Minority carrier recombination lifetimes in n-type CdMgSe mixed crystals measured by means of the photothermal infrared radiometry

Minority recombination lifetimes of n-type CdMgSe mixed crystals were estimated by using infrared photothermal radiometry (PTR) amplitude and phase frequency spectra. The results obtained by the PTR method indicate that the lifetimes of optically generated carriers in CdSe and Cd_xMg_1?xSe crystals are about 0.1 μs. The diffusion length of minority carrier in n-type CdSe single crystal was found to be 4.42 μm and it is in a good agreement with the literature value. It was found that with the increasing thermal-to-plasma component coefficient A the carrier concentration increases as expected from PTR theory.     

牙齿组织光热动态特性仿真与试验研究

调制激光作用牙齿组织发生散射形成光子密度波, 而由于光热效应产生热波, 基于一维介质辐射传输漫射近似方程与一维热传导方程建立了调制激光作用牙齿组织半透明混合介质的一维热波数学模型. 利用该模型仿真分析了牙齿龋损特性参数(牙釉质龋损层光吸收系数、散射系数、热扩散系数及龋损深度)对光热辐射动态响应特性的影响与规律. 利用红外探测器(HgCdTe, 2–12 μm)记录808 nm半导体激光激发牙齿组织产生的热波信号, 由锁相放大器计算热波信号的幅值与相位. 通过频率扫描试验获得了牙齿组织的光热动态响应, 利用多参数最佳统计拟合方法得到了牙齿组织特性参数. 结果表明光热辐射测量对牙齿组织不均匀性和龋损特性均具有较高敏感性与特异性.     

PTR技术测量材料的热扩散系数的线性化方法

报道了一种用光热辐射 (PTR)技术测量不透明材料热扩散系数的优化方法。从光热辐射理论出发 ,在一定条件下 ,推导出位相信号和调制频率的关系表现为线性关系 ,分析实验数据得出材料的热扩散系数。     

Study on thermal diffusivity of materials by laser photothermal reflection technique

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.     

Electron heat transport measured in a stochastic magnetic field

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.     

Mixed layer – structured ferroelectrics on the basis of \mbox{\sffamily\bfseries Bi}_{\hbox{\sffamily\bfseries\fontsize{12}{12}\selectfont 4}} \mbox{\sffamily\bfseries Ti}_{\hbox{\sffamily\bfseries\fontsize{12}{12}\selectfont 3}} \mbox{\sffamily\bfseries O}_{\hbox{\sffamily\bfseries\fontsize{12}{12}\selectfont 12}}

Thermal diffusivities of pure YVO₄ single crystal and single crystals doped with Nd, Tm and Ca ions are measured using a modified ?ngstr?m's method. Measurements were carried out for main crystallographic directions ([100], [010] and [001]). Obtained results show that the thermal diffusivity in [001] direction is considerably higher than in (001) plane. Decrease of the thermal diffusivity is observed with growing concentration of dopants. For the heavier doped sample (5% at. of Tm + 0.4% at. of Ca) a drop of the thermal diffusivity is about 35%.     

Frequency modulated infrared imaging for thermal characterization of nanomaterials

The paper presents frequency modulated thermal wave imaging (FMTWI) as a fast and efficient non-contact technique for in-plane thermal characterization of thin plate nanomaterials. A novel excitation signal in the form of an up-chirp is applied and the thermal response is monitored using an infrared (IR) thermography based temperature sensing system. The in-plane thermal diffusivity of any sample can be measured using the multiple phase information extracted from a single run of the experiment. This feature provides a time efficient approach for thermal measurements using infrared thermography techniques. The theoretical background and experimental details of the technique are discussed, with practical measurement of thermal diffusivity of an empty anodic alumina (AAO) template in direction perpendicular to the nanochannel axis, in support.     

On the solidification front of a dilute binary alloy: Thermal diffusivity effects and breathing solutions

The asymptotic equation derived in [6],

, to describe the interfacial structure of the solidification front of a dilute binary alloy in the limit in which the solute rejection coefficient is close to unity, is demonstrated to be also valid to lowest order when the thermal diffusivities in the liquid and in the solid are unequal. At higher order nonequal thermal diffusivity effects contribute an integral term. A uniformly valid approximation for the interfacial structure is obtained. The integral term is shown to be capable of producing slowly travelling waves or breathing solutions along the interfacial front when the thermal diffusivity of the liquid is sufficiently larger than the thermal diffusivity of the solid. This slowly oscillatory behavior may signal the proximity of a chaotic region located within the region of linear instability. Latent heat of fusion effects are also discussed.     

非线性拟合方法用于透射式脉冲红外技术测试碳/碳复合材料的热扩散系数

为了测试碳/碳复合材料的热扩散系数,本文提出了非线性拟合用于透射式脉冲红外检测的数据处理方法.非线性拟合通过循环迭代的方法持续调整拟合参数,让理论值不断逼近实验值,直至获得最佳结果.传统的透射式脉冲红外成像技术利用半高时间法测试材料的热扩散系数,但通常会受到采集时间不足和信噪比差的限制.本文提出的非线性拟合方法可以有效消除或减弱这两种影响.在使用该方法之前,首先选用常见的304不锈钢评估了该方法的测量精度及拟合长度对测试结果的影响.结果显示304不锈钢的测量精度达到0.3%,且当拟合长度不小于半高时间法采集时间的1/5时,拟合长度对非线性拟合结果影响很小.随后使用该拟合方法测试了不同厚度的碳/碳复合材料试件,并通过热扩散系数测量结果分析了试件之间的热参数差异性和材料自身的均匀性.     

Thermal diffusivity measurements of spherical samples using active infrared thermography

This work presents a method for measuring the thermal diffusivity of spherical samples using active infrared thermography. The principal novelty of this method lies in the deduction of an analytical model to obtain the spatial and temporal distribution of temperature in spherical samples. The model is obtained from the classical theory of heat conduction or the 3D heat diffusion equation. In order to analyze the behavior of the model, an active infrared thermography is used in order to monitor the spatial and temporal temperature distribution. Three different materials are used as spherical samples and they are heated by radiation increasing this way its temperature. The recorded data is fitted to the model by adjusting the diffusivity parameter. The results of the diffusivity values obtained using this model are consistent with those obtained from a standard thermal properties analyzer.     

Influence of ion implantation on the thermal diffusivity of semiconductors

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.     

Application of the flash method to rods and tubes

The flash method is the most used technique to measure the thermal diffusivity of solids. It consists of heating the front face of an opaque slab by a short light pulse and detecting the temperature evolution at its rear surface, from which the thermal diffusivity is retrieved. In this paper we extend the classical flash method to be used with rods and tubes. First, the temperature evolution of the surface temperature of solid and hollow cylinders is calculated. Then, experimental measurements of a set of stainless steel samples using an infrared camera confirm the validity of the method.     

Thermal characterization of film-on-substrate system by photothermal method and genetic algorithm

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.     

Photothermal measurements in determination of the thermal diffusivity of SiC

In this work a measuring method for determination of the thermal diffusivity of SiC substrates commonly used in electronic industry is proposed. Such substrates are (300 900) μm thick plates, The method bases on generation of temperature field disturbance in the sample by modulated light beam. Fitting of theoretical curves to the ratio of signals measured in two experimental geometries as a function of modulation frequency allows determination of the thermal diffusivity and optical absorption of the sample. Optical absorption is also measured independently using typical spectrometer. Results obtained for a few SiC substrates confirm usability of proposed method for investigation of such samples. Determined thermal diffusivities of polycrystalline samples are of the order of (0.2 0.5) cm² s ^{- 1}. The thermal diffusivities of single crystals are considerably higher and reach (1.3 1.5) cm² s^-1.     

The low-temperature diffusion of Hydrogen through annealed,quenched and aged gold

An electrolytic method has been used to measure the diffusivity of hydrogen through gold in the well-annealed state, as-quenched from 1248 K, and in foils formed by aging the quenched material at temperatures in the range 348–673 K. The resulting diffusivities are consistent with a simple statistical model in which a fraction of the H atoms saturate traps formed by quenched-in vacancies, but the mobility is primarily determined by the excess of nontrapped H atoms diffusing through “normal” sites in the fcc lattice.     

Thermal diffusivity of light-emitting diode packaging material determined by photoacoustic piezoelectric technique

Thermal property is one of the most important properties of light-emitting diode (LED).Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface,accordingly having an influence on the light-emitting efficiency and the life-span of the device.In this paper,photoacoustic piezoelectric (PAPE) technique has been employed to investigate the thermal properties of polyvinyl alcohol (PVA) and silicon dioxide,which are the new and the traditional packaging materials in white LED,respectively.Firstly,the theory of PAPE technique has been developed for two-layer model in order to investigate soft materials;secondly,the experimental system has been set up and adjusted by measuring the reference sample;thirdly,the thermal diffusivities of PVA and silicon dioxide are measured and analysed.The experimental results show that PVA has a higher thermal diffusivity than silicon dioxide and is a better packaging material in the sense of thermal diffusivity for white LED.     

应用激光闪光法测定半导体融体的热扩散率

本文开发了半导体融体的热扩散率的测量装置。通过引入石英玻璃试样容器将激光闪光法扩展到适合于融体试样。首先在实验及理论上研究了石英玻璃层对试样的热辐射及温度相应的影响,结果发现在室温以上温度范围,石英玻璃层的存在只减小红外辐射探测器的信号幅度但不改变时阃变化历程。由闪光法的原理,包含石英玻璃层的复合试样则可以作为单层试样处理。根据这一原理,我们首次对三元红外半导体融体In1-xGaxSb在不同组分时,温度范围800K至1200 K的热扩散率进行了测量。     

Probe beam size effect on the measurement of the distance between the probe beam and the sample in photothermal deflection

A distance-scan method to determine the distance between the probe beam and sample, which is not easily measured exactly, in photothermal deflection (PD) was reported, with which the distance and thermal diffusivity of the deflecting medium can be simultaneously measured. Probe beam size effect (PBSE) on PD phase signal was quantitatively analyzed to clearly show its physical meaning. The measured distance was experimentally verified as correct and reliable, and the measured thermal diffusivities of N2 and CO2 are in good agreement with the literature values. They could not be precisely measured by phase signal without considering the PBSE.     

Thermal Diffusivity of Film/Substrate Structures Characterized by Transient Thermal Grating Method

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.     

Influence of the Ar8+ and O6+ ion implantation on the recombination parameters of p and n type implanted Si samples investigated by means of the photothermal infrared radiometry

This paper presents the influence of Ar⁸⁺ and O⁶⁺ ion implantation on the recombination parameters of n and p type Si samples. These parameters were determined from the fitting of theoretical characteristics to the experimental photothermal radiometric (PTR) characteristics. We found that with the increasing ion implantation doses (i) the changes of the bulk recombination lifetimes and the carrier diffusivity were not observed; (ii) the increasing of the surface recombination velocities and the parameter A were observed. This paper also proves that it is possible to interpret the experimental PTR characteristics with a relatively simple effective model of a PTR signal.