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.
Digital in-line holographic microscopy is one of the most efficient methods for particle tracking as it can precisely measure the axial position of particles. However, imaging systems are often limited by detector noise, image distortions and human operator misjudgment making the particles hard to locate. A general method is used to solve this problem. The normalized holograms of particles were reconstructed to the pupil plane and then fit to a linear superposition of the Zernike polynomial functions to suppress the aberrations. Relative experiments were implemented to validate the method and the results show that nanometer scale resolution was achieved even when the holograms were poorly recorded.
Proc. SPIE. 9673, AOPC 2015: Micro/Nano Optical Manufacturing Technologies; and Laser Processing and Rapid Prototyping Techniques
KEYWORDS: 3D image reconstruction, Calibration, Reconstruction algorithms, 3D image processing, Atomic force microscopy, Optical spheres, Image processing, Atomic force microscope, Image resolution, 3D metrology
Atomic force microscope (AFM) is the most prevalent instrument in nanometer measurement. But the tip shape has a great influence on the measurements of surface topography. Blind tip reconstruction (BTR), established by Villarrubia, provides a good solution to this problem, nevertheless, with low precision if the tip characterizer is not appropriate. In order to explore the optimal tip characterizers for precision BTR, a serial of simulation experiments were carried out. First, a tip characterizer was simulated as the combination of a nanosized sphere with a square grating for the BTR of a conical tip. The results show that rotation structures are more suitable for conical tip reconstruction than prismatic structures. Second, a cylinder structure is chosen to verify the validity as an optimal feature for conical tip reconstruction. The simulation results show that if only the equivalent cone angle of the cylinder structure is no more than the tip, such structure is suitable as a tip characterizer. Tip characterizers need to have structure with smaller equivalent cone angle so as to make enough segments of the tip touched by the local maximum point of the sample. The local maximum point of the cylinder is just the top edge. From another point of view, the edge of the pillar has a zero equivalent radius, which is the sharpest feature but not obviously in scale.
Dual-energy x-ray technique, which consists in combining two radiographs acquired at two kilovoltage, can improve the identity of the compositions of object over regular CT, or at least improve image contrast. Dual-energy equations can be easily written and solved for ideally monochromatic x-ray source and perfect detector, but become complex when considering polychromatic x-ray source, detector sensitivity, and system non–linearity. In this paper, a new dual-energy algorithm which employed the basis material decomposition method was investigated for improving material separation capability. Studies by using computer-simulated data were performed to validate and evaluate the algorithm. The preliminary results of the study show that, with the proposed algorithm, separated “material specific” images of dual-material object could be obtained. Also monochromatic image can be acquired at arbitrary desired energy which could enhance image contrast in comparison with conventional reconstructed image.
With nano-level spatial and force resolution, atomic force microscope (AFM) becomes an indispensable nanoindentation measurement instrument for thin films and soft films. To do the research of size effect of the hardness property of thin films, indentation experiments have been done on a gold film with 200 nm thickness and a silicon nitride film with 110 nm thickness. It is possible to change the maximum load forces to get discrete residual depths on the film samples. The contact depths of the gold film are 15.91 nm and 26.67 nm respectively, while the contact depths of the silicon nitride film are 7.82 nm and 10.25 nm respectively. A group of nanoindentation force curves are recorded for the transformation into force-depth curves. Subsequently, a 3D image of the residual indentation can be obtained by in-situ scanning immediately after nanoindentation. The topography data is imported into a Matlab program to estimate the contact area of the indentation. For the gold film, the hardness parameters of 3.31 GPa and 2.57 GPa are calculated under the above two contact depths. And for silicon nitride film, the corresponding results are 6.51GPa and 3.58 GPa. The experimental results illustrate a strong size effect for thin film hardness. The correction of the residual indentation image of the gold film is also done as an initial study. Blind tip reconstruction (BTR) algorithm is introduced to calibrate the tip shape, and more reliable hardness values of 1.15 GPa and 0.94 GPa are estimated.
Optical tweezers has shown its significant advantages in applying pico-Newton force on micro beads and handling them with nanometer-level precision, and becomes a powerful tool for single-molecule biology. Many excellent researching results in use of the optical tweezers have been reported. Most of them focus on the single-trap optical tweezers experiments. However, when a single-trap optical tweezers is applied to biological molecule, there is often an obvious noise from the sample chamber holder to which one end of the sample molecule is tethered. In contrast, a dual-trap optical tweezers can intrinsically avoid this problem because both ends of the sample tethered to microspheres are manipulated with two separate optical traps. In order to force the molecule precisely, it is of importance to do calibrations for both traps. Many approaches have been studied to obtain the stiffness and sensitivity of the trap, but those are not quite suitable for making calibration during experiment. Here, we use a modified method of power spectrum density (PSD) for the calibrations of the stiffness and sensitivity of the traps, which combines a sinusoidal motion of the sample stage. The main strength of the method is that the beads used for the calibration also can be used in experiment later. In addition, the calibration can be performed during experiment. Finally, an experiment using a dsDNA molecule to test the system is presented. The results show that the calibration approach for the dual-trap optical tweezers is efficient and accurate.
In order to measure motion characteristic and dynamic parameters of MEMS resonator in every moment based on the
techniques of stroboscopic imaging clear motion images for every moment in one cycle are obtained. Using technique of
Phase correlation method to process motion images of MEMS resonator the dynamic parameters are got. The results give
important reference to MEMS designation. In this paper we derive a completely analytical N-cubed algorithm based on
Phase correlation method. MEMS motion process is analyzed using the algorithm. The amplitude-phase curve of MEMS
in special driving frequency is got. The phase-frequency character is also analyzed. And the amplitude-frequency curve
is acquired through sweep frequency measurement. Experimental results indicate that the repetition of measurement is
Microscopic interferometry is up to now the most widely used technique for microstructure surface profiling, and is also capable of measuring out-of-plane motion and deflection of microstructures with stroboscopic illumination. In this paper we put forward a stroboscopic Mirau microscopic interferometer system, which is built of commercially available components and instruments based on virtual instrument technology. An improved Fourier transform method (FTM) is described, and two interferograms with different phase shifting are processed for achieving reliable phase demodulation. The system is applied to the measurement of microcantilever surface profile and out-of-plane deflection and motion. Finally, experiment results are compared with that of temporal phase-shifting method for validating the process method.