We have investigated the effects of thermal annealing on ex-situ chemically vapor deposited submonolayer graphene islands on polycrystalline Cu foil at the atomic-scale using ultrahigh vacuum scanning tunneling microscopy. Low-temperature annealed graphene islands on Cu foil (at ∼430 °C) exhibit predominantly striped Moiré patterns, indicating a relatively weak interaction between graphene and the underlying polycrystalline Cu foil. Rapid high-temperature annealing of the sample (at 700-800 °C) gives rise to the removal of Cu oxide and the recovery of crystallographic features of the copper that surrounds the intact graphene. These experimental observations of continuous crystalline features between the underlying copper (beneath the graphene islands) and the surrounding exposed copper areas revealed by high-temperature annealing demonstrates the impenetrable nature of graphene and its potential application as a protective layer against corrosion.

Articles you may be interested inElectronic structure, surface morphology, and topologically protected surface states of Sb2Te3 thin films grown on Si(111) J. Appl. Phys. 113, 053706 (2013); 10.1063/1.4789353 Incorporation, valence state, and electronic structure of Mn and Cr in bulk single crystal β-Ga2O3

Single crystals of transition metal (TM) doped β–Ga2O3, a wide gap semiconductor system of interest for transparent conductive oxide and diluted magnetic semiconductor applications, have been studied in the dilute, non-interacting limit (≤0.06 cation %). Based on optical absorption, particle induced x-ray emission, and Rutherford backscattering measurements, Mn does not incorporate as well as Cr, and Mn degrades the crystal quality. Using superconducting quantum interference device (SQuID) magnetometry, a Brillouin type paramagnetic magnetization is observed for Mn or Cr doped crystals with an effective number of Bohr magnetons per TM ion of 5.88 ± 0.1 or 3.95 ± 0.1, respectively. A trace ferromagnetic signal is consistent with a very small concentration of secondary phases in the Mn-doped crystal. The position of the edge in x-ray absorption near edge structure (XANES) measurements suggests that the Cr takes the 3+ valence, while a mixture of Mn2+ and Mn3+ are present; based on the absence of a prominent pre-edge feature in the XANES, both TM predominantly occupy an octahedral site in β–Ga2O3. Density functional theory (DFT) results, optical absorption and SQuID data are consistent with this assignment. While the Cr-doped crystal is conductive, the Mn-doped crystal is insulating, which is consistent with the Mn2+/Mn3+ mixed valence, assuming the Fermi level is pinned mid-gap at the Mn 2+/3+ transition level, which is predicted by DFT to be 1.8 eV above the valence band maximum.

Graphene is nature's ideal two‐dimensional conductor and is comprised of a single sheet of hexagonally packed carbon atoms. Since the first electrical measurements made on graphene, researchers have been trying to exploit the unique properties of this material for a variety of applications that span numerous scientific and engineering disciplines. In order to fully realize the potential of graphene, large scale synthesis of high quality graphene and the ability to control the electronic properties of this material on a nanometer length‐scale are necessary and remain key challenges. This article will review the efforts at the Center for Nanoscale Materials that focus on the atomic‐scale characterization and modification of graphene via scanning tunneling microscopy and its synthesis on various materials (SiC, Cu(111), Cu foil, etc.). These fundamental studies explore growth dynamics, film quality, and the role of defects. The chemical modification of graphene following exposure to atomic hydrogen will also be covered, while additional emphasis will be made on graphene's unique structural properties.

Molecular diffusion, motion, and conformation are critical to chemical and biological processes. Concurrently, understanding how chirality affects these processes has become a critical challenge for various applications in the pharmaceutical and food industries ranging from drug catalysis to novel sensing. Here, we present a unique way of transferring the chirality of simple amino acids, L-and D-alanine, to large-scale chiral networks on Cu(111). We further utilize the unique geometry of the chiral network as a scaffolding to isolate individual molecules within a 1.2 nm hexagonal pore. These hexagonal pores act as single molecule "race tracks" where excess alanine molecules trapped at the perimeter are observed to hop between six distinct locations around the perimeter. Scanning tunneling microscopy (STM) as well as density functional theory (DFT) calculations have been utilized to directly track, influence, and probe this molecular motion confined to self-assembled, chiral, hexagonal pores which also form quantum corrals.