共查询到20条相似文献,搜索用时 15 毫秒
1.
Field emission characteristics of nano-sheet carbon films deposited by quartz-tube microwave plasma chemical vapour deposition 下载免费PDF全文
Nano-sheet carbon films are prepared on Si wafers by means of quartz-tube microwave plasma chemical vapour deposition (MPCVD) in a gas mixture of hydrogen and methane. The structure of the fabricated films is investigated by using field emission scanning electron microscope (FESEM) and Raman spectroscopy. These nano~carbon films are possessed of good field emission (FE) characteristics with a low threshold field of 2.6 V/μm and a high current density of 12.6 mA/cm^2 at an electric field of 9 V/μm. As the FE currents tend to be saturated in a high E region, no simple Fowler-Nordheim (F-N) model is applicable. A modified F N model considering statistic effects of FE tip structures and a space-charge-limited-current (SCLC) effect is applied successfully to explaining the FE data observed at low and high electric fields, respectively. 相似文献
2.
Field emission from single-walled carbon nanotube (SWNT) nonwoven has been
investigated under high vacuum with different vacuum gaps. A low turn-on
electric field of 1.05\,V/$\mu $m is required to reach an emission current
density of 10 $\mu $A/cm$^{2}$. An emission current density of 10
mA/cm$^{2}$ is obtained at an operating electric field of 1.88\,V/$\mu $m. No
current saturation is found even at an emission current of 5\,mA. With the
vacuum gap increasing from 1 to 10 mm, the turn-on field decreases
monotonically from 1.21 to 0.68\,V/$\mu $m, while the field amplification is
augmented. The good field-emission behaviour is ascribed to the combined
effects of the intrinsic field emission of SWNT and the waved topography of
the nonwoven. 相似文献
3.
This paper reports that the tunable self-phase-stabilized infrared
laser pulses have been generated from a two-stage optical parametric
amplifier. With an 800 nm pump source, the output idler pulses are
tunable from 1.3 μm to 2.3 μm, and the maximum output
energy of the idler pulses is higher than 1 mJ at 1.6 μm by
using 6 mJ pump laser. A carrier-envelope phase fluctuation of
~ 0.15 rad (rms) for the idler pulses is measured for longer
than one hour by using a home build f-to-2f interferometer. 相似文献
4.
A chemical vapour deposition (CVD) diamond film detector was prepared and the main characteristics for pulsed proton detection were studied at Beijing Tandem Accelerator. The result shows that the charge collection efficiency of the detector increases with increasing electric field intensity and reaches to 9.44% at 5 V/μm with the charge collection distance of 15.9 μm. The relationship between the sensitivity of the detector and proton energy is consistent with the Monte Carlo (MC) simulation result. Its plasma time for a pulse with 4.85×10^5 protons is 1l.2ns. The dose threshold for onset of damage under 9MeV proton irradiation in the detector is about 10^13 cm^-2. All of the results show that a CVD diamond detector has fast time response and high radiation hardness, and can be used in pulsed proton detection. 相似文献
5.
Low-field electron emission from pinaster-like MoO2 nanoarrays as two-stage emitters 总被引:1,自引:0,他引:1 下载免费PDF全文
Low-field electron emission is obtained from the pinaster-like MoO2 nanoarrays. The turn-on field of the pinasterlike MoO2 nanoarrays is found to be as low as 2.39 V/μm with the current density of 10μA/cm2. The enhancement factor is extracted to be 3590 from the Fowler-Nordheim plot. These excellent emission properties are attributed to the special structure of the pinaster-like MoO2 nanoarrays and confirmed by the calculation in the frame of the two -stage model. Our results show that the pinaster-like MoO2 nanoarrays are promising candidate in realizing field emission displays. 相似文献
6.
Judd-Oflet analysis of spectrum and laser performance of Ho:YAP crystal end-pumped by 1.91μm Tm:YLF laser 下载免费PDF全文
The Ho:YAP crystal is grown by the Czochralski technique.The room temperature polarized absorption spectra of Ho:YAP crystal was measured on a c cut sample with 1 at% holmium.According to the obtained Judd-Ofelt intensity parameters Ω2 = 1.42 × 10-20 cm2,Ω4 = 2.92 × 10-20 cm2,and Ω6 = 1.71 × 10-20 cm2,this paper calculated the fluorescence lifetime to be 6 ms for 5I7 →5 I8 transition,and the integrated emission cross section to be 2.24×10-18 cm2.It investigates the room temperature Ho:YAP laser end pumped by a 1.91 μm Tm:YLF laser.The maximum output power was 4.1 W when the incident 1.91 μm pump power was 14.4 W.The slope efficiency is 40.8%,corresponding to an optical to optical conversion efficiency of 28.4%.The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm. 相似文献
7.
Judd--Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal 下载免费PDF全文
This paper reports that the Tm^3+:Lu2SiO5 (Tm:LSO) crystal is grown by Czochralski technique. The roomtemperature absorption spectra of Tm:LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Ω2=9.3155×10^-20 cm^2, Ω4=8.4103×10^-20 cm^2, Ω6=1.5908×10^-20 cm^2, the fluorescence lifetime is calculated to be 2.03 ms for ^3F4 → ^3H6 transition, and the integrated emission cross section is 5.81×10^-18 cm^2. Room-temperature laser action near 2μm under diode pumping is experimentally evaluated in Tm:LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuouswave maximum output power of 0.67 W. The emission wavelengths of Tm:LSO laser are centred around 2.06μm with spectral bandwidth of -13.6 nm. 相似文献
8.
Simulated human eye retina adaptive optics imaging system based on a liquid crystal on silicon device 下载免费PDF全文
In order to obtain a clear image of the retina of model eye, an
adaptive optics system used to correct the wave-front error is
introduced in this paper. The spatial light modulator that we use
here is a liquid crystal on a silicon device instead of a
conversional deformable mirror. A paper with carbon granule is used
to simulate the retina of human eye. The pupil size of the model eye
is adjustable (3--7mm). A Shack-Hartman wave-front sensor is used
to detect the wave-front aberration. With this construction, a value
of peak-to-valley is achieved to be 0.086Λ, where
Λ is wavelength. The modulation transfer functions before
and after corrections are compared. And the resolution of this
system after correction (69lp/m) is very close to the diffraction
limit resolution. The carbon granule on the white paper which has a
size of 4.7μm is seen clearly. The size of the retina cell is
between 4 and 10μm. So this system has an ability to image
the human eye's retina. 相似文献
9.
Controlled growth and field emission of vertically aligned AlN nanostructures with different morphologies 下载免费PDF全文
The controllable growth of three different morphologies of AlN
nanostructures (nanorod, nanotip and nanocrater) arrays are
successfully realized by using chemical vapour deposition (CVD)
technology. All three nanostructures are of single crystal h-AlN
with a growth orientation of [001]. Their growth is attributed to
the vapour-liquid-solid (VLS) mechanism. To investigate the factors
affecting field emission (FE) properties of AlN nanostructures, we
compare their FE behaviours in several aspects. Experimental results
show that AlN nanocrater arrays possess the best FE properties, such
as a threshold field of 7.2~V/μm and an emission current
fluctuation lower than 4%. Moreover, the three AlN nanostructures
all have good field emission properties compared with a number of
other excellent cathode nanomaterials, which suggests that they are
future promising FE nanomaterials. 相似文献
10.
Large scale, high density boron carbide nanowires have been synthesized by using an improved carbothermal reduction method with B/B203/C powder precursors under an argon flow at 1100℃. The boron carbide nanowires are 5-10 μm in length and 80-100 nm in diameter. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) characterizations show that the boron carbide nanowire has a B4C rhombohedral structure with good crystallization. The Raman spectrum of the as-grown boron carbide nanowires is consistent with that of a B4C structure consisting of B11C icosahedra and C-B-C chains. The room temperature photoluminescence spectrum of the boron carbide nanowires exhibits a visible range of emission centred at 638 nm. 相似文献
11.
High density Al2O3/TaN-based metal--insulator-- metal capacitors in application to radio frequency integrated circuits 下载免费PDF全文
Metal-insulator-metal (MIM) capacitors with atomic-layer-deposited Al2O3 dielectric and reactively sputtered TaN electrodes in application to radio frequency integrated circuits have been characterized electrically. The capacitors exhibit a high density of about 6.05 fF/μm^2, a small leakage current of 4.8 × 10^-8 A/cm^2 at 3 V, a high breakdown electric field of 8.61 MV/cm as well as acceptable voltage coefficients of capacitance (VCCs) of 795 ppm/V2 and 268ppm/V at 1 MHz. The observed properties should be attributed to high-quality Al2O3 film and chemically stable TaN electrodes. Further, a logarithmically linear relationship between quadratic VCC and frequency is observed due to the change of relaxation time with carrier mobility in the dielectric. The conduction mechanism in the high field ranges is dominated by the Poole-Frenkel emission, and the leakage current in the low field ranges is likely to be associated with trap-assisted tunnelling. Meanwhile, the Al2O3 dielectric presents charge trapping under low voltage stresses, and defect generation under high voltage stresses, and it has a hard-breakdown performance. 相似文献
12.
Rectifying effect of heterojunctions between metals and doped conducting polymer nanostructure pellets 下载免费PDF全文
This paper reports that the Schottky junctions between low work function metals (e.g. Al and In) and doped semiconducting polymer pellets (e.g. polyaniline (PANI) microsphere pellet and polypyrrole (PPy) nanotube pellet) have been prepared and studied. Since Ag is a high work function metal which can make an ohmic contact with polymer, silver paste was used to fabricate the electrodes. The Al/PANI/Ag heterojunction shows an obvious rectifying effect as shown in I - V characteristic curves (rectifying ratio γ = 5 at ±6 V bias at room temperature). As compared to the Al/PANI/Ag, the heterojunction between In and PANI (In/PANI/Ag) exhibits a lower rectifying ratio γ= 1.6 at ±2 V bias at room temperature. In addition, rectifying effect was also observed in the heterojunctions Al/PPy/Ag (γ = 3.2 at ±1.6 V bias) and In/PPy/Ag (γ = 1.2 at ±3.0 V bias). The results were discussed in terms of thermoionic emission theory. 相似文献
13.
This paper reports that a novel type of suspended ZnO nanowire field-effect
transistors (FETs) were successfully fabricated using a
photolithography process, and their electrical properties were
characterized by I--V measurements. Single-crystalline ZnO
nanowires were synthesized by a hydrothermal method, they were used
as a suspended ZnO nanowire channel of back-gate field-effect
transistors (FET). The fabricated suspended nanowire FETs showed a
p-channel depletion mode, exhibited high on--off current ratio of
~105. When VDS=2.5 V, the peak transconductances
of the suspended FETs were 0.396 μS, the oxide capacitance was
found to be 1.547 fF, the pinch-off voltage VTH was about
0.6 V, the electron mobility was on average 50.17 cm2/Vs. The
resistivity of the ZnO nanowire channel was estimated to be
0.96× 102Ω cm at VGS = 0 V. These
characteristics revealed that the suspended nanowire FET fabricated
by the photolithography process had excellent performance. Better
contacts between the ZnO nanowire and metal electrodes could be
improved through annealing and metal deposition using a focused ion
beam. 相似文献
14.
A single layer of CoFeB and a multilayer of CoFeB--MgO films are
prepared by means of DC/RF magnetron sputter deposition. The
excellent microwave properties and high electrical resistivity are
simultaneously achieved in the discontinuous multilayer structure of
[Co44Fe44B12(0.7nm)/MgO(0.4nm)]_{40} film. This
film has a high permeability ({μ \prime }) (larger than 100
below 2.1GHz), a high magnetic loss (μ') (larger than 100 in
a range from 1.5 to 3.3GHz), a resistivity of 3.3× 10* 相似文献
15.
This paper describes a micro thermal shear stress sensor with a cavity underneath, based on vacuum anodic bonding and bulk micromachined technology. A Ti/Pt alloy strip, 2μm×100μm, is deposited on the top of a thin silicon nitride diaphragm and functioned as the thermal sensor element. By using vacuum anodic bonding and bulk-si anisotropic wet etching process instead of the sacrificial-layer technique, a cavity, functioned as the adiabatic vacuum chamber, 200μm×200μm×400μm, is placed between the silicon nitride diaphragm and glass (Corning 7740). This method totally avoid adhesion problem which is a major issue of the sacrificial-layer technique. 相似文献
16.
The KH 2 PO 4 crystal is a key component in optical systems of inertial confinement fusion (ICF).The microwaviness on a KH 2 PO 4 crystal surface is strongly related to its damage threshold which is a key parameter for application.To study the laser induced damage mechanism caused by microwaviness,in this paper the near-field modulation properties of microwaviness to the incident wave are discussed by the Fourier modal method.Research results indicate that the microwaviness on the machined surface will distort the incident wave and thus lead to non-uniform distribution of the light intensity inside the crystal;in a common range of microwaviness amplitude,the light intensity modulation degree increases about 0.03 whenever the microwaviness amplitude increases 10 nm;1 order diffraction efficiencies are the key factors responsible for light intensity modulation inside the crystal;the light intensity modulation is just around the microwaviness in the form of an evanescent wave,not inside the crystal when the microwaviness period is below 0.712 μm;light intensity modulation degree has two extreme points in microwaviness periods of 1.064 μm and 1.6 μm,remains unchanged between periods of 3 μm and 150 μm,and descends above the period of 150 μm to 920 μm. 相似文献
17.
We have proposed a novel noncontact ultrasonic motor based on
non-symmetrical electrode driving. The configuration of this
electrode and the fabrication process of rotors are presented. Its vibration
characteristics are computed and analysed by using the finite element
method and studied
experimentally. Good agreement between them is obtained. Moreover,
it is also shown that this noncontact ultrasonic motor is operated in
antisymmetric radial vibration mode of $B_{21}$ mode. The maximum revolution
speed for three-blade and six-blade rotors are 5100 and 3700\,r/min at an
input voltage of 20V, respectively. Also, the noncontact high-speed
revolution of the rotors can be realized by the parts of I, III of the
electrode or
II, IV of the electrode. The levitation distance between the stator and
rotor is
about 140$\mu $m according to the theoretical calculation and the experimental
measurement. 相似文献
18.
We have studied the radiation of a double-walled carbon nanotube
(DWNT) filament with a length of 4.5\,mm and a diameter of
10\,$\mu$m by applying an electric current through the filament. The
DWNT filament starts emitting incandescent light at voltage
$U=6$\,V. Emission spectra of the DWNT below temperature 1250\,K can
well be fitted to those of the blackbody radiation. The intensity of
the incandescent light shows an exponential dependence on the
voltage applied on the DWNT filaments. The resistance of the DWNT
filaments is very stable at high temperatures between 900 and
1250\,K during the emission of light in the experiments. 相似文献
19.
20.
Polymers are a kind of attractive hosts for laser dyes due to their
high transparency in both pumping and lasing ranges and superior
optical homogeneity. In this paper solid dye samples based on
polymethyl methacrylate (PMMA) doped with different concentrations of
1, 3, 5, 7, 8 -pentamethyl-2, 6-diethylpyrromethene-BF$_{2 }$ (PM567)
are prepared. The absorption, fluorescence and lasing spectra of the
samples are obtained. Wide absorption and fluorescence bands are
obtained and a red shift of the maxima of the lasing emission spectra
is observed. With the second-harmonic generation of Q-switched Nd:YAG
laser (532\,nm, $\sim $20\,ns) pumping the samples longitudinally,
the slope efficiencies of the samples are obtained. There is an
optimal dye concentration for the highest slope efficiency when the
pumping energy is lower than some typical value ($\sim $250\,mJ), and
the highest slope efficiency 35.6{\%} is obtained in the sample with
a dye concentration of $2\times10^{ - 4}$\,mol/L. Pumping the samples
at a rate of 10Hz with a pulse energy as high as 200\,mJ (the fluence
is 0.2\,J/cm$^{2})$, the output energy drops to one-half of its
initial value after approximate 15500 pulses and the normalized
photostability is 5.17\,GJ/mol. A kind of solid dye laser which could
have some applications is built. 相似文献