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1.
S. Faetti M. Nobili I. Raggi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):445-453
In this paper we report an experimental investigation on the dynamics of the azimuthal director reorientation at a nematic-solid
interface. Three qualitatively different kinds of substrates have been investigated: I) intrinsically anisotropic SiO-substrates
(-evaporation), II) isotropic SiO-substrates (-evaporation) and III) rubbed PVA-substrates. In the case II), an in-plane anisotropy was induced cooling slowly the thermotropic
nematic liquid crystal (NLC) from the isotropic phase in the presence of a 0.75 T magnetic field. The reorientation dynamic
of the surface azimuthal director angle at the switching-on and off of a magnetic (or electric) field has been investigated.
All the substrates show comparable azimuthal anchoring energies and two dynamic regimes: a fast dynamic response, driven by
the bulk director reorientation and an extremely slow reorientation. The slow dynamics is explained in terms of anisotropic
adsorption of NLC molecules on the solid substrate and is well represented by a stretched exponential.
Received 7 December 1998 相似文献
2.
S. Schinzer S. Köhler G. Reents 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):161-168
We examine the step dynamics in a 1+1-dimensional model of epitaxial growth based on the BCF-theory. The model takes analytically
into account the diffusion of adatoms, an incorporation mechanism and an Ehrlich-Schwoebel barrier at step edges. We find
that the formation of mounds with a stable slope is closely related to the presence of an incorporation mechanism. We confirm
this finding using a solid-on-solid model in 2+1 dimensions. In the case of an infinite step edge barrier we are able to calculate
the saturation profile analytically. Without incorporation but with inclusion of desorption and detachment we find a critical
flux for instable growth but no slope selection. In particular, we show that the temperature dependence of the selected slope
is solely determined by the Ehrlich-Schwoebel barrier which opens a new possibility in order to measure this fundamental barrier
in experiments.
Received 11 May 1999 and Received in final form 6 November 1999 相似文献
3.
Jolanta Prywer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):61-68
According to contemporary crystal growth theories, crystals are bound by low-index faces which are the most slowly growing.
However, high-index faces are observed in crystal habits more and more often. In this paper the growth of high-index faces
is analysed from a crystallographic perspective. It is shown that the crystallographic structure of a given crystal, expressed
by the trigonometric function of appropriate interfacial angles, influences to great degree the crystallisation process and
the morphology of crystals, in particular the behaviour of high-index faces. Additionally, it is concluded that at particular
crystallographic structure of a crystal, a given high-index face may exist in the habit and develop its size, although it
grows much faster than the neighbouring faces.
Received 31 July 2001 相似文献
4.
The combined effect of an anisotropic surface tension and interface kinetics in dendritic crystal growth is studied numerically
by a fully dynamical front-tracking method in two dimensions. It is shown how kinetic effects can be incorporated into the
algorithm without causing numerical instabilities. The results are compared to the theory of E.A. Brener and V.I. Mel'nikov
(Adv. Phys. 40, 53 (1991)). A particularly interesting case arises when the directions of minimum surface tension and minimum kinetic effect
are different. In this case, when the deviation from local equilibrium is increased, the predicted transition from dendrites
growing into the direction of the minimum surface stiffness to the direction of minimum kinetic effect is confirmed. Dendrites
near this transition show strong oscillations and correlated side-branching. The transition where the oscillating dendrites
change direction shows hysteresis.
Received 30 September 1999 and Received in final form 23 February 2000 相似文献
5.
A simplified version of the model by Elser and Joseph for the process of growth of an entropically stabilized, two-dimensional
quasicrystal with no dynamics in the bulk, is proposed. The phason fluctuations are modeled by a scalar field on a periodic
lattice. The choice of the master equation for the growth is restricted by the requirement that its detailed balance solution
describes the equilibrium fluctuations of the field with a quadratic Hamiltonian. The model is parametrized by the chemical
potential bias and the microscopic surface tension coefficient . The phase diagram of the system on the plane (, ) shows several distinct regimes of growth, separated by relatively narrow transition zones. Within the regions corresponding
to these regimes, the phason fluctuations do not depend on and . Analytic expressions for the spectra of phason fluctuations are obtained and confirmed by numerical simulation.
Received 30 June 2000 相似文献
6.
M. Konôpka V. Bužek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(2):285-293
We propose a method for entangling a system of two-level atoms in photonic crystals. The atoms are assumed to move in void
regions of a photonic crystal. The interaction between the atoms is mediated either via a defect mode or via a resonant dipole-dipole interaction. We show that these interactions can produce pure entangled atomic states. We analyze the problem with parameters typical
for currently existing photonic crystals and Rydberg atoms and we show that the atoms can emerge from photonic crystals in
entangled states. Depending on the linear dimensions of the crystal we estimate that a pair of atoms entangled in a photonic
crystal can be separated by tens of centimeters.
Receive 11 June 1999 and Received in final form 4 October 1999 相似文献
7.
R. Granger J.T. Benhlal O. Ndap R. Triboulet 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):429-436
The dielectric function of ZnSe has been deduced from ellipsometric measurements between 20 K and 380 K. is analysed around each critical point with the standard critical point model. The variations of the different parameters
characterising each transition with temperature are presented and analysed. The temperature coefficients of the energies of
the critical transitions are given. is essentially governed by the Coulomb interaction near the fundamental gap. Thanks to the high binding energy of the exciton
and the low spectral width of the ellipsometer, the fundamental state of the exciton is found completely separated from the
first excited states and the continuum at low temperature. In return the strong transition E1 near the L points of the Brillouin zone can be described equally well with a 2D or an excitonic transition.
Received 5 February 1999 and Received in final form 15 June 1999 相似文献
8.
Some years ago we developed an automatized reflectometric method to measure the surface azimuthal anchoring energy of nematic
liquid crystals on an optically isotropic substrate. This method provides a high accuracy and sensitivity but requires the
use of wedge glass plates and a sufficiently high anisotropy of the intensity reflectivity coefficients. This latter condition
restricts greatly the number of possible substrates that can be investigated with this technique. Here we develop a new reflectometric
method which offers comparable or better accuracy and sensitivity but does not require wedge plates and high anisotropy of
the reflectivity coefficients. The method is fully automated and provides a direct measurement of the azimuthal director angle.
The experimental procedure exploits the dependence of the reflectivity tensor on the surface director orientation. The measurement
of the azimuthal angle does not require any knowledge of the optical parameters of the nematic material and of the optically
isotropic substrate, and provides an absolute accuracy better than 0.2° in the whole range 0-360° and a sensitivity better than 0.1°. This reflectometric method can be also used with weakly anisotropic substrates as well as thin rubbed polymeric layers.
In this latter case, the effective uncertainty in the measurement of the director azimuthal angle depends on the substrate
anisotropy. A simple and direct experimental procedure to estimate this uncertainty is proposed.
Received 8 January 2002 and Received in final form 27 February 2003 / Published online: 15 April 2003
RID="a"
ID="a"e-mail: faetti@df.unipi.it 相似文献
9.
Arkhipkin VG Gunyakov VA Myslivets SA Zyryanov VY Shabanov VF 《The European physical journal. E, Soft matter》2007,24(3):297-302
A one-dimensional ZrO2/SiO2 photonic crystal with a 4-n -pentyl-4' -cyanobiphenyl (5CB) nematic defect layer was used to investigate the transmission spectra of light polarized
parallel and perpendicular to the liquid-crystal director at different angles of incidence. The spectra of the photonic crystal
were shown to split into four polarized components Tij at oblique incidence. When the incident angle increased, the bandgap edges and the defect modes shifted towards short wavelengths,
while the amplitudes of the defect modes increased for the transverse magnetic polarization and decreased for the transverse
electric polarization. The observed discrepancy between the defect mode amplitudes in the center and near the edges of the
photonic bandgap was found to be related to the radiation losses inside the defect layer of a non-ideal photonic crystal.
The simulated transmission spectra obtained using recurrence relations and taking into account the decay of defect modes are
in good agreement with the experimental data. 相似文献
10.
N. Richard 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):411-422
This paper describes the magneto-optical effects and the reflectivity behaviors of bilayers based on magnetic and isotropic
()/anisotropic () layers under the condition of total internal reflection. In the framework of Green's dyadic technique, we show accurately
the optical properties of anisotropic layers deposited on a substrate. We present numerical simulations which account for
the variation of angle of incidence at the HeNe laser wavelength. The Kerr rotation is found to increase significantly around
the optical modes in total reflection. We also discuss the importance of anisotropic effects due to the crystallization of
the dielectric material () which occur in the reflectivity and Kerr rotation spectra.
Received 26 January 2000 相似文献
11.
M. Gartz C. Keutgen S. Kuenneke U. Kreibig 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(1):127-131
In this paper a detailed experimental study of Coherent Population Trapping (CPT) effect on sodium induced by a dye-laser
operating in a three-mode regime is presented and a detailed analysis of the role of velocity changing collisions is made.
These collisions show a very small relaxation effect on the dark resonances which are visible even at high pressures. For
the first time we demonstrate the persistence of the ground state coherence to pressures up to one atmosphere for a relatively
“heavy” buffer gas like argon. The experimental results have been compared with theory and a very good agreement has been
obtained. Preliminary results on the effect of Na-N2 collisions on Coherent Population Trapping are presented.
Received: 5 October 1998 / Received in final form: 3 December 1998 相似文献
12.
D.G. Angelakis P.L. Knight 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):247-250
We show how entangled atomic pairs can be prepared in order to test the Bell inequalities. The scheme is based on the interaction
of the atoms with a highly localized field mode within a photonic crystal. The potential of using optically separated transitions
and the stability of the entangled state to spontaneous emission could lead to the closure of the communication and the detection
loopholes appearing in experiments so far. The robustness of the scheme against detector inefficiencies, the spread in the
atomic velocities and the fact that the entangled pairs are not generated simultaneously is also studied.
Received 31 July 2001 and Received in final form 30 November 2001 相似文献
13.
N. Petit V. Garnier V. Ta Phuoc R. Caillard A.-M. Frelin A. Ruyter I. Laffez J.-C. Soret A. Maignan F. Gervais 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):423-429
The reflectivity spectra of an oriented ceramic of Bi-2223 has been investigated by polarized infrared reflectivity spectroscopy
in the energy range 0.005-2.2 eV. It is shown that the data for the polarization parallel to the c axis cannot be fitted with a one-component Drude or extended-Drude model. The conductivity spectrum is then obtained from
the best fit of a “double-damping Drude” model to reflectivity spectra, itself derived from the factorized form of the dielectric
function, and by a Kramers-Kronig inversion as well. The data and their analysis give a new insight of the 2D character of
the system.
Received 26 April 2001 and Received in final form 28 August 2001 相似文献
14.
G. Zhou D. Wang S. Yang Y. Ren X. Xu Z. Shao X. Zhao M. Jiang Y. Tian F. Hao S. Li P. Shi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):389-393
Linear and nonlinear optical properties of a new organic dye, trans-4-[p-(N-n-butyl-N-n-butylamino)-styryl]-N-methyl-pyridinium tetraphenylborate solution in dimethyl formamide (DMF) have been studied systematically.
When excited with mode-locked picosecond 1 064 nm laser beam, intense upconversion fluorescence and superradiance can be obtained.
The temporal behaviors of one-photon absorption and two-photon absorption (TPA) fluorescence and superradiance have been studied.
The highest upconversion efficiency was found to be 4.1% at a pump energy of 4 mJ. By using an optical parameter amplifier
(OPA) as the pump laser, the nonlinear transmittance and upconversion efficiencies of the dye solution at different wavelengths
were measured. The strongest linear absorption was found at a wavelength of 930 nm whereas the highest upconversion efficiency
was at 1 030 nm. The 100 nm red-shift for the highest upconversion efficiency wavelength compared with the strongest nonlinear
absorption are caused by excited state absorption.
Received 17 October 2001 and Received in final form 21 December 2001 相似文献
15.
S. Scandolo F. Bassani V. Lucarini 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):319-323
We describe a procedure to take into account the spatial dispersion of the optical excitations in the susceptibility sum rules.
We show that this implies that relativistic corrections of the same order must be considered. The final result is a decrease
of the total oscillator strength equal to the ratio of the average electron kinetic energy with mc2. We propose experiments with synchrotron radiation sources on crystals of heavy elements to observe the described effect.
Received 5 June 2001 相似文献
16.
A. Ahmad A. Alsaad 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(1):41-46
Zinc oxide thin films were sputter deposited on (100) silicon substrates at
250 ○C substrates temperature via reactive unbalanced dc magnetron
process using pure zinc target and argon/oxygen gases. The influence of the
applied dc sputtering power (between 100 to 250 Watts, step 50 Watts) on the
optical properties of the grown films was systematically investigated by
variable angle of incidence spectroscopic ellipsometry (VASE) technique. The
refractive indices were found to follow the second-order Sellmeier
dispersion relation. However, Cauchy-like dispersion model was formulated to
account for the absorption tail and excitonic structure near the direct band
gap. The optical properties such as refractive indices, extinction
coefficients, optical band gaps, Urbach's energies, excitonic binding
structure and absorption coefficients of the grown films were reported as a
function of dc power in the photon energy range between 1.2 eV and 4.2 eV.
The films were found to be polycrystalline with (002) preferred orientation. 相似文献
17.
L.-H. Tang P. Smilauer D.D. Vvedensky 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):409-412
Two types of mechanisms are proposed for mound coarsening during unstable epitaxial growth: stochastic, due to deposition
noise, and deterministic, due to mass currents driven by surface energy differences. Both yield the relation H=(RWL)2 between the typical mound height W, mound size L, and the film thickness H. An analysis of simulations and experimental data shows that the parameter R saturates to a value which discriminates sharply between stochastic () and deterministic () coarsening. We derive a scaling relation between the coarsening exponent 1/z and the mound-height exponent which, for a saturated mound slope, yields .
Received: 11 November 1997 / Revised in final form: 28 November 1997 /
Accepted: 28 November 1997 相似文献
18.
C. Benjamin 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):403-410
Reflectance measurements from p-type GaSb:Zn epitaxial films with different hole concentrations (1017–1018 cm-3) have been investigated over the frequency region of
100–1000 cm-1. A minimum broadening feature corresponding to the hole plasmon was observed in the reflectance spectra. The experimental
infrared spectra were well fitted using a
Lorentz-Drude dispersion model. The real part ε1 of the dielectric function decreases with increasing hole concentration. However, the imaginary part ε2
increases with hole concentration in the far-infrared region.
This indicates that the acoustic- and optic-phonons mainly
participate in the free carrier absorption processes. The hole
mobility obtained from Hall-effect measurements is slightly
larger than that derived from optical measurements and the
average ratio of mobilities is estimated to be 1.33. Owing to
overdamping effects, the upper branch of longitudinal-optical
phonon plasmon (LPP) coupled modes was observed. The upper
LPP+ frequency increases with hole concentration and it
shows a transition from phonon-like to plasmon-like behavior. A
theoretical analysis with solutions in the complex frequency
plane describes these experimental results. 相似文献
19.
W. X. Shu Z. Ren H. L. Luo F. Li 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):541-546
We systematically investigate the reflection and refraction of an
electromagnetic wave between two semi-infinite anisotropic
magnetoelectric materials. Using the integral formulation of Hertz
vectors and the principle of superposition, we generalize the
extinction theorem and derive the propagation characteristics of
wave. Applying the results obtained, we find a general origin of
Brewster effect. We also show that, through choosing appropriate
material parameters, oblique or omnidirectional total transmission
can occur to TE and TM waves. Compared to the traditional method,
the method used here discloses the underlying mechanism of wave
propagation between two arbitrary anisotropic materials and can be
applied to other problems of propagation. 相似文献
20.
P. Nozières F. Pistolesi S. Balibar 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):387-394
We consider the shape of crystals which are soft in the sense that their elastic modulus μ is small compared to their surface
tension γ, more precisely μa < γ where a is the lattice spacing. We show that their surface steps penetrate inside the crystal as edge dislocations. As a consequence,
these steps are broad with a small energy which we calculate. We also calculate the elastic interaction between steps a distance
d apart, which is a 1/d
2 repulsion. We finally calculate the roughening temperatures of successive facets in order to compare with the remarkable
shapes of lyotropic crystals recently observed by Pieranski et al. [#!Pieranski!#,#!EPJ!#]. Good agreement is found.
Received 25 June 2001 相似文献