Atomic force microscopy (AFM) indentation is widely used to determine mechanical parameters of various materials. However, AFM tip may lead to phase transition of the cold sample in the region of contact area. It is a long-standing challenge that low-temperature phase-change materials (e.g., ice and hydrate) are hardly characterized by AFM, especially for clathrate hydrates. Here, with theoretical analysis and numerical simulation, we investigated the temperature influence of AFM tip on the tetrahydrofuran (THF) hydrate stability. At first, a steady-state model of heat conduction was established between a v-shaped probe and THF hydrate sample. The temperature of the tip was estimated at different laser spot positions and laser intensities. Through numerical simulation, the heat loss by air convection is less than 1% of the total laser heat, and the influence of ambient air on the AFM probe temperature can be neglected. Meanwhile, the local temperature in the region of contact area was also calculated at the THF hydrate temperature of 0°C, -10°C, -20°C, and -30°C. We found out that the AFM tip causes the cold THF hydrate to melt. The thermal melting thickness decreases with the reduction of laser intensity and THF hydrate temperature. On the contrary, it is positively correlated with the thickness of liquid-like layer on THF hydrate surface and is also linearly increased with the contact radius. This indicates that the thermal melting continues as the press-in depth of the tip into THF hydrate increases. The local temperature rises when the tip touches the THF hydrate. It is easier for THF hydrate to be melted by an external pressure. In addition, the proposed model may be useful for guiding force tests on low-temperature phase-change materials by the AFM indentation.

中文翻译：

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AFM 尖端温度对 THF 水合物稳定性的影响：理论模型和数值模拟

原子力显微镜 (AFM) 压痕广泛用于确定各种材料的机械参数。然而，AFM 尖端可能会导致冷样品在接触区域发生相变。低温相变材料（如冰和水合物）很难被 AFM 表征，尤其是笼形水合物，这是一个长期存在的挑战。在这里，通过理论分析和数值模拟，我们研究了 AFM 尖端对四氢呋喃 (THF) 水合物稳定性的温度影响。首先，建立了V形探头与THF水合物样品之间的稳态热传导模型。在不同的激光光斑位置和激光强度下估计尖端的温度。通过数值模拟，空气对流造成的热损失小于激光总热量的1%，环境空气对原子力显微镜探头温度的影响可以忽略不计。同时，还计算了THF水合物温度0°C、-10°C、-20°C和-30°C时接触区域的局部温度。我们发现 AFM 尖端会导致冷的 THF 水合物熔化。热熔厚度随着激光强度和THF水合物温度的降低而减小。相反，它与THF水合物表面类液层的厚度呈正相关，并随着接触半径的增加而线性增加。这表明随着尖端压入 THF 水合物的深度增加，热熔融继续进行。当尖端接触 THF 水合物时，局部温度升高。THF水合物在外部压力下更容易熔化。此外，