Papers by Author: Xing Fu

Abstract: In this paper, the ablated microstructures on copper film affected by ultraviolet nanosecond pulse laser are presented. The experimental system was consisted of two lasers, optics and controlling electronics. A 3000mW, 355nm Q-switched ultraviolet lasers was used to the micro-polishing experiments in the work. The repetition rate of the ultraviolet pulse laser is from single-shot to 100kHz, and the pulse width is less than 40ns. The sample used in experiment is copper film (200 nm) sputtered on glass. A series of experiments at different laser parameters and speed of work platform are done. The ablating experiments are also carried out on focusing and defocusing application in the laser direct writer. The results were analyzed.

Abstract: In recent years, pulsed laser processing technology is widely used in MEMS device manufacturing, aerospace technology, precision instrument manufacturing and circuit board processing. According to the characteristics of nanosecond laser, this paper designs a novel nanosecond pulsed laser micromachining system with PMAC card as its core unit. The system can achieve automation control of laser parameters and movement pattern of motion system by software, which can easily realize automatic processing of point, line, and plane structure in micron scale. In this paper, several groups of experiments are taken to test the reliability and accuracy of the machining system and find the group to obtain the best processing result.

Abstract: Atomic force microscope (AFM) is widely used to measure nanoforce in the analysis of nanomechanical and biomechanical properties. As the critical factor in the nanoforce measurement, the stiffness of the AFM cantilever must be determined properly. In this paper, an accurate and SI-traceable calibration method is presented to obtain the stiffness of the AFM cantilever in the normal direction. The calibration system consists of a homemade AFM head and an ultra-precision electromagnetic balance. The calibration is based on the Hooke's law i.e. the stiffness is equal to the force divided by the deflection of the cantilever. With this system, three kinds of cantilevers were calibrated. The relative standard deviation is better than 1%. The results of these experiments showed good accuracy and repeatability.

Abstract: A novel faint signal processing method based on phase-lock amplification principle is developed to enhance the sensitivity of pump/probe-based laser generated and laser detected surface acoustic waves (LG/LD SAW) spectroscopy system. This novel method involves a “dead zone” filter located before a common phase-lock amplification unit, which wipes off most of the noise stacked on SAW signal. This paper explored the working principle of this novel signal processing method based on the knowledge of the characteristics of the system noise and the signal. The experiment result shows that the detection system’s sensitivity has been dramatically improved by this new signal processing method.

Abstract: We study some microstructures fabricated by designed 355nm ultraviolet nanosecond pulse laser micromachining system, which consists of LASER, mechanical and optical structure, 3D work platform, and control system. Nanosecond pulse LASER, with 40ns pulse duration, is chosen as the light source. Mechanical and optical structure is designed for laser beam focusing. Computer software resolves the graphics. And control system based on DSP and FPGA is designed to drive the 3D work platform. Raster sensor is used to measure the real distance that the platform moves. Using this system, some experiments are analyzed and some parameters are optimized. Some microstructures are also fabricated on single crystal silicon wafer and organic glass. The lines of fabricated graphics are 20-40um wide and smooth, with less effect of heat.

Abstract: Experiments are carried out on a femtosecond laser micromachining system with the wavelength 775nm. The ablated patterns on Si (100) and Si (111) surfaces affected by femtosecond pulse laser parameters are presented. The periodic structure termed ripples on silicon surface is investigated. Two kinds of ripples on the ablated surface are observed by SEM. The whole ablation region indicates the ablated field of all amount of laser energy. The ablation region forms two circular areas. The cross section image of the ablated region is showed which is cut by FIB in the orthogonal direction of the line of the center ripples. The depth of ripples is measured. Adjusted the laser fluence as about 0.3~0.33J/cm2 and the pulse number as changeable from 1 to 50, the forming process of the ripples is observed and studied by AFM. Another experiment is done that the wave-plates are inserted into the space between the objective and sample, the result of the direction of ripples changed with the wave-plates of 1/2 or 1/4 is reviewed.

Abstract: A 775nm femtosecond laser is applied to single crystal silicon by direct-write processing in air. A series of holes are drilled with 150fs duration pulses, various numbers of laser pulses and laser fluences on silicon wafer. Different laser parameters and material properties influence the size of fabricated holes. The diameter and depth of holes are gradually enlarged with the increase of laser fluence and pulse number. The periodic ripple structure on silicon surface is found and explained at the same time.

Abstract: 3-Dimensional X-Ray Diffraction (3DXRD) microscopy is a tool for fast and non-destructive characterization of the individual grains, sub-grains and domains inside bulk materials. The method is based on diffraction with highly penetrating hard x-rays, enabling 3D studies of millimeter - centimeter thick specimens. The position, volume, orientation, elastic and plastic strain can be derived for hundreds of grains simultaneously. Furthermore, by applying novel reconstruction methods 3D maps of the grain boundaries can be generated. With the present 3DXRD microscope set-up at the European Synchrotron Radiation Facility, the spatial resolution is ~ 5 µm, while grains of size 100 nm can be detected. 3DXRD microscopy enables, for the first time, dynamic studies of the individual grains and sub-grains within polycrystalline materials. The methodology is reviewed with emphasis on recent advances in grain mapping. Based on this a series of general 3DXRD approaches are identified for studies of nucleation and growth phenomena such as recovery, recrystallisation and grain growth in metals.