Nucleation Of Au Research Articles

Heterogeneous nucleation and epitaxial growth of Au on the Co decorated Au(111) surface investigated by scanning tunneling microscopy

The growth of Au on the Co decorated Au(111) surface has been studied by scanning tunneling microscopy. The decoration causes an increased sticking probability of the Au atoms to the Co covered elbows of the herringbone reconstruction until they are totally covered with Au. It is concluded that the attraction of the Co islands is strong enough to prevent the Au atoms from diffusing into subsurface layers (random growth mode) at room temperature, eventhough the Au layer is also far from growing in a layer-by-layer growth mode. The decoration of the substrate steps with Co islands enables the observation of the detailed changes in the morphology of the growing Au steps.

The Nucleation and Epitaxial Growth of Au and Ag on Thin Silicon Studied With a Scanning Transmission Electron Microscope

ABSTRACTAn UHV Scanning Transmission Electron Microscope (STEM) has been used to study the nucleation and epitaxial growth of Au and Ag deposited at room temperature on H-passivated thin silicon (111) and (100) substrates. Direct observations of the initial stages of overlayer growth were made using bright field (BF) and annular dark field (ADF) imaging modes. Gold was found to grow on silicon in a quasi-continuous layer mode, while 3D island growth with density as high as 4×1012/cm2 was observed in Ag/Si systems. Electron diffraction studies reveal a good epitaxial relationship for Ag films grown both on silicon (111) and (100) substrates. Diffraction also indicates that Au (111) grows on the silicon (111) surface but the grains may be azimuthally rotated.

Photoelectrochemically‐Induced Gold Deposition on p ‐ GaAs Electrodes: Part I . Nucleation and Growth

This paper reports on the deposition of Au on cathodically biased electrodes from alkaline solutions in the dark or under illumination. Nucleation and growth of Au have been studied by potentiodynamic and potentiostatic current measurements in combination with scanning and transmission electron microscopy. Au deposition is characterized by progressive nucleation and three‐dimensional growth followed by coalescence of Au particles. Different mechanisms of electron transfer processes occurring during nucleation and growth are discussed. Au nucleation in the dark occurs readily at relatively high‐doped electrodes, both in the absence and presence of excess CN−ions. Selective photoinduced nucleation is possible on low‐doped electrodes in a solution with excess CN−ions. It is observed that the critical size of Au nuclei is smaller than 1 nm. Growth of previously formed Au nuclei can proceed in the dark and is initially controlled both by kinetic factors and diffusion of ions. Our results indicate that only a small potential barrier exists between and deposited Au particles.

Note on a theory of three-dimensional electrochemical nucleation with diffusion-controlled growth

Recently a theory was developed by which the number density of nuclei could be obtained from the current maximum of a single-step potentiostatic experiment in the case of three-dimensional nucleation followed by diffusion-controlled growth. It is shown that this theory is based on unrealistic assumptions which cause the calculated nuclear number densities to be much lower than the densities observed experimentally in an electron microscope. Results of a study of Au nucleation on GaAs are reported to illustrate some of the effects which may hamper an exact analysis of the current transient.

Image Processing for Electron Microscope Investigations of Materials

ABSTRACTA time shared television digital image processing system has been developed for on-line electron microscopy and uses a large mainframe computer. The main component of the system is a digital television frame store which has many standard features for digital analysis such as: digitization, zoom and pan, arithmetic and Boolean processors, alphanumeric generators and so on. Images can be acquired at atomic resolution from a TEM, analyzed in real time and hard copy slides made under full computer control. A full range of computer software has been developed or modified from existing software and is generally compatible with IBM Fortran compilers. Some of the areas where extensive menu driven software has been developed are: particle size and feature analysis, algebraic and geometric image manipulations, Fourier analysis, digitization and process control, image contrast correction, text processing, etc. A number of applications areas have been explored which include: the structure of Si/SiO2interfaces; nucleation of Au on rocksalt; the formation of hexatic structures from amorphous phases under shear, tension and compression; analysis of atomic surface structure and image motion and the analysis of field ion micrographs of amorphous structures. Several of these areas will be discussed in the context of image processing and materials characterization.

New experimental results on nucleation of Au on NaCl: Dependence on deposition rate and time

AbstractSystematic experiments have shown that saturation density, nucleation rate, and condensation coefficient are considerably smaller than previously reported. The low condensation coefficient and the linear deposition rate dependence of the nucleation rate show that the model usually applied for the theoretical explanation of the nucleation process needs some revision. From measured condensation coefficients we have estimated the diffusion length of adatoms, xs = (14.4 ± 2.4) nm, and the difference between desorption and diffusion energy, Ea – Esd = (0.31 ± 0.01) eV. Possible reasons for the deviation of the new results from the earlier ones are discussed.

Preferential nucleation of Au on Mn-doped NaCl crystals

Preferential nucleation of Au on Mn-doped NaCl crystals

Effect of Au nucleation centres and deposition rate on crystallinity and electronic properties of evaporated Te films: K Okuyama et al, J Appl Phys, 46 (1) 1975, 105–111

Effect of Au nucleation centres and deposition rate on crystallinity and electronic properties of evaporated Te films: K Okuyama et al, J Appl Phys, 46 (1) 1975, 105–111

Grain growth of evaporated Te films on a heated and cooled substrate

The effect of the substrate temperatures in a wide range between −150 and 270 °C on the grain size, crystal orientation, Hall mobility, and the carrier concentration of evaporated Te films has been investigated. The grain size and the corresponding Hall mobility were observed to increase remarkably with increasing substrate temperature above 50 °C and with decreasing temperature below 50 °C, contrary to the expectation. The carrier concentration decreased with increasing substrate temperature. The influence of Au nucleation centers on the crystallinity and electronic properties were also investigated. An x−ray diffractometer study indicated c−axis texture to occur with improving grain growth.

Effect of Au nucleation centers and deposition rate on crystallinity and electronic properties of evaporated Te films.

The effect of Au nucleation sites, deposition rates, and the film thickness on the crystallinity and electronic properties of evaporated Te films has been investigated. It has been found that to obtain large−grain Te films there exists an optimum conditoin in the coating ratio of Au nucleation sites and the film thickness of Te, and that a fast deposition rate of Te results generally in large−grain Te films with preferred orientation. The best films obtained have shown a grain size of 20−30 μ diameter with the c axis parallel to the substrate and a Hall mobility of 170 cm2 V−1 sec−1.

The initial stages of thin film growth

Recent developments in theoretical and experimental studies of thin film nucleation and initial growth are reviewed. Theoretical work has been concerned mainly with predicting the variation of cluster density with deposition time, atom impingement rate and substrate temperature. Theories now include cluster coalescence behaviour and explore nucleation, growth and coalescence effects into the stages of growth that are readily studied by experiment. Carefully controlled experiments have recently been carried out on the nucleation of Au and Ag on alkali halide substrates; these are discussed in the light of recent theories. Experiments from which information about adatom loss processes may be deduced are also described. It is concluded that current theoretical approaches need to be modified to include several features that are implied by these experiments, particularly the influence of tight-binding substrate sites and the mobility of clusters on the substrate.

Nucleation of Au and Ag on alkali halide substrates

The nucleation and initial growth model developed by Routledge and Stowell has been used to analyse the experimental data obtained by Robins and co-workers for Au and Ag deposited onto alkali halide substrates. It is shown that, although nucleation parameters can be readily deduced for these systems, the agreement between theory and experiment is not wholly satisfactory. The discrepancies may be partly removed by modifying the original calculations to account for dimer mobility but cluster size distribution effects are significant and need to be incorporated into the theoretical model in order to obtain a more detailed description of the experimental results.

In-Situ Deposition of Gold on MgO

The epitaxial nucleation and growth of Au on (100) MgO substrates has recently been studied by in-situ electron microscopy methods but under poorly controlled environmental and deposition conditions using beam-cleaved thin MgO substrates. Gold on MgO has also been investigated by LEED or replica electron microscopy. Here bulk substrates cleaved in UHV were used under well controlled deposition conditions. The results of the insitu experiments and the studies on bulk substrates, however, showed appreciable differences: The bulk studies produced epitaxy at substrate temperatures as low as 100°C, whereas in the in-situ case the respective substrate temperature for epitaxy was well above 400°C; furthermore, nucleation measurements on bulk MgO seemed impurity-controlled with temperature-independent saturation densities, and strong electron irradiation of the substrate during deposition caused the appearance of an unexpected (111)-orientation.We have repeated such studies in-situ under clean, well-controlled UHV-conditions and confirmed most of the results on bulk substrates except the nucleation kinetics.

Analysis of the nucleation of Au on MgO

The data of Robins and Rhodin for the nucleation rate of Au on MgO are analyzed using classical nucleation theory. When the number of potential nucleation sites is assumed to be 1.1 × 10 15 per cm 2, a “Pound” plot of the data is linear and a reasonable value of θ = 44° is obtained for the contact angle. However, the radius of the critical sized nucleus is only 4 Å and the difference in activation energies for desorption and surface diffusion, Δ G des − Δ G sd, is an unrealistic − 0.19eV. When the number of potential nucleation sites is assumed to be 3.5 × 10 11 per cm 2, the reasonable values of θ = 38° and Δ G des − Δ G sd = 0.16 eV are obtained, but the radius of the critical sized nucleus is still only 4 Å. It is concluded that their data can be interpreted by the formalism of classical nucleation theory only in a phenomonological sense.

Nucleation and Surface Conditions

The nucleation of Ag and Au on alkali halides is discussed excluding the influence of adsorbed gas layers. In particular, the problems of nucleation density and of the orientation of nuclei with respect to the substrate crystal are treated. The influence of defects in the surface on nucleation density is discussed in detail. Some principal aspects necessary for a theoretical treatment are pointed out. A review of the problem of the orientation of nuclei is given. An explanation of some recent results, the possible influence of electrical double layers (Debye-Frenkel layers) in the surface region is discussed.

Nucleation and growth of gold on defined silver faces

A study has been made of nucleation and nucleus growth of Au by evaporation on (111) faces of silver crystals produced by a method which gives atomically smooth surface regions between monoatomic steps at distances up to 1 μm. In the temperature range 20–150°C time-dependent adsorption exists, and re-evaporation of the gold atoms can be neglected. By measurement of the critical time at which the first gold nuclei can be observed electron-microscopically, the critical adatom concentration necessary for nucleation can be determined. After a sufficiently long deposition period, a maximum nucleus density is reached. The growth processes at maximum nucleus density is treated with regard to the most simple case of growth of parallel steps. Provided that in the stationary case the maximum adatom concentration between steps where the nuclei no longer can be observed is equal to the critical concentration necessary for the nucleation, the diffusion coefficient of Au on a (111) Ag face can be calculated from the critical nucleation time and the maximum step distance. During continuous growth the gold nuclei degenerate dendritically to a high degree. An estimation shows that the gold nuclei can have a thickness of only a few atom layers.

Electron microscope studies of the mechanism of nucleation and growth of Cu Au ii from the disordered state

2014 Thin single crystal films of Cu Au prepared by evaporation have been studied on a hot stage inside the electron microscope. The alloy is disordered by annealing at 450 °C, and the nucleation and growth of ordered regions is studied as the temperature is lowered to some value in the range 380-400 °C. By use of dark field microscopy on superlattice reflections, the distri- bution of ordered nuclei within a disordered matrix is studied in detail, as well as the orientation distribution within the ordered nuclei. This latter distribution is explained in terms of (101) twinning of the Cu Au. Evidence is obtained that dislocations modify the growth of the ordered phase in their vicinity, and that in some circumstances preferential nucleation of order occurs on the dislocations. These observations are being compared with studies of the nucleation of order produced in bulk alloy which is thinned after the heat treatment. LE JOURNAL DE PHYSIQUE ET LE RADIUM TOME 23, OCTOBRE 1962,