Amorphous Media Research Articles

Dislocation-Driven Formation of Oriented Macroperiodic Metastructures of Curved Single Crystal Lattices in Glass.

Single crystals fabricated in glass by localized heating can develop uniquely deformed lattices stabilized by the surrounding amorphous medium. The development of lattice curvature appears to be intrinsic to the crystal growth process in some systems, while the result of the locally changing crystallography in others. In this work, a model laser-fabricated rotating lattice Sb2S3 crystal grown in stoichiometric glass is used to demonstrate fabrication of novel macroperiodic metastructures that utilize intrinsic lattice curvature superimposed with subtle crystallographic influences. The limited availability of slip systems drives the lattice curvature magnitude to vary with crystal growth direction, maximizing for lattices aligned with the predominant Burgers vector along with corresponding increases in dislocation density. Misaligned lattice orientations form smaller secondary lattice curvatures arising from misaligned Burgers vectors with further elastic contributions. Over extended crystal growth, these secondary components align the lattice to rotate about either the <001> or <010> crystal axes forming repeating metastructures of lattice orientation with periodicity 20-160 microns in length. The mechanistic approach used in this work may be expanded to other systems with known slip systems to better understand and design macroperiodic metastructures.

Modeling of fluence-dependent hole-burned spectra and hole-growth kinetics using multiple two-level system model.

Numerical formalism is presented that perfectly describes resonant low-temperature hole-burned spectra (including zero-phonon holes, ZPHs) and spectral hole-growth dynamics of Al-phthalocyanine tetrasulphonate embedded in hyperquenched glassy water films over more than seven orders of fluence magnitude (0.4 µJ/cm2-5.9 J/cm2). Frequency changes during spectral hole-burning (HB) are traditionally explained with the help of a single extrinsic two-level-system (TLSext) associated with impurity molecules. The new multiple two-level system (n-TLSext) models and data analysis presented in this work show that each chromophore in an amorphous medium can couple with multiple independent TLSext, which maintain perfect photo-memory, allowing a full return of the photoproduct to the initial ("preburn") state. Modeling reveals that the experimentally observed narrow photoproduct peak at higher energies, in close vicinity of the zero-phonon hole (ZPH), reflects a dynamical feature of the HB process populating so-called "terminal" states (states that do not interact with laser excitation). Within the n-TLSext model, each chromophore possesses multiple possibilities to create a photoproduct when in interaction with the burning laser, i.e., chromophores can interact with burning laser-light multiple times until reaching the terminal states. Due to phonon-assisted absorption, terminal states are typically at higher energies than the ZPH, in agreement with the hole burned spectra reported for many molecules embedded in various amorphous solids. However, many HB systems reveal both blue- (high-energy) and red-shifted (low-energy) antiholes (i.e., photoproducts). We suggest that future modeling of resonant holes in various proteins using our n-TLSext model will provide more insight on the complexity of the protein energy landscape.

Confined fluid dynamics in a viscoelastic, amorphous, and microporous medium: Study of a kerogen by molecular simulations and the generalized Langevin equation.

We combine the use of molecular dynamics simulations and the generalized Langevin equation to study the diffusion of a fluid adsorbed within kerogen, the main organic phase of shales. As a class of microporous and amorphous materials that can exhibit significant adsorption-induced swelling, the dynamics of the kerogen's microstructure is expected to play an important role in the confined fluid dynamics. This role is investigated by conducting all-atom simulations with or without solid dynamics. Whenever the dynamics coupling between the fluid and solid is accounted for, we show that the fluid dynamics displays some qualitative differences compared to bulk fluids, which can be modulated by the amount of adsorbed fluid owing to adsorption-induced swelling. We highlight that working with the memory kernel, the central time correlation function of the generalized Langevin equation, allows the fingerprint of the dynamics of the solid to appear on that of the fluid. Interestingly, we observe that the memory kernels of fluid diffusion in kerogen qualitatively behave as those of tagged particles in supercooled liquids. We emphasize the importance of reproducing the velocity-force correlation function to validate the memory kernel numerically obtained as confinement enhances the numerical instabilities. This route is interesting as it opens the way for modeling the impact of fluid concentration on the diffusion coefficient in such ultra-confining cases.

A novel prussian blue/polyaniline composite gas sensor for fast detection of ammonia

This study aims reporting the development of a gas sensor composite whose phases are Prussian blue (PB) and polyaniline (PANI). Structural characterization techniques confirmed the formation of the characteristic cubic phase of Prussian blue alone and in the composite. The morphology of the particles was uneven and the elemental analysis confirmed the characteristic constituents for PANI and Prussian blue. High-resolution images demonstrated the presence of Prussian blue in an amorphous polymer medium, indicating interaction between the phases. Sensor tests demonstrated fast response time for ammonia (∼150 s) and high sensitivity (4 ppm) under ambient temperature and pressure conditions. These results demonstrate the efficiency of the sensor formed in detecting ammonia even at very low concentrations.

A continuous phase-evolution model for cold and strain-induced crystallization in semi-crystalline polymers

The dynamic crystallization during extreme thermomechanical history under producing or service strongly influences the dimensional stability of the semi-crystalline thermoplastic polymers. To produce high-precision structural components, the proper thermomechanical history needs to be carefully designed to eliminate the crystallization-induced shrinkage. On the contrary, the rapidly developed four-dimensional (4D) printing technology tries to amplify the crystallization-induced shrinkage to directly produce the complex curvatures without supporting materials. However, the crystals formed at different deformation states might have different orientations, leading to an anisotropic residual deformation. Therefore, tracing of all crystals formed with different initial configurations is the key issue to ensure the geometric accuracy of both the high-precision and the deformable components. In this study, we developed a continuous phase-evolution model for both the cold and the strain-induced crystallization in semi-crystalline thermoplastics. The irreversible cold crystallization is analogized as the raindrop falling into the pool, and the reversible strain-induced crystallization is analogized as the nonequilibrium liquid-gas phase transformation. Using the continuous phase-evolution concept, the crystal growth is described by a series of continuously formed crystal phases sequentially added into the initial amorphous medium. Each newly formed crystal phase is in a stress-free state at the formation moment, and therefore the crystallization history coupled with the whole deformation history can be memorized. By introducing the oriented growth tensor representing the stress-free state of all formed crystals, the deformation-history dependent anisotropic crystallization and the corresponding residual deformation can be traced. The developed model is validated by comparing with the experimental data of the dynamic crystallization in amorphous poly l-lactide polymers under thermomechanical loading cycles. Finally, the predictive capability of the model is illustrated by several demonstrations, to show the influences of deformation-history dependent crystallization orientations and the corresponding anisotropic residual deformation.

Coulomb Spike Modelling of Ion Sputtering of Amorphous Water Ice

The effects of electronic excitations on the ion sputtering of water ice are not well understood even though there is a clear dependence of the sputtering yield on the electronic stopping power of high-energy ions. Ion sputtering of amorphous water ice induced by electronic excitations is modelled by using the Coulomb explosion approach. The momentum transfer to ionized target atoms in the Coulomb field that is generated by swift ion irradiation is computed. Positively charged ions produced inside tracks are emitted from the surface whenever the kinetic energy gained in the repulsive electrical field is higher than the surface binding energy. For that, the energy loss of deep-lying ions to reach the surface is taken into account in the sputtering yield and emitted ion velocity distribution. Monte Carlo simulations are carried out by taking into account the interactions of primary ions and secondary electrons (δ-rays) with the amorphous water ice medium. A jet-like anisotropic ion emission is found in the perpendicular direction in the angular distribution of the sputtering yield for normal incidence of 1-MeV protons. This directional emission decreases with an increasing incidence angle and vanishes for grazing incidence, in agreement with experimental data on several oxides upon swift ion irradiation. The role of the target material’s properties in this process is discussed.

Oxynitride Amorphous Carbon Layer for Electrically and Thermally Robust Bipolar Resistive Switching

AbstractAdvanced resistive random‐access memory (ReRAM) devices based on resistive switching (RS) have been intensely studied for future high‐density nonvolatile memory devices owing to their high scalability, simplified integration, fast operation, and ultralow power consumption. Among the recently considered active media, diverse carbon‐based media have emerged because of numerous benefits of simple chemical composition, desirable speed, and cost‐effective scalability. However, these media are still susceptible to undesirable reliability issues, including poor endurance and retention and uncontrollable operation voltage distribution. In this study, an oxynitride amorphous carbon active medium governed by appropriate nitrogen content during growth is introduced to facilitate high electrical stability, such as a distinct pulse endurance of more than 107 cycles, a high retention time of 105 s at 85 °C, and increased uniformity in the SET/RESET distribution with thermally robust RS stability even at a high annealing temperature of 400 °C. The findings are possibly the result of adapting an sp2–sp3 conversion nature assisted by the presence of pyridinic N or pyrrolic N as a substitution reaction.

Effect of Thermochemical Boronizing of Alumina Surface on the Borate Crystals Growth and Interaction with Nickel and Nickel Alloy

Wettability at the metal-ceramic interface is highly important for the development of modern composite materials. Poor wettability by metal melts restricts the use of alumina in protective metal matrix composite (MMC) coatings. In the present experimental study, the possibility to modify wetting properties of alumina by thermochemical surface boronizing was investigated. The results of SEM, EDS, XRD and XPS characterisation of surfaces revealed the formation of oxygen containing Al–B compounds identified as aluminium borates (Al18B4O33/Al4B2O9); no signs of non-oxide Al–B compounds were observed. The shape of the single splats deposited on the boronized alumina surface by the thermal spray and re-melted in the furnace revealed that significant wetting improvement by self-fluxing nickel alloy did not occur. However, the improvement of adhesion between the nickel/nickel alloy and Al2O3 surface was obtained due to formation of an intermediate layer consisting of B, O, Al and Si between the metal and ceramic surfaces at the presence of some silicon at the modified surfaces. The presented study demonstrates that the thermochemical boronizing of alumina in amorphous boron medium is a simple method to obtain a thin aluminium borate layer consisting of oriented nano-rod-like crystals, whose growing direction is predetermined by the orientation of the alumina grains’ faces at surface.

Single-crystal Li-rich layered cathodes with suppressed voltage decay by double-layer interface engineering

Despite lithium-rich layered oxides (LLO) are promising candidates for the next-generation cathode materials, the rapid voltage and capacity decay, caused by structural degradation, are primary challenges towards their real-world applications. Herein, via a facial and large-scale treatment method, a robust double layer (DL) cathode-electrolyte interphase (CEI), with outermost layer of amorphous Li3PO4 (LPO) and medium layer of LixNiyMn3-x-yO4 with disordered spinel structure, is uniformly introduced onto the surface of single-crystal Li1.2Ni0.2Mn0.6O2. The double-layer CEI effectively blocks the phase transition from the layered LLO structure into spinel and then rock salt, and thus relieves the voltage decay in cycling. Meanwhile, the CEI blocks the diffusion of TM-ions into the electrolyte and extra O release in cycling, since there are nearly no voids rich in defected rock-salt structure in their edges in the cycled DL-LLO. We further theoretically disclose that the defected rock-salt phase has indeed a high dissolvability of TM and the large irreversibility of O reactivity, which is an accelerator for the structural degradation in cycling. Accordingly, the problems of voltage decay and capacity fading of the modified DL-LLO are greatly relieved and with a voltage drop of only 0.83 mV per cycle and a capacity retention of 82.5 % over 300 cycles at 1 C. This work provides a guidance for effective surface treatment strategies in developing stable Li-rich layered cathodes with high capacity and cyclability.

A Leaky Integrate-and-Fire Neuron Based on Hexagonal Boron Nitride (h-BN) Monocrystalline Memristor

As a competitive candidate for artificial neurons, memristors have become the focus of intense research owing to their intrinsic ion migration tunability, enabling an authentic implementation of biomimicry. However, they still suffer from variability issues due to 3-D uncontrollable filament dynamics in an amorphous medium and modeling of switching dynamics underlying filament growth and rupture is still under investigation. In this work, we present volatile memristors that exhibit desired characteristics for neuromorphic computing with low performance variations utilizing a hexagonal boron nitride (h-BN) monocrystalline as a switching medium. Theoretical investigations assisted by the Monte Carlo simulation combined with experimentally detected <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> characteristics described that the electric field dominates the set process, whereas the Gibbs–Thomson interfacial energy minimization and heat dissipation influence the relaxation process mostly. Additionally, h-BN memristors with high switching uniformity provide an ideal hardware platform for credible neuron emulation and software identification of digital images.

Athermalized carrier multiplication mechanism for detectors using an amorphous silicon gain medium.

In this paper, we investigate the temperature sensitivity of gain and breakdown voltage of detectors based on cycling excitation process (CEP), an internal signal amplification mechanism found in amorphous silicon (a-Si). Changes in gain and breakdown voltage with temperature can result in pixel-to-pixel signal variation in a focal plane array and variations in photon detection efficiency for single photon detectors. We have demonstrated athermalized CEP detectors with their gain and breakdown voltage being nearly temperature independent from 200 K to 350 K, covering the temperature range for practical applications. The device appears to be more thermally stable than avalanche photodetectors (APDs) with different gain media such as Si, InP, InAlAs, etc. The excellent thermal stability of CEP detectors is attributed to the field-enhanced tunneling process for excitation of localized carriers into the mobile bands, which dominates over the phonon excitation process.

Third harmonic generation enhancement from silicon-based multilayer guided mode resonance structures under a conical mounting condition

We experimentally demonstrate more than four-orders of magnitude enhancement in third harmonic generation from an amorphous silicon layer as thin as 10 nm deposited above silicon nitride guided mode resonance (GMR) structures under a conical mounting condition using a rectangular aperture as a pupil plane mask for the fundamental excitation. The multilayer GMR structure studied here consists of shallow etched one-dimensional silicon dioxide gratings with a silicon nitride intermediate layer and an amorphous silicon nonlinear medium. Under conical mounting, by restricting the fundamental excitation angles along the grating vector direction, while retaining the angles supported by the objective lens along the grating lines, the resonances are made angle insensitive. The forward detected THG enhancement increases from 2860 in the absence of any pupil plane mask, with a uniform fundamental excitation angular span of 2.3° to 4740 and 1.7 × 104 in the presence of rectangular apertures that selectively reduce the excitation angular span along the grating vector direction to 0.86° and 0.43°, respectively. Conical mounting using rectangular aperture pupil masks to engineer the fundamental excitation is a promising approach to enhance nonlinear optical processes from angle sensitive GMR structures.

On the possible mechanism of external infrasonic mechanical stimulating the process of formation of nanocrystals in an amorphous metal film

A kinetic model, a physical reason and a condition for stimulated by external infrasonic mechanical vibrations of the formation of nanocrystals in an amorphous metal film. The nanostructural elements of the amorphous medium are responsible for these processes: locally ordered nanoclusters and nanoregions containing free volume, which contain two-level systems. When glass is deformed, two-level systems are excited, due to which they make a significant contribution to inelastic deformation, structural relaxation, formation of nanoclusters and nanocrystals. The physical mechanism of nanocrystallization of metallic glass during mechanical exposure includes, in addition to the mechanism of local thermal fluctuations, also athermal mechanism of quantum tunneling of atoms or atomic groups stimulated by inelastic deformation. Keywords: Kinetic model, amorphous metal film, nanocrystals, infrasonic mechanical vibrations.

Infrasonic Nanocrystal Formation in Amorphous NiTi Film: Physical Mechanism, Reasons and Conditions

The physical mechanism, reasons and conditions of nanocrystal formation in an amorphous NiTi metal film, stimulated by infrasonic action, are formulated. Nanostructural elements of an amorphous medium (relaxation centers) containing disordered nanoregions with two-level systems are considered to be responsible for this process. When exposed to infrasound, a large number of two-level systems are excited, significantly contributing to inelastic deformation and the formation of nanocrystals. The physical mechanism of the nanocrystallization of metallic glass under mechanical action includes both local thermal fluctuations and the additional quantum tunneling of atoms stimulated by shear deformation. A crystalline nanocluster appears as a result of local atomic rearrangement growing increasingly exposed to infrasound. It is possibly unstable in the absence of infrasound. When the radius of the nanocluster reaches a critical value, a potential well appears, in which a conducting electron is localized to form a phason (stable nanocrystal). Estimated values of the phason’s radius and the depth of the nanometer potential well is about 0.5 nm and 1 eV, respectively. It forms a condition of stable phason formation. The occurrence of the instability of the amorphous state and following transformation to the nanostructured state is based on the accumulation of the potential energy of inelastic deformation to a critical value equal to the latent heat of the transformation of the amorphous state into the nanostructured state.

Correlation between multiple scattering angle and ionization energy loss for fast electrons

A correlation between the angle of multiple scattering and the ionization energy loss for relativistic electrons in an amorphous medium is computed by solving the combined transport equation. The correlation is found to be the most pronounced at deflection angles larger than typical, reflecting the underlying single-scattering kinematical correlation, but is also sizable at typical deflection angles, where the width of the angular distribution increases with the increase of the energy loss. The mean energy loss as a function of the deflection angle is calculated. It grows quadratically both at small and at large angles, but the proportionality coefficient at large angles is greater than at small ones.

Physical, optical, structural and thermoluminescence behaviour of borosilicate glasses doped with trivalent neodymium ions

Trivalent neodymium ion (Nd 3+ ) activated sodium magnesium borosilicate glasses having composition (60 – x) B 2 O 3 –20SiO 2 – 10 Na 2 O – 10 MgO – x Nd 2 O 3 (where x = 0, 0.04, 0.08, 0.12, 0.16, 0.2 mol%) were synthesized by melt quenching method to study the structural, physical, optical and thermoluminescence behaviour. The physical parameters like molar volume, density, molecular weight, average boron-boron separation, field strength, ion concentration, polaron radius, interionic distance, oxygen packing density and optical basicity were obtained. The structural information was acquired through Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). XRD spectra suggested the amorphous nature of present media and FTIR spectra highlighted the bands present in this amorphous media. To study the optical parameters such as direct band gap, indirect band gap, refractive index, optical dielectric constant, reflection loss, dielectric constant, molar refractivity, molar polarizability, metallization, electronic polarizability, oxide ion polarizability, transmission coefficient, energy band gap based metallization criterion, refractive index based metallization criterion, non-linear optical susceptibility, non-linear refractive index and Urbach model, optical absorption spectra was recorded in the range of 190–1100 nm. These glasses were irradiated with gamma rays to study the thermoluminescence glow curve at six different doses such as 50 Gy, 100 Gy, 500 Gy, 1 kGy, 5 kGy and 10 kGy. The trapping or kinetic parameters like frequency factor, activation energy and kinetic order were also studied by using peak shape method. Linear dose response curve indicates that the 59.92 B 2 O 3 – 20 SiO 2 – 10 Na 2 O – 10 MgO – 0.08 Nd 2 O 3 sample can be considered as a potential candidate for radiation dosimetry. • Fabrication of Trivalent neodymium ion (Nd 3+ ) activated sodium magnesium borosilicate glasses. • The density increases from 1.616 to 2.079 (gcm −3 ) with increase in Nd 2 O 3 concentration from 0 to 0.2 mol%. • The direct and indirect band gap energy values decrease from 3.408 to 3.253 eV and 1.537–1.446 eV respectively with increase in content of Nd 2 O 3 . • 59.92 B 2 O 3 – 20 SiO 2 – 10 Na 2 O – 10 MgO – 0.08 Nd 2 O 3 sample can be considered as a potential candidate for radiation dosimetry.

О возможном механизме внешнего инфразвукового механического стимулирования процесса формирования нанокристаллов в аморфной металлической пленке

A kinetic model, a physical reason and a condition for stimulated by external infrasonic mechanical vibrations of the formation of nanocrystals in an amorphous metal film. The nanostructural elements of the amorphous medium are responsible for these processes: locally ordered nanoclusters and nanoregions containing free volume, which contain two-level systems. When glass is deformed, two-level systems are excited, due to which they make a significant contribution to inelastic deformation, structural relaxation, formation of nanoclusters and nanocrystals. The physical mechanism of nanocrystallization of metallic glass during mechanical exposure includes, in addition to the mechanism of local thermal fluctuations, also athermal mechanism of quantum tunneling of atoms or atomic groups stimulated by inelastic deformation.

Формирование кремниевых нанокластеров при диспропорционировании моноокиси кремния

In this work, the processes of disproportionation of solid-phase silicon monoxide, accompanied by the formation of nanocrystalline silicon precipitates in the medium of amorphous SiOx suboxide (initial composition SiO0.9), have been studied. Based on the data of X-ray diffraction analysis and transmission electron microscopy, the dynamics of changes in the amount, concentration and size of phase precipitates of silicon with an increase in the temperature of isochronous annealing from 800 °C to 1200 °C is traced. It was found that with a monotonic increase in the total mass of the precipitated silicon, the number of its crystallization centers per unit volume nonmonotonically depends on temperature. The activation energy of diffusion of silicon atoms in the SiOx matrix was determined to be Ea1= 1.64 eV, and the activation energy of their transfer from the formed precipitates to the growth medium of SiOx was Ea2 = 2.38 eV. Anisotropic deformation of silicon crystallites precipitated during the disproportionation of SiO has been revealed for the first time. This phenomenon is associated with the difference in the specific volumes of the separated phases and the anisotropy of the growth rate of silicon precipitates formed in a solid amorphous medium.

The eikonal approximation of the scattering theory for fast charged particles in a thin layer of crystalline and amorphous media

On the basis of the eikonal approximation of quantum scattering theory, the problem of fast charged particle scattering in a thin crystal when particles fall along one of its planes of atoms and in a thin layer of an amorphous matter is considered. It is shown that the scattering cross section in this problem for parameters which are beyond the scope of application of the Born perturbation theory, differs significantly from the corresponding result of the Born approximation. In this case, the scattering in the transverse to the plane direction is determined mainly by a continuous plane potential which is widely used in the channeling theory. The scattering of a particle in the longitudinal direction has features of scattering in a two-dimensional amorphous medium with the inhomogeneous density of atoms. The concept of a continuous potential of the crystal plane of atoms in the suggested approach appears automatically.

‘15 Days to Slow the Spread’: Covid‐19 and Collective Resilience

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