共查询到20条相似文献,搜索用时 187 毫秒
1.
R.A. Gunasekaran J.D. Pedarnig M. Dinescu 《Applied Physics A: Materials Science & Processing》1999,69(6):621-624
A parametric study of the growth of La0.5Sr0.5CoO3 (LSCO) thin films on (100) MgO substrates by pulsed-laser deposition (PLD) is reported. Films are grown under a wide range
of substrate temperature (450–800 °C), oxygen pressure (0.1–0.9 mbar), and incident laser fluence (0.8–2.6 J/cm2). The optimum ranges of temperature, oxygen pressure, and laser fluence to produce c-axis oriented films with smooth surface morphology and high metallic conductivity are identified. Films deposited at low
temperature (500 °C) and post-annealed in situ at higher temperatures (600–800 °C) are also investigated with respect to their
structure, surface morphology, and electrical conductivity.
Received: 20 November 1998 / Accepted: 6 July 1999 / Published online: 21 October 1999 相似文献
2.
45% semi-crystalline parylene-C (–H2C–C6H3Cl–CH2–)
n
thin films (5.8 μm) polymers have been investigated by broadband dielectric spectroscopy for temperatures above the glass
transition (T
g
=90°C). Good insulating properties of parylene-C were obtained until operating temperatures as high as 200°C. Thus, low-frequency
conductivities from 10−15 to 10−12 S/cm were obtained for temperatures varying from 90 to 185°C, respectively. This conductivity is at the origin of a significant
increase in the dielectric constant at low frequency and at high temperature. As a consequence, Maxwell–Wagner–Sillars (MWS)
polarization at the amorphous/crystalline interfaces is put in evidence with activation energy of 1.5 eV. Coupled TGA (Thermogravimetric
analysis) and DTA (differential thermal analysis) revealed that the material is stable up to 400°C. This is particularly interesting
to integrate this material for new applications as organic field effect transistors (OFETs). Electric conductivity measured
at temperatures up to 200°C obeys to the well-known Jonscher law. The plateau observed in the low frequency part of this conductivity
is temperature-dependent and follows Arrhenius behavior with activation energy of 0.97 eV (deep traps). 相似文献
3.
P. Patzner A.V. Osipov P. Hess 《Applied Physics A: Materials Science & Processing》2006,85(2):145-150
The growth of ultra-thin (<2 nm) silicon-oxide films was investigated on Si(100):H, Si(111):H, and a-Si:H surfaces in a pure water atmosphere (0.1–10 Pa) at low temperatures of 30–250 °C. Oxidation was induced photochemically by pulsed F2-laser radiation at 157 nm. The thickness and composition of the growing oxide films were monitored in real time by spectroscopic ellipsometry in the photon energy range of 1.15–4.75 eV. The mechanism of laser-induced silicon oxidation in a H2O atmosphere is shown to differ fundamentally from the classical Deal–Grove mechanism of thermal oxidation at 900–1200 °C, as well as from the photoinduced low-temperature oxidation in an O2 atmosphere. In particular, the film thickness essentially does not depend on temperature below 250 °C. A kinetic model is developed for low-temperature silicon oxidation in a H2O atmosphere. According to this model, the growth is limited at small thicknesses by the oxidation reaction and at larger thicknesses by reactions of the diffusing oxidizing species in the oxide layer. Very good agreement is established between this kinetic model and the ellipsometric measurements and the temperature and pressure dependence of the water oxidation process. PACS 82.65.+r; 07.60.Fs; 81.65.Mq; 82.50.Hp 相似文献
4.
Jumiah Hassan Farm Mooi Yen Mansor Hashim Zulkifly Abbas Zaidan Abdul Wahab W. Mohd. Daud W. Yusoff Azmi Zakaria 《Ionics》2007,13(4):219-222
NiFe2O4 prepared via the sol–gel technique were pre-sintered at 900 °C and synthesized at different sintering temperatures from 1,000 °C
to 1,200 °C at 100 °C intervals. The samples were characterized for microwave dielectric properties. These samples were measured
using Agilent Impedance/Material Analyzer at frequencies 1 MHz to 1.8 GHz. Results showed a decrease in the dielectric constant
and loss factor with frequency except at the turning point, around 150 MHz, where the loss factor showed a gradual increase.
However, both the dielectric constant and loss factor increase with increasing sintering temperature. The grain size and density
also increased with increasing sintering temperature, but the porosity and grain boundary density showed a decrease.
This paper was presented at the International Conference on Solid State Science and Technology 2006, Kuala Terengganu, Malaysia,
Sept. 4–6, 2006. 相似文献
5.
Jyh-Liang Wang Yi-Sheng Lai Bi-Shiou Chiou Chen-Chia Chou Trent Gwo-Yann Lee Huai-Yuan Tseng Chueh-Kuei Jan Huang-Chung Cheng 《Applied Physics A: Materials Science & Processing》2008,90(1):129-134
Pulsed laser deposition (PLD) of (Pb,Sr)TiO3 (PSrT) film on Pt/SiO2/Si at low substrate temperatures (Ts), ranging from 300–450 °C, has been investigated. As Ts increases, the films reveal coarsening clusters, improved crystallization of the perovskite phase, distinct capacitance–electric
field (C–E) hysteretic loops and a larger dielectric constant. The 350 °C-deposited film shows strong (100) preferred orientation
and optimum dielectric properties with the dielectric constant of ∼620. The current density increases as the measurement temperature
and the electric field increase. Moreover, PSrT films exhibit a strong negative temperature coefficient of resistance (NTCR)
behavior at temperatures ranging from 100 to 390 °C.
PACS 81.15.Fg; 77.22.Ch; 68.60.Dv 相似文献
6.
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
7.
The electrophysical properties and structure of the nonstoichiometric high-temperature superconductor YBa2Cu3O
y
restored at T = 930–950°C after low-temperature decomposition (T = 200°C) into phases different in the oxygen content have been studied. It has been shown that, unlike heat treatments at
T ≤ 900°C, the superconducting properties are almost completely restored for 3–5 h during grain recrystallization, which is
impossible at lower temperatures. After short-term annealing at T = 930–950°C (for 1–2 h), the ceramic material still contains a significant number of structural defects, most likely, in
cation sublattices. These defects can contribute to the pinning of magnetic vortices, which substantially increases the critical
current density in magnetic fields up to 2 T as compared to ceramic materials produced by the conventional technology. 相似文献
8.
650 nm-range AlGaInP multi-quantum well (MQW) laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD)
have been studied and the results are presented in this paper. Threshold current density of broad area contact laser diodes
can be as low as 350 A/cm2. Laser diodes with buried-ridge strip waveguide structures were made, threshold currents and differential efficiencies are
(22–40) mA and (0.2–0.7) mW/mA, respectively. Typical output power for the laser diodes is 5 mW, maximum output power of 15
mW has been obtained. Their operation temperature can be up to 90°C under power of 5 mW. After operating under 90°C and 5
mW for 72 hrs, the average increments for the threshold currents of the lasers at 25°C and the operation currents at 5 mW
(at 25°C) are (2–3) mA and (3–5) mA, respectively. Reliability tests showed that no obvious degradation was observed after
1400 hours of CW operation under 50°C and 2.5 mW.
Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17,
1998. 相似文献
9.
The characteristics of a BaO–Al2O3–B2O3–SiO2–La2O3 glass ceramic prepared by spray pyrolysis were studied. Glass powders with spherical shape and amorphous phase were prepared
by complete melting at a preparation temperature of 1 500°C. The mean size and geometric standard deviation of the powders
prepared at the temperature of 1 500°C were 0.6 μm and 1.3. The glass powders had similar composition to that of the spray
solution. The glass transition temperature (T
g) of the glass powders was 600.3°C. Two crystallization exothermic peaks were observed at 769.3 and 837.8°C. Densification
of the specimen started at a sintering temperature of 600°C, in which Ba4La6O(SiO4)6 as main crystal structure was observed. Complete densification of the specimen occurred at a sintering temperature of 800°C.
The specimens sintered at temperatures above 800°C had main crystal structure of BaAl2Si2O8. 相似文献
10.
Nickel hydroxide powder is prepared by chemical precipitation method, and the effect of synthesis temperature on the phase
structure and electrochemical performances of nickel hydroxide is investigated. The phase structure is characterized by X-ray
diffraction (XRD), and the electrochemical performances are characterized by cyclic voltammetry, electrochemical impedance
spectroscopy, and charge/discharge tests. The XRD results show that low temperatures (0–20 °C) induce the precipitation of
badly crystallized nickel hydroxide while at high temperatures (40–60 °C) crystallized β-nickel hydroxide is formed. Electrochemical
performance tests show that the nickel hydroxide synthesized at low temperature has better electrochemical reversibility,
lower electrochemical reaction impedance, and higher discharge capacity than that of the nickel hydroxide synthesized at high
temperature. 相似文献
11.
Steven Yueh-Hsiu Wu Ching-Li Tseng Feng-Huei Lin 《Journal of nanoparticle research》2010,12(4):1173-1185
In this study, a magnetic iron-doped calcium sulfide (Fe–CaS) nanoparticle was newly developed and studied for the purpose
of hyperthermia due to its promising magnetic property, adequate biodegradation rate, and relatively good biocompatibility.
Fe–CaS nanoparticles were synthesized by a wet chemical co-precipitation process with heat treatment in a N2 atmosphere, and were subsequently cooled in N2 and exposed to air at a low temperature. The crystal structure of the Fe–CaS nanoparticles was similar to that of the CaS,
which was identified by an X-ray diffractometer (XRD). The particle size was less than 40 nm based on a Debye–Scherrer equation
and transmission electron microscope (TEM) examination. Magnetic properties obtained from the SQUID magnetometer demonstrated
that the synthesized CaS was a diamagnetic property. Once the Fe ions were doped, the synthesized Fe–CaS converted into paramagnetism
which showed no hysteresis loop. Having been heated above 600 °C in N2, the Fe–CaS showed a promising magnetic property to produce enough energy to increase the temperature for hyperthermia. 10 mg/ml
of the Fe–CaS was able to generate heat to elevate the media temperature over 42.5 °C within 6 min. The area of the hysteresis
loop increased with the increasing of the treated temperature, especially at 800 °C for 1 h. This is because more Fe ions
replaced Ca ions in the lattice at the higher heat treatment temperature. The heat production was also increasing with the
increasing of heat treatment temperature, which resulted in an adequate specific absorption ratio (SAR) value, which was found
to be 45.47 W/g at 37 °C under an alternative magnetic field of f = 750 KHz, H = 10 Oe. The in vitro biocompatibility test of the synthesized Fe–CaS nanoparticles examined by the LDH assay showed no cytotoxicity
to 3T3 fibroblast. The result of in vitro cell hyperthermia shows that under magnetic field the Fe–CaS nanoparticles were
able to generate heat and kill the CT-26 cancer cells significantly. We believe that the developed Fe–CaS nanoparticles have
great potential as thermo-seeds for cancer hyperthermia in the near future. 相似文献
12.
V. V. Parshin M. Yu. Tretyakov M. A. Koshelev E. A. Serov 《Radiophysics and Quantum Electronics》2009,52(8):525-535
We describe an instrumental complex based on high-Q open Fabry–Perot resonators for the frequency band 36–370 GHz and present
original measurement techniques and the latest results of measuring (i) refractive indices and losses of modern high-quality
dielectrics for high-power electronics (with prognosis for up to the terahertz band) and general-purpose dielectrics including
films, (ii) reflectivities of both antenna reflectors of cryogenic-receiver radiotelescopes and the so-called “hot” antennas
for future Mercurian missions, and (iii) the atmospheric absorption for the development of high-precision wave-propagation
models including the continuum absorption. The instrumentation and the measurement techniques are intended for studying condensed-media
parameters at temperatures 80–900 K and atmospheric parameters at temperatures from −40°C to +60°C and humidities from 0 to
80%. 相似文献
13.
M. Miettinen M. Johansson S. Suvanto J. Riikonen U. Tapper T. T. Pakkanen V.-P. Lehto J. Jokiniemi A. Lähde 《Journal of nanoparticle research》2011,13(10):4631-4645
Silicon–carbon nanoceramics have been synthesised from hexamethyldisilane (HMDS) by the atmospheric pressure chemical vapour
synthesis (APCVS). Direct aerosol phase synthesis enables continuous production of high purity materials in one-stage process.
The particle formation is based on the decomposition of the precursor in a high temperature reactor. Reaction of the gas phase
species leads to homogeneous nucleation and formation of the nanoparticles with a narrow size distribution (geometric mean
diameter range of particle number size distribution 160–200 nm with 1.5–1.6 geometric standard deviation at reaction temperatures
800–1200 °C). A systematic investigation of the influence of the process temperature on the powder characteristics, including
the particle size, crystallinity, chemical structure, surface and bulk composition and surface morphology, was carried out.
At the reactor temperature of 800 °C, the synthesised nanoparticles were amorphous preceramics containing mostly SiC4, Si–CH2–Si and Si–H units. The composition of the powder turned towards nanocrystalline 3C–SiC (crystal size under 2 nm) when the
reaction temperature was increased to 1200 °C. The reaction temperature appeared to be a key parameter controlling the structure
and properties of the synthesised powders. 相似文献
14.
The distinctive features of the low-frequency internal friction Q
−1(T) of (Cu-Sn)-Nb composites at high temperatures (up to 400°C) are investigated for strains in the range 10−5–10−4. Considerable hysteresis of Q
−1(T) in the heating-cooling cycle is recorded, including the presence of a minimum at ∼175°C when the sample is heated to 400°C
and two peaks P
2 (at 280°C) and P
1 (at ∼100°C) when the sample is cooled from 400°C. The activation energy of the anomalous internal friction background (up
to 175°C), the oxygen diffusion parameters, and the oxygen concentration in the niobium fibers (all of which govern the peak
P
2) are calculated, and the value and temperature dependence of the yield point of the bronze matrix (which govern the peak
P
1) are estimated.
Zh. Tekh. Fiz. 68, 114–117 (November 1998) 相似文献
15.
W. F. Lim K. Y. Cheong Z. Lockman 《Applied Physics A: Materials Science & Processing》2011,103(4):1067-1075
The effects of post-deposition annealing temperatures (600–1150°C) in 95%N2–5%H2 ambient on the electrical and physical properties of metal-organic decomposed CeO2 spin-coated on n-type 4H-SiC were investigated. As the annealing temperature increased, oxides changed from polycrystalline
to preferred oriented structures and, eventually, to silicate structures. The oxides also showed an incremental increase in
surface roughness as annealing temperature increased. The Lorentz-Lorenz law was utilized to determine the density of the
oxides. The highest density was obtained by a sample annealed at the highest temperature. Electrical results showed that this
sample obtained the lowest leakage current density. Parameters affecting this observation were also investigated. 相似文献
16.
G. Cruciani M. C. Dalconi M. Dondi C. Meneghini F. Matteucci A. Barzanti G. Lorenzi G. Baldi 《Journal of nanoparticle research》2011,13(2):711-719
Nanocrystalline titania pigments were produced by high temperature-forced hydrolysis in a coordinating high-boiling solvent
(and water for reference). The effect of synthesis conditions and co-doping with Cr–Sb and V–Sb on particle size and anatase-to-rutile
transformation (A → R) was studied by temperature-resolved synchrotron X-ray diffraction. The experiments were performed directly
on low concentration (3.5 vol.%) as-synthesized suspensions of titania nanoparticles (up to 230 °C) and on the corresponding
dried powders (up to 950 °C). Crystallite size of as-synthesized nano-anatase is around 20 nm (glycol) or 70 nm (water); it
exhibits a slow growth rate up to the onset temperature of the A → R. Phase composition and crystallite size are drastically
influenced by both synthesis conditions and doping. Synthesis in water resulted in the simultaneous occurrence of anatase
and brookite; transformation into rutile begins early but with a slower rate with respect to glycol-based samples. Doping
affected the A → R, whose onset temperature in undoped titania (700 °C) was lowered to 650 °C (V–Sb) or prevented up to 950 °C
(Cr–Sb). Both (V–Sb) and (Cr–Sb) dopings reduced the volume thermal expansion rate of anatase. 相似文献
17.
Kalavathy Santhi E. Thirumal S. N. Karthick Hee-Je Kim Marimuthu Nidhin V. Narayanan A. Stephen 《Journal of nanoparticle research》2012,14(5):868
Silver–nickel alloy nanoparticles with an average size of 30–40 nm were synthesized by chemically reducing the mixture of
silver and nickel salts using sodium borohydride. The structure and the magnetic properties of the alloy samples with different
compositions were investigated. The phase stability of the material was analysed after annealing the sample in vacuum at various
temperatures. The material exhibits single fcc phase which is stable up to 400 °C and Ni precipitation sets in when the sample
is annealed to 500 °C. The thermal analysis using DSC was carried out to confirm the same. The alloy compositions are found
to be in close correlation with the metal salt ratios in the precursors. The synthesized samples exhibit weak paramagnetic
to ferromagnetic behaviour. The magnetic measurements reveal that by adjusting the precursor ratio, the Ni content in the
material can be altered and hence its magnetic properties tailored to suit specific requirements. The formation of Ag–Ni alloy
is confirmed by the observed Curie temperature from the magneto thermogram. Annealing the sample helps to produce significant
enhancement in the magnetization of the material. 相似文献
18.
《Solid State Ionics》2006,177(13-14):1237-1242
A hybrid supercapacitor was fabricated with NiO and activated carbon as positive and negative electrode, PVA–KOH–H2O containing 5 M KOH as alkaline polymer gel electrolyte, respectively. Cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements were applied to investigate the dependence of the hybrid supercapacitor on the temperatures from − 20 to 40 °C. The results demonstrated that the capacitive performance of the hybrid supercapacitor turned even better with the temperatures rising up from − 20 to 40 °C. The increase of temperature improved the conductivity of the alkaline polymer gel electrolyte, decreased the charge-transfer resistance and made the better contact at the interface between the electroactive materials and the alkaline gel electrolyte at higher operating temperature. The maximum of the specific capacitance and energy density of the hybrid supercapacitor were 73.4 F/g and 26.1 Wh/kg at the current density of 0.1 A/g and the operating temperature of 40 °C, respectively. 相似文献
19.
Konstantin Tarasov Patricia Beaunier Michel Che Eric Marceau Yanling Li 《Journal of nanoparticle research》2011,13(5):1873-1887
Following procedures formerly developed for the preparation of supported heterogeneous catalysts, carbon-coated cobalt nanoparticles
dispersed on porous alumina have been prepared by impregnation of γ-Al2O3 with (NH4)2[Co(EDTA)] and thermal decomposition in inert atmosphere. Below 350 °C, Co(II) ions are complexed in a hexa-coordinated way
by the EDTA ligand. The thermal treatment at 400–900 °C leads to the EDTA ligand decomposition and recovering of the support
porosity, initially clogged by the impregnated salt. According to X-ray absorption spectroscopy, and due to in situ redox
reactions between the organic ligand and Co(II), both oxidic and metallic cobalt phases are formed. Characterisation by transmission
electron microscopy, X-ray diffraction and magnetic measurements reveals that an increase in the treatment temperature leads
to an increase of the degree of cobalt reduction as well as to a growth of the cobalt metal particles. As a consequence, the
samples prepared at 400–700 °C exhibit superparamagnetism and a saturation magnetisation of 1.7–6.5 emu g−1 at room temperature, whilst the sample prepared at 900 °C has a weak coercivity (0.1 kOe) and a saturation magnetisation
of 12 emu g−1. Metal particles are homogeneously dispersed on the support and appear to be protected by carbon; its elimination by a heating
in H2 at 400 °C is demonstrated to cause sintering of the metal particles. The route investigated here can be of interest for obtaining
porous magnetic adsorbents or carriers with high magnetic moments and low coercivities, in which the magnetic nanoparticles
are protected from chemical aggression and sintering by their coating. 相似文献
20.
V. I. Tomin 《Optics and Spectroscopy》2010,108(4):544-552
The dual fluorescence spectra of 3-hydroxyflavone molecules excited by electromagnetic radiation in the region of the S
1 and S
2 absorption bands in the temperature region of 20–80°C are studied using the dynamic quenching of the excited state. An analysis
of the fluorescence parameters shows that heating the solution from room temperature to 60°C increases the proton transfer
rate by a factor of 1.24 in the case of standard excitation into the main absorption band and even stronger (by a factor of
6.9) in the case of excitation into the second absorption band. The presence of a quencher reduces the yield of the two emission
bands and noticeably increases the proton transfer rate, by a factor of 1.16 at room temperature and by a factor of 1.25 at
80°C. Upon excitation into the second singlet band, the transfer rate increases even more (especially at higher temperatures),
by a factors of 1.24 and 3.5 for the same temperatures. The temperature dependences of the transfer rate constant allowed
us to estimate the activation energies of the proton transfer reaction under different physical conditions and reach conclusions
about the mechanism by which this reaction proceeds. It is found that the proton transfer activation energy decreases from
500 to 360 cm−1 when measured in temperature ranges of 20–40 and 20–60°C. The introduction of a quencher with a concentration of 5 × 10−3 M increases the activation barrier to 534 and 471 cm−1 in the same temperature ranges. 相似文献