Seed layers for the growth of oriented vertical arrays of ZnO nanorods

ZnO is a direct wide bandgap semiconductor crystallizing in the wurtzite structure with a series of unique properties: a large exciton binding energy; good optical transmittance in the visible region; high optical gain; piezoelectricity; room temperature ferromagnetism; mechanical stability given by the high melting point and large cohesive energy; radiation hardness; or biological compatibility. These properties allow for applications of ZnO in UV light-emitting devices and detectors, field-effect transistors, solar cells, piezoelectric nanogenerators, or chemical sensors. For the majority of these applications, upright standing arrays with controlled positioning, sizes, and physical properties are preferred. Chemical bath deposition (CBD) is a low-cost, low-temperature, surface scalable technique to grow ZnO nanostructures on virtually any substrate with a suitable seed layer. We show how the properties of the seed layer such as the texture, roughness, and porosity affect the nucleation and the alignment of ZnO nanorods (fig. 1a,b). The ZnO seed layers were prepared by electrophoretic deposition of a commercially available solution of ZnO nanoparticles dispersed in ethanol and by the sol-gel method, where the seed layers deposited by dip coating of a chemical precursor solution obtained by dissolving zinc acetate dihydrate and monoethanolamine in 2-methoxyethanol onto a (100) Si substrate. The film thickness, porosity, texture, and the size of the crystallites were controlled by varying the molar concentration of precursors, the withdrawal speed, and the number of dip-coating cycles. The ZnO nanorods were grown by CBD in aqueous solution consisting of zinc nitrate hexahydrate and HMTA in batch and continuous-flow reactors. Periodic arrays of ZnO nanorods were obtained on the seed layers patterned by electron or ion beam lithography (fig. 1c). To study the electric charge transport in the nanorods, electrical contacts were formed by the deposition of colloidal graphite, by metal evaporation and by the deposition of Pt using the gas injection system in the SEM. The transport properties were correlated with the structural and optical properties investigated by x-ray diffraction and low-temperature photoluminescence spectroscopy. Please click Additional Files below to see the full abstract

INSIGHT INTO NANOPARTICLE CHARGING MECHANISM IN NONPOLAR SOLVENTS TO CONTROL THE FORMATION OF PT NANOPARTICLE MONOLAYERS BY ELECTROPHORETIC DEPOSITION

Electrophoretic deposition of nanoparticles is considered to be one of the convenient methods for preparation of ordered nanoparticle monolayers. By using a nonpolar suspension of nanoparticles, we can (a) limit the current between the electrodes; (b) reduce the changes in the composition and conductivity of the medium due to the generation of charged species near the electrodes; and (c) suppress electrochemical reactions at the electrodes. One of the important questions about understanding the principle mechanisms of electrophoretic deposition is to identify the origin of electric charge in nonpolar suspension from which the nanoparticles are deposited. We developed a simple model of nanoparticle charging and we explained how the amount of the charge carried by nanoparticles can affect the quality of deposited monolayers. For electrophoretic deposition, we used silicon substrates as electrodes and Pt nanoparticles in water-AOT-isooctane reverse micellar system as a suspension. We used the centrifugation of Pt in combination with DLS measurements for controlling the charge carried by nanoparticles. Prepared nanoparticle monolayers were analyzed by AFM, SEM and electrical measurements. Please click Additional Files below to see the full abstract

Hydrogen sensors based on electrophoretically deposited Pd nanoparticles onto InP

Electrophoretic deposition of palladium nanoparticles prepared by the reverse micelle technique onto InP substrates is addressed. We demonstrate that the substrate pre-deposition treatment and the deposition conditions can extensively influence the morphology of the deposited palladium nanoparticle films. Schottky diodes based on these films show notably high values of the barrier height and of the rectification ratio giving evidence of a small degree of the Fermi level pinning. Moreover, electrical characteristics of these diodes are exceptionally sensitive to the exposure to gas mixtures with small hydrogen content

PD NANOLAYERS FOR HYDROGEN SENSORS

We presented study nanoparticle layers created by electrophoretic deposition. A possibility of using Pd nanolayers for the formation of Schottky barriers with a large Schottky barrier height (SBH) value on n-type tin doped InP is proposed together with its potential application in high-sensitive hydrogen sensors

Optoelectrical characterization of well oriented n-type zno nanorod arrays on p-type GaN templates

A heterojunction formed between a single n-type ZnO nanorod and p-type GaN template was successfully prepared by low cost chemical bath deposition technique. Periodic circular patterns were fabricated by focused ion beam etching through poly(methyl methacrylate) mask to control the size, position, and periodicity of the ZnO nanorods. A possible growth mechanism is introduced to explain the growth process of the nanorods. Optical and electrical properties of the heterojunctions were investigated by low temperature photoluminescence spectroscopy and by the measurement of current-voltage (I-V) characteristics. The I-V characteristics were measured by directly contacting single ZnO nanorods with the conductive atomic force microscopy tip. The diode-like rectifying behavior was observed with a turn-on voltage of 2.3 V and the reverse breakdown voltage was 5

Influence of H2O2 treatment on morphological and photoluminescence properties of hydrothermally grown ZnO nanorods

We report photoluminescence properties of hydrothermally grown ZnO nanorods (NRs) before and after hydrogen peroxide (H2O2) treatment. The H2O2 treatment introduces oxygen related defects and thus enhances chemisorption processes in ZnO NRs. These effects amplify interactions between the gas species and adsorbed oxygen and thus can influence sensing properties of ZnO NR

GROWTH OF InP CRYSTALS WITH RARE-EARTH ELEMENTS

We report on the influence of rare earth (RE) elements (Pr, Er, and Dy) addition during vertical Bridgman low pressure synthesis on the properties of InP crystals. The temperature dependent Hall measurement and low temperature photoluminescence (PL) spectroscopy were employed to study the changes in electrical and optical properties of the crystals. The observed changes are attributed to the gettering effect of REs caused by the high affinity of REs towards shallow impurities in InP