We have grown an atom-thin, ordered, two-dimensional multi-phase film in situ through germanium molecular beam epitaxy using a gold (111) surface as a substrate. Its growth is similar to the formation of silicene layers on silver (111) templates. One of the phases, forming large domains, as observed in scanning tunneling microscopy, shows a clear, nearly flat, honeycomb structure. Thanks to thorough synchrotron radiation core-level spectroscopy measurements and advanced density functional theory calculations we can identify it as a ?3????3 R(30?) germanene layer in conjunction with a ?7????7 R(19.1?) Au(111) supercell, presenting compelling evidence of the synthesis of the germanium-based cousin of graphene on gold.

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Germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene

Recent development in 2D materials beyond graphene

A review on silicene - New candidate for electronics

Germanene, a 2D honeycomb structure similar to silicene, has been fabricated on Al(111). The 2D germanene layer covers uniformly the substrate with a large coherence over the Al(111) surface atomic plane. It is characterized by a (3 × 3) superstructure with respect to the substrate lattice, shown by low energy electron diffraction and scanning tunnelling microscopy. First-principles calculations indicate that the Ge atoms accommodate in a very regular atomic configuration with a buckled conformation.

Continuous germanene layer on Al(111).

The tunneling current from a scanning tunneling microscope was used to image and dissociate single O{sub 2} molecules on the Pt(111) surface in the temperature range of 40 to 150K. After dissociation, the two oxygen atoms are found one to three lattice constants apart. The dissociation rate as a function of current was found to vary as I{sup 0.8{plus_minus}0.2} , I{sup 1.8{plus_minus}0.2} , and I{sup 2.9{plus_minus}0.3} for sample biases of 0.4, 0.3, and 0.2V, respectively. These rates are explained using a general model for dissociation induced by intramolecular vibrational excitations via resonant inelastic electron tunneling. {copyright} {ital 1997} {ital The American Physical Society}

Single Molecule Dissociation by Tunneling Electrons

We provide the first direct observation of a $\ensuremath{\beta}\ensuremath{-}\mathrm{S}\mathrm{i}\mathrm{C}\left(100\right)\ensuremath{-}c\left(4\ifmmode\times\else\texttimes\fi{}2\right)$ surface reconstruction. The experiments are performed using high-resolution scanning tunneling microscopy (STM). Flat surfaces having a long range order are grown. Individual Si dimers are identified and form a centered pseudohexagonal pattern give a $c\left(4\ifmmode\times\else\texttimes\fi{}2\right)$ array. Further support for Si-dimer identification is provided by theoretical STM image calculations. The results suggest a model of dimer rows having alternatively up and down dimers (AUDD) within the row, in an ``undulating'' type of arrangement reducing the surface stress. Hence the $\ensuremath{\beta}\ensuremath{-}\mathrm{S}\mathrm{i}\mathrm{C}\left(100\right)\ensuremath{-}$ and $\mathrm{Si}\left(100\right)\ensuremath{-}c\left(4\ifmmode\times\else\texttimes\fi{}2\right)$ surface reconstructions are very different.

Direct Observation of a β-SiC(100)- c$4×2$ Surface Reconstruction

We study a semiconductor on a close-packed surface of a metal for a system that tends to phase separation. At room temperature, deposition of 1/3 monolayer of Ge on Ag(111) surprisingly induces a surface alloy forming a $p(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ superstructure observed in low energy electron diffraction patterns. Yet high-resolution scanning tunneling microscopy images do not exhibit any chemical contrast between Ge and Ag atoms. This is interpreted with ab initio total-energy calculations, which also show that the Ge atoms are located in substitutional sites forming an ordered two-dimensional surface alloy with almost identical local electronic densities for both elements.

Ge/Ag(111) semiconductor-on-metal growth: Formation of an Ag 2 Ge surface alloy

Atomic Structure of the beta -SiC(100)-(3 x 2) Surface.

We use scanning tunneling microscopy to evidence the controlled formation of straight, very long, and highly stable Si atomic lines self-organizing on the {beta}{minus}SiC(100) surface. These atomic channels, which are composed of Si dimers, form at the phase transition between the 3{times}2 and c(4{times}2) reconstructions by selective Si atom organization. The presence of Si atomic lines is found to coincide systematically with a lateral mismatch between the c(4{times}2) Si-dimer rows. Their number and spacing are mediated by annealing time and temperature, resulting in unprecedented arrangements ranging from a very large superlattice to a single isolated atomic line. {copyright} {ital 1997} {ital The American Physical Society}

Highly Stable Si Atomic Line Formation on the {beta} -SiC(100) Surface

The atomic-scale desorption of hydrogen atoms from the $\mathrm{Si}(100)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1:\mathrm{H}$ surface with the tip of the scanning tunneling microscope has been studied using two different desorption methods, namely the stationary and scanning modes. Both p-type and n-type silicon samples have been investigated and a statistical large data set has been acquired. At low sample voltage (+2.5 V), the desorption yield has been found to follow a power law of the tunnel current ${I}^{\ensuremath{\alpha}},$ with \ensuremath{\alpha} being much smaller (\ensuremath{\approx}1) than in previous reports (\ensuremath{\approx}10--15). This means that highly dissipative inelastic electronic channels with very few electrons involved (\ensuremath{\approx}2) are more favorable than previously proposed schemes involving many (\ensuremath{\approx}11--16) weakly dissipative electrons.

Gérald Dujardin

Papers

Direct Observation of a β-SiC(100)- c\(4×2\) Surface Reconstruction

Ge/Ag(111) semiconductor-on-metal growth: Formation of an Ag 2 Ge surface alloy

Atomic Structure of the beta -SiC(100)-(3 x 2) Surface.

Highly Stable Si Atomic Line Formation on the {beta} -SiC(100) Surface

Atomic-scale desorption of H atoms from the Si(100)-2×1:H surface: Inelastic electron interactions