Iron epitaxial electrodeposition on Au(111) substrates is investigated using in situ scanning tunneling microscopy (STM) and ex situ X-ray diffraction (XRD). STM observations show that Fe grows quasi layer-by-layer at sufficiently negative potentials. XRD results indicate that Fe layers thicker than 3 ML are bcc and present the epitaxial relationship Fe(110) [1–10]||Au(111) [11–2]. They also show that the Fe lattice is uniaxially in-plane strained along Fe[1–10] and that the strain is progressively relieved with increasing layer thickness. The growth of Fe on a Ni layer deposited on Au(111) leads to strain free Fe layers with the same epitaxial relationship. The specific shape of Fe of monatomic islands suggests that the first Fe monolayer deposited on Au(111) presents a centered rectangular lattice similar to that of bcc Fe(110) but is stretched along Fe[1–10] by more than 8%.

Second harmonic generation was observed in N-doped H:SiO2 films after poling under x-ray irradiation from a synchrotron at room temperature. The measurements of the photocurrent confirmed that the vitreous films have been poled. The magnitude of the induced second-order nonlinear coefficients measured from the Maker fringe is in the order of 0.001 pm V-1. This provides direct evidence that poling under x-ray irradiation is achievable at room temperature in amorphous materials.

Chalcogenide semiconductors have been deposited epitaxially from aqueous solutions either chemically or electrochemically at growth rates of up to 0.7 μmhr−1. After recalling the basic principles of these deposition processes, results are presented concerning chemically deposited CdS on InP, GaP and CuInSe2 substrates, electrodeposited CdTe on InP, and CdSAnP heterostructures. Characterisation of these structures by RHEED, TEM, HRTEM, and glazing angle X ray diffraction allows to analyse the effects of substrate orientation, polarity, lattice match plus the influence of temperature on epitaxial growth. These results are discussed in terms of self organisation and a site selective growth mechanisms due to the free enegy of formation of each compound.

In order to grow magnetic layers on silicon substrates, a non-magnetic buffer layer is often needed to avoid silicide formation and to reproduce the perpendicular magnetic anisotropy obtained on metal single crystals, as in the case of Co on Au(111) and Pt(111). In this context, we have studied the electrochemical growth of Au buffer layers, and show that it is possible to obtain different film morphologies on hydrogen-terminated vicinal Si(111) surfaces by varying the electrochemical deposition parameters and solution composition. Two different morphologies have been obtained as observed by atomic force microscopy: continuous 2D Au films (chloride solution at pH 4), and films consisting in flat top 3D Au islands decorating the Si(111) step edges (cyanide solution at pH 14). X-ray diffraction measurements reveal that the gold layer and islands have Au(111) orientation and are in epitaxy with the Si(111) surface. In the case of islands, the lateral facets have also Au(111) orientation. Results are discussed within a model in which the breaking of the Si-H surface bonds plays a major role in the Au nucleation and growth mechanisms. (C) 2009 Elsevier B.V. All rights reserved.

In order to grow magnetic layers on silicon substrates, a non-magnetic buffer layer is often needed to avoid silicide formation and to reproduce the perpendicular magnetic anisotropy obtained on metal single crystals, as in the case of Co on Au(111) and Pt(111). In this context, we have studied the electrochemical growth of Au buffer layers, and show that it is possible to obtain different film morphologies on hydrogen-terminated vicinal Si(111) surfaces by varying the electrochemical deposition parameters and solution composition. Two different morphologies have been obtained as observed by atomic force microscopy: continuous 2D Au films (chloride solution at pH 4), and films consisting in flat top 3D Au islands decorating the Si(111) step edges (cyanide solution at pH 14). X-ray diffraction measurements reveal that the gold layer and islands have Au(111) orientation and are in epitaxy with the Si(111) surface. In the case of islands, the lateral facets have also Au(111) orientation. Results are discussed within a model in which the breaking of the Si–H surface bonds plays a major role in the Au nucleation and growth mechanisms.

Thin metal layers deposited on a substrate (buffer layers) are widely employed in many fields of research and in microelectronic industry. In this work we present x-ray diffraction measurements and atomic force microscopy observations which demonstrate that high quality ultrathin Au(111) epitaxial films can be electrodeposited from a gold chloride solution on a well-defined H-terminated vicinal Si(111) surface. In addition, the obtained films present no apparent grain boundary. This result, which seems in conflict with classical growth theory, requires applying unconventional electrodeposition conditions in which a strong hydrogen evolution reaction is promoted.

Au/Co(4–8ML)/Au single magnetic layers and Au(8ML)/Co(4ML)/Au(8ML)/Co(8ML)/Au bilayer were sequentially grown by electrodeposition on an Au(111) buffer layer electrodeposited on Si(111). The technique used in this work provides full control on the structure and the chemical composition of the different layers (no alloying) as well as on the chemistry at interfaces. scanning tunneling microscopy (STM) and atomic force microscopy (AFM) imaging and X-ray diffraction measurements show that atomically flat continuous Co(0001) layers (4–8ML) can be grown in epitaxy with the Au(111) substrate and that the 2nm-thick spacer is also a continuous Au(111) layer. The Co ultrathin layers (4 and 8ML) exhibit perpendicular magnetic anisotropy. The lateral magnetic homogeneity and magnetization reversal process have been investigated by scanning magneto-optical Kerr effect (MOKE) magnetometry and global Kerr microscopy. The correlation between magnetization switching behaviour in each layer of the Co-bilayer stack has been evidenced from in-depth sensitive MOKE measurements and microscopy. The strong coupling observed between the two Co layers is attributed to magnetostatic interaction at domain wall boundaries.

In the present work, we studied the magnetic and structural properties of Co ultrathin films grown by electrodeposition onto Au substrates. The influence of the solution pH is particularly investigated using in situ and ex situ magnetization measurements. The results indicated that the magnetization is out of plane for both basic and acid solutions. Deposits performed at pH 8.5 keep their perpendicular component up to thickness of 20 monolayers (ML) either in or out of the solution, whereas the magnetization becomes in plane for a much lower thickness for deposits performed at pH 3.5 (above 2 ML in solution and 6−7 ML after capping with Cu).

The relation between the mechanical properties and the structure of AlN/TiN bilayers prepared by reactive magnetron sputtering in the 600nm range is investigated. Al and Ti K-edge extended X-ray absorption fine structure is used in order to determine the local order around Al and Ti by comparison with 300nm thick AlN and TiN single layers. The use of this powerful local probe allows the evidence of intermixing between AlN and TiN deposited layers, which is suggested by glow discharge optical emission spectroscopy experiments. The effect of ionic bombardment applied at various steps of the deposition process is studied. The ionic bombardment applied during the deposit induces substantial changes in the absorption spectra that are assigned to a decrease of intermixing and an improvement of local order. Simulations of (Al,Ti)N ternary alloys Al and Ti K-edge absorption spectra for increasing mean occupation factors CTi (CAl) of Ti(Al) substituting Al(Ti) in hexagonal AlN (cubic TiN) lattice are performed in order to determine the initial parameters for the fit of the experimental data. The refinements performed by using FEFFIT software demonstrate that an ionic bombardment applied during the deposition phase results in a significant reduction of the number of Al–Ti pairs within the bilayer and an improvement of the local order around Ti and Al, which is quantified by a decrease of the Debye–Waller parameters. This structural evolution is tentatively correlated with the improvement of mechanical properties of the bilayers.

The magnetic state of electrodeposited iron on An(111) substrates is investigated during the electrodeposition process by means of in situ alternating gradient force magnetometer (AGFM) and in situ perpendicular magneto-optic Kerr effect measurements (PMOKE). A perpendicular magnetic anisotropy (PMA) is observed for a thickness below 2 monolayers (ML). In situ STM observations of the initial stages of iron growth and ex situ EXAFS are used to correlate the structure of films to their magnetic properties. (C) 2004 Elsevier B.V. All rights reserved.

The possibility of preparing structurally well-defined and periodically arranged metal islands on a semiconductor is very attractive for optical and magnetic applications. In this work we used electrochemical deposition to grow nm-sized gold islands that decorate steps on defect-free vicinal H terminated Si(111) surfaces prepared by chemical etching. The gold deposits were studied by atomic force microscopy and X-ray diffraction. Results show that gold nucleates exclusively along the steps and that the density of nuclei is controlled by the electrode potential. Nearly prefect replication of the periodic array of straight monatomic steps is achieved at sufficiently negative potential. XRD indicates that the structure of gold films evolves from powder-like, close to the onset potential of nucleation (−1.6 V), to strongly epitaxial with the (111) orientation at more negative potentials. A reaction model and a growth mechanism are proposed to account for the origin of the selective nucleation and the excellent epitaxy obtained. In particular they discuss whether or not the H-monolayer remains intact under the deposit.

We have studied the formation of phenyl layers by electrochemical reduction of aryl diazonium salts (+N2–Ph–R with R=Br and CH2Br) on atomically flat H-terminated Si(111) electrodes. The surface density, compactness and thickness of layers are investigated as functions of the electrolysis parameters used during the modification (applied potential, charge passed) and the end group, using Rutherford backscattering measurements, electrochemical capacitance–voltage curves, and AFM/STM observations. Results indicate that some surface polymerization occurs above a critical charge Q*, the value of which depends on both the potential and the R-group. Results are interpreted within the frame of a kinetic model. It is shown that dense and ordered monolayers are nevertheless obtainable by monitoring the charge Q close to Q* and by proper choice of the grafting potential. Kinetic Monte Carlo simulations and structural models of the interface are presented to discuss the formation of 2D domains in monolayers. The electronic properties of the modified interface are discussed briefly.

. The anisotropy of atomic bonds formed by acceptor dopants with nitrogen in bulk wurtzite GaN crystals was studied by means of linearly polarized synchrotron radiation used in measurements of X-ray-absorption spectra for the K -edgeof Mg and Zn dopants. These spectra correspond to i) a single acceptor N bond along the c-axis and ii) three bonds realized with N atoms occupying the ab-plane perpendicular to the c-axis. The Zn dopant formed resonant spectra similar to that characteristic for Ga cations. In the case of the Mg dopant, similarity to Ga cations was observed for triple bonds in the ab-plane, only. Practically no resonant structure for spectra detected along the c-axis was observed. The absorption spectra were compared with ab initio calculations using the full-potential linear muffin-tin-orbital method. These calculations were also used for determination of the bond length for Mg–N and Zn–N in wurtzite GaN crystals and show that introducing dopants causes an increase of the lengths of the bonds formed by both dopants. Extended X-ray-absorption fine-structure measurements performed for bulk GaN:Zn confirmed the prediction of the theory in the case of the Zn–N bond. Finally, it is suggested that the anisotropy in the length of the Mg–N bonds, related to their larger strength in the case of bonds in the ab-plane, can explain preferential formation of a superlattice consisting of Mg-rich layers arranged in ab-planes of several bulk GaN:Mg crystals observed by transmission electron microscopy. Within the sensitivity of the method used, no parasitic metallic clusters or oxide compounds formed by the considered acceptors in GaN crystals were found.

We have studied in detail the structure and the nucleation and growth process of electrodeposited epitaxial hexagonal ZnO on GaN(0001). The crystallites grow with the c-axis perpendicular to substrate and the in-plane relationship is ZnO[100] parallel to GaN[100]. We show that the deposit aspect progressively changes with the deposition time from isolated dispersed dots toward fully covering flat zinc oxide single crystals. A simple model is presented which explains these morphological changes. The nucleation is instantaneous and the growth rate is controlled by the crystal surface reactions. The velocity of crystal growth is found dependent on the crystallographic face of the grain: it is approximately five times faster on the {0001} planes than on the {1010} and {0110} families of planes. We show that nucleation problems are encountered with high-quality GaN presenting a low surface defect density. The difficulty has been overcome by chemically treating the substrate with an aqueous ammonium hydroxide solution prior to the deposition. This treatment allows the nucleation of zinc oxide but has a detrimental effect on the deposit "mosaicity" which is better in the case of GaN with high defect density.

Water has been shown to play a crucial role in the stability and catalytic function of protein. Our purpose is to understand the modification of bulk liquid behavior when water is around myoglobin, in particular, the perturbation of liquid water structure by hydrophobic and hydrophilic sites of the protein. For this, the structure of water adsorbed at two different surfaces of a hydrophobic medium such as activated charcoal and a hydrophilic one such as polyHEMA (a synthetic hydrogel) was studied using both x-ray and neutron scattering techniques in earlier works. Following this study, the structure of water around myoglobin is investigated by x-ray scattering at room temperature and down to 77 K. The structure factors and the corresponding radial distribution functions are determined for several levels of hydration. At high water content (3 g water/g protein) the properties of water are very similar to those of bulk water. In partially hydrated samples (<0.4 g water/g protein), the molecular structure of water determined by water-water radial distribution function exhibits significant change, especially in the range of 3.3<r<3.9 A. These changes correspond to a distortion of the hydrogen-bonded network at the level of the first and second neighbors, and water does not crystallize when the temperature is lowered. (C) 2002 American Institute of Physics.

Epitaxial growth of ZnSe thin films on InP(111) and GaAs(100) substrates has been achieved by electrodeposition from a zinc sulfate/selenosulfate solution. The deposition was observed over a wide range of applied potentials (-1.6-1.9 V vs. mercury/mercury sulfate). The epitaxy was characterized by reflective high energy electron diffraction (see Figure for a ZnSe epitaxial layer) and grazing angle X-ray diffraction.

The local order in YFe2Dx deuterides has been characterized by EXAFS and Fe-57 Mossbauer spectroscopy. For all the deuterides several Fe sites and a large distribution of Fe-Fe distances are observed. The Y-Fe and Y-Y distances are close to those calculated for a cubic C15 type structure, but with significant static disorder. These large distance distributions are related to the influence of hydrogen atoms which induce local distortions of the interstitial sites with a displacement of Y and Fe atoms. However, the bulk and mean local magnetic properties remain sensitive to the long range order structure of the deuterides. (C) 2001 Elsevier Science B.V. All rights reserved.

The structure of the smectic B phase formed by perfluorodecylalkanes has been analyzed through the synthesis of three molecules and a careful investigation of their mesophases. Molecules with C-8, C-10 and a branched C-11 alkyl chain were considered. The structure factor analysis of 001 reflexions is consistent with the picture of alternating electron rich and electron poor sublayers. A structural model with segregated perfluoroalkyl chains in the middle of the layer and disordered alkyl chains on each sides is proposed. This model is discussed in terms of space filling arguments: chain lengths, cross section compatibility in the layer and compactness. Infrared dichroic ratios of the CH2 and CF2 stretching modes confirm that perfluoroalkyl subunits are perpendicular to the S-B layer while alkyl ones, in a quasi molten state, fill the remaining layer space.

Polarization-dependent X-ray absorption spectroscopy was used to examine the influence of crystal growth techniques and substrates type on the bond lengths and the bond structure of the single crystalline, wurtzite GaN in a form of bulk materials and epitaxial layers. The layers were grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) on different substrates such as SiC, sapphire and GaN. From the observed X-ray absorption near edge structure (XANES) of the Ga K-edges, it was found that MOCVD introduces a stronger disorder around Ga atoms than MBE. Comparing the Ga and N K-edges of the epilayers and the bulk crystal, we found a prevailing contribution of N-vacancies in the layers and dominance of Ga-vacancies in the bulk crystal. The bonds along the c-axis are less perfect than the bonds in the c-plane for all investigated epilayers. The performed standard extended X-ray absorption fine structure analysis (EXAFS) resulted in a direct estimate of the bond lengths in the c-plane and along the c-axis.

This work investigates the structure and interface perpendicular magnetic anisotropy (PMA) of electrodeposited Cu/Co/Au(111) sandwiches with variable Co thickness [2-20 monolayers (ML's)]. In optimum deposition conditions, polar magneto-optical Kerr effect measurements show that the axis of easy magnetization is perpendicular to the layers for thicknesses below ca. 7.2 ML's. This value is among the best ever reported for the Cu/Co/Au(111) structure. While extended x-ray-absorption fine structure indicates that layers are hcp, in situ STM imaging suggests that magnetoelastic effects contribute significantly to PMA. The correlation observed between the strength of PMA and film structure is discussed in details.