Lecture Petra Reinke
|04 August 2011||FWN-Building 5114.0004, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Dr. Petra Reinke|
|Affiliation:||University of Virginia, USA|
|Title:||Manganese-doping of group IV semiconductor surfaces and nanostructures|
|Date:||Thu Aug 4, 2011|
|Telephone:||+31 50 363 4736|
The ability to combine group IV (Si, Ge) semiconductors with magnetic elements is highly coveted for the development of future spintronics devices. Many aspects of magnetic doping of Si and Ge with Mn are still discussed controversially, and the very low solubility of the dopant, and competition with the formation of silicide or germanide compounds are the main materials challenges.
Our work focuses on understanding the relation between structure, bonding, and the magnetic signature of Mn-Si and Mn-Ge materials. We are specifically interested in two types of nanostructures: delta-doped Mn layers embedded in a semiconductor matrix, where the magnetism is controlled by the hybridization between the Mn d-band and Si-(Ge)-p-band, and Mn-doped Ge-quantum dots. We combine scanning tunneling microscopy (STM) investigations of the growth process with magnetic measurements with x-ray magnetic circular dichroism (XMCD).
The first part of my presentation will discuss the interaction of Mn with three different surfaces: Si(100)-(2x1), Ge-wetting layer, and the (105) facet of Ge-quantum dots. Particular attention is given to the monoatomic Mn-wires, which self-assemble on the Si(100)-(2x1) surface, and the growth processes on an atomic lengthscale. The formation of monoatomic wires can be described with a kinetic Monte-Carlo simulation, which underscores the role of C-type defects in wire assembly. Several routes to the Mn-doping of Ge-QDs will be discussed including surface-deposition of Mn and the co-deposition of Mn and Ge, where the competition with germanide formation plays a significant role in the growth process. Our results are compared to recent reports in the literature on Mn-doping of Ge-QDs.
The magnetism of Mn-nanostructures, which are embedded in a semiconductor matrix is largely determined by the Mn-Si interaction, any contribution from Mn-Mn bonding depresses the saturation magnetization most likely through the addition of an antiferromagnetic component. The analysis of the orbital moments confirms the 2D nature of the interlayers and the in-plane magnetization.
The second part of this seminar will address some aspects of the formation of metal and semiconductor contacts with molecular materials. Fullerene C60 layers were chosen as a model system, and we will begin with a discussion of the fractal growth mode of fullerene layers. The interaction of fullerene surfaces with Au and V differs substantially: while Au forms well-defined clusters, V will diffuse into the fullerene layer and strongly modulates the local density of states.
|Last modified:||22 October 2012 2.30 p.m.|