Study micromechanism of surface planarization in the polishing technology using numerical simulation method

With the development of semiconductor industry, the chemical mechanical polishing technology has already became the main stream method of realize the surface global flatness. In order to understanding physical essence underlying this technology, the author carried out nanometer polishing experiment of silicon wafer using molecular dynamics (MD) simulation method. The simulation result shows that larger slurry grain generate much more vacancy, dislocation, larger residual stress and intensive plastic deformation than that of small one although the larger grain acquire better surface quality.     

抛光液的pH值对抛光元件表面粗糙度的影响

减小大孔径超光滑玻璃表面的粗糙度是提高抛光质量的关键。实验研究了抛光过程中pH值对抛光元件表面粗糙度的影响。结果表明:抛光液的pH值对抛光元件表面粗糙度有较明显的影响;抛光过程中抛光液的pH值会随抛光时间而变化;抛光过程中,当保持抛光液处于微碱状态,且离抛光粉的等电离点较远时,抛光元件表面具有较小的粗糙度。     

Ultra-smooth polishing of high-precision optical surface

A new method of ultra-smooth uniform polishing was presented, which can avoid high-precision surface figure getting worse after ultra-smooth polishing. At first, the fundamental and process were introduced. Then the process was simulated with “Gauss” and “V” type removal function. It shows that there will be no significant influence on optical surface figure after ultra-smooth uniform polishing with any type removal function. To demonstrate the process, a high-precision Ø100 mm fused silica flat optical element was polished, which was prior figured by IBF. Its surface figure accuracy root-mean-square (rms) value is improved from initial 3.624 nm to final 3.393 nm, the mid-spatial frequency surface roughness rms value is improved from initial 0.477 nm to final 0.309 nm, and the high-spatial frequency surface roughness rms value is improved from initial 0.167 nm to final 0.0802 nm. At last, the surface quality of the lens was analyzed by power spectral density (PSD). The result indicates that the surface roughness of high-precision optical element could be improved by ultra-smooth uniform polishing method without the surface figure destroyed.     

Investigation of the surface generation mechanism of mechanical polishing engineering ceramics using discrete element method

Machining technology about ceramics has been developed very fast over recent years due to the growing industrial demand of higher machining accuracy and better surface quality of ceramic elements, while the nature of hard and brittle ceramics makes it difficult to acquire damage-free and ultra-smooth surface. Ceramic bulk can be treated as an assemblage of discrete particles bonded together randomly as the micro-structure of ceramics consists of crystal particles and pores, and the inter-granular fracture of the ceramics can be naturally represented by the separation of particles due to breakage of bonds. Discrete element method (DEM) provides a promising approach for constructing an effective model to describe the tool–workpiece interaction and can serve as a predicting simulation tool in analyzing the complicated surface generation mechanism and is employed in this research to simulate the mechanical polishing process of ceramics and surface integrity. In this work, a densely packed particle assembly system of the polycrystalline Si₃N₄ has been generated using bonded-particle model to represent the ceramic workpiece numerically. The simulation results justify that the common critical depth of cut cannot be used as the effective parameters for evaluating brittle to ductile transformation in ceramic polishing process. Therefore, a generalized criterion of defining the range of ductile regime machining has been developed based on the numerical results. Furthermore, different distribution of pressure chain is observed with different depth of cut which ought to have intense relationship with special structure of ceramics. This study also justified the advantage of DEM model in its capability of revealing the mechanical behaviors of ceramics at micro-scale.     

光学面形的轮带光学抛光方法研究

鉴于光学零件高陡度凹曲面的抛光是光学加工的一个难题,轮带光学确定性抛光方法是解决此类零件抛光的有效方法之一;提出轮带光学抛光技术的原理和方法。研究了轮带光学抛光方法修形的可行性,采用五轴精密数控机床系统对一块直径Ф80 mm的K9玻璃平面样镜进行了修形试验,经过3次迭代修形使其面形精度均方根误差（RMS）由初始的0.109 提高到0.028 ,平均每次收敛率达到1.3。实验结果表明,应用轮带光学抛光技术进行光学镜面修形,面形收敛速度较快,加工精度较高。本实验验证了轮带光学抛光技术的修形能力,为高陡度光学零件的抛光提供了研究基础。     

On the design of a Nd doped silica fiber-laser using a cholesteric liquid crystal mirror

We report operation of a Nd³⁺-doped fiber-laser using a cholesteric liquid crystal acting as a narrow band reflector. The aim of this work is to apply to a fiber-laser the particular optical properties of an helical structure, whatever is the medium exhibiting this structure, either a liquid crystal or either any other material. The advantage of the use of these mediums in the design of fiber-lasers is that they can favourably take the place, in an easy and compact way, of several optical elements such as a polarizer and a quarter-wave plate at one and the same time. This technology promises to design rugged compact low cost tunable coherent sources the lasing range of which can easily be adjusted. We emphasize here the particular part played by the cholesteric liquid crystal-glass interface in the laser action of the fiber. Received 21 October 1999 and Received in final form 7 February 2000     

光学面形的轮带光学抛光方法研究

鉴于光学零件高陡度凹曲面的抛光是光学加工的一个难题,轮带光学确定性抛光方法是解决此类零件抛光的有效方法之一;提出轮带光学抛光技术的原理和方法。研究了轮带光学抛光方法修形的可行性,采用五轴精密数控机床系统对一块直径Ф80 mm的K9玻璃平面样镜进行了修形试验,经过3次迭代修形使其面形精度均方根误差(RMS)由初始的0109 λ提高到0028 λ,平均每次收敛率达到13。实验结果表明,应用轮带光学抛光技术进行光学镜面修形,面形收敛速度较快,加工精度较高。本实验验证了轮带光学抛光技术的修形能力,为高陡度光学零件的抛光提供了研究基础。     

非球面超光滑加工磨头控制技术研究

为了避免在超光滑加工过程中破坏光学元件的原有面形,同时保证整个表面粗糙度的均匀一致,研究了超光滑加工过程中的磨头控制技术.首先分析了超光滑加工机床的结构形式及超光滑加工工艺特点;然后研究了非球面母线的双圆弧拟合算法以及磨头进给速度的控制方法;最后将所研究的磨头运动控制算法应用于超光滑加工控制软件.以顶点曲率半径为300...     

In situ study of the temperature stability of TiO1.05 titanium monooxide using synchrotron radiation

The temperature stability of cubic TiO_1.05 titanium monooxide is investigated. An in situ X-ray structural analysis is performed using synchrotron radiation in a high temperature vacuum chamber. It is found that under poor vacuum and at high heating rates of up to 1250°C, the structural transformations in TiO_1.05 occur at 630°C. In particular, there is a phase transition from TiO_1.05 (space group Fm-3m) to rhombohedraic Ti₂O₃ (space group R-3c) via Ti_2.5O₃ (space group Immm).     

Computer simulation of the two-stage ion polishing of a silicon surface

Comparative results of the computer simulation of surface sputtering by a focused ion beam with Gaussian density distribution and a uniform ion flux are presented. The experimental angular dependences of the yield of silicon sputtering by nitrogen and argon ions are used. The possibility of the optimization of ion polishing via methods of computer simulation is demonstrated.     

超光滑表面的形成与抛光时间之间的关系研究

由于加工超光滑表面的古典法对加工者的经验要求较高,而且不同的加工者对抛光时间长短的控制也有较大的差别,因而下盘时机的准确判断将会对超光滑表面的加工质量产生严重的影响。为此,对所加工的全反射棱镜的超光滑表面抛光不同的时间,并在全反射条件下,根据全反射棱镜背向散射光斑的大小和亮暗的程度来判断所加工超光滑表面加工质量的检测方法,最终给出超光滑表面的抛光质量随抛光时间的变化。在实验结果的基础上得出了抛光质量随抛光时间交替变化的基本规律,并根据加工经验总结出了超光滑表面加工过程中的注意事项和判断下盘时机的基本方法。     

Investigating the mechanisms of diamond polishing using Raman spectroscopy

Recent research has shown that a phase transformation of diamond to a different form of carbon is involved when diamonds are polished in the traditional fashion. The question as to how this phase transformation is activated and maintained to produce high wear rates is of great technological interest since it may radically change the way we view the processing of diamond. This paper describes the use of Raman spectroscopy to examine debris produced on the diamond polishing wheel, both during its preparation and during polishing. In addition, polished diamond surfaces were examined for the possible existence of non-diamond surface layers in an attempt to identify material removal mechanisms. Raman spectroscopy proves ideal for these analyses because its relatively high spatial resolution is well suited to the analysis of small wear features and debris particles, and because of the wealth of information it reveals about chemical structure. This level of structural information has been lacking in previous analyses of diamond polishing debris. In addition to the non-diamond carbon found in the wear debris, significant quantities of two iron oxides, magnetite (Fe₃O₄) and haematite (α-Fe₂O₃), were also found. An interesting observation was that a transformation from magnetite to haematite could be induced either by using high power laser excitation or by frictional heating during polishing. It is suggested that some of the Raman peaks previously attributed to lonsdaleite might better be explained by the presence of these oxides.     

Ultra-precision figuring using submerged jet polishing

A new removal optimization method called submerged jet polishing(SJP) is reported. Experiments are conducted to obtain the removal shape. Results of SJP indicate that a Gaussian shape removal function can be obtained and that the removal rate is sensitive to variations in the standoff distance. SJP is applied to the corrective figuring of a BK7 optical glass. The flatness is improved from photovolatic(PV) 0.066 λ to 0.024 λ(λ = 632.8 nm) after three iterations,and the root mean square(RMS) value is improved from 0.013 λ to 0.00395 λ. The experimental result indicates that SJP has a capability for ultra-precision figuring and can be applied in polishing complex-shaped surfaces.     

Microdetermination of titanium on the developed silicon surface using cells made of perfluorinated proton-conducting membranes

A technique for microdetermination of titanium on the developed silicon surface is suggested. In this technique, thin titanium layers are dissolved in an aqueous solution of hydrofluoric acid and then the resulting solutions are analyzed using potentiometric cells made of perfluorinated proton-conducting membranes. The feasibility of estimation of titanium on the silicon surface in amounts of 5 × 10^?7 mol or less is demonstrated.     

内凹面磁流变槽路抛光方法的研究

针对高陡度非球面光学元件的内凹面抛光难题,提出了一种内凹面磁流变槽路抛光方法。设计与待加工内凹面形状匹配的凸模,并在凸模上开出供磁流变液循环通过的槽路,当磁流变液经过设有磁场的区域时发生流变作用形成柔性抛光磨头对内凹面产生材料去除作用。通过工件的旋转和外部磁极的移动完成对整个内凹面的抛光加工。建立了实验平台并开展了相关初步实验和分析。结果表明该方法能够适应内凹面抛光加工的需要,可获得较高表面质量,具有一定的可行性和应用潜力。     

铝合金表面的直接光学抛光实验

单点金刚石车削铝合金表面具有较好的表面质量和精度,但车削纹路会产生散射现象,难以满足高品质光学系统要求。对铝合金表面进行直接光学抛光可以去掉表面产生的车削纹路,提高反射表面的光学性能,分析酸性条件下和碱性条件下的铝镜抛光原理,采用新型抛光盘与抛光液对单点金刚石车削后铝合金表面进行抛光实验。实验结果表明:通过合理控制工艺参数,能够消除铝合金表面残留的周期性车削刀纹,并且不会产生新的表面划痕,得到较好的铝镜光学表面质量,测得的铝镜表面粗糙度Ra=2.6 nm。     

Thermal radiation control in the terahertz region using the spoof surface plasmon mode

In this Letter, the enhancement of thermal radiation in the terahertz region is presented theoretically by using the spoof surface plasmon mode on the microcavity array. We found that the terahertz wave is radiated selectively in a vertical direction. As a result, a quasi-monochromatic terahertz source can be created.     

Electro-spark alloying using graphite electrode on titanium alloy surface for biomedical applications

In order to improve the biomedical properties of a titanium alloy surface, electro-spark surface alloying was carried out using a graphite electrode in air, in a nitrogen gas atmosphere and in silicone oil. The morphology and microstructure of the strengthened layers were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The hardness distributions as a function of depth were measured by a micro-hardness tester. Corrosion resistance capacities of the modified layers were evaluated using potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). In addition, wear resistance and corrosive wear properties in a simulated body fluid (SBF) were studied with a pin-on-disk tribometer. Alloyed layers, completely covering the substrate surface and about 40 μm thick mainly composed of the TiC phase and with strong metallurgical bonding and adhesion to the substrate, were obtained. This can markedly improve hardness and wear resistance of the surface layer of the substrate. In comparison to coatings prepared in air and nitrogen gas atmospheres, the coating produced in silicone oil media exhibits a denser and more perfect surface structure. The wear resistance in air and corrosive wear resistance in SBF solution is the best for the coating produced in silicone oil. For instance, the wear rate in air with a GCr15 steel ball counterpart is reduced by a factor of 29 compared with the original titanium alloy and the corrosive wear rate in SBF solution with a corundum ball can decrease by a factor of 13.8. Simultaneously, the effect of electron-spark surface alloying of the titanium alloy surface on biocompatibility and biological activity was also investigated. The electron-spark surface strengthened layer treated in silicone oil shows good biocompatibility and biological activity, and can help cell attachment to the substrate surface.