Coral-like Structures Research Articles

Electroassisted codeposition of sol-gel derived silica nanocomposite directs the fabrication of coral-like nanostructured porous gold.

Herein, we report on a one-step coelectrodeposition method to form gold-silica nanocomposite materials from which high surface area nanostructured gold electrodes can be produced. The as-prepared Au-SiO2 films possess an interconnected three-dimensional porous framework with different silica-gold ratios depending on the deposition solutions and parameters. Chemical etching of the nanocomposite films using hydrofluoric acid resulted in the formation of nanostructured porous gold films with coral-like structures and pores in the nanometer range. The cross-linkage of the gold coral branches resulted in the generation of a porous framework. X-ray photoelectron spectroscopy confirms the complete removal of silica. Well-controlled surface area enhancement, film thickness, and morphology were achieved by manipulating the deposition parameters, such as potential, time, and gold ion and sol-gel monomer concentrations in the deposition solution. An enhancement in the surface area of the electrode up to 57 times relative to the geometric area has been achieved. The thickness of the as-prepared Au-SiO2 nanocomposite films is relatively high and varied from 8 to 15 μm by varying the applied deposition potential while the thickness of the coral-like nanostructured porous gold films ranged from 0.22 to 2.25 μm. A critical sol-gel monomer concentration (CSGC) was determined at which the deposited silica around the gold coral was able to stabilize the coral-like gold nanostructures, while below the CSGC, the coral-like gold nanostructures were unstable and the surface area of the nanostructured porous gold electrodes decreased.

Novel coral-like hexagonal MoO3 thin films: Synthesis and photochromic properties

MoO3 thin films were obtained by varying the precursor concentration (Cp) using a hydrothermal method. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), ultraviolet–visible diffuse reflectance spectroscopy and a color difference meter were employed for the characterization of synthesized thin films. With the increase of precursor concentration, the morphology of MoO3 thin films changed from hexagonal prismatic structures to coral-like structures and finally straw-like structures. XRD results showed that all samples can be indexed to the hexagonal structure of MoO3. Additionally, the band gap of all MoO3 thin films was around 3.16eV calculated from UV–vis diffuse reflectance spectrum. The as-prepared MoO3 film with coral-like structures possessed the maximum color difference value (ΔC=2.33). This result indicates that MoO3 film prepared with the precursor concentration of 0.18M exhibits excellent photochromic properties due to the large exposed surface provided by coral-like hierarchical structure.

Surface-morphology changes and damage in hot tungsten by impact of 80 eV – 12 keV He-ions and keV-energy self-atoms

We report results of measurements on the evolution of the surface morphology of a hot tungsten surface due to impacting low-energy (80 – 12,000 eV) He ions, performed at the ORNL Multicharged Ion Research Facility (MIRF). Surface-morphology changes were investigated over a broad range of fluences, energies and temperatures for both virgin and pre-damaged W-targets. At low fluences, ordered coral-like and ridge-like surface structures are observed, with great grain-to-grain variability. At the largest fluences, individual grain characteristics disappear in FIB/SEM scans, and the entire surface is covered by a multitude of near-surface bubbles with a broad range of sizes, and disordered whisker growth, while in top-down SEM imaging the surface is virtually indistinguishable from the nanofuzz produced on linear plasma devices. These features are evident at progressively lower fluences as the He-ion energy is increased. In addition, simulations were carried out of damage caused by cumulative bombardment of 1 keV W self-atoms, using LAMMPS at the Kraken supercomputing facility of the University of Tennessee. The simulations show strong defect-recombination effects that lead to a saturation of the total defect number after a few hundred impacts, while sputtering and implantation lead to an imbalance of the vacancy and interstitial numbers.

Pulsed and potentiostatic electrodeposition of CuInSe2 on gold-coated alumina substrates

CuInSe2 thin films were deposited on gold-coated alumina electrodes using constant and pulsed potential signals. In situ electrochemical measurements were recorded with an atomic force microscope to follow CuInSe2 electrodeposition. The electrodeposited films were characterized employing scanning electron microscopy, energy dispersive spectroscopy, grazing incidence X-ray diffraction, and Raman spectroscopy. The best stoichiometry is attained for films deposited at pulsed potentials of −0.7 V. These films are also the most compact, showing a homogeneous morphology. In contrast, potentiostatic films presented minor variations in their chemical composition with the deposition potential. The morphology presented porous coral-like structures. X-ray and Raman spectroscopy analysis of as-deposited films by either technique reveal the presence of secondary phases such as Cu x Se and Se, especially at the most positive deposition potentials. After a thermal treatment at 500 °C in Se vapor, the crystallinity of the material is significantly enhanced and no secondary phases are present.

Colloidal CdSe/Cu3P/CdSe Nanocrystal Heterostructures and Their Evolution upon Thermal Annealing

We report the synthesis of colloidal CdSe/Cu(3)P/CdSe nanocrystal heterostructures grown from hexagonal Cu(3)P platelets as templates. One type of heterostructure was a sort of "coral", formed by vertical pillars of CdSe grown preferentially on both basal facets of a Cu(3)P platelet and at its edges. Another type of heterostructure had a "sandwich" type of architecture, formed by two thick, epitaxial CdSe layers encasing the original Cu(3)P platelet. When the sandwiches were annealed under vacuum up to 450 °C, sublimation of P and Cd species with concomitant interdiffusion of Cu and Se species was observed by in situ HR- and EFTEM analyses. These processes transformed the starting sandwiches into Cu2Se nanoplatelets. Under the same conditions, both the pristine (uncoated) Cu(3)P platelets and a control sample made of isolated CdSe nanocrystals were stable. Therefore, the thermal instability of the sandwiches under vacuum might be explained by the diffusion of Cu species from Cu(3)P cores into CdSe domains, which triggered sublimation of Cd, as well as out-diffusion of P species and their partial sublimation, together with the overall transformation of the sandwiches into Cu(2)Se nanocrystals. A similar fate was followed by the coral-like structures. These CdSe/Cu(3)P/CdSe nanocrystals are therefore an example of a nanostructure that is thermally unstable, despite its separate components showing to be stable under the same conditions.

A Study on the Deposition of Al2O3 Coatings on Polymer Substrates by a Plasma Spray/Micro-Arc Oxidation Two-Step Method

To increase the wear resistance of polymer matrix composites, alumina coatings were deposited on polymer substrates by a two-step method combining plasma spraying and micro-arc oxidation. The microstructures and phase compositions of the processed coatings were investigated for different treatment times. Uniformly distributed pores were found in addition to the presence of various coral-like structures and floccules on the surface of the coatings. The presence of α-Al2O3 and γ-Al2O3 phases was identified by XRD. The distribution of alumina was analyzed by EDS and is discussed. The maximum bond strength of the coatings was found to be 5.89 MPa. There was little thermal damage in the polymer substrates after the coatings were produced.

Control of cultured human cells with femtosecond laser ablated patterns on steel and plastic surfaces

The purpose of the present study is to explore topographical patterns produced with femtosecond laser pulses as a means of controlling the behaviour of living human cells (U2OS) on stainless steel surfaces and on negative plastic imprints (polycarbonate). The results show that the patterns on both types of material strongly affect cell behaviour and are particularly powerful in controlling cell spreading/elongation, localization and orientation. Analysis by fluorescence and scanning electron microscopy shows that on periodic 1D grating structures, cells and cell nuclei are highly elongated and aligned, whereas on periodic 2D grid structures, cell spreading and shape is affected. The results also show that the density and morphology of the cells can be affected. This was observed particularly on pseudo-periodic, coral-like structures which clearly inhibited cell growth. The results suggest that these patterns could be used in a variety of applications among the fields of clinical research and implant design, as well as in diagnosis and in cell and drug research. Furthermore, this article highlights the noteworthy aspects and the unique strengths of the technique and proposes directions for further research.Electronic supplementary materialThe online version of this article (doi:10.1007/s10544-012-9726-8) contains supplementary material, which is available to authorized users.

Highly sensitive gas sensor based on coral-like SnO2 prepared with hydrothermal treatment

A novel sensor material of SnO2 nanocrystals with coral-like porous structures was prepared via a simple wet-chemical approach combining with an annealing process. The microstructure of obtained SnO2 powders were characterized by X-ray diffraction, scanning electron microscope and nitrogen adsorption–desorption experiment. We also investigated their gas sensing performance toward several volatile organic compounds. The obtained sample is found to show excellent sensing performances to the target ethanol owing to the nano coral-like structure providing many quick passages to absorb and desorb gas. Such an unexpected morphology holds substantial promise for rendering SnO2 as a potential gas sensing material for a broad range of future sensor applications.

Superhydrophobic surface based on a coral-like hierarchical structure of ZnO.

BackgroundFabrication of superhydrophobic surfaces has attracted much interest in the past decade. The fabrication methods that have been studied are chemical vapour deposition, the sol-gel method, etching technique, electrochemical deposition, the layer-by-layer deposition, and so on. Simple and inexpensive methods for manufacturing environmentally stable superhydrophobic surfaces have also been proposed lately. However, work referring to the influence of special structures on the wettability, such as hierarchical ZnO nanostructures, is rare.MethodologyThis study presents a simple and reproducible method to fabricate a superhydrophobic surface with micro-scale roughness based on zinc oxide (ZnO) hierarchical structure, which is grown by the hydrothermal method with an alkaline aqueous solution. Coral-like structures of ZnO were fabricated on a glass substrate with a micro-scale roughness, while the antennas of the coral formed the nano-scale roughness. The fresh ZnO films exhibited excellent superhydrophilicity (the apparent contact angle for water droplet was about 0°), while the ability to be wet could be changed to superhydrophobicity after spin-coating Teflon (the apparent contact angle greater than 168°). The procedure reported here can be applied to substrates consisting of other materials and having various shapes.ResultsThe new process is convenient and environmentally friendly compared to conventional methods. Furthermore, the hierarchical structure generates the extraordinary solid/gas/liquid three-phase contact interface, which is the essential characteristic for a superhydrophobic surface.

The synthesis of zinc oxide nanoparticles from zinc acetylacetonate hydrate and 1-butanol or isobutanol

ZnO nanoparticles of different sizes, from 20 to 200 nm in length, and morphologies, nanorods and coral-like structures, were synthesized via a simple one-pot synthesis by refluxing an oversaturated solution of zinc acetylacetonate hydrate in 1-butanol and isobutanol. On the basis of 1H and 13C NMR experiments, the reactions in both alcohols were found to proceed via the alcoholytic C–C cleavage of the acetylacetonate ligand, followed by the hydrolytic formation of the reactive Zn–OH intermediate from the water molecules present in the precursor hydrate species and/or those released during the condensation cycle. The zinc acetylacetonate conversion into ZnO in isobutanol is significantly slower than in the case when 1-butanol was used as both the medium and the reagent. FE-SEM studies showed that in 1-butanol the growth of the rod-shaped particles occurs via the agglomeration of ZnO primary particles that are less than 10 nm in size. The morphology of the particles formed in the isobutanol is time dependent, with the final coral-like structures developing from initially formed bundle-like structures.

A new lineage of lichenized basidiomycetes inferred from a two‐gene phylogeny: The Lepidostromataceae with three species from the tropics

The lichen habit has apparently evolved independently in at least five major clades of mushroom-forming basidiomycetes (Agaricomycetes). Tracing the origin of lichenization in these groups depends on a clearer understanding of the phylogenetic relationships of basidiolichens to other fungi. We describe here a new family of basidiolichens made up of tropical, soil-inhabiting fungi that form lichenized, scale-like squamules and erect, coral-like fruiting structures. These structures are common to two basidiolichen genera, Multiclavula and Lepidostroma. Molecular studies have confirmed the phylogenetic position of Multiclavula species in the Cantharellales, but Lepidostroma species have never been sequenced. We obtained nuclear small and large subunit ribosomal sequences from specimens of L. calocerum collected in Costa Rica and Mexico and also from specimens of two Multiclavula spp. recently described from Rwanda. The phylogenetic placement of these fungi within the Agaricomycetes was investigated using likelihood and Bayesian analyses. Our results indicate that L. calocerum and the Rwandan species form a natural group unrelated to Multiclavula and sister to the Atheliales, members of which are neither lichen-forming nor clavarioid. The independent evolution of morphologically similar forms in so many groups of basidiomycetes is a remarkable example of convergence, indicating similar pathways to lichenization in these fungi.

Synthesis and characterization of nanocrystalline and mesostructured CeO 2: Influence of the amino acid template

Mesostructured and nanocrystalline cerium oxide materials with a coral-like structure were self-assembled using amino acids as templates. The samples were characterized by N 2-adsorption, XRD, SEM, and Raman spectroscopy. The influence of the amino acid structure and composition on the final CeO 2 nanodomain structure and crystal size was investigated. The XRD and Raman data indicate a direct correlation between the amino and carboxylic group positions in the structure of linear-, branched, and ring-amino acids and the crystal size of CeO 2, which ranges from 6 to 30 nm in diameter. In contrast, the final coral-like nanodomain structures are independent on the amino acid used as template. The results demonstrate a synthetic method for hierarchical architectures in which the final CeO 2 crystal size can be controlled by the use of amino acids in the self-assembly process.

Colloidal aqueous dispersion of polyaniline nanotubes grafted non-covalently with poly(ethylene oxide)-block-poly(acrylic acid) copolymer

Polyaniline (PANI) nanotubes were prepared by oxidative polymerization of aniline in the presence of two structure-directing agents—salicylic acid (SA) and sodium dodecyl sulfate (SDS). When using only SA, mainly aggregated nanotube dendrites or coral-like structures have been obtained. Addition of a very small amount of the surfactant SDS, much less than the critical micelle concentration, results in substantial reduction of the aggregated nanotube morphology on the account of isolated PANI nanotubes, which is the favorable structure from the point of view of further modification. In order to make the isolated nanotubes water dispersible, their surface was modified by complex formation (non-covalent grafting) with hydrophilic poly(ethylene oxide)-block-poly(acrylic acid) copolymer. These water-dispersible PANI nanotubes might be good candidates for some biochemical and biomedical applications.

Carbon whisker formation under fast particle irradiation

The well known synthesis methods for carbon whiskers and carbon nano-tubes are dc arc discharge, laser ablation and catalytic processes. The configurations obtained are strongly influenced by the working conditions such as temperature, pressure and patterning substrates. In the present contribution, we report a simple process where carbon whiskers were produced by MeV D + irradiated graphite. Scanning probe microscopy and X-ray diffraction methods were used to analyze the samples which consist of polished silicon used to collect the ejected matter. The results of the analysis revealed the presence of carbon nanoparticles embedded in a highly heated environment. SEM images clearly illustrate that these materials have highly complex structures. Initially, the carbon whiskers form well-separated spheroidal particles and subsequently transform into coral-like structures through step by step deposition. It is believed that the chaotic environment associated with the irradiation leads to the complex structures obtained. A scenario to explain such unexpected results is proposed.

Scale formation in flash chambers of high-temperature MSF distillers

The general overhaul of a high-temperature (112°C) MSF distiller provided the opportunity for the collection and examination of scales formed on the bottom of the first nine flash chambers. These scales were inspected visually and subjected to wet chemical analysis as well as various spectral investigations. The scales of cells 1–3 were composed exclusively of brucite (Mg(OH) 2), having started as layers and developed with time to become coral-like structures. In cells 4 and 5 the scales acquired a hard glassy texture. In cell 4, the scales were a 50:50 mixture of brucite and anhydrite (CaSO 4). Calcium sulphate constituted the entire deposit in cell 5. The sulphate scale disappeared completely in subsequent cells while in cells 6–9 brucite reappeared with increasing amounts of calcite (CaCO 3). The two theories accounting for the formation of alkaline scales are reviewed in short. These are based on the thermal decomposition of the HCO − 3 ion of seawater to yield CO 2− 3 or OH −, which trigger the precipitation of CaCO 3 and Mg(OH) 2, respectively. Thermodynamic calculations of the free energy changes of the various probable reactions were carried out at 25°C and 100°C, and their implications are discussed. The scaling process cannot be explained purely by thermodynamics, and kinetics must be taken into consideration. A unified theory, that the primary, rate determining-step in HCO − 3 decomposition is the first order reaction — HCO − 3 = OH − + CO 2 — is proposed to explain the variation of scale composition between CaCO 3 and Mg(OH) 2. The resulting OH − can either neutralize a second HCO − 3 ion or react with a Mg 2+ ion, depending on the temperature. These reactions are assumed to have temperature-dependent activation energies. Calcium sulphate can exist in six different modifications. These are the α- and β-(soluble) and insoluble anhydrite (CaSO 4), the α- and β-hemihydrate (CaSO 4.½H 2O) and gypsum (CaSO 4.2H 2O). The free energy changes accompanying the formation of all compounds were computed at 25°C and 100°C. The implications of these figures are discussed, and the concept of scaling threshold is mentioned. A comparison is made between the conditions prevailing in the distiller under consideration and those described in the literature for CaSO 4 precipitation. Sulphate scaling in thermal desalination plants can be surmounted by lowering the operation temperature, by reducing the concentration factor, or by softening seawater. Antiscale agents specific to sulphate deposits have recently been developed and tested on a laboratory scale.

Anaerobic Methane Oxidation and Sulfate Reduction in Bacterial Mats on Coral-Like Carbonate Structures in the Black Sea

A detailed study of the processes of anaerobic methane oxidation and sulfate reduction in the bacterial mats occurring on coral-like carbonate structures in the region of methane seeps in the Black Sea, as well as of the phenotypic diversity of sulfate-reducing bacteria developing in this zone, has been performed. The use of the radioisotopic method shows the microbial mat structure to be heterogeneous. The peak activity of the two processes was revealed when a mixture of the upper (dark) and underlying (intensely pink) layers was introduced into an incubation flask, which confirms the suggestion that methanotrophic archaea and sulfate-reducing bacteria closely interact in the process of anaerobic methane oxidation. Direct correlation between the rate of anaerobic methane oxidation and the methane and electron acceptor concentrations in the medium has been experimentally demonstrated. Several enrichment and two pure cultures of sulfate-reducing bacteria have been obtained from the near-bottom water and bacterial mats. Both strains were found to completely oxidize the substrates to CO2 and H2S. The bacteria grow at temperatures ranging from -1 to 18 (24) degrees C, with an optimum in the 10-18 degrees C range, and require the presence of 1.5-2.5% NaCl and 0.07-0.2% MgCl2 x 6H2O. Regarding the aggregate of their phenotypic characteristics (cell morphology, spectrum of growth substrates, the capacity for complete oxidation), the microorganisms isolated have no analogues among the psychrophilic sulfate-reducing bacteria already described. The results obtained demonstrate the wide distribution of psychrophilic sulfate-reducing bacteria in the near-bottom water and bacterial mats covering the coral-like carbonate structures occurring in the region of methane seeps in the Black Sea, as well as the considerable catabolic potential of this physiological group of psychrophilic anaerobes in deep-sea habitats.

Synthesis of coral-like nickel nanocrystallites via a dipolar-interaction-directed self-assembly process

Coral-like nickel structures composed of polycrystalline nanowires with an average diameter of 100 nm were synthesized via a convenient dipolar-interaction-directed self-assembly process. Studies show that the acicular nanocrystallites may magnetize one another by dipolar interaction in an arbitrary direction, leading to the formation of coral-like structures. It is found that the coercivity ( H c) value of the as-prepared sample (ca. 193 Oe) is higher than that of bulk Ni (100 Oe), which is probably related to the coral-like structures of nickel nanocrystallites.

Catalysed growth of novel aluminium oxide nanorods

Micron-scale coral-like aluminium oxide structures have been generated by heating a mixture of AlB2 and Co powders in a quartz boat at ca. 1050 °C under N2. Upon sonication in acetone, the structures break down into elongated single-crystal aluminium oxide nanorods ranging from 20 to 200 nm in diameter and up to 5 μm in length. Single Co particles are often found attached to nanorod tips. A vapour–liquid–solid (V–L–S) mechanism appears to be responsible for the aluminium oxide nanorod growth.

Phylogenetic diversity of the archaeal component in microbial mats on coral-like structures associated with methane seeps in the Black Sea

With the use of molecular ecology methods, the archaea component of microbial mats on coral-like structures associated with methane seeps occurring at a depth of about 200 m in the Black Sea was investigated without the isolation of pure cultures. Using archaea-specific 16S rRNA-targeted oligonucleotide primes, long fragments of genes were amplified, cloned, and sequenced and their phylogenetic analysis was carried out. It was shown that archaea in microbial mats on coral-like structures are represented by two dominant phylotypes that belong to the kingdoms Crenarchaeota and Euryarchaeota and are not specifically related to any described archaea species. The possible role of the revealed archaea in the process of anaerobic methane oxidation is discussed.

Zinc alloy plating

3,4-dihydro-1,3-2H-benzoxazines as novel one-electron donators for silver(I) ion into nano-metallic silver was firstly found and reported. The silver formation from nano-spherical particles to coral-like and dendrite-like structures was presented. With respect to the characterization results, the feasible reaction mechanism of the silver formation was proposed as an electron donated from benzoxazine to silver(I) ion, resulting in a radical cationic species of benzoxazine and silver(0). Based on this reduction process, a new approach for nano-silver coating on various surfaces such as fumed silica (SiO2), titanium dioxide (TiO2), carbon black (CB), chitosan (CS) including plastic sheet (polycarbonate, PC) and pellet (polyvinyl alcohol, PVA), was also revealed. Besides the nano-silver coated products were applied as antimicrobials fillers for Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633, Micrococcus luteus ATCC 9341, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 2785 and Candida albicans ATCC 10231.