Epitaxial Growth Of Au Research Articles

Pd–Au Heteropentamers: Selective Growth of Au on Pd Tetrahedral Nanoparticles with Enhanced Electrocatalytic Activity

We developed a seed-mediated approach for the selective growth of Au-on-Pd tetrahedral nanoparticles giving rise to Pd–Au heteropentamers. The size of the Au domains in the heterostructures could be finely tuned from 5 to 8 nm. High-resolution transmission electron microscopy characterization demonstrated that the heteromers are single crystalline indicating an epitaxial growth of Au on Pd. The modification of screen-printed carbon electrodes with Pd–Au heteromers shows an improved electrocatalytic activity.

Simultaneous determination of hydroquinone and catechol using a glassy carbon electrode modified with Au@Pd loaded on reduced graphene oxide

Au@Pd core–shell nanoplates were synthesized successfully through the heterogeneous, epitaxial growth of Au on Pd nanoplates.

Evolution of the electronic structure during the epitaxial growth of Au on Pt(100)

We report an angle-resolved photoemission study of the electronic structure of Au layers grown epitaxially on Pt(100) in the coverage range 1–10monolayers (ML). Our results include an analysis of the electronic band structure and the Fermi surface, combined with structural information from low-energy electron diffraction. The Au films grow epitaxially with a (1×1) pattern up to 4–5ML. We monitor the electronic band structure near the surface X¯-point vs. Au coverage. In the 1–3ML range we observe interface electronic states related to the formation of a Au–Pt alloy in this coverage range. Starting at 2–3ML coverage, we identify quantum well states from the incipient Au sp band, which converge into a bulk like Au sp band near 6ML. After 5–6ML, a (1×7) pattern is observed, due to the formation of a surface reconstruction in the epitaxial Au film with a topmost hexagonal layer, as in the reconstruction of bulk Au(100). We identify specific electronic states of quasi-one-dimensional character coming from the corrugated hexagonal layer. We obtain a complete picture and understanding of the electronic structure of Au/Pt(100), including sp Au band formation, hybridization and electronic confinement, and with implications in the understanding of the distinct electronic behavior of Au layers and particles in the nm size range.

Epitaxial Growth of Au on Pt (111) and Pt (poly) by Surface Limited Redox Replacement of Pb UPD Layer

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The synthesis and optical properties of the heterostructured ZnO/Au nanocomposites

ZnO/Au heterostructured nanoparticles were formed through epitaxial growth of Au on the ZnO seeds. The morphology and structure of ZnO/Au nanocomposites were investigated by TEM and XRD analysis. The nanocontact between Au and ZnO results in red-shift of surface plasmon of the Au and increase the intensity of Raman signals of ZnO. Heterostructured ZnO/Au nanocomposites also enhance chemical stability of ZnO in aqueous solution.

Epitaxial growth of Au(1 1 1) on α-Al 2O 3(0 0 0 1) by using a Co seed layer

The influence of a Co seed layer on the structure of Au films grown onto α-Al 2O 3(0 0 0 1) single crystal substrates by molecular beam epitaxy has been studied by reflection high energy electron diffraction (RHEED). The RHEED results proved that the initial deposition of a few monolayers of Co onto Al 2O 3(0 0 0 1) prior to the Au deposition yielded high-quality fcc Au(1 1 1)-oriented epitaxial films and a well-known (23×1) surface reconstruction structure. Based on the RHEED results, it was concluded that the adhesion energy between the Co seed layer and Al 2O 3 substrate was rather important than the lattice mismatch between them.

Growth of thin Co films on W( [formula omitted]) and Au( [formula omitted]) layers prepared on Al 2O 3( [formula omitted

Thin epitaxial W(1 1 0)/Co and Au(1 1 1)/Co films were prepared by molecular beam epitaxy on single crystal sapphire Al 2O 3(1 1 2 ̄ 0) substrates and investigated by means of low energy electron diffraction and Auger electron spectroscopy. The growth of W on Al 2O 3(1 1 2 ̄ 0) was found to depend strongly on substrate temperature and film thickness. W films deposited at a substrate temperature T p=1200 K with a film thickness d W⩾100 Å revealed a bcc(1 1 0) structure with a mean terrace size of 40 Å. Epitaxial growth of Au was achieved at T p=300 K with a layer thickness d Au=30 Å for a deposition onto the W(1 1 0) substrate layers. The structural properties of thin Co films grown at T p=300 K on the W(1 1 0) and Au(1 1 1) substrate layers were studied as a function of Co film thickness for wedge-shaped layers. The Co films were found to grow epitaxially in both cases with distinct growth modes and lattice strains.

Effect of substrate temperature on the epitaxial growth of Au on TiO 2(1 1 0)

We have studied the effects of substrate temperature on the epitaxial growth of Au on TiO 2(1 1 0) surface by combined high resolution scanning electron microscopy and electron backscatter diffraction. The Au was evaporated under UHV conditions onto stoichiometric and unreconstructed (1×1) TiO 2(1 1 0) surfaces. Two deposition conditions were used consisting of RT deposition followed by annealing at 775 K and direct deposition at 775 K. Two different epitaxial orientations have been observed for the two conditions. After room temperature deposition and annealing, the epitaxial orientation relationship is (1 1 1)Au//(1 1 0)TiO 2 with 〈1 1 0〉 Au//[0 0 1]TiO 2. While for direct deposition at high temperature the epitaxial orientation relationship is (1 1 2)Au//(1 1 0)TiO 2 with 〈1 1 0〉 Au//(0 0 1)TiO 2. For both orientations, two epitaxial variants are observed which are rotated from each other by 180° around the TiO 2(1 1 0) surface normal. These two variants are in a twin orientation relationship. For the high temperature deposition, extensive (1 1 1) twinning of the Au islands is observed which are the boundaries separating two orientation variants.

Real-time x-ray scattering study of surface morphology evolution during ion erosion and epitaxial growth of Au(111)

We describe a detailed real-time x-ray scattering study of the evolution of the surface morphology of Au(111) both during ion erosion with 500-eV ${\mathrm{Ar}}^{+}$ ions, and during homoepitaxial growth. We monitor the erosion and growth morphologies as a function of substrate temperature. We also monitor the surface reconstruction, since it is known to play an important role in determining growth regimes on Pt(111). Ion irradiation of Au(111) leads to surface morphology evolution by step retraction above 270 \ifmmode^\circ\else\textdegree\fi{}C and quasi-layer-by-layer removal at 90--220 \ifmmode^\circ\else\textdegree\fi{}C. The extent of the surface reconstruction on Au(111) during ion irradiation gradually decreases with decreasing temperature. While the herringbone reconstruction remains during ion irradiation at 270 \ifmmode^\circ\else\textdegree\fi{}C, the long range order is lost and only the (22\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$) reconstruction is present at 170 \ifmmode^\circ\else\textdegree\fi{}C. We also observe layer-by-layer growth in the Au/Au(111) system at 55--145 \ifmmode^\circ\else\textdegree\fi{}C, a result that differs from the usual behavior of homoepitaxy on fcc(111) surfaces. As in the layer-by-layer erosion regime, only the (22\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$) reconstruction is present during layer-by-layer growth. Room temperature ion irradiation leads to a (1\ifmmode\times\else\texttimes\fi{}1) surface structure and a three-dimensional rough morphology exhibiting pattern formation with a characteristic lateral length scale. Line-shape analysis of the diffuse scattering in transverse x-ray scans taken during low temperature ion irradiation, indicates that the characteristic lateral length scale increases with time consistent with a power law $l\ensuremath{\sim}{t}^{0.28}.$ This agrees with a simple analysis of the position of the satellite peak in the diffuse scattering in these transverse x-ray scans.

Temperature induced change of surface roughness of Au(1 1 1) epitaxial films on mica

The epitaxial growth of Au(1 1 1) on mica was studied using scanning tunneling microscopy (STM). Structure and surface roughness of 100 nm thick films evaporated at substrate temperature in the range 580–890 K was examined at deposition rates of 0.2 and 0.5 nm/s. Decrease of the surface roughness at some temperature depending on the deposition rate was observed. It can be explained considering a critical island size R c at which a new layer nucleates on top of the Au(1 1 1) island. The critical size increases with temperature much faster than the size of available 3D islands formed during coalescence on mica substrate. Consequently, at lower temperatures 2D nucleation on the top of pre-deposited 3D Au islands can be observed while at higher temperatures no nucleation takes place and adatoms fill gaps between islands.

Cross-sectional time-resolved high-resolution electron microscopy of epitaxial growth of Au on MgO

Vapor phase epitaxial growth techniques are indispensable for production of thin film electric devices. Various structural analyses have been attempted to evaluate the epitaxial growth. Conventional transmission electron microscopy (CTEM) is a most useful method. In particular, it is known that a plan-view time-resolved CTEM of in-situ vacuum-deposition in a microscope can analyze each process of epitaxial growth. The nucleation in vacuum-deposition was also in-situ observed by a time-resolved high resolution electron microscopy (TRHREM). However many unresolved problems still remain in the studies of the epitaxial growth because it is difficult to observe the epitaxial interfaces less than a few nanometer under appropriate conditions. Much more advanced techniques are required for electron microscopy to obtain detailed information.In the present study, a TRHREM for the cross-sectional observation was developed to elucidate the epitaxial growth process in vacuum-deposition.Gold (Au) was vacuum-deposited on (001) surfaces of the magnesium oxide (MgO) substrates at room temperature in a specimen chamber of a 200-kV high-resolution electron microscope (JEOL, JEM2010).

Gold growth on Si(111) √3 × √3 Ag and √3 × √3 Au surfaces

Epitaxial growth of gold on Si(111) √3 × √3 Ag and √3 × √3 Au surfaces is investigated by reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). A stable RHEED oscillation is observed during the epitaxial growth of Au(111) on both surfaces at room temperature after 2 monolayer (ML) deposition (1 ML = 1.39 × 10 15 atoms/ cm 2). Before the oscillation, at about 0.5 ML, a diffuse RHEED pattern due to formation of a disordered structure appears for both surfaces. During RHEED oscillations, gold silicide segregates on the grown surfaces. The roles of the disordered structure formation and the silicide segregation in the layered epitaxial growth are discussed.

Structure of Au on Ag(110) studied by scanning tunneling microscopy

The epitaxial growth of Au on Ag(110) has been studied by scanning tunneling microscopy up to 8 ML. In the submonolayer range the results show that gold atoms are intermixed with the silver atoms in the top two layers. Above 1 ML a two‐dimensional fingerlike growth gives rise to anisotropic three‐dimensional islands of gold, which appear to be thermal equilibrium structures. Above 5 ML, the gold overlayer forms a (1×3) reconstruction which is manifested as double rows of atoms growing along [11̄0]. The development of this reconstruction is followed as a function of coverage.

Epitaxial growth of Au on Ag(110) studied by scanning tunneling microscopy

The epitaxial growth of Au on Ag(110) has been investigated by scanning tunneling microscopy up to 3 ML. A very consistent “intermixed Stranski-Krastanov” growth mode is demonstrated. Below 1 ML the open structure of the (110) surface allows the Au atoms to be incorporated mainly in the second layer. At higher coverages three-dimensional anisotropic islands of gold are observed. The anisotropic shape, the island density and the transition from two-dimensional to three-dimensional growth are discussed.

Epitaxial growth of Au on Ag(110) studied by scanning tunneling microscopy

Epitaxial growth of Au on Ag(110) studied by scanning tunneling microscopy

Intermixing and three-dimensional islands in the epitaxial growth of Au on Ag(110)

The epitaxial growth of Au on Ag(110) has been studied by scanning tunneling microscopy up to 2.5 ML. In the submonolayer range the results show that gold atoms are intermixed with the silver atoms in the top two layers. Above 1 ML, a two-dimensional fingerlike growth gives rise to anisotropic three-dimensional islands of gold. This intermixed Stranski-Krastanov growth mode is in quantitative agreement with ion channeling data which were previously interpreted as a bilayer growth mode [Fenter and Gustafson, phys. Rev. Lett. 64, 1142 (1990)]

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

Abstract 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.

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.

Model bimetallic catalysts: The preparation and characterisation of Au/Ru(0001) surfaces and the adsorption of carbon monoxide

We have studied the growth and structure of gold films deposited onto a Ru(0001) single-crystal substrate in UHV using LEED, Auger electron spectroscopy (AES) and thermal desorption mass spectroscopy (TDS). The gold concentrations ( θ Au) varied from fractions of a monolayer up to several monolayers with the Ru substrate held at either 540 K (low-temperature series) or at 1110 K (high-temperature series) during deposition. A correlation between the AES signal heights of Ru and Au in conjunction with TDS peak areas revealed a layer-by-layer growth of Au, particularly for the high- T series. TDS revealed three different Au binding states which are subsequently populated, viz., a β 3 state around 1320 K desorbing in a first-order kinetics and associated with the first Au monolayer, followed by a β 2 state ( T des around 1180–1280 K, fractional-order desorption) reflecting the second monolayer and a β 1 state ( T des around 1160–1260 K, zero-order desorption) corresponding to the third and all following Au layers. The activation energy of desorption. ΔE des, increases with increasing coverage in the submonolayer regime; it rises from 330 J mol −1 at θ Au = 0.1 to about 400 J mol −1 at θ = 0.6 ML. As a general tendency, the lower substrate temperatures favour an island growth of the Au whereas higher Ru temperatures lead to a more pronounced spreading and dispersion of the Au atoms. Epitaxial growth of Au can be observed at higher coverages ( θ Au ≲ 3 ML) as indicated by double-scattering LEED features. The CO adsorption data support the conclusions about the lateral dispersion of the Au on the Ru substrate in that the high- T Au films suppress the CO uptake more effectively than the low- T films.