Preferred structures of the atomic Ag islands on silicone oil surfaces

Varying the substrate temperature T(s) from 285 to 353 K, both the aggregation behavior of Ag atoms and the preferred structures of the atomic Ag islands on silicone oil surfaces are investigated. After deposition, the deposited Ag atoms form isolated islands with a preferred height. Our observations reveal that, as T(s) increases, the preferred island height increases from 20.0 to 33.0 nm, which results in the decrease of the Ag apparent coverage, from 9.6 ± 0.1% to 6.5 ± 0.3%. Further, the crystal structure of the Ag islands changes from amorphous to polycrystalline as the substrate temperature T(s) goes up. Subsequently a 3D aggregation mechanism of the Ag atoms on the liquid substrates is proposed.     

硅油基底表面铁薄膜的生长机理及表面有序结构

利用直流溅射方法在液体基底(硅油)表面成功制备出金属铁薄膜系统，研究了其生长机理及特征的表面有序结构.实验发现铁薄膜的生长过程与液相基底表面非磁性金属薄膜的情况类似，基本服从二阶段生长模型.连续铁薄膜中可观测到尺寸巨大的圆盘形有序结构，其生长演化与溅射功率、沉积时间和真空环境中的生长时间等实验条件密切相关.实验证明，此类有序结构是在薄膜内应力作用下，铁原子及原子团簇在液体表面自由扩散迁移，并最终在硅油基底表面某些区域成核凝聚所致.在较大溅射功率和沉积时间条件下，圆盘外部区域的铁薄膜中形成周期分布的波纹褶皱，其波长约为10 μm，波峰基本与圆盘的边界平行.进一步研究表明：在沉积过程中，由于沉积铁原子的局域能量作用，导致硅油的表面层结构发生改变而形成一聚合物层；在随后的冷却过程中，聚合物层的强烈收缩使铁薄膜处于很大的压应力场中，促使薄膜起皱形成波纹结构. 关键词： 液体基底 铁薄膜 生长机理 有序结构     

Comparison of electronic structures of mass-selected Ag clusters and thermally grown Ag islands on sputter-damaged graphite surfaces

Ag cluster anions consisting of 3–16 atoms were deposited on sputter-damaged HOPG surfaces using a soft-landing technique (mean deposition energy less than 0.2 eV/atom) at room temperature. For investigations of the structures of deposited clusters, X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were used. In addition, the chemical properties of deposited clusters were studied using atomic oxygen and CO. Comparison of the properties of deposited Ag clusters and Ag islands with similar sizes grown by evaporating Ag atoms on the same substrate shows different results, implying that two different preparation methods give either different shapes of Ag clusters and islands, or dissimilar metal–support interactions. PACS 73.22.-f     

Unified phase-field model for epitaxial growth of multi-scale three-dimensional islands on insulating surfaces

In this paper we present a unified phase-field model for non-equilibrium growths of various three-dimensional metal islands on insulating surfaces. We introduce a phase-field variable to distinguish the island from the non-island regions and substrate and a density variable to describe local density of deposited adatoms. Two partial differential equations with appropriate boundary conditions, as the governing equations, are used to describe the evolution of the three-dimensional metal islands and the diffusion of adatoms. We solve the equations by using an adaptive mesh refinement method so that we can simulate the non-equilibrium growth of three-dimensional metal islands from tens of nanometers to several micrometers. We investigate the dependence of simulated results on the model parameters and experimental conditions. Equilibrium shape of such islands can be obtained through sufficient post-deposition relaxation. Experimental trends of island size and shape on various scales are obtained with reasonable parameters. This method should be a good approach to non-equilibrium growths of multi-scale three-dimensional metal islands.     

液相基底温度对沉积银原子及其团簇凝聚过程的影响

研究了沉积银原子及其团簇在液相基底(硅油)表面的凝聚过程随基底温度的变化关系.实验结果表明:当硅油基底温度升高时,沉积银原子及其团簇的凝聚过程仍基本符合二阶段生长模型; 样品具有明显的边缘效应,在样品中心区域,凝聚体的覆盖率比边缘的相应值小,样品中心区域的凝聚体覆盖率先随薄膜名义厚度的增加迅速增大,然后逐渐趋于饱和,覆盖率趋于饱和时的膜厚值随基底温度的升高而降低; 对于一定的薄膜名义厚度,硅油基底温度越高,中心区域的凝聚体覆盖率越小.银原子凝聚体的分枝平均长度随基底温度的演化过程也具有类似的规律.对沉积银 关键词： 薄膜 液相基底 分枝状凝聚体 生长模型     

Effect of Polymer-Substrate Interactions on the Surface Morphology of Polymer Blend Thin Films

Surface structures and compositions of poly(Styrene-block-Ethylene/Butylene-block-Styrene) (SEBS)/Poly(Methyl Methacrylate) (PMMA) blend films have been studied by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). Substrates with different hydrophobicity and SEBS with and without Maleic Anhydride (MA) grafting were used to study the effect of polymer-substrate interactions. It is indicated that the surface energy of the substrate (substrate/air) plays a crucial role on the surface composition of the polymer component. For a fixed surface, the adsorption of polymer on the substrate is also important. The hydrophilic sites of SEBS-g-MA can prevent the dewetting of the SEBS-g-MA from the substrate. The dewetting of PMMA from the SEBS-g-MA will make the PMMA protrusions more pronounced, and the SEBS-g-MA phase domains are enlarged after annealing treatment. An adsorption scheme is suggested to explain the phase inversion and height difference observed in the various polymers used. In addition, SEBS triblock copolymers form wormlike and meshlike microphase separation morphologies on the hydrophilic and hydrophobic substrates, respectively.     

Fractal microstructure of Ag film via plasma discharge as SERS substrates

According to the atmospheric pressure plasma (APP) technology, we propose a rapid synthetic approach of the substrates for enhanced Raman spectroscopy. The plasma is used to modify and etch the surface of silver film, which generates large scale hotspots' aggregation. By switching the discharge polarity and adjusting the film thickness, different surface morphologies are formed due to the oxidation, reactive etch and accumulation of the plasma product in a certain space. Especially under positive corona discharge condition, dense snake-like microstructures are formed by the gradual connection of individual nanoparticles, which are driven by the influence of the electric field on surface diffusion. In addition, the experiments verify that the corresponding enhancement factor (EF) raises at least five orders of magnitude and the treatment time is about 10 min.     

纳秒激光烧蚀下液态金属表面微结构的形成

首次发现了在不同保护气体及多脉冲uV—IR激光的照射下,液态金属的微型突起和微结构的形成。测量表明,针对不同的金属和保护气,这种结构的单脉冲生成速率可达（5—20）μm／pulse,形成了长度为1～2mm,直径约为焦点两倍的单个微型突起。最后,介绍了控制微结构形状的可能性,并讨论了它们的应用潜力。     

Structure and reactivity of Pd doped Ag surfaces

We have performed first principles calculations for clean and Pd doped Ag(1 1 1) and Ag(1 0 0) surfaces, with and without adsorbed O and CO. Our results for the structure of the Pd doped Ag surfaces indicate that Pd atoms are located lower than the surrounding Ag surface atoms. We find that O atoms adsorbed on Pd doped Ag(1 1 1) reside at the fcc hollow sites, the site next to Pd being slightly favored. Moreover, we provide results for O and CO co-adsorption on the clean and Pd doped Ag(1 1 1) surfaces, indicating that Pd can act as an electronic promoter for the CO oxidation reaction.     

纳秒激光烧蚀下液态金属表面微结构的形成(英文)

首次发现了在不同保护气体及多脉冲UV-IR激光的照射下,液态金属的微型突起和微结构的形成。测量表明,针对不同的金属和保护气,这种结构的单脉冲生成速率可达(5～20)μm/pulse,形成了长度为1～2 mm,直径约为焦点两倍的单个微型突起。最后,介绍了控制微结构形状的可能性,并讨论了它们的应用潜力。     

Morphologies of epitaxial islands on a lattice-misfitted substrate

Under certain growth conditions for systems with a film/substrate lattice misfit, the deposited material is known to aggregate into island-like shapes. We have obtained an analytical expression of the total free energy, which consists of strain energy, surface energy and interfacial energy of a coherent island/substrate system, and the change of equilibrium aspect ratio versus the volume of the island and the misfit of lattices in the system, which provides a broad perspective on island behaviour. These then were used to study the equilibrium shapes of the system. The results show that in order to minimize the total free energy, a coherent island will have a particular height-to-width aspect ratio, called equilibrium aspect ratio, that is a function of the island volume and misfit. The aspect ratio is increased with increasing island volume at a fixed misfit, and with increasing misfit strain between the island and substrate at a fixed island volume. Moreover, the effect of misfit dislocation on the equilibrium shape of the island is also examined. The results obtained are in good agreement with experiment of observations and thus can serve as a basis for interpreting the experiments.     

Growth and stability of carbon islands on platinum surfaces

Details of the growth of C(graphite) islands and their stability on Pt surfaces were studied by FEM, UHV-SEM and very high resolution scanning AES. Initial nucleation of the C occurs on dislocations in the curved high index surface areas. Above 1150 K these randomly distributed islands dissolve and face specific layers are formed on {110} which can extend along the 〈100〉 zones all the way to the {100} planes. The sequence of stability of graphite layers on Pt is: {110} > all other {hk0} on the 〈100〉 zone except {100} > {100} followed closely by {111}. Concerning this layer stability, epitaxial mismatch plays a subservient role to the dipole interaction between metal substrate and graphite layer.     

Preferential heights in the growth of Ag islands on Si(1 1 1)-(7 × 7) surfaces

Growth behavior of thin Ag films on Si substrates at room temperature has been investigated by scanning tunneling microscopy and reflection high energy electron diffraction. In the layer-plus-island growth Ag islands show strongly preferred atomic scale heights and flat top. At low coverage (1 ML), islands containing two atomic layers of Ag are overwhelmingly formed. At higher coverages island height distribution shows strong peaks at relative heights corresponding to an even number (2, 4, 6, …) of Ag atomic layers. Beyond some coverage the height preference vanishes due to the appearance of screw dislocations and spiral growth.     

Magnetism of Fe clusters and islands on Pt surfaces

Clusters and islands of Fe atoms have been prepared by noble gas buffer layer assisted growth as well as by standard molecular beam epitaxy on Pt substrates. Xe buffer layers have been utilized to promote the formation of compact, relaxed Fe clusters with narrow size distribution. Without the Xe buffer, strained Fe islands with a characteristic misfit dislocation network are formed. Magnetization loops obtained by magneto-optical Kerr effect measurements reveal that in-plane easy magnetization axis is only found for the relaxed clusters, pointing out the important role of epitaxial lattice deformations for the magnetic anisotropy. PACS 61.46.+w; 68.37.Ef; 36.40.Cg; 75.75.+a     

Modification of bonding properties and microstructure of resin-cement interface by coupling agents

To solve the problem of organic-inorganic light conductive composite interface features, transparent resin and cement matrix were used as carriers to further study features of the organic-inorganic interface formed by transparent resin and cement matrix and the interface modification of the coupling agent. The bond strength, micro-hardness, microstructure and surface morphology of a resin light conductive cementitious materials (RLCCM) interface were evaluated by tests of tensile and oblique shear, micro-hardness, environmental scanning electron microscopy, and atomic force microscope. The results show that the silane A-151 and aluminate coupling agent could significantly improve interface bond properties of RLCCM. At 7 d, the interface tensile bond strength of the silane A-151 and aluminate coupling agent increased by 117 and 105%, respectively. At 28 d, strength on average increased by 73%. At 7 d, interface shear strength the silane A-151 and aluminate coupling agent of 45° increased by 43 and 53%, respectively, At 28 d, strength on average increased by 40%. The transparent resin performance weakened region thickness up to 100 μm; the hardness of the transparent resin in the transition region was increased by 19.6 and 39.9%, respectively. Silane coupling agent A-151 and cement hydration products formed flat spherical particles with diameter of approximately 78 nm, and these particles mosaicked and fused in the surface of the hydrate; therefore, the surface became denser and smoother.     

Structural evolution of silicone oil liquid exposed to Ar plasma

Structure properties of silicone oil serving as a liquid substrate exposed to Ar plasma are investigated in this paper. Under the action of energetic Ar ions, the surface of silicone oil liquid substrate exhibits a branch-like fractal aggregation structure, which is related to the structure evolution of silicone oil liquid from Si--O chain to Si--O network. The radicals from the dissociation of silicone oil molecule into the Ar plasma turns the plasma into a reactive environment. Therefore, the structural evolution of silicone oil liquid substrate and the reactive radicals in the plasma space become possible factors to affect the aggregation of nanoparticles and also the structures and the compositions of nanoparticles.     

真空热退火温度对单相Ag2O薄膜微结构和光学性质的影响

利用直流磁控反应溅射技术在玻璃衬底上沉积了单相Ag₂O薄膜,并采用真空热退火对单相Ag₂O薄膜在不同热退火温度 (T _{A) 下进行了1 h热处理.利用X射线衍射谱、扫描电子显微镜和分光光度计研究了 T A对单相Ag2O薄膜微结构和光学性质的影响.研究结果表明, T}A= 300 ℃ 时Ag₂O薄膜中开始出现Ag纳米颗粒,且随着 T _{A的升高薄膜中Ag的含量 关键词： 2}O薄膜')" href="#">Ag₂O薄膜 热退火温度 微结构 光学性质     

Effect of temperature on the phase behavior and microstructure of aggregates in SDS/Triton X-100/aH2O systems

The phase behavior and microstructure of a system containing polyoxyethylene tert-octylphenyl (Triton X-100), sodium dodecyl sulfate (SDS) and water were investigated using polarized optical microscopy (POM), differential scanning calorimetry (DSC) and small-angle X-ray diffraction (XRD). Phase-behavior study revealed that lamellar and hexagonal phases occurred in different compositions, and that lyotropic liquid crystal phases tended to form an H phase with increased Triton X-100 content. The effects of temperature on the phase behavior and microstructure of lyotropic liquid crystals were also studied. Heating induced a change from hexagonal to lamellar phase and from gel to hexagonal phase. POM and small-angle X-ray diffraction (SXRD) revealed that the phase-transition temperature of LLCs increased with increased Triton X-100 content, as further supported by DSC data.     

基底显微结构对薄膜生长影响的Monte Carlo模拟研究

利用Monte Carlo方法研究了基底显微结构对薄膜生长的影响. 对不同显微结构基底上薄膜生长的初始阶段岛的形貌和尺寸与薄膜覆盖度和入射粒子沉积速率之间的关系进行了模拟和分析. 模型中考虑了粒子沉积、吸附粒子扩散和蒸发等过程. 结果表明,基底显微结构对薄膜生长具有明显影响. 当沉积温度为300K、沉积速率为0.005ML/s（Monolayer/second,简称ML/s）、覆盖度为0.05ML时,四方基底上薄膜生长呈现凝聚生长. 随着覆盖度增加,岛的尺寸变大,岛的数目减少. 而对于六方基底,当覆盖度从0.05ML变化到0.25ML时,薄膜生长经历了一个从分散生长过渡到分形生长的过程. 无论是四方还是六方基底,随着沉积速率的增加,岛的形貌由少数聚集型岛核分布状态向众多各自独立的离散型岛核分布状态过渡.     

Role of patterning in islands nucleation on semiconductor surfaces

Quantum dots (QDs) grown on semiconductors surfaces are actually the main researchers' interest for applications in the forthcoming nanotechnology era. New frontiers in nanodevice technology rely on the precise positioning of the nucleation site and on controlling the shape and size of the dots. In this article we will review some recent studies regarding the control of the nucleation process on semiconductor surfaces. A few approaches to form ordered patterns on surfaces are described: natural patterning induced by surface instabilities (as step bunching or step meandering), in situ substrate patterning by Scanning Tunneling Microscopy (STM), high resolution patterning by Focused Ion Beam (FIB). Growth of epitaxial layers of semiconductors (Ge/Si(100) and InAs/GaAs(100)) on patterned surfaces has been studied by STM or Atomic Force Microscopy (AFM) unveiling the way in which the first atoms start to aggregate and identifying their exact nucleation site. Control of the dot size to match the patterning typical wavelength has been achieved by using surfactants on misoriented substrates. STM images acquired in real time allows one to identify the mechanism of Ge cluster formation on patterned Si(100), and to follow the island transition from pre-pyramid to pyramid. Nucleation of ordered Ge dots on SiO₂ substrates has been obtained thanks to FIB tight patterning, achieving island densities of 3.5×10¹⁰/cm². To cite this article: N. Motta et al., C. R. Physique 7 (2006).