This thesis summarizes the present status of the nanofabrication of diffractive optics, i.e. zone plates, and test objects for soft x-ray microscopy at KTH. The emphasis is on new and improved fabrication processes for nickel and germanium zone plates. A new concept in which nickel and germanium are combined in a zone plate is also presented. The main techniques used in the fabrication are electron beam lithography for the patterning, followed by plasma etching and electroplating for the structuring of the optical materials. The process for fabricating nickel zone plates has been significantly improved. The reproducibility of the electroplating step has been increased by the implementation of an in-situ rate measurement and an end-point detection method. We have also shown that pulse plating can be used to obtain zone plates with a uniform height profile. New plating mold materials have been introduced and electron-beam curing of the molds has been investigated and implemented to increase their mechanical stability so that pattern collapse in the electroplating step can be avoided. The introduction of cold development has improved the achievable resolution of the process. This has enabled the fabrication of zone plates with outermost zone widths down to 16 nm. The nickel process has also recently been adapted to fabrication of gold structures intended for test objects and hard x-ray zone plates. For the fabrication of germanium zone plates we developed a highly anisotropic plasma-etch process using Cl2 feed and sidewall passivation. Germanium zone plates have been fabricated with zone widths down to 30 nm. The diffraction efficiency is comparable to that of nickel zone plates, but the process does not involve electroplating and thus has for potential for highyield fabrication. The combination of nickel and germanium is a new fabrication concept that provides a means to achieve high diffraction efficiency even for thin nickel. The idea is to fabricate a nickel zone plate on a germanium film. The nickel zone plate itself is then used as etch mask for a highly selective CHF3- plasma etch into the germanium layer. Proof of principle experiments showed an efficiency increase of about a factor of two for nickel zone plates with a 50- nm nickel thickness. / QC 20100728

<p>Scanning transmission x-ray microscopes (STXM) focus monochromatic x-rays into an intense sub-30 nm diameter spot. Samples are then positioned at the focal plane and raster scanned through the spot while the transmitted x-rays are acquired to build up images at x-ray photon energies. In addition, x-ray absorption spectroscopy (XAS) can be performed by recording image sequences over a photon energy range of interest. STXMs excel at characterizing thin sections of inhomogeneous soft matter with their combination of high spatial (<30 nm) and photon energy (<0.1 eV) resolution. However, the overarching theme of this thesis is to apply the intense, tightly focused spot of x-rays to induce spatially resolved chemical and physical changes, and directly pattern materials, primarily thin polymer films. The irradiated areas are then investigated using several types of microscopy (scanning transmission x-ray, atomic force, scanning electron) and XAS. The experiments cover three broad areas: i) Nanofabrication; realization of the smallest possible feature sizes, and fabrication schemes unique to focused x-rays with applications including nanofluidics. ii) Radiation chemistry and physics; investigating the mechanisms of radiation-induced processes such as bond formation/loss, morphological change, carbon contamination, and temperature increase. iii) X-ray optics; the spatial distribution of x-rays at a focal plane can be recorded in a thin polymer film and later read out using an atomic force microscope. Applications include feedback for optics fabrication and enhanced image processing, the ultimate goal being increased spatial resolution.</p> / Doctor of Philosophy (PhD)

The X-ray optics of synchrotron radiation beamlines are considered in this paper. The characteristics of synchrotron radiation which make it the premier source of light for studies in many regions of the electromagnetic spectrum are given. A chapter is devoted to the collimating, focusing and monochromating optics of two X-ray diffraction beamlines at the National Synchrotron Light Source. The beamlines are operated by the Naval Research Laboratory (NRL) and the Oak Ridge National Lab (ORNL). The major optical components of these beamlines are reviewed in regards to their function and their flexibility. A detailed analysis is performed on the NRL X-ray collimating mirror. The mirror is treated as an elastically bent beam. Deflection and slope error equations are developed which relate the shape of the bent mirror to its ideal surface. Visible light diffraction patterns collected from the mirror helped to establish operating conditions which provide good collimation. When the observed patterns are wed to the theoretical calculations, estimates of the average figure error are made. Finally, the effect of a highly collimated synchrotron beam on the reproducibility of the integrated intensities from polycrystalline materials is considered. The calculations show that except for the most fine grained materials, representative intensity measurements can only be made when the sample is permitted to move. / M.S.

Soft x-ray microscopes routinely perform high-resolution 3D imaging of biological cells in their near-native environment with short exposure times at synchrotron radiation facilities. Some laboratory-sized microscopes are aiming to make this imaging technique more accessible to a wider scientific community. However, these systems have been hampered by source instabilities hindering routine imaging of biological samples with short exposure times. This Thesis presents work performed on the Stockholm laboratory x-ray microscope. A novel heat control system has been implemented, improving the stability of the laser-produced plasma source. In combination with recent upgrades to the imaging system and an improved cryofixation method, the microscope now has the capability to routinely produce images with 10-second exposure time of cryofixed biological samples. This has allowed for tomographic imaging of cell autophagy and cell-cell interactions. Furthermore, a numerical 3D image formation model is presented as well as a novel reconstruction approach dealing with the limited depth of focus in x-ray microscopes. / <p>QC 20170505</p>

Este trabalho é uma contribuição às análises de forças de aprisionamento óptico exercidas sobre partículas esféricas por superposições discretas de feixes de Bessel. Um estudo teórico-numérico foi realizado no regime de óptica geométrica, completando as pesquisas já realizadas com tais feixes e no caso escalar, tanto no regime de Rayleigh quanto através de um formalismo eletromagnético completo. Investigam-se padrões longitudinais de intensidade de possível interesse prático, com potenciais de fornecer múltiplas armadilhas ópticas simultâneas utilizando dois métodos de análise. O primeiro parte da observação de que no regime paraxial todos os raios associados aos feixes se encontram quase paralelos entre si quando se toma como aproximação uma superposição de raios paralelos que incidem completamente sobre um hemisfério do espalhador. Tal método, entretanto, é naturalmente restrito pelas forças transversais. O segundo, que torna mais confiáveis e precisas as predições acerca da componente longitudinal de força, adota procedimentos mais robustos que levam em consideração tanto a contribuição da pressão de radiação (força de espalhamento) quanto a força gradiente devido a gradientes locais de intensidade associados a raios não-paralelos. Assim, acredita-se que este trabalho traz como contribuição um reforço a esta classe específica e promissora de feixes não difrativos como feixes de luz interessantes para aplicações em aprisionamento e micromanipulação óptica. / This work is a contribution to the analyses of optical trapping forces exerted on spherical particles by discrete superpositions of Bessel beams. A theoretical-numerical study has been carried out in the ray optics regime, completing the pre-existing research performed with such beams, in the scalar case, both in the Rayleigh regime and through a complete electromagnetic formalism. We investigate longitudinal intensity patterns of possible practical interest with potential to provide multiple simultaneous optical traps, by using two methods of analysis. The first assumes that, in the paraxial regime, all rays associated to the beams are almost parallel to each other, taking a superposition of parallel rays that are completely incident on a hemisphere of the scatterer as a suitable approximation. Such a method, however, is naturally constrained by the transverse forces. The second one, which makes the predictions about the longitudinal force component more reliable and accurate, adopts more robust procedures that take into consideration the contribution of the radiation pressure (scattering force) as well as the gradient force due to local intensity gradients associated to non-parallel rays. Thus it is hoped that this work will contribute to reinforce this specific and promising class of non-diffractive beams as interesting light beams for applications in optical trapping and micromanipulation.

Thin films and multilayers are widely used in many applications, ranging from X-ray optics to microelectronic devices. In service, the X-ray optics elements are exposed to the X-ray beam, which heats up the structure resulting in the thermal deformations, and consequently in distortions of the reflective surface. In addition, the excessive heating may activate interdiffusion in the multilayers coatings and result in degradation of their reflective performance and even film cracking. Therefore, analysis of the thermally-induced deformations and stresses in the X-ray optical elements is important. The presented work is organized in two major parts. The first part examines formation of the peculiar periodic crack patterns observed in the thermally loaded Mo/Si multilayers. Film stress evolution during thermal cycling of the multilayers on Si substrate is analyzed. Results of the high-speed microscopic observations of crack propagation in the annealed Mo/Si multilayers are presented. The observations provide experimental evidence of the mechanism underlying formation of the periodic crack patterns. In the second part, thermal deformations and the resulting surface curvature changes in the X-ray optics elements are analyzed. Finite element modeling is used to assess the potential to thermally control curvature in the X-ray mirrors consisting of the Mo/Si multilayers on a Si substrate. Influence of heating due to the X-ray beam irradiation on thermal deformations in the X-ray mirror bonded to a thick substrate is analyzed in-depth. The detailed consideration includes analysis of the thermal and structural mechanics simulations. Based on simulations of different model configurations, influence of structural composition on thermal distortions of the optics elements is addressed. Results of this analysis can be used to mitigate distortions of the X-ray optics caused by the X-ray beam and provide basis for further studies of thermally controlling surface curvature in the optical elements.

Soft x-ray microscopy in the water-window (λ = 2.28 nm – 4.36 nm) is based on zone-plate optics and allows high-resolution imaging of, e.g., cells and soils in their natural or near-natural environment. Three-dimensional imaging is provided via tomographic techniques, soft x-ray cryo tomography. However, soft x-ray microscopes with such capabilities have been based on large-scale synchrotron x‑ray facilities, thereby limiting their accessibility for a wider scientific community. This Thesis describes the development of the Stockholm laboratory soft x-ray microscope to three-dimensional cryo tomography and to new optics-based contrast mechanisms. The microscope relies on a methanol or nitrogen liquid-jet laser-plasma source, normal-incidence multilayer or zone-plate condenser optics, in-house fabricated zone-plate objectives, and allows operation at two wavelengths in the water-window, λ = 2.48 nm and λ = 2.48 nm. With the implementation of a new state-of-the-art normal-incidence multilayer condenser for operation at λ = 2.48 nm and a tiltable cryogenic sample stage the microscope now allows imaging of dry, wet or cryo-fixed samples. This arrangement was used for the first demonstration of laboratory soft x-ray cryo microscopy and tomography. The performance of the microscope has been demonstrated in a number of experiments described in this Thesis, including, tomographic imaging with a resolution of 140 nm, cryo microscopy and tomography of various cells and parasites, and for studies of aqueous soils and clays. The Thesis also describes the development and implementation of single-element differential-interference and Zernike phase-contrast zone-plate objectives. The enhanced contrast provided by these optics reduce exposure times or lowers the dose in samples and are of major importance for harder x-ray microscopy. The implementation of a high-resolution 50 nm compound zone-plate objective for sub-25-nm resolution imaging is also described. All experiments are supported by extensive numerical modelling for improved understanding of partially coherent image formation and stray light in soft x-ray microscopes. The models are useful tools for studying effects of zone plate optics or optical design of the microscope on image formation and quantitative accuracy in soft x-ray tomography. / QC 20110221

Diffractive zone-plate lenses are widely used as optics in high-resolution x-ray microscopes. The achievable resolution in such microscopes is presently not limited by the x-ray wavelength but by limitations in zone-plate nanofabrication. Thus, for the advance of high-resolution x-ray microscopy, progress in zone-plate nanofabrication methods are needed.   This Thesis describes the development of new nanofabrication processes for improved x-ray zone-plate optics. Cold development of the electron-beam resist ZEP7000 is applied to improve the resolution of soft x-ray Ni zone plates. The influence of developer temperature on resist contrast, resolution, and pattern quality is investigated. With an optimized process, Ni zone plates with outermost zone widths down to 13 nm are demonstrated. To enhance the diffraction efficiency of Ni zone plates, the concept of Ni-Ge zone plates is introduced. The applicability of Ni-Ge zone plates is first demonstrated in a proof-of-principle experiment, and then extended to cold-developed Ni zone plates with outermost zone widths down to 13 nm. For 15-nm Ni-Ge zone plates a diffraction efficiency of 4.3% at a wavelength of 2.88 nm is achieved, which is about twice the efficiency of state-of-the-art 15-nm Ni zone plates. To further increase both resolution and diffraction efficiency of soft x-ray zone plates, a novel fabrication process for W zone plates is developed. High resolution is provided by salty development of the inorganic electron-beam resist HSQ, and cryogenic RIE in a SF6 plasma is investigated for high-aspect-ratio W structuring. We demonstrate W zone plates with 12-nm outermost zone width and a W height of 90 nm, resulting in a 30% increase in theoretical diffraction efficiency compared to 13-nm efficiency-enhanced Ni-Ge zone plates. In addition to soft x-ray zone plates, some lenses for hard x-ray free-electron-laser applications were also fabricated during this Thesis work. Fabrication processes for the materials W, diamond, and Pt were developed. We demonstrate Pt and W-diamond zone plates with 100-nm outermost zone width and respective diffraction efficiencies of 8.2% and 14.5% at a photon energy of 8 keV. / QC 20111114

Este trabalho é uma contribuição às análises de forças de aprisionamento óptico exercidas sobre partículas esféricas por superposições discretas de feixes de Bessel. Um estudo teórico-numérico foi realizado no regime de óptica geométrica, completando as pesquisas já realizadas com tais feixes e no caso escalar, tanto no regime de Rayleigh quanto através de um formalismo eletromagnético completo. Investigam-se padrões longitudinais de intensidade de possível interesse prático, com potenciais de fornecer múltiplas armadilhas ópticas simultâneas utilizando dois métodos de análise. O primeiro parte da observação de que no regime paraxial todos os raios associados aos feixes se encontram quase paralelos entre si quando se toma como aproximação uma superposição de raios paralelos que incidem completamente sobre um hemisfério do espalhador. Tal método, entretanto, é naturalmente restrito pelas forças transversais. O segundo, que torna mais confiáveis e precisas as predições acerca da componente longitudinal de força, adota procedimentos mais robustos que levam em consideração tanto a contribuição da pressão de radiação (força de espalhamento) quanto a força gradiente devido a gradientes locais de intensidade associados a raios não-paralelos. Assim, acredita-se que este trabalho traz como contribuição um reforço a esta classe específica e promissora de feixes não difrativos como feixes de luz interessantes para aplicações em aprisionamento e micromanipulação óptica. / This work is a contribution to the analyses of optical trapping forces exerted on spherical particles by discrete superpositions of Bessel beams. A theoretical-numerical study has been carried out in the ray optics regime, completing the pre-existing research performed with such beams, in the scalar case, both in the Rayleigh regime and through a complete electromagnetic formalism. We investigate longitudinal intensity patterns of possible practical interest with potential to provide multiple simultaneous optical traps, by using two methods of analysis. The first assumes that, in the paraxial regime, all rays associated to the beams are almost parallel to each other, taking a superposition of parallel rays that are completely incident on a hemisphere of the scatterer as a suitable approximation. Such a method, however, is naturally constrained by the transverse forces. The second one, which makes the predictions about the longitudinal force component more reliable and accurate, adopts more robust procedures that take into consideration the contribution of the radiation pressure (scattering force) as well as the gradient force due to local intensity gradients associated to non-parallel rays. Thus it is hoped that this work will contribute to reinforce this specific and promising class of non-diffractive beams as interesting light beams for applications in optical trapping and micromanipulation.

Eine grundlegende Schwierigkeit in der Röntgenoptik liegt in der Bereitstellung geeigneter Optiken. So ist aufgrund der schwachen Wechselwirkung der Röntgenstrahlung mit Materie der Einsatz brechender Optiken nicht sinnvoll, und es wird auf alternative Konzepte wie Röntgenwellenleiter zurückgegriffen. Röntgenwellenleiter sind nicht-dispersive strahlführende Optiken, welche die Kohärenz der Röntgenstrahlung filtern und als quasi-Punktquellen fungieren. Hierbei wird der Röntgenstrahl in einer oder zwei Dimensionen räumlich beschränkt, wobei der Wellenlängenbereich der Röntgenstrahlung eine Abmessung im sub-100 nm-Bereich erfordert. In der vorliegenden Arbeit wurde ein Verfahren etabliert, mit welchem die Herstellung von Wellenleiterkanälen im sub-50 nm-Bereich in Silizium gelingt. Die Prozessierung basiert hierbei auf einem Schema aus elektronenstrahllithographischer Belichtung, Reaktivem Ionenätzen und Wafer bonding. Das Verfahren ist variabel in Bezug auf verschiedene Wellenleitergeometrien, beispielsweise gekreuzte Wellenleiter und Kanalwellenleiter, ist auf alternative Materialien übertragbar, und erlaubt die Strahlführung auf in einer Dimension gekrümmten Pfaden. Die im Rahmen der vorliegenden Arbeit hergestellten Wellenleiter wurden erfolgreich an verschiedenen Synchrotron-Messplätzen eingesetzt und ihre Fernfelder charakterisiert, und der kohärente Wellenleiterstrahl wurde in der Röntgenmikroskopie und der holographischen Bildgebung eingesetzt. Es finden sich sowohl für die Quellgröße der Wellenleiter als auch für die Auflösung in der Bildgebung Werte im sub-50 nm-Bereich.