Bimodal growth of Au on SrTiO3(001)

We have investigated the vapor phase growth of Au on SrTiO3(001)-(2 x 1) substrates by UHV scanning tunneling microscopy. Submonolayer (ML) coverages below 300 degrees C wet the surface as disordered metastable 2D islands. Beyond 0.75 ML fcc nanocrystals with a (111) interface are nucleated and ripen by dewetting the surrounding layer. Some multiply twinned fivefold symmetric clusters are also created. Above 400 degrees C dewetting occurs for all coverages and the surface is only populated by nanocrystals and fivefold clusters. A planar ground state configuration for small Au clusters and a higher interface energy for crystals than for wetted 2D ML films explains these results.     

The growth and chemisorptive propertles of Ag and Au monolayers on platinum single crystal surfaces: An AES,TDS and LEED study

The growth and chemisorptive properties of monolayer films of Ag and Au deposited on both the Pt(111) and the stepped Pt(553) surfaces were studied using Auger electron spectroscopy (AES), thermal desorption spectroscopy (TDS), and low energy electron diffraction (LEED). AES studies indicate that the growth of Au on Pt(111) and Pt(553) and Ag on Pt(111) proceeds via a Stranski-Krastanov mechanism, whereas the growth of Ag on the Pt(553) surface follows a Volmer-Weber mechanism. Au dissolves into the Pt crystal bulk at temperatures > 800 K, whereas Ag desorbs at temperatures > 900 K. TDS studies of Ag-covered Pt surfaces indicate that the AgPt bond (283 kJ mol^?1) is ～25 kJ mol^?1 stronger than the AgAg bond (254 kJ mol^?1). On the Pt(553) surface the Au atoms are uniformly distributed between terrace and step sites, but Ag preferentially segregates to the terraces. The decrease in CO adsorption on the Pt crystal surfaces is in direct proportion to the Ag or Au coverage. No CO adsorption could be detected for Ag or Au coverages above one monolayer at 300 K and 10^?8 Torr. The heat of adsorption of CO on Pt is unaltered by the presence of Ag or Au.     

Kinetic Monte Carlo simulations of Au clusters on Si(111)-7 × 7 surface

Self-assembled growth of Au nanoclusters on the Si(111)-7 × 7 surface has been studied using kinetic Monte Carlo simulations. A model considering various atomic processes of deposition, adsorption, diffusion, nucleation, and aggregation is introduced, and the main energetic parameters are optimized based on the experimental results. The evolution of surface morphology during Au growth is simulated in real time, from which the atomic behaviors of Au could be really captured. Most of Au atoms diffuse on the substrate in the very early stage of growth, and Au clusters nucleate and grow with the increasing coverage. The competition among various atomic processes results in the distinct distribution of Au clusters under different coverages. The growth conditions are further optimized, showing that the higher uniformity of Au clusters would be obtained at a low deposition rate and an optimal substrate temperature of about 380 K.     

Transmission of low-energy (< 10 eV) O ions through Au films on TiO2(110)

In an attempt to identify the fundamental processes that influence ion transport through metallic surface layers, we have studied the transmission of O⁺ ions through discontinuous Au films adsorbed on TiO₂(110). A low energy (< 10 eV) O⁺ ion beam is generated via electron stimulated desorption when an Au-dosed TiO₂(110) substrate is bombarded with a focused 250 eV electron beam. Low energy ion scattering data indicate that Au evaporated under ultrahigh vacuum conditions at 300 K forms three-dimensional clusters on TiO₂(110). As the Au coverage increases, the formation of Au clusters on TiO₂(110) blocks a fraction of the TiO₂ surface and the O⁺ yield is attenuated. However, for high coverages (≥30% Au covered substrate) the O⁺ signal decreases at a faster rate than the TiO₂ open area fraction. We attribute the attenuation of the O⁺ yield for high Au coverages mainly to blocking of O⁺ by Au clusters, to deflection of trajectories by the image force between ions and Au clusters, and to charge transfer between desorbing O⁺ and neighboring Au clusters.     

Ag growth on Si(111) with an Sb surfactant investigated by scanning tunneling microscopy

We have investigated a room-temperature growth mode of ultrathin Ag films on a Si(111) surface with an Sb surfactant using STM in a UHV system. On the Sb-passivated Si surface, small sized islands were formed up to 1.1 ML. Flat Ag islands were dominant at 2.1 ML, coalescing into larger islands at 3.2 ML. Although the initial growth mode of Ag films on the Sb-terminated Si(111) surface was Volmer-Weber (island growth), the films were much more uniform than Ag growth on clean (Si(111) at the higher coverages. From the analysis of STM images of Ag films grown with and without an Sb surfactant, the uniform growth of Ag films using an Sb surfactant appears to be caused by the kinetic effects of Ag on the preadsorbed Sb layer. Our STM results indicated that Sb suppresses the surface diffusion of Ag atoms and increases the Ag-island density. The increased island density is believed to cause coalescence of Ag islands at higher coverages of Ag, resulting in the growth of atomically flat and uniform Ag islands on the Sb surfactant layer.     

Electronic structure of Ag adsorbed on Si(111); experiment and theory

Experimental results (low energy electron loss spectroscopy) and band structure calculations relating to the early stages of Ag growth on a Si(111) surface are presented. Crystallography and thermal desorption kinetics studies of this interface, previously published, gave rise to the following conclusions. At room temperature and below 200°C, two-dimensional (2D) (111) epitaxial layers develop on top of a first ordered layer (√3 × √3), while at higher temperatures three-dimensional (3D) clusters develop over this first layer. Low energy electron loss experiments were performed at various surface coverages θ. They display different evolutions according to the growth modes. For the 2D epitaxial growth, one observes the disappearance of the peaks characteristic of a Si surface and the onset of Ag induced peaks located at 7.1 and 4.6 eV at completion of the √3 layer. These peaks narrow and shift to the bulk Ag excitation energies at 7.5 and 4 eV when a second Ag layer is deposited. In order to explain these results, we present a theoretical calculation of the electronic density of states of the interface using a tight binding approximation. This calculation accounts for the development of the Ag d band from the √3 coverage range to the (111) epitaxial Ag planes. The evolution of the spectra when θ is increased is discussed in view of these results.     

Ag(111)和Au(111)上铋的初始生长行为

半金属铋(Bi)的表面合金具有的Rashba效应,和其具体结构性质有重要关联.本文结合扫描隧道显微镜(STM)和密度泛函理论(DFT),系统地研究了Bi原子在Ag(111)和Au(111)上的不同初始生长行为.在室温Ag(111)上,连续的Ag2Bi合金薄膜会优先在Ag台阶边缘形成;在570 K Ag(111)上,随着...     

SURFACE PLASMON OF Ag CLUSTERS ON ALUMINA FILMS

The deposition of silver on an ordered alumina film prepared on Re(0001) surface has been studied by Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS). The results show that Ag grows initially as clusters at 90K and 300K. A red shift of the Ag surface plasmon as a function of decreasing coverage is observed, which is related to the cluster size effect. A surface plasmon characteristic of metallic Ag appears at coverages higher than 2.8 monolayer equivalent.     

Nucleation, growth and morphology of Co thin films on Ag(1 1 0)

Scanning tunneling microscopy (STM) experiments reveal that Co growth on Ag(1 1 0), at coverages of Co < 1 ML and low substrate temperatures (150 K), involves a concomitant insertion of Co into the top Ag layer and exchange of Ag out onto the surface. At 300 K, coverages of Co > 1 ML gives rise to a 3D nanocluster growth on the surface, with the clusters covered by Ag. Depending slightly on coverage, the clusters have a typical diameter of 3 nm and a height of 0.4 nm. Upon annealing to 500 K, major changes are observed in the morphology of the surface. STM and AES show that there is a reduction of the number of Co islands on the surface, partly due to subsurface Co cluster migration and partly due to sintering into larger clusters.     

Dy@C82分子在Au(111)表面依赖于覆盖度的取向研究

利用超高真空扫描隧道显微镜, 在低温(80 K)下研究了同分异构体分子Dy@C₈₂在Au(111)表面的吸附与分子取向．在低覆盖度下,Dy@C₈₂分子优先吸附于台阶边缘形成分子团簇与分子链结构．这种吸附取决于分子-衬底的相互作用,并存在多种不同的分子取向．增大分子覆盖度后,Dy@C₈₂在金表面形成二维有序密排的单层膜结构．Dy@C₈₂分子在金表面的取向倾向于其C₂长轴与金表面近乎平行．具有三种取向的分子最具优势,而同种取向的分子组成许多局限于一个个小区域内的取向有序结构畴．随着覆盖度的增加,Dy@C₈₂分子在Au(111)表面趋向于短程有序取向排列,这是由分子-衬底作用与分子间的偶极-偶极作用共同决定的．     

The surface structures growth’s features caused by Ge adsorption on the Au(111) surface

The initial stage of the adsorption of Ge on an Au(111) surface was investigated. The growth and stability of the structures formed at the surface were studied by ultrahigh-vacuum low-temperature scanning tunneling microscopy and analyzed using density functional theory. It was established that the adsorption of single Ge atoms at the Au(111) surface at room temperature leads to the substitution of Au atoms by Ge atoms in the first surface layer. An increasing of surface coverage up to 0.2–0.4 monolayers results in the growth of an amorphous binary layer composed of intermixed Au and Ge atoms. It was shown that the annealing of the binary layer at a temperature of T _s ? 500 K, as well as the adsorption of Ge on the Au(111) surface heated to T _s ? 500 K for coverages up to 1 monolayer lead to a structural transition and the formation of an Au–Ge alloy at least in the first two surface layers. Based on experimental and theoretical data, it was shown that the formation of single-layer germanene on the Au(111) surface for coverages ≤1 monolayer in the temperature range of T _s = 297–500 K is impossible.     

Gold at the Si(111)-Pd interface; modification of atomic interdiffusion

We present the results of an angle integrated photoemission (hv = 21.2eV) and Auger investigation of the effect of Au interlayers on the growth of the Si(111)-Pd interface. Gold does not remain totally blocked at the interface with increasing amounts of deposited Pd. As a consequence the same amount of Au (around 6 monolayers) acts as a promotor of Si-Pd mixing at low Pd coverages (below about 8 monolayers) and as an inhibitor at higher Pd coverages. The effect is dependent on the amount of Au so that Au at 10 monolayers is an inhibitor independent of the Pd coverage. The implications on the interface growth mechanism are discussed.     

LEED study of the epitaxial growth of the thin film Au(111)/Ag(111) system

An analysis of LEED data from the Ag(111) surface at room temperature and 5° ? Θ ? 16°, φ = 12° has been carried out in order to test three different model potentials for the exchange and correlation part of the one-electron LEED potential. Clean Au(111) surfaces have been grown on Ag(111) at room temperature at a deposition rate of 0.15 Å s^?1. Similar method of calculation and potentials have been employed for the Au overlay er on Ag(111). After the deposition of ? 2.5 monolayers of Au/Ag(111) the growth of Au can proceed in two different ways. One of them matches satisfactorily with the theoretical calculation for the Au(111) overlayer on Ag(111) following the fcc sequence. The other seems to be concerned with the diffusion of Ag during the Au growth. Similar curves have been obtained during the diffusion of Ag through 350 Å of Au(111).     

Adsorption of gold on hydrogen terminated Si(0 0 1): Formation of chain structure

Possible formation of stable Au atomic wire on the hydrogen terminated Si(0 0 1): 3×1 surface is investigated under the density functional formalism. The hydrogen terminated Si(0 0 1): 3×1 surface is patterned in two different ways by removing selective hydrogen atoms from the surface. The adsorption of Au on such surfaces is studied at different sub-monolayer coverages. At 4/9 monolayer (ML) coverage, zigzag continuous Au chains are found to be stable on the patterned hydrogen terminated Si(0 0 1): 3×1 surface. The reason for the stability of the wire structures at 4/9 ML coverage is explained. It is to be noted that beyond 4/9 ML coverage, the additional Au atoms may introduce clusters on the surface. The continuous atomic gold chains on the substrate may be useful for the fabrication of atomic scale devices.     

1-Hexadecylamine as both reducing agent and stabilizer to synthesize Au and Ag nanoparticles and their SERS application

1-Hexadecylamine (HDA)-capped Au and Ag nanoparticles (NPs) have been successfully prepared by a one-pot solution growth method. The HDA is used as both reducing agent and stabilizer in the synthetic process is favorable for investigating the capping mechanism of Au and Ag NPs’ surface. The growth process and characterization of Au and Ag NPs are determined by Ultraviolet–visible (UV–vis) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). Experimental results demonstrate that the HDA-capped Au and Ag NPs are highly crystalline and have good optical properties. Furthermore, surface-enhanced Raman scattering (SERS) spectra of 2-thionaphthol are obtained on the Au and Ag NPs modified glass surface, respectively, indicating that the as-synthesized noble metal NPs have potentially high sensitive optical detection application.     

Electron energy loss spectroscopy of the vibration modes of water on Ag(100) and Ag(115) surfaces and comparison to Au(100), Au(111) and Au(115)

Motivated by rather similar behavior of the Helmholtz capacitances of stepped Au(11n) and Ag(11n) electrodes we have extended a previous study on the vibration spectrum of water adsorbed at low temperatures on stepped gold surfaces to Ag(100), Ag(115) and Au(111) surfaces. On Ag(100) surfaces, the spectra show the presence of the typical H-bonded network of water molecules. The rather weak intensity, the absence of non-hydrogen bonded hydrogen atoms, the similarity to the infrared spectrum of ice crystallites, and the increase in the angular spread of the elastic peak are indicative of adsorption in form of three-dimensional clusters. This is stark contrast to Au(100) and Au(111) where the spectra match to a model involving stacks of water bilayers. The low coverage spectra on Ag(115) resemble the results on Au(115): A considerable fraction of the H-atoms remains in the non-H-bonded state and spectral features of water adsorbed at step-sites are identified. The first layer of water on Ag(115) surfaces should therefore have a similar structure as recently proposed in a theoretical study concerning water on Au(115). For larger doses, the experimental results on Ag(115) suggests the formation of three-dimensional clusters. This is contrary to Au(115) where the layered structure with a constant fraction of non-hydrogen-bonded H-atoms persists at higher doses.     

Theoretical study of structure and segregation in 38-atom Ag-Au nanoalloys

Ag–Au bimetallic “nanoalloy” clusters with 38 atoms have been studied using a Gupta many-body potential combined with a genetic algorithm search technique. Clear changes in structure are observed as a function of Ag/Au composition and there is a clear tendency for surface segregation of the Ag atoms. Cluster stability is found to increase with increasing number of Au-Au and Ag-Au bonds and the segregation has been rationalised in terms of bonds strengths and elemental surface energies.     

Synchrotron-Radiation Photoemission Study of Growth and Stability of Au Clusters on Rutile TiO2(110)-1×1

利用同步辐射高分辨光电子能谱研究了金团簇在部分还原TiO₂-(1×1)表面的生长和稳定性．价带谱实验结果观察到非常少量金团簇的沉积导致了Ti3+的3d峰完全消失,表明金团簇成核在TiO₂-(1×1)表面的氧缺陷位．Au4f芯电子光电子能谱实验结果证明了TiO₂-(1×1)表面氧缺陷位向金团簇转移电荷．还对比研究了化学剂量比和部分还原的TiO₂-(1×1)表面上金团簇的热稳定性．当金团簇尺寸相近时部分还原的TiO₂-(1×1)表面上金团簇要比化学剂量比的TiO₂-(1×1)面上金团簇稳定;在相同的表面上尺寸大的金团簇要比尺寸小的金团簇稳定．     

Growth and thermal stability of ultra-thin Ag and Au layers on Mo(1 1 1) surface

The influence of temperature on the growth process of ultra-thin Ag and Au layers on the Mo(1 1 1) surface was investigated. At 300 K growth of the Stranski-Krastanov type was found for Ag; for Au growth of the monolayer plus simultaneous multilayers type was found, where a base layer is one physical layer. The first three geometrical adsorbed layers for Ag are thermally stable. For annealed Au layers triangle features with base side length from 15 to 35 Å were formed for θ < 6 monolayer (ML), and for θ > 6 ML part of the Au formed a flat adlayer with Au atoms grouped in equilateral triangles with side length 7 Å. The presence of Au layers does not cause faceting, layers are not smooth which could be caused by the fact that Au does not wets the substrate. For Ag thick layers reversible wetting/non-wetting transition was observed at 600 K. Ag layers on Mo(1 1 1) surface did not lead to faceting.     

Photochemical Synthesis and Properties of Colloidal Copper,Silver and Gold Adsorbed on Quartz

Original methods for the photochemical production of stable copper, silver and gold colloids in the form of films on quartz, and dispersion in liquids were devised. It is shown that photochemical synthesis of colloidal metals is a difficult multiphase process, and includes the formation of low-valence forms of Cu(I), Au(I) and nonmetal clusters, colloidal particles and their agglomerates. Cluster stabilization and further growth to colloidal particles are achieved by adsorption onto the solid surface (quartz) or by increasing the viscosity of photolyte. In the absence of these methods of stabilization, the processes of intermediate reoxidation to Cu(II) and Au(III) and agglomeration of Ag and Au colloids proceed in a photolyte. Adsorption and the rate of cluster growth on a quartz surface are speeded up by the action of monochromatic UV light. Experimental models of the mechanism of colloidal formation are suggested. The dependence of the growth rate and the properties of the colloids on conditions of the photochemical procedure (energy and light intensity, concentration of initial complex) has been established.