Search results for "Amorphous solid"
showing 10 items of 622 documents
Do we understand the solid-like elastic properties of confined liquids?
2021
Recently, in polymeric liquids, unexpected solid-like shear elasticity has been discovered, which gave rise to a controversial discussion about its origin (1⇓–3). The observed solid-like shear modulus G depends strongly on the distance L between the plates of the rheometer according to a power law G ∝ L − p with a nonuniversal exponent ranging between p = 2 and p = 3 . Zaccone and Trachenko (4) have published an article in which they claim to explain these findings by a nonaffine contribution to the liquid shear modulus. The latter is represented as Δ G ∝ − ∑ λ = L , T 1 V … [↵][1]1To whom correspondence may be addressed. Email: giancarlo.ruocco{at}roma1.infn.it. [1]: #xref-corresp-1-1
Alteration of the structural properties of inulin gels
2019
Abstract In this work, inulin particle gels, prepared with a type of long chain inulin, were examined in terms of their structural properties and mechanical response, depending on the applied shear rates and temperature during gel preparation. The results are interpreted on the basis of a particle gel model, which takes into account the varying gel structure, depending on the sample preparation parameters. X-ray measurements of the inulin powder, used for the experiments, revealed a mostly amorphous powder. The temperature profiles for the sample preparation, chosen from 25 °C to 60 °C with constant stirring at 600 rpm, yielded viscoelastic particle gels with decreasing hardness. By applica…
Diffusion and outgassing of O<inf>2</inf> in amorphous SiO<inf>2</inf> silica nanoparticles with specific surface properties
2014
Self-limiting and complete oxidation of silicon nanostructures produced by laser ablation in water
2016
Oxidized Silicon nanomaterials produced by 1064 nm pulsed laser ablation in deionized water are investigated. High-resolution transmission electron microscopy coupled with energy dispersive X-ray spectroscopy allows to characterize the structural and chemical properties at a sub-nanometric scale. This analysis clarifies that laser ablation induces both self-limiting and complete oxidation processes which produce polycrystalline Si surrounded by a layer of SiO2 and amorphous fully oxidized SiO2, respectively. These nanostructures exhibit a composite luminescence spectrum which is investigated by time-resolved spectroscopy with a tunable laser excitation. The origin of the observed luminescen…
Molecular dynamics simulation of epitaxial growth of the Si(001) surface
1988
Abstract Molecular beam epitaxy on a Si(100) substrate has been studied using a molecular dynamics method with the Stillinger-Weber model potential. At high substrate temperature, 800 K, well ordered crystalline layers are found to grow underneath an amorphous overlayer of approximately 5 A thick. A limiting temperature for epitaxial growth is found to be 480 K, below which the growth does not produce ordered layers. When the sample deposited below 480 K is heated up to 800 K and the deposition is started again the original adatoms start to form ordered atomic layers. Thus the collisions of the deposited atoms in addition to the substrate temperature seem to play an essential role in the gr…
Role of the strain in the epitaxial regrowth rate of heavily doped amorphous Si films
2008
Solid phase epitaxial regrowth (SPER) of p -doped preamorphized Si was studied by time resolved reflectivity. Strain and dopant concentration were opportunely varied by implanting neutral (Ge) and isovalent (B, Ga) impurities in order to disentangle the two different effects on SPER. Larger SPER rate variations occurred in strained doped Si with respect to undoped samples. The generalized Fermi level shifting model was implemented to include the role of the strain and to fit the experimental data over a large range of temperature for p - and n -type doping. We introduced a charged defect, whose energy level is independent of the dopant species. © 2008 American Institute of Physics.
Cathodoluminescence decay kinetics in Ge+, Si+, O+ implanted SiO2 layers
2003
Abstract Cathodoluminescence spectral shapes and respective band decay times show no similarity between luminescence centers in different crystal and amorphous modifications of SiO2 and GeO2. On the other hand, the additionally produced red luminescence centers (650 nm) by oxygen implantation into SiO2 layers are of the same nature as in stoichiometric SiO2 and are attributed to the non-bridging oxygen hole center (NBOHC). On the other hand, the elevated blue luminescence (460 nm) in Si implanted SiO2 belongs to the silicon related oxygen deficient center (SiODC) as in stoichiometric layers also. Ge implantation into SiO2 and thermal post-annealing leads to a huge violet luminescence (400 n…
Bimodal Acidity at the Amorphous Silica/Water Interface
2015
International audience; Understanding the microscopic origin of the acid base behavior of mineral surfaces in contact with water is still a challenging task, for both the experimental and the theoretical communities. Even for a relatively simple material, such as silica, the origin of the bimodal acidity behavior is still a debated topic. In this contribution we calculate the acidity of single sites on the humid silica surface represented by a model for the hydroxylated amorphous surface. Using a thermodynamic integration approach based on ab initio molecular dynamics, we identify two different acidity values. In particular, some convex geminals and some type of vicinals are very acidic (pK…
Crystalline nanorods as possible templates for the synthesis of amorphous biosilica during spicule formation in Demospongiae.
2009
In tandem: High-resolution TEM shows that during the initial stages of demosponge spicule formation, a primordial crystalline structure is formed within the axial filament. The recently developed electron diffraction tomography technique (ADT) reveals that the nanorods have a layered structure that matches smectitic phyllosilicates. These intracellular nanorods have been considered as precursors of mature spicules. High-resolution microscopy shows that, during the initial stages of demosponge spicule formation, a primordial crystalline structure is formed within the axial filament. The recently developed electron diffraction tomography technique reveals that the nanorods have a layered stru…
Preface: Special Issue on Structure in Glassy and Jammed Systems
2016
This special issue presents new developments in our understanding of the role of structure in dynamical arrest and jamming. Articles highlight local geometric motifs and other forms of amorphous order, in experiment, computer simulation and theory.