<p>Steam explosions are possible during granulation of Si and FeSi75. These explosions are a great hazard, and must be avoided. Norwegian ferroalloy producers have initiated a research program to learn more about such violent melt-water interactions, in a joint effort with NTNU and SINTEF. The focus has primarily been on important parameters that can be controlled industrially, such as water temperature and metal composition. This thesis-work has focused on the effect of small additions of Al and Ca in Si-metal and FeSi75. However, within the same project, experiments on the effect of water temperature have also been carried out.</p><p>The work has primarily been of experimental character. Two experimental apparatuses have been used. The first apparatus allows us to rapidly melt a sample of metal in an inert atmosphere to a desired temperature, expose the surface of the melt to an oxidizing agent (i.e. water) and then rapidly cool the sample to room temperature. The oxide that forms at the surface is examined with a microprobe. Thus, information regarding the composition and substance of the oxide layer is available. The second apparatus is suitable for releasing single drops of melt into a water tank, where they can be triggered and explode. A variety of techniques have been used in order to monitor the experiment: regular video, high-speed film, high-speed video, open-shutter imaging and pressure transducer measurements. </p><p>Both Si and FeSi75 must be triggered in order to explode. Trigger pressures range from 0.3 MPa (FeSi75) to 2 MPa (Si-metal). We have established at which depths the molten drops can be triggered. Molten drops of FeSi75 can be triggered at depths twice of those of molten drops of Si. The latter can be triggered even if they are partially solidified.</p><p>The explosion itself is strong enough to trigger neighbor drops as far away as 400 mm. Thus, we cannot rule out the possibility of large-scale steam explosions during granulation of molten Si or FeSi75, which is in accordance with industrial practice.</p><p>By the use of high-speed imaging techniques and pressure measurements, we have been able to describe qualitatively what happens when a molten drop of Si/FeSi75 fragments rapidly in water. As the melt fragments, the rapid heat transfer generates vapor as bubbles, which expand and collapse in a cyclic manner. Large pressure pulses are generated upon collapse of the steam bubble, that is, when water jets impact in the center of the collapsing bubble.</p><p>The first step in the oxidation of liquid silicon is the formation of gaseous SiO. The fate of this gas now depends on the flow conditions at the surface of the melt. In the case of a molten drop descending in water, most of the gas is flushed away from the surface. Thus, there are only minor traces of oxygencontaining material (i.e. silica) at the surface of the solidified drop.</p><p>The addition of small amounts of Al and/or Ca dramatically changes the behavior of the molten drop. A strange effect is the two-fold increase in the fall velocity for molten drops of silicon. A similar effect was detected for molten drops of FeSi75. Alloying elements such as Al and Ca greatly reduce the risk for a steam explosion of molten Si. The significance of these elements is related to the oxidation reactions at the surface of the molten drop of metal. As silicon reacts with water vapor and oxidizes, hydrogen gas is formed. If Al and Ca are present in the melt, these elements will speed up the hydrogen generation considerably. This gas is strongly influencing on the probability for a steam explosion to occur. H2 stabilizes the vapor film around the drop, that is, much stronger trigger pressures are needed to collapse the film. Even if the trigger pressure is strong enough to collapse the vapor film, violent interactions are almost completely absent. A fragmentation of the melt is observed, but the heat transfer is apparently not rapid enough to generate steam bubbles, i.e. the generation of steam is below the critical limit.</p>

<p>This thesis work consists of two parts, each with a different motivation. Part II is the main part and was partly conducted in industry, at ScanWafer ASA’s plant no.2 in Glomfjord.</p><p>The large growth in the Photo Voltaic industry necessitates a dedicated feedstock for this industry, a socalled Solar Grade (SoG) feedstock, since the currently used feedstock rejects from the electronic industry can not cover the demand. Part I of this work was motivated by this urge for a SoG- feedstock. It was a cooperation with the Sintef Materials and Chemistry group, where the aim was to study the kinetics of the removal reactions for dissolved carbon and boron in a silicon melt by oxidative gas treatment. The main focus was on carbon, since boron may be removed by other means. A plasma arc was employed in combination with inductive heating. The project was, however, closed after only two experiments. The main observations from these two experiments were a significant boron removal, and the formation of a silica layer on the melt surface when the oxygen content in the gas was increased from 2 to 4 vol%. This silica layer inhibited further reactions.</p><p>Multi-crystalline (mc) silicon produced by directional solidification constitutes a large part of the solar cell market today. Other techniques are emerging/developing and to keep its position in the market it is important to stay competitive. Therefore increasing the knowledge on the material produced is necessary. Gaining knowledge also on phenomenas occurring during the crystallisation process can give a better process control.</p><p>Part II of this work was motivated by the industry reporting high inclusion contents in certain areas of the material. The aim of the work was to increase the knowledge of inclusion formation in this system. The experimental work was divided into three different parts;</p><p>1) Inclusion study</p><p>2) Extraction of melt samples during crystallisation, these were to be analysed for carbon- and nitrogen. Giving thus information of the contents in the liquid phase during soldification.</p><p>3) Fourier Transform Infrared Spectroscopy (FTIR)-measurements of the substitutional carbon contents in wafers taken from similar height positions as the melt samples. Giving thus information of the dissolved carbon content in the solid phase.</p><p>The inclusion study showed that the large inclusions found in this material are β-SiC and β-Si3N4. They appear in particularly high quantities in the top-cuts. The nitrides grow into larger networks, while the carbide particles tend to grow on the nitrides. The latter seem to act as nucleating centers for carbide precipitation. The main part of inclusions in the topcuts lie in the size range from 100- 1000 µm in diameter when measured by the Coulter laser diffraction method.</p><p>A method for sampling of the melt during crystallisation under reduced pressure was developed, giving thus the possibility of indicating the bulk concentration in the melt of carbon and nitrogen. The initial carbon concentration was measured to ~30 and 40 ppm mass when recycled material was employed in the charge and ~ 20 ppm mass when no recycled material was added. Since the melt temperature at this initial stage is ~1500 °C these carbon levels are below the solubility limit. The carbon profiles increase with increasing fraction solidified. For two profiles there is a tendency of decreasing contents at high fraction solidified.</p><p>For nitrogen the initial contents were 10, 12 and 44 ppm mass. The nitrogen contents tend to decrease with increasing fraction solidified. The surface temperature also decreases with increasing fraction solidified. Indicating that the melt is saturated with nitrogen already at the initial stage. The proposed mechanism of formation is by dissolution of coating particles, giving a saturated melt, where β-Si3N4 precipitates when cooling. Supporting this mechanism are the findings of smaller nitride particles at low fraction solidified, that the precipitated phase are β-particles, and the decreasing nitrogen contents with increasing fraction solidified.</p><p>The carbon profile for the solid phase goes through a maximum value appearing at a fraction solidified from 0.4 to 0.7. The profiles flatten out after the peak and attains a value of ~ 8 ppma. This drop in carbon content is associated with a precipitation of silicon carbide. It is suggested that the precipitation of silicon carbide occurs after a build-up of carbon in the solute boundary layer.</p><p>FTIR-measurements for substitutional carbon and interstitial oxygen were initiated at the institute as a part of the work. A round robin test was conducted, with the Energy Research Centre of the Netherlands (ECN) and the University of Milano-Bicocci (UniMiB) as the participants. The measurements were controlled against Secondary Ion Mass Spectrometer analyses. For oxygen the results showed a good correspondence between the FTIR-measurements and the SIMS. For carbon the SIMS-measurements were significantly lower than the FTIR-measurements. This is probably due to the low resistivity of the samples (~1 Ω cm), giving free carrier absorption and an overestimation of the carbon content.</p>

<p>Ceramic membranes made from mixed oxygen-ionic and electronic conducting perovskite oxides can selectively separate oxygen from air at elevated temperatures. These membranes have several potential applications that require a continuous supply of oxygen. For example, they may be an alternative for cryogenic production of oxygen or alternative electrode materials in solid oxide fuel cells. Of particular significance is the partial oxidation of methane to syngas (CO + H₂). By combining air separation and partial oxidation of natural gas into a single step, the need for expensive oxygen production by cryogenic means may be eliminated. Combined with existing processes for gas-to-liquid production such as Fisher-Tropsch and methanol synthesis, the MIEC membrane technology represents a very attractive route for conversion of natural gas to liquid fuels.</p><p>The research in this field was initially concerned with the search for materials with the optimum oxygen flux. Today, the long term stability of the membranes is probably the main issue. The membranes have to be stable under operating conditions, which include mechanical stability and chemically compatibility with other materials like sealing and support materials. However, the current understanding of the long term chemical and mechanical reliability is poor and this is one of the major challenges for solid state ionic research. The aim of this work has been to investigate the mechanical properties and the chemical stability of La_0.5Sr_0.5Fe_1-xCo_xO_3-δ (x = 0, 0.5, 1) materials when they are exposed to thermal and chemical gradients.</p><p>The chemically induced stresses due to reduction of the valence state of the transition metals are of particular importance with respect to the mechanical stability. In paper I, the oxygen non-stoichiometry, investigated by thermogravimetrical analysis, and thermal end chemical expansion, studied by dilatometry and high temperature X-ray diffraction, of La_0.5Sr_0.5Fe_1-xCo_xO3-δ materials are reported. The oxygen deficiency was observed to increase with decreasing partial pressure of oxygen and increasing temperature corresponding to expectations and previous reports. At ambient temperature the thermal expansion coefficient of the materials were in the range 15- 18·10^-6 K^-1. Above a certain temperature thermal reduction of the material take place, and the thermal expansion coefficient due to chemical expansion raise to 16-36·10^-6 K^-1. The chemical expansion ε_c, defined as the linear expansion due to a change in partial pressure of oxygen at constant temperature, reached a maximum in the range 0.036-0.039 for the materials studied at 800ºC. The change in ionic radii of the transition metals is the main contribution to the chemical expansion. The crystal structure of the perovskite materials were shown to be slightly rhombohedral at ambient temperatures and a transition to cubic phase were observed above 300ºC.</p><p>This non-linear thermal expansion behavior is a major challenge for the applications of the mixed conductor materials. La_0.5Sr_0.5Fe_1-xCo_xO_3-δ membranes in an oxygen partial pressure gradient will have different oxygen deficiency on either side of the membrane. The increasing oxygen deficiency is accompanied by a volume expansion as shown in paper I, and this will lead to chemically induced stresses. These stresses and the failure that might follow can be prevented by creep of the materials. Creep is also important due to dimensional stability. In paper II, the steady-state creep performance under compression of La_0.5Sr_0.5Fe_1-xCo_xO_3-δ (x = 0.5, 1) as a function of temperature, atmosphere, load and two different grain sizes is reported. The stress exponent found for the materials was close to unity and an unusual low inverse grain size exponent close to one was found for one of the materials. The activation energy of the two materials was not equal and the influence of secondary phases on the creep was discussed. The obtained creep behavior and microstructural investigation after measurements point to a diffusion related mechanism for the creep. Higher creep rates are found under reducing conditions and this suggest that creep relaxation of mechanical or chemical induced stresses may enhance the mechanical stability of oxygen permeable membranes.</p><p>In Paper III, the mechanical properties of La_0.5Sr_0.5Fe_1-xCo_xO_3-δ (x = 0.5, 0.75, 1) were investigated by several methods. Fracture strength was measured by four-point bending, fracture toughness was measured by SENB and SEVNB methods and finally Young’s modulus were investigated by four-point bending and resonant ultrasound spectroscopy. Four-point bending showed a non-linear ferroelastic behavior at ambient temperature due to rhombohedral crystal structure. Above the ferroelastic to paraelastic transition temperature the materials showed elastic behavior, however, at temperatures from about 800ºC a non-elastic respond was observed due to creep. The measured fracture strength and fracture toughness were observed to increase with increasing temperature, which was attributed to frozen-in stress gradients in the materials during cooling due to different oxygen stoichiometry. These stress gradients caused the low fracture strength and fracture toughness at ambient temperature. At higher temperatures, the stresses are assumed to relax resulting in a higher strength and fracture toughness. At high temperature, the non-linear respond made systematic errors in the calculated strength and fracture toughness. The Young’s modulus was measured from four-point bending and by resonant ultrasound spectroscopy for two of the materials. These data obtained by these two different methods were not in good agreement, which demonstrate the difficulty to obtain reliable data for the Young’s modulus of such materials by four-point bending. The presented findings have demonstrated the importance of understanding ferroelasticity and chemically induced stresses in order to comprehend the mechanical properties of such mixed valence state perovskite materials.</p><p>A high oxygen flux is required in order to realize the oxygen permeable membrane technology. At the same the chemical stability of the materials in a pO₂ gradient must be good for a sufficient long period of time. The oxygen flux performance and the long term stability of La_0.5Sr_0.5Fe_1-xCo_xO_3-δ (x = 0, 0.5, 1) are the topics of Paper IV and V.</p><p>Oxygen fluxes through the membranes are found as a function of oxygengradient and temperature in a oxygen permeation cell using air and inert gas on each side. The oxygen flux was observed to increase with decreasing pO₂on the secondary side until the surface exchange became rate limiting and the fluxes reach a constant value. By further increase of the pO₂ gradient, the flux seemed to decrease and this was attributed to the pO₂ dependence of the surface exchange coefficient. The apparent activation energy of the oxygen permeation was in good accordance with previous investigation of similar materials.</p><p>After about 5 week of exposure in an oxygen gradient at about 1150°C, the membranes were carefully examined by electron microscopy for evidence for kinetic demixing and decomposition. Dependent of the overall composition of the membrane, different secondary phases were formed at the primary surface of the membrane. For the cobalt containing materials, isolated grains or clusters of grains of cobalt oxide were formed. In case of the La_0.5Sr_0.5FeO_3-δ membrane, a dense and about 20 µm thick layer of the secondary phase SrFe₁₂O₁₉was formed at the primary side. The overall (La+Sr)/(Fe+Co) ratio was also seen to influence on the phase formed at the primary side. Kinetic demixing was also demonstrated in all the membranes although the metal concentration profiles were not drastically changed from the initial concentrations. The formation of secondary phases was reflected in the (La+Sr)/(Fe+Co) ratio across the membrane. The largest deviation from the nominal stoichiometry was seen close to the surfaces indicating steeper chemical gradients close to the surfaces. These phenomena may strongly limit the long term stability of thinner membranes e. g. films on a porous substrate.</p>

No description available.

<p>Slagsegheten hos stål är komplext beroende av ett antal olika parametrar, som i olika grad påverkar varandra.</p><p>Många betydande och viktiga ledtrådar har hittats som förhoppningsvis kan ge en bredare förståelse varför slagsegheten varierar och varför den inte alltid uppnås i nuvarande process.</p><p>Studien har utförts på kalldragna sömlösa rör, med stålsort EN 10305-1. Projektet innefattar ett antal olika produkt specifikationer med olika dimensioner, med lite olika kemiska sammansättning. På grund av slagseghetskraven på industriella produkter var det viktigt att utvärdera vilka parametrar som påverkar. En utvärdering gjordes dels av resultat från slagseghetsprovning efter påverkande processer, och dels från utvärdering av stålets mikrostruktur.</p><p>Förutom dimension och kemisk sammansättning, varierar processlinjens faktorer. Den första processen som påverkar är kalldragningen som i denna studie har haft reduktioner mellan 15% och 31%. Avspänningsglödgningens temperatur påverkar även, där temperaturerna 525 oC, 575 oC och 600 oC är de som använts på produkterna i projektet. Vissa av projektets produkter har även normaliserats, och resultaten tyder på att detta är en mycket viktig process om man ser till slagseghet.</p><p>Målsättningen var att får fram omslagskurvor vid olika tillstånd av stålet. Utifrån dessa tillsammans med utvärdering av stålets mikrostruktur och kemisk sammansättning kunde flera diskussioner föras.</p><p>Den viktiga slutledningen som kunde dras var att inga faktorer är ensam avgörande för slagsegheten i den här studien. Den kemiska sammansättningen påverkar ihop med processlinjens olika faktorer. Man bör ligga på en temperatur för avspänningsglödgning över 550 oC. Projektet visar även på att större dimensioner påverkar slagsegheten negativt.</p><p>Två viktiga felmarginaler kan ha påverkat resultaten i projektet, dels positionen för vart anvisningen görs på provstaven i förhållande till rören och dels användandet av en praxis som beräknar resultat från provning med reducerade provstavar. En undersökning av dessa felmarginaler gjordes, och resultaten var tydliga. En mer noggrann provuttagning bör göras, och man bör vara mer försiktig vid användandet av praxisen.</p>

<p>This thesis deals with the preparation, optical characterization and analyses of experimental work and theoretical modeling on selective solar absorbers used in solar thermal collectors. The overall goal has been to obtain efficient absorbers by optimizing the optical properties, and to improve their durability using cost-effective techniques.</p><p>A Ni-Al₂O₃ absorber was pyrolytically coated with SnO₂ to improve its coating quality. Undesirable increase of solar reflectance obtained as a result of the SnO₂ was reduced by applying a silica antireflection layer produced by a dipping technique from colloidal silica sol. Annealing of Ni particles in an Al₂O₃ matrix was also carried out and compared to particles heated without the matrix. Due to the Al₂O₃ matrix, a much slower oxidation rate was found for the embedded particles. In addition, the optical performance of commercial Ni-Al₂O₃ and Ni-NiO_x absorbers were experimentally compared at oblique incidence. A better solar-absorptance of the Ni-Al₂O₃ at higher angles of incidence was found. This is due to enhanced optical interference in the double-layer structure of Ni-Al₂O₃, which could not be achieved in the graded index film of Ni-NiO_x.</p><p>The optical properties of Si-Al₂O₃ films of different thicknesses have been investigated by preparing the films using an integral coloration method. The solar-absorptance and thermal-emittance were found to increase with increasing film thickness. Due to high thermal-emittance, the Si-Al₂O₃ coating shows non-selective absorbing properties. Its feasibility for a selective solar absorber was studied by modeling the coating as a function of coating thickness for different particle size and volume fraction using four-flux theory. The results indicated that the Si-Al₂O₃ coating is not a suitable candidate for selective solar absorbers.</p><p>Scattering and absorption cross-sections of FeMnCuO_x and black carbon pigments have been obtained from reflectance and transmittance measurements in the solar wavelength range. The cross-sections were determined by using pellets consisting of low pigment volume fractions dispersed in KBr matrix. The cross-sections exhibit linear dependence of the volume fraction, indicating that single scattering dominates. The cross-sections were used to model the optical properties of solar selective paints using four-flux model resulting in good agreement between calculations and experiments.</p>

<p>An angle-resolved scatterometer and an integrating sphere for reflectance measurements at oblique angles of incidence have been designed and evaluated. The integrating sphere has a centre-mounted sample holder and the detector sits at the end of the sample holder and therefore always faces the same sphere wall area. The sphere geometry plays an important role for the modelling of detected signals and the reflected intensity has to be divided into a specular and a diffuse component. These components must be treated separately in the modelling. These two instruments, as well as traditional spectrophotometers, have been used for the evaluation of solar energy materials. Scattering as well as non-scattering surfaces have been studied, requiring different measurement techniques.</p><p>By using angle-resolved scatterometry it has been demonstrated that a solar reflector does not need to be perfectly specular provided the concentration factor is low. Thus it is possible to use inexpensive aluminium foil as the reflector material. The possibility of increasing the reflectance of aluminium with thin dielectric films of silicon and titanium oxides for pv-cell and solar thermal collector application has been investigated. Particular attention has been paid to the angular optical properties since thin films strongly affect them owing to interference effects. In an under-glazing application for pv-cells, the use of aluminium coated with titania and silica is recommended. The long-term stability of several reflector materials has been studied and anodised aluminium protected by a UV-stabilised polymer coating is recommended for solar collector reflectors.</p><p>Antireflective films consisting of porous silicon oxide for solar collector cover glazings have been studied. The films were prepared by a dip-coating process using a suspension of nano-sized silicon oxide particles. This treatment increased the solar transmittance by 5.5 percentage points. It has also been shown that it is possible to temper antireflection treated glazings without seriously affecting the optical performance. The tempering also strongly improves the mechanical stability of the film.Some of the measurements presented in this thesis were used as input data to simulation programs, which calculate the collected annual energy as a function of the optical properties of the different components. It was found that spectrophotometric laboratory measurements agree well with outdoor collector testings.</p>

<p>During recent decades, huge amount of radioactive waste has been dumped into the earth's surface environments. ¹²⁹I (T_1/2= 15.6 My) is one of the radioactive products that has been produced through a variety of processes, including atomic weapon testing, reprocessing of nuclear fuel and nuclear accidents. This thesis describes development of the Accelerator Mass Spectrometry (AMS) ultra-sensitive atom counting technique at Uppsala Tandem Laboratory to measure ¹²⁹I and discusses investigations of its distribution in the hydrosphere (marine and fresh water) and precipitation. The AMS technique provides a method for measuring long-lived radioactive isotopes in small samples, relative to other conventional techniques, and thus opens a new line of research. The optimization of the AMS system at Uppsala included testing a time of flight detector, evaluation of the most appropriate charge-state, reduction of molecular interference and imporvement of the detection limit. Furthermore, development of a chemical procedure for separation of iodine from natural water samples has been accomplished. </p><p>The second part of the thesis reports investigations of ¹²⁹I in natural waters and indicates that high concentrations of ¹²⁹I (3-4 orders of magnitude higher than in the pre-nuclear era) are found in most of the considered natural waters. Inventory calculations and results of measurements suggest that the major sources of radioactive iodine are the two main European nuclear reprocessing facilities at Sellafield (U.K.) and La Hague (France). This information provides estimates of the transit time and vertical mixing of water masses in the central Arctic Ocean. Results from precipitation, lakes and runoff are used to elucidate mechanisms of transport of ¹²⁹I from the point sources and its pathways in the hydrological environment. This study also shows the need for continuous monitoring of the ¹²⁹I level in the hydrosphere and of its future variability.</p>

<p>By the introduction of machine elements made of light metals, e.g. Al or Mg alloys, which are coated with a material providing high wear resistance and low friction coefficient, both economical and environmental benefits can be gained. A high resistance against wear results in increased lifetime and lower costs for spare parts and maintenance. This also means fewer production stops and less machine downtime. Moreover, a vehicle of lower weight and with reduced friction losses will consume less fuel.</p><p>The light metal alloys display low hardness and elastic modulus and in addition they have a high tendency to stick to the countersurface in sliding contact. Hence, to be used in tribologically demanding applications, they must be coated with a material providing low friction and wear. Due to the thin and brittle nature of the available coatings an intermediate load-carrying layer has to be introduced to protect the base material from large deformations and the brittle surface coating from cracking.</p><p>In this thesis both experiments and theoretical simulations has shown that the load-carrying layer between the soft and compliant base material and the thin brittle coating should have high elastic modulus and hardness as well as a for the contact situation sufficient thickness.</p><p>A number of vapour deposited coatings have been investigated regarding their tribological behaviour with special emphasis on the mechanisms providing low friction. When sliding against steel, it was found that carbon-rich coatings show much lower friction and wear of the countersurface than nitrogen-rich coatings. The explanation is that steel has a tendency to stick to nitrogen-rich coatings, leading to steel against steel contact, but not to carbon-rich coatings. Another explanation is that material is transferred from a carbon-rich coating to the steel and this gives an easily sheared contact with low friction coefficient.</p>

<p>This thesis deals with studies of thin films using soft x-ray emission spectroscopy. Thin films are frequently used in optical, semiconductor and magnetic applications, and along with the development of thin film deposition techniques, there is a growing need for thin film characterisation and production control. Soft x-ray spectroscopy provides elemental as well as chemical bonding information and has the advantage of being relatively insensitive to electric and magnetic fields. It may thus be used <i>in-situ</i> during deposition for monitoring sputtering deposition.</p><p>Thin films of TiVN were reactively co-sputtered using two targets, and soft x-ray spectroscopy and optical emission spectroscopy were used to determine the film composition <i>in-situ</i>. These measurements were compared with <i>ex-situ </i>elemental analysis<i> </i>as well as with computer simulations. The results agree qualitatively and indicate that soft x-ray spectroscopy can be used for <i>in-situ</i> determination of film composition. In another study, the composition of chromium nitride was studied <i>in-situ</i> under varying deposition conditions. The fraction of different stoichiometric phases in the deposited films as a function of nitrogen flow was determined <i>in-situ</i>.</p><p>The thesis also deals with the angular dependence of soft x-ray emission spectroscopy. The angular dependence of the emission was measured and compared to simulations for layered samples consisting of different transition metals, one sample consisting of Fe(50Å)/Cu(100Å)/V(100Å)/Si and another set of samples consisting of Fe(XÅ)/V(100Å)/MgO, where X = 25, 50 and 100 Å. The measured angular variation can be described qualitatively by calculations including refractive effects. For measurements below the critical angle of reflection, only the top layer corresponding to the evanescent wave region of 20-50 Å is probed, whereas for larger grazing angles the probe depth reaches thousands of Å. This demonstrates the feasibility of using the angular dependence as a way of studying composition and layer thickness of thin films.</p>