Strain induced atomic structure at the Ir-doped LaAlO3/SrTiO3 interface.

The structure of Ir-doped LaAlO3/SrTiO3(001) interfaces was investigated on the atomic scale using probe-corrected transmission electron microscopy in high-angle annular dark-field scanning mode (HAADF-STEM) and electron energy loss spectroscopy (EELS), combined with first-principles calculations. We report the evolution of the strain state experimentally measured in a 5 unit-cell thick LaAlO3 film as a function of the Ir concentration in the topmost SrTiO3 layer. It is shown that the LaAlO3 layers remain fully elastically strained up to 3% of Ir doping, whereas a higher doping level seems to promote strain relaxation through enhanced cationic interdiffusion. The observed differences between the energy loss near edge structure (ELNES) of Ti-L2,3 and O-K edges at non-doped and Ir-doped interfaces are consistent with the location of the Ir dopants at the interface, up to 3% of Ir doping. These findings, supported by the results of density functional theory (DFT) calculations, provide strong evidence that the effect of dopant concentrations on the properties of this kind of interface should not be analyzed without obtaining essential information from the fine structural and chemical analysis of the grown structures.

Inhomogeneous spatial distribution of the magnetic transition in an iron-rhodium thin film.

Monitoring a magnetic state using thermal or electrical activation is mandatory for the development of new magnetic devices, for instance in heat or electrically assisted magnetic recording or room-temperature memory resistor. Compounds such as FeRh, which undergoes a magnetic transition from an antiferromagnetic state to a ferromagnetic state around 100 °C, are thus highly desirable. However, the mechanisms involved in the transition are still under debate. Here we use in situ heating and cooling electron holography to quantitatively map at the nanometre scale the magnetization of a cross-sectional FeRh thin film through the antiferromagnetic-ferromagnetic transition. Our results provide a direct observation of an inhomogeneous spatial distribution of the transition temperature along the growth direction. Most interestingly, a regular spacing of the ferromagnetic domains nucleated upon monitoring of the transition is also observed. Beyond these findings on the fundamental transition mechanisms, our work also brings insights for in operando analysis of magnetic devices.

Evidence of a minority monoclinic LaNiO2.5 phase in lanthanum nickelate thin films.

LaNiO3 (LNO) thin films of 14 nm and 35 nm thicknesses grown epitaxially on LaAlO3 (LAO) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) substrates are studied using High Resolution Transmission Electron Microscopy (HRTEM) and High Angle Annular Dark Field (HAADF) imaging. The strain state of the films is studied using Geometric Phase Analysis (GPA). Results show the successful in-plane adaptation of the films to the substrates, both in the compressive (LAO) and tensile (LSAT) cases. Through the systematic analysis of HRTEM superstructure contrast modulation along different crystal orientations, localized regions of the monoclinic LaNiO2.5 phase are detected in the 35 nm films.

The gold/ampicillin interface at the atomic scale.

In the fight against antibiotic resistance, gold nanoparticles (AuNP) with antibiotics grafted on their surfaces have been found to be potent agents. Ampicillin-conjugated AuNPs have been thus reported to overcome highly ampicillin-resistant bacteria. However, the structure at the atomic scale of these hybrid systems remains misunderstood. In this paper, the structure of the interface between an ampicillin molecule AMP and three flat gold facets Au(111), Au(110) and Au(100) has been investigated with numerical simulations (dispersion-corrected DFT). Adsorption energies, bond distances and electron densities indicate that the adsorption of AMP on these facets goes through multiple partially covalent bonding. The stability of the AuNP/AMP nanoconjugates is explained by large adsorption energies and their potential antibacterial activity is discussed on the basis of the constrained spatial orientation of the grafted antibiotic.

Fully Crystalline Faceted Fe-Au Core-Shell Nanoparticles.

Fe-Au core-shell nanoparticles displaying an original polyhedral morphology have been successfully synthesized through a physical route. Analyses using transmission electron microscopy show that the Au shell forms truncated pyramids epitaxially grown on the (100) facets of the iron cubic core. The evolution of the elastic energy and strain field in the nanoparticles as a function of their geometry and composition is calculated using the finite-element method. The stability of the remarkable centered core-shell morphology experimentally observed is attributed to the weak elastic energy resulting from the low misfit at the Fe/Au (100) interface compared to the surface energy contribution.

Design of FeBi nanoparticles for imaging applications.

A variety of imaging technologies are now routinely used in the medical field, their use being continuously enlarged through the development of contrast agents. Recently nanoparticles (NPs) proved efficient to improve imaging in vivo by increasing contrast and targeting capabilities. The current trend is now focused on the development of dual contrast agents combining two or more functionalities on the same NP. Motivated by this new challenge we developed FeBi NPs as new nanomaterials with potential application as a contrast agent for MRI and CT imaging. In addition to the well-known use of iron in the development MRI contrast agents, we chose Bi as a CT imaging agent rather than the more documented gold, because it possesses a larger X-ray attenuation coefficient and is much less expensive. Two sets of NPs, with sizes around 150 nm and 14 nm, were synthesized using organometallic approaches. In both cases, the NPs are spherical, and contain distinct domains of Fe and Bi, with the surface being enriched with Fe, and a hydrophobic coating. This coating differs from one sample to the other: the surfaces of the 150 nm large NPs are coated by amine ligands, while those of the 14 nm large NPs are coated by a mixture of an amine and its hydrochloride salt. Exchange of the surface ligands to afford water soluble NPs has been attempted. We show that only the larger NPs could be functionalized with water soluble ligands, which is in agreement with the lability of their initial surface coating. Colloidal aqueous solutions of FeBi NPs with glycoPEG ligands have been obtained.

Development of bi-metallic Fe-Bi nanocomposites: synthesis and characterization.

We investigate the formation of bi-metallic particles in the Fe-Bi system, well known as totally immiscible in the bulk, using a large combination of structural and element-sensitive techniques, well-adapted to the nanoscale. The synthesis approach makes use of the kinetics of decomposition of the different precursors to achieve a controlled sequential growth of the different elements. Different ligands have also been used in order to limit the size and ensure dispersion of the synthesized particles. Our results give evidence for the presence of body-centered cubic ferromagnetic iron nanograins together with larger bismuth crystallites. Interestingly, while the iron particles remain very small, the resistance to oxidation of the Fe-Bi nanocomposites highly depends on the stabilizing ligand used in the synthesis. The presence of both metals, Fe and Bi, in a single cluster has been clearly revealed in the oxidation resistant composite synthesized using the HMDS ligand.

Chemical solution approaches to YBa2Cu3O7_delta-Au nanocomposite superconducting thin films.

We explore the feasibility of preparing YBa2CU3O7-Au (YBCO-Au) nanocomposite thin films by chemical solution deposition (CSD). Two approaches were used: (i) A standard in-situ methodology where Au metallorganic salts are added into the precursor solution of YBCO trifluoroacetate (TFA) salts and (ii) a novel approach where stable colloidal solutions of preformed gold nanoparticles (5-15 nm) were homogeneously mixed with TFA-YBCO solutions. A detailed analysis of the microstructure of the films showed that in both cases, there is a strong tendency of gold nanoparticles to migrate to the film surface. However the kinetics of this migration evidences important differences and in the case of preformed nanoparticles their size remains unchanged (a few nanometers) whereas for the in-situ nanocomposites gold ripening leads to large particles (hundreds of nanometers). The grown YBCO-Au films showed good superconducting characteristics (J(c) 2 MA/cm2 at 77 K) but the absence of Au inclusions inside the YBCO matrix explains the fact that no enhancement of vortex pinning was observed.

Magnetic properties of Co(N)RhM nanoparticles: experiment and theory?

The magnetism of Co-Rh nanoparticles is investigated experimentally and theoretically. The particles (approximately 2 nm) have been synthesized by decomposition of organometallic precursors in mild conditions of pressure and temperature, under hydrogen atmosphere and in the presence of a polymer matrix. The magnetic properties are determined by SQUID, Mössbauer spectroscopy, and X-ray magnetic circular dichroism (XMCD). The structural and chemical properties are characterized by wide angle X-ray scattering, transmission electronic microscopy and X-ray absorption near edge spectroscopy. All the studied Co-Rh clusters are magnetic with an average spin moment per atom mu that is larger than the one of macroscopic crystals or alloys with similar concentrations. The experimental results and comparison with theory suggest that the most likely chemical arrangement is a Rh core, with a Co-rich outer shell showing significant Co-Rh mixing at the interface. Measured and calculated magnetic anisotropy energies (MAEs) are found to be higher than in pure Co clusters. Moreover, one observes that the MAEs can be tuned to some extent by varying the Rh concentration. These trends are well accounted for by theory, which in addition reveals important spin and orbital moments induced at the Rh atoms as well as significant orbital moments at the Co atoms. These play a central role in the interpretation of experimental data as a function of Co-Rh content. A more detailed analysis from a local perspective shows that the orbital and spin moments at the Co-Rh interface are largely responsible for the enhancement of the magnetic moments and magnetic anisotropy.

New approach for the dynamical simulation of CBED patterns in heavily strained specimens.

A new method for the dynamical simulation of convergent beam electron diffraction (CBED) patterns is proposed. In this method, the three-dimensional stationary Schrödinger equation is replaced by a two-dimensional time-dependent equation, in which the direction of propagation of the electron beam, variable z, stands as a time. We demonstrate that this approach is particularly well-suited for the calculation of the diffracted intensities in the case of a z-dependent crystal potential. The corresponding software has been developed and implemented for simulating CBED patterns of various specimens, from perfect crystals to heavily strained cross-sectional specimens. Evidence is given for the remarkable agreement between simulated and experimental patterns.

Effect of sample bending on diffracted intensities observed in CBED patterns of plan view strained samples.

Convergent beam electron diffraction is used to study the effect of the sample bending on diffracted intensities as observed in transmission electron microscopy (TEM). Studied samples are made of thin strained semiconductor Ga(1-)(x)In(x)As epitaxial layers grown on a GaAs substrate and observed in plan view. Strong variations of the diffracted intensities are observed depending on the thinning process used for TEM foil preparation. For chemically thinned samples, strong bending of the substrate occurs, inducing modifications of both kinematical and dynamical Bragg lines. For mechanically thinned samples, bending of the substrate is negligible. Kinematical lines are unaffected whereas dynamical lines have slightly asymmetric intensities. We analyse these effects using finite element modelling to calculate the sample strain coupled with dynamical multibeam simulations for calculating the diffracted intensities. Our results correctly reproduce the qualitative features of experimental patterns, clearly demonstrating that inhomogeneous displacement fields along the electron beam within the substrate are responsible for the observed intensity modifications.

Quantitative analysis of HOLZ line splitting in CBED patterns of epitaxially strained layers.

A SiGe layer epitaxially grown on a silicon substrate is experimentally studied by convergent beam electron diffraction (CBED) experiments and used as a test sample to analyse the higher-order Laue zones (HOLZ) line splitting. The influence of surface strain relaxation on the broadening of HOLZ lines is confirmed. The quantitative fit of the observed HOLZ line profiles is successfully achieved using a formalism particularly well-adapted to the case of a z-dependent crystal potential (z being the zone axis). This formalism, based on a time-dependent perturbation theory approach, proves to be much more efficient than a classical Howie-Whelan approach, to reproduce the complex HOLZ lines profile in this heavily strained test sample.

Ligand-stabilized ruthenium nanoparticles: synthesis, organization, and dynamics.

The decomposition of the ruthenium precursor Ru(COD)(COT) (1, COD = 1,5-cyclooctadiene; COT = 1,3,5-cyclooctatriene) in mild conditions (room temperature, 1--3 bar H(2)) in THF leads, in the presence of a stabilizer (polymer or ligand), to nanoparticles of various sizes and shapes. In THF and in the presence of a polymer matrix (Ru/polymer = 5%), crystalline hcp particles of uniform mean size (1.1 nm) homogeneously dispersed in the polymer matrix and agglomerated hcp particles (1.7 nm) were respectively obtained in poly(vinylpyrrolidone) and cellulose acetate. The same reaction, carried out using various concentrations relative to ruthenium of alkylamines or alkylthiols as stabilizers (L = C(8)H(17)NH(2), C(12)H(25)NH(2), C(16)H(33)NH(2), C(8)H(17)SH, C(12)H(25)SH, or C(16)H(33)SH), leads to agglomerated particles (L = thiol) or particles dispersed in the solution (L = amine), both displaying a mean size near 2--3 nm and an hcp structure. In the case of amine ligands, the particles are generally elongated and display a tendency to form worm- or rodlike structures at high amine concentration. This phenomenon is attributed to a rapid amine ligand exchange at the surface of the particle as observed by (13)C NMR. In contrast, the particles stabilized by C(8)H(17)SH are not fluxional, but a catalytic transformation of thiols into disulfides has been observed which involves oxidative addition of thiols on the ruthenium surface. All colloids were characterized by microanalysis, infrared spectroscopy after CO adsorption, high-resolution electron microscopy, and wide-angle X-ray scattering.

Selective synthesis of novel in and in3 sn nanowires by an organometallic route at room temperature.

Simply decomposing InCp at room temperature in the presence of hexadecylamine leads to the formation of indium nanowires with a crystalline bct structure, a mean diameter of about 200 nm, and lengths in the micrometer range. The method can be extended to the preparation of In3 Sn nanowires of about 100 nm in diameter (a transmission electron micrograph is shown in the picture). Cp=C5 H5 (-) .