Category Archives: Invited Abstracts

Atomic Carbon Chains: A Perfectly One-Dimensional Carbon Phase Beyond Nanotubes 

F. Banhart¹, O. Cretu¹, A. La Torre¹, A. Botello-Mendez², J.-C. Charlier²

¹Institut de Physique et Chimie des Matériaux, University of Strasbourg, France 

²Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Belgium 

Carbon chains can be considered as sp1-hybridized strings of carbon atoms of monoatomic thickness, constituting the logical one-dimensional phase of carbon. They have been proposed since a long time until they were observed by electron microscopy. Recent experiments show that, by using a measuring system with an STM tip in a TEM specimen stage, carbon chains can not only be made but also characterized (O. Cretu et al., Nano Lett. 13, 3487 (2013)). By passing a current through the chains, their electrical properties have been measured for the first time. The chains are obtained by unraveling carbon atoms from nanotubes or graphene ribbons while an electrical current flowed through the tubes or ribbons and, successively, through the chain. The electrical conductivity of the chains was found to be much lower than predicted for ideal chains. First-principles calculations show that strain in the chains determines the conductivity in a decisive way. Indeed, carbon chains are always under varying non-zero strain that transforms their atomic structure from cumulene (double bonds throughout the chain) to polyyne (alternating single/triple bonds), thus inducing a tunable band gap. New experiments show the bonding characteristics at contacts between metals and carbon chains as well as characteristic current-voltage curves, depending on the type of contact. The experiments show a perspective toward the synthesis of carbon chains and their application as the smallest possible interconnects or even as one-dimensional semiconducting devices.

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Electronic properties in moiré superlattice in rotationally stacked atomic layers 

Mikito Koshino¹, Pilkyung Moon²

¹Department of Physics, Tohoku University, 

²Korean Institute for Advanced Study 

We report recent theoretical studies on the electronic properties of rotationally stacked atomic layer systems, including graphene-graphene bilayer, and graphene-hBN (hexagonal boron nitride) composite bilayer. The misoriented atomic structure gives rise to a moiré superlattice structure with a long spatial period, and it strongly modifies the band structure in the low-energy region. We develop an effective continuum model based the tight-binding Hamiltonian, which correctly describes the electronic structure of moiré superlattice [1]. In a magnetic field, the coexistence of the moiré pattern and the Landau quantization causes the fractal energy spectrum so-called Hofstadter’s butterfly. We calculate the spectral evolution as a function of magnetic field, and demonstrate that the quantized Hall conductivity changes in a complicated manner in changing Fermi energy and the magnetic field amplitude [2]. We also calculate the optical absorption in the fractal band regime, and find that the absorption spectrum and the optical selection rule exhibit recursive self-similar structure as well, reflecting the fractal nature of the energy spectrum.[3]

[1] P. Moon and M. Koshino, Phys. Rev. B 87, 205404 (2013)

[2] P. Moon and M. Koshino, Phys. Rev. B 85, 195458 (2012).

[3] P. Moon and M. Koshino, Phys. Rev. B 88, 241412(R) (2013).

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Strategic Functionalization of Nanomaterials for Potential Biomedical Applications 

Giorgia Pastorin

Pharmacy Department, National University of Singapore, 3 Science Drive 2, Block S15#05-PI-03, Singapore 117543 

Recent advances in nanomaterials have led to several opportunities in biomedical research. The current and most promising applications of these nanomaterials include, but are not limited to, drug delivery and tissue repair. Indeed, drug delivery systems represent one of the most interesting results deriving from the development of advanced materials, among which carbon nanotubes (CNTs) seem to embody an intriguing option; this is due to some favorable attributes including CNTs’ unique shape, which promotes cellular-uptake, and large aspect-ratio that facilitates functionalization of bioactive molecules on their surface [1,2].

In our group we have investigated several strategies for the incorporation of different drug molecules both via covalent linkage [2] and via encapsulation in form of “nano-bottles” [3-5]. The efficacy of drugs released from our drug delivery systems was improved in vitro in comparison with the free drug, probably due to remarkable mitochondrial injury, as demonstrated by the decrease in mitochondrial membrane potential resulting from accumulation of CNT-drug constructs at the mitochondrial level. Conversely, empty carriers neither reduced cell viability significantly nor incurred mitochondrial damage.

Also, we have demonstrated that carbon-based materials might provide a promising biocompatible scaffold in tissue engineering, since they do not hamper the proliferation of human mesenchymal stem cells (hMSCs) and accelerate their specific differentiation into bone cells [6,7]. Interestingly, cell differentiation occurred even in the absence of additional biochemical inducing agents, as evidenced by multiple independent criteria at the transcriptional, protein expression and functional levels [6]. Since the differentiation rate is comparable to the one achieved with currently used growth factors, these results pave the way for the potential use of these nanomaterials for stem cell research. OOOnOHINNER FUNCTIONALIZATION: NANOBOTTLEDRUG DELIVERYEXTERNAL FUNCTIONALIZATIONTISSUE ENGINEERING & REPAIRGRAPHENE

References 
[1] B.S. Woong et al. Adv. Drug Deliv. Rev. 2013, 65, 1964.
[2] G. Pastorin et al. Chem. Commun. 2006, 21,1182.
[3] Zhao C. et al. Biotechnol. Adv. 2013, 31, 654.
[4] W. Wu et al. Angew. Chem. Int. Ed., 2005, 44, 6358.
[5] R. Yupeng and G. Pastorin. Adv.Mater. 2008, 20, 2031.
[6] J. Li et al. Chem. Sci. 2012, 3, 2083.
[7] S. L. Yoong et al. Biomaterials, 2014, 35, 748.
[8] T. R. Nayak et al. ACS Nano. 2010, 4, 7717.
[9] T. R. Nayak et al. ACS Nano. 2011, 5, 4670.

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