Problems with Evaluation of Micro-Pore Size in Silicon Carbide Using Synchrotron X-ray Phase Contrast Imaging.

Tatiana S Argunova,Victor G Kohn

doi:10.3390/ma15030856

Abstract

We report near- and far-field computer simulations of synchrotron X-ray phase-contrast images using a micropipe in a SiC crystal as a model system. Experimental images illustrate the theoretical results. The properties of nearly perfect single crystals of silicon carbide are strongly affected by μm-sized pores even if their distribution in a crystal bulk is sparse. A non-destructive technique to reveal the pores is in-line phase-contrast imaging with synchrotron radiation. A quantitative approach to evaluating pore sizes is the use of computer simulations of phase-contrast images. It was found that near-field phase-contrast images are formed at very short distances behind a sample. We estimated these distances for tiny pores. The Fresnel zones did not provide any information on the pore size in the far-field, but a contrast value within the first Fresnel zone could be used for simulations. Finally, general problems in evaluating a micro-pore size via image analysis are discussed.

Highlights

We report near- and far-field computer simulations of synchrotron X-ray phase-contrast images using a micropipe in a silicon carbide (SiC) crystal as a model system
The properties of nearly perfect single crystals of silicon carbide are strongly affected by μm-sized pores even if their distribution in a crystal bulk is sparse
The Fresnel zones did not provide any information on the pore size in the far-field, but a contrast value within the first Fresnel zone could be used for simulations

Summary

Introduction

The structural homogeneity and perfection of silicon carbide (SiC) single crystals have been improved in recent years by developing physical vapor transport technology. In-line phasecontrast imaging (PCI) allows one to visualize micro-objects in the volume of materials if absorption contrast is weak. Other imaging techniques such as x-ray microscopy (XRM), coherent diffraction imaging (CDI), or x-ray ptychography can provide nano-level resolution. A wide, diverging, partially coherent SR beam makes it possible to detect the crystal defects by the total phase shift along the beam path In this technique, image features depend on the sample-to-detector distance z. This paper presents experimental and simulated phase-contrast images corresponding to different distances behind the sample to evaluate a proper transverse size of a micro-pore from image analysis. We must conclude that the distance is too small and practically unattainable

Experiment

Numerical Simulation