Optimum Deposition Conditions Research Articles

Efficient Nanocrystal Photovoltaics via Blade Coating Active Layer.

CdTe semiconductor nanocrystal (NC) solar cells have attracted much attention in recent year due to their low-cost solution fabrication process. However, there are still few reports about the fabrication of large area NC solar cells under ambient conditions. Aiming to push CdTe NC solar cells one step forward to the industry, this study used a novel blade coating technique to fabricate CdTe NC solar cells with different areas (0.16, 0.3, 0.5 cm2) under ambient conditions. By optimizing the deposition parameters of the CdTe NC’s active layer, the power conversion efficiency (PCE) of NC solar cells showed a large improvement. Compared to the conventional spin-coated device, a lower post-treatment temperature is required by blade coated NC solar cells. Under the optimal deposition conditions, the NC solar cells with 0.16, 0.3, and 0.5 cm2 areas exhibited PCEs of 3.58, 2.82, and 1.93%, respectively. More importantly, the NC solar cells fabricated via the blading technique showed high stability where almost no efficiency degradation appeared after keeping the devices under ambient conditions for over 18 days. This is promising for low-cost, roll-by-roll, and large area industrial fabrication.

Copper Oxide Thin Films for Sub-Ppm Acetone Detection Obtained By Glancing Angle Magnetron Sputtering Deposition

Introduction The number of gas-sensing applications increases year by year including industrial application as well as new approaches such as medical diagnostics, where gas sensors are used for measurement of volatile organic compounds present in the exhaled human breath. Over 3500 various VOCs have been already detected in the exhaled human breath, and a single breath consists of 500 various VOCs [1]. Apart from the conventional breath alcohol detectors, the novel applications appeared such as the detection of biomarkers [2]. One of the promising compounds that can be used as a biomarker is acetone, which is considered to be the biomarker of diabetes since people with diabetes tend to have higher acetone detection that healthy people [3,4]. The exhaled acetone is usually in the range of 0.2 - 0.8 ppm and over 2.5 ppm for people without and with diabetes, respectively. In order to measure such low, sub-ppm, concentrations, laboratory systems are applied including GC-MS [5], PTR-MS [6], and recently e-noses [7] as well as single sensors [8]. In this paper, the investigation results on the copper oxide (CuO) deposited by utilization of magnetron sputtering technology with glancing angle technique are presented, where CuO was deposited at various parameters such as deposition angle, argon/oxygen ratio. The responses to various sub-ppm acetone concentrations are presented.CuO depositionThe gas-sensing applications of CuO have been previously confirmed and described [9]. Here, the CuO thin films were deposited by the UHV magnetron sputtering system from Kurt J. Lesker with a glancing angle deposition technique realized by utilization of a commercial ECR manipulator, which allows us to change the deposition angle, substrate rotation, and it has integrated heater that can be heated up to 850oC. The base vacuum pressure and deposition vacuum pressure were 0.001 Pa and 0.3 Pa, respectively. The temperature was fixed at 200oC, the power at 100W, the argon/oxygen ratios were 33%, 50%, 66%, 80% and 100% (pure oxygen without argon). After deposition, the samples were annealed at 400oC for 4 hours in the air. Gas-sensing measurements The developed sensors were tested in the dedicated measurement setup based on the quartz-tube oven with gas-dosing lines, where various target gas concentrations are obtained by utilization of mass flow controllers 1179B (MKS Instruments, USA) and acetone canisters with 5 ppm of acetone (Air Products, UK). The gas sensor response (S) was defined as resistance ratio S=(Rgas-Rair)/Rair, where Rgas and Rair are electrical resistances in gas and air, respectively. Results and Conclusions The sensors have been measured under exposure to acetone in the 0.25–2.5 ppm range, which covers the exhaled acetone range. The results have confirmed the influence of the glancing angle deposition for gas detection, in this case for acetone detection. The highest responses have been obtained for samples deposited at 85o (Fig.1b), however, the SEM verification will be carried out to compare the morphology and nanorods distribution. Moreover, the deposition system allows us to deposit the copper oxides at various argon/oxygen concentrations including deposition in pure oxygen. The results presented in Fig.1a shows, that the highest responses have been obtained for samples deposited at 20%/80% Ar/O2 ratio. It has been underlined, that the samples were annealed after deposition and preheated for 4h at 300oC, 350oC, and 400oC before the measurements. Further investigations are focused on choosing the optimal deposition conditions for acetone-sensors as well as long-term stability tests are performing.Fig.1. The sensors’ responses under exposure to acetone in the 0.25–2.5 ppm range at various operating temperatures for gas-sensing layer deposited at various (a) oxygen concentrations; (b) deposition angles.

Electrochemical detection of flavin mononucleotide using mineral-filmed microelectrodes

• Hematite and maghemite were deposited onto carbon fiber microelectrode tips. • Square wave voltammetry was used to detect flavin mononucleotide. • Hematite-filmed microelectrodes have improved sensitivity, LOD, and LOQ. Microelectrodes with tip diameters of tens of micrometers have higher resolution and faster response times than traditional large electrodes with diameters of millimeters or centimeters. The response of the microelectrode can be improved with a thin film that has an affinity to the analyte of interest, flavin mononucleotide (FMN). FMN is an electron transfer mediator in biological systems. Previously, we have developed two methods of detecting FMN. We have shown that a bare carbon fiber microelectrode can be used to detect flavin and, in a follow-up study, we demonstrate that a thin film of hematite on a large glassy carbon electrode improves flavin detection. The technology for depositing minerals onto carbon microelectrode surfaces needs to be improved and applied to multiple minerals. We selected maghemite and hematite as minerals to deposit because of their affinity to redox active compounds. Our goal was to develop a technology to deposit a thin film of minerals (maghemite and hematite) to the bare carbon microelectrode tip. First, we optimized deposition conditions; then we compared the performance of these microelectrodes. The maghemite-filmed microelectrodes only improved the sensitivity of the microelectrode toward FMN at low concentrations as compared to the bare carbon fiber. Alternatively, hematite, deposited at the same conditions as maghemite, increased the sensitivity by 20-times, the limit of detection (LOD) by 7-times, and the limit of quantification (LOQ) by 7-times, compared to the bare carbon fiber microelectrode. Ultimately, a hematite film, deposited at pH 5 and −0.4 V Ag/AgCl, achieved a sensitivity of 14.1 ± 1.6nA/μM between 0.1 and 20 μM, an LOD of 0.018 μM, and a LOQ of 0.063 μM.

RF magnetron sputtering processed transparent conductive aluminum doped ZnO thin films with excellent optical and electrical properties

Aluminum doped ZnO thin films (AZO), which simultaneously transmit light and conduct electrical current, are widely applied in photovoltaic devices. To achieve high performance AZO thin films, the effects of RF magnetron sputtering conditions on the optical and electrical properties of the films have been explored. The optimized AZO thin films exhibit strong (002) orientated growth with hexagonal wurtzite structure. The minimum resistivity of 0.9 × 10−3 Ω cm, the highest carrier concentration of 2.8 × 1020 cm−3, the best Hall mobility of 22.8 cm2 (V s)−1 and average transmittance above 85% can be achieved at the optimum deposition condition of 0.2 Pa, 120 W and 200 °C. Considering the single parabolic band model, the bandgap shift by carrier concentration of the films can be attributed to the Burstein-Moss effect. The results indicate that RF magnetron sputtered AZO thin films are promising for solar cell applications relying on front contact layers.

Reversible 100 mA Current Switching in a VO₂/Al₂O₃-Based Two-Terminal Device Using Focused Far-Infrared Laser Pulses.

In this study, we implemented reversible current switching (RCS) of 100 mA in a two-terminal device based on a vanadium dioxide (VO₂) thin film, which could be controlled by far-infrared (FIR) laser pulses. The VO₂ thin films used for fabrication of two-terminal devices were grown on sapphire (Al₂O₃) substrates using a pulsed laser deposition method. An optimal deposition condition was determined by analyzing the resistance-temperature curves of deposited VO₂ thin films and the current-voltage characteristics of two-terminal devices based on these films, which were suggested in our previous works. The film surface of the VO₂-based device was directly irradiated using focused CO₂ laser pulses, and the insulator-metal transition or metal-insulator transition of the VO₂ thin film could be triggered depending on laser irradiation. Consequently, RCS of up to 100 mA could be accomplished. This on-state current is close to the upper limit of the current flowing through our VO₂ device. The switching contrast, defined as the ratio between on-state and off-state currents, was evaluated and found to be ˜11,962. The average rising and falling times of the switched current were found to be ˜29.2 and ˜71.7 ms, respectively. In comparison with our previous work, the improved heat dissipation structure and the high-quality thin film could maintain the switching contrast at a similar level, although the on-state current was increased by about two times.

ALD Growth of MgxCa1–xO on GaN and Its Band Offset Analysis

Atomic layer deposition (ALD) processes were developed for growing MgO and CaO on GaN substrates using a home-built ALD reactor with amidinate-based precursors. An optimal deposition condition was ...

Out of stoichiometry CuCrO2 films as a promising p-type TCO for transparent electronics

Optimal deposition conditions to synthesize highly conductive and transparent CuCrO2 films out of stoichiometry and Cu2O + CuCrO2 nanocomposite films by AA-MOCVD at a low temperature and atmospheric pressure.

Study of electrochemical deposition of Ni-Mo thin films from alkaline electrolytes

The process of co-deposition of Ni with Mo from alkaline electrolytes was studied by taking linear and cyclic polarization curves of Pt electrode at various concentrations of initial components and potential scan rates. Solutions of Na2MoO4∙2H2O and NiSO4∙7H2O were used as sources of ions of the main components in NH4OH electrolyte. It was found that co-deposition of nickel with molybdenum goes through the oxide formation stage, and a solid solution of these two metals is deposited on the cathode surface. The film obtained at constant current on Ni electrode under optimal conditions was found amorphous, but additional thermal treatment at 500 °C for one hour made it polycrystalline. This was confirmed by peaks in X-ray diffraction patterns, corresponding to NiMoO4, Ni, and MoO3. The proposed electrolyte and electrolysis conditions allow to obtain thin films with molybdenum content ranging from 17.1 to 50.9 at.%. The co-deposition of Ni with Mo is limited by diffusion of these ions to the cathode surface. The knowledge of the mechanism of co-deposition of Ni and Mo will make possible a selection of optimal conditions for deposition of alloys of the required composition with satisfactory electrocatalytic properties.

Preparation of ZnTe thin films using chemical bath deposition technique

Chemical bath deposition was used to prepare thin films of ZnTe. The density of compounds (0.5–2) ml in 50 ml of distilled water, the precipitation time (10–80 min), and the solution temperature during the precipitation process (15–85 °C) have been changed during the preparation of the ZnTe thin films to get the optimal deposition conditions of a semiconductor. The effect of these parameters has been determined by studying the optical properties of the films which included the transmittance and absorbance as a function of the wavelength and energy gap. The energy gap remains constant at about 2.7 eV over all precipitation times for each density of compound. We have also found that the energy gap of the films decreases with increasing solution temperature, reaching approximately 2.9-3eV at 15 °C and decreasing to 2.4 eV at 85 °C.

Influence of electrodeposition techniques and parameters towards the deposition of Pt electrocatalysts for methanol oxidation

Deposition of platinum catalysts on a titanium substrate (Pt/Ti) was performed using various electrodeposition techniques, and an optimum deposition condition attributing to enhanced activity towards methanol oxidation reaction (MOR) was identified. Physical characterization confirmed that the variation of deposition parameters resulted in Pt nanostructures with various morphologies. The final morphology of the Pt catalyst was strongly influenced by the average potential applied or observed during the deposition. Dynamic applied waveform electrodeposition techniques, namely cyclic voltammetry deposition and pulse current deposition, were found to offer efficient deposition and homogeneous distribution of Pt on Ti compared to constant applied waveform deposition techniques such as potentiostatic and galvanostatic deposition, which could be attributed to the improved homogeneity of metal ion concentration during deposition. Among the various deposition techniques and parameters studied, results indicate that Pt catalysts deposited by pulse electrodeposition with a low-duty cycle was found to be the optimum to achieve high catalytic activity towards MOR. The results of this study not only reflect the fundamental understanding of Pt morphology at different deposition modes but also highlight the importance of performing the deposition with an optimal deposition technique and parameters to have a better and more efficient metal deposition from its precursor.

Design of advanced one-step hydroxyapatite coatings for biomedical applications using the electrostatic spray deposition

Calcium phosphate ceramics (CaP), particularly hydroxyapatite Ca10(PO4)6(OH)2 (HAP), are widely used as surface coatings on top of titanium and its alloys in biomedical applications thanks to their ability to form strong bonds with natural bone tissues. In this paper, the electrostatic spray deposition technique (ESD) by using an organic phosphorus (V) precursor is proposed as an alternative to the widely used plasma-spraying process. This bottom-up approach enables the one-step fabrication of single-phase crystalline HAP coatings with unique morphologies. The microstructure and composition of the deposited CaP layers result from a delicate compromise between the physicochemical properties of the precursor solution and the ESD deposition conditions. An in-depth study of their structural, microstructural, compositional properties and their reactivity with Ti6Al4V is undertaken. It shows that the Ca/P molar ratio and the nature of phases are strongly dependent on hydrolysis and evaporation of the P(V) precursor in the ESD process. Optimized deposition conditions are found by using solvents of low-boiling point, for which the coatings deposited above 325 °C correspond to a well crystalline, nanostructured, and single-phase HAP. Infrared heat treatment of a coating prepared from the one optimized precursor solution promotes nanostructured HAP.

Texture evolution in PLD grown ferroelectric Strontium Barium Niobate (SBN) thin films with processing parameters

Abstract Texture evolution along c-axis has been optimized for Strontium Barium Niobate (SBN) thin films prepared using Pulsed laser Deposition (PLD) technique for two different compositions i.e., S r 0.60 B a 0.40 N b 2 O 6 ( S B N 60 ) , S r 0.75 B a 0.25 N b 2 O 6 (SBN75). At an optimized deposition pressure of 10 mTorr, substrate temperature of 800 °C and laser fluence of 1.0 J c m − 2 , a preferred c-axis oriented (001) SBN60 thin film was obtained on different substrates. The film possesses minimum stress ( − 0.98 × 10 10 d y n e / c m 2 ) , strain (−0.76 ( - 0 . 76 × 10 2 ) and maximum texture coefficient ( T 001 ) of about 1.77 along the c-axis. Similarly, a preferred c-axis oriented growth of SBN75 films was obtained at 30 m T o r r pressure with 1.5 J c m − 2 laser fluence and 800 °C substrate temperature with minimum stress ( − 0.99 × 10 10 d y n e / c m 2 ) , strain (−0.77 ( - 0 . 77 x 10 2 ) and maximum texture coefficient ( T 001 ) of about 2.59 along the c-axis. Structural and morphological properties of the SBN thin films were studied using X-ray diffraction (XRD), Atomic force Microscopy (AFM) and Scanning electron microscopy (SEM). Root mean square roughness of about 2.07 nm and 2.85 nm was obtained for the SBN60 and SBN75 thin film at optimized deposition conditions.

Sputtered VO2 coatings on commercial glass substrates for smart glazing applications

VO2 is a well-known thermochromic material that can be potentially applied as a coating on “smart” glazing systems. In this work VO2 thermochromic films, were grown by the rf sputtering technique on two different types of commercial glass substrates, namely fused silica and float glass, at the low deposition temperature of 300 °C. The optimum deposition conditions, in order to succeed the thermochromic monoclinic phase of VO2(M), were investigated and found to be subject to substrate and thickness. It was observed that on the float glass substrate, only films with thicknesses below 50 nm grown with 3% O2 in plasma exhibited a thermochromic behavior, displaying a critical transition temperature of TC = 46.1 °C, width of transmittance hysteresis loop at 2000 nm ΔTC = 9.1 °C, IR-switching ΔTrIR = 14.6%, integrated solar transmittance modulation ΔTrsol = 1.3% and integrated luminous transmittance at 25 °C equal to Trlum = 36.6%. In contrast, films deposited on fused silica glass demonstrated a thermochromic phase, for all thicknesses, when grown with 1% O2 in the plasma. These thermochromic films were characterized by much lower TC(<40 °C) and ΔTC<10 °C, along with significant thickness variations of the ΔTrIR, ΔTrsol and Trlum parameters. Finally, rapid thermal annealing (RTA) was used and found to enhance the thermochromic performance of films deposited on float glass, with thickness greater than 50 nm. These differences might be attributed to the different composition of each kind of glass, as well as to diffusion phenomena between film and substrate.

Multifunctional cobalt coating with exceptional amphiphobic properties: self-cleaning and corrosion inhibition

Wetting ability is a crucial property for self-cleaning applications. Amphiphobic surfaces have an excellent repellency for both water and organic droplets. Herein, we electrodeposited an amphiphobic cobalt coating. First, a hydrophobic coating with the contact angle (CA) of 121° is achieved through the optimization of deposition condition (current density of 92 mA.cm−2 and pH of 3.25). Surface hydrophobicity is attributed to the uniform hierarchical morphology of the coating achieved by deposition process along with the gradual removal of molecular water and adsorption of airborne hydrocarbons during 5 days. Then, we modified the coating with a fluorinated solution. So, the surface becomes superhydrophobic with a water CA of 161° and a very low contact angle hysteresis (CAH) of approximately 8°. The hydrophobic coating demonstrated oleophilic property against glycerol (CA = 39°) and octane (CA = 18°), in which after the modification through fluorinated solution, the CAs of glycerol and octane increased to 141° and 130°, respectively. AFM results showed that the roughness of the modified coating remained constant, and thus it was concluded that the enhanced liquid repellency is originated from the low surface energy. The modified surface preserved its amphiphobic property after 6 months of exposure to air at ambient temperature. Eventually, the corrosion behavior assessments reveal that the modified coating enhanced the corrosion inhibition compared to the pure cobalt coating by reducing the corrosion current density by 82%.

Investigation for the Thermodynamic Polarization Degradation of the BaTiO3 Crystal Thin Films

According to the latest development of memory, it is found that the motion of ferroelectric domain wall is very important for the high-density non-volatile devices of ferroelectric materials. This paper mainly studies the microstructure of barium titanate (BaTiO3) crystal films with the molecular dynamics of crystal domain motion and then models the polarization degradation with the conservation of the nucleation energy-focusing and free energy thermodynamic processes in the crystalline domains. First, by the means of XRD diffractometer and JADE software, the crystal axis orientation of BaTiO3 thin film is analysed, and then the crystal axis orientation is determined by referring the published measurement results. Further, for the ferroelectric crystal BaTiO3 thin film, the thermodynamic process is studied and the temperature dependences of the polarization ratio with respect to the spontaneous polarization is modelled. Numerical simulations have shown the much higher temperature dependence on the nucleation energy than on the free energy in a domain wall system, leading to the possibility to reach a high polarization ratio with the optimal deposition conditions to control the local energy and the nucleation energy cost of crystalline domains.

Synthesis and catalytic performance of highly dispersed platinum nanoparticles supported on alumina via supercritical fluid deposition

Highly dispersed platinum nanoparticles (NPs) supported on alumina were prepared by supercritical fluid deposition (SFD) with the aid of co-solvent ethanol using inorganometallic Na2PtCl6·6H2O as Pt precursor. The mean Pt particle size (1.5 nm) was obtained at the optimized deposition conditions of 40 °C and 110 bar and 3 h of deposition time. The catalysts were characterized by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP-OES) and hydrogen-oxygen titrations to investigate the structure-activity relationship. Compared with the catalyst prepared via an impregnation method, the Pt was highly dispersed to smaller particles for Pt/Al2O3 catalysts prepared by SFD and showed much higher catalytic activity of catalytic reforming of cyclohexane dehydrogenation.

Improved Corrosion Resistance and Increased Hardness of Copper Substrates from Cu-Ni/Ni-P Composite Coatings

To improve the corrosion resistance and to increase the hardness of copper substrate in marine environment, the Cu-Ni/Ni-P composite coatings were prepared on the copper substrate using the galvanostatic electrolytic deposition method. The deposition current densities were explored to find the optimized deposition conditions for forming the composite coatings. Corrosion resistance properties were analyzed using the polarization curves and electrochemical impedance spectroscopy (EIS). Considering the corrosion resistance and hardness, the −20 mA/cm2 was selected to deposit Cu-Ni coatings on copper substrate and the −30 mA/cm2 was selected to deposit Ni-P coating on the Cu-Ni layer. The Cu-Ni/Ni-P composite coatings not only exhibited superior corrosion resistance compared to single Cu-Ni coating in 3.5 wt.% NaCl solution, but also showed much better mechanical properties than single Cu-Ni coating.

Structure and mechanical performance for TiAlN films that are grown with a low Al composition

An orthogonal array L9 (34) is used with the grey Taguchi design to optimize the performance of TiAlN films that are grown by direct current magnetron co-sputtering, using a low Al concentration. The structure, mechanical performance and the cutting properties of a coated TiAlN tool for which the films are deposited using various parameters are determined. For the optimal deposition conditions, the (111) diffraction peak intensity increases, which demonstrates an improvement in the crystallinity of the TiAlN films. A TiAlN film coated cutter insert is used for the dry milling of a Cr-Mo alloy steel workpiece and it is shown that the tool flank wear decreases and there are fewer surface defects proved. In the confirmation cutting tests the surface roughness is decreased by 26.08% and the flank wear is 16.15% less. The TiAlN films exhibit good mechanical performance, using grey relational analysis, the improvement rate in hardness H is 14.74%, in friction coefficient is 45.88%, in elastic modulus E is 9.56%, in H/E is 9.09% and in H3/E2 is 25.92%.

Assembly of chitosan-graphite oxide nanoplatelets core shell microparticles for advanced 3D scaffolds supporting neuronal networks growth

This manuscript reports the development of functional 3D scaffolds based on chitosan (CHI) and graphite oxide nanoplatelets (GO) for neuronal network growth. To this aim, CHI microparticles, produced by alkaline gelation method, were coated with GO exploiting a simple template-assisted assembly based on the electrostatic attraction in an aqueous medium. The optimal deposition conditions were evaluated by optical microscopy and studied by quartz crystal microbalance. FE-SEM observations highlight the formation of a core-shell structure where the porous chitosan core is completely wrapped by a uniform GO layer. This outer shell protects the inner chitosan from enzymatic degradation thus potentially extending the scaffold viability for in vivo applications. The presence of hydrophilic oxygen-containing functionalities on the outermost layer of GO and its inner conductive graphitic core maintained the bioactivity of the scaffold and promoted neuronal cell adhesion and growth. The proposed approach to modify the surface of CHI microparticles makes it possible for the design of 3D scaffolds for advanced neuronal tissue engineering applications.

Development of hybrid metallic coatings on carbon fiber-reinforced polymers (CFRPs) by cold spray deposition of copper-assisted copper electroplating process

Metallization of polymeric materials such as carbon fiber-reinforced polymers (CFRPs) by the cold spray technique has gained significant interest to enhance their electrical conductivity. Copper is a very good electrical conductor, which makes it favorable for applications that require high electrical conductivity. However, previous studies showed that continuous copper coatings could not be fabricated directly on CFRPs by cold spraying. In this study, a hybrid fabrication process was used to enable cold spray deposition of copper onto CFRPs, making them electrically conductive. The CFRP substrate was first metallized with an electroless Ni coating; subsequently, a thick copper layer was electroplated onto the Ni interlayer. Copper was then cold spray deposited onto the electroplated CFRP as well as on a Cu control panel. Deposition efficiency (DE) of the cold-sprayed coatings was measured for both the CFRP and the control Cu coupons to determine optimal deposition conditions. Surface and cross-sectional morphologies of the coated CFRP were investigated, and both the electroplated CFRP and control panels were characterized for mechanical properties and surface roughness before cold spray deposition. The electrical resistivity of the cold-sprayed CFRPs was evaluated. It was found that the DE of copper particles is sensitive to the surface characteristics of the substrate. The electrical resistivity of the cold-sprayed coatings was slightly higher than that of the bulk copper due to porosity and small defects on the coating surface. The results suggest that Cu coatings can be successfully fabricated onto CFRPs if a copper inter-layer is present. This layer not only protects the CFRP from any possible damage, but also improves the cold sprayability of copper particles as compared to the conventional cold spraying copper powder/copper panel due to its favorable mechanical, thermal and surface properties. The fabricated coatings can serve as conductive surfaces for application as lightning strike protection coatings.