Bipolar Resistive Switching of Single Gold-in-Ga₂O₃ Nanowire

We have fabricated single nanowire chips on gold-in-Ga₂O₃ core–shell nanowires using the electron-beam lithography techniques and realized bipolar resistive switching characteristics having invariable set and reset voltages. We attribute the unique property of invariance to the built-in conduction path of gold core. This invariance allows us to fabricate many resistive switching cells with the same operating voltage by simple depositing repetitive metal electrodes along a single nanowire. Other characteristics of these core–shell resistive switching nanowires include comparable driving electric field with other thin film and nanowire devices and a remarkable on/off ratio more than 3 orders of magnitude at a low driving voltage of 2 V. A smaller but still impressive on/off ratio of 10 can be obtained at an even lower bias of 0.2 V. These characteristics of gold-in-Ga₂O₃ core–shell nanowires make fabrication of future high-density resistive memory devices possible

Lead-Free NaNbO₃ Nanowires for a High Output Piezoelectric Nanogenerator

Perovskite ferroelectric nanowires have rarely been used for the conversion of tiny mechanical vibrations into electricity, in spite of their large piezoelectricity. Here we present a lead-free NaNbO₃ nanowire-based piezoelectric device as a high output and cost-effective flexible nanogenerator. The device consists of a NaNbO₃ nanowire–poly(dimethylsiloxane) (PDMS) polymer composite and Au/Cr-coated polymer films. High-quality NaNbO₃ nanowires can be grown by hydrothermal method at low temperature and can be poled by an electric field at room temperature. The NaNbO₃ nanowire–PDMS polymer composite device shows an output voltage of 3.2 V and output current of 72 nA (current density of 16 nA/cm²) under a compressive strain of 0.23%. These results imply that NaNbO₃ nanowires should be quite useful for large-scale lead-free piezoelectric nanogenerator applications

Liquid–Solid Process for Growing Gold Nanowires on an Indium Tin Oxide Substrate as Excellent Field Emitters

Gold nanowires are successfully grown on an ITO substrate by a liquid–solid process. An excellent field emission behavior of the nanowires, as indicated by the field enhancement factor (β) of up to 7585, indicates a significant decrease in energy barrier between the nanowires and the ITO substrate. A single Au nanowire demonstrates a strong emission current up to 800 nA at an applied voltage of 200 V. The outstanding reliability of the nanowires warrants their potential applications as effective electron field emitters and chemical and/or biological sensors in future microelectronics

Gallium Nitride Nanowire Based Nanogenerators and Light-Emitting Diodes

Single-crystal n-type GaN nanowires have been grown epitaxially on a Mg-doped p-type GaN substrate. Piezoelectric nanognerators based on GaN nanowires are investigated by conductive AFM, and the results showed an output power density of nearly 12.5 mW/m². Luminous LED modules based on n-GaN nanowires/p-GaN substrate have been fabricated. CCD images of the lighted LED and the corresponding electroluminescence spectra are recorded at a forward bias. Moreover, the GaN nanowire LED can be lighted up by the power provided by a ZnO nanowire based nanogenerator, demonstrating a self-powered LED using wurtzite-structured nanomaterials

Coaxial Metal-Silicide Ni₂Si/C54-TiSi₂ Nanowires

One-dimensional metal silicide nanowires are excellent candidates for interconnect and contact materials in future integrated circuits devices. Novel core–shell Ni₂Si/C54-TiSi₂ nanowires, 2 μm in length, were grown controllably via a solid–liquid–solid growth mechanism. Their interesting ferromagnetic behaviors and excellent electrical properties have been studied in detail. The coercivities (Hcs) of the core–shell Ni₂Si/C54-TiSi₂ nanowires was determined to be 200 and 50 Oe at 4 and 300 K, respectively, and the resistivity was measured to be as low as 31 μΩ-cm. The shift of the hysteresis loop with the temperature in zero field cooled (ZFC) and field cooled (FC) studies was found. ZFC and FC curves converge near room temperature at 314 K. The favorable ferromagnetic and electrical properties indicate that the unique core–shell nanowires can be used in penetrative ferromagnetic devices at room temperature simultaneously as a future interconnection in integrated circuits

In Situ Observation of Dehydration-Induced Phase Transformation from Na₂Nb₂O₆–H₂O to NaNbO₃

We have monitored the phase transformation from a Sandia octahedral molecular sieve Na₂Nb₂O₆–H₂O to a piezoelectric NaNbO₃ nanowire through in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements at high temperatures. After dehydration at 288 °C, the Na₂Nb₂O₆–H₂O becomes significantly destabilized and transforms into NaNbO₃ with the increase of time. The phase transformation time is exponentially proportional to the inverse of temperature, for example, ∼10⁵ s at 300 °C and ∼10¹ s at 500 °C, and follows an Arrhenius equation with the activation energy of 2.0 eV. Real time TEM investigation directly reveals that the phase transformation occurs through a thermally excited atomic rearrangement due to the small difference of Gibbs free energy between two phases. This work may provide a clue of kinetic control for the development of high piezoelectric lead-free alkaline niobates and a deep insight for the crystallization of oxide nanostructures during a hydrothermal process

In Situ Observation of Dehydration-Induced Phase Transformation from Na₂Nb₂O₆–H₂O to NaNbO₃

We have monitored the phase transformation from a Sandia octahedral molecular sieve Na₂Nb₂O₆–H₂O to a piezoelectric NaNbO₃ nanowire through in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements at high temperatures. After dehydration at 288 °C, the Na₂Nb₂O₆–H₂O becomes significantly destabilized and transforms into NaNbO₃ with the increase of time. The phase transformation time is exponentially proportional to the inverse of temperature, for example, ∼10⁵ s at 300 °C and ∼10¹ s at 500 °C, and follows an Arrhenius equation with the activation energy of 2.0 eV. Real time TEM investigation directly reveals that the phase transformation occurs through a thermally excited atomic rearrangement due to the small difference of Gibbs free energy between two phases. This work may provide a clue of kinetic control for the development of high piezoelectric lead-free alkaline niobates and a deep insight for the crystallization of oxide nanostructures during a hydrothermal process

Realizing High-Efficiency Omnidirectional n‑Type Si Solar Cells <i>via</i> the Hierarchical Architecture Concept with Radial Junctions

Hierarchical structures combining micropyramids and nanowires with appropriate control of surface carrier recombination represent a class of architectures for radial p-n junction solar cells that synergizes the advantageous features including excellent broad-band, omnidirectional light-harvesting and efficient separation/collection of photoexcited carriers. The heterojunction solar cells fabricated with hierarchical structures exhibit the efficiency of 15.14% using cost-effective as-cut Czochralski n-type Si substrates, which is the highest reported efficiency among all n-type Si nanostructured solar cells. We also demonstrate the omnidirectional solar cell that exhibits the daily generated power enhancement of 44.2% by using hierarchical structures, as compared to conventional micropyramid control cells. The concurrent improvement in optical and electrical properties for realizing high-efficiency omnidirectional solar cells using as-cut Czochralski n-type Si substrates demonstrated here makes a hierarchical architecture concept promising for large-area and cost-effective mass production