Bowan Tao

Reliable operation of thin-film strain gauges (TFSG) in high-temperature aero-engine environment is essential for in situ structural health monitoring. However, the long-term stability of metallic TFSGs is governed not only by the intrinsic thermal resistance of the sensing alloy, but also interrelated with oxygen penetration, cation migration and the associated degradation of electron transport. In this study, magnetron-sputtered FeCrAl sensing layers were integrated with two protective architectures: a single-layer Al₂O₃-ZrO₂ coating and a heterolayer Al₂O₃-ZrO₂/Al₂O₃ coating. Structural, compositional, and electrical analyses demonstrated that the heterolayer structure served as a more effective diffusion barrier than the single-layer coating, suppressing oxygen penetration and Al depletion from the FeCrAl lattice. As a result, S2 exhibited lower resistance drift and a lower temperature coefficient of resistance (TCR) after repeated annealing at 600 to 1000 °C. The FeCrAl TFSG protected by heterolayer coating also maintained more stable gauge factors of 2.61, 2.45, 2.35, and 2.15 at 25, 400, 600, and 800 °C respectively, while achieving higher accuracy than single-layer coating. Finally, dynamic strain above 1 kHz was successfully resolved on a vibrating turbine blade at temperature up to 800 °C using frequency-domain signal extraction. These results confirmed a protective-layer design strategy for stabilizing performance of FeCrAl TFSG for high-temperature component monitoring.

Due to the intrinsic fast response characteristic of the atomic layer thermopile (ALTP) structure compared to the conventional thin film thermopile, the ALTP thermal gas flow sensor shows encouraging potential in fast gas flow detection. However, the thermal conduction delay between the ALTP film and the heating film still restricts the response speed. In this work, the prepared Si₃N₄/AlN composite films significantly reduced the thickness of the insulating layer while ensuring reliable insulation properties. Therefore, the response time of the ALTP thermal gas flow sensor was significantly reduced to 0.1 ms. Meanwhile, the sensor also demonstrated reliable and regular response signals in the tests of different gases, with different thermal sensitivity S*(N₂) > S*(O₂) > S*(Ar), conforming to the characteristics of thermal gas flow sensors. This work may promote the application of the ALTP sensor in high-speed gas flow detection.

Excellent biaxial texture is key to mitigating grain boundary weak links in REBa₂Cu₃O₇-δ (REBCO) superconducting tapes. While ion beam-assisted deposition of MgO (IBAD-MgO) is widely used for initial textured templates, this approach still encounters challenges, including environmental sensitivity and lattice defects. This work investigates the chemical evolution of atmospherically exposed IBAD-MgO layers and its impact on the texture of the subsequent metal-organic chemical vapor deposition (MOCVD) grown homoepitaxial-MgO (homo-MgO). Exposure causes surface hydroxylation and carbonation, resulting in the degradation of the MgO texture. Therefore, exposure should ideally be limited to within ~60 min. Optimizing thickness (~100 nm) of MgO layer and deposition rate (16 nm/min) of the homo-MgO layer yields superior biaxial texture, crystallinity, and roughness. The full-width-at-half-maximum value of the out-of-plane (Δω) and in-plane (Δφ) of MgO reached 2.9° and 6.3°, respectively, with a root-mean-square roughness (Rq) of 2.3 nm. This work not only reveals the chemical evolution of the IBAD-MgO template layer under exposure conditions and its impact on subsequent coatings, but also synergistically optimizes thickness and deposition rate to improve the texture and morphology of the MgO layer, thereby providing a reference for the controlled preparation of high-quality MgO buffer layers.

High-temperature oxidation of PdCr thin film strain gauges causes significant resistance drift, compromising measurement accuracy in aero-engine turbine monitoring. Traditional oxidation studies relying on mass gain or oxide thickness measurements are impractical for microscale thin films. Here we establish an oxidation kinetic model based on Wagner's theory and the Arrhenius equation that enables quantification of oxidation parameters through in-situ resistance measurements. Isothermal oxidation experiments of PdCr thin films at 500–800 °C reveal temperature-dependent mechanism transitions: grain boundary diffusion control at 500 °C with accelerating rates; mixed control at 600 °C with limited protection; self-healing behavior at 700 °C where initially non-protective oxide densifies into an effective diffusion barrier; and linear kinetics at 800 °C indicating complete loss of protectiveness. The Al2O3-ZrO2 protective layer reduces resistance drift across all temperatures, decreasing oxidation rate constants. At 700 °C it eliminates the self-healing transition, enabling immediate formation of a protective oxide scale. At 800 °C, the protective layer significantly mitigates oxidation severity and prevents catastrophic failure. Activation energy analysis confirms the layer functions as a physical oxygen barrier without altering intrinsic oxidation mechanisms.

High-temperature thin-film strain gauges (TFSGs) face challenges in balancing high strain sensitivity (Gauge Factor, GF), low temperature coefficient of resistance (TCR), and long-term stability. This study presents a novel bilayer FeCrAl/PdCr composite TFSG designed to overcome these limitations through strategic material combination and thickness ratio optimization. Comprehensive characterization revealed that the thickness ratio critically governs microstructure and electrical properties of the composite thin-film. Electrical testing demonstrated that the 1:1 ratio achieved the lowest resistivity, attributed to minimized combined grain boundary and interface scattering. Crucially, it also yielded the most stable TCR and lowest resistance drift rate, resulting from effective self-compensation between FeCrAl’s higher positive TCR and PdCr’s superior stability/oxidation resistance. Multilayer TFSGs employing the optimized 1:1 FeCrAl/PdCr composite as the strain-sensitive element were also fabricated on DD6 nickel-based superalloy substrates and turbine blades. Static strain tests demonstrated excellent linearity and significantly enhanced GF. This represents a 30–50% improvement over PdCr gauges. The GF decrease with temperature correlated primarily with the reduction in the substrate’s elastic modulus. High repeatability was confirmed over three cycles. Dynamic strain response tests on turbine blades showed the TFSG reliably captured resonant frequencies. The FeCrAl/PdCr (1:1) composite TFSG successfully mitigates the traditional trade-off between high sensitivity and temperature stability, and reliable static/dynamic response. This demonstrates its strong potential for accurate strain monitoring in high-temperature aerospace applications, particularly turbine blade health monitoring.

基于超导体临界特性、微波特性及约瑟夫森特性延伸出的超导电子学应用，在超高速计算、超高灵敏度探测和量子信息等领域展现出革命性潜力，为突破传统半导体电子学应用瓶颈提供了一个重要的方向。随着超导镀膜与低温制冷技术的迅速发展，高温超导薄膜已被用于制成各类现代电子器件。REBa2Cu3O7-δ(REBCO，RE=稀土元素)高温超导薄膜因高临界参数、优异的微波特性及抗干扰性受到更多关注。但基于材料弱连接属性，要实现REBCO在现代电子器件中应用，获得满足要求的高质量双轴织构薄膜是应用的基础。本文总结了目前REBCO薄膜制备工艺，包括脉冲激光沉积法、磁控溅射法、蒸发法、金属有机化学气相沉积法和金属有机沉积法。分别从镀膜工艺原理、特点、研究进展及REBCO薄膜性能优化策略等进行总结，最后对REBCO镀膜工艺未来发展方向做出初步展望。

Atomic Layer Thermopile (ALTP) heat flux sensors are pivotal for monitoring heat flux in high-frequency heat flux environments. In thermal conditions above room temperature, ensuring sensors’ behavior such as temperature tolerance and drift, particularly for YBa₂Cu₃O₇-δ(YBCO)-based sensitive films is paramount. In this paper, we first investigate the response characteristics and material properties of YBCO-based ALTP sensors, thereby evaluating the temperature tolerance of the YBCO film. Then, we performed sensitivity measurements under different temperatures and verified the repeatability and linearity of the ALTP above room temperature for the first time. Further, we innovated a dual-measurement structure capable of concurrently assessing the heat flux and temperature of the YBCO-sensitive film, verifying its feasibility through mathematical modeling and simulation. Finally, based on the structure, we introduced temperature compensation of the YBCO ALTP sensor in a test, dramatically reducing the relative error from 7.47% to 1.56%. This work not only refines the understanding of ALTP sensors’ behavior under thermal loading but also contributes a novel approach to improve their performance.

The atomic layer thermopile (ALTP) heat flux sensor has been applied to detect the heat flux of the hot end component surface to optimize the thermal protection design for important aerospace equipment. To meet the demand for accurately measuring on special-shaped component surfaces, the flexible ALTP heat flux sensor composed of the MgO biaxial texture template fabricated by Inclined Substrate Deposition (ISD) and a textured inclined La _1-x Ca _x MnO ₃ (LCMO) sensitive film has been reported in past work. Compared to the typical single crystal substrate, the MgO template has inherent defects like large surface roughness and gaps among the adjacent columns, which could affect the epitaxial quality of subsequent sensitive films and further influence the sensor’s performance. In this work, the homoepitaxial MgO (homo-MgO) film, fabricated by the MOCVD process, was introduced as the interface modification layer. The most intuitive modification effect is filling the step height difference and gaps of the ISD-MgO, the RMS value is optimized to 10.838 nm and the step height difference is reduced considerably by controlling the epitaxial temperature. Based on the optimized homo-MgO layer, the LCMO sensitive film gets the well biaxial texture, and the corresponding sensor represents the optimized sensitivity of 2.51 μV/(kW/m ² ) and response time of 82 ns.

Strain engineering is an important way to control the physical properties of manganite thin films. Here, the effect of strain mode on the transverse thermoelectric (TTE) effect of inclined La1xCaxMnO3 (LCMO) thin films is investigated. The compressive strain enhances the electrical conductivity of the LCMO thin film, resulting in larger laser-induced voltage and faster response speed, which is suitable for high-energy pulse laser detection. Compared to that, the LCMO thin film on the STO substrate is ideal for heat-flux detection due to higher heat-flux sensitivity originating from lower conductivity. Still, it also has to withstand the loss of response speed. Moreover, it is first observed that the TTE voltage polarity of the LCMO thin film changes under different strain states. The measured results of LCMO thin films deposited LaAlO3 (LAO) substrate buffered with the SrTiO3 (STO) thin film and STO substrate buffered with the LAO thin film strongly support that the above results are indeed caused by the lattice strain. This work may be suitable for other material systems to modulate thermoelectric transport anisotropy and the TTE effect by strain.