Aqueous Deposition Research Articles

Aqueous chemical solution deposition of lanthanum zirconate and related lattice-matched single buffer layers suitable for YBCO coated conductors: A review

Abstract The main focus of this review article is to present an overview of the present status of the water-based buffer layers for YBa 2 Cu 3 O 7− x coated conductors. In the present time, the development of second generation superconducting YBa 2 Cu 3 O 7− x coated on flexible substrates are attractive for the researchers around the world due to their possible application potential in long distance electric power transmission systems and for high magnetic field applications. For this to be realized, buffer layers are required. They play an important role for the protection of the YBa 2 Cu 3 O 7− x layer coated on top of the flexible substrates. However, people are interested to find an improvement in the buffer layer materials that has the most suitability for the YBa 2 Cu 3 O 7− x superconductors, using low-cost manufacturing processes. In accordance to this, chemical solution deposition is a method that can offer a solution for this problem. This deposition method is highly versatile and cost-effective technique for fabricating buffer layers and YBa 2 Cu 3 O 7− x coated conductors for high performance applications. In effect to that, aqueous methods can additionally offer cost-effective and environmentally-friendly solution. In the following work, the preparation and characterization of buffer layers including that of lanthanum zirconate, lanthanum doped cerium oxide, lattice tuned cerium doped lanthanum zirconate films and non-stoichiometric lanthanum zirconate buffer layers on metallic Ni-5%W substrates using chemical solution deposition (CSD), starting from aqueous precursor solutions is discussed in detail. Their performance in terms of crystallinity, buffer layer action is presented.

Intumescent Multilayer Nanocoating, Made with Renewable Polyelectrolytes, for Flame-Retardant Cotton

Thin films of fully renewable and environmentally benign electrolytes, cationic chitosan (CH) and anionic phytic acid (PA), were deposited on cotton fabric via layer-by-layer (LbL) assembly in an effort to reduce flammability. Altering the pH of aqueous deposition solutions modifies the composition of the final nanocoating. CH-PA films created at pH 6 were thicker and had 48 wt % PA in the coating, while the thinnest films (with a PA content of 66 wt %) were created at pH 4. Each coating was evaluated at both 30 bilayers (BL) and at the same coating weight added to the fabric. In a vertical flame test, fabrics coated with high PA content multilayers completely extinguished the flame, while uncoated cotton was completely consumed. Microcombustion calorimetry confirmed that all coated fabric reduces peak heat release rate (pkHRR) by at least 50% relative to the uncoated control. Fabric coated with pH 4 solutions shows the greatest reduction in pkHRR and total heat release of 60% and 76%, respectively. This superior performance is believed to be due to high phosphorus content that enhances the intumescent behavior of these nanocoatings. These results demonstrate the first completely renewable intumescent LbL assembly, which conformally coats every fiber in cotton fabric and provides an effective alternative to current flame retardant treatments.

Atom Probe Tomography Characterization of Thin Copper Layers on Aluminum Deposited by Galvanic Displacement

″Ultrathin″ metallization layers on the order of nanometers in thickness are increasingly used in semiconductor interconnects and other nanostructures. Aqueous deposition methods are attractive methods to produce such layers due to their low cost, but formation of ultrathin layers has proven challenging, particularly on oxide-coated substrates. This work focused on the formation of thin copper layers on aluminum, by galvanic displacement from alkaline aqueous solutions. Analysis by atom probe tomography (APT) showed that continuous copper films of approximately 1 nm thickness were formed, apparently the first demonstration of deposition of ultrathin metal layers on oxidized substrates from aqueous solutions. The APT reconstructions indicate that deposited copper replaced a portion of the surface oxide film on aluminum. The results are consistent with mechanisms in which surface hydride species on aluminum mediate deposition, either by directly reducing cupric ions or by inducing electronic conduction in the oxide, thus enabling cupric ion reduction by Al metal.

An experimental-theoretical analysis of protein adsorption on peptidomimetic polymer brushes.

Surface-grafted water-soluble polymer brushes are being intensely investigated for preventing protein adsorption to improve biomedical device function, prevent marine fouling, and enable applications in biosensing and tissue engineering. In this contribution, we present an experimental-theoretical analysis of a peptidomimetic polymer brush system with regard to the critical brush density required for preventing protein adsorption at varying chain lengths. A mussel adhesive-inspired DOPA-Lys (DOPA = 3,4-dihydroxy-phenylalanine; Lys = lysine) pentapeptide surface grafting motif enabled aqueous deposition of our peptidomimetic polypeptoid brushes over a wide range of chain densities. Critical densities of 0.88 nm(-2) for a relatively short polypeptoid 10-mer to 0.42 nm(-2) for a 50-mer were identified from measurements of protein adsorption. The experiments were also compared with the protein adsorption isotherms predicted by a molecular theory. Excellent agreements in terms of both the polymer brush structure and the critical chain density were obtained. Furthermore, atomic force microscopy (AFM) imaging is shown to be useful in verifying the critical brush density for preventing protein adsorption. The present coanalysis of experimental and theoretical results demonstrates the significance of characterizing the critical brush density in evaluating the performance of an antifouling polymer brush system. The high fidelity of the agreement between the experiments and molecular theory also indicate that the theoretical approach presented can aid in the practical design of antifouling polymer brush systems.

Copper Layers Deposited on Aluminum by Galvanic Displacement

Metallization layers nanometers to tens of nanometers thick are desirable for semiconductor interconnects, among other technologically relevant nanostructures. Whereas aqueous deposition of such films is economically attractive, fabrication of continuous layers is particularly challenging on oxidized substrates used in many applications. Here it is demonstrated that galvanic displacement can deposit thin adherent copper layers on aluminum foils and thin films from alkaline copper sulfate baths. According to scanning electron microscopy and quartz crystal microbalance measurements, the use of relatively low CuSO4 concentrations produced films composed of copper nanoparticles overlying a uniform continuous copper layer on the order of nanometers in thickness. It seems that there are no precedents for such thin layers formed by aqueous deposition on oxidized metals. The thin copper layers are explained by a mechanism in which copper ions are reduced by surface aluminum hydride on Al during alkaline dissolution.

Aqueous deposition of calcium phosphates and silicate substituted calcium phosphates on magnesium alloys

Abstract Attempts were made to deposit homogeneous films of calcium phosphates (CaPs) on two magnesium alloy systems, AZ31 and Mg–4Y, through an aqueous phosphating bath method. The deposition of silicate substituted CaPs by this aqueous method was also explored as silicate substitution is believed to increase the bioactivity of CaPs. The effect of doped and undoped coatings on the in vitro degradation and bioactivity of both alloy systems was studied. FTIR and EDX confirmed the deposition of Ca, P, and Si on both alloys and the coatings appeared to consist primarily biphasic mixtures of hydroxyapatite and β-TCP. These largely inhomogeneous coatings, as observed by SEM, were not shown to have any significant effect on maintaining the physiological pH of the culture medium in comparison to the uncoated samples, as the pH remained approximately in the 8.4–8.7 range. Interestingly, despite similar pH profiles between the coated and uncoated samples, CaP coatings affected the degradation of both alloys. These doped and undoped calcium phosphate coatings were observed to decrease the degradation of AZ31 whereas they increased the degradation of Mg–4Y. In vitro studies on cell attachment using MC3T3-E1 mouse osteoblasts showed that between the uncoated alloys, Mg–4Y appeared to be the more biocompatible of the two. Silicate substituted CaP coatings were observed to increase the cell attachment on AZ31 compared to bare and undoped CaPs coated samples, but did not have as great of an effect on increasing cell attachment on Mg–4Y.

Efficiency Improvement of Solar Cell with ZnO Nanotip Array Prepared by Aqueous Solution Deposition

ZnO nanotips were synthesized on a sputtered ZnO buffer layer/ITO/glass by aqueous solution deposition with precursors of zinc nitrate and ammonia. Growth direction of ZnO nanotips can be controlled by the thickness of sputtered ZnO buffer layer. The average height of 13 μm was obtained at 70 °C for 24 hr and the diameter of ZnO nanotips was ranged from 60 nm to 100 nm.

Superpixel segmentation for analysis of hyperspectral data sets, with application to Compact Reconnaissance Imaging Spectrometer for Mars data, Moon Mineralogy Mapper data, and Ariadnes Chaos, Mars

[1] We present a semiautomated method to extract spectral end-members from hyperspectral images. This method employs superpixels, which are spectrally homogeneous regions of spatially contiguous pixels. The superpixel segmentation is combined with an unsupervised end-member extraction algorithm. Superpixel segmentation can complement per pixel classification techniques by reducing both scene-specific noise and computational complexity. The end-member extraction step explores the entire spectrum, recognizes target mineralogies within spectral mixtures, and enhances the discovery of unanticipated spectral classes. The method is applied to Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) images and compared to a manual expert classification and to state-of the-art image analysis techniques. The technique successfully recognizes all classes identified by the expert, producing spectral end-members that match well to target classes. Application of the technique to CRISM multispectral data and Moon Mineralogy Mapper (M3) hyperspectral data demonstrates the flexibility of the method in the analysis of a range of data sets. The technique is then used to analyze CRISM data in Ariadnes Chaos, Mars, and recognizes both phyllosilicates and sulfates in the chaos mounds. These aqueous deposits likely reflect changing environmental conditions during the Late Noachian/Early Hesperian. This semiautomated focus-of-attention tool will facilitate the identification of materials of interest on planetary surfaces whose constituents are unknown.

Biomimetic formation of Titania Thin Films: Effect of Amino Acids on the Deposition Process

Different types of amino acids have been used as additives to control the aqueous deposition of titanium dioxide thin films on single-crystal Si wafers. Thin titania films can be obtained through a chemical bath deposition (CBD) process using TiCl₄ as a precursor in an aqueous solution at temperatures below 100 °C. The addition of amino acids to the deposition solution was shown to reduce the thickness and roughness of the films and to increase their density. These protein building blocks were employed to modify the deposition rate as well as the size of aggregates that form the film. The thickness, crystallinity, morphology and composition of the grown films were characterized by a variety of techniques, including XRD, XPS, AFM and SEM. The consequences of the type of the amino acid additive (and its concentration in the solution) on the microstructural evolutions of the deposed films are thus revealed and discussed on the basis of the organic-inorganic interactions in solution and at the film surface.

Electrodeposition of Semiconductor n-CdTe and p-CdTe in Aqueous Medium and Aluminum Metal in a Nonaqueous Medium

Both n-type and p-type semiconductor CdTe were synthesized by electrodeposition from an aqueous deposition bath. Electrodeposition potential was found to be the key factor to synthesize the CdTe semiconductor of any specific conductivity type. The electrodeposition potentials of -0.4 V and 0.4 V versus Ag/AgCl generated the p-type and n-type CdTe respectively. The optimum deposition time was found to be 90 minutes for the best photoresponce of CdTe during water-splitting reaction. The indirect band gap energy of CdTe was found tunable from 1.55 to 2.00 eV by controlling both electrodeposition potential and the annealing time. Crystalline aluminum metal was deposited on a platinum electrode tip at room temperature in a non-aqueous deposition bath of anhydrous toluene containing aluminum bromide and the supporting electrolyte, tetra butyle ammonium bromide. Anhydrous condition was found to be the critical factor for the success of electrodeposition and production of aluminum metal at room temperature in a non-aqueous deposition bath.

Columbus crater and other possible groundwater-fed paleolakes of Terra Sirenum, Mars

Columbus crater in the Terra Sirenum region of the Martian southern highlands contains light-toned layered deposits with interbedded sulfate and phyllosilicate minerals, a rare occurrence on Mars. Here we investigate in detail the morphology, thermophysical properties, mineralogy, and stratigraphy of these deposits; explore their regional context; and interpret the crater's aqueous history. Hydrated mineral-bearing deposits occupy a discrete ring around the walls of Columbus crater and are also exposed beneath younger materials, possibly lava flows, on its floor. Widespread minerals identified in the crater include gypsum, polyhydrated and monohydrated Mg/Fe-sulfates, and kaolinite; localized deposits consistent with montmorillonite, Fe/Mg-phyllosilicates, jarosite, alunite, and crystalline ferric oxide or hydroxide are also detected. Thermal emission spectra suggest abundances of these minerals in the tens of percent range. Other craters in northwest Terra Sirenum also contain layered deposits and Al/Fe/Mg-phyllosilicates, but sulfates have so far been found only in Columbus and Cross craters. The region's intercrater plains contain scattered exposures of Al-phyllosilicates and one isolated mound with opaline silica, in addition to more common Fe/Mg-phyllosilicates with chlorides. A Late Noachian age is estimated for the aqueous deposits in Columbus, coinciding with a period of inferred groundwater upwelling and evaporation, which (according to model results reported here) could have formed evaporites in Columbus and other craters in Terra Sirenum. Hypotheses for the origin of these deposits include groundwater cementation of crater-filling sediments and/or direct precipitation from subaerial springs or in a deep (∼900 m) paleolake. Especially under the deep lake scenario, which we prefer, chemical gradients in Columbus crater may have created a habitable environment at this location on early Mars.

From nanowires to hierarchical structures of template-free electrodeposited ZnO for efficient dye-sensitized solar cells

A new and original method for the electrochemical growth of ZnO nanocrystalline porous layers and multiscale hierarchical structures is described. The structures are designed by simply playing with the growth conditions and without any use of template or additive in the aqueous deposition bath. Two types of hierarchical structures are described combining electrodeposited ZnO nanowire arrays and a nanoporous layer: nanowire arrays covered by a conformal nanoporous layer and nanowire arrays embedded in a nanoporous layer. The global performances of dye sensitized solar cells (DSSCs) fabricated using the hierarchical structures are higher than those found for nanoparticulate sol–gel ZnO films and for the two basic electrodeposited structures. Films made of nanowires embedded in a nanocrystalline matrix show a maximum energy conversion efficiency of ∼4.1%. The wires play several important beneficial roles in the presented structures since they permit the electrodeposition of thick nanoporous ZnO films which immobilize a large amount of dye, they act as preferential electron pathways for efficient charge collection and, due to their size, they enhance the light trapping in the photoanode and hence increase the light diffusion length before its harvesting by the dye. Another interest of the proposed ZnO hierarchical structures is a synthesis as well as an applied post-growth thermal treatment performed below 150 °C in soft environments which are then perfectly compatible with lightweight plastic flexible and other fragile substrates.

Gold/silicon nanocomposites: synthesis, characterization, and application in detection of dopamine

Silicon nanowires (SiNWs) with the length of several hundreds of micrometers and an average diameter of 15 nm were successfully synthesized via a thermal-evaporation oxide-assisted process. Then, a convenient method was applied to metallize the SiNWs just by dipping them into an aqueous deposition solution. During the metallization process, which is a redox reaction, gold nanoparticles (NPs) were prepared on SiNWs surface to confine the particle size and prevent agglomeration during the preparation and utilization of gold NPs. The synthesized SiNWs decorated with gold NPs were utilized to modify the glassy carbon electrode. Electrochemical measurements displayed that the modified electrode showed high sensitivity for dopamine (DA) detection.

Carbon Nanotube/Manganese Oxide Ultrathin Film Electrodes for Electrochemical Capacitors

Multiwall carbon nanotube (MWNT)/manganese oxide (MnO2) nanocomposite ultrathin film electrodes have been created via redox deposition of MnO2 on layer-by-layer (LbL)-assembled MWNT films. We demonstrate that these LbL-assembled MWNT (LbL-MWNT)/MnO2 thin films consist of a uniform coating of nanosized MnO2 on the MWNT network structure using SEM and TEM, which is a promising structure for electrochemical capacitor applications. LbL-MWNT/MnO2 electrodes yield a significantly higher volumetric capacitance of 246 F/cm3 with good capacity retention up to 1000 mV/s due to rapid transport of electrons and ions within the electrodes. The electrodes are generated with two simple aqueous deposition processes: the layer-by-layer assembly of MWNTs followed by redox deposition of MnO2 at ambient conditions, thus providing a straightforward approach to the fabrication of high-power and -energy electrochemical capacitors with precise control of electrode thickness at nanometer scales.

Bioinspired Deposition of TiO2 Thin Films Induced by Hydrophobins

The deposition of ceramic thin films from aqueous solutions at low temperature using biopolymers as templates has attracted much attention due to economic and environmental benefits. Titanium dioxide is one of the most attractive functional materials and shows a wide range of applications across vastly different areas because of its unique chemical, optical, and electrical properties. In the present work, we deposited smooth, nanocrystalline titania thin films by an aqueous deposition method on surface active and amphipathic proteins of fungal origin called hydrophobins. Initially, the hydrophobin molecules were self-assembled on a silicon substrate and characterized by angle-resolved X-ray photoelectron spectroscopy (AR-XPS), atomic force microscopy (AFM) and surface potential measurements. Thin films of titanium dioxide were deposited on the surface of hydrophobin self-assembled monolayers from aqueous titanium(IV) bis(ammonium lactate) dihydroxide solution at near-ambient conditions. The microstructure of the as-deposited films was analyzed by AFM, scanning and transmission electron microscopy, which revealed the presence of nanocrystals. The titania films were also characterized using AR-XPS and Fourier transform infrared spectroscopic (FTIR) techniques. Appropriate mechanisms involved in film deposition are suggested. Additionally, nanoindentation tests on as deposited titania films showed their high resistance against mechanical stress.

The synthesis of polyacrylonitrile/carbon nanotube microspheres by aqueous deposition polymerization under ultrasonication

Polyacrylonitrile (PAN)/carbon nanotube (CNT) microspheres with diameters approximately 300–500 nm were synthesized by aqueous deposition polymerization under ultrasonication. A new absorption band appeared in the Fourier transform infrared spectrum of the PAN/CNT microspheres indicated that the functionalized CNTs interacted chemically with the itaconic acid on the PAN macromolecules. The results from the UV–vis and Raman spectra suggested that the functionalized CNTs and PAN macromolecules had interfacial interaction. The peak shift for the radical breathing modes in Raman spectra indicated that the functionalized CNTs were debundled by the PAN macromolecules during polymerization under ultrasonication. X-ray diffraction data showed that the PAN/CNT microspheres had higher degree of crystallization and larger crystal size than those of PAN, which was confirmed by the second exothermic peak of the differential scanning calorimeter scan in a nitrogen atmosphere. Thermogravimetric analysis showed that the addition of the functionalized CNTs improved the thermal stability of PAN.

Effect of P addition on the thermal stability and electrical characteristics of NiSi films

Immersion Ni–P deposition is undoubtedly one of the most important catalytic deposition process, due to its simplicity in operation and low equipment cost. In this study, immersion deposited Ni–P films were used to form Ni-silicide films. Ni–P films with a thickness of 100nm were fabricated by immersing Si(100) substrates in an aqueous deposition solution. Ni-silicide films were then formed by annealing the samples in a furnace at temperatures ranging from 400°C to 900°C for 1h in an argon ambient. Experimental results indicate that a phosphor addition in Ni films increased the transformation temperature of NiSi to NiSi2 to 900°C. Moreover, the feasibility of enhancing the thermal stability of NiSi by varying the interface energy at the NiSi2/Si interface and the surface energy of a Ni–P–Si capping layer on the NiSi surface is discussed.

Preparation of a SERS substrate and its sample-loading method for point-of-useapplication

A simple approach was demonstrated to prepare a silver (Ag) nanoparticle(NP) assembly as a SERS substrate. Just by dipping a flat silicon (Si)wafer into an aqueous deposition solution of hydrogen fluoride (HF) + silvernitrate (AgNO3), a monolayer of Ag NPs was uniformly deposited onto the Si wafer surface. In order toload the to-be-detected sample onto the as-prepared SERS substrate, three methodshave been individually tested, (i) by incubating the SERS substrate in the samplesolution, (ii) by dropping and drying a small volume of the sample solution (1–2 µl) onto the SERS substrate surface, or (iii) by directly introducing the sample into thedeposition solution. The last approach was also employed to metalize a Si nanowire(NW). Due to the NW’s highly curved surface, the Ag NPs self-assembled andaggregated along the NW with a close interdistance. The aggregated Ag NPs on theNW surface can also be used as a SERS substrate. The demonstrated approachholds the promise to prepare a fresh SERS substrate at the point-of-use with thesample already loaded to promptly collect the SERS signal for the field application.

Metallization of Silicon Nanowires and SERS Response from a Single Metallized Nanowire

A simple method was demonstrated to metallize silicon (Si) nanowire (NW) just by dipping it into an aqueous deposition solution for several minutes. During the metallization process, metal ions were reduced and deposited on the top of the Si NW (where surface Si was oxidized). The surface silicon oxide was simultaneously dissolved and removed by hydrogen fluoride (HF), so that the deposition reaction was sustainable and controllable. The deposited silver (Ag) nanoparticles (NPs) uniformly self-assembled along the Si NW and developed into a metal covering with the NW as its core. Not only Ag+ but also Cu2+, Pd2+, Co2+, Au3+, and Pt4+ were deposited to metallize the Si NW using the simplified metallization process. Applications of the new nanocomposite materials were also explored. When the resulting Ag NP/Si NW was tested as a surface-enhanced raman scattering (SERS) substrate, an extremely strong signal was observed and a detection limit of ∼600 molecules or 200−300 Ag NPs per laser spot was reached. The ...

Spectral and thermodynamic constraints on the existence of gypsum at the Juventae Chasma on Mars

The spectral imaging of the Mars obtained with the Mars Express/OMEGA experiment demonstrates that a majority of the sulfates-rich regions are associated with the interior light-toned layered deposits within the canyon system in the equatorial zone of the planet. While all sulfates-rich deposits inside the canyons are characterized by the presence of the kieserite and hydrated magnesium sulfates, the spectral features of gypsum were detected only in the Juventae Chasma and the Iani Chaos. The detection of gypsum in the upper part of the layered deposits, stacking the erosional remnant on the floor of the Juventae Chasma (above the spectral signature of the kieserite and polyhydrated sulfates detected on the flanks of the remnant) represents a more intriguing case. To clarify the question of the presence of gypsum in the Juventae Chasma, we present reanalyzed OMEGA spectra within that area and performed the chemical equilibrium modelling of sulfates precipitation sequence at the freezing and the evaporation of a hypothetical aqueous solution which could have existed within the Chasma in the past. Our results did not confirm the presence of distinct spectral signatures of gypsum. The results of equilibrium modelling also exclude significant precipitation of gypsum during the latest stage of the aqueous sedimentation, responsible for the formation of the upper part of the erosional remnant.