共查询到20条相似文献,搜索用时 15 毫秒
1.
Archer P Dierking I Görtz V Goodby JW 《The European physical journal. E, Soft matter》2008,25(4):385-393
The full Landau potential of several, widely varying ferroelectric liquid-crystalline materials has been experimentally determined. Tilt angle and polarisation data is analysed across the SmA to SmC transition for varying applied electric-field amplitudes, allowing the determination of all the coefficients of the generalised Landau model of ferroelectric liquid crystals. The materials investigated encompass different materials, including low-polarisation mixtures to high-polarisation single-component materials. The materials also possess a variation in the order of the SmA to SmC phase transition from strongly first order to strongly second order. The effects of both the polarisation and order of phase transition of the system are discussed with respect to the various terms of the generalised Landau model. Further, the mechanisms behind the difference between a first- and second-order phase transition are discussed with respect to the Landau potential and the second Landau coefficient b . 相似文献
2.
K. L. Sandhya Yu. P. Panarin V. P. Panov J. K. Vij R. Dabrowski 《The European physical journal. E, Soft matter》2008,27(4):397-405
Results of the experimental study on different antiferroelectric liquid crystal (AFLC) materials are presented using a number
of techniques such as the optical birefringence, electro-optics and the measurements of optical thickness of free-standing
films. Despite differences in the molecular structures of the various AFLC materials studied, these are found to exhibit a
de Vries type of smecticA* (SmA
*) properties in a temperature range higher than SmC
* . This correlation leads to the conclusion that these two classes of liquid crystals are related to each other. Furthermore,
we suggest that these arise from the same physical mechanism, namely the existence of the weak synclinic (or reduced anticlinic)
correlations between the neighbouring molecular tilt directions. 相似文献
3.
High-resolution photorefractive gratings in nematic liquid crystals sandwiched with photoconductive polymer film 总被引:1,自引:1,他引:0
F. Yao Y. Pei Yu Zhang J. Zhang C. Hou X. Sun 《Applied physics. B, Lasers and optics》2008,92(4):573-576
Photorefractive gratings with high grating resolution were observed in the 20 μm thick low-molar-mass nematic liquid crystal
(NLC) cell with a separate photoconductive (PC) poly(N-vinylcarbazole) layer. An orientational grating with a grating spacing of 1.9 μm was produced. It is believed that a space–charge
field with small fringe spacing forms in the PC layer and its evanescent component penetrates into the NLC layer. The penetrated
evanescent field drives the NLC to reorient, and consequently the orientational grating forms. The model indicates that the
modulated field exists in several hundred nanometers near the surface, and thus the orientational grating is not full of the
NLC film, which is consistent with the observed phenomena of the multiple diffractions. Besides, asymmetric two-beam coupling
of 11.2% was achieved for the grating with a grating spacing of 1.9 μm, and a net gain coefficient of larger than 62 cm−1 was obtained. 相似文献
4.
Wenhui Ma 《Applied Physics A: Materials Science & Processing》2009,96(4):915-920
The effect of surface tension associated internal pressure on the Curie phase transition in ferroelectric nanowires and nanodots
has been investigated using a modified Landau–Ginzburg–Devonshire phenomenological approach. Based on experimental data on
the size- dependent phase transition in freely suspended single-crystalline ferroelectric nanocrystals, bulk surface tension
coefficients for BaTiO3 and PbTiO3 have been determined to be of the order of 1–2 N/m. The present theoretical study reproduces the size dependence of the transition
temperature experimentally acquired in individual BaTiO3 single-crystalline nanowires. In the case of PbTiO3 single-crystalline nanodots, however, in order to fit the theoretically calculated size-dependent ferroelectric transition
with the experimental data, an effective surface tension coefficient has been introduced, which is size dependent and can
be much higher than the bulk value.
An erratum to this article can be found at 相似文献
5.
T. Dekola D. Isakov E. de Matos Gomes V. H. Nunes Rodrigues M. M.R. Costa 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(4):519-522
Glycine glycinium perrhenate is a new hydrogen bonded crystalline material that exhibits several phase transitions at low
and high temperature. At room temperature the structure shows some special features. One dimensional polar chains, linked
by strong hydrogen bonds exist parallel to [100], [010] and [–110]. The structural, thermal and dielectric properties of this
new perrhenic salt are presented and a relationship is established. 相似文献
6.
This paper presents a design of sharp transmission filters using band edge resonance effects in a hetero-structure composed
of one-dimensional photonic crystals with different periods. Assuming that the photonic crystals are made of identical pairs
of transparent materials, the band-edge resonance occurs when the periods are distributed in a geometrical progression with
a common ratio, r=r
c
, where r
c
is a known function of refractive-index modulation, incident angle and the polarization of light. The band-edge resonance
results in sharp resonant peaks in the transmission spectrum, with the full width at half maximum of the peaks increasing
with an increase in the number of unit cells in each photonic crystal. Furthermore, if M photonic crystals are used to construct the hetero-structure, M−1 resonant peaks with the spacing between kth (1<k<M) and (k−1)th peaks equal to the band gap of the kth photonic crystal form in the transmission spectrum. 相似文献
7.
The influence of controllable parameters like temperature and wavelength on the trajectories of light in a nematic liquid crystal with topological defects is studied through a geometric model. The model incorporates phenomenological details as how the refractive indices depend on such parameters. The deflection of light by the topological defect is then shown to be greater at lower temperatures and shorter wavelengths. 相似文献
8.
M. Humar M. Škarabot M. Ravnik S. Žumer I. Poberaj D. Babič I. Muševič 《The European physical journal. E, Soft matter》2008,27(1):73-79
We show that diffraction of visible light from 2D dipolar nematic colloidal crystals can be tuned electrically. When the external
electric field of ∼ 1V/μm is applied in a direction perpendicular to the plane of the 2D colloidal crystal, the induced strain
is highly anisotropic, and the inter-colloidal spacing changes by as much as 20% along one direction and ∼ 2% along the perpendicular
one. Although the speed of response is in the range of several seconds, this novel mechanism could provide interesting photonic
applications. 相似文献
9.
X. F. Xu N. Xu W. Hu J. D. Wu Y. Q. Shen Z. F. Ying 《Applied Physics A: Materials Science & Processing》2009,96(2):415-421
The Fourier transform infrared (FTIR) spectra and switching current response in sodium nitrite:poly(vinyl alcohol) nanocomposite
films have been studied as a function of composition of NaNO2. The switching current data fitted well to infinite-grain model (IGM) in the region t<t
s
and to finite-grain model (FGM) in the region t≥t
s
. The microscopic parameters like the dimensionality, the domain wall velocity, and the nucleation rate have been evaluated
which provide more physical insight of the switching phenomena in the composite films. The polarization current and nucleation
rate are optimum in 50 wt.% composite film and have been discussed in terms of grain size and strain variations with the composition.
The effect of applied field and pulse width variation on the switching behavior of 50 wt.% composition has also been studied.
The exponential field dependence of the domain wall velocity and the nucleation rate indicate that nucleation mechanism is
responsible for switching phenomena in the composite films. The writing pulse width affects significantly on the switching
behavior of the composite films. 相似文献
10.
Shichun Jiang Chaoliang He Yongfeng Men Xuesi Chen Lijia An Sérgio S. Funari Chi-Ming Chan 《The European physical journal. E, Soft matter》2008,27(4):357-364
The reversible transitions of the lamellae of a crystalline-crystalline diblock copolymer from the melt to crystallites were
studied using simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) measurements with synchrotron
radiation. A symmetric poly(ethylene oxide)-poly( -caprolactone) diblock copolymer was chosen for this study. We showed in the course of the block copolymer crystallisation
that the time-resolved integrated intensity I
int was proportional to the product of the volume fractions of the PEO and PCL phases and the scattering contrast due to the
electron density difference. These results demonstrated that simultaneous SAXS/WAXS measurements could be used to monitor
the crystallisation process in two domains of different sizes at the same time. 相似文献
11.
I.?A.?Santos R.?G.?Mendes J.?A.?Eiras J.?de?Los?S.?Guerra E.?B.?Araújo 《Applied Physics A: Materials Science & Processing》2009,95(3):757-760
The dielectric properties of Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films were carefully analyzed. In contrast to bulk samples which present three distinct dielectric
relaxation phenomena Sr0.75Ba0.25Nb2O6 thin films present only two of them. The suppression of the third anomaly can be mainly attributed to the narrow grain size
distribution of nanograins and weak tensile strains imposed to the film from the substrate. The whole set of results point
to the interpretation of a dielectric response characteristic of mesoscopic structure, which is composed of clusters and nanodomains. 相似文献
12.
We report on the experimental observation of the beaming effect in photonic crystals using experimentally mapped spatial field
distributions of energy emitted from a subwavelength photonic crystal waveguide into free-space, rendering with crisp clarity
the diffractionless beaming of energy. Our experimental data agree well with our numerical studies of the beaming enhancement
in photonic crystals with modulated surfaces. Without loss of generality, we study the beaming effect in a photonic crystal
scaled to microwave frequencies and demonstrate the technological capacity to deliver long-range wavelength-scaled beaming
of energy. 相似文献
13.
T. P. J. Han E. Cantelar G. Lifante F. Cusso F. Jaque 《Applied physics. B, Lasers and optics》2009,94(2):209-214
This paper reports on the spectroscopy properties, absorption and luminescence, of Cr3+ ions in singly doped, ZnO-codoped, and Zn in-diffused LiNbO3:Cr crystals. In addition to the broad absorption, inter-ionic transitions ascribed to Cr3+ ions located in Li+ and Nb5+ sites; [Cr]Li and [Cr]Nb centres two absorption bands at higher energy are reported and ascribed to the charge transfer transitions of the Cr3+ ions of the two defect centres.
The charge transfer transitions are used as optical probe to study the role of the Zn ions in the Zn in-diffused LiNbO3:Cr samples. It has been observed that the Zn-in-diffused processes created [Cr]Nb centres in the diffusion zone. The location of the diffused Zn2+ ions is considered to be in Li+ site, displacing the Cr3+ ions from the Li+ sites, [Cr]Li, to the Nb5+ positions, [Cr]Nb. 相似文献
14.
M. van Leeuwen 《The European Physical Journal C - Particles and Fields》2009,61(4):569-574
We present selected recent results of multi-hadron correlation measurements in azimuth and pseudorapidity at intermediate
and high p
T
in Au+Au collisions at
, from the STAR experiment at RHIC. At intermediate p
T
, measurements are presented that attempt to determine the origin of the associated near-side (small Δφ) yield at large pseudo-rapidity difference Δη that is found to be present in heavy ion collisions. In addition, results are reported on new multi-hadron correlation measures
at high-p
T
that use di-hadron triggers and multi-hadron cluster triggers with the goal to constrain the underlying jet kinematics better
than in the existing measurements of inclusive spectra and di-hadron correlations. 相似文献
15.
Li Wang Sasa Zhang Qingpu Wang Jiaqi Chen Wei Jiang Ray T. Chen 《Applied Physics A: Materials Science & Processing》2009,95(2):329-334
Photonic crystal based superprism offers a way to design new optical components for beam steering and DWDM (Dense Wavelength
Division Multiplexing) application. Three-dimensional (3D) photonic crystals are especially attractive as they could offer
more control of the light beam. A FCT (Face-Centered-Tetragonal) woodpile structure has been fabricated using layer by layer
stacking techniques with E-Beam lithography. Special planarizations and processes have been introduced to ensure the survivability
and good alignment of the fabricated nanostructures. Scanning electron microscopy results proved the structure uniformity.
With the proper design, the structure exhibits superprism effects around 1550 nm, and such effects have been observed in the
experiments. 相似文献
16.
By performing optical two-wave mixing in a liquid crystal light valve, we are able to slow down optical pulses to group velocities
as slow as a few tenths of mm/s, corresponding to a very large group index. We present experiment and model of the slow light
process occurring in liquid crystal light valves. The large group index corresponds to having a large sensitivity for phase
variations, a property that can be used to increase the sensitivity of Fourier transform interferometer. We show that when
a liquid crystal light valve is inserted in a Mach–Zehnder interferometer, the effect of frequency perturbations at the input
of the system is amplified by a factor related to the group delay. 相似文献
17.
M. Cazayous A. Sacuto D. Lebeugle D. Colson 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(2):209-212
We have performed Raman measurements on high energy excitations in BiFeO3 single crystals as a function of both temperature and laser excitation lines. A strong feature observed at 1250 cm-1 in the Raman spectra has been previously assigned to two phonon overtone. This peak exhibits an unusual frequency shift with
the laser lines and the temperature dependence of its Fano lineshape shows two singularities at 150 K and 200 K which can
be related to magnetic excitations. In the same energy range, we have also identified the two-magnon excitation with a temperature
dependence very similar to the one measured for the one-magnon modes. 相似文献
18.
Two-photon induced photorefraction in undoped lithium tantalate crystals with different compositions
I. S. Steinberg I. E. Kalabin P. E. Tverdokhleb 《Applied physics. B, Lasers and optics》2009,95(3):407-411
Two-photon interband photorefraction in undoped lithium tantalate crystals with composition ranging from 47.95 to 49.6 mol%
of lithium oxide was demonstrated at the wavelength of 532 nm. The photorefractive properties were examined with holographic
method. Two-photon holograms were recorded with high holographic sensitivity, large refractive index change, and fast hologram
writing time. Permanent changes of the refractive index have been obtained. These holograms can be read nondestructively at
the wavelength of 660 nm using heterodyne method. Holographic characteristics strongly depend on composition. 相似文献
19.
Zhi-Bing Wang Yong-Hong Ye Yu-An Zhang Jia-Yu Zhang 《Applied Physics A: Materials Science & Processing》2009,97(1):225-228
Large-scale periodically structured metal films with enhanced optical transmission in visible frequencies were fabricated
by depositing silver onto colloidal crystals. The obtained transmission properties are similar to those observed through periodical
hole arrays in planar metal films. We have experimentally observed two enhanced transmission pass bands in visible frequencies
in these metal films due to the excitation of surface plasmon polaritons. The peak positions of the pass bands depend on the
size of the colloidal spheres. The transmission spectra highly depend on the incident angle for p-polarized light but are
weak for s-polarized light. Our fabrication method provides a promising approach for the fabrication of large-scale low-cost
plasmonic crystals with submicrometer periodicity. 相似文献
20.
Gomathi Natarajan David C. Cameron 《Applied Physics A: Materials Science & Processing》2009,95(3):621-627
In this paper we report on the influence of film thickness on the electrical and gas-sensing properties of tin oxide thin
films grown by atomic layer deposition (ALD) technique. The nature of the carrier and post-flow gases used in ALD was found to have a dramatic influence on the electrical conductance of the deposited films. Up to a film
thickness of 50 nm the sheet conductance of the films increased with the thickness, and above 50 nm the sheet conductance
was not significantly influenced by the film thickness. This effect was attributed to oxygen depletion at the film surface.
When the depth of oxygen depletion (d
dep) was greater than or equal to the film thickness (t), the sheet conductance was thickness dependant. On the other hand, when d
dep≤t, the sheet conductance was independent of the film thickness but depended on the depth of the oxygen depletion. This proposed
explanation was verified by subjecting the films to different lengths of post-annealing in an oxygen depleted atmosphere.
Gas-sensing functionality of the films with various thicknesses was examined. It was observed that the film thickness had
a significant influence on the gas-sensing property of the films. When the thickness was greater than 40 nm, the sensitivity
of the films to ethanol was found to follow the widely reported trend, i.e., the sensitivity decreases when the film thickness
increases. Below the film thickness of 40 nm the sensitivity decreases as film thickness decreases, and we propose a model
to explain this observation based on the increase in resistance due to multiple grain boundaries. 相似文献