fengliu's blog

Strain induced self-assembly provides an attractive route to nanofabrication of semiconductor quantum dots on surfaces. Recent experiments have demonstrated that combining the strain induced self-assembly with surface patterning provides an effective method to further improve the size uniformity and spatial ordering of quantum dots. However, the underlying mechanisms responsible for such improvement remain poorly understood. Recently, we have developped theoretical models to elucidate the strain induced growth instability and island nucleation on patterned substrates.

We demonstrate, by theoretical analysis and molecular dynamics simulation, a mechanism for fabricating nanotubes by self-bending of nanofilms under intrinsic surface stress imbalance due to surface reconstruction. A freestanding Si nanofilm may spontaneously bend itself into a nanotube without external stress load, and a bilayer SiGe nanofilm may bend into a nanotube with Ge as the inner layer, opposite of the normal bending configuration defined by misfit strain.

In this chapter of "Hankbook of Theoretical and Computational Nanotechnology", I will provide an overview of the progress made in the last decade on theoretical modeling and computer simulation of strain-mediated formation of nanostructures on surface, focusing on strain-induced self-assembly and self-organization of two-dimensional (2D) patterns and structures. As part of a handbook, the main objective of the chapter is not to provide an extensive literature review on the topic. Instead, I will try to provide a general introduction and overview of the basic concepts and physical models along with some relatively detailed discussion of mathematical derivations and technical treatments so that readers (especially graduate students) who are interested in this topic can use this chapter as a guide and reference to start their own modeling and simulation.

The nanotechnology of the future demands controlled fabrication of nanostructures. Much success has been made in the last decade in fabricating nanostructures on surface with desirable size and shape, either in serial using scanned-probe techniques or in parallel using self-assembly/self-organization processes sometimes combined with lithographic patterning techniques. However, controlled fabrication of nanostructures remains in general a formidable challenge. For example, despite the enormous success we have so far enjoyed with carbon nanotubes (CNTs), it is still very difficult (if not impossible) to synthesize CNTs with a degree of control that we would like in terms of their size and chirality. Fabrication of nanostructures in many other forms and with other materials is even less developed. There exists a strong need for the development of nanofabrication techniques with higher degree of control. Here, we demonstrate the general design principles of an emerging nanofabrication approach based on nanomechanical architecture of strained bi-layer thin films, which allows fabrication of a variety of nanostructures, such as nanotubes, nanorings, nanodrills, and nanocoils, with an unprecedented level of control.