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Based on the correlation between Raman shift and bond parameters, and further combined with experimental values of the Raman shift composition effect, the relationship between the composition and bond parameters of the 2D-M1−xM′xX2 and 2D-MX′2xX2(1−x) alloy materials was established. Numerical reproduction of the measurements clarified that the host atom phonons involved interaction with all of its z neighbors, whereas the doping atom phonon only involved interaction with a dimer. The doping of large atoms resulted in an elongation of the bond length, an increase in the equivalent coordination number, and enhancement of the binding energy. The doping of small atoms led to a contraction of the bond length, a decrease in the equivalent coordination number, and a weakening of binding energy. By quantifying the relationship between composition and bond parameters from Raman shifts, a deep understanding of two-dimensional alloy properties can be achieved. [ABSTRACT FROM AUTHOR]

In this paper, we clarified a robust mechanism of magnetism generated by excess electrons captured by edge-quantum well of diamagnetic armchair edges. Consistency between density functional theory calculations and electron cyclotron resonance experiments verified that: (1) Multi-layer armchair nanoribbons are stable with proper amounts of excess electrons which can provide net spin; (2) Since under-coordination induces lattice relaxation and potential well modulation, electrons tend to be trapped at edges; and (3) Neither large amount of excess electrons nor positive charges can induce magnetism. This work shed light on the development of graphene devices in its magnetic applications. [ABSTRACT FROM AUTHOR]

Strain-induced graphene phonon softening and phonon band splitting are indeed fascinating, which were attributed to the phonon double resonant scattering without intrinsic involvement of C-C bond relaxation. Here, we show that the lengthening and weakening of the C-C bond softens the phonon and that the mismatching between the uniaxial strain and the C3v bond geometry splits the band. In addition to the force constant of 11.8 N/m for a C-C bond in graphene, consistency between theory and measurements derives that if the strain is along a bond, maximal band splitting happens; if the strain is perpendicular, no band splitting occurs. [ABSTRACT FROM AUTHOR]

From the perspective of bond order-length-strength correlation and the local bond averaging approach, we have formulated the number-of-layer resolved Raman shifts of graphene, with quantification of the referential origins from which the Raman shifts proceed and clarification of their origins. It is found that the primary D mode and the secondary 2D mode are dominated by the interaction between a specific atom and its nearest neighbors while the G mode by the dimer interaction, and therefore red shift happens to the D/2D phonons and blue shift to the G mode upon the number-of-layer is reduced. [ABSTRACT FROM AUTHOR]

The thermally softened and the mechanically stiffened graphene phonons have been formulated from the perspective of bond order-length-strength correlation with confirmation of the C-C bond length in the single-layer graphene contracting from 0.154 to 0.125 nm and the binding energy increasing from 0.65 to 1.04 eV. Matching theory to the measured temperature- and pressure-dependent Raman shift has derived that the Debye temperature drops from 2230 to 540 K, the atomic cohesive energy drops from 7.37 to 3.11 eV/atom, and the binding energy density increases from 250 to 320 eV/nm3 compared with the respective quantities of bulk diamond. [ABSTRACT FROM AUTHOR]

Although the size- and shape-induced blueshift in the photoluminescence and photoabsorption of nanostructured ZnO has been extensively investigated, the underlying mechanism remains yet unclear. Here we show that theoretical reproduction of the observed trends clarifies that the blueshift originates from the Hamiltonian perturbation due to the broken-bond-induced local strain and quantum trapping and electron-phonon coupling in the surface skin up to two atomic layers in depth while bonds in the core interior retain their bulk nature. The extent of the blue shift depends on the tunable fraction of undercoordinated atoms in the surface skin. Therefore, the quantum confinement effect is indeed more “superficial” than first thought [H. Winn, OE Mag. 8, 10 (2005)]. [ABSTRACT FROM AUTHOR]

The Hg2CuTi-type structure is found to be preferable energy wise than the Cu2MnAl-type structure for full-Heusler Cr2MnAl and exhibits half-metallic ferromagnetism based on first principles. The calculations for the mixed compounds with disorder between B and D sublattices reveal that the case of exchanging one atom maintains the half-metallicity while the case of exchanging two atoms loses it. The electronic structures of the atoms at sites A or C are affected mainly by the nearest-neighboring coordination while that of the atoms at site B are determined by the next-nearest-neighboring coordination. [ABSTRACT FROM AUTHOR]

It has long been puzzling regarding the trends and physical origins of the size-effect on the elasticity of ZnO nanostructures. An extension of the atomic “coordination-radius” correlation premise of Pauling and Goldschmidt to energy domain has enabled us to clarify that the elastic modulus is intrinsically proportional to the sum of bond energy per unit volume and that the size-induced elastic stiffening arises from (i) the broken-bond-induced local strain and skin-depth energy pinning and (ii) the tunable fraction of bonds between the undercoordinated atoms, and therefore, the elastic modulus of ZnO nanostructures should increase with the inverse of feature size. [ABSTRACT FROM AUTHOR]

A model has been developed for the P-E hysteresis behavior from the perspective of dipole switching. Hysteresis loops have been reproduced with the model to agree reasonably well with the experimental data measured from various ferroelectric thin films. The model can also predict asymmetric hysteresis loop measured under unconventional situation. Additionally, the mathematical description can be easily combined with electronic design automation software in circuit simulation of ferroelectric capacitor or ferroelectric field effect transistor. [ABSTRACT FROM AUTHOR]

The authors have computationally designed ultraincompressible materials, namely, rhenium carbide, in the WC and NiAs structures with a very high shear modulus. The corresponding calculated bulk modulus is comparable with that of diamond. Especially for the WC-typed rhenium carbide (ReC), the incompressibility along the c axis is demonstrated to exceed the linear incompressibility of diamond. The unique mechanical properties would make it suitable for applications under extreme conditions. [ABSTRACT FROM AUTHOR]

A single band of photoluminescence (PL) has been detected at room temperature from the Pb(Zr[sub x]Ti[sub 1-x])O[sub 3] (x=0–1.0) surface. The intense and stable PL band covers 475±50 nm (or 2.67±0.25 eV) wavelengths and the corresponding photoexcitation (PE) band is in the range of 305±45 nm. It is found that changing the x value causes a negligible shift of the PL and PE peaks, and the light emission is subject to the Pb presence. The minimal lifetime of the excited photons was found to be 0.03 ms at x=0.5 and the maximum lifetime of 0.60 ms can be achieved by either decreasing or increasing the x values. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The dielectric behavior of nanostructured diamond films has been investigated by using an impedance analyzer up to 500 °C. Impedance data are presented in the form of the Cole-Cole plot. It is found that: (i) the resistivity contributed both from bulk grain interior and grain boundary decreases with increasing temperature; (ii) above 250 °C, the impurities at grain boundaries are thermally activated, and thus contribute to the dielectric relaxation; and (iii) the electrical conductivity of diamond films follows an Arrhenius law with an activation energy transition from 0.13 to 0.67 eV at 250 °C. Similar activation energy is found for the Arrhenius plot of relaxation frequencies from 0.14 to 0.73 eV. The dielectric transition is explained as the change of crystal field caused by the thermal expansion or by surface bond contraction of nanosized particles. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on laser-like mechanoluminescence in zinc manganese telluride-diluted magnetic semiconductor. Bond order-length-strength correlation mechanism; Coordination number; Bond contraction coefficient.

Correlation between chemical bonds, energy bands, and the corresponding properties of oxides and nitrides is established. It is proposed that an oxygen or nitrogen atom can hybridize and form a tetrahedron with its four neighbors through bonding orbitals and nonbonding lone pairs. As a result, the energy states of the host material are modified with four additional features, namely, sp[sup 3]-hybrid bonding, nonbonding (lone pair), antibonding (dipole), and hole states. Therefore, oxygen and nitrogen possess the special ability of not only enlarging the band gap by hole production but also adding an antibonding subband above the Fermi level. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]