Coverage dependence ofSb∕Si(111)adsorption and desorption modes: Interplay between chemical interactions and site transitions

Abstract

The kinetic and thermodynamic properties of adsorption and desorption of Sb onto a Si͑111͒ surface are analyzed by mass spectrometry and ab initio calculations. Two domains of temperature are evidenced. At T Ͻ 600°C there is an irreversible adsorption involving a subtle competition between sticking, adsorption, then dissociation of Sb 4 tetramers associated to a partial reflection of Sb 4 molecules on the Sb-covered surface. At T Ͼ 800°C, Sb 4 molecules are dissociated close to the surface leading to a simple reversible adsorption/ desorption of Sb monomers. In this temperature range, adsorption/desorption isotherms can be recorded for various temperatures, which reveal a surprising behavior since quasi-Langmuir isotherms appear to be the consequence of a two-dimensional ͑2D͒ phase transition. More precisely, as shown by ab initio calculations, during the submonolayer adsorption process, the adsorption site evolves ͑as a function of coverage͒ from ternary towards on-top position and the character of the Sb-Sb effective interactions changes from repulsive towards attractive. The 2D phase transition close to Ϸ 0.7 ML seems to be associated to characteristic signatures in many other experiments. Then for high enough supersaturations, it is possible to overpass =1 ML by the formation of dimers, first partially located on top sites which repel one another, up to a second phase transition around = 1.3 ML in which dimers leave the on top sites and stand up to occupy almost vertically the hollow ones for building the second Sb layer. Lastly surfactant effect is quantified.

Comparative analysis of germanium–silicon quantum dots formation on Si(100), Si(111) and Sn/Si(100) surfaces

“…During the modeling of quantum dots growth processes in the presence of tin increase in the diffusion coefficient by 5 times and decrease in surface energy by 200 erg cm −2 were supposed [24,25,43,47]. The value of surface energy reduction in the presence of Sn quantitatively corresponds to the results of the work [48], where surface energy reduction in the presence of Sb (the closest neighbor of Sn in the periodic table of the chemical elements) is reported.…”

Estudo de filmes ultrafinos de óxidos high/K crescidos sobre semicondutores

“…Isto pôde ser estimado através da razão das áreas dos fotopicos Sb3d/Si2p e comparações com trabalhos da literatura [94] que correlacionam a razão Sb3d/Si2p em função do número de monocamadas de Sb. Na sequência, o filme de Sb foi submetido a um tratamento térmico no qual o cristal de Si foi aquecido a uma temperatura de 360 o C por 5 minutos, esta temperatura foi escolhida com base em trabalhos da literatura [94], [95], [96] que mostram que Sb começa a sublimar da superfície em temperaturas acima de 400 o C. A figura 5.1 mostra o espectro de XPS "long scan" da superfície após a evaporação e tratamento térmico do filme de Sb. A figura 5.2 mostra a comparação dos fotopicos de Sb3d e Si2p antes e depois do tratamento térmico, no qual pode ser observada uma diminuição no sinal do Sb3d e conseqüente aumento no sinal do Si2p.…”