| 1. |
- Muthukumar, Kaliappan, et al.
(författare)
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Cerium doped Fullerenes (Ce@C82 & Ce2@C80) adsorbed on Cu(111) surface : Theoretical Explanation for Surprising Experimental Findings
- 2008
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Konferensbidrag (refereegranskat)abstract
- Cerium is one of the most reactive elements of the rare earth group; and the complex physics accompanying its single occupied 4f band; close to the Fermi level; has baffled scientists for many decades. Cerium can be encapsulated into fullerene (C82 & C80) cages;1-4 which works as an n-dopant and in the incarcerated form it can be used as quantum bits in quantum computing2. Theoretical studies aiming at the detailed picture of metal-cage interaction and a closer look on the electronic structure of these Ce doped fullerenes have been reported.3-4 But; only a few theoretical studies have been conducted with an aim to address the nature of interaction of these endohedral fullerene molecules with semiconductors and metal surfaces. Hence; in this study; we apply density functional theory (DFT) to expand the investigation of Ce@C82 and Ce2@C80 on Cu (111) surface to have a more detailed study from both a fundamental and applied viewpoint to what extent the fullerene-surface interaction influences the encapsulated atom. Our calculations reveal a surprising observation in the electronic structure of doped Ce fullerenes on Cu (111) surface. We discuss and elucidate our results with the measured STM/STS spectra
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| 2. |
- Muthukumar, Kaliappan, et al.
(författare)
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Cerium Endohedral fullerenes (Ce@C82 and Ce2@C80) Theoretical Interpretations for Experimental observation
- 2008
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Konferensbidrag (refereegranskat)abstract
- Many questions remain unanswered for the endohedral fullerenes. Owing to the improvement in separation of isomers and in theoretical studies (DFT and ab-initio) evolving as imperative tool for characterization; these can be addressed.1;2 Understanding of the position and binding configuration of the metal atom inside the cage is crucial as it controls the structural and electronic properties of the molecule.3 Theoretical calculations proved to be efficient in explaining many controversies in the field of lanthanoid endohedral fullerenes.2-5 Fig; Ce2@C80; Ce2@C78) DFT optimized structures of Ce2@C80 D3d and Ce2@C78 D3h Here in this study we use DFT to characterize Ce doped metallofullerenes and report some surprising theoretical findings on the binding of cerium inside various carbon cages; (C60; C78; C80; C82). We observe that the presence of an additional Ce atom puts restrictions on the binding in the C80 cage6; but this does not happen in the C78 cage. We explain the reason behind this by analyzing the electronic structure. Further various spectra (RESPES; IETS; STM/STS) have been simulated for Ce@C82 and Ce2@C80 which we compare and discuss with experiments
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| 3. |
- Muthukumar, Kaliappan, et al.
(författare)
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Endohedral Fullerene Ce@C82 on Cu(111): Orientation, Electronic Structure, and Electron-Vibration Coupling
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:4, s. 1656-1662
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Tidskriftsartikel (refereegranskat)abstract
- Structural, electronic, and vibrational properties of the endohedral fullerene Ce@C82 on Cu(111) have been studied by scanning tunneling microscopy (STM) and density functional theory (DFT). Ce@C82 forms islands on the substrate. Our STM measurements show relatively large differences in morphology and electron spectra of molecules within these islands indicating multiple molecular orientations on the substrate, while the vibrational spectra are more uniform. We have determined molecular orientations by comparing STM and DFT molecular morphology, and we have calculated Ce@C82 bound to Cu(111) and found that it is chemisorbed. We show that Ce@C82 adopts orientations on the surface that enables Ce to remain at its most favorable binding site inside C82. The effect of chemisorption on the structural and electronic properties of Ce@C82 is thus small, and the orientations are limited to configurations with Ce in the upper hemisphere of the molecular configurational space. We show that the variations in the dI/dV spectra between molecules of different orientations is due to Ce-cage orbitals that are localized in space and their involvement in tunneling depends on the molecular orientation on the substrate. The observed electron-vibration coupling modes in the STM-IETS (in-elastic tunneling spectroscopy) of Ce@C82 arise from cage modes only, and therefore, electron transport properties are expected to be different compared to Ce2@C80, which has active Ce-cage vibrations.
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| 4. |
- Muthukumar, Kaliappan, et al.
(författare)
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Endohedral fullerenes and their implications in technology
- 2009
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Konferensbidrag (refereegranskat)abstract
- The interest in nanoscale materials is due to their positive impact in various scientific areas such as energy; environmental and in biomedical sciences. Carbon has a wide range of interesting properties; which makes it a versatile element and special attention has been paid to carbon based nanostructures such as fullerenes and nanotubes among several other investigated materials. Fullerenes; with their distinctive carbon cage structure; have been the object of intense research since their discovery and they have become a building block of nanoscience and a base for novel molecular materials. Fullerenes have also played a central role in the development of a variety of single molecule techniques and spectroscopies; each of which is currently an intensely active sub-field of nanoscience and nanotechnology. These include: single molecule manipulation; single molecule electronic and optical microscopy; and monomolecular electronic devices
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| 5. |
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| 6. |
- Muthukumar, Kaliappan, et al.
(författare)
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Surprising Findings for Ce Doped Fullerenes and Understanding of Experiments through Theoretical Modelling A DFT Approach
- 2008
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Endohedral fullerenes; which have one metal atom encapsulated; are relatively well studied compared to species that have two elements inside the cage.1-5 Cerium; the most reactive elements of the rare earth group can be encapsulated into fullerene (C78; C80; C82) cages;1 which works as a n-dopant and in the incarcerated form it can be used as quantum bits in quantum computing2. Understanding of the position and binding pattern of the metal atom inside the cage is important as it controls the structural and electronic properties of the molecule. We found that Ce in Ce@C82 has a specific and unique binding site in C82-C2v and has a C2v symmetric structure; which is explained by the specific charge pattern of this binding site and the symmetry of the MO s that comply well with the Ce d orbital bonding.6 This six-membered ring binding site is also favored by La in La@C82. Each of the six-membered rings of C80-Ih fulfills this symmetry criterion and therefore a similar kind of binding site is expected for Ce in Ce2@C80. But; we observe a novel binding site for Ce in presence of an additional cerium atom; while La preserve its usual binding pattern in La2@C80 as in La@C82.7 We here discuss and analyze the reason for the preference of novel binding site of Ce atoms in C80-Ih by explaining the competitive binding nature of Ce-Ce and Ce-C. Surprisingly; Ce in Ce2@C78 unlike Ce2@C80 has its binding pattern as in Ce@C60 and in Ce@C82 (binding to a six-membered ring). We explain this variation in binding together with the nature of the charge transfer between the Ce atoms and the cage (C82 and C80). In addition; we explain experimental observations for Ce@C82 and Ce2@C80 from RESPES; IETS; STM/STS spectra by comparison with simulated properties
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| 7. |
- Muthukumar, Kaliappan, et al.
(författare)
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Theoretical explanation of the nature of free and surface bound cerium endohedral fullerenes
- 2009
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Konferensbidrag (refereegranskat)abstract
- Cerium is one of the most reactive elements of the rare earth group, and its complex physics accompanying its single occupied 4f band, close to the Fermi level, has baffled scientists for many decades. Cerium can be encapsulated into fullerene (C72, C78, C80 and C82) cages, which works as an n-dopant. Metallofullerenes can be used as quantum bits in quantum computers, as molecular devices and as MRI contrasting agents. Here we address the challenges in modelling cerium endohedral fullerenes using density functional theory (DFT) and report our theoretical inspection that gives a detailed picture of metal-cage interaction and a closer look on the electronic structure of these cerium doped fullerenes. Experimental and theoretical results for these endohedral species bound to Cu(111) will also be presented with a fundamental and applied viewpoint to expand our knowledge about endohedral fullerene-surface interaction. We have found that the conductance of empty C60 to be much higher than the endohedrally doped cerium fullerene Ce2@C80 when bound to the same Cu(111) surface using low-temperature scanning tunnelling microscopy (LT-STM), which we explain through DFT calculations.
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| 8. |
- Muthukumar, Kaliappan, et al.
(författare)
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Theoretical Predictions and Explanation of Experimental Observations for Ce Doped Fullerenes
- 2008
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Konferensbidrag (refereegranskat)abstract
- Fullerenes that have one metal atom encapsulated; for example M@C60; M@C70; M@C82; (M= Sc; Y; La; Ce; etc.) are relatively well studied compared to species that have two elements inside the cage.1-4 We recently reported the structure of Ce@C82 and explained the preferential binding site of Ce to only one of the thirty-one 6-membered rings of C82-C2v cage by identifying its specific charge pattern and the symmetry of the MO s that comply well with the Ce d orbital bonding.5 Since; each of the six-membered rings of C80-Ih fulfill the proposed criteria; similar kind of binding site is expected for Ce in Ce2@C80. But; we observe a novel binding site for Ce in presence of an additional cerium atom; while La in La2@C80 does bond with six-membered rings.6 In this study; we discuss and analyze the reason for the preference for a novel binding site by Ce atoms in C80-Ih through density functional calculations. Further; we explain the nature of the charge transfer between the Ce atoms and the cage (C82 and C80) and elucidate the oxidation state of Ce in these metallofullerenes by comparing the charge transfer in the conventional Ce tri halides (CeF3; CeBr3). In addition; we explain experimental observations for Ce@C82 and Ce2@C80 from RESPES; IETS; STM/STS spectra by comparison with simulated properties
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| 9. |
- Stróecka, Anna, et al.
(författare)
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Electron-induced excitation of vibrations of Ce atoms inside a C 80 cage
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:16
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Tidskriftsartikel (refereegranskat)abstract
- Inelastic electron tunneling spectroscopy of Ce 2@C 80 dimetallofullerenes reveals a low-energy inelastic excitation that is interpreted using ab initio calculations and associated with the movements of encapsulated Ce atoms inside the C 80 cage. The electron-vibration interaction in Ce 2@C 80 is unusually high, inducing a pronounced zero-bias anomaly in differential conductance of Ce 2@C 80. Our observations show that the atoms encapsulated in fullerene cages can actively participate in determining the properties of molecular junctions
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| 10. |
- Stróecka, Anna, et al.
(författare)
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Modification of the conductance of single fullerene molecules by endohedral doping
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:13
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Tidskriftsartikel (refereegranskat)abstract
- We use scanning tunneling microscopy to establish controlled contacts to single molecules of endohedrally doped Ce 2@C 80 fullerenes with C 60 as a reference. The stability of the experimental setup allows for the determination of the conductance of Ce 2@C 80 relative to the conductance of C 60. The endohedral doping reduces the conductance of Ce 2@C 80 by a factor of about five with respect to C 60. Ab initio calculations show that the reason for this reduced conductance is the absence of electron orbitals delocalized over the cage of Ce 2@C 80 in the energy window of the conductance measurement
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