Novel formation and decay mechanisms of nanostructures on surface
Introduction
Nanoscale structures on surface are at the forefront of exploratory work for the next generation devices in the fields of electronic and optical industry, which rely on materials of ever increasing complexity and decreasing size. In most cases these nanostructures must be fabricated either through homoepitaxial or heteroepitaxial growth. The understanding of the kinetics involved in the formation and stability of nanostructures on surface is of importance for the fast-growing area of nanotechnology. So far, substantial experimental and theoretical studies have been focused on the evolution of morphological features on the surface and the growth modes, and also the decay of 3D islands. In this paper we will summarize the recent study of the novel formation and decay mechanisms of nanostructures on surface.
Section snippets
Reaction-limited aggregation in surfactant-mediated epitaxy
In heteroepitaxial growth, the presence of strain often leads to 3D growth mode since the equilibrium structure involves strain-relieving effects. A breakthrough was made in 1989 when Copel et al. [1] demonstrate that the use of a single layer of As can improve the heteroepitaxial growth of Ge on Si. This remarkable behavior was termed the “surfactant effect”. Since then, a large number of experimental and theoretical efforts have been devoted to understand the surfactant effect [2]. Now
Pattern election in the presence of adsorbates
In the earliest stages of Pt(1 1 1) homoepitaxy where only single-layer islands are formed, Michely et al. [12] found that the islands develop fractal or dendritic shapes at low growth temperatures, but are compact at higher temperatures. In particular, the compact islands can select triangular, hexagonal, and inverted triangular shapes as the growth temperature is increased. This set of observations on the shape evolution of the Pt islands has defied a consensus explanation for years, despite
Island evolution controlled by condensation energy
A deposited adatom on a surface will dissipate its latent condensation heat, which is of the order of several eV. Such a condensation energy is much higher than the thermal activation energy required for an adatom to diffuse on a surface, which amounts to only a few tenths of an eV. This condensation energy will assist diffusion, namely, the transient mobility [18], [19], [20], [21]. Our first attempt is to make use of the condensation energy of adatoms to control the island evolution [22].
Kinetic stability of nanostructures at surface
In order to assess the stability of 3D nanostructures, it requires an understanding of the nature of the processes responsible for the decay of nanostructures and furthermore a precise knowledge of the activation energies involved in the relevant processes. Among these the diffusion of adatoms across step edges is most important because it influences the mass transport between terraces of different height. A new effective mechanism of inter-layer mass transport was proposed in the decay of
Concluding remarks
The study on the formation and decay mechanisms is very important in the practice of electronic and optoelectronic devices. By STM and theoretical modeling, we can uncover some of the building regulations down to the atomic scale.
Acknowledgments
Financial support from the NSF of China, the Chinese Academy of Sciences, the Key Project on Basic Research (G2000067103), US DOE National and US NSF is acknowledged. We also thank I.-S. Hwang, T.T. Tsong and T. Micheley for stimulating discussions.
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