Photoemission yield spectroscopy of electronic surface states on germanium (111) surfaces

The electronic surface states of cleaved and annealed Ge(111) surfaces have been investigated by photoemission yield spectroscopy and contact potential measurements on a set of differently doped samples. On the 2 × 1 cleaved surface, a surface state band centered about 0.7 eV below the valence band maximum is found. The variations of the work function with the doping level show that an empty surface state band exists above the Fermi level. After annealing at temperatures of the order of 350°C, this surface exhibits a 2 × 8 superstructure. A new surface state band is then found closer to the valence band maximum. This variation of the surface state distribution is correlated to a change in the surface potential. The variation of the electronic characteristics upon oxygen adsorption are also reported and an evaluation of the sticking coefficient is made for both structures.     

Passivation of Si (111) surfaces by ordered metal layers

The properties of √3 × √3 ordered gold and silver monolayers on a Si(111) substrate have been investigated by Auger, low energy electron diffraction and photo-emission analysis. It has been found that oxygen adsorption on these surfaces is considerably weaker than on clean Si surfaces. This new result clearly emphasizes the correlation between the oxidation properties of Si atoms and their local environment. A comparison is made with previous results concerning Au-Si amorphous metallic alloys where gold atoms act as a catalyst for the oxidation.     

Dangling bond surface state of Si(111): New results

By angle resolved photoemission on Si(111) 2 × 1 surfaces, the main surface structure at ?0.85 eV below E_F is shown to exhibit a strong s?p_z character in contradiction with previous measurements. The similarity of the results on the 2 × 1 and 7 × 7 surfaces, together with theoretical calculations lead us to favor a buckled model for the 2 × 1 surface and a model based on ring like arrangements of lowered and raised atoms for the 7 × 7 surface.     

Angle resolved photoemission measurements on AgSi(111) 7 × 7 interfaces

The AgSi(111) interface is investigated by LEED, AES and angle resolved photoemission spectroscopy using 50 eV synchrotron radiation in p-polarization. Results on room temperature (RT) silver growth on Si(111) 7 × 7 are characterized by an evolution of the LEED pattern and of the d band shape which is consistent with 2D island formation in the submonolayer range. When the Ag coverage (Θ) is increased, a progressive build-up of Ag layers occurs with a possible interdiffusion of the atomic constituents. The ordered $\text{Si(111)}\text{3}\text{×}\text{3}\text{R(30°)Ag}$ structure (R₃) obtained by annealing a 1 ML RT deposit gives rise to new interface states near E_F. In contrast to the RT deposit at the same Θ, two well defined d band peaks are present while the bulk Si emission near 3.4 eV is clearly seen. The R₃ data would favour recent crystallographic models which conclude to an embedment of the Ag atoms in a threefold hollow adsorption site.     

Structure dependent oxidation of clean Si(111) surfaces

The initial process of oxygen adsorption is investigated by high resolution photoemission yield spectroscopy on (2 × 1) and (7 × 7)Si(111) surfaces. The corresponding changes in work function, ionization energy and surface state distribution, within and close to the gap, depend strongly on the initial structure. It is shown for the first time that, after completion of a “monolayer” of oxygen, the dangling bond states completely disappear on the (7 × 7) structure while a few percents remain unaffected on the (2 × 1).     

Association of Molybdenum Ionic Species with Alumina Surface

The adsorption isotherms at 25, 45, and 65 degrees C of molybdenum solutions of concentration ranges between 10(-3) and 3x10(-2) M(Mo) (pH 4-5) on different alumina samples are investigated. The analysis is conducted using a modified Frumkin isotherm which takes a more realistic account of the lateral interaction between adsorbed species and considers that the adsorption takes place on the most basic OH groups on the surface of alumina. The results are discussed in view of the difference in solutions speciation, and the changes in the pH of the remaining supernatant solutions. The solution temperature, PZC of the used aluminas, the configuration of the basic OH groups on their surface, and the pore structure have been shown to intervene effectively. Copyright 2000 Academic Press.