Non-invasive transmission electron microscopy of vacancy defects in graphene produced by ion irradiation.

Irradiation with high-energy ions has been widely suggested as a tool to engineer properties of graphene. Experiments show that it indeed has a strong effect on graphene's transport, magnetic and mechanical characteristics. However, to use ion irradiation as an engineering tool requires understanding of the type and detailed characteristics of the produced defects which is still lacking, as the use of high-resolution transmission microscopy (HRTEM)--the only technique allowing direct imaging of atomic-scale defects--often modifies or even creates defects during imaging, thus making it impossible to determine the intrinsic atomic structure. Here we show that encapsulating the studied graphene sample between two other (protective) graphene sheets allows non-invasive HRTEM imaging and reliable identification of atomic-scale defects. Using this simple technique, we demonstrate that proton irradiation of graphene produces reconstructed monovacancies, which explains the profound effect that such defects have on graphene's magnetic and transport properties. This finding resolves the existing uncertainty with regard to the effect of ion irradiation on the electronic structure of graphene.

Ion-irradiation-induced defects in isotopically-labeled two layered graphene: enhanced in-situ annealing of the damage.

Contrary to theoretical estimates based on the conventional binary collision model, experimental results indicate that the number of defects in the lower layer of the bi-layer graphene sample is smaller than in the upper layer. This observation is explained by in situ self-annealing of the defects.

Self-assembly of oxide-supported metal clusters into ring-like structures.

Self-assembly is a phenomenon that continuously occurs at the nanoscale, as atoms form predetermined building blocks such as molecules and clusters, which then themselves gather into structures of a larger scale. The interplay of competing forces is a decisive factor in the emergence of these organized systems, but the precise mechanism by which this self-assembly progresses is seldom known. Using a combination of physical cluster deposition and atomic force microscopy, we have investigated the spontaneous formation of µm-sized rings of SiO(x)-supported metal nanoclusters. With the help of molecular dynamics simulations, we show that the competition between short-range van der Waals attractions and long-range repulsive dipolar forces, induced by the ionic surface, plays a key role in the self-assembly of these structures.

Analysis of ALD-processed thin films by ion-beam techniques.

This review introduces the possibilities of ion-beam techniques for the analysis of thin films and thin-film structures processed by atomic layer deposition (ALD). The characteristic features of ALD are also presented. The analytical techniques discussed include RBS, NRA and ERDA with its variants, viz. the TOF-ERDA and HI-ERDA. The thin film examples are taken from flat-panel display technology (TFEL structures) and the semiconductor industry (high-k insulators).