Ph. Mathiez

7 × 7 Si(111)Cu interfaces: Combined LEED, AES and EELS measurements

Abstract CuSi(111) interfaces have been examined as a function of substrate temperature and deposition time using different surface sensitive techniques. At room temperature a layer by layer growth was found. Strong intermixing of Cu and Si takes place and beyond 10 monolayers an ordered α Si phase in Cu was found. At high temperature, the growth follows the layer plus island or Stranski-Krastanov growth mode. Three-dimensional crystallites, probably consisting of Cu 3 Si, grow epitaxially on an ordered intermediate layer.

Formation and properties of the copper silicon(111) interface

The initial stages of the Cu growth on top of a 7×7 Si(111) surface were monitored with LEED, AES, UPS, and XPS techniques. Results suggest that at room temperature the Cu growth proceeds by a laminar fashion. An intermixing between Si and Cu takes place giving rise to a diffuse interface extending to several first monolayers. This fact is testified by the splitting of the Si LVV transition in AES spectra, by the deviation of the AES and XPS Cu and Si signal plot versus coverage from a perfect layer by layer growth plot, and by a strong diffuse background intensity in LEED diagram. Moreover, at this coverage range, a slight narrowing and a shift (0.7 eV±0.2 eV) of the 3d Cu peak towards higher binding energy as compared with the bulk metal are observed in valence band photoemission spectra. With increasing coverage, a metal rich phase is found displaying an ordered 1×1 Cu(111) planelike structure. No Si enrichment at the topmost metallic layer is observed by XPS. Core level spectroscopy gives similar resu...

Combined AES, LEED, SEM and TEM characterizations of CuSi(100) interfaces

CuSi(100) interfaces prepared under UHV at different substrate temperatures (TS) have been characterized using in-situ Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) as well as ex-situ scanning and transmission electron microscopy (SEM, TEM). At room temperature (RT), the film grows in a layer by layer like mode. With increasing TS, the intensity of the Cu M2,3VV (61 eV) Auger transition decreases and at TS = 500°C no Cu Auger signal could be measured below θ ∼ 100. Yet SEM and TEM observations of these deposits show islands in epitaxial relation with the substrate. It can be determined from TEM images that these islands are covered with a Si skin (∼ 50 A; thick) and that they are deeply implanted in the Si substrate. This explains the AES measurements.

CuSi(111) interfaces: Oxidation properties in relation with their structural properties

The oxidation properties of CuSi(111) interfaces prepared either at room temperature (RT) or at high temperatures starting from a 7 × 7−Si(111) surface, are investigated in relation with their structural properties. At low oxygen exposures (104 langmuirs), at room temperature, enhanced oxidation effects are observed for a RT Cu deposit while an annealed interface which displays a nearly 5 × 5 LEED structure is completely passivated as regard to oxidation under the same conditions. With a stronger oxidation (3 × 107 L), we always measure an enhanced oxidation at the RT CuSi interface as compared with the virgin Si surface while the passivity property of the annealed CuSi interface is weakened.

Cooperative Segregation of Boron at Si(111)

Interface segregation of boron at Si(111) surfaces has been studied at the atomic scale using a scanning tunnelling microscope (STM). During the segregation process (produced by thermal annealing), strong cooperative effects take place which cannot be explained by a simple nearest-neighbour pair interaction model. Although average surface concentrations of boron in the investigated temperature range could be calculated in terms of a Fowlers model, the comparison between STM and simulated images suggests that one must introduce longer-range interactions to describe the atomic-scale configurations.

Characterization of Cu/Si(100) interfaces by different surface-sensitive techniques

Abstract Room-temperature (RT) and high-temperature (HT) Cu/Si(100) have been investigated by in-situ Auger and electron energy loss spectroscopies and ex-situ SEM and TEM. At RT, a quasi-layer-by-layer growth of a CuSi compound is observed in the early stages. Beyond θ = 10 ML, metallicity of Si in Cu environment is observed. Estimation of the stoichiometry of the film by the plateau of the Auger growth curve suggests a composition near Cu 3 Si in agreement with the position of the Cu-induced peaks in EELS. At high temperature (130°–500°C), the growth of 3D crystallites occurs while a wetting by a Si film is revealed by both SEM and TEM.

√3 structure of Boron enriched Si(111) surfaces investigated by Auger, leed and scanning tunneling microscopy

Abstract Boron enrichment of the Si(111) surface was realized by long time annealing at 900 ° C of highly boron doped Si samples ( p ≈10 19 cm −3 ). Boron Auger peak (179 eV) and LEED patterns of boron induced 3 × 3 R 30° reconstructions could be detected after such a treatment. Preparation and characterization of the samples by averaging surface sensitive techniques have been performed in an UHV chamber equipped with a STM unit. High resolution STM images of the 3 structure have been obtained. Simultaneous imaging in both polarities, thus probing filled or empty surface states, allowed us to observe spectroscopic effects which are discussed in this paper. On the basis of our data, a modification of the T 4 adatom model of the 3 structure is proposed.

The Au/Si(111)7×7 interface: Correlation between electronic and morphological properties by high‐resolution electron energy‐loss spectroscopy, ultraviolet photoemission spectroscopy, and transmission electron microscopy

We have studied the diffusive Au/Si(111)‐7×7 interface by surface sensitive techniques (high‐resolution electron energy‐loss and ultraviolet photoemission spectroscopies) and by transmission electron microscopy (TEM). The combination of the spectroscopic methods with TEM allows us to propose a new morphological description of the layer growing at room temperature, namely, that there are crystallites of pure Au embedded in an amorphous AuxSi1−x alloy matrix.

Early stages of Cu growth on boron segregated Si(111) surfaces: A scanning tunneling microscopy study

Out segregation of boron from the bulk of highly doped Si samples leads to surfaces which present a B–Si(111)√3×√3 R(30°) reconstruction (hereafter abbreviated B√3). Scanning tunneling microscopy investigations show that, depending on the annealing temperatures, different boron equilibrium surface concentrations are obtained in the B√3 substrates. Comparisons of Cu growth on such substrates show that copper nucleation is highly correlated to the density of dangling bonds at the surface.

Scanning tunneling microscopy investigations on Pb/Si(111)

Abstract We present results on the early stages of room-temperature (RT) deposition of Pb on the Si(111)-7 × 7 surface on the basis of STM characterization coupled with Auger and LEED analysis. These data show that in the submonolayer range of coverage no intermixing of Pb and Si occurs, while the 7 × 7 periodicity remains. Further deposition of Pb in the monolayer range gives rise to the observation of well shaped atomically flat Pb islands whose edges are oriented along the equivalent 〈1 1 0〉 directions.