Coherent x-ray micro-diffraction and local mechanical loading can be combined to investigate the mechanical deformation in crystalline nanostructures. Here we present measurements of plastic deformation in a copper crystal of sub-micron size obtained by loading the sample with an Atomic Force Microscopy tip. The appearance of sharp features in the diffraction pattern, while conserving its global shape, is attributed to crystal defects induced by the tip.

The strain field of individual epitaxial sub-micrometric copper islands is studied using coherent X-ray diffraction and finite element modelling. The strain inhomogeneity in each island is so large that the characteristic features of the island shape tend to disappear in the diffraction pattern, which is dominated by strain effects. The model confirms the tensile strain imposed to the island by the thermal mismatch occurring during the preparation of the samples. An evaluation of the residual strain is obtained by qualitatively fitting the diffraction data. (C) 2012 Elsevier B. V. All rights reserved.

The effect of epitaxial stress on the stability of Au-Ni solid solutions grown by MBE on Au(001) is investigated. Experimental studies (TEM, GIXD) have shown that the elastic energy of the AuNi alloys is relaxed via two competing ways: twinning and an ordering process in which pseudo-periodic antiphase structures based on the L10 unit cell are found. The stabilisation of a metastable ordered L10 phase in the stressed Au-Ni system is explained using thermodynamic calculations based on the minimisation of free energy including elastic contributions.

FePd(001) thin films have been grown by the molecular beam epitaxy (MBE) technique. At room temperature, these films are chemically disordered whereas at 350 °C a well ordered L1 0 structure is found with the c-axis oriented in the growth direction. By combining RHEED, STM and Auger measurements, it is suggested that ordering occurs at the growing surface by the development of bi-atomic steps of the ordered structure. We have put in evidence that the surfactant behavior of the Pd atoms is mainly involved in the ordering process and selects the single orientation of the c-axis. For intermediate temperatures between RT and 350 °C, TEM and X-rays have evidenced a pseudo-periodic arrangement of anti-phased domains having a columnar shape. The variation of the long-range order parameter is related to the average size of these ordered domains.

Au(100)/Ni(100) periodic superlattices have been grown by the MBE technique specially for X-ray diffraction experiments. The nominal number of Ni planes deposited were 1.5, 2, 4 and 5 ML and the thickness of the gold layers was always 1.5 nm. The X-ray profiles have been simulated using a kinematical structure refinement program. The obtained strain profiles are in very good agreement with earlier HREM results. It is shown that a strong interdiffusion occurs during the growth.

Abstract This communication deals with the early stage of the growth of Cu on Si(0 0 1)–H at room temperature. A copper silicide layer of about 1–2 nm of thickness is evidenced by reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy and transmission electron microscopy (TEM). HRTEM experiments show that the silicide structure is in agreement with the bcc β-Cu0.84Si0.16 structure. With further deposition of Cu, TEM reveals a highly textured fiber structure with a weak in-plane misorientation (few degrees). Scanning tunneling microscope (STM) observations for different thicknesses show a quasi-continuous film structure with mounds of well-defined sizes and well-defined separation distances. The mean distance L deduced from the height–height autocorrelation function varies as L ( t ) ∼ t 0.5 with Cu thickness t. This particular growth morphology evolution does not correspond to the expected self-affine behavior supported by most kinetic models (based on KPZ model). As a matter of fact, the characteristic distance L is comparable with the size of the grains revealed by TEM. Therefore, it seems that silicide formation at the early stage of copper deposition play an important role in subsequent copper film microstructure.

This communication deals with the early stage of the growth of Cu on Si(0 0 1)-H at room temperature. A copper silicide layer of about 1-2 nm of thickness is evidenced by reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy and transmission electron microscopy (TEM). HRTEM experiments show that the silicide structure is in agreement with the bcc beta-Cu0.84Si0.16 structure. With further deposition of Cu, TEM reveals a highly textured fiber structure with a weak in-plane misorientation (few degrees). Scanning tunneling microscope (STM) observations for different thicknesses show a quasi-continuous film structure with mounds of well-defined sizes and well-defined separation distances. The mean distance L deduced from the height-height autocorrelation function varies as L(t) similar to t(0.5) with Cu thickness t. This particular growth morphology evolution does not correspond to the expected self-affine behavior supported by most kinetic models (based on KPZ model). As a matter of fact, the characteristic distance L is comparable with the size of the grains revealed by TEM. Therefore, it seems that silicide formation at the early stage of copper deposition play an important role in subsequent copper film microstructure. (C) 2004 Published by Elsevier B.V.

We have studied bilayers and trilayers of FePd thin-film alloys. where each of the constituting layers has a different magnetic-anisotropy, as controlled by the growth conditions. The competition between the magnetocrystalline anisotropy and the shape anisotropy in these films lends to the formation of stripe domains with a period of similar to 100 nm, which has been imaged by magnetic force microscopy (MFM). The average magnetic anisotropy has been obtained from the in-plane and perpendicular magnetic field dependence, measured using vibrating sample magnetometry (VSM). We measured the soft x-ray resonant magnetic scattering (SXRMS) at the Fe L-3 edge using sigma linearly polarized light, which is sensitive to the magnetization profile in the layers. The magnetic configuration of the layer systems was modeled using micromagnetic software (GL-FFT, @CNRS). The results of the micromagnetic modeling were used for a numerical simulation of the reflectivity scan and the magnetic rod scans of the SXRMS. This allowed us to determine parameters, such as the lateral roughness, the magnetic period, the magnetic correlation length, and the magnetic layer thickness. The good agreement obtained with the experimental results demonstrates that SXRMS Provides in-depth information that cannot be obtained from either MFM or VSM.

We report on the growth of alloys ( CrPt 3 , VPt 3 , FePt) on the (0 0 0 1) surface of the layered compound WSe 2 , by co-deposition of 3d-metal and Pt atoms under ultra-high vacuum conditions. Because of weak interactions with the Se hexagonal dense planes and the strong lattice mismatch, the adatoms self-assemble and form epitaxial 3D nanostructures, which adopt lattice parameters very close to those of bulk phases. This type of growth is called quasi-van der Waals epitaxy and would allow the fabrication of nanostructured media of potential interest for magnetic recording technology. The structure and morphology of the nanostructures were studied by reflection high-energy electron diffraction, scanning tunnelling microscope and grazing incidence small angle X-ray scattering. These first results suggest that both the type of long-range chemical ordering ( L 1 2 or L 1 0 ) and the elastic properties of alloys play a role in the final morphology of nanostructures.

We report the dependence of the growth and the optical properties of self-assembled CdTe/Zn1−xMgxTe quantum dots on the barrier Mg content x (0⩽x⩽0.3). Due to the decrease of the lattice mismatch between CdTe and Zn1−xMgxTe with increasing x, we use a technique for inducing dot formation, based on efficient reduction of the surface energy by deposition of amorphous Te, which is then desorbed. Mg incorporation in the barriers leads to a better heavy-hole confinement along the growth axis, which is manifested in photoluminescence (PL) studies by both an extension of the radiative regime temperature range (up to 150 K for 30% Mg) and a strong increase of the activation energy for the nonradiative recombination. However, the in-plane confinement is less enhanced, which allows observation of interdot carrier transfer with increasing temperature, as evidenced directly by the analysis of PL intensities for different single dots. Our temperature-dependent data (time-resolved and microphotoluminescence) suggest that this transfer consists of a thermally activated process via the two-dimensional wetting-layer states rather than a direct tunneling (hopping) process.

Metallic multilayers offer a fantastic playground to investigate elastic stresses in films of nanometer thickness. We will present and discuss a few examples from our recent work on Au–Ni and Ag–Cu systems where we combined plate bending measurements and electron or X-ray diffraction to investigate stress buildup and interfacial mixing. Comparing these two cases we discuss the results with respect to basic parameters like the misfits in lattice parameters and in elastic moduli, the mixing enthalpies and the surface energies.

We report on the growth of FePt nanostructures by self-assembling on the van der Waals surface of WSe2 (0001) under ultra-high vacuum conditions. The morphology and crystalline structure of nanostructures were investigated by reflection high energy electron diffraction (RHEED), scanning tunnelling microscopy (STM) and x-ray diffraction. The FePt nanostructures grow with the (111) plane azimuthally aligned to the WSe2 (0001) plane with a narrow size distribution centred around 4.5 nm showing a rounded shape for deposition temperatures in the 300-500 degreesC range. They develop the L1(0)-type structure starting at a relatively low deposition temperature of about 200 degreesC with the occurrence of three possible variants. Moreover, segregation of Se at the growing surface was observed even in films deposited at room temperature. However, such a surfactant effect does not prevent the L1(0) ordering and could explain the perpendicular magnetic anisotropy observed in previously studied CoPt3 films grown at room temperature on WSe2. Magnetic measurements in 3 nm thick FePt(111) deposits have revealed an easy axis of magnetization in the film plane, with a coercivity strongly enhanced with L1(0) order.

Chemically disordered FePd epitaxial layers are grown at room temperature by molecular beam epitaxy on a Pd(001) buffer layer and then annealed in order to induce the chemically ordered L1(0) (AuCu I) structure. Contrary to what is observed in the case of ordering during growth above room temperature, the ordered structure appears here with the three possible variants of the L1(0) phase. The ratio of the three different variant volumes is set by the residual epitaxial strain in the layer before annealing. It thus explains that for long annealing times, the long-range order parameter associated with the L1(0) variant with c along the (100) growth direction saturates at a value close to 0.65, and never reaches unity. Magnetic consequences of the ordering are studied.

Soft X-ray resonant magnetic scattering (SXRMS) was performed on a FePd alloy thin film at the L3-edge of Fe. This film exhibits perpendicular magnetic anisotropy giving rise to periodic alternation of up and down magnetisation domains with closure domains. Rocking curves performed in transverse geometry allowed us to measure the magnetic periodicity and correlation length of domains. Micromagnetic simulations of the FePd layers and SXRMS calculations were made to analyse the asymmetry ratio of magnetic satellite intensities, hence allowing us to quantify the magnetic anisotropy.

We observed that the relaxation mechanism of the epitaxial strain is dramatically dependent on the chemical ordering within the L1{sub 0} structure in FePd(Pt) thin films. In disordered or weakly ordered layers, the relaxation takes place though perfect (1/2)[101] dislocations, whereas well-ordered films relax through the partial 1/6[112] Shockley dislocations, piled-up within microtwins, with a huge impact on both the morphology and the magnetic properties of the film. We show that the antiphase boundary energy is the key factor preventing the propagation of perfect dislocations in ordered alloys.

A method for growing self-assembled II–VI quantum dots (QDs) is demonstrated: A highly strained CdTe layer, grown onto Zn(Mg)Te, is covered with an amorphous Te layer which is then desorbed. This induces QD formation, observed as an abrupt change of both the reflection high-energy electron diffraction pattern and the surface morphology studied by atomic force microscopy in an ultrahigh vacuum. The dots are also characterized after capping by microphotoluminescence. This morphology transition, which occurs after and not during the growth, can be understood in terms of variation of the surface energy in presence of the group-VI element, which compensates for the natural trend toward plastic relaxation in II–VI compounds. This method shows the strong influence of the surface energy (and not just the lattice mismatch) in inducing the formation of coherent islands for mismatched systems having a low dislocation formation energy such as CdTe/ZnTe and CdSe/ZnSe.

In recent years, Ni/Cu films and multilayers with perpendicular magnetic anisotropy (PMA) have attracted much interest due to their potential advantage in magneto-optical recording. While the magnetic anisotropy of this system has been intensively investigated and interpreted, a major question concerning the magnitude of the magnetic moments remains unresolved. In this report, using Auger electron spectroscopy (AES) on a Ni/Cu/Si(001) epitaxied wedge sample, we show that Cu atoms diffuse in the growing Ni layer. We have used a dynamical segregation model to reproduce our experimental results and to calculate the Cu concentration profile. The observed chemical mixing may explain the dramatic decrease of the atomic magnetic moment for ultra-thin films reported in previous experimental works [Phys. Rev. B 55 (17) (1997) 11422].