8 research outputs found
Lattice Expansion in Seamless Bi layer Graphene Constrictions at High Bias
Our understanding of sp2 carbon nanostructures is still emerging and is
important for the development of high performance all carbon devices. For
example, in terms of the structural behavior of graphene or bi-layer graphene
at high bias, little to nothing is known. To this end we investigated bi-layer
graphene constrictions with closed edges (seamless) at high bias using in situ
atomic resolution transmission electron microscopy. We directly observe a
highly localized anomalously large lattice expansion inside the constriction.
Both the current density and lattice expansion increase as the bi-layer
graphene constriction narrows. As the constriction width decreases below 10 nm,
shortly before failure, the current density rises to 4 \cdot 109 A cm-2 and the
constriction exhibits a lattice expansion with a uniaxial component showing an
expansion approaching 5 % and an isotropic component showing an expansion
exceeding 1 %. The origin of the lattice expansion is hard to fully ascribe to
thermal expansion. Impact ionization is a process in which charge carriers
transfer from bonding states to antibonding states thus weakening bonds. The
altered character of C-C bonds by impact ionization could explain the
anomalously large lattice expansion we observe in seamless bi-layer graphene
constrictions. Moreover, impact ionization might also contribute to the
observed anisotropy in the lattice expansion, although strain is probably the
predominant factor.Comment: to appear in NanoLetter
Single-wall-carbon-nanotube/single-carbon-chain molecular junctions
Stable junctions between a single carbon chain and two single-wall carbon nanotubes were produced via coalescence of functionalized fullerenes filled into a single-wall carbon nanotube and directly imaged by in situ transmission electron microscopy. First principles quantum chemical calculations support the observed stability of such molecular junctions. They also show that short carbon chains bound to other carbon structures are cumulenes and stable semiconductors due to Peierls-like distortion. Junctions like this can be regarded as archetypical building blocks for all-carbon molecular electronics. © 2010 The American Physical Society
In situ observations of self-repairing single-walled carbon nanotubes
Single-walled carbon nanotubes are shown to have self-repairing capabilities exceeding that predicted by theory. Time-series aberration-corrected low-voltage transmission electron microscopy is used to study the defect dynamics of single-walled carbon nanotubes in situ. We confirm experimentally previous theoretical predictions for the agglomeration of adatoms forming protrusions and subsequent ejection. An explanation for the preferred destruction of smaller-diameter tubes is proposed. The complete healing of a ∼20 -atom multivacancy in a nanotube wall is shown while theory only predicts the healing of much smaller holes. © 2010 The American Physical Society
Enhanced pi-pi interactions between a C-60 fullerene and a buckle bend on a double-walled carbon nanotube
In situ low-voltage aberration corrected transmission electron microscopy (TEM) observations of the dynamic entrapment of a C60 molecule in the saddle of a bent double-walled carbon nanotube is presented. The fullerene interaction is non-covalent, suggesting that enhanced π-π interactions (van der Waals forces) are responsible. Classical molecular dynamics calculations confirm that the increased interaction area associated with a buckle is sufficient to trap a fullerene. Moreover, they show hopping behavior in agreement with our experimental observations. Our findings further our understanding of carbon nanostructure interactions, which are important in the rapidly developing field of low-voltage aberration corrected TEM and nano-carbon device fabrication. © The Author(s) 2010