Fe Nanoclusters on the Ge（001） Surface Studied by Scanning Tunneling Microscopy,Density Functional Theory Calculations and X-Ray Magnetic Circular Dichroism

The growth of Fe nanoclusters on the Ge(001) surface has been studied using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. STM results indicate that Fe nucleates on the Ge(001) surface, forming well-ordered nanoclusters of uniform size. Depending on the preparation conditions, two types of nanoclusters were observed having either four or sixteen Fe atoms within a nanocluster. The results were confirmed by DFT calculations. Annealing the nanoclusters at 420 K leads to the formation of nanorow structures, due to cluster mobility at such temperature. The Fe nanoclusters and nanorow structures formed on the Ge(001) surface show a superparamagnetic behaviour as measured by X-ray magnetic circular dichroism.      

Dehydrogenation properties of La-doped NaAlH4 (001) surface: A first-principle approach

First-principles calculations based on density functional theory have been performed to study the effects of La atom on the structural, electronic, and dehydrogenation properties of NaAlH₄ (001) surface. A LaAl₄H₁₈ complex structure is found in the La atom doped NaAlH₄ (001) surface. Two new peaks are imported into the density of state of La-doped NaAlH₄ (001) surface at −1.46 and Fermi level due to the effect of La d orbitals. The analyses of bond length and electronic properties show that it is favorable to form LaAl phase. The average hydrogen removal energy of La-doped NaAlH₄ (001) surface decreases to 2.390 eV, which is smaller than that of pristine NaAlH₄ (001) surface. The characteristic illustrates that doping La favors the dehydrogenation reaction of NaAlH₄. The improved dehydrogenation in the La-doped NaAlH₄ (001) surface may be attributed to the weakening of Al–H bond.     

Energy level of compensator states in (001) phosphorus-doped diamond

The energy level of acceptor-type compensator states in (001) phosphorus-doped diamond is examined by combining the techniques of cathodoluminescence analysis, Hall-effect measurements, secondary ion mass spectroscopy, and capacitance-voltage measurements. The capacitance-voltage properties of metal/n-type semiconductor contact are known to be a sensitive tool for evaluating deep levels. The slope of the inverse of the square of capacitance provides the distribution of space charge density in the n-type layer, and this density strongly depends on the relationship between the deep level and the surface Fermi level. In this study, we use this relationship to characterize the energy level of compensator states. The donor and acceptor densities in (001) n-type diamond are determined by low-temperature cathodoluminescence analysis and Hall-effect measurements. The electrical activity of doped phosphorus atoms is also discussed.     

GaSb(001) Surface Reconstructions Measured at the Growth Front by Surface X-ray Diffraction

Surface x-ray diffraction was employed, in situ, to measure the GaSb(001)-(1 × 5) and (1 × 3) surface phases under technologically relevant growth conditions. We measured a large set of fractional-order in-plane diffraction peaks arising from the superstructure of the surface reconstruction. From the data we calculated two-dimensional (2D) Patterson functions, the peaks of which represent inter-atomic distances weighted by the number of electrons in the individual atoms. For the (1 × 3) phase we obtained good agreement between our data and the β(4 × 3) model proposed in recent experimental and theoretical work. Our measurements on the Sb-rich (1× 5) phase provide evidence that the structure under growth conditions is, in fact, different from that of the models previously suggested on the basis of scanning tunneling microscopy (STM). We discuss reasons for this discrepancy as well as the identified structural elements for these reconstructions, which include surface relaxations and subsurface rearrangement.     

Surface effects on the Frenkel pair defects stability in the vicinity of the Si(001) surface

A systematic first-principles pseudo-potential study of the stability of tetrahedral Frenkel pairs generated in the vicinity of the silicon Si(001)-(2×1) surface is reported. The defect formation energies and associated structures are discussed. We demonstrate that vacancies that are generated close to the surface are subject to annihilation processes either through recombination of the Frenkel pairs or through surface amorphization. On the other hand, interstitials that are positioned on the subsurface exhibit specific behaviors compared to those located deeper inside the bulk Si. Calculations indicate that the tetrahedral interstitial is unstable when located close to the surface and it relaxes to form a split-110 (dumbbell) configuration. In deeper layers, the tetrahedral interstitial remains rarely stable; it relaxes to hexagonal or to fourfold-coordinated configurations. The defect formation energies are given as a function of surface–vacancy and interstitial–vacancy distances. Results indicate that the formation energy is considerably reduced as the interstitial approaches the surface.     

Fabrication of GaN epitaxial films on Al_2O_3/Si (001) substrates

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The synthesis of nitrogen/sulfur co-doped TiO2 nanocrystals with a high specific surface area and a high percentage of {001} facets and their enhanced visible-light photocatalytic performance

In this article, we study superfluid behavior of a gas of spatially indirect magnetoexcitons with reference to a system of two graphene layers embedded in a multilayer dielectric structure. The system is considered as an alternative of a double quantum well in a GaAs heterostructure. We determine a range of parameters (interlayer distance, dielectric constant, magnetic field, and gate voltage) where magnetoexciton superfluidity can be achieved. Temperature of superfluid transition is computed. A reduction of critical parameters caused by impurities is evaluated and critical impurity concentration is determined.     

Nitrogen doped anatase TiO2 sheets with dominant {001} facets for enhancing visible-light photocatalytic activity

The photocatalytic activity of TiO₂ can be mainly improved from three approaches: (1) enhancing surface energy; (2) increasing availability of visible light and (3) improving the separation efficiency of photo-induced electrons and holes. Here, we report a one-step route to obtain nitrogen (N) doped TiO₂ sheets with dominant {001} facets by a hydrothermal process. The XRD patterns confirm the better crystallinity. XPS spectrums show nitrogen acting as interstitial N or an O–Ti–N structure in TiO₂ sheets. Compared with that of TiO₂ sheets, the N doped TiO₂ sheets not only absorb visible light, but also have a large percentage of high reactive {001} facets, so the photocatalytic activities are greatly enhanced, as confirmed by the decomposition of methylene orange.     

Atomistic simulations of the Fe(001)–Li solid–liquid interface

Using EAM potentials and molecular dynamic simulations, the Fe(001)–Li solid–liquid interface is characterized in details with density, potential energy, stress, diffusion coefficient profiles, interface width and two-dimensional density map. In addition, the temperature effect on these quantities is also studied. The diffusion coefficient profile indicates Li atoms near the interface diffuse more difficultly. The interface width, calculated from coarse-grained density profile or potential energy profile, increases exponentially with increasing temperature. A “prefreezing” Li layer is observed. Moreover, the two-dimensional density maps for Li and Fe atoms in the first interfacial layer show clearly that Fe and Li formed immiscible two-dimensional domains, rather than an intermixed interfacial alloy.     

川东南丁山与焦石坝地区五峰组—龙马溪组页岩气富集条件差异分析与思考

四川盆地东南缘（川东南）丁山构造五峰组—龙马溪组页岩气勘探已取得突破,但相比涪陵页岩气田焦石坝构造,其富集高产因素又体现出其自身的特殊性。以四川盆地丁山和焦石坝地区五峰组—龙马溪组为研究对象,综合利用钻井、测井、地震及分析化验等资料,明确了两地区主要富集条件的差异性,建立了2种目标类型页岩气成藏富集模式,研究发现：（1）丁山优质页岩层段TOC≥3%的页岩仅发育于五峰组—龙马溪组一段①—③层,厚15~19 m,明显比焦石坝薄（焦页1井近38 m）;（2）丁山构造保存条件明显受齐岳山断裂控制,平面上远离齐岳山断裂、埋深更大的斜坡带和深埋平缓带页岩气层压力系数、孔隙度和含气量明显增大,而焦石坝构造保存条件明显受周边控制构造的断裂影响,压力系数、孔隙度和含气量仅在断裂附近出现明显的降低;（3）丁山优质页岩层段在自身脆性方面与焦石坝无明显差异,但由于埋深变化较大,埋深处于3 500~4 500 m富集区的优质页岩层段的地应力、岩石破裂压力明显增大。研究认为沉积环境造成了两地区页岩原生品质具有一定的差异,其中丁山属于“较快速海退型”陆棚相沉积,而焦石坝属于“缓慢海退型”陆棚相沉积;而控制构造的断裂是造成页岩气逸散方式和程度不同的主要因素。根据以上特点,建立了丁山 “齐岳山断裂带主体控制、浅埋藏区垂向、横向联合逸散、深埋藏区富集”的盆缘“鼻状断背斜富集型”、焦石坝盆内“控边断裂垂向逸散为主、横向逸散微弱、主体稳定区富集”的“断背斜富集型”成藏富集模式。