Matthias Meixner

Sin2ψ-based residual stress gradient analysis by energy-dispersive synchrotron diffraction constrained by small gauge volumes. II. Experimental implementation

On the basis of the theoretical concept for the use of small gauge volumes to study near-surface residual stress fields with high spatial resolution [Meixner, Klaus & Genzel (2013). J. Appl. Cryst. 46, 610–618], the experimental implementation of the approach is demonstrated. It is shown that specifically designed slit systems are required to avoid effects such as diffuse scattering at the slit blades and total external reflection, both giving rise to a reduced resolution. Starting from the characterization of the small gauge volume, practical guidance on how to control the alignment of the sample relative to the gauge volume for different geometrical conditions of energy-dispersive diffraction is given. The narrow-slit configuration as well as the formalism for data evaluation introduced in the first part of this series is applied to the analysis of a very steep in-plane residual stress gradient in a shot-peened Al2O3 ceramic sample. The results are compared with those obtained by means of a conventional wide-slit setup using the classical universal plot method for residual stress analysis on the one hand, and with the simulations performed in the first part on the other hand.

Influence of the Grain Size on the Properties of CH3NH3PbI3 Thin Films

Hybrid perovskites have already shown a huge success as an absorber in solar cells, resulting in the skyrocketing rise in the power conversion efficiency to more than η = 22%. Recently, it has been established that the crystal quality is one of the most important parameters to obtain devices with high efficiencies. However, the influence of the crystal quality on the material properties is not fully understood. Here, the influence of the morphology on electronic properties of CH3NH3PbI3 thin films is investigated. Postannealing was used to vary the average grain size continuously from ≈150 to ≈1000 nm. Secondary grain growth is thermally activated with an activation energy of Ea = 0.16 eV. The increase in the grain size leads to an enhancement of the photoluminescence, indicating an improvement in the material quality. According to surface photovoltage measurements, the charge-carrier transport length exhibits a linear increase with increasing grain size. The charge-carrier diffusion length is limited by grain boundaries. Moreover, an improved morphology leads to a drastic increase in power conversion efficiency of the devices.

Diffraction analysis of strongly inhomogeneous residual stress depth distributions by modification of the stress scanning method. II. Experimental implementation

The modified stress scanning method [Meixner, Fuss, Klaus & Genzel (2015). J. Appl. Cryst. 48, 1451–1461] is experimentally implemented for the analysis of near-surface residual stress depth distributions that are strongly inhomogeneous. The suggested procedure is validated by analyzing the very steep in-plane residual stress depth profile of a shot-peened Al2O3 ceramic specimen and comparing the results with those that were obtained by well established X-ray diffraction-based gradient methods. In addition, the evaluation formalism is adapted to the depth-dependent determination of the residual stresses inside of multilayer thin-film systems. The applicability for this purpose is demonstrated by investigating the residual stress depth distribution within the individual sublayers of a multilayered coating that consists of alternating Al2O3 and TiCN thin films. In this connection, the specific diffraction geometry that was used for the implementation of the stress scanning method at the energy-dispersive materials science beamline EDDI@BESSYII is presented, and experimental issues as well as limitations of the method are discussed.

Residual stress analysis of diamond‐coated WC–Co cutting tools: separation of film and substrate information by grazing X‐ray diffraction

Chemical vapour deposition (CVD) of diamond surface layers is an effective way of improving the properties of cemented carbide cutting tools. Inadequate coating adhesion is one of the main issues and it may be affected by the residual stresses of the CVD diamond films. The most common methods for nondestructive residual stress analysis are based on X-ray diffraction. The present paper deals with the particular case of determining the residual stress state of thin CVD diamond layers deposited on cobalt cemented tungsten carbide (WC–Co) substrates. It will be shown that the application of the conventional sin2ψ method might lead to erroneous results, as a result of superimposing diffraction lines originating from cobalt and the diamond coating. An approach to separating information on the substrate and film, based on grazing conditions in the symmetrical Ψ mode of diffraction, is presented. The results, revealing large compressive stresses within the coating, are compared with those obtained by supplementary micro-Raman spectroscopy investigations.

Residual Stress Analysis by Energy-Dispersive Synchrotron Diffraction: Concepts for High Resolution Depth Profiling in Real Space

Recently, the ‘stress scanning method’ has been introduced in the field of depth resolved residual stress analysis. The principle of this method is based on depth scans that are performed in several inclination angles with a gauge volume characterized by a height dimension in the range of 10 µm. This method has been used in the energy-dispersive mode of diffraction for rather long-range depth gradients. In this case the variation of the residual stresses is negligible on the scale of the gauge volume height dimension. In this contribution it is shown that the stress scanning method can be extended to the analysis of steep residual stress depth gradients that vary significantly even within the height dimension of the gauge volume, but a careful evaluation of the measured data is necessary and must be adapted to the special case.