Characterization of interface abruptness and material properties in catalytically grown III-V nanowires: exploiting plasmon chemical shift

We have studied the assessment of chemical composition changes in III-V heterostructured semiconductor nanowires (NWs) with nanometric spatial resolution using transmission electron microscopy methods. These materials represent a challenge for conventional spectroscopy techniques due to their high sensitivity to electron beam irradiation. Radiation damage strongly limits the exposure time to a few (5-10) s, which reduces the sensitivity of the traditionally used x-ray spectroscopy. The rather low counting statistics results in significant errors bars for EDS chemical quantification (5-10%) and interface width determination (few nanometers). Plasmon chemical shift is ideal in this situation, as its measurement requires very short exposure times (similar to 100 ms) and the plasmon peak energy can be measured with high precision (similar to 20 meV in this work). This high sensitivity allows the detection of subtle changes (1-2%) in composition or even the detection of a small plasmon energy (33 +/- 7) meV change along usually assumed pure and homogeneous InAs segments. We have applied this approach to measure interface widths in heterostructure InAs/InP NWs grown using metal catalysts and also to determine the timescale (similar to 10 s) in which beam irradiation induces material damage in these wires. In particular, we have detected small As concentrations (4.4 +/- 0.5)% in the final InP segment close to the Au catalyst, which leads to the conclusion that As diffuses through the metal nanoparticle during growth.