Higher Deposition Time Research Articles

Optical band gap, photocatalysis, surface structures and depth profile properties of Cu2Se nanostructured thin films

The optical behaviour, stoichiometry, surface configuration of Cu2Se nanostructured thin layers prepared at different reaction times by the chemical process has been considered. The optical band gap of the deposited thin films decreases from 2.92 eV to 2.08 eV for the first transition and from 2.18 to 1.2 eV for the second transition. In addition, it was shown that Urbach energy is independent from the film thickness, and tail values of the localized states has decreased from 1.15 to 0.33 eV. It was found that the concentration of Cu: Se remains approximately constant across the depth of the deposited film at higher deposition time. The degradation efficiency of 98% was achieved by Congo red for the prepared Cu2Se thin film at optimal condition which make it a good candidate for organic dye. From these measurements and by controlling the band gap energy, the Cu2Se can find application in solar cell application.

Nano-TiO2 Coating Layers with Improved Anticorrosive Properties by Aerosol Flame Synthesis and Thermophoretic Deposition on Aluminium Surfaces.

TiO2 in the form of nanoparticles is characterized by high photocatalytic activity and high resistance to oxidation, making it an excellent candidate to realize coatings for improving the corrosion resistance of aluminium surfaces. Different coating technologies have been proposed over the years, which often involve the use of toxic compounds and very high temperatures. In this work, an alternative and novel one-step method for the coating of aluminium alloy surfaces with titania nanoparticles is presented. The method is based on the combination of aerosol flame synthesis and direct thermophoretic deposition and allows to produce nanostructured thin coating layers of titania with different features. Specifically, 3.5 nm anatase nanoparticles were synthesized and deposited onto aluminium alloy AA2024 samples. The thickness of the coating was changed by modifying the total deposition time. A thermal annealing treatment was developed to improve the adhesion of nano-titania on the substrates, and the morphology and structures of the coatings were characterized using (ultra violet) UV-vis absorption, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The corrosion resistance behavior of the coatings was evaluated by means of electrochemical polarization measurements, coupled with a numerical analysis using COMSOL software. Both the experimental and numerical electrochemical polarization curves showed a significant increase in the corrosion potential of coated substrates with respect to the bare aluminium and a decrease in the current density. The coatings obtained with higher deposition time and greater thickness showed the best performances in terms of the resistance of the aluminium surfaces to corrosion.

Influence of adding Pluronic F127 in the electrolyte on the morphology, structure and biofilm adhesion of calcium phosphate coatings

In this work, we have investigated the addition of Pluronic F127 (PF127) into the electrolyte solution on the structure, morphology and antibacterial growth of calcium phosphate (CaP) coatings synthesized by an electrochemical method on Ti substrate. Different parameters of the deposition process were investigated, which were temperature, time and PF127 wt%. The coatings were characterized by X-ray diffraction (XRD), gravimetric analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In vitro antimicrobial assays against S. aureus were performed. XRD analysis confirmed the formation of dicalcium phosphate dihydrate (DCPD) or anhydrous dicalcium phosphate (DCPA) and octacalcium phosphate (OCP). The structure and morphology depended mainly on PF127 wt% and deposition temperature in lower deposition time. Interestingly, structure and morphology were not influenced by adding PF127 at higher deposition time using higher PF127 concentrations. The morphology by SEM changed from plate-like to fiber by varying the PF127 concentration as well as blocks at higher temperatures. Moreover, all coatings were crystalline, uniform and crack-free. Antibacterial assays showed that biofilm formation was prevented when a coating of PF127 is deposited on the surface. Bacterial growth depended on the phase and morphology of washed coatings. Thus, the structure, morphology and consequently bacterial growth resistance can be tailored by the use of PF127 in the electrochemical processing at shorter deposition times.

Effect of deposition time and complexing agents on hierarchical nanoflake-structured CdS thin films

Hierarchical nanoflake-structured CdS thin films have been prepared using chemical bath deposition method at two deposition intervals with different complexing agents. As complexing agents, ammonia and ammonia with triethanolamine or ethylene-diamine-tetra-acetic acid were taken. Structural, optical and morphological studies of the as-deposited CdS films have been studied using X-ray diffraction, UV–Vis and Raman spectroscopy, atomic force and field emission scanning electron microscopy. Compositional analysis reveals that near stoichiometric thin films of CdS were deposited at higher deposition time. X-ray diffraction patterns confirmed the cubic phase of the deposited films and the calculated crystallite sizes increased with higher deposition time while both dislocation densities and micro-strains were found to decrease with increase in deposition time. Field emission scanning electron microscopy shows the formation of hierarchical nanoflakes having small voids at lower deposition time, however, the density of the nanoflakes increases with increase in deposition duration. UV–Vis–NIR spectroscopy was performed in the spectral range 350–1100 nm which confirmed that the synthesized films contain good optical transparency in the range of 85–95% and the calculated bandgaps were found in the range of 2.20–2.42 eV. Raman spectroscopy indicated a strong electron–phonon coupling for films deposited for longer duration as the particle size increased.

Electrodeposited Ni-Cu alloy coatings on mild steel for enhanced corrosion properties

Ni rich single-phase Ni-Cu alloy coatings were obtained on mild steel substrates by electrodeposition from stable alkaline citrate baths. Three different baths were prepared with varying Cu2+ concentration. Electrodeposition experiments were performed in the galvanostatic mode at three different current densities of 10, 20 and 30 mA cm−2. The coating compositions calculated from EDAX analysis showed that copper content in the coating increased with an increase in copper content of the bath, but decreased with an increase in current density. It was observed that the morphology of the deposits changed from globular to cauliflower with an increase in current density. Deposits from baths containing lower copper content showed more separated and localised cauliflower structures. The roughness of the deposits was also observed to increase with an increase in current density and to some extent with increase in deposition time. The corrosion potential for all coatings was less negative compared to mild steel, indicating barrier protection properties. Corrosion rate was largely affected by the morphology and roughness of the coatings. At higher current densities and higher deposition time, rougher surfaces and gaps and separations between the cauliflower structures were responsible for higher corrosion rate.

Structural, optical and ac electrical characterization of CBD synthesized NiO thin films: Influence of thickness

We have studied the electrical conductivity, dielectric relaxation mechanism and impedance spectroscopy characteristics of nickel oxide (NiO) thin films synthesized by chemical bath deposition (CBD) method. Thickness dependent structural, optical and ac electrical characterization has been carried out and deposition time was varied to control the thickness. The material has been characterized using X-ray diffraction and UV-VIS spectrophotometer. Impedance spectroscopy analysis confirmed enhancement of ac conductivity and dielectric constant for films deposited with higher deposition time. Decrease of grain size in thicker films were confirmed from XRD analysis and activation energy of the material for electrical charge hopping process was increased with thickness of the film. Decrease in band gap in thicker films were observed which could be associated with creation of additional energy levels in the band gap of the material. Cole-Cole plot shows contribution of both grain and grain boundary towards total resistance and capacitance. The overall resistance was found to decrease from ~ 14.6 × 105Ω for 30min deposited film (~ 120nm thick) to ~ 2.42 × 105Ω for 120min deposited film (~307nm thick). Activation energy value to electrical conduction process evaluated from conductivity data was found to decrease with thickness. Identical result was obtained from relaxation time approach suggesting hopping mechanism of charge carriers.

The Effect of Electrodeposition Parameters and Morphology on the Performance of Au Nanostructures for the Detection of As (III)

A series of Au nanospikes and dendrites were electrodeposited with either an inorganic (Pb2+) or organic (cysteine) growth directing agent for different times to obtain varied morphology. These structures were compared with gold nanoparticles of three different shapes (Octahedral, Cubic and Rhombic Dodecahedral) for detection of As (III) by Square Wave Anodic Stripping Voltammetry (SWASV). The sensitivity and limit of detection (LOD) was dependent on the surface crystallographic orientations and the morphology, with superior sensitivity confirmed with a maximum amount of Au (111) facets on the surface for the nanoparticles. XRD studies suggested that the shape directing influence of Pb2+ is lost on the gold nanospikes at higher deposition time, and that the size of the (111) terraces on the polycrystalline surfaces decreased, which led to a loss of performance. For gold dendrites, as the cysteine maintained shape directing behavior through hierarchical dendritic branching, deposition time did not affect the sensitivity. The study confirms that electrodeposition parameters or nanoparticle synthesis methods for Au surfaces in arsenic sensing needs to be carefully controlled, to either maximize the (111) facets, or minimize the steps on a polycrystalline Au surface, and that inorganic and organic shape directing agents will have differing effects.

The influence of different silicon adhesion interlayers on the tribological behavior of DLC thin films deposited on steel by EC-PECVD

Diamond-like carbon (DLC) is a hydrogenated amorphous carbon (a-C:H) thin film material owing to its unique tribological properties that may open great opportunities for new applications. However, DLC presents low chemical affinity with metallic alloys and high intrinsic stress, prompting film delamination and poor adherence on the substrate. In the present work, we performed a systematic study about structural and tribological properties of a-C:H thin films grown on steel by introducing adhesive silicon-containing interlayers deposited at different processing temperatures and times. The studied bi-layers were deposited by electrostatic confinement plasma enhanced chemical vapor deposition (EC-PECVD) and were characterized by several techniques. The results showed that the adhesive interlayers produced from tetramethylsilane are chemically structured as a non-stoichiometry hydrogenated amorphous silicon carbide alloy (a-SiCx:H). Its structure, chemical composition and thickness are very dependent on deposition conditions. The thickness of the interlayers increases with deposition time and decreases with deposition temperature. The interlayer contains less hydrogen and silicon atoms at higher deposition temperatures, with enhanced formation of Si–C bonds in its structure. This last chemical event is correlated with the rise in the critical load values found for a-C:H film delamination when the a-SiCx:H interlayers are deposited from 573K to 823K. On the other hand, the interlayer contains less carbon atoms at higher deposition times, decreasing the critical load values for a-C:H film delamination when the a-SiCx:H interlayers are deposited from 5min to 10min.

Preparation and characterization of transparent NiO thin films deposited by spray pyrolysis technique

Nickel oxide thin films were successfully fabricated with various deposition time (td=5, 10, and 15min) on glass substrates using spray pyrolysis technique. The deposited films undergo thermal treatment at 350°C for various annealing time (ta=0, 15, 30 and 60min). In this study, the effect of td and ta on film thickness was observed and their influence on structural, morphological and optical properties were investigated. The films deposited with td=5min showed amorphous structure while the films grown at higher deposition time became partially crystallized with preferred growth along (111) direction. Heat treatment carried out in air allowed us to tune the polycrystalline structure and the diffraction intensity at preferred peak increases with the increase in ta which is a consequence of better crystallinity. This was reflected in the AFM micrographs of the films which suggested that the thermal annealing (or increasing ta) facilitates the process of grain-growth, and improves the crystalline microstructure. The optical transmission of the films was found to vary with td and ta and thus film thickness. The thinner films show higher transparency in the UV–vis spectral region. The optical band gap was blue-shifted from 3.35eV to 3.51eV depending on ta. The effect of ta on the various optical constants of the NiO films has also been discussed.

CHARACTERIZATION OF NICKEL OXIDE THIN FILM — DC REACTIVE MAGNETRON SPUTTERING

Nickel oxide ( NiO ) thin films were deposited on glass substrates by reactive direct current (DC) magnetron sputtering of a Ni target in an Ar / O 2 mixture. The effect of thickness (0.2 μm, 0.4 μm and 1 μm) on the structural and surface morphological properties of NiO thin films was investigated. These films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). The films were cubic NiO , with preferred orientation in the (111) direction at lower deposition time (10 mins). At higher deposition time (60 mins) the preferred orientation shifted to (200) plane. Electrochemical behavior of NiO thin films for different thickness samples were analyzed between the electrode potential ‑0.2 and 0.8 V vs scanning calomel electrode (SCE) in both anodic and cathodic directions and the current responses were measured.

Surface evolution of amorphous nanocolumns of Fe–Ni grown by oblique angle deposition

The growth of Fe–Ni based amorphous nanocolumns has been studied using atomic force microscopy. The root mean square roughness of the film surface increased with the deposition time but showed a little change at higher deposition time. It was found that the separation between the nanostructures increased sharply during the initial stages of growth and the change was less pronounced at higher deposition time. During the initial stages of the column growth, a roughening process due to self shadowing is dominant and, as the deposition time increases, a smoothening mechanism takes place due to the surface diffusion of adatoms.

The characterization and elimination of the external acidity of ZSM-5

The external acidity of ZSM-5 was modified either by coating the crystals with a silicalite shell or by chemical vapour deposition (CVD) of tetraethoxysilane (TEOS). Temperature programmed desorption (TPD) techniques were used to characterize the acidity changes arising from these modifications. Ammonia and pyridine were used as probes for the total acidity, and 4-methylquinoline was used to probe the external acidity of the modified and unmodified ZSM-5 samples. Si/Al ratios of the modified samples were also used to characterize the samples. Both methods of modification were able to make the external acid sites inert. Chemical vapour deposition was found to be a better method, because the external surface acidity was eliminated without significantly changing the catalyst in terms of total acidity. Optimum elimination of the external surface acidity by CVD was obtained for the sample with the higher deposition time (16 h) and temperature (400°C). Optimum elimination of the external surface acidity using the silicalite shell method was obtained using the detemplated NH 4-form of the parent crystal as seed material. The channel structures of crystals modified by both processes remained accessible to ammonia and pyridine.