Large Surface Features Research Articles

Visible and Near-infrared Spectral Properties of Martian Slope Streaks

Martian slope streaks are large surface features with lower albedo than their surroundings that are one of the few active geologic processes occurring on Mars today. We investigated the slope streaks’ spectral properties using images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) at nine sites, including three sites with observations over multiple years to enable time-series analysis. For each individual slope streak within each image, we determined the average spectra of each streak and of the slope immediately adjacent to account for changes in geology across a CRISM image or within slopes containing streaks. We find a trend where the visible spectral continuum (0.4–0.6 μm) is strongly negative for the darkest slope streaks, and the spectral continuum increases as the slope streaks fade, consistent across all sites and over multiple observations of the same site. We do not find absorption at 1.4 or 1.9 μm associated with hydration. In some slope streaks, we see evidence of Fe-bearing minerals, but these signatures are also found in the streak-free slope directly adjacent, suggesting that the streaks have a similar mineralogy to their surroundings. The spectral changes that we see are most consistent with changes in the fine dust component and support a dry flow mechanism whereby slope streaks are formed by processes that trigger dust removal from the slope in particular locations, with the streaks slowly fading as dust resettles on the surface.

Advanced morphological characterization of DC sputtered copper thin films

In this paper, Cu thin films were successfully deposited on glass substrates using DC magnetron sputtering at varying deposition times. The deposition time was varied as 5, 9, 11 and 17[Formula: see text]min. The obtained Cu thin films were analyzed for morphology and topography using atomic force microscopy (AFM). The size of the surface structures/grains was seen to evolve with deposition time. The conventional/statistical, fractal and multifractal analyses were carried out on AFM images using existing imaging algorithms. The arithmetic roughness and interface width parameters were seen to evolve with the sputtering time. The autocorrelation and height–height correlation functions revealed that the surfaces of all the Cu thin films exhibited self-affine character, but were not mounded properties. The fractal dimensions computed using box counting and power spectral density functions revealed that larger dimensions were associated with larger surface features. The lacunarity coefficients were too small indicating that the surfaces were generally deficient in porosity and other defects. The multifractal analyses revealed that spatial roughness does not exhibit linear relationship with the deposition time. The study reveals that surface evolution and nanoscale behavior is significantly influenced by the deposition time although a linear relationship is not established.

N/C doped nano-size IrO2 catalyst of high activity and stability in proton exchange membrane water electrolysis

It is highly desirable to synthesize and deploy low-cost and highly efficient catalysts for the oxygen evolution reaction (OER) to catalyze water splitting. We show that N/C doped amorphous iridium oxide combines the benefits of nano-size (approximately 2 nm), which results in exposure to large active surface areas and features of oxygen defects, which make for an electronic structure suitable for the OER. Systematic studies indicate that the OER activity of the iridium oxide catalyst is accelerated by the effect of the structure and chemical state of the iridium element. Remarkably, the N/C doped amorphous iridium oxide catalyst shows a lower cell voltage of 1.774 V at 1.5 A cm−2, compared with IrO2 (1.847 V at 1.5 A cm−2), and it can maintain such a high current density for over 200 h without noticeable performance deterioration. This work provides a promising method for the improving OER electrocatalysts and the construction of an efficient and stable PEM water cracking system.

Multifractal Analysis to Determine the Effect of Surface Topography on the Distribution, Density, Dispersion and Clustering of Differently Organised Coccal-Shaped Bacteria.

The topographic features of surfaces are known to affect bacterial retention on a surface, but the precise mechanisms of this phenomenon are little understood. Four coccal-shaped bacteria, Staphylococcus sciuri, Streptococcus pyogenes, Micrococcus luteus, and Staphylococcus aureus, that organise in different cellular groupings (grape-like clusters, tetrad-arranging clusters, short chains, and diploid arrangement, respectively) were used. These differently grouped cells were used to determine how surface topography affected their distribution, density, dispersion, and clustering when retained on titanium surfaces with defined topographies. Titanium-coated surfaces that were smooth and had grooved features of 1.02 µm-wide, 0.21 µm-deep grooves, and 0.59 µm-wide, 0.17 µm-deep grooves were used. The average contact angle of the surfaces was 91°. All bacterial species were overall of a hydrophobic nature, although M. luteus was the least hydrophobic. It was demonstrated that the 1.02 µm-wide featured surface most affected Strep. pyogenes and S. sciuri, and hence the surfaces with the larger surface features most affected the cells with smaller dimensions. The 0.59 µm featured surface only affected the density of the bacteria, and it may be suggested that the surfaces with the smaller features reduced bacterial retention. These results demonstrate that the size of the topographical surface features affect the distribution, density, dispersion, and clustering of bacteria across surfaces, and this is related to the cellular organisation of the bacterial species. The results from this work inform how surface topographical and bacterial properties affect the distribution, density, dispersion, and clustering of bacterial retention.

Fabrication of PVDF-blended ultrafiltration membranes incorporated by chiral mesoporous silica for enantioseparation

Novel poly(vinylidene fluoride) (PVDF) ultrafiltration membranes blending with chiral mesoporous SiO2 materials were constructed to improve the anti-fouling and separation performance of PVDF-blended membranes. The formation of asymmetric mesoporous structure of chiral mesoporous SiO2 caused their large hydrophilic surface and significant chiral features, which enhanced the hydrophilicity and polarity of the resulting PVDF membranes blended with chiral mesoporous SiO2. So, the PVDF-blended membranes containing chiral mesoporous SiO2 had a high permeation performance and anti-fouling property. After blending with chiral mesoporous SiO2, the maximum flux of membranes exceeded 500 L·m−2·h−1 and was 6.5-fold higher than that of neat PVDF. Due to the stereo-specific interaction between enantiomers and chiral recognition sites introduced by chiral mesoporous SiO2 in the membranes, all PVDF-blended membranes had evident enantioseparation performance for DL-racemic tryptophan. The C-SiO2-20/PVDF-blended membranes had the highest enantioseparation performance under the same addition content and the maximum enantiomeric excess (e.e.%) was more than 20 %. Given the strong stereo-specific interaction and hydrogen bonding between d-tryptophan and β-cyclodextrin (β-CD), the addition of more β-CD would introduce more chiral recognition sites into the membranes, thereby enhancing the enantioseparation performance of the membranes for d-tryptophan. The maximum e.e.% of C-SiO2-20/β-CD/PVDF-blended membranes for the tryptophan enantiomer reached 55%.

Impacts of the San Francisco Bay Area shelter-in-place during the COVID-19 pandemic on urban heat fluxes

The purpose of this study was to make quantitative connections between changes in social and economic activities in northern California urban areas and related Earth system environmental responses to the COVID-19 pandemic in 2020. We tested the hypothesis that the absence of worker activities during Shelter-in-Place in the San Francisco Bay Area detectably altered the infrared heat flux from parking lots, highways, and large building rooftops, caused primarily by quantitative changes in the reflective properties in these different classes of urban surfaces. The Landsat satellite's thermal infrared (TIR) sensor imagery for surface temperature (ST) was quantified for all the large urban features in the Bay Area that have flat (impervious) surfaces, such parking lots, wide roadways, and rooftops. These large impervious surface features in the five-county Bay Area were first delineated and classified using sub-meter aerial imagery from the National Agriculture Imagery Program (NAIP). We then compared Landsat ST data acquired on (or near) the same dates from the three previous years (2017–2019) for all these contiguous impervious surfaces. Results showed that all the large parking lots, roadway corridors, and industrial/commercial rooftops across the entire Bay Area urban landscape were detected by Landsat ST time series as significantly cooler (by 5o C to 8o C) during the unprecedented Shelter-in-Place period of mid-March to late-May of 2020, compared to same months of the three previous years. The explanation for this region-wide cooling pattern in 2020 that was best supported by both remote sensing and ground-based data sets was that relatively low atmospheric aerosol lower (PM2.5) concentrations from mid-March to late May of 2020 resulted in weaker temperature inversions over the Bay Area, higher diurnal surface mixing, and lowered urban surface temperatures, compared to the three previous years.

Advanced textured monocrystalline silicon substrates with high optical scattering yields and low electrical recombination losses for supporting crack‐free nano‐ to poly‐crystalline film growth

AbstractCrystalline silicon tandem devices with perovskites, CIGS, and nanocrystalline silicon, as well as the TOPCon design, are incompatible with the conventional pyramidal surface texture of silicon. This is a result of crack formation in nano to polycrystalline growth on large sharp surface features. In this work, three texturing approaches are investigated, using alkaline and/or acidic wet chemical etches, that can lead to the crack‐free growth of nano to polycrystalline materials on textured surfaces. In this work, we show that without acidic smoothening, the fraction of <111> pyramidal surface coverage has to remain relatively small to prevent crack formation during crystalline growth on these surfaces. Applying an acidic etch as a function of time continuously smoothens surface features. This shifts the reflection to wider scattering angles and results in higher total reflected intensity with respect to the conventional texture, making it an interesting option for a wide variety of tandem pv applications. Finally, we demonstrate crater‐like features on a <100> monocrystalline silicon surface using an etching process including a sacrificial layer. These craters increase light scattering into wider angles, but to a lesser extent than the former approach. In terms of passivation, we demonstrate the positive effect of a post deposition hydrogen treatment. Initial dilution of the silane plasma improves passivation on a <111> surface, but is detrimental to passivation on a <100> surface, likely because the hydrogen dilution results in epitaxial growth at the c‐Si/a‐Si:H hetero‐interface. A minority carrier lifetime of over 3 ms has been achieved for all texturing approaches, after deposition of a 15 nm a‐Si:H layer on both sides of the wafer, for different a‐Si:H deposition and annealing schemes.

A Smaller Bearing Ratio, as a Surface Texture Measure, Promotes Faster Sliding on Ice

Abstract Surfaces only characterized by a roughness Ra or Sa may have a totally different surface texture and include complex patterns such as grooves, dimples, or a mirror-polish. Here, the bearing ratio is proposed as an additional characterization measure to determine the sliding performance of a steel–ice friction pair. Different steel surfaces were produced by milling, shot blasting, and scratching, followed by texture assessment with a stylus type three-dimensional (3D) profilometer. The bearing ratio and other 3D roughness parameters were determined. Tribology experiments involved a 3 m long inclined plane tribometer and the speed measured at four points during the sliding experiment. Correlation between the steel sliding speed and the bearing ratio was observed under two different regimes: at warmer conditions and at colder conditions. Experiment 1 depicting warmer conditions exhibited a relative humidity of 64%, an air temperature of −2 °C, and an ice temperature of −9 °C. Experiment 2 for colder conditions showed a relative humidity of 78%, an air temperature of 1 °C, and an ice temperature of −4 °C. The sliding speed correlated with the bearing ratio in these two conditions showing −0.91 and −0.96, respectively. A strong correlation between the sliding speed and the bearing ratio shows the value of the bearing ratio as an additional surface characteristic for considering larger surface features.

The effect of nozzle internal flow on spray atomization

The effect of nozzle surface features on the overall atomization behavior of a liquid jet is analyzed in the present computational work by adopting three representative geometries, namely a single X-ray tomography scan of the Engine Combustion Network’s Spray A nozzle (Unprocessed), a spline reconstruction of multiple scans (Educated), and a purely external flow configuration. The latter configuration is often used in fundamental jet atomization studies. Numerically, the two-phase flow is solved based on algebraic volume-of-fluid methodology utilizing the OpenFoam solver, interFoam. Quantitative characterization of the surface features concerning the first two geometries reveals that while both of them have similar levels of cylindrical asymmetries, the nozzle configuration pertaining to the Unprocessed geometry has much larger surface features along the streamwise direction than the Educated geometry. This produces for the Unprocessed configuration a much larger degree of non-axial velocity components in the flow exiting the orifice and also a more pronounced disturbance of the liquid surface in the first few diameters downstream of the nozzle orifice. Furthermore, this heightened level of surface destabilization generates a much shorter intact liquid core length, that is, it produces faster primary atomization. The surprising aspect of this finding is that the differences between the Unprocessed and Educated geometries are of [Formula: see text](1) μm, and they are able to produce [Formula: see text](1) mm effects in the intact liquid core length. In spite of more pronounced atomization for the Unprocessed geometry, the magnitude of the turbulent liquid kinetic energy is roughly the same as the Educated geometry. This highlights the important role of mean field quantities, in particular, non-axial velocity components, in precipitating primary atomization. At the other end of the spectrum, the external-only configuration has the mildest level of surface disturbances in the near field resulting in the longest intact liquid core length.

Combined atomic force microscopy and photoluminescence imaging to select single InAs/GaAs quantum dots for quantum photonic devices

We report on a combined photoluminescence imaging and atomic force microscopy study of single, isolated self-assembled InAs quantum dots. The motivation of this work is to determine an approach that allows to assess single quantum dots as candidates for quantum nanophotonic devices. By combining optical and scanning probe characterization techniques, we find that single quantum dots often appear in the vicinity of comparatively large topographic features. Despite this, the quantum dots generally do not exhibit significant differences in their non-resonantly pumped emission spectra in comparison to quantum dots appearing in defect-free regions, and this behavior is observed across multiple wafers produced in different growth chambers. Such large surface features are nevertheless a detriment to applications in which single quantum dots are embedded within nanofabricated photonic devices: they are likely to cause large spectral shifts in the wavelength of cavity modes designed to resonantly enhance the quantum dot emission, thereby resulting in a nominally perfectly-fabricated single quantum dot device failing to behave in accordance with design. We anticipate that the approach of screening quantum dots not only based on their optical properties, but also their surrounding surface topographies, will be necessary to improve the yield of single quantum dot nanophotonic devices.

Substrate effects and diffusion dominated roughening in Cu2O electrodeposition

Cuprous oxide (Cu2O) films from 25 nm to 1500 nm were electrodeposited on n-Si(100) and Ni/n-Si(100) substrates from aqueous solution at room temperature. X-ray diffraction and transmission electron microscopy imaging show that the Cu2O structure and morphology are strongly affected by the substrate choice, with V shape and U shape columnar growth on n-Si(100) and Ni/n-Si(100), respectively. Atomic force microscopy reveals the presence of rounded grains at the surface in both cases. Anomalous and normal roughening are observed in films grown on n-Si and Ni, respectively, but estimates of scaling exponents are not conclusive. On the other hand, the distributions of local heights, roughness, and extremal heights show good agreement with those of the fourth order linear stochastic equation of Mullins and Herring (MH). Thus, surface dynamics in both systems is dominated by diffusion of adsorbed molecules, with no large scale effect of possible inhomogeneities in mass flux from the solution or in reaction and adsorption rates. In growth on n-Si substrates, the noise amplitude of the MH equation increases in time as t0.8, while the coefficient of the curvature-related term is time-independent. Step edge energy barriers restrict the mass flux across grain boundaries, thus a broad size distribution of initial grains leads to coarsening of the larger ones. This explains their V shape in the thickest films and establishes a connection with the anomalous roughening. These effects are reduced in films grown on Ni/n-Si, which initially have much larger grains with narrower size distributions and, consequently, smaller fluctuations in coarse grained growth rates. Thus, despite the relevance of electrochemical conditions for Cu2O films to grow and their influence on crystallographic orientation, large scale surface features are determined by physical properties of the material and its interactions with the substrate, with a universal microscopic dynamics similar to vapor deposition.

APCVD of dual layer transparent conductive oxides for photovoltaic applications

We report the atmospheric pressure chemical vapour deposition (APCVD) of a dual layer transparent conductive oxide (TCO). This combines a fluorine doped tin oxide (FTO) base layer with a fluorine doped zinc oxide (FZO) top layer, where we seek to utilise the respective advantages of each material and the differences in their associated industrial deposition process technologies. Deposition of a 250nm thick FZO layer on FTO was enough to develop features seen with FZO only layers. The crystallographic orientation determined by the FZO dopant concentration. Changes to the deposition parameters of the underlying FTO layer effected stack roughness and carrier concentration, and hence optical scattering and absorption. Photovoltaic cells have been fabricated using this TCO structure showing promising performance, with efficiencies as high as 10.21% compared to reference FTO only values of 9.02%.The bulk of the coating was FTO, providing the majority of conductivity and the large surface features associated with this material, whilst keeping the overall cost low by utilising the very fast growth rates achievable. The FTO was capped with a thinner FZO layer to provide a top surface suitable for wet chemical or plasma etching, allowing the surface morphology to be tuned for specific applications.

3D SEM for surface topography quantification – a case study on dental surfaces

3D analysis of surface topography is becoming a more used tool for industry and research. New ISO standards are being launched to assist in quantifying engineering surfaces. The traditional optical measuring instrumentation used for 3D surface characterization has been optical interferometers and confocal based instrumentation. However, the resolution here is limited in the lateral dimension to the wavelength of visible light to about 500 nm. The great advantage using the SEM for topography measurements is the high flexibility to zoom from low magnifications and locating interesting areas to high magnification of down to nanometer large surface features within seconds. This paper presents surface characterization of dental implant micro topography. 3D topography data was created from SEM images using commercial photogrammetric software. A coherence scanning interferometer was used for reference measurements to compare with the 3D SEM measurements on relocated areas. As a result of this study, measurements emphasizes that the correlation between the accepted CSI measurements and the new technology represented by photogrammetry based on SEM images for many areal characterization parameters are around or less than 20%. The importance of selecting sampling and parameter sensitivity to varying sampling is high-lighted. Future work includes a broader study of limitations of the photogrammetry technique on certified micro-geometries and more application surfaces at different scales.

Time dependence of effective slip on textured hydrophobic surfaces

In this paper, we present results on water flow past randomly textured hydrophobic surfaces with relatively large surface features of the order of 50 μm. Direct shear stress measurements are made on these surfaces in a channel configuration. The measurements indicate that the flow rates required to maintain a shear stress value vary substantially with water immersion time. At small times after filling the channel with water, the flow rates are up to 30% higher compared with the reference hydrophilic surface. With time, the flow rate gradually decreases and in a few hours reaches a value that is nearly the same as the hydrophilic case. Calculations of the effective slip lengths indicate that it varies from about 50 μm at small times to nearly zero or “no slip” after a few hours. Large effective slip lengths on such hydrophobic surfaces are known to be caused by trapped air pockets in the crevices of the surface. In order to understand the time dependent effective slip length, direct visualization of trapped air pockets is made in stationary water using the principle of total internal reflection of light at the water-air interface of the air pockets. These visualizations indicate that the number of bright spots corresponding to the air pockets decreases with time. This type of gradual disappearance of the trapped air pockets is possibly the reason for the decrease in effective slip length with time in the flow experiments. From the practical point of usage of such surfaces to reduce pressure drop, say, in microchannels, this time scale of the order of 1 h for the reduction in slip length would be very crucial. It would ultimately decide the time over which the surface can usefully provide pressure drop reductions.

Synthesis and characterization of Nb 2AlC thin films

We report on the synthesis and characterization of epitaxial c-axis oriented Nb 2AlC thin films deposited on c-axis sapphire (Al 2O 3) substrates by magnetron sputtering. Selected area electron diffraction reveal that independent of substrate temperature or film stoichiometry, there is the growth of a secondary phase not found in bulk, Nb 5Al 3C x with a- and c-axis lattice constants of 7.746 Å and 5.246 Å, respectively. Scanning electron micrographs reveal large surface features, many with hexagonal shape and faceted texture. Atomic force microscopy topographical measurements indicate a surface roughness of approximately 15% of the total film thickness. Electrical transport measurements show typical metal-like conduction with a room temperature resistivity of ≈ 0.9 μΩ-m and a residual resistivity ratio of 2.5. A superconducting transition was found at ≈ 440 mK.

A new instrument for automated microcontact printing with stamp load adjustment

An instrument for automated microcontact printing (microCP) on microscope slides is described. The movement of the stamp, which is actuated by a computer controlled pneumatic actuator, is precisely guided until it makes contact with the substrate. As a consequence, the absolute position of the microprinted patterns is reproducible over a series of substrates with 1 mum standard deviation. Exchange of substrates and stamps is a quick and simple procedure. This makes possible the microprinting of adjacent or superimposable patterns, with different products, in a reproducible manner. Furthermore, a novel approach is described for adjusting the load on the stamp during contact. Two adjustable screws are set up so that their length (with reference to the substrate holder) limits the stamp compression during contact. The load on the stamp is proportional to the stamp compression and from the experimental point of view, this is controlled by the operator adjusting the screws. This makes possible the microCP with stamps incorporating large surface features as well as stamps with isolated features raised on the surface. For proof of concept, automated microCP of a single parallelepiped polydimethylsiloxane feature, with a surface of 2 cm x 30 microm and a height of 25 mum, is demonstrated inside a microfluidic channel without roof collapse. A second example is provided with a single cross feature, possessing an overall surface of 140 x 140 microm(2) and a height of 14 microm. Potential applications of this versatile, inexpensive and compact instrument are discussed. The machine's potential for high throughput also makes it suitable for mass production applications.

Effects of Inhibited Acid Cleaning of Steel Fracture Surfaces for Failure Analyses

To Clean Or Not To Clean? In many failure analyses, adherent rust limits the scope of the fracture surface examinations and presents dilemmas for the failure analyst. The rust must be removed to identify fracture initiation sites and crack propagation modes, and the cleaning methodology varies with service life and type of environmental exposure that the component experienced. In this study, failure analysts examined laboratory fracture samples in a scanning electron microscope (SEM). The fractures were then subjected to controlled rusting conditions, and subsequently varying exposures to inhibited acid were used to remove the rust. The fracture surfaces were again examined in the SEM, after rust removal. The ideal immersion time in the inhibited acid varied with the desired inspection. Although large fracture surface features remained visible after long cleaning times, fine features were damaged by even brief exposure to inhibited acid. However, inhibited acid cleaning is extremely helpful and remains the only means of obtaining useable fractographic results in many situations.

Retention of microbial cells in substratum surface features of micrometer and sub-micrometer dimensions

Surfaces were produced with defined topographical features and surface chemistry. Silicon wafers, and wafers with attached nucleopore filters and quantifoils were coated with titanium using ion beam sputtering technology. Irregularly spaced, but regularly featured surface pits, sizes 0.2 and 0.5 μm, and regularly spaced pits with regular features (1 and 2 μm) diameter were produced. The smallest surface feature that could be successfully produced using this system was of diameter 0.2 μm. Ra, the average absolute deviation of the roughness irregularities from the mean line over one sampling length, Rz, the difference in height between the average of the five highest peaks, and the five lowest valleys along the assessment length of the profile and surface area values increased with surface feature size, with Ra values of 0.04–0.217 μm. There was no significant difference between the contact angles observed for smooth titanium surfaces with 0.2 and 0.5 μm features. However, a significant difference in contact angle was observed between the 1 and 2 μm featured surfaces ( p < 0.005). Substrata were used in microbial retention assays, using a range of unrelated, differently sized microorganisms. Staphylococcus aureus (cells 0.5–1 μm diameter) were retained in the highest numbers. S. aureus was well retained in the 0.5 μm sized pits and began to accumulate within larger surface features. Rod shaped Pseudomonas aeruginosa (1 μm × 3 μm) were preferentially retained, often end on, within the 1 μm surface features. Some daughter cells of Candida albicans blastospores were retained in 2 μm pits. For S. aureus and P. aeruginosa, the greatest numbers of cells were retained in the largest (2 μm) surface features. The number of C. albicans was similar across all the surfaces. The use of defined surfaces in microbial retention assays may lead to a better understanding of the interaction occurring between cells and surface features.

Measuring starspot temperature from line depth ratios

Gray and collaborators have recently demonstrated that line-depth ratios are a powerful tool for temperature discrim- ination, able to resolve dierences10 K. The method has been applied to detect temperature variations in the 5-15 K range due to activity cycles (e.g. Gray et al. 1996a, 1996b) or to rotation modulation produced by large surface features, called star-patches, like that detected in Boo A by Toner & Gray (1988). Cool starspots of a few tenths of the stellar surface produce bumps in a line profile, which migrate through the line profile allowing Doppler-imaging in fast rotating stars. In the hypothesis that in slowly-rotating stars the passage of dark spots pro- duces modulation of the center line depth of dierent amount in lines of dierent sensitivity to temperature, we have made test observations on three active binaries of the RS CVn type. Based on observations made at the Catania Astrophysical Observatory at a resolution R= 14 000, we show that line-depth ratios can be eectively used to determine spot temperatures of active binary systems. Using, on average, ten line pairs, selected in the 6100-6300 A wavelength range, with the help of observations of 30 main sequence and giant stars, we have derived a calibration relation of line-depth ratios (LDR) in an absolute temperature scale, taking into account the gravity eect in the calibration relation. Single LDRs converted to temperature through the calibration relations have led to clear rotational modulation of the average surface temperature with amplitudes of 177 K, 119 K, and 127 K for VY Ari, IM Peg and HK Lac, with average estimated errors of about 10 K. We show that the observed temperature variation amplitude allows us to define a minimum fractional spotted area coverage as a function of spot-photosphere temperature ratio. Adopting the maximum value of average temperature, determined from the LDRs, as that of the unspotted photosphere, we computed the average spot temperature corresponding to the minimum spot coverage. Although not univocally constrained, the temperature dierence (T = Tph Tsp) obtained for the three systems,T= 890 K for VY Ari,T= 750 K for IM Peg, andT= 810 K for HK Lac, are in good agreement with values derived with other methods.

ITO coated flexible transparent substrates for liquid crystal based devices

Indium tin oxide (ITO) thin films were successfully deposited onto transparent flexible substrates of hydroxypropylcellulose crosslinked with 1,4-Di-isocyanatobutane (BDI). According to our results, flexible substrates produced with a sol/gel fraction of 0.16 can reach, under vacuum conditions, a working temperature, T s≈150°C. The effect of O 2 plasma exposure on the transmittance and sheet resistance of the ITO coated flexible substrates has been studied. Atomic force microscopy shows that these type of substrates have a large surface roughness (4.8 nm) which originates high values in the diffuse transmittance. A memory of the large surface features of the flexible substrate is retained in the growing of ITO thin film. The best properties of the resulting ITO coated flexible substrates are an average total transmittance in the visible region of about 80% and a sheet resistance of about 4×10 4 Ω/sq.