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1.
D. Sands 《Applied Physics A: Materials Science & Processing》2007,88(1):179-189
A new theory of undercooling has been developed based on the Fickian form of heat flux expressed in terms of a gradient in
enthalpy density. It is shown that heat diffusion is more fundamental than Fourier’s law of heat conduction. During the solid–liquid
phase change, diffusion requires continuity of the enthalpy density across the phase-change boundary, which has two important
consequences. First, the calculated melt-depth during rapid heating is reduced, and second, during cooling the rate of loss
of heat is independent of both the rate of release of latent heat and the temperature of the interphase layer. The cause of
undercooling is diffusive heat loss without recrystallisation, which simply causes the temperature of the liquid to drop.
Both the nature of melting and classical nucleation have been examined and shown to support diffusion over conduction. In
particular, it is established that the literature supports a model of melting in which phase fluctuations at the melting point
occur, and that these phase fluctuations must inevitably lead to thermal transport at uniform temperature. Hitherto unrecognized
inconsistencies in classical nucleation theory also support the diffusive framework. The model is applied to pulsed laser
melting and amorphisation of (111) silicon.
PACS 64.70.Dv; 66.30.Xj; 68.18.Jk 相似文献
2.
Ikurou Umezu Muneyuki Naito Daisuke Kawabe Yusuke Koshiba Katsuki Nagao Akira Sugimura Tamao Aoki Mitsuru Inada Tadashi Saitoh Atsushi Kohno 《Applied Physics A: Materials Science & Processing》2014,117(1):155-159
Hyperdoping with deep-level impurity is a promising method to prepare intermediate band semiconductors. We prepared silicon hyperdoped with deep-level impurities, sulfur and titanium, by ion implantation followed by pulsed YAG laser melting. The processes of sulfur and titanium hyperdoping are comparatively studied. The amorphous sulfur and titanium ion-implanted layers changed to monocrystal by following pulsed laser melting. The depth profile of sulfur impurity after pulsed laser melting is similar to that of ion-implanted sample, while large segregation is observed for titanium hyperdoping. The crystallinity and degree of segregation depend on the laser shot number and initially implanted titanium dose. There is a trade-off between crystallinity and depth profile of impurity for titanium hyperdoping. From a viewpoint material processing, formation of high-quality silicon monocrystal hyperdoped with sulfur is easier than that with titanium. Correlation between the mid-infrared optical absorption and photoconductivity is also discussed for sulfur-hyperdoped sample. 相似文献
3.
利用准分子脉冲激光晶化非晶硅薄膜是制备高密度尺寸可控的硅基纳米结构的有效方法之一.本文将脉冲激光对非晶硅超薄膜的影响处理为热传导问题,采用了基于Tersoff势函数的分子动力学方法模拟了在非晶氮化硅衬底上2.7 nm超薄非晶硅膜的脉冲激光晶化过程.研究了不同激光能量对非晶硅薄膜晶化形成纳米硅的影响,发现在合适的激光能量窗口下,可以获得高密度尺寸可控的纳米硅薄膜,进而模拟了在此能量作用下非晶硅膜中成核与生长的机理与微观过程,并对晶化所获得的纳米硅薄膜的微结构进行了分析.
关键词:
非晶硅
分子动力学
脉冲激光晶化 相似文献
4.
The two-dimensional Laplace integral transform technique is used to solve the problem of melting a semi-infinite target induced by surface absorption of a laser pulse.Mathematical expressions for the temperature distribution within the solid part of the target and the thickness of its liquified part were obtained considering cooling, temperature dependent absorption coefficient of the irradiated surface and constant temperature in the molten layer. As an illustrative example computations were carried out on a semi-infinite aluminium (Al) target. 相似文献
5.
Lester Guttman 《Solid State Communications》1983,45(7):551-552
The entropy and melting point of amorphous silicon cannot be measured in a thermodynamic sense. 相似文献
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8.
Polycrystalline silicon (poly-Si) thin film has been prepared by means of
nickel-disilicide (NiSi多晶硅 受激准分子激光器结晶 结晶化 界面晶粒生长 polycrystalline silicon, excimer laser crystallization,Ni-disilicide, Ni-metal-induced lateral crystallization, two-interface grain growth Project supported by the National High Technology Development Program of China (Grant No 2002AA303250) and by the National Natural Science Foundation of China (Grant No 60576056). 9/7/2005 12:00:00 AM 3/6/2006 12:00:00 AM Polycrystalline silicon (poly-Si) thin film has been prepared by means of nickel-disilicide (NiSi2) assisted excimer laser crystallization (ELC). The process to prepare a sample includes two steps. One step consists of the formation of NiSi2 precipitates by heat-treating the dehydrogenated amorphous silicon (a-Si) coated with a thin layer of Ni. And the other step consists of the formation of poly-Si grains by means of ELC. According to the test results of scanning electron microscopy (SEM), another grain growth model named two-interface grain growth has been proposed to contrast with the conventional Ni-metal-induced lateral crystallization (Ni-MILC) model and the ELC model. That is, an additional grain growth interface other than that in conventional ELC is formed, which consists of NiSi2 precipitates and a-Si. The processes for grain growth according to various excimer laser energy densities delivered to the a-Si film have been discussed. It is discovered that grains with needle shape and most of a uniform orientation are formed which grow up with NiSi2 precipitates as seeds. The reason for the formation of such grains which are different from that of Ni-MILC without migration of Ni atoms is not clear. Our model and analysis point out a method to prepare grains with needle shape and mostly of a uniform orientation. If such grains are utilized to make thin-film transistor, its characteristics may be improved. 相似文献
9.
S. Tosto 《Applied Physics A: Materials Science & Processing》2000,71(3):285-297
The paper introduces a 3D computer simulation model of the melting and recrystallization process of amorphous Si induced by
pulsed laser irradiation. The model takes into account the temperature dependence of thermal and optical properties of crystalline,
amorphous and liquid Si. The melting process is described by introducing for each volume element of melt pool the characteristic
times of beginning of melting, end of melting and nucleation of a stable nucleus. The solution of heat equations of liquid
and solid phases also provides one with the nucleation rates and temperatures. These data enable one to discriminate whether
amorphous or crystalline phases are really allowed to be formed. Two examples of computer simulation are carried out to show
the outputs of the model.
Received: 7 February 2000 / Accepted: 28 March 2000 / Published online: 9 August 2000 相似文献
10.
Polycrystalline copper film microstructures produced by laser melting and rapid lateral solidification are analyzed using transmission electron microscopy. The microstructure is predominantly composed of directionally solidified grains up to 22 μm long and 1 μm wide lying in the plane of the film. We identify four morphologically solidification zones, corresponding to occlusion, steady lateral growth, defective growth, and nucleation. Electron diffraction analysis indicates clustering of 1 0 0 orientations around the direction of solidification for the grains in the steady lateral growth zone. Simple estimates of solidification times based on heat flow modeling and a critical nucleation temperature suggest that interface velocities of several hundred m/s may be attained during solidification. 相似文献
11.
A. A. Ionin S. I. Kudryashov L. V. Seleznev D. V. Sinitsyn A. F. Bunkin V. N. Lednev S. M. Pershin 《Journal of Experimental and Theoretical Physics》2013,116(3):347-362
The space-time dynamics of thermal melting, subsurface cavitation, spallative ablation, and fragmentation ablation of the silicon surface excited by single IR femtosecond laser pulses is studied by timeresolved optical reflection microscopy. This dynamics is revealed by monitoring picosecond and (sub)nanosecond oscillations of probe pulse reflection, which is modulated by picosecond acoustic reverberations in the dynamically growing surface melt subjected to ablation and having another acoustic impedance, and by optical interference between the probe pulse replicas reflected by the spalled layer surface and the layer retained on the target surface. The acoustic reverberation periods change during the growth and ablation of the surface melt film, which makes it possible to quantitatively estimate the contributions of these processes to the thermal dynamics of the material surface. The results on the thermal dynamics of laser excitation are supported by dynamic measurements of the ablation parameters using noncontact ultrasonic diagnostics, scanning electron microscopy, atomic force microscopy, and optical interference microscopy of the modified regions appearing on the silicon surface after ablation. 相似文献
12.
Karen Birkelund Matthias Müllenborn François Grey Flemming Jensen Steen Madsen 《Superlattices and Microstructures》1996,20(4):555-560
We report a novel combination of AFM lithography and laser direct writing on hydrogen-passivated amorphous silicon surfaces to fabricate combined silicon milli-, micro- and nanostructures. Selective oxidation is performed by focusing a laser beam (λ=458 nm) on a hydrogen-terminated silicon surface, forming the millimetre-size contact pads for connection of nanometre-scale patterns. The nanostructures are made by electric-field-enhanced oxidation using a contact mode AFM equipped with a metal-coated tip. Both techniques are based on selective oxidation of hydrogen-passivated amorphous silicon, where the oxide is used as an etch mask in a single etch step. The lithographic process has also been demonstrated using a reflection mode scanning near-field optical microscope with an uncoated fiber probe. 相似文献
13.
Nanosecond pulsed laser ablation of silicon in liquids 总被引:2,自引:0,他引:2
R. Karimzadeh J. Zamir Anvari N. Mansour 《Applied Physics A: Materials Science & Processing》2009,94(4):949-955
Laser fluence and laser shot number are important parameters for pulse laser based micromachining of silicon in liquids. This
paper presents laser-induced ablation of silicon in liquids of the dimethyl sulfoxide (DMSO) and the water at different applied
laser fluence levels and laser shot numbers. The experimental results are conducted using 15 ns pulsed laser irradiation at
532 nm. The silicon surface morphology of the irradiated spots has an appearance as one can see in porous formation. The surface
morphology exhibits a large number of cavities which indicates as bubble nucleation sites. The observed surface morphology
shows that the explosive melt expulsion could be a dominant process for the laser ablation of silicon in liquids using nanosecond
pulsed laser irradiation at 532 nm. Silicon surface’s ablated diameter growth was measured at different applied laser fluences
and shot numbers in both liquid interfaces. A theoretical analysis suggested investigating silicon surface etching in liquid
by intense multiple nanosecond laser pulses. It has been assumed that the nanosecond pulsed laser-induced silicon surface
modification is due to the process of explosive melt expulsion under the action of the confined plasma-induced pressure or
shock wave trapped between the silicon target and the overlying liquid. This analysis allows us to determine the effective
lateral interaction zone of ablated solid target related to nanosecond pulsed laser illumination. The theoretical analysis
is found in excellent agreement with the experimental measurements of silicon ablated diameter growth in the DMSO and the
water interfaces. Multiple-shot laser ablation threshold of silicon is determined. Pulsed energy accumulation model is used
to obtain the single-shot ablation threshold of silicon. The smaller ablation threshold value is found in the DMSO, and the
incubation effect is also found to be absent. 相似文献
14.
Th. Dittrich I. Sieber W. Henrion S. Rauseher N. Wanderka J. Rappich 《Applied Physics A: Materials Science & Processing》1996,63(5):467-470
Short laser pulses (wavelength 337 nm, duration time 0.5 ns) are used for thermal processing of ultra thin nanoporous silicon layers (UPSL) prepared electrochemically on n- and p-type Si(1 1 1) in aqueous NH4F solution. The theoretical threshold for melting (W
m
) of UPSL is about 0.01 J/cm2. This is about one order of magnitude belowW
m
of crystalline silicon. A selective laser induced melting regime can be realized for which an UPSL is practically completely molten on the top of an unmolten crystalline silicon substrate. Investigations with scanning and high resolution transmission electron microscopy show the formation of crystalline silicon spheres with diameters in the range of some of ten nm in this regime. 相似文献
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16.
Chang Woo Lee Choochon Lee Yong Tae Kim 《Applied Physics A: Materials Science & Processing》1993,56(2):123-126
Effects of multi-step rapid thermal annealing of plasma-deposited amorphous silicon films on Corning 7059 glass are investigated. A three-step rapid thermal annealing for 10 s/step at 730° C after film deposition reduces the activation energy of electrical conductivity for silicon films from 0.64 to 0.51 eV and causes (111) grain growth with a size of 1500 Å, which is determined using scanning electron microscopy, Raman spectroscopy and X-ray diffractometry. 相似文献
17.
F. Delachat F. Antoni A. Slaoui C. Cayron C. Ducros J.-F. Lerat T. Emeraud R. Negru K. Huet P.-L. Reydet 《Applied Physics A: Materials Science & Processing》2013,111(3):807-812
An attempt has been made to achieve the crystallization of silicon thin film on metallic foils by long pulse duration excimer laser processing. Amorphous silicon thin films (100 nm) were deposited by radiofrequency magnetron sputtering on a commercial metallic alloy (N42-FeNi made of 41 % of Ni) coated by a tantalum nitride (TaN) layer. The TaN coating acts as a barrier layer, preventing the diffusion of metallic impurities in the silicon thin film during the laser annealing. An energy density threshold of 0.3 J?cm?2, necessary for surface melting and crystallization of the amorphous silicon, was predicted by a numerical simulation of laser-induced phase transitions and witnessed by Raman analysis. Beyond this fluence, the melt depth increases with the intensification of energy density. A complete crystallization of the layer is achieved for an energy density of 0.9 J?cm?2. Scanning electron microscopy unveils the nanostructuring of the silicon after laser irradiation, while cross-sectional transmission electron microscopy reveals the crystallites’ columnar growth. 相似文献
18.
《中国物理 B》2015,(8)
It is interesting that in preparing process of nanosilicon by pulsed laser, the periodic diffraction pattern from plasmonic lattice structure in the Purcell cavity due to interaction between plasmons and photons is observed. This kind of plasmonic lattice structure confined in the cavity may be similar to the Wigner crystal structure. Emission manipulation on Si nanostructures fabricated by the plasmonic wave induced from pulsed laser is studied by using photoluminescence spectroscopy.The electronic localized states and surface bonding are characterized by several emission bands peaked near 600nm and 700nm on samples prepared in oxygen or nitrogen environment. The electroluminescence wavelength is measured in the telecom window on silicon film coated by ytterbium. The enhanced emission originates from surface localized states in band gap due to broken symmetry from some bonds on surface bulges produced by plasmonic wave in the cavity. 相似文献
19.
F. Kokai S. Inoue H. Hidaka K. Uchiyama Y. Takahashi A. Koshio 《Applied Physics A: Materials Science & Processing》2013,110(1):1-7
Carbon nanotubes (CNTs) appear to be ideal tip materials of atomic force microscopy (AFM) due to their small diameter and high stiffness. In this study, double-walled carbon nanotube (DWCNT) structures with different lengths of inner and outer layers are proposed as AFM tips. Both the vibration response and mode shapes of the tipped nanotubes under axial compression are studied by a theoretical nanobeam model. The results show that the natural frequencies of DWCNTs are significantly affected by the compressive loads and the length difference between the inner and outer nanotubes. The natural frequency associated with certain vibrational modes decreases with increasing compressive loads. This research may provide a useful reference for practical design for AFM tips with CNTs. 相似文献
20.
A. V. Nezhdanov A. Yu. Afanaskin A. V. Ershov A. I. Mashin 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(1):1-5
The effect of laser radiation power on the Raman spectra of amorphous silicon obtained by electron-beam evaporation has been
revealed. The formation of nanocrystalline inclusions in the amorphous matrix under exposure to a laser with a power of more
than 2.5 mW is established by Raman spectroscopy and photoluminescence. The influence of the fabrication conditions (substrate
temperature and annealing in a vacuum) of source amorphous silicon films on the formation of nanocrystalline inclusions formed
by subsequent laser treatment has been investigated. The features of silicon nanocrystal formation in cases when the original
amorphous silicon film is obtained at a substrate temperature of ∼250°C have been revealed. These features may be associated
with the presence of silicon-silicon multiple bonds. 相似文献