SEARCH · Searcharxiv

Results for “cond-mat.mtrl-sci”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources

arXiv2013

Copper Replaces Tin: A Copper based Gelling Catalyst for Poly-Urethane from Discarded Motherboard

A discarded motherboard based eco-friendly copper catalyst has been programmed to replace the industrially used tin based catalyst DBTDL. The catalyst has been characterized by UV-Vis spectroscopy, FT-IR and TEM. Using the catalyst reaction conditions is optimized and under the optimized condition, both polyurethane and polyurethane foam are prepared, thus proving the generality of the catalyst to be used in industries. A possible mechanism has also been proposed.

cond-mat.mtrl-sci↗

arXiv2013

Seeding ice growth at ambient conditions using nano graphene oxide

Water wetting on a hydrophobic surface at ambient conditions is disallowed by the nonpolar nature of the surface and high vapor pressure of water. However, the presence of sub-millimeter sized hydrophilic patches allows the waxy wings of desert beetles to become wettable by morning mist. Here, we show that a sprinkle of graphene oxide nanoflakes (nanoGOs) is effective in condensing water nanodroplets and seeding ice epitaxy on graphite at ambient conditions. By controlling relative humidity and nanoGO density, we are able to study the formation of a complete ice wetting layer on a time scale of 20 hours. This presents an unprecedented opportunity to visualize ice nucleation and growth in real time using non-contact atomic force microscopy. The stages of crystallization, as proposed by Ostwald in 1897, is fully unfolded at a microscopic level for the first time. We obtain real-time imaging of sequential phase transition from amorphous ice to a transient cubic ice Ic stage and finally to the stable hexagonal ice Ih. Most interestingly, we discover that ice nucleation and growth can be influenced by modifying the functional groups of nanoGO, and by intermolecular hydrogen-bonding between nanoGOs. This affords a strategy to control heterogenous ice nucleation and snow crystal formation.

cond-mat.mes-hall↗

arXiv2013

On the microscopic origin of the magneto-electronic phase separation in Sr doped LaCoO3

The nanoscopic magneto-electronic phase separation in doped La1-xSrxCoO3 perovskites was studied with local probes. The phase separation is directly observed by Mössbauer spectroscopy in the studied doping range of 0.05 <= x <= 0.25 both at room-temperature as well as in the low temperature magnetic phase. Extended with current synchrotron based X-ray spectroscopies, these data help to characterize the volume as well as the local electric and magnetic properties of the distinct phases. A simple model based on a random distribution of the doping Sr ions describes well both the evolution of the separated phases as well as the variation of the Co spin state. The experiments suggest that Sr doping initiates small droplets and a high degree of doping driven cobalt spin-state transition, while the Sr-free second phase vanishes rapidly with increasing Sr content.

cond-mat.str-el↗

arXiv2013

Barrier Height Formation in Organic Blends / Metal Interfaces: Case of (TTF-TCNQ) / Au(111)

The interface between the tetrathiafulvalene / tetracyanoquinodimethane (TTFTCNQ) organic blend and the Au(111) metal surface is analyzed by Density Functional Theory calculations, including the effect of the charging energies on the molecule transport gaps. Given the strong donor and acceptor characters of the TTF and TCNQ molecules, respectively, there is a strong intermolecular interaction, with a relatively high charge transfer between the two organic materials. We find that the TCNQ LUMO peak is very close to the Fermi level; due to the interaction with the metal surface, the organic blend molecular levels are broadened, creating an important induced density of interface states. We show that the interface energy level alignment is controlled by the charge transfer between TTF, TCNQ and Au, and by the molecular dipoles created in the molecules because of their deformations when adsorbed on Au(111); in particular the TCNQ molecules present a bent adsorption geometry with the N atoms bonded to the Au surface. A generalization of the Unified-IDIS model, to explain how the interface energy levels alignment is achieved for the case of this blended organic layer, is presented by introducing matrix equations associated with the Charge Neutrality Levels of both organic materials and with their intermixed screening properties.

cond-mat.mtrl-sci↗

arXiv2013

PVC composite internal process of current-voltage time delay formation and conductivity levels lifetimes origin

In the previously described model of interpreting the numerous results in the switching states of the conduction in the films of PVC composites [1,2] was noted the need to involve hopping mechanism and percolation theory to explain the phenomenon of giant jumps conductivity, just as was done for the interpretation of such jumps for disordered semiconductor films. It was also shown that to explain the totality of spontaneous and stimulated transitions between states of the conduction in PVC composites requires the existence of an internal process that is able to produce a fixed observable current - voltage delay and switching electrical conductivity levels lifetime. In this paper one of the possible relaxation processes that lead to the emergence of the delay time, and the occurrence of spontaneous and stimulated transitions sample conductivity of nanocomposites PVC is presented. In particular, as a mechanism for determining time delay and lifetimes of the conduction states the reaction of dehydrochlorination is proposed, which should be reversible in case when HCl molecules separated from macromolecule physically can not "travel" far from "their place" in the macromolecule, as it just takes place within a local PVC free volume. In a frame of developed model all previously observed and called "anomalous" electrical phenomena receive a reasonable and predictable behavior.

cond-mat.mtrl-sci↗

arXiv2013

A short circuit in the electrical cables with polymer insulation: a new look at the cause of its occurrence and non-traditional ways of solving the problem

It is known that most of the electrical cables use as insulation compositions based on polyvinyl chloride. Like most polymers, the latter is quite sensitive to thermal aging, which is not without reason, to be one of the main causes of the various types of faults in the polymeric insulation, leading eventually to a short circuit and fire. On the example of the most common polymer insulator-PVC subjected to preliminary partial thermolysis, simulating the process of accelerated aging, we for the first time show that in this case as a result of the aging process, the electrical conductivity of PVC can acquire abnormal (not obeying Ohm's law) character. In this case, transitions from a state with normal (low) conductivity of PVC into the state with an ab-normally high conductivity was clearly observed, being spontaneous uncontrollable process. Es-pecially the large-scale nature of these changes allowing easily transferring polyvinylchloride from a state of typical dielectric (insulator) in a class of conductors attracts attention.). Thus, an-other one of the most important features of a short circuit in the PVC insulation is opened. It is noted that the reduction of fire hazards in this case (by the maximum possible elimination of the phenomenon of short circuit due to thermal aging of polymeric insulation) should be preventive in nature, as the most effective, simple and convenient way.

cond-mat.mtrl-sci↗

arXiv2013

Spinodal Gap Dependence on Size and Boundary Reaction Rate for Intercalation in Nanoparticles

Using mathematical model for intercalation dynamics in phase-separating materials proposed in (Singh, G. K.; Ceder, G.; Bazant, M. Z. Electrochimica Acta 2008, 53, 7599) and developed further in (Burch, D.; Bazant, M. Z. Nano Letters 2009, 9, 3795) we found that the spinodal gap generally shrinks as the particle size decreases. We also got that for some range of boundary reaction rate parameter and particle size the concentration spinodal gap is not continuous but it has stable "islands" where no spinodal decomposition is expected. In fact the presence of infinitesimally small boundary reaction rate parameter will destabilize nano particle even for infinitesimal length of particle. But then further continuous raise of this parameter will stabilize the system till some limit. We made careful analysis to study the dependence of spinodal decomposition on boundary reaction rate and size parameters which can be used for LiFePO4 battery material application. Our model predicted that for nanoparticles having size less than diffusion length and enough small boundary reaction rate spontanious charge or discharge will occur.

cond-mat.mtrl-sci↗

arXiv2013

Flaw-driven Failure in Nanostructures

Understanding failure in nanomaterials is critical for the design of reliable structural materials and small-scale devices that have components or microstructural elements at the nanometer length scale. No consensus exists on the effect of flaws on fracture in bulk nanostructured materials or in nanostructures. Proposed theories include nanoscale flaw tolerance and maintaining macroscopic fracture relationships at the nanoscale with virtually no experimental support. We explore fracture mechanisms in nanomaterials via nanomechanical experiments on nanostructures with pre-fabricated surface flaws in combination with molecular dynamics simulations. Nanocrystalline Pt cylinders with diameters of 120 nm with intentionally introduced surface notches were created using a template-assisted electroplating method and tested in uniaxial tension in in-situ SEM. Experiments demonstrate that 8 out of 12 samples failed at the notches and that tensile failure strengths were 1.8 GPa regardless of whether failure occurred at or away from the flaw. These findings suggest that failure location was sensitive to the presence of flaws, while strength was flaw-insensitive. Molecular dynamics simulations support these observations and show that incipient plastic deformation commences via nucleation and motion of dislocations in concert with grain boundary sliding. We postulate that such local plasticity reduces stress concentration ahead of the flaw to levels comparable with the strengths of intrinsic microstructural features like grain boundary triple junctions, a phenomenon unique to nano-scale solids that contain an internal microstructural energy landscape. This mechanism causes failure to occur at the weakest link, be it an internal inhomogeneity or a surface feature with a high local stress.

cond-mat.mtrl-sci↗

arXiv2013

Microstructure evolution and heterogeneous nucleation in ternary Al-Cu-Ni alloys

The simulations of the solidification of ternary Al-Cu-Ni alloys by means of a general multi-phase-field model for an arbitrary number of phases reveal that the real microstructure can be generated by coupling the real thermodynamic parameters of the phases and the evolution equations. The stability requirements on individual interfaces for model functions guarantee an absence of "ghost" phases in a $n$-dimensional phase-field space. The special constructed thermal noise terms disturb the stability and can produce the heterogeneous nucleation of product phases in accordance to the energetic and concentration conditions. Of particular interest is that in triple points the nucleation of the forth phase occurs without additional noise. Another observation is the growth of the eutectic-like or peritectic-like structure in various alloys.

cond-mat.mtrl-sci↗

arXiv2013

Novel linear algebraic theory and one-hundred-million-atom electronic structure calculation on the K computer

A novel linear-algebraic algorithm, multiple Arnoldi method, was developed in an interdisciplinary study between physics and applied mathematics and realized one-hundred-million-atom (100-nm-scale) electronic state calculations on the K computer. The algorithms are Krylov-subspace solvers for generalized shifted linear equations and were implemented in our order-N calculation code ELSES (http://www.elses.jp/). Moreover, a method for calculating eigen states is presented as a theoretical extension.

cond-mat.mtrl-sci↗

arXiv2013

Avalanches in 2D Dislocation Systems: Plastic Yielding is not Depinning

We study the properties of strain bursts (dislocation avalanches) occurring in two-dimensional discrete dislocation dynamics models under quasistatic stress-controlled loading. Contrary to previous suggestions, the avalanche statistics differs fundamentally from predictions obtained for the depinning of elastic manifolds in quenched random media. Instead, we find an exponent τ=1 of the power-law distribution of slip or released energy, with a cut-off that increases exponentially with the applied stress and diverges with system size at all stresses. These observations demonstrate that the avalanche dynamics of 2D dislocation systems is scale-free at every applied stress and, therefore, can not be envisaged in terms of critical behavior associated with a depinning transition.

cond-mat.mtrl-sci↗

arXiv2013

Dynamics of Self-retracting motion of graphite micro-flakes

A sheared microscopic graphite mesa retracts spontaneously to minimize interfacial energy. Using an optical knife-edge technique, we report comparative measurements of the speeds of such self-retracting motion (SRM) in air and low vacuum (about 1 Pa). We found that the retracting speed Vm of SRM is almost the same in the two environments at both room temperature and high temperature (above 150 celsius degree). We also extract the acceleration of the SRM, and found some typical behaviors. In the high speed range (above 5 m/s), the acceleration decreases linearly with the logarithm of the SRM speed. We attribute this phenomenon to the thermally activated sliding process in SRM. In the low speed region (between 0.1 m/s and 1 m/s), the acceleration increases linearly with the logarithm of the SRM speed.

cond-mat.mtrl-sci↗

arXiv2013

Electric moulding of dispersed lipid nanotubes into a nanofluidic device

Hydrophilic nanotubes formed by lipid molecules have potential applications as platforms for chemical or biological events occurring in an attolitre volume inside a hollow cylinder. Here, we have integrated the lipid nanotubes (LNTs) by applying an AC electric field via plug-in electrode needles placed above a substrate. The off-chip assembly method has the on-demand adjustability of an electrode configuration, enabling the dispersed LNT to be electrically moulded into a separate film of parallel LNT arrays in one-step. The fluorescence resonance energy transfer technique as well as the digital microscopy visualised the overall filling of gold nanoparticles up to the inner capacity of an LNT film by capillary action, thereby showing the potential of this flexible film for use as a high-throughput nanofluidic device where not only is the endo-signalling and product in each LNT multiplied but also the encapsulated objects are efficiently transported and reacted.

cond-mat.soft↗

arXiv2013

Tailoring Plasmonic Metamaterials for DNA Molecular Logic Gates

Structural and functional information encoded in DNA combined with unique properties of nanomaterials could be of use for the construction of novel biocomputational circuits and intelligent biomedical nanodevices. However, at present their practical applications are still limited by either low reproducibility of fabrication, modest sensitivity, or complicated handling procedures. Here, we demonstrate the construction of label-free and switchable molecular logic gates that use specific conformation modulation of a guanine- and thymine- rich DNA, while the optical readout is enabled by the tunable alphabetical metamaterials, which serve as a substrate for surface enhanced Raman spectroscopy (MetaSERS). By computational and experimental investigations, we present a comprehensive solution to tailor the plasmonic responses of MetaSERS with respect to the metamaterial geometry, excitation energy, and polarization. Our tunable MetaSERS-based DNA logic is simple to operate, highly reproducible, and can be stimulated by ultra-low concentration of the external inputs, enabling an extremely sensitive detection of mercury ions.

cond-mat.mtrl-sci↗

arXiv2013

Local Electron Field Emission Study of Two-dimensional Carbon

A systematic field-emission study has been carried out on different types of two-dimensional carbons in ultrahigh vacuum with the cathode-anode distance ranging from near-contact to about 124 nm. An analytical model has been developed to explain the increase of field enhancement factor with the cathode-anode distance. Good agreement has been achieved between the calculation results and experimental data, including those reported in literature. The work provides useful insights into the characteristics of field emission from two-dimensional carbon.

cond-mat.mes-hall↗

arXiv2013

Coulomb interaction and charge neutrality: Pariser, Parr and Pople Hamiltonian versus the Extended Hubbard Hamiltonian

The Extended Hubbard Hamiltonian used by the Condensed Matter community is nothing but a simplified version of the Pariser, Parr and Pople Hamiltonian, well established in the Quantum Chemistry community as a powerful tool to describe the electronic structure of π-conjugated planar Polycyclic Aromatic Hydrocarbons (PAH). We show that whenever the interaction potential is non-local, unphysical charge inhomogeneities may show up in finite systems, provided that electrons are not neutralized by the ion charges. Increasing the system size does not solve the problem when the potential has an infinite range, and for finite range potentials these charge inhomogeneities become slowly less important as the potential range decreases and/or the system size increases. Dimensionality does also play a major role. Examples in bi-dimensional systems, such as planar PAH and graphene, are discussed to some extent.

cond-mat.mtrl-sci↗

arXiv2013

A Nonlinear Theory of Prestressed Elastic Stick-and-Spring Structures

The discrete modeling of a large class of mechanical structures can be based on a stick-and-spring concept. We here present a stick-and-spring theory with potential application to the statics and the dynamics of such nanostructures as graphene, carbon nanotubes, viral capsids, and others. A key feature of our theory is its geometrical nonlinearity: we combine exactly defined strain measures with a general linear stress response; another, rarely found feature is a careful account of prestress states. A linear version is firstly proposed, where attention is restricted to study small displacements from an unstressed reference placement. Next, a theory linearized about a prestressed (preloaded or not) placement is displayed, which is based on a careful analysis of the tangent stiffness operator and its two parts, the elastic and prestress stiffness operators. Finally, two examples are proposed and solved; when an analytical solution is of prohibitive complication, numerical solutions are given, by the use of a specifically implemented `stick-and-spring' code.

cond-mat.mtrl-sci↗

arXiv2013

Melting curve of face-centred-cubic nickel from first principles calculations

The melting curve of Ni up to 100 GPa has been calculated using first principles methods based on density functional theory (DFT). We used two complementary approaches: i) coexistence simulations with a reference system and then free energy corrections between DFT and the reference system, and ii) direct DFT coexistence using simulation cells including 1000 atoms. The calculated zero pressure melting temperature is slightly underestimated at $1637 \pm 10$ K (experimental value is 1728 K), and at high pressure is significantly higher than recent measurements in diamond anvil cell experiments [Phys. Rev. B {\bf 87}, 054108 (2013)]. The zero pressure DFT melting slope is calculated to be $30 \pm 2$ K, in good agreement with the experimental value of 28 K.

cond-mat.mtrl-sci↗