共查询到20条相似文献,搜索用时 125 毫秒
1.
L. Guo S. Y. Zhang X. R. Zhang J. He Z. N. Zhang 《Applied Physics A: Materials Science & Processing》1995,60(4):395-398
The influence of ion implantation on the thermal diffusivities of semiconductors are studied using the mirage effect. The dependences of the thermal diffusivities on the implantation doses are obtained. For silicon wafers implanted by boron, phosphorus and arsenic ions, with constant implantation energy, the thermal diffusivities decrease with increasing dose, when the doses are less than some critical values. The theoretical calculation results by using a one-dimensional multilayer model are in good agreement with the experimental ones. On the other hand, for gallium-arsenide wafers implanted with silicon ions, it is found experimentally that the thermal diffusivity increases with the implantation dose. 相似文献
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Z. J. Chen J. W. Fang S. Y. Zhang 《The European physical journal. Special topics》2008,153(1):195-198
For a film-on-substrate system, in the case of thin films
with lower thermal diffusivities compared to substrates, the phase
characterization of the photothermal signals is analyzed. Moreover, the
numerical estimations of multiparameter are performed, which show the
feasibility of simultaneous determination of the thermal diffusivities of
the film and the substrate, as well as the thermal interface resistance of
the film/substrate. Because the thermal diffusivity of the thin-film and the
thermal interface resistance may be highly correlated, a genetic algorithm
is used as an estimation method for the determination of the thermal
properties of thin films with low thermal diffusivity. 相似文献
4.
In this paper we present results of noncontact measurements of the thermal diffusivity of infrared semi-transparent n-CdMgSe mixed semiconductor crystals by means of the photothermal radiometry (PTR) in a transmission configuration. In order to overcome an influence of the infrared semi-transparency and plasma waves on the PTR signal from n-CdMgSe mixed crystals the samples were covered by thin aluminum foils on both sides. The thermal diffusivities of n-CdMgSe mixed crystals were estimated from PTR phase frequency characteristics using a well-known formula. It was found that the obtained results are underestimated in comparison to thermal diffusivities estimated from the PPE (photopyro-electric) measurements. A three layer model of a PTR signal was applied in order to estimate an error in determination of the thermal diffusivity of a sample caused by aluminum foils. 相似文献
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A PVDF piezoelectric film transducer is used in
a photoacoustic piezoelectric technique for studying thermal diffusivities
of biological tissues. The experimental precision may be improved by using
PVDF films because the acoustic impedance of PVDF films is close to that of
biological tissues. Thermal diffusivities of several fresh porcine tissues
in vitro are studied and the results are compared with previously obtained
ones. 相似文献
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To elucidate the key mechanisms responsible for the transition from deflagrative to detonative combustion in smooth-walled channels, a reactive flow with anisotropic thermal and molecular diffusivities is considered. Setting the transverse diffusivities large compared to longitudinal diffusivities, the initially formed deflagration (despite no-slip boundary conditions) appears to be nearly planar and not accelerating. This, however, does not prevent its eventual abrupt transition to Chapman–Jouguet detonation. 相似文献
9.
Transient thermal gratings at surfaces for thermal characterization of bulk materials and thin films
O. W. Käding H. Skurk A. A. Maznev E. Matthias 《Applied Physics A: Materials Science & Processing》1995,61(3):253-261
Transient Thermal Gratings (TTGs) at surfaces of absorbing materials have been utilized for investigating heat diffusion in bulk materials and thin films. In this report, we describe the theoretical background of the technique and present experimental data. TTGs were excited in the surface plane by interference of two pulsed laser beams and monitored by a cw probe beam, either via temperature dependence of the reflectivity or by deflection from the displacement pattern. A theoretical model describing the thermal and thermoelastic surface response was developed, both for a homogeneous material and a multilayer structure. The potential of the technique will be demonstrated by experimental results on (i) thermal diffusivities of bulk materials, (ii) anisotropic lateral heat transport, and (iii) thermal diffusivities of metal and diamond films. Furthermore, we will show that TTGs allow thermal depth profiling of inhomogeneous materials whenever there is a vertical gradient in thermal conductivity. 相似文献
10.
Study on thermal diffusivity of materials by laser photothermal reflection technique 总被引:1,自引:0,他引:1
A method of measuring thermal diffusivity of materials at room temperature by photothermal reflection technique is described. An intensity-modulated Ar+ laser beam is used as incident light. The beam is focused to about 1 mm diameter spot and illuminates the sample surface. HgCdTe infrared detector is used to receive photothermal signal. Using this technique, the photothermal signals are experimentally measured as the function of different frequencies. The thermal diffusivities can be obtained by fitting the experimental data. On the other hand, the thermal diffusivities of one-way composite and orthogonal symmetric arranged composites Al2O3/Al are measured in transverse, longitudinal and arbitrary directions. The results show that the diffusivity of one-way material decreases with the increase of the measurement angle; the diffusivity of orthogonally arranged material almost keeps the same when measurement angle changes. 相似文献
11.
Clifton W. Draper Gerd M. Rosenblatt 《Journal of Physics and Chemistry of Solids》1977,38(11):1265-1268
A flash method, employing a pulsed flashlamp-pumped dye laser has been used to determine the thermal diffusivities of elemental arsenic, antimony, and bismuth. Measurements were made both on poly-crystalline samples and on oriented single crystal (111) wafers in the form of small disks 3.0?7.0 mm in diameter, and 0.43–1.33 mm thick. Thermocouples (0.076 mm dia) monitor the back surface temperature as a function of time after the front of the sample is exposed to a single laser pulse of pulse width (τ) <1.0 μsec. The room temperature thermal diffusivities α (cm2/sec) of polycrystalline As, Sb and Bi are respectively: 0.234, 0.182 and 0.0651. The diffusivities parallel to the trigonal crystal axis α1 are: 0.119,0.142 and 0.0350. Measurements on polycrystalline Cu, Al and Ti yield 1.13, 0.96 and 0.085 cm2/sec, in agreement with literature values. 相似文献
12.
Thermal Diffusivity of Film/Substrate Structures Characterized by Transient Thermal Grating Method 下载免费PDF全文
Transient thermal grating method is used to measure the thermal diffusivity of absorbing films deposited on transparent substrates. According to periodically modulated dielectric constant variations and thermoelastic deformations of the thin films caused by the transient thermal gratings, an improved optical diffraction theory is presented. In the experiment, the probing laser beam reflectively diffracted by the thermal grating is measured by a photomultiplier at different grating fringe spaces. The thermal diffusivity of the film can be evaluated by fitting the theoretical calculations of diffraction signals to the experimental measured data. The validity of the method is tested by measuring the thermal diffusivities of absorbing ZnO films deposited on glass substrates. 相似文献
13.
E. Matthias M. Reichling J. Siegel O. W. Käding S. Petzoldt H. Skurk P. Bizenberger E. Neske 《Applied Physics A: Materials Science & Processing》1994,58(2):129-136
Single-shot ablation thresholds of nickel and gold films in the thickness range from 50 nm to 7 m have been measured for 14 ns laser pulses at 248 nm, using photoacoustic shock wave detection in air. The metal films were deposited on fused silica substrates. The ablation threshold was found to increase linearly with film thickness up to the thermal diffusion length of the film. Beyond this point it remains independent of film thickness. The proportionality between threshold fluence and thickness allows the prediction of ablation thresholds of metal films from the knowledge of their optical properties, evaporation enthalpies and thermal diffusivities. Physically it proves that ablation is driven by the energy density determined by the thermal diffusion length. A simple thermodynamic model describes the data well. Thermal diffusivities, an essential input for this model, were measured using the technique of transient thermal gratings. In addition, the substrate dependence of the ablation threshold was investigated for 150 nm Ni films. 相似文献
14.
The exact analytical solution for the thermal wave multiple reflections and interference in a normally cut layered structure is derived. The analysis predicts the existence of the new characteristic spatial scale in the considered phenomena—the length of thermal wave synchronism, which depends on the modulation frequency of the laser-induced head flux and the thermal diffusivities of the alternating layers. Both the amplitude and the phase of the photothermal response exhibit pronounced variation with modulation frequency when the length of the thermal wave synchronism is close to the spatial period of the structure. 相似文献
15.
Amorphous silicon nitride is a model system for a covalently bound amorphous solid with a low atomic mobility where reasonable values of self-diffusivities are still lacking. We used neutron reflectometry on isotope enriched Si3 14N4/Si3 15N4 multilayers to determine nitrogen self-diffusivities ranging from 10(-24) to 10(-21) m2/s between 950 and 1250 degrees C. Time dependent diffusivities observed at 1150 degrees C indicate the presence of structural relaxation. For long annealing times (relaxed state) the diffusivities follow an Arrhenius law with an activation enthalpy of (3.6 +/- 0.4) eV. The results are indicative of a direct diffusion mechanism without the involvement of thermal point defects. 相似文献
16.
Honggang Zhou 《哲学杂志》2013,93(25):3401-3420
In many situations, failures such as spallation or cracking occur when chromia-forming alloys are subjected to high-temperature thermal treatment. On the other hand, a small amount of reactive element addition can remarkably increase the adherence between chromia scales and alloys. A two-dimensional finite element model has been developed to analyze the effects of reactive elements on the selective oxidation of chromia scale-forming binary alloys. The quantitative relation between the diffusivities of chromium ions and the activities of reactive element (yttrium) has been derived for the first time and has been incorporated with a continuum thermodynamic model accounting for stress–diffusion interaction in the oxidation of Cr–Fe alloys. The model predicts that the diffusivities of Cr ions are affected by the activities of reactive element compounds, which eventually leads to a decrease of the interfacial spallation driving force, as well as an increase of the interfacial adherence. 相似文献
17.
K. Muthukkumaran P. Kuppusami R. Srinivasan K. Ramachandran E. Mohandas S. Selladurai 《Ionics》2007,13(1):47-50
Thermal properties of 15-mol% gadolinia doped ceria thin films (Ce0.85Gd0.15 O1.925) prepared by pulsed laser ablation on silicon substrates in the temperature range 473–973 K are presented. Thermal diffusivities
and thermal conductivities were evaluated using photoacoustic spectroscopy. The influence of grain size on thermal properties
of the films as a function of deposition temperature is studied. It is observed that the thermal diffusivity and the conductivity
of these films decreases up to 873 K and then increases with substrate temperatures. The thermal properties obtained in these
films are discussed on the basis of influence of grain size on phonon scattering. 相似文献
18.
X.J. Liu Q.J. Huang S.Y. Zhang A.H. Luo C.X. Zhao 《Journal of Physics and Chemistry of Solids》2004,65(7):1247-1251
The thermal diffusivity has been investigated in double perovskite Sr2MMoO6 (M=Fe, Mn and Co) by means of the mirage effect. We have found that the thermal diffusivity of metallic Sr2FeMoO6 is 0.39 cm2/s, which is larger than that (0.33 cm2/s) of insulating Sr2MnMoO6 and Sr2CoMoO6. We further investigate the substitution effects of the La3+ ions for the Sr2+ ions in Sr2FeMoO6 and Sr2MnMoO6, and have found that the thermal diffusivities of both samples significantly increase with the La concentration. Such an enhancement of the thermal diffusivities has been ascribed to occupation of the extra itinerant electrons on the conduction Mo4d band. 相似文献
19.
Biewer TM Forest CB Anderson JK Fiksel G Hudson B Prager SC Sarff JS Wright JC Brower DL Ding WX Terry SD 《Physical review letters》2003,91(4):045004
New profile measurements have allowed the electron thermal diffusivity profile to be estimated from power balance in the Madison Symmetric Torus where magnetic islands overlap and field lines are stochastic. The measurements show that (1) the electron energy transport is conductive not convective, (2) the measured thermal diffusivities are in good agreement with numerical simulations of stochastic transport, and (3) transport is greatly reduced near the reversal surface where magnetic diffusion is small. 相似文献
20.
Diffusivities of two-dimensional electron-hole pairs in thin GaAs/AlGaAs Quantum Wells (QWs) are studied experimentally and theoretically as functions of temperature and well-width. With growing well-widths, increasing diffusivities are observed for fixed Al-contents. Experimental diffusivities for the lateral carrier motion in continuously as well as in interrupted-grown thin QWs of different barrier Al-content are presented for T>150 K. Increasing diffusivities are observed for rising temperatures in the range T190 K. A comparison of the experimental data and results of theoretical model calculations indicates that the increase is partly related to thermal dissociation of excitons into free carrier pairs. The effective diffusivity of this two-component system is calculated using a system of rate equations and considering acoustic-deformation-potential scattering, polar-optical scattering and barrier-alloy-disorder scattering.The experimental data were obtained at: 4. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, W-7000 Stuttgart 80, Germany 相似文献