The pyrolytic decomposition of metal alkoxides (di-acetoxy-di-t-butoxy-silane, DADBS) during chemical vapour deposition of thin oxide films

In this study the effects of the nature of metal alkoxides on their vapour pressures and thermal decomposition chemistry are reported. The vapour pressure and the volatility of a metal alkoxide strongly depends on the steric effect of its alkoxy group.\ud \ud The thermal decomposition chemistry of one metal alkoxide (di-acetoxy-di-t-butoxy-silane, DADBS) has been studied by mass spectrometry at temperatures between 423 and 923 K. The pyrolytic products were acetic acid anhydride and 2-methyl propene. The acetic acid anhydride is formed at temperatures above 473 K and 2-methyl propene is formed above 673 K by a ß -hydride elimination mechanism. In these steps, a 6-ring intermediate is supposed to be formed. The silicon acid finally remaining is proposed to react by poly-condensation to SiO2 coatings or powder

Oxometalate-glass composites and thin films

New glass-composites with ion exchange properties have been developed. Ammonium 12-molybdophosphate (AMP) (ΝΗ4)3ΡΜοΐ2θ4ο, and ammonium 12-tungstophosphate (AWP) (Nh4)3PW12O40, known for their ion exchange capabilities, are included either in preformed aerogels with defined pore size, or are added to sol-gel mixtures during the process of gel formation. Characterization is carried out by FTIR, Raman and EXAFS spectroscopy. Ion exchange capacities for the oxometalate precursors are determined for silver and rubidium and are compared to those of the glass composites. Glass composites show high ion exchange capacity, but some portion of the metalate complexes leaches from the glass during the procedure. This is in contrast to thin composite films, which have almost no porosity and do not show loss of metalate. EXAFS spectroscopy demostrates that the oxometalate microstructure is maintained in glass composites and that rubidium ions after ion exchange in glasses occupy similar cation positions as in the precursor compounds

Alkoxide complexes of rhenium, niobium and tantalum

This thesis describes two major methods for preparation of new mono-, bi- and trimetallic complexes on the basis of Rhenium, Niobium and Tantalum: (1) - the electrochemical method for the synthesis of Re4O4(OEt)12 and (2) - the interaction of Rhenium heptoxide, Re2O7, with alkoxo-derivates of Niobium and/or Tantalum, M2(OR)10 for the synthesis of bi- and trimetallic complexes of common formula (M1-xM'x)4O2(OR)14(ReO4)2 (M = Nb; M' = Ta; R = Me, Et), where x = 0–1. The structures of these complexes were determined by single-crystal X-ray diffraction. The products were also characterized by IR, NMR and X-ray powder diffraction. The influence of the increasing ligand size on the solubility and stability of the complexes Re4O4(OEt)12 and M4O2(OR)14(ReO4)2 (M = Nb, Ta; R = Me, Et) has been established. The effect of the ligand and metal ion ratio on the conditions and the chemical composition of the products of thermal treatment have been investigated. Nanosized Rhenium metal particles (approximately 3 nm in diameter) were obtained from Re4O4(OEt)12 by thermal decomposition in inert atmosphere at as low temperature as 380 °C. Semi-ordered macro porous monoliths with the pore size in the range 100 – 250 nm, with the crystal structure related to the block structures of the L-modification of Ta2O5, were produced from trimetallic complexes of the common formula (Nb1-xTax)4O2(OMe)14(ReO4)2 (x = 0.3, 0.5, 0.7) via thermal decomposition in air at the temperatures ≤ 1000 °C. The thermal decomposition in dry nitrogen atmosphere provides formation of solid solutions, which possess the structures related to the block structure of the H-modification of Nb2O5 for the Niobium-rich precursors and block structure of the L-modification of Ta2O5 for Ta:Nb ≤ 1:1 at the temperatures ≤ 1000 °C

Kombineeritud sool-geel ja aatomkihtsadestatud struktuurid

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Vedela materjali tahkestamise võimalused on mitmete teiste rakenduste seas omandanud tehnoloogilise tähtsuse kuna nad võimaldab valmistada vedelatest lähteainejugadest tahkeid fiibrilisi kehandeid ehk kiudusid. Käesolevates teesides keskendutakse metallialkoksiidide põhiste vedelikjugade tahkestumisele eesmärgiga sünteesida metalloksiidseid seest õõnsaid fiibreid ehk mikrotorusid. Uuringute põhiobjektiks on 8% üütriumoksiidiga faasistabiliseeritud tsirkooniumi oksiid (8%YSZ), mis on teada-tuntud tehnoloogiline materjal. Sünteesitud materjalid on ligemale 100%liselt tetragonaalses faasis, materjalidel on hea mehaaniline-termiline vastupidavus, kannatades kuumutamist 1000 ˚C ja enam, ning võimaldades näiteks rakenda toru sees 1000 atm ülerõhku. Tulenevalt neist omadustest pakume me torudele välja rea erinevaid rakendusi. Optiline kvaliteet – nanohomogenne materjali struktuur – võimaldab kasutada materjale vastavate lainejuhtidena, näiteks optilise lainejuhtivuse põhiste sensoritena. 8%YSZ torude ioonjuhtivus lubab asuda konstrueerima nende põhiseid ioonmembraanseadmeid, nagu näiteks tahkeoksiidsed kütuselemendid ja gaasisensorid. Teesides on demonstreeritud üksiku toru põhist mikroplasmaseadet, mis võimaldab plasma teket üleatmosfäärirõhulistes tingimustes ja perspektiivis plasmaergastud aktiivsete osakeste suunamist lokaalsesse pinnapunkti. Viimane rakendus võiks olla huvipakkuv näiteks meditsiinis. Keraamiliste mikrotorustruktuuride täiendavaks funktsionaliseerimiseks on näidatud aatomkihtsadestamistehnoloogiate sobilikkust. Magneesiumoksiidkiled sadestati mikrotorude pinnale kasutades β-diketonate tüüpi lähteainet 2,2,6,6-tetramethyl-heptanedionato-3,5magnesium(II). Aatomkihtsadestmine on torude funktsionaliseerimiseks oluline, kuna ta võimaldab torude ühtlast katmist nii seest, kui väljast.Curing processes enabling transformation of liquid threads into solid fiber material have gained technological importance. The theis are focusing on curing mechanisms for metal alkoxide-derived liquid threads in order to prepare novel structures metal oxide hollow fibres (microtubes). The focus is on YSZ (8% Y2O3 stabilized ZrO2), which exhibits a stable 100% tetragonal phase nanocrystalline structure up to 1000 ˚C. These tubes have excellent mechanical characteristics and can withstand 1000atm pressure inside the tubes. Owing to these and other physical, chemical and mechanical properties, there are many potential applications for these tubes, one example being that the high optical quality of the YSZ tubes could be useful for guiding of light. Ionic conductivity with no electronic component makes these tubes suitable for ionic membrane applications like solid oxide fuel cells (SOFCs) or corresponding gas sensors. We demonstrate a single-tube-based miniature plasma jet device potentially applicable as an ion source for local surface treatment. For the purpose of functionalization, deposition of MgO thin film on nanocrystalline YSZ microtubes was investigated. MgO films were atomic layer deposited from β-diketonate-type precursor 2,2,6,6-tetramethyl-heptanedionato-3,5-magnesium(II)

Pengaruh elemen gamifikasi terhadap motivasi pelajar menggunakan aplikasi quizizz

Pelajar generasi abad ke 21 sekarang lebih berminat belajar menggunakan gadjet atau alat-alat komunikasi canggih tanpa wayar yang berasaskan teknologi. Sejajar dengan hasrat kerajaan dalam mempraktikkan Pendidikan Abad ke-21 (PAK 21) dalam melahirkan pelajar yang berkolaboratif dan berfikiran kritis, satu kajian telah dilaksanakan untuk mengkaji tahap motivasi intrinsik dan ekstrinsik pelajar terhadap kaedah pembelajaran gamifikasi menggunakan aplikasi Quizizz. Reka bentuk kajian yang digunakan dalam kajian ini adalah berbentuk tinjauan deskriptif dan infrensi dengan menggunakan pendekatan kuantitatif melalui instrumen soal selidik. Lokasi sampel kajian dilakukan di Kolej Kemahiran Tinggi Mara (KKTM) Sri Gading, Batu Pahat, Johor terhadap pelajar Diploma Kejuruteraan Bangunan yang mengambil kursus Kejuruteraan Matematik 3. Kajian rintis telah dijalankan kepada pelajar Diploma Kejuruteraan Awam UTHM seramai 30 orang. Manakala responden bagi kajian ini adalah sebanyak 63 orang pelajar KKTM. Data dianalisis menggunakan SPSS versi 22.0 bagi menentukan purata skor min dan analisis regresi berganda. Secara keseluruhannya, hasil analisis data menunjukkan bahawa tahap motivasi intrinsik adalah (min=3.52) dan tahap motivasi ekstrinsik adalah (min=3.53) selepas menggunakan kaedah gamifikasi. Kedua-dua nilai purata skor min tahap motivasi intrinsik dan ekstrinsik pelajar berada pada tahap sederhana. Manakala hasil daripada ujian infrensi menggunakan analisis regresi berganda menunjukkan 48.6% variasi tahap motivasi intrinsik dipengaruhi oleh elemen tahap dan kutipan mata. Seterusnya bagi tahap motivasi ekstrinsik, sejumlah 62.5% variasi tahap motivasi ekstrinsik dipengaruhi oleh elemen kutipan mata, tahap, ganjaran dan avatar. Oleh itu, kajian ini dapat membantu tenaga pengajar agar mudah mencipta dan menggunakan kaedah gamifikasi yang boleh meningkatkan motivasi intrinsik dan ekstrinsik pelajar dalam sesi pengajaran dan pembelajaran mereka selaras dengan visi PAK 21

Nanostructured sonogels

Acoustic cavitation effects in sol-gel liquid processing permits to obtain nanostructured materials, with size-dependent properties. The so-called "hot spots" produce very high temperatures and pressures which act as nanoreactors. Ultrasounds force the dissolution and the reaction stars. The products (alcohol, water and silanol) help to continue the dissolution, being catalyst content, temperature bath and alkyl group length dependent. Popular choices used in the preparation of silica-based gels are tetramethoxysilane (TMOS), Si(OCH3)4 and tetraethoxysilane (TEOS), Si(OC 2H5)4. The resultant "sonogels" are denser gels with finer and homogeneous porosity than those of classic ones. They have a high surface/volume ratio and are built by small particles (1 nm radius) and a high cross-linked network with low -OH surface coverage radicals. In this way a cluster model is presented based on randomly-packed spheres in several hierarchical levels that represent the real sonoaerogel. Organic modified silicates (ORMOSIL) were obtained by supercritical drying in ethanol of the corresponding alcogel producing a hybrid organic/inorganic aerogel. The new material takes the advantages of the organic polymers as flexibility, low density, toughness and formability whereas the inorganic part contributes with surface hardness, modulus strength, transparency and high refractive index. The sonocatalytic method has proven to be adequate to prepare silica matrices for fine and uniform dispersion of CdS and PbS quantum dots (QDs), which show exciton quantum confinement. We present results of characterization of these materials, such as nitrogen physisorption, small angle X-ray/neutrons scattering, electron microscopy, uniaxial compression and nanoindentation. Finally these materials find application as biomaterials for tissue engineering and for CO2 sequestration by means the carbonation reaction.Ministerio de Ciencia y Tecnología MAT2005-158

Solid solutions of rare earth cations in mesoporous anatase beads and their performances in dye-sensitized solar cells

Solid solutions of the rare earth (RE) cations Pr3+, Nd3+, Sm3+, Gd3+, Er3+ and Yb3+ in anatase TiO2 have been synthesized as mesoporous beads in the concentration range 0.1-0.3% of metal atoms. The solid solutions were have been characterized by XRD, SEM, diffuse reflectance UV-Vis spectroscopy, BET and BJH surface analysis. All the solid solutions possess high specific surface areas, up to more than 100 m2/g. The amount of adsorbed dye in each photoanode has been determined spectrophotometrically. All the samples were tested as photoanodes in dye-sensitized solar cells (DSSCs) using N719 as dye and a nonvolatile, benzonitrile based electrolyte. All the cells were have been tested by conversion efficiency (J-V), quantum efficiency (IPCE), electrochemical impedance spectroscopy (EIS) and dark current measurements. While lighter RE cations (Pr3+, Nd3+) limit the performance of DSSCs compared to pure anatase mesoporous beads, cations from Sm3+ onwards enhance the performance of the devices. A maximum conversion efficiency of 8.7% for Er3+ at a concentration of 0.2% has been achieved. This is a remarkable efficiency value for a DSSC employing N719 dye without co-adsorbents and a nonvolatile electrolyte. For each RE cation the maximum performances are obtained for a concentration of 0.2% metal atoms. © 2015, Nature Publishing Group. All rights reserved

Metalloksiidsete süsiniknanotorukomposiitide süntees: sool-geel protsess, reoloogia ning struktuurilised ja funktsionaalsed omadused

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Antud töö käsitleb materjaliteaduses väga aktuaalset teemat – kahe (või enama) erineva materjali sidumist üheks liit(komposiit)materjaliks selliselt, et säilivad mõlema algmaterjali parimad omadused. Saadud materjalide kasutamiseks praktilistes rakendustes on oluline, et saadud komposiitmaterjale oleks võimalikult lihtne vormida väga erineva geomeetrilise kujuga struktuurideks (pinnakatted, fiibrid, monoliidid, jne.). Käesoleva töö eesmärgiks oli seatud sool-geel meetodil valmistatud oksiidsete mikro- ja nanostruktuuride moodustumise mehhanismide uurimine, sellistesse struktuuridesse süsiniknanotorude viimise metoodika väljatöötamine ning saadud struktuursete komposiitmaterjalide omaduste uurimine. Sool-geel meetodil saadavate geelstruktuuride moodustumist mõjutavad kõige enam kasutatava sooli viskoossus ja reoloogilised parameetrid. Sooli viskoossus sõltub omakorda temas sisalduvate osakeste mõõtmetest ning omadustest. Erinevaid mõõtemeetodeid kasutades leiti, et termiliselt töödeldud ning hüdrolüüsitud alkoksiidide soolid sisaldasid keskmiselt 4 nanomeetrit pikki ja 2 nanomeetrilise läbimõõduga piklike osakesi. Metallialkoksiidide ja neist valmistatud soolide reoloogilised mõõtmised näitasid, et need käituvad nagu tüüpilised anomaalviskoossusega vedelikud. Süsiniknanotorude lisamisel metallialkoksiidide soolidesse vähenes materjali viskoossus. Käesoleva doktoritöö käigus töötati välja mitu meetodit erinevate struktuuride valmistamiseks viskoossetest metallialkoksiidide soolidest. Näidati, et on võimalik valmistada fiibreid pikkuse ja diameetri suhtega kuni 10 000 ning minimaalse diameetriga 200 nanomeetrit. Demonstreeriti, et lähteaine ning ümbritseva keskkonna omadusi optimeerides ja metalli alkoksiidist tõmmatud joa katkemist ära kasutades on võimalik valmistada väga väikese tipuraadiusega oksiidseid teravike. Samuti näidati, et kasutades nn. modifitseeritud määrimismeetodit, on kõrge viskoossusega lähtematerjalidest võimalik valmistada struktuurseid kilesid ja/või siledaid kilesid paksusega kuni mõni mikromeeter. Lisaks eelnevale demonstreeriti, et materjali joaks tõmbamine orienteerib nanotorusid tõmbamise suunas. Kõige parema elektrijuhtivusega (10 S/m) olid materjalid, millesse oli lisatud 1 massi % süsiniknanotorusid. Demonstreeritud meetod süsiniknanotorudega dopeeritud komposiitmaterjalide valmistamiseks võimaldab formeerida väga erineva geomeetriaga struktuure väga erinevate metallide oksiididest.Integration of two naturally very different classes of materials to bring out their best properties, while “cancelling” their worst ones, to make a better material is one of the main challenges of modern material science. The thesis deals with the synthesis and characterization of composite materials based on metal oxides and carbon nanotubes. The goal of this dissertation was to study formation mechanisms of oxide nano- and microstructures from metal alkoxides by sol-gel methods, and to search for ways to increase their electrical properties by doping with carbon nanotubes. Viscosity and rheological properties of metal alkoxide sols are the main parameters responsible for formation of the specific shape of oxide structures via sol-gel processes. Sol precursor’s viscosity in turn is affected by the sol particle size, in this study evaluated to be approximately 4 nm in length and 2 nm in diameter. Multiple metal alkoxides polymerization-condensation processes and the corresponding materials properties were investigated and characterized. The best spinnability conditions, i.e. material ability to form liquid thread, were also determined for different metal alkoxides. Rheological tests proved that the metal alkoxide precursors behave as typical non-Newtonian fluids. Rheological studies of precursors doped with carbon nanotubes demonstrated unusual decreasing of viscosity. During this Ph. D. study, preparation of structures with different shapes was demonstrated. Metal oxide fibers with a high aspect ratio of up to 10 000 and as small as 200 nm were drawn from different concentrated metal alkoxide precursors. The pinching-off of alkoxide based jets in air was demonstrated as a reproducible route for preparing nanometer level sharp oxide needles. Also, it was also shown that the modified tape casting can be used to prepare either smooth and/or linearly structured sol–gel films from high-viscosity sol. Using pristine CNTs and metal alkoxides, it was demonstrated that pulling concentrated alkoxide/CNT viscous threads orients the nanotubes inside the matrix. At 1% CNT loadings, the final CNT reinforced CMC material electrical conductivity was measured to be in the range of 10 S/m. Demonstrated method is applicable to obtain a variety of shapes from CNT reinforced CMCs with different metal oxide matrices

Low Temperature MOCVD-Processed Alumina Coatings

We first present a Review about the preparation of alumina as thin films by the technique of MOCVD at low temperature (550°C and below). Then we present our results about thin films prepared by the low pressure MOCVD technique, using aluminium tri-isopropoxide as a source, and characterized by elemental analysis (EMPA, EDS, ERDA, RBS), FTIR, XRD and TGA. The films were grown in a horizontal, hot-wall reactor, with N2 as a carrier gas either pure or added with water vapour. The deposition temperature was varied in the range 350-550°C. The films are amorphous. Those prepared at 350°C without water added in the gas phase have a formula close to AlOOH. Those deposited above 415°C are made of pure alumina Al2O3. When water is added in the gas phase, the films are pure alumina whatever the deposition temperature

Synthesis, chemical vapour deposition and structural studies of group 13 alkoxides

This work is concerned with the synthesis of precursors to group 13 oxide thin films, and the subsequent chemical vapour deposition (CVD) of group 13 mixed metal oxide films. Investigations into the mechanisms at work during their decomposition via various techniques including gas phase electron diffraction (GED) is also discussed. A wide variety of group 13 alkoxides have been synthesised and characterised and described in this thesis. Significant findings support previous investigations showing the reaction of trialkyl group 13 complexes [MR3] with an excess of a donor functionalised alcohol does not yield a group 13 bis(alkoxide). However, compounds of the type [Ga(OR)nCl3-n] (n = 1, 2) have been synthesised using direct routes from gallium amido precursors, which are also described herein. In addition a wide variety of novel group 13 precursors incorporating a mixture of ligands leading to enhanced properties, desirable for CVD are presented. The gas phase structures of the dimethylalkoxygallanes, [Me2GaOCH2CH2NMe2]2 and [Me2GaOCH2CH2OMe]2 have been obtained via gas-phase electron diffraction from studying the vapour produced upon heating. Ab initio molecular orbital calculations are presented for these compounds, as well as the gas phase structure of [Me2GaOtBu]2. Only the monomeric forms [Me2GaOCH2CH2NMe2] and [Me2GaOCH2CH2OMe] are observed in the gas phase with donor functionalised ligands, whereas the dimer [Me2GaOtBu]2 remains intact in the gas phase. Gallium oxide films were grown via AACVD using a variety of group 13 precursors. The films deposited were not oxygen deficient and little carbon contamination was observed, which is attributed to being a direct result of precursor design. Thin films of indium gallium oxide, and zinc gallium oxide were also produced from the in situ reactions of InMe3, GaMe3 and HOCH2CH2OMe (for GaxIn2-xO3) and ZnEt2, GaMe3 and HOCH2CH2OMe (for GaxZnyO) via AACVD on silica substrates