Possible charge ordering and anomalous transport in graphene/graphene quantum dot heterostructure.

Observations of superconductivity and charge density waves (CDW) in graphene have been elusive thus far due to weak electron-phonon coupling (EPC) interactions. Here, we report a unique observation of anomalous transport and multiple charge ordering phases at high temperatures (T1∼213K,T2∼325K) in a 0D-2D van der Waals (vdW) heterostructure comprising of single layer graphene (SLG) and functionalized (amine) graphene quantum dots (GQD). The presence of functionalized GQD contributed to charge transfer with shifting of the Dirac point ∼ 0.

WO Nanowhiskers Decorating SiO Nanofibers: Lessons from SEM/TEM Growth to Large Scale Synthesis and Fundamental Structural Understanding.

Tungsten suboxide WO nanowhiskers are a material of great interest due to their potential high-end applications in electronics, near-infrared light shielding, catalysis, and gas sensing. The present study introduces three main approaches for the fundamental understanding of WO nanowhisker growth and structure. First, WO nanowhiskers were grown from γ-WO/-SiO nanofibers in a scanning electron microscope (SEM) utilizing a specially designed microreactor (μReactor).

Impact of d-states on transition metal impurity diffusion in TiN.

In this work, we studied the energetics of diffusion-related quantities of transition-metal impurities in TiN, a prototype ceramic protective coating. We use ab-initio calculations to construct a database of impurity formation energies, vacancy-impurity binding energies, migration, and activation energies of 3d and selected 4d and 5d elements for the vacancy-mediated diffusion process. The obtained trends suggest that the trends in migration and activation energies are not fully anti-correlated with the size of the migration atom.

Long-Range Magnetic Order in Nickel Hydroxide-Functionalized Graphene Quantum Dots.

In this work, we demonstrate the prospect of chemically synthesizing transition metal (Ni) doped magnetic graphene quantum dots (GQDs) with the sole aim of shedding light on their magnetic properties. Our results show that adsorption of nickel hydroxide on predominantly paramagnetic GQDs reveals antiferromagnetic ordering in the M-T profile around 10 K with change of the spin exchange coupling deviating from = 1/2 to = 1, mainly arising from the d-p mixing hybridization between the p orbital of carbon from the GQD and the d orbital of Ni. Furthermore, our results are well complemented by simulations showing asymmetry of the up and down spins around the Fermi level for nickel hydroxide-doped GQDs with long-range spin polarization.

Probing the charge transfer and electron-hole asymmetry in graphene-graphene quantum dot heterostructure.

In recent years, graphene-based van der Waals (vdW) heterostructures have come into prominence showcasing interesting charge transfer dynamics which is significant for optoelectronic applications. These novel structures are highly tunable depending on several factors such as the combination of the two-dimensional materials, the number of layers and band alignment exhibiting interfacial charge transfer dynamics. Here, we report on a novel graphene based 0D-2D vdW heterostructure between graphene and amine-functionalized graphene quantum dots (GQD) to investigate the interfacial charge transfer and doping possibilities.

Surface Energy of Au Nanoparticles Depending on Their Size and Shape.

Motivated by often contradictory literature reports on the dependence of the surface energy of gold nanoparticles on the variety of its size and shape, we performed an atomistic study combining molecular mechanics and ab initio calculations. We show that, in the case of Au nanocubes, their surface energy converges to a value for ( 0 0 1 ) facets of bulk crystals. A fast convergence to a single valued surface energy is predicted also for nanospheres.

An Ab Initio Study of Magnetism in Disordered Fe-Al Alloys with Thermal Antiphase Boundaries.

We have performed a quantum-mechanical study of a B2 phase of Fe 70 Al 30 alloy with and without antiphase boundaries (APBs) with the {001} crystallographic orientation of APB interfaces. We used a supercell approach with the atoms distributed according to the special quasi-random structure (SQS) concept. Our study was motivated by experimental findings by Murakami et al.

An Ab Initio Study of Vacancies in Disordered Magnetic Systems: A Case Study of Fe-Rich Fe-Al Phases.

We have performed quantum-mechanical calculations to examine the impact of disorder on thermodynamic, structural and electronic (magnetic) properties of Fe-Al systems with vacancies. A series of supercells was used and their properties were computed employing density-functional theory (DFT) as implemented in the VASP package. Our case study is primarily aimed at a disordered solid solution Fe 81.

Thermal Expansion and Other Thermodynamic Properties of -TiAl and -TiAl Intermetallic Phases from First Principles Methods.

Anisotropic thermal expansion coefficients of tetragonal γ -TiAl and hexagonal α 2 -TiAl phases were calculated using first principles methods. Two approaches with different computational costs and degrees of freedom were proposed. The predicted values were compared with available experimental data showing that for γ -TiAl, the more computational demanding method with decoupled impact of volume and temperature effects on the cell shape leads to significantly better results than that with only ground-state optimised unit cell geometry.

Experimental Chemistry and Structural Stability of AlNb₃ Enabled by Antisite Defects Formation.

First-principles evolutionary algorithms are employed to shed light on the phase stability of Al⁻Nb intermetallics. While the tetragonal Al₃Nb and AlNb₂ structures are correctly identified as stable, the experimentally reported Laves phase of AlNb₃ yields soft phonon modes implying its dynamical instability at 0 K. The soft phonon modes do not disappear even upon elevating the temperature in the simulation up to 1500 K.

Impact of Nano-Scale Distribution of Atoms on Electronic and Magnetic Properties of Phases in Fe-Al Nanocomposites: An Ab Initio Study.

Quantum-mechanical calculations are applied to examine magnetic and electronic properties of phases appearing in binary Fe-Al-based nanocomposites. The calculations are carried out using the Vienna Ab-initio Simulation Package which implements density functional theory and generalized gradient approximation. The focus is on a disordered solid solution with 18.

Quantum-Mechanical Study of Nanocomposites with Low and Ultra-Low Interface Energies.

We applied first-principles electronic structure calculations to study structural, thermodynamic and elastic properties of nanocomposites exhibiting nearly perfect match of constituting phases. In particular, two combinations of transition-metal disilicides and one pair of magnetic phases containing the Fe and Al atoms with different atomic ordering were considered. Regarding the disilicides, nanocomposites MoSi 2 /WSi 2 with constituents crystallizing in the tetragonal C11 b structure and TaSi 2 /NbSi 2 with individual phases crystallizing in the hexagonal C40 structure were simulated.

An Ab Initio Study of Pressure-Induced Reversal of Elastically Stiff and Soft Directions in YN and ScN and Its Effect in Nanocomposites Containing These Nitrides.

Using quantum-mechanical calculations of second- and third-order elastic constants for YN and ScN with the rock-salt (B1) structure, we predict that these materials change the fundamental type of their elastic anisotropy by rather moderate hydrostatic pressures of a few GPa. In particular, YN with its zero-pressure elastic anisotropy characterized by the Zener anisotropy ratio A Z = 2 C 44 / ( C 11 - C 12 ) = 1.046 becomes elastically isotropic at the hydrostatic pressure of 1.

An Ab Initio Study of Connections between Tensorial Elastic Properties and Chemical Bonds in Σ5(210) Grain Boundaries in Ni₃Si.

Using quantum-mechanical methods we calculate and analyze (tensorial) anisotropic elastic properties of the ground-state configurations of interface states associated with Σ 5(210) grain boundaries (GBs) in cubic L1 2 -structure Ni 3 Si. We assess the mechanical stability of interface states with two different chemical compositions at the studied GB by checking rigorous elasticity-based Born stability criteria. In particular, we show that a GB variant containing both Ni and Si atoms at the interface is unstable with respect to shear deformation (one of the elastic constants, C 55 , is negative).

Origin of the Low Magnetic Moment in Fe₂AlTi: An Ab Initio Study.

The intermetallic compound Fe 2 AlTi (alternatively Fe 2 TiAl) is an important phase in the ternary Fe-Al-Ti phase diagram. Previous theoretical studies showed a large discrepancy of approximately an order of magnitude between the ab initio computed magnetic moments and the experimentally measured ones. To unravel the source of this discrepancy, we analyze how various mechanisms present in realistic materials such as residual strain effects or deviations from stoichiometry affect magnetism.

Surface energy of nanoparticles - influence of particle size and structure.

The surface energy, particularly for nanoparticles, is one of the most important quantities in understanding the thermodynamics of particles. Therefore, it is astonishing that there is still great uncertainty about its value. The uncertainty increases if one questions its dependence on particle size.

An Study of Thermodynamic and Mechanical Stability of Heusler-Based Fe₂AlCo Polymorphs.

We use quantum-mechanical calculations to test a hypothesis of Glover et al. (J. Mag.

Ab initio inspired design of ternary boride thin films.

The demand to discover new materials is scientifically as well as industrially a continuously present topic, covering all different fields of application. The recent scientific work on thin film materials has shown, that especially for nitride-based protective coatings, computationally-driven understanding and modelling serves as a reliable trend-giver and can be used for target-oriented experiments. In this study, semi-automated density functional theory (DFT) calculations were used, to sweep across transition metal diborides in order to characterize their structure, phase stability and mechanical properties.

Au, a stable glassy cluster: results of ab initio calculations.

Structure and properties of small nanoparticles are still under discussion. Moreover, some thermodynamic properties and the structural behavior still remain partially unknown. One of the best investigated nanoparticles is the Au cluster, which has been analyzed experimentally and theoretically.

Tensorial elastic properties and stability of interface states associated with Σ5(210) grain boundaries in Ni(Al,Si).

Grain boundaries (GBs) represent one of the most important types of defects in solids and their instability leads to catastrophic failures in materials. Grain boundaries are challenging for theoretical studies because of their distorted atomic structure. Fortunately, quantum-mechanical methods can reliably compute their properties.

Surface energies of AlN allotropes from first principles.

In this letter we present first-principles calculations of the surface energies of rock-salt (B1), zinc-blende (B3) and wurtzite (B4) AlN allotropes. Of several low-index facets, the highest energies are obtained for monoatomic surfaces (i.e.

Interfacial coherency stress distribution in TiN/AlN bilayer and multilayer films studied by FEM analysis.

The development of interfacial coherency stresses in TiN/AlN bilayer and multilayer films was investigated by finite element method (ABAQUS) using the four-node bilinear quadrilateral axisymmetric element CAX4R. The TiN and AlN layers are always in compression and tension at the interface, respectively, as may be expected from the fact TiN has larger lattice parameter than AlN. Both, the bi-layer and the multilayer stacks bend due to the coherency stresses.

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Transition metal aluminium nitride (TM-Al-N) thin films are valued for their excellent mechanical (e.g. hardness) as well as protective (e.

Influence of Zr on structure, mechanical and thermal properties of Ti-Al-N.

Multinary Ti-Al-N thin films are used for various applications where hard, wear and oxidation resistant materials are needed. Here, we study the effect of Zr addition on structure, mechanical and thermal properties of Ti(1-x)Al(x)N based coatings under the guidance of ab initio calculations. The preparation of Ti(1-x-z)Al(x)Zr(z)N by magnetron sputtering verifies the suggested cubic (NaCl-type) structure for x below 0.