Search results for "Electron diffraction"
showing 10 items of 191 documents
Superficial oxidation of molybdenum at high pressure and low temperature: RHEED and AES analyses of the molybdenum oxide formation
1991
Abstract Numerous studies relate to the interaction of the molybdenum surface with oxygen at low pressure and high temperature. They give results about oxygen chemisorption, surface facetting and the epitaxial formation of MoO 2 crystallites. This work deals with the interaction of Mo(100), Mo(110) and Mo(111) surfaces with oxygen at high pressure (10 4 Pa) and low temperature (620–820 K). RHEED and AES analyses results prove that, in these oxidation conditions: MoO 2 and non-stoichiometric molybdenum oxide such as Mo 4 O 11 are not evidenced in any of the molybdenum oxidation steps. The MoO 3 phase nucleates directly from any Mo surface. The structure and orientation of MoO 3 nuclei are ch…
Accurate and precise lattice parameters by selected-area electron diffraction in the transmission electron microscope
2009
8 páginas, 6 figuras, 7 tablas.
Interaction of oxygen with Mo(100), Mo(110), and Mo(111) surfaces. RHEED and AES analyses of the molybdenum oxide nucleation and growth
1991
Abstract A study of the nucleation and growth of MoO 3 generated by interaction of oxygen with Mo(100), Mo(110), and Mo(111) single crystalline surfaces is investigated at high oxygen pressure (10 4 Pa) and low temperature (620 to 820 K). The results of RHEED and AES analyses prove that under these oxidation conditions, MoO 3 nucleates directly from the metal without intermediate formation of MoO 2 or nonstoichiometric molybdenum oxide such as Mo 4 O 11 . The structure and orientation of MoO 3 nuclei are characterized in relation with the parent molybdenum surface. On the Mo(110) and Mo(111) surfaces, which are faceting, the nucleation and growth of MoO 3 takes place by successive structura…
Morphology and magnetoresistance of Co2Cr0.6Fe0.4Al-based tunnelling junctions
2009
Some ferromagnetic Heusler compounds are theoretically predicted to be half metallic materials, i.e. to be characterized by a huge spin polarization at the Fermi energy. We investigate the correlations between junction preparation conditions, morphology and transport properties of planar MgO/Co2Cr0.6Fe0.4Al/AlOx/Co/CoOx/Pt tunnelling junctions. Epitaxial Co2Cr0.6Fe0.4Al thin films were deposited by dc and rf magnetron sputtering on different buffer layers (Cr, Fe, MgO) on MgO(1 0 0) substrates. By RHEED, LEED and in situ STM investigations different surface morphologies were observed. Atomically flat surfaces with Co2Cr0.6Fe0.4Al unit cell sized steps (B2 structure) were obtained by rf sput…
Electron Diffraction Reinvestigation of CdCr<sub>2</sub>Se<sub>4</sub> and ZnCr<sub>2-x</sub>V<sub>x</su…
2013
Crystal structure of two spinel single crystals CdCr2Se4 and ZnCr2-xVxSe4 have been reinvestigated using automated electron diffraction tomography method with beam precession. 3D reciprocal space have been reconstructed base on recorded tilt series. For both samples crystal structure was refined and the cubic symmetry with space group Fd-3m was confirmed. No additional electron potential has been located beside occupied atom sites.
Ex situ investigations of MOCVD-grown gallium nitride nanowires using reflection high energy electron diffraction
2011
Vertically oriented nanowires (NWs) of single-crystalline wurtzite GaN have been fabricated on sapphire substrates, via metal organic chemical vapor deposition (MOCVD). We present ex situ investigations on orientation and structure of grown GaN nanowires on GaN(0001) surface using reflection high energy electron diffraction (RHEED). Both ordered and randomly oriented GaN crystalline structures have been detected.
Isolated self-assembled InAs/InP(001) quantum wires obtained by controlling the growth front evolution
2007
6 páginas, 5 figuras. In this work we explore the first stages of quantum wire (QWR) formation studying the evolution of the growth front for InAs coverages below the critical thickness, θc, determined by reflection high energy electron diffraction (RHEED). Our results obtained by in situ measurement of the accumulated stress evolution during InAs growth on InP(001) show that the relaxation process starts at a certain InAs coverage θRθR this ensemble of isolated nanostructures progressively evolves towards QWRs that cover the whole surface for θ = θc. These results allow for a better understanding of the self-assembling process of QWRs and enable the study of the individual properties of In…
Crystalline nanorods as possible templates for the synthesis of amorphous biosilica during spicule formation in Demospongiae.
2009
In tandem: High-resolution TEM shows that during the initial stages of demosponge spicule formation, a primordial crystalline structure is formed within the axial filament. The recently developed electron diffraction tomography technique (ADT) reveals that the nanorods have a layered structure that matches smectitic phyllosilicates. These intracellular nanorods have been considered as precursors of mature spicules. High-resolution microscopy shows that, during the initial stages of demosponge spicule formation, a primordial crystalline structure is formed within the axial filament. The recently developed electron diffraction tomography technique reveals that the nanorods have a layered stru…
Crystal structure determination of a new LaPO4 phase in a multicomponent glass ceramic via 3D electron diffraction
2022
Abstract A glass ceramic from the MgO–Al2O3–SiO2 system containing additives of ZrO2, TiO2, La2O3 and P2O5 was investigated. Via x-ray powder diffraction (XRPD) and Transmission electron microscopy(TEM) the crystalline phases present could be identified as MgAl2O4 (Spinel), orthorhombic ZrTiO4 and a polymorph of LaPO4 with a previously unknown crystal structure. The crystal structure of this LaPO4 phase was solved ab initio via 3D ED Data. The polymorph occurs in a distorted barite structure type in the same space group (P21/n) as the stable monazite type polymorph, however the density is higher and the La has a higher coordination number. Furthermore the LaPO4 is present in a spinodal reli…
Two-dimensional dye crystals with controllable optical properties
1993
The structure, molecular ordering and optical properties of single crystals of cyanine dyes grown by adsorption from a water subphase to a positively charged lipid monolayer are discussed. These crystals are one monolayer thick, of uniform dimensions between 10 and 100μm (depending on nucleation conditions) and of rectangular shape. Single crystals were studied by transmission electron diffraction and by polarized absorption and emission spectroscopy. We show that the crystals consist of two rows of densely stacked molecules with two different orientations of the long molecular axes. This leads to two perpendicularly polarized absorption bands. The measured splitting is in accordance with r…