共查询到20条相似文献,搜索用时 31 毫秒
1.
X. Xu C. P. Grigoropoulos R. E. Russo 《Applied Physics A: Materials Science & Processing》1995,62(1):51-59
A nanosecond-time-resolution pyrometer has been developed for measuring the transient surface temperature of a solid material heated by pulsed excimer-laser irradiation. Fast germanium diodes are employed to capture the transient thermal emission signals in the wavelength range between 1.2 and 1.6rwm. The surface temperature is derived from the measured spectral thermal emission. The directional spectral emissivity is determined in situ by measuring the transient directional spectral reflectivity and applying Kirchhoff's law. The experimental results are in good agreement with numerical thermal modeling predictions. The pyrometric thermal emission measurement also yields the solid/liquid interface temperature during the pulsed excimer-laser-induced melting. The relation between the measured interface superheating temperature and the interface velocity reveals the melting kinetic relation during the high-power, short-pulse laser-induced phase-change processes. 相似文献
2.
A composite material of Zinc oxide and carbon nano-tubes (ZnO-CNTs) paste was synthesized by mixing multi-wall CNTs, ZnO nano-grains and organic vehicles. The microstructures and the morphologies of screen-printed films were characterized by field-emission scanning electron microscope. Results show that ZnO flakes geometrically matched with CNTs by filling into the interspaces of CNTs or directly covering upon CNTs. The field emission characteristics of films are found to be greatly effected by ZnO nano-grains. Especially, the turn-on electric field of ZnO-CNT film (1.17 V/μm) which is far lower than that of usual CNT films (1.70 V/μm). Furthermore, except that better emission stability is achieved, brightness and emission uniformity are notably enhanced as well. It can be speculated that the special microstructures of ZnO mixed CNT films dominate the enhanced electrical conductivity, thermal conductivity, and effective emitters. 相似文献
3.
Design and optimization of a SiC thermal emitter/absorber composed of periodic microstructures based on a non-linear method
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
《中国物理 B》2015,(9)
Spectral and directional control of thermal emission based on excitation of confined electromagnetic resonant modes paves a viable way for the design and construction of microscale thermal emitters/absorbers. In this paper, we present numerical simulation results of the thermal radiative properties of a silicon carbide(Si C) thermal emitter/absorber composed of periodic microstructures. We illustrate different electromagnetic resonant modes which can be excited with the structure,such as surface phonon polaritons, magnetic polaritons and photonic crystal modes, and the process of radiation spectrum optimization based on a non-linear optimization algorithm. We show that the spectral and directional control of thermal emission/absorption can be efficiently achieved by adjusting the geometrical parameters of the structure. Moreover, the optimized spectrum is insensitive to 3% dimension modification. 相似文献
4.
A. F. Vyatkin V. I. Zinenko A. I. Il’in O. V. Trofimov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(6):1180-1184
The dynamics of ion-beam etching of test microstructures, simulating fragments of the surface structure of very large-scale
modern integrated circuits, has been studied. Aluminum strip microstructures, 0.5 μm high and 1 μm wide deposited on the surface
or embedded into SiO2, were used as test samples. 1 keV Ar+ ion beam 1 with a current density 0.5 mA/cm2, incident on the surface of a sample, rotating at a speed of 60 r/min, at an angle of 87°, has been used in the experiments.
The surface morphology evolution was studied using atomic-force microscopy. The experiments demonstrate that physical ion
sputtering at glancing incident angles can be used for the planarization of originally inhomogeneous structures. The achieved
planarization degree allows one to use this method for defect detection in the metallization multilevel layers of very large-scale
modern integrated circuits. 相似文献
5.
We report recent progress to date on the UT‐MSL/KEK “Ultra Slow Muon” project, in which thermal muonium (Mu) atoms are generated
from the surface of a hot tungsten target placed at the primary 500 MeV proton beam line and resonantly ionized by intense
u.v. lasers synchronized with the emission of the Mu. The positive muon ionization fragments are collected by electrostatic
beam optics to form a beam of slow positive muons.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
The viscose flow and microstructure formation of Fe-Cu peritectic alloy melts are investigated by analyzing the velocity and
temperature fields during rapid solidification, which is verified by rapid quenching experiments. It is found that a large
temperature gradient exists along the vertical direction of melt puddle, whereas there is no obvious temperature variation
in the tangent direction of roller surface. After being sprayed from a nozzle, the alloy melt changes the magnitude and direction
of its flow and velocity rapidly at a height of about 180 μm. The horizontal flow velocity increases rapidly, but the vertical
flow velocity decreases sharply. A thermal boundary layer with 160–300 μm in height and a momentum boundary layer with 160–240
μm in thickness are formed at the bottom of melt puddle, and the Reynolds number Re is in the range of 870 to 1070 in the
boundary layer. With the increase of Re number, the cooling rate increases linearly and the thickness of thermal boundary
layer increases monotonically. The thickness of momentum boundary layer decreases slowly at first, then rises slightly and
decreases sharply. If Re < 1024, the liquid flow has remarkable effects on the microstructure formation due to dominant momentum
transfer. The separated liquid phase is likely to form a fiber-like microstructure. If Re>1024, the heat transfer becomes
dominating and the liquid phase flow is suppressed, which results in the formation of fine and uniform equiaxed microstructures.
Supported by the National Natural Science Foundation of China (Grant Nos. 50121101 and 50395105) 相似文献
7.
P. Mandal S. S. Talwar R. S. Srinivasa S. S. Major 《Applied Physics A: Materials Science & Processing》2009,94(3):577-584
CdS nanocrystallites formed in ordered fatty acid LB multilayers exhibited strong surface states emission ∼550 nm and weak
excitonic emission ∼400 nm. Treatment with aqueous CdCl2 resulted in the suppression of surface states emission and enhancement of the blue excitonic emission. Subsequent annealing
in air at 200°C caused an order of magnitude enhancement of excitonic emission. The growth of nanocrystallites during annealing
as seen from the red-shift of excitonic absorption and emission is suppressed by the CdCl2 treatment. The hindered growth of nanocrystallites, the significant enhancement of excitonic emission from CdS, and the suppression
of surface states emission are attributed to surface passivation of CdS nanocrystallites by surface oxide formation. 相似文献
8.
G. V. Valsky A. M. Gagarski I. S. Guseva D. O. Krinitsin G. A. Petrov Yu. S. Pleva V. E. Sokolov V. I. Petrova T. A. Zavarukhina T. E. Kuzmina 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(6):767-771
The angular dependence of the γ-ray asymmetry relative to the plane formed by the directions of fission-fragment separation
and longitudinal polarization of the thermal neutrons inducing 235U(n, f) fission was investigated. The results obtained confirm the existence of γ-ray emission asymmetry and the dependence of its
coefficient on the angle between the axes of the fission-fragment and γ-ray detectors, revealed for the first time by the
ITEP group at the FRM-II reactor in Munich. The observed T-odd effect of around ∼2 × 10−4 can be explained by the angular anisotropy of the γ-ray emission from fission fragments with large angular momenta oriented
relative to the fission axis. 相似文献
9.
B.K. Nayak M.C. Gupta K.W. Kolasinski 《Applied Physics A: Materials Science & Processing》2008,90(3):399-402
We report for the first time that a regular array of sharp nano-textured conical microstructures are formed on the titanium
metal surface by irradiation with ultrafast laser pulses of 130 fs duration, 800 nm wavelength in vacuum (∼1 mbar) or in 100 mbar
He. The microstructures are up to 25 μm tall, and taper to about 500 nm diameters at the tip. Irradiation in the presence
of SF6, air or HCl creates a textured surface but does not create sharp conical microstructures. The surfaces of these microstructures
exhibit periodic nano-texture of feature size comparable to the wavelength of light consistent with ripple formation. Contrary
to pillar formation by femtosecond laser irradiation of silicon where the initial ripples evolve into the pillars and the
ripples disappear, the ripples on titanium pillars have a much smaller periodicity than the pillars and remain on the surface
of the pillars. The textured surface is pitch black compared to its original silver-grayish color, i.e, it exhibits greatly
reduced reflectivity throughout the measured visible spectrum.
PACS 52.38.Mf; 79.20.Ds; 81.07.-b; 81.16.-c; 82.53.-k 相似文献
10.
A. Matsushita Y. Miyake Y. Murata K. Nishiyama K. Nagamine D. G. Fleming M. Morita T. Ohmi 《Hyperfine Interactions》1991,65(1-4):1071-1080
Evidence for the emission of slow muonium atoms from a 3.0-nm-thick SiO2 layer covered on an n-type Si is reported. Also, upon applying an rf-resonance technique at the muon frequency, a time-differential
observation of a delayed state-change from muonium to diamagnetic muon at room temperature was observed. Combining results
obtained by use of longitudinal field decoupling and transverse spin rotation methods, the conversion rate was estimated to
be 5 to 10 μs−1. Both of the above results, namely the observation of the emission and state-change of muonium, suggest a process in which
μ+ initially captures an electron from Si, then quickly converts to μ+ again during thermal diffusion in the Si towards the SiO2 layer. Within the oxide layer, muonium is again formed and subsequently is emitted from the SiO2 surface. 相似文献
11.
Ye Wu Irene Ling Li Ling Fu Jian pang Zhai Shuang Chen Ruan 《Applied Surface Science》2009,255(23):9409-9412
Excimer laser emitting at 248 nm is applied to produce microstructures on the surface of aluminum alloy. The surface morphology shows that hotspots and thermal fluidic structures both come to light. Two possible mechanisms of hotspots formation are proposed: near-field diffraction and interference, and extremely fast rapid thermal annealing. And for the formation of thermal fluidic pattern structure, a thin film model is applied. 相似文献
12.
Sword-like (diameter ranging from 40 nm to 300 nm) and needle-like zinc oxide (ZnO) nanostructures (average tip diameter ∼40 nm)
were synthesized on annealed silver template over silicon substrate and directly on silicon wafer, respectively via thermal
evaporation of metallic zinc followed by a thermal annealing in air. The surface morphology, microstructure, chemical analysis
and optical properties of the grown samples were investigated by field emission scanning electron microscopy, X-ray diffraction,
energy dispersive X-ray analysis, room temperature photoluminescence and Raman spectroscopy. The sword-like ZnO nanostructures
grown on annealed silver template are of high optical quality compared to needle-like ZnO nanorods for UV emission and show
enhanced Raman scattering. 相似文献
13.
Mathew S Ani Joseph S Radhakrishnan P Nampoori VP Vallabhan CP 《Journal of fluorescence》2011,21(4):1479-1484
CdS nanoparticles with different size are prepared by chemical bath deposition method. These particles show strong fluorescence
at emission wavelength of 507 nm. It has been observed that this emission peak changes through a range of 147 nm, by varying
the excitation wavelengths through 370–480 nm.The emission peak can thus be tuned by varying the excitation wavelengths. This
peak emission wavelength shift is due to the selective excitation of vibronic levels in the surface state of the CdS nanoparticles. 相似文献
14.
A series of electroplating works have been conducted to investigate the best condition for the coelectrodeposition of nickel–alumina
(Ni/α–Al2O3) composite coating. Co-electrodeposition was done onto mild steel as cathode at ambient temperature (27°C) with current density
of 30 mA/cm2 under α-Al2O3 concentration of 2 g/l and various agitation speeds of 50, 100, 150, 200, and 250 rpms. The cross-section of the composite
coatings portrayed α-Al2O3 particles was co-deposited. Under field emission scanning electron microscopy analysis, the coating shows a coarse surface
morphology, while cross-sectional microstructures shows a compact embedding of α-Al2O3 particle in the Ni matrix. Elemental analysis by EDX detected the presence of Ni and α-Al2O3. Vickers microhardness testing shows that the coating hardness increases almost 60% at the highest agitation speed, i.e.,
250 rpm. 相似文献
15.
Yu. K. Zemtsov A. Yu. Sechin A. N. Starostin A. G. Leonov D. I. Chekhov 《JETP Letters》1997,65(11):839-844
The purely thermal infrared emission spectra of a resonance medium (sodium vapor) are investigated experimentally. It is shown
that the emission intensity in the 2–3 μm range at temperatures of 600–1200 K is several orders of magnitude higher than the
intensity obtained from the standard theory of resonance radiation transfer. This phenomenon can be conventionally termed
an “infrared catastrophe.” The form of the recorded spectra and the absolute intensity of the emission in both the infrared
and visible regions of the spectrum are in agreement with the theory developed by Yu. L. Zemtsov and A. M. Starostin, Zh.
éksp. Teor. Fiz. 103, 345 (1993) [JETP 76, 186 (1993)], in which the Boltzmann spectral distribution of the population of the resonance level is proportional to exp(−ħω/T).
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 807–811 (10 June 1997) 相似文献
16.
Three-dimensional photochemical microfabrication of conductive polymers in transparent polymer sheet
By focused illumination at the wavelength of 800 nm using a femtosecond laser, the tris(2,2′-bipyridyl)ruthenium complex displayed
a two-photon excitation as observed by the quadratic dependence of the emission intensity on the incident laser power. Since
the oxidation of pyrrole is induced by the oxidative quenching of the excited state, polypyrrole can be formed by a continuous
illumination. The polymerization area showed a high spatial selectivity which can be scanned in the XYZ axis by a piezo device. In the present study, three-dimensional (3D) polypyrrole microstructures were formed in the transparent
polymer sheet. 相似文献
17.
Suruchi Anand Prabhat Verma S C Abbi K P Jain M J Tafreshi K Balakrishnan R Dhansekaran 《Pramana》1996,47(2):133-143
The single crystal ZnSe:I sample was grown by the chemical vapor transport (CVT) method using iodine as the transporting agent.
The iodine incorporates itself effectively as a donor in the lattice. The sample shows a 〈111〉 optical quality surface and
has an absorption edge at 2.55 eV due to a deep impurity band nearly 0.15eV below the conduction band. The photoluminescence
emission spectra of this crystal have been measured for its temperature dependence as well as for excitation energy dependence.
The photoluminescence is in accordance with a donor-acceptor complex formation involving iodine activated donors and self-activated
acceptors. The configuration coordinate model has been used to explain the temperature dependent changes in the peak position
and the bandwidth of the emission band. The decrease in luminescence efficiency with increasing temperature is explained by
using a simple model for thermal quenching. The activation energy at low temperature range (T<200K) is different from that at high temperature range (200K<T<300K). 相似文献
18.
D. I. Vaisburd S. I. Tverdokhlebov T. A. Tukhfatullin 《Russian Physics Journal》1997,40(11):1064-1082
A dense pulsed electron beam and nanosecond pulse length has been used to inject negative electric charge into various dielectric
materials (single crystals, glasses, composites, plastics) for initiation of electron field emission from the dielectric into
a vacuum. It has been shown that upon reaching a critical electric field in the bulk and at the dielectric surface there is
intense critical electron emission. The local current density from the emission centers reaches a record value (for dielectrics)
of the order of 106 A/cm2. The emission occurs in the form of a single gigantic pulse. The measured amplitude of the emission current averaged over
the emitting surface is the same order of magnitude as the injected electron current: 10–1000 A. the emission current pulse
lages behind the current pulse of the primary electron beam injected into the sample. The delay time is in the range 1–20
nsec and decreases with increasing current density of the injected beam. Direct experimental evidence is found for intense
generation of carriers (band or quasifree electrons) in the near-surface layer of the dielectric in a strong electric field
due to the Frenkel-Poole effect and collisional ionization of traps, usually various donor levels. This process greatly strengthens
the field emission from the dielectric. It has been shown experimentally that the emission is nonuniform and is accompanied
by “point bursts” at the surface of the dielectric and ionized plasma spikes in the vacuum interval. These spikes are the
main reason that the transition of the field emission into “bursts” is critical, similar to the current which has been previously
observed in metals and semiconductors. However there are a number of substantial differences. For example the critical field
emission current density needed for the transition into “bursts” is three orders of magnitude less than for metals. If we
provide sufficient electron current at the surface or from the bulk of the dielectric to the emission centers, then the critical
emission is always accompanied by a vacuum discharge between the surface of the dielectric and a metallic collector. A detailed
computer model of the processes in the dielectric during injection of a high-density electron beam has been developed which
allows one to understand the complex physical pattern of the phenomenon.
Tomsk Polytechnic University. Institute of High-Current Electronics, Siberian Section, Russian Academy of Sciences. Translated
from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 45–67, November, 1997. 相似文献
19.
S.G. Li G. Fu I. Reading S.B. Tor N.H. Loh P. Chaturvedi S.F. Yoon K. Youcef-Toumi 《Applied Physics A: Materials Science & Processing》2007,89(3):721-728
Micro powder injection molding (μPIM) is one of the potential processes for the mass production of metallic microstructures
and micro components. Here, μPIM is the miniaturization of conventional PIM, which involves four processing steps: mixing,
injection molding, debinding and sintering. This paper looks into the feasibility and effectiveness of μPIM as a key mass
production process for the fabrication of metallic micro components. For it to be an effective re-production process, it is
imperative to examine how well parts can be duplicated/fabricated from a master mold. In this work, the dimensional variation
of high-aspect-ratio micro-pillars arrays, in particular the dimensional shrinkage, global warpage, and surface roughness
at each stage of the μPIM process for a range of molding pressures, are quantified and compared in detail. The sensitivity
of the dimensional variation of the microstructures to the packing pressure is reported. The mechanism behind the dimensional
variation is analyzed.
PACS 81.20.Ev; 81.20.Hy; 81.70.Fy; 07.60.Ly; 81.05.-t 相似文献
20.
The well-known defects of the surface of a solid, microscopic projections and spikes, play a decisive role in electron emission
induced by an electric field. If there are mobile electrons of holes in the solid, then the electric field is enhanced by
a factor of 10–100 at the tip of a microscopic projection. This effect was discovered in electrostatics more than a century
ago. In turn, the probability of tunnel emission of an electron from a metal into a vacuum is an exponential function of the
electric field strength. Correspondingly the electron emission current density at the tip of a microscopic spike can be larger
than that on a smooth surface by an astronomical factor. This effect is particularly strikingly manifested when picosecond
pulses of infrared laser radiation of moderate power are used to initiate autoelectronic emission. Relative to a smooth surface,
the emission current density is enhanced by hundreds of orders of magnitude. These experimental conditions can be used to
scan the surface of a conducting material with a laser beam and to detect all the microscopic projections, in order to male
detailed observations with subpicosecond time resolution of the phase transition from autoelectronic emission to explosive
emission.
Polytechnic University, Tomsk. Institute of Electrophysics, Ural Branch of the Russian Academy of Sciences. French National
Scientific Center, Saclay, France. Translated from Izvestiya Vysshikh Uchenbnykh Zavedenii, Fizika, No. 11, pp. 42–44, November,
1997. 相似文献