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

LPE Growth of III-V Semiconductors from rare-earth Treated Melts

We focus on the characterization of InP and InGaAsP layers prepared by liquid phase epitaxy with rare-earth admixtures. We applied photoluminescence spectroscopy (PL), capacitance-voltage measurements, and secondary ion mass spectroscopy in order to explain: (i) the gettering effect and conductivity crossover of InP layers for Pr treated samples, (ii) narrowing of the PL and elecroluminescent spectra of the active InGaAsP region of a double-heterostructure LED

Physical properties of InP epitaxial layers prepared with dysprosium admixture

Physical properties of commonly prepared InP layers grown by LPE technique and those grown from Dy treated melt are compared. The layers were examined by SEM, low temperature PL spectroscopy, C-V measurements and temperature dependent Hall effect. Structural, electrical and optical properties of InP layers exhibit a significant dependence on the presence of Dy and its concentration in the melt. When increasing the concentration of Dy the reversal of electrical conductivity occurs

Příprava a charakterizace struktur ZnO malých rozměrů

ZnO low dimensional structures were prepared in order to study their unique electronic and optical properties. ZnO nanocrystals were obtained by ball milling of commercially available powders. This process was found to produce particles with sizes of tens to hundreds nanometers being composed of nanocrystals down to a few nanometers. ZnO micro and nanorods mainly of hexagonal shape as well as nanotubes and nanocombs were grown by vapor-solid method in a muffle furnace under the flow of high purity argon

Influence of rare-earth elements on InP-based semiconductor structures for radiation detectors

Preparation and characterization of InP epitaxial layers with Tb admixture in the growth melt is reported. Structural, electrical and optical properties of InP layers exhibit a signaficant dependence on the presence of Tb and its concentration in the melt. When increasing the concentration of Tb in the growth melt the reversal of electrical conductivity occurs

Characterisation of InP layers prepared by the LPE method with Pr and Nd addition in the growth melt

High purity InP epitaxial layers were grown by LPE from the melt conataining, besides essential components, also rare-earth elements admixture. The layers were examined by SEM, low temperature PL spectroscopy, C-V measurements and temperature dependent Hall effect. The behaviour and the impact of Pr and Nd were compared. The concentration of shallow impurities was reduced by up to three orders of magnitude. PL spectra were markedly narrowed and fine spectral features were resolved

Růst InP metodou LPE s přídavkem prvků vzácných zemin do taveniny

Addition of REs to the growth melt is known to have purifying effect on AIIIBV LPE layers. Each member of REs family acts in its own way. Small addition of Tb, Dy, Tm, and Pr leads to pronounced gettering of shallow donors, the high purity n-type InP can be grown. Exceeding certain concentration, reversal of conductivity type from n to p occurs. Addition of Tm during growth on InP:Fe substrates always results in the preparation of semi-insulating layers due to Fe out-diffusion mediated by RE admixture