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We have studied electronic transport in undoped GaAs/SrTiO3 coreâ€"shell nanowires standing on their Si substrate with two-tip scanning tunneling microscopy in ultrahigh vacuum. The resistance profile along the nanowires is proportional to the tip separation with resistances per unit length of a few GΩ/ ÎĽ m. Examination of the different transport pathways parallel to the nanowire growth axis reveals that the measured resistance is consistent with a conduction along the interfacial states at the GaAs{110} sidewalls, the 2 nm thick SrTiO3 shell being as much as resistive, despite oxygen deficient growth conditions. The origin of the shell resistivity is discussed in light of the nanowire analysis with transmission electron microscopy and Raman spectroscopy, providing good grounds for the use of SrTiO3 shells as gate insulators. [ABSTRACT FROM AUTHOR]

Increasing quantum confinement in semiconductor quantum dot (QD) systems is essential to perform robust simulations of many-body physics. By combining molecular beam epitaxy and lithographic techniques, we developed an approach consisting of a twofold selective area growth to build QD chains. Starting from 15 nm-thick and 65 nm-wide in-plane In 0.53 Ga 0.47 As nanowires on InP substrates, linear arrays of In 0.53 Ga 0.47 As QDs were grown on top, with tunable lengths and separations. Kelvin probe force microscopy performed at room temperature revealed a change of quantum confinement in chains with decreasing QD sizes, which was further emphasized by the spectral shift of quantum levels resolved in the conduction band with low temperature scanning tunneling spectroscopy. This approach, which allows the controlled formation of 25 nm-thick QDs with a minimum length and separation of 30 nm and 22 nm respectively, is suitable for the construction of scalable fermionic quantum lattices., (© 2024 IOP Publishing Ltd.)

We have studied electronic transport in undoped GaAs/SrTiO 3 core-shell nanowires standing on their Si substrate with two-tip scanning tunneling microscopy in ultrahigh vacuum. The resistance profile along the nanowires is proportional to the tip separation with resistances per unit length of a few GΩ/ μ m. Examination of the different transport pathways parallel to the nanowire growth axis reveals that the measured resistance is consistent with a conduction along the interfacial states at the GaAs{110} sidewalls, the 2 nm thick SrTiO 3 shell being as much as resistive, despite oxygen deficient growth conditions. The origin of the shell resistivity is discussed in light of the nanowire analysis with transmission electron microscopy and Raman spectroscopy, providing good grounds for the use of SrTiO 3 shells as gate insulators., (© 2022 IOP Publishing Ltd.)

Improved performance in flexible organic light-emitting diodes (OLEDs) is demonstrated by using a hybrid nanostructured plasmonic electrode consisting of silver nanowires (AgNWs) decorated with silver nanoparticles (AgNPs) and covered by exfoliated graphene sheets. Such all-solution processed electrodes show high optical transparency and electrical conductivity. When integrated in an OLED with super yellow polyphenylene vinylene as the emissive layer, the plasmon coupling of the NW-NP hybrid plasmonic system is found to significantly enhance the fluorescence, demonstrated by both simulations and photoluminescence measurements, leading to a current efficiency of 11.61 cd A -1 and a maximum luminance of 20 008 cd m -2 in OLEDs. Stress studies reveal a superior mechanical flexibility to the commercial indium-tin-oxide (ITO) counterparts, due to the incorporation of exfoliated graphene sheets. Our results show that these hybrid nanostructured plasmonic electrodes can be applied as an effective alternative to ITO for use in high-performance flexible OLEDs.

The surface morphology of III-V semiconductor nanowires (NWs) protected by an arsenic cap and subsequently evaporated in ultrahigh vacuum is investigated with scanning tunneling microscopy and scanning transmission electron microscopy. We show that the changes of the surface morphology as a function of the NW composition and the nature of the seed particles are intimately related to the formation and reaction of surface point defects. Langmuir evaporation close to the congruent evaporation temperature causes the formation of vacancies which nucleate and form vacancy islands on {110} sidewalls of self-catalyzed InAs NWs. However, for annealing temperatures much smaller than the congruent temperature, a new phenomenon occurs: group III vacancies form and are filled by excess As atoms, leading to surface As Ga antisites. The resulting Ga adatoms nucleate with excess As atoms at the NW edges, producing monoatomic-step islands on the {110} sidewalls of GaAs NWs. Finally, when gold atoms diffuse from the seed particle onto the {110} sidewalls during evaporation of the protective As cap, Langmuir evaporation does not take place, leaving the sidewalls of InAsSb NWs atomically flat.

We report a significant and persistent enhancement of the conductivity in free-standing non-intentionally doped InAs nanowires upon irradiation in ultra-high vacuum. Combining four-point probe transport measurements performed on nanowires with different surface chemistries, field effect based measurements and numerical simulations of the electron density, the change in the conductivity is found to be caused by an increase in the surface free carrier concentration. Although an electron beam of a few keV, typically used for the inspection and the processing of materials, propagates through the entire nanowire cross-section, we demonstrate that the electrical properties of the nanowire are predominantly affected by radiation-induced defects occurring at the nanowire surface and not in the bulk.

III-V antimonide nanowires are among the most interesting semiconductors for transport physics, nanoelectronics and long-wavelength optoelectronic devices due to their optimal material properties. In order to investigate their complex crystal structure evolution, faceting and composition, we report a combined scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) study of gold-nucleated ternary InAs/InAs(1-x)Sb(x) nanowire heterostructures grown by molecular beam epitaxy. SEM showed the general morphology and faceting, TEM revealed the internal crystal structure and ternary compositions, while STM was successfully applied to characterize the oxide-free nanowire sidewalls, in terms of nanofaceting morphology, atomic structure and surface composition. The complementary use of these techniques allows for correlation of the morphological and structural properties of the nanowires with the amount of Sb incorporated during growth. The addition of even a minute amount of Sb to InAs changes the crystal structure from perfect wurtzite to perfect zinc blende, via intermediate stacking fault and pseudo-periodic twinning regimes. Moreover, the addition of Sb during the axial growth of InAs/InAs(1-x)Sb(x) heterostructure nanowires causes a significant conformal lateral overgrowth on both segments, leading to the spontaneous formation of a core-shell structure, with an Sb-rich shell.

The paper reports on self-assembly of silicon nanowire junctions assisted by protocollagen, a low cost soluble long fiber protein and precursor of collagen fibrils. First, the collagen was combed on an octadecyl-terminated silicon surface with gold electrodes. Then the combed surface was exposed to an aqueous suspension of silicon nanowires. In order to increase electrostatic interactions between the positively charged collagen and the nanowires, the nanowires were chemically modified with negatively charged sulfonate groups. The interaction of collagen with the sulfonated nanowires, which mimics the native collagen/heparin sulfate interaction, induced self-assembly of the nanowires localized between gold electrodes. The proof of concept for the formation of spontaneous electrode-nanowire-electrode junctions using collagen as a template was supported by current-voltage measurements.