A. Sgarlata

Copper phthalocyanine on Si(111)-7 × 7 and Si(001)-2 × 1: an XPS/AES and STM study

Abstract Silicon surfaces with different reconstruction, Si (111)-7 × 7 and Si (001)-2 × 1, are exposed to a molecular beam of copper phthalocyanine. On Si(111) the adsorbate-substrate interaction is strong, as suggested by a partial reduction of copper shown in the XPS spectra and by the evidence provided by STM of a chemical reaction involving some of the Si adatoms. As a consequence, the molecules are not imaged at atomic scale by STM. At variance with this behaviour, on the single-domain Si (001)-2 × 1 face, the adsorbed molecules are clearly imaged by STM, suggesting an adsorption state more weakly bonded. This is the first observation of Cu phthalocyanine molecules imaged on a silicon surface, and it further illustrates the potential of STM for surface chemistry.

Porphyrin thin films coated quartz crystal microbalances prepared by electropolymerization technique

Quartz crystal microbalances (QMB) have been coated by thin films of different metal complexes of protoporphyrin IX dimethyl ester (M-PPIX), deposited by electropolymerization technique. The structure of these films has been characterized by scanning tunnelling microscopy (STM). The sensory behaviour of the obtained QMB have been studied in the presence of four volatile organic compounds (VOC).

Self-ordering of Ge islands on step-bunched Si(111) surfaces

By using step-bunched Si(111) surfaces as templates, we demonstrate the self-assembly of an ordered distribution of Ge islands without lithographic patterning. Initially, islands nucleate and evolve at step edges, up to complete ripening, forming long ribbons. Subsequently, island nucleation takes place at the center of flat terraces. Ge islands appear to be regularly spaced in scanning tunneling microscope images. The exploitation of this effect provides a possible route to grow ordered arrays of semiconducting nanostructures.

Ge-Si intermixing in Ge quantum dots on Si

We have provided direct evidence for the presence of considerable Si-Ge intermixing in strained and unstrained Ge quantum dots deposited on Si(001) and Si(111). The local structure around Ge was probed by using Ge K-edge X-ray absorption spectroscopy; complementary evidence for intermixing was provided by AFM and STM studies. These results implied that the strain energy in the dots was reduced by Si atoms diffusing into the dots, resulting in a modified form of Stranski-Krastanov growth.

Composition of Ge — Si – islands in the growth of Ge on Si — 111 – by x-ray spectromicroscopy

The stoichiometry of Ge∕Si islands grown on Si(111) substrates at temperatures ranging from 460to560°C was investigated by x-ray photoemission electron microscopy (XPEEM). By developing a specific analytical framework, quantitative information on the surface Ge∕Si stoichiometry was extracted from laterally resolved XPEEM Si 2p and Ge 3d spectra, exploiting the chemical sensitivity of the technique. Our data show the existence of a correlation between the base area of the self-assembled islands and their average surface Si content: the larger the lateral dimensions of the 3D structures, the higher their relative Si concentration. The deposition temperature determines the characteristics of this relation, pointing to the thermal activation of kinetic diffusion processes.

Composition of Ge(Si) islands in the growth of Ge on Si(111)

X-ray photoemission electron microscopy (XPEEM) is used to investigate the chemical composition of Ge/Si individual islands obtained by depositing Ge on Si(111) substrates in the temperature range 460–560 °C. We are able to correlate specific island shapes with a definite chemical contrast in XPEEM images, at each given temperature. In particular, strained triangular islands exhibit a Si surface content of 5%–20%, whereas it grows up to 30%–40% for “atoll-like” structures. The island’s stage of evolution is shown to be correlated with its surface composition. Finally, by plotting intensity contour maps, we find that island centers are rich in Si.

Self-assembly of InAs and Si/Ge quantum dots on structured surfaces

We discuss the self-aggregation process of InAs and Si–Ge quantum dots (QDs) on natural and patterned GaAs(001) and Si(001) and Si(111) surfaces, with reference to our recent studies with scanning tunnelling and atomic force microscopy and current experimental and theoretical works. Various methods for obtaining naturally structured surfaces are briefly surveyed, as the patterning formed by the surface instability and by the strain in mismatched heteroepitaxy, and the latest methods of pre-patterning and growth at selected sites are discussed. Basic topics are also addressed that determine the final morphology of QDs, such as the wetting layer formation, the elastic strain field and the two-dimensional to three-dimensional phase transition.

Metal phthalocyanines (MPc, MNi, Cu) on Cu(001) and Si(001) surfaces studied by XPS, XAS and STM

Abstract The growth mode of metal phthalocyanines (MPc, MNi, Cu) on clean Cu(001) and Si(001) (i.e. bonding and adsorption geometry) and their electronic structure are studied by a combination of spectroscopic techniques: x-ray photoemission, x-ray absorption at Metal L 2,3 edges and scanning tunnelling microscopy.

Evolution of the intermixing process in Ge/Si(111) self-assembled islands

In this contribution we present a study of the Ge–Si intermixing process that arises during the growth of Ge/Si(111) self-assembled islands. The samples, grown by means of a molecular beam epitaxy (MBE)-like technique, have been characterized by in-situ scanning tunneling microscopy (STM) and atomic force microscopy (AFM) complemented by ex-situ X-ray absorption fine structure (XAFS). We have observed by STM a change in the island morphological evolution, from truncated tetrahedra to atoll-like islands, that can be related to the misfit the reduction effect induced by the intermixing process. We have evaluated the intermixing by measuring the average coordination numbers of Si and Ge around a Ge atom by XAFS. We show that the Si content in the nominally pure Ge wetting layer reaches 50% while in the three-dimensional (3-D) islands it is about 25%, and that the intermixing increases with increasing deposition temperature in the 450–530 °C range.

Morphological instabilities of the InAs/GaAs(001) interface and their effect on the self-assembling of InAs quantum-dot arrays

The morphology of the InAs/GaAs(001) system has been imaged by atomic force microscopy (AFM) at different stages of the epitaxial growth from the initial formation of a pseudomorphic two-dimensional (2D) interace up to the self-aggregation of InAs quantum dots (QDs). The substrate texture and the dependence of the cation diffusion on the elastic strain field fully control the lateral ordering of the nanoparticles in the self assembling process and determine the final morphology of multistacked InAs QD arrays.