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1.
C. Schick 《The European physical journal. Special topics》2010,189(1):3-36
Calorimetry is an effective analytical tool to characterize the glass transition and phase transitions under confinement.
Calorimetry offers a broad dynamic range regarding heating and cooling rates, including isothermal and temperature modulated
operation. Today 12 orders of magnitude in scanning rate can be covered by combining different types of calorimeters. The
broad dynamic range, comparable to dielectric spectroscopy, is especially of interest for the study of kinetically controlled
processes like crystallization or glass transition.
Accuracy of calorimetric measurements is not very high. Commonly it does not reach 0.1% and often accuracy is only a few percent.
Nevertheless, calorimetry can reach high sensitivity and reproducibility. Both are of particular interest for the study of
confined systems. Low addenda heat capacity chip calorimeters are capable to measure the step in heat capacity at the glass
transition in nanometer thin films. The good reproducibility is used for the study of glass forming materials confined by
nanometer sized structures, like porous glasses, semicrystalline structures, nanocomposites, phase separated block copolymers,
etc. Calorimetry allows also for the frequency dependent measurement of complex heat capacity in a frequency range covering
several orders of magnitude.
Here I exclusively consider calorimetry and its application to glass transition in confined materials. In most cases calorimetry
reveals only a weak dependence of the glass transition temperature on confinement as long as the confining dimensions are
above 10 nm. Why these findings contradict many other studies applying other techniques to similar systems is still an unsolved
problem of glass transition in confinement. 相似文献
2.
W. Jiang M. Du Q. Gu J. Jiang H. Huth D. Zhou G. Xue C. Schick 《The European physical journal. Special topics》2010,189(1):187-195
Miscibility in blends of polystyrene and poly(phenylene oxide) (PS/PPO) confined in thin films (down to 6 nm) was investigated
using a recently developed sensitive differential alternating current (AC) chip calorimeter. Comparison of composition dependence
of glass transition in thin films with common models should provide information on miscibility. This study focuses on the
blend system polystyrene and poly(phenylene oxide) (PS/PPO) because it is thought as a miscible model system in the whole
composition range. Furthermore, its local dynamic heterogeneity is already identified by dynamic mechanic thermal analysis
(DMTA) and solid state NMR techniques. For this blend, we find that even for the thinnest films (6 nm, corresponding to about
half of PPO’s radius of gyration R
g) only one glass transition is observed. The composition dependence of T
g is well described by the Fox, Couchman or Gordon-Taylor mixing law that are used for the miscible bulk blends. Although there
is a contradicting result on whether T
g decreases with decreasing film thickness between our calorimetric measurements and Kim’s elipsometric measurements on the
same blend (Kim et al. Macromolecules 2002, 35, 311–313), the conclusion that the good miscibility between PS and PPO remains in ultrathin films holds for both
studies. Finally, we show that our chip calorimeter is also sensitive enough to study the inter-layer diffusion in ultrathin
films. PS chain in a thin PS/PPO double layer that is prepared by spin coating PPO and PS thin film in tandem will gradually
diffuse into the PPO layer when heated above T
g of PS, forming a PSxPPO100−x blend. However, above the PSxPPO100−x blend, there exists an intractable pure PS like layer (∼30 nm in our case) that does not diffuse into the blend beneath
even staying at its liquid state over 10 hours. 相似文献
3.
A. Schönhals H. Goering C. Schick B. Frick M. Mayorova R. Zorn 《The European physical journal. Special topics》2007,141(1):255-259
The effect of a nanometer confinement on the molecular
dynamics of poly(methyl phenyl siloxane) (PMPS) was studied by
dielectric spectroscopy (DS), temperature modulated DSC (TMDSC) and
neutron scattering (NS). Nanoporous glasses with pore sizes of
2.5–20 nm have been used. DS and TMDSC experiments show that for
PMPS in 7.5 nm pores the molecular dynamics is faster than in the
bulk which originates from an inherent length scale of the
underlying molecular motions. For high temperatures the temperature
dependence of the relaxation rates for confined PMPS crosses that of
the bulk state. Besides finite states effects also the thermodynamic
state of nano-confined PMPS is different from that of the bulk. At a
pore size of 5 nm the temperature dependence of the relaxation
times changes from a Vogel/Fulcher/Tammann like to an Arrhenius
behavior where the activation energy depends on pore size. This is
in agreement with the results obtained by NS. The increment of the
specific heat capacity at the glass transition depends strongly on
pore size and vanishes at a finite length scale between 3 and 5 nm
which can be regarded as minimal length scale for glass transition
to appear in PMPS. 相似文献
4.
M. K. Mundra C. J. Ellison P. Rittigstein J. M. Torkelson 《The European physical journal. Special topics》2007,141(1):143-151
Confinement effects in polystyrene and poly(methyl
methacrylate) films and nanocomposites are studied by fluorescence.
The ability to employ an intensive measurable, the excited-state
fluorescence lifetime, in defining the glass transition temperature,
Tg, of polymers is demonstrated and compared to the use of an
extensive measurable, fluorescence intensity. In addition, intrinsic
fluorescence from the phenyl groups in polystyrene is used to
determine the Tg-confinement effect in films as thin as
~15 nm. The decrease in Tg with decreasing film thickness
(below ∼60 nm) agrees well with results obtained by extrinsic
pyrene fluorescence. Dye label fluorescence is used to quantify the
enhancement in Tg observed with decreasing thickness (below
~90 nm) in poly(methyl methacrylate) films; addition of
2–4 wt% dioctyl phthalate plasticizer reduces or eliminates the
Tg-confinement effect in films down to 20 nm
thickness. Intrinsic polystyrene fluorescence, which is sensitive to
local conformation, is used to quantify the time scales (some tens
of minutes) associated with stress relaxation in thin and ultrathin
spin-coated films at Tg + 10 K. Finally, the shape of the
fluorescence spectrum of pyrene doped at trace levels in polystyrene
films and polystyrene-silica nanocomposites is used to determine
effects of confinement on microenvironment polarity. 相似文献
5.
K. Fukao Y. Oda K. Nakamura D. Tahara 《The European physical journal. Special topics》2010,189(1):165-171
The glass transition temperature and the dynamics of the α-process have been investigated using dielectric relaxation spectroscopy
for single and stacked thin films of poly(2-chlorostyrene) (P2CS). The stacked film consists of 10 layers of single thin films
with thickness of 12 nm or 18 nm. The glass transition temperature T
g
of the single thin films of P2CS is found to decrease with decreasing film thickness in a similar way as observed for polystyrene
thin films. The magnitude of the depression of T
g
for the stacked thin films is larger than that of the single thin films with corresponding thickness. The depression of the
temperature at which the dielectric loss shows a peak due to the α-process at a given frequency, T
α, is larger than that of the single thin films, although the magnitude is smaller than that of T
g
. Annealing at a high temperature could cause the T
g
and T
α of the stacked thin films to approach the values of the bulk system. 相似文献
6.
Silver-doped indium oxide thin films have been prepared on glass and quartz substrates at room temperature (300 K) by a reactive dc magnetron sputtering technique using an alloy target of pure indium and silver (80:20 at. %). During sputtering, the oxygen flow rates are varied in the range 0.00–2.86 sccm keeping the magnetron power constant at 40 W. The resistivity of these films is in the range 100–10-3 Ω cm and they show a negative temperature coefficient of resistivity. The films exhibit p-type conductivity at an oxygen flow rate of 1.71 sccm. The work function of these silver–indium oxide films has been measured by a Kelvin probe technique. The refractive index of the films (at 632.8 nm) varies in the range 1.13–1.20. Silver doping in indium oxide narrows the band gap of indium oxide (3.75 eV). PACS 73.30.+y; 81.15.Cd; 78.20.Ci; 73.61.Le 相似文献
7.
A. N. Chumakov S. A. Petrov N. A. Bosak E. N. Shcherbakova 《Journal of Applied Spectroscopy》2012,79(4):664-669
We have obtained carbon thin films on silicon and glass substrates with multipulse pulsed laser irradiation of graphite under vacuum (p ≈ 2.6 Pa) using a high-frequency series of nanosecond laser pulses (τ = 85 ns, λ = 1060 nm) with pulse repetition frequency f ≈ 10–20 kHz and laser power density q ≈ 15–40 MW/cm2. We established the optimal laser power density and laser pulse repetition frequency for obtaining amorphous nanostructured diamond-like films. 相似文献
8.
Determination of the optimal parameters for the fabrication of ZnO thin films prepared by spray pyrolysis method 总被引:1,自引:0,他引:1
In this work, ZnO thin films have been prepared by spray pyrolysis deposition method on the glass substrates. The effect of
deposition parameters, such as deposition rate, substrate temperature and solution volume has been studied by X-ray diffraction
(XRD) method, UV–Vis–NIR spectroscopy, scanning electron microscopy (SEM), and electrical measurements. The XRD patterns indicate
polycrystalline wurtzite structure with preferred direction along (0 0 2) planes. Thin films have transparency around 90%
in the visible range. The optical band gap was determined at 3.27 eV which did not change significantly. Evolution of electrical
results containing the carriers’ density, sheet resistance and resistivity are in agreement with structural results. All the
results suggest the best deposition parameters are: deposition rate, R = 3 ml/min, substrate temperature, T
s = 450°C and thickness of the thin films t = 110–130 nm. 相似文献
9.
Dhananjay Satyendra Singh J. Nagaraju S.B. Krupanidhi 《Applied Physics A: Materials Science & Processing》2007,88(2):421-424
Sol–gel route was employed to grow polycrystalline thin films of Li-doped ZnO thin films (Zn1-xLixO, x=0.15). Polycrystalline films were obtained at a growth temperature of 400–500 °C. Ferroelectricity in Zn0.85Li0.15O was verified by examining the temperature variation of the real and imaginary parts of dielectric constant, and from the
C–V measurements. The phase transition temperature was found to be 330 K. The room-temperature dielectric constant and dissipation
factor were 15.5 and 0.09 respectively, at a frequency of 100 kHz. The films exhibited well-defined hysteresis loop, and the
values of spontaneous polarization (Ps) and coercive field were 0.15 μC/cm2 and 20 kV/cm, respectively, confirming the presence of ferroelectricity.
PACS 77.22Ch; 77.22Ej; 77.80Bh 相似文献
10.
The ultrasensitive differential scanning calorimetry is used to observe the glass transition in thin (1-400 nm) spin-cast films of polystyrene, poly (2-vinyl pyridine) and poly (methyl methacrylate) on a platinum surface. A pronounced glass transition is observed even at a thickness as small as 1-3 nm. Using the high heating (20-200 K/ms) and cooling (1-2 K/ms in glass transition region) rates which are typical for this technique, we do not observe appreciable dependence of the glass transition temperature over the thickness range from hundreds of nanometers down to 3 nm thick films. The evolution of calorimetric data with film thickness is discussed in terms of broadening of transition dynamics and loss of transition contrast. 相似文献
11.
LiCoO2 thin films were prepared by electron beam evaporation technique using LiCoO2 target with Li/Co ratio 1.1 in an oxygen partial pressure of 5 × 10−4 mbar. The films prepared at substrate temperature T
s < 573 K were amorphous in nature, and the films prepared at T
s > 573 K exhibited well defined (104), (101), and (003) peaks among which the (104) orientation predominates. The X-ray photoelectron
spectroscopy (XPS) and inductively coupled plasma (ICP) data revealed that the films prepared in the substrate temperature
range 673–773 K are nearly stoichiometric. The grain size increases with an increase of substrate temperature. The Co–eg absorption bands, are empty and their peak position lies at around 1.7 eV above the top to the Co–t2g bands. The fundamental absorption edge was observed at 2.32 eV. The films annealed at 1,023 K in a controlled oxygen environment
exhibit (104) out plane texture with large grains.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006 相似文献
12.
Thin films of molybdenum trioxide were deposited on glass substrates employing direct current (DC) magnetron sputtering by
sputtering of molybdenum at different oxygen partial pressures in the range 8 × 10−5–1 × 10−3 mbar and at a substrate temperature of 473 K. The glow discharge characteristics of magnetron cathode target of molybdenum
were studied. The influence of oxygen partial pressure on the structural and optical properties of molybdenum trioxide films
was investigated. The films formed at an optimum oxygen partial pressure of 2 × 10−4 mbar were polycrystalline in nature with orthorhombic α- phase and an optical band gap of 3.16 eV. The refractive index of
the films formed at an oxygen partial pressure of 2 × 10−4 mbar decreased from 2.08 to 1.89 with increase of wavelength from 450 to 1,000 nm, respectively.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006. 相似文献
13.
D. R. Lee S. H. Choi H. H. Lee J.-Y. Kim C.-J. Yu 《The European physical journal. Special topics》2009,167(1):163-169
We studied ~0.5 μm and 30–80 ? thick films of a normal dielectric
liquid, tetrakis(2-ethylhexoxy)silane (TEHOS), at temperature range 228–286 K,
deposited onto silicon (111) substrate with native oxide using X-ray
reflectivity. TEHOS is spherical with size ~10 ?, non-polar,
non-reactive, and non-entangling; TEHOS has been reported to show interfacial
layering at room temperature and surface layering at 0.23 Tc (Tc≈
950 K). For films m thick, the reflectivity data did not change
significantly as a function of temperature; for films 30–80 ? thick, the
reflectivity data did change. The data could be fitted with an electron density
model composed of a minimum necessary number of Gaussians and a uniform density
layer with error-function broadened interfaces. When the film thickness is 60–80 ? below 246 K, we found that the interface
and the surface layering coexist
but do not overlap. When the film thickness is 30–40 ? below 277 K, they
overlap and the electron density profile shows slowly decreasing molecular
oscillations at the air-liquid interface. 相似文献
14.
Z. Yang D. Peng A. Clough C.-H. Lam O.K.C. Tsui 《The European physical journal. Special topics》2010,189(1):155-164
Experiments in the past 1.5 decades have found that the glass transition temperature of polymer films can be noticeably different
from the bulk when the film thickness is decreased below ∼100 nm. On the other hand, many dynamic measurements have found
results inconsistent with the observed change in the glass transition temperature. One frequently cited reason is that the
dynamic properties being probed may not be directly related to the glass transition. Viscosity is a property traditionally
used to characterize the dynamic slowing down occurring to a material at the glass transition. In this paper, we report experimental
result showing that the viscosity of polystyrene films supported by oxide-coated silicon decreases with decreasing film thickness,
consistent with the observed glass transition temperature of the films. 相似文献
15.
W. Deng T. Ohgi H. Nejo D. Fujita 《Applied Physics A: Materials Science & Processing》2001,72(5):595-601
Highly conductive and transparent indium tin oxide (ITO) thin films, each with a thickness of 100 nm, were deposited on glass
and Si(100) by direct current (DC) magnetron sputtering under an argon (Ar) atmosphere using an ITO target composed of 95%
indium oxide and 5% tin oxide for photon-STM use. X-ray diffraction, STM observations, resistivity and transmission measurements
were carried out to study the formation of the films at substrate temperatures between 40 and 400 °C and the effects of thermal
annealing in air between 200 and 400 °C for between1 and 5 h. The film properties were highly dependent on deposition conditions
and on post-deposition film treatment. The films deposited under an Ar atmosphere pressure of ∼1.7×10-3 Torr by DC power sputtering (100 W) at substrate temperatures between 40 and 400 °C exhibited resistivities in the range
3.0–5.7×10-5 Ω m and transmissions in the range 71–79%. After deposition and annealing in air at 300 °C for 1 h, the films showed resistivities
in the range 2.9–4.0×10-5 Ω m and transmissions in the range 78–81%. Resistivity and transmission measurements showed that in order to improve conductive
and transparent properties, 2 h annealing in air at 300 °C was necessary. X-ray diffraction data supported the experimental
measurements of resistivity and transmission on the studies of annealing time. The surface roughness and film uniformity improve
with increasing substrate temperature. STM observations found the ITO films deposited at a substrate temperature of 325 °C,
and up to 400 °C, had domains with crystalline structures. After deposition and annealing in air at 300 °C for 1 h the films
still exhibited similar domains. However, after deposition at substrate temperatures from 40 °C to 300 °C, and annealing in
air at 300 °C for 1 h, the films were shown to be amorphous. More importantly, the STM studies found that the ITO film surfaces
were most likely to break after deposition at a substrate temperature of 325 °C and annealing in air at 300 °C for 2 or 3 h.
Such findings give some inspiration to us in interpreting the effects of annealing on the improvement of conductive and transparent
properties and on the transition of phases. In addition, correlations between the conductive/transparent properties and the
phase transition, the annealing time and the phase transition, and the conductive/transparent properties and the annealing
time have been investigated.
Received: 10 July 2000 / Accepted: 27 October 2000 / Published online: 9 February 2001 相似文献
16.
Properties of reactively sputtered W–B–N thin film as a diffusion barrier for Cu metallization on Si
L. C. Leu D. P. Norton L. McElwee-White T. J. Anderson 《Applied Physics A: Materials Science & Processing》2009,94(3):691-695
Thin films of W–B–N (10 nm) have been evaluated as diffusion barriers for Cu interconnects. The amorphous W–B–N thin films
were prepared at room temperature via reactive magnetron sputtering using a W2B target at various N2/(Ar + N2) flow ratios. Cu diffusion tests were performed after in-situ deposition of 200 nm Cu. Thermal annealing of the barrier stacks
was carried out in vacuum at elevated temperatures for one hour. X-ray diffraction patterns, sheet resistance measurement,
cross-section transmission electron microscopy images, and energy-dispersive spectrometer scans on the samples annealed at
500°C revealed no Cu diffusion through the barrier. The results indicate that amorphous W–B–N is a promising low resistivity
diffusion barrier material for copper interconnects. 相似文献
17.
The film thickness dependence of both the glass transition temperature (T(g)) and the 1 kHz alpha relaxation were studied for thin films of isotactic Poly (methylmethacrylate) (i-PMMA) supported on aluminium substrates. Films in the thickness range 7-200 nm were studied. The ellipsometrically determined T(g) was found to show reductions for films thinner than 60 nm, with the largest observed reduction being 12 K for a 7 nm thick film. Measurements of the T(g) were also performed on i-PMMA films supported on silicon substrates. Dielectric studies of the temperature dependent 1 kHz alpha relaxation peak, showed that the position (T(alpha)) and shape of the peak have no film thickness dependence. This was shown to hold for films with one free surface and films with a 30 nm thermally evaporated capping layer. Capping the films was shown to have no effect on the thickness dependence of either T(g) or T(alpha). The implications of these results are discussed further and the different film thickness dependencies of T(g) and T(alpha) are discussed. This is done within the framework of the Vogel-Fulcher-Tamann (VFT) theory of glass forming materials and also in the context of the existence of a dynamic correlation length xi. 相似文献
18.
Antimony telluride thin films were prepared on the well-cleaned glass substrates under a pressure of 10 – 5 torr by thermal
evaporation method. The thicknesses of the films were measured using Multiple Beam Interferometer (MBI) technique. The structure
of the sample was analyzed by X-ray diffraction technique. The film attains crystalline structure as the temperature of the
substrate is increased to 373 K. The d spacing and the lattice parameters of the sample were calculated. Optical behavior
of the film samples with the various thicknesses was analyzed by obtaining their transmittance spectra in the wavelength range
of 400 – 800 nm. The transmittance is found to decrease with increase in film thickness and also it falls steeply with decreasing
wavelength. The optical constants were estimated and the results are discussed. The optical band gap energy decreases with
increase in the film thickness. The optical transition in these films is found to be indirect and allowed.
Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003. 相似文献
19.
B. I. Turko V. B. Kapustyanyk V. P. Rudyk M. V. Partika M. V. Kvasnytsya A. P. Vas’kiv 《Journal of Applied Spectroscopy》2007,74(2):310-312
We have studied the behavior of the intrinsic absorption edge in zinc oxide thin films in the temperature range 80–300 K.
We have observed that the intrinsic absorption edge in films with crystal sizes of ≈45 nm or larger is described by the empirical
Urbach’s rule, while in films with crystallite sizes of ≈15 nm, it is described by a modified Urbach’s rule. We have calculated
the effective frequency of phonons taking part in formation of the absorption edge.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 275–277, March–April, 2007. 相似文献
20.
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