Pressure dependence of the Boson peak in glassy As2S3 studied by Raman Scattering

A detailed pressure-dependence study of the low-energy excitations of glassy As2S3 is reported over a wide pressure range, up to 10 GPa. The spectral features of Boson peak are analysed as a function of pressure. Pressure effects on the Boson peak are manifested as an appreciable shift of its frequency to higher values, a suppression of its intensity, as well as a noticeable change of its asymmetry leading to a more symmetric shape at high pressures. The pressure-induced Boson peak frequency shift agrees very well with the predictions of the soft potential model over the whole pressure range studied. As regards the pressure dependence of the Boson peak intensity, the situation is more complicated. It is proposed that in order to reach proper conclusions the corresponding dependence of the Debye density of states must also be considered. Employing a comparison of the low energy modes of the crystalline counterpart of As2S3 as well as the experimental data concerning the pressure dependencies of the Boson peak frequency and intensity, structural or glass-to-glass transition seems to occur at the pressure ~4 GPa related to a change of local structure. Finally, the pressure-induced shape changes of the Boson peak can be traced back to the very details of the excess (over the Debye contribution) vibrational density of states.Comment: To appear in J. Non-Cryst. Solids (Proceedings of the 5th IDMRCS, Lille, July 2005

Understanding the dynamics of biological colloids to elucidate cataract formation towards the development of methodology for its early diagnosis

The eye lens is the most characteristic example of mammalian tissues exhibiting complex colloidal behaviour. In this paper we briefly describe how dynamics in colloidal suspensions can help addressing selected aspects of lens cataract which is ultimately related to the protein self-assembly under pathological conditions. Results from dynamic light scattering of eye lens homogenates over a wide protein concentration were analyzed and the various relaxation modes were identified in terms of collective and self-diffusion processes. Using this information as an input, the complex relaxation pattern of the intact lens nucleus was rationalized. The model of cold cataract - a phase separation effect of the lens cytoplasm with cooling - was used to simulate lens cataract at in vitro conditions in an effort to determine the parameters of the correlation functions that can be used as reliable indicators of the cataract onset. The applicability of dynamic light scattering as a non-invasive, early-diagnostic tool for ocular diseases is also demonstrated in the light of the findings of the present paper.Comment: Slightly different version from the published one 10 pages, 2 figure

On the analysis of the vibrational Boson peak and low-energy excitations in glasses

Implications of reduction procedures applied to the low energy part of the vibrational density of states in glasses and supercooled liquids are considered by advancing a detailed comparison between the excess - over the Debye limit - vibrational density of states g(w) and the frequency-reduced representation g(w)/w^2 usually referred to as the Boson peak. Analyzing representative experimental data from inelastic neutron and Raman scattering we show that reduction procedures distort to a great extent the otherwise symmetric excess density of states. The frequency of the maximum and the intensity of the excess experience dramatic changes; the former is reduced while the latter increases. The frequency and the intensity of the Boson peak are also sensitive to the distribution of the excess. In the light of the critical appraisal between the two forms of the density of states (i.e. the excess and the frequency-reduced one) we discuss changes of the Boson peak spectral features that are induced under the presence of external stimuli such as temperature (quenching rate, annealing), pressure, and irradiation. The majority of the Boson peak changes induced by the presence of those stimuli can be reasonably traced back to simple and expected modifications of the excess density of states and can be quite satisfactorily accounted for the Euclidean random matrix theory. Parallels to the heat capacity Boson peak are also briefly discussed.Comment: To appear in J. Non-Cryst. Solids (Proceedings of the 5th IDMRCS, Lille, July 2005

The Essential Elements of a Risk Governance Framework for Current and Future Nanotechnologies

Societies worldwide are investing considerable resources into the safe development and use of nanomaterials. Although each of these protective efforts is crucial for governing the risks of nanomaterials, they are insufficient in isolation. What is missing is a more integrative governance approach that goes beyond legislation. Development of this approach must b

Zno nanowires: Growth, properties and advantages

One-dimensional anisotropic nanostructures, and in particular nanowires, are under intensive investigations over the last decade owing to their unique physical properties and their documented performance in a wide range of opto-electronic and nano-photonic devices. Here, we present a short overview of the main assets of nanowire arrays with particular emphasis as materials for solar energy harvesting and conversion. A brief survey on the main growth techniques of ZnO nanowires, i.e. chemical vapor deposition and solution chemistry is also presented. © Springer Science+Business Media Dordrecht 2015

Complex dynamics in nanoscale phase separated supercooled liquids

The relaxation properties of supercooled AsxS100-x liquids are investigated using a combination of infrared photon correlation spectroscopy and topological constraint theory. Results reveal two channels of relaxation for sulfur-rich compositions that manifest by an unusual profile in the density-density autocorrelation function involving two typical timescales. This indicates a reduced temperature-dependent dynamics for one of the channels associated with a sulfur-rich segregated nanoscale phase that furthermore displays a low liquid fragility. Conversely, the dynamics of the emerging cross-linked As-S network is associated with a growth of the glass transition temperature with As content. These results can be quantitatively understood from topological constraint theory applied to a phase separated network for which a dedicated constraint enumeration must be achieved. The vanishing of this peculiar behavior occurs close to the reported isostatic reversibility window observed at the glass transition. © 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI

Optical Properties and Structure of As-Sb Chalcohalide Glasses by Raman Scattering and Density Functional Theory Calculations

We report an investigation of the optical properties, structure, and vibrational modes of SbxAs37-xS48I15 glasses (0 at. % < x < 37 at. %). Optical parameters such as the refractive index, the absorption coefficient, and the optical band gap are correlated with the glass composition. All parameters were found to follow an almost linear dependence with the antimony content x. Both the refractive index and the absorption edge wavelength exhibit a systematic increase against x. Off-resonant Raman spectra of the glasses spectra were measured and analyzed. Structural units, representative of the glass structure, were optimized by density functional theory (DFT) calculations, providing vibrational spectra in agreement with the experiments. Raman spectra were interpreted based on the harmonic frequencies and the activities of vibrational modes obtained by the DFT analysis. The results showed evidence in favor of statistical mixing of iodine atoms, among the various pyramidal units, hence discarding structural models suggesting the presence of isolated pyramidal molecules of the types AsI3/SbI3. Both experimental data and DFT results suggested that iodine atoms exhibit much higher propensity to replace sulfur atoms in antimony than in arsenic-based pyramids. In addition, comparison of experimental and simulated spectra of selected clusters in mixed glasses indicates that it is more probable to find corner-sharing Sb-based pyramids than As-based ones. Copyright © 2020 American Chemical Society

Laser-assisted explosive synthesis and transfer of turbostratic graphene-related materials for energy conversion applications

International audienceProduction of high-grade graphene-like materials using a simple, reliable processes and its simultaneous transfer onto soft surfaces have not yet achieved; hence impeding wide-ranging graphene applications. Even more complex processes are required to prepare graphene-based nanohybrids, which offer additional synergistic functionalities in relation to graphene. Here, an uncomplicated and scalable process to prepare high-purity few-layer turbostratic graphene and graphene/SiOx nanohybrids is demonstrated employing laser-mediated explosive synthesis and transfer of graphene flakes. The process is capable of producing, and simultaneously transferring, graphene flakes on any substrate, such as polymer, glass, metal, ceramics, etc. Graphene and nanohybrids exhibit sp2 structures of turbostratic stacking, with low sheet resistance and very high (~30) C/O ratio. The merits of the method are showcased by two energy-related examples, flexible single-electrode triboelectric nanogenerators and electric double-layer capacitors. This method emerges as a paradigm of additive manufacturing for graphene-based devices with impact for applications in flexible electronics. © 2022, The Author(s)