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This chapter reviews progress both in the fabrication of multilayer zone plate optics for focusing X-rays, as well as in imaging experiments using these optics. The fabrication based on pulsed laser deposition is accompanied by analytical and numerical treatment of X-ray propagation to control volume diffraction effects. On the imaging side, different schemes are presented; these include scanning-scattering with focused X-rays, holography, as well as recent advances in lens-enhanced phase-reconstruction.

The influence of a thin polycarbonate de-adhesion layer on the hydrogen concentration is studied on 30 nm vanadium films deposited on glass substrates, using electrochemical hydrogenography in an optical microscopy and scanning tunneling microscopy. It is shown that the optical reflection provides information about the de-adhesion morphology (buckles) while the optical transmission signal gives information about concentration and film thickness changes. Artificially patterned samples allow simultaneous studying adhered and de-adhered film parts, for similar mean concentrations. The optical data clearly show a different hydrogen behavior of the two parts. Data interpretation suggests higher local hydrogen content in the adhered film parts than for the detached films parts. Strong changes in the optical transmission of the adhered film parts can be attributed to strong morphological changes at the film surface. These changes are mainly attributed to grain sliding processes in the vanadium film.

In-situ transmission electron microscopy is used to investigate crack propagation parallel to the interfaces of a Ti/ZrO 2 multilayer. The cracks propagate along the middle of the 100 nm thick polycrystalline Ti layers, causing extensive dislocation activity, void coalescence, and crack bridging. The plastic zone size has been determined from the range of dislocation activity and agrees well with estimates of the toughness obtained from the measured crack tip opening displacement. The toughness is much smaller than in bulk Ti, which we attribute to the constraint on dislocation activity and cropping of the plastic zone by the small Ti layer dimensions.

An efficient way for minimizing phonon thermal conductivity in solids is to nanostructure them by means of reduced phonon mean free path, phonon scattering and phonon reflection at interfaces. A sophisticated approach toward this lies in the fabrication of thin multilayer films of different materials. In this paper, we show by femtosecond-pump-probe reflectivity measurements that in different multilayer systems with varying acoustic mismatch (consisting of metals, semiconductors, oxides and polymers), oscillations due to phonon localization can be observed. For the growth of multilayer films with well-defined layer thicknesses, we used magnetron sputtering, evaporation and pulsed laser deposition. By altering the material combinations and reducing the layer thicknesses down to 3 nm, we observed different mechanisms of phonon blocking, reaching in the frequency regime up to 360 GHz.

Multilayer zone plates can be used for holographic imaging without an order-sorting aperture., This article describes holographic imaging experiments using a hard X-ray multilayer zone plate (MZP) with an outermost zone width of 10 nm at a photon energy of 18 keV. An order-sorting aperture (OSA) is omitted and emulated during data analysis by a ‘software OSA’. Scanning transmission X-ray microscopy usually carried out in the focal plane is generalized to the holographic regime. The MZP focus is characterized by a three-plane phase-retrieval algorithm to an FWHM of 10 nm.

Hard x-ray imaging methods are routinely used in two and three spatial dimensions to tackle challenging scientific questions of the 21st century, e.g. catalytic processes in energy research and bio-physical experiments on the single-cell level [1–3]. Among the most important experimental techniques are scanning SAXS to probe the local orientation of filaments and fluorescence mapping to quantify the local composition. The routinely available spot size has been reduced to few tens of nanometres; but the real-space resolution of these techniques can degrade by (i) vibration or drift, and (ii) spreading of beam damage, especially for soft condensed matter on small length scales. We have recently developed new Multilayer Zone Plate (MZP) optics for focusing hard (14 keV) and very hard (60 keV to above 100 keV) x-rays down to spot sizes presumably on 5 or 10nm scale. Here we report on recent progress on a new MZP based sample scanner, and how to tackle beam damage spread. The Eiger detector synchronized to a piezo scanner enables to scan in a 2D continuous mode fields of view larger than 20μm squared, or for high resolution down to (virtual) pixel sizes of below 2nm, in about three minutes for 255×255 points (90 seconds after further improvements). Nano-SAXS measurements with more than one million real-space pixels, each containing a full diffraction image, can be carried out in less than one hour, as we have shown using a Siemens star test pattern.

X-Ray Microscopy Conference 2016, XRM 2016, Oxford, UK, 15 Aug 2016 - 19 Aug 2016; Journal of physics / Conference Series 849, 012049 (2017). doi:10.1088/1742-6596/849/1/012049, With Pulsed Laser Deposition, Multilayer Zone Plates can be fabricated to focus hard x-ray beams into 2D spots smaller than 10 nm. To put these optics into use for imaging applications, we have commissioned a new dedicated sample tower as a high-resolution module for the GINIX instrument, stationed at the P10 beamline at PETRA III. Here we summarise the motorisation and show first imaging benchmark results obtained with a "traditional" Fresnel Zone Plate. The first 2D continuous STXM scan using the new EigerX 4M detector at full 750 Hz speed is shown: a field of view of roughly about 1 μm squared has been recorded with 255 × 255 images within 96 seconds., Published by IOP Publ., Bristol

Advances in X-Ray/EUV Optics and Components XII : [Proceedings] - SPIE, 2017. - ISBN 97815106122979781510612303 - doi:10.1117/12.2271139 Advances in X-Ray/EUV Optics and Components XII, San Diego, United States, 6 Aug 2017 - 10 Aug 2017; SPIE 6 pp. (2017). doi:10.1117/12.2271139, Penetration lengths in the millimetre range make hard x-rays above 60 keV a well-suited tool for non-invasive probing of small specimens buried deep inside their surroundings, and enable studying individual components inside assembled, complex devices (solar cells, batteries etc.). The real-space resolution of typical imaging modalities like fluorescence mapping, scanning SAXS and WAXS depend on the available beam size. Although routine in the 5–25keV regime [1-4], spot sizes below 50nm are very challenging at x-ray energies above 50 keV: Compound refractive lenses lack in refractive power, the multilayer thickness of coated mirrors is bounded by interfacial diffusion, and lithographic Fresnel Zone Plates loose their efficiency in the two-digit keV regime. Multilayer Laue Lenses and Multilayer Zone Plates (MZP) are promising candidates for high-keV focusing to small spot sizes; compared to Fresnel Zone Plates, the aspect ratio comparing outermost layer width (~focal spot size) to optical thickness (efficiency) is virtually unlimited by the fabrication. Using Pulsed Laser Deposition on a rotating wire (several millimetre long), we have fabricated an MZP with 10nm outermost zone widths and optical thickness of 30 μm(optimum phase shift at 60 keV), yielding an unprecedented ultra-high aspect ratio of 1:3000 (outermost zone width compared to optical thickness). We present experimental results obtained at ESRF’s high energy beamline ID31, where for the first time scanning experiments with real-space resolutions below 50nm even at x-ray energies ranging from 60 keV to above 100 keV have been achieved., Published by SPIE

During growth of multilayers by pulsed laser deposition (PLD), often both intermixing and resputtering occur due to the high kinetic energy of the particles transferred from the target to the substrate surface. In order to obtain a fundamental understanding of the underlying processes, W/Si multilayers have been studied by the complementary methods of transmission electron microscopy (TEM), X-ray reflectivity (XRR) and in-situ rate monitoring. For the experiments, deposition conditions were chosen that result in high energetic Si ions and mainly low energetic W atoms for the multilayer growth. Under these conditions, interface mixing of up to 3 nm occurs at the W/Si interfaces, while the Si/W interfaces remain sharp. Furthermore, enhanced resputtering of Si leads to a Si thickness deficit of up to 2 nm at the W/Si interfaces. The presented results can be understood by a combination of theoretical calculations as well as SRIM and TRIDYN simulations, which match perfectly to the experimentally obtained intermixing and enhanced resputtering of Si at the W/Si interfaces. peerReviewed

Nanoscale thin-film multilayer materials are of great research interest since their large number of interfaces can strongly hinder phonon propagation and lead to a minimized thermal conductivity. When such materials provide a sufficiently small thermal conductivity and feature in addition also a high thermal stability, they would be possible candidates for high-temperature applications such as thermal barrier coatings. For this article, we have used pulsed laser deposition in order to fabricate thin multilayers out of the thermal barrier material ZrO2 in combination with W, which has both a high melting point and high density. Layer thicknesses were designed such that bulk thermal conductivity is governed by the low value of ZrO2, while ultrathin W blocking layers provide a high number of interfaces. By this phonon scattering, reflection and shortening of mean free path lead to a significant reduction in overall thermal conductivity even below the already low value of ZrO2. In addition to this, X-ray reflectivity measurements were taken showing strong Bragg peaks even after annealing such multilayers at 1300 K. Those results identify W/ZrO2 multilayers as desired thermally stable, low-conductivity materials.

One of the major advantages of pulsed laser deposition (PLD) is the ability to transfer complex multicomponent materials stoichiometrically from a target to the growing film on a substrate. Nevertheless, in some systems small deviations from stoichiometry were found. In this paper, we show that it is possible to grow homogeneous alloy films with concentrations over an unprecedented large range of 0–97 wt% W from a single W80Cu20 target by just varying the laser fluence and additionally tilting the substrate during deposition. This is probably the largest deviation from stoichiometry transfer possible in a binary system.

In common, one of the most characteristic properties of pulsed laser deposition is the stoichiometry transfer between target and substrate, which has been used heavily for many complex systems. In this paper we show that it is yet possible to obtain drastic deviations from stoichiometry transfer in a binary system by just varying the fluence during laser deposition. In the W–Cu system, the W concentration of films grown from a composite W60Cu40 target (60 wt% W) was indeed continuously changed over an unprecedented large range of 0–70 wt% W. Close to the deposition threshold, pure Cu films are formed due to the much higher vapor pressure of Cu. At higher laser fluences, more and more W-rich W–Cu alloy samples are obtained, since ion implantation and intermixing processes occur. These alloys can reach W contents even higher than that of the target because of enhanced resputtering and reflection of the lighter Cu atoms at the film surface. Stoichiometric films with 60 wt% of W are only obtained at laser fluences around 2.7 J/cm2, when the strong Cu evaporation from the target and reflection and resputtering effects of Cu at the film surface are in balance.

As a novel approach, the combination of pulsed laser deposition and focused ion beam was applied to fabricate different types of multilayer zone plate structures for soft X-ray applications. For this purpose, high quality non-periodic ZrO2/Ti multilayers were deposited by pulsed laser deposition on planar Si substrates and on rotating steel wires with layer thicknesses according to the Fresnel zone plate law. Linear focusing optics were fabricated by cutting slices out of the multilayers by focused ion beam and placing them directly over pinholes within Si3N4 substrates. Additionally, it was shown that laser deposition of depth-graded multilayers on a wire is also a promising way for building up multilayer zone plates with point focus. First experiments using a table-top X-ray source based on a laser-induced plasma show that the determined focal length and spatial resolution of the fabricated multilayer Laue lens corresponds to the designed optic.

Different polymer–metal nanocomposites, metal clusters on a polymer surface and for the first time also polymer/metal multilayers, were pulsed laser deposited at a wavelength of 248 nm. Poly(methyl methacrylate) (PMMA) and Bisphenol A dimeth-acrylate (BisDMA), which strongly differ in their hardness of 3 and 180 N/mm 2 , respectively, were taken as polymer components. Metals Ag and Cu were chosen because of their different reactivity to polymers. When depositing Ag on PMMA, spherical clusters are formed due to high diffusion and total coalescence. For Cu, much smaller grains with partially elongated shapes occur because of lower diffusivity and incomplete coalescence. Compared to the results on the soft PMMA, the clusters formed on the harder BisDMA are much larger due to higher diffusivity on this underlayer. In PMMA/Cu multilayers, wavy layered structures and buckling is observed due to relaxation of compressive stress in the Cu layers. Smooth Cu layers with higher thicknesses can only be obtained, when the hardness of the polymer is sufficiently high, as in the case of BisDMA/Cu multilayers.

The focusing properties of a one-dimensional multilayer Laue lens (MLL) were investigated using monochromatic soft X-ray radiation from a table-top, laser-produced plasma source. The MLL was fabricated by a focused ion beam (FIB) structuring of pulsed laser deposited ZrO2/Ti multilayers. This novel method offers the potential to overcome limitations encountered in electron lithographic processes. Utilizing this multilayer Laue lens, a line focus of XUV radiation from a laser-induced plasma in a nitrogen gas puff target could be generated. The evaluated focal length is close to the designed value of 220 μm for the measurement wavelength of 2.88 nm. Divergence angle and beam waist diameter are measured by a moving knife edge and a far-field experiment, determining all relevant second-order moments based beam parameters. The waist diameter has been found to be approximately 370 nm (FWHM). peerReviewed

Smooth poly(methyl methacrylate) (PMMA) films without any droplets were pulsed laser deposited at a wavelength of 248 nm and a laser fluence of 125 mJ/cm2. After deposition at room temperature, the films possess low universal hardness of only 3 N/mm2. Thermal treatments up to 200°C, either during deposition or afterwards, lead to film hardening up to values of 200 N/mm2. Using a combination of complementary methods, two main mechanisms could be made responsible for this temperature induced hardening effect well above the glass transition temperature of 102°C. The first process is induced by the evaporation of chain fragments and low molecular mass material, which are present in the film due to the ablation process, leading to an increase of the average molecular mass and thus to hardening. The second mechanism can be seen in partial cross-linking of the polymer film as soon as chain scission occurs at higher temperatures and the mobility and reactivity of the polymer material is high enough. peerReviewed

Poly(methyl methacrylate) (PMMA) was pulsed laser deposited at a wavelength of 248 nm using different laser fluences between 30 and 9000 mJ/cm 2 . While the composition of the films obtained after deposition at high laser fluences is close to that of the target, the molecular mass of the film material is reduced to about M w = 8000 g/mol due to incubation processes independent on the high starting mass of the target. The microstructure of the films strongly depends on the laser fluence. After deposition at laser fluences above 500 mJ/cm 2 , the illuminated PMMA targets show a rough and molten surface with holes and bubbles resulting from strong subsurface heating. The corresponding PMMA films are very rough and exhibit a high number of droplets. In contrast, at laser fluences close to the deposition threshold of about 60 mJ/cm 2 completely smooth films are obtained. Below the deposition threshold, the target performs incubation processes and colour changes occur, but it is only partially molten, and almost no ablation is observed. Only in a narrow fluence range above the deposition threshold (between about 80 and 160 mJ/cm 2 ) a crater with a smooth surface is formed at the target leading to a high ablation rate and to completely smooth films without any droplets.

Hard x-ray focusing and imaging on the few nano metre scale has gained a lot of attraction in the last couple of years. Thanks to new developments in fabrication and inspection of high-N.A. optics, focusing of hard x-rays has caught up with the focusing performance for soft x-rays. Here we review the latest imaging experiments of the Gottinger Multilayer zone plate collaboration, summarising our route from 1D to 2D lenses for different hard x-ray energies, and recapitulate recent progress on a journey from focusing to imaging.

Efficient focusing optics are a key ingredient for high-resolution (few nanometer) hard x-ray imaging. In recent years, a combined optical scheme using prefocusing to match the coherent fraction of the synchrotron’s x-ray beam to a high-resolution multilayer zone plate (MZP) has been presented. This scheme allows sub-5 nm focusing of hard x-rays in two dimensions. Nevertheless, the first lenses prepared by pulsed laser deposition of alternating WW and Si layers were limited by a low deposition rate of W and the formation of lots of Si-droplets during film growth. Thus, the material combination has been changed to Ta 2 O 5 and ZrO 2 , allowing a much faster and more accurate layer growth. Here we present latest developments achieved in both design and fabrication of high-resolution MMZPs: A MZP with a lens diameters of about 15 micrometers, sharp layer interfaces, 5 nm outermost zone widths and a focal length of 0.5 mm. Too increase the focusing efficiency even more, a tilted geometry using a pulled glass fibre was successfully implemented.

Pulsed laser deposition was used to grow complex polymer–metal nanocomposites consisting of Ag, Cu and Nb clusters embedded in a poly(methyl-methacrylate) (PMMA) matrix. During deposition at room temperature, the size and amount of the metal clusters can be tuned in different ways. First, it is controlled by the number of laser pulses hitting the respective targets. In the case of Ag, a bimodal size distribution of the clusters is observed, induced by total coalescence and secondary nucleation processes. For Cu and Nb, much smaller clusters and higher cluster densities are obtained due to a stronger reactivity with the polymer and thus a lower diffusivity in the PMMA. Additionally, the microstructure of the Ag clusters is affected by the degree of cross linking of the polymer and can be influenced by pre-deposition of nucleation seeds in the form of small Cu clusters.

The reduction in the length scale of materials to the nanometer range brings about fundamental changes that lead to novel and unusual phenomena, very different from their coarse-grained counterparts. These differences are not only due to the different physical properties of the small-size system but it is also affected by the type of the stabiliser used on these materials. In situ X-ray diffraction (XRD) investigations of the hydrogen absorption behaviour in different nanometer sized palladium samples were performed during loading and unloading. Pressure-lattice parameter isotherms were constructed for three different samples: surfactant stabilised clusters, and two types of polymer stabilised samples (clusters and closed clusters layers sample). The pressure-lattice parameter isotherms for the samples show a narrowed lattice parameter miscibility gap . The closed clusters layers sample shows the smallest lattice parameter expansion values. The effect of the samples morphology on the lattice expansion will be discussed. It will be shown that not only the sample sizes affect the expansion but also the cluster surrounding plays an important rule.

Modifications of magnetic properties upon heavy-ion irradiation have been recently investigated for films of ferromagnetic 3d-elements (Fe, Ni, Co) and alloys (permendur, permalloy), in relation to changes of their microstructure. Here we report on Xe-ion irradiation of a highly textured iron film prepared via pulsed-laser deposition on a MgO(100) single crystal and containing a thin 57Fe marker layer for magnetic orientation Mossbauer spectroscopy (MOMS). We compare the results with those obtained for a polycrystalline Fe/Si(100) sample produced by electron evaporation and premagnetized before Xe-irradiation in a 300 Oe external field. Characterization of the samples also included magneto-optical Kerr effect (MOKE), Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD).

In situ stress measurements were performed on polycrystalline Permalloy and Ag thin films laser deposited in ultrahigh vacuum (UHV) and at different Ar gas pressures. In UHV, when the kinetic energy of the particles is high (about 100 eV), in the initial growth stage the stress is dominated by the surface energy and intermixing effects. With increasing deposition time, capillary-induced compressive growth stress is observed. Additionally, the film stress is strongly influenced by the growth mode (island growth or layer-by-layer growth). In the case of Volmer–Weber growth, island zipping generates tensile stress, as soon as island impingement and coalescence occurs. In the late stages, compressive stress due to shot-peening and implantation dominates the measurements, similar as in sputtered films. The depth of influence of the impinging particles is determined to be about 3 nm. With increasing Ar pressure (or at low laser fluence) the impinging particles are slowed down and implantation or intermixing eff...

Pd/Nb- and Fe/V multilayers were prepared by either ion sputtering or laser ablation. They were deposited on tungsten tips for field ion microscopy using the 3-dimensional atom probe. D was added by doping from the gas phase. In agreement with thermodynamic data D is accumulated in the metal with the more negative heat of solution, i.e. V or Nb. However, SIMS depth profiles of H concentration measured at room temperature show a pronounced enrichment in the top regions of both Nb- and V layers. This is also observed in a deuterium depth profile obtained by the 3d atom probe measured at 60 K despite the moderate removal of atoms by field evaporation which does not give rise to the formation of lattice defects when compared to sputtering. Thus we assume that surface segregation is the reason for H/D accumulation in surface near regions. The effect vanishes if measurements by the atom probe were made at 20 K where the D mobility is too low to allow D transport to the surface during the time of measurements. With the superior depth resolution of the 3d atom probe being less than 0.5 nm we were able to show that at both the V/Fe and the Nb/W interface depletion of deuterium occurs in a range of about 0.5 nm within the Nb- or V layer due to intermixing of adjacent metals.

Nb—Pd multilayers were prepared by laser deposition. Samples were loaded electrolytically with hydrogen up to 0.3 H/Nb, others were submitted to four complete loading—unloading cycles and remained loaded. The microstructure of these samples as well as that of as-prepared samples were studied by high resolution electron microscopy. After several hydrogen loading and unloading cycles the change in microstructure consists mainly of a new arrangement of dislocations. Further transmission electron microscopy studies reveal that β-NbH grows in columns parallel to the growth direction of the films after phase separation. X-ray studies show that after unloading from the p-NbH phase the stress in the film changes to the reverse mode. This is valid for completely loaded as well as partially loaded specimens.

Using Cu/Ag multilayers, we show that the deposition of a significant number of highly energetic ions, characteristic of pulsed laser deposition, leads to resputtering of the already-deposited film and implantation into the existing film. The consequent film growth is described by a ‘subsurface growth mode’, in which the material does not grow on top of the already-deposited film, but rather within the topmost few monolayers. This hypothesis is confirmed using three in situ diagnostic methods: rate monitoring which was found to exhibit a non-linearity at the beginning of each new layer, a result of resputtering of the growing film; resistance measurements showing a drop in conductance after beginning a new Cu layer, an effect attributed to implantation and alloying at the interface; and electron diffraction to determine the variation in lattice parameters during growth, which can be interpreted as a consequence of alloying.

A new model of light–target interaction, which takes into account multiple interaction of the scattered laser beam with the surface structure of a target, is reported. The model is based on calculations of the local intensity of the electromagnetic wave, from which the local amount of ablated material can be obtained after each simulated laser pulse. The simulations of the sequence of laser pulses was employed to explain the observed development of the particular surface topography. It is shown that during laser ablation a small initial surface roughness is sufficient to initiate further deepening of the surface relief. During this preliminary development of the relief, the 1st-order scattering plays a dominant role. But, as soon as the surface acquired a relatively deep relief, the 2nd-order interaction leads to the appearance of “hot” valleys, where the electromagnetic energy of the light wave is significantly more concentrated and, therefore, the ablation is more efficient. As a result of this effect the depth of the valleys increases and the cone structure becomes more and more pronounced.

One of the most significant features of pulsed-laser deposition (PLD) in vacuum as compared to conventional deposition methods is that a significant number of ions are deposited with a high kinetic energy of about 100 eV. Using Fe/Ag multilayers, we show that the deposition of energetic particles during PLD leads to implantation into the existing film. The film growth can be described by a growth mode in which the material does not grow on top, but rather within the topmost few monolayers of the already deposited film. To examine this “subsurface growth”, in situ resistance measurements and electron diffraction experiments were performed. Resistance measurements show a drop in conductance after beginning a new Fe layer, an effect attributed to implantation and alloying at the interface. Electron diffraction experiments allow the observation of the structural change from fcc-Ag to bcc-Fe and vice versa. These experiments are interpreted by the use of a Bain transformation to describe a homogeneous transformation between the two structures.

Metastable, supersaturated alloys of the thermally immiscible systems Ag/Fe ( 111 In tracers. In both systems the magnetic hyperfine fields B n were found to decrease linearly with the number n of Ag or In neighbor atoms next to the probe site (10.9% per Ag atom; 4.5% per In atom). From the observed distribution of the fractions f n in the laser-deposited samples, the maximum solubility S =15(5) at% of In in Fe was determined after laser deposition. This concentration compares well with the maximum solubility S =16(3) at% of Ag in Fe previously found for supersaturated Ag/Fe alloys. The solubility of In in Fe in thermal equilibrium at room temperature and at 970–1370 K was determined for samples having In concentrations of less than 0.1–2.1 at%.

Pulsed laser deposited (PLD) metallic alloys and multilayers are characterized by the formation of amorphous or metastable nanocrystalline phases with high solid solubilities, unusually enlarged lattice spacings in growth direction and intermixed interfaces. The differences to sputtered and evaporated samples are discussed with respect to the high instantaneous deposition rate, which is about 105 times larger than during sputtering or thermal evaporation, and the high kinetic energy of the deposited particles of up to more than 100 eV at high laser fluences inducing atomic mixing, a large number of defects and a high stress in the deposited films.

During pulsed laser deposition (PLD) of metals (and other materials) one typical problem occurs: beside atoms and ions macroscopic droplets (up to some μm) are expelled from the roughening target and are deposited on the film surface. In the case of metals two kinds of droplets are observed during laser ablation, which have different sizes, angular distributions, velocities, and dependencies on the number of pulses, target roughening and energy density. These experiments indicate different origins for the two types of droplets: expelling from the cones growing out of the target and expelling from the molten surface. Consequences for the reduction and avoidance of these droplets are discussed.

Laser deposited FeAg alloys exhibit a supersaturation of the Fe(Ag) solid solution of up to 13 at.% Ag and an unusual lattice expansion in the growth direction. The relaxation process, grain coarsening, decomposition and mixing processes occurring during 350 keV Ar + irradiation at 77 K in these alloys were studied by X-ray diffraction. Depending on the original state of the samples, different processes dominate, but always lead to the same dynamic phase equilibrium under irradiation.

We present experiments carried out using a combined hard x-ray focusing set-up preserving the benefits of a large-aperture Kirckpatrick-Baez (KB) mirror system and a small focal length multilayer zone plane (MZP). The high gain KB mirrors produce a pre-focus of 400 nm × 200 nm; in their defocus, two MZP lenses of diameter of 1.6 μm and 3.7 μm have been placed, with focal lengths of 50 μm and 250 μm respectively. The lenses have been produced using pulsed laser deposition (PLD) and focused ion beam (FIB). Forward simulations including error models based on measured deviations, auto-correlation analysis and three-plane phase reconstruction support two-dimensional focus sizes of 4.3 nm × 4.7 nm (7:9 keV, W/Si)1 and 4.3 nm ×5.9 nm (13:8 keV, W/ZrO2), respectively.

Optics express 21(16), 19311 (2013). doi:10.1364/OE.21.019311, Published by Soc., Washington, DC

The structure of metallic alloys and multilayers prepared by pulsed laser deposition using KrF radiation (248 nm) and a pulse duration of 30 ns was investigated by X-ray diffraction. In comparison with conventional deposition techniques, the structural properties of laser-deposited FeNb and FeAg films can be characterized by the formation of amorphous or metastable nanocrystalline phases with higher solubilities, unusually enlarged lattice spacings in the growth direction and different film textures. Often these films are in a state further away from the equilibrium state than sputtered or evaporated samples. Fe Nb multilayers exhibit much broader amorphous interfaces, while Fe Ag superlattices show a different texture and sharp interfaces visible by satellite reflections in the X-ray spectra. These differences can be understood by the about 105 times higher instantaneous deposition rate and the high kinetic energy of the deposited particles in the range of up to 100 eV.

Numerical calculations are presented, which describe the processes of target heating and ablation of pure metals (for instance Fe) during irradiation by 30 ns laser pulses at 248 nm. The following effects are taken into account: the absorption of the laser radiation and the heat conduction within the target, the evaporation of material from the target surface, the cooling of the target surface by the heat of evaporation and the partial absorption of the incident laser beam in the evaporated material. As results of the calculations, the temperature profile in the target and the ablated material can be obtained. Furthermore, by energy balance, an energy of the ablated material of up to some 100 eV is obtained. Experiments performed concerning the threshold energy of ablation, the removed mass from the target and the kinetic energy of the deposited ions (by time-of-flight measurements) are in good agreement with the performed calculations.

The structural and mechanical properties of polymethyl methacrylate (PMMA) thin films produced by pulsed laser deposition in ultra-high vacuum were investigated by infrared spectroscopy, electron microscopy, size-exclusion chromatography and microhardness measurements. After preparation, the film hardness and elastic modulus are found to be increased. This is caused by a reduced chain length of the polymer film to values of 5800 g/mol and by cross links of an amount of about 20% of the polymer, while the chemical structure of the deposited films is comparable to the target material. During annealing, relaxation processes lead to a reduction of the film hardness, without changing the cross-linked part in the samples.

Ceramic–metal (MgO combined with Fe, Ti and Ni80Nb20) and polymer–metal (polycarbonate combined with Ag and Pd) nanocomposite multilayers were deposited at room temperature by laser ablation (at 248 nm). The multilayers were characterized by X-ray reflectometry, infrared spectroscopy and transmission electron microscopy. In the case of MgO/metal multilayers, well-layered structures are produced down to layer periodicities of 1.2 nm, necessary for tunneling magnetoresistance devices and X-ray mirrors in the ‘water window’. The interface roughness in the case of polymer/metal multilayers is found to be a strong function of the metal layer thickness and also the nature of the metal.

The changes in the properties of laser deposited metal thin films were investigated in different inert gas atmospheres (He, Ne, Ar and Xe). With increasing inert gas pressure, the reduction of particle energy is accompanied by a strong increase of the deposition rate (especially in He atmosphere), a transition from compressive to tensile stress, and changes in structure and texture. This is explained by a reduction of surface mobility of the deposited particles, a decrease of implantation, resputtering and shot-peening effects. At high gas pressures, deposition conditions similar to sputtering or even thermal deposition are obtained.

The structure of metallic alloys grown by pulsed KrF laser deposition is examined by x‐ray diffraction and compared with results from literature on sputtered and evaporated films. In general, the phases and structures obtained are similar, while laser deposited films often exhibit unusually enlarged lattice parameters in direction of growth, small grain sizes, larger extensions of the single‐phase regions and sometimes better alignment of the grains. These differences can be explained by the approximately 105 times higher instantaneous deposition rate of the pulsed laser ablation process and the high kinetic energy of the deposited particles of up to more than 100 eV.

During 350 keV Ar+ irradiation at 77K, laser-deposited Fe−Ag multilayers first show stress relaxation and demixing processes at the interfaces followed by grain coarsening and a supersaturation of the bcc α-Fe phase with Ag due to ballistic mixing. At high fluence, the fcc γ-Fe(Ag) phase (a=3.65 A) is formed, which can be explained by either chemically guided ballistic short-range relocations or by the occurrence of thermal spikes, where all atoms possess sufficient energy to allow collective structural rearrangements, but only during such a short time that a decomposition due to long-range diffusion is suppressed.

The structure of laser‐deposited and sputtered Fe/Nb and Fe/Ag multilayers was investigated by x‐ray diffraction. Significant differences in the textures, sharpness of the interfaces, and critical bilayer thicknesses for alloys are obtained for these two deposition processes. For small bilayer thicknesses, the measured x‐ray‐diffraction patterns were analyzed by computer simulations using a one‐dimensional model, which includes the occurrence of amorphous or disordered interlayers between the crystalline layers and takes layer thickness fluctuations into account. These simulations indicate that already in as‐prepared Fe/Nb multilayers thin amorphous interlayers exist and describe the thickness increase during an interdiffusion reaction already in the early stages of the transformation. In the case of Fe/Ag multilayers, the interfaces are disordered after deposition and first sharpen during annealing at about 250 °C, before grain coarsening occurs.

The characteristic behaviours of pulsed excimer laser deposition (at 248 nm) of metallic alloys and multilayers are: high deposition rates of up to 3 nm/s above an ablation threshold of about 5 J/cm 2 , a nearly congruent transfer between target and film, droplets on the film surface, and a strong thickness dependence of the obtained films. Compared to sputtered or evaporated films the alloys obtained are characterized by similar structures in most cases, but often larger extensions of single-phase regions and enlarged lattice parameters in the growth direction, while multilayers sometimes have different textures, often a better alignment of the grains in the growth direction and in systems with a negative heat of mixing sometimes a different critical bilayer thickness for the formation of fully amorphous films. Therefore, the pulsed laser deposition is an attractive alternative thin-film technique for the deposition of metallic alloys and multilayers.

The structure of metallic elements and alloy thin films grown by pulsed KrF laser deposition was examined by X-ray diffraction and Mossbauer spectroscopy, and compared with results on triode sputtered films. While, in general, the obtained phases and structures are similar, laser ablated films often exhibit smaller grain sizes, enlarged lattice parameters in the growth direction, larger extensions of the single-phase regions and sometimes a better alignment of the grains. It can be concluded, that often laser deposited metallic material is in a state further away from equilibrium than after preparation by classical thin film techniques . The differences can be explained by the 10 5 –10 6 times higher momentary deposition rate of the pulsed laser ablation process.

During scanning tunneling microscopy measurements on YBa2Cu3O7 thin films with positive sample bias voltages, different kinds of surface modifications appear. While in the topography condition no surface modification occurs, the cleaning and etching conditions irreversibly change the surface topography. In the deformation condition a strong elastic deformation of the tip and/or the surface is observed. It is shown that field evaporation of material from the surface to the tip is responsible for the observed surface modification. In consequence, the tip is contaminated with different oxides. Localized states in the oxides make resonant tunneling of electrons through the oxide layer possible. The configuration of these localized states determines the kind of surface modification by the scanning tunneling microscope.

Grazing incidence Xe${}^{+}$ ion sputtering was used to create a nanoscale ripple pattern on a thin Fe film, epitaxially grown on MgO(001). The Fe film has a thickness gradient of 0--20 nm and a ripple height of about 3 nm, giving rise to a transition from a continuous film to separated nanorods with decreasing film thickness. This allowed the investigation of the competition between the uniaxial and biaxial anisotropy of the irradiated sample as a function of thickness. From magneto-optical Kerr effect measurements, we determine accurately the cubic magnetocrystalline anisotropy and the uniaxial anisotropy that originates from the ripple pattern using a coherent rotation model. Our results show that the uniaxial anisotropy strength increases, whereas the contribution of the biaxial crystal anisotropy decreases, when going from the continuous film to the nanorod structures.

Y 1 Ba 2 Cu 3 O y films were grown in situ on oxidized Zr foils by pulsed laser ablation. The substrate temperature and the oxygen partial pressure were varied from 500 °C to 800 °C and between 0.01 mbar and 1 mbar, respectively, in order to determine the optimum conditions for a c-textured growth. Particular attention was paid to the special features of metallic substrates as oxidation, surface roughness, and rolling texture. X-ray diffraction experiments and resistance measurements were performed in order to study the texture and the superconducting properties of the films. For a substrate temperature of 750 °C and an oxygen partial pressure of 0.3 mbar a superconducting transition temperature of 89 K (midpoint) was obtained.

YBaCuO thin films were deposited on polycrystalline Zr sheets (T c = 89 K) and single-crystalline MgO (T c − 90 K) by KrF laser ablation. The oxygen loading was studied by resistance measurements. In the case of films on Zr the oxygen diffusion coefficients are similar to values determined for sintered pellets by thermogravimetric measurements. For films on MgO, the values are reduced by a factor of more than 100. These differences can be understood by the different microstructures of these films. In the case of films on Zr-sheets, the c-texture is not perfect and large-angle grain boundaries are ‘open channels’ for the diffusion of oxygen. The diffusion into the grains occurs parallel to the YBaCuO planes in a/b-direction. On the other side, in the case of high quality films on MgO with critical densities j c (77 K) = 3·10 6 A/cm 2 , the grain boundaries seem to be ‘dense’ and, therefore, the oxygen diffusion has to take place in c-direction, which increases the loading times by a factor of about 100 due to the anisotropic oxygen diffusion in the layered YBaCuO structure.

The kinetics of oxygen diffusion was investigated in Y1Ba2Cu3OY bulk material and laser ablated thin films on MgO. From isothermal annealing experiments in different oxygen partial pressures the diffusion coefficients, activation energies and time-temperature-transformation (TTT) diagrams were determined and discussed in regard to the oxygen content and the different microstructure of the bulk pellets and the thin films. Diffusion coefficients for the oxygen diffusion in the bulk material of between 1·10−12 and 2·10−10 cm2/s were determined by thermogravimetric measurements in the temperature range of 300°C to 700°C. Within the same temperature region in the laser ablated films (T x =92 K,j x (77K)=3·106 A/cm2) diffusion coefficients of between 3·10−15 to 3·10−12 cm2/s were obtained by in-situ resistance measurements. In both materials the activation energies for the oxygen diffusion decrease with decreasing oxygen content.