| 1. |
- Muthukumar, Kaliappan, et al.
(författare)
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A Joint Theoretical and Experimental Characterization of the In-elastic Tunneling modes of Ce@C82 and Ce2@C80
- 2008
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Konferensbidrag (refereegranskat)abstract
- The drive for miniaturization of electronic devices involves nanotechnology; where single molecules are investigated for the use as electric components.1 Owing to their electronic and magnetic flexibility; endohedral fullerenes have been suggested as one of a possible molecular candidate in future electronics.2 Such molecular components differ from the conventional electronic materials by the degree to which mechanical degrees of freedom affect electrical conductivity.3;4 Understanding of these processes are still in its infancy and in this study in-elastic tunnelling spectroscopy (IETS) which probes the tunnelling current of a single molecule using scanning tunnelling microscopy (STM); with controlled excitation of their vibration modes has been applied to cerium endohedral fullerenes (Ce@C82 and Ce2@C80) to investigate the interplay between electrons and vibrations of these molecules on Cu(111).5 We report here our measured IETS spectrum of single Ce@C82 and Ce2@C80 on Cu (111) and explain the observed IETS peaks by analysing the molecular vibrational spectra simulated using density functional theory calculations.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
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| 6. |
- 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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| 7. |
- 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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| 8. |
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| 9. |
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