This thesis treats the reflective and structural properties of multilayer structures. Soft X-ray multilayer mirrors intended as near-normal incidence reflective optics and polarizers in the water window (λ=2.4-4.4 nm) are the main focus. Such mirrors require multilayer periodicities between 1.2-2.2 nm, a large number ~600of multilayer periods (N), and atomically flat interfaces. Bi-metallic multilayers were deposited by dual-target magnetron sputtering on Si(001) Geometrical roughness and intermixing/interdiffusion at the interfaces were investigated in connection with the impact of ion-surface interactions during growth of Cr/Ti, Cr/Sc, and Ni/V multilayers. This was achieved by comparing multilayers grown with or without high-flux low energy (Eion<30 eV) ion assistance. The use of modulated ion assistance resulted in a substantial improvement of interface flatness and abruptness in each of theAb-initio calculations indicate that the stabilization of the amorphous layer structure is due to a lowering of the total energy of the system by eliminating high energy incoherent interfaces between crystalline Sc and Cr. Light element incorporation in Cr/Sc multilayers was investigated through residual gas pressure variation. It is shown that multilayers retain their structural and optical properties within the high vacuum range of 2×10-7-to-2×10-6 Torr. The incorporation of 34 at.% nitrogen at a higher residual gas pressure ( ~2×10-5 Torr) resulted in highly textured understoichiometricx/ScNy multilayers. As a result of nitrogen incorporation, interface widths as small as 0.29 nm, and near-normal incidence reflectivity enhancement (at λ=3.11 nm) by 100 % (compared to pure Cr/Sc multilayers) was achieved. Light element incorporation was also found to be advantageous for the thermal stability of the multilayers. In-situ hard X-ray reflectivity measurements performed during isothermal annealing in thex/ScNy are stable up to 350 °C. As an alternative route to metallic multilayers, single crystal CrN/ScN superlattices, grown by reactive sputtering in N atmosphere onto MgO(001), were also investigated. The superlattice synthesis at 735 °C, resulted in highly abrupt interfaces with minimal interface widths of 0.2 nm. As-deposited superlattices with only 61 periodsλ=3.11 nm as well as very high thermal stability up to 850 °C. / Denna avhandling behandlar syntes, analys, och materialvetenskap rörande så kallade multilagerspeglar för mjuk röntgenstrålning. Speglarna är lämpade som optiska komponenter för instrument såsom röntgenmikroskop i våglängdsområdet 2,4 nm till 4,4 nm, även kallat vattenfönstret. Tack vare de senaste decenniernas stora teknologiska och vetenskapliga framsteg i att framställa mycket intensiva källor för mjuk röntgenstrålning, såsom tex synkrotronljuskällor, frielektronlasrar, och plasmagenererade källor, är det nu tänkbart att utnyttja denna strålning till nya tillämpningar som tidigare inte varit möjliga. Några exempel är; röntgenmikroskopi av biologiska preparat med upplösning ca 1/100 av det som är möjligt med synligt ljus, fotolitografi av Det finns flera stora utmaningar för att lyckas tillverka multilagerspeglar. Först och främst måste man hitta materialkombinationer som ger upphov till reflektion i mellanytorna mellan materialen men som inte samtidigt absorberar all röntgenstrålning. Dessutom måste materialen gå att belägga på varandra i flera hundra tunna lager, vart och ett endast ca 1 nanometer tjockt, med en ytojämnhet om endast några tiondels nanometer. Den absoluta tjockleks precision i varje I det här arbetet har fyra olika typer av multilagerbeläggningar undersökts: krom/titan (Cr/Ti), krom/skandium (Cr/Sc), nickel/vanadin (Ni/V) samt kromnitrid/skandiumnitrid (CrN/ScN). Materialvalen har baserats på teoretiska beräkningar som visat att dessa materialsystem genererar mycket god reflektans i vattenfönstret. Varje kombination av metaller är optimal för en specifik våglängd och de individuella lagertjocklekarna måste optimeras teoretiskt för varje enskilt För Cr/Sc multilager har vi visat att lagren som beläggs har en oordnad, så kallad amorf, struktur mellan metallatomerna som har sitt ursprung i att multilagrets totala energi kan sänkas om mellanytor mellan kristallint Cr och kristallint Sc kan undvikas. Studier av effekterna av kväveupptag hos Cr/Sc multilagerspeglar under sputtringsprocessen har lett till ökad förståelse av materialsystemet. Till exempel har vi visat att kvävet framförallt binder till de inre regionerna av Sc och inte så mycket till Cr-lagren eller i mellanytorna. Med kväve i strukturen har vi gjort speglar som tål höga temperaturer, vilket är av stor betydelse för tillämpningar baserade högintensiva ljuskällor. Så kallade supergitter, dvs multilager

<p>A part of the Ph.D. project focused on growth and characterization of metal multilayers is presented in this licentiate thesis. The main interest in carrying out this research is to develop highly reflective normal-incidence condenser mirrors for soft X-ray microscopy studies in the water window (λ=2.4-4.2 nm) wavelength regime.</p><p>Transition metals like Sc, Ti V, etc. have been considered because of the presence of their 2p-absorption edges within the water window. An anomalous dispersion at absorption edges has been utilized to get enhanced reflectance of soft X-rays. Since a single surface exhibits a very poor X-ray reflectivity, Cr/Sc, Cr/Ti, and Ni/V multilayers were grown in order to coherently add many reflections from several interfaces. The selection of Cr and Ni, as spacer layer, was made on the basis of their X-ray optical contrasts with the above-mentioned transition metals. The multilayer design, i.e., the individual layer thicknesses and the total number of bilayers, directly influences the resultant reflectance and careful determination was therefore made with the aid of computer simulations.</p><p>All multilayers were grown on chemically cleaned Si substrates by ion-assisted dual target magnetron sputtering under high vacuum (~10^-7 Torr) conditions. The effect of low and high ion-flux bombardment of low energy (<50 eV) Ar ions, on growing surfaces was studied for all material systems. Furthermore, a two-stage deposition of each individual layer with modulated ion-energies was applied in order to obtain smooth and abrupt interfaces with as small intermixing as possible. Ion-surface interactions were also theoretically considered for estimating an appropriate ion-flux and ion-energy range desired for sufficient ad-atom mobilities.</p><p>X-ray reflectivity and transmission electron microscopy have been the main probes for multilayer characterization in this work. For the Cr/Ti multilayer designed for normal incidence and grown with optimized two-stage ion-energy modulation, a peak reflectance of 2.1% was achieved at the Ti-2p absorption edge (λ=2.74 nm). For a multilayer mirror designed for the Brewster angle a maximum reflectance of 4.3% was accomplished. These measurements were made at the synchrotron radiation source BESSY in Berlin. Specular reflectivity and diffuse scattering scans were utilized for quantitative and qualitative analysis of the vertical and lateral structure of the multilayers. At-wavelength measurements of a series of Cr/Ti multilayers revealed the accumulation of roughness with increasing number of bilayers (N>100) for this material system. Hard X-ray reflectivity and diffractometry were used for quality checks of the multilayers for rapid feedback to the deposition. In-situ annealing using hard X-ray reflectivity was also performed to assess the thermal stability of Cr/Ti multilayers. It was found that probably due to a strong thermal diffusion the degradation of multilayers (with bilayer period of 1.37 nm) in this material system occurs just above the growth temperature (~40°C). The accumulation of a low spatial frequency "waviness" with increasing number of layers in Cr/Ti multilayers was investigated by transmission electron microscopy. The influence of process conditions on multilayer structure with different periodicities was investigated by TEM analyses of a series of three samples for each of the above-mentioned material system. The Cr/Sc multilayers have shown the most flat and abrupt interface structure without any significant roughness evolution when grown with optimum process parameters.</p> / Report code: LiU-TEK-LIC-2005:48. On the day of the defence data the status of article I was: Accepted.

With the availability of high reflectivity multilayer mirrors and zone plate lenses, the EUV region (5nm - 40nm) of the electromagnetic spectrum is currently being explored for applications of nanoscale printing and imaging. Advances made in this area have consequences for many areas of science. Research for producing a compact, bright EUV source for laboratory use has gained momentum in recent years. For this study, EUV radiation is produced by irradiating target materials using a focused laser beam. Focused laser beam ionizes the target to create a hot, dense, pulsed plasma source, where emission is a result of the relaxation of excited levels. Spectroscopy is used as the main diagnostic to obtain the spectral signature of the plasma. Spectral characteristics are used to deduce the physical state of plasma, thus enabling the tuning of laser irradiance conditions to maximize the needed emission bandwidth. Various target materials are studied, as well as different target geometries, with spectroscopy below 200 nm on pulsed micro-plasmas being a particularly daunting task. Total range spectroscopy from 1 nm to greater than 1 micron is completed for tin-doped spherical droplet plasma source. Reliable plasma diagnostics require both accurate measurements and solid theoretical support in order to interpret the experimental results. Using existing 1D-hydrocode, temperature and density characteristics of the expanding plasma is simulated for any set of experimental conditions. Existing atomic codes written for calculating one-electron radial wavefunctions with LS-coupling scheme via Hartree-Fock method is used in order to gain details of the ion stages, populations, transitions, etc, contributing to the spectral data.

A part of the Ph.D. project focused on growth and characterization of metal multilayers is presented in this licentiate thesis. The main interest in carrying out this research is to develop highly reflective normal-incidence condenser mirrors for soft X-ray microscopy studies in the water window (λ=2.4-4.2 nm) wavelength regime. Transition metals like Sc, Ti V, etc. have been considered because of the presence of their 2p-absorption edges within the water window. An anomalous dispersion at absorption edges has been utilized to get enhanced reflectance of soft X-rays. Since a single surface exhibits a very poor X-ray reflectivity, Cr/Sc, Cr/Ti, and Ni/V multilayers were grown in order to coherently add many reflections from several interfaces. The selection of Cr and Ni, as spacer layer, was made on the basis of their X-ray optical contrasts with the above-mentioned transition metals. The multilayer design, i.e., the individual layer thicknesses and the total number of bilayers, directly influences the resultant reflectance and careful determination was therefore made with the aid of computer simulations. All multilayers were grown on chemically cleaned Si substrates by ion-assisted dual target magnetron sputtering under high vacuum (~10-7 Torr) conditions. The effect of low and high ion-flux bombardment of low energy (&lt;50 eV) Ar ions, on growing surfaces was studied for all material systems. Furthermore, a two-stage deposition of each individual layer with modulated ion-energies was applied in order to obtain smooth and abrupt interfaces with as small intermixing as possible. Ion-surface interactions were also theoretically considered for estimating an appropriate ion-flux and ion-energy range desired for sufficient ad-atom mobilities. X-ray reflectivity and transmission electron microscopy have been the main probes for multilayer characterization in this work. For the Cr/Ti multilayer designed for normal incidence and grown with optimized two-stage ion-energy modulation, a peak reflectance of 2.1% was achieved at the Ti-2p absorption edge (λ=2.74 nm). For a multilayer mirror designed for the Brewster angle a maximum reflectance of 4.3% was accomplished. These measurements were made at the synchrotron radiation source BESSY in Berlin. Specular reflectivity and diffuse scattering scans were utilized for quantitative and qualitative analysis of the vertical and lateral structure of the multilayers. At-wavelength measurements of a series of Cr/Ti multilayers revealed the accumulation of roughness with increasing number of bilayers (N&gt;100) for this material system. Hard X-ray reflectivity and diffractometry were used for quality checks of the multilayers for rapid feedback to the deposition. In-situ annealing using hard X-ray reflectivity was also performed to assess the thermal stability of Cr/Ti multilayers. It was found that probably due to a strong thermal diffusion the degradation of multilayers (with bilayer period of 1.37 nm) in this material system occurs just above the growth temperature (~40°C). The accumulation of a low spatial frequency "waviness" with increasing number of layers in Cr/Ti multilayers was investigated by transmission electron microscopy. The influence of process conditions on multilayer structure with different periodicities was investigated by TEM analyses of a series of three samples for each of the above-mentioned material system. The Cr/Sc multilayers have shown the most flat and abrupt interface structure without any significant roughness evolution when grown with optimum process parameters. / <p>Report code: LiU-TEK-LIC-2005:48. On the day of the defence data the status of article I was: Accepted.</p>

L’observation d’échantillons biologiques à une échelle nanométrique est actuellement un thème majeur pour la biologie. En particulier, la microscopie à rayons X dans la fenêtre de l’eau (entre les seuils d’absorption K-alpha de l’oxygène et du carbone, soit entre 2,4 et 4,4 nm de longueur d’onde) présente un intérêt remarquable car elle permet à la fois l’observation d’échantillons biologiques avec un fort contraste d’absorption naturel, mais également une haute résolution grâce à la courte longueur d’onde d’utilisation. Plusieurs microscopes basés sur des composants diffractifs ont d’ores et déjà été développés et ont montré une résolution allant jusqu’à 12 nm. Dans ce contexte, nous développons au Laboratoire Charles Fabry un microscope X plein champ à miroirs en incidence proche de la normale. Le schéma optique du microscope a dans un premier temps été étudié et optimisé. Il est basé sur un objectif de Schwarzschild, et dispose donc d’une longue distance de travail ce qui permettra de faciliter l’installation de l’échantillon à observer. Les miroirs doivent être traités avec un revêtement multicouche à très faible période à base de chrome et de scandium. Plusieurs systèmes multicouches à couches sub nanométrique ont été étudiés pour maximiser la réflectivité des revêtements à une longueur d’onde proche de 3,14 nm, parmi lesquels : Cr/Sc, Cr/B4C/Sc, CrN/Sc et CrN/B4C/Sc. Une réflectivité pic de plus de 23% a été mesurée pour un revêtement multicouche CrN/B4C/Sc à un angle d’incidence inférieur à 5°. / The observation of biological samples at a nanometer scale is currently a major topic for biology. In particular, X-ray microscopy in the water-window (between Oxygen and Carbon K-alpha edges, corresponding to a wavelength between 2.4 and 4.4 nm) is off remarkable interest since it enables the visualization of biological samples with a natural high absorption contrast and a high resolution thanks to the short working wavelength. Several such x-ray microscopes have already been developed and showed resolutions down to 12 nm. In this context, we develop at Laboratoire Charles Fabry a full field, near normal incidence mirror based X-ray microscope. The optical design of the microscope was studied and optimized in a first place. It is based on a Schwarzschild objective, with a rather long working distance so that the installation of the sample will be facilitated. The mirrors are to be coated with very short period multilayer coatings containing chromium and scandium. Several multilayer systems with sub-nanometer thick layers ere studied in order to obtain the highest reflectance possible near normal incidence at a wavelength near 3.14 nm. Those systems were Cr/Sc, Cr/B4C/Sc, CrN/Sc and CrN/B4C/Sc. A peak reflectance of 23% has been measured for CrN/B4C/Sc at an incidence angle lower than 5°.

Absorption plays a critical role in a variety of optical applications – sometimes it is desirable to minimize it as in optical fibers and waveguides, or to enhance it as in solar cells and photodetectors. We describe here a new optical scheme that controllably produces high optical absorption over a broad wavelength range (hundreds of nm) in systems that have low intrinsic absorption over the same range. This effect, 'coherent perfect absorption' or CPA, arises from a subtle interplay between interference and absorption of two beams incident on a weakly absorbing medium. In the first part of this study, we present an analytical model that captures the relevant physics of CPA in one-dimensional photonic structures. This model elucidates an absorption-mediated interference effect that underlies CPA – an effect that is normally forbidden in Hermitian systems, but is allowed when conservation of energy is violated due to the inclusion of loss. As a concrete example, we consider a Fabry-Pérot resonator containing a lossy dielectric and confirm this model through a computational study of a 1-micron-thick silicon layer in a cavity formed of dispersive mirrors with aperiodic multilayer design. We confirm that one may achieve 100% absorption in this thin silicon layer (whose intrinsic absorption is only ~ 3%) in the near-infrared. We then design two device models using few-micron-thick aperiodic planar dielectric mirrors and demonstrate (computationally, as well as experimentally) spectrally flat, coherently enhanced absorption at the theoretical limit in a 2-micron-thick film of polycrystalline silicon embedded in symmetric and asymmetric cavities. This coherent effect is observed over an octave-spanning wavelength range of ~800 – 1600 nm utilizing incoherent light in the near-infrared, exploiting mirrors that have wavelength-dependent reflectivity devised to counterbalance the decline in silicon's intrinsic absorption at long wavelengths. We anticipate that the design principles established here may be extended to other materials, broader spectral ranges, and large surface areas. Finally, we study the effect of the angle of incidence on CPA in planar structures. The results of this study point to a path for realizing CPA in such systems continuously over large bandwidths.

Les plus brefs flashs de lumière qui puissent être produits en laboratoire actuellement ont des durées de quelques dizaines d’attosecondes (1 as = 10-18 s), et ne peuvent être créés que dans le domaine extrême-ultraviolet (XUV). Le développement de composants optiques capables de contrôler et de mettre en forme ce rayonnement attoseconde est crucial pour permettre à ces impulsions de se généraliser. Cette thèse porte donc sur l’étude et la réalisation de tels composants.Les impulsions attosecondes ont la particularité de comporter une dérivée de fréquence intrinsèque au processus utilisé pour leur génération. Cela a pour effet d’augmenter leur durée. Nous avons donc développé des miroirs multicouches capables d’induire une dérive de fréquence opposée sur les impulsions s’y réfléchissant, permettant ainsi de les compresser. En caractérisant les impulsions attosecondes réfléchies par ces miroirs, nous avons pour la première fois observé une telle compression des impulsions attosecondes. Nous avons également développé des miroirs multicouches théoriquement capables de compresser des impulsions sous la barre symbolique des 50 as, soit en dessous du record actuel de durée d’une impulsion lumineuse.La mesure de ces impulsions requiert leur focalisation dans un spectromètre. Or les miroirs focalisants généralement utilisés peuvent très rapidement introduire des aberrations géométriques. A l’aide de simulations numériques et d’une étude analytique, nous avons montré que ces aberrations pouvaient très fortement déformer la structure spatio-temporelle des impulsions attosecondes, provoquant une augmentation de leur durée. Enfin, nous avons montré que ces effets n’étaient pas pris en compte par les techniques actuelles de caractérisation d’impulsions attosecondes, cela pouvant amener à mesurer une impulsion attoseconde plus courte qu’elle ne l’est en réalité. / The shortest flashes of light ever produced so far have durations of a few tens of attoseconds (1 as = 10-18 s), and can only be generated in the extreme ultraviolet spectral range (XUV). Developing optical components able to control and shape such attosecond radiation is crucial to generalize the use of these light pulses. This is the topic of this work.Attosecond pulses happen to be chirped due to the physical process used to generate them. This phenomenon leads to an increase in their duration. Consequently, we developed inversely chirped multilayer mirrors, allowing one to compress the pulses during their reflection off the mirrors. By measuring these reflected pulses, we observed for the first time such a compression of attosecond pulses. Moreover, we developed another set of multilayer mirrors theoretically able to compress pulses below 50 as. That is below the current pulse duration record.Furthermore, the measurement of these pulses requires that they be focussed into a spectrometer. However, typically used focusing mirrors can add geometric aberrations. By the use of numerical simulations and thanks to an analytic study, we showed that these aberrations could strongly distort the spatio-temporal structure of the pulses, and increase their duration. Moreover, we showed that this phenomenon was not taken into account by current attosecond pulse characterization techniques. This could lead to determining the pulse duration to be shorter than it actually is.