New features of the layer-by-layer deposition of microcrystalline silicon films revealed by spectroscopic ellipsometry and high resolution transmission electron microscopy

Spectroscopic ellipsometry and high resolution transmission electron microscopy have been used to characterize microcrystalline silicon films. We obtain an excellent agreement between the multilayer model used in the analysis of the optical data and the microscopy measurements. Moreover, thanks to the high resolution achieved in the microscopy measurements and to the improved optical models, two new features of the layer-by-layer deposition of microcrystalline silicon have been detected: i) the microcrystalline films present large crystals extending from the a-Si:H substrate to the film surface, despite the sequential process in the layer-by-layer deposition; and ii) a porous layer exists between the amorphous silicon substrate and the microcrystalline silicon film.

The Electronic Structure of Co-Sputtered Zinc Indium Tin Oxide Thin Films

Zinc indium tin oxide (ZITO) transparent conductive oxide layers were deposited via radio frequency (RF) magnetron co-sputtering at room temperature. A series of samples with gradually varying zinc content was investigated. The samples were characterized with x-ray and ultraviolet photoemission spectroscopy (XPS, UPS) to determine the electronic structure of the surface. Valence and conduction bands maxima (VBM, CBM), and work function were determined. The experiments indicate that increasing Zn content results in films with a higher defect rate at the surface leading to the formation of a degenerately doped surface layer if the Zn content surpasses 50%. Furthermore, the experiments demonstrate that ZITO is susceptible to ultraviolet light induced work function reduction, similar to what was earlier observed on ITO and TiO2 films.

Quality potential of DIP and hardwood CTMP based raw materials in woodcontaining printing paper

The objective of the thesis was to define the quality potential of DIP and hardwood CTMP based raw material furnish for a printing paper production and to define the end product's pulp-based boundary conditions especially when thinking of Chinese markets. Although the Chinese paper industry expands rapidly, the production of some paper grades is still exiguous. Especially the softwood resources are limited in Asia, thus the purpose of the thesis was to find out the possibilities to produce printing paper in China from local raw materials. Bleached CTMP can be produced, for example, from fast-growing hardwood species like eucalyptus and poplar. Therefore in this thesis it was examined if good quality printing paper is possible to produce by using deinked pulp and hardwood CTMP based furnish. In the first section of experimental part, various deinked pulps and chemithermomechanical pulps were compared. The deinked pulps were from China, Central Europe and Finland. Central European was made for magazine papers, and the Chinese as well as the Finnish pulps were made for newsprints. Two of the BCTMPs were from China and those both were made from poplar, whereas one BCTMP was made from eucalyptus in a pilot plant. There were significant differences especially between BCTMPs and their paper properties. In the second section of experimental part, the deinked pulp and eucalyptus BCTMP were blended to produce handsheets. The results show that producing the highest quality printing paper would be difficult from these raw materials. Deinked pulp affected especially the strength and optical properties as well as calender blackening. The BCTMP was found to have effects mostly on the smoothness, strength and optical properties as well as calender blackening.

Mikrokontrolleriohjaus led-ryhmälle

Luonnonvarojen ehtyminen ja ympäristön saastuminen on luonut kysyntää uusille, energiaa säästäville ja ympäristöystävällisille teknologioille. Valaistuksessa tällainen teknologia on led-tekniikka. Led-tekniikalla on useita etuja verrattuna kilpaileviin tekniikoihin kuten pitkä elinikä, ympäristöystävällisyys ja mekaaninen kestävyys. Ledejä käytetään nykyään laajalti erilaisissa erikoissovelluksissa, erityisesti jos vaatimuksena on valon värillisyys. Näihin päiviin asti ledien hinta ja heikko valontuotto ovat rajoittaneet led-valaisimien yleistymistä hehkulamppujen ja muiden valaisintyyppien korvaajina. Tekniikan nopea kehittyminen on tehnyt led-tekniikasta varteenotettavan vaihtoehdon myös yleisvalaistukseen. Uusimpien valkoisten ledien valotehokkuus on 2 - 5 -kertainen hehkulamppuun verrattuna. Led-tekniikassa on vielä paljon käyttämätöntä potentiaalia, tulevaisuudessa päästäneen 10 - 15 -kertaiseen valotehokkuuteen hehkulamppuun verrattuna. Työssä suunnitellaan mikrokontrolleripohjainen ohjausjärjestelmä valkoista valoa tuottavalle led-valaisimelle, jonka värisävyä ja kirkkautta käyttäjä voi säätää. Valkoinen valo synnytetään sekoittamalla neljän erivärisen led-rivin valoa. Mikrokontrolleri ohjaa kutakin led-riviä väriensekoitusteoriaan perustuen. Mikrokontrolleriohjaus huomioi myös ledien optisten ominaisuuksien muutokset lämpötilan suhteen. Mikrokontrolleriohjauksen suorituskyky todetaan käytännön mittauksilla.

LWC-paperin opasiteetin parantaminen

LWC-syväpainopaperilta vaaditaan hyvän ajettavuuden, kiillon ja sileyden ohella hyvää opasiteettia. Tämä on asettanut haasteita LWC-paperin valmistajille paperin neliömassojen laskiessa. Tässä diplomityössä etsittiin keinoja parantaa kevyiden LWC-syväpainolajien opasiteettia heikentämättä oleellisesti muita tärkeitä paperin ominaisuuksia. Tavoitteena oli nostaa CR48-lajin opasiteetti tavoitearvoon 90 %. Työn kirjallisuusosassa perehdyttiin paperin optisten ominaisuuksien teoriaan sekä raaka-aineisiin ja prosessin osiin, joilla on vaikutusta paperin opasiteettiin. Työn kokeellisessa osassa tutkittiin olemassa olevan aineiston perusteella tekijöitä, joilla uskottiin olevan vaikutusta CR48-lajin opasiteettiin. Tutkimuksen ja kirjallisuuden perusteella ajettiin tehdaskoeajoa, joiden avulla pyrittiin parantamaan paperin opasiteettia. CR48-lajin opasiteettitavoite saavutettiin kolmella eri tavalla. Opasiteettitavoite saavutettiin, kun paperin vaaleus säädettiin tavoitearvoon pigmenttivärin avulla tumman hierteen sijasta. Tällöin väripigmentin määrää päällystyspastassa nostettiin 0,01 osaa ja valkaistun hierteen osuus kokonaishierteen määrästä oli 100 %. Vaaleuden säätö pastavärillä oli käytännössä hidasta ja hankalaa. Opasiteettitavoite saavutettiin myös, kun hierre jauhettiin täysin koeterillä. Koeterillä tapahtuva jauhatus oli rajumpaa ja katkovampaa kuin perinteisillä terillä, joten hienoaineen lisääntyminen ja kuidun lyheneminen paransivat paperin opasiteettia, mutta lujuudet huononivat. Lisäksi tavoiteopasiteetti saavutettiin, kun sellun osuutta vähennettiin 8 %-yksikköä. Lujuuden säilymisen kannalta sellun vähennys oli parempi keino opasiteetin parantamiseksi kuin hierteen jauhaminen koeterillä. Koeajojen perusteella pohjapaperin tuhkapitoisuuden nostolla ja hierteen CSF-luvun alentamisella ei ollut vaikutusta paperin opasiteettiin. Lisäksi 100 %:nen koeterillä jauhettu sahahakehierre antoi paperille huonomman opasiteetin kuin hierre, josta puolet oli jauhettu koeterillä ja raaka-aineesta 25 % oli sahahaketta.

Paperin ominaisuuksiin vaikuttaminen kuitulajeilla ja valmistuksen osaprosesseilla

Työn tarkastellaan massalaatujen valmistusmenetelmiä ja paperinvalmistuksen osaprosesseja pitäen silmällä massalaadun ja jälkikäsittelyn vaikutusta paperin optisiin ja reologisiin ominaisuuksiin. Pääpaino oli käytössä olevilla prosesseilla, mutta myös muutaman viimeisen vuosikymmenen aikaisiin valmistusmenetelmiin tutustuttiin suppeasti. Koska asiakkaat ja kuluttajat vaativat yhä vaaleampia, kestävämpiä ja lujempia papereita, on tärkeää kyetä tunnistamaan eri osa-prosessit, joilla voidaan vaikuttaa näihin ominaisuuksiin. Asiakaslähtöisyyden ohella prosessien pitää nykyisten tiukkojen päästömääräysten vuoksi pyrkiä ympäristöystävälliseen liiketoimintaan. Myös keräyspaperin käytöstä on säädetty asetus, jonka mukaan keräyspaperin pitää päätyä ensisijaisesti uusiopaperin raaka-aineeksi. Ympäristövaatimukset ja kierrätyskuidun käyttö antavatkin omat haasteensa hyvien optisten ja reologisten ominaisuuksien saavuttamisessa.

Monte Carlo simulation of x-ray spectra generated by kilo-electron-volt electrons

We present a general algorithm for the simulation of x-ray spectra emitted from targets of arbitrary composition bombarded with kilovolt electron beams. Electron and photon transport is simulated by means of the general-purpose Monte Carlo code PENELOPE, using the standard, detailed simulation scheme. Bremsstrahlung emission is described by using a recently proposed algorithm, in which the energy of emitted photons is sampled from numerical cross-section tables, while the angular distribution of the photons is represented by an analytical expression with parameters determined by fitting benchmark shape functions obtained from partial-wave calculations. Ionization of K and L shells by electron impact is accounted for by means of ionization cross sections calculated from the distorted-wave Born approximation. The relaxation of the excited atoms following the ionization of an inner shell, which proceeds through emission of characteristic x rays and Auger electrons, is simulated until all vacancies have migrated to M and outer shells. For comparison, measurements of x-ray emission spectra generated by 20 keV electrons impinging normally on multiple bulk targets of pure elements, which span the periodic system, have been performed using an electron microprobe. Simulation results are shown to be in close agreement with these measurements.

Decomposição de precursores metalorgânicos: uma técnica química de obtenção de filmes finos

This review focus the more relevant foundations and applications of the Metallo-Organic Decomposition (MOD) technique, mainly within the last decade. The technique has grown significantly, mainly due to the good results concerning the preparation of multicomponent oxide systems with composition, structural and morphologic control, in a relatively simple way. This opened new opportunities to obtain materials with well-defined electrical and optical properties.

Fundamentals and applications of spectroscopic ellipsometry

This paper describes the use of ellipsometry as a precise and accurate technique for characterizing substrates and overlayers. A brief historical development of ellipsometry and the basic principles necessary to understand how an ellipsometer works are presented. There are many examples of studies performed in addressing materials science issues, and several are presented here: measurements of thickness, optical properties, and modeling of surface roughness. These selected results obtained in our laboratory for substrates, Si/SiO2 interfaces, and polymers provide evidence that ellipsometry can play a critical role in characterizing different types of materials.

Formação e caracterização óptica de filmes automontados de POMA/PPV

A study is presented of the formation and optical properties of polymeric heterostructures from poly(p-phenylene vinylene) (PPV) and poly(o-methoxyaniline) (POMA) produced via the self-assembly technique. POMA layers were obtained in a non self-limiting process from its emeraldine salt, semiconducting form in HCl solution. Thermal conversion of PPV was performed at low temperatures with the substitution of the counter-ion Cl in the PPV precursor by a long sulfonic chain, the dodecylbenzenesulfonate (DBS) ion. The optical properties of PPV films converted in this way are not affected by POMA, which can be used as transparent electrode of PPV luminescent devices.

The Impact of Aspen and Alder on the Quality of NHBK

The purpose of this work was to study the effect of aspen and alder on birch cooking and the quality of the pulp produced. Three different birch kraft pulps were studied. As a reference, pure aspen and alder were included. The laboratory trials were done at the UPM Research Centre in Lappeenranta, Finland. The materials used were birch, aspen and alder mill chips that were collected around the area of South-Carelia in Finland. The chips used in the study were pulped using a standard kraft process. The pulps including birch fibres were ECF-bleached at laboratory scale to a target brightness of 85 %. The bleached pulps were beaten at low consistency by a laboratory Voith Sulzer refiner and tested for optical and physical properties. The theoretical part is a study of hardwoods that takes into accounts the differences between birch, aspen and alder. Major sub-areas were fibre and paper-technical properties as well as chemical composition and their influence on the different properties. The pulp properties of birch, aspen and alder found in previous studies were reported. Russian hardwood forest resources were also investigated. The fundamentals of kraft pulping and bleaching were studied at the end of theoretical part. The major effect of replacing birch with aspen and alder was the deterioration (lowering) of tensile and tear strengths. In other words, addition of aspen and alder to a birch furnish reduced strength properties. The reinforcement ability of the tested pulps was the following: 100 % birch > 80 % birch, 20 % aspen > 70 % birch, 20 % aspen, 10 % alder. The second thing noted was that blending of birch together with aspen and alder give better smoothness, optical properties and also formation. It can be concluded, that replacement of birch with alder during cooking by more than 10 % can negatively affect on the paper-technical properties of birch pulp. Mixing pure birch and aspen pulps would be more beneficial when producing printing paper made from chemical pulp.

Correlação entre parâmetros da cinética de intumescimento com características estruturais e hidrofílicas de hidrogéis de poliacrilamida e metilcelulose

In this paper, the effects of acrylamide (AAm), methylcellulose (MC) contents, pH and ionic strength on kinetic, network and hydrophilic properties of polyacrylamide and methylcellulose hydrogels were investigated. The hydrogels were characterized by evaluating of network [average molecular weight between crosslinks (M C), crosslink density (q) and the number of elastically effective chains (Ve)], and kinetic parameters [diffusional exponent (n), diffusion constant (k) and diffusion coefficient (D)]. Such properties were controlled by adjusting of the AAm, MC contents, pH and ionic strength factors. Due to high hydrophilicity and fast water-uptake, the PAAm-MC hydrogels can be considered as materials for potential applications in agricultural fields, mainly in controlled release of water or pesticides.

O estado da arte da síntese de semicondutores nanocristalinos coloidais

Colloidal semiconductor nanocrystals, also known as quantum dots, have attracted great attention since they have interesting size-dependent properties due to the quantum confinement effect. These nanoparticles are highly luminescent and have potential applications in different technological areas, including biological labeling, light-emitting diodes and photovoltaic devices. The synthetic methods of semiconductor nanocrystals have progressed in the last 30 years, and several protocols were developed to synthesize monodisperse nanocrystals with good optical properties, different compositions and morphologies. This review describes the main methods used to synthesize nanocrystals in the II-VI and III-V systems, and the recent approaches in this field of research.

Preparação de nanopartículas de prata e ouro: um método simples para a introdução da nanociência em laboratório de ensino

A new practical experiment involving silver and gold nanoparticle syntheses was introduced in an inorganic chemistry laboratory course for undergraduate students at the Institute of Chemistry, UNICAMP. The nanoparticles were synthesized by the reduction of silver nitrate and tetrachloroauric acid with sodium borohydride and sodium citrate in an aqueous medium. Stabilities of the suspensions were tested using several different reactants including sodium chloride, polyvinylpyrrolidone, polyvinyl alcohol and cistamine. Changes in optical properties were observed by electronic spectra and also by transmission electronic microscopy, which also yielded data for estimating particle size.

EFEITO DA ESTRUTURA MOLECULAR DE LIGANTES DE SUPERFÍCIE EM PONTOS QUÂNTICOS DE CdTe DISPERSOS EM ÁGUA

Water-soluble CdTe quantum dots are synthesized to investigate how short-chain surface ligands bearing -SH, -COOH, and -NH2 groups interact with CdTe during nucleation/growth processes. Their optical properties and colloidal stability after the ligand exchange are also investigated. We then characterize the resulting CdTe by fluorescence, UV–Vis absorption, and infrared spectroscopies. The stability of the colloidal dispersions was determined by their Zeta potentials. The results show that in the synthesis of water-soluble CdTe, surface ligands with at least two functional groups are required and the hard/soft character of them is an important factor in the stability of CdTe.