If graphene is ever going to live up to the promises of future nanoelectronic devices, an easy and cheap route for mass production is an essential requirement. A way to extend the capabilities of plasma-enhanced chemical vapour deposition to the synthesis of freestanding few-layer graphene is presented. Micrometre-wide flakes consisting of four to six atomic layers of stacked graphene sheets have been synthesized by controlled recombination of carbon radicals in a microwave plasma. A simple and highly reproducible technique is essential, since the resulting flakes can be synthesized without the need for a catalyst on the surface of any substrate that withstands elevated temperatures up to 700• C. A thorough structural analysis of the flakes is performed with electron microscopy, x-ray diffraction, Raman spectroscopy and scanning tunnelling microscopy. The resulting graphene flakes are aligned vertically to the substrate surface and grow according to a three-step process, as revealed by the combined analysis of electron microscopy and x-ray photoelectron spectroscopy.

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Enhancing the transport contribution of surface states in topological insulators is vital if they are to be incorporated into practical devices. Such efforts have been limited by the defect behaviour of Bi2Te3 (Se3) topological materials, where the subtle bulk carrier from intrinsic defects is dominant over the surface electrons. Compensating such defect carriers is unexpectedly achieved in (Cu0.1Bi0.9)2Te3.06 crystals. Here we report the suppression of the bulk conductance of the material by four orders of magnitude by intense ageing. The weak antilocalization analysis, Shubnikov–de Haas oscillations and scanning tunnelling spectroscopy corroborate the transport of the topological surface states. Scanning tunnelling microscopy reveals that Cu atoms are initially inside the quintuple layers and migrate to the layer gaps to form Cu clusters during the ageing. In combination with first-principles calculations, an atomic tunnelling–clustering picture across a diffusion barrier of 0.57 eV is proposed.

Chemical vapor deposition (CVD) is widely considered to be the most economically viable method to produce graphene for high-end applications. However, this deposition technique typically yields undesired grain boundaries in the graphene crystals, which drastically increases the sheet resistance of the layer. These grain boundaries are mostly caused by the polycrystalline nature of the catalytic template that is commonly used. Therefore, to prevent the presence of grain boundaries in graphene crystals, it is crucial to develop a large scale, single-crystalline template. In this paper, we demonstrate the deposition of a single-crystalline Cu(111) film on top of a 2″ sapphire wafer. The crystalline quality of the Cu(111) templates is optimized by controlled modification of the sapphire surface termination and by tuning the Cu deposition conditions. Moreover, we find that the Cu layer transforms into an untwinned single-crystalline Cu(111) structure after annealing at typical graphene growth temperatures. This allows for the growth of high-quality graphene by the CVD technique. The findings presented in this paper are an important step forward in the production of wafer scale, single-crystalline graphene.

Pyramidal Au20 clusters are intactly deposited and visualized at the single cluster level.

We investigated the growth and the electronic properties of crystalline NaCl layers on Au(111) surfaces by means of cryogenic scanning tunneling microscopy and spectroscopy under ultra-high vacuum conditions. Deposition of NaCl on Au(111) at room temperature yields bilayer NaCl islands, which can be transformed into trilayer NaCl islands by post-annealing. Upon NaCl adsorption, the Au(111) Shockley surface state becomes an interface state (IS) at the NaCl/Au(111) interface. Using Fourier-transform images of maps of the local density of states, the energy versus wave vector dispersions of the IS and the Au(111) bulk states are determined. The dispersion of both states is found to depend strongly on the thickness of the adsorbed NaCl layer.

Single magnetic Co atoms are deposited on atomically thin NaCl films on Au(111). Two different adsorption sites are revealed by high-resolution scanning tunneling microscopy (STM), i.e., at Na and at Cl locations. Using density functional based simulations of the STM images, we show that the Co atoms substitute with either a Na or Cl atom of the NaCl surface, resulting in cationic and anionic Co dopants with a high thermal stability. The dependence of the magnetic coupling between neighboring Co atoms on their separation is investigated via spatially resolved measurement of the local density of states.

We investigated the local influence of the Au(111) herringbone reconstruction on the properties of thin adsorbed NaCl films using cryogenic scanning tunneling microscopy (STM) and spectroscopy. Depending on the local hcp versus fcc character of the reconstruction, NaCl adsorption gives rise to a different shift of the Au(111) surface state toward the Fermi level, in agreement with ab initio calculations. Such lateral modulation may allow for tunable nanostructuring of thin insulating films, which opens up new perspectives for molecular electronics applications. Furthermore, we demonstrate the simultaneous visualization of both the alkali and the halogen atoms in hcp regions of the NaCl/Au(111) surface using a functionalized STM tip. Ab initio calculations relate this simultaneous visualization to the larger electron density in the hcp regions.