We employ the sub-atomically focused beam of a scanning transmission electron microscope (STEM) to introduce and controllably manipulate individual dopant atoms in a 2D graphene lattice. The electron beam is used to create defects and subsequently sputter adsorbed source materials into the graphene lattice such that individual vacancy defects are controllably passivated by Si substitutional atoms. We further document that Si point defects may be directed through the lattice via e-beam control or modified (as yet, uncontrollably) to form new defects which can incorporate new atoms into the graphene lattice. These studies demonstrate the potential of STEM for atom-by-atom nanofabrication and fundamental studies of chemical reactions in 2D materials on the atomic level.

The ability to engineer the thermal conductivity of materials allows us to control the flow of heat and derive novel functionalities such as thermal rectification, thermal switching and thermal cloaking. While this could be achieved by making use of composites and metamaterials at bulk length-scales, engineering the thermal conductivity at micro- and nano-scale dimensions is considerably more challenging. In this work, we show that the local thermal conductivity along a single Si nanowire can be tuned to a desired value (between crystalline and amorphous limits) with high spatial resolution through selective helium ion irradiation with a well-controlled dose. The underlying mechanism is understood through molecular dynamics simulations and quantitative phonon-defect scattering rate analysis, where the behaviour of thermal conductivity with dose is attributed to the accumulation and agglomeration of scattering centres at lower doses. Beyond a threshold dose, a crystalline-amorphous transition was observed.

Chemical vapor deposition (CVD) grown graphene used in (scanning) transmission electron microscopy [(S)TEM] studies must undergo a careful transfer of the one-atom-thick membrane from the growth surface (typically a Cu foil) to the TEM grid. During this transfer process, the graphene invariably becomes contaminated with foreign materials. This contamination proves to be very problematic in the (S)TEM because often >95% of the graphene is obscured, and imaging of the pristine areas results in e-beam-induced hydrocarbon deposition which further acts to obscure the desired imaging area. In this article, the authors examine two cleaning techniques for CVD grown graphene that mitigate both aspects of the contamination problem: visible contamination covering the graphene, and “invisible” contamination that deposits onto the graphene under e-beam irradiation. The visible contamination may be removed quickly by a rapid thermal annealing to 1200 °C in situ and the invisible e-beam-deposited contamination may be removed through an Ar/O2 annealing procedure prior to imaging in the (S)TEM.