We report the incorporation of substitutional Mn atoms in high-quality, epitaxial 1 graphene on Cu(111), using ultra-low energy ion implantation. We characterize in detail the atomic structure of substitutional Mn in a single carbon vacancy and quantify its concentration. In particular, we are able to determine the position of substitutional Mn atoms with respect to the Moiré superstructure (i.e. local graphene-Cu stacking symmetry) and to the carbon sublattice; in the out-of-plane direction, substitutional Mn atoms are found to be slightly displaced towards the Cu surface, i.e. effectively underneath the graphene layer. Regarding electronic properties, we show that graphene doped with substitutional Mn to a concentration of the order of 0.04%, with negligible structural disorder (other than the Mn substitution), retains the Dirac-like band structure of pristine graphene on Cu(111), making it an ideal system in which to study the interplay between local magnetic moments and Dirac electrons. Our work also establishes that ultra-low energy ion implantation is suited for substitutional magnetic doping of graphene; given the flexibility, reproducibility and scalability inherent to ion implantation, our work creates numerous opportunities for research on magnetic functionalization of graphene and other 2D materials.

Over the last ten years, signatures of high temperature ferromagnetism have been found in thin films and nanoparticles of various materials which are non-ferromagnetic in bulk, from semiconductors to superconductors. These studies often involve state-ofthe-art magnetometers working close to the limits of their sensitivity, where magnetic contaminations and measurement artefacts become non-negligible. Because such spurious effects may be involved, the reliability of magnetometry techniques for the detection of ferromagnetism in these new magnetic nanomaterials has been questioned. In this paper, we present a detailed study on magnetic contamination arising from sample processing and handling, describing how it may occur and how it can be avoided or otherwise removed. We demonstrate that, when proper procedures are followed, extrinsic magnetic signals can be reproducibly kept below 5 × 10 −7 emu (5 × 10 −10 Am 2). We also give an overview of the expected levels of contamination when such optimum conditions can not be guaranteed and analyze the characteristics of the resulting magnetic behaviour, discussing which features may or may not be used as criteria to distinguish it from intrinsic ferromagnetism. Although the measurements were performed using superconducting quantum interference device (SQUID) magnetometers, most of what we describe can also be applied when using alternating-gradient force (AGFM) and vibrating-sample (VSM) magnetometers.

Radioactive27 Mg (t 1/2 =9.5 min) was implanted into GaN of different doping types at CERN's ISOLDE facility and its lattice site determined via β − emission channeling. Following implantations between room temperature and 800°C, the majority of 27 Mg occupies the substitutional Ga sites, however, below 350°C significant fractions were also found on interstitial positions ~0.6 Å from ideal octahedral sites. The interstitial fraction of Mg was correlated with the GaN doping character, being highest (up to 31%) in samples doped p-type with 2×1019 cm −3 stable Mg during epilayer growth, and lowest in Si-doped n-GaN, thus giving direct evidence for the amphoteric character of Mg. Implanting above 350°C converts interstitial 27 Mg to substitutional Ga sites, which allows estimating the activation energy for migration of interstitial Mg as between 1.3 and 2.0 eV.

In-plane compressively strained α-Sn films have been theoretically predicted and experimentally proven to possess nontrivial electronic states of a 3D topological Dirac semimetal. The robustness of these states typically strongly depends on purity, homogeneity and stability of the grown material itself. By developing a reliable fabrication process, we were able to grow pure strained α-Sn films on InSb(100), without heating of the substrate during growth, nor using any dopants. The α-Sn films were grown by molecular beam epitaxy, followed by experimental verification of the achieved chemical purity and structural properties of the film's surface. Local insight into the surface morphology was provided by scanning tunneling microscopy. We detected the existence of compressive strain using Mössbauer spectroscopy and we observed a remarkable robustness of the grown samples against ambient conditions. The topological character of the samples was confirmed by angle-resolved photoemission spectroscopy, revealing the Dirac cone of the topological surface state. Scanning tunneling spectroscopy, moreover, allowed obtaining an improved insight into the electronic structure of the 3D topological Dirac semimetal α-Sn above the Fermi level.

Using ion implantation, the electrical as well as the magnetotransport properties of individual ZnO nanowires (NWs) can be tuned. The virgin NWs are configured as field-effect transistors which are in the enhancement mode. Al-implanted NWs reveal a three-dimensional metallic-like behavior, for which the magnetoresistance is well described by a semiempirical model that takes into account the presence of doping induced local magnetic moments and of two conduction bands. On the other hand, one-dimensional electron transport is observed in Co-implanted NWs. At low magnetic fields, the anisotropic magnetoresistance can be described in the framework of weak electron localization in the presence of strong spin-orbit scattering. From the weak localization, a large phase coherence length is inferred that reaches up to 800 nm at 2.5 K. The temperature-dependent dephasing is shown to result from a one-dimensional Nyquist noise-related mechanism. At the lowest temperatures, the phase coherence length becomes limited by magnetic scattering.