title: Catalyst Composition Tuning: The Key for the Growth of Straight Axial Nanowire Heterostructures with Group III Interchange.
abstract: Au-catalyzed III-V nanowire heterostructures based on the group III interchange usually grow straight only in one of the two growth sequences, whereas the other sequence produces kinked geometries; thus, the realization of double heterostructures remains challenging. Here, we investigate the growth of Au-assisted InAs-GaAs and GaAs-InAs axial nanowire heterostructures. A detailed study of the heterostructure morphology as a function of growth parameters and chemical composition of the catalyst nanoparticle is performed by means of scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analysis. Our results clearly demonstrate that the nanoparticle composition, rather than other growth parameters, as postulated so far, controls the growth mode and the resulting nanowire morphology. Although GaAs easily grows straight on InAs, straight growth of InAs on GaAs is achieved only if the nanoparticle composition is properly tuned. We find that straight InAs segments on GaAs require high group III-to-Au ratios in the nanoparticle (greater than 0.8); otherwise, the droplet wets the sidewalls and the nanowire kinks. We discuss the observed behavior within a theoretical model that relates the nanoparticle stability to the group III-to-Au ratio. Based on this finding, we demonstrate the growth of straight nanowire heterostructures for both sequences. The proposed strategy can be extended to other III-V nanowire heterostructures based on the group III interchange, allowing for straight morphology regardless of the growth sequence, and ultimately for designing nanowire heterostructures with the required properties for different applications.
authors.affiliation: NEST, Istituto Nanoscienze - CNR and Scuola Normale Superiore , Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Zannier
authors.affiliation: NEST, Istituto Nanoscienze - CNR and Scuola Normale Superiore , Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Ercolani
authors.affiliation: NEST, Istituto Nanoscienze - CNR and Scuola Normale Superiore , Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Umesh Prasad
authors.initials: UP
authors.lastname: Gomes
authors.affiliation: Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia , Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Jérémy
authors.initials: J
authors.lastname: David
authors.affiliation: Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia , Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Gemmi
authors.affiliation: St. Petersburg Academic University , Khlopina 8/3, 194021 Saint Petersburg, Russia.|ITMO University , Kronverkskiy Prospekt 49, 197101 Saint Petersburg, Russia.
authors.forename: Vladimir G
authors.initials: VG
authors.lastname: Dubrovskii
authors.affiliation: NEST, Istituto Nanoscienze - CNR and Scuola Normale Superiore , Piazza San Silvestro 12, 56127 Pisa, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Sorba
keywords: Nanowires; VLS growth; axial heterostructures; catalyst composition