A Review on Principles and Applications of Scanning Thermal Microscopy (SThM)

As the size of materials, particles, and devices shrinks to nanometer, atomic, or even quantum scale, it is more challenging to characterize their thermal properties reliably. Scanning thermal microscopy (SThM) is an emerging method to obtain local thermal information by controlling and monitoring probe–sample thermal exchange processes. In this review, key experimental and theoretical components of the SThM system are discussed, including thermal probes and experimental methods, heat transfer mechanisms, calibration strategies, thermal exchange resistance, and effective heat transfer coefficients. Additionally, recent applications of SThM to novel materials and devices are reviewed, with emphasis on thermoelectric, biological, phase change, and 2D materials.     

Direct Synthesis of Large‐Scale WTe2 Thin Films with Low Thermal Conductivity

Large‐scale, polycrystalline WTe₂ thin films are synthesized by atmospheric chemical vapor reaction of W metal films with Te vapor catalyzed by H₂Te intermediates, paving a way to understanding the synthesis mechanism for low bonding energy tellurides and toward synthesis of single‐crystalline telluride nanoflakes. Through‐plane and in‐plane thermal conductivities of single‐crystal WTe₂ flakes and polycrystalline WTe₂ thin films are measured for the first time. Nanoscale grains and disorder in WTe₂ thin films suppress the in‐plane thermal conductivity of WTe₂ greatly, which is at least 7.5 times lower than that of the single‐crystalline flakes.     

激光扫描显微镜的探讨

本文探讨在满足象素密度要求的条件下,充分利用电视监视器可分辨光点数,具有大扫描视场的激光扫描显微镜的设计。     

用扫描热显微镜测量亚微米尺度的局域热参数分布

从集总参数模型出发 ,分析了热敏电阻型热探针的热传导机制和热物性测量机理 ,说明了扫描热探针的信号与样品表面温度 ,样品与探针间的热阻以及样品热导率等因素有关 .在不同的工作条件下 ,可用以进行表面的温度分布和局域热导分布等热参数的测量 .把扫描热显微镜用于半导体激光器结区温度分布和室温下热桥样品的实际测量 ,得到的热象图提供了亚微米尺度的热参数信息     

Understanding of the Extremely Low Thermal Conductivity in High‐Performance Polycrystalline SnSe through Potassium Doping

P‐type polycrystalline SnSe and K_0.01Sn_0.99Se are prepared by combining mechanical alloying (MA) and spark plasma sintering (SPS). The highest ZT of ≈0.65 is obtained at 773 K for undoped SnSe by optimizing the MA time. To enhance the electrical transport properties of SnSe, K is selected as an effective dopant. It is found that the maximal power factor can be enhanced significantly from ≈280 μW m^?1 K^?2 for undoped SnSe to ≈350 μW m^?1 K^?2 for K‐doped SnSe. It is also observed that the thermal conductivity of polycrystalline SnSe can be enhanced if the SnSe powders are slightly oxidized. Surprisingly, after K doping, the absence of Sn oxides at grain boundaries and the presence of coherent nanoprecipitates in the SnSe matrix contribute to an impressively low lattice thermal conductivity of ≈0.20 W m^?1 K^?1 at 773 K along the sample section perpendicular to pressing direction of SPS. This extremely low lattice thermal conductivity coupled with the enhanced power factor results in a record high ZT of ≈1.1 at 773 K along this direction in polycrystalline SnSe.     

扫描探针显微镜在激光纳米加工技术上的应用和进展

综述了扫描探针显微镜在激光纳米加工技术上应用的最新进展,介绍了纳米结构的形成机理。     

衬底热导对Mn-Co-Ni-O薄膜热敏 红外探测器性能的影响

研究了用Mn-Co-Ni-O薄膜材料制备的热敏红外探测器件,并主要通过调控衬底热导改进了器件性能。对于较薄的探测元,研究了具有微桥结构的红外器件。结果表明,该器件的响应率比非微桥器件高80%左右,探测率高44%左右。这主要是因为其独特的结构形式降低了器件热导,且对光的全反射效应提高了探测元对光的吸收率。对于较厚的探测元,在衬底上增加了抛光的散热铜片,使器件衬底的导热系数提高了47%左右,但响应电压降低了50%左右。因此需要合理选择散热铜片,以获得合适的时间常数和响应率。     

Tuning Thermal Transport Through Atomically Thin Ti3C2Tz MXene by Current Annealing in Vacuum

Heat transport across vertical interfaces of heterogeneous 2D materials is usually governed by the weak Van der Waals interactions of the surface‐terminating atoms. Such interactions play a significant role in thermal transport across transition metal carbide and nitride (MXene) atomic layers due to their hydrophilic nature and variations in surface terminations. Here, the metallicity of atomically thin Ti₃C₂T_z MXene, which is also verified by scanning tunneling spectroscopy for the first time, is exploited to develop a self‐heating/self‐sensing platform to carry out direct‐current annealing experiments in high (<10^?8 bar) vacuum, while simultaneously evaluating the interfacial heat transport across a Ti₃C₂T_z/SiO₂ interface. At room temperature, the thermal boundary conductance (TBC) of this interface is found, on average, to increase from 10 to 27 MW m^?2 K^?1 upon current annealing up to the breakdown limit. In situ heating X‐ray diffraction and X‐ray photo‐electron spectroscopy reveal that the TBC values are mainly affected by interlayer and interface spacing due to the removal of absorbents, while the effect of surface termination is negligible. This study provides key insights into understanding energy transport in MXene nanostructures and other 2D material systems.     

Thermal Conductivity of HfTe5: A Critical Revisit

Hafnium pentatelluride (HfTe₅) has attracted extensive interest due to its exotic electronic, optical, and thermal properties. As a highly anisotropic crystal (layered structure with in‐plane chains), it has highly anisotropic electrical‐transport properties, but the anisotropy of its thermal‐transport properties has not been established. Here, accurate experimental measurements and theoretical calculations are combined to resolve this issue. Time‐domain thermoreflectance measurements find a highly anisotropic thermal conductivity, 28:1:8, with values of 11.3 ± 2.2, 0.41 ± 0.04, and 3.2 ± 2.0 W m^-1 K^-1 along the in‐plane a‐axis, through‐plane b‐axis, and in‐plane c‐axis, respectively. This anisotropy is even larger than what was recently established for ZrTe₅ (12:1:6), but the individual values are somewhat higher, even though Zr has a smaller atomic mass than Hf. Density‐functional‐theory calculations predict thermal conductivities in good agreement with the experimental data, provide comprehensive insights into the results, and reveal the origin of the apparent anomaly of the relative thermal conductivities of the two pentatellurides. These results establish that HfTe₅ and ZrTe₅, and by implication their alloys, have highly anisotropic and ultralow through‐plane thermal conductivities, which can provide guidance for the design of materials for new directional‐heat‐management applications and potentially other thermal functionalities.     

IC Surface Corrosion Inspection by C-Mode Scanning Acoustic Microscopy

C-mode scanning acoustical microscopy, C-SAM, is widely used in plastic package evaluations and for failure analysis. It permits to detect subsurface delaminations, cracks and pores （air bubbles） for different microelectronics packages. In this study, abnormality was observed in C-SAM daily test, the images showed no delaminations but inhomogeneities on the IC surface. Corrosion was found by optical microscope and scanning electron microscope after decapsulation. It can be revealed as the acoustic impedance is different between corrosion and normal area. The presence of inhomogeneities and discontinuities along ultrasonic waves＇ propagation paths inside the matter causes modifications in the amplitude and polarity of ultrasonic waves. However, C-SAM＇s capability in detecting IC surface corrosion has not been presented. The capability will be illustrated and the inspection mechanism will be discussed in this paper.     

SIMOX硅片埋氧层垂直方向热导率的测量

提出了一种简单、有效而且准确的测量SOI硅片埋氧层垂直方向热导率的方法,并采用这种方法测量了用SIMOX工艺制作的SOI硅片的埋氧层垂直方向的热导率.测量结果显示至少在5 5nm以上的尺度上对于SIMOX硅片的埋氧层垂直方向经典的热导率定义仍然成立,且为一明显小于普通二氧化硅的热导率(1 4W/mK)的常数1 0 6W/mK .测量中发现硅/二氧化硅边界存在边界热阻,并测量了该数值.结果表明,边界热阻在SOI器件尤其是薄二氧化硅背栅的双栅器件热阻的计算中不可忽略.     

在线检测多晶硅薄膜热导率测试结构的设计与模拟

提出了一种在线测试表面加工多晶硅薄膜热导率的结构,推导了热学模型,给出了测试方法,用ANSYS验证了热学模型.该方法避免了测试结构放置在真空中的缺点,有望在工艺线上得到应用.     

范德堡多晶硅热导率的测试结构

在O.M.Paul等研究的范德堡热导率测试结构的基础上,提出了一种改进结构,利用一组测试结构来测得多晶硅薄膜的热导率。在十字型结构中一个含有多晶硅薄膜,而另一个不含有多晶硅薄膜,根据建立的热学模型,可以获取多晶硅薄膜的热导率。用有限元分析软件ANSYS进行了模拟分析,分析表明模拟值与实验值能较好地吻合,且辐射散热是基本可以忽略的,从而验证了模型建立的正确性,说明该方法能够实现对多晶硅薄膜的测量,且具有较高的测试精确度。     

热导式氢气纯度分析仪的设计

热导检测器是利用被测组分和参考气的热导系数不同而响应的浓度型检测器,是一种非破坏性检测器,可与其他检测器联用。本文介绍了一种利用热导检测器测量氢气纯度的方法,提出了热导式氢气纯度分析仪的总体设计方案。本设计的特点是将参考气(氮气)直接密封于热导检测器中,测量时不用再向仪器持续输入参考气,再利用数字温度传感器DS18B20检测温度,对恒流源及运放的温漂进行补偿。主要介绍了氢气热导池检测器、信号处理电路、键盘显示等电路的工作原理及部分程序的设计思想。并给出了样机的应用测试数据。     

Thermal Conductivity of Amorphous Materials

Thermal conductivity is one of the most fundamental properties of solid materials. The thermal conductivity of ideal crystal materials has been widely studied over the past hundreds years. On the contrary, for amorphous materials that have valuable applications in flexible electronics, wearable electrics, artificial intelligence chips, thermal protection, advanced detectors, thermoelectrics, and other fields, their thermal properties are relatively rarely reported. Moreover, recent research indicates that the thermal conductivity of amorphous materials is quite different from that of ideal crystal materials. In this article, the authors systematically review the fundamental physical aspects of thermal conductivity in amorphous materials. They discuss the method to distinguish the different heat carriers (propagons, diffusons, and locons) and the relative contribution from them to thermal conductivity. In addition, various influencing factors, such as size, temperature, and interfaces, are addressed, and a series of interesting anomalies are presented. Finally, the authors discuss a number of open problems on thermal conductivity of amorphous materials and a brief summary is provided.     

A 0D Lead‐Free Hybrid Crystal with Ultralow Thermal Conductivity

Organic–inorganic hybrid materials are of significant interest owing to their diverse applications ranging from photovoltaics and electronics to catalysis. Control over the organic and inorganic components offers flexibility through tuning their chemical and physical properties. Herein, it is reported that a new organic–inorganic hybrid, [Mn(C₂H₆OS)₆]I₄, with linear tetraiodide anions exhibit an ultralow thermal conductivity of 0.15 ± 0.01 W m^?1 K^?1 at room temperature, which is among the lowest values reported for organic–inorganic hybrid materials. Interestingly, the hybrid compound has a unique 0D structure, which extends into 3D supramolecular frameworks through nonclassical hydrogen bonding. Phonon band structure calculations reveal that low group velocities and localization of vibrational energy underlie the observed ultralow thermal conductivity, which could serve as a general principle to design novel thermal management materials.     

Van der Waals Heteroepitaxy of GaSe and InSe,Quantum Wells,and Superlattices

Bandgap engineering and quantum confinement in semiconductor heterostructures provide the means to fine-tune material response to electromagnetic fields and light in a wide range of the spectrum. Nonetheless, forming semiconductor heterostructures on lattice-mismatched substrates is a challenge for several decades, leading to restrictions for device integration and the lack of efficient devices in important wavelength bands. Here, it is shown that the van der Waals epitaxy of 2D GaSe and InSe heterostructures occur on substrates with substantially different lattice parameters, namely silicon and sapphire. The GaSe/InSe heteroepitaxy is applied in the growth of quantum wells and superlattices presenting photoluminescence and absorption related to interband transitions.     

显微拉曼光谱法对多孔硅热导率的研究

多孔硅优良的热学性能使其成为MEMS领域新兴的热绝缘材料。文中采用一种简便且无损的多孔硅热导率测量技术——显微拉曼光谱技术对电化学腐蚀法制备的不同孔隙率和厚度的多孔硅试样热导率进行了测量,结果表明在多孔硅的拉曼谱峰位置与其温度间存在线性对应关系。在所有样品中,厚度为110μm空隙率为65%的多孔硅显示出最好的绝热性能,其热导率为0.624W/mK。且随多孔硅孔隙率和厚度的减小,其热导率有迅速增加的趋势(厚度和孔隙率为9μm和40%时,其热导率升至25.32W/mK)。     

LiNbO3铁电畴结构扫描力显微镜表征

为了分析评价铌酸锂(LiNbO3)单晶单畴化的效果,应用扫描力显微镜(SFM),对LiNbO3单晶片的电畴微观结构进行了分析表征。由于在压电力模式下,电畴的成像受到了样品本身结构的影响,畴图中出现的图像结构多与划痕相关。电畴的图像结构随着电压的加大越趋明显,可以断定,检测信号的确为样品本身压电响应。实验中对厚为1 mm的LiNbO3单晶加10 V直流偏压2 min,极化强度发生改变,但远没达到反转电压。这些对电畴结构的表征为表面加工工艺的改进提供了微观分析依据。     

Phonon Scattering and Thermal Conductivity in p‐Type Nanostructured PbTe‐BaTe Bulk Thermoelectric Materials

Transmission electron microscopy studies show that a PbTe‐BaTe bulk thermoelectric system represents the coexistence of solid solution and nanoscale BaTe precipitates. The observed significant reduction in the thermal conductivity is attributed to the enhanced phonon scattering by the combination of substitutional point defects in the solid solution and the presence of high spatial density of nanoscale precipitates. In order to differentiate the role of nanoscale precipitates and point defects in reducing lattice thermal conductivity, a modified Callaway model is proposed, which highlights the contribution of point defect scattering due to solid solution in addition to that of other relevant microstructural constituents. Calculations indicate that in addition to a 60% reduction in lattice thermal conductivity by nanostructures, point defects are responsible for about 20% more reduction and the remaining reduction is contributed by the collective of dislocation and strain scattering. These results underscore the need for tailoring integrated length‐scales for enhanced heat‐carrying phonon scattering in high performance thermoelectrics.