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1.
Hartmann L Gorbatschow W Hauwede J Kremer F 《The European physical journal. E, Soft matter》2002,8(2):145-154
The molecular dynamics in thin films (18 nm-137 nm) of isotactic poly(methyl methacrylate) (i-PMMA) of two molecular weights
embedded between aluminium electrodes are measured by means of dielectric spectroscopy in the frequency range from 50 mHz
to 10 MHz at temperatures between 273 K and 392 K. The observed dynamics is characterized by two relaxation processes: the
dynamic glass transition (α-relaxation) and a (local) secondary β-relaxation. While the latter does not depend on the dimensions
of the sample, the dynamic glass transition becomes faster (≤2 decades) with decreasing film thickness. This results in a
shift of the glass transition temperature T
g to lower values compared to the bulk. With decreasing film thickness a broadening of the relaxation time distribution and
a decrease of the dielectric strength is observed for the α-relaxation. This enables to deduce a model based on immobilized
boundary layers and on a region displaying a dynamics faster than in the bulk. Additionally, T
g was determined by temperature-dependent ellipsometric measurements of the thickness of films prepared on silica. These measurements
yield a gradual increase of T
g with decreasing film thickness. The findings concerning the different thickness dependences of T
g are explained by changes of the interaction between the polymer and the substrates. A quantitative analysis of the T
g shifts incorporates recently developed models to describe the glass transition in thin polymer films.
Received 12 August 2001 and Received in final form 16 November 2001 相似文献
2.
We have studied the effect of physical ageing in thin supported glassy polystyrene films by using ellipsometry to detect overshooting
in the expansivity-temperature curve upon heating of aged samples. Films with thickness 10-200 nm have been aged at 70°
C and 80°
C (below the bulk glass transition temperature). We observe clear relaxation peaks in the expansivity-temperature curve for
films thicker than 18 nm but not for the 10 nm film. The intensity of the relaxation peak is inversely proportional to the
film thickness, while the temperatures characteristic to the relaxation peak are almost independent of the film thickness.
These observations are successfully interpreted by the idea that the surface layer of the order of 10 nm has liquid-like thermal
properties.
Received 28 October 2002 / Published online: 1 April 2003
RID="a"
ID="a"Present address: Yokohama Research Center, Mitsubishi Chemical Corporation, 1000 Kamoshida-chou, Aoba-ku, Yokohama 227-8502, Japan; e-mail:
kawana@rc.m-kagaku.co.jp 相似文献
3.
Ngai KL 《The European physical journal. E, Soft matter》2002,8(2):225-235
Large increases of mobility of local segmental relaxation observed in polymer films as the film thickness is decreased, as
evidenced by decreases of the glass temperature, are not found for relaxation mechanisms that have longer length scales including
the Rouse relaxation modes and the diffusion of entire polymer chains. We show that the coupling model predictions, when extended
to consider polymer thin films, are consistent with a large increase of the mobility of the local segmental motions and the
lack of such a change for the Rouse modes and the diffusion of entire polymer chains. There are two effects that can reduce
the coupling parameter of the local segmental relaxation in thin films. One is the chain orientation that is induced parallel
to the surface when the film thickness h becomes smaller than the end-to-end distance of the chains and the other is a finite-size effect when h is no longer large compared to the cooperative length scale. Extremely thin ( ≈ 1.5 nm) films obtained by intercalating a
polymer into layered silicates have thickness significantly less than the cooperative length scale near the bulk polymer glass
transition temperature. As a result, the coupling parameter of the local segmental relaxation in such thin films is reduced
almost to zero. With this plausible assumption, we show the coupling model can explain quantitatively the large decrease of
the local segmental relaxation time found experimentally.
Received 1 August 2001 and Received in final form 1 December 2001 相似文献
4.
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both
by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that
the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose
here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus
of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations
in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that
the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous
dynamics close to T
g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and
we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results
of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the
slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T
g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T
g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation.
Received 21 March 2000 and Received in final form 4 December 2000 相似文献
5.
S. Djordjevic E. Farber G. Deutscher N. Bontemps O. Durand J.P. Contour 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):407-416
We report results obtained with two different experimental set-ups in state-of-the-art YBCO thin films as similar as possible,
prepared by pulsed laser deposition on LaAlO3 substrates: a surface impedance measurement on 4000 ? thick films using a parallel plate resonator (10 GHz), and a far infrared
transmission (100-400 GHz) measurement which requires thinner (1000 ?) samples. The former measurement yields the temperature
variation of the penetration depth λ(T) and the real part of the conductivity, provided the absolute value of λ(T) is known. The latter yields the imaginary part of the conductivity, hence the absolute value of the penetration depth, as
well as its temperature dependence at the measuring frequency. Combining these two experiments, we establish a quasi-linear
temperature variation of λ(T), with a 2 ? K-1 low temperature slope, and a fairly large zero temperature value λ(T = 0)=(1800±200) ? . The scattering rate of the quasi-particles calculated from a two-fluids model shows that the films compare
to good quality single crystals, where twice a larger slope has been found. This surprising behavior is described in detail,
including an in-depth structural analysis of the samples in order to evaluate their similarities. We find that the 10 GHz
data obtained in the thickest films can be fitted to the dirty d-wave mode in the unitarity limit, with an extrapolated slope of 3 ? K-1, but yield a scattering rate that is difficult to reconcile with the high T
c (92 K) of the films.
Received 7 May 2001 and Received in final form 18 October 2001 相似文献
6.
Ellison CJ Kim SD Hall DB Torkelson JM 《The European physical journal. E, Soft matter》2002,8(2):155-166
Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine
the effects of decreasing film thickness on glass transition temperature, T
g, the relative strength of the glass transition, and the relative rate of physical aging below T
g in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state
of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine)
(P2VP) differs from that in the rubbery state with a transition at T
g. Positive deviations from bulk T
g are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T
g are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence
intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength
of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful
information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when
used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of
physical aging in films as thin as 10 nm.
Received 21 August 2001 相似文献
7.
V. Milosavljević S. Djeniže 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):99-104
Characteristics of the Stark broadened and overlapping 447.1 nm He I spectral line and its forbidden 447.0 nm components have
been measured at electron densities between 4.4×1022 m-3 and 8.2×1022 m-3 and electron temperatures between 18 000 K and 33 000 K in plasmas created in five various discharge conditions using the
low pressure pulsed arc as an optically thin plasma source operated in helium-nitrogen-oxygen gas mixture. Good agreement
was found among our measured line characteristics and their existing calculated values, based on the quasistatic approximation.
Possible influence of the singly ionized oxygen impurity atoms (O II) on the intensity values of the dip between allowed and
forbidden components was found that can explain the disagreement among some existing experimental and calculated line characteristics
data, at higher electron temperatures and densities. On the basis of the observed asymmetry of the 447.1 nm spectral line
profile we have obtained the ion contribution parameter at 1022 m-3 electron density and 8 000 K electron temperature.
Received 20 February 2001 and Received in final form 25 April 2001 相似文献
8.
Ultra thin films of glassy polymers such as polystyrene (PS) can show a) anomalously large thickness changes, b) unexpected
dewetting properties, c) large shifts in the glass temperature Tg. The present discussion focusses mainly on point a). A certain cascade of metastable states is presented together with (tentative)
explanations.
Received 1 March 2001 and Received in final form 10 May 2001 相似文献
9.
T. Grenet F. Giroud 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):165-170
We present a study of the electrical transport properties of thin i-Al-Cu-Fe films. We observe clear signatures of a dimensional
crossover in the temperature and magnetic field dependence of the conductivity for films thinner that ≃ 103?. In particular for the thinnest sample the magnetoconductivity is strongly anisotropic, as is expected for the weak localisation
contribution in two dimensions. These experiments show direct qualitative manifestations of the disorder induced quantum interference
effects occurring in quasicrystals. Estimates of the electronic microscopic parameters are in accordance with those obtained
in bulk samples. Their values and significance are discussed.
Received 16 February 2001 and Received in final form 20 June 2001 相似文献
10.
S. Djeniže A. Srećković S. Bukvić 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):11-16
We have obtained transition probabilities (Einstein's A values) of thirteen transitions in doubly (N III), six in triply (N IV) and two in four times (N V) ionized nitrogen spectra
belonging to the 3s-3p and 3p-3d transitions using a relative line intensity ratio (RLIR) technique. The linear low-pressure pulsed arc was used as an optically
thin plasma source operated at 51 400 K electron temperature and 2.2×1023 m-3 electron density in nitrogen plasma. Our A values are compared to recent theoretical and experimental data.
Received 18 December 2001 / Received in final form 29 January 2002 Published online 28 June 2002 相似文献
11.
A. Brioude F. Lequevre J. Mugnier C. Bovier J. Dumas J.C. Plenet 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):115-119
Very thin ZrO
2
films (few nanometers) have been prepared by sol-gel process. These films were deposited onto a stack of a thin silver layer
evaporated on a glass substrate for Surface Plasmons Resonance (SPR) experiments. The first aim of this work is to study the
high densification of the sol-gel films followed by the refractive index and thickness accurate measurements at each step
of the annealing procedure, using an optical set-up based on SPR. Secondly, SPR excitation coupled with micro-Raman experiment
has also been performed to determine the thin films structure depending on layer thickness. Finally, Conventional Transmission
Electron Microscopy (CTEM) and High Resolution (HRTEM) studies have been conducted to check and complete Raman spectroscopy
results. A discussion compares the optical results and the Transmission Electron Microscopy observations and shows that ultra
thin layers structure is strongly depends on films thickness.
Received 14 May 2001 and Received in final form 2 January 2002 相似文献
12.
M. Bonelli A.C. Ferrari A. Fioravanti A. Li Bassi A. Miotello P.M. Ossi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):269-280
Tetrahedral amorphous carbon films have been produced by pulsed laser deposition, at a wavelength of 248 nm, ablating highly
oriented pyrolytic graphite at room temperature, in a 10-2 Pa vacuum, at fluences ranging between 0.5 and 35 Jcm-2. Both (100) Si wafers and wafers covered with a SiC polycrystalline interlayer were used as substrates. Film structure was
investigated by Raman spectroscopy at different excitation wavelength from 633 nm to 229 nm and by transmission Electron Energy
Loss Spectroscopy. The films, which are hydrogen-free, as shown by Fourier Transform Infrared Spectroscopy, undergo a transition
from mainly disordered graphitic to up to 80% tetrahedral amorphous carbon (ta-C) above a threshold laser fluence of 5 J cm-2. By X-ray reflectivity roughness, density and cross-sectional layering of selected samples were studied. Film hardness as
high as 70 GPa was obtained by nanoindentation on films deposited with the SiC interlayer. By scratch test film adhesion and
friction coefficients between 0.06 and 0.11 were measured. By profilometry we obtained residual stress values not higher than
2 GPa in as-deposited 80% sp3 ta-C films.
Received 25 June 2001 相似文献
13.
E. Jahier J. Guéna Ph. Jacquier M. Lintz M.A. Bouchiat 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):221-229
We demonstrate the production of an electric field inside a high temperature cesium vapor cell with external electrodes. This external control of the electric field, which is not possible with a glass cell in presence of a cesium
vapor, is achieved using a cell made of sapphire, and is of particular interest for our ongoing Parity Violation experiment.
We describe the main components and the implementation on the set-up, including the pulsed high voltage generator. With pulse
duration not exceeding 200 ns the system provides a reversible longitudinal E-field of up to 2 kV/cm in the vapor at a density of ∼ 2×1014 at/cm3 without discharge. Atomic signals attest the application of the electric field in the cell, with the predicted value. Further
improvements obtained with sapphire cells are also presented.
Received 15 September 2000 相似文献
14.
Structure distortion, optical and electrical properties of ZnO thin films co-doped with Al and Sb by so--gel spin coating 下载免费PDF全文
ZnO thin films co-doped with Al and Sb with different concentrations and a fixed molar ratio of AlCl3 to SbCl3 at 1:2, are prepared by a sol--gel spin-coating method on glass annealed at 550 ℃ for 2 h in air. The x-ray diffraction results confirm that the ZnO thin films co-doped with Al and Sb are of wurtzite hexagonal ZnO with a very small distortion, and the biaxial stresses are 1.03×108, 3.26×108, 5.23×108, and 6.97×108 Pa, corresponding to those of the ZnO thin films co-doped with Al and Sb in concentrations of 1.5, 3.0, 4.5, 6.0 at% respectively. The optical properties reveal that the ZnO thin films co-doped with Al and Sb have obviously enhanced transmittance in the visible region. The electrical properties show that ZnO thin film co-doped with Al and Sb in a concentration of 1.5 at% has a lowest resistivity of 2.5Ω·cm. 相似文献
15.
The T
g of organic liquids confined to nanoporous matrices and that of thin polymer films can decrease dramatically from the bulk
value. One possible explanation for this phenomenon is the development of hydrostatic tension during vitrification under confinement
that results in a concomitant increase in the free volume. Here we present experimental evidence and modeling results for
ortho-terphenyl (o-TP) confined in pores as small as 11.6 nm that indicate that, although there is an important hydrostatic
tension in the liquid in the pores, it does not develop until near the reduced T
g of the constrained material --well below the bulk T
g. Enthalpy recovery for the o-TP in the nanopores exhibits accelerated physical aging relative to the bulk, as well as a leveling
off of the fictive temperature at equilibrium values greater than the aging temperature. An adaptation of the structural recovery
model that incorporates vitrification under isochoric conditions is able to provide a quantitative explanation for the apparently
anomalous aging observed in nanopore confined liquids and in thin polymeric films. The results strongly support the existence
of an intrinsic size effect as the cause of the reduced T
g.
Received 3 September 2001 相似文献
16.
G. Riou S. Jandl M. Poirier V. Nekvasil M. Diviš P. Fournier R.L. Greene D.I. Zhigunov S.N. Barilo 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):179-182
We present an infrared crystal-field study of Pr2CuO4 single crystals and thin films. Excitations from the ground state multiplet 3H4 to the 3H5, 3H6, 3F2 and 3F3 excited multiplets are observed in both single crystals and thin films. A precise set of crystal-field parameters, that reproduces
the energy and the symmetry of the levels, is determined.
Received 25 April 2001 相似文献
17.
Higgins AM Sferrazza M Jones RA Jukes PC Sharp JS Dryden LE Webster J 《The European physical journal. E, Soft matter》2002,8(2):137-143
We investigate the dynamics of spinodal dewetting in liquid-liquid polymer systems. Dewetting of poly(methyl-methacrylate)
(PMMA) thin films on polystyrene (PS) “substrates” is followed in situ using neutron reflectivity. By following the development of roughness at the PS/PMMA interface and the PMMA surface we extract
characteristic growth times for the dewetting process. These characteristic growth times are measured as a function of the
molecular weight of the two polymers. By also carrying out experiments in the regime where the dynamics are independent of
the PS molecular weight, we are able to use dewetting to probe the scaling of the PMMA thin film viscosity with temperature
and molecular weight. We find that this scaling reflects bulk behaviour. However, absolute values are low compared to bulk
viscosities, which we suggest may be due in part to slippage at the polymer/polymer interface.
Received 25 June 2001 and Received in final form 5 December 2001 相似文献
18.
The branched crystal morphology of linear polyethylene formed at various temperatures from thin films has been studied by
atomic-force microscopy (AFM), transmission electron microscopy (TEM), electron diffraction (ED) pattern and polymer decoration
technique. Two types of branched patterns, i.e. dendrite and seaweed patterns, have been visualized. The fractal dimension d
f = 1.65 of both dendrite and some of seaweed patterns was obtained by using the box-counting method, although most of the
seaweed patterns are compact. Selected-area ED patterns indicate that the fold stems tilt about 34.5° around the b-axis and polymer decoration patterns show that the chain folding direction and regularity in two (200) regions are quite
different from each other. Because of chain tilting, branched crystals show three striking features: 1) the lamella-like branches
show two (200) regions with different thickness; 2) the crystals usually bend towards the thin region; 3) the thick region
grows faster by developing branches, thus branches usually occur outside the thick region. The branched patterns show a characteristic
width w, which gives a linear relationship with the crystallization temperature on a semilogarithmic plot.
Received 15 March 2002 and Received in final form 29 April 2002 相似文献
19.
R.A. Ganeev A.I. Ryasnyansky M.K. Kodirov S.R. Kamalov V.A. Li R.I. Tugushev T. Usmanov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):129-131
The results of third-order nonlinear susceptibilities studies of Fe- and Zn-doped polyvinylpyrrolidone (PVP) aqueous solution
in processes of third harmonic generation of Nd:YAG laser radiation are presented. Nonlinear susceptibilities of PVP:Fe and
PVP:Zn were calculated to be 5×10-13 esu and 3×10-13 esu respectively. Third harmonic conversion efficiencies in these metallocomplexes were measured to be 8×10-7 and 5×10-7 respectively. The Z-scan method was applied to determine Kerr effect influence on frequency conversion process. The value
of nonlinear refractive index of PVP:Fe at the wavelength of λ = 1064 nm was measured to be n
2 = - 6.7×10-13 esu.
Received 30 November 2001 / Received in final form 27 March 2002 Published online 28 June 2002 相似文献
20.
Grohens Y Hamon L Reiter G Soldera A Holl Y 《The European physical journal. E, Soft matter》2002,8(2):217-224
We have measured, the thickness dependence of the glass transition temperature T(g)( h), using ellipsometry at variable temperature, for poly(methyl-methacrylate) (PMMA) of various tacticity in confined geometry. We report that several factors significantly affect T(g)( h): i) polymer microstructure (stereoregularity of PMMA) related to local dynamics; ii) interfacial interactions; iii) conformation of the polymer chains. These results raise many fundamental questions on the origin of the thickness-dependent glass transition. Why and how do the interactions with the substrate significantly affect T(g)( h)? Does T(g)( h) depend on the modifications of conformational parameters of the chains (their entropy)? What is the correlation between local dynamics and T(g)( h) in thin films? The aim of this paper is to summarise these open questions, which should stimulate further investigations in the thin polymer film scientific community. 相似文献