The main focus of this thesis is ab initio modeling of core level spectra with a high-level quantum chemical description both of the chemical interactions and of local atomic multiplet effects. In particular, the combination of calculations and synchrotron-based core-level spectroscopy aims at understanding the local structure of the electronic valence in transition metal complexes, and the details of the solvation mechanisms of electrolyte solutions, systems relevant for the dye-sensitized solar cell. Configurational sampling in solution is included through molecular dynamics simulations. Transition metal complexes are studied with x-ray absorption (XA) and resonant inelastic scattering (RIXS) spectroscopy, characterizing excited states with atomic site specificity. The theoretical multiconfigurational method, applying an active-space partitioning of the molecular orbitals (RASSCF), is used to assign the transitions observed in spectra of hydrated Ni2+ explicitly, including charge transfer and multiplet effects. Furthermore, the solvent-induced binding energy properties of the I- and I3- anions in aqueous, ethanol, and acetonitrile solutions are analyzed using photoelectron spectroscopy (XPS). The study shows that specific ion–solvent interactions are important for the core-level binding energy shifts in solution. The special case with I3- dissolved in water, where hydrogen bonding causes breaking of the molecular symmetry, is treated and proves that the geometry changes influence the photoelectron spectrum of aqueous I3- directly.

This talk was presented in the 14th International Conference on Atomic Layer Deposition (ALD 2014) in Kyoto, Japan on 18th June 2014. Abstract Atomic Layer Deposition (ALD) is emerging as a ubiquitous method for the deposition of conformal and homogeneous ultra-thin films on complex topographies and large substrates in microelectronics. Electrochemical deposition (ECD) is the first choice for the deposition of copper (Cu) into the trenches and vias of the interconnect system for ULSI circuits. The ECD of Cu necessitates an electrically conductive seed layer for filling the interconnect structures. ALD is now considered as a solution for conformal deposition of Cu seed layers on very high aspect ratio (AR) structures also for technology nodes below 20 nm, since physical vapor deposition is not applicable for structures with high AR. Cu seed layer deposition by the reduction of Cu2O, which has been deposited from the Cu(I) β-diketonate [(nBu3P)2Cu(acac)] (1) used as Cu precursor, has been successfully carried out on different substrates like Ta, TaN, SiO2, and Ru [1, 2]. It was found that the subsequent gas-phase reduction of the Cu2O films can be aided by introducing catalytic amounts of a Ru precursor into the Cu precursor, so that metallic copper films could potentially obtained also on non-catalytic substrates [3, 4]. In this work, in situ X-ray photoelectron spectroscopy (XPS) investigation of the surface chemistry during Cu2O ALD from the mixture of 99 mol % of 1 and 1 mol % of [Ru(η5 C5H4SiMe3)(η5-C7H11)] (2) as ruthenium precursor, and the reduction of Cu2O to metallic Cu by formic acid carried out on SiO2 substrate are demonstrated. Oxidation states of the Cu in the film are identified by comparing the Cu Auger parameter (α) [5] with literature data. α calculated after ALD equals 362.2 eV and after reduction equals 363.8 eV, comparable to the Cu2O and metallic Cu in thin-films [6] respectively. In addition, <10 % of Cu(I), Cu(II), and Cu(OH)2 species are identified from the Cu 2p3/2 and Cu L3VV Auger spectrum after reduction. Consequently, the ALD Cu2O is successfully reduced to metallic copper by in-situ thermal reduction using formic acid. [1] T. Waechtler et al., J. Electrochem. Soc., 156 (6), H453 (2009). [2] T. Waechtler et al., Microelectron. Eng., 88, 684 (2011). [3] S. Mueller et al., Conference Proceedings SCD 2011, Semiconductor Conference Dresden, pp. 1-4. [4] T. Waechtler et al., US Patent Application Publication, US 2013/0062768. [5] C. D. Wagner, Faraday Discuss. Chem. Soc., 60, 291 (1975). [6] J. P. Espinós et al., J. Phys. Chem. B, 106, 6921 (2002).

Sodium borohydride is stable in alkaline solution, however, it hydrolyses and generates hydrogen gas in the presence of suitable catalyst. By this way hydrogen can be generated safely for the fuel cells. All of the catalyst having been used in the hydrolysis of sodium borohydride, with one exception, are heterogeneous. The limited surface area of the heterogeneous and therefore, have limited activity because of the surface area. Thus, the use of metal nanoclusters as catalyst with large surface area is expected to provide a potential route to increase the catalytic activity. In this dissertation we report for the first time the use of ruthenium(0) nanoparticles as catalyst in the hydrolysis of sodium borohydride. The water dispersible ruthenium(0) nanoparticles were prepared by the reduction of RuCl3.xH2O with sodium borohydride and were stabilized by three different ligands dodecanethiol, ethylenediamine and acetate. Among these three colloidal materials the acetate stabilized ruthenium(0) nanoparticles were found to have the highest catalytic activity in catalyzing the hydrolysis of sodium borohydride. The acetate stabilized ruthenium(0) nanoparticles were characterized by tranmission electron microscopy (TEM), X-ray photoelectron spectroscopy and FT-IR spectroscopy. The particle size of the acetate stabilized ruthenium(0) nanoparticles was determined to be 2.62&plusmn / 1.18 nm from the TEM analysis. The kinetic of the ruthenium(0) nanoparticles catalyzed hydrolysis of sodium borohydride was studied depending on the catalyst concentration, substrate concentration and temperature. The activation parameters of this reaction were also determined from the evaluation of the kinetic data. This catalyst provides the lowest activation energy ever found for the hydrolysis of sodium borohydride.

ABSTRACT CARBON SUPPORTED AND SURFACTANT STABILIZED METAL NANOPARTICLE CATALYSTS FOR DIRECT METHANOL FUEL CELLS &Ccedil / elik, &Ccedil / aglar M.S., Department of Chemistry Supervisor: Assoc. Prof. Dr. G&uuml / ls&uuml / n G&ouml / kaga&ccedil / August 2005, 72 pages Carbon supported surfactant, such as 1-decanethiol and octadecanethiol, stabilized platinum and platinum/ruthenium species have been prepared recently. In this thesis, for the first time, 1-hexanethiol has been used as an organic stabilizer for the preparation of carbon supported platinum and platinum/ruthenium nanoparticle catalysts. These new catalysts were employed for methanol oxidation reaction, which were used for direct methanol fuel cells. Cyclic voltammetry, X-ray photoelectron spectroscopy and transmission electron microscopy have been used in order to determine the nature of the catalysts. The effect of temperature and time on catalytic activity of catalysts were examined and the maximum catalytic activity was observed for carbon supported 1-hexanethiol stabilized platinum nanoparticle catalyst (with 1:1 thiol/platinum molar ratio) which was heated up at 200oC for 5 hours. The particle size of platinum nanoparticles was determined to be ~ 10 nm in diameter. The size and distribution of metal nanoparticles on carbon support, the Pt/Ru surface composition, the relative amount of Pt(0), Pt(II) and Pt(IV) and the removal of organic surfactant molecules around the metal nanoparticles were found to be important in determining the catalytic activity of electrodes towards methanol oxidation reaction. A significant decrease in catalytic activity was observed for carbon supported 1-hexanethiol stabilized Pt75Ru25 and Pt97Ru3 (with 1:1 thiol/PtRu molar ratio) with respect to carbon supported 1-hexanethiol stabilized Pt (with 1:1 thiol/platinum molar ratio). This result might be due to unremoved stabilizer shell around platinum/ruthenium nanoparticles and increase in amount of Pt(II) and Pt(IV) compared to Pt(0) where the methanol oxidation occured.

The development of new storage materials will facilitate the use of hydrogen as a major energy carrier in near future. In hydrogen economy, chemical hydrides such as NaBH4, KBH4, LiH, NaH have been tested as hydrogen storage materials for supplying hydrogen at ambient temperature. Among these chemical hydrides, sodium borohydride seems to be an ideal hydrogen storage material because it is stable under ordinary conditions and liberates hydrogen gas in a safe and controllable way in aqueous solutions. However, self hydrolysis of sodium borohydride is so slow that it requires a suitable catalyst. All of the prior catalysts tested for the hydrolysis of sodium borohydride are heterogeneous and, therefore, have limited activity because of the small surface area. Here, we report for the first time the employment of water dispersible metal(0) nanoclusters having a large portion of atoms on the surface as a catalyst for the hydrolysis of sodium borohydride. In-situ formation of nickel(0) nanoclusters and catalytic hydrolysis of sodium borohydride were performed in the same medium. Nickel(0) nanoclusters are prepared from the reduction of nickel(II) acetylacetonate by sodium borohydride in aqueous solution and stabilized with hydrogenphosphate anions. The nickel(0) nanoclusters were characterized by using XPS, Powder XRD, FT-IR, UV-Vis and NMR spectroscopic methods. The kinetics of the nickel(0) nanoclusters catalyzed hydrolysis of sodium borohydride was studied depending on the catalyst concentration, substrate concentration, stabilizing agent concentration and temperature. Tha kinetic study shows that the nickel(0) nanocluster-catalyzed hydrolysis of sodium borohydride is first order with respect to catalyst concentration and zero order with respect to substrate concentration The activation parameters of this reaction were also determined from the evaluation of the kinetic data. The hydrogenphosphate-stabilized nickel(0) nanoclusters provide a lower activation energy (Ea= 55 kJ/mol) than bulk nickel (Ea=73 kJ/mol) for the hydrolysis of sodium borohydride.

Designing novel nanostructures which exploit the self-assembly capabilities of biomolecules yields a promising approach to control matter at the nanoscale. Here, the homochiral molecular self-assemblies of the methionine and tyrosine amino acids on the monocrystalline Ag(111) and Cu(111) surfaces are characterized by means of scanning tunneling microscopy (STM) and spectroscopy (STS), helium atom scattering (HAS), x-ray photoelectron spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) in ultrahigh vacuum (UHV). On Ag(111), methionine self-assembles into supramolecular chains following the <110> substrate axis, forming regular nanogratings with tunable periodicity. Within the nanowires, a zwitterionic dimerization scheme is revealed. STS shows that the biomolecular nanostructures act as tunable one-dimensional quantum resonators for the surface state electrons. Zero-dimensional electronic confinement is achieved by positioning single iron atoms in the molecular trenches. This shows a novel approach to control the dimensionality of surface state electrons. The nanogratings were exploited to steer the spontaneous one-dimensional ordering of cobalt and iron atoms. For T > 15 K, the metal species self-align into homogeneously distributed chains in between the biomolecular trenches with ~25 Å interatomic distace. For Co, the dynamics of the self-alignment was monitored, revealing a reduced mobility in comparison with isolated Co atoms on bare Ag(111). On Cu(111), the self-assembly of methionine is influenced by the substrate reactivity and its temperature during molecular deposition. For T < 273 K, the biomolecules assemble in anisotropic extended clusters oriented with a -10° rotation off the <110> substrate orientations, whereas above 283 K a regularly ordered 1D phase arises with a +10° rotation off these high-symmetry axis. XPS reveals a structural transformation triggered by a thermally activated deprotonation of the zwitterionic ammonium group. On Ag(111), tyrosine self-assembles above a critical temperature into linear structures primarily following the substrate crystalline symmetry. A zwitterionic non-covalent molecular dimerization is demonstrated, NEXAFS data providing evidence of a non-flat adsorption of the phenyl ring. This recalls the geometrical pattern of methionine on Ag(111) and supports a universal self-assembling scheme for amino acids on close-packed noble metal surfaces, the different mesoscopic ordering being determined by the side chain reactivity.

The oxidative dissolution of chalcopyrite in ferric media often produces incomplete copper recoveries. The incomplete recoveries have been attributed to inhibition caused by the formation of a metal deficient sulphide and the deposition of elemental sulphur and jarosite. Although these phases have been qualitatively identified on the surface of chalcopyrite, none have been quantitatively identified. The aim of the project was to quantitatively analyse the surface before and after oxidative dissolution, with X-ray photoelectron spectroscopy (XPS), and to use the phases identified as the basis for mechanisms of dissolution and inhibition. / XPS analysis was performed on chalcopyrite massive fractured under anaerobic atmosphere and chalcopyrite massive and concentrate oxidised in 0.1 M ferric sulphate (pH 1.9) and 0.2 M ferric chloride (pH 1.6) at 50, 65 and 80ºC. Quantitative XPS analysis of the chalcopyrite surfaces required the development of programs that accounted for the observed XPS spectra. The output of these programs was used to construct profiles of the chalcopyrite surfaces and the deposited phases. These surface profiles were correlated with copper recoveries determined for chalcopyrite concentrate dissolution under the same conditions. / The surface of chalcopyrite before oxidative dissolution reconstructs to form a `pyritic' disulphide phase. This phase is oxidised in ferric media to form thiosulphate via the incorporation of oxygen atoms from the hydration sphere. The thiosulphate reacts in the oxidising conditions of low pH to form elemental sulphur, sulphite and sulphate. The sulphate complexes with ferric to produce hydronium jarosite. This reaction occurs at the surface during the initial stages of dissolution and in the bulk solution during the latter stages. This precipitation of hydronium jarosite during the latter stages of dissolution corresponds to inhibition of the dissolution reaction. It is therefore concluded hydronium jarosite is responsible for inhibiting the oxidative dissolution of chalcopyrite in ferric media. / The identification of hydronium jarosite as the inhibiting phase is consistent with the industrial practice of removing `excess' iron from the ferric solution before oxidative dissolution. However, additional iron and sulphate are generated at the chalcopyrite surface during oxidative dissolution. These high iron and sulphate concentrations combine with the low pH and high temperatures favoured for the oxidative dissolution of chalcopyrite to produce ideal conditions for jarosite precipitation. Therefore, pH must be lowered further to prevent jarosite precipitation and enhance copper recoveries from chalcopyrite in ferric media.

Στην παρούσα εργασία μελετήθηκε η ανάπτυξη και η επακόλουθη συμπεριφορά κατά τη θέρμανση υμενίων μεταλλικού νικελίου και χρωμίου σε μονοκρυσταλλικό οξείδιο του νικελίου, NiO(100). Οι αποθέσεις έγιναν κοντά στη θερμοκρασία δωματίου σε περιβάλλον υπερυψηλού κενού 2 x 10-10 mbar χρησιμοποιώντας πηγές θερμικής εξάχνωσης, ενώ η χημική κατάσταση των επιφανειών προσδιορίστηκε με την χρήση φασματοσκοπίας φωτοηλεκτρονίων ακτίνων-Χ (XPS) και στην περίπτωση της απόθεσης Cr επιπλέον με φασματοσκοπία σκέδασης ιόντων (ISS). Οι φασματοσκοπικές μετρήσεις έγιναν με το υπόστρωμα σε θερμοκρασίες από 550 Κ έως 680 Κ, ώστε να αυξηθεί η αγωγιμότητα και να αποφευχθεί η διαφορική φόρτιση της επιφάνειας του κρυστάλλου. Η θέρμανση μέχρι 2 μονοστρώματα (ML) νικελίου αποτεθειμένου σε NiO(100) είχε πρόσφατα βρεθεί ότι οδηγεί σε σταδιακή εξαφάνιση του Ni0, φαινόμενο που αποδόθηκε σε οξείδωσή του με οξυγόνα από το υπόστρωμα. Καθώς η ποσότητα αυτή είναι σημαντικά μεγαλύτερη από τις τυχόν διαθέσιμες ποσότητες επιφανειακού οξυγόνου (π.χ. προσροφημένα υδροξύλια) και δεν υπάρχουν ενδείξεις για την παρουσία μη στοιχειομετρικού οξυγόνου στο εσωτερικό του μονοκρυστάλλου NiO(100), επιδιώχθηκε η διερεύνηση της προέλευσης των οξυγόνων που συμμετείχαν στην οξείδωση. Προς τούτο έγιναν διαδοχικές αποθέσεις Ni0 1,6 ML, 3,8 ML και 7,5 ML, ενώ μετά από κάθε απόθεση και πριν από την επόμενη το δείγμα θερμάνθηκε μέχρι τους 940 Κ, όπου στις δύο πρώτες περιπτώσεις επήλθε πλήρης οξείδωση του Ni0 ενώ στην τρίτη η οξείδωση δεν ολοκληρώθηκε στα χρονικά περιθώρια του πειράματος. Μια κατ’ αρχήν μοντελοποίηση της κινητικής της οξείδωσης υποδεικνύει προέλευση του διαθέσιμου οξυγόνου από πηγή σταθερής συγκέντρωσης στο εσωτερικό του κρυστάλλου. Η μοντελοποίηση των εντάσεων των φωτοκορυφών XPS με βάση σωματιδιακά υμένια νικελίου σταθερού μέσου πάχους που καλύπτουν κλάσμα της επιφάνειας, οδηγεί στο συμπέρασμα ότι η θέρμανση αρχικά οδηγεί σε γρήγορη συσσωμάτωση του νικελίου, ενώ στην συνέχεια τα μεγάλα σωματίδια Ni0 που σχηματίζονται καλύπτονται αρχικά από NiO και στην συνέχεια η οξείδωση προχωρά προς τον μεταλλικό τους πυρήνα. Καθώς από το πείραμα δεν προκύπτει άλλη πληροφορία για την προέλευση των οξυγόνων, διεξάχθηκαν προσομοιώσεις Μοριακής Δυναμικής προκειμένου να διερευνηθεί η δυνατότητα του τέλειου μονοκρυστάλλου να παρέχει πλεγματικά οξυγόνα στην επιφάνεια. Οι προσομοιώσεις έγιναν στο ισόθερμο κανονικό στατιστικό σύνολο χρησιμοποιώντας τη μέθοδο του Nose πάνω σε μονοκρύσταλλο από 1728 ιόντα με εφαρμογή περιοδικών οριακών συνθηκών. Η ολοκλήρωση των εξισώσεων κίνησης έγινε με τον αλγόριθμο του Verlet, με χρονικό βήμα 2x10-15 s και χρησιμοποιήθηκε δυναμικό του τύπου σκληρών ιόντων, ενώ οι συνεισφορές Coulomb υπολογίστηκαν με την μέθοδο του Ewald. Πραγματοποιήθηκαν προσομοιώσεις για αποθέσεις με 8 ιόντα νικελίου (0,06ML), 16 ιόντα νικελίου (0,11ML) και 32 ιόντα νικελίου (0,22ML) σε θερμοκρασία 0,37Tm, με καταγραφή της συνάρτησης τοπικής πυκνότητας κατανομής των ιόντων οξυγόνου ανά 2000 βήματα. Οι προσομοιώσεις δείχνουν ότι ο τέλειος μονοκρύσταλλος μπορεί να σχηματίσει μεγάλο αριθμό οπών ιόντων οξυγόνου της τάξης του 10%, γεγονός που επιτρέπει την ερμηνεία του πειράματος, όπου περίπου 8ML Ni0 οξειδώθηκαν με οξυγόνα από το υπόστρωμα, χωρίς την ανάγκη υπόθεσης της παρουσίας άλλης πηγής μη στοιχειομετρικού οξυγόνου στο εσωτερικό του μονοκρυστάλλου. Για την μελέτη της αλληλεπίδρασης του Cr με το NiO(100), η οποία δεν είχε μελετηθεί συστηματικά μέχρι τώρα σε κλίμακα νανομετρικών υμενίων, έγιναν 4 πειράματα απόθεσης, που κατέληξαν σε 1,10 nm , 0,12 nm, 0,05 nm και 0,30 nm Cr0. Η απόθεση μεταλλικού χρωμίου σε θερμοκρασία δωματίου οδήγησε σε πλήρη κάλυψη της επιφάνειας του NiO(100), ενώ θέρμανση στους 550 Κ προκάλεσε συσσωμάτωση του χρωμίου και οξείδωσή του με παράλληλη αναγωγή του νικελίου του υποστρώματος. Περαιτέρω θερμάνσεις σε υψηλότερες θερμοκρασίες προκάλεσαν την εκ νέου οξείδωση του νικελίου. Η μοντελοποίηση των εντάσεων των φωτοκορυφών XPS με βάση σωματιδιακά υμένια χρωμίου και νικελίου δείχνει ότι το χρώμιο οξειδώνεται από κάτω προς τα πάνω και τελικά καλύπτει το μεταλλικό νικέλιο, χωρίς να αποκλείεται η ενδιάμεση ανάμειξη των δύο μετάλλων. Η μοντελοποίηση της οξείδωσης του ανηγμένου νικελίου σε μεγαλύτερη θερμοκρασία, δείχνει ότι ακολουθείται γενικά η ίδια πορεία , όπως και για απόθεση καθαρού Νi, με το οξείδιο του χρωμίου αρχικά να καλύπτει το σχηματιζόμενο NiO. Κατά την παρατεταμένη θέρμανση της διεπιφάνειας στους 940 Κ, η απόκλιση των πειραματικών σημείων από τις προβλέψεις του μοντέλου υποδεικνύει διεπιφανειακή ανάμειξη των υμενίων NiO και Cr2O3 και πιθανό σχηματισμό σπινελίου NiCr2O4, όπως αναφέρεται και στην βιβλιογραφία. Τα αποτελέσματα της φασματοσκοπίας ISS επιβεβαιώνουν σε ποιοτικό επίπεδο την ερμηνεία που αποδίδουν τα μοντέλα στις μετρήσεις XPS. / Deposition and annealing of Ni and Cr on a NiO(100) single crystal was studied using X-ray photoelectron spectroscopy (XPS) and Molecular Dynamics Simulations (MD) for the case of Ni and using XPS and Ion Scattering Spectroscopy (ISS) for the case of Cr. Depositions were carried out near room temperature in ultra high vacuum with base pressure of 2 x 10-10 mbar using Ni and Cr thermal evaporation sources . Both XP and IS spectra were taken while the sample was kept at an elevated temperature between 550K and 680K in order to avoid differential substrate charging. Annealing of up to 2 monolayers (ML) Ni deposited on NiO(100) has been reported to result in the gradual elimination of metallic Ni, attributed to oxidation via the substrate. Since the necessary quantity of oxygen is far greater than any possibly available surface oxygen (e.g. adsorbed hydroxyl species) and there is no evidence of non stoichiometric oxygen within the NiO(100) single crystal, it was decided to investigate the origin of the oxygen species involved. To that purpose, three successive depositions of Ni0 on NiO(100) were conducted, 1.6 ML 3.8 ML and 7.5 ML. After each deposition and before the next one, the sample was annealed up to 940 K resulting in the complete oxidation of the deposited Nio , with the exception of the final deposition of 7.5 ML whereby the oxidation was not completed within the time frame of the experiment. Simple kinetic modelling of the oxidation is consistent with oxygen originating from a constant concentration source within the substrate. Modelling of the XPS photoelectron intensities based on particulate films covering part of the substrate surface indicates that annealing leads initially to sintering and then to oxidation of the Ni0 particles, whereby they are covered by NiO as oxidation proceeds toward the metallic core. Since the experiment cannot provide any more information with respect to the origin of the oxygen, MD simulations where performed in order to investigate the ability of the perfect crystal to provide lattice oxygen to its surface. The Molecular Dynamics simulations were carried out in the constant temperature canonical ensemble using the Nose scheme, with a slab geometry consisting of 1728 ions and applying periodic boundary conditions. The equations of motion were integrated by means of Verlet’s algorithm and with a time step of 2 x10-15 s, whereas a rigid ion potential was adopted for the atomic interactions and the Coulombic contributions were evaluated with the use of the Ewald summation. Results are presented for depositions of 8 Ni (0.06ML), 16 Ni (0.11ML) and 32 Ni (0.22ML) ad-cations. The evolution of these systems was followed for up to 300000 time steps at a temperature corresponding to 0.37Tm , while the oxygen ions local density distribution function was recorded every 2000 time steps during each simulation run. The simulations show that the perfect crystal can successively form up to 10% of oxygen vacancies in each layer, which can explain the experimental results whereby 8ML of Ni0 where oxidized, without affecting the equivalent concentration of the available oxygen in the substrate and without having to assume any non stoichiometric oxygen inside the NiO(100) single crystal. In order to study the interaction of Cr with NiO(100), which has not been studied systematically so far in the nanometric film thickness range, four quantities of Cr0 , 10 nm, 0,12nm, 0,05 nm and 0,30 nm , were deposited. Deposition at room temperature resulted in complete coverage of the NiO(100) surface, while annealing at 550 K caused sintering and oxidation of Cr as well as reduction of NiO to Ni0 while farther annealing at higher temperatures caused the re-oxidation of the reduced Ni. Modelling of the XPS photoelectron intensities based on particulate films, indicated that Cr0 particles are oxidized from the bottom and finally cover the Ni0 film produced by reduction of the NiO(100) substrate, however the possibility that metallic Cr mixes with metallic Ni forming surface alloy during the process cannot be excluded. The XPS-based modelling of the oxidation process of the reduced Ni at higher temperatures shows that these particles are initially covered by NiO while the oxidation proceeds toward the metallic core, just as in the case of pure deposited Ni. Upon extensive annealing of the interface at 940 K, the deviation of the experimental results from the predictions of the model suggests that mixing of Cr2O3 and NiO occurs at the interface and possibly a NiCr2O4 spinel is formed, as reported in the literature. The ISS results qualitatively support the interpretation of the XPS results provided by the models.

Un-doped, Er3+ doped (TiO2:Er3+) as well as Er3+/Yb3+ co-doped (TiO2:Er3+/Yb3+) nanocrystals with different concentrations of RE3+ (Er3+, Yb3+) were successfully synthesized using the sol-gel method. The powder X-ray diffraction (XRD) spectra revealed that all undoped and doped samples remained in anatase after annealing at 400°C. The presence of RE3+ ions in the TiO2 host lattice was confirmed by conducting elemental mapping on the samples using Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDX), which was in agreement with X-ray photoelectron spectroscopy (XPS) results. Transmission electron microscope (TEM) images approximated particle sizes of the samples to be between 1.5 – 3.5 nm in diameter and this compares well with XRD analyses. Phonon quantification in TiO2 was achieved using Fourier transform infrared (FT-IR) spectroscopy. Optical bandgap from Ultraviolet/Visible/Near-Infrared was extrapolated from Kubelka-Munk relation and the narrowing of the bandgap for the doped samples as compared to the undoped sample was observed. The photoluminescence PL study of the samples revealed two emission peaks attributed to direct band-gap and defect-related emissions. A laser beam with 980 nm wavelength was used to irradiate the samples, and the displayed emission lines of the TiO2: Er3+ in the visible region of the electromagnetic spectrum confirmed up-conversion luminescence. Enhancement of up-conversion luminescence intensity due to Yb3+ co-doping was observed, indicating an efficient energy transfer process from the sensitizer Yb3+ to the activator Er3+. / Physics / M. Sc. (Physics)

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