Neutron visualization of inhomogeneous buried interfaces in thin films.

When designing some functions in thin film systems, one of the key concepts is the structure of the constituent layers and interfaces. In an actual system, the layers and interfaces are often inhomogeneous in different scales, from hundreds of microns to several nanometers, causing differences in properties, despite very similar average structures. In this case, the choice of the observation point is critical to clarify the problem. Another critical aspect is the identification of these points by surveying the entire inhomogeneous thin film system. This article presents a description of a novel promising solution that is suitable for nondestructive visualization of inhomogeneous buried layers and interfaces in thin films. Such observations have been impossible until now. In this investigation, a unique extension of neutron reflectometry is proposed. While conventional neutron reflectivity just gives average depth-profiling of the scattering length density of layered thin films, the present method provides full picture of the inhomogeneity. In general, achieving a high spatial-resolving power for neutron scattering is not straightforward because the neutron counts become fairly limited at the sample or the detector position when the beam size is reduced. As a result, XY scanning of a sample with a small neutron beam is fairly difficult because of the required long measurement time. To address these issues, new concepts have been introduced for neutron reflectivity. The proposed method uses a wide beam instead of reducing the beam size. In addition, it measures the projection reflection profile instead of the total integrated intensity. These profiles are collected at a set of different in-plane angles. Similar to computed tomography, it is possible to obtain the specimen's two-dimensional (2D) neutron reflectivity distribution as one image. Because the spatial resolution is limited by the detection method, a Hadamard coded mask is employed to measure the reflection projection with only 50% loss of the primary neutron intensity. When the time-of-flight (ToF) mode is used for the neutron experiment, one can obtain many images as a function of ToF, i.e., the wavevector transfer. Such series of images can be displayed as a video. This indicates that the neutron reflectivity profiles of local points can be retrieved from the above video images. This paper presents the first report on the development of neutron reflectivity with imaging capability, and the analysis of local points in inhomogeneous layered thin-films without utilizing a small neutron beam. In the present work, the feasibility of the proposed method with approximately 1 mm spatial resolution was examined. In addition, further improvements of the approach are discussed. It is anticipated that this technique will facilitate new opportunities in the study of buried function interfaces.

X-ray reflection tomography: a new tool for surface imaging.

We report here a novel technique of surface imaging by X-ray reflection tomography utilizing an ordinary laboratory X-ray source. The technique utilizes the line projection, at different rotation angles, of the reflected beam from a highly reflecting patterned sample at grazing incidence. Filtered back-projection algorithm is applied to the line projection data to reconstruct an image of the pattern on the sample surface. Spatial resolution currently obtained is ~1.6 mm. Nonetheless, we have achieved high correlation between the original image and the reconstructed image. This work is the first step in future efforts of nondestructive X-ray imaging for buried surfaces and interfaces.

X-ray diffraction imaging of anatase and rutile.

Both anatase and rutile are well-known as stable phases of TiO(2). In real-life samples, TiO(2) is most likely to be a mixture of those phases rather than pure anatase and rutile, and therefore quantitative analysis is extremely important. It is basically possible to determine the average ratio by X-ray diffraction (XRD) using differences in the crystal structure, but it is not easy to do so when attempting mapping by point-by-point scanning. The present paper describes the successful application of newly developed projection-type XRD imaging, which is an extremely rapid and highly efficient method.

Spectrometer for lanthanides' K x-ray fluorescence.

X-ray fluorescence analysis is a highly useful technique for determining the chemical composition of matter. The present article describes the successful development of a wavelength-dispersive x-ray fluorescence spectrometer for a fairly high-energy range, 30-60 keV, that can contribute to studying lanthanides' Kbeta spectra with high-energy resolution. By combining a new high-energy synchrotron light source and the present spectrometer, it has been demonstrated that the full width at half maximum for lanthanum's Kbeta(1) is 32 eV and that all the peaks in the spectra are fully resolved. This corresponds to an energy resolution EDeltaE of 1180, which is ten times better than a conventional system based on a Ge detector, which can detect only two peaks, Kbeta(1) and Kbeta(2), in seven peaks. The present spectrometer can open up a new field in x-ray spectrometry.

XAFS imaging of Tsukuba gabbroic rocks: area analysis of chemical composition and local structure.

Gabbroic rocks were collected at Mount Tsukuba in Japan, and their XAFS images were studied using a projection-type X-ray fluorescence (XRF) microscope, which is a powerful new tool recently developed for extremely rapid imaging. The instrument employs a grazing-incidence arrangement in order that primary X-rays illuminate the whole sample surface, as well as parallel-beam optics and an extremely close geometry in order to detect XRF by a high-performance X-ray CCD system with 1024 x 1024 pixels. The XRF image indicated that black amphibole and white feldspar, both of which are typical mineral textures of the rock, contain iron. The origin has been suggested to be several small yellowish-brown minerals contained there. The XAFS imaging has been carried out by repeating the exposure of XRF images during the energy scan of the primary X-rays. It has been found that the structure is qualitatively close to that of olivine, and the main differences found in both areas can be explained as a difference in iron and magnesium concentration, i.e. the mixed ratio of forsterite (Mg(2)SiO(4)) and fayalite (Fe(2)SiO(4)). The feasibility of the present XAFS imaging method has been demonstrated for realistic inhomogeneous minerals.