Jahng Junghoon, Lee Eun Seong
Hyperspectral Nanoimaging Team, Korea Research Institute of Standards and Science (KRISS), Daejeon 34113, South Korea.
Nanophotonics. 2023 Sep 7;12(19):3817-3827. doi: 10.1515/nanoph-2023-0424. eCollection 2023 Sep.
To comprehensively describe the operation of photo-induced force microscopy (PiFM), we have developed a model based on coupled harmonic oscillators. This model features two point masses connected by massless elastic wires, offering greater intuitiveness compared to existing PiFM models. It simplifies these models into a unified theoretical framework. By solving the equations of motion using adjusted oscillator parameters, we have successfully replicated all dynamic features from previous theories. These features include resonance frequencies and shapes of eigenmodes, as well as the responses to various external forces in the two PiFM modes: direct coupling and sideband coupling. Furthermore, by integrating our model with a recently developed photo-induced thermal expansion force model, which covers both tip-enhanced and global expansions, we have managed to uncover the underlying physical mechanism responsible for the unique signal behaviors observed in sideband coupling mode, where the signal plot, as a function of sample thickness, unexpectedly exhibits a peak followed by a valley, rather than a proportionally increasing signal. Our study has the potential to enhance the comprehension of various other physical phenomena associated with PiFM in the future.
为了全面描述光致力显微镜（PiFM）的操作，我们开发了一种基于耦合谐振子的模型。该模型的特点是两个质点由无质量的弹性线连接，与现有的PiFM模型相比更具直观性。它将这些模型简化为一个统一的理论框架。通过使用调整后的振子参数求解运动方程，我们成功地复制了先前理论中的所有动态特征。这些特征包括共振频率和本征模形状，以及在PiFM的两种模式（直接耦合和边带耦合）中对各种外力的响应。此外，通过将我们的模型与最近开发的光致热膨胀力模型相结合，该模型涵盖了尖端增强和整体膨胀，我们成功地揭示了边带耦合模式中观察到的独特信号行为的潜在物理机制，在该模式下，信号图作为样品厚度的函数，意外地呈现出一个峰值，随后是一个谷值，而不是成比例增加的信号。我们的研究有可能在未来增强对与PiFM相关的各种其他物理现象的理解。
