AVS 51st International Symposium
    Nanometer-scale Science and Technology Thursday Sessions
       Session NS2-ThM

Paper NS2-ThM7
Strain Mapping in Nanowire Heterostructures

Thursday, November 18, 2004, 10:20 am, Room 213D

Session: Nanowires I
Presenter: J.L. Taraci, Arizona State University
Authors: J.L. Taraci, Arizona State University
M.J. Hÿtch, Centre National de Recherche Scientifique, France
T. Clement, Arizona State University
J.W. Dailey, Arizona State University
D.J. Smith, Arizona State University
P. Peralta, Arizona State University
J. Drucker, Arizona State University
S.T. Picraux, Arizona State University
Correspondent: Click to Email
A new method for the detailed strain analysis of nanowires and nanowire heterostructures will be discussed. This technique enables strain mapping of nanowires based on the combination of high resolution electron microscopy and image analysis. The accuracy to which strain may be determined using this method is better than 0.3%, which allows for the accurate strain mapping of core-shell and heterostructure nanowires. The technique is applied to nanowires grown by vapor-liquid-solid CVD using disilane and digermane. We will show how this technique can be used to obtain detailed distributions of @epsilon@@sub xx@, @epsilon@@sub yy@, @epsilon@@sub xy@, mean dilatation, and rotation maps within individual nanowire heterostructures. We first demonstrate the method by analysis of a single Ge nanowire which displayed a linear rotation along the growth axis, with the nanowire in compression and tension on either side of the central axis. The measured results are shown to be in agreement with a nanomechanics description of the nanowire for a bending moment applied at the end of the cantilevered nanowire beam. We then present preliminary results for Si-Ge core-shell and heterointerface nanowires. This technique allows for the direct strain mapping at heterostructure interfaces due to the lattice mismatch. In these studies the Si/Ge growth is carried out at 400°C and below to minimize any chemical interdiffusion effects on the strain profiles. The resulting strain maps of nanowire heterostructures can then be directly compared with Stillinger Weber modeling of the anticipated Si-Ge strain distributions, assuming chemically abrupt interfaces. The large aspect ratio nanowire structures allow rapid lateral relaxation with distance from the interface and thus provide an interesting contrast to conventional strained layer heterostructures.