R.C. Cinti

The influence of steps on the epitaxial growth of iron-silicide on Si(001)

Abstract Iron deposition up to ~ 25 A on planar and stepped Si(001) surfaces was studied by LEED, AES, UPS, and ELS measurements. On both surfaces iron nucleation is of 3D type with notable interdiffusion at room temperature. Annealing of the overlayers up to 800 K enhances the interdiffusion and above 800 K semiconducting FeSi 2 is formed on both surfaces, unstructured on the planar and epitaxially on the stepped one.

Directional UV photoemission from clean and sulphur saturated (100), (110) and (111) nickel surfaces

Abstract Angle resolved photoemission energy distribution curves (EDCs) were obtained on clean and sulphur saturated (100), (110) and (111) nickel surfaces for excitation energies equal to 10.2, 13.5, 16.8 and 21.2 eV. The EDCs of clean surfaces are weakly structured at θ = 0° and become more rich in features for oblique angles. In the explored energy range, adsorption of sulphur produces two extra-structures at initial energies depending on surface orientation. One of which situated at about −4.5 eV below the Fermi level is in good agreement with Hagstrum ion neutralization spectroscopy results, the other at around −1.8 cV has never been observed before. A remarkable similarity of adsorption effects on the three surfaces is found. These results are compared with experimental data obtained previously on equivalent sulphur saturated surfaces by INS and discussed in relation to recent theoretical calculations on chalcogen adsorption on nickel.

Scanning tunneling microscopy study of the Si(111)-(√3 × √3)-Pb mosaic phase

Abstract The atomic and electronic structure of the Pb-induced (√3 × √3)R30 mosaic phase on Si(111) substrates has been studied by means of scanning tunneling microscopy (STM). A systematic voltage dependent STM imaging analysis combined with scanning tunneling spectroscopy measurements have enabled us to interpret the different height contrast between Si and Pb adatoms observed on STM images. This contrast difference may be attributed to a large charge-transfer between the different adatom dangling-bond orbitals.

Interface formation of W evaporated on Si(111) (7 × 7)

Abstract XPS, XAES, UPS and LEED have been used to study the interface formation of W evaporated onto Si(111) (7×7) surfaces, with samples maintained at room temperature and after subsequent annealing of the deposits. The intensity variations of the core levels (Si 2p and W 4f) and of the Auger signals (Si KLL, Si LVV and W NOO) as a function of surface coverage θ correspond to an abrupt junction and a layer-by-layer growth mode. This hypothesis is confirmed by work function measurements. The W 4 f 7 2 undergoes an energy shift of − 0.4 eV (towards lower binding energy) at low coverage, θ ⪷ 1 monolayer (ML), and reaches its bulk metal value at θ ≈ 10 ML; this shows in addition a rather short transition region. Meanwhile, the only variations observed with Si core levels are energy shifts of −0.2 eV for Si 2p and +0.2 eV for Si KLL, which take place at the very first deposition of a submonolayer amount of W. These shifts are attributed to a surface band bending variation. When the metal deposit attains a surface coverage θ ≈ 0.1 ML the Si characteristic surface states disappear from the UPS spectra, while the (7×7) LEED pattern is replaced by a (1×1) diagram which afterwards vanishes in the background for θ⪸1 ML . UPS indicates a rapid predominance of d-metal emission, and a W valence band is fully developed at θ ⪸ 4 ML . Upon annealing of 5–100 ML deposits at temperatures above 750°C, XPS and UPS testify the completion of WSi2 formation and LEED patterns indicate an epitaxial overlayer.

Chemisorption of indium on (111) silicon substrates: II. Adsorption by flash desorption technique — Adsorption energy

Abstract The adsorption of indium on clean (111) silicon surfaces is studied by flash desorption. Two adsorption phases are found: a 59.5 kcal mole constant-energy phase which saturates at 7 × 10 13 atoms cm 2 and a second phase which increases with the adatom population n. The temperature of the desorption peak of this phase decreases when n increases. The adsorption energy of In on (111) Si is calculated by the Gyftopoulos theory, and the calculated and experimental results are compared. A very small charge transfer between the adatoms and the surface, equal to or smaller than 0.02 electron per adatom, is found.

Préparation et oxydation superficielle d'une face (110) de vanadium

Resume In the first part a method for obtaining a (110) plane of acceptable purity is described. This surface is characterized by LEED and Auger spectroscopy; effects of annealing and ion-bombardment are given, and the major importance of sulfur diffusing out the crystal in the cleaning process is demonstrated. In the second part the interactions between the surface and oxygen are studied, in the low pressure range, by LEED and work function measurements. No ordered surface structures are found; these observations show that oxygen dissolves in vanadium even at low temperature.

Interfaces formed by evaporation of Si on Ni and Mo surfaces

Abstract The interfaces formed by Si evaporated onto Ni(100) and Mo polycrystalline surfaces are studied by XPS, XAES and UPS, with the samples at room temperature (RT) and after annealing of deposits of ∼ 20 monolayers. The RT interfacial reactions are different for the two metals; with Ni strong interaction occurs leading to an intermixed and gradual interface, while the junction is rather abrupt with Mo. On both metals, the Si 2p energy shift is negligible in the monolayer range and attains ∼ −0.3 eV in “thick” deposit. In comparison with the inverse systems, i.e. metals deposited on Si, it is found that the Si-metal and metal-Si interfaces formed at RT are similar, but their subsequent annealings produce fairly different composite layers.

LEED and UPS study of Ni ≅ (001) vicinal surfaces

Abstract Two stepped surfaces of nickel in the vicinity of the (001) plane have been studied by LEED and UPS. On clean surfaces, diffraction patterns show reversible step rearrangements when temperature and contamination are varied. A simple model is proposed describing this reconstruction. UPS spectra measured on these vicinals show no remarkable differences with corresponding EDCs for the clean simple Ni(001) surface, suggesting a large similarity in their respective local density of states. Some results concerning the stability of the surface morphologies upon sulphur adsorption are described.

Structure et orientation des noyaux élémentaires sur un substrat cristallin

Abstract With a simple atomistic model we have investigated the structure and the orientation energetically the most probable of a four-atom nucleus on a crystalline substrate assumed perfect. If Qaa is the interaction energy between two atoms of the nucleus at the distance raa and Qab the interaction energy between a substrate atom and a deposit atom separated by rab, the formation energy of the nucleus is: E= ∑ 4, m Q ab + ∑ 4 Q aa , where m is the number of the nearest neighbours considered on the substrate. With the energies Qi in the form of Morse functions, one can obtain the configuration of the nucleus and its relative position on the surface which minimise the formation energy. These values, versus the ratio of the substrate atomic diameter, can be calculated systematically by means of machine programming. Results are given for (100) and (111) fcc crystalline substrates and are compared with experimental data.

Adsorption and diffusion of single Pb atoms on Si(111)7 × 7 and Si(111)5 × 5 surfaces studied by scanning tunneling microscopy

Abstract We have shown very recently by means of scanning tunneling microscopy (STM) that single Pb atoms are highly mobile at room temperature (RT) when adsorbed on Si(111)7 × 7 surfaces. In the present work we have undertaken a further STM investigation of RT adsorption and diffusion of Pb on another DAS (dimer-adatom-stacking fault) reconstruction. To do so, substrates with large terraces presenting the Si(111)5 × 5 reconstruction were prepared and ultra-low coverage (≈0.01–0.02 ML) of Pb were deposited at RT. The STM results measured on these surfaces show that single Pb atoms are highly mobile at RT inside (5 × 5) half-cells but diffuse at very low rate to neighboring half-cells, as is the case for (7 × 7) substrates. The implications of these findings on the possible adsorption sites are discussed in comparison with the Pb Si 1117 × 7 system.