Ab initio investigation of the elasticity and stability of aluminium

On the basis of the pseudopotential plane-wave (PP-PW) method in combination with the local density functional theory (LDFT), complete stress-strain curves for the uniaxial loading and uniaxial deformation along the [001] and [111] directions, and the biaxial proportional extension along [010] and [001] for aluminium are obtained. During the uniaxial loading, certain general behaviours of the energy versus the stretch and the load versus the stretch are confirmed; in each case, there exist three special unstressed structures: f.c.c., b.c.c., and f.c.t. for [001]; f.c.c., s.c., and b.c.c. for [111]. Using stability criteria, we find that all of these states are unstable, and always occur together with shear instability, except the natural f.c.c. structure. A Pain transformation from the stable f.c.c. structure to the stable b.c.c. configuration cannot be obtained by uniaxial compression along any equivalent [001] and [111] direction. The tensile strengths are similar for the two directions. For the higher energy barrier of the [111] direction, the compressive strength is greater than that for the [001] direction. With increase in the ratio of the biaxial proportional extension, the stress and tensile strength increase; however, the critical strain does not change significantly. Our results add to the existing ab initio database for use in fitting and testing interatomic potentials.

Spectral properties and stability of Er3+-doped TeO2-WO3 glass

Er3+-doped TeO2-WO3 glass was fabricated and characterized by absorption spectrum, fluorescence spectrum, Raman spectrum and stability. The Judd-Ofelt parameter ohm(t)(t = 2, 4, 6) were calculated from the absorption spectrum by the Judd-Ofelt theory. The fluorescence spectrum indicates that the fluorescence width at half-maximum (FWHM) is 66nm. The stimulated emission cross-section of Er3+ in TeO2-WO3 glass at 1532 nm was calculated to be 0.80 x 10(-20) cm(2) by McCumber theory. The phonon energy of TeO2-WO3 glass is found to be 931 cm(-1). The difference between crystallization onset temperature and glass transition temperature Delta T is 112 degrees C. These results show that Er3+-doped TeO2-WO3 glass has higher stability and good spectral properties, which were useful for broadband amplifier. (c) 2005 Elsevier B.V. All rights reserved.

The formation and stability of Si1-xCx alloys in Si implanted with carbon

Si1-xCx alloys of carbon (C) concentration between 0.6%-1.0% were grown in Si by ion implantation and high temperature annealing. The formation of Si1-xCx alloys under different ion doses and their stability during annealing were studied. If the implanted dose was less than that for amorphizing Si crystals, the implanted C atoms would like to combine with defects produced during implantation and it was difficult to form Si1-xCx alloys after being annealed at 850 degreesC. With the increment of implanted C ion doses, the lattice damage increased and it was easier to form Si1-xCx alloys. But the lattice strain would become saturate and only part of implanted carbon atoms would occupy the substitutional positions to form Si1-xCx alloys as the implanted carbon dose increased to a certain degree. Once Si1-xCx alloys were formed, they were stable at 950 degreesC, but part of their strain would release as the annealing temperature increased to 1 000 degreesC. Stability of the alloys became worse with the increment of carbon concentration in the alloys.

Structure, fluorescence and stability of CdS nanoparticles prepared in air

CdS nanoparticies were prepared in air and their stability by air annealing was studied. A small change in crystal structure and particle size was observed by air annealing, but a rapid reduction in fluorescence was found. Through investigation, it is revealed that it is the surface change or reconstruction rather than the variation of the size or structure that decreases the fluorescence. The emission of the particles consists with two peaks which are dependent on the excitation energy. The two peaks are considered to be arisen from "two" different sizes of nanoparticles and may be explained in terms of selectively excited photoluminescence. Finally we discuss why the discrete state of nanoparticles are able to be resolved in the photoluminescence excitation spectrum, but could not be differentiated in the absorption spectrum.

The role of molybdenum oxide as anode interfacial modification in the improvement of efficiency and stability in organic light-emitting diodes

It has been experimentally found that molybdenum oxide (MoO3) as the interfacial modification layer on indium-tin-oxide (ITO) in organic light-emitting diodes (OLEDs) significantly improves the efficiency and lifetime. In this paper, the role of MoO3 and MoO3 doped N,N '-di(naphthalene-1-yl)-N,N '-diphenyl-benzidine (NPB) as the interface modification layer on ITO in improvement of the efficiency and stability of OLEDs is investigated in detail by atomic force microscopy (AFM), polarized optical microscopy, transmission spectra, ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS).

Improved performance and stability by an Al/Ni bilayer cathode in organic light-emitting diodes

Al/Ni bilayer cathode was used to improve the electroluminescent (EL) efficiency and stability in N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1' biphenyl 4,4'-dimaine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq(3))-based organic light-emitting diodes. The device with LiF/Al/Ni cathode achieved a maximum power efficiency of 2.8 lm/W at current density of 1.2 mA/cm(2), which is 1.4 times the efficiency of device with the state-of-the-art LiF/Al cathode. Importantly, the device stability was significantly enhanced due to the utilization of LiF/Al/Ni cathode. The lifetime at 30% decay in luminance for LiF/Al/Ni cathode was extrapolated to 400 It at an initial luminance of 100 cd/m(2), which is 10 times better than the LiF/Al cathode.