Nanoscale elemental quantification in heterostructured SiGe nanowires

Abstract

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 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.

From Solid-State Dewetting of Ultrathin, Compressively Strained Silicon–Germanium-on-Insulator Films to Mastering the Stoichiometry of Si1–xGex Nanocrystals

“…This feature, well-known for silicon nanostructures deposited on the SiO 2 layer, does not permit one to quantify properly the fraction of silicon within the SiGe agglomerates. On the other hand, the higher contrast on the agglomerate edges is assigned to SAM edge effects , coupled with the finite size of the electron beam nanoprobe, which also induces Auger transitions in the BOx layer. Despite the fact that it is difficult to extract information from the silicon Auger map (Figure e), no size effects can be pointed out, suggesting that the silicon distribution is homogeneous within as-dewetted nanocrystals.…”

“…In the case of such nanostructures, as the primary electron penetration depth is large with respect to the nanocrystal height, the electron beam may induce Auger transitions in the BOx via secondary electrons. 55 These transitions can then be dominant in the total Auger signal and are able to explain the low contrast on the particle center compared to the BOx layer. This feature, well-known for silicon nanostructures deposited on the SiO 2 layer, 55 does not permit one to quantify properly the fraction of silicon within the SiGe agglomerates.…”

“…55 These transitions can then be dominant in the total Auger signal and are able to explain the low contrast on the particle center compared to the BOx layer. This feature, well-known for silicon nanostructures deposited on the SiO 2 layer, 55 does not permit one to quantify properly the fraction of silicon within the SiGe agglomerates. On the other hand, the higher contrast on the agglomerate edges is assigned to SAM edge effects 55,56 coupled with the finite size of the electron beam nanoprobe, which also induces Auger transitions in the BOx layer.…”

“…The silicon Auger KLL transition mapping displayed in Figure e presents a low contrast between nanodot centers and the BOx layer, while a higher contrast is observed on the agglomerate’s edges. In the case of such nanostructures, as the primary electron penetration depth is large with respect to the nanocrystal height, the electron beam may induce Auger transitions in the BOx via secondary electrons . These transitions can then be dominant in the total Auger signal and are able to explain the low contrast on the particle center compared to the BOx layer.…”

Thin film depth profiling by ion beam analysis

“…• SAM 44 uses the non-radiative atomic relaxation AES (Auger electron spectroscopy) process after excitation by an electron beam. The great advantage of AES is that it can be mounted into a (modified) scanning electron microscope (SEM), and the AES signal is used for imaging.…”