Blue phosphorene, a two-dimensional, hexagonal-structured, semiconducting phosphorus, has gained attention as it is considered easier to synthesize on metal surfaces than its allotrope, black phosphorene. Recent studies report different structures of phosphorene, for example, on Cu(111), but the underlying mechanisms of their formation are not known. Here, using a combination of in situ ultrahigh vacuum low-energy electron microscopy and in vacuo scanning tunneling microscopy, we determine the time evolution of the surface structure and morphology during the deposition of phosphorus on single-crystalline Cu(111). We find that during the early stages of deposition phosphorus intermixes with Cu, resulting in copper phosphide structures. With the increasing surface concentration of phosphorus, the phosphide phase disappears, and a blue phosphorene layer forms, followed by the self-assembly of highly ordered phosphorus clusters that eventually grow into multilayer islands. We attribute the unexpected transformation of stable phosphide to a phosphorene layer to the presence of a large concentration of P2 dimers on the surface. Our results constitute direct evidence for a growth mode leading to a flat phosphorene layer via an intermediary phase, which could underpin the growth of other 2D materials on strongly interacting substrates.
- Klíčová slova
- 2D materials, copper phosphide, growth mode, phase transformation, phosphorene,
- Publikační typ
- časopisecké články MeSH
The work is focused on the mechanical behavior description of porous filled composites that is not based on simulations or exact physical models, including different assumptions and simplifications with further comparison with real behavior of materials with different extents of accordance. The proposed process begins by measurement and further fitting of data by spatial exponential function zc = zm · p1b · p2c, where zc/zm is mechanical property value for composite/nonporous matrix, p1/p2 are suitable dimensionless structural parameters (equal to 1 for nonporous matrix) and b/c are exponents ensuring the best fitting. The fitting is followed by interpolation of b and c, which are logarithmic variables based on the observed mechanical property value of nonporous matrix with additions of further properties of matrix in some cases. The work is dedicated to the utilization of further suitable pairs of structural parameters to one pair published earlier. The proposed mathematical approach was demonstrated for PUR/rubber composites with a wide range of rubber filling, various porosity, and different polyurethane matrices. The mechanical properties derived from tensile testing included elastic modulus, ultimate strength and strain, and energy need for ultimate strain achievement. The proposed relationships between structure/composition and mechanical behavior seem to be suitable for materials containing randomly shaped filler particles and voids and, therefore, could be universal (and also hold materials with less complicated microstructure) after potential following and more exact research.
- Klíčová slova
- mechanical properties, polymer matrix composite, porosity,
- Publikační typ
- časopisecké články MeSH
This study describes a new mathematical approach to the relationship between mechanical properties (tensile modulus, ultimate strength, and strain), composition as well as structure of porous-filled reinforced composites. The composite system consisted of a polyurethane matrix, a rubber filler, and a small amount of polyethylene terephthalate as a reinforcement. The newly proposed equations are based on a special mixing rule with the same basic form for all studied properties. The mixing rule contains a correction parameter η, which differs in different filler content in the filled part of the composite. Here, a cubic exponential function including the product of suitable structural parameters and exponents ensuring the best fitting and describable by matrix properties were successfully defined to fit the different values of correction parameter. The proposed equations should be a suitable step to obtain a relationship for describing the mechanical behavior of porous-filled and reinforced composites in the case of a small amount of reinforcement.
- Klíčová slova
- composite, porosity, reinforcement, tensile modulus, tensile strength,
- Publikační typ
- časopisecké články MeSH
We performed a quantum-mechanical study of the effect of antiphase boundaries (APBs) on structural, magnetic and vibrational properties of Fe3Al compound. The studied APBs have the {001} crystallographic orientation of their sharp interfaces and they are characterized by a 1/2〈111〉 shift of atomic planes. There are two types of APB interfaces formed by either two adjacent planes of Fe atoms or by two adjacent planes containing both Fe and Al atoms. The averaged APB interface energy is found to be 80 mJ/m2 and we estimate the APB interface energy of each of the two types of interfaces to be within the range of 40-120 mJ/m2. The studied APBs affect local magnetic moments of Fe atoms near the defects, increasing magnetic moments of FeII atoms by as much as 11.8% and reducing those of FeI atoms by up to 4%. When comparing phonons in the Fe3Al with and without APBs within the harmonic approximation, we find a very strong influence of APBs. In particular, we have found a significant reduction of gap in frequencies that separates phonon modes below 7.9 THz and above 9.2 THz in the defect-free Fe3Al. All the APBs-induced changes result in a higher free energy, lower entropy and partly also a lower harmonic phonon energy in Fe3Al with APBs when compared with those in the defect-free bulk Fe3Al.
- Klíčová slova
- Fe-Al, ab initio, antiphase boundaries, magnetism, phonons, stability,
- Publikační typ
- časopisecké články MeSH
The response of three covalent crystals with a diamond lattice (C, Si and Ge) to uniaxial and a special triaxial (generally nonhydrostatic) loading is calculated from first principles. The lattice deformations are described in terms of variations of bond lengths and angles. The triaxial stress state is simulated as a superposition of axial tension or compression and transverse (both tensile and compressive) biaxial stresses. The biaxial stresses are considered to be adjustable parameters and the theoretical strengths in tension and compression along <100>, <110>, <111> crystallographic directions are calculated as their functions. The obtained results revealed that the compressive strengths are, consistently to fcc metals, almost linear functions of the transverse stresses. Tensile transverse stresses lower the compressive strength and vice versa. The tensile strengths, however, are not monotonic functions of the transverse biaxial stresses since they mostly exhibit maxima for certain values of the transverse stresses (e.g., tensile for <100> and <110> loading of Si and Ge or compressive for <100> loading of C).
- MeSH
- germanium chemie MeSH
- křemík chemie MeSH
- krystalizace * MeSH
- mechanické jevy * MeSH
- pevnost v tahu MeSH
- testování materiálů MeSH
- uhlík chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- germanium MeSH
- křemík MeSH
- uhlík MeSH
Lattice dynamics and stability of four fcc crystals (Al, Ir, Pt and Au) under isotropic (hydrostatic) tensile loading are studied from first principles using the linear response method and the harmonic approximation. The results reveal that, contrary to former expectations, strengths of all the studied crystals are limited by instabilities related to soft phonons with finite or vanishing wavevectors. The critical strains associated with such instabilities are remarkably lower than those related to the volumetric instability. On the other hand, the corresponding reduction of the tensile strength is by 20% at the most. An analysis of elastic stability conditions is also performed and the results obtained by means of both approaches are compared.
- MeSH
- anizotropie MeSH
- chemické modely * MeSH
- kovy chemie MeSH
- krystalizace * MeSH
- mechanický stres MeSH
- pevnost v tahu MeSH
- počítačová simulace MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- kovy MeSH
