G. Le Lay

Physics and electronics of the noble-metal/elemental-semiconductor interface formation: A status report

Abstract The object of this report is to given a systematic overview of the characteristics of the formation of the noble-metal/elemental-semiconductor interface. The growth mechanisms, the structural and energetic properties of the different phases, are described and discussed in connection with the electronic properties of the system. The interaction of these interfaces with oxygen is also analyzed. Besides individual behavior, general trends in these interfaces formation are derived.

Isothermal desorption spectroscopy for the study of two-dimensional condensed phases: Investigation of the Au (deposit)/Si(111) (substrate) system; application to the Xe/(0001)graphite system

Abstract A study with LEED and AES of Au deposits on Si(111) permits one to characterize three well-organised two-dimensional (2D) phases ( 5 × 1; 3 ; 6 ) according to coverage ratios and temperature. Isothermal desorption experiments show three distinct kinetics, each being connected to the vanishing of one 2D phase. In each case the reaction is zero order. A general model for the desorption of condensed 2D phases is elaborated. It is shown that the order of the reaction has two extrema, 0 and 1 2 , depending on whether surface diffusion is important or not. This kinetic model is applied to the experimental results obtained with the Au/Si(111) system and also with the simpler Xe/(0001) graphite system. Physical parameters such as the cohesive energy and the vibrational frequencies of the atoms in the 2D phases are derived. These values are in good agreement with the ones independently obtained for these systems from measurements of another kind.

Synthesis and electrical conductivity of multilayer silicene

The epitaxial growth and the electrical resistance of multilayer silicene on the Ag(111) surface has been investigated. We show that the atomic structure of the first silicene layer differs from the next layers and that the adsorption of Si induces the formation of extended silicene terraces surrounded by step bunching. Thanks to the controlled contact formation between the tips of a multiple probe scanning tunneling microscope and these extended terraces, a low sheet resistance, albeit much higher than the electrical resistance of the underlying silver substrate, has been measured, advocating for the electrical viability of multilayer silicene.

AES study of the very first stages of condensation of gold films on silicon (111) surfaces

Abstract To analyse the very first stages of condensation of gold films on Si(111) substrates we record Auger amplitudes upon deposition at room and high temperatures, and observe LEED patterns. With those experimental data we can infer the mechanism leading to the formation of the low temperature silicides and to the high temperature superstructures.

Desorption kinetics of condensed phases Two-dimensional phases of silver on Ge(111)

Abstract Silver condenses on germanium (111) according to the Stranski-Krastanov growth mechanism. It forms initially a two-dimensional Ge(111)4 × 4-Ag phase with four silver atoms per sixteen germanium atoms, then a more dense two-dimensional phase Ge(111)√3 × √3-Ag with 0.85 Ag per germanium atom. These two-dimensional phases are followed by the epitaxial condensation of three-dimensional silver crystallites on Ge(111). The desorption kinetics of the two-dimensional phases are studied in the monophased domain as well as in the biphased domain. We find for both domains an island model according to which the desorption occurs indirectly via surface diffusion.

Formation of noble-metal-Si(100) interfaces

Abstract From the very first stages of adsorption, in the course of the build up of the interfaces, the noble metals condensed on clean Si(111) surfaces behave quite distinctively. A large number of investigations has been devoted to the characterization of these systems, which appear in many aspects as prototypes for further studies in semiconductor interface physics. Although of increasing practical interest, the interfaces of Cu, Ag and Au with Si(100) have been comparatively much less studied in a fundamental way. In this paper we review the knowledge acquired on these systems, adding new experimental results (electron spectroscopy and -microscopy). A comparison between noble-metal/Si(100) and noble-metal/Si(111) interface properties will be included.

Complementary data obtained on the metal-semiconductor interface by LEED, AES and SEM: Pb/Ge(111)

Abstract AES, LEED and scanning electron microscopy analysis performed on the Pb/Ge(111) system under UHV lead to the following main results. The Pb/Ge(111) system exhibits the Stranski-Krastanov growth mode. The stoichiometry of the complete 2D layer is one. This monolayer undergoes a reversible phase transformation √3 × √3 ⇄ 1 × 1 at around 300°C. The value of the bonding energy of one lead atom on (111)Ge is found to be equal to φ Pb − Ge = 31 ± 2 kcal mol . The adhesion energy of a 3D lead crystallite on (111)Ge has been estimated to be β = 918 ± 9 erg cm 2 .

Surface spectroscopy studies of Pb monolayers on Si(111)

We have studied the adsorption process and the thermal desorption process of Pb on clean Si(111)7 × 7 substrates using LEED and AES. The growth kinetics follows a Stranski-Krastanov mode (2D adlayer + 3D islands). The adlayer is completed at one monolayer when deposited below the lead melting point. Upon heat treatment, three different surface phases resulting in a (3×3)R30 ° unit cell are identified. The last one, saturated at 1 ML, undergoes a reversible phase transition to a 1×1 structure. This phase transition is attributed to an order-order solid phase transition.

Formation of a one-dimensional grating at the molecular scale by self-assembly of straight silicon nanowires

Upon submonolayer deposition of silicon onto the anisotropic silver (110) surface flat lying individual Si nanowires, all oriented along the [−110] direction, can be grown at room temperature with a high aspect ratio. Upon deposition at ∼200°C, these one-dimensional nanostructures self-assemble by lateral compaction to form a regular array of essentially identical nanowires, ∼1.6nm in width, covering uniformly the entire substrate surface. They realize, at macroscopic sizes, a highly perfect one-dimensional grating with a molecular-scale pitch of just 2nm.Upon submonolayer deposition of silicon onto the anisotropic silver (110) surface flat lying individual Si nanowires, all oriented along the [−110] direction, can be grown at room temperature with a high aspect ratio. Upon deposition at ∼200°C, these one-dimensional nanostructures self-assemble by lateral compaction to form a regular array of essentially identical nanowires, ∼1.6nm in width, covering uniformly the entire substrate surface. They realize, at macroscopic sizes, a highly perfect one-dimensional grating with a molecular-scale pitch of just 2nm.

Synchrotron radiation investigation and surface spectroscopy studies of prototypical systems: lead-semiconductor interfaces

Abstract Reviewing recent works on the formation of a variety of lead-semiconductor Schottky barriers we emphasize the fact that in many cases lead appears as a “prototype” metal forming unreacted, very sharp interfaces with many different semiconductors. We add also new experimental evidence, mostly derived from synchrotron radiation core level and valence band spectroscopy based on lead-silicon interfaces.