arXiv subjects

Ulrich Kuetgens

Publications and source records attributed to Ulrich Kuetgens.

2 recordsLinked to original sources

arXiv2013

Finite element analysis of surface-stress effects in the Si lattice-parameter measurement

A stress exists in solids surfaces, similarly to liquids, also if the underlying bulk material is stress-free. This paper investigates the surface stress effect on the measured value of the Si lattice parameter used to determine the Avogadro constant by counting Si atoms. An elastic-film model has been used to provide a surface load in a finite element analysis of the lattice strain of the x-ray interferometer crystal used to measure the lattice parameter. Eventually, an experiment is proposed to work a lattice parameter measurement out so that there is a visible effect of the surface stress.

cond-mat.mtrl-sci↗

arXiv2010

Measurement of the \{220\} lattice-plane spacing of a $^{28}$Si crystal

The spacing of the \{220\} lattice planes of a $^{28}$Si crystal was measured by combined x-ray and optical interferometry to a $3.5\times 10^{-9}$ relative accuracy. The result is $d_{220}=(192014712.67 \pm 0.67)$ am, at 20.0 $^\circ$C and 0 Pa. This value is greater by $(1.9464 \pm 0.0067)\times 10^{-9} d_{220}$ than the spacing in natural Si, a difference which confirms quantum mechanics calculations. Subsequently, this crystal has been used to determine the Avogadro constant by counting the Si atoms, a key step towards a realization of the mass unit based on a conventional value of the Planck or the Avogadro constants.

physics.atom-ph↗