Lateral deformation and defect resistance of compacted silica glass: Quantification of the scratching hardness of brittle glasses

Human interaction with multimedia devices occurs predominantly over inorganic glass surfaces. Scratch-induced damage is a primary limitation in the suitability of brittle glasses for this purpose. However, neither truly quantitative data nor a topo-chemical understanding of the underlying deformation process which would allow for the development of improved materials is presently available. Here, we present lateral nano-indentation experiments for determining the work of deformation which is involved in the process of glass scratching. Using a series of hot-compressed vitreous silica with mild degrees of structural densification, we derive relations between quantitative scratch hardness and the underlying glass structure. We show that Young's modulus provides a clear rational for the observed variations in scratching hardness. In the specific case of silica, the energy needed to generate a certain scratch volume corresponds to roughly one tenth of Young's modulus. This relationship formally indicates that only about one tenth of the bonds which are involved in the deformation process are broken in its course. However, comparison with a more complex glass material with a certain fraction of two dimensional structural units and a strong ability for topological adaption to local stress clearly indicates a deviation from this behavior. This opens a pathway to topo-chemical engineering of scratch-resistant glasses

Tunable broadband photoluminescence from bismuth‐doped calcium aluminum germanate glasses prepared in oxidizing atmosphere

Tunable photoluminescence (PL) from transparent inorganic glass matrices is of interest for applications demanding a semitransparent photoconverter that does not elastically scatter incoming light. For this purpose, bismuth (Bi)‐doped optical materials exhibit unique spectral characteristics in terms of bandwidth and emission tunability. Here, we demonstrate a facile route for preparing such converters from Bi‐doped calcium‐aluminate and calcium‐aluminogermanate glasses. These glasses offer tunable PL across the near violet and visible‐to‐near‐infrared (NIR) spectral range, with an emission lifetime in the range of 300 μs. The addition of GeO 2 exerts a decrease in optical basicity, which in turn enables the stabilization of NIR‐active low‐valence Bi species for broadband NIR PL

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

The TEMPO Survey I: Predicting Yields of the Transiting Exosatellites, Moons, and Planets from a 30-day Survey of Orion with the Nancy Grace Roman Space Telescope

We present design considerations for the Transiting Exosatellites, Moons, and Planets in Orion (TEMPO) Survey with the Nancy Grace Roman Space Telescope. This proposed 30-day survey is designed to detect a population of transiting extrasolar satellites, moons, and planets in the Orion Nebula Cluster (ONC). The young (1-3 Myr), densely-populated ONC harbors about a thousand bright brown dwarfs (BDs) and free-floating planetary-mass objects (FFPs). TEMPO offers sufficient photometric precision to monitor FFPs with ${\rm M}\geq1{\rm M}_{\rm J}$ for transiting satellites. The survey is also capable of detecting FFPs down to sub-Saturn masses via direct imaging, although follow-up confirmation will be challenging. TEMPO yield estimates include 14 (3-22) exomoons/satellites transiting FFPs and 54 (8-100) satellites transiting BDs. Of this population, approximately $50\%$ of companions would be "super-Titans" (Titan to Earth mass). Yield estimates also include approximately $150$ exoplanets transiting young Orion stars, of which $>50\%$ will orbit mid-to-late M dwarfs and approximately ten will be proto-habitable zone, terrestrial ($0.1{\rm M}_{\oplus} - 5{\rm M}_{\oplus}$) exoplanets. TEMPO would provide the first census demographics of small exosatellites orbiting FFPs and BDs, while simultaneously offering insights into exoplanet evolution at the earliest stages. This detected exosatellite population is likely to be markedly different from the current census of exoplanets with similar masses (e.g., Earth-mass exosatellites that still possess H/He envelopes). Although our yield estimates are highly uncertain, as there are no known exoplanets or exomoons analogous to these satellites, the TEMPO survey would test the prevailing theories of exosatellite formation and evolution, which limit the certainty surrounding detection yields.Comment: Submitted to PAS

Metal-organic framework and inorganic glass composites

Abstract: Metal-organic framework (MOF) glasses have become a subject of interest as a distinct category of melt quenched glass, and have potential applications in areas such as ion transport and sensing. In this paper we show how MOF glasses can be combined with inorganic glasses in order to fabricate a new family of materials composed of both MOF and inorganic glass domains. We use an array of experimental techniques to propose the bonding between inorganic and MOF domains, and show that the composites produced are more mechanically pliant than the inorganic glass itself

Strain-rate sensitivity of glasses

Although glasses are commonly thought of as ideal brittle materials, a local plastic deformation can be induced by the penetration of sharp objects, such as the indenter tips commonly employed for hardness testing. Since the first experimental verification of this phenomenon, considerable research effort has been devoted to the underlying microscopic mechanisms, which govern the indentation deformation of glasses, but also to associated properties of technological relevance, like crack initiation and defect tolerance, fracture toughness, brittleness or even scratchability. In early indentation studies, this has been achieved through a post-mortem topographic or spectroscopic analysis of the residual hardness imprints left on the glass surface. However, with the ongoing demand for a mechanical characterization at small-scales, advanced indentation protocols have been developed, which nowadays allow for a more comprehensive description of the fundamental deformation processes in amorphous materials and by extension, the design of more defect-tolerant glasses. But regardless of the numerous studies on the contact damage resistance of glasses, the time or rate dependence of the indentation deformation, commonly referred to as creep, still remains poorly understood. To overcome this issue, the influence of the imposed strain-rate on the hardness of a variety of glasses with covalent, ionic and metallic bonding character as well as varying degrees of network dimensionality and atomic packing density was characterized in a nanoindentation strain-rate jump test. Based on these results, a qualitative mechanistic description of the topological principles that determine the rate dependence of the glass hardness has been proposed

Family Exit in Family Firms: How Network Ties Affect the Owner’s Intention to Follow the Private Equity Succession Route

Kreer F, Mauer R, Limbach P, Brettel M. Family Exit in Family Firms: How Network Ties Affect the Owner’s Intention to Follow the Private Equity Succession Route. Schmalenbach Business Review. 2015;67(4):454-488.We study private equity as a succession route in family firms. Using survey data from Germany, we empirically examine the role owner-managers and their network ties play in the early process of firm succession. Our evidence suggests that network ties, strong ties in particular, matter to owner-managers when they consider a sale to private equity. Applying the Theory of Planned Behavior, we find that subjective norms and attitude explain the intention to sell to private equity investors, while entrepreneurial network ties explain the subjective norm component. We further show that subjective norm mediates the relationship of network ties on intention