Quantitative Thermal Microscopy Measurement with Thermal Probe Driven by dc+ac Current

Quantitative thermal measurements with spatial resolution allowing the examination of objects of submicron dimensions are still a challenging task. The quantity of methods providing spatial resolution better than 100 nm is very limited. One of them is scanning thermal microscopy (SThM). This method is a variant of atomic force microscopy which uses a probe equipped with a temperature sensor near the apex. Depending on the sensor current, either the temperature or the thermal conductivity distribution at the sample surface can be measured. However, like all microscopy methods, the SThM gives only qualitative information. Quantitative measuring methods using SThM equipment are still under development. In this paper, a method based on simultaneous registration of the static and the dynamic electrical resistances of the probe driven by the sum of dc and ac currents, and examples of its applications are described. Special attention is paid to the investigation of thin films deposited on thick substrates. The influence of substrate thermal properties on the measured signal and its dependence on thin film thermal conductivity and film thickness are analyzed. It is shown that in the case where layer thicknesses are comparable or smaller than the probe–sample contact diameter, a correction procedure is required to obtain actual thermal conductivity of the layer. Experimental results obtained for thin SiO\(_{\mathrm {2}}\) and BaTiO\(_{\mathrm {3 }}\)layers with thicknesses in the range from 11 nm to 100 nm are correctly confirmed with this approach.     

Thermal Wave-Based Scanning Probe Microscopy and Its Applications

In the last two decades scanning thermal microscopes (SThM) with DC- and AC-heating have been developed offering resolutions down to the nanometer scale. The SThM is based on an atomic force microscope (AFM) that is equipped with a temperature sensitive nanoprobe. Most frequently a tip with a temperature-dependent electrical resistor is used which can be operated as a thermometer or as a heater. The lateral resolution of about 100 nm is determined by the tip radius. Alternatively, if the thermoelastic response is detected by a smaller AFM probe, a spatial resolution of about 10 nm can be attained. Thermal wave-based SThM-techniques (AC-SThM) are used (i) to control the thermal management of electronic devices and to image thermal parameters with submicron resolution and (ii) to study resonance absorption processes of optical, infrared, and microwave radiation on the nanometer scale. Examples presented comprise the thermal imaging of hot spots in high power and in-plane-gate transistors and local studies of the temperature dependence of the thermal conductivity of nano-structured NiTi shape memory alloys by the $3\!\upomega $ method. The use of the SThM as a tool for a spatially resolved spectroscopy is demonstrated by locally resolved ferromagnetic resonance measurements in thin iron and nickel films deposited on various substrates.     

Realizing the Accurate Measurements of Thermal Conductivity over a Wide Range by Scanning Thermal Microscopy Combined with Quantitative Prediction of Thermal Contact Resistance

Quantitative thermal performance measurements and thermal management at the micro-/nano scale are becoming increasingly important as the size of electronic components shrinks. Scanning thermal microscopy (SThM) is an emerging method with high spatial resolution that accurately reflects changes in local thermal signals based on a thermally sensitive probe. However, because of the unclear thermal resistance at the probe-sample interface, quantitative characterization of thermal conductivity for different kinds of materials still remains limited. In this paper, the heat transfer process considering the thermal contact resistance between the probe and sample surface is analyzed using finite element simulation and thermal resistance network model. On this basis, a mathematical empirical function is developed applicable to a variety of material systems, which depicts the relationship between the thermal conductivity of the sample and the probe temperature. The proposed model is verified by measuring ten materials with a wide thermal conductivity range, and then further validated by two materials with unknown thermal conductivity. In conclusion, this work provides the prospect of achieving quantitative characterization of thermal conductivity over a wide range and further enables the mapping of local thermal conductivity to microstructures or phases of materials.     

高空间分辨率的热测试技术——扫描热显微技术

简述了用扫描热显微技术进行高空间分辨率热测量 试的技术特点和研究现状,介绍了实际测试的情况,初步分析了扫描热地和样品表面间的传热机理,提出了进一步研究的方向。     

Local thermal property analysis by scanning thermal microscopy of an ultrafine-grained copper surface layer produced by surface mechanical attrition treatment

Scanning thermal microscopy (SThM) was used to map thermal conductivity images in an ultrafine-grained copper surface layer produced by surface mechanical attrition treatment (SMAT). It is found that the deformed surface layer shows different thermal conductivities that strongly depend on the grain size of the microstructure: the thermal conductivity of the nanostructured surface layer decreases obviously when compared with that of the coarse-grained matrix of the sample. The role of the grain boundaries in thermal conduction is analyzed in correlation with the heat conduction mechanism in pure metal. A theoretical approach, based on this investigation, was used to calculate the heat flow from the probe tip to the sample and then estimate the thermal conductivities at different scanning positions. Experimental results and theoretical calculation demonstrate that SThM can be used as a tool for the thermal property and microstructural analysis of ultrafine-grained microstructures.     

Imaging of Thermal Conductivity with Sub-Micrometer Resolution Using Scanning Thermal Microscopy

With the development of new emerging technologies, many objects in scientific research and engineering are of sub-micrometer and nanometer size, such as microelectronics, micro-electro-mechanical systems (MEMS), biomedicines, etc. Therefore, thermal conductivity measurements with sub-micrometer resolution are indispensable. This paper reports on the imaging of various micrometer and sub-micrometer size surface variations using a scanning thermal microscope (SThM). The thermal images show the contrasts indicating the differences of the local thermal conductivity in the sample. Thermal resistance circuits for the thermal tip temperature are developed to explain the heat transfer mechanism between the thermal tip and the sample and to explain the coupling between the local thermal conductivity and the topography in the test results.     

Local thermal property analysis by scanning thermal microscope of ultrafine-grained surface layer in copper and in titanium produced by surface mechanical attrition treatment

Ultrafine-grained surface layers were obtained by surface mechanical attrition treatment (SMAT) in copper and titanium samples. The thermal properties of the deformed layers were characterized using a scanning thermal microscope (SThM) that allows thermal conductivity to be mapped down to the submicrometer scale. A theoretical approach, based on this investigation, was used to calculate the heat flow from the probe tip to the sample and then estimate the thermal conductivities at different scanning positions. Experimental results and theoretical calculation demonstrate that scanning thermal microscope can be used as a powerful tool for the thermal property and microstructural characterization of ultrafine-grained microstructures.     

Simultaneous Measurement of Local Magnetic and Thermal Parameters by Thermal Wave Scanning Microscopy

To characterize magnetic materials on nanoscales, a new technique has been developed which is based on the combination of two scanning thermal near-field techniques: the thermally modulated ferromagnetic resonance induced by the probe of a scanning thermal wave microscope and the detection of the 3?? signal from the same thermal probe. The simultaneous detection of the thermally modulated microwave absorption and of the 3?? response of the nanoprobe offers a means to control the thermal contact between probe and sample during scans across the sample. In this contribution, the experimental setup is described and results of measurements conducted on Fe-based structures deposited on a MgO substrate are presented.     

Micro- and Nano-scale Measurement of the Thermophysical Properties of Polymeric Materials Using Atomic Force Microscopy

To realize the benefits and optimize the performance of micro- and nano-structured materials and thin films, designers need to understand and thus be able to characterize their thermal, thermophysical, and thermomechanical properties on appropriate length scales. This paper describes the determination of glass-transition temperatures of polymers on the micro-scale, obtained from contact force–distance curves for poly(methyl methacrylate) and poly(vinyl acetate) measured using an atomic force microscope (AFM). Measurements were made using a standard AFM tip where thin films were heated using a temperature controlled hot stage and by using a scanning thermal microscopy (SThM) probe. The latter was used either with the hot stage or with the SThM probe providing a localized heating source via Joule heating. Differences in the glass-transition temperature measured using the hot stage and Joule heating were apparent and considered to be due to heat transfer effects between the probe, specimen, and surroundings. Gradients of force–distance curves, pull-off and snap-in forces, and adhesion energy were obtained. The results suggest that the onset of changes in the material’s mechanical properties at the glass transition was found to be dependent on the mechanical property measured, with pull-off force values changing at lower temperatures than the snap-in force and adhesion energy.     

A combined imaging,microthermal and spectroscopic study of a multilayer packaging system

The effectiveness of a packaging solution for the pharmaceutical and food industry is dependent on the integrity of the constituent layers and the interfaces formed between them. The deconvolution and analysis of the many intimate layers found in packaging is analytically challenging, requiring techniques capable of identifying sub‐micron regions. Here we have characterized the chemical and physical nature of the layers in a multilayer packaging system along with the interfaces, using a combination of high‐resolution atomic force microscopy (AFM), microthermal analysis using scanning thermal microscopy (SThM), and Fourier transform infrared (FT‐IR) spectroscopy. In particular, localized thermal analysis is shown to reveal the thermal transitions of the individual layers, but it was found that care must be exercised when melting through one layer to the next, as this can result in overestimates of melting temperatures of the underlying layer due to excess power loss from the SThM probe to the already molten top layer surrounding the probe. Copyright © 2004 John Wiley & Sons, Ltd.     

Comparison of Thermal Conductivity and Thermal Boundary Conductance Sensitivities in Continuous-Wave and Ultrashort-Pulsed Thermoreflectance Analyses

Thermoreflectance techniques are powerful tools for measuring thermophysical properties of thin film systems, such as thermal conductivity, Λ, of individual layers, or thermal boundary conductance across thin film interfaces (G). Thermoreflectance pump–probe experiments monitor the thermoreflectance change on the surface of a sample, which is related to the thermal properties in the sample of interest. Thermoreflectance setups have been designed with both continuous wave (cw) and pulsed laser systems. In cw systems, the phase of the heating event is monitored, and its response to the heating modulation frequency is related to the thermophysical properties; this technique is commonly termed a phase sensitive thermoreflectance (PSTR) technique. In pulsed laser systems, pump and probe pulses are temporally delayed relative to each other, and the decay in the thermoreflectance signal in response to the heating event is related to the thermophysical properties; this technique is commonly termed a transient thermoreflectance (TTR) technique. In this work, mathematical models are presented to be used with PSTR and TTR techniques to determine the Λ and G of thin films on substrate structures. The sensitivities of the models to various thermal and sample parameters are discussed, and the advantages and disadvantages of each technique are elucidated from the results of the model analyses.     

金属基复合材料界面导热性能的扫描热探针测试

利用扫描热探针方法,以微米级的空间分辨率,分析测试了三种馆长在复合材料（ＭＭＣ）界面特征和界面导热性能,应用数学统计方法对扫描热显微镜（ＳＴhM)的形貌和热电压数据进行处理和转换,获得 面宽度和界面导热率数据,结果表明,金属基复合材料宏观导热性能与增强相一基体界面的导热性能密切相关。     

DC Experiments in Quantitative Scanning Thermal Microscopy

This paper presents experimental results of quantitative DC measurements carried out by the use of a scanning thermal microscope equipped with nanofabricated thermal probes, and their numerical simulations done by finite element analysis. In the proposed method, the probe resistance variations are measured for the sample-to-air transition. It is shown that taking the signal measured in air as a reference makes the measurement less sensitive to instabilities of ambient conditions. This paper also presents a simple theoretical model describing the phenomena associated with heat transfer in the probe–sample system. Both experimental and numerical results confirm the theoretical findings. The registered signal can be related to the thermal conductivity of different materials, which makes the method useful for determining the local thermal conductivity.     

Analysis of Possibilities of Application of Nanofabricated Thermal Probes to Quantitative Thermal Measurements

A steady-state thermal model of the nanofabricated thermal probe was proposed. The resistive type probe working in the active mode was considered. The model is based on finite element analysis of the temperature field in the probe-sample system. Determination of the temperature distribution in this system allows calculations of relative changes in the probe electrical resistance. It is shown that the modeled probe can be used for measurements of the local thermal conductivity with the spatial resolution determined by the probe apex dimensions. The probe exhibits the maximum sensitivity to the changes in the thermal conductivity of the sample between 2 W·m⁻¹ ·K⁻¹ and 200 W·m⁻¹ ·K⁻¹. The influence of the thermal conductivity of the probe substrate on metrological characteristics of the probe as well as the thermal resistance of the probe-sample contact on the determination of the sample thermal conductivity were also analyzed. The selected results of numerical analysis were compared with data of preliminary experiments.     

Experimental Measurements and Theoretical Prediction of the Thermal Conductivity of Two- and Three-Phase Water/Olivine Systems

The thermal conductivity of olivine, dry and mixed with water, up to saturation, has been measured with a thermal probe, using the step heating method. The olivine is composed of solid particles with dimensions in the range from 0.8 to 1 mm. Dry olivine has been measured in the range of temperatures between –17° to +50°C. Olivine mixed with water has been measured at +50°C. The cubic cell model has been used to make predictions to compare with the measured data. Comparisons of the experimental thermal conductivities and the predicted values of dry and water-mixed olivine show good agreement. The cubic cell model can be used to evaluate the porosity of olivine and the thermal conductivity of the solid particles, from the values measured at dryness and saturation, with reasonably good agreement. In this way, it is not necessary to measure the mineral composition of the particles of the porous media. Also, the porosity of the medium is predicted with reasonable agreement, which takes into account the phenomenon of the porosity increase near the probe, since the diameter of the probe is smaller than that of the solid particles.     

Theoretical Modeling of Obliquely Crossed Photothermal Deflection for Thermal Conductivity Measurements of Thin Films

A three-dimensional theoretical model has been developed to calculate the normal probe beam deflection of the obliquely crossed photothermal deflection configuration in samples which consist of thin films deposited on substrates. Utilizing the dependence of the normal component of probe beam deflection on the cross-point position of the excitation and probe beams, the thermal conductivity of the thin film can be extracted from the ratio of the two maxima of the normal deflection amplitude, which occurs when the cross-point is located near both surfaces of the sample. The effects of other parameters, including the intersect angle between the excitation and the probe beams in the sample, the modulation frequency of the excitation beam, the optical absorption and thickness of the thin films, and the thermal properties of substrates on the thermal conductivity measurement of the thin film, are discussed. The obliquely crossed photothermal deflection technique seems to be well suited for thermal conductivity measurements of thin films with a high thermal conductivity but a low optical absorption, such as diamond and diamond-like carbon, deposited on substrates with a relatively low thermal conductivity.     

Thermal stress singularities at tips of a crack in a semi-infinite medium under uniform heat flow

In the framework of plane thermoelastic problems is discussed the thermal stress field near the tips of an arbitrarily inclined crack in an isotropic semi-infinite medium with the thermally insulated edge surface under uniform heat flow. The crack is replaced by continuous distributions of quasi-Volterra dislocations corresponding to line heat sources and edge dislocations, and we obtain a set of simultaneous singular integral equations for dislocation density functions, whose solution is given in the forms of series in terms of Tchebycheff polynomials of the first kind. By means of this method, the thermal stress singularities at the crack tips are estimated exactly and the stress intensity factors can be readily evaluated. Numerical results are given for the particular case where the surface of the inclined crack is maintained at constant temperature and the heat supplied across the surface of the crack vanishes as a whole. The effects of the distance from the crack tip to the edge surface of the semi-infinite medium and the angle of inclination of the crack on the stress intensity factors and the initial direction of crack extension are shown graphically.     

(YCa)F3助烧AlN陶瓷的显微结构和热导率

采用（ＣａＹ）Ｆ_３为助烧结剂，低温烧结（１６５０℃， ６ｈ）制备出热导率为２０８Ｗ／ｍ·Ｋ的ＡＩＮ陶瓷，在烧结过程中，热导率随保温时间的变化服从方程：λ（ｔ）＝λ∞－△λ（０）·ｅ~（－ｔ／ｒ）·用ＳＥＭ、 ＳＴｈＭ、 ＴＥＭ和 ＨＲＥＭ对 ＡＩＮ陶瓷的显微结构及其对热导率的影响进行了研究，结果表明，晶粒尺寸对ＡＩＮ陶瓷热导率的影响可以忽略，而分隔在ＡＩＮ晶粒之间的晶界相会降低热导率。     

On the theory of near-field magneto-optical microscopy via plasmonic modes of nanowire

The results of a theory of near-field magneto-optical microscopy with a linear probe scanning the near-surface region of a sample are presented. A cylindrical nanowire supporting surface plasmons is considered as a model of the probe. The polar magneto-optical Kerr effect is studied in scattering of light by near-surface nanowire and magnetic nanodomain. The problem is solved self-consistently in the dipolar interactions of the nanowire with the sample surface and in magnetization-linear approximation of magneto-optics. The near-field magneto-optical response depending on the distance between probe and domain is obtained, and the microscopy resolving power is estimated.     

Thermal radiation of nanoparticles occurring at a heated flat surface in vacuum

The most general expression for the rate of radiative heating (cooling) of an electrically neutral nanoparticle occurring in vacuum near a flat surface of a homogeneous polarizable medium is obtained for the first time. The magnetic polarizability of a conducting nanoparticle radically influences the rate of heat exchange between this particle and a metal surface. The rate of radiative cooling is several orders of magnitude higher than the power density of thermal radiation from a blackbody of the same size. This ratio is retained for micron size particles occurring at a distance of several hundred microns from the surface.