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Gd silicide nanostructures epitaxially grown on Si(001) are studied by plan-view transmission electron microscopy and associated nanobeam electron diffraction, as well as scanning tunneling microscopy. The nanobeam diffraction measurements show a direct correlation between the nanostructure morphology, either nanowires or islands, and the silicide crystal structure. Scanning tunneling microscopy shows a phase transformation from nanowires to islands that nucleate at nanowire intersections. A specific mechanism for this transformation is proposed that explains nanowire growth behavior previously observed on vicinal Si surfaces.
Ferromagnetic/non-magnetic (F/N) metallic multilayers in the Current-Perpendicular-to-Plane (CPP) geometry show giant Magnetoresistance (MR) and are promising candidates for potential use in high density storage devices. F/Al interfaces were recently shown to have large interface specific resistances that enhance the CPP-resistance. However, the CPP resistances showed instability over time at room temperature and also upon annealing to 453K. To help understand both the large interface specific resistances and their instabilities, we have undertaken cross-sectional High Resolution Transmission Electron Microscopy (HRTEM) and Electron Energy Loss Spectroscopy (EELS) studies of both as-sputtered and annealed Py/Al and Co/Al multilayers. We find well-layered, but rough structures with local F/Al interfaces being tilted up to ˜15°from the plane perpendicular to the growth direction. HRTEM images appear to show diffuse interfaces, but a through-focus series of images suggests considerable grain overlap in the electron beam direction, thereby complicating interpretation. This combination of HRTEM imaging and EELS analysis suggests that any interfacial mixing is limited in scale, and shows no evidence of intermetallic compound formation. No obvious differences are seen between assputtered and annealed samples.
There has been considerable interest in the properties of rare earth metal nanostructures grown epitaxially on Si(001) surfaces. The questions arises as to what extent the nanometer scale lateral dimensions (width and thickness) affect the material properties. We compare thin film Gd silicide samples with Gd nanostructures grown on Si(001) using high resolution transmission electron microscopy (HRTEM). The nanostructures have the same orthorhombic crystal structure as the thicker silicide films. Electron energy loss spectroscopy measurements from metallic Gd and the thin film silicides are also shown as references for similar measurements on the nanostructures.
Self-assembled gadolinium silicide (GdSi2) nanostructures grown on Si(001) were studied by transmission electron microscopy (TEM) and scanning tunneling microscopy (STM). Cross-sectional TEM and plan-view TEM moiré fringe pattern analyses show that the GdSi2 nanostructures can be divided into two classes: elongated nanowires with hexagonal crystal structure and rectangular islands with orthorhombic or tetragonal crystal structure.
High resolution electron microscopy has been used to study the core structure of a/2 and a/3<112> dislocations in Ni3Al deformed in the range of increasing strength with temperature. a/3<112> coupled SISFs were found to lie on (111) and their structure agreed well with theoretical predictions. a/2 superpartials were always dissociated on (111) or (111) planes while the APB plane was found to be (010). Computer simulation of dislocation core structures were found to agree well with the observed dissociations. The APB width was found to increase significantly with increasing deformation temperature near the peak yield strength temperature.
Melt spinning was used to produce rapidly solidified ribbons of the B2 intermetallics NiAl and FeAl. Both Fe-40Al and Fe-45A1 possessed some bend ductility in the as spun condition. The bend ductility of Fe-40Al, Fe-45Al, and equiatomic NiAl increased with subsequent heat treatment. Heat treatment at approximately 0.85 Tm resulted in significant grain growth in equiatomic FeAl and in all of the NiAl compositions. Low bend ductility in both FeAl and NiAl generally coincided with intergranular failure, while increased bend ductility was characterized by increasing amounts of transgranular cleavage fracture.
High-resolution transmission electron microscopy has been used to investigate the structure and growth behavior of three separate multilayer systems composed of spin-glass alloys(AuFe.03,CuMn.15, and AgMn.09) alternating with amorphous silicon. Each of the three systems was fabricated with two different sample configurations. The first consisted of bilayers with 3 nm spinglass alloy and 7 nm amorphous siliconlayers. The second consisted of 7 nm spin-glass alloy and 7 nm amorphous silicon layers. HRTEM images of ion-milled cross-sectioned samples revealed variations in the degree of crystallinity of the spin-glass material. Variations in the amount and symmetry of interlayer formation were also observed. Systematic studies of such variations should help to explain differences in their measured spin-glass properties.
To gain a better understanding of the ductility limitations in TiAl alloys, the mechanisms involved in deformation strain transfer and/or microcrack initiation at grain boundaries have been examined in an equiaxed near-γ alloy. These studies have been carried out on both in-situ and ex-situ deformed bulk samples using scanning electron microscopy (SEM) techniques for both orientation analysis and deformation defect imaging. Selected area electron channeling patterns (SACPs) have allowed determination of grain orientations, eliminating ambiguity between the a and c axes. Deformation twins and dislocations have been imaged in the bulk samples using electron channeling contrast imaging (ECCI). A combination of ECCI contrast analysis and trace analysis based on orientations determined from SACP has allowed identification of the active deformation systems. Microcracks have been found to initiate at γ-γ boundaries as a result of an inability to adequately transfer twin strain from grain to grain. Once initiated, cracks propagate through cleavage and re-nucleation of grain boundary microcracks in front of the advancing crack. A geometric based predictive factor has been developed that accounts for microcrack initiation at γ-γ boundaries based in deformation twinning and strain accommodation by ordinary dislocations.
Growth orientation and type of internal structures are both observed to change abruptly as a function of growth temperature in catalyst free growth of gallium nitride nanowires. In the present work, corresponding temperature-dependent changes in the growth matrix substrate that can affect the availability of nucleation sites and influence the reactivity of constituent adatom materials in catalyst-free nanowire growth are investigated. The influence of Ga vapor pressure and an abrupt change in the availability of single versus molecular adatom constituents is identified as a possible controlling parameter.
The evolution of carbon onion structure from spherical to polyhedral is correlated with changes in the sp3/sp2 ratio as a function of increasing synthesis temperature using electron energy loss spectroscopy, scanning electron microscopy, and high resolution electron microscopy. Results that are obtained using asymmetric f-variance versus symmetric Gaussian deconvolution of electron energy loss spectra are compared. The possibility of a separate peak at 287 eV is discussed.
Martin Crimp is one of the most exciting British playwrights to have emerged since the 1980s: his work is characterized by its vision of contemporary society as a place of social decay, moral compromise, and barely suppressed violence. He is also a writer whose work engages with both British and European theatre traditions. He started his career in 1981 at the Orange Tree Theatre, a fringe venue in Richmond, and this theatre produced all his early work, including Dealing with Clair and Play with Repeats. But it was when he became a Royal Court playwright in 1990, with No One Sees the Video, that he achieved international success and recognition. Three plays in particular – The Treatment, Attempts on Her Life and The Country – have become recognized masterpieces. Crimp has also pursued a parallel career as a translator and adapter of classics such as Molière's The Misanthrope and Sophocles' The Women of Trachis (as Cruel and Tender). The interview with Aleks Sierz which follows is assembled from conversations with Martin Crimp in London during February and March 2006, and the NTQ Checklist of Crimp's work on page 361 is derived from materials assembled by Sierz for his forthcoming book from Methuen, The Theatre of Martin Crimp.
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