Direct imaging of single Au atoms within GaAs nanowires
by Maya Bar-Sadan, Juri Barthel, Hadas Shtrikman and Lothar Houben
Incorporation of catalyst atoms during the growth process of semiconductor nanowires reduces the electron mean free path and degrades their electronic properties. Aberration-corrected scanning transmission electron microscopy (STEM) has been demonstrated to be capable of directly imaging single Au atoms within the dense matrix of a GaAs crystal, by slightly tilting the GaAs lattice planes with respect to the incident electron beam. Au doping values in the order of 1E[17...18] per cube centimetre were measured, making ballistic transport through the nanowires practically inaccessible.
Scientists from ER-C together with collaborators have demonstrated that the detection of single foreign atoms within a III-V crystal lattice is feasible even in cases where the Z number ratio between the dopant and the host lattice is rather low, by avoiding strong channelling conditions. The volume of detection, where single Au atoms can be imaged, is only a fraction of the sample volume, close to the focal plane of the electron beam. The present work has put this technique on a firm foundation with quantitative modelling considering varying focal depths and positions of atoms. In GaAs nanowires, this technique allowe to identify single Au atoms within the lattice, proving that Au atoms are incorporated within the nanowire during the growth process. The high doping level in the wires encourages pursuing alternative, self-assisted synthetic routes for GaAs nanowires for ballistic transport. Since the presented method is general, the present study lays the groundwork for other doped semiconductor nanostructures and for correlating dopant atom positions with their physical properties.
Maya Bar-Sadan, Juri Barthel, Hadas Shtrikman and Lothar Houben: Direct imaging of single Au atoms within GaAs nanowires, Nano Letters 12 (2012) 2352-2356.