ABSTRACT:Frictional, adhesive, and elastic characteristics of graphene edges are determined through lateral force microscopy. Measurements reveal a significant local frictional increase at exposed graphene edges, whereas a single overlapping layer of graphene removes this local frictional increase. Comparison of lateral force and atomic force microscopy measurements shows that local forces on the probe are successfully modeled with a vertical adhesion in the vicinity of the atomic-scale graphene steps which also provides a new low-load calibration method. Lateral force microscopy performed with carefully maintained low-adhesion probes shows evidence of elastic straining of graphene edges. Estimates of the energy stored of this observed elastic response is consistent with out-of-plane bending of the graphene edge. PACS (81.05.ue, 81.07.Lk, 46.55.+d, 68.35.Af, 62.20.de) 2

Carbon nanotubes are grown on few-layer graphene films using chemical vapor deposition without a carbon feedstock gas. We find that the nanotubes show a striking alignment to specific crystal orientations of the few-layer graphene films. The nanotubes are oriented predominantly at 60 degree intervals and are offset 30 degrees from crystallographically oriented etch tracks, indicating alignment to the armchair axes of the few-layer graphene films. Nanotubes grown on various thicknesses of few-layer graphene under identical process conditions show that the thinnest films, in the sub-6 atomic layer regime, demonstrate significantly improved crystallographic alignment. Intricate crystallographic patterns are also observed having sharp kinks with bending radii less than the ∼10 nm lateral resolution of the electron and atomic force microscopy used to image them. Some of these kinks occur independently without interactions between nanotubes while others result when two nanotubes intersect. These intersections can trap nanotubes between two parallel nanotubes resulting in crystallographic back and forth zigzag geometries. These interactions suggest a tip-growth mechanism such that the catalyst particles remain within several nanometers of the few-layer graphene surface as they move leaving a nanotube in their wake.

Memristors have recently generated significant interest due to their potential use in nanoscale logic and memory devices. Of the four passive circuit elements, the memristor (a two-terminal hysteretic switch) has so far proved hard to fabricate out of a single material. Here we employ electromigration to create a reversible passive electrical switch, a memristive device, from a single-component metallic nanowire. To achieve resistive switching in a single-component structure we introduce a new class of memristors, devices in which the state variable of resistance is the system's physical geometry. By exploiting electromigration to reversibly alter the geometry, we repeatedly switch the resistance of single-component metallic nanowires between low and high states over many cycles. The reversible electromigration causes the nanowire to be cyclically narrowed to approximately 10 nm in width, resulting in a change in resistance by a factor of two. As a result, this work represents a potential route to the creation of nanoscale circuits from a single metallic element.

Lateral force microscopy (LFM) is used to probe the nanoscale elastic and frictional characteristics of molybdenum disulfide (MoS2).