Search results for "Amorphous solid"
showing 10 items of 622 documents
Fluctuating hydrodynamics and diffusion in amorphous solids
1994
The fluctuating hydrodynamic description for an isotropic fluid is extended to include the displacement field u, reflecting the freezing of the local structures in an amorphous solid. The fluctuating nonlinear equations for the set of hydrodynamic variables including u has been obtained. The role of u is manifested through its longitudinal part, i.e., \ensuremath{\nabla}\ensuremath{\cdot}u, in terms of which we define the variable c(x,t). It refers to the diffusion of the free volume or vacancies, signifying configurational rearrangements in the amorphous solid. The analysis here shows that one recovers the earlier result obtained by Das and Mazenko [Phys. Rev. A 34, 2265 (1986)] for mode c…
In situobservation of the formation, diffusion, and reactions of hydrogenous species inF2-laser-irradiatedSiO2glass using a pump-and-probe technique
2006
We quantitatively studied the formation, diffusion, and reactions of mobile interstitial hydrogen atoms $({\mathrm{H}}^{0})$ and molecules $({\mathrm{H}}_{2})$ in ${\mathrm{F}}_{2}$-laser-irradiated silica $(\mathrm{Si}{\mathrm{O}}_{2})$ glass between 10 and $330\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Two key techniques were used: single-pulse ${\mathrm{F}}_{2}$ laser photolysis of silanol (SiOH) groups to selectively create pairs of ${\mathrm{H}}^{0}$ and oxygen dangling bonds (nonbridging oxygen hole centers, NBOHC), and in situ photoluminescence measurements of NBOHCs to monitor their reactions with ${\mathrm{H}}^{0}$ and ${\mathrm{H}}_{2}$ as a function of time and temperature. A smalle…
Corrigendum: Fabrication and heating rate study of microscopic surface electrode ion traps
2012
We report heating rate measurements in a microfabricated goldon-sapphire surface electrode ion trap with a trapping height of approximately 240 μm. Using the Doppler recooling method, we characterize the trap heating rates over an extended region of the trap. The noise spectral density of the trap falls in the range of noise spectra reported in ion traps at room temperature. We find that during the first months of operation, the heating rates increase by approximately one order of magnitude. The increase in heating rates is largest in the ion-loading region of the trap, providing a strong hint that surface contamination plays a major role for excessive heating rates. We discuss data found i…
Understanding the glass transition and the amorphous state of matter: can computer simulation solve the challenge?
1999
The glass transition of supercooled fluids is one of the big puzzles of condensed matter physics, because there occurs a dramatic slowing down (the viscosity η can increase from about η = 1 Poise at the melting transition to η 10 13 Poise at the glass transition temperature T g ), but one hardly sees any accompanying change in the static structure. Theoretical concepts are very controversial - e.g., the Gibbs-di Marzio theory attributes glassy freezing to an underlying entropy catastrophe (the entropy of the supercooled fluid would fall below the crystal entropy at the Kauzmann temperature T 0 T g . Computer simulations offer the advantage that atomistically detailed information on structur…
EXAFS study of mixed nickel molybdenum oxide thin films at the Ni and Mo K-edges
2004
Mixed nickel molybdenum oxide thin films were produced by DC magnetron co-sputtering technique with the nickel content about 8, 16 and 25 at%. X-ray absorption spectroscopy at the Ni and Mo K-edges was used to study the local atomic structure in the films. The best-fit analysis of the EXAFS signals suggests that (i) the films are amorphous, except for the highest nickel content (25 at%), at which a segregation of NiO phase was observed; (ii) nickel and molybdenum atoms are octahedrally coordinated by oxygen atoms. Opposite to the NiO6 octahedra, the MoO6 octahedra are strongly distorted, that results in an existence of two groups of oxygen atoms—four nearest at B1.76 ( A and two distant at …
Surface relief grating formation in amorphous As40S15Se45 and As2S3 films under 0.532 μm wavelength illumination
2014
In this research we have studied the influence of λ = 0.532 μm laser light illumination on the formation and properties of surface relief gratings in amorphous As2S3 and As40Se15Se45 films, as well as a bulk As2S3 sample. The surface relief grating formation was studied for a wide range of grating periods (∼1 – ∼80 μm) for the variable thicknesses of the samples. The examination of the relief depth, Δh, and its dependence on the grating period at constant exposures shows that the impact of sample thickness could manifest itself as a shift in the optimal grating period at holographic surface relief formation (As2S3) and affect the process itself.
The dynamics of sodium in sodium disilicate: Channel relaxation and sodium diffusion
2001
We use molecular dynamics computer simulations to study the dynamics of amorphous (Na_2O)2(SiO_2). We find that the Na ions move in channels embedded in a SiO_2 matrix. The characteristic distance between these channels gives rise to a prepeak in the structure factor at around q=0.95 A^-1. The dynamics of sodium is given by a fast process which can be seen in the incoherent scattering function and a slow process which is seen in the coherent function. The relaxation time of the latter coincides with the alpha-relaxation time of the matrix. The Kohlrausch exponent of the fast process for q>1.6 A^1 is the same as the von Schweidler exponent for the slow one, demonstrating that the two proc…
Isotropic Chiral Acoustic Phonons in 3D Quasicrystalline Metamaterials.
2020
International audience; The elastic properties of three-dimensional (3D) crystalline mechanical metamaterials, unlike those of amorphous structures, are generally strongly anisotropic—even in the long-wavelength limit and for highly symmetric crystals. Aiming at isotropic linear elastic wave propagation, we therefore study 3D periodic approximants of 3D icosahedral quasicrystalline mechanical metamaterials consisting of uniaxial chiral metarods. Considering the increasing order of the approximants, we approach nearly isotropic effective speeds of sound and isotropic acoustical activity. The latter is directly connected to circularly polarized 3D metamaterial chiral acoustic phonons—for all …
Sound attenuation and anharmonic damping in solids with correlated disorder
2010
We study via self-consistent Born approximation a model for sound waves in a disordered environment, in which the local fluctuations of the shear modulus G are spatially correlated with a certain correlation length The theory predicts an enhancement of the density of states over Debye's omega(2) law (boson peak) whose intensity increases for increasing correlation length, and whose frequency position is shifted downwards as lg. Moreover, the predicted disorder-induced sound attenuation coefficient r(k) obeys a universal scaling law F(k) = f (ke) for a given variance of G. Finally, the inclusion of the lowest-order contribution to the anharmonic sound damping into the theory allows us to rec…
Spherulite formation in a ?noncrystalline? two-dimensional hydrogen-bond assembly
1996
4-Urazoyl benzoic acid groups 1 are attached as terminal end group to an oligoisobutene. According to wide-angle X-ray scattering the material is amorphous. Differential scanning calorimetry, small-angle X-ray scattering, transmission electron microscopy, and polarizing microscopy show that the polar head groups form ordered two-dimensional assemblies which organize into spherulites. Temperature-dependent SAXS measurements and the d.s.c. analysis give a close insight into the order-disorder (“melting”) process of the two-dimensional clusters which form macroscopic spherulites. The order-disorder transition of the clusters is closely related to the dynamics and order of the polyisobutene cha…