Laser-induced Surface Acoustic Waves (LSAWs) has been promisingly and widely used in recent years due to its rapid, high accuracy and non-contact evaluation potential of layered and thin film materials. For now, researchers have applied this technology on the characterization of materials' physical parameters, like Young's Modulus, density, and Poisson’s ratio; or mechanical changes such as surface cracks and skin feature like a melanoma. While so far, little research has been done on providing practical guidelines on pulse laser parameters to best generate SAWs. In this paper finite element simulations of the thermos-elastic process based on human skin model for the generation of LSAWs were conducted to give the effects of pulse laser parameters have on the generated SAWs. And recommendations on the parameters to generate strong SAWs for detection and surface characterization without cause any damage to skin are given.
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.
Atomic force microscope (AFM) is very useful in nano-scale force measurement. Lateral force is typically used in nanoscratch and surface friction measurement based on AFM. As one of the most important parameters to obtain lateral force, the lateral spring constant of AFM cantilever probe is of great significance and needs to be quantitative calibrated. Lateral torsion and lateral force of the cantilever are two parameters need to be measured in lateral spring constant calibration. In this article, we develop a calibration system and introduce a calibration method using an AFM head and an electromagnetic balance. An aluminium column with a known angel on top is placed on the weighing pan of the balance. The cantilever is precisely positioned in the AFM head, then approaches and bends on the aluminium column. During this procedure, the bending force and the lateral torsion of the cantilever are synchronously measured by the balance and an optical lever system, respectively. Then the lateral spring constant is calculated with a formula. By using this method, three kinds of rectangular cantilever are calibrated. The relative standard deviations of the calibration results are smaller than 2%.
Proc. SPIE. 9673, AOPC 2015: Micro/Nano Optical Manufacturing Technologies; and Laser Processing and Rapid Prototyping Techniques
KEYWORDS: Optical spheres, 3D image reconstruction, Calibration, Image processing, Image resolution, Atomic force microscopy, 3D metrology, Atomic force microscope, Reconstruction algorithms, 3D image processing
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.