Nanoscrolls are papyrus-like nanostructures which present unique properties due to their open ended morphology. These properties can be exploited in a plethora of technological applications, leading to the design of novel and interesting devices. Dur
ing the past decade, significant advances in the synthesis and characterization of these structures have been made, but many challenges still remain. In this mini review we provide an overview on their history, experimental synthesis methods, basic properties and application perspectives.
Graphene is one of the most important materials in science today due to its unique and remarkable electronic, thermal and mechanical properties. However in its pristine state, graphene is a gapless semiconductor, what limits its use in transistor ele
ctronics. In part due to the revolution created by graphene in materials science, there is a renewed interest in other possible graphene-like two-dimensional structures. Examples of these structures are graphynes and graphdiynes, which are two-dimensional structures, composed of carbon atoms in sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and some of them are intrinsically nonzero gap systems. These systems can be easily hydrogenated and the relative level of hydrogenation can be used to tune the band gap values. We have investigated, using fully reactive molecular dynamics (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. Our results showed that the hydrogen bindings have different atom incorporation rates and that the hydrogenation patterns change in time in a very complex way. The formation of correlated domains reported to hydrogenated graphene is no longer observed in graphdiyne cases.
Recently, it was proposed that graphene membranes could act as impermeable atomic structures to standard gases. For some other applications, a higher level of porosity is needed, and the so-called Porous Graphene (PG) and Biphenylene Carbon (BPC) mem
branes are good candidates to effectively work as selective sieves. In this work we have used classical molecular dynamics simulations to study the dynamics of membrane permeation of He and Ar atoms and possible selectivity effects. For the graphene membranes we did not observe any leakage through the membrane and/or membrane/substrate interface until a critical pressure limit, then a sudden membrane detachment occurs. PG and BPC membranes are not impermeable as graphene ones, but there are significant energy barriers to diffusion depending on the atom type. Our results show that this kind of porous membranes can be effectively used as selective sieves for pure and mixtures of gases.
In this work we have investigated the mechanical properties and fracture patterns of some graphene nanowiggles (GNWs). Graphene nanoribbons are finite graphene segments with a large aspect ratio, while GNWs are nonaligned periodic repetitions of grap
hene nanoribbons. We have carried out fully atomistic molecular dynamics simulations using a reactive force field (ReaxFF), as implemented in the LAMPPS (Large-scale Atomic/Molecular Massively Parallel Simulator) code. Our results showed that the GNW fracture patterns are strongly dependent on the nanoribbon topology and present an interesting behavior, since some narrow sheets have larger ultimate failure strain values. This can be explained by the fact that narrow nanoribbons have more angular freedom when compared to wider ones, which can create a more efficient way to accumulate and to dissipate strain/stress. We have also observed the formation of linear atomic chains (LACs) and some structural defect reconstructions during the material rupture. The reported graphene failure patterns, where zigzag/armchair edge terminated graphene structures are fractured along armchair/zigzag lines, were not observed in the GNW analyzed cases.
We have studied the effect of thermal effects on the structural and transport response of Ag atomic-size nanowires generated by mechanical elongation. Our study involves both time-resolved atomic resolution transmission electron microscopy imaging an
d quantum conductance measurement using an ultra-high-vacuum mechanically controllable break junction. We have observed drastic changes in conductance and structural properties of Ag nanowires generated at different temperatures (150 and 300 K). By combining electron microscopy images, electronic transport measurements and quantum transport calculations, we have been able to obtain a consistent correlation between the conductance and structural properties of Ag NWs. In particular, our study has revealed the formation of metastable rectangular rod-like Ag wire (3/3) along the (001) crystallographic direction, whose formation is enhanced. These results illustrate the high complexity of analyzing structural and quantum conductance behaviour of metal atomic-size wires; also, they reveal that it is extremely difficult to compare NW conductance experiments performed at different temperatures due to the fundamental modifications of the mechanical behavior.
