Short Deposition Times Research Articles

Growth of Uranyl Hydroxide Nanowires and Nanotubes by the Electrodeposition Method and Their Transformation to One‐Dimensional U3O8 Nanostructures

AbstractActinide nanomaterials have great potential for application in the fabrication of nuclear fuels and spent fuel reprocessing in advanced nuclear energy systems. In this work, we used track‐etched nanoporous membranes as hard templates to synthesize uranium‐based nanomaterials with new structures by electrodeposition. Through electrochemical behavior investigations and subsequent product characterization, the chemical compositions of the deposition product has been confirmed to be uranyl hydroxide. More importantly, accurate control of the morphologies of the deposition product (i.e., nanowires and nanotubes) could be achieved by carefully adjusting the growth parameters such as deposition time and current density. The preferred morphology of the electrodeposition product was nanowires when a low current density was applied, whereas nanotubes could be formed only when a high current density and a short deposition time were both applied. The formation of nanotubes is attributed to the hydrogen bubbles generated by water electrolysis under the overpotential electroreduction conditions. Additionally, we transformed the main chemical composition of the deposition products from uranyl hydroxide to triuranium octoxide by calcination, and SEM results showed that the morphologies of the nanowires and nanotubes were very well maintained after the calcination. Our work provides a useful protocol for the synthesis of one‐dimensional uranium‐based nanomaterials.

The Initial Stages of Electrodeposition of Re-Ni Alloys

The early stages of Re-Ni alloy deposition from citrate electrolytes were studied in terms of the apparent faradaic efficiency (FE) of the deposition process, the composition of the deposits and their morphology. The deposition time was varied in the range of 0.05 to 60 seconds. The apparent FE of the deposition process was calculated as the ratio between the charge consumed in electrochemical stripping of the deposit and the charge consumed during electrodeposition. The apparent FE and Re-content in the deposits (measured by energy dispersive X-ray spectroscopy) were shown to decrease with deposition time. Anomalous values of the FE, well above 100%, were observed at short deposition times. Under these conditions, the deposition of material consisting of nanoparticles with diameters of 50–80 nm was observed by scanning electron microscopy studies, supporting the anomalous high deposition rates. This behavior is indicative of chemical reactions taking place at short times in parallel with electrodeposition. The effects of deposition time on the apparent FE and Re-content in the deposits are explained by the changes in catalytic activity of the cathode surface during deposition.

Improving the Gas Barrier Property of Clay–Polymer Multilayer Thin Films Using Shorter Deposition Times

Relatively fast exposure times (5 s) to aqueous solutions were found to improve the gas barrier of clay-polymer thin films prepared using layer-by-layer (LbL) assembly. Contrary to the common belief about deposition time (i.e., the longer the better), oxygen transmission rates (OTRs) of these nano-brick-wall assemblies are improved by reducing exposure time (from 1 min to 5 s). Regardless of composition, LbL films fabricated using shorter deposition time are always thicker in the first few layers, which correspond to greater clay spacing and lower OTR. A quadlayer (QL) assembly consisting of three repeat units of branched polyethylenimine (PEI), poly(acrylic acid) (PAA), PEI and montmorillonite (MMT) clay is only 24 nm thick when deposited with 1 min exposure to each ingredient. Reducing the exposure time of polyelectrolytes to 5 s not only increases this film thickness to 55 nm but also reduces the oxygen transmission rate (OTR) to 0.05 cm3/(m2 day atm), which is 2 orders of magnitude lower than the same film made using 1 min exposures. A conceptual model is proposed to explain the differences in growth and barrier, which are linked to polyelectrolyte relaxation, desorption, and interdiffusion. The universality of these findings is further exemplified by depositing clays with varying aspect ratios. This ability to quickly deposit high-barrier nanocomposite thin films opens up a tremendous opportunity in terms of commercial-scale processing of LbL assemblies.

Submicron coating of SiO2 nanoparticles from electrophoretic deposition

Anodic electrophoretic deposition (EPD) of SiO2 nanoparticles is investigated for the formation of submicron coatings. The deposition yield is studied relative to the nature of the working electrode (platinum, silicon wafer) implying de facto some different applied voltage range, the deposition time and the nanoparticle concentration. The composition of the films and the thickness of the deposited material are analyzed by energy dispersive X-ray spectroscopy through X-film software. The kinetic deposition and also the deposition mechanisms are discussed. For short deposition times, the linear Hamaker relation fits the experimental results, which implies that the migration–coagulation step would be the initial deposit mechanism of the silica nanoparticles. For long deposition times, the thickness of the film reaches a saturation value that is dependent on the applied electric field. This phenomenon is mainly due to an increase in the deposit resistance. For low applied voltage, the adhesion and the cohesion of the film obtained by EPD are clearly enhanced by comparison with simple dip-coating. Thin solid films, nearly uniform and crack-free up to 300nm of thickness, are obtained by optimization of the EPD parameters. For high applied voltages, some electrochemical reactions occur towards electrodes during EPD and disturb the deposition of nanoparticles, which limits the final thickness.

One- and two-dimensional cuprous oxide nano/micro structures fabricated on highly orientated pyrolytic graphite (HOPG) by electrodeposition

One- and two-dimensional cuprous oxide (Cu2O) nanostructures were fabricated on highly orientated pyrolytic graphite (HOPG) by electrodeposition in CuSO4 at room temperature (25°C) with no additives. For short deposition times, 1D Cu2O single nanocrystals were generally of an octahedral shape with sizes ranging from 50nm to 400nm, while 2D Cu2O nanowires with diameters ranging from 100nm to 300nm had lengths of more than 100μm. With longer deposition times, microwires were found to have diameters ranging from 1μm to 2μm with lengths up to 60μm, while microcrystals were also produced with sizes 1μm to 6μm. The highly aligned Cu2O nano/microwires were found to be deposited on the step edges of the HOPG substrate. Various crystal morphologies including flower-like and butterfly-like structures, and dendrites and truncated octahedra were observed on the working electrode of HOPG. Some of the morphologies are revealed for the first time by one step electrodeposition and these are confirmed to be single Cu2O crystals.

Growth of InAs quantum dots on Si-based GaAs nanowires by controlling the surface adatom diffusion

InAs/GaAs dots-on-nanowire (NW) hybrid heterostructures are grown on Si substrate by metal organic chemical vapor deposition. The formation of InAs quantum dots (QDs) is intimately associated with the NW density as well as the substrate surface properties, both of which strongly affect the surface adatom diffusion. InAs QDs are realized with a short deposition time by reducing the NW density. The QDs exhibit specific facets and pure zinc blende structure, residing on a wetting layer of several nanometers. Photoluminescence emission from the QDs is observed at room temperature, with a linewidth of 186meV. The results are promising for future integration of III–V NW hybrid devices, especially photovoltaic cells on Si.

Long-term stabilization of sprayed zinc oxide thin film transistors by hexafluoropropylene oxide self assembled monolayers

Surface functionalization of solution processed zinc oxide layers was studied in transistors with bottom-gate bottom-contact configuration aiming at suppression of trapping processes to increase device stability. Saturation of electrically active surface sites and formation of a moisture barrier to decrease the impact of humid atmosphere was successfully shown by binding hexafluoropropylene oxide (HFPO) on the metal oxide semiconductor. Deep trap level related electrical parameters, i.e., stability, hysteresis, and on-set voltage, improved rapidly within 60 s of exposure which was attributed to occupation of sites characterized by low adsorption energies, e.g., at edges. In contrast, shallow trap level related parameters, i.e., mobility, showed a much slower process of improvement. Identical behavior was determined for the contact angle. A physical model is presented by applying first order reaction kinetics equation to Young's law and multiple trapping and release model which relates the dependence of the contact angle and the mobility to the hexafluoropropylene oxide deposition time. Consistent time constants of τ = ≪1 min, 2 min, and 250 min were extracted for mobility and contact angle which implies a direct dependence on the surface coverage. Mobility decreased at short deposition times, recovered at medium deposition times and improved strongly by 2.4 cm2 V−1 s−1 for long deposition times of 1400 min. A microscopic model of these phenomena is given with interpretation of the different time constants found in the experiment.

Bismuth sulfide sensitized TiO2 arrays for photovoltaic applications

We report the use of chemically deposited bismuth sulfide (Bi2S3) for sensitization of TiO2 nanotube arrays (TNA) obtained by electrochemical anodization. Deposition of Bi2S3 onto TNA was carried at 25°C for 20min, 1h and 3h, showing structural changes and different Bi/S ratio at shorter deposition time. The best photocurrent and external quantum efficiency was obtained at 1h. Electrochemical impedance measurements were correlated with the structural, optical, and electronic properties of the sensitized arrays, finding a decisive role of the recombination resistance and chemical capacitance in determining the photoelectrochemical behavior. A three-order of magnitude difference in electron life time (τn) was found in sensitized arrays with different Bi/S ratio, suggestive of the separation of the limiting phenomena inside the oxide (τn=ms) and chalcogenide (τn=s) films.

Formation of Polymer–Ionic Liquid Gels Using Vapor Phase Precursors

We studied a new method for preparing polymer–ionic liquid (IL) gels via deposition of vapor phase precursors onto thin layers of IL. The solubility of 2-hydroxyethyl methacrylate in 1-ethyl-3-methylimidazolium tetrafluoroborate enabled polymerization at both the IL–vapor interface and within the IL layer. We observed a transition from a viscous liquid to a gel with increasing polymer concentration. At short deposition times, there were two distinct molecular weights reflecting polymerization at the IL–vapor interface and within the IL layer, while at longer deposition times the molecular weight distribution within the IL layer broadened. The polymer chains within the IL were orders of magnitude larger than the polymer chains at the IL–vapor interface, and increasing the reactor pressure was shown to increase the molecular weight. Our ability to form high molecular weight polymer chains allows for the formation of gels for utilization as fuel-cell membranes and thin-film transistors.

Sputtering angle effects by Kr mixing in N+ ion beam on the lifetime of nitrided carbon stripper foils

Nitrided carbon stripper (NCS) foils with high nitrogen content were produced by ion beam sputtering of reactive nitrogen gas. Such foils seem to be very useful as strippers in high-intensity heavy ion accelerators. We have conducted comprehensive research, development, and production of such foils with high reproducibility. Krypton, a heavy noble gas, was mixed with the reaction nitrogen gas (IBSRN) in the ion beam sputtering process to produce stripper foils with short sputtering deposition time and long lifetimes in the high intensity ion beam irradiation. With the (N2 + Kr) mixed gas ions we investigated the influence of different sputtering angles (α) on the lifetime of the NCS-foils in case of poly-graphite material. The lifetime measurement of these foils of 20 ± 5 μg/cm2 was performed with a 3.2 MeV Ne+ ion beam as usual. The foils made at a sputtering angle of 15° showed a maximum of 11.0 and 7.5 C/cm2 average charge density, respectively, which corresponded to about 275 and 187 times the lifetime of the best commercially available foils.

Characterization of Polydopamine Thin Films Deposited at Short Times by Autoxidation of Dopamine

Current interest in melanin films derived from the autoxidation of dopamine stems from their use as a universal adhesion layer. Here we report chemical and physical characterization of polydopamine films deposited on gold surfaces from stirred basic solutions at times ranging from 2 to 60 min, with a focus on times ≤10 min. Data from Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical methods suggest the presence of starting (dopamine) and intermediate (C=N-containing tautomers of quinone and indole) species in the polydopamine films at all deposition times. A uniform overlayer analysis of the XPS data indicates that film thickness increased linearly at short deposition times of ≤10 min. At deposition times ≥10 min, the films appeared largely continuous with surface roughness ≈ ≤ 2 nm, as determined by atomic force microscopy (AFM). Pinhole-free films, as determined by anionic redox probe measurements, required deposition times of 60 min or greater.

Correlation between topographic structures and local field emission characteristics of graphene-sheet films

In an early report, some of us have demonstrated that graphene-sheet films prepared by electrophoretic deposition (EPD) method have great potential as high-performance field emission cathode. We report that the field emission performance from such graphene-sheet films may be enhanced. We have investigated the correlation between topographic structures and local field emission characteristics of graphene-sheet films, prepared with changing EPD deposition time. Detailed experiments show that samples prepared with longer deposition time have better field emission performance. Both scanning electron microscopy and high resolution transmission electron microscopy images show that the topographic structure of the surface layer of the samples deposited with longer time is formed with higher density of graphene sheets with shorter length and fewer graphene layers, in comparison with those with shorter deposition times. Such topographic structure is found experimentally to give large field enhancement. Computer simulation further confirms that a thinner graphene sheet will give more significant geometrical field enhancement at the corner of graphene sheet. Theoretical analysis shows that in an EPD process, longer-length graphene sheets will be deposited before shorter ones, explaining why with longer deposition time, the topographic structure of surface layer consists of shorter-length graphene sheets.

Electrochemically active surface area effects on the performance of manganese dioxide for electrochemical capacitor applications

The specific surface area, morphology and electrochemical performance of thin films of electrodeposited manganese dioxide have been examined. Electrodeposition of these films was carried out using chronoamperometry, using times ranging from 10 to 120s in order to obtain deposits with different masses. Using a novel approach to analysing the chronoamperometric i–t data, the specific surface area of the electrodeposited material was found to range from 13 to 67m2/g across the range of deposition times, with short deposition times leading to higher specific surface areas. This has implications on the electrodeposition mechanism of manganese dioxide, which favours crystallite nucleation initially, leading to a high surface area material, followed by growth of these crystallites leading to a denser, lower surface area electrode material. This is the first time that the electrochemically active surface area of porous electrode materials has been determined. This decrease in surface area with deposition time was also reflected in the specific capacitance values of the material, which decreased slightly with increased deposition time, and hence lower surface area.

Dielectric Properties of Boron Nitride in THz Region Synthesized with Nonenergetic CVD

Pyrolytic boron nitride (pBN) was prepared with a nonenergetic chemical vapor deposition. Two tests were performed (i) short time deposition to investigate rate and volume deposition of injected reaction gases and (ii) long time deposition to characterize possible qualitative differences of the formed BN layer. SEM, XRD, FTIR, Raman spectroscopy, and Terahertz time‐domain spectroscopy proved that there are small qualitative differences in the pBN deposited at various distances from the blast pipe. The quality of the phase synthesized was resolved with highly sensitive THz‐TDS technique, the index of refraction npBN varied at 2.0 THz (66.6 cm) from 2.018 ± 0.003 to 2.124 ± 0.005.

Femtosecond pulsed laser deposition of cobalt ferrite thin films

The insertion of different elements in the cobalt ferrite spinel structure can drastically change the electric and magnetic characteristics of CoFe2O4 bulks and thin films. Pulsed Laser Deposition (PLD) is a widely used technique that allows the growth of thin films with complex chemical formula. We present the results obtained for stoichiometric and Gadolinium-doped cobalt ferrite thin films deposited by PLD using a femtosecond laser with 1kHz repetition rate. The structural properties of the as obtained samples were compared with other thin films deposited by ns-PLD. The structural characteristics and chemical composition of the samples were investigated using profilometry, Raman spectroscopy, X-Ray diffraction measurements and ToF-SIMS analysis. Cobalt ferrite thin films with a single spinel structure and a preferential growth direction have been obtained. The structural analysis results indicated the presence of internal stress for all the studied samples. By fs-PLD, uniform thin films were obtained in a short deposition time.

Corrosion protection of electrodeposited multilayer nanocomposite Zn-Ni-SiO2 coatings

Multilayer nanocomposite coatings of Zn-Ni-SiO2 were deposited galvanostatically on mild steel (MS) from Zn-Ni bath, having Zn+2 and Ni+2 ions and uniformly dispersed nano-SiO2 particles. The corrosion characteristics and properties of multilayered nanocomposite (MNC) coatings were evaluated by electrochemical polarization and impedance methods. Such deposition conditions as, bath composition, cyclic cathode current densities (CCCD’s) and number of layers were optimized for peak performance of coatings against corrosion. A significant improvement in the corrosion performance of MNC coatings was observed when a coating was changed from a monolayer to multilayer type. Corrosion rate (CR) of MNC coating decreased progressively with number of layers up to an optimal level, and then started increasing. The increase of CR at a higher degree of layering is attributed to diffusion of layers due to a very short deposition time, failing to give the enhanced corrosion protection. The formation of layers, inclusion of silica particle in MNC coating matrix were confirmed by SEM and XRD study. At optimal current densities, i.e. at 3.0–5.0 A/cm2, the Zn-Ni-SiO2 coating having 300 layers, represented as (Zn-Ni-SiO2)30/5.0/300 is found to be about 107 times more corrosion resistant than a monolayer Zn-Ni-SiO2 coating, developed from the same bath for the same time. The reasons responsible for the extended corrosion protection of MNC Zn-Ni-SiO2 coatings, compared to corresponding monolayer Zn-Ni and (Zn-Ni-SiO2) coatings were analyzed, and results were discussed.

Novel spongelike nanostructured ZnO films: Properties and applications

In this work spongelike nanostructured zinc oxide films are proposed and compared to ZnO vertical nanostructures described in literature in terms of crystalline, optical, electrical and piezoelectric properties. Spongelike nanostructured zinc films were grown by room temperature sputtering processes on different kinds of substrates, and wurzitic zinc oxide nanostructured films were successfully obtained by a subsequent low temperature oxidation treatment. This method allowed growing films with thickness of a few micrometers with relatively short deposition time. In order to provide a comprehensive knowledge of their morphological, structural, optical and functional properties, different kinds of measurements, such as FESEM, TEM, XRD, UV–Vis–NIR spectroscopy and electrical and piezoelectric properties assessment, were performed. The interesting results achieved suggest spongelike ZnO as a promising material for photovoltaic and sensing applications.

Graphite‐Composite Electrodes Bulk‐Modified with (BiO)2CO3 and Bi2O3 Plates‐Like Nanostructures for Trace Metal Determination by Anodic Stripping Voltammetry

AbstractWe describe the preparation of bismutite ((BiO)2CO3) and bismuth‐oxide (Bi2O3) plates‐like nanostructures and their incorporation within graphite‐composite electrodes for the determination of trace metals by anodic‐stripping‐voltammetry. The bismuth nanostructures were produced under microwave‐hydrothermal conditions followed by thermal conversion of as‐prepared precursor and characterized by X‐ray diffraction, Fourier‐transformed infrared and field‐emission scanning‐electron‐microscopy. Graphite‐composite electrodes bulk‐modified with Bi2O3 nanostructures provided higher sensitivity and lower detection limits for determinations of cadmium, lead and zinc (0.26; 0.52; and 2.23 µg L−1, respectively) employing short deposition time (60 s). The results indicate that the modification of graphite‐composite electrodes with Bi2O3 nanostructures improved analytical characteristics of electrochemical sensors for trace‐metal determinations.

Oxygen Concentration Control of Dopamine-Induced High Uniformity Surface Coating Chemistry

Material surface engineering has attracted great interest in important applications, including electronics, biomedicine, and membranes. More recently, dopamine has been widely exploited in solution-based chemistry to direct facile surface modification. However, unsolved questions remain about the chemical identity of the final products, their deposition kinetics and their binding mechanism. In particular, the dopamine oxidation reaction kinetics is a key to improving surface modification efficiency. Here, we demonstrate that high O(2) concentrations in the dopamine solution lead to highly homogeneous, thin layer deposition on any material surfaces via accelerated reaction kinetics, elucidated by Le Chatelier's principle toward dopamine oxidation steps in a Michael-addition reaction. As a result, highly uniform, ultra-smooth modified surfaces are achieved in much shorter deposition times. This finding provides new insights into the effect of reaction kinetics and molecular geometry on the uniformity of modifications for surface engineering techniques.

Electrochemical methods for corrosion testing of Ce-based coating prepared on AA6060 alloy by dip immersion method

Dip-immersion is simple and cost-effective method for the preparation of Ce-based conversion coatings (CeCCs), a promising alternative to the toxic chromate coatings, on the metal substrates. In this work CeCCs were prepared on Al-alloy AA6060 from aqueous solution of cerium chloride at room temperature. Effect of immersion time and post-treatment in phosphate solution on the microstructure and corrosion properties of the coatings was studied. The longer immersion time, the thicker but nonhomogeneous and cracked CeCCs. The post-treatment contributed to the sealing of cracks, as proven by an increase in corrosion resistance compared with as-deposited coatings. CeCCs prepared at longer deposition time and post-treated showed much better corrosion protection than those prepared at short deposition time. A detailed EIS study was undertaken to follow the evolution of corrosion behaviour of CeCCs with time of exposure to aggressive chloride environment (3.5 % NaCl). For the sake of comparison, the EIS properties of bare AA6060 were also investigated. A linear voltammetry was performed to complete the study. Results confirmed a formation of protective CeCCs on AA6060 surface. However, even CeCCs prepared at longer deposition time and post-treated provided a short term protection in aggressive environment, due to the small thickness.