The atomic structure of low-index surfaces of the intermetallic compound InPd.

The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to ∼580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above ∼660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (≥750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and "global" measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature.

Oxygen adsorption on the Al9Co2(001) surface: first-principles and STM study.

Atomic oxygen adsorption on a pure aluminum terminated Al9Co2(001) surface is studied by first-principle calculations coupled with STM measurements. Relative adsorption energies of oxygen atoms have been calculated on different surface sites along with the associated STM images. The local electronic structure of the most favourable adsorption site is described. The preferential adsorption site is identified as a 'bridge' type site between the cluster entities exposed at the (001) surface termination. The Al-O bonding between the adsorbate and the substrate presents a covalent character, with s-p hybridization occurring between the states of the adsorbed oxygen atom and the aluminum atoms of the surface. The simulated STM image of the preferential adsorption site is in agreement with experimental observations. This work shows that oxygen adsorption generates important atomic relaxations of the topmost surface layer and that sub-surface cobalt atoms strongly influence the values of the adsorption energies. The calculated Al-O distances are in agreement with those reported in Al2O and Al2O3 oxides and for oxygen adsorption on Al(111).

Structural investigation of the (010) surface of the Al13 Fe4 catalyst.

We have investigated the structure of the Al(13)Fe(4)(010) surface using both experimental and ab initio computational methods. The results indicate that the topmost surface layers correspond to incomplete puckered (P) planes present in the bulk crystal structure. The main building block of the corrugated termination consists of two adjacent pentagons of Al atoms, each centered by a protruding Fe atom. These motifs are interconnected via additional Al atoms referred to as "glue" atoms which partially desorb above 873 K. The surface structure of lower atomic density compared to the bulk P plane is explained by a strong Fe-Al-Fe covalent polar interaction that preserves intact clusters at the surface. The proposed surface model with identified Fe-containing atomic ensembles could explain the Al(13)Fe(4) catalytic properties recently reported in line with the site-isolation concept [M. Armbrüster et al., Nat. Mater. 11, 690 (2012)].

Al13Fe4 as a low-cost alternative for palladium in heterogeneous hydrogenation.

Replacing noble metals in heterogeneous catalysts by low-cost substitutes has driven scientific and industrial research for more than 100 years. Cheap and ubiquitous iron is especially desirable, because it does not bear potential health risks like, for example, nickel. To purify the ethylene feed for the production of polyethylene, the semi-hydrogenation of acetylene is applied (80 × 10(6) tons per annum; refs 1-3). The presence of small and separated transition-metal atom ensembles (so-called site-isolation), and the suppression of hydride formation are beneficial for the catalytic performance. Iron catalysts necessitate at least 50 bar and 100 °C for the hydrogenation of unsaturated C-C bonds, showing only limited selectivity towards semi-hydrogenation. Recent innovation in catalytic semi-hydrogenation is based on computational screening of substitutional alloys to identify promising metal combinations using scaling functions and the experimental realization of the site-isolation concept employing structurally well-ordered and in situ stable intermetallic compounds of Ga with Pd (refs 15-19). The stability enables a knowledge-based development by assigning the observed catalytic properties to the crystal and electronic structures of the intermetallic compounds. Following this approach, we identified the low-cost and environmentally benign intermetallic compound Al(13)Fe(4) as an active and selective semi-hydrogenation catalyst. This knowledge-based development might prove applicable to a wide range of heterogeneously catalysed reactions.

PdGa intermetallic hydrogenation catalyst: an NMR and physical property study.

The PdGa intermetallic compound is a highly selective and stable heterogeneous hydrogenation catalyst for the semi-hydrogenation of acetylene. We have studied single crystals of PdGa grown by the Czochralski technique. The (69)Ga electric-field-gradient (EFG) tensor was determined by means of NMR spectroscopy, giving experimental confirmation of both the recently refined structural model of PdGa and the theoretically predicted Pd-Ga covalent bonding scheme. The hydrogenation experiment has detected no hydrogen uptake in the PdGa, thus preventing in situ hydride formation that leads to a reduction of the catalytic selectivity. We have also determined bulk physical properties (the magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient, the thermal conductivity and the specific heat) of single-crystalline PdGa. The results show that PdGa is a diamagnet with metallic electrical resistivity and moderately high thermal conductivity. The thermoelectric power is negative with complicated temperature dependence, whereas the Hall coefficient is positive and temperature-dependent, indicating complexity of the Fermi surface. Partial fulfillment of the NMR Korringa relation reveals that the charge carriers are weakly correlated. Specific heat measurements show that the density of electronic states (DOS) at the Fermi energy of PdGa is reduced to 15% of the DOS of the elemental Pd metal.

Pseudomorphy, surface alloys and the role of elementary clusters on the domain orientations in the Cu/Al13Co4(100) system.

We have used the pseudo-tenfold surface of the orthorhombic Al(13)Co(4) crystal as a template for the adsorption of Cu thin films of various thicknesses deposited at different temperatures. This study has been carried out by means of low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), x-ray photoelectron spectroscopy (XPS) and x-ray photoelectron diffraction (XPD). From 300 to 573 K, Cu adatoms grow pseudomorphically up to one monolayer. At 300 K, the ß-Al(Cu, Co) phase appears for coverages greater than one monolayer. For higher temperature deposition, the ß-Al(Cu, Co) phase further transforms into the γ-Al(4)Cu(9) phase. Both ß and γ phases grow as two (110) domains rotated by 72° ± 1° from each other. Instead of following the substrate symmetry, it is the orientations of the bipentagonal motifs present on the clean Al(13)Co(4)(100) surface that dictate the growth orientation of these domains. The initial bulk composition and structural complexity of the substrate have a minor role in the formation of the γ-Al(4)Cu(9) phase as long as the amount of Al and the Cu film thickness reach a critical stoichiometry.

Achieving epitaxy between incommensurate materials by quasicrystalline interlayers.

Epitaxial interfaces of commensurate periodic materials can be characterized by a locking into registry of their atomic structure. This characteristic is identified as a natural framework to capture the essence of epitaxy also for systems including quasicrystalline materials. The resulting general definition for epitaxy requires a matching of reciprocal lattice points. The consequences for the real space structure of an epitaxial interface between quasiperiodic and periodic materials are explored and an experimental realization of such an interface is presented. It is demonstrated that due to their higher number of reciprocal lattice basis vectors (exceeding three), quasicrystals can provide interlayers epitaxially linking incommensurate materials.

Quasicrystalline epitaxial single element monolayers on icosahedral Al-pd-mn and decagonal Al-ni-co quasicrystal surfaces.

Single element quasicrystalline monolayers were prepared by deposition of antimony and bismuth on the fivefold surface of icosahedral Al71.5Pd21Mn8.5 and the tenfold surface of decagonal Al71.8Ni14.8Co13.4. Elastic helium atom scattering and low energy electron diffraction of the monolayers show Bragg peaks at the bulk derived positions of the clean surfaces, revealing highly ordered quasicrystalline epitaxial films. Their adatom densities of (0.9+/-0.2)x10(15) cm(-2) and (0.8+/-0.2)x10(15) cm(-2) on Al-Pd-Mn and Al-Ni-Co, respectively, correspond to roughly one adatom per Al atom of the quasicrystalline substrate surfaces.

Quasicrystalline valence bands in decagonal AlNiCo

Quasicrystals are metallic alloys that possess perfect long-range structural order, in spite of the fact that their rotational symmetries are incompatible with long-range periodicity. The exotic structural properties of this class of materials are accompanied by physical properties that are unexpected for metallic alloys. Considerable progress in resolving the geometric structures of quasicrystals has been made using X-ray and neutron diffraction, and concepts such as the quasi-unit-cell model have provided theoretical insights. But the basic properties of the valence electronic states--whether they are extended as in periodic crystals or localized as in amorphous materials--are still largely unresolved. Here we investigate the electronic bandstructure of quasicrystals through angle-resolved photoemission experiments on decagonal Al71.8Ni14.8Co13.4. We find that the s-p and d states exhibit band-like behaviour with the symmetry of the quasiperiodic lattice, and that the Fermi level is crossed by dispersing d-bands. The observation of free-electron-like bands, distributed in momentum space according to the surface diffraction pattern, suggests that the electronic states are not dominated by localization.

Comparison of gas chromatographic-mass spectrometric methods for screening of chlorotriazine pesticides in soil.

The performance of a coupled technique resulting from the combination of gas chromatography with a selective mass spectrometric technique (tandem mass spectrometry) (GC-MS-MS) with collisionally activated dissociation (CAD) and multi-reaction monitoring (MRM) was compared with that of GC-low resolution MS (GC-LRMS) at a resolving power of 1000 and GC-high-resolution MS (GC-HRMS) at resolving powers of 5000 and 10,000 for the determination of atrazine, simazine, cyanazine, deethylatrazine and deisopropylatrazine in polluted soil samples. GC-MS-MS daughter ion spectra for the parent ions [M]+. and [M - CH3]+ were generated using collisionally activated dissociation and studied. Also, by optimizing the collision energy for maximum sensitivity a method for screening chlorotriazines by MRM was developed. Analyses of soil sample extracts showed that GC-MS-MS overcomes interferences from other chlorotriazines and interfering compounds that could not be removed by GC-HRMS or GC-LRMS at resolving powers of 10,000 and 1000, respectively. The limits of detection for GC-MS-MS and GC-HRMS at a signal-to-noise ratio of 10 ranged between 1 and 24 pg, with a mean relative standard deviation of 25-30%. Soil samples known to contain chlorotriazines and their degradation products were analysed by GC-MS-MS and the results obtained were compared with those given by GC-HRMS at resolving powers of 5000 and 10,000, with quantification differences of 25-30%.

[Antecedents of pediatric pathology in adolescents hospitalized in a department for pediatric psychiatry]. / Antécédents de pathologie pédiatrique des adolescents hospitalisés en pédopsychiatrie.

The antecedents of pediatric hospitalization and previous history of somatic disturbance in 101 adolescents aged 12-16 yr hospitalized in a pedopsychiatric unit were compared to those of a representative population of 101 high school adolescents without psychiatric problems. Patients and controls were matched according to age, sex and parents nationality. The result showed that adolescents with psychiatric disorders were significantly more frequently hospitalized during infancy and childhood, particularly for medical reasons. They also presented many more algic syndromes, recurrent headaches, recurrent vomiting and epilepsy. Thus, recurrent pediatric hospitalization and chronic somatic disturbance appear to be warning signals of a possible psychiatric risk and should lead to a psychological investigation of the child and his relations with the family.

Osteoid osteoma of the acetabulum: two cases.

We report two cases of osteoid osteoma of the acetabulum associated with severe chronic synovitis. The diagnosis is difficult and usually delayed because the acetabulum is a rare site for this tumor and clinical signs are nonspecific. Computed tomography (CT) scanning is the best diagnostic technique. An intraarticular surgical approach allows complete resection, but one case required spongy bone grafts. Postoperative results are excellent.

[Carpal tunnel syndrome in children. Apropos of 4 personal cases]. / Le syndrome du canal carpien chez l'enfant. A propos de 4 observations personnelles.

Four cases of Carpal Tunnel syndrome during childhood are reported. Two of them are post traumatic cases; for one child, the syndrome was caused by hypertrophic cal six months after trauma. The other child has been operated because of a median and ulnar nerve deficit syndrome, which appeared one month after fracture. In the third observation, the authors have seen an abnormal muscle just in front of annular anterior ligament of the carpus during surgery. This muscle was assimilated to hypertrophic Palmaris Brevis muscle. In the last observation, the adolescent had a Poland syndrome with Sprengel malformation. In this paper, the authors point out clinical particularities due to musculo-tendinous malformation which can lead to Carpal Tunnel syndrome.

Allergy to nickel or cobalt: tolerance to nickel and cobalt samples in man and in the guinea pig allergic or sensitized to these metals.

The aim of this study was to evaluate, in animals and humans sensitive to nickel or cobalt, the tolerance to manufactured metal samples of nickel and cobalt of a defined metallographic structure, plated or not with a layer of chrome or copper/chrome of a determined thickness. Under the defined experimental conditions, a guinea pig sensitized to one metal (nickel or cobalt) was intolerant to both metals (nickel and cobalt). A plating of chrome or copper/chrome did not act as a protection. In the human, it was not the same: the tolerance to metal samples was determined by the specific sensitivity. A plating of chrome or copper/chrome did not act as protection.

[Percutaneous epiphysiodesis. First trials with the long bones of the lower limbs]. / L'épiphysiodèse percutanée. Premiers essais concernant les os longs des membres inférieurs.

Ten children underwent a percutaneous drilling. The growth plate is destroyed under X ray control. The results are usually good, except in one analysed case. The percutaneous epiphysiodesis is minimally traumatic, cosmetically preferable and safe.

Nickel allergy: tolerance to metallic surface-plated samples in nickel-sensitive humans and guinea pigs.

The purpose of this work is to evaluate in nickel-sensitive patients and guinea pigs the tolerance to nickel samples, surface-plated with one or several metals of varying structures and thicknesses. All the metal samples elicited allergic reactions in the guinea pig. In humans, absolute tolerance was not observed for any sample. In humans, the interposing of a layer of bright copper between nickel and surface chrome greatly increased the tolerance.

[The urorectal syndrome caused by abdomen-levator incoordination in children]. / Le syndrome urorectal par incoordination abdomino-lévatorienne chez l'enfant.

We have studied thirty four children (mean age 6.6 years) with severe functional constipation, associated or not with encopresis. In twenty three cases the defecography showed a persistent anorectal angle due to failure of puborectalis sling relaxation during defecation straining. Voiding disorders, unknown to parents, but demonstrated by obstructive uroflowmetry, are also seen in nineteen of these children. Therefore is definite a true urorectal outlet obstruction syndrome by spastic pelvic floor mechanism. The exact etiologic factor of these functional abnormalities remains undefined. All children were managed by biofeedback training. A satisfactory result (with six months follow up), has obtained in fourteen cases.

[Aggressive fibrous dysplasia of the mandible. Resection of the lower portion of the mandible]. / Dysplasie fibreuse agressive de la mandibule. Résection de la partie gauche de la mandibule.

Report of a case of swelling monostotic fibrous dysplasia in the left part of the mandible in a girl 8 years old. Two rapid recurrences after total curettage require the sus periostal resection of the left part of the mandible, without bone graft. Total recovery with 6 years follow up, with good cosmetic and functional result because of bone regeneration and growth stimulation by orthesis.

Intraoperative radioactive localization of osteoid osteomas: four case reports.

We have excised four osteoid osteomas in four children, aided by intraoperative radioactive localization. Here we report these cases and describe the equipment used. Exact detection and elective excision are the two advantages of this technique.

[Advantages and disadvantages of peroperative isotopic localization in the excision of osteoid osteoma. Considerations apropos of 6 cases]. / Intérêts et pièges du repérage isotopique peropératoire dans l'exérèse de l'ostéome ostéoïde. Réflexions à propos de 6 observations.

We have excised six cases of osteoid osteoma in children, by using intra-operative accurate radioactive localization. The value of this technique is considerable and allows a better localization of the lesion. Exact detection and elective excision are the two advantages of this technique. We are reporting these case and describing the equipment being used.