The macro and micro morphology of the Si surface, depending on noble metal ion concentration in etching solution, prepared by metal assisted etching were investigated. We defined the morphology of etched Si in four types, and developed the phase diagram of Si morphology. Mixture of silver nitrate (AgNO3) and hydrofluoric acid (HF) was used as an electroless-plating bath of Ag, as well as etching solution of Si. The morphology of the etched Si surface as function of concentration of AgNO3 in etching solution was observed by SEM. With increasing concentration of the AgNO3 in the etching solution, the surface of etched Si tended to be porous structure with very fine pores of a few nm (porous Si). When concentration of AgNO3is low, single crystal Si nanowires with a smooth surface without pores were observed.

To realize applications based on nanowires, the development of methods that allow the organization of nanostructures into integrated arrangements is crucial. While many different methods exist, the direct synthesis of complex nanowire structures is one of the most suitable approaches to efficiently connect numerous nanostructures to the macroscopic world. The fabrication of various 3D nanowire assemblies including arrays, networks, and hierarchical structures by combining specifically designed template materials with electrochemical deposition is demonstrated. The ion track template method is extended to create more complex structures by changing template production and electrodeposition parameters. In contrast to current synthesis routes, it is possible to independently control many of the parameters defining both (i) characteristics of individual nanowires (including dimensions and composition) and (ii) the arrangement of the nanoscale building blocks into nanowire assemblies determined by nanowire orientation and integration level. Results that highlight the benefits arising from the design of advanced 3D nanowire architectures are presented.

Highly densely packed, self-organized silicon nanowires with very narrow diameter distribution were synthesized within porous anodic alumina templates with electrodeposited catalytic metal nanoparticles. For successful catalytic metal nanoparticle deposition, electrochemical-, and chemical barrier layer thinning process was investigated following anodization process. Controlled pulsed electrodeposition process was carried out for a volume calibration of desired catalytic metal nanoparticle deposition inside nanopore arrays using different metal-ion containing electrolyte. Not only single metal nanoparticles, but also multi metal nanoparticles layers were filled inside PAA to enhance metal filling aspect, and to control the volume of nanoparticles more precisely. Using multilayered metal nanoparticles resulted on different SiNW’s growth behavior depending on the types of underlying metal nanoparticles.

SiNWs were successfully synthesized using hot-filament assisted chemical vapor deposition system. Although silicon precursor gas can generally be dissociated at relatively low temperatures, the use of a hot filament activation help decreasing process temperature, and also, highly activated atomic hydrogen generation via the tungsten hot filament placed at gas inlet helps preventing parasitic amorphous silicon deposition on either the alumina membrane surface or the pore wall which hinders appropriate growth of SiNWs in PAA by nanopores clogging. Such densely packed, self-organized SiNWs are of high interest in many application fields like nanoelectronics, optoelectronics, and energy storage/conversion devices etc.

GaN nanowires and nanorods have been successfully synthesized on Si (111) substrates by magnetron sputtering through ammoniating Ga2O3/Nb thin films and the effects of ammoniation temperatures on growth of GaN nanowires and nanorods were analyzed in detail. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and photoluminescence spectra were carried out to characterize microstructures, morphologies, and optical properties of GaN samples. The results demonstrate that sample after ammoniation at 950 °C is single crystal GaN with hexagonal wurtzite structure and high crystalline quality, having the size of 30 - 80 nm in diameter. After ammoniation at 1000 °C, GaN nanorods appear with smooth and clean surface and more than 100 nm in diameter. The optical properties of GaN nanowires grown at 950 °C and nanorods grown at 1000 °C are best with strong emission intensities.

Morphologies of silicon nanowires grown by plasma-assisted metalorganic chemical vapor deposition were studied in the presence of various dopant precursors. The varied precursors affected the axial and radial growth rates over orders of magnitude where triethylborane showed the strongest enhancements for both axial and radial growth, and triethylarsenic and triethylantimony retarded axial growth. Native oxide thickness is also shown to depend strongly on doping condition resulting in increased oxide thicknesses for increased carrier concentration, using shifts in the measured binding energy of the silicon 2p3/2 state as a proxy for carrier concentration.

A nanofluid is a solid-liquid composite material consisting of a stable suspension of nanometric particles in a conventional refrigerant liquid expected to exhibit enhanced heat transfer properties. Elemental silver (Ag) was selected in this research because of its high electrical and thermal conductivity that are likely to be dependent on the crystal size and shape at the nanoscale. Accordingly, we have synthesized highly monodisperse silver nanowires and nanocrystals by reducing silver nitrate solutions with ethylene glycol in presence of polyvinylpyrrolidone, (PVP). The shape-control in the silver nanostructures was achieved by a proper selection of the type and level of chloride salts, e.g. KCl and CaCl2, and specific PVP/Ag mole ratios in starting solutions. The development of the metal phase was confirmed by X-ray diffractometry. Transmission electron microscopy analyses evidenced the formation of silver nanowires exhibiting a very uniform thickness that could be tuned in the 40-130nm range. UV-vis measurements evidenced the plasmon peak at ∼387nm and clear shoulders at ∼357nm that are indicative of the formation of elongated nanostructures.

ZnO nanostructures such as nanorods and nanoneedles were prepared on both cotton textiles and electrospun cellulosic nanofibers by a simple, two-step hydrothermal process at low temperature in aqueous solution. Commercially available cotton fabrics were used. Cellulosic nanofibers (average diameters of 100 nm) were obtained by electrospinning of cellulose acetate/polyvinyl acetate/polyethylene glycol mixture on glass slides to form non-woven mats.

On cotton textiles, the systematic change of the seed-to-growth solution concentration ratio caused a noticeable variation on the morphology of the nanostructures. The loading ratio of ZnO nanorods and nanoneedles were 37.5% and 18.1 wt%, respectively. Durable superhydrophobicity was achieved with a static water contact angle of 160.7° upon fluorosilane treatment, even after prolonged exposure to UV and plasma irradiation. The surface wettability was found to slightly vary from nanorods (160.7°) to nanoneedles (159.8°). The ZnO nanostructures did not lose their superhydrophobicity after 1 h of agitation in DI water. Excellent UV blocking activities were observed for nanorods and nanoneedles in the wavelength region analyzed. On electrospun cellulosic nanofibers of approximately 100 nm diameter, the loading ratio of ZnO nanorods were found to be 33.3 wt% which are densely and uniformly distributed the entirety of the nanofibers. Although diameters of the nanofibers and cotton fibers are very different in size (around 100 nm and 15-20 micron, respectively) the ZnO loading on electrospun fibers are very close to that of cotton fabric due to the high surface area and coiled nature of electrospun fibers, resulting in high packing density. ZnO nanorods grown on electrospun nanofibers exhibited hydrophilic behavior.

GaP, GaAs, and InP nanowires were grown on graphitic layers by the vapor-liquid-solid method in a metalorganic vapor phase epitaxy chamber. On graphene/SiC(0001), Au particles as catalyst were formed at the steps by controlling the Au deposition rate and the annealing temperature in a low-energy electron microscopy system. GaP nanowires were grown on this substrate, and it was found that vertical nanowires were formed at the steps of the surface. We also performed GaP, GaAs, and InP nanowire growth on graphite substrates. Free-standing nanowires were obtained for all three materials, although they were vertically, diagonally, and laterally-oriented at the same time. The results suggested that the growth at the steps is the key to growing nanowires vertically on graphene surface.

Materials with a remarkable combination of high electrical conductivity as well as optical transparency are playing a key role for opto-electronic devices. In addition to these specific electro-optical properties, transparent conductive materials should, for many applications, be lightweight, flexible, low-cost, non toxic and compatible with mass production techniques. In these regards, the use of Ag nanowire (Ag NW) networks appears to be a promising approach. In this study, Ag NW electrodes were fabricated by a novel spray injection method. The number of pulses was varied resulting in different network morphologies. Coatings were systematically characterised structurally, electrically and optically via SEM, four-point probe measurements and spectrophotometry, respectively. Semi uniform layers of nanowires with large haze coefficients have been obtained over large areas. Thermal annealing was shown to increase the nanowire film conductance resulting in 16 Ω/sq surface resistance and up to 73% maximal total transmittance. Films showed average optical transparencies superior to that of ITO over the 250-2500 nm range. Finally, encapsulation of Ag NWs within a matrix of ZnO nanoparticles greatly enhanced the thermal stability of these networks.

This article applies a recently discovered gas phase nanocluster electrodeposition process to the formation and combinatorial improvement of 3D bulk heterojunction photovoltaic cells. The gas phase deposition process used here is a single reactor system that forms charged nanoclusters (gold, silver, tungsten, and platinum) at atmospheric pressure. The clusters deposit onto selected surface areas with sub 100 nm lateral resolution using a programmable concept similar to liquid phase electrodeposition such that biased electrodes turn ON or OFF deposition in selected areas. Continued deposition of the nanoparticles results in a tower array with different lengths and density on a single substrate which is used as contacts to the active organic layer of 3D bulk heterojunction photovoltaic cells. Applying a combinatorial approach identifies in a massively parallel way electrode designs and topologies that improve light scattering, absorption, and minority carrier extraction. We report photovoltaic cells with higher and denser nanocluster tower arrays that improve the power conversion efficiency of bulk heterojunction photovoltaic cells by approximately 47.7%.

In the present global environmental context, it becomes more and more critical to find efficient solutions to lower our energy consumption on one hand, and to produce energy from clean renewable sources on the other hand. Consequently, research efforts on materials for energy applications are intensifying.

The present work aims at developing optoelectrical components usable for both energy saving (light emitting diodes) and renewable energy production (solar cells) by fabricating p-n heterojunctions based on a single semiconductor, titanium dioxide. TiO2 is indeed a very promising candidate: it is chemically and physically stable under irradiation, transparent to visible and near-infrared light (Eg= 3 – 3.5 eV), presents photocatalytic activity, is non-toxic and low cost, which permits to envisage its large scale use.

In the present paper, the proposed architecture for both solar cells and LEDs is original as well as common for both applications: a three-dimensional architecture based on an anodic alumina nanoporous membrane which serves as nanomask for TiO2 growth in order to enlarge the effective surface of the components. TiO2is synthesized by Atomic Layer Deposition (ALD), a technique particularly well adapted to the deposition of ultrathin films (from one monolayer to few tens of nanometers) on 3D porous substrates patterned with high aspect ratio nanopores.

In this work, the capacity of synthesizing 3D nanostructures is demonstrated. TiO2ultrathin films (10 to 100 nm) were grown by ALD on flat, micropatterned, microporous and nanoporous anodic alumina membranes (AAM) substrates. The films were highly conformal, as confirmed by SEM and TEM imaging. Both EDS and XPS analyses validated the dioxide film stoichiometry.

With a wide band gap of greater than 3.0 eV and the ability to self-heal from radiation damage, icosahedral boron arsenide (B12As2) is an apt candidate for use in next-generation betavoltaics. By capturing and converting high energy electrons from radioisotopes into usable electricity, “nuclear batteries” made from B12As2 could potentially power devices for decades. Compared to bulk crystals or epitaxial films, B12As2 nanowires may have lower defect densities or may even be defect-free, leading to better electrical properties and device performance. In our study, B12As2 nanowires were synthesized via vapor-liquid-solid (VLS) growth using platinum powder and nickel powder on silicon carbide and 20 nm thick nickel film on silicon substrates from 700 °C to 1200 °C. Platinum yielded the highest quality nanowires from 900 °C to 950 °C, resulting in platinum particles densely covered with wires formed by straight segments connected by sharp angular kinks. At these growth temperatures, diameters ranged from less than 30 nm to about 300 nm as determined by scanning electron microscopy and transmission electron microscopy. Growth temperatures of 850 °C or less produced curled wires 200-1000 nm in diameter. Transmission electron microscopy and selected area electron diffraction revealed excellent crystallinity in wires grown above 850 °C, while wires grown at or below 850 °C were partially amorphous. Wires grown from the 20 nm nickel film displayed similar morphologies at temperatures up to 850 °C; from 900 °C to 950 °C, straight, isolated wires were grown with diameters of 200-400 nm. Nickel powder only produced wires larger than 1 μm in diameter. The comparative quality and growth of B12As2nanowires will be discussed.

We study the photocurrent from photoexcited charged carriers excited with lasers of energy both above and below the energy gap in CdS nanostructures. We observe non-linear photocurrents in CdS nanosheet devices in the metal-semiconductor-metal configuration with Schottky contacts for sub-band gap excitations. Analysis of two-photon absorption dominated photocurrents reveals a nonlinear coefficient of β = 2 cm/GW for these nanosheet devices, which is comparable to those of bulk CdS. We demonstrate the use of the photocurrent polarization measurements to determine the orientation of atoms in the nanosheet.

Si-doped GaAs nanowires (NWs) were grown on (111)Si substrate by MBE-VLS method. The electrical characteristics of the GaAs NWs were measured. A joule heater was arranged near the tip of NW for making the gradient of substrate temperature. The obtained Seebeck coefficient of the GaAs NW increases linearly with a rise in temperature. The thermoelectric power of the Si doped GaAs NW was determined by the hole diffusion. It was estimated that the hole density in the Si-doped GaAs NW at room temperature was 5.9×1018 cm-3 from the slope of the temperature dependence of the Seebeck coefficient in the Si-doped GaAs NW. At room temperature, the Seebeck coefficient, thermoelectric power factor, and thermoelectric figure of merit (ZT) were 429 μV/K, 271μW/mK2, and 1.5×10-3, respectively.

In this work, Dopant Segregated Schottky Barrier (DSSB) and Schottky Barrier (SB) vertical silicon nanowire (VSiNW) diodes were fabricated on p-type Si substrate using CMOS-compatible processes to investigate the effects of segregated dopants at the silicide/silicon interface and different annealing processes on nickel silicide formation in DSSB VSiNW diodes. With segregated dopants at the silicide/silicon interface, VSiNW diodes showed higher on-current, due to an enhanced carrier tunneling, and much lower leakage current. This can be attributed to the altered energy bands caused by the accumulated Arsenic dopants at the interface. Moreover, DSSB VSiNW diodes also gave ideality factor much closer to unity and exhibited lower electron SBH (ΦBn) than SB VSiNW diodes. This proved that interfacial accumulated dopants could impede the inhomogeneous nature of the Schottky diodes and simultaneously, minimize the effect of Fermi level pinning and ionization of surface defect states. Comparing the impact of different silicide formation annealing using DSSB VSiNW diodes, the 2-step anneal process reduces the silicide intrusion length within the SiNW by ~ 5X and the silicide interface was smooth along the (100) direction. Furthermore, the 2-step DSSB VSiNW diode also exhibited much lower leakage current and an ideality factor much closer to unity, as compared to 1-step DSSB VSiNW diode.

We produce four distinct ZnO nanorod diode structures that are based on ZnO nanorods produced at pH 6 and pH 11 and have the p-type material PEDOT:PSS (hybrid device) or CuSCN (all inorganic device). After testing the performance of the diodes we show a rectification of 1050 at ±1V in the dark for the inorganic device. The device also exhibits good UV photodetection showing a rapid ca0.1ms turn on and off to a source of illumination. The hybrid devices performed as previously reported with a rectification of 25 at ±1V in both dark and under illumination. We ascribe the performance of the devices to the differences in morphology in the ZnO brought about by the processing conditions and the way in which the p-type layer coats the nanostructure.

The authors present the technological routes used to build planar and vertical gate all-around (GAA) field-effect transistors (FETs) using both Si and SiGe nanowires (NWs) and the electrical performances of the as-obtained components. Planar FETs are characterized in back gate configuration and exhibit good behavior such as an ION/IOFF ratio up to 106. Hysteretic behavior and sub-threshold slope values with respect to surface and oxide interface trap densities are discussed. Vertical devices using Si NWs show good characteristics at the state of the art with ION/IOFF ratio close to 106 and sub-threshold slope around 125 mV/decade while vertical SiGe devices also obtained with the same technological processes, present an ION/IOFF ratio from 103 to 104but with poor dynamics which can be explained by the high interface traps density.

Light-emitting diodes (LEDs) based on p-GaN/ZnO heterojunction were fabricated. GaN was deposited on sapphire using metal-organic chemical vapor deposition (MOCVD), and two kinds of ZnO i.e. ZnO thin film deposited by sputtering and ZnO nanorods (NRs) grown by hydrothermal method were used as n-type layer respectively. MgO film with the thickness around 10 nm was deposited by electron-beam deposition to act as an interlayer between GaN and ZnO. Photoluminescence, electroluminescence and I-V curves were measured to compare the properties of GaN based heterojunction LEDs with different architectures. The existence of MgO interlayer as well as the morphology of ZnO obviously influenced the electrical and optical properties of GaN based LEDs. The effect of MgO interlayer on ZnO growth, properties and I-V curves and emission spectra of LEDs is discussed in detail.

We report the formation and optical properties of site-controlled InAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition for application to single photon sources. InAs/GaAs QD-in-NWs with various InAs thicknesses are realized on patterned GaAs(111)B substrates in the form of InAs/GaAs heterostructures and identified by structural analyses using scanning transmission electron microscopy and photoluminescence characterization. Sharp excitonic emission peaks at 10 K from single QD-in-NWs with the narrowest exciton linewidth of 87 μeV are observed. Light emission from the single QD-in-NW shows photon antibunching which evidences single photon emission from high-quality QD-in-NWs.

Lasing characteristics of a single Zinc oxide (ZnO) nanosheet and a single ZnO nanowire were investigated by an ultraviolet light excitation. ZnO nanocrystals were synthesized by chemical vapor deposition (CVD) method, and those ZnO nanocrystals were excited by a third-harmonic Q-switched Nd:YAG laser beam (355 nm, 5 ns). The emission spectra from a single ZnO nanocrystal was collected by an objective lens with a magnification factor of 100 or 50, coupled with a spectrometer with a light fiber. The area observed by the spectrometer is about 10 μm in diameter, and therefore the emission spectra from a single ZnO nanocrystal can be observed. The emission spectra showed the obvious lasing characteristics having mode structure and a threshold for lasing. The lasing threshold power density of a ZnO nanosheet and a ZnO nanowire were measured to be about 60 kW/cm2 and 150 kW/cm2, respectively. ZnO nanosheet can be a superior laser medium due to the lower threshold for lasing compared to the threshold of the ZnO nanowire. However, since the lasing spectra had mode structure, a single-longitudinal mode lasing would be required for a practical application. The single longitudinal mode lasing can be realized by a nanomachining of a grating on the ZnO nanocrystal surface due to distributed bragg reflector (DBR) laser. The minimum DBR pitch was estimated to be about 81 nm, which can be machined by focused-ion beam (FIB) focused up to 7 nm at minimum, and therefore, we demonstrated the nanomachining on a single ZnO nanowire. However, the single-longitudinal mode lasing was not observed so far, and thus optimization of experimental conditions such as the DBR pitch, ion dose amount and increasing the number of repetition of DBR would be required.