The immense potential of carbon nanoprobes (CNPs) for using as contrast agents has propelled much recent research and development in the field of thermoacoustic (TA) molecular imaging, while the proper engineering and design of such materials with required high TA conversion efficiency is still a highly challenging task. In this work, we proposed a controllable strategy to amplify the TA conversion efficiency of the CNPs by constructing vacancy defect (VD) dipoles, and systematically demonstrated the amplification mechanism through theoretical and experimental investigations. First-principles calculation results indicate that, when a carbon atom is removed from the CNPs by chemical approach, owing to local electron density redistribution, the VDs are formed at the positions of the original carbon atoms and act as the structural origin of permanent electric dipoles with the dipole moment several orders higher than that of non-defect sites. Under pulsed microwave irradiation, the VD dipoles are polarized repeatedly and significantly contribute to the conversion efficiency from absorbed electromagnetic waves to ultrasound through enhanced dielectric relaxation losses. We experimentally synthesized graphene samples with different VD densities and VD types to demonstrate the efficiency of the proposed strategy, and results coincide well with the theoretical proposition. This work offers feasible guidance to the systematic development and rational design of new high-conversion-efficiency TA CNPs via VD engineering.

碳纳米探针（CNP）用作造影剂的巨大潜力推动了热声（TA）分子成像领域的许多最新研究和开发，而对具有所需高TA转换效率的此类材料进行适当的工程设计仍是一个重要课题。极具挑战性的任务。在这项工作中，我们提出了一种可控策略，通过构建空缺（VD）偶极子来放大CNP的TA转化效率，并通过理论和实验研究系统地证明了这种放大机理。第一性原理计算结果表明，当通过化学方法从CNP中去除碳原子时，由于局部电子密度的重新分布，VDs在原始碳原子的位置形成，并作为永久电偶极子的结构起源，其偶极矩比无缺陷部位高几倍。在脉冲微波辐射下，VD偶极子反复极化，并通过增强的介电弛豫损耗显着提高了从吸收的电磁波到超声的转换效率。我们通过实验合成了具有不同VD密度和VD类型的石墨烯样品，以证明所提出策略的有效性，并且结果与理论命题非常吻合。这项工作为通过VD工程对新型高转化率TA CNP的系统开发和合理设计提供了可行的指导。