“Atomic-scale Growth on Si(001)”
J.H.G. Owen, University of Geneva
There are two competing paradigms for growth of precise structures on the atomic scale. I have proposed the use of self-assembled templates based on the Bi nanoline on Si(001) as a means to form structures which are very precise in dimensions, and form many identical structures in parallel, but at the cost of control over the location of these structures. Patterned lithography on the H:Si(001) surface, which can be realized with near-atomic precision, followed by atomic layer epitaxy (ALE), on the other hand, requires more work to create the pattern with atomic accuracy but then provides complete control over the resulting structure.
Bi nanolines are exactly 1.54 nm wide and can be over 1um in length. Their average spacing at high density is around 4 nm. We determined their unusual subsurface reconstruction into 5- and 7-membered rings of Si, which we dubbed the Haiku structure, and which is responsible for their extreme length and perfection. Many metals show preferential deposition onto the Bi nanolines relative to a H-passivated background. I found that noble metals and transition metals form arrays of nanoclusters on these templates, while indium and aluminium react with the Bi dimers, forming epitaxial nanowires, 1-2 layers thick and over 100 nm long, with a unique zigzag structure. We are developing techniques to grow atomic chains of metal atoms on these templates, which are likely to have interesting electronic and spin properties that we will characterize. In the process, we have developed a new Si-in-Si nanoline, which I will describe.
In-situ studies of disilane decomposition on the Si(001) surface by hot STM, imaging at temperature under a flux of disilane, allowed us to observe many dynamic features of the growth process, such as the breakdown of the disilane fragments, nucleation of islands in the first and second layers, hydrogen diffusion and ultimately the growth of the first monolayers of Si. In close collaboration with DFT modeling, we thereby mapped out a complete reaction pathway from the initial adsorption as SiH3 to epitaxial Si islands. I will offer some thoughts on the implications of the details of this reaction process for the development of patterned ALE processes.
James Owen is a senior postdoc in the Department of Condensed Matter Physics at the University of Geneva. He earned a D.Phil. from the Materials Department of Oxford University in 1996. He is interested in the mechanisms that control epitaxial growth at the atomic scale forming nanostructures by self-assembly and the characterization of their properties. He has over a decade’s experience in atomic-resolution imaging and characterization of this and other semiconductor surfaces, specializing in elevated-temperature imaging required for the observation of dynamic diffusion, nucleation and growth processes. His aspiration is to look beyond the fabrication of isolated single-nm wires to the ability to put together complete nanoelectronic devices, comprising a mixture of components, which may be “prefabricated” ex-situ, self-assembled in-situ or defined by lithography. Details at http://homepage.mac.com/jhgowen/research/research.html.