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891.
High quality, straight GaN nanowires (NWs) with diameters of 50 nm and lengths up to 3 μm have been grown on Si(0 0 1) using Au as a catalyst and the direct reaction of Ga with NH3 and N2:H2 at 900 °C. These exhibited intense, near band edge photoluminescence at 3.42 eV in comparison to GaN NWs with non-uniform diameters obtained under a flow of Ar:NH3, which showed much weaker band edge emission due to strong non-radiative recombination. A significantly higher yield of β-Ga2O3 NWs with diameters of ≤50 nm and lengths up to 10 μm were obtained, however, via the reaction of Ga with residual O2 under a flow of Ar alone. The growth of GaN NWs depends critically on the temperature, pressure and flows in decreasing order of importance but also the availability of reactive species of Ga and N. A growth mechanism is proposed whereby H2 dissociates on the Au nanoparticles and reacts with Ga giving GaxHy thereby promoting one-dimensional (1D) growth via its reaction with dissociated NH3 near or at the top of the GaN NWs while suppressing at the same time the formation of an underlying amorphous layer. The higher yield and longer β-Ga2O3 NWs grow by the vapor liquid solid mechanism that occurs much more efficiently than nitridation. 相似文献
892.
Qun Li Andreas Ricoeur Meinhard Kuna 《Archive of Applied Mechanics (Ingenieur Archiv)》2011,81(6):685-700
The axisymmetric problem of a penny-shaped crack embedded in an infinite three-dimensional (3D) piezoelectric body is considered.
A general formulation of Coulomb traction on the crack surfaces can be obtained based on thermodynamical considerations of
electromechanical systems. Three-dimensional electroelastic solutions are derived by the classical complex potential theory
when Coulomb traction is taken into account and the poling direction of piezoelectric body is perpendicular to the crack surfaces.
Numerical results show that the magnitude of Coulomb tractions can be large, especially when a large electric field in connection
with a small mechanical load is applied. Unlike the traditional traction-free crack model, Coulomb tractions induced by an
applied electric field influence the Mode I stress intensity factor for a penny-shaped crack in 3D piezoelectric body. Moreover,
compared to the current model, the traditional traction-free crack model always overestimates the effect of the applied electric
load on the field intensity factors and energy release rates, which has consequences for 3D piezoelectric fracture mechanics. 相似文献
893.
894.
895.
Gideon Steyl Gert J. Kruger Andreas Roodt 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(10):m473-m475
The molecules of the title complex, [Rh(Trop)(CO)2] (Trop is 2‐hydroxycyclohepta‐2,4,6‐trienonate, C7H5O2), exhibit symmetrical but non‐crystallographic square‐planar molecular geometry, with Rh—C distances of 1.825 (10) and 1.826 (9) Å, Rh—O distances of 2.021 (5) and 2.032 (5) Å, and an O—Rh—O bite angle of 79.4 (2)°. Strong Rh⋯Rh and Rh⋯C intermolecular interactions of 3.683 (3) and 3.650 (5) Å, respectively, are also observed. 相似文献
896.
897.
898.
Trithiaazapentalene derivatives were prepared by the reaction of 2-alkylidene-4-oxothiazolidines with Lawesson's reagent. They are classified as two structurally different trithiaazapentalene compounds that have different contributions of monocyclic 1,2-dithiole and 1,2,4-dithiazole structures and degrees of aromaticity of the bicyclic trithiaazapentalene system. The electron-donating ability of substituents at the C(5) position of the trithiaazapentalene system is recognized as the main cause for changes in π-electron distribution. This is the first complete study of substituent effects on the structure of trithiapentalenes. 相似文献
899.