高气压反射式高能电子衍射仪监控脉冲激光外延氧化物薄膜

在超高真空分子束外延（MBE）生长技术中，反射式高能电子衍射仪（RHEED）能实时显示半导体和金属外延生长过程，给出薄膜表面结构和平整度的信息，成为MBE必备的原位表面分 析仪.为了研究氧化物薄膜如高温超导（YBa₂Cu₃O₇） 、铁电薄膜（Sr_1-xBa_x TiO₃）及它们的同质和异质外延结构的生长机理，获得高质量的符合各种应用 需要的氧化 物多层薄膜结构，在常规的制备氧化 关键词： 高温超导薄膜 RHEED     

XPS,AFM, ATR and TPD evidence for terraced,dihydrogen terminated, 1×1 (100) silicon

Heating (100) silicon at high temperature (say, higher than 850 °C) in H₂, cooling to 670–700 °C in the same ambient, and quenching to room temperature in N₂ results in environmentally robust, terraced 1 × 1 (100) SiH₂. Evidence for this conclusion is based on angle‐resolved x‐ray photoelectron spectroscopy, atomic force microscopy, infrared absorption spectroscopy in the attenuated total reflection mode, thermal programmed desorption, and reflection high‐energy electron diffraction. Copyright © 2005 John Wiley & Sons, Ltd.     

Investigation of surface structure and composition of in situ annealed Fe–Mn binary alloy samples using RHEED and electron spectroscopy

The formation of oxides at the surface of Fe–1.5%Mn and Fe–0.6%Mn binary alloys was investigated as a function of the conditions of the heat treatments. Both the influence of temperature and the atmosphere under which the experiments were performed were studied. The range of annealing temperatures was adjusted to 800°C. The atmosphere consisted of a mixture of N₂–5%H₂ and traces of water vapour, with different fixed dew points ranging from −10°C to −30°C. The state of the annealed surfaces was determined using in situ analytical devices attached to the annealing reactor in order to avoid surface contamination or the formation of native oxides after the experiments due to contact with air. The structure and composition of the surfaces were determined by reflection high-energy electron diffraction (RHEED) and electron spectroscopy (XPS, AES). Copyright © 2002 John Wiley & Sons, Ltd.     

RHEED study on continuously repeated step flow and layer-by-layer growth modes in SrRuO3/SrMnO3 superlattice

Nanolayered superlattices composed of ferromagnetic SrRuO₃ and antiferromagnetic SrMnO₃ layers were grown on SrTiO₃ (100) substrates by pulsed laser deposition. Multilayers were grown under predetermined synthesis conditions resulting in growth of SrRuO₃ and SrMnO₃ by step flow and layer-by-layer modes, respectively. The growth of SrMnO₃ was observed to occur through the layer-by-layer during the entire deposition process despite the expected increase in surface roughness because of the incorporation of SrRuO₃ upper layers. Monitoring by reflection high-energy electron diffraction (RHEED) revealed that the growth of every SrMnO₃ layer consisted of a pre-stage during which the gaps on the relatively rough SrRuO₃ surface were filled before the actual growth of the SrMnO₃ layer, which resulted in incomplete half oscillation and change from spot patterns to streaky patterns. The in-plane lattice constant did not show any considerable change in the case of SrRuO₃ and SrMnO₃ layers, despite the considerable lattice mismatch between the two materials (SrRuO₃, SrMnO₃) and SrTiO₃. On the other hand, the RHEED patterns showed the existence of lattice mismatch effects in the out-of-plane lattice constant, which showed significant strains of opposite signs in the different layers, indicating a strong dependence on the composition of the layers and superlattice periodicity. In this paper, the growth characteristics of a SrRuO₃/SrMnO₃ multilayer along with its magnetic properties will be discussed.     

Molecular beam epitaxy

Molecular beam epitaxy (MBE) is a process for growing thin, epitaxial films of a wide variety of materials, ranging from oxides to semiconductors to metals. It was first applied to the growth of compound semiconductors. That is still the most common usage, in large part because of the high technological value of such materials to the electronics industry. In this process beams of atoms or molecules in an ultra-high vacuum environment are incident upon a heated crystal that has previously been processed to produce a nearly atomically clean surface. The arriving constituent atoms form a crystalline layer in registry with the substrate, i.e., an epitaxial film. These films are remarkable because the composition can be rapidly changed, producing crystalline interfaces that are almost atomically abrupt. Thus, it has been possible to produce a large range of unique structures, including quantum well devices, superlattices, lasers, etc., all of which benefit from the precise control of composition during growth. Because of the cleanliness of the growth environment and because of the precise control over composition, MBE structures closely approximate the idealized models used in solid state theory.

This discussion is intended as an introduction to the concept and the experimental procedures used in MBE growth. The refinement of experimental procedures has been the key to the successful fabrication of electronically significant devices, which in turn has generated the widespread interest in the MBE as a research tool. MBE experiments have provided a wealth of new information bearing on the general mechanisms involved in epitaxial growth, since many of the phenomena initially observed during MBE have since been repeated using other crystal growth processes. We also summarize the general types of layered structures that have contributed to the rapid expansion of interest in MBE and its various offshoots. Finally we consider some of the problems that remain in the growth of heteroepitaxial structures, specifically, the problem of mismatch in lattice constant between layers and between layer and substrate. The discussion is phenomenological, not theoretical; MBE has been primarily an experimental approach based on simple concepts.     

Role of gallium wetting layer in high-quality ZnO growth on sapphire (0001) substrates

ZnO is a wide direct bandgap (Eg=3.37 eV at room temperature) II-VI compound semiconductor of wurtzite structure (a = 3.249 ? c = 5.207 ?. Compared to GaN and ZnS, ZnO has a larger exciton binding energy, ~60 meV (cf. ~25 meV for GaN and ~40 meV for ZnS), which is advantageous to realizing low-threshold excitonic lasers. Since optically pumped UV lasing of ZnO at room temperature was reported in 1997[1], much attention has been paid to the crystal quality improvement and p-type conduc…     

Epitaxial growth of cobalt clusters on the bare and the oxide film grown on NiAl(1 0 0) surfaces

The structure of the nano-sized cobalt clusters on bare NiAl(1 0 0) and an oxidized NiAl(1 0 0) surfaces have been investigated by AES, LEED and RHEED. The deposition of Co onto bare NiAl(1 0 0) at room temperature led to small crystalline Co grains and surface asperities of substrate. The latter is likely induced by replacement of surface Al, Ni atoms by Co deposit. At 800 K Co particles aggregate to form clusters, but incorporation of Co into bulk NiAl(1 0 0) could occur upon annealing at 900 K. On the other hand, pure face-centered cubic (fcc) phase of Co crystallites of ≈1 nm in diameter with inclusion of smaller-sized particles (D < 1 nm) are observed on Θ-Al₂O₃ after Co deposition at room temperature. After annealing the Co nano-clusters grow larger at expense of small particles (D ≈ 3 nm), where the [1 1 0] and [−1 1 0] axis of the Co(0 0 1) facets are parallel to the [1 0 0] and [0 1 0] directions of (0 0 1)oxide, respectively. The in-plane lattice constant of Co clusters is ca. 4% larger than that of bulk Co, yielding less strain at the Co/oxide interface. A 15° ± 10% random orientation of the normal to (0 0 1) facet of Co clusters with respect to (0 0 1)oxide surface was deduced from the “arc”-shape reflection spots in RHEED. These results suggest that both orientation and phase of Co clusters are strongly affected by the nature and structure of oxide surface.     

Growth of Pt thin films on WSe2

The morphology and structure of Pt deposited on a WSe₂(0 0 0 1) van der Waals surface have been investigated by reflection high energy electron diffraction and scanning tunneling microscopy. At room temperature, the initial growth is characterized by the formation of three-dimensional fcc Pt islands with (1 1 1) orientation. In contrast, at higher temperatures of about 450 °C the formation of a novel chemically ordered Pt-Se alloy is observed. Based on the diffraction patterns, a tetragonal DO₂₂-type structure of a Pt₃Se compound is suggested. With increasing Pt thickness, this chemically ordered alloy disappears and an additional superstructure occurs, which is accompanied by the coalescence of the islands. The observed superstructure is attributed to a strong Se diffusion towards the growth surface, forming most likely a PtSe₂ alloy with the CdI₂-type layered structure on the top surface. Due to the lateral lattice mismatch between the Pt(1 1 1) layers and the PtSe₂(1 1 1) top layer, a Moiré pattern with a period of 1.1 nm is created, which might be used as a long-range atomic pattern for further nanostructure growth.     

Texture of molybdenum thin films on SrTiO3(1 0 0): A RHEED study

The structure of ultrathin Mo films on SrTiO₃(1 0 0) was studied by in situ reflection high-energy electron diffraction (RHEED). A different structure was observed for films less than 20 Å thick than for thicker films. These films were epitaxial and had a metastable structure. Thicker films had the dimensions of equilibrium bcc Mo(1 1 0). Relaxation processes transformed the metastable Mo into bcc Mo, resulting in the following orientation relationships between Mo and SrTiO₃: (1 1 0)[0 0 1]_bcc Mo ∥ (1 0 0)[0 0 1]_SrTiO3 and (1 1 0)[1 1 1]_bcc Mo ∥ (1 0 0)[0 1 1]_SrTiO3. The formation of such specific orientations is related to transformations via the Bain and Needle Path, respectively.     

Valuing of the critical layer thickness from the deading time constant of RHEED oscillation in the case of InxGa1−xAs/GaAs heterojunction

In this work, we have looked for the correlation between the observed decay of reflection high-energy electron diffraction intensity oscillation and the critical layer thickness in the case of strained In_xGa_1−xAs/GaAs heterojunctions. The value of deading time constant of oscillation depends on the mismatch and on growth parameters, too. The decay of oscillation was described by two deading time constants which are responsible for the influences of the parameters mentioned above. The critical layer thickness was valued from the deading time constant responsible for the influence of mismatch only. The critical layer thickness determined this way shows good agreement with the theoretical model.