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1.
A simplified collisional-radiative model is applied to a high velocity plasma flow through the arcjet nozzle to investigate the temporal evolution of excited level population densities in the selected spatial positions inside arcjet thruster. Oomputations are carried out for various sets of input parameters such as electron temperature, electron number density, atom temperature, and pressure. The numerical results illustrate that the exter~t of the ionization-recombination non-equilibrium is strongly dependent on the electron temperature and pressure, and is significantly affected by resonance radiation. 相似文献
2.
Intertwisted fibrillar diamond-like carbon films prepared by electron cyclotron resonance microwave plasma enhanced chemical vapour deposition 下载免费PDF全文
In this paper, the structures, optical and mechanical properties of diamond-like carbon films are studied, which are prepared by a self-fabricated electron cyclotron resonance microwave plasma chemical vapour deposition method at room temperature in the ambient gases of mixed acetylene and nitrogen. The morphology and microstructure of the processed film are characterized by the atomic force microscope image, Raman spectra and middle Fourier transform infrared transmittance spectra, which reveal that there is an intertwisted fibrillar diamond-like structure in the film and the film is mainly composed of sp^3 CH, sp^3 C—C, sp^2 C═C, C═N and C_{60}. The film micro-hardness and bulk modulus are measured by a nano-indenter and the refractive constant and deposition rate are also calculated. 相似文献
3.
Columnar growth of crystalline silicon films on aluminium-coated glass by inductively coupled plasma CVD at room temperature 下载免费PDF全文
Silicon films were grown on aluminium-coated glass by inductively
coupled plasma CVD at room temperature using a mixture of SiH4
and H2 as the source gas. The microstructure of the films was
evaluated using Raman spectroscopy, scanning electron microscopy and
atomic force microscopy. It was found that the films are composed of
columnar grains and their surfaces show a random and uniform
distribution of silicon nanocones. Such a microstructure is highly
advantageous to the application of the films in solar cells and
electron emission devices. Field electron emission measurement of
the films demonstrated that the threshold field strength is as low
as ~9.8V/μm and the electron emission characteristic is
reproducible. In addition, a mechanism is suggested for the columnar
growth of crystalline silicon films on aluminium-coated glass at room
temperature. 相似文献
4.
Study of runaway electron behaviour during electron cyclotron resonance heating in the HL-2A Tokamak 下载免费PDF全文
During the current flat-top phase of electron cyclotron
resonance heating discharges in the HL-2A Tokamak, the behaviour of
runaway electrons has been studied by means of hard x-ray detectors
and neutron diagnostics. During electron cyclotron resonance
heating, it can be found that both hard x-ray radiation intensity
and neutron emission flux fall rapidly to a very low level, which
suggests that runaway electrons have been suppressed by electron
cyclotron resonance heating. From the set of discharges studied in
the present experiments, it has also been observed that the
efficiency of runaway suppression by electron cyclotron resonance
heating was apparently affected by two factors: electron cyclotron
resonance heating power and duration. These results have been
analysed by using a test particle model. The decrease of the
toroidal electric field due to electron cyclotron resonance heating
results in a rapid fall in the runaway electron energy that may lead
to a suppression of runaway electrons. During electron cyclotron
resonance heating with different powers and durations, the runaway
electrons will experience different slowing down processes. These
different decay processes are the major cause for influencing the
efficiency of runaway suppression. This result is related to the
safe operation of the Tokamak and may bring an effective control of
runaway electrons. 相似文献
5.
Silicon thin films are deposited by inductively coupled plasma chemical vapour deposition (ICP-CVD) at a low temperature of 350℃ using a mixture of SiH4 and H2. The structures of the films are characterized by x-ray diffraction and Raman spectra. Under the optimum experimental conditions, we observe that the crystallinity of Si films becomes more excellent and the preferred orientation changes from (111) to (220) with the decreasing dilution of SiH4 in H2. Such an abnormal crystallization is tentatively interpreted in term of the high density, low electron temperature and spatial confinement of the plasma in the process of ICP-CVD. 相似文献
6.
Fundamentals of the Schottky contacts and the
high-temperature current conduction through three kinds of Schottky
diodes are studied. N-Si Schottky diodes, GaN Schottky diodes and
AlGaN/GaN Schottky diodes are investigated by I--V--T
measurements ranging from 300 to 523~K. For these Schottky diodes, a
rise in temperature is accompanied with an increase in barrier
height and a reduction in ideality factor. Mechanisms are
suggested, including thermionic emission, field emission,
trap-assisted tunnelling and so on. The most remarkable finding in
the present paper is that these three kinds of Schottky diodes are
revealed to have different behaviours of high-temperature reverse
currents. For the n-Si Schottky diode, a rise in temperature is
accompanied by an increase in reverse current. The reverse current
of the GaN Schottky diode decreases first and then increases with
rising temperature. The AlGaN/GaN Schottky diode has a trend
opposite to that of the GaN Schottky diode, and the dominant
mechanisms are the effects of the piezoelectric polarization field and
variation of two-dimensional electron gas charge density. 相似文献
7.
Polymerization of C60 is realized under high temperature and high pressure. X-ray diffraction reveals a rhombohedral lattice structure in the product, and solid-state ^13C nuclear magnetic resonance spectroscopy confirms the formation of sp^3 bonds between C60 molecules. Specific heat is then measured over the temperature range of 300-2 K. It is found that its specific heat values are significantly less than those in fullerite within the region of 80-2K, and this huge reduction is attributed to the suppression of intermolecular librational modes in polymerized C60. An excellent fit to the experimental data over the entire temperature range is provided by a model, which needs to include only three-dimensional and two-dimensional translational modes in various contributions at different temperatures. 相似文献
8.
Structure and photoluminescence properties of Er3+-doped TiO2-SiO2 powders prepared by sol-gel method 下载免费PDF全文
Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions. 相似文献
9.
Spatially-resolved spectroscopic diagnosing of aluminum wire array Z-pinch plasmas on QiangGuang-I facility 下载免费PDF全文
Spatially-resolved crystal spectrometers with a high spectral resolution are developed to diagnose K-shell x-ray radiation from Z-pinch plasmas. These diagnostic apparatuses are successfully applied to aluminum wire array Z-pinch experiments on QiangGuang-I facility, a driver with a pulsed current up to about 1.5 MA in 80 ns. Time-integrated experimental results show that the K-shell x-ray emission lines of aluminum Z-pinch plasmas are dominated by line emissions from helium-like ionisation state. Bright spots that might have higher electron temperature or density are produced randomly in location and size along the z-axis during implosions. According to the experimental data, the electron temperature and the ion density are estimated to be between 250 eV and 310 eV, and between 7.0×1019cm-3 and 4.0×1019 cm-3 respectively, while the ion temperature is inferred to be about 10.2 keV, which is much higher than the electron temperature. 相似文献
10.
Influence of annealing treatment on as-grown Ib-type diamond crystal at a high temperature and high pressure 下载免费PDF全文
In this paper,we report on the influence of annealing treatment on as-grown Ib-type diamond crystal under high pressure and high temperature in a china-type cubic anvil high-pressure apparatus.Experiments are carried out at a pressure of 7.0 GPa and temperatures ranging from 1700 C to 1900 C for 1 h.Annealing treatment of the diamond crystal shows that the aggregation rate constant of nitrogen atoms in the as-grown Ib-type diamond crystal strongly depends on diamond morphology and annealing temperature.The aggregation rate constant of nitrogen remarkably increases with the increase of annealing temperature and its value in octahedral diamond is much higher than that in cubic diamond annealed at the same temperature.The colour of octahedral diamond crystal is obviously reduced from yellow to nearly colorless after annealing treatment for 1 h at 1900 C,which is induced by nitrogen aggregation in a diamond lattice.The extent of nitrogen aggregation in an annealed diamond could approach approximately 98% indicated from the infrared absorption spectra.The micro-Raman spectrum reveals that the annealing treatment can improve the crystalline quality of Ib-type diamond characterized by a half width at full maximum at first order Raman peak,and therefore the annealed diamond crystals exhibit nearly the same properties as the natural IaA-type diamond stones of high quality in the Raman measurements. 相似文献
11.
By using the Villain transformation, the Heisenberg ferrimagnetic spin chain is calculated. Two branches of the low-lying excitation in both the absence and presence of magnetic field are obtained. The thermodynamic quantities (such as free energy, magnetization, specific heat and static magnetic susceptibility) are also evaluated at finite temperature. This & the first time to calculate the Ferrimagnetic spin chain by using Villain's method, and we find that the results at a low temperature are quite similar to the previous calculation. The results of free energy and magnetization in zero temperature suggest that the Villain transformation has a good efficiency. 相似文献
12.
Effects of Dislocation on High Temperature Transport Characteristics of Unintentionally Doped GaN 下载免费PDF全文
High temperature transport characteristics of unintentionally doped GaN have been investigated by means of high temperature Hall measurements from room temperature to 500^o C. The increment of electron concentration from room temperature to 500^o C is found to vary largely for different samples. The dispersion of temperature dependence of electron concentration is found to be directly proportional to the density of dislocations in GaN layers calculated by fitting the FWHM of the rocking curves in x-ray diffraction measurements (XRD). The buildup levels in persistent photoconductivity (PPC) are also shown to be directly proportionM to the density of dislocations. The correlation of XRD, Hall and PPC results indicate that the high temperature dependence of electron density in unintentional doped GaN is directly dislocation related. 相似文献
13.
Characteristics of a large gap uniform discharge excited by DC voltage at atmospheric pressure 下载免费PDF全文
A large-gap uniform discharge is ignited by a coaxial dielectric barrier discharge and burns between a needle anode and a plate cathode under a low sustaining voltage by feeding with flowing argon. The basic aspects of the large-gap uniform discharge are investigated by optical and spectroscopic methods. From the discharge images, it can be found that this discharge has similar regions with glow discharge at low pressure except a plasma plume region. Light emission signals from the discharge indicate that the plasma column is invariant with time, while there are some stochastic pulses in the plasma plume region. The optical emission spectra scanning from 300 nm to 800 nm are used to calculate the excited electron temperature and vibrational temperature of the large-gap uniform discharge. It has been found that the excited electron temperature almost keeps constant and the vibrational temperature increases with increasing discharge current.Both of them decreases with increasing gas flow rate. 相似文献
14.
In this paper, we apply the two-time Green's function method, and provide a simple way to study the magnetic properties of one-dimensional spin-(S, s) Heisenberg ferromagnets. The magnetic susceptibility and correlation functions are obtained by using the Tyablikov decoupling approximation. Our results show that the magnetic susceptibility and correlation length are a monotonically decreasing function of temperature regardless of the mixed spins. It is found that in the case of S = s, our results of one-dimensional mixed-spin model is reduced to be those of the isotropic ferromagnetic Heisenberg chain in the whole temperature region. Our results for the susceptibility are in agreement with those obtained by other theoretical approaches. 相似文献
15.
<正>This paper reports that GaSb thin films have been co-deposited on soda-lime glass substrates.The GaSb thin film structural properties are characterized by Raman spectroscopy.The Sb-A1g/GaSb-TO ratio decreases rapidly with the increase of substrate temperature,which suggests a small amount of crystalline Sb in the GaSb thin film and suggests that Sb atoms in the thin film decrease.In Raman spectra,the transverse optical(TO) mode intensity is stronger than that of the longitudinal optical(LO) mode,which indicates that all the samples are disordered.The LO/TO intensity ratio increases with increasing substrate temperature which suggests the improved polycrystalline quality of the GaSb thin film.A downshift of the TO and LO frequencies of the polycrystalline GaSb thin film to single crystalline bulk GaSb Raman spectra is also observed.The uniaxial stress in GaSb thin film is calculated and the value is around 1.0 GPa.The uniaxial stress decreases with increasing substrate temperature.These results suggest that a higher substrate temperature is beneficial in relaxing the stress in GaSb thin film. 相似文献
16.
Highly ordered BiFeO3(BFO) nanotubes with about 200nm in diameter and 60μm in length are fabricated by a sol-gel AAO template method. A perovskite-type structure of BFO is confirmed in the nanotubes by transmission electron microscopy and selected area electron diffraction analysis. The coexistence of ferroelectric and ferromagnetic ordering of these BFO nanotubes at room temperature is demonstrated, giving a remnant polarization of 26μC/cm2, a low coercive electric field of 60kV/cm, and a magnetization of 0.18emu/g. In addition, it is found that the leakage behavior of these nanotubes is dominated by the ohmic contact mechanism. 相似文献
17.
Effect of the annealing temperature on the long-term thermal stability of Pt/Si/Ta/Ti/4H–SiC contacts 下载免费PDF全文
《中国物理 B》2015,(10)
The Pt/Si/Ta/Ti multilayer metal contacts on 4H–Si C are annealed in Ar atmosphere at 600°C–1100°C by a rapid thermal processor(RTP). The long-term thermal stability is evaluated by aging the annealed contact at 600°C in air. The contact's properties are determined by current–voltage measurement, and the specific contact resistance is calculated based on the transmission line model(TLM). Transmission electron microscope(TEM) and energy-dispersive x-ray spectrometry(EDX) are used to characterize the interface morphology, thickness, and composition. The results reveal that a higher annealing temperature is favorable for the formation of an Ohmic contact with a lower specific contact resistance, and causes the rapid degradation of the Ohmic contact in the aging process. 相似文献
18.
The phase behaviour of a single polyethylene chain is studied by using molecular dynamics simulations. A free chain and a chain with fixing one end are considered here, since the atomic force microscope (AFM) tip can play a significant role in polymer crystallization in experiment. For a free chain, it is confirmed in our calculation that the polymer chain exhibits an extended coil state at high temperatures, collapses into a condensed state at low temperatures, i.e. the coil-to-globule transition that is determined by a high temperature shoulder of the heat capacity curve, and an additional liquid-to-solid transition that is described by a low temperature peak of the same heat curve. These results accord with previous studies of square-well chains and Lennard-Jones homopolymers. However, when one of the end monomers of the same chain is fixed the results become very different, and the chain cannot reach an extended coil-like state as a free chain does at high temperatures, i.e. there exists no coil-to-globule-like transition. These results may provide some insights into the influence of AFM tip when it is used to study the phase behaviour of polymer chains. If the interaction force between AFM tip and polymer monomers is strong, some monomers or one of them can be seen as being fixed by the tip, which is similar to our simulation model, and it is also found that AFM tip could induce polymer crystallization. 相似文献
19.
Multi-walled carbon nanotubes (MWCNTs) are grown by arc discharge method in a controlled methane environment. The arc discharge is produced between two graphite electrodes at the ambient pressures of 100 tort, 300 torr, and 500 torr. Arc plasma parameters such as temperature and density are estimated to investigate the influences of the ambient pressure and the contributions of the ambient pressure to the growth and the structure of the nanotubes. The plasma temperature and density are observed to increase with the increase in the methane ambient pressure. The samples of MWCNT synthesized at different ambient pressures are analyzed using transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. An increase in the growth of MWCNT and a decrease in the inner tube diameter are observed with the increase in the methane ambient pressure. 相似文献
20.
Electrical properties of an AlInN/GaN high-electron mobility transistor (HEMT) on a sapphire substrate are investi-gated in a cryogenic temperature range from 295 K down to 50 K. It is shown that drain saturation current and conductance increase as transistor operation temperature decreases. A self-heating effect is observed over the entire range of temperature under high power consumption. The dependence of channel electron mobility on electron density is investigated in detail. It is found that aside from Coulomb scattering, electrons that have been pushed away from the AlInN/GaN interface into the bulk GaN substrate at a large reverse gate voltage are also responsible for the electron mobility drop with the decrease of electron density. 相似文献