Sub-monolayer physical layer deposition of Zn on Ag(111) substrate at room temperature is investigated using Auger electron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. We identified an original Zn highly-anisotropic structure in the shape of finger-like inserted dendrite in front of Zn monolayer growth. On the basis of STM observations, a mechanism of inserted dendritic growth and a mechanism of its transition to layered growth are proposed.

Auger Electron Spectroscopy, Low Energy Electron Diffraction and Scanning Tunneling Microscopy have been used to study the atomic structure of a Zn monolayer deposited on Ag(111) and Ag(110) substrates at room temperature. On both faces, there is formation of a close packed monolayer of Zn covering the entire substrate surface and giving rise to specific Moire patterns. From a comprehensive LEED and STM data analysis, we deduce that the Zn monolayer adopts a (111) structure equivalent to a pure Zn layer rotated with respect to the silver substrate, of about 1.5 degrees on the Ag(111) face and of about 4.5 degrees on the Ag(110) face giving rise respectively to (root 156x root 156)R18 degrees and c(12 x 6) superstructures.

Using Auger Electron Spectroscopy (AES), Scanning Tunneling Microscopy/Spectroscopy (STM/STS) and Low Energy Electron Diffraction (LEED), we report an in-situ study of amorphous magnesium silicide (Mg2Si) ultra-thin films grown by thermally enhanced solid-phase reaction of few Mg monolayers deposited at room temperature (RT) on a Si(100) surface. Silicidation of magnesium films can be achieved in the nanometric thickness range with high chemical purity and a high thermal stability after annealing at 150 degrees C, before reaching a regime of magnesium desorption for temperatures higher than 350 degrees C. The thermally enhanced reaction of one Mg monolayer (ML) results in the appearance of Mg2Si nanometric crystallites leaving the silicon surface partially uncovered. For thicker Mg deposition nevertheless, continuous 2D silicide films are formed with a volcano shape surface topography characteristic up to 4 Mg MLs. Due to high reactivity between magnesium and oxygen species, the thermal oxidation process in which a thin Mg2Si film is fully decomposed (0.75 eV band gap) into a magnesium oxide layer (6-8 eV band gap) is also reported. (C) 2017 Elsevier B.V. All rights reserved.

Generation of ultra-thin oxide layers (in the nanometer range) is currently a technological lock for numerous applications such as microelectronics, spintronics or even molecular electronics. A precise study of the stages of growth of Mg is essential before studying the growth of the oxide. In this work we report and discuss an experimental study of the very first stages of Mg growth onto Si(100) by Scanning Tunneling Microscopy-Spectroscopy (STM-STS), Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED). First, we have shown that an amorphous underlayer is formed onto the silicon substrate for Mg deposits of 0.25 monolayers (ML). This underlayer is attributed to a Mg2Si silicide formed at RT during Mg deposition. Then, using an original growth method based on alternate cycles of magnesium monolayer adsorption and room temperature (RT) oxidation, we did grow ultra-thin magnesium oxide films onto Si(100). Our study revealed that the ultra-thin Mg2Si layer at the MgO/Si(100) interface acts as a diffusion barrier and prevents oxidation of the highly-reactive silicon during magnesium oxide growth.

The indium oxide In2O3 is among the transparent Conducting oxides (TCO) appropriate for solar cells and optoelectronics. The physical properties are based on the electron distribution on the core levels and in the valence band of material.. The knowledge of the electron distribution on the different states is fundamental to predict the possibilities of electron transitions. In this respect, we adopt calculations based on the generalized gradient approximation (GGA) and modified Becke Johnson (mBJ) to show the electron state density. We associate to the numerical simulation the experimental analysis techniques auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), and UV photoelectron spectroscopy (UPS) of great sensitivity to characterize the material surfaces. The analysis technique AES is used for proving the chemical composition of the In2O3 compound through the In-M45N45N45 and O-KLL signals. The energy loss peak at 16.3 eV on the EELS spectra is related to plasmons. The energy losses lower than 16.3 eV are related to interband transitions (ITs). They arise from the hybridation of states (s, p, and d) of indium and (s, p)of oxygen. The energy loss at 19 eV is mainly related to IT transition from the d states of indium in hybridation with a slight contribution of p and s states of indium and oxygen. The calculation is useful to predict the states from which the interband transitions occur. The EELS associated with UPS constitutes powerful techniques to show the energy states of the electron distribution. The irradiation of In2O3 by the UV photons at, 320 nm leads to the photoluminescence emission at low energy around 580 nm, appropriate to laser applications.

The growth of two-dimensional oxide films with accurate control of their structural and electronic properties is considered challenging for engineering nanotechnological applications. We address here the particular case of MgO ultrathin films grown on Ni (100), a system for which neither crystallization nor extended surface ordering has been established previously in the monolayer range. Using Scanning Tunneling Microscopy and Auger Electron Spectroscopy, we report on experiments showing MgO monolayer (ML) epitaxy on a ferromagnetic nickel surface, down to the limit of atomic thickness. Alternate steps of Mg ML deposition, O2 gas exposure, and ultrahigh vacuum thermal treatment enable the production of a textured film of ordered MgO nano-domains. This study could open interesting prospects for controlled epitaxy of ultrathin oxide films with a high magneto-resistance ratio on ferromagnetic substrates, enabling improvement in high-efficiency spintronics and magnetic tunnel junction devices.

In this paper, we use a multi-levels modeling approach to describe the elaboration of directly integrated energetic materials. The deposition of copper oxide on aluminum substrate is described. Atomic scale calculations are first conducted to identify local mechanisms involved during the growth of CuO on Al(111). These atomic scale data are then used to parameterize a macroscopic code, inspired on a kinetic Monte Carlo methodology dedicated to simulate vapor like deposition process. The objective is to establish the link between the microstructure of materials and the way they are achieved, i.e. the process parameters such as temperature and gas pressure. This work is conducted in the context of the integration of nano-structured energetic thermites used as micro energy source in microelectronic devices. We show that the temperature of the deposition process appears as the driving parameter to tailor the thickness of interfacial layers.

First principles calculations, scanning tunneling microscopy, and Auger spectroscopy experiments of the adsorption of Mg on Ag(111) substrate are conducted. This detailed study reveals that an atomic scale controlled deposition of a metallic Mg monolayer perfectly wets the silver substrate without any alloy formation at the interface at room temperature. A liquid-like behavior of the Mg species on the Ag substrate is highlighted as no dot formation is observed when coverage increases. Finally a layer-by-layer growth mode of Mg on Ag(111) can be predicted, thanks to density functional theory calculations as observed experimentally.

First principles calculations are conducted to investigate kinetic behavior of oxygen species at the surface of clean and defective Al(111) substrate. Oxygen island, aluminum vacancy, aluminum sub-vacancy, aluminum ad-atom and aluminum terraces defects are addressed. Adsorption of oxygen molecule is first performed on all these systems resulting in dissociated oxygen atoms in main cases. The obtained adsorbed configurations are then picked to study the behavior of atomic oxygen specie and get a detailed understanding on the effect of the local environment on the ability of the oxygen atom to diffuse on the surface. We pointed out that local environment impacts energetics of oxygen atom diffusion. Close packed oxygen island, sub-vacancy and ad-atoms favor oxygen atom stability and decrease mobility of oxygen atom on the surface, to be seen as surface area for further nucleation of oxygen island.

An ultra-thin MgO film of two monolayers (ML) was successfully grown onto Ag(111) by repeating twice RT adsorption of Mg atomic monolayer, RT oxidation and 725K thermal annealing under UHV conditions. Using Auger electron spectroscopy, low electron energy diffraction and scanning tunneling microscopy/spectroscopy, we report here formation of MgO(1x1) and MgO(1x1)-R30 epitaxial layers, consistent with the growth of a MgO(111) polar film onto the silver surface and composed of patches having extended slight corrugation oriented along defined directions with respect to the substrate. (C) 2015 Elsevier B.V. All rights reserved.

Using scanning tunneling microscopy and spectroscopy, Auger electron spectroscopy, and low energy electron diffraction, we have studied the growth of Mg deposited on Si(100)-(2 × 1). Coverage from 0.05 monolayer (ML) to 3 ML was investigated at room temperature. The growth mode of the magnesium is a two steps process. At very low coverage, there is formation of an amorphous ultrathin silicide layer with a band gap of 0.74 eV, followed by a layer-by-layer growth of Mg on top of this silicide layer. Topographic images reveal that each metallic Mg layer is formed by 2D islands coalescence process on top of the silicide interfacial layer. During oxidation of the Mg monolayer, the interfacial silicide layer acts as diffusion barrier for the oxygen atoms with a decomposition of the silicide film to a magnesium oxide as function of O2 exposure.

Surface interfaces of thin magnesium oxide films elaborated onto Si(100)–(2×1) substrates were characterized using scanning tunneling microscopy and spectroscopy, Auger electron spectroscopy, atomic force microscopy, and high-resolution transmission electron microscopy. We report that a flat and highly homogeneous magnesium oxide with well-defined interfaces could be grown at room temperature (RT) by repeating alternate adsorption of Mg atomic monolayer and O2 on Si(100). RT oxidation process of the first Mg monolayer plays a crucial role as driving force allowing a partial decomposition of amorphous ultra-thin Mg2Si at the Mg/Si interface to form more magnesium oxide in the surface. This process induces crystallization of the interfacial Mg2Si thin film and then gives arise to an unexpected MgOx/Mg2Si(11–1)/Si(100) heterostructure. MgOx monolayer displays a band gap of about 6eV and exhibits a weak RMS roughness on large areas.

Using scanning tunneling microscopy (STM), Auger electron spectroscopy, and low energy electron diffraction, we have observed a surprising complete dissolution at room temperature of one lead monolayer deposited by evaporation on an aluminum oxide thin film (∼0.8 nm thick) previously grown on Ag (111). We have observed the quasi-instantaneous diffusion of the lead deposit through the oxide layer to the silver/oxide interface. After the diffusion process, lead atoms form a Moiré superstructure, which is characterized by STM through the oxide layer. This unexpected behavior puts in light the very weak interaction between the aluminum oxide and the silver substrate.

In this paper we report on several structures of silicene, the analog of graphene for silicon, on the silver surfaces Ag(100), Ag(110) and Ag(111). Deposition of Si produces honeycomb structures on these surfaces. In particular, we present an extensive theoretical study of silicene on Ag(111) for which several recent experimental studies have been published. Different silicene structures were obtained only by varying the silicon coverage and/or its atomic arrangement. All the structures studied show that silicene is buckled, with a Si-Si nearest neighbor distance varying between 2.28 and 2.5 Å. Due to the buckling in the silicene sheet, the apparent (lateral) Si-Si distance can be as low as 1.89 Å. We also found that for a given coverage and symmetry, one may observe different scanning tunneling microscopy images corresponding to structures that differ by only a translation.

We report on experimental evidence for the formation of a two dimensional Si/Au(110) surface alloy. In this study, we have used a combination of scanning tunneling microscopy, low energy electron diffraction, Auger electron spectroscopy, and ab initio calculations based on density functional theory. A highly ordered and stable Si-Au surface alloy is observed subsequent to growth of a sub-monolayer of silicon on an Au(110) substrate kept above the eutectic temperature.

Silicene–the silicon-based counterpart of graphene–has a two dimensional structure that is responsible for the variety of potentially useful chemical and physical properties. The existence of silicene has been achieved recently owing to experiments involving epitaxial growth of silicon as stripes on Ag(001), ribbons on Ag(110), and sheets on Ag(111). The nano-ribbons observed on Ag(110) were found–by both high definition experimental scanning tunneling microscopy images and density functional theory calculations–to consist of an arched honeycomb structure. Angle resolved photo-emission experiments on these silicene nano-ribbons on Ag(110), along the direction of the ribbons, showed a band structure which is analogous to the Dirac cones of graphene. Unlike silicon surfaces, which are highly reactive to oxygen, the silicene nano-ribbons were found to be resistant to oxygen reactivity.