Characterization of interface abruptness and material properties in catalytically grownIII–V nanowires: exploiting plasmon chemical shift

Abstract

We have studied the assessment of chemical composition changes in III–V heterostructuredsemiconductor nanowires (NWs) with nanometric spatial resolution using transmissionelectron microscopy methods. These materials represent a challenge for conventionalspectroscopy 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 thesensitivity of the traditionally used x-ray spectroscopy. The rather low countingstatistics results in significant errors bars for EDS chemical quantification (5–10%)and interface width determination (few nanometers). Plasmon chemical shift isideal in this situation, as its measurement requires very short exposure times (∼100 ms) and the plasmon peak energy can be measured with high precision (∼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. Wehave applied this approach to measure interface widths in heterostructureInAs/InP NWs grown using metal catalysts and also to determine the timescale (∼10 s) in which beam irradiation induces material damage in thesewires. 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 Asdiffuses through the metal nanoparticle during growth.