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1.
The temperature dependence of the dc conductivity and thermoelectric power was determined for five different amorphous chalcogenide Se–Ge–Te films, with Ge?=?3.0–22?at.%, Se?=?0–97?at.% and Te?=?0–97?at.%. The films were prepared by thermal evaporation of GeSe4, GeTe4 and GeSe2Te2 quenched bulk materials. Values of the activation energy calculated from the temperature dependence of both electrical conductivity and thermoelectric power showed a decrease with increasing Ge content in the Se–Ge films as well as with replacement of Te for Se in the Se–Ge–Te films. The results showed an Anderson transition, with the conductivity showing insulating behaviour on the Ge–Se side to metallic behaviour at the binary composition Ge–Te. The radius of localization was obtained for the different compositions investigated. The wave function associated with the charge carriers at the composition Ge3.3Te96.7 is non-localized. A minimum metallic conductivity of 237?±?5?(Ω?cm)?1 was found. 相似文献
2.
The current–voltage characteristics and electrical switching behavior of bulk As30Te70-xSix (2x22) and As40Te60-xSix (2x17) glasses have been investigated over a wide range of compositions. The glasses studied have been found to exhibit a current-controlled negative-resistance behavior and memory switching. Further, the switching voltage (Vt) is found to increase linearly with sample thickness in the range of 0.15 mm to 0.45 mm, and it decreases linearly with temperature (300–353 K). It is also observed that the variation of the switching voltage Vt of As–Te–Si glasses exhibits a sharp slope change at an average coordination number r=2.46 (for both tie lines), which is associated with the rigidity percolation in the system. Further, a minimum is seen in the switching voltage Vt at an average coordination number r=2.66, which is likely to be the chemical threshold of the system. PACS 71.55.Jv; 72.20.Ht; 72.80.Ng; 73.61.Jc; 77.80.Fm; 78.66.Jg 相似文献
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Three types of elastic modulation in atomic layers of epitaxial Ge films on the surface of Si(111) observed in scanning tunnel microscopy are discussed. Two types of modulation are associated with misfit dislocations accumulating at the interface. Modulation of the third type arises on the surfaces of dislocation-free pseudomorphic films and could be due to the presence on a Si substrate surface of two-dimensional silicon islands with a height of three atomic bilayers and lateral dimensions of 15–20 nm. Measured bending values Δh for the third type of modulation (Δh ≤ 0.1 nm) agree with data calculated within the theory of elasticity 相似文献
5.
The elastic stress fields caused by a dislocation in Ge_xSi_(1-x) epitaxial layer on Si substrate are investigated in this work. Based on the previous results in an anisotropic bimaterial system,the image method is further developed to determine the stress field of a dislocation in the film-substrate system under coupled condition. The film-substrate system is firstly transformed into a bimaterial system by distributing image dislocation densities on the position of the free surface. Then,the unknown image dislocation densities are solved by using boundary conditions,i.e.,traction free conditions on the free surface. Numerical simulation focuses on the Ge0.1Si0.9/Si film-substrate system. The effects of layer thickness,position of the dislocation and crystallographic orientation on the stress fields are discussed. Results reveal that both the stresses σxx,σxz at the free surface and the stress σxy,σyy,σyz on the interface are influenced by the layer thickness,but the former is stronger. In contrast to the weak dependence of stress field on the crystallographic orientation the stress field was strongly affected by dislocation position. The stress fields both in the film-substrate system and bimaterial system are plotted. 相似文献
6.
A two-stage model of the capture of electrons and holes in traps in amorphous silicon nitride Si3N4 has been proposed. The electronic structure of a “Si–Si bond” intrinsic defect in Si3N4 has been calculated in the tight-binding approximation without fitting parameters. The properties of the Si–Si bond such as a giant cross section for capture of electrons and holes and a giant lifetime of trapped carriers have been explained. It has been shown that the Si–Si bond in the neutral state gives shallow levels near the bottom of the conduction band and the top of the valence band, which have a large cross section for capture. The capture of an electron or a hole on this bond is accompanied by the shift of shallow levels by 1.4–1.5 eV to the band gap owing to the polaron effect and a change in the localization region of valence electrons of atoms of the Si–Si bond. The calculations have been proposed with a new method for parameterizing the matrix elements of the tightbinding Hamiltonian taking into account a change in the localization region of valence electrons of an isolated atom incorporated into a solid. 相似文献
7.
The object of the present study is to design a methodology to follow the kinetics of T1 precipitation, in an AA2198 alloy, in terms of precipitate size, morphology (thickness, diameter) and volume fraction, during a two-temperature isothermal heat treatment. We used in situ small-angle X-ray scattering (SAXS) as a way to measure the evolution of the T1 mean thickness and diameter during the heat treatment. Transmission electron microscopy (TEM) was then performed in order to calibrate these evolutions. Furthermore, we demonstrate that the volume fraction evolution can be described successfully using a simple analysis of the differential scanning calorimetry (DSC) thermograms. The latter was calibrated by selected observations in high angular annular dark field scanning transmission electron microscopy (HAADF-STEM). Microstructure evolution during DSC heating ramps was analysed using in situ SAXS: the T1 phase transformation is found to consist in a two-step thickening process explained by two consecutive diffusion stages. The enthalpy of formation of the T1 phase is deduced from the DSC measurements. 相似文献
8.
Improvement of Electrical Properties of the Ge2Sb2Te5 Film by Doping Si for Phase-Change Random Access Memory 总被引:1,自引:0,他引:1
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Si-doped Ge2Sb2Te5 films have been prepared by dc magnetron co-sputtering with Ge2Sb2Te5 and Si targets. The addition of Si in the Ge2Sb2Te5 film results in the increase of both crystallization temperature and phasetransition temperature from face-centred-cubic (fcc) phase to hexagonal (hex) phase. The resistivity of the Ge2Sb2Te5 film shows a significant increase with the Si doping. When doping 11.8 at.% of Si in the film, the resistivity after 460℃ annealing increases from 1 to 11 mΩ.cm and dynamic resistance increase from 64 to 99Ω compared to the undoped Ge2Sb2Te5 film. This is very helpful to writing current reduction of phase-change random access memory. 相似文献
9.
Evidence for a Bose—Einstein Condensate in Dilute Rb Gas by Absorption Image in a Quadrupole and Ioffe Configuration Trap 总被引:3,自引:0,他引:3
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《中国物理快报》2003,20(6):799-801
10.
Lihui Huang Shiqing Xu Meiquan Guo Chenyue Wang Youjie Hua Shilong Zhao Degang Deng Huanping Wang Guohua Jia 《Journal of Physics and Chemistry of Solids》2012,73(7):886-889
Eu3+-doped Sr2Si1?xGexO4 (x=0–1) phosphors have been prepared by the high temperature solid-state reaction method. The luminescent properties of these phosphors were investigated. Red fluorescence of Eu3+ is enhanced gradually in the samples with increasing substitution of Si by Ge upon the excitation of 393 nm light. The intensity is increased by 50% with full substitution of Si by Ge. These results are originated from the structural changes and the phonon energy reduction in the samples due to the substitution of Si by Ge. The CIE chromaticity coordinates of the phosphors vary slightly around (0.62, 0.37) and all are in the red color region. The results indicate that these phosphors could be promising red phosphors for white light emitting diodes. 相似文献
11.
Eva A. Mørtsell Sigmund J. Andersen Jesper Friis Calin D. Marioara Randi Holmestad 《哲学杂志》2013,93(11):851-866
AbstractBonding energies and volume misfits for alloying elements and vacancies in multicomponent Al–Mg–Si alloys have been calculated using density functional theory (DFT). A detailed atomic scale analysis has been done for characteristic precipitate structures, using high-angle annular dark-field scanning transmission electron microscopy. Two new stacking configurations of the important strengthening phase β′′ were discovered in the Ge-added alloy. All three stacking variations were found to be energetically favourable to form from DFT calculations. The second stacking configuration, β2′′, contains vacated columns in its unit cell, consequently requiring less solute to create the same volume fraction of precipitate needles. DFT suggests a lower formation enthalpy per atom for β2′′ when Si is exchanged with Ge. In the alloy containing Ag additions, a new Q’/C-like local configuration containing Ag instead of Cu was discovered, also this phase was deemed energetically favourable from DFT. 相似文献
12.
We examine the effects of a phenomenological pseudogap on the
T=0 K phase diagram of a high temperature superconductor within
a self-consistent model which exhibits a d-wave pairing
symmetry. At the mean-field level the presence of a pseudogap in
the normal phase of the high temperature superconductor is proved
to be essential for the existence of a metallic–like state in the
density versus interaction phase diagram. In the small density
limit, at high attractive interaction, bosonic–like degrees of
freedom are likely to emerge. Our result should be relevant for
underdoped high temperature superconductors, where there is a
strong evidence for the presence of a pseudogap in the excitation
spectrum of the normal state quasiparticles. 相似文献
13.
P. K. Manna S. M. Yusuf M. D. Mukadam J. Kohlbrecher 《Applied Physics A: Materials Science & Processing》2012,109(2):385-390
We report the evidence of a core?Cshell structure in the antiferromagnetic La0.2Ce0.8CrO3 nanoparticles by using a combination of neutron diffraction, polarized neutron small angle scattering (SANSPOL), and dc magnetization techniques. The neutron diffraction study establishes that the present nanoparticles are antiferromagnetic in nature. The magnetic scattering in the SANSPOL study arises from the shell part of the nanoparticles due to the disordered surface spins. The analysis of the SANSPOL data shows that these nanoparticles have a mean core diameter of 12.3±1.1?nm, and a shell thickness of 2.8±0.4?nm, giving a core?Cshell structure with an antiferromagnetic core, and a shell with a net magnetic moment under an applied magnetic field. 相似文献
14.
The structural and the thermodynamic properties of potassium nitrate KNO3 and its composites with nanosized aluminum oxide Al2O3 have been studied by differential scanning calorimetry. It has been found that an amorphous phase forms in composites (1–x)KNO3–xAl2O3. The thermal effect corresponding to this phase has been observed at 316°C. It has been found that the phase transition heats of potassium nitrate decreased as the aluminum oxide fraction increased. 相似文献
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Sorayut Glomglome Itsara Srithanachai Chat Teeka Somsak Mitatha Surasak Niemcharoen Preecha P. Yupapin 《Optics & Laser Technology》2012,44(5):1294-1297
A new concept of an optical spin generation using bright and dark soliton conversion behaviors within a modified optical add–drop filter known as PANDA ring resonator is proposed. The orthogonal solitons can be formed within the system and detected simultaneously at the output ports. Under the resonant condition, the dark and bright soliton pair corresponding to the left-hand and right-hand rotating solitons (photons) can be generated. When a soliton is absorbed by an object, an angular momentum of either +? or ?? is imparted to the object, in which two possible spin states known as optoelectronic(soliton) spins are exhibited. Furthermore, an array of soliton spins, i.e. particles can be generated and detected by the proposed system, which can be used to form large scale spin generation. 相似文献
17.
R. De Renzi G. Allodi S. Fanesi G. Guidi F. Licci M. Hennion L. Pinsard 《Applied magnetic resonance》2000,19(3-4):421-430
We detected two spontaneous precession frequencies in antiferromagnetic pure LaMnO3, the end member of different families of charge-doped manganites. The muon site and local field orientation are identified for one frequency, which provides a measure of the staggered magnetization. We present additional zero and longitudinal field muon relaxation data on an LaMnO3.045 sample in which a new regime appears above an intermediate temperatureT*, where regions of magnetic order coexist with domains of fluctuating moments. These results are discussed in terms of nucleation of the ordered phase in a superparamagnetic matrix. 相似文献
18.
V. S. Airapetyan 《Journal of Applied Spectroscopy》2009,76(2):268-272
We have developed, built, and tested an automated differential lidar system for measuring low concentrations of atmospheric
gases, based on an optical parametric oscillator tunable in the near IR region. We have calculated the spectral shift of the
relative intensities of the individual lines in the ν3 absorption band of methane. In comparing the measured and calculated spectra, we did not observe any shifts in the ν3 absorption band of methane. At the same time, in the experimental spectra we observe broadening of the Q branch and the individual lines of the P branch.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 285–290, March–April, 2009. 相似文献
19.
The potentiality of a phoxonic crystal for sensing of biodiesel in a binary mixture of diesel and biodiesel is theoretically investigated. Using the transfer matrix method, the transmission of acoustic and optical waves through a periodic one-dimensional crystal of Si–SiO2 layers is studied. A pass band is created in the band gap region by introducing a cavity in the considered one-dimensional crystal structure. This pass band can also be considered as a defect mode, and it is found that its position is highly dependent on mole concentration of binary mixture of biodiesel and diesel present in the cavity. The sensitivity of the sensor for a binary mixture of biodiesel and diesel in the cavity with various mole concentrations is estimated. Simulated results provide a valuable guidance for designing a phoxonic crystal sensor consisting of a defect layer. 相似文献
20.
JETP Letters - A two-stage optical parametric amplifier is fabricated on the basis of type-II BBO crystals pumped by the intense radiation of a Ti:sapphire laser. Femtosecond radiation tunable from... 相似文献