Nanoscale metallic multilayer films (NMMFs) have captured scientific interests on their mechanical responses. Compared with the properties of monolithic films, multilayers possess unique high strength as the individual layer thickness reduces to the nanoscale, which is benefited from the plentiful hetero-interfaces. However, NMMFs always exhibit a low fracture toughness and ductility, which seriously hinders their practical applications. While there have been reviews on the strengthening and deformation mechanisms of microlaminate, rapid developments in nanotechnology have brought an urgent requirement for an overview focused on the cracking and toughening mechanisms in nanoscale metallic multilayers. This article provides an extensive review on the structure, standard methodology and fracture mechanisms of NMMFs. A number of issues about the crack-related properties of NMMFs have been displayed, such as fracture toughness, wear resistance, adhesion energy, and plastic instability. Taken together, it is hoped that this review will achieve the following two purposes: (1) introducing the size-dependent cracking and toughness performance in NMMFs; and (2) offer a better understanding of the role interfaces displayed in toughening mechanisms. Finally, we list a few questions we concerned, which may shed light on further development.

Graphene grown on Cu by chemical vapor deposition is rough due to the surface roughening of Cu for releasing interfacial thermal stress and/or graphene bending energy. The roughness degrades the electrical conductance and mechanical strength of graphene. Here, by using vicinal Cu(111) and flat Cu(111) as model substrates, we investigated the critical role of original surface topography on the surface deformation of Cu covered by graphene. We demonstrated that terrace steps on vicinal Cu(111) dominate the formation of step bunches (SBs). Atomically flat graphene with roughness down to 0.2 nm was grown on flat Cu(111) films. When SB-induced ripples were avoided, as-grown ultraflat graphene maintained its flat feature after transfer. The ultraflat graphene exhibited extraordinary mechanical properties with Young’s modulus ≈ 940 GPa and strength ≈ 117 GPa, comparable to mechanical exfoliated ones. Molecular dynamics simulation revealed the mechanism of softened elastic response and weakened strength of graphene with rippled structures.

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In this work, HfOx/HfO2 homo-bilayer structure based resistive random access memory devices were fabricated, and the resistive switching characteristics of the devices were investigated.

Inorganic boron nitride (BN) nanosheets with excellent oil solubility were essential to replacing the traditional sulfur/ phosphate-containing additives because of their long practical services. However, serious agglomerated BN nanosheets without proper modification hamper their application in lubricant as green oil additives. Here, we developed a simple and robust method for fabricating highly oil-dispersed ultrathin alkyl-functionalized BN nanosheets via a ball-milling process combined with surface modification. Such a chemical-assisted exfoliation process endows ultrathin BN nanosheets with a superior dispersion ability in nonpolar lubricant. Because of the ultrathin structure and good compatibility, the resulting BN nanosheets significantly display great antifriction and antiwear performance as oil additives, as well as reduced surface pitting. As a result, about 45% friction reduction and 89% wear reduction, together with 2.67 times load capacity improvement, were achieved with the help of BN nanosheets in lubricant. High lubrication performance could be attributed to the continuous delivery of BN nanosheets to the contact region and the chemical formation of a protecting boron-based tribofilm. The present work highlights the significance of designing welldispersed functional 2D nanosheets as green additives for boosting lubrication performance as well as reducing surface pitting.