共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Nayak G.L. Bhalla G.C. Trigunayat 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):319-323
Highly purified single crystals of cadmium iodide obtained through repeated zone refining have been subjected to laser beam
exposure (Argon ion laser), both for various time durations and to various beam intensities, and then subjected to band gap
determination by UV spectroscopy. The band gap has been found to decrease gradually with increase in the laser beam intensity,
whereas its variation with increase in time of exposure shows an unusual behaviour such that it initially falls sharply followed
by a gradual rise back to its original value. The results have been analysed and interpreted in terms of indirect band gap
character of the material and an unusual variation in phonon frequency. The interpretation is well supported by X-ray diffraction
and scanning electron microscopy (SEM) studies.
Received: 26 May 1997 / Revised: 6 August 1997 / Accepted: 15 September 1997 相似文献
2.
M. I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):151-153
Using the Landauer formula approach, it is proven that
minimal conductivity of order e2/h found experimentally in
bilayer graphene is an intrinsic property. For the case of ideal
crystals, the conductivity turns out to be equal to e2/2h per
valley per spin. A zero-temperature shot noise in bilayer graphene
is considered and the Fano factor is calculated. Its value
1–2/π is close to the value 1/3 found earlier for single-layer
graphene. 相似文献
3.
D.V. Rao R. Cesareo G.E. Gigante 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(1):45-53
Elastic scattering cross-sections for Pd, Ag, Cd, In, Sn, Sb, Pt, Au and Pb are measured at an angle of 90 in the X-ray region 5.41 keV. These energies fall between the high-energy side of the L- and M-shell absorption edges of the atoms considered. The present atomic region is significant for solid X-rays to assess the contribution
of resonance and solid-state environmental effects. Also it is the anomalous scattering region for many of the atoms of the
periodic table. Experimental results are compared with theoretical calculations based on form factor formalisms including
the anomalous corrections and available recent S-matrix values. Based on the experimental evidence, the present results indicate the influence of solid-state environmental
effects, the importance of anomalous corrections nearer to absorption edges, the correctness of revised high-energy limit
values, the superiority of S-matrix predictions over form factor values on measured elastic scattering cross-sections in the X-ray regime and also show
the resonance behavior around K, L and M absorption edges.
Received: 27 January 1998 / Received in final form: 4 January 1999 相似文献
4.
Guangqing Pei Changtai Xia Shixun Cao Jungang Zhang Feng Wu Jun Xu 《Journal of magnetism and magnetic materials》2006
Polycrystalline Zn1−xNixO diluted magnetic semiconductors have been successfully synthesized by an auto-combustion method. X-ray diffraction measurements indicated that the 5 at% Ni-doped ZnO had the pure wurtzite structure. Refinements of cell parameters from powder diffraction data revealed that the cell parameters of Zn0.95Ni0.05O were a little bit larger than ZnO. Transmission electron microscopy observation showed that the as-synthesized powders were of the size ∼60 nm. Magnetic investigations showed that the nanocystalline Zn0.95Ni0.05O possessed room temperature ferromagnetism with the saturation magnetic moment of 0.1 emu/g (0.29 μB/Ni2+). 相似文献
5.
R. Ferrini G. Guizzetti M. Patrini F. Nava P. Vanni C. Lanzieri 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):213-216
GaAs Schottky diodes, made on semi-insulating liquid encapsulated Czochralski grown material with concentrations of acceptor
dopants varying from 1014 to 1017 cm-3, were investigated as alpha particle detectors. The charge collection efficiency (CCE) was found to decrease dramatically
with increasing . Optical spectra in transmittance and reflectance were accurately measured to determine the concentrations of both neutral
and ionised EL2 defects as a function of . The concentration of ionised EL2+ centres was shown to increase with , and to be quasi inversely proportional to the CCE values. This behaviour strongly supports the hypothesis that the EL2 defects
play the main role in the compensation of the material and in limitation of the detection properties.
Received 21 March 2000 相似文献
6.
M.G. Donato G. Faggio M. Marinelli G. Messina E. Milani A. Paoletti S. Santangelo A. Tucciarone G. Verona Rinati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):133-139
High quality synthetic diamonds were grown on single-crystal silicon by microwave plasma enhanced chemical vapour deposition
(CVD). A careful optimisation of both the experimental setup and the growth parameters was necessary before that the achievement
of the best results was made possible. The films were deposited using a CH4-H2 gas mixture at methane concentrations variable in the range 0.6-2.2%, while the substrate temperature was fixed at 750 °C. Raman spectroscopy and photoluminescence (PL) were utilised to monitor the quality of the deposited films and to study
the spatial distribution of defects, respectively. Micro-Raman analysis shows that linewidths of the diamond peak lower than
2.4 cm-1 can be easily measured at the growth surface, indicating that the crystalline quality of individual grains is comparable
to that of the best natural diamonds. The excellent phase purity of the diamond microcrystals at the growth surface is witnessed
by the complete absence of any non-diamond carbon feature and by a very weak luminescence background in the 1.6-2.4 eV spectral
range. A worsening of the quality of the diamond particles is found moving from the growth surface towards the film-substrate
interface. A photoluminescence feature at about 1.68 eV, commonly associated to Si impurities, is distinctly observed as the
exciting laser beam is focused close to the interface. A progressive degradation of the global quality of the films is found
with increasing methane concentration in the gas mixture, as witnessed by an increased PL background in the films grown at
higher methane concentrations.
Received 24 November 2000 相似文献
7.
Zitterbewegung, chirality, and minimal conductivity in graphene 总被引:3,自引:0,他引:3
M. I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):157-160
It has been recently demonstrated experimentally that
graphene, or single-layer carbon, is a gapless semiconductor with
massless Dirac energy spectrum. A finite conductivity per channel
of order of e2/h in the limit of zero temperature and zero
charge carrier density is one of the striking features of this
system. Here we analyze this peculiarity based on the Kubo and
Landauer formulas. The appearance of a finite conductivity without
scattering is shown to be a characteristic property of Dirac
chiral fermions in two dimensions. 相似文献
8.
M. I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):225-228
A theory of electron states for graphene nanoribbons
with a smoothly varying width is developed. It is demonstrated
that the standard adiabatic approximation allowing to neglect the
mixing of different standing waves is more restrictive for the
massless Dirac fermions in graphene than for the conventional
electron gas. For the case of zigzag boundary conditions, one can
expect a well-pronounced conductance quantization only for highly
excited states. This difference is related to the relativistic
Zitterbewegung effect in graphene. 相似文献
9.
A. John Peter K. Gnanasekar K. Navaneethakrishnan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(3):283-288
A variational formalism for the calculation of the binding energies
of hydrogenic donors in a parabolic diluted magnetic semiconductor quantum
dot is discussed. Results are obtained for Cd
Mn
Te/Cd
Mn
Te structures as a
function of the dot radius in the presence of external magnetic and electric
fields applied along the growth axis. The donor binding energies are
computed for different field strengths and for different dot radii. While
the variation of impurity binding energy with dot radii and electric field
are as expected, the polarizability values enhance in a magnetic field.
However, for certain values of dot radii and in intense magnetic fields the
polarizability variation is anomalous. This variation of polarizability is
different from non- magnetic quantum well structures. Spin polaronic shifts
are estimated using a mean field theory. The results show that the spin
polaronic shift increases with magnetic field and decreases as the electric
field and dot radius increase. 相似文献
10.
Space-time dispersion of graphene conductivity 总被引:1,自引:0,他引:1
L. A. Falkovsky A. A. Varlamov 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(4):281-284
We present an analytic calculation of the conductivity of pure graphene as a
function of frequency ω, wave-vector k, and temperature for the
range where the energies related to all these parameters are small in
comparison with the band parameter γ≃3 eV, but much larger than
the collision rate τ-1. The simple asymptotic expressions are given
in various limiting cases. For instance, the conductivity for kv0≪
T≪ω is equal to σ(ω,k)=e2/4ħ and independent
of the band structure parameters γ and v0. Our results are also
used to explain the known dependence of the graphite conductivity on
temperature and pressure. 相似文献
11.
V. Tsurkan St. Plogmann M. Demeter D. Hartmann M. Neumann 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):401-403
X-ray photoelectron spectroscopy was used to investigate ACr2S4 (, Zn, Mn, Fe, Fe:Cu) and BCr2Se4 (, Cu, Hg, Hg:Cu) single crystals. Well defined splitting of the Cr 2p core level has been found. The local magnetic moments of the Cr ions are responsible for the observed effect.
Received 2 November 1999 相似文献
12.
A. Thränhardt C. Ell G. Khitrova H.M. Gibbs 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):571-576
We calculate energy levels, dipole moments and radiative broadening of interface fluctuation quantum dots. For optically allowed
states, the dipole moment grows proportionally to the lateral quantum dot radius while the radiative broadening saturates
towards the quantum well radiative broadening for large lateral quantum dot radii. This is accompanied by a change in the
angular emission pattern, concentrating emission in forward and backward direction. Optically forbidden states do not couple
to light propagating in the growth direction yet they may have a considerable radiative broadening due to spontaneous emission
in other directions.
Received 20 March 2002 Published online 25 June 2002 相似文献
13.
We synthesized the Mn-doped Mg(In2−xMnx)O4 oxides with 0.03?x?0.55 using a solid-state reaction method. The X-ray diffraction patterns of the samples were in a good agreement with that of a distorted orthorhombic spinel phase. Their lattice parameters and unit-cell volumes decrease with x due to the substitution of the smaller Mn3+ ions to the larger In3+ ions. The undoped MgIn2O4 oxide presents diamagnetic signals for 5 K?T?300 K. The M(H) at T=300 K reveals a fairly negative-sloped linear relationship. Neither magnetic hysteresis nor saturation behavior was observed in this parent sample. For the Mn-doped samples, however, positive magnetization were observed between 5 and 300 K even if the x value is as low as 0.03. The mass susceptibility enhances with Mn content and it reaches the highest value of 1.4×10−3 emu/g Oe (at T=300 K) at x=0.45. Furthermore, the Mn-doped oxides with x=0.06 and 0.2, respectively, exhibit nonlinear magnetization curves and small hysteretic loops in low magnetic fields. Susceptibilities of the Mn-doped samples are much higher than those of MnO2, Mn2O3 oxides, and Mn metals. These results show that the oxides have potential to be magnetic semiconductors. 相似文献
14.
We present the first-principles calculations of digital magnetic heterostructures Si/M, Ge/M. GaAs/M, GaSb/M, GaN/M and GaN/M (50%) with M=Cr, Mn, Fe, and Co. The interaction between magnetic dopants results in a wide spin-polarized two-dimensional band inside the gap. It is found that beginning occupation of the minority-spin band greatly increases the energy of the ferromagnetic (FM) state and leads, as a rule, to the antiferromagnetic (AFM) spin ordering. This mechanism causes transition to the AFM state, when interaction between magnetic atoms is too strong, and defines the optimum of Curie temperature as a function of transition element concentration in magnetic layers. 相似文献
15.
H.D. Gan H.Z. Zheng J.J. Deng J.F. Bi H. Zhu Y. Ji P.H. Tan F.H. Yang J.H. Zhao 《Solid State Communications》2007,141(8):453-458
A series of (Ga, Mn)As epilayers have been prepared on semi-insulating GaAs (001) substrates at 230 °C by molecular-beam epitaxy under fixed temperatures of Ga and Mn cells and varied temperatures of the As cell. By systematically studying the lattice constants, magnetic and magneto-transport properties in a self-consistent manner, we find that the concentration of As antisites monotonically increases with increasing As flux, while the concentration of interstitial Mn defects decreases with it. Such a trend sensitively affects the properties of (Ga, Mn)As epilayers. 相似文献
16.
X.Q. Zhao B.X. Liu Y. Liang Z.Q. Hu 《Applied Physics A: Materials Science & Processing》1997,64(5):483-486
5 . The γ-Fe particles, because of their paramagnetic nature, are very convenient for investigation on the attributes of iron
oxide layers formed on the particle surfaces. Structures, morphologies and magnetic properties of the oxide layers covering
the iron ultrafine particles have been studied using transmission electron microscopy observation, magnetic property measurement,
X-ray diffraction and annealing treatment. Convincing evidences established that the iron oxide layers are not continuous
and consist of very fine crystallites, and that these layers are non-ferromagnetic and have no contribution to the saturation
magnetization of the iron particles. The iron oxide layers formed at room temperature was determined to be Fe3O4. Additionally, a brief annealing of the iron particles in air were performed to examine magnetic properties of the formed
iron oxide layers and ultrafine oxide particles.
Received: 30 April 1996/Accepted: 5 November 1996 相似文献
17.
We report on the ferromagnetic characteristics of Zn1−xMnxO films (x=0.1-0.3) prepared by the sol-gel method on silicon substrates using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and superconducting quantum interference device (SQUID) magnetometry at various temperatures. Magnetic measurement show that the Curie temperature (TC) and the coercive field (HC) were ∼39 K and ∼2100 Oe for the film of x=0.2, respectively. EDS and TEM measurements indicate that Mn content at the interface is significantly higher than that at the center of the Zn0.8Mn0.2O film showing the ratio, Zn:Mn:O≅1:12:15. This experimental evidence suggests that ferromagnetic precipitates containing manganese oxide may be responsible for the observed ferromagnetic behavior of the film. 相似文献
18.
E. Kogan M. Auslender M. Kaveh 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):373-376
Localization and dephasing of conduction electrons in a low carrier density ferromagnet due to scattering on magnetic fluctuations
is considered. We claim the existence of the “mobility edge”, which separates the states with fast diffusion and the states
with slow diffusion; the latter is determined by the dephasing time. When the “mobility edge” crosses the Fermi energy a large
and sharp change of conductivity is observed. The theory provides an explanation for the observed temperature dependence of
conductivity in ferromagnetic semiconductors and manganite pyrochlores.
Received 17 January 1999 and Received in final form 12 March 1999 相似文献
19.
E. Barborini C. Lenardi P. Piseri P. Milani R. G. Agostino T. Caruso E. Colavita S. La Rosa M. Bertolo C. Ducati 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):273-276
Inclusions of metals in the growth process of carbon
cluster assembled materials (ns-C) induce modifications in the
structural and electronic properties of the material. A novel
pulsed microplasma cluster source (PMCS) is able to deliver
highly intense, collimated and stable beams suitable for
producing bulk quantities of cluster-assembled nanocomposite
films. Loading of metal nanoparticles into carbon cluster based
films is obtained either by mixing a gas phase metallorganic
compound with the carrier gas (He) before entering into the
source (for example molybdenum (V) isopropoxide), or by using a
double component sputtering target (metal (Ti, Ni)/graphite). The study of film
morphology on nanometer scale, carried out by transmission
electron microscopy (TEM), reveals the dispersion in a ns-C
matrix of metallic particles and, in the case of molybdenum
containing films, also of carbide particles. Spatially resolved
ultraviolet photoemission spectroscopy confirms the segregation
of metal particles and exhibits evident anisotropy in the
Mo:ns-C films, mainly ascribable to the formation of carbide
nanoparticles. 相似文献
20.
Fucheng Yu Cunxu GaoSe Young Jeong P.B. ParchinskiyDojin Kim Hyojin KimYoung Eon Ihm 《Journal of magnetism and magnetic materials》2006
GaMnAs and Be-codoped GaMnAs films grown via molecular beam epitaxy (MBE) were heat treated and the stability of Mn in the matrix was investigated. MnAs had a stable phase at the low growth temperature, but MnGa was stable at the annealing temperature. Be-codoping did not prevent the precipitation processes, but Be itself was stable during the annealing process to maintain the GaAs matrix at the high conductivity. 相似文献