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We report on the intercalation of a submonolayer of copper at 775 K underneath graphene epitaxially grown on Ir(111) studied by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) at 77 K. Nucleation and growth dynamics of Cu below graphene have been investigated, and, most importantly, the intercalation mechanism has been identified. First, LEED patterns reveal the pseudomorphic growth of Cu on Ir under the topmost graphene layer resulting in a large Cu in-plane lattice parameter expansion of about 6% compared to Cu(111). Second, large-scale STM topographs as a function of Cu coverage show that Cu diffusion on Ir below graphene exhibits a low energy barrier resulting in Cu accumulation at Ir step edges. As a result, the graphene sheet undergoes a strong edges reshaping. Finally, atomicallyresolved STM images reveal a damaged graphene sheet at the atomic scale after metal intercalation. Point defects in graphene were shown to be carbon vacancies. According to these results, a Cu penetration path beneath graphene is proposed to occur via metal aided defect formation with no or poor self healing of the graphene sheet. This work illustrates the fact that Cu intercalation is harmful for graphene grown on Ir(111) at the atomic scale. [ABSTRACT FROM AUTHOR]

From scanning tunneling spectroscopy measurements, we recently found evidence for the effect of electron-phonon interactions on the lifetime of hot electrons and holes. This information was obtained by measuring the linewidth of quantum well states resulting from the confinement of Shockley states in truncated hexagonal Ag nanopyramids. In the present paper, we show that a careful analysis allows us to obtain both the intrinsic and extrinsic broadening contributions. This latter contribution results from the lossy boundary scattering which is strongly reduced in this peculiar geometry. Indeed, we deduce the energy dependence of the reflection coefficient which remains higher, as usually observed in nanostructures like adatom islands and quantum corrals. [ABSTRACT FROM AUTHOR]

Due to their extreme surface sensitivity, the Shockley states of (111) noble metal surfaces can be used to study the modifications of atomic and electronic properties of epitaxial ultra thin films and self-organized nanostructures. In metallic interfaces, the different parameters of the Shockley surface state bands (energy, effective mass and eventually spin-orbit splitting) have been shown to be strongly thickness dependent. It was also possible by scanning tunneling spectroscopy to evidence a spectroscopic signature of buried interfaces. Moreover, superperiodic surface structures like the reconstruction on Au(111) vicinal surfaces or self-organized nanodots, lead to spectacular spectroscopic effects. In the vicinal Au(23 23 21) surface, the opening of tiny energy gaps associated with the reconstruction potential of such surfaces has been evidenced. Peculiar growth on these Au vicinal surfaces allows us to obtain high quality self-assembled metallic nanostructures which exhibit homogeneous electronic properties on a large spatial scale resulting from a coherent scattering of the Shockley states. [ABSTRACT FROM AUTHOR]

In this paper the effect of oxygen on the vanadium homoepitaxial growth process is analyzed by using Auger spectroscopy, electron diffraction and scanning tunneling microscopy. As the oxygen induced 1× 5 surface structure got a lattice spacing 6% different from the pure V lattice, relaxation is observed by electron diffraction during the growth. The average in-plane lattice spacing is thus shown to be proportional to the oxygen surface concentration. The surface lattice relaxation is observed to exponentially vary with the number of deposited atomic planes. A kinetic model is proposed and allows us to explain these observations. Furthermore, it helps us to distinguish two regimes depending on growth temperature. At high temperature, the oxygen surface concentration during growth is due to oxygen upward diffusion from the underneath V layer. For lower temperature however, this upward diffusion is not efficient and another source of oxygen contamination is evidenced. When the oxygen surface concentration is sufficient, a spectacular self-organization is observed at the surface by surface microscopy. Ribbons shape islands are observed and are tentatively explained as a consequence of oxygen surface concentration and stress induced by the surface reconstruction. Graphical abstractImage 1Highlights· Self-organization during homoepitaxial growth of vanadium in presence of oxygen· Evidence of oxygen segregation during the growth that plays a role in the self-organization· Evidence of strain induced by oxygen that explains the self-organization· A simple kinetic model accounts for the results. [ABSTRACT FROM AUTHOR]

The non-centro-symmetric semiconductor BiTeI exhibits two distinct surface terminations that support spin- split Rashba surface states. Their ambipolarity can be exploited for creating spin-polarized p-n junctions at the boundaries between domains with different surface terminations. We use scanning tunneling microscopy (STM) and spectroscopy (STS) to locate such junctions and investigate their atomic and electronic properties. The Te- and I-terminated surfaces are identified owing to their distinct chemical reactivity and an apparent height mismatch of electronic origin. The Rashba surface states are revealed in the STS spectra by the onset of a van Hove singularity at the band edge. Eventually, an electronic depletion is found on interfacial Te atoms, consistent with the formation of a space-charge area in typical p-n junctions. [ABSTRACT FROM AUTHOR]

The commensurate-incommensurate phase transition in chlorine monolayer on Ag(111) has been studied with low-temperature scanning tunneling microscopy and low-energy electron diffraction. We report the observation of self-interstitial defects: two-dimensional (2D) crowdions formed at the initial stage of the (x√-3 x x√-3)R30° lattice compression. After critical coverage of 0.34 monolayer (ML) the crowdions condense into a domain-wall fluid. As coverage further increases, the domain-wall crystal solidifies with average wall separation of 23 Å. [ABSTRACT FROM AUTHOR]

Epitaxial Ag ultra-thin films grown on Au(1 1 1) have been studied by scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES). In the submonolayer range, the spectroscopic measurements reveal the existence of two parabolic dispersive surface Shockley bands associated with the Au substrate and the Ag islands, respectively. The surface state in the Ag region is shifted by about 160 meV towards the Fermi level. High resolution measurements on Au(1 1 1) reveal the splitting of each band in two spin–orbit contributions. A reduction of this spin–orbit splitting is observed for a 1 ML Ag film. Moreover, an annealing of the interface leads to an interdiffusion and to an additional shift of the surface state. [Copyright &y& Elsevier]

A self-ordered nanoporous lattice formed by individual chlorine atoms on the Au(111) surface has been studied with low-temperature scanning tunneling microscopy, low-energy electron diffraction, and density functional theory calculations. We have found out that room-temperature adsorption of 0.09-0.30 monolayers of chlorine on Au(111) followed by cooling below 110 K results in the spontaneous formation of a nanoporous quasihexagonal structure with a periodicity of 25-38 A depending on the initial chlorine coverage. The driving force of the superstructure formation is attributed to the substrate-mediated elastic interaction. [ABSTRACT FROM AUTHOR]

Adsorption of chlorine atoms on the Cu(111) surface has been studied with low-temperature scanning tunneling microscopy (LT-STM) in a combination with density functional theory (DFT) calculations. At submonolayer coverage range ( θ ≤ 0.10 ML), chlorine forms quasi-one dimensional chains. Atoms in the chains alternately occupy fcc and hcp positions, with nearest-neighbor distance of ≈ 3.9 Å. At coverage of 0.10–0.33 ML, a simple 3 × 3 R 30 ° structure is formed, in which all chlorine atoms occupy fcc positions with nearest neighbor distances of 4.4 Å. [ABSTRACT FROM AUTHOR]

Abstract: Atomic structures formed on the Ag(111) surface as a result of molecular chlorine adsorption have been studied with a low-temperature scanning tunneling microscopy (LT-STM) in a combination with DFT calculations. We have found that saturated chlorine coverage on Ag(111) is a complex system consisting of two different structural phases: small anti-phase domains of a (3×3) reconstruction and nanoclusters Ag3Cl7. [Copyright &y& Elsevier]

Abstract: The surface structure of alkali doped Si(111):B ultra-thin films has been studied by low-energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). A comparative study of K/Si(111)-3×1 and K/Si(111):B- interfaces allowed us to determine the saturation coverage to be 0.5 monolayer in the later case. The -surface reconstruction is shown to be a common property of pure K, Rb, Cs materials and K0.4Rb0.6 alloys but progressively disappears if Rb is replaced by Ca. Taking into account the existence of two distinct boron sites in the ratio 1/3 as seen from B-1s core levels spectra, LAPW-DFT calculations have been carried out in order to optimize the atomic structure. As a result, alkali adatoms are shown to form trimers leading to a large modulation of the Siccompanied by an inhomogeneous doping of the dangling bonds in agreement with voltage dependent STM images. [Copyright &y& Elsevier]

We investigate the structural and electronic properties of strained Ge/Si(111)-(5×5) surfaces by means of scanning tunneling microscopy and high-resolution angle-resolved photoemission spectroscopy. The homogeneous (5×5) reconstructed overlayers are characterized by three electronic surface states, similar to the Si(111)-(7×7) surface. The dispersion of the dangling bond related surface state exhibits the same periodicity as that of the (5×5) reconstruction. Moreover, a careful analysis of the shape and width of this surface state provides striking evidence of electron-phonon coupling at low temperatures. By considering the spectral function within a simple Debye model, we determine both the Debye energy and the electron-phonon coupling strength. The latter value is further confirmed by analyzing the temperature-dependent phonon broadening of the dangling bond related surface state linewidth. [ABSTRACT FROM AUTHOR]

Ab initio density-functional theory calculations, photoemission spectroscopy (PES), scanning tunneling microscopy, and spectroscopy (STM, STS) have been used to solve the 2√3 x 2√3R30 surface reconstruction observed previously by LEED on 0.5 ML K/Si:B. A large K-induced vertical lattice relaxation occurring only for 3/4 of Si adatoms is shown to quantitatively explain both the chemical shift of 1.14 eV and the ratio 1/3 measured on the two distinct B 1s core levels. A gap is observed between valence and conduction surface bands by ARPES and STS which is shown to have mainly a Si-B character. Finally, the calculated STM images agree with our experimental results. This work solves the controversy about the origin of the insulating ground state of alkali-metal/Si(111):B semiconducting interfaces which were believed previously to be related to many-body effects. [ABSTRACT FROM AUTHOR]

In this paper, we report on the experimental determination of alkali absolute coverage in the K/Si(111):B- 2√3 x 2√3R30° surface. To this end, we carried out a comparative study with the closest system, namely, K/Si(111)-3 x 1, for which potassium coverage has been widely demonstrated to be 1/3 of a monolayer. We used x-ray photoemission spectroscopy to count and compare the number of potassium atoms in both surfaces, together with a scanning tunneling microscopy in order to check the completion of these ultrathin layers. The analysis leads to a 1/2 monolayer coverage in the 2√3 x 2√3R30° surface, that is six potassium atoms per unit cell. Assuming this coverage, we can propose a simple model structure with potassium atoms arranged in trimers; we discuss the effect of such a reconstruction in terms of two distinct "up" and "down" Si adatom sites as well as the resulting surface electronic properties. [ABSTRACT FROM AUTHOR]

The atomic structure and surface electronic properties of Ag epitaxial ultra-thin films on Cu(111) substrate have been studied by scanning tunneling microscopy (STM) and angle-resolved photoemission (ARPES). In the submonolayer range, Ag films exhibit a surface reconstruction which depends on the preparation temperature. At T=150 K, a 9×9 moire´ superstructure is observed resulting from the superposition of Ag and Cu lattices whereas at room temperature a triangular structure is stabilized. Photoemission spectroscopy shows that the surface state energy reflects the morphology and the structure of the Ag films. Below one monolayer, two parabolic dispersions indicate the presence of confined surface states in the Cu terraces and in the Ag islands. The different surface state energies associated with the two Ag layer reconstructions allow to study the irreversible transition from the moire´ to the triangular structure. [Copyright &y& Elsevier]

Shockley surface states have been studied in Ag epitaxial ultra-thin films on Cu(111) by angle-resolved photoemission (ARPES), scanning tunneling microscopy (STM) and spectroscopy (STS). The morphology of these films is characterized by large Ag islands growing along the step edges of the substrate. In the submonolayer range, the two spectroscopic techniques indicate the existence of two surface states associated with the Cu terraces and the Ag islands suggesting the confinement of the electronic states. Moreover, two different atomic reconstructions depending on the preparation temperature have been evidenced and lead to different surface state energies. [Copyright &y& Elsevier]