Modeling diffraction in free-space optical interconnects by the mode expansion method

Free-space optical interconnects (FSOIs), made up of dense arrays of vertical-cavity surface-emitting lasers, photodetectors and microlenses can be used for implementing high-speed and high-density communication links, and hence replace the inferior electrical interconnects. A major concern in the design of FSOIs is minimization of the optical channel cross talk arising from laser beam diffraction. In this article we introduce modifications to the mode expansion method of Tanaka et al. [IEEE Trans. Microwave Theory Tech. MTT-20, 749 (1972)] to make it an efficient tool for modelling and design of FSOIs in the presence of diffraction. We demonstrate that our modified mode expansion method has accuracy similar to the exact solution of the Huygens-Kirchhoff diffraction integral in cases of both weak and strong beam clipping, and that it is much more accurate than the existing approximations. The strength of the method is twofold: first, it is applicable in the region of pronounced diffraction (strong beam clipping) where all other approximations fail and, second, unlike the exact-solution method, it can be efficiently used for modelling diffraction on multiple apertures. These features make the mode expansion method useful for design and optimization of free-space architectures containing multiple optical elements inclusive of optical interconnects and optical clock distribution systems. (C) 2003 Optical Society of America.

Bifacial dye-sensitized solar cells: a strategy to enhance overall efficiency based on transparent polyaniline electrode

Dye-sensitized solar cell (DSSC) is a promising solution to global energy and environmental problems because of its clean, low-cost, high efficiency, good durability, and easy fabrication. However, enhancing the efficiency of the DSSC still is an important issue. Here we devise a bifacial DSSC based on a transparent polyaniline (PANI) counter electrode (CE). Owing to the sunlight irradiation simultaneously from the front and the rear sides, more dye molecules are excited and more carriers are generated, which results in the enhancement of short-circuit current density and therefore overall conversion efficiency. The photoelectric properties of PANI can be improved by modifying with 4-aminothiophenol (4-ATP). The bifacial DSSC with 4-ATP/PANI CE achieves a light-to-electric energy conversion efficiency of 8.35%, which is increased by ,24.6% compared to the DSSC irradiated from the front only. This new concept along with promising results provides a new approach for enhancing the photovoltaic performances of solar cells.

Effect of selenization conditions on the growth and properties of Cu2ZnSn(S,Se)4 thin films

The opto-electronic properties of copper zinc tin sulfide can be tuned to achieve better cell efficiencies by controlled incorporation of selenium. In this paper we report the growth of Cu2ZnSn(S,Se)4 (CZTSSe) using a hybrid process involving the sequential evaporation of Zn and sputtering of the sulfide precursors of Cu and Sn, followed by a selenization step. Two approaches for selenization were followed, one using a tubular furnace and the other using a rapid thermal processor. The effects of annealing conditions on the morphological and structural properties of the films were investigated. Scanning electron microscopy and energy dispersive spectroscopy were employed to investigate the morphology and composition of the films. Structural analyses were done using X-ray diffraction (XRD) and Raman spectroscopy. Structural analyses revealed the formation of CZTSSe. This study shows that regardless of the selenization method a temperature above 450 °C is required for conversion of precursors to a compact CZTSSe layer. XRD and Raman analysis suggests that the films selenized in the tubular furnace are selenium rich whereas the samples selenized in the rapid thermal processor have higher sulfur content.

Three transducers for one photodetector: essays for optical communications

Dissertation presented to obtain the PhD degree in Electrical and Computer Engineering - Electronics

Gd2O3: Eu Nanoparticle-Based Poly(vinylidene fluoride) Composites for Indirect X-ray Detection

Polymer based scintillator composites have been fabricated by combining poly(vinylidene fluoride) (PVDF) and Gd2O3:Eu nanoparticles (50nm). PVDF has been used since it is a flexible and stable binder matrix and highly resistance to thermal and light deterioration. Gd2O3:Eu has been selected as scintillator material due to its wide band gap, high density and suitable visible light yield. The structural, mechanical, thermal and electrical characteristics of the composites were studied as a function of filler content, together with their performance as scintillator material. The introduction of Gd2O3:Eu nanoparticles into the PVDF matrix does not influence the morphology of the polymer or the degree of crystallinity. On the other hand, an increase of the Young´s modulus with respect to PVDF matrix is observed for filler contents of 0.1-0.75 wt.%. The introduction of Gd2O3:Eu into the PVDF matrix increases dielectric constant and DC electrical conductivity as well as the visible light yield in the nanocomposite, being this increase dependent upon Gd2O3:Eu content and X-ray input power. In this way, Gd2O3:Eu/PVDF composites shows suitable characteristics to be used as X-ray radiation transducers, in particular for large area applications.

Titanium oxide adhesion layer for high temperature annealed Si/Si3N4/TiOx/Pt/LiCoO2 battery structures

This work describes the influence of a high annealing temperature of about 700C on the Si(substrate)/Si3N4/TiOx/Pt/LiCoO2 multilayer system for the fabrication of all-solid-state lithium ion thin film microbatteries. Such microbatteries typically utilize lithium cobalt oxide (LiCoO2) as cathode material with a platinum (Pt) current collector. Silicon nitride (Si3N4) is used to act as a barrier against Li diffusion into the substrate. For a good adherence between Si3N4 and Pt, commonly titanium (Ti) is used as intermediate layer. However, to achieve crystalline LiCoO2 the multilayer system has to be annealed at high temperature. This post-treatment initiates Ti diffusion into the Pt-collector and an oxidation to TiOx, leading to volume expansion and adhesion failures. To solve this adhesion problem, we introduce titanium oxide (TiOx) as an adhesion layer, avoiding the diffusion during the annealing process. LiCoO2, Pt and Si3N4 layers were deposited by magnetron sputtering and the TiOx layer by thermal oxidation of Ti layers deposited by e-beam technique. Asdeposited and annealed multilayer systems using various TiOx layer thicknesses were studied by scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS). The results revealed that an annealing process at temperature of 700C leads to different interactions of Ti atoms between the layers, for various TiOx layer thicknesses (25–45 nm).

Aprender verbos semánticamente similares: materiales didácticos electrónicos para estudiantes de ELE

El trabajo consiste en un análisis y la evaluación de materiales electrónicos existentes sobre parejas de verbos con significados parecidos, además de la ampliación de estos materiales y la creación de un blog para poner-los a disposición de los estudiantes de ELE

Kymenlaakson kirjastojen verkkopalveluosaamisen kehittäminen

Tässä työssä tutkittiin kirjastohenkilökunnan tiedollisia, taidollisia ja asenteellisia valmiuksia, jotka liittyvät verkon kautta käytettäviin e-aineistoihin sekä verkkopalvelusovellusten käyttöön. Työn olennaisina osina olivat käyttökoulutuksen suunnittelu ja toteutus sekä siihen liittyvän ennakkotehtävän ja koulutuksen lopuksi kerätyn palautteen analysointi. Koulutustarve oli todettu ennen tätä tutkimusta tehdyllä kyselytutkimuksella. Koulutukseen osallistuneiden osaamistasoa mitattiin ennen koulutusta ennakkotehtävällä. Saatujen tutkimustulosten perusteella e aineistojen ja verkkopalvelusovellusten tuntemus ja käyttökokemus oli vahaista. Koulutuksen jälkeen tehdyn palautekyselyn perusteella vastanneet vaikuttivat motivoituneilta ja tyytyväisiltä koulutuksen antiin. Koulutuksesta saatu hyöty nähtiin yleissivistyksen, tiedonhaun sekä asiakkaiden opastuksen kannalta. Saadun palautteen perusteella koulutusta tulee edelleen kehittää ajankäytön, sisällön suunnittelun ja arvioinnin osalta. Tämän vuoksi tarvitaan tavoiteltavien tietojen ja taitojen tarkempaa määrittelyä. Koulutuksen onnistumisen ja vaikutusten lopullinen arviointi, joka tulisi suorittaa noin vuoden kuluessa koulutuksen päättymisen jälkeen, jäi tämän tutkimuksen ulkopuolelle.

Key factors in transforming university internationalization into commercial activity in Finland. Case of University of Turku

Globalization, developments in ICT, emergence of knowledge society and other changes have reformed the environment for international higher education during the past few decades. Consequently, higher education sector has moved towards more marketing-oriented system, and universities have started to undertake commercial activities as part of their internationalization. This development has emerged to Finland as well, which forms the basis for this study. The purpose is to examine commercialization in Finnish university landscape and to investigate the ways Finnish university could capitalize its international activities and educational knowledge for export. The research question of the study is: What are the key factors in transforming university internationalization into commercial activity in the Finnish university landscape? The main problem is further divided into three sub-questions: 1) How can a university internationalize; 2) what are the motivational factors behind university internationalization and commercialization; and 3) how can higher education be developed into export services and products? The research was conducted as a qualitative case study of University of Turku. Methods used for gathering and examining data were interviewing and document analysis. Primary data was collected through four individual semi-structured interviews, which were conducted face-to-face. Secondary data that included reports, articles and electronic materials such as university web pages, was used to complement the primary data. The results were analyzed by theming the data into three broader categories of internationalization activities; drivers and motivations and; education export activities. After the data was organized in themes, analysis continued by comparing different parts of data and finding patterns that would explain the phenomenon in Finnish universities. According to the empirical data, University of Turku is currently on the growth state of internationalization with strategies such as internationalization of curriculum, establishment of international research groups, mobility of students and academics, international networking and support services. Commercialization phenomenon is still rather new to the case university, but it has already developed educational products and services for export. The study concludes that university internationalization cannot be directly transformed into commercial activities in the Finnish context, but the universities need to be active in actually creating educational products. The key factors found in this study include: 1) the Finnish government policies behind the current hype of export education; 2) the potential and knowledge capacity of universities for exports; 3) need for additional profits; 4) further internationalization through commercial activities; 5) recognizing and exploiting the specific areas of strength and 6) establishing of cooperative partnerships for better products.

Electrical Characteristics of n-ZnO/p-Si Heterojunction Diodes Grown by Pulsed Laser Deposition at Different Oxygen Pressures

Heterojunction diodes of n-type ZnO/p-type silicon (100) were fabricated by 12 pulsed laser deposition of ZnO films on p-Si substrates in oxygen ambient at 13 different pressures. These heterojunctions were found to be rectifying with a 14 maximum forward-to-reverse current ratio of about 1,000 in the applied 15 voltage range of -5 V to +5 V. The turn-on voltage of the heterojunctions was 16 found to depend on the ambient oxygen pressure during the growth of the ZnO 17 film. The current density–voltage characteristics and the variation of the 18 series resistance of the n-ZnO/p-Si heterojunctions were found to be in line 19 with the Anderson model and Burstein-Moss (BM) shift.

Automation of Chemical Spray Pyrolysis Unit and Fabrication of Sprayed CuInS2/In2S3 Solar Cell

Aim of the present work was to automate CSP process, to deposit and characterize CuInS2/In2S3 layers using this system and to fabricate devices using these films.An automated spray system for the deposition of compound semiconductor thin films was designed and developed so as to eliminate the manual labour involved in spraying and facilitate standardization of the method. The system was designed such that parameters like spray rate, movement of spray head, duration of spray, temperature of substrate, pressure of carrier gas and height of the spray head from the substrate could be varied. Using this system, binary, ternary as well as quaternary films could be successfully deposited.The second part of the work deal with deposition and characterization of CuInS2 and In2S3 layers respectively.In the case of CuInS2 absorbers, the effects of different preparation conditions and post deposition treatments on the optoelectronic, morphological and structural properties were investigated. It was observed that preparation conditions and post deposition treatments played crucial role in controlling the properties of the films. The studies in this direction were useful in understanding how the variation in spray parameters tailored the properties of the absorber layer. These results were subsequently made use of in device fabrication process.Effects of copper incorporation in In2S3 films were investigated to find how the diffusion of Cu from CuInS2 to In2S3 will affect the properties at the junction. It was noticed that there was a regular variation in the opto-electronic properties with increase in copper concentration.Devices were fabricated on ITO coated glass using CuInS2 as absorber and In2S3 as buffer layer with silver as the top electrode. Stable devices could be deposited over an area of 0.25 cm2, even though the efficiency obtained was not high. Using manual spray system, we could achieve devices of area 0.01 cm2 only. Thus automation helped in obtaining repeatable results over larger areas than those obtained while using the manual unit. Silver diffusion on the cells before coating the electrodes resulted in better collection of carriers.From this work it was seen CuInS2/In2S3 junction deposited through automated spray process has potential to achieve high efficiencies.

Defect analysis of semiconductor thin films for photovoltaic applications using photo-luminescence and photo-conductivity

The present thesis can be divided into three areas:1) the fabrication of a low temperature photo-luminescence and photoconductivity measuring unit 2) photo-luminescence in the chalcopyrite CulnSez and CulnS2 system for defect and composition analysis and 3) photo-luminescence and photo-conductivity of In:JS3. This thesis shows that photo-luminescence is one of most essential semiconductor characterization tool for a scientific group working on photovoltaics. Tools which can be robust, non-destructive, requiring minimal sample preparation for analysis and most informative of the device applications are sought after by industries and this thesis is towards establishing photo-luminescence as "THE" tool for semiconductor characterization. The possible application of photo-luminescence as a tool for compositional and quality analysis of semiconductor thin films has been worked upon by this thesis. Photo-conductivity complement photo-luminescence and together they provide all the information required for the fabrication of an opto-electronic device.

Growth And Characterization Of Diammonium Hydrogen Citrate And Citric Acid Monohydrate Single Crystals

Over the past years there has been considerable interest in the growth of single crystals both from the point of view of basic research and technological application. With the revolutionary emergence of solid state electronics which is based on single crystal technolo8Ys basic and applied studies on crystal growth and characterization _have gained a-more significant role in material science. These studies are being carried out for single crystals not only of semiconductor and other electronic materials but also of metals and insulators. Many organic crystals belonging to the orthorhombic class exhibit ferroelectric, electrooptic, triboluminescent and piezoelectric properties. Diammonium Hydrogen Citrate (DAHC) crystals are reported to be piezoelectric and triboluminescent /1/. Koptsik et al. /2/ have reported the piezoelectric nature of Citric Acid Monohydrate (CA) crystals. And since not much work has been done on these crystals, it has been thought useful to grow and characterize these crystals. This thesis presents a study of the growth of these crystals from solution and their defect structures. The results of the microindentation and thermal analysis are presented. Dielectric, fractographic, infrared (IR) and ultraviolet (UV) studies of DAHC crystals are also reported

Erfahrungsbericht: Praktische Umsetzung des Informationsmanagements

Das Handling digitaler Informationen und ihre Integration in bestehende Bibliotheksdienstleistungen sind heutzutage eine der wichtigsten Aufgaben von Bibliotheken. Am Beispiel der Bibliothek der Gesamthochschule Kassel wird gezeigt, wie die entwickelten Lösungen von den organisatorischen, funktionalen und baulichen Gegebenheiten beeinflußt worden sind. Beschrieben werden zudem die technische Plattformen sowie das Zusammenwirken unterschiedlicher Dienste bis hin zum Aufbau eines eigenen Verlages für elektronische Publikationen.