Black magnetite beach sands from Milos and Kimolos islands: research of minerals' origin through mineral analysis, and potential enrichment in specific trace elements through geochemical analysis.

Μαύρες μαγνητιτκές άμμοι έχουν παρατηρηθεί σε διαφορετικές τοποθεσίες κατά μήκος των ακτογραμμών των νήσων Μήλος και Κίμωλος. Σε αυτή τη διπλωματική εργασία μελετάται η ορυκτολογική και τη γεωχημική σύσταση αυτών των άμμων. Τα δείγματα συγκεντρώθηκαν από επτά (7) παραλίες της Μήλου και μία (1) παραλία της Κιμώλου. Στόχος της εργασίας είναι να ερευνήσει την προέλευση των βαρέων ορυκτών των μαύρων άμμων, εστιάζοντας ιδιαίτερα στον μαγνητίτη, και να εξετάσει τον πιθανό εμπλουτισμό τους στα βαρέα μέταλλα: Ba, Mn, Ni, Pb, Zn, Cr. Οι μαύρες μαγνητιτικές άμμοι αποτελούνται συνήθως από βαρέα μέταλλα όπως μαγνητίτη, ιλμενίτη, τιτανιομαγνητίτη, αιματίτη, τα οποία απαντώνται σε μαύρη άμμο σε ρέματα, κολπίσκους, ποτάμια, ακτές, παραλίες και όρμους, μέσω διαδικασιών διάβρωσης και συγκέντρωσης οφειλόμενες στη δράση του νερού. Ο μαγνητίτης εμφανίζεται συνήθως στη φύση σε μορφή κοκκώδη και είναι κοινό συστατικό των πυριγενών-ηφαιστειακών πετρωμάτων (κυρίως μαφικής σύστασης), μεταμορφομένων πετρωμάτων, ή γρανιτών. Η υπόθεση της εργασίας είναι ότι οι μαύρες μαγνητιτικές άμμοι από τα νησιά της Μήλου και της Κιμώλου προέρχονται (κυρίως στην περίπτωση της Μήλου) από τα ηφαιστειακά προϊόντα ενδιάμεσης σύστασης που καλύπτουν το μεγαλύτερο μέρος του νησιού, δηλαδή ανδεσιτικά πετρώματα (λάβες, πυροκλαστικά, τόφφοι). Έτσι, το γεωλογικό πλαίσιο των νησιών μελετάται σε αυτή την εργασία όντας κρίσιμης σημασίας. Σύμφωνα με την ορυκτολογική και γεωχημική ανάλυση (ανάλυση XRD (Περίθλαση ακτίνων Χ) και ανάλυση SEM / EDS (Φασματοσκοπία Ενεργειακής Διασποράς ακτίνων Χ)), των μαύρων μαγνητιτικών άμμων, συμπεραίνουμε ότι τα ορυκτά του σιδήρου, ιδιαίτερα ο μαγνητίτης, προέρχονται από ηφαιστειακά προϊόντα της ανδεσιτικής σύστασης . Στην περίπτωση της Μήλου, τα ανδεσιτικά προϊόντα των ηφαιστειακών περιόδων 2.7-1.4 Ma (Άνω Πλειόκαινο - Κάτω-Μέσο Πλειστόκαινο) και 3.5-3.0 M.a. (Μέσο έως Άνω Πλειόκαινο) φαίνεται να αποτελούν την πηγή του μαγνητιτικού υλικού. Στην περίπτωση της Κιμώλου, το υλικό του μαγνητίτη μπορεί επίσης να προέρχεται από τα ανδεσιτικά προϊόντα των δύο διακεκριμένων ηφαιστειακών κύκλων μεταξύ 3,5-0,9 Μ.a., ή τη γρανιτική διείσδυση που εμφανίζεται διάσπαρτα στο κέντρο του νησιούί. Όσον αφορά το ανδεσιτικό υλικό, δεν έχει ακόμη εξακριβωθεί εάν ο μαγνητίτης προέρχεται από λάβες, τόφφους ή άλλο σχηματισμό ανδεσιτικής σύστασης. Οι άμμοι έχουν επίσης υποβληθεί σε γεωχημική ανάλυση, για τη μελέτη της χημικής τους σύνθεσης και του δυνητικού εμπλουτισμού στα βαρέα μέταλλα: Ba, Mn, Ni, Pb, Zn, Cr. Είναι γενικά γνωστό ότι τα βαρέα ορυκτά των μάυρων άμμων αποτελούν κοιτάσματα, οπότε ο εμπλουτισμός σε βαρέα μέταλλα ενδιαφέροντος θα μπορούσε να οδηγήσει σε περαιτέρω έρευνα. Σύμφωνα με την ανάλυση, τα κύρια στοιχεία έδωσαν αποτελέσματα σε συμφωνία με την ασβεσταλκαλική γεωχημεία της ηφαιστειότητας στη γενική περιοχή της Μήλου. Τα αποτελέσματα για τα έξι βαρέα ιχνοστοιχεία (Ba, Ni, Mn, Pb, Cr, Zn) συνδέουν την εμφάνιση και τις αναλογίες στα δείγματα με την ήδη υπάρχουσα μεταλλογένεση και υδροθερμική δραστηριότητα και των δύο νησιών, ειδικά για το βάριο και το μαγγάνιο, ως κράματα και αντικαταστάσεις στο πλέγμα των ορυκτών του σιδήρου και άλλων βαρέων ορυκτών.Black magnetite sands have been observed in different locations across the coastline of Milos and Kimolos islands. This thesis studies the mineralogy and geochemistry of these black magnetite beach sands from both islands. The samples were gathered from seven (7) beach locations from Milos and one (1) specific location from Kimolos. The aim of this project is to propose the origin of the black sands’ heavy minerals, focusing especially on magnetite, and examine the potential enrichment in the heavy metals: Ba, Mn, Ni, Pb, Zn, Cr, according to geochemical analysis. Black magnetite sands typically consist of heavy minerals such as magnetite, ilmenite, titanomagnetite, hematite, which are found in black sands in streams, creeks, rivers, seashores, and bays, via erosion and concentration by high water’s action. Magnetite most commonly occurs in nature in a granular form as a sand or grit and it is a common constituent of igneous-volcanic (basically mafic), metamorphic rocks, or as inclusion in granites too. The hypothesis of this project is that the black beach magnetite sands from the islands of Milos and Kimolos derive (especially in Milos case) from the volcanic products of intermediate composition that occur in most of the islands extent, which is andesitic rocks, (lavas, pyroclastics, tuffs). So, the geological framework of the islands is studied in this thesis as being of critical importance. The mineralogical and geochemical analysis (XRD (X-ray Diffraction) analysis and on SEM/EDS (Energy-dispersive X-ray spectroscopy)),of the black magnetite sands gave that iron minerals, especially magnetite, originate from volcanic products of andesitic composition. In Milos case, the magnetite material may derive from the andesitic products of the volcanic periods around and between 2.7-1.4 Ma (Upper Pliocene - Lower-Middle Pleistocene) and 3.5-3.0 M.a. (Middle to Upper Pliocene). In Kimolos case, the magnetite material may also derive from the andesitic products of the two distinguished volcanic circles between 3.5-0.9 M.a., or the granitic intrusion that occurs scattered in the central island. As it concerns the andesitic material, is yet to be ascertained whether magnetite derives from lavas, tuffs or other formation of andesitic composition. The sands have been also subjected on geochemical analysis, for the study of their chemical composition and the potential enrichment in the heavy metals: Ba, Mn, Ni, Pb, Zn, Cr. It is general known that heavy mineral sands consist ore deposits, so enrichment in heavy metals of interest could lead in further research. According to the analysis, the main elements gave results in agreement with the calc-alkaline geochemistry of the volcanism in Milos general area. The results for the six heavy trace elements (Ba, Ni, Mn, Pb, Cr, Zn) relates the occurrence and ratios in the samples with the already existed mineralization and hydrothermal activity of both islands, especially for barium and manganese, and their presence as alloys and replacements in the mineral plexus of ferrous-ferric and other heavy minerals

Doping controlled resistive switching dynamics in transition metal oxide thin films

Transition metal oxide thin films have attracted increasing attention due to their potential in non-volatile resistive random access memory (RRAM) devices, where such thin films are used as active layers in metal-insulator-metal (MIM) configurations. Titanium dioxide is one of the most celebrated oxides among the ones that exhibit resistive switching behaviour due to its wide band gap, high thermal stability, and high dielectric constant. RRAM devices with various materials as active layers, have demonstrated very fast switching performance but also huge potential for miniaturisation, which is the bottleneck of FLASH memory. Nevertheless, these devices very often suffer poor endurance, physical degradation, large variability of switching parameters and low yields. In most cases, the physical degradation stems from high electroforming and switching voltages. Doping of the active layer has been often employed to enhance the performance of RRAM devices, like endurance, OFF/ON ratio, forming voltages, etc. In this work, doping in TiO2-x RRAM devices was used to engineer the electroforming and switching thresholds so that device degradation and failure can be delayed or prevented. Al and Nb were selected with basic criteria the ionic radius and the oxidation state. The doped RRAM devices, showed improved switching performance compared to their undoped counterparts. Alternative approaches to doping were also investigated, like multilayer stacks comprising Al2O3-y and TiO2-x thin films. Furthermore, Al:TiO2-x/Nb:TiO2-x bilayer RRAM devices were fabricated, to prove whether a diode behaviour of the p-n interface inside the RRAM was feasible. The latest would be a particularly interesting finding towards active electronics

Data for 'Impact of ultra-thin Al2O3–y layers on TiO2–x ReRAM switching characteristics'

Data accompanying the paper: Prodromakis, Themistoklis; Trapatseli, Maria; Cortese, Simone; Serb, Alexantrou / Improved switching characteristics of TiO2-x ReRAM with embedded ultra-thin 2 Al2O3-y layers. In: Journal of Applied Physics, 28.03.2017. Abstract for accompanying paper: Transition metal-oxide resistive random access memory (RRAM) devices have demonstrated excellent performance in switching speed, versatility of switching and low-power operation. However, this technology still faces challenges like poor cycling endurance, degradation due to high electro-forming switching voltages and low yields. Engineering of the active layer by doping or addition of thin oxide buffer layers, are approaches that have been often adopted to tackle these problems. Here, we have followed a strategy that combines the two; we have used ultra-thin Al2O3-y buffer layers incorporated between TiO2-x thin &#12;lms taking into account both 3+/4+ oxidation states of Al/Ti cations. Our devices were tested by DC and pulsed voltage sweeping and in both cases demonstrated improved switching voltages. We believe that the Al2O3-y layers act as reservoirs of oxygen vacancies which are injected during EF, facilitate a &#12;lamentary switching mechanism and provide enhanced &#12;lament stability as shown by the cycling endurance measurements.</span

A TiO2-based volatile threshold switching selector service with 10^7 non linearity and sub 100 pA Off Current

Data for the conference paper: A TiO2-based volatile threshold Switching Selector Device with 10^7 non linearity and sub 100 pA Off Current. The file features the Resistive Switching Characteristics of the volatile selector at both polarities, including electroforming step, showing a non linearity of 10^7 between high and low resistance states. Also, the linearity of the low resistance states is presented, showing that the resistance values are the same at both polarities.</span

Al-doping engineered electroforming and switching dynamics of TiO_x ReRAM devices

TiO2 thin films have drawn a lot of attention for their application in emerging memory devices, such as resistive random access memory (ReRAM). However, TiO2 ReRAM still faces reliability issues, including poor endurance, large device-to-device and cycle-to-cycle variability of switching parameters and low yields. Moreover, high electroforming voltages have been often associated with irreversible damage to devices. Doping of TiO2 has been employed as a strategy for overcoming these issues. Therefore in this work, we used Al as a dopant in TiO2 thin films to investigate its effect on electroforming and switching voltages of ReRAM devices. Conductive atomic force microscopy (C-AFM) measurements on these thin films, suggested that Al doping decreased the switching voltages compared to the undoped thin films. This result was confirmed by pulse voltage sweeping of ReRAM devices employing the same doped thin films. The Al-doped devices were on average electroforming at -5.7 V, compared to -6.4 V for the undoped ones, and they were switching with potentials as low as ±0.9 V. These findings suggest a potential pathway for implementing low-power ReRAM systems<br/

Spike sorting using non-volatile metal-oxide memristors

Electrophysiological techniques have improved substantially over the past years to the point that neuroprosthetics applications are becoming viable. This evolution has been fuelled by the advancement of implantable microelectrode technologies that have followed their own version of Moore's scaling law. Similarly to electronics, however, excessive data-rates and strained power budgets require the development of more efficient computation paradigms for handling neural data in situ; in particular the computationally heavy task of events classification. Here, we demonstrate how the intrinsic analogue programmability of memristive devices can be exploited to perform spike-sorting on single devices. Leveraging the physical properties of nanoscale memristors allows us to demonstrate that these devices can capture enough information in neural signal for performing spike detection (shown previously) and spike sorting at no additional power cost.</p

Field emission properties of low-temperature, hydrothermally grown tungsten oxide

Tungsten oxide layers have been prepared on conductive glass substrates using aqueous chemical growth from a sodium tungstate precursor at low-temperature hydrothermal conditions. The deposits were then tested as cold electron emitters. Traceable layers could be deposited only within a narrow pH range of 1.5-2 at a time length not exceeding 4 h. Transmittance in the visible spectrum was found to decrease with deposition time. The presence of both monoclinic and hexagonal phases was always detected. At the longest deposition times and highest precursor concentrations, morphologies comprise randomly oriented spikes or rods. The overall emission performance is found to improve with growth time and precursor concentration. The role of morphology on the emission properties of the films is discussed. Field Emission Properties of Low-Temperature, Hydrothermally Grown Tungsten Oxide. Available from: https://www.researchgate.net/publication/51234194_Field_Emission_Properties_of_Low-Temperature_Hydrothermally_Grown_Tungsten_Oxide [accessed May 7, 2015]