We review the position-controlled growth of III-V nanowires (NWs) by selective-area metal-organic vapor-phase epitaxy (SA-MOVPE). This epitaxial technique enables the positioning of the vertical NWs on (111) oriented surfaces with lithographic techniques. Core-shell structures have also been achieved by controlling the growth mode during SA-MOVPE. The core-shell III-V NW-based devices such as light-emitting diodes, photovoltaic cells, and vertical surrounding-gate transistors are discussed in this article. Nanometer-scale growth also enabled the integration of III-V NWs on Si regardless of lattice mismatches. These demonstrated achievements should have broad applications in laser diodes, photodiodes, and high-electron mobility transistors with functionality on Si not made possible with conventional Si-CMOS techniques.

A cornerstone in the successful application of semiconductor nanowire devices is controlled impurity doping. In this review article, we discuss the key results in the field of semiconductor nanowire doping. Considerable development has recently taken place in this field, and half of the references in this review are less than 3 years old. We present a simple model for dopant incorporation during in situ doping of particle-assisted growth of nanowires. The effects of doping on nanowire growth are thoroughly discussed since many investigators have seen much stronger and more complex effects than those observed in thin-film growth. We also give an overview of methods of characterizing doping in nanowires since these in many ways define the boundaries of our current understanding.

Semiconductor nanowires (NWs) are characterized by an extraordinarily large surface-to-volume ratio. Consequently, surface effects are expected to play a much larger role than in thin films. Here, we review a research focused on the impact of the surface on the electrical and optical properties of catalyst-free GaN NWs with growth direction <0001>. Using a combination of complementary experimental techniques, it has been shown that the Fermi level is pinned at the NW sidewall surfaces, resulting in internal electric fields and in full depletion for NWs below a critical diameter. Deoxidation of the surfaces unpins the Fermi level, leading to enhanced radiative recombination of excitons. Prominent absorption below the bandgap is caused by the Franz-Keldysh effect. Close to the surface, the ionization energy of donors is reduced. The consideration of surface-induced effects is mandatory for an understanding of the physical properties of NWs as well as their application in devices.

Ferromagnetic resonance investigations on Ni nanowires are reported. The angular dependence of the resonance line position is analyzed within a thermodynamic approach that includes shape anisotropy (ellipsoids of revolution), magnetocrystalline anisotropies (cubic and uniaxial), and dipole–dipole interactions. The results are supported by hysteresis loops, obtained on the same sample.

Vanadium oxide nanowires have gained increasing interest as the electrode materials for Li-ion batteries. This article presents the recent developments of vanadium oxide nanowire materials and devices in Li-ion batteries. First, we will describe synthesis and construction of vanadium oxide nanowires. Then, we mainly focus on the electrochemical performances of vanadium oxide nanowires, such as VO2, V2O5, hydrated vanadium oxides, LiV3O8, silver vanadium oxides, etc. Moreover, design and in situ characterization of the single nanowire electrochemical device are also discussed. The challenges and opportunities of vanadium oxide nanowire electrode materials will be discussed as a conclusion to push the fundamental and practical limitations of this kind of nanowire materials for Li-ion batteries.

The morphology of semiconducting nanowires, including kinked and branched wires, must be controlled in order to produce functional devices. Here, we describe some of the experimental and theoretical work involving complex morphologies of Au-catalyzed Si nanowires grown using the vapor–liquid–solid technique. Although there is a broad parameter space to explore, experiments have highlighted the importance of the precursor and impurity partial pressures on kinking behavior. Theoretical and modeling work has indicated that the stability of and transitions in droplet configuration are important for growth direction changes that can lead to complex morphologies. We describe recent phase-field simulations of nanowire growth that address the dynamics of liquid droplets during vapor–liquid–solid growth, as well as the implications of these results for the formation of wires with complex morphology.

The growth kinetics of Si bulk crystals and nanowires (NWs) in contact with Au–Si liquids is studied by molecular dynamics simulations using an empirical potential fitted to the Au–Si binary phase diagram. The growth speed v is predicted as a function of Si concentration xSi in the Au–Si liquid at temperature T = 1100 K and as a function of T at xSi = 75%. For both bulk crystals and NWs, the {111} surface grows by the nucleation and expansion of a single two-dimensional island at small supersaturations, whereas the {110} surface grows simultaneously at multiple sites. The top surfaces of the NWs are found to be curved near the edges. The difference in the growth velocity between NWs and bulk crystals can be explained by the shift of the liquidus curve for NWs. For both bulk crystals and NWs, the growth speed diminishes in the low temperature limit because of reduced diffusivity.

Epitaxially oriented silicon nanowires (SiNWs) were grown on (111) Si substrates by the vapor–liquid–solid technique in an atmospheric-pressure chemical vapor deposition (APCVD) system using Au as the catalyst and SiCl4 as the source gas. The dependencies of SiNW growth rate on the growth temperature and SiCl4 partial pressure (PSiCl4) were investigated, and the experimental results were compared with calculated supersaturation curves for Si obtained from a gas phase equilibrium model of the SiCl4–H2 system. The SiNW growth rate was found to be weakly dependent on temperature but strongly dependent on the PSiCl4, exhibiting a maximum value qualitatively similar to that predicted from the equilibrium model. The results indicate that SiNW growth from SiCl4 is limited by gas phase chemistry and transport of reactant species to the growth surface under APCVD conditions. The experimental results are discussed within the context of a gas phase mass transport model that takes into account changes in equilibrium partial pressure due to curvature-related Gibbs–Thomson effects.

In this work, we compare the synthesis of germanium nanowires (GeNWs) using a highly localized heat source with GeNWs synthesized in a uniform temperature environment. With the exception of thermal environment, identical synthesis parameters were maintained in all experiments. The localized heat source, a suspended silicon microscale heater, enabled site-specific synthesis and thus the direct integration of GeNWs which is presented for the first time. The effect of heat source implementation and local temperature gradients on the resulting nanowires is assessed in terms of resulting nanowire geometry, growth rate, and quality. Overall, we note a reduction in growth rate and elevated kinking levels in locally synthesized nanowires when compared to nanowires synthesized in uniform temperature processes. The taper which typically characterizes GeNWs, however, is significantly reduced. Finally, we explore branching behavior which hints of instabilities in the synthesis process as nanowires grow away from the heat source.

Lateral ZnO nanowires (NWs) were selectively grown from the edge of a SiO2/Si–Al2O3–SiO2/Si multilayer structure for potential integration into devices using Si processing technology. Microstructural studies demonstrate a two-step growth process in which the tip region, with a diameter of ~10 nm, rapidly grew from the Al2O3 surface and, later, a base growth with a diameter of ~22 nm overgrew the existing narrow ZnO NW, halting further tip growth. Kinetics studies showed that surface diffusion on the alumina seed surface determined ZnO NW growth rate.

A novel and previously unreported, high temperature solid–liquid–solid (SLS) silica nanowire (NW) growth mode has been observed and investigated. In this mode, SLS NW nucleation and subsequent growth was uniquely promoted by—and coupled to—the formation of thermally etched pyramidal pits in the Si substrate that formed during a high temperature anneal phase before the onset of SLS NW formation. The silicon oxide-mediated thermal pit formation process enhanced Si transport to Au–Si alloy droplets directly adjacent to the pyramidal pits. Consequently, SLS NW nucleation and growth was preferentially promoted at the pit edges. The promotion of SLS NW growth by the pyramidal pits resulted in the observation of SLS NW “blooms” at the pit locations. Subsequent NW growth, occurring both at the pit sites and from Au–Si alloy droplets distributed across the planar surfaces of the Si wafer, eventually occluded the pits. This newly observed process is termed as “thermal pit-assisted growth.”

In this study, we show that the volatile monoxide species generated during the active oxidation of Ge and Si substrates can be utilized in the presence of Au catalytic nanoparticles to nucleate and grow GeOx and SiOx nanowires. A simple thermodynamic model is developed to ascertain the critical O2 partial pressure as a function of temperature required for the active oxidation of Ge and Si substrates and is experimentally verified. The ideal conditions for uniform nanowire growth across the substrate are shown to be primarily dependent on the O2 partial pressure, the annealing temperature and thicknesses of the surface oxide, and deposited Au. The role of a metastable surface oxide separating the active oxidation and NW nucleation processes is also discussed.

A rich research history exists for crystalline growth by vapor–liquid–solid (VLS) methods, but not for amorphous growth. Yet VLS growth in the absence of crystallographic influences provides an ideal laboratory for exploring surface energy effects, including the role of line tension. We discuss the growth of amorphous silica nanowires from indium droplets by a modified VLS method. Multiple strands issue from each droplet, each strand having <1% (i.e., < 5 nm) of the radius of the droplet. We analyze the surface forces for this system, including line tension, and combine data in a novel way to estimate the surface energy of silica, the interfacial energy of liquid indium on silica, and the line tension at the three-phase boundary. The results suggest that the growth of these silica strands would be impossible without the presence of a negative line tension that also serves to stabilize the strand radii against perturbation.

We exploit a facile synthetic route to fabricate dendritic SnO2/TiO2 nanodentrites with a twofold point symmetry by a combination of vapor transport deposition method for the SnO2 nanowire backbones and subsequent hydrothermal heteroepitaxial growth of TiO2 nanorod branches. As a result of the good lattice matching and same rutile crystal structures between SnO2 and TiO2, an interface epitaxy is established accounting for the high symmetry. Proof-of-principle demonstration of the function in photoelectrochemical water splitting is presented.

The cathodic electrodeposition of crystalline ZnO nanowires and amorphous FeO(OH) nanotubes in polycarbonate track-etched membranes with pore diameters of 50–200 nm is reported. Nitrate was used as a sacrificial precursor for the electrochemical generation of hydroxyl ions that raised the pH of the interior of the nanopore, leading to precipitation of a metal oxide or hydroxide phase. The crystalline and semiconducting ZnO phase formed directly above 60 °C at sufficiently high pH and led to the formation of dense nanowires with preferential (0001) orientation. The morphology of the wire could be influenced by the deposition temperature. Axially segmented gold–ZnO and silver–ZnO nanowires were made. In contrast, the iron hydroxide phase deposited inside the pore as a permeable gel that collapsed and transformed into hollow FeO(OH) tubes during drying. The as-formed nanotubes were amorphous and could be filled with nickel in a subsequent electrodeposition step, yielding core-shell nickel iron-oxohydroxide nanowires. The cathodic efficiency of nitrate reduction was low in both cases, suggesting that diffusional supply of metal ions may be the rate-determining step.

Urchin-like γ-MnO2 nanostructures, composed of nanowires with diameters in the range 40–70 nm were prepared through the direct reaction between MnSO4 and KClO3 via a mild hydrothermal route. Reaction time and temperature were found to influence both the phase and morphology of as-prepared products. For longer reaction times, the initially formed γ-phase transformed to α-MnO2 nanowires along with the loss of urchin-like morphology. Powder x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetry and differential scanning calorimetry were used to characterize the as-prepared products. On the basis of XRD patterns and SEM images, a possible growth mechanism for the time-dependant morphological evolution of various MnO2 nanostructures has been suggested and discussed.

Gd silicide nanostructures epitaxially grown on Si(001) are studied by plan-view transmission electron microscopy and associated nanobeam electron diffraction, as well as scanning tunneling microscopy. The nanobeam diffraction measurements show a direct correlation between the nanostructure morphology, either nanowires or islands, and the silicide crystal structure. Scanning tunneling microscopy shows a phase transformation from nanowires to islands that nucleate at nanowire intersections. A specific mechanism for this transformation is proposed that explains nanowire growth behavior previously observed on vicinal Si surfaces.

For development and integration of Si nanowires into nanoelectronic devices, an understanding of Ni silicide formation in electrical contacts to Si nanowires is necessary. Here, we examine the kinetics of Ni silicide phase formation. For Si nanowires with [111] growth directions, NiSi2 is the only phase to form in the temperature range 400–550 °C, and the NiSi2 growth exhibits linear kinetics from 400 to 500 °C with an activation energy of 0.76 ± 0.10 eV. In the case of Si nanowires with [112] growth directions, growth of the θ-Ni2Si phase in contact with the Si nanowire occurs with parabolic kinetics over the temperature range 400–550 °C, and an activation energy of 1.45 ± 0.07 eV/atom is extracted. Differences in the growth rates for Ni silicide phases with different SiNW growth directions implies that for simultaneous preparation of SiNW devices with Ni silicide contacts, SiNWs with the same growth direction are necessary.

Metallic nanostructures and specifically nanowires can be used for technological breakthroughs. Experimental measurements have provided insights on the mechanical properties of metallic nanostructures. In conjunction, modeling analyses provide an understanding of the underlying deformation and strengthening mechanisms in nanostructures. Most modeling studies on nanostructures are based on atomistic and molecular dynamics simulations, and though invaluable, they are limited to nanoscale dimensions of a few tens of nanometers, at small temporal scales, and physically unrealistic strain rates. Furthermore, most of the current applications for free-standing metallic nanostructures require high aspect ratios with at least one dimension greater than a few hundred nanometers. A continuum microstructurally based approach can, therefore, provide insights on design of one-dimensional nanowires on a physically relevant scale. Hence, we use a multiple-slip crystal plasticity formulation that is adapted to single crystal gold nanowires to simulate the experimental setup for a two-end fixed nanowire subjected to bending.