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Coatings
Volume 4
Issue 2
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Coatings, Volume 4, Issue 2 (June 2014) – 10 articles , Pages 203-379

Cover Story (view full-size image): ZnO/Cu2O heterojunction solar cells were fabricated by spin-coating and electrodeposition methods, and photovoltaic properties and microstructures were investigated. ZnO and Cu2O were used as n- and p-type semiconductors, respectively. The conversion efficiency increased by Al doping in the ZnO layer, and the efficiency was improved further by growing ZnO and Cu2O layers with larger crystallite sizes. View this paper.
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2091 KiB  
Article
A Study of the Abrasion of Squeegees Used in Screen Printing and Its Effect on Performance with Application in Printed Electronics
by Christopher O. Phillips, David G. Beynon, Simon M. Hamblyn, Glyn R. Davies, David T. Gethin and Timothy C. Claypole
Coatings 2014, 4(2), 356-379; https://doi.org/10.3390/coatings4020356 - 12 Jun 2014
Cited by 17 | Viewed by 12727
Abstract
This article presents a novel method for accelerated wear of squeegees used in screen printing and describes the development of mechanical tests which allow more in-depth measurement of squeegee properties. In this study, squeegees were abraded on the screen press so that they [...] Read more.
This article presents a novel method for accelerated wear of squeegees used in screen printing and describes the development of mechanical tests which allow more in-depth measurement of squeegee properties. In this study, squeegees were abraded on the screen press so that they could be used for subsequent print tests to evaluate the effect of wear on the printed product. Squeegee wear was found to vary between different squeegee types and caused increases in ink transfer and wider printed features. In production this will lead to greater ink consumption, cost per unit and a likelihood of product failure. This also has consequences for the production of functional layers, etc., used in the construction of printed electronics. While more wear generally gave greater increases in ink deposition, the effect of wear differed, depending on the squeegee. There was a correlation between the angle of the squeegee wear and ink film thickness from a worn squeegee. An ability to resist flexing gave a high wear angle and presented a sharper edge at the squeegee/screen interface thus mitigating the effect of wear. There was also a good correlation between resistance to flexing and ink film thickness for unworn squeegees, which was more effective than a comparison based on Shore A hardness. Squeegee indentation at different force levels gave more information than a standard Shore A hardness test and the apparatus used was able to reliably measure reductions in surface hardness due to solvent absorption. Increases in ink deposition gave lower resistance in printed silver lines; however, the correlation between the amount of ink deposited and the resistance, remained the same for all levels of wear, suggesting that the wear regime designed for this study did not induce detrimental print defects such as line breakages. Full article
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660 KiB  
Article
Polymerization of Vinylpyrrolidone to Form a Neutral Coating on Anionic Nanomaterials in Aqueous Suspension for Rapid Sedimentation
by Edward P. C. Lai, Zafar Iqbal and Sherif Nour
Coatings 2014, 4(2), 340-355; https://doi.org/10.3390/coatings4020340 - 20 May 2014
Cited by 2 | Viewed by 9080
Abstract
Nanomaterials in water present an array of identifiable potential hazards to ecological and human health. There is no general consensus about the influence of anionic or cationic charge on the toxicity of nanomaterials on environmental ecology. One challenge is the limited number of [...] Read more.
Nanomaterials in water present an array of identifiable potential hazards to ecological and human health. There is no general consensus about the influence of anionic or cationic charge on the toxicity of nanomaterials on environmental ecology. One challenge is the limited number of scalable technologies available for the removal of charged nanomaterials from water. A new method based on polymer coating has been developed in our laboratory for rapid sedimentation of nanomaterials in aqueous suspension. Using colloidal silica as a model inorganic oxide, coating of polyvinylpyrrolidone (PVP) around the SiO2 nanoparticles produced SiO2@PVP particles, as indicated by a linear increase of nephelometric turbidity. Purification of the water sample was afforded by total sedimentation of SiO2@PVP particles when left for 24 h. Characterization by capillary electrophoresis (CE) revealed nearly zero ionic charge on the particles. Further coating of polydopamine (PDA) around those particles in aqueous suspension produced an intense dark color due to the formation of SiO2@PVP@PDA. The SiO2@PVP@PDA peak appeared at a characteristic migration time of 4.2 min that allowed for quantitative CE-UV analysis to determine the original SiO2 concentration with enhanced sensitivity and without any ambiguous identity. Full article
(This article belongs to the Special Issue Effects of Polymer Coatings on Toxicity of Nanomaterials)
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1221 KiB  
Article
Microstructural Evolution of (Ti,W,Cr)B2 Coatings Deposited on Steel Substrates during Annealing
by Aleksandra Newirkowez, Benjamin Cappi, Rainer Telle and Harald Schmidt
Coatings 2014, 4(2), 329-339; https://doi.org/10.3390/coatings4020329 - 07 May 2014
Cited by 1 | Viewed by 5988
Abstract
The topic of the present experiments are transition metal diboride coatings of composition (Ti0.49W0.51)B2 and (Ti0.44W0.30Cr0.26)B2. The coatings were deposited on steel substrates using dc magnetron sputtering. We investigated how [...] Read more.
The topic of the present experiments are transition metal diboride coatings of composition (Ti0.49W0.51)B2 and (Ti0.44W0.30Cr0.26)B2. The coatings were deposited on steel substrates using dc magnetron sputtering. We investigated how annealing in argon at elevated temperatures modifies microstructure. The as-deposited films are amorphous. Annealing between 700 and 1100 °C results in the formation of nano-crystalline precipitates with average grain diameters of about 10–50 nm. A TiC phase (Fm-3m; a ≈ 4.3 Å) is observed as the dominating precipitate phase. In addition, small amounts (10%–20%) of a Cr23C6 phase (Fm-3m; a ≈ 10.6 Å) are observed. In contrast to literature data on the same coatings deposited on silicon substrates, the formation of boride precipitate phases is strongly suppressed here. From investigations with X-ray diffractometry, electron microscopy and secondary ion mass spectrometry we conclude that the nanostructure of the coatings is formed by reactive phase formation of the boride coating with the carbon containing steel substrate. Full article
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846 KiB  
Article
Tin Oxide-Silver Composite Nanomaterial Coating for UV Protection and Its Bactericidal Effect on Escherichia coli (E. coli)
by Gil Nonato C. Santos, Eduardo B. Tibayan, Gwen B. Castillon, Elmer Estacio, Takashi Furuya, Atsushi Iwamae, Kohji Yamamoto and Masahiko Tani
Coatings 2014, 4(2), 320-328; https://doi.org/10.3390/coatings4020320 - 06 May 2014
Cited by 7 | Viewed by 8293
Abstract
SnO2-Ag composite nanomaterials of mass ratio 1:4, 2:3, 3:2 and 4:1 were fabricated and tested for toxicity to E. coli using the pour-plate technique. The said nanomaterials were mixed with laminating fluid and then coated on glass slides. The intensity [...] Read more.
SnO2-Ag composite nanomaterials of mass ratio 1:4, 2:3, 3:2 and 4:1 were fabricated and tested for toxicity to E. coli using the pour-plate technique. The said nanomaterials were mixed with laminating fluid and then coated on glass slides. The intensity of UVA transmitted through the coated glass slides was measured. Results revealed that the 1:4 ratios of SnO2-Ag composite nanomaterials have the optimum toxicity to E. coli. Furthermore, the glass slides coated with SnO2 nanomaterial showed the lowest intensity of transmitted UVA. Full article
(This article belongs to the Special Issue Photocalytic Coatings for Air-Purifying, Self-Cleaning and Antimicrobial Properties)
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769 KiB  
Communication
The Effect of Cr Content on the Oxidation Behavior of Ti-Cr-N Films
by James E. Krzanowski and Daniel J. Foley
Coatings 2014, 4(2), 308-319; https://doi.org/10.3390/coatings4020308 - 30 Apr 2014
Cited by 6 | Viewed by 5696
Abstract
Ti1−xCrxN thin-film samples were sputter-deposited with lateral composition gradients x = 0.1–0.9 across each sample. In order to determine the effect of Cr content on oxidation, samples were air-oxidized at temperatures ranging from 650 to 950 °C. The [...] Read more.
Ti1−xCrxN thin-film samples were sputter-deposited with lateral composition gradients x = 0.1–0.9 across each sample. In order to determine the effect of Cr content on oxidation, samples were air-oxidized at temperatures ranging from 650 to 950 °C. The extent and type of oxide formed was characterized using X-ray diffraction. Only minor oxidation was observed for the 650–750 °C temperature range. At 850 °C, films below x = 0.7 showed poor oxidation resistance, with the formation of TiO2 and Cr2O3 oxides, but little oxidation occurred above x = 0.7. At 950 °C, films above x = 0.7 again exhibited the best oxidation resistance. Chromium nitride films, which deposited as Cr2N, were found to begin oxidizing at 750 °C, indicating that the increased oxidation resistance of the higher-Cr Ti-Cr-N films can be attributed to the Ti-induced stabilization of the B1-structured phase. A compositionally-uniform film (x = 0.79) was also deposited and analyzed by XPS before and after oxidation. Oxidation resulted in primarily Cr2O3 at the surface, with some TiO2 also present, with the oxide richer in Cr than the starting film composition. These results suggested that at higher Cr compositions in the film, the oxidation mechanism was controlled by Cr diffusion to the surface. Full article
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1142 KiB  
Review
Review of the CdCl2 Treatment Used in CdS/CdTe Thin Film Solar Cell Development and New Evidence towards Improved Understanding
by I. M. Dharmadasa
Coatings 2014, 4(2), 282-307; https://doi.org/10.3390/coatings4020282 - 30 Apr 2014
Cited by 124 | Viewed by 14039
Abstract
Cadmium chloride treatment is a key processing step identified in the late 1970s to drastically improve the solar to electric conversion efficiency of CdS/CdTe thin film solar cells. Although a large body of experimental results are available to date, this process is yet [...] Read more.
Cadmium chloride treatment is a key processing step identified in the late 1970s to drastically improve the solar to electric conversion efficiency of CdS/CdTe thin film solar cells. Although a large body of experimental results are available to date, this process is yet to be understood even after three decades of research. This paper reviews the experimental results available, presents some new clues leading to improved understanding and suggests key research areas necessary to fully understand this crucial processing step. Improved understanding will lead to further increase in conversion efficiency of CdS/CdTe solar cells well beyond 20%. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
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1583 KiB  
Article
Completely Analytical Tools for the Next Generation of Surface and Coating Optimization
by Norbert Schwarzer
Coatings 2014, 4(2), 253-281; https://doi.org/10.3390/coatings4020253 - 23 Apr 2014
Cited by 4 | Viewed by 6856
Abstract
Usually, some severe efforts are required to obtain tribological parameters like Archard’s wear depth parameter kd. Complex tribological experiments have to be performed and analyzed. The paper features an approach where such parameters are extracted from effective interaction potentials in combination [...] Read more.
Usually, some severe efforts are required to obtain tribological parameters like Archard’s wear depth parameter kd. Complex tribological experiments have to be performed and analyzed. The paper features an approach where such parameters are extracted from effective interaction potentials in combination with more physical-oriented measurements, such as Nanoindentation and physical scratch. Thereby, the effective potentials are built up and fed from such tests. By using effective material potentials one can derive critical loading situations leading to failure (decomposition strength) for any contact situation. A subsequent connection of these decomposition or failure states with the corresponding stress or strain distributions allows the development of rather comprehensive tribological parameter models, applicable in wear and fatigue simulations, as demonstrated in this work. From this, a new relatively general wear model has been developed on the basis of the effective indenter concept by using the extended Hertzian approach for a great variety of loading situations. The models do not only allow to analyze certain tribological experiments, such as the well known pin-on disk test or the more recently developed nano-fretting test, but also to forward simulate such tests and even give hints for structured optimization or result in better component life-time prediction. The work will show how the procedure has to be applied in general and a small selection of practical examples will be presented. Full article
(This article belongs to the Special Issue Advances in Multifunctional Coatings for Next Generation Applications)
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1455 KiB  
Article
Ni-Al and NiO-Al Composite Coatings by Combustion-Assisted Flame Spraying
by Galina Xanthopoulou, Amalia Marinou, George Vekinis, Aggeliki Lekatou and Michalis Vardavoulias
Coatings 2014, 4(2), 231-252; https://doi.org/10.3390/coatings4020231 - 17 Apr 2014
Cited by 26 | Viewed by 8635
Abstract
A new, cost-efficient and on-site-applicable thermal spraying process for depositing NiAl metallic overlay or bond-coat coatings for high temperature applications by synthesizing the desired intermetallic phases in-flight during oxy-acetylene flame spraying is presented. Base-metal powders were used for spraying and, by adjusting the [...] Read more.
A new, cost-efficient and on-site-applicable thermal spraying process for depositing NiAl metallic overlay or bond-coat coatings for high temperature applications by synthesizing the desired intermetallic phases in-flight during oxy-acetylene flame spraying is presented. Base-metal powders were used for spraying and, by adjusting the spraying conditions, excellent NiAl-based coatings were achieved on various substrates, including mild steel, stainless steel and aluminium alloys. Expensive, pre-alloyed or agglomerated powders are avoided and the method is very promising for in-situ work and repairs. We call the new method “Combustion-Assisted Flame Spraying” (CAFSY) and its viability has been demonstrated at a pre-industrial level for coating metallic substrates. The NiAl-based coatings produced by CAFSY exhibit very high integrity with good adhesion, very low porosity, high surface hardness and high erosion resistance at a substantially lower cost than equivalent coatings using pre-prepared alloy powders. Full article
(This article belongs to the Special Issue Advanced Thermal Spray Coatings for Emerging Applications)
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866 KiB  
Article
The Effect of Bias Voltage and Gas Pressure on the Structure, Adhesion and Wear Behavior of Diamond Like Carbon (DLC) Coatings With Si Interlayers
by Liam Ward, Fabian Junge, Andreas Lampka, Mark Dobbertin, Christoph Mewes and Marion Wienecke
Coatings 2014, 4(2), 214-230; https://doi.org/10.3390/coatings4020214 - 01 Apr 2014
Cited by 23 | Viewed by 11658
Abstract
In this study diamond like carbon (DLC) coatings with Si interlayers were deposited on 316L stainless steel with varying gas pressure and substrate bias voltage using plasma enhanced chemical vapor deposition (PECVD) technology. Coating and interlayer thickness values were determined using X-ray photoelectron [...] Read more.
In this study diamond like carbon (DLC) coatings with Si interlayers were deposited on 316L stainless steel with varying gas pressure and substrate bias voltage using plasma enhanced chemical vapor deposition (PECVD) technology. Coating and interlayer thickness values were determined using X-ray photoelectron spectroscopy (XPS) which also revealed the presence of a gradient layer at the coating substrate interface. Coatings were evaluated in terms of the hardness, elastic modulus, wear behavior and adhesion. Deposition rate generally increased with increasing bias voltage and increasing gas pressure. At low working gas pressures, hardness and modulus of elasticity increased with increasing bias voltage. Reduced hardness and modulus of elasticity were observed at higher gas pressures. Increased adhesion was generally observed at lower bias voltages and higher gas pressures. All DLC coatings significantly improved the overall wear resistance of the base material. Lower wear rates were observed for coatings deposited with lower bias voltages. For coatings that showed wear tracks considerably deeper than the coating thickness but without spallation, the wear behavior was largely attributed to deformation of both the coating and substrate with some cracks at the wear track edges. This suggests that coatings deposited under certain conditions can exhibit ultra high flexible properties. Full article
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760 KiB  
Article
Microstructures and Photovoltaic Properties of Zn(Al)O/Cu2O-Based Solar Cells Prepared by Spin-Coating and Electrodeposition
by Takeo Oku, Tetsuya Yamada, Kazuya Fujimoto and Tsuyoshi Akiyama
Coatings 2014, 4(2), 203-213; https://doi.org/10.3390/coatings4020203 - 31 Mar 2014
Cited by 39 | Viewed by 10975
Abstract
Copper oxide (Cu2O)-based heterojunction solar cells were fabricated by spin-coating and electrodeposition methods, and photovoltaic properties and microstructures were investigated. Zinc oxide (ZnO) and Cu2O were used as n- and p-type semiconductors, respectively, to fabricate photovoltaic devices based on [...] Read more.
Copper oxide (Cu2O)-based heterojunction solar cells were fabricated by spin-coating and electrodeposition methods, and photovoltaic properties and microstructures were investigated. Zinc oxide (ZnO) and Cu2O were used as n- and p-type semiconductors, respectively, to fabricate photovoltaic devices based on In-doped tin oxide/ZnO/Cu2O/Au heterojunction structures. Short-circuit current and fill factor increased by aluminum (Al) doping in the ZnO layer, which resulted in the increase of the conversion efficiency. The efficiency was improved further by growing ZnO and Cu2O layers with larger crystallite sizes, and by optimizing the Al-doping by spin coating. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
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