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234 results on '"Castell, Martin R."'

2. Out- versus in-plane magnetic anisotropy of free Fe and Co nanocrystals: tight-binding and first-principles studies

Author

Li, Dongzhe, Barreteau, Cyrille, Castell, Martin R., Silly, Fabien, and Smogunov, Alexander

Subjects
Condensed Matter - Materials Science
Abstract

We report tight-binding (TB) and Density Function Theory (DFT) calculations of magnetocrystalline anisotropy energy (MAE) of free Fe (body centerd cubic) and Co (face centered cubic) slabs and nanocrystals. The nanocrystals are truncated square pyramids which can be obtained experimentally by deposition of metal on a SrTiO$_3$(001) substrate. For both elements our local analysis shows that the total MAE of the nanocrystals is largely dominated by the contribution of (001) facets. However, while the easy axis of Fe(001) is out-of-plane, it is in-plane for Co(001). This has direct consequences on the magnetic reversal mechanism of the nanocrystals. Indeed, the very high uniaxial anisotropy of Fe nanocrystals makes them a much better potential candidate for magnetic storage devices., Comment: 8 pages, 7 figures

Published
2014
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3. Deriving molecular bonding from macromolecular self-assembly

Author

Silly, Fabien, Weber, Ulrich K., Shaw, Adam Q., Burlakov, Victor M., Castell, Martin R., Briggs, G. A. D., and Pettifor, David G.

Subjects
Condensed Matter - Materials Science
Abstract

Macromolecules can form regular structures on inert surfaces. We have developed a combined empirical and modeling approach to derive the bonding. From experimental scanning tunneling microscopy (STM) images of structures formed on Au(111) by melamine, by PTCDA, and by a 2:3 mixture of the two, we determine the molecular bonding morphologies. Within these bonding morphologies and recognizing the distinction between cohesive and adhesive molecular interactions we simultaneously simulated different molecular structures using a lattice Monte Carlo method. Within these bonding morphologies there is a distinction between cohesive and adhesive molecular interactions. We have simulated different molecular structures using a lattice Monte Carlo method.

Published
2008

6. Ultrathin Oxide Films on Au(111) Substrates

Author

Wu, Chen, Castell, Martin R., Hull, Robert, Series editor, Jagadish, Chennupati, Series editor, Osgood, Richard M., Series editor, Parisi, Jürgen, Series editor, Seong, Tae-Yeon, Series editor, Uchida, Shin-ichi, Series editor, Wang, Zhiming M., Series editor, Kawazoe, Yoshiyuki, Series editor, Netzer, Falko P., editor, and Fortunelli, Alessandro, editor

Published
2016
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7. Planar NbnOm Clusters on the Au(111) Surface.

Author

Wang, Shuqiu, Zhu, Yuhan, Van den Bossche, Maxime, Goniakowski, Jacek, Noguera, Claudine, and Castell, Martin R.

Subjects
SCANNING tunneling microscopy, ATOMIC clusters, ATOMIC structure, GOLD clusters, DENSITY functional theory, ULTRAHIGH vacuum, MICROCLUSTERS
Abstract

Planar oxide atomic clusters are of considerable scientific interest because of their potential for enhanced catalytic activity versus their three‐dimensional counterparts. This enhancement is the result of the substrate stabilizing novel planar configurations that have an extensive periphery where catalytic reactions can occur. A class of planar NbnOm atomic clusters that are synthesized by the evaporation of metallic Nb onto an Au(111) substrate in an ultrahigh vacuum environment and subsequent oxidation at elevated temperatures is reported. The atomic structures of the clusters are determined using a combination of scanning tunneling microscopy and density functional theory. The clusters are composed of structural units with four‐, five‐, and sixfold rotational symmetry and these units can assemble to form larger planar clusters. The theoretical comparison of supported structures with their hypothetical freestanding counterparts shows that the atomic and electronic structures of the oxide clusters are significantly altered by the interaction with the Au substrate. The substrate effects include interfacial charge transfer and structural relaxation to relieve the strain in the Nb‐O bonds. The substrate interactions also reduce the energy differences between clusters of different configurations and this enables the coexistence of a large variety of cluster configurations. [ABSTRACT FROM AUTHOR]

Published
2023
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8. Defects on Strontium Titanate

Author

Marshall, Matthew S. J., Becerra-Toledo, Andres E., Marks, Laurence D., Castell, Martin R., Ertl, Gerhard, Series editor, Lüth, Hans, Series editor, Car, Roberto, Series editor, Rocca, Mario Agostino, Series editor, Freund, Hans-Joachim, Series editor, Jupille, Jacques, editor, and Thornton, Geoff, editor

Published
2015
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34. 2020 roadmap on solid-state batteries

Author

Pasta, Mauro, primary, Armstrong, David, additional, Brown, Zachary L., additional, Bu, Junfu, additional, Castell, Martin R, additional, Chen, Peiyu, additional, Cocks, Alan, additional, Corr, Serena A, additional, Cussen, Edmund J, additional, Darnbrough, Ed, additional, Deshpande, Vikram, additional, Doerrer, Christopher, additional, Dyer, Matthew S, additional, El-Shinawi, Hany, additional, Fleck, Norman, additional, Grant, Patrick, additional, Gregory, Georgina L., additional, Grovenor, Chris, additional, Hardwick, Laurence J, additional, Irvine, John T S, additional, Lee, Hyeon Jeong, additional, Li, Guanchen, additional, Liberti, Emanuela, additional, McClelland, Innes, additional, Monroe, Charles, additional, Nellist, Peter D, additional, Shearing, Paul R, additional, Shoko, Elvis, additional, Song, Weixin, additional, Jolly, Dominic Spencer, additional, Thomas, Christopher I, additional, Turrell, Stephen J, additional, Vestli, Mihkel, additional, Williams, Charlotte K., additional, Zhou, Yundong, additional, and Bruce, Peter G, additional

Published
2020
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46. Shapes of epitaxial gold nanocrystals on SrTiO3 substrates.

Author

Chen, Peiyu, Murugappan, Krishnan, and Castell, Martin R.

Abstract

Morphological control of gold nanocrystals is important as their catalytic and optical properties are highly shape dependent. In this paper we report the shapes of gold nanocrystals which deviate from the equilibrium Wulff shape due to the influence of the SrTiO3 single crystal substrates. The gold crystals are characterized by scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). The nanocrystals have an equilibrium shape of a truncated octahedron with {111} and {001} facets. On all three substrate surfaces, i.e., SrTiO3(001)-(2 × 1), SrTiO3(001)-c(4 × 2), and SrTiO3(111)-(4 × 4) + (6 × 6), the height-to-width ratio of the gold crystals is not a constant as would be expected for equilibrium crystals, but instead it increases with crystal height. We propose that as the crystals increase in size, their aspect ratio heightens to relax the interfacial strain. The ratio between the {111} and {001} surface areas of our gold crystals is found to differ on the three substrates, which we speculate is due to the selective adsorption of surfactants on the {111} and {001} gold facets resulting from the different substrate surfaces. Reentrant facets of gold crystals that should be present according to their Wulff shape are not observed because these concave sites typically grow out due to kinetic considerations. This study demonstrates the significant effect of the crystal facet termination and surface reconstruction of an oxide substrate on the shape of supported gold nanocrystals. [ABSTRACT FROM AUTHOR]

Published
2020
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49. Template ordered open-grid arrays of paired endohedral fullerenes

Author

Deak, David S., Silly, Fabien, Porfyrakis, Kyriakos, and Castell, Martin R.

Subjects
Scanning tunneling microscopy -- Observations, Chemistry
Abstract

Oxide crystal surfaces are used as a template to controllably order endohedral fullerenes into two-dimensional (2D) open-grid arrays and are compared to ordinary close-packed ordering of endohedral fullerenes. The results have shown how topographic features of a substrate induce fullerenes to assemble into unique configurations.

Published
2006

50. Ordering of TiO2-based nanostructures on SrTiO3(001) surfaces

Author

Deak, David S., Silly, Fabien, Newell, David T., and Castell, Martin R.

Subjects
Titanium dioxide -- Structure, Nanotechnology -- Research, Electron spectroscopy -- Usage, Chemicals, plastics and rubber industries
Abstract

A class of nanostructured surface phases on SrTiO3(001) is characterized through atomic-resolution scanning tunneling microscopy and Auger electron spectroscopy. The nanostructures are composed of TiO2-derived complexes surrounded by a TiO2 surface termination and this surface ordering phenomena has introduced another level of complexity in the chemistry of perovskite oxide surfaces and has provided a basis from which potential photocatalytic and molecular-ordering applications might be developed.

Published
2006

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