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High-precision measurement of lenses and mirrors of free-form surface figures is necessary owing to the increasing functionality of optical elements. Previously, we developed a nanoprofiler measurement technology. The nano-profiler calculates the form from a slope distribution on the measurement surface. The slope distribution is calculated from the measurement result of the optical system that directly measures the slope of the surface using laser light and a quadrant photodiode, as well as the rotary encoder output that indicates the position of the optical system and the object to be measured. The slope distribution and optical path length are required to calculate the form. The geometrical length is between the measured surface of the object and the photodetector's surface. The optical path length was designed to be 400 mm when the instrument was manufactured; however, because assembly errors were included, the optical path length must be calibrated to obtain measurements with higher accuracy. Therefore, we herein propose a multistep self-calibration method to calibrate the optical path length. In this method, a plurality of forms is measured on the surface to be measured while changing the optical path length by a known amount. The optical path length was estimated based on the results of the multiple form measurements. Before the evaluation was performed, the optimum measurement conditions for the evaluation were determined via simulation, and the optical path length was obtained from the actual measurement results under the optimum conditions. The results show that the optical path length is 399.698 mm, and the standard deviation of the calculated variation in the optical path length is 5.3 μm. • This paper reviews self-calibration method of the optical path length. • Multiple measured results are used for self-calibration. • The optimum measurement conditions for self-calibration were determined from prior simulations. • Self-calibration was performed with an actual instrument and the results were discussed. [ABSTRACT FROM AUTHOR]

To realize the damage-free finishing of CVD-SiC substrates, which are used as materials for space telescope mirrors and glass lens molds, plasma chemical vaporization machining (PCVM) and plasma-assisted polishing (PAP) were combined. In this study, the properties of such CVD-SiC substrates, including their surface morphology, composition and crystalline orientation, were investigated. Lapping using diamond abrasives and conventional chemical mechanical polishing (CMP) using CeO 2 slurry were conducted for comparison with the proposed atmospheric-pressure-plasma-based finishing process. Many scratches and a subsurface damage (SSD) layer were formed by the diamond lapping of CVD-SiC. Conventional CMP using CeO 2 slurry was conducted for the damage-free finishing of CVD-SiC. However, the polishing efficiency was very low. In the proposed process, PCVM, which is a noncontact dry etching process, was performed to remove the SSD layer while PAP, which combines plasma modification and soft abrasive polishing, was performed for damage-free surface finishing. PCVM was conducted on a diamond-lapped CVD-SiC surface. After PCVM for a short duration of 5 min, the scratches and SSD layer formed by lapping were completely removed, although the surface roughness was slightly increased. PAP using a resin-bonded CeO 2 grindstone was conducted to decrease the surface roughness of CVD-SiC processed by diamond lapping and PCVM for 5 min, for which a loose-held-type grindstone was demonstrated to be very useful. A flat and scratch-free surface with an rms roughness of 0.6 nm was obtained after PAP finishing. [ABSTRACT FROM AUTHOR]

Single-crystal silicon carbide (4H-SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for fabrication of next-generation semiconductor devices. In this work, we report a hybrid polishing process combining thermal oxidation pretreatment and soft abrasive polishing to realize the damage-free and atomic-scale smooth finishing of the carbon face of 4H-SiC. By thermal oxidation pretreatment, the hardness of the carbon face has been reduced from 4.6 GPa to 1.7 GPa, which enables highly efficient polishing using CeO 2 slurry. For conventional CeO 2 slurry polishing without pretreatment, scratches still existed after a long polishing duration for 16 h. The probable scratch removal mechanism in CeO 2 slurry polishing has been proposed based on surface morphology changes during polishing. Whereas a scratch-free surface with well-ordered SiC atomic steps was obtained within a short polishing duration of only 3 h when polishing was conducted on a thermally oxidized surface. Our results demonstrate that hybrid polishing combining surface pretreatment and soft abrasive polishing is a promising approach to realize the damage-free and atomic-scale smooth finishing of the carbon face of 4H-SiC. [ABSTRACT FROM AUTHOR]

Abstract: The paper overviews research activities at the “Research Center for Ultra Precision Science & Technology of Osaka University”. It describes the motivation of the research, and the physical concepts of new ultraprecision machining methods; i.e. elastic emission machining (EEM), plasma chemical vaporization machining (PCVM), atmospheric pressure plasma chemical vapor deposition (PCVD), and hydroxyl electrochemical machining (H-ECM), and some application examples achieved by utilizing above methods are introduced. [Copyright &y& Elsevier]

The demand for high-accuracy aspheric optical elements has increased significantly in recent years. The surface shapes of such optical elements must be measured with 1 nm Peak-to-Valley(PV) accuracy; however, it is difficult to achieve 1 nm PV accuracy with conventional methods. In this research, we developed a nanoprofiler based on the normal vector tracing method that can achieve the required accuracy. An aspheric mirror was measured by using the nanoprofiler, and repeatable, sub-nanometer measurements were achieved. Furthermore, we compared our nanoprofiler results with those of a Fizeau interferometer and found that the difference was within the systematic error. [ABSTRACT FROM AUTHOR]

We have developed a nanoprofiler that relies on the use of the normal vector. Our aim was to enable the measurement of the profile of free-form surfaces with high precision. Since the nanoprofiler does not use a reference surface, it should be capable of measuring free-form surfaces with a high degree of accuracy. Repeatability at the sub-nanometer level has been achieved. In this study, with a goal of reducing and evaluating the related uncertainty, we set out to estimate the degree of systematic error. We investigated the effect of the systematic error on the measurement results by computer simulation. Then, by comparing the measured results with those of the simulation, we estimated the systematic error. [ABSTRACT FROM AUTHOR]

Abstract: Electrochemical etching enables processing with an atomic-level accuracy, without deteriorating the physical properties of the workpiece; however, contamination of its surface with electrolytes is unavoidable. If it is possible to carry out electrochemical etching without using electrolytes, such a process will be applicable to electronic device manufacturing and precision nanoscale processing of semiconductor materials. In addition, this process does not require the use of chemicals, cleaning after processing or disposal of waste fluid, which results in a low-cost and environmentally friendly process. To develop an electrochemical etching process that does not require the use of electrolytes, we proposed a method in which a functional-group-modified electrode is used as the cathode. A carboxylated graphite electrode was prepared by treating a graphite electrode with sulfuric acid. Electrolysis of ultrapure water was carried out using the obtained electrode as a cathode. The results indicate that the electrolysis current obtained using the modified electrode is approximately six-fold that obtained using an unmodified electrode. Furthermore, we can etch a Cu surface conically in ultrapure water. The current efficiency increases by 70% at maximum, and the minimum current required for electrochemical etching decreases compared with that in the case of using an unmodified electrode. [Copyright &y& Elsevier]

We have studied the dissociative adsorption process of halogen molecules (Cl2 and F2) on the Si(0 0 1) surface by first-principles molecular-dynamics (FPMD) calculations and scanning tunneling microscopy (STM) observations. From FPMD calculations, we demonstrate that Cl2 and F2 molecules adsorb dissociatively at dangling bonds of a buckled dimer with no energy barrier, so that the buckled dimer becomes geometrically flat. In addition, STM observations show that the dissociative adsorptions of Cl2 and F2 induce buckled dimers at the SA step on the Si(0 0 1)-(2×1) surface to become symmetric dimers, in good agreement with the results of FPMD calculations. [Copyright &y& Elsevier]