The atomic force microscopy (AFM) was proposed to characterize the surfaces of various materials with high sensitivity and resolution(sub-nanometer) since 1980s, but it intrinsically lacks amongst others chemical sensitivity. These limitations of AFM can be overcome by coupling with optical microscope, which allows to obtain more comprehensive characterization data by in-situ measurement. To integrate the AFM into the upright optical microscope easily, this paper proposed a novel design of AFM. The corresponding Raman-AFM system was developed which adopts the sample scanning structure with a self-developed ultra-thin AFM head. The AFM head employs an innovative multi-reflected laser beam to detect the deformation of the cantilever, which greatly reduces the Z-direction thickness of the head, making its Z-direction thickness smaller than the working distance of the objective lens. Therefore, the AFM probe can be directly mounted under the objective lens of the upright optical microscope without changing the existing optical path. To evaluate the performance of the proposed AFM system, a standard grid was imaged using the Raman-AFM system. Then, a sample of two-dimensional material, black phosphorus(BP)/molybdenum disulfide(MoS2) heterojunction, was characterized. The physicochemical information of the heterojunction was obtained by in-situ measurement of the surface topography and Raman spectra.
Metrological AFM (mAFM) has high-resolution three-dimensional measurement capability, and its measurement results can be traced back to the SI. Most of mAFMs utilize the optical beam deflection (OBD) method to detect the deflection of cantilever probe, which has simple structure and high sensitivity. A novel 3D traceable OBD system was designed based on the flatbed scanner. In the design, the propagation direction of the laser beam can always be parallel to the motion direction of the scanner so that the relative positions of the laser focal spot and the cantilever probe remain unchanged in any scanning range. All the scanners in the X, Y, Z directions are connected in series, and their motion directions are strictly orthogonal without mutual coupling. The application of the compensation scanner achieves the synchronous movement of the aspherical lens and the Z-direction scanner, which avoids the defocusing phenomenon of the cantilever probe during the large-stroke scanning with the Z-direction scanner. A series of experiments were performed to evaluate the proposed design, including the measurement of the laser tracking errors caused by the scanner motion and imaging results of a standard grid under contact mode. The results demonstrated the imaging capabilities of this system.
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