Number Of Deposition Cycles Research Articles

Correlated effects of preparation parameters and thickness on morphology and optical properties of ZnO very thin films

Nano-granular ZnO layers have been grown using a sol–gel synthesis and spin-coating deposition process. Thin films with thicknesses ranging from 15 to 150nm have been obtained by varying the number of deposition cycles and prepared with different synthesis conditions. Morphologies and optical properties have been carefully investigated by joint spectroscopic ellipsometry and atomic force microscopy. A correlation between the evolution of optical properties and grains morphology has been observed. It is shown that both synthesis temperature and concentration similarly allow us to change the correlated growth and properties evolution rate. Thickness variation associated to choice of synthesis parameters could be a useful way to tune morphology and optical properties of the nanostructured ZnO layers.

Electrochemical Deposition of Pt Nanoclusters on WC for Hydrogen Evolution Reaction in Acid

Water splitting by electrolysis is an effective and renewable way to produce hydrogen fuel from acid or alkaline electrolytes. Presently, alkaline water electrolyzers are being the most widely employed, largely due to the use of low-cost catalysts. Yet, there is strong interest for expanded use of acid water electrolyzers in future because of better device performance than the alkaline. In this work, we explore and develop new fabrication techniques that could minimize the use of the Pt catalyst that is highly active, but too expensive to be used for hydrogen evolution reaction (HER) in acid water electrolyzers. Of our particular interest is to grow Pt monolayer films and nanostructures on tungsten carbide (WC) supports by electrodeposition. Fig. 1 shows Pt deposition as a function of applied potential from a NaCl-supporting electrolyte. An interesting finding is that the deposition of Pt is prevented at potentials below -0.5 V, in spite of high driving forces for Pt clusters to form and grow. This talk will present ways in which this anomalous deposition behavior can be exploited for preparing novel Pt catalysts. A brief summary will be given for Pt deposition on Au [[1]] and Ni [[2]] electrodes where a monolayer-thick Pt film is deposited at -0.8 V but additional growth is quenched. For WC substrates, we will discuss challenges associated with the lack of Pt depositing at -0.80 V, before introducing to a new approach that is developed to facilitate the formation of Pt nuclei. The proposed method involves cycling the potential between -0.8 V and -0.45 V at a fast rate of 50 mV/s. As shown in Fig. 2, Pt nanoclusters with high particle density could be grown on WC, and their average size is about 5 nm. To gain mechanistic insights on Pt nanostructure nucleation and growth, the deposits were analyzed using scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and underpotentially deposited (UPD) hydrogen and copper. Correlations between deposition potential cycle and particle growth and particle density will be discussed. Finally, Pt deposits were examined as catalysts for HER in 0.5 M sulfuric acid. The dependence of HER activity on the number of deposition cycles is shown in Fig. 3 where the HER activity approaches that of bulk platinum as the deposition cycles increase even though the expected total amount of platinum is far less than a complete coverage. This work illustrates that electrodeposition provides a simple and scalable way for preparing Pt nanocluster/WC catalysts, which exhibit high activity and durability toward HER in acid media. [1] Y. Liu, D. Gokcen, U. Bertocci, T. P. Moffat, Science, 338, 1327 (2012). [2] Y. Liu, C. M. Hangarter, D. Garcia, T. P. Moffat, Surf. Sci. (2014) dx.doi.org/10.1016/j.susc.2014.06.002 Figure 1

Ultrathin hematite film for photoelectrochemical water splitting enhanced with reducing graphene oxide

Ultrathin hematite films have been prepared on FTO using a separated two-phase hydrolysis–solvothermal reaction. The film thickness can be controlled by the number of deposition cycles. The Photoanode based on hematite film with 7 deposition cycles generated a photocurrent of 0.61 mA cm−2 at +1.5 V vs. RHE. The photocurrent can be improved by coating a layer of reducing graphene oxide (RGO) through spin coating. The enhanced performance is attributed to the promoting effects of RGO which acted as hole collector and transporter in the electrodes. This research demonstrates that graphene can be used as an alternative co-catalyst to enhance photoelectrochemical water splitting activity of ultrathin hematite film. The as-prepared photoanodes were notably stable under water oxidation conditions.

Preparation of SnS quantum dots for solar cells application by an in-situ solution chemical reaction process

SnS quantum dots (QDs) with size of 8nm were synthesized by an in-situ room temperature solution chemical reaction process. Stannous chloride, as Sn precursor, was coated on the TiO2 photo-anodes to form a solid precursor film. Ammonium sulfide was dissolved into ethanol to form anionic reaction solution. SnS quantum dots were generated by immersing the Sn-coated TiO2 photo-anodes into the anionic solution. The structure, morphology and optical absorption properties of the SnS/TiO2 photoanodes were investigated by means of XRD, SEM, TEM and UV–vis measurements. The photovoltaic properties of the SnS QDs sensitized TiO2 solar cells were optimized by changing the number of deposition cycles of the SnS QDs. It turns out that the SnS/TiO2 solar cell with 20 deposition cycles exhibited the best photovoltaic performance with an open-circuit voltage Voc of 510mV, a short-circuit current density Jsc of 2.41mA, a fill factor FF of 0.49 and a power conversion efficiency η of 0.61% under AM 1.5 illumination. This result is interpreted in terms of minimization of the charge transfer resistance. The performance will drop for further deposition because the charge transfer resistance will increase due to QDs agglomeration.

Synthesis and Photo-Response of CuS Thin Films by an In Situ Multi-Deposition Process at Room Temperature: A Facile and Eco-Friendly Approach

Uniform hexagonal covellite CuS thin films were deposited at room temperature by an in situ solution chemical reaction using copper precursor solid films as cationic source and ammonium sulfide ethanol solution as anionic reaction medium. We investigated the influence of both ethanolamine and butanol contents used in copper nitrate/ethylene glycol monomethylether (EGME) cationic solution for the preparation of copper precursor solid films, deposition cycle numbers and annealing treatment of the as-grown thin films by X-ray diffraction (XRD), FESEM, energy dispersive X-ray fluorescence EDX, transmission electron microscopy–Selected area electronic diffraction (TEM–SAED), atomic force microscopy (AFM) and ultraviolet-visible-near-infrared (UV-Vis–NIR) measurements. Photo-response of the CuS thin films was characterized by linear sweep voltammetry. The deposited CuS thin films were used to sensitize TiO 2 anodes for solar cell application. The results showed that the CuS films had two-dimension oriented, half-sheet shaped growing morphology standing disorderly but vertically to substrates, and the calculated texture coefficient TC(102) verified that the half-sheet shaped crystallites had (102) plane orientation. This in situ multi-deposition process had an average deposited rate of 9 nm per cycle, and a self-perfect function to grow smooth, uniform and 2D oriented morphology with increase in the dip-cycle numbers. The photocurrent density was 14.5 Ma/cm2 at 1 V versus Ag / AgCl electrode for the annealed CuS thin films. CuS -sensitized TiO 2 solar cells had a maximum conversion efficiency of 0.224%.

Layer-by-layer assembly of manganese–cobalt–nickel oxide nanosheets/graphene composite films

Two different nanosheets, poly(diallyldimethylammonium chloride)-functionalized graphene nanosheets (FRGO) and manganese–cobalt–nickel oxide nanosheets (MnCoNiO2) are used as building blocks for the assembly of manganese–cobalt–nickel oxide nanosheets/graphene composite films (MnCoNiO2–FRGO). Sequential adsorption of these oppositely-charged nanosheets yields multilayer films, whereas simple mixing produces a lamellar flocculate. UV–visible spectra exhibit a progressive increase of absorbance with increasing number of deposition cycles, providing strong evidence for the regular growth of multilayer films. The combination of FRGO and MnCoNiO2 nanosheets produces a new layered structure with a planar spacing of 2.36nm, which is in agreement with the sum of the thicknesses of MnCoNiO2 and FRGO nanosheets. The MnCoNiO2–FRGO composite films show a higher specific capacitance and good electrochemical stability because of a synergistic effect existed between the FRGO nanosheets and MnCoNiO2 nanosheets.

On the electrochemical synthesis and charge storage properties of WO3/polyaniline hybrid nanostructures

The aim of this study is to tailor the electrochemical synthesis of hybrid materials consisting of nanoporous tungsten trioxide (WO3) and polyaniline (PANI) for application as supercapacitor electrodes. Nanoporous WO3, synthesized by the anodization of tungsten foils, acted as the active material framework for this assembly. With the variation of the anodization voltage, host materials with different morphological features were prepared. Subsequently, electrodeposition of PANI was carried out by potentiodynamic cycling in highly acidic media. Through alteration of the number of deposition cycles, the amount of deposited PANI was varied. This parameter had a decisive impact on the morphology of the resulting hybrids as confirmed by SEM images. Cyclic voltammetry and galvanostatic charge–discharge measurements were carried out to characterize the charge storage properties of the synthesized hybrids. By comparing electrochemical data with structural properties, structure–property relationships were established, and under optimal conditions, 350 F g−1 and 200 mF cm−2 were obtained.

Some Features of CdS/CdSe Quantum Dot‐sensitized Solar Cell Incorporating Carbon Nanotubes#

Quantum dot‐sensitized solar cells (QDSSCs) were synthesized using CdS and CdSe quantum dots (QDs) incorporated onto one‐dimensional ZnO nanorods by successive ionic layer adsorption. In order to get the highest performance of the synthesized cell, the concentration of precursor QD solution and the number of deposition cycles in the QD solution were varied together. The photovoltaic performance of each cell was compared with the ultraviolet/visible absorption spectra and incident photon to current efficiency graphs. QDSSCs incorporating single‐walled carbon nanotubes (SWNTs), sprayed onto the substrate before deposition of the next layer, exhibited enhanced or decreased photocell efficiency compared to that of the pristine cell. In particular, a maximum rate increase of 17% was obtained with the solar cell containing SWNTs in CdSe QDs.

Platinum–Ruthenium Heterogeneous Catalytic Anodes Prepared by Atomic Layer Deposition for Use in Direct Methanol Solid Oxide Fuel Cells

Heterogeneous Pt–Ru catalysts are synthesized by atomic layer deposition (ALD) of Ru onto a porous Pt mesh and employed as the anode in direct methanol solid oxide fuel cells (DMSOFCs). The degree of Ru coverage is controlled by the number of deposition cycles employed in catalyst preparation; samples are prepared using 50, 100, 200, 300, and 400 cycles. The dispersed nature of the ALD Ru coating is confirmed by auger electron spectroscopy and high-resolution transmission electron microscopy. DMSOFC performance is measured at several temperatures between 300 and 450 °C. Optimal ALD Ru coverage results in DMSOFC power and electrode impedance values close to ones from SOFCs with Pt electrodes running on hydrogen. Thermal stability is also improved significantly, preventing agglomeration of the Pt mesh. X-ray photoelectron spectroscopy is used to analyze the chemical properties of the surface and confirms that increased ALD Ru coverage results in a dramatic reduction in the amount of surface-bound carbon mon...

Optically monitored spray coating system for the controlled deposition of the photoactive layer in organic solar cells

A spray deposition process equipped with an in situ optical thickness monitoring system has been developed to fabricate the photoactive layer of solar cells. Film thickness is monitored by a photodiode–LED couple after each deposition cycle. Using optimized conditions, the thickness of the spray deposited photoactive films can be tuned to increase linearly with the number of deposition cycles over a wide range of deposition conditions. After instrument calibration, optimization of the active layer thickness can be accomplished by simply setting the desired absorbance of the film. The simple process outlined here may be used for the rapid optimization of thin film photovoltaic devices. As proof of this, we fabricate a poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester as well as a P3HT and indene-C60 bis-adduct organic solar cells, which achieve a champion power conversion efficiency of 4.2%.

Thermal annealing of sequentially deposited SnS thin films

The influence of thermal treatment with the number of deposition cycles on the properties of SnS films on CdS and ZnS substrates was investigated. Annealing under an argon atmosphere made amorphous SnS films formed in one deposition cycle crystalline, but did not markedly change the crystallinity of SnS films formed after multiple deposition cycles. All annealed films were consistent with the orthorhombic phase of herzenbergite SnS, and no additional Sn-containing phases were identified. The CdS/SnS films maintained their initial stoichiometric composition of tin monosulphide after annealing. The films deposited on ZnS substrate films were rich in tin and poor in sulphur and their composition was unaffected by thermal annealing. Both the deposited and thermally annealed films possessed uniform pinhole-free surfaces. Only minor changes in the optical transmittance and reflectance spectra of the CdS/SnS films were observed after annealing, whereas the spectra of the ZnS/SnS films exhibited substantial changes after annealing. As the annealing temperature increased, the absorption edge of the ZnS/SnS films shifted to a longer wavelength. The optical bandgap of the CdS/SnS films was indirect and decreased from 1.28 eV for the three-deposition- cycle CdS/SnS film to 1.22 eV after annealing at 460 °C. The ZnS/SnS films showed a similar change: the bandgap of 1.39 eV for the unannealed films decreased to 1.23 eV after annealing. All deposited and annealed SnS films showed p-type conductivity and their photoconductivity increased with the increasing annealing temperature. Solar cells with reverse structures were fabricated; their performance decreased with the increasing annealing temperature of the SnS film.

Co3O4-modified TiO2 nanotube arrays via atomic layer deposition for improved visible-light photoelectrochemical performance.

Composite Co3O4/TiO2 nanotube arrays (NTs) were fabricated via atomic layer deposition (ALD) of Co3O4 thin film onto well-aligned anodized TiO2 NTs. The microscopic morphology, composition, and interfacial plane of the composite structure were characterized by scanning electron microscopy, energy dispersion mapping, X-ray photoelectron spectra, and high-resolution transmission electron microscopy. It was shown that the ultrathin Co3O4 film uniformly coat onto the inner wall of the high aspect ratio (>100:1) TiO2 NTs with film thickness precisely controlled by the number of ALD deposition cycles. The composite structure with ∼4 nm Co3O4 coating revealed optimal photoelectrochemical (PEC) performance in the visible-light range (λ > 420 nm). The photocurrent density reaches as high as 90.4 μA/cm(2), which is ∼14 times that of the pristine TiO2 NTs and 3 times that of the impregnation method. The enhanced PEC performance could be attributed to the finely controlled Co3O4 coating layer that enhances the visible-light absorption, maintains large specific surface area to the electrolyte interface, and facilitates the charge transfer.

Deposition and characteristics of bismuth sulfide thin films by an in situ chemical reaction process at room temperature: a facile and eco-friendly approach

Uniform, smooth and densely packed Bi2S3 thin films were prepared at room temperature by an in situ solution chemical reaction using bismuth nitrate as precursor in a form of thin solid film which was reacted with ammonium sulfide ethanol solution. Bi2S3 thin films both as-deposited and annealed at different temperatures were characterized by XRD, SEM, EDS, AFM, UV–Vis–NIR and LSV measurements. The thin films growth with deposition cycle numbers was investigated. The results showed that the as-deposited Bi2S3 thin films were almost amorphous and near to chemical stoichiometry. The annealing promoted crystallization to orthorhombic structure as well as crystal growth from very small particles to short-rod shaped nanocrystals. The optical band-gap energy was in the range of 1.34–1.69 eV depended on crystal size on films. The eight dip-cycles Bi2S3 films annealed at 300 °C had a better photoelectrochemical performance with photocurrent density of 5.03 mA/cm2 bias 0.5 V vs. Ag/AgCl reference electrode. This in situ deposition had an average deposited rate of 40 nm per cycle and a self-perfect function to grow smooth with increase of dip-cycle numbers.

Non-noble metal copper nanoparticles-decorated TiO2 nanotube arrays with plasmon-enhanced photocatalytic hydrogen evolution under visible light

Cu nanoparticles (Cu NPs) were successful deposited on the TiO2 nanotube arrays (TNAs) through pulsed electrochemical deposition method. By adjusting the number of deposition cycles, the amount of Cu NPs can be controlled. Compared with pure TNAs, a new strong absorption peak appeared on Cu/TNAs under visible light region due to the surface plasmon resonance (SPR) of Cu NPs. Photoelectrochemical performance and photocatalytic hydrogen evolution characteristic of the Cu/TNAs catalysts were investigated under visible light irradiation. The novel Cu/TNAs heterogenous architectures show a stable and high photocatalytic activity for hydrogen evolution without the Pt co-catalyst.

Photocatalytic activity of TiO2 films on Si support prepared by atomic layer deposition

TiO2 films were deposited on the native oxide covered Si(100) with ALD method. The films were grown applying various numbers of deposition cycles at different temperatures. The resulting coatings possessed different thickness, crystallinity, morphology and roughness. The photocatalytic activity of the films has been studied in the presence of terephthalic acid, Azur B and two herbicides: 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid. Coatings deposited at 350°C (anatase–rutile composites) show the highest activity in the process of TA oxidation (the highest efficiency of hydroxyl radical generation). The influence of film thickness on photoactivity is more complex and depends on the mechanism of processes to be photocatalysed.

Amorphous and perovskite Li3xLa(2/3)−xTiO3 (thin) films via chemical solution deposition: solid electrolytes for all-solid-state Li-ion batteries

Thin films of amorphous and crystalline perovskite Li3xLa(2/3)−xTiO3 (LLT) (x = 0.117) are prepared by means of aqueous chemical solution deposition onto rutile TiO2 thin films as an anode, yielding an electrochemical half-cell. The Li-ion conductivity of the pin-hole free, amorphous LLT thin film (90 nm thick) is 3.8 × 10−8 S cm−1 on Pt and 1.3 × 10−8 S cm−1 on rutile TiO2, while measuring perpendicular to the thin film direction with impedance spectroscopy. Grazing angle attenuated total reflectance-Fourier transform infrared spectroscopy shows that all organic precursor molecules have been decomposed at 500 °C. In addition, in situ (heating) X-ray diffraction analysis shows that phase pure crystalline perovskite LLT (x = 0.117) is formed on top of the rutile TiO2 anode at 700 °C. Furthermore, thickness control is possible by varying the precursor solution concentration and the number of deposition cycles. The current study presents a promising synthesis route to develop all-solid-state battery devices based on multi-metal oxide materials using aqueous precursor chemistry.

Preparation of silicon-substituted hydroxyapatite coatings on Ti–30Nb–xTa alloys using cyclic electrochemical deposition method

Silicon-substituted hydroxyapatite coatings on Ti–30Nb–xTa alloys, prepared using a cyclic electrochemical deposition method, have been investigated using a variety of surface analytical experimental methods. The silicon-substituted hydroxyapatite (Si-HA) coatings were prepared by electrolytic deposition in electrolytes containing Ca2+, PO43− and SiO32− ions. The deposited layers were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and a wettability test. Phase transformation from (α″+β) to largely β occurred with increasing Ta content in the Ti–30Nb–xTa alloys, yielding larger grain size. The morphology of the Si-HA coatings was changed by increasing the number of deposition cycles, with the initial plate-like structures changing to mixed rod-like and plate-like shapes, and finally to a rod-like structure. From the ATR-FTIR spectra, Si existed in the form of SiO44− groups in Si-HA coating layer. The lowest aqueous contact angles and best wettability were found for the Si-HA coatings prepared with 30 deposition cycles.

Iron oxide nanostructured electrodes for detection of copper(II) ions.

Iron oxide nanostructured (ION) electrodes were assembled layer-by-layer onto ITO-coated glass substrates and their structure, morphology, and electrochemical properties were investigated, the latter aiming at the development of a chemical sensor for Cu2+. The electrodes were built by immersing the substrate alternately into an aqueous colloidal suspension of positively charged magnetite nanoparticles (np-Fe3O4, 8 nm) and an aqueous solution of anionic sodium sulfonated polystyrene (PSS). The adsorbed amount of both materials was monitored ex-situ by UV-vis spectroscopy and it was found to increase linearly with the number of deposition cycles. The resulting films feature a densely-packed structure of magnetite nanoparticles, as suggested by AFM and Raman spectroscopy, respectively. Cyclic voltammograms of electrodes immersed in acetate buffer (pH 4.6) displayed three electrochemical events that were tentatively ascribed to the reduction of Fe(III) oxy-hydroxide to magnetite, reduction of maghemite to magnetite, and finally oxidation of magnetite to maghemite. The effect of np-Fe3O4/PSS bilayers on the ION electrode performance was to increase the anodic and cathodic currents produced during electrochemical oxidation-reduction of the Fe(CN)(3-/4-) redox couple. With more bilayers, the ION electrode provided higher anodic/cathodic currents. Moreover, the redox couple exhibited a quasi-reversible behavior at the ION electrode as already observed with other working electrode systems. Fitting of voltammetry data provided the apparent electron transfer constants, which were found to be higher in ION electrodes for both redox couples (Fe(CN)(3-/4-) and Cu(2+/0)). By means of differential pulsed anodic stripping voltammetry, the ION electrodes were found to respond linearly to the presence of Cu2+ in aqueous samples in the range between 1.0 and 8.0 x 10(-6) mol x L(-1) and displayed a limit of detection of 0.3 x 10(-8) mol x L(-1). The sensitivity was - 0.6μA/μmol x L(-1). In standard addition and recovery experiments performed with tap water the recovery was about 102%-119%. In similar experiments conducted with ground and instant coffee samples the recovery was 92.5% and 103%, respectively. Furthermore, the ION electrodes were almost insensitive to the presence of common interfering ions, such as Zn2+, Mn2+, Ni2+, and Fe3+, even at concentrations ten times higher than that of Cu2+.

Atomic layer deposition and characterization of Bi₂Te₃ thin films.

Bi2Te3 thin films were deposited by atomic layer deposition (ALD) from BiCl3 and (Et3Si)2Te at 160-300 °C. The process was studied in detail, and growth properties typical of ALD were verified. Films were stoichiometric with low impurity content. The film thickness was easily controlled with the number of deposition cycles. Properties of the ALD Bi2Te3 thin films were found to be comparable to those reported in literature for Bi2Te3 films made by other methods. Films crystallized to a rhombohedral phase, and there was a preferred orientation to the growth. Electrical and thermoelectric properties were also determined to be comparable to literature values.

Synthesis and Photoluminescence Properties of Monodisperse Spherical SiO<sub>2</sub>@Lu<sub>2</sub>O<sub>3</sub>: Eu<sup>3+</sup> Particles with Core-Shell Structure

Spherical submicron SiO2 particles have been coated with luminescent Lu2O3: Eu3+ layers by a Pechini sol-gel process, resulting in the formation of SiO2@Lu2O3: Eu3+ core-shell particles(300, 500 nm). The obtained core–shell phosphors have perfect spherical shape with narrow size distribution, smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (50 nm for four deposition cycles). Under the excitation of ultraviolet, the Eu3+ ion mainly shows its characteristic emissions in the core-shell particles from Lu2O3: Eu3+) shells. The PL intensity of Eu3+ increases with the number of coating cycles.