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Photoinduced phenomena in thin films of amorphous selenium (a-Se) have been a subject of intensive researches so far. Thin films of a-Se were deposited on corning glass by thermal evaporation, with several thicknesses. The influence of light exposure, with different colors (blue or red or natural white light), on the optical and structural properties of a-Se thin films was carried out by using ultraviolet-visible transmittance spectroscopy. It was found that the gap of the samples illuminated with blue and natural white light at room temperature shifts to lower energies. This photodarkening is stable at room temperature and is irreversible even after several days. On the other hand the photodarkening in the samples illuminated with red light is much smaller than that for samples illuminated with blue and natural white light. The photodarkening is accompanied by an increase in the refractive index. These results are discussed with results, previously obtained, about the photoinduced changes of the negative-U centers in, [T.sup.-] and [T.sup.+], studied using time-of-flight (TOF) traces recorded on samples prepared in the same conditions. These TOF measurements show that the defect level [T.sup.-] at 0.4 eV above the valence band edge shifts to 0.5 eV under illumination with white light at room temperature. This effect is not seen if the illumination is done at 35°C. These phenomena are attributed to nanocrystallization in the a-Se films. PACS Nos.: 81.40.Tv. Les phenomenes photo-induits dans des films de selenium amorphe (a-Se) ont fait l'objet de recherches intensives jusqu'il maintenant. Nous deposons par evaporation thermique des films minces de plusieurs epaisseurs de a-Se sur substrat de verre. Utilisant la spectroscopie par transmittance UV-visible. nous etudions l'effet de l'exposition a la lumiere de differentes couleurs (bleu ou rouge ou blanc) sur les proprietes optiques et structurales des films de a-Se Nous observons un deplacement du gap vers des energies plus basses dans les echantillons eclaires a la lumiere bleue ou blanche a la temperature de la piece. Ce photo-noircissement est stable a la temperature de la piece et est irreversible meme apres plusieurs jours. D'un autre cote, le photo-noircissement dans les echantillons eclaires a la lumiere rouge est beaucoup plus faible. Le photo-noircissement s'accompagne d'une augmentation de l'indice de refraction. Nous comparons nos resultats avec des resultats obtenus precedemment sur les changements de photo- noircissement de centres U negatifs dans [T.sup.-] et [T.sup.+], etudies par temps de vol (TOF) sur des echantillons prepares de facon similaire. Ces mesures TOF montrent que le niveau defaut [T.sup.-] a 0.4 eV au dessus du seuil de la bande de valence subit un deplacement de 0.5 eV sous illumination par lumiere blanche ou bleue a la temperature de la piece. Nous n'observons pas cet effet si l'illumination est a 35°C, ce qui est attribute a une nano-cristallisation dans les films de a-Se. [Traduit par la Redaction], 1. Introduction Amorphous chalcogenide films are known to exhibit a number of photoinduced phenomena [1-5], because of their structural flexibility (low coordination of chalcogens) and their high-lying lone-pair p states [...]

Light trapping effect using rough surface transparent conductive oxide (TCO) is one of the best ways to achieve high efficiency thin-film silicon solar cells. Several types of rough ZnO film fabricated by metal organic chemical vapor deposition technique onto the glass, which are etched by reactive ion etching, have been proposed so far as promising TCO substrates. In this paper, newly developed ZnO substrate with extremely high light scattering property comparing with typical pyramidal texture one was developed. By applying this newly developed ZnO substrate to the solar cell, higher short circuit current of about 2% has been achieved comparing with typical pyramidal texture one without sacrificing other parameters. This result showed that the newly developed substrate is suitable as a front TCO substrate for high performance thin-film silicon solar cell. PACS Nos.: 78.55.Qr, 88.40H-. La captation de la lumiere en utilisant un oxyde conducteur transparent a surface rugueuse (TCO) est l'une des meilleures facons pour atteindre une haute efficacite dans les cellules solaires faites de films minces de silicium. Plusieurs types de films de ZnO rugueux fabriques par deposition organometallique en phase vapeur sur du verre et qui sont graves par attaque ionique reactive, ont ete proposes jusqu'il maintenant comme des substrats TCO prometteurs. Nous developpons ici des substrats nouvellement developpes de ZnO avec des proprietes de diffusion de la lumiere extremement elevees si on les compare aux textures pyramidales typiquement proposees. En appliquant ces nouveaux substrats aux cellules solaires, un courant de courtcircuit plus grand de 2 % est atteint, compare a l'habituelle texture pyramidale, et ce sans sacrifier les autres parametres. Ces resultats montrent que ce substrat nouvellement developpe est un substrat avant approprie pour des films minces de silicium utilises comme cellules solaires. [Traduit par la Redaction], 1. Introduction Thin-film silicon solar cells have been expected to be a low cost solar cell for more than 30 years. However, amorphous silicon (a-Si:H) solar cell, which is one [...]

Optical transition properties of nanocrystalline silicon (nc-Si) doped Si[O.sub.2] thin films prepared by cosputtering with Si[O.sub.2] target and Si-chips followed by high temperature annealing were investigated as a function of ratio of target area (Si/Si[O.sub.2]) in the range of 0 to 0.19. Optical transmission measurements revealed that the indirect band-gap of nc-Si decreased from 4.87 to 2.32 eV with increasing Si/Si[O.sub.2] from 0.04 to 0.19, whereas no noticeable absorption was observed for the samples with Si/Si[O.sub.2] = 0.00. Photoluminescence (PL) measurements showed that considerably weak emissions due to oxygen deficient center (ODC) in Si[O.sub.2] films were observed at 514-539 nm for samples with lower Si/Si[O.sub.2] of 0.0-0.09, while the strong emissions due to an interfacial layer between the nc-Si core and the Si[O.sub.2] surface layer were observed at 746-808 nm for samples with higher Si/Si[O.sub.2] of 0.13-0.19. PL excitation spectrum monitored at 800 nm showed that the PL at 800 nm was excited through nc-Si. On the other hand, cathodoluminesncence peaks were observed at 455 and 465 nm for the samples with 0.04 and 0.13, respectively, in which both peaks were assigned to originate from oxygen vacancies created during electron beam irradiation. The mechanisms of three types of luminescence, due to the ODC in Si[O.sub.2] band-to-band transition of nc-Si, and the interfacial layer between the nc-Si core and the Si[O.sub.2] surface layer, are discussed. PACS Nos.: 78.67.Bf, 78.55.Hx, 81.15.Cd. Nous analysons, en fonction d'un rapport de surface de cible (Si/Si[O.sub.2]) variant de 0 a 0,19, les proprietes des transitions optiques de films minces de Si[O.sub.2] dopes au silicium nanocristallin, nc-Si, prepares par une co-pulverisation avec des cibles de Si[O.sub.2] et des puces de Si, suivie d'un recuit a haute temperature. Les mesures de transmission optique revelent que la bande interdite indirecte du nc-Si decroit de 4,87 a 2,32 eV lorsque Si/Si[O.sub.2] augmente de 0,04 a 0,19, alors qu'on n'observe aucune absorption pour les echantillons avec Si/Si[O.sub.2] = 0,0. Des mesures de photoluminescence (PL) montrent qu'une tres faible emission due au centre deficient en oxygene (ODC) dans les films de Si[O.sub.2] est observee a 514-539 nm pour les echantillons avec Si/Si[O.sub.2] = 0,0-0,09, alors qu'une forte emission due a une couche inter-faciale entre le coeur de nc-Si et la couche de surface de Si[O.sub.2] est observee a 706-808 nm pour des echantillons avec Si/Si[O.sub.2] = 0,13-0,19. Le spectre d'excitation de PL observe a 800 nm montre que le PL a 800 nm est excite par le nc-Si. D'autre part, les pics de cathodoluminescence sont observes a 455 et 465 nm pour les echantillons avec 0,04 et 0,13 respectivement, dans lesquels les deux pics proviennent de lacunes en oxygene crees pendant l'irradiation par faisceau d'electrons. Nous discutons des trois mecanismes de luminescence, due aux ODC dans le Si[O.sub.2], aux transitions bande-a-bande du nc-Si et a la couche interfaciale entre le coeur de nc-Si et la couche de surface de Si[O.sub.2]. [Traduit par la Redaction], 1. Introduction Multifunctional electronic devices are attractive for the realization of optoelectronic integrated circuits because one electronic device has many functions (e.g., light emitting device and flash memory), which can [...]

The concept of photonic random textures for application as a light-trapping scheme in thin-film solar cells is introduced. Those textures consist of a randomly textured interface, as commonly applied in thin-film solar cells, which is superimposed with a two-dimensional grating structure. The light-scattering properties of those textures are investigated by scalar scattering theory for transmission into the absorber layer and reflection at the back contact. A quantity to describe the light-trapping efficiency is derived and verified by rigorous diffraction theory. The photonic random textures outperform the random textures and the grating structures significantly. PACS Nos.: 42.25.Dd, 42.79.Dj, 88.40.fc. Nous introduisons le concept de texture photonique aleatoire dans le schema de captation de la lumiere dans les cellules minces photovoltaiques. Ces textures nouveau genre consistent en une interface texturee aleatoirement, frequemment utilisee en cellules minces photovoltaiques, superposee a un reseau de diffraction 2D. Nous utilisons la theorie scalaire de la diffraction pour etudier les proprietes de diffusion de la lumiere par ces textures pour la transmission vers la couche absorbante et la reflexion arriere. Nous utilisons la theorie rigoureuse de la diffraction pour evaluer et verifier une quantite qui decrit l'efficacite de captation de la lumiere. Les textures photoniques aleatoires surpassent les textures aleatoires et les reseaux de diffraction de facon significative. [Traduit par la Redaction], Introduction Light trapping in silicon-based thin-film solar cells is an important issue, because the absorption near the band gap is quite low for flat devices [1,2] and the device thickness [...]

In this work we have performed an exploratory study of the infrared (IR) sensing properties of polymorphous silicon-germanium (pm-[Si.sub.x][Ge.sub.y]:H) thin films. Our objective was to study the characteristics that are important parameters for infrared detection, as activation energy ([E.sub.a]), thermal coefficient of resistance (TCR), room temperature conductivity ([σ.sub.RT]), and responsivity to IR radiation. After characterization, our results demonstrated that pm-SiGe:H films have advantages over a-Si:H,B, pm-Si:H, and pm-Ge:H, because of the possibility to tailor its properties as [σ.sub.-RT], [E.sub.a], and TCR, and moreover, the possibility to adjust those values for specific applications. PACS Nos.: 61.72.uf, 81.05.Gc, 07.57.Kp. Nous completons ici une etude exploratoire des proprietes de detection dans l'infrarouge (IR) de films minces de silicium-germanium polymorphe (pm-[Si.sub.x][Ge.sub.y]:H). Notre objectif est d'etudier les caracteristiques qui sont d'importants parametres pour la detection dans l'infrarouge, comme l'energie d'activation ([E.sub.a]), le coefficient thermique de resistance (TCR), la conductivite a temperature de la piece ([σ.sub.RT]) et la responsivite a la radiation IR. Apres analyse, nos resultats montrent que les films de pm-[Si.sub.x][Ge.sub.y]:H ont des avantages sur ceux de a-Si:H,B, pm-Si:H et pm-Ge:H, a cause de la possibilite d'ajuster ses proprietes, comme [σ.sub.RT], [E.sub.a] et TCR, en plus de la possibilite d'ajuster ces valeurs a des applications specifiques. [Traduit par la Redaction], 1. Introduction Infrared (IR) detection technology based on amorphous semiconductors has experienced significant progress in the last 10 years. At present, thermal imaging systems containing monolithic infrared focal plane arrays [...]

In order to study the effect of defects on the laser-induced damage of different optical thin films, we carried out damage experiments on two kinds of thin films with a 1 ms long-pulse laser. Surface-defect and subsurface-defect damage models were used to explain the damage morphology. The two-dimensional finite element method was applied to calculate the temperature and thermal-stress fields of these two films. The results show that damages of the two films are due to surface and subsurface defects, respectively. Furthermore, the different dominant defects for thin films of different structures are discussed. [c] 2010 Optical Society of America OCIS codes: 140.3330, 310.6870.

We report the construction and testing of a chirped diffraction grating, which serves as a substrate for surface plasmon-enhanced optical transmission. This grating possesses a spatial variation in both pitch and amplitude along its surface. It was created by plasma oxidation of a curved poly(dimethoxysilane) sheet, which resulted in nonuniform buckling along the polymer surface. A gold-coated replica of this surface elicited an optical response that consisted of a series of narrow, enhanced transmission peaks spread over the visible spectrum. The location and magnitude of these transmission peaks varied along the surface of the grating and coincided with conditions where surface plasmons were excited in the gold film via coupling to one or more of the grating's diffracted orders. A series of measurements were carried out using optical diffraction, atomic force microscopy, and normal incidence optical transmission to compare the grating topology to the corresponding optical response. In addition, the impact of a thin dielectric coating on the transmission response was determined by depositing a thin silicon oxide film over the grating surface. After coating, wavelength shifts were observed in the transmission peaks, with the magnitude of the shifts being a function of the film thickness, the local grating structure, and the diffracted order associated with each peak. These results illustrate the ability of this surface to serve as an information-rich optical sensor whose properties can be tuned by control of the local grating topology. 10.1021/ac100497w

We fabricate low-noise visible-blind ultraviolet photodetectors of indium tin oxide/SrTi[O.sub.3]/Ag (ITO/STO/ Ag) based on the properties of STO bandgap excitation and the conductance of ITO thin film. The ITO films are epitaxially grown on STO wafers as electrodes and windows of the photodetectors, simultaneously. The photodetectors have low noise and very good electromagnetic shielding. The dark current is as low as 270 pA even at a 200 V bias. The peak responsivity reaches to 30 mA/W at the wavelength of 360 nm. From the experimental results, the same ideas can be generalized to develop visible-blind and solar-blind UV photodetectors based on wide bandgap materials, such as LaA1[O.sub.3], LiNb[O.sub.3], LiTa[O.sub.3], BaTi[O.sub.3], ZnO, MgO, and Zr[O.sub.2]. OCIS codes: 040.5160, 040.5150, 040.7190, 310.7005.

In this paper, we derive the unpolarized infrared (IR) emissivity of thin oil films over anisotropic Gaussian seas from a refined physical surface spectrum model of damping due to oil. Since the electromagnetic wavelength is much smaller than the surface mean curvature radius and than the surface root mean square height, the Kirchhoff--tangent plane approximation, reduced to the geometric optics approximation, can be used. The surface can then be replaced by its local infinite tangent plane at each point of each rough surface. The multiple reflections at each interface are ignored (i.e., for both the upper air/oil interface and the lower oil/sea interface of the contaminated sea). Nevertheless, the multiple reflections between the upper and the lower interfaces of the oil film are taken into account, by assuming a locally flat and planar thin oil film, which forms a local Fabry--Perot interferometer. This means that the Fresnel reflection coefficient of a single interface can be substituted for the equivalent Fresnel reflection coefficient of the air/oil/sea film, calculated by considering an infinite number of reflections inside the layer. Comparisons of the emissivity between a clean sea and a contaminated sea are presented, with respect to emission angle, wind speed, wind direction, oil film thickness, oil type, and wavelength. Thus, oil detection, characterization, and quantization are investigated in the IR window regions. [c] 2010 Optical Society of America OCIS codes: 290.5880, 000.5490, 010.4458, 260.3060, 280.4991, 240.0310.

As a kind of Na-incorporating control method, NaF co-evaporation or soda-lime glass thin films (SLGTFs) are useful to improve the photovoltaic performance of Cu(In, Ga)[Se.sub.2] (CIGS) cells fabricated on low-Na substrates. X-ray diffraction (XRD) patterns and scanning electron microscope pictures demonstrate that the grain size of CIGS thin film is reduced with the addition of Na. In addition, a variance of the preferred orientation is found by XRD patterns in terms of SLGTF samples. By a use of 100 nm thick SLGTF as a Na source, the best CIGS solar cell with an efficiency of 13.42% has been obtained. [c] 2010 Optical Society of America OCIS codes: 160.6000, 310.6845.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.08.016 Byline: Constantin Romanescu, Jochen Marschall, Deena Kim, Ajeeta Khatiwada, Konstantinos S. Kalogerakis Keywords: Ices; Ices; IR spectroscopy; Spectroscopy Abstract: Optical constants in a broad temperature and wavelength range are important input parameters in radiative transfer models used in studies of planetary atmospheres. In the laboratory, the refractive index values of ices at the HeNe laser wavelength (632.8nm) are often used to monitor the growth rate and thickness of ice films. In this report we present laboratory measurements determining the refractive index at 632.8nm of ammonia and hydrocarbon ices in the temperature range 80-100K. Thin ice films are vapor-deposited on a cryogenically cooled mirror located inside a high-vacuum apparatus. The real component of the refractive index of these ice films is determined by a two-angle interferometric technique. Optical modeling calculations of the transmittance and reflectance through the thin ice films assist in the interpretation of the experimental results. We discuss our results and compare them with other measurements available in the literature. The results reported here are relevant to the spectroscopy of icy objects in the solar system; they are needed to perform laboratory characterization of ices, derive optical constants, and model spectra. Author Affiliation: Molecular Physics Laboratory, SRI International, Menlo Park, CA 94025, USA Article History: Received 20 March 2009; Revised 12 July 2009; Accepted 20 August 2009

Thin films of A1N doped with chromium were deposited on flat Si (100) substrates and optical fibers by rf magnetron sputtering, using 100-200 W rf power and 5-8 mTorr nitrogen. The thickness of the films on the flat silicon substrate was 400 nm and on optical fibers with 80 [micro]m and smaller diameters was up to 10 [micro]m. Surface characterization and luminescence properties were investigated to fabricate resonant laser cavities. X-ray diffraction and scanning electron microscope studies showed that films deposited on flat silicon were amorphous, while those deposited on the fibers show columnar growth and some gain structure, most probably due to a temperature rise at the substrate during deposition. Cathodoluminescence and photoluminescence of the as-deposited and thermally activated A1N:Cr films showed an emission peak at 702 nm as a result of the [sup.4][T.sub.2] [right arrow] [sup.4][A.sub.2] transition. OCIS codes: 160.4670, 160.3380, 160.5293, 180.5810, 240.0310, 240.6490.

We present a simple method for simultaneous measurement of thermo-optic and stress-optic coefficients of polymer thin films by measuring the film refractive indices as a function of temperature (dn/dT). Usually, such dn/dT value is considered as the thermo-optic coefficient. However, in the thin film systems, the measured dn/dT values result from both the thermo-optic and stress-optic effects. To demonstrate the stress-induced effects, the dn/dT values have been investigated for two different polymers: benzocyclobutene (high film stress) and epoxy 3505 (negligible film stress), using a prism coupler technique. The finite element method has been used so as to predict the stresses in the polymer film and, by combining them with the experimental dn/dT values, the individual thermo-optic and stress-optic coefficients have been determined. We found that the obtained thermo-optic coefficient is significantly different than the measured dn/dT values. The method is generic in nature and can thus be applied to a wide range of polymer waveguide materials. [c] 2010 Optical Society of America OCIS codes: 120.4530, 130.5460, 160.6840, 310.6860.

To deduce the location of absorptive inclusions in thin films, temperature distributions in pure Ti[O.sub.2] films and Ti[O.sub.2] films with high-absorptance inclusions are analyzed based on temperature field theory. According to our theoretic simulations, the surface temperature rise increases when absorptive inclusions are incorporated into thin films and shows different values for different inclusions. With the increase of inclusion thickness, the surface temperature rise varies and has a maximum value. A potential method is presented to deduce the location of absorptive inclusion through calculating the surface temperature rise at two modulated frequencies, if it is possible to know in advance the inclusion material or to prejudge this from a thin-film deposition process. [c] 2010 Optical Society of America OCIS codes: 310.6870, 140.6810.

By modifying some structural characteristics, the annealing process can have considerable effects on the optical performance and laser-induced damage resistance of Zr[O.sub.2] thin films deposited by electron-beam deposition. Annealing at increased temperature gives rise to an increase of refractive index, the evolutions of packing density, and the structure order of the films due to the removal of adsorbed water in advance, material crystallization, and phase transformation. Thus, the combined effects of greatly strengthened endurance, crystal structure ordering, and stress transition after the annealing leads to an increase of the laser-induced damage threshold in a vacuum environment from 12 to 16J/[cm.sup.2] (at 1064 nm, 12 ns pulse duration, and 1-on-1 testing mode). [c] 2009 Optical Society of America OCIS codes: 310.1620, 310.3840, 310.6860, 310.6870.

We employed the atomic layer deposition technique to grow [Al.sub.2][O.sub.3] films with nominal thicknesses of 400, 300, and 200 nm on silicon and soda lime glass substrates. The optical properties of the films were investigated by measuring reflection spectra in the 400-1800 nm wavelength range, followed by numerical fitting assuming the Sellmeier formula for the refractive index of [Al.sub.2][O.sub.3]. The films grown on glass substrates possess higher refractive indices as compared to the films on silicon. Optical waveguiding is demonstrated, confirming the feasibility of high-index contrast planar waveguides fabricated by atomic layer deposition. OCIS codes: 310.6860, 310.2790, 160.4760, 160.4670.

Ellipsometry is an optical technique that is widely used for determining optical and geometrical properties of optical thin films. These properties are in general extracted from the ellipsometric measurement by solving an inverse problem. Classical methods like the Levenberg--Marquardt algorithm are generally too long, depending on direct calculation and are very sensitive to local minima. In this way, the neural network has proved to be an efficient tool for solving these kinds of problems in a very short time. Indeed, it is rapid and less sensitive to local minima than the classical inversion method. We suggest a complete neural ellipsometric characterization method for determining the index dispersion law and the thickness of a simple Si[O.sub.2] or photoresist thin layer on Si, Si[O.sub.2], and BK7 substrates. The influence of the training couples on the artificial neural network performance is also discussed. OCIS codes: 120.2130, 200.4260.

In various everyday situations, a characteristic interference pattern can be observed on water surfaces. This pattern can be divided into two overlapping components: a corona and a system of Quetelet's rings, often with only a section of these visible in the form of fringes. We attribute this phenomenon to thin films of small spheres located just above the reflecting water surface. Due to differences in the optical arrangement, explanatory models applicable for conventionally produced Quetelet's rings are not transferable. We present a compatible mathematical model and some obvious analogies in order to explain the occurrence and properties of this phenomenon. OCIS codes: 290.5850, 260.3160.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2009.04.008 Byline: N.R. Mathews (a)(b), Erik R. Morales (b)(c), M.A. Cortes-Jacome (a), J.A. Toledo Antonio (a) Keywords: TiO.sub.2; Sol-gel growth; Raman spectroscopy; Porosity; Photocatalysis Abstract: Nanostructured TiO.sub.2 thin films were deposited on glass substrates by sol-gel dip coating technique. The structural, morphological and optical characterizations of the as deposited and annealed films were carried out using X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and UV-vis transmittance spectroscopy. As-deposited films were amorphous, and the XRD studies showed that the formation of anatase phase was initiated at annealing temperature close to 400[degrees]C. The grain size of the film annealed at 600[degrees]C was about 20nm. The lattice parameters for the films annealed at 600[degrees]C were a =3.7862C* and c =9.5172C*, which is close to the reported values of anatase phase. Band gap of the as deposited film was estimated as 3.42eV and was found to decrease with the annealing temperature. At 550nm the refractive index of the films annealed at 600[degrees]C was 2.11, which is low compared to a pore free anatase TiO.sub.2. The room temperature electrical resistivity in the dark was of the order of 4.45x10.sup.6 ohm-cm. Photocatalytic activity of the TiO.sub.2 films were studied by monitoring the degradation of aqueous methylene blue under UV light irradiation and was observed that films annealed above 400[degrees]C had good photocatalytic activity which is explained as due to the structural and morphological properties of the films. Author Affiliation: (a) Programa de Ingenieria Molecular, IMP, Eje Central Lazaro Cardenas #152 Col. San Bartolo Atepehuacan, Mexico D.F C.P 07730, Mexico (b) Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, Morelos, Temixco 62580, Mexico (c) CIMAV, Miguel de Cervantes, No.120, Chihuahua, Mexico Article History: Received 19 September 2008; Revised 28 February 2009; Accepted 14 April 2009 Article Note: (miscellaneous) Communicated by: Associate Editor Dr. Gion Calzaferri

In 1892 Drude and Nernst reported the first observation of a standing light wave by using a fluorescent thin film, which is a real-time version of Wiener's first experiment on standing light wave. We reproduce the experiment by Drude and Nernst with improved efficiency using modern laser technology and a highly fluorescent [pi]-conjugated polymer. We also used a glass plate scratched slightly on one surface to visualize the same phenomenon using diffuse reflection instead of fluorescence. This method has the advantage of being a wavelength-independent observation compared to the fluorescence method. [DOI: 10.1119/1.3027506]

We report experimental characterization of a very small rectangular phase shift (< 0.3 rad) obtained from the far-field diffraction patterns using a closed aperture Z-scan technique. The numerical simulations as well as the experimental results reveal a peak-valley configuration in the far-field normalized transmittance, allowing us to determine the sign of the dephasing. The conditions necessary to obtain useful Z-scan traces are discussed. We provide simple linear expressions relating the measured signal to the phase shift. A very good agreement between calculated and experimental Z-scan profiles validates our approach. We show that a very well known nonlinear characterization technique can be extended for linear optical parameter estimation (as refractive index or thickness). OCIS codes: 120.5050, 120.2830, 310.6860, 050.1970, 050.5080, 070.7345.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2008.12.015 Byline: A.A. Dakhel Keywords: Optical properties; Cadmium-dysprosium oxide; Dy-doped CdO; Mobility; Oxides; Rare earth oxides; TCO Abstract: Lightly Dy-doped CdO thin films (molar 0.5%, 1%, 2%, and 2.5%) have been prepared by a vacuum evaporation method on glass and Si wafer substrates. The prepared films were characterised by X-ray fluorescence, X-ray diffraction, UV-vis-NIR absorption spectroscopy, and dc-electrical measurements. Experimental data indicate that Dy.sup.3+ doping slightly stretchy-stresses the CdO crystalline structure and changes the optical and electrical properties. The bandgap of CdO was suddenly narrowed by about 20% due to a little doping with Dy.sup.3+ ions. Then, as the Dy doping level was increased, the energygap was also increased. This variation was explained by the effect of Burstein-Moss energy shift (or bandgap widening effect) together with a bandgap shrinkage effect. The electrical behaviour of the samples shows that they are degenerate semiconductors. However, the 2% Dy-doped CdO sample shows an increase in its mobility by about 3.5 times, conductivity by 35 times, and carrier concentration by 10 times relative to undoped CdO film. From transparent conducting oxide point of view, Dy is sufficiently effective for CdO doping. Author Affiliation: Department of Physics, College of Science, University of Bahrain, P.O. Box 32038, Bahrain Article History: Received 20 May 2008; Revised 6 November 2008; Accepted 18 December 2008 Article Note: (miscellaneous) Communicated by Associate Editor: Dr. Takhir Razykov

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2008.11.001 Byline: E. Elangovan, G. Goncalves, R. Martins, E. Fortunato Keywords: Indium molybdenum oxide thin films; Hall measurements; Optical properties; Radio-frequency sputtering Abstract: Indium molybdenum oxide (IMO) thin films were deposited by RF magnetron sputtering on glass substrates at room temperature. The deposition and argon partial pressures were maintained at 6.0x10.sup.-1 Pa and 3.0x10.sup.-1 Pa, respectively. The oxygen partial pressure (OPP) was varied in the range 1.0-6.0x10.sup.-3 Pa. The films were sputtered at 40W for 30min using the target consisted In.sub.2O.sub.3 (98wt%): Mo (2wt%). The films are polycrystalline with a slight preferential orientation along (222) plane. The crystallinity is increased with the increasing OPP. The negative sign of Hall coefficient confirmed the n-type conductivity. A maximum mobility [approximately equal to]19cm.sup.2 V.sup.-1 s.sup.-1 is obtained for the films deposited with OPP of 3.6x10.sup.-3 Pa. The average visible transmittance calculated in the wavelength ranging 500-800nm is ranging between 2% and 77%. The optical band gap calculated from the absorption data is varied between 3.69 and 3.91eV. A striking feature is that the work function of the films is wide ranging 4.61-4.93eV. A possibility of using the produced IMO films as transparent conducting oxide in photovoltaic applications such as organic solar cells is discussed in this article. Author Affiliation: CENIMAT-I3N, Materials Science Department, FCT-UNL, 2829-516 Caparica, Setubal, Portugal Article History: Received 6 May 2008; Revised 29 September 2008; Accepted 3 November 2008 Article Note: (miscellaneous) Communicated by: Associate Editor Razykov

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2008.11.006 Byline: N.M. Shah, C.J. Panchal, V.A. Kheraj, J.R. Ray, M.S. Desai Keywords: CuInSe.sub.2 thin film; Thermal evaporation; X-ray diffraction; Energy dispersive X-ray analysis; Atomic force microscopy; Transmission measurements Abstract: Copper indium diselenide (CuInSe.sub.2) compound was synthesized by reacting its constituent's elements copper, indium and selenium in near stoichiometric proportions (i.e. 1:1:2 with 5% excess selenium) in an evacuated quartz ampoule. Synthesized pulverized compound material was used as an evaporant material to deposit thin films of CuInSe.sub.2 onto organically cleaned sodalime glass substrates, held at different temperatures (300-573 K), by means of single source thermal evaporation method. The phase structure and the composition of chemical constituents present in the synthesized compound and thin films have been investigated using X-ray diffraction and energy dispersive X-ray analysis, respectively. The investigations show that CuInSe.sub.2 thin films grown above 423 K are single phase, having preferred orientation of grains along the (112) direction, and having near stoichiometric composition of elements. The surface morphology of CuInSe.sub.2 films, deposited at different substrate temperatures, has been studied using the atomic force microscopy to estimate its surface roughness. An analysis of the transmission spectra of CuInSe.sub.2 films, recorded in the wavelength range of 500-1500 nm, revealed that the optical absorption coefficient and the energy band gap for CuInSe.sub.2 films, deposited at different substrate temperatures, are [approximately equal to]10.sup.4 cm.sup.-1 and 1.01-1.06 eV, respectively. The transmission spectrum was analyzed using iterative method to calculate the refractive index and the extinction coefficient of CuInSe.sub.2 thin film deposited at 523 K. The Hall effect measurements and the temperature dependence of the electrical conductivity of CuInSe.sub.2 thin films, deposited at different substrate temperatures, revealed that the films had electrical resistivity in the range of 0.15-20 ohm cm, and the activation energy 82-42 meV, both being influenced by the substrate temperature. Author Affiliation: Applied Physics Department, Faculty of Technology and Engineering, M.S. University of Baroda, Vadodara 390001, Gujarat, India Article History: Received 12 June 2008; Revised 8 November 2008; Accepted 17 November 2008 Article Note: (miscellaneous) Communicated by: Associate Editor Dr. Takhir Razykov

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2008.10.004 Byline: N. Muthukumarasamy (a), S. Jayakumar (b), M.D. Kannan (b), R. Balasundaraprabhu (b) Keywords: CdSeTe; Hot wall deposition; Band gap bowing Abstract: CdSe.sub.x Te.sub.1- .sub.x thin films of different compositions have been deposited on glass substrates by hot wall deposition method under conditions very close to thermodynamical equilibrium with minimum loss of material. The structural studies carried out on the deposited films revealed that they are crystalline in nature and exhibit either cubic zinc blende or hexagonal phase or both depending on the composition of the material. The lattice parameter values for both cubic and hexagonal phases have been determined and are observed to vary with composition according to Vegard's law. The optical properties of the deposited CdSe.sub.x Te.sub.1- .sub.x thin films have been studied using transmittance spectra. The spectra shows a sharp fall in transmittance at wavelength corresponding to the band gap of the material. The optical band gap has been determined and found to be direct allowed. The band gap has been observed to strongly depend on film composition. The variation of band gap with composition has been observed to be quadratic in nature exhibiting a bowing behaviour. Author Affiliation: (a) Department of Physics, Coimbatore Institute of Technology, Coimbatore, Tamilnadu, India (b) Thin Film Center, PSG College of Technology, Coimbatore, Tamilnadu, India Article History: Received 27 April 2008; Revised 20 September 2008; Accepted 2 October 2008 Article Note: (miscellaneous) Communicated by: Associate Editor Tahir M. Razykov

A photothermal experiment with mirage detection was used to determine the thermal conductivity of various thin films deposited on semiconductor substrates. The first type consisted of conducting oxide films: ZnO and CdO deposited on GaSb:Te, while the other contained high dielectric constant Hf[O.sub.2] layers on Si. All films were fabricated using a magnetron sputtering technique. Experimental results showed that the value of the thermal conductivity of ZnO and CdO films is lower than the value obtained for Hf[O.sub.2]. Thermal conductivities of investigated thin films are about 2 orders of magnitude lower than those corresponding to bulk materials. OCIS codes: 310.0310, 310.6870, 310.7005, 310.1210.

This study investigates the optical properties and microstructure of [Ta.sub.2][O.sub.5] film deposited with the glancing angle deposition technique. The tilted nanocolumn microstructure, examined with scanning electron microscopy, induces the optical anisotropy of thin film. The optical properties of thin film are characterized with an inverse synthesis method. Based on the Cauchy model, the dispersion equations of optical constants of film are determined from the transmittance spectra measured at normal and oblique incidence over 400-800 nm. The starting values derived with an envelope method quicken the optimization process greatly. The dispersion of the principal indices [N.sub.1], [N.sub.2], and [N.sub.3] and the thickness d of thin film are presented statistically. A good agreement between the measured optical properties and theoretical calculation is obtained, which validates the model established for thin film produced by glancing angle deposition. OCIS codes: 310.6860, 120.4530, 260.1440, 230.4000.

Soap bubbles became popular in 17th century paintings and prints primarily as a metaphor for the impermanence and fragility of life. The Dancing Couple (1663) by the Dutch painter Jan Steen is a good example which, among many other symbols, shows a young boy blowing soap bubbles. In the 18th century the French painter Jean-Simeon Chardin used soap bubbles not only as metaphor but also to express a sense of play and wonder. In his most famous painting, Soap Bubbles (1733/ 1734) a translucent and quavering soap bubble takes center stage. Chardin's contemporary Charles Van Loo painted his Soap Bubbles (1764) after seeing Chardin's work. In both paintings the soap bubbles have a hint of color and show two bright reflection spots. We discuss the physics involved and explain how keenly the painters have observed the interaction of light and soap bubbles. We show that the two reflection spots on the soap bubbles are images of the light source, one real and one virtual, formed by the curved surface of the bubble. The faint colors are due to thin film interference effects.

An infrared reflectance--absorbance spectroscopy method for characterizing the ultrathin fluid film retained on a surface upon forced dewetting from a fluid has been developed for investigation of interfacial molecular structure at reflective substrates. This report details the optical considerations and constraints necessary to acquire IR spectral data from nanometer-thick films retained upon forced dewetting of a solid substrate from a fluid into a vapor-saturated environment. The feasibility of this method is demonstrated through successful spectral acquisition from Ag surfaces modified with 11-mercaptoundecanol forcibly dewet from water. The IR spectral results clearly illustrate that information is acquired only from the interracial region with no contribution from the bulk liquid. Residual layer thicknesses calculated from IR absorbance values are substantiated by ellipsometry. The spectra make clear that the molecular structure of the residual layer is distinctly different from that of the bulk liquid, confirming that this method is viable for interracial structure elucidation of thin fluid films at a variety of solid substrates.

A straightforward approach for estimation of thickness (d), real ([[epsilon].sub.1]) and imaginary parts ([[epsilon].sub.2]) of the complex permittivity of very thin films from spectrophotometric measurements is presented. The uncertainties in [[epsilon].sub.1], [[epsilon].sub.2], and d due to methodical error and the uncertainties in the measured quantities are investigated. It is shown that the influence of these factors is considerable when [[epsilon].sub.1], [[epsilon].sub.2], and d are obtained simultaneously for each wavelength. The accuracy of [[epsilon].sub.1], [[epsilon].sub.2], and d is significantly increased if the value of d is evaluated first, its value is kept constant over the whole spectral region, and then [[epsilon].sub.1] and [[epsilon].sub.2] are calculated for each wavelength. OCIS codes: 120.4530, 120.5240, 120.5700, 120.7000.

We present the continuous wavelet transform (CWT) method for determining the dispersion curves of the refractive index and extinction coefficient of absorbing thin films by using the transmittance spectrum in the visible and near infrared regions at room temperature. The CWT method is performed on the transmittance spectrum of an a - [Si.sub.1-x][C.sub.x]:H film, and the refractive index and extinction coefficient of the film are continuously determined and compared with the results of the envelope and fringe counting methods. Also the noise filter property of the method is depicted on a theoretically generated noisy signal. Finally, the error analyses of the CWT, envelope, and fringe counting methods are performed. OCIS codes: 070.4560, 310.6860, 070.4790.

This work discusses the experimental determination of the optical constants (refractive index) of DC-magnetron-sputtered boron carbide films in the 30-770 eV photon energy range. Transmittance measurements of three boron carbide films with thicknesses of 54.2, 79.0, and 112.5 nm were performed for this purpose. These are believed to be the first published experimental data for the refractive index of boron carbide films in the photon energy range above 160 eV and for the near-edge x-ray absorption fine structure regions around the boron K (188 eV), carbon K (284.2 eV), and oxygen K (543.1 eV) absorption edges. The density, composition, surface chemistry, and morphology of the films were also investigated using Rutherford backscattering, x-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and extreme ultraviolet reflectance measurements. OCIS codes: 340.7480, 120.4530, 310.6860, 310.6870.

A test was made of the ability of Kramers--Kronig-constrained variational dielectric fitting to extract the optical conductivity of a thin film from reflectance data containing structure due to both thin film and substrate. The reflectance of a series of well-characterized thin films of Sr[Ru.sub.x][Mg.sub.1-x][O.sub.3] and Sr[Ru.sub.x][O.sub.3] with a variety of thicknesses ([approximately equal to] 56-300 nm) and dc resistivities ([approximately equal to] 250-2200 [micro][ohms]cm) was measured. The low frequency values of the extracted optical conductivities agree with the dc measurements, however, removal of features due to the substrate improves with increasing film thickness. OCIS codes: 300.6270, 310.6860.

Series of samples of lightly Ga-doped CdO thin films (3%, 6%, and 9%) have been prepared by evaporation method on glass substrate. The prepared films were characterised by X-ray diffraction (XRD), UV-VIS-NIR absorption spectroscopy, and de-electrical measurements. The investigation shows that Ga doping widens the energygap of CdO. The optical properties were easily explained by using Tauc et al. band-to-band transitions and classical Drude theory. The electrical behaviour of the samples shows that they are degenerate semiconductors. The 6% Ga-doped CdO sample shows increase its mobility by 3.2 times, increase its conductivity by 1.5 times, increase its intrinsic bandgap, and a slight increase its transmittance relative to undoped CdO film. Explanation was given concerning these variations. From transparent conducting oxide (TCO) point of view, Ga is not sufficiently effective for CdO doping comparing to other dopants like In, Sn, Sc, and Y. Keywords: Optical properties; Gallium-cadmium oxide; Ga-doped CdO; Mobility; Oxides; Degenerate semiconductors