Qingliang Zhao

Atomic force microscope using a diamond tip: a tool for micro/nanomachining on single-crystal silicon surface

When the AFM cantilever is mounted with a sharp diamond tip, in addition to controlling both the applied normal load on the tip and other machining parameters by the AFM electrical components, it is capable of conducting micro/nano-machining on the surface of single crystal silicon. Firstly in this research work the diamond tip based single asperity cutting experiments are conducted on silicon surface with different normal loads and cutting speed, in aiming to investigate the AFM based microcutting process and material removal mechanism for silicon-like brittle material on nanoscale. Secondly, the micro/nano-machining experiments are conducted on single crystal silicon surface with different detecting approaches for characterizing the features of the micro/nano-machined region in terms of material removal mechanism and chips forming characteristic under different normal loads. Furthermore, the contact interaction mechanism existed between the AFM diamond tip and the machined silicon surface during the micro/nano-machining process is simulated with finite element method. Finally, the wear mechanism of an atomic force microscope (AFM) diamond tip when conducting micro/nano-machining on a single crystal silicon surface is empirically analyzed. The results indicate that the AFM based v has a precisely dimensional controllability and a good surface quality on nanometer scale.

Deformation analysis of micro/nano indentation and diamond grinding on optical glasses

The previous research of precision grinding optical glasses with electrolytic in process dressing (ELID) technology mainly concentrated on the action of ELID and machining parameters when grinding, which aim at generating very “smoothed” surfaces and reducing the subsurface damage. However, when grinding spectrosil 2000 and BK7 glass assisted with ELID technology, a deeply comparative study on material removal mechanism and the wheel wear behaviors have not been given yet. In this paper, the micro/nano indentation technique is initially applied for investigating the mechanical properties of optical glasses, whose results are then refereed to evaluate the machinability. In single grit diamond scratching on glasses, the scratching traces display four kinds of scratch characteristics according to different material removal modes. In normal grinding experiments, the result shows BK7 glass has a better machinability than that of spectrosil 2000, corresponding to what the micro/nano indentation vent revealed. Under the same grinding depth parameters, the smaller amplitude of acoustic emission (AE) raw signals, grinding force and grinding force ratio correspond to a better surface quality. While for these two kinds of glasses, with the increasing of grinding depth, the variation trends of the surface roughness, the force ratio, and the AE raw signals are contrary, which should be attributed to different material removal modes. Moreover, the SEM micrographs of used wheels surface indicate that diamond grains on the wheel surface after grinding BK7 glass are worn more severely than that of spectrosil 2000. The proposed research analyzes what happened in the grinding process with different material removal patterns, which can provide a basis for producing high-quality optical glasses and comprehensively evaluate the surface and subsurface integrity of optical glasses.

Ultraprecision grinding machining of optical aspheric surface in ductile mode

In this paper, in order to grind optical aspheric surfaces with high quality and high precision, some factors that influence the roughness and profile accuracy of machined surfaces were theoretically analyzed. At the same time, all kinds of parameters of ultra-precision grinding optical aspheric surface in ductile mode were optimized. Afterwards author developed the ultra-precision aspheric grinding system. Its principal axis of the workpiece, traverse guide, longitudinal guide and principal axis of the grinder were aero-static bearing form. Turning accuracy of principal axis of the workpiece was 0.05 micrometers . The highest rotate speed of the grinder was 80000 rev/min. Its turning accuracy was 0.1 micrometers . The resolution of linear displacement of the traverse and longitudinal guide was 4.9 nm. Micro-adjusting accuracy of the center high micro-adjusting machine of the grinder was 0.1 micrometers . Finally, we performed grinding aspheric surface experiments on this grinding system. The results show that to obtain high accuracy and high quality aspheric surface, the mean size of grains of diamond wheels should be smaller than 10 micrometers , and also the high speed of the wheel and small feed rate are needed. After optimizing these grinding parameters, the final machined aspheric profile accuracy can reach 0.4 micrometers and surface roughness can be less than 0.01 micrometers .

Nanostructure and optical properties of SiO2 films prepared by reactive midfrenquency magnetron sputtering

Nanocrystalline silicon dioxide (SiO2) films for optical applications were deposited on aluminium substrates by reactive midfrenquency magnetron sputtering. The composition of the coating is varied by changing the oxygen gas flow during the depositiongs. The structural properties and the surface morphology of films deposited with various deposition parameters were investigated by x-ray photoelectron spectroscopy and atomic force microscopy. The optical properties were measured and calculated by spectrophotometer and thin-film analyzer. It was found that the composition of silicon dioxide films varies from nearly pure Si, SiO to SiO2, controlled by O2 flow rate. The reflection index of nanocrystalline SiO2 film-aluminum system accords with the mixture rule. All SiO2 films are transparent and the evolution of the transmittance as a function of the films is investigated, and opportunities for their optimization are described.

Ultra-precision diamond turning of microstructure with FTS

In order to fabricate optical microstructures at a high efficiency but low cost way, ultra-precision diamond machining technology with fast tool servo (FTS) was developed in this study and a typical sine-wave microstructure with a form accuracy of 0.65 μm and surface roughness of 45 nm was fabricated by this technology. Moreover, the effects of cutting conditions such as feed rate and spindle speed on surface quality were discussed, the experimental results suggested that better surface quality can be obtained when a higher spindle speed but a relatively lower feed rate were employed. In addition, the cutting experiments also showed that the surface machined with FTS was much better than that machined without FTS. At last, the tool wear behaviour in ultra-precision diamond machining of sine-wave microstructure was explored.

Subsurface damage mechanisms in diamond grinding of BK7 on tetraform 'C'

This research investigates the diamond grinding mechanism of optical glass and the resulted surface and sub-surface by a novel ultra-stiff machine tool, Tetraform C. During the grinding process, an acoustic emission (AE) sensor and a piezoelectric dynamometer were used to monitor the grinding process and the grinding force components correlating to different characteristics of the material removal transition. SEM and AFM microscopes were used to evaluate the ground workpiece surface topography and sub-surface integrity. The nano-indentation technique was applied to evaluating the ground glass surface properties in terms of nano-hardness and elastic modulus. The Experimental results show that for BK7, nanometric quality surfaces (Ra < 5 nm) with minimal subsurface damage depth (< 1μm) could be achieved with a relatively large diamond grit size (6-12μm) metal bonded grinding wheel at a high material removal rate, due to the ultra high closed loop stiffness of Tetraform C.

Effects of diamond cutting tool's rake angle and edge radius on the diamond turned surface quality

For the purpose of realizing the brittle materials turning in ductile mode on the basis of optimizing the diamond cutting tools geometrical parameters, the Linear Elastic Fracture Mechanics and Finite Element Method are applied to stimulate the stress distribution and micro-cracks propagation in the cutting region generated under different rake angles and edge radius. The cutting experiments on single crystal silicon surface are then conducted to verify the stimulation results, which show that the propagation of micro-cracks can be restrained from atomic-size cracks when utilizing the diamond cutting tools with -15 degree to -25 degree rake angles. As a result of increasing the critical depth of cut value of brittle-ductile transition, the goal of ductile-mode turning can be achieved. In addition, with a smaller cutting edge radius, the turning of brittle material in ductile-mode can be easily realized, resulting in good diamond turned surface quality.