Graphene removal by water-assisted focused electron-beam-induced etching - unveiling the dose and dwell time impact on the etch profile and topographical changes in SiO2 substrates.

Graphene is one of the most extensively studied 2D materials, exhibiting extraordinary mechanical and electronic properties. Although many years have passed since its discovery, manipulating single graphene layers is still challenging using standard resist-based lithography techniques. Recently, it has been shown that it is possible to etch graphene directly in water-assisted processes using the so-called focused electron-beam-induced etching (FEBIE), with a spatial resolution of ten nanometers. Nanopatterning graphene with such a method in one single step and without using a physical mask or resist is a very appealing approach. During the process, on top of graphene nanopatterning, we have found significant morphological changes induced in the SiO2 substrate even at low electron dose values (<8 nC/µm2). We demonstrate that graphene etching and topographical changes in SiO2 substrates can be controlled via electron beam parameters such as dwell time and dose.

Conductance steps in electromigrated Bi nanoconstrictions.

Bismuth nanostructures of initial lateral size of about 150 nm were successfully electromigrated at room temperature under high vacuum conditions through the application of voltage ramps and accurate control of their conductance. The imaging of the nanogap formation was followed by scanning electron microscopy. An appropriate design of the initial Bi nanostructures has made the electromigration process of semimetallic Bi feasible. Beyond the intrinsic interest in the generation of Bi structures with size tailored at the nanoscale, remarkable features have been observed in the time-dependent conductance curves of the Bi nanoconstrictions. In particular, sub-quantum conductance plateaus can be detected before the rupture of the constriction. An alternative procedure to study the transport through Bi nanoconstrictions has been explored using a focused-Ga-ion etching process with simultaneous control of the conductance. This second approach confirms the transport behavior observed in electromigrated Bi nanoconstrictions.

Three dimensional magnetic nanowires grown by focused electron-beam induced deposition.

Control of the motion of domain walls in magnetic nanowires is at the heart of various recently proposed three-dimensional (3D) memory devices. However, fabricating 3D nanostructures is extremely complicated using standard lithography techniques. Here we show that highly pure 3D magnetic nanowires with aspect-ratios of ~100 can be grown using focused electron-beam-induced-deposition. By combining micromanipulation, Kerr magnetometry and magnetic force microscopy, we determine that the magnetisation reversal of the wires occurs via the nucleation and propagation of domain walls. In addition, we demonstrate that the magnetic switching of individual 3D nanostructures can be directly probed by magneto-optical Kerr effect.