Combining scanning probe microscopy and x-ray spectroscopy

A new versatile tool, combining Shear Force Microscopy and X-Ray Spectroscopy was designed and constructed to obtain simultaneously surface topography and chemical mapping. Using a sharp optical fiber as microscope probe, it is possible to collect locally the visible luminescence of the sample. Results of tests on ZnO and on ZnWO4 thin layers are in perfect agreement with that obtained with other conventional techniques. Twin images obtained by simultaneous acquisition in near field of surface topography and of local visible light emitted by the sample under X-Ray irradiation in synchrotron environment are shown. Replacing the optical fibre by an X-ray capillary, it is possible to collect local X-ray fluorescence of the sample. Preliminary results on Co-Ti sample analysis are presented

XAS-XEOL and XRF spectroscopies using Near-Field Microscope probes for high-resolution photon collection

Scanning Probe Microscopes allow to obtain sample topography up to atomic resolution. Local surface properties such as potential, elasticity, density of states... can also be determined. However, an a priori knowledge of the sample chemistry is required to completely identify the objects present on the sample surface. X-ray spectroscopies allow elemental and structural analysis of a sample with accuracy better than 1 Å. The lateral resolution is limited by the primary beam diameter, currently a few μm². Two different ways can be followed to enhance the lateral resolution: - further primary beam focusing - detector aperture shrinking to collect the fluorescence coming only from a part of the emitting volume, while keeping a significant signal/noise ratio. This is ensured approaching the detector as much as possible toward the surface. We have chosen to develop this second option. Local sample visible luminescence is collected through a low aperture sharp optical fibre, probe of a shear force microscope. This technique was used to characterize microstructured semiconducting samples to achieve simultaneously the surface topography and luminescence mapping. The results were obtained using either synchrotron radiation or a laboratory microsource equipped with a polycapillary lens. To extend this concept to a wider variety of materials, local XRF collection by an EDX detector equipped with a cylindrical X-ray capillary was tested. A cobalt sample irradiated with the microsource was used for technique evaluation. The signal magnitude dependence with the capillary diameter was measured. Modelling and numerical calculations were developed to estimate the signal magnitude that could be detected using a 1 μm diameter capillary. The optimal system geometry was determined. Scanning Probe Microscopy combined to XRF analysis could thereby lead to simultaneous acquisition of sample topography and chemical mapping. The expected lateral resolution using synchrotron radiation is 100 nm while sub 1 μm resolution is realistic with a laboratory source. This technique would allow to point a peculiar micro- or nano-object on the surface and to perform its chemical analysis.Les microscopes en champ proche permettent d'obtenir la topographie d'un échantillon avec une résolution pouvant atteindre la résolution atomique. Ces techniques permettent également d'accéder à certaines propriétés locales de la surface telles que le potentiel, l'élasticité, la densité d'états... Ces spectroscopies locales sont de type 'contraste' et ne permettent pas de dresser la cartographie chimique de la surface sans connaissance a priori des éléments qui la composent. Les spectroscopies de rayons-X sont des méthodes de caractérisation puissantes qui permettent de déterminer la composition et la structure élémentaire de l'échantillon avec une précision inférieure à l'Ångström. La résolution latérale est essentiellement limitée par la taille du faisceau primaire, couramment de plusieurs μm². Deux voies sont possibles pour l'améliorer: - réduire l'étendue du faisceau primaire excitateur; - limiter la collecte du rayonnement émis à une portion du volume excité, tout en approchant le détecteur au maximum pour garder un rapport signal/bruit suffisant. C'est cette deuxième option que nous avons choisi de développer. Pour cela nous avons collecté localement la luminescence visible issue de l'échantillon par la pointe-sonde d'un microscope à force de cisaillement, constituée d'une fibre optique effilée de faible ouverture. Cette technique a été utilisée pour caractériser des échantillons semiconducteurs micro- et nano-structurés afin d'en obtenir simultanément la topographie et la cartographie de luminescence locale. Ces résultats ont été obtenus non seulement sur une ligne synchrotron mais également à l'aide d'une microsource de laboratoire équipée d'une lentille polycapillaire. Afin de pouvoir étendre ce concept à d'autres types de matériaux, la faisabilité de la collecte de la fluorescence X locale a été évaluée avec la microsource. Pour cela la fluorescence X émise par un échantillon de cobalt a été collectée par un capillaire cylindrique équipant un détecteur EDX. L'influence du diamètre du capillaire sur le niveau de signal a été mesurée. Une simulation numérique a été développée afin d'estimer le niveau de signal obtenu en utilisant un capillaire de 1 μm de diamètre et d'optimiser la géométrie du système. En couplant la microscopie en champ proche et l'analyse XRF, à la lumière de ces résultats, il sera possible d'atteindre 100 nm de résolution latérale en environnement synchrotron et moins de 1 μm à l'aide d'une source de laboratoire. Il serait alors possible de sélectionner un objet particulier sur une surface et d'en faire l'analyse élémentaire

High resolution XRF using capillary optics

International audienceClassical XRF measurements are commonly performed in synchrotron facilities because the technique requires a high brightness X-ray source. Thanks to the development of polycapillary lens, sharply focusing X-ray beams on samples, the technique can now be performed in laboratory. The lateral resolution is essentially linked to the incident beam geometry and is currently in the range of tens of micrometers. On the other hand, imaging chemical composition and structure at nanometer dimensions is a keypoint in nanoscience, especially for structures and properties characterization of embedded interface. For this purpose, non-destructive techniques, based on X-ray irradiation have a leader place. We have developed an experimental test-bed to estimate the ultimate resolution reachable by XRF. This equipment includes a microfocused X-ray low power source, and an EDX detector equipped with a cylindrical glass capillary, increasing the X-ray fluorescence collection yield. It is based on a confocal configuration since the detected signal comes from the intersect between the volume excited nearby the source lens focal plane and the analyzed volume in the aperture of the capillary. The setup was evaluated using test samples consisting in a molybdenum grid (250µm mesh) glued on an iron substrate. Significant XRF signal level with 50s acquisition time was recorded through a 25µm radius capillary for detection. Spectra were recorded along a scan line crossing the grid. The spectroscopic signal shows good correlation between molybdenum Kα and iron Kα signals. A similar grid was then used as a mask for thin titanium pattern evaporation on a cobalt sample. A 5 µm radius capillary was used to collect the sample X-ray fluorescence. The Cobalt Kα line is detected on the whole line scanned, since titanium is thin enough to allow the Co-Kα photons to escape. The titanium spectroscopic trace fits with the expected pattern. The use of thin capillaries for XRF detection opens the way to 500 nm lateral resolution in lab and 50 nm using brighter sources such as synchrotron facilities. Furthermore, approaching the capillary extremity towards the surface in near field mechanical interaction would allow to image the surface topography simultaneously to sample chemical mapping. This concept has already been demonstrated in previous works

Design, deposition and metrology of EUV multilayer coatings for SR, FEL and space applications (Orale)

International audienceWe will report and discuss on some aspects of the design, deposition and characterization of reflecting multilayer coatings with specific spectral characteristics and enhanced temporal, thermal and radiation stability for extreme ultra-violet (EUV) applications, such as synchrotron radiation (SR), free-electron lasers (FEL) and solar plasma diagnostics.We will present our recent results on multilayer-coated beamline optics with high uniformity of the period (in the order of ± 0.5 %) along the entire length of 250 mm. We will also show some examples of highly reflective Al-based tri-component multilayers, which were fabricated in our laboratory and characterized by grazing x-ray reflectometry and with EUV radiation. These coatings were realized for various applications in the EUV range from 17 to 35 nm including a delay line project of FEL facility in Trieste and, very recently, the FSI (full Sun imager) and HRI (high-resolution imager) EUV telescopes of future Solar Orbiter space mission

Al-based multilayer coatings for space applications

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