Ion beam figuring machine for ultra-precision silicon spheres correction

Abstract

a b s t r a c tIn the framework of the Avogadro project, isotopically enriched 28 Si spheres had been manufactured as artifacts for the assessment of various physical quantities including the sphere volume which finally leads to a very accurate determination of the Avogadro constant N A . The Avogadro constant is an important input datum for the redefinition of the unit of mass, the kilogram, on the basis of fundamental physical constants. During the recent measurement campaign, it has turned out that one of the main contributions to the overall uncertainty of N A is the sphericity error and consequently the interferometric volume measurement. Since chemical-mechanical polishing has reached its limits with respect to form accuracy due to the sensitivity of material removal rate to crystal orientation, it has been proposed to use ion beam figuring for further reduction of sphericity error from currently 50 nm PV to values <10 nm PV. In this paper, a new concept and realization of a multi-axis ion beam figuring machine dedicated for deterministic correction of silicon spheres is presented. Aspects of long term tool stability and alignment procedures in order to relate the ion beam footprint to the sphere surface are covered. Furthermore, a process dwell time calculation and tool path generation method dedicated for spheres manufacturing will be presented and discussed.

Contributions of precision engineering to the revision of the SI

“…However, if the weighing and moving mechanism differ or there are effects, such as unwanted horizontal forces and torques which may generate small movements of the coil, this can prevent cancellation of the bracketed terms in equations 1 and 3 and then it is necessary to consider all terms in the virtual power equation (5) or (6) Equation 6gives a concise picture of the Kibble balance problem in such cases and is useful for assessing alignment uncertainties [74]. The measurand of interest among the terms on the right hand side of Equation 5is the virtual mechanical power , and the signal that is detected to represent this quantity is the virtual electrical power UI.…”

“…35. Another approach to further reduce the topography deviations of the Si spheres was reported, which uses ion beam figuring techniques for targeted modification of the Si surface [6].…”

A Novel Force-Controlled Spherical Polishing Tool Combined With Self-Rotation and Co-Rotation Motion

“…Nowadays, many scholars have made fruitful achievements in the optical polishing based on the CCOS principle [4], [5]. Manual polishing is gradually replaced by computer numerically controlled (CNC) machines [6].…”

Ion beam figuring and optical metrology system for synchrotron x-ray mirrors

“…This level of surface quality for non-planar optics cannot easily be achieved using traditional mechanical polishing techniques. This motivates the use of advanced deterministic polishing methods, such as ion beam figuring 1,2 , for the final stages of optic production. Such specialized tools are possessed by only a few suppliers of X-ray optics for synchrotron and free electron laser beamlines, which presents a significant procurement cost and time risk.…”