共查询到11条相似文献,搜索用时 0 毫秒
1.
R. R. Gareev D. E. Bü rgler M. Buchmeier R. Schreiber P. Grü nberg 《Journal of magnetism and magnetic materials》2002,240(1-3):235-237
Fe/Fe1−xSix/Fe (x=0.4–1.0) wedge-type epitaxial trilayers with improved homogeneity are grown by co-evaporation from two electron-beam sources. The coupling strengths of the bilinear (J1) and biquadratic (J2) coupling terms are derived from Brillouin light scattering (BLS) spectra and longitudinal MOKE hysteresis loops. The total coupling strength J=J1+J2 increases dramatically with increasing x and reaches values in excess of 6 mJ/m2. 相似文献
2.
A pseudopotential formalism within the virtual crystal approximation in which the effects of composition disorder are involved is applied to the GaxIn1−xAsyP1−y quaternary alloys in conditions of lattice matching to GaAs, InP and ZnSe substrates so as to predict their energy band gaps. Very good agreement is obtained between the calculated values and the available experimental data for the alloy lattice matched to InP and GaAs. The alloy is found to be a direct-gap semiconductor for all y compositions whatever the lattice matching to the substrates of interest. The (Γ→Γ) band-gap ranges and the ionicity character are found to depend considerably on the particular lattice-matched substrates suggesting therefore that, for an appropriate choice of y and the substrate, GaxIn1−xAsyP1−y could provide more diverse opportunities to obtain desired band gaps, which opens up the possibility of discovering new electronic devices with special features and properties. 相似文献
3.
A crystal chemistry study of LiNi1 − yCoyO2 phases, used as positive electrode in lithium batteries, is presented. These materials crystallize in the rhombohedral system (space group: R
m) with a layered structure. Rietveld profile refinement of the X-ray data shows that for low substitution amounts ( ≤ 0.20) extra-nickel ions are always present leading to the Li1 − zNi1 + z − tCotO2 (t = y(1 + z)) formula (z * > 0), while for y ≥ 0.30, a pure 2D structure is obtained (z = 0). The stabilization of the 2D character of the structure by cobalt substitution in lithium nickelate leads to the improvement of the electrochemical properties. 相似文献
4.
5.
V. K. Dixit K. S. Keerthi H. L. Bhat Parthasarathi Bera M. S. Hegde 《Applied Surface Science》2003,220(1-4):321-326
The growth of epitaxial InBixAsySb(1−x−y) layers on highly lattice mis-matched semi-insulating GaAs substrates has been successfully achieved via the traditional liquid phase epitaxy. Orientation and single crystalline nature of the film have been confirmed by X-ray diffraction. Scanning electron micrograph shows abrupt interface at micrometer resolution. Surface composition of Bi(x) and As(y) in the InBixAsySb(1−x−y) film was measured using energy dispersive X-ray analysis and found to be 2.5 and 10.5 at.%, respectively, and was further confirmed with X-ray photoelectron spectroscopy. Variation of the composition with depth of the film was studied by removing the layers with low current (20 μA) Ar+ etching. It was observed that with successive Ar+ etching, In/Sb ratio remained the same, while the As/Sb and Bi/Sb ratios changed slightly with etching time. However after about 5 min etching the As/Sb and Bi/Sb ratios reached constant values. The room temperature band gap of InBi0.025As0.105Sb0.870 was found to be in the range of 0.113–0.120 eV. The measured values of mobility and carrier density at room temperature are 3.1×104 cm2 V−1 s−1 and 8.07×1016 cm−3, respectively. 相似文献
6.
Anomalies are found in the near-band-edge luminescence properties of Δ2-light-hole indirect excitons in Si1−yCy-based tensilely strained quantum wells (QWs). The experimental spectra exhibit a clear signature of phonon-assisted transitions on the lower energy side of the “no-phonon” transition, which indicates the relevance of “virtual” indirect valleys and in-plane k-dispersion, as opposed to the theoretical prediction that the zone-centered Δ2 valleys take over the conduction band edge. Intervalley scattering between [0 0 1]-Δ2 valleys and in-plane Δ4 valleys is suggested as the underlying mechanism. On the other hand, the experimental evidence was found for “apparently enhanced” quantum-confined Stark red shifts for Si1−yCy-based QWs. However, quantitative estimates are in conflict with the experimental results and predict a blue shift due to exciton weakening which masks the Stark effect as in the case of Δ4-heavy hole excitons in Si1−xGex-based QWs. 相似文献
7.
A. Polimeni A. Patan M. Henini L. Eaves P. C. Main G. Hill 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
The optical properties of InAs/AlyGa1−yAs self-assembled quantum dots are studied as a function of temperature from 10 K to room temperature. The temperature dependence of carrier hopping between dots is discussed in terms of the depth of the dot confinement potential and the dispersion in dot size and composition. We show that carrier hopping between dots influences both the electrical and optical properties of laser devices having dots as active medium. 相似文献
8.
kos Nemcsics 《Applied Surface Science》2002,190(1-4):294-297
In this work, we have looked for the correlation between the observed decay of reflection high-energy electron diffraction intensity oscillation and the critical layer thickness in the case of strained InxGa1−xAs/GaAs heterojunctions. The value of deading time constant of oscillation depends on the mismatch and on growth parameters, too. The decay of oscillation was described by two deading time constants which are responsible for the influences of the parameters mentioned above. The critical layer thickness was valued from the deading time constant responsible for the influence of mismatch only. The critical layer thickness determined this way shows good agreement with the theoretical model. 相似文献
9.
J.A. Sans J.F. Snchez-Royo J. Pellicer-Porres A. Segura E. Guillotel G. Martinez-Criado J. Susini A. Muoz-Pez V. Lpez-Flores 《Superlattices and Microstructures》2007,42(1-6):226
In this paper, we investigate the Co site configuration in Zn1−xCoxO thin films by means of different spectroscopic techniques. Thin films were prepared by pulsed laser deposition with Co proportion from 1% to 30%. The Co 2p doublet observed in the X-ray photoelectron spectra exhibits the spin–orbit splitting and shake-up satellites typical of Co+2 ionization states. X-ray absorption spectra at the Co K-edge, taken in fluorescence mode, unambiguously show that Co atoms are in tetrahedral configuration substituting for Zn over the whole composition range. Optical absorption spectra provide further evidence of the tetrahedral coordination of Co cations, both through the internal transitions in the Co 3d shell and through the shift to higher energies of the band-to-band absorption edge with the increase of the Co proportion. 相似文献
10.
S.K. Srivastava Manoranjan Kar S. Ravi 《Journal of magnetism and magnetic materials》2008,320(14):e107-e110
The mixed valent manganites (La0.85Ag0.15)MnO3 with perovskite structure has been prepared by doping up to 50% of Co at the Mn site. Paramagnetic (PM) to ferromagnetic (FM) transitions have been observed in all the prepared materials. However, the long-range magnetic ordering observed in (La0.85Ag0.15)MnO3 is systemically reduced to cluster glass-type (short-range) of FM ordering due to the introduction of Co. The FM transition temperature was found to decrease with increase in Co doping up to 20% and for further increase in Co doping, the Tc was found to increase. They are explained on the basis of competition between FM double exchange interactions in Mn–O–Mn and Co–O–Co networks. In addition to PM–FM transition, evidences of FM to antiferromagnetic (AFM), and AFM to reentrant spin-glass transitions have been observed. The shift in spin-glass freezing temperature, Tf has been observed from the frequency variation of ac susceptibility measurements. The observed magnetic transitions are explained on the basis of magnetic interactions in different Mn–O–Mn, Mn–O–Co and Co–O–Co networks and such transitions are also observed from the measurement of third harmonic susceptibility. Metal–insulator transition and colossal magneto-resistivity have been observed up to 10% of Co doping. 相似文献
11.
Y. V. Piskunov K. N. Mikhalev Yu. I. Zhdanov A. P. Gerashenko S. V. Verkhovskii K. A. Okulova E. Yu. Medvedev A. Yu. Yakubovskii L. D. Shustov P. V. Bellot A. Trokiner 《Physica C: Superconductivity and its Applications》1998,300(3-4)
and
NMR measurements in the normal and superconducting states of Tl2Ba2Ca2Cu3O10−δ with different δ are reported. In the overdoped Tl2223 sample with Tc=117 K (Tcopt=123 K) and δ1<δopt different temperature dependencies of the Knight shift
are revealed for inequivalent CuO2 layers. For the inner CuO2 layer with the square oxygen coordination of Cu the decrease of
with temperature is more gradual. In going towards the underdoped Tl2223 with Tc=104 K and δ2>δopt the changes of
with temperature are found to be the same for both types of copper layers. The quadrupole coupling constants for copper and oxygen from different CuO2 layers were obtained. From the variations with doping of the valence contribution to the electric field gradient at copper sites, we estimate both the hole numbers at Cu and oxygen sites and the real concentration of mobile hole carriers nh in each of inequivalent CuO2 layers. In the overdoped Tl2223 sample the charge density in the inner layer differs from the one in the outer plane (with five-fold oxygen coordination for Cu). Our results show that the inhomogeneity of the charge distribution disappears in the underdoped regime. The results are compared with calculations of the charge distribution among the CuO2 planes in multilayered cuprates reported by Haines and Tallon [E.M. Haines, J.L. Tallon, Phys. Rev. B 45 (1992) 3127]. 相似文献