Littérature scientifique sur le sujet « Nanoscale multilayer mirror »

AbstractNanoscale multilayers of ZnS/Ag/ZnS were deposited on Corning glass substrates at different substrate temperatures. The depositions were carried out in high vacuum using electron beam deposition technique at 20, 60, 100 and 150 °C, respectively. The optical and electrical performance of each single layer and the accomplished ZnS/Ag/ZnS multilayer system were characterized using spectroscopic ellipsometry analysis, XRD and finally AFM. Based on these analyses and associated theories, such as the characteristic matrix theory, the optimized multilayer system was speculated and tested. Crystallographic structures of the films were studied by X-ray diffraction. In addition to X-ray diffraction, morphological characterizations were carried out by AFM in order to observe the deposited particle size, packing and roughness of the films. The optimum performance was achieved at the substrate temperature of 60 °C.

Extreme ultraviolet (XUV) and X-ray free-electron lasers enable new scientific opportunities. Their ultra-intense coherent femtosecond pulses give unprecedented access to the structure of undepositable nanoscale objects and to transient states of highly excited matter. In order to probe the ultrafast complex light-induced dynamics on the relevant time scales, the multi-purpose end-station CAMP at the free-electron laser FLASH has been complemented by the novel multilayer-mirror-based split-and-delay unit DESC (DElay Stage for CAMP) for time-resolved experiments. XUV double-pulses with delays adjustable from zero femtoseconds up to 650 picoseconds are generated by reflecting under near-normal incidence, exceeding the time range accessible with existing XUV split-and-delay units. Procedures to establish temporal and spatial overlap of the two pulses in CAMP are presented, with emphasis on the optimization of the spatial overlap at long time-delays via time-dependent features, for example in ion spectra of atomic clusters.

Short-period multilayer mirrors are used in wavelength-dispersive x-ray fluorescence to extend the wavelength range available with naturally occurring Bragg-crystals. W/Si multilayer mirrors with a period of 2.5 nm are used to reflect and disperse elements in the O-Kα–Al-Kα range. However, the reflectance is far from theoretical due to nanoscale W-Si intermixing and formation of WSix. In this work, B4C diffusion barriers were applied in sputter deposited 2.5 nm W/Si multilayers to inhibit W–Si interaction. A peak reflectance of 45% at 9.7° grazing was measured at a wavelength of 0.834 nm—the highest reported in the literature so far. Diffuse scattering measurements revealed no change in interfacial roughness when applying B4C barriers compared to W/Si. A hybrid grazing incidence x-ray reflectivity and x-ray standing wave fluorescence analysis revealed an increase in W concentration of the absorber layer after the application of B4C barriers. Chemical analysis suggests a partial replacement of W silicide bonds with W carbide/boride bonds from the B4C barrier. The formed WxBy and WxCy instead of WxSiy is hypothesized to increase reflectance at 0.834 nm due to its higher W atomic density.

The rapid growth of nanotechnology has increased the need for fast nanoscale imaging. X-ray free electron laser (XFEL) facilities currently provide such coherent sources of directional and high-brilliance X-ray radiation. These facilities require large financial investments for development, maintenance, and manpower, and thus, only a few exist worldwide. In this article, we present an automated table-top system for XUV coherent diffraction imaging supporting the capabilities for multispectral microscopy at high repetition rates, based on laser high harmonic generation from gases. This prototype system aims towards the development of an industrial table-top system of ultrafast soft X-ray multi-spectral microscopy imaging for nanostructured materials with enormous potential and a broad range of applications in current nanotechnologies. The coherent XUV radiation is generated in a semi-infinite gas cell via the high harmonic generation of the near-infrared femtosecond laser pulses. The XUV spectral selection is performed by specially designed multilayer XUV mirrors that do not affect the XUV phase front and pulse duration.

AbstractThe large surface area of porous silicon provides numerous sites for many potential species to attach, which makes it an ideal host for sensing applications. The average pore size can be easily adjusted to accommodate either small or large molecular species. When porous silicon is fabricated into a structure consisting of two high reflectivity multilayer mirrors separated by an active layer, a microcavity is formed. Multiple narrow and visible luminescence peaks are observed with a full width at half maximum value of 3 nm. The position of these peaks is extremely sensitive to small changes in refractive index, such as that obtained when a biological object is attached to the large internal surface of porous silicon. We demonstrate the usefulness of this microcavity resonator structure as a DNA optical biosensor which displays appropriate sensitivity, selectivity, and response speed. A probing strand of DNA is initially immobilized in the porous silicon matrix, and then subsequently exposed to its sensing complementary DNA strand. Red-shifts in the luminescence spectra are observed and detected for various DNA concentrations. The spectral shifts confirm successful recognition and binding of DNA molecules within the porous structure. Detailed device fabrication procedures and the results of extensive testing will be presented. The detection scheme has also been extended to include the detection of viral DNA, proteins, and potentially bacteria. This work will lead to the development of a “smart bandage”, where the detection of bacteria or viruses can be diagnosed and an antibiotic treatment can be recommended.

La FCI (fusion par confinement inertiel) est une voie privilégiée pour accéder expérimentalement aux conditions extrêmes de la matière, via l'implosion d'une cible par laser. Pour caractériser la symétrie d'implosion, un microscope de résolution micrométrique, opérant dans le domaine des rayons X durs, est développé par le CEA (Commissariat à l'énergie atomique). TXI (Toroidal X-ray Imager) qui sera installé au NIF (National Ignition Facility) est un diagnostic X de type Wolter, où les miroirs coniques sont remplacés par des miroirs toriques. Il est également un diagnostic multicanal, fonctionnant à un angle de rasance nominal de 0.6°, et permettant d'imager des énergies de 8.7 keV, 13 keV et 17.5 keV. Les épaisseurs requises de revêtements multicouches doivent être de plus en plus fines pour imager ces énergies. Différentes formules de multicouches (alternances de deux matériaux dont la période totale permet de réfléchir une certaine longueur d'onde, conformément à la loi de Bragg) ont été optimisés, afin de satisfaire le cahier des charges de TXI. La réponse optique de l'instrument a été simulée à l'aide d'un logiciel de tracé de rayon. Les revêtements ont ensuite été réalisés par pulvérisation cathodique. Pour la suite de la thèse, une pré-étude sur la conception d'un imageur fonctionnant jusqu'à 60 keV a été menée, ainsi qu'une pré-étude sur la technologie HiPIMS (High Power Impulse Magnetron Sputtering) pour en étudier les bénéfices sur la qualité des films minces
Inertial Confinement Fusion (ICF) is a preferred experimental approach to access extreme matter conditions, through the implosion of a laser-driven target. To characterize the implosion symmetry, a micrometer-resolution microscope, operating in the hard X-ray range, is being developed by the CEA (Commissariat à l'énergie atomique). TXI (Toroidal X-ray Imager), which will be installed at the NIF (National Ignition Facility), is a Wolter-type X-ray diagnostic where conical mirrors are replaced by toroidal mirrors. It is also a multi-channel diagnostic, operating at a nominal grazing angle of 0.6°, allowing imaging at 8.7 keV, 13 keV, and 17.5 keV. The required thicknesses of the multilayer coatings must become increasingly thin to image these energies. Different multilayer formulas (alternating two materials whose total period allows reflection of a certain wavelength, according to Bragg's law) have been optimized to meet TXI's specifications. The instrument's optical response was simulated using ray-tracing software. The coatings were then produced by sputtering deposition. For the next phase of the thesis, a preliminary study was conducted on designing an imager capable of operating up to 60 keV, as well as a pre-study on HiPIMS (High Power Impulse Magnetron Sputtering) technology to assess its benefits for thin-film quality

One of the many technology areas that lie on the critical-path to the success of soft X-ray projection lithography (SXPL) is the fabrication and metrology of aspheric mirrors. I will review the progress of our collaboration with a number of companies to determine if the mirror fabrication and metrology technologies can be developed so that SXPL can meet the early next century demand for 0.1 μm design rule devices. The figure and finish tolerances for these mirrors are well beyond the current state-of-the-art for aspheres and even beyond industry's capability to fabricate spheres. To achieve the desired imaging capability will require mirrors with subnanometer figure errors over the full spatial frequency bandwidth, from 10 nm to 250 mm. Although exact full bandwidth tolerances have not been determined, we have estimated that the nanoscale rms roughness (as measured over a bandwidth of 10 nm to 1.0 μm) must be less than 0.1 - 0.2 nm so that high reflectivity multilayers can be attained. Specifications for the figure errors of a 5X reduction system being developed by GCA/Tropel range from 1.0 to 3.0 nm PV (depending on the mirror) for a 36 term Zernike polynomial fit. Although we have not yet estimated the specification for spatial frequencies between 1.0 μm and 25 mm, there is evidence that they could have a significant effect on imaging performance at X-ray wavelengths near 14 nm.1