Abstract
Coherent X-ray diffraction techniques play an increasingly significant role in the imaging of nanoscale structures, ranging from metallic and semiconductor to biological objects. In material science, X-rays are usually considered to be of a low-destructive nature, but under certain conditions they can cause significant radiation damage and heat loading on the samples. The qualitative literature data concerning the tolerance of nanostructured samples to synchrotron radiation in coherent diffraction imaging experiments are scarce. In this work the experimental evidence of a complete destruction of polymer and gold nanosamples by the synchrotron beam is reported in the case of imaging at 1-10 nm spatial resolution. Numerical simulations based on a heat-transfer model demonstrate the high sensitivity of temperature distribution in samples to macroscopic experimental parameters such as the conduction properties of materials, radiation heat transfer and convection. However, for realistic experimental conditions the calculated rates of temperature rise alone cannot explain the melting transitions observed in the nanosamples. Comparison of these results with the literature data allows a specific scenario of the sample destruction in each particular case to be presented, and a strategy for damage reduction to be proposed.
Highlights
X-ray microscopy and coherent diffractive imaging (CDI; Miao et al, 1999; Nugent et al, 2003; Eisebitt et al, 2004; Pfeifer et al, 2006; Quiney et al, 2006; Chapman et al, 2006; Chapman & Nugent, 2010) and their modifications are rapidly developing as ultra-high spatial-resolution imaging techniques that exploit coherent, ultra-bright X-ray sources
Whilst searching for the best position to record experimental data suitable for phase-retrieval reconstruction of the kapton–gold sample, we briefly observed a few diffraction patterns with satellite peaks positioned on both sides of the central reflection from the crystal analyzer (Fig. 1)
While the spatial resolution in a diffraction-imaging experiment is inversely proportional to the radiation energy, the linear absorption coefficient away from the absorption edge decreases approximately as the inverse-square of the photon energy
Summary
X-ray microscopy and coherent diffractive imaging (CDI; Miao et al, 1999; Nugent et al, 2003; Eisebitt et al, 2004; Pfeifer et al, 2006; Quiney et al, 2006; Chapman et al, 2006; Chapman & Nugent, 2010) and their modifications are rapidly developing as ultra-high spatial-resolution imaging techniques that exploit coherent, ultra-bright X-ray sources. 580 doi:10.1107/S0909049511016335 between sample and its environment, soft X-rays are much better suited to image materials with low electron densities (Sayre & Chapman, 1995; Chapman et al, 2006). Their use is limited owing to high vacuum requirements, so hard X-rays are preferred (Chapman et al, 2006). From an analysis of maximum tolerable doses in both the CDI-based X-ray microscopy and macromolecular crystallography, Howells, Beetz et al (2009) predicted that a particular feature of biological protein can be imaged with 10 nm resolution at a dose $ 109 Gy. Based on the assumption that the material science samples have higher radiation tolerance, the authors (Howells, Beetz et al, 2009) predicted the possibility of coherent diffraction imaging of such samples with 1 nm resolution. In this paper we present experimental evidence for the destructive influence of synchrotron X-rays on nanoscale samples of both organic and metallic nature, show the role of heat loading in each case, and propose a tentative scenario to explain the observations
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