Structural characterisation of thin films advanced materials with microscopy techniques: Pd on 6H-SiC(0001), BN /Si(100) and CeO2/Si(100)

This thesis deals with structural characterisation of three different systems of thin films with great technological impact: a) Pd/6H-SiC(0001) b) BN/Si(100) and c) CeO2/Si(100). Various complementary microscopy techniques were employed such as Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM) and Atomic Force Microscopy (AFM) to identify the structural profile via detailed study, analysis and modeling. The scientific results of this thesis contributed to parameterization and optimization of deposition condition leading to high degree of reproducibility of thin film fabrication. The structural study of Pd/6H-SiC(0001) revealed that deposition at room temperature leads to epitaxial growth. During deposition, structural defects and twinning are observed with two different twin interfaces {111} Σ=3 and {11} Σ=3 existing between the two crystals. This study also included modelling and quantitative simulation analysis found in good agreement with experimental results. The study of the second system BN/Si(100) revealed the growth of the cubic phase (c-BN) during deposition via RF magnetron sputtering. The existence of c-BN triangular shape crystals self-organizing (by pointing always towards to the substrate) was attributed to the influence of the deposition parameters. It is remarkable, that the Si substrate and the observed c-BN nanostructures share a common crystallographic axis (texture formation). The third system studied was the cubic phase of polycrystalline CeO2 during its deposition on Si(100) via ΕΒΕ. Specially designed software package (Process Diffraction) was used alternatively to identify the structure, except the standard method. No evidence of hexagonal phase crystals Ce2O3 was found. Additionally, the increase of temperature during deposition seems to increase the size of the crystals. The analysis of diffraction patterns revealed various crystallographic orientations and correlations between thin film and substrate.Το αντικείμενο της εργασίας αυτής, είναι ο δομικός χαρακτηρισμός λεπτών υμενίων τριών συστημάτων που παρουσιάζουν σημαντικό τεχνολογικές ενδιαφέρον: α) Pd/6H-SiC(0001) β) BN/Si(100) και γ) CeO2/Si(100). Οι τεχνικές που χρησιμοποιήθηκαν είναι η Συμβατική Ηλεκτρονική Μικροσκοπία (TEM), η Ηλεκτρονική Μικροσκοπία Υψηλής Διακριτικής Ικανότητας (HRTEM) και η Μικροσκοπία Ατομικών Δυνάμεων (AFM). Ως κύριος στόχος της παρούσας εργασίας ορίστηκε, η λεπτομερής παρατήρηση, μελέτη, πιστοποίηση και μοντελοποίηση των δομικών χαρακτηριστικών που εμφανίζουν τα τρία αυτά συστήματα. Τα αποτελέσματα της εργασίας αυτής συνέβαλλαν σημαντικά στην παραμετροποίηση και βελτιστοποίηση των συνθηκών ανάπτυξης αυξάνοντας σημαντικά το βαθμό επαναληψιμότητας στην παραγωγή λεπτών υμενίων με ιδιαίτερο τεχνολογικό αντίκρισμα. Το πρώτο σύστημα που εξετάζεται είναι το σύστημα Pd/6H-SiC(0001). Ο δομικός χαρακτηρισμός έδειξε ότι η εναπόθεση του υμενίου σε θερμοκρασία δωματίου οδηγεί σε πολύ καλή επιταξιακή ανάπτυξη. Κατά την ανάπτυξη διαπιστώνονται σφάλματα δομής, με την παρουσία πολλών διδυμιών. Δύο κύριοι τύποι διεπιφανειών {111} Σ=3 και {11} Σ=3 εμφανίζονται μεταξύ των διδύμων κρυστάλλων. Οι τύποι αυτοί αναλύθηκαν και προτάθηκαν δομικά μοντέλα, τα οποία οδήγησαν στην υπολογιστική προσομοίωση των διεπιφανειών αυτών. Η σύγκριση των προσομοιωμένων εικόνων με τις αντίστοιχες πειραματικές έδειξε πολύ καλή συμφωνία γεγονός που κατέδειξε την ορθότητα και την αξιοπιστία του εφαρμοζόμενου μοντέλου. Στο δεύτερο σύστημα BN/Si(100) παρατηρήθηκε ανάπτυξη κυβικής φάσης ΒΝ (c-BN) κατά την εναπόθεση του υμενίου ΒΝ με την τεχνική RF magnetron sputtering. Ο καθοριστικός ρόλος των συνθηκών ανάπτυξης στη διαμόρφωση δομικών χαρακτηριστικών φαίνεται από την εμφάνιση νανοδομών, (τριγωνικού σχηματισμού c-ΒΝ), οι οποίες τείνουν να αναπτύσσονται σε διεύθυνση πάντοτε κάθετη προς το υπόστρωμα, δηλ. παρουσιάζουν μια τάση να αυτο-οργανώνονται. Είναι σημαντικό το γεγονός ότι, οι παρατηρούμενοι προσανατολισμοί των νανοκρυστάλλων c-BN έχουν μεταξύ τους, ένα κοινό κρυσταλλογραφικό άξονα του τύπου , ο οποίος είναι επίσης κοινός και με το υπόστρωμα του Si (texture formation). Στην περίπτωση του τρίτου συστήματος παρατηρήθηκε ανάπτυξη πολυκρυσταλλικού CeO2 κυβικής φάσης κατά την εναπόθεση οξειδίου του δημητρίου (CeO2) σε υπόστρωμα Si(100) με την τεχνική ΕΒΕ. Η πιστοποίηση έγινε εκτός του κλασσικού τρόπου υπολογισμού και με την χρησιμοποίηση ειδικού λογισμικού (Process Diffraction). Δεν υπήρξε καμιά ένδειξη για ανάπτυξη έστω και μικρών νανοκρυσταλλιτών εξαγωνικής φάσης Ce2O3. Είναι γεγονός ότι εξαιτίας της αύξησης της κινητικότητας των ατόμων, παρατηρείται αύξηση του μεγέθους των νανοκρυσταλλιτών, σε συνάρτηση με την θερμοκρασία. Από την ανάλυση των εικόνων περίθλασης διαπιστώθηκαν κρυσταλλογραφικοί προσανατολισμοί και συσχετίσεις μεταξύ υποστρώματος και υμενίου

Effect of Ag doping on the microstructure and photoluminescence of ZnO nanostructures

ZnO nanostructures were obtained by metal-organic chemical vapor deposition via Ag catalyst-assisted growth in a temperature range of 200-500 degrees C. Growth at temperatures above 500 degrees C resulted in vertically aligned ZnO nanorods (NLs). Ag incorporation into ZnO up to 0.4 at.% promoted creation of basal plane stacking fault (BSF) defects and corrugation of the side facets of the NLs. The presence of BSFs give rise to an additional photoluminescence peak with a wavelength of similar to 386 nm, which is slightly red-shifted compared to the commonly observed NBE emission at similar to 375 nm. The observed emission was found to be specifically observed from the side facets of the NLs. It is suggested that this emission is due to a high concentration of BSFs in the ZnO as a result of an incorporation of Ag as acceptor dopant. [GRAPHICS] SEM image of an Ag-doped ZnO nanorod with corrugated side facets. The observed corrugation is accompanied by a high concentration of basal plane stacking faults.Funding Agencies|Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM)</p

Effect of Ag doping on the microstructure and photoluminescence of ZnO nanostructures

ZnO nanostructures were obtained by metal-organic chemical vapor deposition via Ag catalyst-assisted growth in a temperature range of 200-500 degrees C. Growth at temperatures above 500 degrees C resulted in vertically aligned ZnO nanorods (NLs). Ag incorporation into ZnO up to 0.4 at.% promoted creation of basal plane stacking fault (BSF) defects and corrugation of the side facets of the NLs. The presence of BSFs give rise to an additional photoluminescence peak with a wavelength of similar to 386 nm, which is slightly red-shifted compared to the commonly observed NBE emission at similar to 375 nm. The observed emission was found to be specifically observed from the side facets of the NLs. It is suggested that this emission is due to a high concentration of BSFs in the ZnO as a result of an incorporation of Ag as acceptor dopant. [GRAPHICS] SEM image of an Ag-doped ZnO nanorod with corrugated side facets. The observed corrugation is accompanied by a high concentration of basal plane stacking faults.Funding Agencies|Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM)</p

Influence of flash annealing on structure and electrical properties of multilayered TiO2/TiO/Ti thin films

POSTER - European Materials Research Symposium - EMRS2013, Strasbourg, 27 - 31 May 2013Influence of flash annealing on structure and electrical properties of multilayered TiO2/TiO/Ti thin film

The interdependence of structural and electrical properties in TiO2/TiO/Ti periodic multilayers

International audienceMultilayered structures with 14-50 nm periods composed of titanium and two different titanium oxides, TiO and TiO2, were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. The structure and composition of these periodic TiO2/TiO/Ti stacks were investigated by X-ray diffraction and transmission electronic microscopy techniques. Two crystalline phases, hexagonal close packed Ti and face centred cubic TiO, were identified in the metallic-rich sub-layers, whereas the oxygen-rich ones comprised a mixture of amorphous TiO2 and rutile phase. DC electrical resistivity rho measured for temperatures ranging from 300 to 500 K exhibited a metallic-like behaviour (rho(473K) = 1.05 x 10(-5) to 1.45 x 10(-6) Omega m) with a temperature coefficient of resistance ranging from 1.20 x 10(-3) K-1 for the highest period (Lambda = 50.0 nm) down to negative values close to -4.97 x 10(-4) K-1 for the smallest one (Lambda = 14.0 nm). A relationship between the dimensions of periodic layers and their collective electrical resistivity is proposed where the resistivity does not solely depend on the total thickness of the film, but also depends on the chemical composition and thickness of each sub-layer. Charge carrier mobility and concentration measured by the Hall effect were both influenced by the dimension of TiO2/TiO/Ti periods and the density of ionized scattering centres connected to the titanium concentration in the metallic sub-layers. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Oral Bacteria and Intestinal Dysbiosis in Colorectal Cancer

The human organism coexists with its microbiota in a symbiotic relationship. These polymicrobial communities are involved in many crucial functions, such as immunity, protection against pathogens, and metabolism of dietary compounds, thus maintaining homeostasis. The oral cavity and the colon, although distant anatomic regions, are both highly colonized by distinct microbiotas. However, studies indicate that oral bacteria are able to disseminate into the colon. This is mostly evident in conditions such as periodontitis, where specific bacteria, namely Fusobacterium nucrelatum and Porphyromonas gingivalis project a pathogenic profile. In the colon these bacteria can alter the composition of the residual microbiota, in the context of complex biofilms, resulting in intestinal dysbiosis. This orally-driven disruption promotes aberrant immune and inflammatory responses, eventually leading to colorectal cancer (CRC) tumorigenesis. Understanding the exact mechanisms of these interactions will yield future opportunities regarding prevention and treatment of CRC

Flash annealing influence on structural and electrical properties of TiO2/TiO/Ti periodic multilayers

International audienceMultilayered structures with a 40 nm period composed of titanium and two different titanium oxides, TiO and TiO2, were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. These multilayers were sputtered onto Al2O3 sapphire to avoid substrate compound diffusion during flash annealing (ranging from350 °C to 550 °C). Structure and composition of these periodic TiO2/TiO/Ti stackswere investigated by X-ray diffraction, X-ray photoemission spectroscopy and transmission electronic microscopy techniques. Two crystalline phases α-Ti and fcc-TiO were identified in the metallic-rich sub-layers whereas the oxygen-rich ones were composed of amixture of amorphous and rutile TiO2 phase. DC electrical resistivity ρ measured for temperatures ranging from 25 to 200 °C was influenced by the thermal treatments. The temperature coefficients of resistance of these periodic TiO2/TiO/Ti multilayers were modified from 11.7 × 10−04 to −8.81 × 10−04 K−1. Local changes of crystallinity were reported and the resistivity responses of these annealed films could be linked to the typical electrical behavior of a metal-oxide mixtur

Synthesis and Characterization of Cerium Oxide Nanoparticles: Effect of Cerium Precursor to Gelatin Ratio

Hemocompatible nanoparticles with reactive oxygen species (ROS) scavenging properties for titanium implant surface coatings may eliminate implant failure related to inflammation and bacterial invasion. Cerium (Ce) is a rare earth element, that belongs to the lanthanide group. It exists in two oxidation states, Ce+3 and Ce+4, which contribute to antioxidant, catalytic, antibacterial, and ROS-scavenging properties. The purpose of the present study was to synthesize ceria nanoparticles and to evaluate their hemocompatibility and ROS scavenging properties. The synthesis of Ce-NPs was performed via the sol-gel method, and five different ratios of cerium precursors to gelatin were evaluated. Their characterization was achieved through FTIR, XRD, SEM, and TEM. Hemocompatibility and ROS analysis were evaluated at different concentrations with human erythrocytes. The morphology and size distribution were certified by TEM and the cubic CeO2 fluorite structure was identified by selected area electron diffraction and high-resolution TEM. The particle size of the lowest Ce concentration presented a mean diameter of 10 nm. At concentrations of 2 NPs unique candidates as nanofillers or nanocoatings with antibacterial properties

Magnetic Anisotropies and Exchange Bias of Co/CoO Multilayers with Intermediate Ultrathin Pt Layers

Co/CoO multilayers are fabricated by means of radio-frequency magnetron sputtering. For the formation of each multilayer period, a Co layer is initially produced followed by natural oxidation. Platinum is used not only as buffer and capping layers, but also in the form of intermediate ultrathin layers to enhance perpendicular magnetic anisotropy. Three samples are compared with respect to the magnetic anisotropies and exchange bias between 4–300 K based on superconducting quantum interference device magnetometry measurements. Two of the multilayers are identical Co/CoO/Pt ones; one of them, however, is grown on a Co/Pt “magnetic substrate” to induce perpendicular magnetic anisotropy via exchange coupling through an ultrathin Pt intermediate layer. The third multilayer is of the form Co/CoO/Co/Pt. The use of a “magnetic substrate” results in the observation of loops with large remanence when the field applies perpendicular to the film plane. The CoO/Co interfaces lead to a significant exchange bias at low temperatures after field cooling. The largest exchange bias was observed in the film with double Co/CoO/Co interfaces. Consequently, significant perpendicular anisotropy coexists with large exchange bias, especially at low temperatures. Such samples can be potentially useful for applications related to spintronics and magnetic storage