Kelvin Probe Force Microscopy (KPFM) characterization of lanthanum lutetium oxide high-k dielectric thin films

Lanthanum lutetium oxide (LaLuO3) thin films were investigated considering their perspective application for industrial microelectronics. Scanning probe microscopy (SPM) techniques permitted to visualize the surface topography and study the electric properties. This work compared both the material properties (charge behavior for samples of 6 nm and 25 nm width) and the applied SPM modes. Particularly, Kelvin probe force microscopy (KPFM) was applied to characterize local potential difference with high lateral resolution. Measurements showed the difference in morphology, chargeability and charge dissipation time for both samples. The polarity effect was detected for this material for the first time. Lateral spreading of the charged spots indicate the diffusive mechanism to be predominant in charge dissipation. This allowed to estimate the diffusion coefficient and mobility. Using simple electrostatic model it was found that charge is partly leaking into the interface oxide layer.

Ammoniumin, fosfaatin ja nitraatin poisto adsorption avulla

Kiinnostus ravinneionien ammoniumin, fosfaatin ja nitraatin poistoon liittyy niiden ne-gatiivisiin ympäristövaikutuksiin ja niiden poistoon jätevesistä on olemassa erilaisia tekniikoita. Tässä työssä ionien poistoa tutkittiin adsorptiotekniikan avulla. Siinä perus-ajatuksena on ionin kiinnittyminen adsorbentin pintaan, jolloin sen poistaminen käsitel-tävästä vedestä on mahdollista. Tässä diplomityössä tutkittiin eri adsorbentteja ammoniumin, fosfaatin ja nitraatin poistoon, ja päämääränä oli niiden yhtäaikainen poistaminen. Kokeita tehtiin niin laboratoriossa valmistetuille ravinneliuoksille kuin Yara Suomi Oy:n Siilinjärven (Yara) toimipaikalta toimitetuille vesille. Yaran vesien osalta pääpaino oli ammoniumin poistossa. Tutkimuksen haasteina olivat ionien erilaiset varaukset, jolloin esimerkiksi positiivisesti varautunut ammoniumioni kiinnittyi negatiivisesti varautuneen adsorbentin pintaan hel-poiten. Toisaalta negatiivisesti varautuneet anionit fosfaatti ja nitraatti suosivat positiivi-sesti varautuneita adsorbentteja. Myös muiden ionin läsnäolo joko edisti tai esti adsorboitumista ja joissain tapauksissa pH:lla oli suuri merkitys prosessin onnistumiseen. Saatuja tuloksia tarkasteltiin tutkittujen ionien poistoprosenttien ja isotermimallinnuksien kautta unohtamatta muita esille tulleita seikkoja. Saatujen tulosten mukaan etenkin kalsinoitu hydrotalsiitti poisti fosfaattia ja nitraattia, mutta se ei mainittavasti toiminut ammoniumille. Ammoniumille sen sijaan toimi par-haiten zeoliitit ja bentoniitti, jotka vähensivät myös Yaran vesien ammoniumpitoisuutta. Ionien yhtäaikainen poistaminen oli haastavaa ja sen parempi ymmärtäminen edellyttää jatkotutkimuksia. Yksi jatkotutkimuskohde voisi olla eri adsorbenttien yhdistäminen keskenään, ja tästä saatiin jo alustavia, rohkaisevia tuloksia.

The pH-dependent phase distribution of wood pitch components in papermaking processes

Wood contains only a very small amount of lipophilic extractives, commonly known as wood pitch. The pitch is known to cause severe problems in papermaking processes. The amount of pitch in process waters can be decreased by seasoning of the raw material prior to pulping, pulp washing, removal of pitch by flotation, adsorption of pitch onto various mineral surfaces, and retention of pitch to the fibre material by cationic polymers. The aim of this study was to determine the influence of pH on some of the methods used for pitch control. Experiments were performed using laboratory-made wood pitch emulsions with varying pH, salt concentration, hemicellulose concentration and pitch composition. These emulsions were used to study the phase distribution of resin and fatty acids, the colloidal stability of pitch with and without steric stabilisation by galactoglucomannans, and the interactions between wood pitch and mineral particles. Purification of unbleached and peroxidebleached mill process water was performed by froth flotation in combination with a foaming agent. The distribution of resin and fatty acids (RFAs) between colloidal pitch droplets and the water phase was very dependent on pH. At pH 3, almost all of the RFAs were attached to the pitch droplets, while increasing the pH led to increasing concentration of dissolved RFAs in the water phase. The presence of salt shifted the release of RFAs towards higher pH, while lower ratio of neutral pitch in the emulsion resulted in release of RFAs at lower pH. It was also seen that the dissolution and adsorption of RFAs at sudden pHchanges takes place very quickly. Colloidal pitch was more stable against electrolyte-induced aggregation at higher pH, due to its higher anionic charge. The concentration of cationic polymers needed to aggregate colloidal pitch also increased with increasing pH. The surface characteristics of solid particles, such as amount of charged groups, were very important for understanding their interactions with colloidal wood pitch. Water-soluble galactoglucomannans stabilised the colloidal pitch sterically against aggregation, but could not completely prevent interactions between wood pitch and hydrophilic particles. Froth flotation of unbleached and peroxidebleached process water showed that the pitch could be removed more effectively and selectively at low pH, compared to at neutral pH. The pitch was removed more effectively, using lower concentrations of foaming agent, from peroxide-bleached water than from unbleached water. The results show that pH has a major impact on various pulping and papermaking processes. It determines the anionic charge of the colloidal pitch and the solubility of certain pitch components. Because of this, the pH influences the effectiveness of pitch retention and removal of pitch. The results indicate that pitch problems could be diminished by acknowledging the importance of pH in various papermaking processes.

Enhancing the Usability of Drug Materials by Electrostatic Atomisation

Electrospraying or electrostatic atomisation is a process of liquid disruption by electrostatic forces. When liquid is brought into an electric field, charge is induced to its surface. Once the repulsive electrostatic force exceeds the liquid surface tension, the liquid disrupts into small highly charged droplets. The size of the electrosprayed droplets can range from hundreds of micrometers down to a few tens of nanometers. Electrospraying can be used not only to produce droplets, but also solid particles. The research presented in this thesis concentrates on producing drug particles by this method. In the experiments, a drug powder was dissolved in a convenient solvent and the solution was atomised. The solvent was then evaporated from the formed droplets in a drying medium and inside each droplet, a dense cluster of the dissolved drug remained. From the pharmaceutical point of view, the most important characteristics of the produced particles are size distribution, porosity, crystal form and degree of crystallinity. These properties affect the dissolution behaviour and ultimately the drug bioavailability in the body. The effects of electrostatic atomization on the aforementioned characteristics are generally not well understood. The research focused on studying these particle properties and finding possible correlations with the spraying parameters. The produced droplets were dried either under atmospheric or reduced pressure, the latter in order to improve the drying process. Special emphasis was put on implementing the spraying under reduced pressure, and the effects of the drying pressure on particle properties. Based on the results, the possibilities to enhance the dissolution of poorly soluble drugs by this method were estimated. In the course of experiments, it was also discovered that electrospraying may have a profound effect on the polymorphic form of the produced drug particles. In the light of the obtained results, it was concluded that electrospraying may offer a valuable tool to overcome some of the challenges met in modern drug development and formulation.

Numerical simulation of two-chamber plasma sources using finite element method

Numerical simulation of plasma sources is very important. Such models allows to vary different plasma parameters with high degree of accuracy. Moreover, they allow to conduct measurements not disturbing system balance.Recently, the scientific and practical interest increased in so-called two-chamber plasma sources. In one of them (small or discharge chamber) an external power source is embedded. In that chamber plasma forms. In another (large or diffusion chamber) plasma exists due to the transport of particles and energy through the boundary between chambers.In this particular work two-chamber plasma sources with argon and oxygen as active mediums were onstructed. This models give interesting results in electric field profiles and, as a consequence, in density profiles of charged particles.

Emission, kinetic and magnetic phenomena in rare-earth and transition metal doped ZnSe single crystals

In this work emission, optical, electrical and magnetic properties of the d- and f- elements doped zinc selenide crystals were investigated within a wide temperature range. Doping was performed in various technological processes: during the growth by chemical vapor transport method; by thermal diffusion from the Bi or Zn melt. Concentration of the doping impurity in the crystals was controlled by amount of the dopant in the source material or by its concentration in the doping media. Special interest in the work was paid to the influence of the different concentrations of Cr and Yb impurities on ZnSe crystals’ properties, correlations between observed effects and similarities with the Ni, Mn and Gd dopants are analysed. Possibility of formation of the excitons bound to the doping d-ions was shown. In contrast to this, it was observed that f-elements do not bound excitons, but prevent formation of excitons bound to some uncontrolled impurities. A mechanism of Cr doping impurity interaction with background impurities and zinc selenide structural defects was proposed based on experimental data. An assumption about resonant energy transfer between double charged chromium ions and complexes based on crystals’ vacancy defects was made. A correlation between emission and magnetic properties of the d- ions doped samples was established. Based on this correlation a mechanism explaining the concentration quench of the emission was proposed. It was found that f-ions bind electrically active shallow and deep donor and acceptor states of background impurity to electrically neutral complexes. This may be observed as “purification” of ZnSe crystals by doping with the rare-earth elements, resulting i tendency of the properties of f-ion doped crystals to the properties of intrinsic crystals, but with smaller concentration of uncontrolled native and impurity defects. A possible interpretation of this effect was proposed. It was shown that selenium substituting impurities decrease efficiency of the Yb doping. Based on this experimental results an attempt to determine ytterbium ion surroundings in the crystal lattice was made. It was shown that co-doping of zinc selenide crystals with the d- and f- ions leads to the combination of the impurities influence on the material’s properties. On the basis of obtained data an interaction mechanism of the d- and f-elements co-dopants was proposed. Guided by the model of the ytterbium ion incorporation in the selenide sublattice of the ZnSe crystals, an assumption about stabilization of single charged chromium ions in the zinc sublattice crystal nodes, by means of formation of the local charge compensating clusters, was made.