S. Di Fonzo

Non-destructive determination of local strain with 100-nanometre spatial resolution

Structure sizes of ∼180 nm are now standard in microelectronics, and state-of-the-art fabrication techniques can reduce these to just a few tens of nanometres (ref. 1). But at these length scales, the strain induced at interfaces can locally distort the crystal lattice, which may in turn affect device performance in an unpredictable way. A means of non-destructively characterizing such strain fields with high spatial resolution and sensitivity is therefore highly desirable. One approach is to use Raman spectroscopy, but this is limited by the intrinsic ∼0.5-µm resolution limit of visible light probes. Techniques based on electron-beam diffraction can achieve the desired nanometre-scale resolution. But either they require complex sample preparation procedures (which may alter the original strain field) or they are sensitive to distortional (but not dilational) strain within only the top few tens of nanometres of the sample surface. X-rays, on the other hand, have a much greater penetration depth, but have not hitherto achieved strain analysis with sub-micrometre resolution. Here we describe a magnifying diffraction imaging procedure for X-rays which achieves a spatial resolution of 100 nm in one dimension and a sensitivity of 10-4 for relative lattice variations. We demonstrate the suitability of this procedure for strain analysis by measuring the strain depth profiles beneath oxidized lines on silicon crystals.

Phase contrast hard x-ray microscopy with submicron resolution

In this letter we present a hard x-ray phase contrast microscope based on the divergent and coherent beam exiting an x-ray waveguide. It uses lensless geometrical projection to magnify spatial variations in optical path length more than 700 times. Images of a nylon fiber and a gold test pattern were obtained with a resolution of 0.14 μm in one direction. Exposure times as short as 0.1 s gave already visible contrast, opening the way to high resolution, real time studies.

High gain beam compression in new-generation thin-film x-ray waveguides

X-ray waveguides can compress an incident beam for microscopy applications above 8 keV photon energy to sizes smaller than 100 nm in one dimension, a range which is not routinely accessed with other x-ray optics (e.g., Fresnel zone plates). Beryllium, because of its low absorption, is expected to provide the highest intensity gain. Measured gains for a beryllium waveguide of 74 nm thickness exceed values of 100 at 13 and 20 keV photon energy, which is an improvement by an order of magnitude compared to previously reported performances. The same object works also at 8 keV with gain 43.

Advances in Microdiffraction with X-Ray Waveguide

birthday The x-ray waveguides are a novel optical component for hard x-rays able to produce submicrometer beams. In this article we review the operating principle and describe the characteristics of the exiting beam. We will give two significant examples of applications in microdiffract ion obtained with an unprecedented spatial resolution of 100 nm.

Sub-micrometre coherent beams from x-ray waveguides: principles and applications

The operating principle and some applications of the x-ray waveguides are revised. Significant improvements in waveguide fabrication with respect to the first ones yielded gain of about a factor six with respect to the incident intensity. The high degree of coherence and the divergence of the beam exiting the waveguide allowed phase contrast experiments with unprecedented spatial resolution of 140 nm. An innovative geometry for microdiffraction experiments is proposed which can open the way to very high spatial resolution measurements. The results of a very recent test experiment on a patterned silicon crystal are presented.

X-ray micro-diffraction analysis of reconstructed bone at Zr prosthetic surface with sub-micrometre spatial resolution

The purpose of the present investigation is to demonstrate the power of the x-ray micro-diffraction technique in biological studies. In particular the reported experiment concerns the study of the interface between a Zr prosthetic device implanted in a rat femur and the newly-formed bone, with a spatial resolution of 0.5 µm. The obtained results give interesting information on the Zr deformation and on the crystallographic phase, the grain size and the orientation of the new bone. Moreover the study reveals a marked difference in the structure of the reconstructed bone with respect to the native bone, which cannot be appreciated with other techniques.

Density fluctuations of water–glucose mixtures studied by inelastic ultra-violet scattering

The dynamics of density fluctuations of aqueous glucose solutions were studied in the water-rich region by means of Brillouin ultra-violet scattering. The temperature dependence of the position and line-width of inelastic peaks gives evidence of a strong relaxation process located in the picosecond timescale. In the approximation of a single exponential process, the relaxation time, τ, was obtained for different glucose concentrations; its temperature dependence is well described by an Arrhenius law characterized by an activation energy comparable to that of pure water. This result supports the hypothesis that the microscopic mechanism responsible for the main relaxation process in sugar–water solutions is the continuum rearrangement of the hydrogen-bond network. A comparison is also reported with previous results on aqueous trehalose solutions, showing the acoustic absorption scales with the number of glucoside units for both glucose and trehalose aqueous solutions.

Thin film X-ray waveguides: ‘Condenser systems’ for experiments with X-ray beams of 0.1 μm dimension

This report discusses the latest performance data for X-ray waveguides applied in the production of hard X-ray micro-spots. It is possible to compress an X-ray radiation beam in a thin film waveguide in one direction down to the level of about 0.1 μm, a value which has not been achieved routinely with any other device. A gain factor of about 5 could be achieved in this case for a photon energy of 17 keV. The thin film waveguides were found to provide increasing transmission from 11 keV to 25 keV. As the exiting beam is not only of small size but also highly coherent and divergent it can be used in a number of microscopic techniques: e.g. micro-diffraction, micro-fluorescence, Gabor-holography, phase contrast microscopy.

Submicrometre Beams from a Hard X-ray Waveguide at a Third-Generation Synchrotron Radiation Source

The use of an X-ray waveguide for scattering experiments at an undulator of a third-generation synchrotron radiation source is discussed. The performance with a perfect crystal monochromator, multilayer monochromator and focusing mirror is explored. A maximum flux of 8 x 109 photons s(-1) at lambda = 0.083 nm was obtained for a 0.15 (V) x 600 (H) micron(2) beam at the exit of the waveguide with a multilayer monochromator. The combination of an Si (111) monochromator and ellipsoidal mirror resulted in a flux of approximately 10(9) photons s(-1) but with a horizontal compression of the beam to approximately 30 micron. The use of the waveguide in diffraction experiments is addressed.

Soft X-ray resonant magnetic reflectivity of Gd/Fe multilayers

We report on resonant magnetic scattering of elliptically polarized soft X-rays from Gd/Fe multilayers. At the Fe 2p and, in particular at the Gd 3d edges a strong magnetic circular dichroism (MCD) has been observed even at room temperature. The MCD was investigated as a function of incident angle, energy and degree of circular polarization leading to application for quantitative polarization analysis between 700 and 1250 eV.