In the past decades, bubbles have been gaining extensive attentions for their wide range of applications, especially those at the micro-scale. Research on the bubbles' mechanical properties is necessary for better implementations. Precise measurement of the microbubbles' mechanical properties (e.g. stiffness and adhesion) relies largely on delicate manipulation technologies in aqueous environment. As a consequence, atomic force microscopy (AFM) has been widely adopted in this field. Bubble stiffness is an important indicator to reflect the stability. Existing studies mainly focused on statistic property of the microbubbles' stiffness, which may omit delicate specific characteristics of a single microbubble. In this letter, as an instance, AFM-based stiffness measurement of a single hydrogen microbubble has been carried out. The electrochemistry method was adopted to generate stable hydrogen microbubbles. By using force volume mode of a commercial AFM, the temperature-dependent stiffness property of the microbubble was studied. Furthermore, stiffness map of a single microbubble was captured, which shows location-dependent anisotropic characteristic, contradicting the preassumption that stiffness of bubbles should be isotropic. To explain this phenomenon, the contact condition between the AFM tip and the bubble surface is considered as the key reason that induces the anisotropic observation, and a corresponding model is established to verify this hypothesis.

中文翻译：

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使用原子力显微镜表征氢微泡的刚度特性


在过去的几十年里，气泡因其广泛的应用，特别是在微观尺度上的应用而受到广泛关注。为了更好地实施，有必要研究气泡的机械性能。微泡机械性能（例如刚度和粘附力）的精确测量很大程度上依赖于水环境中精密的操纵技术。因此，原子力显微镜（AFM）已在该领域得到广泛采用。气泡刚度是反映气泡稳定性的重要指标。现有的研究主要集中在微泡刚度的统计特性上，可能忽略了单个微泡的微妙的具体特征。在这封信中，作为一个例子，我们对单个氢微泡进行了基于 AFM 的刚度测量。采用电化学方法产生稳定的氢气微泡。利用商用原子力显微镜的力体积模式，研究了微泡随温度变化的刚度特性。此外，捕获了单个微泡的刚度图，该图显示了位置相关的各向异性特征，与气泡刚度应该是各向同性的假设相矛盾。为了解释这一现象，AFM针尖与气泡表面之间的接触条件被认为是引起各向异性观察的关键原因，并建立了相应的模型来验证这一假设。