal orientation is A-type only when Ag is deposited slowly. The interface does not reconstruct to the √3 × √3-Ag structure, which is normally observed for Ag deposition above 200°C on the Si(111)7 × 7 surface, but retain bulk-like structure. The presence of hydrogen at the interface is demonstrated after deposition of thick (1100 Å) Ag films. However, the amount of hydrogen at the interface is not a full monolayer. This partial desorption of hydrogen from the interface explains why the Schottky barrier heights of Ag/Si(111):H diodes are close to those of Ag/Si(111)7 × 7 and Ag/Si(111)2 × 1.     

Controlled surface nanopatterning with buried dislocation arrays

Self-assembled configurations of nanostructures are expected to play an increasing role in devices design, as an alternative to conventional microelectronics. The key limitation is the lack of control on localisation, density and size uniformity of the structures. Here we show how to create a template to overcome these problems. A periodic nanometre scale patterning can be induced at a silicon surface by buried dislocation networks obtained by twist wafer bonding, using stress selective etching of the surface. These templates are morphologically characterised by scanning tunnelling microscopy and grazing incidence X-ray diffraction. Stress fields and elastic energy densities are calculated for the non-etched solid, and the selective etching mechanisms are discussed. Germanium growth experiments on such a Si patterned surface give a demonstration of the ordering efficiency. This study provides a general method to create a template, which organises nanostructures with controlled periodicity over the full size of a Si wafer.     

透射式GaAs光电阴极AlGaAs窗层和GaAs光电发射层界面应变状况的X射线衍射研究

本文介绍了应变和弛豫的概念以及倒易点在倒易空间的分布,阐明了GaAs光电阴极AlGaAs窗层和GaAs光电发射层界面应变状况的X射线衍射的分析方法,最后给出了实例.     

Deposition and dielectric characterization of strontium and tantalum-based oxide and oxynitride perovskite thin films

We have synthesized the composition x = 0.01 of the (Sr_1-xLa_x)₂(Ta_1-xTi_x)₂O₇ solid solution, mixing the ferroelectric perovskite phases Sr₂Ta₂O₇ and La₂Ti₂O₇. Related oxide and oxynitride materials have been produced as thin films by magnetron radio frequency sputtering. Reactive sputter deposition was conducted at 750 °C under a 75 vol.% (Ar) + 25 vol.% (N₂,O₂) mixture. An oxygen-free plasma leads to the deposition of an oxynitride film (Sr_0.99La_0.01) (Ta_0.99Ti_0.01)O₂N, characterized by a band gap E_g = 2.30 eV and a preferential (001) epitaxial growth on (001) SrTiO₃ substrate. Its dielectric constant and loss tangent are respectively Epsilon' = 60 (at 1 kHz) and tanDelta = 62.5 × 10⁻³. In oxygen-rich conditions (vol.%N₂ ≤ 15%), (110) epitaxial (Sr_0.99La_0.01)₂(Ta_0.99Ti_0.01)₂O₇ oxides films are deposited, associated to a larger band gap value (E_g = 4.55 eV). The oxide films permittivity varies from 45 to 25 (at 1 kHz) in correlation with the decrease in crystalline orientation; measured losses are lower than 5.10⁻³. For 20 ≤ vol.% N₂ ≤ 24.55, the films are poorly crystallized, leading to very low permittivities (minimum Epsilon' = 3). A correlation between the dielectric losses and the presence of an oxynitride phase in the samples is highlighted.     

Instability of an elastic film on a viscous layer

A flat, compressed elastic film on a viscous layer is unstable. The film can form wrinkles to reduce the elastic energy. In this paper, we are interested in the two-dimensional models for thin films bonded to a viscous layer and in particular we focus on generic instabilities evidenced in this context by Suo and coworkers [Huang, Z., Hong, W., Suo, Z., 2005. Non linear analyses of wrinkles in a film bonded to a compliant substrate. J. Mech. Phys. Solids 53, 2101–2118; Lo, Y.H., 1991. New approach to grow pseudomorphic structures over the critical thickness. Appl. Phys. Lett. 59, 2311–2320]. We present a rigorous linear perturbation analysis for anisotropic materials, that allows the prediction of both the orientation of the corrugations of the thin film, and the wavelength that maximize the growth velocity. Finally, we compare our theoretical estimates to experimental results for a In_0.65Ga_0.35As alloy constraint to InP.     

SiC epitaxy growth using chloride-based CVD

The growth of thick epitaxial SiC layers needed for high-voltage, high-power devices is investigated with the chloride-based chemical vapor deposition. High growth rates exceeding 100 μm/h can be obtained, however to obtain device quality epilayers adjustments of the process parameters should be carried out appropriately for the chemistry used. Two different chemistry approaches are compared: addition of hydrogen chloride to the standard precursors or using methyltrichlorosilane, a molecule that contains silicon, carbon and chlorine. Optical and electrical techniques are used to characterize the layers.     

Magnetoelectric coupling induced multistate magnetization

Complex oxides provide an ideal playground for exploring the interplay among the fundamental degrees of freedom: structural (lattice), electronic (orbital and charge), and magnetic (spin). With trends toward device miniaturization, there is growing interest in combining electronic and magnetic properties into multifunctional thin-film materials for potential applications in novel versatile devices. Here, we report growth of ferromagnetic nanostructures on ferroelectric ($1?x$)[Pb(Mg_1/3Nb_2/3)O₃]???x[PbTiO₃] (PMN-PT) single crystals. With careful control of material composition and application of electric field direction and amplitude, we realized stabilization of both monoclinic and orthorhombic phases in the PMN-PT single crystals with the intrinsic rhombohedral phase. Multistate magnetization modulation has been realized through phase transformation control in the ferroelectric component. This finding promises multistate information recording through magnetoelectric effect.