arXiv subjects

David Stifter

Publications and source records attributed to David Stifter.

7 recordsLinked to original sources

arXiv2020

Effects of Alloying Elements on Surface Oxides of Hot-Dip Galvanized Press Hardened Steel

Effects of steel alloying elements on the formation of the surface oxide layer of hot-dip galvanized press hardened steel after austenitization annealing were examined with various advanced microscopy and spectroscopy techniques. The main oxides on top of the original thin Al2O3 layer, originating from the primary galvanizing process, are identified as ZnO and (Mn,Zn)Mn2O4 spinel. For some of the investigated steel alloys, a non-uniform, several nanometer thick Cr enriched, additional film was found at the Al2O3 layer. At a sufficiently high concentration, Cr can act as a substitute for Al during annealing, strengthening and regenerating the original Al2O3 layer with Cr2O3. Further analysis with secondary ion mass spectrometry allowed a reliable distinction between ZnO and Zn(OH)2.

physics.app-ph↗

arXiv2014

Bond Model and Group Theory of Second Harmonic Generation in GaAs(001)

A comprehensive analysis of second harmonic generation (SHG) in a diatomic zincblende crystal based on the Simplified Bond Hyperpolarizability Model (SBHM), Group Theory (GT) is presented. The third rank tensor between the two approaches are compared and applied to reproduce rotational anisotropy (RA) SHG experimental result.It is well known that such a crystal is noncentrosymmetric, therefore the second harmonic generation source is dominated by bulk dipoles with a SHG polarization $P_{BD}=\chi_{ijk}^{(2)}E(\omega)E(\omega)$. We show that the SBHM previously applied to mono crystal system such as Silicon can also be applied to an atomic cell containing two different atoms e.g. GaAs by introducing an effective hyperpolarizability $\alpha_{2GaAs}=\left(\alpha_{2Ga}-\alpha_{2As}\right)$ . Comparison with GT yields the same third rank tensor for a $T_d$ point group corresponding to bulk tetrahedral structure. Interestingly, SBHM gives good agreement with RASHG experiment of GaAs using only one single fitting parameter when Fresnel analysis is also incorporated in the model.

cond-mat.mtrl-sci↗

arXiv2013

XPS on corrosion products of ZnCr coated steel: on the reliability of Ar+ ion depth profiling for multi component material analysis

X-ray photoelectron spectroscopy combined with Ar+ ion etching is a powerful concept to identify different chemical states of compounds in depth profiles, important for obtaining information underneath surfaces or at layer interfaces. The possibility of occurring sputter damage is known but insufficiently investigated for corrosion products of Zn-based steel coatings like ZnCr. Hence, in this work reference materials are studied according to stability against ion sputtering. Indeed some investigated compounds reveal a very unstable chemical nature. On the basis of these findings the reliability of depth profiles of real samples can be rated to avoid misinterpretations of observed chemical species.

physics.chem-ph↗

arXiv2012

Simplified bond-hyperpolarizability model of second-harmonic-generation in Si(111): theory and experiment

Second-harmonic-generation (SHG) in centrosymmetric material such as Si(111) is usually understood either from the phenomenology theory or more recently using the Simplified Bond-Hyperpolarizability Model (SBHM) [G. D. Powell, J. F. Wang, and D. E. Aspnes, Phys. Rev. B 65, 205320/1 (2002)]. Although SBHM is derived from a classical point of view, it has the advantage over the former that it gives-especially for lower symmetry systems- a clear physical picture and a more efficient explanation of how nonlinearity is generated. In this paper we provide a step-by-step description of the SBHM in Si(111) for the linear and second harmonic case. We present a SHG experiment of Si(111) and show how it can be modelled by summing up the contribution of the fields produced by the anharmonic motion along the bonds.

cond-mat.mtrl-sci↗

arXiv2012

Bulk dipole contribution to second harmonic generation in diamond lattices

It is generally argued that material classes with inversion symmetry do not produce bulk dipole related second harmonic generation (SHG). So, SHG is then either ascribed to surface effects or bulk related electric quadrupole or magnetic dipole effects. Using symmetry and \emph{ab-initio} potentials we show analytically that due to the fact of the decaying harmonic electric field certain diamond crystal orientations, as e.g. Si(111), produce a bulk dipole SHG response. For fcc and bcc lattices with a single atom basis, i.e. for the most important metals, however, SHG can purely arise due to the disturbance induced by the surface. Finally we propose an experiment, exploiting the different dispersion for the fundamental as well as frequency doubled radiation to determine this effect.

physics.optics↗

arXiv2011

Quantitative phase reconstruction for orthogonal-scanning differential phase-contrast optical coherence tomography

We present differential phase-contrast optical coherence tomography (DPC-OCT) with two transversally separated probing beams to sense phase gradients in various directions by employing a rotatable Wollaston prism. In combination with a two-dimensional mathe- matical reconstruction algorithm based on a regularized shape from shading (SfS) method accurate quantitative phase maps can be determined from a set of two orthogonal en-face DPC-OCT images, as exemplified on various technical samples.

physics.optics↗

arXiv2011

Spatially resolved stress measurements in materials with polarization-sensitive optical coherence tomography: image acquisition and processing aspects

We demonstrate that polarization-sensitive optical coherence tomography (PS-OCT) is suitable to map the stress distribution within materials in a contactless and non-destructive way. In contrast to transmission photoelasticity measurements the samples do not have to be transparent but can be of scattering nature. Denoising and analysis of fringe patterns in single PS-OCT retardation images are demonstrated to deliver the basis for a quantitative whole-field evaluation of the internal stress state of samples under investigation.

physics.optics↗