Formation Of Black Spots Research Articles

Sub-micron pinhole detection in the cathode of organic light-emitting diodes

A technique is presented on tracing the sub-micron pinholes that result in black spots in organic light-emitting diodes (OLED) when exposed to ambient atmosphere. The mystery about the type and nature of tiny pinholes present in the OLED cathode that allow oxygen and/or moisture ingress in minute quantities causing black spot formation, is clarified. The technique can accurately locate nanodefects or pinholes in the center of black spots of various sizes, even on a centimeter scale. Pinholes in the investigated OLEDs were shown to be caused by different particles originating from various locations in the device stack. Defects in the Ba-Al cathode of a solution processed polymer LED (PLED) and pinholes in the LiF-Al cathode of a thermally evaporated small molecule organic LED (smOLED) were investigated and compared. The technique is a powerful tool for inspection and can, thereby, accelerate the process optimization for OLED fabrication.

High-performance thin-film encapsulation for organic light-emitting diodes

Organic light-emitting diodes degrade rapidly by means of local cathode oxidation when exposed to the ambient atmosphere, resulting in visible non-emissive areas called black spots. High performance inorganic based encapsulations are required to protect the OLED. We have applied a hybrid thin-film encapsulation stack consisting of two inorganic barrier layers of silicon nitride deposited at low temperature with an organic layer in between. The resulting water permeation mechanism into the OLED is solely by means of lateral pinhole-to-pinhole transport. With the application of CaO nanoparticles in the organic layer the lateral water transport rate is reduced and we show that black spot formation in 8 cm2 OLEDs is delayed by 6000 h at accelerated climate conditions of 60°C/90% relative humidity. This is estimated to correspond to 20 years at ambient conditions.

Identification and control of moulds responsible for black spot spoilage in dry-cured ham

The aims of this work were to identify moulds responsible for black spot spoilage in the drying and cellar stages of dry-cured ham processing and evaluate the effectiveness of preventive actions for controlling this alteration. Four mould strains isolated from spoiled hams were identified by morphological characteristics and the ITS and β-tubulin sequencing. Two of them were Cladosporium oxysporum, one was C. cladosporioides and the remaining one was C. herbarum. These spoiling strains reproduced the black spots on dry-cured ham-based media and ham slices. Additionally, the effect of water activity (aw) conditions reached throughout dry-cured ham ripening and the activity of the protective culture Penicillium chrysogenum CECT 20922 against the spoiling moulds were evaluated. In the dry-cured ham model system the growth of the Cladosporium strains was minimised when the aw approaches 0.84 or in P. chrysogenum CECT 20922 inoculated dry-cured ham slices. Therefore such combination could be used to avoid the black spot formation in dry-cured ham.

Multi-breakdown model for explaining the formation and growth of black spots in PZT capacitor under DC bias

Lead zirconate titanate (PZT) is widely used in various electro-mechanical devices because of its piezoelectric function. In some of its applications, the piezo ceramic will be subjected to a DC bias. The applied DC bias will stress the PZT ceramic and can undergo an electrical degradation process. This electrical degradation process demonstrates itself as resistance decreases and leakage current increases. Therefore, the electrical degradation phenomenon can severely impact on device performance and reliability. It has been found that, accompany this electrical breakdown process, black spots will appear in the ceramic body. In this paper, the formation and growth of the black spots in a PZT capacitor under DC bias is investigated. The black spot area is further characterized with various analytical methods. Based on previous research, a multi-breakdown model is proposed for explaining the mechanism of black spot growth.

Surface, structural and tensile properties of proton beam irradiated zirconium

This paper reports the surface, structural and tensile properties of proton beam irradiated pure zirconium (99.8%). The Zr samples were irradiated by 3.5MeV protons using MC-50 cyclotron accelerator at different doses ranging from 1×1013 to 1×1016 protons/cm2. Both un-irradiated and irradiated samples were characterized using Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD) and Universal Testing Machine (UTM). The average surface roughness of the specimens was determined by using Nanotech WSxM 5.0 develop 7.0 software. The FESEM results revealed the formation of bubbles, cracks and black spots on the samples’ surface at different doses whereas the XRD results indicated the presence of residual stresses in the irradiated specimens. Williamson–Hall analysis of the diffraction peaks was carried out to investigate changes in crystallite size and lattice strain in the irradiated specimens. The tensile properties such as the yield stress, ultimate tensile stress and percentage elongation exhibited a decreasing trend after irradiation in general, however, an inconsistent behavior was observed in their dependence on proton dose. The changes in tensile properties of Zr were associated with the production of radiation-induced defects including bubbles, cracks, precipitates and simultaneous recovery by the thermal energy generated with the increase of irradiation dose.

Characterisation and detection of spoilage mould responsible for black spot in dry-cured fermented sausages

Moulds responsible for black spot spoilage of dry-cured fermented sausages were characterised. For this purpose, samples were taken from those dry-cured fermented sausages which showed black spot alteration. Most of the mould strains were first tentatively identified as Penicillium spp. due to their morphological characteristics in different culture conditions, with one strain as Cladosporium sp. The Cladosporium strain was the only one which provoked blackening in culture media. This strain was further characterised by sequencing of ITS1-5.8S-ITS2 rRNA and β-tubulin genes. This mould strain was able to reproduce black spot formation in dry-cured fermented sausage ‘salchichón’ throughout the ripening process. In addition, a specific and sensitive real-time PCR method was also developed to detect Cladosporium oxysporum responsible for the black spot formation in sausages. This method could be of great interest for the meat industry to detect samples contaminated with this mould before spoilage of product avoiding economic losses for this sector.

Modified Atmosphere Packaging (MAP) for Control of Black Spot Formation in Chilled Prawns

The marketing of organically labeled prawns is predominately in a cooked or raw frozen form to avoid the development of melanosis (black spot). Certification for organic status prohibits the use of any added chemicals. The application of 60% CO2/40%N2 modified atmosphere to chilled (raw) prawns using two species of prawn was investigated for the ability to control black spot formation. Sensory assessment and microbiological counts were used to determine the end of product shelf life. Modified atmosphere packaged (MAP) prawns exhibited no melanosis for up to 16 days. The high quality life was retained for 12 days; shelf life of 16 days, according to standard microbiological criteria, was achieved, which is more than twice previously reported for non-MAP prawns. Results suggest MAP may be an effective method for the marketing of organically grown prawns as well as those produced by conventional prawn aquaculture without application of the normal chemicals used to prevent black spot.

OLED compatible water-based nanolaminate encapsulation systems using ozone based starting layer

Highly efficient nanolaminate diffusion barriers made of TiO2/Al2O3 multilayers using low temperature atomic layer deposition optimized for organic light emitting diodes are presented. Water vapour transmission rates (WVTR) show values of the order of 10−3g/m2/d at 38°C, 90% RH on planarized PEN webs (pPEN) when ozone is used as the oxidizing precursor for Al2O3 deposition. OLED encapsulated with such diffusion barriers display few dark spots observed over 2000h after deposition and for aging under ambient conditions. Diffusion barriers deposited using water as the oxidizing precursor for Al2O3 result in at least 10 times lower WVTR on pPEN webs (10−4g/m2/d). However, these water based diffusion barriers are incompatible with OLEDs such that the latter show extensive black spot formation (areas of no visible luminescence) immediately after deposition. Finally through the growth of these initial black spots, more than 40% loss in initial luminescence occurs after merely 900h of operation. In this report, we introduce a new methodology for OLED encapsulation using a two step process where 10nm thick ozone Al2O3 based nanolaminate diffusion barrier is followed by a 90nm thick water Al2O3 based diffusion barrier (keeping TiO2 precursors always the same). With this novel diffusion barrier stack, no visible black spot growth is observed over 2000 continuous operation hours under ambient conditions. Simultaneously, high OLED luminescence representing 90% of the initial luminescence value, which is measured at t=0 is maintained after 2000h of operation. Low WVTR values in the 10−4g/m2/d range on pPEN webs are consistently measured in these essentially water based barrier layers with only 10nm thick starting ozone Al2O3 based nanolaminate diffusion barriers. The results reported here have implications on developing methodologies for ultra high performance, OLED compatible diffusion barriers by ALD.

Mechanistic features of nanodiamonds in the lapping of magnetic heads.

Nanodiamonds, which are the main components of slurry in the precision lapping process of magnetic heads, play an important role in surface quality. This paper studies the mechanistic features of nanodiamond embedment into a Sn plate in the lapping process. This is the first study to develop mathematical models for nanodiamond embedment. Such models can predict the optimum parameters for particle embedment. From the modeling calculations, the embedded pressure satisfies p 0 = (3/2)·(W/πa 2) and the indentation depth satisfies . Calculation results reveal that the largest embedded pressure is 731.48 GPa and the critical indentation depth δ is 7 nm. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and Auger electron spectroscopy (AES) were used to carry out surface quality detection and analysis of the disk head. Both the formation of black spots on the surface and the removal rate have an important correlation with the size of nanodiamonds. The results demonstrate that an improved removal rate (21 nm·min−1) can be obtained with 100 nm diamonds embedded in the plate.

Self-Recovery and Re-Degradation Phenomena for PZT Ceramic

Lead zirconate titanate (PZT) ceramic as a kind of widely used piezoelectric material is developing very fast for these years because of its high piezoelectric properties. Therefore, various theories have been developed for describing the mechanism of the degradation process of the PZT ceramic [1-4]. However, there are still many contentions in these reported theories. In this paper, experiments on commercially available lead zirconate titanate (PZT) ceramic samples have been designed. Through this work, it has been found that the leakage current is increasing with the electrical degradation process of the PZT ceramic. Self-recovery and re-degradation phenomena and formation of black spots have also been observed. It has suggested that the duration of the re-degradation process depends on the duration of the self-recovery and the re-degradation process would not produce any black spots and the black spots are only formed during electrical degradation process.

Reversible luminance decay in polymer light-emitting electrochemical cells

The luminance decay of generic sandwich polymer light-emitting electrochemical cells has been investigated. Under constant current operation, the apparent luminance decay is caused by both the formation of non-emitting black spots, which decreases the active emitting area, and the in situ electrochemical doping, which quenches the luminescence of the light-emitting electrochemical cell film. The latter's effect on luminance, however, can be mostly reversed by letting the electrochemical doping relax. A dramatic recovery of luminance is observed when the device is stored without voltage bias and/or moderately heated between consecutive operations. The decay/recovery cycle can be repeated multiple times with little loss of luminance despite the high current density (167 mA/cm2) applied. At lower current density, a freshly made device loses less than 10% of its peak luminance after over 200 h of continuous operation. Polymer light-emitting electrochemical cells therefore possess vastly longer operating lifetime if allowed to recover from the effect of reversible doping.

Drainage and critical thickness of foam films from mixed solutions of bovine serum albumin and n-dodecyl-β-D-maltoside

Data for the kinetic stability of foam films from ``bovine serum albumin'' (BSA) solution, or from its mixed solutions with non-ionic surfactant ``n-dodecyl-β-D-maltoside'' (C12G2) are presented and discussed based on the specificity of interactions between the components analyzed by tensiometry and fluorescence spectroscopy.The thickness as a function of time in different areas of BSA or BSA/ C12G2 films formed at different experimental conditions (different molar ratios between protein and surfactant, film radius) is measured interferometrically from a video recording of the film evolution. The thinning velocity presented via drainage coefficient, α, in the areas where first, or other black spots appear, or in other film areas was determined from the lnh (t) dependences up to the critical state (first black spot formation in the film). It is found that BSA film has the slowest thinning and the most regular thickness. The thinning velocity of the both BSA and BSA/surfactant films in the area where first spot appears decreases considerably with increasing of the film radius. The thinning velocity values in other film areas are close to those obtained in areas with spots, but only in the initial period of film drainage. The thinning in these places almost stops around the critical state. In above mentioned different film areas the thicknesses, corresponding to the critical state are measured and compared. It is found that the values of critical thickness in areas with spots are noticeably smaller, than critical thickness in other areas, irrespectively of the film radius and molar ratio of the stabilizers. It means that the value of critical thickness for a protein film can not be obtained as an average value of the thickness values determined in different film areas just before the first black spot formation.

Gene expression analysis identifies new candidate genes associated with the development of black skin spots in Corriedale sheep

The white coat colour of sheep is an important economic trait. For unknown reasons, some animals are born with, and others develop with time, black skin spots that can also produce pigmented fibres. The presence of pigmented fibres in the white wool significantly decreases the fibre quality. The aim of this work was to study gene expression in black spots (with and without pigmented fibres) and white skin by microarray techniques, in order to identify the possible genes involved in the development of this trait. Five unrelated Corriedale sheep were used and, for each animal, the three possible comparisons (three different hybridisations) between the three samples of interest were performed. Differential gene expression patterns were analysed using different t-test approaches. Most of the major genes with well-known roles in skin pigmentation, e.g. ASIP, MC1R and C-KIT, showed no significant difference in the gene expression between white skin and black spots. On the other hand, many of the differentially expressed genes (raw P-value < 0.005) detected in this study, e.g. C-FOS, KLF4 and UFC1, fulfil biological functions that are plausible to be involved in the formation of black spots. The gene expression of C-FOS and KLF4, transcription factors involved in the cellular response to external factors such as ultraviolet light, was validated by quantitative polymerase chain reaction (PCR). This exploratory study provides a list of candidate genes that could be associated with the development of black skin spots that should be studied in more detail. Characterisation of these genes will enable us to discern the molecular mechanisms involved in the development of this feature and, hence, increase our understanding of melanocyte biology and skin pigmentation. In sheep, understanding this phenomenon is a first step towards developing molecular tools to assist in the selection against the presence of pigmented fibres in white wool.

Characterization of plasma-sprayed Y2O3 coating and investigation of its visual aspect change

Abstract Yttria (Y2O3) has been commonly used as a protective coating material because it has strong resistance to plasma erosion with reducing the amount of reaction products generated during the semiconductor/LCD fabrication process. We have investigated the visual aspect of the plasma-sprayed Y2O3 coating both experimentally and numerically to propose the process conditions proper for white Y2O3 coating. It was demonstrated that heating of the particle surface in oxygen deficient plasma jet core resulted in the reduction of coating materials associated with the formation of black spots, while the re-oxidation of reduced feed stock materials at long spray distance, where they were exposed to relatively lower temperature of plasma and abundant oxygen, caused the whitening of coating. Based on the results, we proposed a spray coating condition proper for reducing the black spots formed in protective Y2O3 ceramic coating.

Time course effects on primary metabolism of potato ( Solanum tuberosum) tuber tissue after mechanical impact

An important feature relevant to potato ( Solanum tuberosum) tuber quality management is the susceptibility to blackspot bruising caused by melanin production after exposure to severe mechanical stress. We analyzed the previously neglected nature and sequence of responses in primary metabolism and compared the cultivars ‘Afra’ and ‘Milva’ that differ in tissue elasticity and susceptibility to blackspot bruising. Mechanical stress application was highly standardized and differential formation of bruising damage and occurrence of small cracks in the outer tuber layers were demonstrated. Concomitant GC–TOF-MS based metabolite profiling revealed characteristic changes in central metabolism, namely in intermediates of the TCA cycle and linked parts of amino acid metabolism, with the clear exception of phenylalanine and tyrosine, the immediate precursor of melanin biosynthesis. We conclude that the initial metabolic responses and the initiation of blackspot formation are distinct, and that melanin biosynthesis is not driven by early precursor accumulation through activation of the aromatic amino acid biosynthesis pathway.

New Modified Dipping Method Using 4-hexylresorcinol for Preventing Blackspot Formation in Prawns

Industry acceptance of alternative sulphite treatments for preventing blackspot in prawns is limited. This study demonstrated that dipping prawns (Penaeus monodon and Fenneropenaeus merguiensis) in a less concentrated solution for longer times provides better control of blackspot formation than the recommended 2 minute dip in 50 mg/L 4-hexylresorcinol. Protection improved as modified dipping times and solution concentrations increased. Blackspot protection provided by most of the modified dip methods was more effective than a 1 minute dip in 1% sodium metabisulphite. The recommended 2 minute dip method should be limited to 125 kg when used on consecutive 25-kg batches of prawns. Yields increased by less than 10% even after 72-hour exposure in the modified dip. The new dipping method meets most international residue standards when applying the modified treatments evaluated.

Impact of discards of beam trawl fishing on the nematode community from the Tagus estuary (Portugal)

The impact of dead discards, originating from beam trawl fishing on the nematode community from the Tagus estuary was investigated in terms of vertical distribution of the dominant nematode groups. Sediment cores were collected from a mud-flat from the Tagus estuary. Crangon crangon (Linnaeus, 1758) carcasses were added to the surface of the cores, simulating the settling of dead discards on the sediment. The vertical distribution of the dominant nematode groups was determined up to 4 cm deep at four different moments in time post deposition (0, 2, 4 and 6 h) and compared to control cores. The C. crangon addition to the sediment led to the formation of black spots and therefore oxygen depleted areas at the sediment surface. The Chromadora/ Ptycholaimellus group, normally dominant at the surface layer, migrated downwards due to their high sensibility to toxic conditions. Sabatieria presented the opposite trend and became the dominant group at the surface layer. Since Sabatieria is tolerant to oxygen stressed conditions and high sulphide concentrations, we suggest that it migrated opportunistically towards an unoccupied niche. Daptonema, Metachromadora and Terschellingia did not show any vertical migration, reflecting their tolerance to anoxic and high sulphidic conditions. Our study showed that an accumulation of dead discards at the sediment surface might therefore alter the nematode community vertical distribution. This effect is apparently closely related to toxic conditions in the sediment, induced by the deposition of C. crangon at the sediment surface. These alterations might be temporal and reflect an adaptation of the nematode community to dynamic intertidal environments.

Phenoloxidase Activity of Hemocyanin in Whiteleg Shrimp Penaeus vannamei: Conversion, Characterization of Catalytic Properties, and Role in Postmortem Melanosis

Latent phenoloxidase activity of hemocyanin (Hc) in whiteleg shrimp Penaeus vannamei was assayed to determine its potential involvement in postmortem melanosis. Conversion of pure 12-mer, but not 6-mer, hemocyanin to phenoloxidase by endogenous (serine proteinases) and exogenous (SDS) effectors demonstrated the need of complex aggregation for displaying enzyme activity. Because Hc was converted to Hc-phenoloxidase (HcPO) by hemocytes extracts, the mechanism of conversion seems to be the same for polyphenoloxidases. HcPO has similar biochemical and kinetic properties as real polyphenoloxidases and uses mono- and diphenols as substrates. The kinetics of hydroxygenation of monophenols has a lag phase, typical for tyrosinases, contrary to oxidation of diphenols. Regardless of the structure of the substrate, melanin is finally formed. Because of the abundance, distribution, and resistance of Hc to freezing-thawing, involvement of Hc in black spot formation postmortem is suggested. This has important implications for commercialization of shrimp and related seafood.

Polyphenol Uses in Seafood Conservation

Oxidative reactions are the main culprits in color alterations associated with seafood spoilage. Black spot formation or melanosis is a natural post-mortem oxidative mechanism, which cause crustaceans rejection by consumers because of their appearance. The use of phenolic compounds, such as 4-hexylresorcinol, appears to be a good alternative to the conventional sulphites, allowing longer conservation periods. Lipidic oxidation is also one of the main restrictive factors in the preservation of fish products. The application of natural plant extracts to prevent oxidative rancidity has been studied in a number of fish products. However, polyphenol-protein interactions may have a masking effect on the free radical scavenging activity of polyphenols and may also have a detrimental effect on the in vivo bioavailability of both phenolics and proteins. Polyphenolic plant extracts may be included into fish gelatin-based films in order to obtain an edible film with antioxidant properties. These films applied on the surface of raw or mild processed salted or smoked fish may increase the shelf life of fish products by reduction the lipid oxidation during the chilled storage.

The Effects of Process Parameters on Mechanical Property and Visual Aspect of Plasma Sprayed Y2O3 Coating

The effects of process parameters on the mechanical property and visual aspect of Y203 coating formed by plasma spraying were investigated. For the experiments, granular Y203 powders were plasma sprayed using plasma gun with external powder-feeding system. When an asymmetric spraying was introduced by one-side powder-feeding, bigger pores and more frequent black spots were found in the region formed in opposite side from powder feeding direction, where the droplets of relatively lower temperature and lower flying velocity impinged to form coating. The optimum conditions for highest Vickers hardness were found to be different from those for white visual aspect of the Y203 coatings. Among the process parameters such as Ar flow rate, H2 flow rate, 02 contents, spraying distance, spraying distance was known to be most important for the formation of black spots in Y203 coating. The black spots formed in Y203 coating are thought to have relationship with the breakdown of stoichiometry between Y and O during plasma spraying. Consequently, the processing route not to form black spots in Y203 coating is described.