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We discuss the conversion of a pure screw dislocation into a helical (single helix) dislocation through absorption of vacancies. These helical dislocations having some edge and mostly screw character can pair up through attractive interaction to form a double helix. This attractive interaction between two helices is derived through the edge component of mixed dislocations and from the presence of vacancy jogs. Recent results on the growth of GeS [] and PbS [] nanowires with Eshelby twist showed large disagreements between experimental and theoretical Burgers vectors for these crystal structures, which can be resolved by introducing the double helix of screw dislocations.

Growth of high-quality III–V nanowires at a low cost for optoelectronic and electronic applications is a long-term pursuit of research. Still, controlled synthesis of III–V nanowires using chemical vapor deposition method is challenge and lack theory guidance. Here, we show the growth of InP and GaP nanowires in a large area with a high density using a vacuum chemical vapor deposition method. It is revealed that high growth temperature is required to avoid oxide formation and increase the crystal purity of InP nanowires. Introduction of a small amount of Ga into the reactor leads to the formation of GaP nanowires instead of ternary InGaP nanowires. Thermodynamic calculation within the calculation of phase diagrams (CALPHAD) approach is applied to explain this novel growth phenomenon. Composition and driving force calculations of the solidification process demonstrate that only 1 at.% of Ga in the catalyst is enough to tune the nanowire formation from InP to GaP, since GaP nucleation shows a much larger driving force. The combined thermodynamic studies together with III–V nanowire growth studies provide an excellent example to guide the nanowire growth. Supplementary Information The online version contains supplementary material available at 10.1186/s11671-021-03505-2.

Self-supported membranes consisting of entangled 2 to 6 μm long ZnO nanowires (NWs) on graphite with excellent UV emission were fabricated by a vapor transport technique at high temperature in a tubular furnace. The NWs grew on catalyst-free graphite flakes that had been mechanically compacted within an alumina boat crucible (the “substrate crucible”). The self-supported ZnO NW/graphite membrane detached spontaneously from the graphite substrate during the cooling stage after NW growth. The inversion of the substrate crucible orientation to an upside down position (usually used by our group for rigid substrates) resulted in strong reductions of the UV/visible emission ratio; by a factor of ~20 for NWs grown on compacted graphite and of ~1000 for NWs grown on Au-catalyzed Si wafers. Simulations of the transport fluid dynamics within the synthesis tube demonstrate that the substrate holder shape and substrate position within the holder play crucial roles in the reduction of precursor velocities, which is likely a key factor for achieving the long entangled NWs with enhanced UV/visible emission ratios that conform the self-supported ZnO NW/graphite membranes. Fil: Tosi, Ezequiel. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina Fil: Marín Ramírez, Oscar Alonso. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina Fil: Tirado, Monica Cecilia. Universidad Nacional de Tucumán. Instituto de Física del Noroeste Argentino. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet Noa Sur. Instituto de Física del Noroeste Argentino; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina Fil: Comedi, David Mario. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Departamento de Nanomateriales y Propiedades Dieléctricas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física; Argentina

We demonstrate the self-assembled formation of AlN nanowires by molecular beam epitaxy on sputtered TiN films on sapphire. This choice of substrate allows growth at an exceptionally high temperature of 1180 {\deg}C. In contrast to previous reports, the nanowires are well separated and do not suffer from pronounced coalescence. This achievement is explained by sufficient Al adatom diffusion on the substrate and the nanowire sidewalls. The high crystalline quality of the nanowires is evidenced by the observation of near band edge emission in the cathodoluminescence spectrum. The key factor for the low nanowire coalescence is the TiN film, which spectroscopic ellipsometry and Raman spectroscopy indicate to be stoichiometric. Its metallic nature will be beneficial for optoelectronic devices employing these nanowires as the basis for (Al,Ga)N/AlN heterostructures emitting in the deep ultraviolet spectral range.

Nanowires can serve as flexible substrates for hybrid epitaxial growth on selected facets, allowing for design of heterostructures with complex material combinations and geometries. In this work we report on hybrid epitaxy of semiconductor - ferromagnetic insulator - superconductor (InAs/EuS/Al) nanowire heterostructures. We study the crystal growth and complex epitaxial matching of wurtzite InAs / rock-salt EuS interfaces as well as rock-salt EuS / face-centered cubic Al interfaces. Because of the magnetic anisotropy originating from the nanowire shape, the magnetic structure of the EuS phase are easily tuned into single magnetic domains. This effect efficiently ejects the stray field lines along the nanowires. With tunnel spectroscopy measurements of the density of states, we show the material has a hard induced superconducting gap, and magnetic hysteretic evolution which indicates that the magnetic exchange fields are not negligible. These hybrid nanowires fulfil key material requirements for serving as a platform for spin-based quantum applications, such as scalable topological quantum computing., 15 pages, 5 figures

One-dimensional nanostructures with controllable morphologies and defects are appealing for use in nanowire devices. This paper details the influence of colloidal magnetite iron oxide nanoparticle seeds to regulate the radial dimension and twin boundary formation in Ge nanowires grown through a liquid-injection chemical vapor deposition process. Control over the mean nanowire diameter, even in the sub-10 nm regime, was achieved due to the minimal expansion and aggregation of iron oxide nanoparticles during the growth process. The uncommon occurrence of heterogeneously distributed multiple layer {111} twins, directed perpendicular to the nanowire growth axis, were also observed in 〈111〉-directed Ge nanowires, especially those synthesized from patterned hemispherical Fe3O4 nanodot catalysts. Consecutive twin planes along 〈111〉-oriented nanowires resulted in a local phase transformation from 3C diamond cubic to hexagonal 4H allotrope. Localized polytypic crystal phase heretostructures were formed along 〈111〉-oriented Ge nanowire using magnetite nanodot catalysts.

This review focuses on the emerging field of core–multishell (CMS) semiconductor nanowires (NWs). In these kinds of wires, a NW grown vertically on a substrate acts as a template for the coaxial growth of two or more layers wrapped around it. Thanks to the peculiar geometry, the strain is partially released along the radial direction, thus allowing the creation of fascinating heterostructures, even based on lattice mismatched materials that would hardly grow in a planar geometry. Enabling the unique bridging of the 1D nature of NWs with the exciting properties of 2D heterostructures, these novel systems are becoming attractive for material science, as well as fundamental and applied physics. We will focus on NWs made of III-V and III-V-based alloys as they represent a model system in which present growth techniques have reached a high degree of control on the material structural properties, and many physical properties have been assessed, from both the theoretical and experimental points of view. In particular, we provide an overview on the growth methods and structural properties of CMS NWs, on the modulation doping mechanisms enabled by these heterostructures, on the effects of a magnetic field, and on the phononic and optical properties typical of CMS NWs. Moreover, we review the main technological applications based on these systems, such as optoelectronic and photovoltaic devices.