薄膜材料横向热扩散率的热辐射检测

利用薄膜材料横向尺寸远大于其厚度的特点，通过测量横向传播热波的幅值和相位来确定薄膜的热扩散率是可行的．本文介绍带有背树的薄膜的横向热扩散率的检测理论，以及利用非接触的热辐射技术对金刚石一硅复合膜的检测结果．     

采用激光光热透射技术测量材料的热扩散率

介绍利用激光光热透射技术测量材料热扩散率的方法，用该方法测量黄铜，纯铁、铝、纯铜及锗的热扩散率，其结果与能常采用的检测手段一致。     

横向激光光热偏转相位法测量金刚石薄片的热扩散率

本文介绍横向激光光热偏转装置的优化设计及其利用相位信息测量CVD金刚石薄片的热扩散率,并和脉冲激光光热辐射方法测量的结果相比较.     

利用Mirage效应确定非均匀材料厚度方向的热扩散率分布

在热导率沿试样厚度按指数规律渐变的假设下，利用两种基本数学变换，求解了非均匀材料的热传导方程，得到了试样内及与其相邻媒质内的温度场解析解。再根据光热光偏转理论，确定了检测光束切向偏转分量的位相与调制频率之间的函数关系，如果利用熟知的由检测光束法向偏转分量测定试样热扩散率的技术，测定试样两表面的热扩散率，这样就可以由Mirage效应的两个偏转分量来测定试样热扩散率沿厚度方向的分布。本文给出有关的理论推导，同时也给出了人造金刚石试样内热扩散率分布的实验结果。     

钽掺杂对钛酸钡导热性能影响的研究

利用光热检测技术测量了钛酸钡材料的导热性能，得到了不同成型压力、烧结温度以及不同 掺杂量下的钛酸钡材料的热扩散率.研究了钽掺杂对钛酸钡材料导热性能的影响，发现了钽 元素掺杂量小于1.5mol%时，钛酸钡材料的热扩散率随掺杂量的增加而增大，当钽元素掺杂 量大于1.5mol%时，热扩散率随掺杂量的增加而减少.对钛酸钡材料的导热性能做了进一步的 分析. 关键词： 光热检测 钛酸钡 导热性能 钽掺杂     

碳纳米管纤维及薄膜的热导率和热扩散率研究

宏观碳纳米管(Carbon nanotube,CNT)薄膜的成功制备是发展有机热电材料的一个重要方向。由于CNT薄膜厚度仅为200 nm且多孔、粗糙度大,对其热学特性表征极为困难。本文提出应用3ω技术测量由单壁(Single-walled,SW)CNT薄膜卷曲成的宏观纤维的热导率和热扩散率,讨论了卷曲层数对结果的影响及估算薄膜面向热导率和热扩散率的思路。所研究的两个SWCNT薄膜的面向热导率为3.4 W/(m·K)和2.0 W/(m·K),热扩散率为24 mm~2/s和21mm~2/s。结果表明SWCNT薄膜将为发展低成本有机热电材料领域做出贡献。     

非均匀材料热学参量的光声效应检测理论

利用两种基本的数学变换，得到了非均匀材料以及相邻介质的温度场表达式，在非均匀材料的热扩散率随指数渐变的条件下，得到了气体介质温度场的解析式，利用传声器检测理论，求得光声信号的相位表达式，在非均匀材料两表面热扩散率已知的情况下，通过固体传声器测量出光声信号的相位与频率的关系，即可确定出非均匀材料热扩散率的分布，该方法具有计算量小、实验简单的特点。本文给出了有关的理论推导及理论模拟情况．     

退火处理对磁控溅射制备LaCoO_3薄膜性能的影响

采用磁控溅射法在硅衬底上制备了LaCoO_3(LCO)薄膜,研究了退火温度对LCO薄膜组织结构、表面形貌及热电特性的影响,并利用X射线衍射仪、原子力显微镜(AFM)、激光导热仪等对LCO薄膜的晶体结构、表面形貌、热扩散系数等进行测量与表征.结果表明:退火温度对LCO薄膜的结晶度、晶粒尺寸和薄膜表面形貌都有较大影响;退火前后LCO薄膜的热扩散系数都随温度的升高而减小,且变化速率逐渐减缓; LCO薄膜的热扩散系数随退化温度的升高先增大后减小.LCO薄膜经过700℃退火后得到最佳的综合性能,其薄膜表面致密、平整,结晶质量最好,热扩散系数最小,热电性能最好.     

光热偏转检测技术自动测量的研究

介绍了光热偏转技术自动测量材料热物性的原理及实验方法。根据光热偏转检测理论建立了一套自动检测系统,从自动控制、数据采集和数据处理等方面实现了光热偏转检测技术的自动化测量。设计出了步进电机自动控制和数据处理软件。利用该系统对钛酸锶钡材料的热扩散率进行了测量,发现随着掺杂量铈的增加,钛酸锶钡的热扩散率逐渐减小,当掺杂量铈增加到一定值时,其热扩散率又开始增加。     

周期热流法测量薄膜材料热扩散率的二维效应分析

符号表A无量纲温度幅值L。热扩散长度。1二维效应作用区边界AD温度幅值。试样表面法向Yd样品无量纲厚度AO特征温度q热源热流。材料热扩散率C材料体积比热容qb热源热流幅值。”测量热扩散率d样品厚度T试样上某点温度A材料导热系数h表面等效换热系数几边界温度p温度相位He无量纲换热系数。。光源边界。测量角频率1前言使用周期热流法测量薄膜材料面向热扩散率的基本原理如图1所示，调制光对试样加热，遮光板沿V方向以一定速度V移动，引起试样上热源边界l变化，假设没有热损失，试样上经历沿。方向的一维导热过程，则热电偶测得之温度幅…     

Perturbation theories behind thermal mode spectroscopy for high-accuracy measurement of thermal diffusivity of solids

Thermal mode spectroscopy (TMS) has been recently proposed for accurately measuring thermal diffusivity of solids from a temperature decay rate of a specific thermal mode selected by three-dimensional (anti)nodal information [Phys. Rev. Lett., 117, 195901 (2016)]. In this paper, we find out the following advantages of TMS by use of perturbation analyses. First, TMS is applicable to the measurement of high-thermal diffusivity with a small-size specimen. Second, it is less affected by thermally resistive films on a specimen in the sense that the resistance at the interface does not affect the first-order correction of thermal diffusivity. Third, it can perform doubly accurate measurement of the thermal diffusivity specified at a thermal equilibrium state even if the diffusivity depends on temperature in the sense that the measurement can be performed within tiny temperature difference from the given state and that the decay rate of the slowest decaying mode is not affected by the dependence.     

Photothermal techniques applied to the study of thermal properties in biodegradable films

The objective of the present work was to determine the thermal diffusivity and effusivity of biodegradable films by using photothermal techniques. The thermal diffusivity was studied by using the open photoacoustic cell technique. On the other hand the thermal effusivity was obtained by the photopyroelectric technique in a front detection configuration. The films were elaborated from mixtures of low density polyethylene (LDPE) and corn starch. The results showed that at high moisture values, the thermal diffusivity increased as the starch concentration was higher in the film. However at low moisture conditions (<9%) the thermal diffusivity diminished when the starch content in the sample was increased. On the other hand the thermal effusivity has a behavior in opposition to the thermal diffusivity. The thermal effusivity increased with the increase of the starch content in the film, at low extrusion moisture conditions (6.55%). As the moisture and starch concentration in the films were increased, the thermal effusivity diminished.     

Thermal conductivity and interface thermal resistance of Si film on Si substrate determined by photothermal displacement interferometry

An in situ, noncontact, photothermal displacement interferometer for performing thermal diffusivity measurements on bulk and thin-film materials has been developed. Localized transient surface motion is generated through photothermoelastic coupling of a pulsed, heating laser beam to the sample under investigation. The maximum surface displacement is found to be linearly dependent on the laser power while the proportionality is a function of the thermal diffusivity. Both thin-film conductivity and film/substrate interface thermal resistance are derived from the measured, effective thermal conductivity by employing simple heat-flow analysis. Wedge-shaped Si films, vacuum deposited on single crystal Si wafers are studied with this technique. A sample with oxide layer removed by ion bombardment of the wafer surface prior to film deposition shows the same film conductivity as a sample film deposited on an as-cast wafer, while the uncleaned sample exhibits higher interface thermal resistance. It is found that the thin-film thermal conductivity is somewhat smaller than the bulk value. However, the existence of an interface thermal resistance, when combined with film thermal conductivity, can result in an effective thermal conductivity as low as two orders of magnitude lower than the bulk value.Currently supported by the LLE fellowship     

A thermoelastic method to determine the thermal diffusivity

We present a method to measure the thermal diffusivity of metals. A homogeneous small heat source is fed into a cyclindrical sample of titanium by thermoelastic compression. This heating process is followed by a thermal relaxation controlled by the thermal diffusivity. The resulting temperature variation is detected by a miniature temperature sensor mounted on the lateral surface of the sample. The value so obtained for the thermal diffusivity of titanium is (6.6±0.2)·10⁻⁶ m²/s. Gruppo Nazionale Struttura della Materia del Consiglio Nazionale delle Ricerche     

An analytical model for thermal diffusivity measurements of film substrate composite using the mirage technique

The thermal diffusivity h of a thin film on a substrate is measured by using the mirage technique. The photothermal deflection of the probe beam is caused by the heat field and the substrate, heated by the pump beam. From the experimental data a two-dimensional algorithm is proposed to obtain the measurements of the diffusivity of film and substrate in one set of mirage detection.     

Scanning thermal microwave resonance microscopy

Local detection of ferromagnetic resonance in magnetically ordered materials is achieved by local thermal modulation of the microwave resonance absorption with a scanning thermal microscope. A scanning thermal microwave resonance microscope was constructed based on a microwave bridge with an X-band cavity and a thermal nano-probe contacted to the sample at the wall of the cavity. The technique has been tested on an epitaxial iron film which exhibited lateral inhomogeneities due to a partial oxidation of iron. Different types of oxidation could be distinguished. The locally resolved ferromagnetic resonance spectra are compared with the result of an integral measurement using conventional detection techniques of the ferromagnetic resonance with the same set-up. The lateral resolution achievable with the thermally modulated ferromagnetic resonance measurements was about 200 nm for the investigated iron film.     

Characterization of thermal diffusivity of micro/nanoscale wires by transient photo-electro-thermal technique

In this work, a transient photon-electro-thermal (TPET) technique based on step laser heating and electrical thermal sensing is developed to characterize the thermophysical properties of one-dimensional micro/nanoscale conductive and nonconductive wires. In this method, the to-be-measured thin wire/tube is suspended over two electrodes and is irradiated with a step cw laser beam. The laser beam induces a transient temperature rise in the wire/tube, which will lead to a transient change of its electrical resistance. A dc current is applied to the sample, and the resulting transient voltage variation over the wire is measured and used to extract the thermophysical properties of the sample. A 25.4-μm thick Pt wire is used as the reference sample to verify this technique. Sound agreement is obtained between the measured thermal diffusivity and the reference value. Applying the TPET technique, one can measure the thermal diffusivity of conductive single-wall carbon nanotube (SWCNT) bundles and nonconductive cloth fibers. For nonconductive wires, a thin (∼ nm) metallic film is coated on the outside of the wire for electrical thermal sensing. The measured thermal diffusivity for the SWCNT bundle is 2.53×10^-5 m²/s, much less than the thermal diffusivity of graphite in the layer direction. For microscale cloth fibers, our experiment shows its thermal diffusivity is at the level of 10^-7 m²/s. PACS 78.20.Nv; 42.62.-b; 65.80+n; 66.30.Xj     

Ageing evaluation of thermal barrier coatings by thermal diffusivity

Ceramic thermal barrier coatings (TBC) are widely applied for protecting from combustion gases hot path components of gas turbines for both aero- and land-based applications. In order to prevent the detachment of TBC, it would be essential to monitor their degradation in terms of sintering kinetic. As sintering strongly affects also the thermal diffusivity of TBC, the idea is to measure the latter parameter to account for the former. The technique to measure thermal diffusivity using pulsed thermography is described, together with the model that leads to the identification of TBC diffusivity. Tests and results on specimens artificially aged are reported.     

Elastic modulus and in-plane thermal diffusivity measurements in thin polyimide films using symmetry-selective real-time impulsive stimulated thermal scattering

We describe a technique for extending the utility of the real-time Impulsive Stimulated Thermal Scattering (ISTS) method for thin film characterization. Using weakly absorbed excitation pulses, we show how to selectively drive acoustic waveguide modes that are unobservable when strongly absorbed pulses are used. The ability to excite and monitor these modes is important because it allows for a significant increase in the experimental sensitivity to the film longitudinal velocity. This arrangement also greatly simplifies determination of the in-plane thermal diffusivity. The technique is illustrated through study of unsupported polyimide films with six different thicknesses.