April 21-25, 2014 | San Francisco
Meeting Chairs: Jose A. Garrido, Sergei V. Kalinin, Edson R. Leite, David Parrillo, Molly Stevens
ZnO nanorods can be readily produced by hydrothermal methods on glass substrates at low temperature (95°C) in a short period time (4 hours). The initial pH value of the aqueous solution makes a big difference on the morphology of ZnO nanorod arrays. Under acid condition (pH=5), ZnO nanorods are much bigger and sparser than the final products under neutral condition (pH=7). Another significant feature is that the nanorods from pH=5 randomly tilt from the substrate to a certain angle, whereas, the nanorods from pH=7 are standing vertically.In order to explain how the direction of ZnO crystal growth was influenced under distinct condition, the growing process of the nanorods was monitored by SEM. The initial pH value is believed to have a great effort on the appearance of the ZnO crystal nucleation in the early stage, and continuously affects the nanorod development. The crystalline structure and optical properties of ZnO nanorods were also studied by using XRD, TEM and Photoluminescence techniques.
Designing, fabricating and integrating arrays of nanodevices into a functional system is the key for transferring nano-scale science into applicable nanotechnology. Despite of the numerous efforts devoted to achieve uniformly ordered assembly of various low-dimensional nanomaterials, planar metal-oxide-semiconductor field-effect-transistor (MOSFET) is still the dominant configuration for implementing functional nanodevices. Novel architecture like 3D integrated circuits has also been adopted to facilitate integration of nanostructure-based planar building blocks by sequentially assembling them into vertically stacked layers. Nevertheless, lack of cost-effective technology for aligning and integrating these nanodevices into circuitry with sufficiently high density hinders further practical applications. For the emerging applications of bio-integrated electronics such as smart skin and human/machine interfacing, schemes for integrating functional nanomaterials with peripheral circuits on deformable/stretchable substrates at low temperature and low cost are highly desirable. To address these application needs, we demonstrate the first and by far the largest 3D array integration of vertical ZnO nanowire (NW) piezotronic transistors circuitry on 4-inch PET flexible substrates, by combining the patterned bottom-up solution synthesis of vertically aligned ZnO NWs at low-temperature (85 oC) with state-of-the-art top-down microfabrication. The as-fabricated array circuit possesses device density of 8464/cm2, which is much larger than the number of mechanoreceptors embedded in the human fingertip skins and enables a 15-to-25-fold increase in number of taxels and 300-to-1000-fold increase in taxel area density compared to recent reports.The position, dimension, crystal orientation, morphology and material properties of synthesized ZnO NWs can be well controlled by the hydrothermal solution synthesis and optimized via engineering measures. The solution-synthesized ZnO NWs array exhibits good uniformity in electrical characteristics and response to applied pressure among all of the devices. The reliability and stability of device operations have also been probed, which indicates a good stability of the array operation for future applications like in vivo physiological sensing in complex environments. Moreover, the feasibility of the fabricated array for self-powered active and adaptive artificial skin without external bias has been presented as well. The scalability of this demonstrated technology in integrating solution-derived single-crystalline with interfacing circuitry at low temperature and low cost enables future implementation of nanomaterials for bio-integrated applications in human-machine interfacing and biomedical diagnosis/therapy.Ref: Wu W. Z.*, Wen X. N.*, Wang Z. L. Taxel-addressable matrix of vertical-nanowire piezotronic transistors for active and adaptive tactile imaging. Science 340, 952-957, 2013.*Authors with equal contributions
ZnO continues to attract considerable attention due to its potential applications in UV detection, LEDs, spintronics, gas sensors, field effect transistors, field emission, photovoltaics and photocatalysis. Many of these applications require epitaxial films or nanostructured morphologies and ZnO is popular for these applications due to the ease of synthesizing a myriad of nano-forms (e.g. rods, rings, particles, belts) by solution methods. Solution methods are of particular interest because of the low temperatures employed (often < 100oC) and the ease of forming single crystal films and nanostructures.This talk will present our observations concerning the growth of ZnO in water both as nanostructures and in film form. In the film form, epitaxial films have been grown at <100oC and much of the work has looked at reducing the defects in the grown films. Epitaxial films with threading dislocation densities in the low 108 cm-2 values utilizing lateral epitaxial overgrowth with and without photolithographic masking will be discussed. Recent results from initial works on the growth of homoepitaxial ZnO and MgZnO films and also nanostructured polycrystalline films will also be presented. For the latter, functional surface properties such as wetting will also be reported.In addition, post growth annealing is required to optimize properties of solution grown ZnO and this study shows that such annealing leads to the formation of pores within epitaxial films and also in single crystal rods. It is believed that these pores form upon coalescence of anion and cation vacancies. Pore formation can be detrimental, adversely affecting transparency and mobility and as such, more detailed investigations has been undertaken utilizing a variety of characterization techniques such as scanning transmission electron microscopy (STEM), tomography and absorption spectroscopy.
As the most promising candidates for Diluted magnetic semiconductors (DMSs) with high Curie temperature (Tc), TM-doped ZnO has attracted considerable attention of scientific community due to its attractive advantages such as low cost, abundance, friendly environment and optoelectronic property. Although there are many reports on room-temperature ferromagnetism (RTFM) of ZnO diluted magnetic semiconductors doped with transition-metal (TM), the origin of RTFM is still quite controversial. Recently, some computational results calculated using the first-principles method based on density functional theory (DFT) show that codoping appears to be a potential approach to obtain intrinsic and enhanced ferromagnetism in TM-doped ZnO.[1,2] Stirred from the above mentioned facts, it would be quite interesting to synthesize and investigate the properties of codoping ZnO DMS, such as Cr-Ni codoped ZnO DMS. Meanwhile, magnetic field has been used as an efficient way to modulate the growth, morphology and the properties of the crystalline materials while it is applied in the synthesis process. In this work, Cr-Ni codoped ZnO powders were synthesized by hydrothermal method under the high pulsed magnetic field. The effects of pulsed magnetic field on the morphology, structure and magnetic properties of Cr-Ni codoped ZnO were investigated by X-ray diffraction, scanning electron microscope, high resolution transmission electron microscope, Raman scattering spectra and vibrating sample magnetometer. It was found that high pulsed magnetic field processing not only affects on the morphology of ZnO nanocrystallines, but also improves the Cr-Ni ions doping into the ZnO matrix. The room temperature ferromagnetism observed in the samples demonstrates clearly that codoping is an optional method to fabricate intrinsic ferromagnetism in TM-doped ZnO. According the bound magnetic polaron model (BMPs) proposed by Coey et al, Cr and Ni ions incorporation may prompt the formation of bound polaron (oxygen vacancies, Vo), which may be the reason for the field processing sample with better ferromagnetism.AcknowledgementsThe authors thank the project supported by Shanghai Science and Technology Commission(11nm0501600), and the Analysis and Research Center of Shanghai University for their technical supports.Reference B. Lu et al. Appl. Phys. Lett, 101:242401, 2012.  P. Gopal et al. Phys. Rev. B, 74:094418, 2006. J.M.D. Coey et al. Nat. Mater, 4:173, 2005*Corresponding author contact: email@example.com
We recently put forward a solution based method of laser induced chemical deposition for nanomaterials. The grow rate of SnO2 nanotube by laser induced chemical deposition can reach a value more than 300 nm/s. The method can be applied to produce various chalcogenide nanomaterials. Nanomaterials synthesized by laser-induced chemical deposition share the characteristic of uniform fine microstructure. In this paper, we demonstrate that this method can be used to coat 3 dimensional porous structure with uniform nanoparticles. Paper fibers coated with iron oxide nanoparticle as an example is studied in this paper. Heavy loading of Iron Oxide nanoparticles can achieved in a short time. The relationship between the laser power and production rate is shown. The size and crystal structure of the coated nanoparticle are investigated by SEM and TEM. The hybrid structure of nanoparticle coated paper fibers is used as an effective sorbent for heavy metal in water treatment.
In this presentation, we discuss our recent results in developing an electrochemical-liquid-liquid-solid (ec-LLS) growth process that relies on an unconventional aqueous electrodeposition strategy to produce crystalline covalent Group IV and III-V semiconductor nanomaterials. This process employs a liquid metal as a traditional cathode substrate and as a recrystallization flux to directly produce crystalline Group IV and III-V semiconductors at or near lab ambient conditions. The first half of the talk will focus on general features of the ec-LLS process used for the direct electrodeposition of crystalline GaAs and InAs thin films from aqueous solutions without any thermal annealing. Here, dissolved As2O3(aq) in water is electrochemically reduced on reactive Ga or In to produce the respective binary crystalline semiconductor. The necessity for clean (i.e. oxide free) group III metal interfaces will be discussed. Spectroelectrochemical data will then be presented that detail the extent of this electrodeposition process at low and elevated temperatures, highlighting a key balance between the rates of several electrochemical, metallurgical, and transport processes.. The second half of the presentation will highlight recent data that extends the ec-LLS strategy to using arrays of liquid gallium (Ga(l)) nanodroplet electrodes supported on Ge or Si wafers for the electrodeposition of epitaxial and single crystal Ge nanowires from dissolved GeO2(aq). High resolution transmission electron microscopy investigations will be presented which verify the epitaxial nature between the nanowire/substrate interface as well confirm the position of the Ga(l) nanodroplet at the tip of the nanowire following growth. The influence of the substrate crystal orientation on the resultant nanowire growth direction will be revealed by scanning electron microscopy. The observed uniformity in as-grown nanowire height will be discussed within the context of the traditional instantaneous electrochemical nucleation model. In the same vein, the propensity for this ec-LLS strategy to be used for wafer-scale preparation of homogenous Ge nanowire arrays will be described.
Titanium dioxide (TiO2) has found its applications in many important areas including dye-sensitized solar cells, p