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Ex situ atomic force microscopy and x-ray photoelectron spectroscopy are employed to characterise the adsorption of calcium phosphate from an aqueous solution of CaCl 2 .H 2 O and KH 2 PO 4 onto rutile-TiO 2 (110) and α-Al 2 O 3 (0001). Prior to immersion, the substrates underwent wet chemical preparation to produce well-defined surfaces. Calcium phosphate adsorption is observed on both rutile-TiO 2 (110) and α-Al 2 O 3 (0001), with atomic force microscopy images indicating island-type growth. In contrast to other studies on less well-defined TiO 2 and Al 2 O 3 substrates, the induction period for calcium phosphate nucleation appears to be comparable on these two surfaces. [ABSTRACT FROM AUTHOR]

Nanoparticles of one element or compound dispersed across the surface of another substance form the basis for many materials of great technological importance, like catalysts, fuel cells, sensors and biomaterials. Nanoparticles also often grow during thin film deposition. The size and number density of such nanoparticles are important, often estimated with electron or scanning tunneling microscopies. However, these are slow and often unavailable with sufficient resolution for particles near 1 nm. Because the probe depth of low-energy ion scattering spectroscopy (LEIS) with He + and Ne + is so shallow (less than one atom), it provides quantitative information on the fraction of the surface that is covered by such nanoparticles. Combined with the total amount per unit area, this fraction provides the average particle thickness. When the ions are incident or detected at some angle away from the surface normal, macroscopic screening effects cause interpretation of LEIS signals in terms of area fraction covered to be complicated. In this paper, we report a geometric analysis of particles with the shape of hemispherical caps so that LEIS signals obtained in any measurement geometry can also be used to quantitatively determine the area fraction, average particle thickness and diameter, or number density of particles. [ABSTRACT FROM AUTHOR]

Abstract: Using molecular dynamics, nudged elastic band and modified analytic embedded atom methods, the diffusion behaviors of Pd adatom on stepped Pd(001) surface have been investigated. Lower than 975K, Pd adatom just hops along the perfect [110]-direction step. The diffusion dynamics equation is derived from the Arrhenius law between 875 and 975K, and the corresponding migration energy and prefactor are 0.76eV and 5.2×10−2 cm2/s respectively, which shows that they adhere to the step in case of adatom moving to the step. The adatom diffuses across the perfect step with an Ehrlich–Schwoebel barrier of 0.09eV by exchange mechanism. Our calculations show the kink at step can markedly decrease the static energy barrier across the step with a negative Ehrlich–Schwoebel barrier, and it contributes to form layer-by-layer growth model in the epitaxial experiment. Our calculations show that the kink can also markedly improve the adatom's mass transport of interlayer, contributing to the formation of the compact film. Lastly, a quantitative result at 300K shows that the kink affects tremendously the diffusion mobility of adatom near it, which indicates that the kink plays a key role in the formation of the compact and uniform film on Pd(001) surface in an epitaxial growth experiment. [Copyright &y& Elsevier]

Abstract: We have used scanning tunneling microscopy to probe the effect of oxygen exposure on an ensemble of Ag islands separated by a Ag wetting layer on Si(111)-7×7. Starting from a distribution dominated by islands that are 1 layer high (measured with respect to the wetting layer), coarsening in ultrahigh vacuum at room temperature leads to growth of 2-layer islands at the expense of 1-layer islands, which is expected. If the sample is exposed to oxygen, 3-layer islands are favored, which is unexpected. There is no evidence for oxygen adsorption on top of Ag islands, but there is clear evidence for adsorption in the wetting layer. Several possible explanations are considered. [Copyright &y& Elsevier]

Abstract: We report the results of a Surface X-Ray Diffraction (SXRD) study of Fe nanostructured films deposited on c(2×2)-N/Cu(100) at room temperature (RT), with Fe coverage ΘFe =0.5ML and ΘFe =1ML. The c(2×2)-N/Cu(100) surface is an example of self-organised system, that can be used for growth of arrays of metal nano-islands and organic molecules assemblies. We chose two different values of N coverage, ΘN =0.3ML and ΘN =0.5ML, the second value corresponding to N saturation. We monitored the presence of surface diffraction peaks in hk scans and we performed Crystal Truncation Rods (CTR) analysis with ROD fitting programme. In the case of ΘN =0.5ML, i.e. at saturation coverage, the CTR could be fitted with one surface domain with p4gm(2×2) symmetry. In the surface cell adopted, N atoms occupy four-fold hollow sites, with Fe (intermixed with Cu) giving rise to a “clock” reconstruction previously observed on iron nitride films obtained by co-deposition and annealing. This result is an indirect confirmation of N surface segregation on top of the Fe films, occurring during the growth at RT. When subsaturation N coverage (ΘN =0.3ML) is used as a substrate for Fe deposition, the best results could be obtained with a model where two surface domains are present: the first one corresponds to a surface cell with Fe sitting in four-fold hollow sites on bare Cu areas, with possible interdiffusion in the second lattice. The second domain is assigned to growth of Fe on the N-covered square islands occurring once the bare Cu areas are fully covered. The SXRD analysis on N-covered surface domains shows that the mechanism of reconstruction and of N segregation on top layer is already active at RT for all N-coverage values. [Copyright &y& Elsevier]

Abstract: Classical molecular dynamics simulations are used to examine the growth of SrO and TiO2 thin films on SrTiO3 (STO). In particular, the simulations consider the deposition of SrO and TiO2 molecules at incident energies of 0.1, 0.5, and 1.0eV/atom onto the (001) surface of STO. The role of surface termination layer (SrO vs. TiO2) is analyzed. In the case of SrO deposition, smooth, ordered films are produced for all incident energies considered and for both surface terminations. By contrast, in the case of TiO2 deposition, three-dimensional islands are formed under all conditions. These predictions are in good agreement with experimental data. Importantly, the simulations explain why these differing morphologies are produced for SrO and TiO2 deposition. [Copyright &y& Elsevier]

Abstract: Thin films containing both the azo-dye disperse red 1 (DR1) and the poly(methylmetacrylate) (PMMA) or the poly(phenylenevinylene) (PPV) are deposited by Langmuir–Blodgett and spin coating techniques on various substrates. The morphology, surface structure and growth pattern of the azo-dye-polymers were studied by atomic force microscopy. Nucleation and growth processes are responsible for the generation of different structures. The spin coated films were additionally oriented using the electric field poling method (corona poling). The film homogeneity is improved by this method in all cases. Due to the polar character of DR1 molecules, rod-like sub-structures are observed after the corona poling process in DR1–MMA films. The indium tin oxide surface enhances reorientation of the azo-dye-polymer molecules during corona poling and results in a significant reduction of the surface roughness. [Copyright &y& Elsevier]

Abstract: Different growth modes were identified using scanning tunnelling microscopy (STM) in the initial stages of ultra-thin films growth of copper phthalocyanine (CuPc) on Si(001) surfaces terminated with ammonia (Si(001):NH3) and hydrogen (Si(001):H), depending on the surface chemistry. At the onset of the growth, defect sites are saturated with strongly-pinned flat-lying CuPc molecules. Subsequently, molecules arrange in a standing manner, with two macroscopic island directions along the [110] and directions. The Si surface termination influences the shape and coverage of the molecular layer before the onset of multilayer formation: on NH3 terminated surfaces, large elongated islands are formed, and nucleation of the second layer begins after the first layer is only 50% complete. This is in contrast to the H passivated surfaces, where a high density of smaller islands form and a higher coverage is reached before second layer nucleation, which we have attributed to a difference in molecular mobility on the substrate. STM shows that the islands contain columns of molecules, which on both surfaces are aligned by 64° with respect to the macroscopic island direction. From these observations, we have derived a model in which the molecular orientation observed in these studies is very similar to the bulk -phase CuPc. This rationalises the reduced crystallite size characteristic of thicker phthalocyanine films. [Copyright &y& Elsevier]

Abstract: The morphology and structure of Pt deposited on a WSe2(0001) van der Waals surface have been investigated by reflection high energy electron diffraction and scanning tunneling microscopy. At room temperature, the initial growth is characterized by the formation of three-dimensional fcc Pt islands with (111) orientation. In contrast, at higher temperatures of about 450°C the formation of a novel chemically ordered Pt–Se alloy is observed. Based on the diffraction patterns, a tetragonal DO22-type structure of a Pt3Se compound is suggested. With increasing Pt thickness, this chemically ordered alloy disappears and an additional superstructure occurs, which is accompanied by the coalescence of the islands. The observed superstructure is attributed to a strong Se diffusion towards the growth surface, forming most likely a PtSe2 alloy with the CdI2-type layered structure on the top surface. Due to the lateral lattice mismatch between the Pt(111) layers and the PtSe2(111) top layer, a Moiré pattern with a period of 1.1nm is created, which might be used as a long-range atomic pattern for further nanostructure growth. [Copyright &y& Elsevier]

Abstract: Electrodeposition is used to produce epitaxial single-crystal films on Au(111) substrates without annealing or other post-deposition modification. X-ray techniques show that the Bi(012) plane is parallel to the underlying Au(111) surface, and the azimuthal orientation of the films is determined. Combination of the X-ray data with in situ scanning tunneling microscopy (STM) images suggests a common growth mode from the first few layers up to thick films. [Copyright &y& Elsevier]

Abstract: The adsorption of tetracene (Tc) on Ag(111) was investigated by high resolution LEED (SPA-LEED) and temperature programmed desorption (TPD). Two long-range ordered monolayer phases (α,β) were found after Tc evaporation at sample temperatures of 300K and 230K, respectively, and subsequent cooling below 230K. The metastable β phase exhibits a 44% larger coverage than the α phase, and can be transformed into the α phase by annealing. At room temperature the long-range order is lost. At submonolayer coverage, only short-range order was observed, even at low temperatures. The unit cell of the α phase contains one molecule in planar geometry. There are two molecules within the unit cell of the β phase, which are presumably tilted with respect to the surface. Multilayer growth proceeds in a pronounced Stranski–Krastanov mode, leaving a large part of the monolayer uncovered. The TPD peak of the monolayer is very broad (300–550K). The zero-order multilayer TPD peak has its onset at about ∼280K and yields a desorption energy of 120–130kJmol−1. [Copyright &y& Elsevier]