Development of Scanning Photothermal Microscope for Nanoscale Sub-surface Structural Defect Characterization

本项目的目标是开展基于激光耦合扫描探头光热概念的突破性亚表面结构缺陷表征研究，以实现纳米级空间分辨率的深度剖析。所提出的亚表面表征具有纳米级的空间分辨率，使用调频近场激光聚焦和热膨胀传感。将研究亚表面表征中的物理现象，包括近场激光聚焦、纳米尺度加热、热输运和弹性表面位移。建立了周期性纳米级激光加热下表面动态位移的物理模型，为亚表面结构缺陷的纳米级空间分辨率表征开辟了一条新的引人注目的途径，而现有的扫描探针技术大多用于表征表面性质。该表征中的表面位移传感利用了原子力的声学机理，具有响应速度快的特点。通过改变激光入射到扫描探头尖端的调制频率，我们将能够改变表征长度和诊断不同深度的亚表面缺陷。此外，交付成果将包括一个全面的物理模型，以解释表征数据，以获得关于结构缺陷的大小和深度的定量信息。所提出的亚表面表征的强大能力将使其在纳米结构材料的结构诊断和纳米材料加工中亚表面结构的评价中具有广泛的应用。拟议研究的结果将通过广泛的出版物传播。此外，研究成果将被整合到爱荷华州立大学的新课程开发和传统课堂教学中。将安排本科生通过暑期研究广泛参与。爱荷华州立大学的ESPP计划将促进对K-12学生的外展服务。

The objectives of this project are to conduct research on break-through sub-surface structural defect characterization based on laser-coupled scanning probe photothermal concept to achieve depth profiling with nanoscale spatial resolution. The proposed sub-surface characterization features nanoscale spatial resolution using frequency-modulated near-field laser focusing and thermal expansion sensing. Research will be carried out to study the physical phenomena in sub-surface characterization, including near-field laser focusing, nanoscale heating, thermal transport, and elastic surface displacement. A physical model will be developed for dynamic surface displacement under periodical nanoscale laser heating.Upon accomplishment, the proposed research will open a new compelling way for sub-surface structural defect characterization with nanoscale spatial resolution while most of the existing scanning probe technologies are for characterizing surface properties. The surface displacement sensing in the proposed characterization takes advantage of the atomic force acoustic mechanism and features fast response. By varying the modulation frequency of the laser beam incident on the scanning probe tip, we will be able to vary the characterization length and diagnose sub-surface defect of different depth. Furthermore, deliverables will include a comprehensive physical model to interpret the characterization data to obtain quantitative information about the size and depth of structural defect. The strong capability of the proposed sub-surface characterization will make it have broad applications in structural diagnostics of nanostructured materials and evaluation of sub-surface structure in nanoscale material processing. Results of the proposed research will be disseminated through broad publications. Furthermore, the research results will be integrated into new course development and conventional class teaching at Iowa State University. Extensive undergraduate participation via summer research will be arranged. Outreach services to K-12 students will be facilitated through the ESPP program of Iowa State University.