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Cite this: DOI: 10.1039/c4nr07503j
Nanoscale elemental quantiﬁcation in heterostructured SiGe nanowires† W. Hourani,*a,b P. Periwal,c,d F. Bassani,c,d T. Baron,c,d G. Patriarchee and E. Martinez*a,b The nanoscale chemical characterization of axial heterostructured Si1−xGex nanowires (NWs) has been performed using scanning Auger microscopy (SAM) through local spectroscopy, line-scan and depth proﬁle measurements. Local Auger proﬁles are realized with suﬃcient lateral resolution to resolve individual nanowires. Axial and radial composition heterogeneities are highlighted. Our results conﬁrm the phenomenon of Ge radial growth forming a Ge shell around the nanowire. Moreover, quantiﬁcation is performed
Received 19th December 2014, Accepted 5th April 2015
after verifying the absence of preferential sputtering of Si or Ge on a bulk SiGe sample. Hence, reliable results are obtained for heterostructured NW diameters higher than 100 nm. However, for smaller sizes, we
have noticed that the sensitivity factors evaluated from bulk samples cannot be used because of edge
eﬀects occurring for highly topographical features and a modiﬁed contribution of backscattered electrons.
The growth of axial heterostructured semiconductor nanowires (NWs) with a one-dimensional modulated composition and/or doping has attracted much attention1–4 as they can serve as basic building blocks of future generation field-eﬀect transistors (FETs). In particular, Si/Si1−xGex axial heterostructured NWs can be used as channels for charge carrier transport in vertically aligned NW tunnel-FETs for high speed and low power operations.5–8 Band-gap tuning along the charge carrier transport direction can be performed by the axial growth of lattice mismatched heterostructures.9 For this purpose, an adequate control of the atomic concentrations of Si and Ge along the axial and radial directions of the NWs is of upmost importance. Few characterization methods are able to provide quantitative information about the chemical composition of such nanostructures. Scanning transmission electron microscopy (STEM) combined with electron dispersive spectroscopy (EDS) or electron energy loss spectroscopy (EELS) can provide useful information together with atom probe tomography (APT).10 However, regarding APT, needle-shaped specimens are
required and potential artifacts such as surface amorphization, or gallium implantation have been reported during milling by focus ion beam (FIB).11 Scanning Auger microscopy (SAM) is another technique of interest for surface and in-depth chemical analysis at the nanometer scale. This technique is becoming more and more interesting to investigate the chemical composition of nanomaterials.12–18 New generation Auger nanoprobes combine high lateral resolution (