Very low-temperature epitaxial growth of Mn5Ge3 and Mn5Ge3C0.2 films on Ge(111) using molecular beam epitaxy

International audienceC-doped Mn5Ge3 compound is ferromagnetic at temperature up to 430 K. Hence it is a potential spin injector into group-IV semiconductors. Segregation and diffusion of Mn at the Mn5Ge3 /Ge interface could severely hinder the efficiency of the spin injection. To avoid these two phenomena we investigate the growth of Mn5Ge3 and C-doped Mn5Ge3 films on Ge(111) substrates by molecular beam epitaxy at room-temperature. The reactive deposition epitaxy method is used to deposit these films. Reflection high energy electron diffraction, X-ray diffraction analysis, transmission electron microscopy and atomic force microscopy indicate that the crystalline quality is very high. Magnetic characterizations by superconducting quantum interference device and ferromagnetic resonance reinforce the structural analysis results on the thin films quality

The contribution of condensation-corrosion in the morphological evolution of caves in semi-arid regions: preliminary investigations in the Kyrenia Range, Cyprus

The condensation-corrosion process occurs when airflow cools at the contact with colder cave walls. Condensed water becomes aggressive for soluble rocks and corrodes the walls. This process is particularly active close to cave entrances in high thermal gradient zones where external air enters caves. Condensation appears to be important where bat colonies are also present. Bat metabolism and guano decomposition release heat, vapour, and acids. Hence, bat colonies contribute to the increase of condensation- corrosion, especially by providing permanent moisture and chemical aggressiveness. Corrosive air convections produce rounded morphologies, such as ceiling channels, cupolas, and corroded older flowstones. This process has been overlooked in previous research, since related morphologies were often confused with those produced by early phreatic flow. Kyrenia Range in Cyprus has a semi-arid climate. All the studied caves developed along open-fractures. They are located both in recrystallized carbonates (limestone and dolostone, such as Smoky and Pigeons Caves), or in gypsum (First Day and Angry Bat Caves). We also studied a maze cave that acted as a spring in gypsum that initially developed under phreatic conditions, followed by an epiphreatic phase that allowed the development of notches (Fig Tree Cave, also named İncirli Show Cave). Due to the semi-arid climate, external air is very dry in summer, thus condensation seems to occur mainly in winter, when cave atmosphere instability allows large air exchanges between caves and surface atmosphere. In summer, evaporation prevails, allowing the development of popcorn lines in carbonate caves and massive gypsum crusts, stalagmites, and sidewalk rims in gypsum caves. However, the presence of a bat colony in a semi-confined chamber in Smoky Cave is probably the origin of the permanent moisture, also during the dry season, leading to a strong development of condensation-corrosion features such as ceiling cupolas, and possibly to the permanent activity of flowstones. In addition, we detected high concentrations of sulphur dioxide (SO2) and radon (Rn) in Fig Tree Cave, possibly related to the activity of the neighbouring overthrust. Based on the five studied caves in the Kyrenia Range and surroundings, the open-fracture caves in carbonates and gypsum have not undergone the typical initial phreatic stage, but have formed in a short time during Pleistocene as a result of the fast uplift of the range and were later reshaped by condensation-corrosion morphologies. Some gypsum caves may have formed entirely by this latter process, after initial minor fracture development. Cyprus is an outstanding area for studying the condensation-corrosion in caves, since a phreatic origin can be ruled out for most of the rounded morphologies. Prispevek kondenzacijske korozije pri razvoju jam v polsuhih območjih: predhodni rezultati v jamah Kirenijskega gorovja, CiperKondenzacijska korozija se pojavi ob stiku vlažnega zračnega toka s hladnimi jamskimi stenami. Pri tem na jamsko steno iz zraka kondenzira film vode, ki kemično korodira vodotopno kamnino. Proces je najbolj izrazit v bližini jamskih vhodov, kjer ob visokem temperaturnem gradientu zunanji zrak vstopa v jamo. Kondenzacijo in kondenzacijsko korozijo lahko pomembno povečajo kolonije netopirjev. Metabolizem netopirjev in razpadanje gvana sproščata toploto, vlago in kisline. Kondenzacijska korozija iz konvekcijskih tokov vlažnega zraka ustvarja zaobljene skalne oblike, kot so kupole, stropni kanali in korodirana siga. Kirenijsko gorovje na Cipru ima polsuho podnebje. Večina jam v tej raziskavi so odprte razpoke v prekristaljenem karbonatu (apnenec in dolomit) ali v sadri. Poleg teh obravnavamo tudi blodnjake v sadri, ki so se oblikovali v freatični coni in so v preteklosti delovali kot izviri. V njih najdemo stenske zajede, ki so nastale v epifreatični fazi. Ker je zrak poleti zelo suh, je kondenzacija omejena na zimski čas, ko se intenzivno izmenjuje zrak med jamsko in zunanjo atmosfero. Poleti prevladuje izhlapevanje, kar omogoča razvoj cvetačastih oblik v karbonatnih jamah ter sadrinih skorij, stalagmitov in stranskih obrob v jamah v sadri. Kolonija netopirjev v eni od polzaprtih dvoran v jami Smoky Cave verjetno vzdržuje visoko vlago tudi poleti. Posledica so močno izražene oblike kondenzacijske korozije (kupole) in stalna aktivna rast sige. V eni od jam smo izmerili visoko vsebnost SO2 in radona, ki je verjetno povezana z aktivno narivno tektoniko. Pet obravnavanih jam je tektonskega izvora in so verjetno nastale v kratkem obdobju hitrega dvigovanja v pleistocenu ter bile kasneje preoblikovane s kondenzacijsko korozijo. Nekatere jame v sadri so nastale skoraj izključno s kondenzacijsko korozijo, ki je preoblikovala prvotne majhne razpoke. Ciper je izjemno območje za podobne študije, saj lahko zaradi odsotnosti freatične faze večino zaobljenih jamskih oblik pripišemo kondenzacijski koroziji.Ključne besede: Vzhodno Sredozemlje, kondenzacijska korozija, gvano, Kirenijsko gorovje, jame v odprtih razpokah, hitri tektonski dvig, sadra, jamska mikroklima, pleistocen

Electrodéposition sous champ magnétique de zinc et de fer.Propriétés magnétiques des arborescences de fer

President du jury: A. Alemany ; Raporteurs : J-P. Chopart, J.M.D. Coey ; Examinateurs : J-L. Porteseil, R. Ballou, P. MolhoThis work is concerned with the effects of magnetic fields on arborescence of zinc and iron obtained by electrochemical deposition in thin cell and with the magnetic properties of iron arborescences. For zinc under normal magnetic field, the macroscopic morphology changes are explained by the mechanical action, on the growing aggregate, of fluid convection induced by the Lorentz force. A weak effect is observed at the microscopic scale but none on the crystal structure. An in-plane magnetic field influences the growth only very weakly. For iron, a normal magnetic field has a weak effect. An in-plane magnetic field transforms a morphology with circular symmetry to a morphology with two perpendicular axes of symmetry, one parallel to the field. This is explained by the minimisation of the Zeeman and magnetic dipolar energy. It is shown that magnetic properties are very sensitive to the morphology. Unusual anisotropy and coercivity are observed.Ce travail concerne les effets de champ magnétique sur les arborescences de zinc et de fer obtenues par électrodéposition en cellule fine et les propriétés magnétiques des arborescences de fer. Pour le zinc et sous champ magnétique normal, les changements de morphologie macroscopiques variés sont expliqués par l'action mécanique sur l'agrégat en croissance de convections fluides induites par la force de Lorentz. Un faible effet est observé à l'échelle microscopique mais pas sur la structure cristalline. Un champ plan n'influence que faiblement la croissance. Pour le fer, un champ magnétique normal a un effet faible. Un champ plan transforme une morphologie de symétrie circulaire en une morphologie à deux axes de symétrie perpendiculaires, une parallèle au champ. Ceci est expliqué par la minimisation des énergies Zeeman et dipolaires. Il est montré que les propriétés magnétiques sont tres sensibles à la morphologie. Une anisotropie et une coercivité inhabituelles sont observées

Electrodéposition sous champ magnétique de zinc et de fer (propriétés magnétiques des arborescences de fer)

: Ce travail concerne les effets de champ magnétique sur les arborescences de zinc et de fer obtenues par électrodéposition en cellule fine et les propriétés magnétiques des arborescences de fer. Pour le zinc et sous champ magnétique normal, les changements de morphologie macroscopiques variés sont expliqués par l'action mécanique sur l'agrégat en croissance de convections fluides induites par la force de Lorentz. Un faible effet est observé à l'échelle microscopique mais pas sur la structure cristalline. Un champ plan n'influence que faiblement la croissance. Pour le fer, un champ magnétique normal a un effet faible. Un champ plan transforme une morphologie de symétrie circulaire en une morphologie à deux axes de symétrie perpendiculaires, une parallèle au champ. Ceci est expliqué par la minimisation des énergies Zeeman et dipolaires. Il est montré que les propriétés magnétiques sont très sensibles à la morphologie. Une anisotropie et une coercivité inhabituelles sont observées.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Magnetic properties of Fe arborescences grown by electrodeposition

International audienceMagnetization measurements were performed on Fe arborescent aggregates grown by electrodeposition. ‘Sparse' arborescences with few thick branches and ‘dense' arborescences with many thin branches can be generated. A change in the magnetic behavior is observed in connection with these morphologies. Sparse arborescences show a soft magnetism not too different from that of bulk Fe. Dense arborescences show a behavior akin to that of ‘fine grains': a remanent magnetization about half of the saturation and a coercive field of about 0.1 T are measured at low temperature. On increasing the temperature, a superparamagnetic contribution is detected up to room temperature

Step flow growth of Mn5Ge3 films on Ge(111) at room temperature

International audienceThe very first stages of the non-diffusive growth of Mn5Ge3 thin films on Ge(111) substrates are characterized by several techniques. Mn5Ge3 films are grown by molecular beam epitaxy using the co-deposition of Mn and Ge atoms at room temperature. XRD measurements demonstrate that the thin films are monocrystalline. The evolution of the RHEED intensity during the deposition and the AFM images show a step-flow growth mode. RHEED patterns, combined with TEM images, prove that the lattice mismatch of 3.7% is accommodated by the formation of an array of interfacial dislocations and by the presence of a residual strain in the thin films. These observations are supported by the numerical calculations of the critical nucleation volumes exhibiting very similar values, in the case of a pseudomorphic growth or in the case of an accommodation of the lattice mis-match by interfacial dislocations. Furthermore, the effect Ge/Mn stoichiometric and Mn-rich fluxes on the surface morphology is examined

Synchrotron high-resolution XRD and thermal expansion of synthetic Mg calcites

International audienceThe structural parameters and the thermal behavior of a complete series of Ca–Mg carbonates synthesized at high pressure and temperature (1–1.5 GPa, 1273–1373 K) in the range 0–50 mol% MgCO3 have been investigated by in situ powder synchrotron high-resolution X-ray diffraction at ambient and up to 1073 K under self-controlled CO2 partial pressure. The crystal structures are disordered Mg calcite in the range 1–41 mol% MgCO3, and Ca dolomite at 49 mol% MgCO3. New calibration curves of the cell parameters for the Mg content and thermal expansion from ambient to 1073 K are given. Short-range structural effects of cation substitution and ordering and their thermal behavior as a function of Mg content were identified from three sets of data: the peak broadening, the cell parameter strains and the Raman band enlargements. Both intra- and inter-crystalline levels of compositional heterogeneity are identified and allow splitting the Mg calcites into two groups: low- and high-Mg calcites. The low-Mg calcites (up to 22 mol% MgCO3) are homogeneous in Mg content with short-range ordering. High-Mg calcite (up to 41 mol% MgCO3) displays domains with different local ordering configurations and similar or slightly different Mg contents, and to which is added a compositional variation between crystals, as determined by EMP, of the order of  ± 0.8 mol% MgCO3. The cation ordering in Ca-rich dolomites similarly occurs in high-Mg synthetic calcites. The role of (CO3)2− group ordering is shown to be an important factor in the formation of Ca–Mg carbonates

Regular Arrays of Pt Clusters on Alumina: A New Superstructure on Al 2 O 3 /Ni 3 Al(111)

International audienceAlumina ultrathin films obtained by high temperature oxidation of a Ni3Al (111) surface are a good template to grow regular arrays of metal clusters. Up to now two hexagonal organizations called 'dot' and 'network' structures have been observed with distances between clusters of 4.1 and 2.4 nm, respectively. In the present article we report on an investigation by in situ Grazing Incidence Small Angle X-ray Scattering (GISAXS), showing that Pt deposited at room temperature (RT) and for a low coverage forms a new hexagonal structure with a distance between clusters of 1.38 nm. For the first time, an assembly of tiny Pt clusters (1-6 atoms) with a very high density (5.85x10 13 cm-2) and presenting a good organization on an alumina surface, is obtained. This system could be used to investigate by surface science techniques the new emerging field of Single Atom Catalysis (SAC). By deposition at 573 K small Pt clusters are organized on the network structure. By deposition of Pt at 573 K on pre-formed Pd seeds, large Pt (Pd) clusters containing a hundred of atoms are organized on the dot structure and they remain organized up to 733 K. We show that the three structures are interrelated. The different organizations of the Pt clusters on the alumina surface are explained by the presence of 3 types of sites corresponding to different adsorption energy for Pt atoms

Modular microfluidic platform for solubility measurement, nucleation statistics and polymorph screening of active pharmaceutical ingredients: Irbesartan, Rimonabant, Aripiprazole and Sulfathiazole

Drug efficacy strongly relies on the solid state of the active pharmaceutical ingredient. Classical solid-state screening methods involve different solvent compositions and supersaturations. Moreover, the many repeat experiments needed to address the stochasticity of nucleation make this approach costly. This paper presents a newly developed modular microfluidic platform that provides a universal and flexible plug-and-play tool for crystallisation studies without use of surfactants. By dissolving a powder, our setup generates saturated solutions that can be used for solubility measurements or distributed in microdroplets. Here, we describe solubility measurements performed on different forms, stable and metastable, of pharmaceutical molecules (Irbesartan, Rimonabant and Aripiprazole) in organic and aqueous solvents. In addition, we provide nucleation statistics obtained for Sulfathiazole in water and in acetonitrile. Reporting polymorph screening on Sulfathiazole and statistics for nucleated forms, we find that the cooling rate influences both nucleation and polymorphism results, reflecting the competition between thermodynamics and kinetics. Three unknown forms were discovered, with XRD patterns and Raman spectra that do not match any referenced form. We also demonstrate the limitations of microfluidics for crystallisation by cooling: reducing the crystalliser volume considerably increases nucleation induction time