Nov 8, 2012
Native adatoms on III–V semiconductor surface repositioned to form nanostructures
Scanning tunnelling microscopy tips can be invaluable tools in atomic-scale patterning. Apart from probing surfaces with atomic resolution, the metal tips can be used as an operative tool to reposition single adsorbed atoms (adatoms) with ultimate precision. First demonstrated by Don Eigler at IBM's Almaden Research Center in California in the late 1980s, this experimental approach is setting new standards in the investigation of solid-state matter at the atomic scale.
Reporting the results in J. Phys.: Condens. Matter 24 354008, we show that the technique of STM-based atom manipulation can be extended to III-V semiconductors, offering the prospect of constructing functional nanostructures on a semiconductor platform atom-by-atom.
In our work, we used InAs(111)A samples grown by molecular beam epitaxy (MBE). The generic properties of this III-V semiconductor surface make it a promising candidate for successfully performing atom manipulation and exploring new functions in individual nanostructures arising from quantum-physical effects. Firstly, InAs(111)A is chemically nonreactive due to completely saturated surface dangling bonds. Secondly, the MBE-grown surface exhibits donor-type indium adatoms serving as atomic building blocks with a charge state of +1e. Thirdly, the presence of a surface-localized two-dimensional electron gas (2DEG) allows us to explore the interaction of tailored nanostructures with itinerant 2DEG electrons.
Our study reveals the elementary processes governing the reversible transfer of an adatom between the tip and the semiconductor surface, opening up the possibility of assembling nanostructures of various sizes and shapes (see the image above). To carry out the investigations, we used a state-of-the-art cryogenic STM instrument operated in ultrahigh vacuum and at liquid-helium temperature.
The atom manipulation procedures enable the construction of semiconductor-based nanostructures that host confined quantum states (electronic coupling along atomic chains) and exhibit physical multistability driven by the tunnelling current (atomic switching and storage capability). The feasibility of deliberately positioning charged adatoms together with the reduced electronic screening found in a semiconductor makes the InAs(111)A surface an interesting model system for manipulating electronic structure at the nanometre scale: the electrostatic potential at a specific surface location can be tuned by placing point charges nearby, providing a means to, for example, perform a local gating of an individual nanostructure or adsorbed molecule within the STM tunnel junction.
More details are available in the Journal of Physics: Condensed Matter.
About the author
The work presented is based on a collaboration between the NTT Basic Research Laboratories (BRL) in Atsugi, Japan, and the Paul-Drude-Institut für Festkörperelektronik (PDI) in Berlin, Germany. The STM portion of the work was carried out at PDI's low-temperature STM group by Jianshu Yang, Christophe Nacci and Jesús Martínez-Blanco (PDI postdoctoral scientists), as well as Kiyoshi Kanisawa (NTT BRL senior scientist) and Stefan Fölsch (PDI senior scientist). Samples were grown at the MBE facilities of NTT BRL. The research was supported by the Japan Science and Technology Agency (JST), and the German Research Foundation (DFG) within the Japanese-German Cooperative Program 'Nanoelectronics' (FO 362/1-3).