Sets Of Nanowires Research Articles

Vibration Damping Mechanism of Fiber-Reinforced Composites with Integrated Piezoelectric Nanowires.

Here, both piezoelectric and nonpiezoelectric nanostructures are used within fiber-reinforced composites to improve the damping capabilities of the host material. This work investigates and isolates the role of both piezoelectricity and the mechanical redistribution of strain on the damping properties of fiber-reinforced composites through the integration of a nanowire interphase between the fiber and matrix. Prior works have successfully studied and reported the effectiveness of modifying the surface of the reinforcing fibers in a composite material using nanowires and other nanostructured interfaces to increase mechanical damping, however, have yet to fully investigate the mechanism dictating the observed behavior. This study analyzes the effects of nonpiezoelectric nanowire interfaces in comparison to piezoelectric nanowire interfaces of the same microscale morphology. The damping properties of carbon fiber-reinforced composites containing both sets of nanowires are investigated via dynamic mechanical analysis over a range of temperatures as well as modal analysis at the first resonant frequency. The results conclusively indicate that a combination of both mechanical and piezoelectric effects contributes to the significant increase in damping properties of fiber-reinforced composites and quantifies the individual contributions.

Measurement of anisotropic thermal conductivity of a dense forest of nanowires using the 3ω method.

The 3ω method is a dynamic measurement technique developed for determining the thermal conductivity of thin films or semi-infinite bulk materials. A simplified model is often applied to deduce the thermal conductivity from the slope of the real part of the ac temperature amplitude as a function of the logarithm of frequency, which in-turn brings a limitation on the kind of samples under observation. In this work, we have measured the thermal conductivity of a forest of nanowires embedded in nanoporous alumina membranes using the 3ω method. An analytical solution of 2D heat conduction is then used to model the multilayer system, considering the anisotropic thermal properties of the different layers, substrate thermal conductivity, and their thicknesses. Data treatment is performed by fitting the experimental results with the 2D model on two different sets of nanowires (silicon and BiSbTe) embedded in the matrix of nanoporous alumina templates, having thermal conductivities that differ by at least one order of magnitude. These experimental results show that this method extends the applicability of the 3ω technique to more complex systems having anisotropic thermal properties.

Universal conductance fluctuations and localization effects in InN nanowires connected in parallel

The low-temperature quantum transport of InN nanowires grown by plasma-assisted molecular beam epitaxy is investigated. Two sets of nanowires with diameters of 100 and 45 nm originating from two different growth runs are studied. Magnetic-field-dependent as well as gate-dependent measurements of universal conductance fluctuations are performed to gain information on the phase-coherence in the electron transport. By analyzing the correlation field and the average fluctuation amplitude a phase-coherence length of several hundred nanometers is extracted for both sets of nanowires at temperatures below 1 K. Conductance fluctuations are also observed when the Fermi wavelength is varied by applying a bias voltage to a back-gate. The results on the electron phase-coherence obtained from the gate-dependent measurements are consistent with the findings from the magnetic field dependent measurements. A considerable damping of the fluctuation amplitude by ensemble averaging is achieved by connecting nanowires in parallel. The suppression of the fluctuation amplitude is studied systematically by measuring samples with different numbers of nanowires. By utilizing the damping of the conductance fluctuations by connecting nanowires in parallel in combination with an averaging over the gate voltage, weak localization effects are resolved. For both sets of nanowires a clear evidence of the weak antilocalization is found, which indicates the presence of spin-orbit coupling. For the spin-orbit scattering length lso values in the order of 100 nm are extracted.

A Statistics-Guided Approach to Precise Characterization of Nanowire Morphology

Precise control of nanomaterial morphology is critical to the development of advanced nanodevices with various functionalities. In this paper, we developed an efficient and effective statistics-guided approach to accurately characterizing the lengths, diameters, orientations, and densities of nanowires. Our approach has been successfully tested on a zinc oxide nanowire sample grown by hydrothermal methods. This approach has three key components. First, we introduced a novel geometric model to recover the true lengths and orientations of nanowires from their projective scanning electron microscope images, where a statistical resampling method is used to mitigate the practical difficulty of relocating the same sets of nanowires at multiple projecting angles. Second, we developed a sequential uniform sampling method for efficiently acquiring representative samples in characterizing diameters and growing density. Third, we proposed a statistical imputation method to incorporate the uncertainty in the determination of nanowire diameters arising from nonspherical cross-section spinning. This approach enables precise characterization of several fundamental aspects of nanowire morphology, which served as an excellent example to overcome nanoscale characterization challenges by using novel statistical means. It might open new opportunities in advancing nanotechnology and might also lead to the standardization of nanocharacterization in many aspects.

Analysis of Mask-Based Nanowire Decoders

Stochastically assembled nanoscale architectures have the potential to achieve device densities 100 times greater than today's CMOS. A key challenge facing nanotechnologies is controlling parallel sets of nanowires (NWs), such as those in crossbars, using a moderate number of mesoscale wires. Three similar methods have been proposed to control NWs using a set of perpendicular mesoscale wires. The first is based on NW differentiation during manufacture, the second makes random connections between NWs and mesoscale wires, and the third, a mask-based approach, interposes high-K dielectric regions between NWs and mesoscale wires. Each of these addressing schemes involves a stochastic step in their implementation. In this paper, we analyze the mask-based approach and show that, when compared to the other two schemes, a large number of mesoscale control wires are necessary for its realization.

Ordered growth of tilted ZnO nanowires: morphological, structural and opticalcharacterization

Tilted ZnO nanowires have been grown by high-pressure pulsed laser deposition (PLD) onm-plane sapphire without employing any catalyst species. The nanowires are inclined30° with respect to the substrate normal and show well-defined epitaxial relationships with them-plane sapphire substrate, the projection of the nanowires’ axis being parallel to the in-plane sapphire direction. Two sets of nanowires, differing in diameter and length, coexist within theinitial growth stages, but only the narrowest and longest nanowires are found to keep ongrowing as deposition proceeds. A systematic study of the effects of growth conditions,including number of pulses, temperature, total pressure and oxygen partial pressure, hasbeen carried out to determine those conditions under which a completely ordered array oftilted nanowires, with a minimum angular distribution, is obtained. Among thegrowth conditions, temperature and oxygen partial pressure are seen to mainlyaffect the nanowires’ axial and lateral growth rates, respectively, while the totalchamber pressure allows monitoring of the evolution from thin film growth, at lowpressure, to a mixture of nanowire/nanobelt growth, at high pressure. Finally,cathodoluminescence (CL) shows that low growth temperatures and high oxygenpartial pressures improve the overall optical quality of the ZnO nanowire arrays.