High spatial resolution X-ray microdiffraction applied to biomaterial studies and archeometry

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Abstract

The high spatial resolution X-ray microdiffraction by using X-ray optics can provide unique information on regions with very high gradients in physical quantities, as in the case of interfaces. Among the several available X-ray optics for synchrotron radiation producing high intensity micron and sub-micron beams, the X-ray waveguide (WG) can provide the smallest X-ray beam in one direction. Moreover, its applicability has been widened by an improved set-up installed at ID13 beamline at ESRF, where a new undulator is combined with an horizontally focusing mirror. In this work, we show different applications of waveguide-based microdiffraction, the first two regard biological problems and in particular the structural analysis of newly formed bone in ceramic scaffolds. The second application regards archeometry and in particular the sulphatation process and the thin gypsum crust formation on the surface of carbonate rocks (travertine, marbles), due to the exposure of the monuments at aggressive atmospheres. In the three cases, the local structural information derived thanks to the high spatial resolution demonstrates the power of the microdiffraction technique based on WG, and the possibility to apply this new methododogy in different scientific fields.

Introduction

The high demand of thorough characterization of materials and processes requires development of advanced diagnostic methods. One of the important figures of merit in many cases is the spatial resolution. The X-ray microdiffraction technique combines diffraction, which is a powerful tool for structural analysis, with the high spatial resolution. To this purpose, the X-ray beam must, in general, be conditioned. In principle, a simple pinhole could do this task, but photon flux would be lost. Therefore, focusing X-ray optics must be employed to concentrate photon flux in small dimensions, as lenses do in the visible spectrum. Unfortunately, there are severe problems in fabricating optical elements for hard X-rays capable to reach sub-micrometer spatial resolution. The advent of the high brilliant synchrotron radiation sources gave new impulse to research for innovative X-ray optics. At present, the available optics for hard X-rays are the Fresnel Zone Plates [1] based on diffraction, the refractive lenses [2] based on refraction, the capillaries [3] and curved mirrors [4] based on total reflection and the X-ray waveguides (WGs) [5], [6], [7] based on standing waves which have demonstrated the capability to provide the highest spatial resolution (in one dimension) up to now.

Since the initial experiments using the WG [5], remarkable improvements have been done with respect to optics efficiency [8], and with respect to integration of the optical element in a microdiffraction set-up and to experimental procedures [9], [10]. In this work, we present three recent applications of microdiffraction using the WG in the field of biology and archeometry.

Section snippets

X-ray waveguides

A typical waveguide structure (see Fig. 1) consists (from bottom to top) of an ultra-flat substrate, a metal layer few tens of nm thick, a guiding layer made of a low-density material having a thickness of the order of 100 nm and a metal cap layer a few nm thick. This structure allows the formation of a strong X-ray standing wave (XSW) field inside the guiding layer with the spatial periodicity depending on the incident angle. When the XSW periodicity is equal to an integer fraction of the

Newly formed bone at prosthesis interface

Events leading to the integration of an implant into a bone, determining the performance of the device, take place largely at the tissue/implant interface [10], [11], [12]. After implantation, reactions occur at the tissue/implant interface that lead to time-dependent changes in the tissues and in the surface characteristics of the implant material.

Up to now, the details of the interactions between tissue and implant are still poorly understood being a complex problem. In particular, as it is

Conclusions

In this work, the power of the microdiffraction technique using the waveguide has been shown presenting three examples carried out at the ID13 beamline of ESRF regarding different scientific fields. Mainly in the cases of bone formation, the high spatial resolution provides unique information on regions with very high gradients in physical quantities, as in the case of interfaces.

In particular, the first two examples regarded the local structural analysis of the newly formed bone and the

Acknowledgement

It is a pleasure to thank Dr. N.N. Aldini and Prof. R. Giardino who provide the thin sections of the samples with the coated and uncoated orthopaedic devices.

This work was partially supported by the program PURS of the National Institute for the Physics of Matter (INFM).

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    This paper was presented at the International Congress on X-Ray Optics and Microanalysis (ICXOM XVII), held in Chamonix, Mont Blanc, France, 22–26 September 2003, and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference.

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