Extinction Coefficient Values Research Articles

Determination of optical parameters of organic and inorganic thin films using both surface plasmon resonance and Abelès-Brewster methods

We present two methods to characterize organic and inorganic thin films. The thin films characterization was performed employing an opto-mechanical system, which uses light with p polarization from a He-Ne laser operating at 632.8nm. This system is based on the methods of Abelès-Brewster and surface plasmon resonance in the prism-based Kretschmann configuration. The metallic thin films characterization is made using surface plasmon resonance method while dielectric thin films (organic and inorganic) are characterized using both methods The optical parameters were obtained through a LabVIEW program based on the Fresnel equations by matrix method. The proposed system was proved through the optical characterization of gold, zinc sulfide and bovine serum albumin thin films with a fast, simple and accurate response and the optical parameters were obtained for each tested film. The refractive index and extinction coefficient values obtained for the gold thin film were 0.1758 and 3.3895, respectively, with a thickness of 53nm; a refractive index of 2.3501 was measured for the zinc sulfide thin film showing a thicknesses of 28.42nm; meanwhile bovine serum albumin presented a refractive index of 1.5595 with a thickness of 143.75nm.

Copper oxide nanocrystallites fabricated by thermal oxidation of pre-sputtered copper films at different temperatures and under oxygen and argon flows

Copper oxide nanocrystallites were synthesized from Cu thin films via controlled thermal treatment under O2 and Ar flows. The nanocrystallites were synthesized at 350, 400 and 500°C. XRD revealed that substoichiometric copper oxides such as Cu4O3 and Cu64O were emerged with Cu and CuO for samples treated at 350°C and 450°C, respectively, whereas single monoclinic CuO was emerged for the samples treated at 500°C. EDAX quantitative analysis confirmed the presence of both Cu and oxygen in the films with slightly excess oxygen for films treated at 400 and 500°C. SEM examinations confirmed the nanocrystallite morphologies for the examined samples and that more coalescent nanocrystallites, with diameters in the range 42–75nm, were obtained for the samples treated at 500°C. With increasing treatment temperature from 350 to 500°C, the films vary from highly reflecting reddish brown color to highly transparent. The estimated band gap values for the mixed copper oxide phases, samples treated at 450°C, and pure CuO phase were 1.27eV and 2.00eV, respectively. High refractive index and moderate extinction coefficient values were calculated for the samples containing mixed phases which may find new application in optoelectronics. The refractive index values for pure CuO were matched with the previously reported values. The samples treated at 350°C had very low resistivity and metallic behavior, whereas a semiconducting behavior was observed for the samples treated at 400 and 500°C.

Mass extinction spectra and size distribution measurements of quartz and amorphous silica aerosol at 0.33–19 µm compared to modelled extinction using Mie, CDE, and T-matrix theories

Simultaneous measurements were made of the spectral extinction (from 0.33–19 µm) and particle size distribution of silica aerosol dispersed in nitrogen gas. Two optical systems were used to measure the extinction spectra over a wide spectral range: a Fourier transform spectrometer in the infrared and two diffraction grating spectrometers covering visible and ultraviolet wavelengths. The particle size distribution was measured using a scanning mobility particle sizer and an optical particle counter. The measurements were applied to one amorphous and two crsystalline silica (quartz) samples. In the infrared peak values of the mass extinction coefficient (MEC) of the crystalline samples were 1.63 ± 0.23 m2g−1 at 9.06 µm and 1.53 ± 0.26 m2g−1 at 9.14 µm with corresponding effective radii of 0.267 and 0.331 µm, respectively. For the amorphous sample the peak MEC value was 1.37 ± 0.18 m2g−1 at 8.98 µm and the effective radius of the particles was 0.374 µm. Using the measured size distribution and literature values of the complex refractive index as inputs, three scattering models were evaluated for modelling the extinction: Mie theory, the Rayleigh continuous distribution of ellipsoids (CDE) model, and T-matrix modelling of a distribution of spheroids. Mie theory provided poor fits to the infrared extinction of quartz (R2 < 0.19), although the discrepancies were significantly lower for Mie theory and the amorphous silica sample (R2=0.86). The CDE model provided improved fits in the infrared compared to Mie theory, with R2 > 0.82 for crsytalline sillica and R2=0.98 for amorphous silica. The T-matrix approach was able to fit the amorphous infrared extinction data with an R2 value of 0.995. Allowing for the possibility of reduced crystallinity in the milled crystal samples, using a mixture of amorphous and crystalline T-matrix cross-sections provided fits with R2 values greater than 0.97 for the infrared extinction of the crystalline samples.

Influence of doping fluorine on the structural, surface morphological and optical properties of CdO films

CdO and CdO:F films were prepared by ultrasonic spray pyrolysis method on glass substrates at temperature of 250 ± 5 °C. The structural and optical properties of pure and fluorine doped CdO films were characterized by XRD measurements and UV–VIS spectra, respectively. X-ray diffraction patterns show that the films have the polycrystalline structure with preferred orientation along (111) plane. Scherrer Method and Williamson Hall Method were used for calculating of the crystalline grains and strains of films. It is observed that the films at 8% F doped has better crystallinity level, and F doping decreases the defects in CdO films and improves crystallite quality. By UV–VIS spectra, it is revealed that the film with 8% F doped has a high transmittance about 65% in the visible region together with a direct band gap of 2.70 eV. Thicknesses, refractive indices and extinction coefficient values are determined by spectroscopic ellipsometry technique using Cauchy–Urbach model.

Studies on Lower Tropospheric Aerosols over New Delhi, India Using Lidar

This study reports the altitude distribution of physical and optical properties of aerosols in the lower troposphere over the urban tropical region Delhi measured using an UV (355 nm) lidar which is capable of operating in both day and night time. It is observed that there is strong seasonal variation in the altitude (from 0.4 to 4 km) distribution of aerosols during the observation period from July 2009 to May 2010. The aerosol extinction coefficient and depolarization values range from 0.02 to 0.6 km−1 and 0.02 to 0.05 respectively during the observation period. Relatively high aerosol extinction coefficient values were observed below 1.5 km altitude during the autumn season may be due the festivals and bio-mass burning activities. In all the seasons except winter, the aerosol loading from 0.4 km to 4 km range contributes more than 38% to the atmospheric column optical depth.

Mass extinction efficiency and extinction hygroscopicity of ambient PM2.5 in urban China

The ambient PM2.5 pollution problem in China has drawn substantial international attentions. The mass extinction efficiency (MEE) and hygroscopicity factor (f(RH)) of PM2.5 can be readily applied to study the impacts on atmospheric visibility and climate. The few previous investigations in China only reported results from pilot studies and are lack of spatial representativeness. In this study, hourly average ambient PM2.5 mass concentration, relative humidity, and atmospheric visibility data from China national air quality and meteorological monitoring networks were retrieved and analyzed. It includes 24 major Chinese cities from nine city-clusters with the period of October 2013 to September 2014. Annual average extinction coefficient in urban China was 759.3±258.3Mm−1, mainly caused by dry PM2.5 (305.8.2±131.0Mm−1) and its hygroscopicity (414.6±188.1Mm−1). High extinction coefficient values were resulted from both high ambient PM2.5 concentration (68.5±21.7µg/m3) and high relative humidity (69.7±8.6%). The PM2.5 mass extinction efficiency varied from 2.87 to 6.64m2/g with an average of 4.40±0.84m2/g. The average extinction hygroscopic factor f(RH=80%) was 2.63±0.45. The levels of PM2.5 mass extinction efficiency and hygroscopic factor in China were in comparable range with those found in developed countries in spite of the significant diversities among all 24 cities. Our findings help to establish quantitative relationship between ambient extinction coefficient (visual range) and PM2.5 & relative humidity. It will reduce the uncertainty of extinction coefficient estimation of ambient PM2.5 in urban China which is essential for the research of haze pollution and climate radiative forcing.

Technical note: optical extinction coefficient of polydisperse spherical gold nanoparticles in water

The extinction coefficients of polydispersed gold nanoparticles up to σ = 360 nm were computed via exact solution of Mie theory. A narrow extinction peak around 520 nm occurs for mean particle sizes &lt;d&gt; within dipole approximation limit. Spectral characteristics for extinction coefficient computed based on increasing mean particle sizes, degree of polydispersity, composition ratio of bimodal size distributions and changes in dispersant temperature are compared. As mean particle sizes increases, the plasmon resonance peak red-shifts and broadens skewing towards infrared. Increasing polydispersity on mean particle diameter beyond dipole approximation limit decreases peak extinction coefficient values. Increasing temperature from ambient to boiling changes the peak extinction coefficient intensity value by an order of 10^-13 while resonance wavelength remains unchanged.

Effect of sulphur and different irrigation regimes on par distribution, canopy temperature, yield and water use efficiency of groundnut (Arachis hypogaea L.)

A field experiment was conducted to study the effect of different levels of irrigation and sulphur on leaf area index, on distribution pattern of photosynthetically active radiation, consumptive use, water use efficiency, Canopy-Air Temperature Difference as well as yield attributes and yield of summer groundnut (Arachis hypogaea) during two consecutive years (2009 and 2010) at the ‘C’ block farm of Bidhan Chandra Krishi Viswavidyalaya, Kalyani, Nadia, West Bengal during pre-kharif season in a sandy loam soil with 24 treatment combinations (eight irrigation level in main plot and three level of sulphur in sub-plot) in a split plot design replicated thrice. The study revealed that both the levels of irrigation and sulphur significantly influenced all the yield attributing characters and the kernel yield. The highest values of yield attributing characters and kernel yield were recorded when sulphur applied @ 15 kg ha−1. The highest consumptive use, and water use efficiency were recorded under three irrigations applied at flowering, pegging and pod filling stage followed by two irrigations at pegging and pod filling stage. No irrigation treatment recorded lower photosynthetically active radiation absorption percentage value but higher photosynthetically active radiation extinction coefficient and Canopy-Air Temperature Difference value as compare to irrigation treatments, respectively.

Measuring the Spectrum of Extinction Coefficient and Reflectance for Cadmium Compounds from 400 to 900 nm

The key to extract the contents of cadmium in water by using remote sensing technique is to measure the spectrum of extinction coefficient per g·L(-1) and reflectance for its compounds. So in this paper, firstly, we choose two kinds of cadmium compounds, cadmium sulfide (CdS) and cadmium oxide (CdO), which are most commonly exsit in natural water, to measure the spectrums of extinction coefficient and reflectance for them. We use the equipment, designed on our own, which can adjust the path length of light passing and make our measuring results more accurate at visible and near-infrared wavelength range than others. Then we use Analytical Spectral Devices (ASD) spectrometer to measure the radiance of the light spot, which is from the direct light passed through cadmium compounds solutions of different concentrations reflected by the standard board. Using the ratio method to eliminate environmental errors and the effects of the thimbleful of suspended solids in water, we obtain the extinction coefficient per g·L(-1) of these two kinds of cadmium compounds from 400 to 900 nm. Secondly, we use ASD spectrometer to measure the reflectance spectrum of them in the sunny day at outdoor. The reflectance we obtain in this paper can help us to calculate the absorption and scattering coefficient per g·L(-1) in the future. The measuring results show that the extinction coefficient spectrum of CdS has two troughs at 550 and 830 nm and one peak at 675 nm. And the extinction coefficient spectrum of CdO decrease from purple to near-infrared. Both of their coefficient spectrums in blue are larger than green and red. And the value of the extinction coefficient per g·L(-1) of CdS is larger than CdO in the whole measuring wavelength range. The reflectance of CdS in yellow and red is larger than purple and blue, which increases rapidly from 500 to 650 nm and then leveling off. While the reflectance of CdO increase linearly from 525 to 900 nm. Both have obvious spectral characteristic. According to our results, the largest extinction coefficient appear at blue color, while the largest reflectance appear at yellow and red, which means that those bands are the most sensitive wavelength to detect the change of cadmium concentration in water. This study carries out with optical parameters measurements for optical activity of cadmium compounds specifically for water quality remote sensing for the first time. We conclude that the extinction coefficient and reflectance spectrums we obtained are reasonable, and the results can be used as the base parameter in the remote sensing inversion model for cadmium contents in water, which provides a breakthrough on using remote sensing technique to extract the heavy metal contents in water. Obtained these two optical parameters in this paper can provide powerful reference for band selection of the remote sensing image, which is used to extract cadmium contents in water, as well as provide the necessary important parameters of the remote sensing inversion model of cadmium contents in water.

Samarium colloids prepared in organic solvents and active solids

Samarium colloids in organic solvents (2-methoxyethanol, 2-propanol, 2-propanone, and 1,2-dimethoxyethane) were obtained by the chemical liquid deposition (CLD) method at 77 K. The colloids were characterized by electron diffraction, energy-dispersive X-ray (EDX), UV-Vis spectroscopy, kinetic stability, and electrophoretic measurements. The colloid stability depends on the solvent used and the metal concentration. The higher stability was obtained in 2-methoxyethanol, which is in agreement with previous results for other lanthanide colloids. The zeta potential (ζ) of the colloids ranges between 0.138 and 1.945 mV. The UV-Vis spectra exhibit bands characteristic of the solvent. The 2-methoxyethanol shows bands at 205 and 234 nm very similar to the 2-propanol which exhibits bands at 202 and 253 nm for 2.5E−4 M concentration. However, bands for 1,2-dimethoxyethane and 2-propanone colloids were impossible to determine due to their highest extinction coefficient values. A dependence of the UV/Vis spectral properties of these new sol materials with Sm(III) is described. In all cases, the EDX analyses confirm the presence of metal in the colloids. The electron diffraction gives the most common (hkl) planes corresponding to Sm and Sm2O3 (211) and (100), respectively. As shown by the particle size distribution determined from transmission electron microscopy (TEM), the Sm-2-methoxyethanol colloids exhibit ranges from 1.6 and 2.9 nm, but the Sm-2-propanol colloids show ranges from 2.3 to 2.5 nm; the medium particle size of Sm-1,2-dimetoxyethane colloid is 0.8 nm, and the Sm-2-propanone colloids have a range from 1.0 and 4.3 nm, exhibiting a solvent polarity dependence. Also, active solids from the evaporation of the colloids which have been fully characterized by several chemical and physical techniques have been obtained.

Theoretical investigation about the optical characterization of cone‐shaped pin‐Si nanowire for top cell application

AbstractCone‐shaped semiconductor silicon nanowires (CS‐Si‐NWs) grown in vapor liquid solid mode are promising for the fabrication of low‐cost high‐performance solar cells because of their low processing cost and lower use of Si materials, as compared to planar devices. In this article, the effect of injected charge carriers on the refractive indices and extinction coefficient values in a cone‐shaped pin Si NW (CS‐pin‐Si NW) were considered. Then, the influence of top diameters and periods on the optical absorption was investigated using a finite difference time‐domain (FDTD) modeling method. The absorption increased when we decreased the period from 300 to 150 nm for a light wave with a wavelength of 700 nm. However, in the case of incident light at a wavelength of 500 nm, the absorption significantly increased by up to 100% and was found to be independent of the period. On the other hand, we varied the period and the top diameter of the NWs with a fixed bottom diameter. In this case, we found that the period did not significantly affect the absorption value. A high value of the short circuit current density of 19.5 mA/cm2 was found in the case of NWs with a top diameter of 110 nm and a period of 150 nm. Combined with the analysis of the ultimate photocurrents, an optimum geometric structure with a top diameter of 70 nm and a period of 150 nm for a CS‐pin‐Si NW‐based top cell for tandem solar cell applications was proposed.

Role of substrate in electrodeposited copper telluride thin films

Copper telluride thin films have been prepared on different substrates using an electrodeposition technique. Stylus profilometry has been carried out to find out thickness value of the deposited films. X-ray diffraction analysis revealed that the prepared films possess polycrystalline in nature. Film composition with surface morphology has been analyzed using an energy dispersive analysis by X-rays and scanning electron microscopy. Optical absorption analysis showed that the prepared films possess band gap value in the range between 2.02 and 2.26 eV. Value of refractive index, extinction coefficient, real and imaginary dielectric constants are estimated for films obtained on transparent substrates.

Columnar aerosol characteristics and radiative forcing over the Doon Valley in the Shivalik range of northwestern Himalayas.

Spectral aerosol optical depth (AOD) measurements obtained from multi-wavelength radiometer under cloudless conditions over Doon Valley, in the foothills of the western Himalayas, are analysed during the period January 2007 to December 2012. High AOD values of 0.46±0.08 and 0.52±0.1 at 500nm, along with low values of Ångström exponent (0.49±0.01 and 0.44±0.03) during spring (March-May) and summer (June-August), respectively, suggest a flat AOD spectrum indicative of coarse-mode aerosol abundance compared with winter (December-February) and autumn (September-November), which are mostly dominated by fine aerosols from urban/industrial emissions and biomass burning. The columnar size distributions (CSD) retrieved from the King's inversion of spectral AOD exhibit bimodal size patterns during spring and autumn, while combinations of the power-law and unimodal distributions better simulate the retrieved CSDs during winter and summer. High values of extinction coefficient near the surface (∼0.8-1.0km-1 at 532nm) and a steep decreasing gradient above are observed via CALIPSO profiles in autumn and winter, while spring and summer exhibit elevated aerosol layers between ∼1.5 and 3.5km due to the presence of dust. The particle depolarisation ratio shows a slight increasing trend with altitude, with higher values in spring and summer indicative of non-spherical particles of dust origin. The aerosol-climate implications are evaluated via the aerosol radiative forcing (ARF), which is estimated via the synergy of OPAC and SBDART models. On the monthly basis, the ARF values range from ∼ -30 to -90Wm-2 at the surface, while aerosols cause an overall cooling effect at the top of atmosphere (approx. -5 to -15Wm-2). The atmospheric heating via aerosol absorption results in heating rates of 1.2-1.6Kday-1 during March-June, which may contribute to changes in monsoon circulation over northern India and the Himalayas.

Tethered balloon-born and ground-based measurements of black carbon and particulate profiles within the lower troposphere during the foggy period in Delhi, India

The ground and vertical profiles of particulate matter (PM) were mapped as part of a pilot study using a Tethered balloon within the lower troposphere (1000m) during the foggy episodes in the winter season of 2015–16 in New Delhi, India. Measurements of black carbon (BC) aerosol and PM <2.5 and 10μm (PM2.5 & PM10 respectively) concentrations and their associated particulate optical properties along with meteorological parameters were made. The mean concentrations of PM2.5, PM10, BC370nm, and BC880nm were observed to be 146.8±42.1, 245.4±65.4, 30.3±12.2, and 24.1±10.3μgm−3, respectively. The mean value of PM2.5 was ~12 times higher than the annual US-EPA air quality standard. The fraction of BC in PM2.5 that contributed to absorption in the shorter visible wavelengths (BC370nm) was ~21%. Compared to clear days, the ground level mass concentrations of PM2.5 and BC370nm particles were substantially increased (59% and 24%, respectively) during the foggy episode. The aerosol light extinction coefficient (σext) value was much higher (mean: 610Mm−1) during the lower visibility (foggy) condition. Higher concentrations of PM2.5 (89μgm−3) and longer visible wavelength absorbing BC880nm (25.7μgm−3) particles were observed up to 200m. The BC880nm and PM2.5 aerosol concentrations near boundary layer (1km) were significantly higher (~1.9 and 12μgm−3), respectively. The BC (i.e BCtot) aerosol direct radiative forcing (DRF) values were estimated at the top of the atmosphere (TOA), surface (SFC), and atmosphere (ATM) and its resultant forcing were - 75.5Wm−2 at SFC indicating the cooling effect at the surface. A positive value (20.9Wm−2) of BC aerosol DRF at TOA indicated the warming effect at the top of the atmosphere over the study region. The net DRF value due to BC aerosol was positive (96.4Wm−2) indicating a net warming effect in the atmosphere. The contribution of fossil and biomass fuels to the observed BC aerosol DRF values was ~78% and ~22%, respectively. The higher mean atmospheric heating rate (2.71Kday−1) by BC aerosol in the winter season would probably strengthen the temperature inversion leading to poor dispersion and affecting the formation of clouds. Serious detrimental impacts on regional climate due to the high concentrations of BC and PM (especially PM2.5) aerosol are likely based on this study and suggest the need for immediate, stringent measures to improve the regional air quality in the northern India.

Tuning of photoluminescence properties of functional phthalides for OLED applications

Abstract With an objective to develop simple organic systems and tailor their properties for optoelectronic applications, we have synthesized three functionalized phthalide derivatives and have investigated their electroluminescence and photophysical properties under different conditions. These derivatives showed good solubility in common organic solvents and exhibited strong absorption in the range 320–400 nm, having molar extinction coefficient values of ca. 10 4 M −1 cm −1 . The monomeric solution of these derivatives exhibited very low fluorescence quantum yields (Φ F ) of ca. 0.003–0.04 owing to their inherent structural features such as intramolecular free rotation and decay to the dark triplet states. However, upon complexation with Lewis acids, such as BCl 3 , these derivatives showed increased fluorescence quantum yields up to ca. 0.21 ± 0.01 and also exhibited aggregation induced emission (AIE) in water/acetonitrile mixtures with the emission yields in the range ca. 0.11–0.16. The morphological analysis of the aggregates through SEM and TEM showed the formation of rod-like structures in 90% water/acetonitrile mixture with an average size of ca. 100 nm. Supporting the observed aggregation induced enhancement in emission properties, these derivatives also exhibited significantly enhanced solid state fluorescence quantum yields of ca. 0.58–0.60. As a representative example, organic light emitting diode (OLED) fabricated using the derivative 3 as the emissive layer showed an efficient electroluminescence centered at 524 nm with a turn on voltage of 9 V, demonstrating thereby their potential use in optoelectronic applications.

Aerosols and lightning activity: The effect of vertical profile and aerosol type

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite has been utilized for the first time in a study regarding lightning activity modulation due to aerosols. Lightning activity observations, obtained by the ZEUS long range Lightning Detection Network, European Centre for Medium range Weather Forecasts (ECMWF) Convective Available Potential Energy (CAPE) data and Cloud Fraction (CF) retrieved by MODIS on board Aqua satellite have been combined with CALIPSO CALIOP data over the Mediterranean basin and for the period March to November, from 2007 to 2014. The results indicate that lightning activity is enhanced during days characterized by higher Aerosol Optical Depth (AOD) values, compared to days with no lightning. This study contributes to existing studies on the link between lightning activity and aerosols, which have been based just on columnar AOD satellite retrievals, by performing a deeper analysis into the effect of aerosol profiles and aerosol types. Correlation coefficients of R=0.73 between the CALIPSO AOD and the number of lightning strikes detected by ZEUS and of R=0.93 between ECMWF CAPE and lightning activity are obtained. The analysis of extinction coefficient values at 532nm indicates that at an altitudinal range exists, between 1.1km and 2.9km, where the values for extinction coefficient of lightning-active and non-lightning-active cases are statistically significantly different. Finally, based on the CALIPSO aerosol subtype classification, we have investigated the aerosol conditions of lightning-active and non-lightning-active cases. According to the results polluted dust aerosols are more frequently observed during non-lightning-active days, while dust and smoke aerosols are more abundant in the atmosphere during the lightning-active days.

Effects of Shade on Microclimate, Canopy Characteristics and Light Integrals in Dry Season Field-Grown Cocoa (Theobroma cacao L.) Seedlings

Effect of shade regimes on gradients of microclimate, canopy extent (leaf area index: LAI) and light integrals in dry season field-grown cocoa (cacao) seedlings was investigated in a rainforest zone of Nigeria. The shade regimes tested were: unshaded/open-to-sun, dense shade and moderate shade. Shade intensity affected solar radiation transmission through cacao canopy, photosynthetic active radiation (PAR) and canopy light attenuation (extinction coefficient, k). Intensity of transmitted radiation below the canopy from incident radiation was highest for open-to-sun, followed by moderate and dense shade, respectively. The temporal trend of intercepted radiation showed that intercepted radiation increased from December to May, and, the values were highest for open-to-sun, followed by moderate and dense shade. The ratio of transmitted (Io) to incident (I) radiation (IO/I) was higher for open sun. Significant differences were found between open-to-sun (unshaded) and moderate and dense shade intensity for value of canopy extinction coefficient (k). The association of growing degree days (GDD), and, total leaf number (TLN) and leaf area index (LAI), were characterized by high coefficient of determination (R2) for the respective open, dense and moderate shade treatments. Inverse of the slope of the regression of relationship between estimated thermal time (°Cdays) and corresponding total leaf number (TLN) denotes leaf appearance rate (phyllochron, in °Cdays/leaf). Rate of leaf appearance was faster in open sun compared with to that in moderate or dense shade intensity. Characteristics of the cacao canopy development were measured by leaf area index (LAI), a parameter which affects the intercepted photosynthetic active radiation (PAR). Higher LAI was obtained in no shade (open sun) compared to that in moderate or dense shade treatments. Unshaded plants had a higher radiation use efficiency (RUE) and RUE values were significantly higher compared to the other two treatments. Low light intensity and LAI for under-storey cacao had negative implications for growth and biomass development. Air temperatures within the cacao field were highest for open sun cacao, followed by moderate and dense shade, respectively; the values increased from December to April, with peak values seen in April.

Optical and electrical properties of boron doped diamond thin conductive films deposited on fused silica glass substrates

This paper presents boron-doped diamond (BDD) film as a conductive coating for optical and electronic purposes. Seeding and growth processes of thin diamond films on fused silica have been investigated. Growth processes of thin diamond films on fused silica were investigated at various boron doping level and methane admixture. Two step pre-treatment procedure of fused silica substrate was applied to achieve high seeding density. First, the substrates undergo the hydrogen plasma treatment then spin-coating seeding using a dispersion consisting of detonation nanodiamond in dimethyl sulfoxide with polyvinyl alcohol was applied. Such an approach results in seeding density of 2×1010cm−2. The scanning electron microscopy images showed homogenous, continuous and polycrystalline surface morphology with minimal grain size of 200nm for highly boron doped films. The sp3/sp2 ratio was calculated using Raman spectra deconvolution method. A high refractive index (range of 2.0–2.4 @550nm) was achieved for BDD films deposited at 500°C. The values of extinction coefficient were below 0.1 at λ=550nm, indicating low absorption of the film. The fabricated BDD thin films displayed resistivity below 48Ohm cm and transmittance over 60% in the visible wavelength range.

Photoluminescence, ellipsometric, optical and morphological studies of sprayed Co-doped ZnO films

In this study, undoped and cobalt (Co)-doped zinc oxide (ZnO) films were successfully produced by ultrasonic spray pyrolysis (USP) technique at low temperature (350[Formula: see text]C). The optical and surface properties were investigated as a function of Co content. The optical parameters (thickness, refractive index and extinction coefficient) were determined using spectroscopic ellipsometry (SE) and it was seen that the refractive index and extinction coefficient values of Co-doped ZnO films decreased slightly depending on the increasing of Co doping. For investigation, the transmittance and photoluminescence (PL) spectra of the films, UV–Vis spectrophotometer and PL spectroscopy were used at room temperature. The transmittance spectra show that transmittance values decreased and Co[Formula: see text] ions substitute Zn[Formula: see text] ions of ZnO lattice. The optical band gap values decreased from 3.26 eV to 2.85 eV with the changing of Co content. The results of PL spectra exhibit the position of the different emission peaks unchanged but the intensity of peaks increased with increasing Co doping. Also, the surface properties of the films were obtained by atomic force microscopy (AFM) and these results indicated that the surface morphology and roughness values were prominently changed with Co doping.

Effects of cloud and humidity on atmospheric extinction coefficient derived from visual range observations in Iranian major airports

ABSTRACTVisibility impairment, one of the restricting phenomena for aviation, results from light scattering and absorption. In this study, the historical visibility database for the period of 1981–2010 is used to obtain extinction coefficient according to the Koschmieder theory in the four busiest airports in Iran, including Tehran‐Mehrabad, Mashhad, Shiraz and Isfahan. The long‐term trend of extinction coefficient and its seasonal variations are investigated using 10th and 90th percentiles of extinction data to show the visual range in each airport. Correlation of the long‐term visibility trend with relative humidity (RH) and cloudiness is also examined. The comparison of seasonal mean extinctions shows the noticeable effect of local climate. The highest extinction coefficient value in each airport is seen during winter, while the lowest value occurs in summer. The seasonal mean extinction coefficient level in winter is about 0.1 km−1 higher than those of the other seasons. This is likely due to pollutants trapped by the stagnant cold air that partly obstruct visibility and increase the extinction in wintertime. There is not an outstanding variation of the tenth percentile of the extinction coefficient in the four airports. The low variation may relate to the definition of the upper threshold in visibility. Analysis shows that there is a positive correlation between extinction and humidity in all the airports that indicates the increase of scattering by hygroscopic particles with increasing humidity, such effect would be accentuated in high RH. The same result is seen for different percentages of cloudiness. To minimize the effects of humidity and cloudiness on the long‐term visibility trend, the days with the relative humidity values more than 70% and cloudiness of more than 5/8 of the sky are removed from the visibility trend analysis. The trends of the screened days are nearly parallel to the trends of raw data, but with a slight difference in each airport. The overall filtered long‐term trends show the increase of extinction coefficient at all the airports that emphasize the effect of pollution on the trend of light extinction within the whole period of this study. Eliminating the meteorological factors from the raw data does not change the overall increasing trend of extinction at Tehran and Isfahan airports. It suggests that the changes in air quality are responsible for the long‐term visibility degradation at these two stations that are located in the two most highly industrialized and polluted cities in Iran.