Controlled formation of gold nanoparticles with tunable plasmonic properties in tellurite glass

Silicate glasses with metallic nanoparticles (NPs) have been of intense interest in art, science and technology as the plasmonic properties of these NPs equip glass with light modulation capability. The so-called striking technique has enabled precise control of the in situ formation of metallic NPs in silicate glasses for applications from coloured glasses to photonic devices. Since tellurite glasses exhibit the unique combination of comparably easy fabrication, low phonon energy, wide transmission window and high solubility of luminescent rare earth ions, there has been a significant amount of work over the past two decades to adapt the striking technique to form gold or silver NPs in tellurite glasses. Despite this effort, the striking technique has remained insufficient for tellurite glasses to form metal NPs suitable for photonic applications. Here, we first uncover the challenges of the traditional striking technique to create gold NPs in tellurite glass. Then, we demonstrate precise control of the size and concentration of gold NPs in tellurite glass by developing new approaches to both steps of the striking technique: a controlled gold crucible corrosion technique to incorporate gold ions in tellurite glass and a glass powder reheating technique to subsequently transform the gold ions to gold NPs. Using the Mie theory, the size, size distribution and concentration of the gold NPs formed in tellurite glass are determined from the plasmonic properties of the NPs. This fundamental research provides guidance for designing and manipulating the plasmonic properties in tellurite glass for photonics research and applications

Indentation-Induced Structural Changes in Vitreous Silica Probed by in-situ Small-Angle X-Ray Scattering

The transient (or permanent) structural modifications which occur during local deformation of oxide glasses are typically studied on the basis of short-range data, for example, obtained through vibrational spectroscopy. This is in contrast to macroscopic observations, where variations in material density can usually not be explained using next-neighbor correlations alone. Recent experiments employing low-frequency Raman spectroscopy have pointed-out this issue, emphasizing that the deformation behavior of glasses is mediated through structural heterogeneity and drawing an analogy to granular media. Here, we provide additional support to this understanding, using an alternative experimental method. Structural modification of vitreous silica in the stress field of a sharp diamond indenter tip was monitored by in-situ small-angle X-ray scattering. The influenced zone during loading and after unloading was compared, demonstrating that changes in the position of the first sharp diffraction peak (FSDP) directly in the center of the indent are of permanent character. On the other hand, variations in the amplitude of electron density fluctuations (AEDF) appear to fully recover after load release. The lateral extent of the modifications and their relaxation are related to the short- to intermediate-range structure and elastic heterogeneity pertinent to the glass network. With support from Finite Element Analysis, we suggest that different structural length scales govern shear deformation and isotropic compaction in vitreous silica

Pressure dependence of the topological heterogeneity of glasses

Der amorphe bzw. glasige Zustand besitzt, per Definition keine langreichende symmetrische atomare Anordnung. Um die Struktur eines Glases dennoch beschreiben zu können, wurde der theoretische Formalismus der „Topologie“ eingeführt. Dieser definiert eine geometrische Grundanordnung der Struktureinheiten und deren atomare Besetzung. Experimentell lässt sich die Topologie jedoch schwer erfassen. Übliche Methoden zur Strukturanalyse von Gläsern (z.B. Kernspinresonanz, Röntgenbeugung, Ramanspektroskopie, Infrarotspektroskopie) können Nahordnung, bzw. Strukturen mittlerer Größenordnung aufklären, geben aber keinerlei Hinweise auf Strukturen im Fernordnungsbereich. Die vorliegende Studie fokussiert deshalb auf die experimentelle Beschreibung der Topologie von Gläsern über die Analyse der jeweils vorliegenden nanoskaligen Heterogenität und betrachtet im Speziellen deren Druckabhängigkeit. Wird eine unterkühlte Schmelze eingefroren, zeigen die entstehenden Strukturen bzw. die strukturelle Heterogenität, sowie zahlreiche makroskopisch beobachtbare Eigenschaften des so entstandenen Glases, eine deutliche Abhängigkeit von den angewandten Einfrierbedingungen, d.h. von der Kinetik des Glasübergangs. Diese kann dann über die jeweils vorliegende fiktive Temperatur und den fiktiven Druck, welche den Punkt des Einfrierens aller atomaren Bewegungen repräsentieren, beschrieben werden. Bisher existieren jedoch nur wenige experimentelle Studien, welche den Einfluss variierender Einfrierbedingungen, besonders des Drucks, auf die Struktur, bzw. die Topologie untersuchen. In dieser Arbeit konnte anhand des Borosilikatglassystems gezeigt werden, dass die Hauptverdichtung des Materials durch die Homogenisierung der Topologie geregelt wird. Konkret wurde eine Reduktion der eingefrorenen Dichtefluktuationen von ca. 27 % mit einem scheinbaren fiktiven Druck von Pa,f = 470 MPa festgestellt. Des Weiteren wurde eine inelastische Komprimierung im Borosilikatglas im Bereich von 10 GPa < p < 20 GPa nachgewiesen. Strukturell ist die Umwandlung durch die Bildung von tetragonal koordiniertem Bor und direkte Verknüpfungen von Silizium mit Bor über ein gemeinsames Sauerstoffatom charakterisiert. Thermodynamisch gesehen, bleibt die Frage, ob es sich um Polyamorphismus handelt. Außerdem wurden Gläser des Sulfophosphatsystems, das durch eine variable Netzwerkverknüpfung bis zu einer rein ionischen Struktur mit steigendem Schwefelgehalt gekennzeichnet ist, analysiert. Im Niedrigdruckbereich bis Pa,f < 0.5 GPa, ist unabhängig vom Polymerisationsgrad, die topologische Heterogenität der Gläser kaum beeinflusst. Vor allem in den hauptsächlich ionisch gebundenen Glaszusammensetzungen ist jedoch ein Anstieg der topologischen Heterogenität mit Pa,f angedeutet.By definition, glasses miss a strict symmetrical atomic arrangement on intermediate or higher length scale. The term "topology" was introduced as a theoretical formalism to describe the basic geometrical arrangement of the structural units and their atomic decoration. Experimentally, such "topology" is rather difficult to access. Tools for analyzing glass structure (e.g. nuclear magnetic resonance, X-ray diffraction, Raman spectroscopy, infrared spectroscopy) usually address only the short or mid-range order, but are quite ineffective in resolving higher length-scale features. Therefore, this study is focusing on the experimental description of the topology of glasses by considering nanoscale heterogeneity and especially considering its pressure dependency. When a supercooled melt is frozen-in, structures, structural heterogeneity and various macroscopic properties of the obtained glass are largely dependent on the freezing kinetics. The values of fictive temperature and fictive pressure may be employed to describe the point at which freezing ultimately occurred. So far, little experimental data is available on the structural and particularly, topological implications of variations in freezing kinetics, especially variations in pressure, which are therefore addressed in the present study. On the basis of borosilicate systems, it could be shown that the main compaction of the materials network occurs though the homogenization of topological heterogeneity. For a glass with Pa,f = 470 MPa a reduction of global frozen in density fluctuations of about 27 % was found. For borosilicate glass, additionally an inelastic compression between 10 GPa < p < 20 GPa was detected. The transition is characterized by the formation of tetragonal coordinated boron and direct linking of silicon to boron via bridging oxygen. From a thermodynamic point of view the question of polyamorphism in this context is still open. Furthermore glasses of the sulfophosphate system, which is characterized by variable network connectivity up to purely ionic with highest sulfur contents, are analyzed. Independent of the degree of polymerization, these glasses are nearly unaffected in the low compression regime up to Pa,f < 0.5 GPa. However, for the highly depolymerized ionic glass compositions an increased topological heterogeneity with Pa,f is indicated

Glass and circularity

EditorialGreen Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Architectural Technolog

Controlled formation of gold nanoparticles with tunable plasmonic properties in tellurite glass

Abstract Silicate glasses with metallic nanoparticles (NPs) have been of intense interest in art, science and technology as the plasmonic properties of these NPs equip glass with light modulation capability. The so-called striking technique has enabled precise control of the in situ formation of metallic NPs in silicate glasses for applications from coloured glasses to photonic devices. Since tellurite glasses exhibit the unique combination of comparably easy fabrication, low phonon energy, wide transmission window and high solubility of luminescent rare earth ions, there has been a significant amount of work over the past two decades to adapt the striking technique to form gold or silver NPs in tellurite glasses. Despite this effort, the striking technique has remained insufficient for tellurite glasses to form metal NPs suitable for photonic applications. Here, we first uncover the challenges of the traditional striking technique to create gold NPs in tellurite glass. Then, we demonstrate precise control of the size and concentration of gold NPs in tellurite glass by developing new approaches to both steps of the striking technique: a controlled gold crucible corrosion technique to incorporate gold ions in tellurite glass and a glass powder reheating technique to subsequently transform the gold ions to gold NPs. Using the Mie theory, the size, size distribution and concentration of the gold NPs formed in tellurite glass are determined from the plasmonic properties of the NPs. This fundamental research provides guidance for designing and manipulating the plasmonic properties in tellurite glass for photonics research and applications

Indentation densification of fused silica assessed by raman spectroscopy and constitutive finite element analysis

Inelastic deformation of anomalous glasses manifests in shear flow and densification of the glass network; the deformation behavior during indentation testing is linked strongly to both processes. In this paper, the indentation densification field of fused silica is investigated using depth‐resolved Raman spectroscopy and finite element simulations. Through affecting the size of the indent, the normal load and the Raman laser spot size determine the spatial sampling resolution, leading to a certain degree of structural averaging. For appropriate combinations of normal load (indent size) and laser spot diameter, a maximum densification of 18.4% was found at the indent center. The indentation behavior was modeled by extended Drucker‐Prager‐Cap (DPC) plasticity, assuming a sigmoidal hardening behavior of fused silica with a densification saturation of 21%. This procedure significantly improved the reproduction of the experimental densification field, yielding a maximum densification of 18.2% directly below the indenter tip. The degree of densification was found to be strongly linked to the hydrostatic pressure limit below the indenter in accordance to Johnson's expanding cavity model (J. Mech. Phys. Solids, 18 (1970) 115). Based on the good overlap between FEA and Raman, an alternative way to extract the empirical correlation factor m, which scales structural densification to Raman spectroscopic observations, is obtained. This approach does not require the use of intensive hydrostatic compaction experiments

Indentation densification of fused silica assessed by raman spectroscopy and constitutive finite element analysis

Inelastic deformation of anomalous glasses manifests in shear flow and densification of the glass network; the deformation behavior during indentation testing is linked strongly to both processes. In this paper, the indentation densification field of fused silica is investigated using depth‐resolved Raman spectroscopy and finite element simulations. Through affecting the size of the indent, the normal load and the Raman laser spot size determine the spatial sampling resolution, leading to a certain degree of structural averaging. For appropriate combinations of normal load (indent size) and laser spot diameter, a maximum densification of 18.4% was found at the indent center. The indentation behavior was modeled by extended Drucker‐Prager‐Cap (DPC) plasticity, assuming a sigmoidal hardening behavior of fused silica with a densification saturation of 21%. This procedure significantly improved the reproduction of the experimental densification field, yielding a maximum densification of 18.2% directly below the indenter tip. The degree of densification was found to be strongly linked to the hydrostatic pressure limit below the indenter in accordance to Johnson's expanding cavity model (J. Mech. Phys. Solids, 18 (1970) 115). Based on the good overlap between FEA and Raman, an alternative way to extract the empirical correlation factor m, which scales structural densification to Raman spectroscopic observations, is obtained. This approach does not require the use of intensive hydrostatic compaction experiments

Studium und Berufseinstieg: Ergebnisse der ersten Sächsischen Absolventenstudie

In der vorliegenden Studie werden die wichtigsten Ergebnisse der ersten Sächsischen Absolventenstudie vorgestellt, an der alle Hochschulen im Geschäftsbereich des Sächsischen Staatsministeriums für Wissenschaft und Kunst teilgenommen haben, welches Auftraggeber der Untersuchung war. Der Freistaat Sachsen ist nach Bayern und Rheinland-Pfalz das dritte Bundesland, das eine landesweite Absolventenstudie durchführt bzw. durchgeführt hat. Das Ziel der Untersuchung bestand darin, primär Informationen und Ergebnisse zur Einschätzung des Studiums, zum Prozess der Berufseinmündung, zu Beschäftigungsverhältnissen, zur Zufriedenheit mit der beruflichen Situation und zur regionalen Mobillität zu erhalten