Li Jian, Jahng Junghoon, Ma Xuezhi, Liang Jing, Zhang Xue, Min Qianhao, Wang Xiao-Liang, Chen Shuangjun, Lee Eun Seong, Xia Xing-Hua
State Key Lab of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
Hyperspectral Nano-Imaging Team, Korea Research Institute of Standards and Science, Daejeon 34113, South Korea.
Natl Sci Rev. 2024 Mar 18;11(5):nwae101. doi: 10.1093/nsr/nwae101. eCollection 2024 May.
The photoinduced dipole force (PiDF) is an attractive force arising from the Coulombic interaction between the light-induced dipoles on the illuminated tip and the sample. It shows extreme sample-tip distance and refractive index dependence, which is promising for nanoscale infrared (IR) imaging of ultrathin samples. However, the existence of PiDF in the mid-IR region has not been experimentally demonstrated due to the coexistence of photoinduced thermal force (PiTF), typically one to two orders of magnitude higher than PiDF. In this study, we demonstrate that, with the assistance of surface phonon polaritons, the PiDF of c-quartz can be enhanced to surpass its PiTF, enabling a clear observation of PiDF spectra reflecting the properties of the real part of permittivity. Leveraging the detection of the PiDF of phonon polaritonic substrate, we propose a strategy to enhance the sensitivity and contrast of photoinduced force responses in transmission images, facilitating the precise differentiation of the heterogeneous distribution of ultrathin samples.
光致偶极力（PiDF）是一种吸引力，它源于被照射的探针尖端与样品上光致偶极子之间的库仑相互作用。它表现出对样品-探针距离和折射率的极端依赖性，这对于超薄样品的纳米级红外（IR）成像很有前景。然而，由于光致热力（PiTF）的共存，中红外区域PiDF的存在尚未得到实验证明，PiTF通常比PiDF高一个到两个数量级。在本研究中，我们证明，在表面声子极化激元的辅助下，c-石英的PiDF可以增强到超过其PiTF，从而能够清晰观察到反映介电常数实部特性的PiDF光谱。利用对声子极化激元基底PiDF的检测，我们提出了一种提高透射图像中光致力响应灵敏度和对比度的策略，有助于精确区分超薄样品的异质分布。
