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1.	Akan, Rabia, et al. (author) Investigation of Metal-Assisted Chemical Etching for Fabrication of Silicon-Based X-Ray Zone Plates 2018 In: Microscopy and Microanalysis. - 1431-9276 .- 1435-8115. Journal article (peer-reviewed)
2.	Akan, Rabia (author) Metal-assisted chemical etching for nanofabrication of hard X-ray zone plates 2021 Doctoral thesis (other academic/artistic)abstract Hard X-ray scanning microscopes, or nanoprobes, make it possible to image samples and probe their chemical, elemental and structural properties at nanoscale resolution. This is enabled by the use of nanofocusing optics. Commonly used optics in nanoprobes for high resolution X-ray experiments are zone plates. Zone plates are circular diffraction optics with radially decreasing grating periods. Their performance depends on their geometrical properties and material. The width of the outermost zone, which today is in the order of a few tens of nanometers, defines the zone plate resolution, while the zone thickness and the material define the X-ray focusing efficiency. For hard X-ray zone plates, the required zone thickness is several micrometers. Therefore, high-aspect ratio nanostructures are a prerequisite for high-resolution, high-efficiency zone plates. The very small structures together with the high-aspect ratios make zone plates one of the most challenging devices to fabricate. A wet-chemical nanofabrication process that has proved its capability of providing silicon nanostructures with ultra-high aspect ratios is metal-assisted chemical etching (MACE). MACE is an electroless, autocatalytic pattern transfer method that uses an etching solution to selectively etch a predefined noble metal pattern into silicon. In this thesis, MACE is optimized specifically for zone plate nanostructures and used in the development of a new zone plate device nanofabrication process. The MACE optimization for silicon zone plate nanostructures involved a systematic investigation of a wide parameter space. The preferable etching solution composition, process temperature, zone plate catalyst design and silicon type were identified. Parameter dependencies were characterized with respect to etching depth and verticality, mechanical stability of zones and silicon surface roughness. Zone plate molds with aspect ratios of 30:1 at 30 nm zone widths were nanofabricated using the optimized MACE process. For use with hard X-rays, the silicon molds were metallized with palladium using electroless deposition (ELD). The first order diffraction efficiency of such a palladium/silicon zone plate was characterized as 1.9 %. Both MACE for the zone plate pattern transfer and ELD for the silicon mold metalization are conceptually simple, relatively low-cost and accessible methods, which opens up for further developments of zone plate device nanofabrication processes.
3.	Akan, Rabia, et al. (author) Reaction control of metal-assisted chemical etching for silicon-based zone plate nanostructures Other publication (other academic/artistic)abstract Metal-assisted chemical etching (MACE) reaction parameters were investigated for the fabrication of specially designed silicon-based x-ray zone plate nanostructures using a gold catalyst pattern and etching solutions composed of HF and H2O2. Etching depth, zone verticality and zone roughness were studied as a function of etching solution composition, temperature and processing time. Homogeneous, vertical etching with increasing depth is observed at increasing H2O2 concentrations and elevated processing temperatures, implying a balance in the hole injection and silica dissolution kinetics at the gold-silicon interface. The etching depth decreases and zone roughness increases at the highest investigated H2O2 concentration and temperature. Possible reasons for these observations are discussed based on reaction chemistry and zone plate design. Optimum MACE conditions are found at HF:H2O2 concentrations of 4.7 M:0.68 M and room temperature with an etching rate of 0.7 micrometers per minute, which is about an order of magnitude higher than previous reports. Moreover, our results show that a grid catalyst design is important for successful fabrication of vertical high aspect ratio silicon nanostructures.
4.	Akan, Rabia, et al. (author) Reaction control of metal-assisted chemical etching for silicon-based zone plate nanostructures 2018 In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 8:23, s. 12628-12634 Journal article (peer-reviewed)abstract Metal-assisted chemical etching (MACE) reaction parameters were investigated for the fabrication of specially designed silicon-based X-ray zone plate nanostructures using a gold catalyst pattern and etching solutions composed of HF and H2O2. Etching depth, zone verticality and zone roughness were studied as a function of etching solution composition, temperature and processing time. Homogeneous, vertical etching with increasing depth is observed at increasing H2O2 concentrations and elevated processing temperatures, implying a balance in the hole injection and silica dissolution kinetics at the gold-silicon interface. The etching depth decreases and zone roughness increases at the highest investigated H2O2 concentration and temperature. Possible reasons for these observations are discussed based on reaction chemistry and zone plate design. Optimum MACE conditions are found at HFH2O2 concentrations of 4.7 M:0.68 M and room temperature with an etching rate of ≈0.7 μm min-1, which is about an order of magnitude higher than previous reports. Moreover, our results show that a grid catalyst design is important for successful fabrication of vertical high aspect ratio silicon nanostructures.
5.	Seiboth, Frank, et al. (author) Aberration Correction for Hard X-ray Focusing at the Nanoscale 2017 In: Advances in X-Ray/EUV Optics and Components XII. - : SPIE - International Society for Optical Engineering. - 9781510612303 - 9781510612297 Conference paper (peer-reviewed)abstract We developed a corrective phase plate that enables the correction of residual aberration in reflective, diffractive, and refractive X-ray optics. The principle is demonstrated on a stack of beryllium compound refractive lenses with a numerical aperture of 0.49 x 10(-3) at three different synchrotron radiation and x-ray free-electron laser facilities. By introducing this phase plate into the beam path, we were able to correct the spherical aberration of the optical system and improve the Strehl ratio of the optics from 0.29(7) to 0.87(5), creating a diffraction-limited, large aperture, nanofocusing optics that is radiation resistant and very compact.
6.	Seiboth, Frank, et al. (author) Perfect X-ray focusing via fitting corrective glasses to aberrated optics 2017 In: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 8 Journal article (peer-reviewed)abstract Due to their short wavelength, X-rays can in principle be focused down to a few nanometres and below. At the same time, it is this short wavelength that puts stringent requirements on X-ray optics and their metrology. Both are limited by today’s technology. In this work, we present accurate at wavelength measurements of residual aberrations of a refractive X-ray lens using ptychography to manufacture a corrective phase plate. Together with the fitted phase plate the optics shows diffraction-limited performance, generating a nearly Gaussian beam profile with a Strehl ratio above 0.8. This scheme can be applied to any other focusing optics, thus solving the X-ray optical problem at synchrotron radiation sources and X-ray free-electron lasers.
7.	Uhlén, Fredrik, et al. (author) Ronchi test for characterization of X-ray nanofocusing optics and beamlines 2014 In: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 21, s. 1105-1109 Journal article (peer-reviewed)abstract A Ronchi interferometer for hard X-rays is reported in order to characterize the performance of the nanofocusing optics as well as the beamline stability. Characteristic interference fringes yield qualitative data on present aberrations in the optics. Moreover, the visibility of the fringes on the detector gives information on the degree of spatial coherence in the beamline. This enables the possibility to detect sources of instabilities in the beamline like vibrations of components or temperature drift. Examples are shown for two different nanofocusing hard X-ray optics: a compound refractive lens and a zone plate.
8.	Abend, Sven, et al. (author) Terrestrial very-long-baseline atom interferometry : Workshop summary 2024 In: AVS Quantum Science. - : American Institute of Physics (AIP). - 2639-0213. ; 6:2 Research review (peer-reviewed)abstract This document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more kilometer--scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions.
9.	Akan, Rabia, et al. (author) Metal-Assisted Chemical Etching and Electroless Deposition for Fabrication of Hard X-ray Pd/Si Zone Plates 2020 In: Micromachines. - : MDPI. - 2072-666X. ; 11:3 Journal article (peer-reviewed)abstract Zone plates are diffractive optics commonly used in X-ray microscopes. Here, we present a wet-chemical approach for fabricating high aspect ratio Pd/Si zone plate optics aimed at the hard X-ray regime. A Si zone plate mold is fabricated via metal-assisted chemical etching (MACE) and further metalized with Pd via electroless deposition (ELD). MACE results in vertical Si zones with high aspect ratios. The observed MACE rate with our zone plate design is 700 nm/min. The ELD metallization yields a Pd density of 10.7 g/cm3, a value slightly lower than the theoretical density of 12 g/cm3. Fabricated zone plates have a grid design, 1:1 line-to-space-ratio, 30 nm outermost zone width, and an aspect ratio of 30:1. At 9 keV X-ray energy, the zone plate device shows a first order diffraction efficiency of 1.9%, measured at the MAX IV NanoMAX beamline. With this work, the possibility is opened to fabricate X-ray zone plates with low-cost etching and metallization methods.
10.	Akan, Rabia, et al. (author) Optimization of metal-assisted chemical etching for deep silicon nanostructures Other publication (other academic/artistic)
11.	Akan, Rabia, et al. (author) Optimization of Metal-Assisted Chemical Etching for Deep Silicon Nanostructures 2021 In: Nanomaterials. - : MDPI AG. - 2079-4991. ; 11:11 Journal article (peer-reviewed)abstract High-aspect ratio silicon (Si) nanostructures are important for many applications. Metal-assisted chemical etching (MACE) is a wet-chemical method used for the fabrication of nanostructured Si. Two main challenges exist with etching Si structures in the nanometer range with MACE: keeping mechanical stability at high aspect ratios and maintaining a vertical etching profile. In this work, we investigated the etching behavior of two zone plate catalyst designs in a systematic manner at four different MACE conditions as a function of mechanical stability and etching verticality. The zone plate catalyst designs served as models for Si nanostructures over a wide range of feature sizes ranging from 850 nm to 30 nm at 1:1 line-to-space ratio. The first design was a grid-like, interconnected catalyst (brick wall) and the second design was a hybrid catalyst that was partly isolated, partly interconnected (fishbone). Results showed that the brick wall design was mechanically stable up to an aspect ratio of 30:1 with vertical Si structures at most investigated conditions. The fishbone design showed higher mechanical stability thanks to the Si backbone in the design, but on the other hand required careful control of the reaction kinetics for etching verticality. The influence of MACE reaction kinetics was identified by lowering the oxidant concentration, lowering the processing temperature and by isopropanol addition. We report an optimized MACE condition to achieve an aspect ratio of at least 100:1 at room temperature processing by incorporating isopropanol in the etching solution.
12.	Beck, M., et al. (author) A pulse-train laser driven XUV source for picosecond pump-probe experiments in the water window 2001 In: Optics Communications. - 0030-4018 .- 1873-0310. ; 190:06-jan, s. 317-326 Journal article (peer-reviewed)abstract We describe the development of a table top soft X-ray source based on a laser produced plasma. The plasma is produced by a Nd:YLF pulse-train laser which delivers pulse trains of up to 400 pulses each of about 25 ps duration, Number and energy of the micropulses are fully computer controlled adjustable for an optimum interaction with a rotating solid target. Spectral, spatial and temporal characteristics of the X-ray emission from Mylar and copper targets have been studied. A calibrated back-illuminated CCD camera together with a slit grating spectrograph were utilized for the measurement of the absolute soft X-ray photon fluxes. The temporal measurements were performed using a streak camera while the plasma size was measured with a zone plate. An application of the system in a X-ray absorption experiment is shown, The advantages of the system in view of possible optical pump and soft X-ray probe experiments will be discussed.
13.	Beck, M., et al. (author) Evaluation of the energetic position of the lowest excited singlet state of beta-carotene by NEXAFS and photoemission spectroscopy 2001 In: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728 .- 1879-2650. ; 1506:3, s. 260-267 Journal article (peer-reviewed)abstract In carotenoids the lowest energetic optical transition belonging to the pi -electron system is forbidden by symmetry, therefore the energetic position of the S-1 (2(1)A(g)) level can hardly be assessed by optical spectroscopy. We introduce a novel experimental approach: For molecules with ir-electron systems the transition C1s --> 2p(pi*) from inner-atomic to the lowest unoccupied molecular orbital (LUMO) appears in X-ray absorption near edge spectra (NEXAFS) as an intense, sharp peak a few eV below the carbon K-edge. Whereas the peak position reflects the energy of the First excited singlet state in relation to the ionization potential of the molecule, intensity and width of the transition depend on hybridization and bonding partners of the selected atom. Complementary information can be obtained from ultraviolet photoelectron spectroscopy (UPS): At the low binding energy site of the spectrum a peak related to the highest occupied molecular orbital (HOMO) appears. We have measured NEXAFS and UPS of beta -carotene. Based on these measurements and quantum chemical calculations the HOMO and LUMO energies can be derived.
14.	Bertilson, Michael C., et al. (author) Zone plate efficiency measurements with a laser-plasma source 2007 In: Advances in X-Ray/EUV Optics and Components II. - : SPIE. - 9780819468536 ; , s. F7050-F7050 Conference paper (peer-reviewed)abstract We demonstrate a compact instrument for rapid and accurate measurements of the absolute and local efficiency of soft x-ray zone plates in the water window [M. Bertilson, et al, Rev. Sci. Instrum 78, 026103 (2007)]. The arrangement is based on a new single-line lambda = 2.88 nm liquid-nitrogen-jet laser-plasma source. The versatility of the instrument enables micro and condenser zone plates with focal lengths in the range from similar to 200 mu m to similar to 100 mm to be measured. We demonstrate an accurate local efficiency map of a in-house fabricated micro zone plate. Furthermore, we show how this compact instrument allows rapid feedback to the fabrication process which is important for future improvements.
15.	Bertilson, Michael, et al. (author) Compact high-resolution differential interference contrast soft x-ray microscopy 2008 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:064104 Journal article (peer-reviewed)abstract We demonstrate high-resolution x-ray differential interference contrast (DIC) in a compact soft x-ray microscope. Phase contrast imaging is enabled by the use of a diffractive optical element objective which is matched to the coherence conditions in the microscope setup. The performance of the diffractive optical element objective is evaluated in comparison with a normal zone plate by imaging of a nickel siemens star pattern and linear grating test objects. Images obtained with the DIC optic exhibit typical DIC enhancement in addition to the normal absorption contrast. Contrast transfer functions based on modulation measurements in the obtained images show that the DIC optic gives a significant increase in contrast without reducing the spatial resolution. The phase contrast operation mode now available for our compact soft x-ray microscope will be a useful tool for future studies of samples with low absorption contrast.
16.	Bertilson, Michael, et al. (author) First application experiments with the Stockholm compact soft x-ray microscope 2009 In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 186 Journal article (peer-reviewed)abstract Most soft x-ray microscopes operating in the water window (lambda = 2.3 - 4.4 nm) rely on synchrotron radiation sources. In the future we believe scientists will use soft x-ray microscopes as one imaging tool among others in their own laboratory. For this purpose we have developed a full field soft x-ray microscope with a laser-plasma source compact enough to fit on an optical table. In this contribution we describe the current status of this microscope now featuring stable operation at lambda = 3.37 nm or lambda = 2.48 nm. In-house fabricated single element zone plates offering the possibility to perform phase contrast imaging have been implemented. We also report on the first application experiments for compact soft x-ray microscopy, including results from studies of clay minerals and colloids existing in nature and results from phase optics experiments. Planned upgrades of the microscope include increasing the source brightness, implementing more efficient condenser optics, and installing a cryo sample stage for tomography. These improvements will open up for further applications, especially in the field of biological imaging.
17.	Bertilson, Michael, et al. (author) High-resolution computed tomography with a compact soft x-ray microscope 2009 In: Optics Express. - 1094-4087. ; 17:13, s. 11057-11065 Journal article (peer-reviewed)abstract Computed tomography based on high-resolution soft x-ray microscopy utilizes the natural contrast for biological specimens provided by the water window (lambda = 2.4 - 4.4 nm) and the high resolving power of zone plate objectives. It is capable of revealing the 3D structure of biological specimens at sub-visible-microscopic resolution. To date, the technique has only been available at synchrotron-based microscopes, which limits the researchers access. In the present paper we demonstrate high-resolution soft x-ray tomography with a laboratory zone-plate-based soft x-ray microscope. The specimen, a diatom mounted on a glass capillary, was reconstructed from a tilt series of 53 images covering 180 using a filtered back projection algorithm. The resolution of the tomogram was estimated to a half period of 140 nm using a differential-phase-residual method. Cryo-fixation, increased source brightness and extended-depth-of-focus objectives are important for pushing the resolution of compact systems for biological samples.
18.	Bertilson, Michael, et al. (author) Laboratory Soft X-Ray Cryo Tomography Other publication (other academic/artistic)abstract X-rays allow quantitative high-spatial-resolution three-dimensional (3D) imaging of intact unstained cells. Such 3D imaging is provided by soft x-ray lens-based methods (water-window cryo tomography) and hard x-ray lens-less methods (coherent diffraction imaging) are emerging. However, both methods rely on high-brightness synchrotron-radiation sources, which limit the accessibility of a wider scientific community. Here we show 3D water-window cryo tomography with a laboratory-source-based microscope arrangement. The system relies on a λ=2.48-nm liquid-jet laser-plasma source, normal- incidence multilayer condenser optics, 30-nm zone-plate optics, and a cryo sample chamber. We demonstrate imaging of intact unstained yeast, protozoan parasites and mammalian cells. 3D images show noise-limited features close to ~100 nm and intra-cellular structure is classified based on the local absorption coefficient. A comprehensive theoretical model of the tomographic imaging system allows optimization of system parameters and a quantitative estimate of the 3D imaging accuracy. The model includes issues such as non-geometric projections of the thick samples and stray light, and is applicable to laboratory as well as synchrotron-based x-ray microscopes. The model shows that laboratory x-ray cryo tomography will allow quantitative 3D imaging with ~30-nm (half-period) resolution over a full 5 µm object.
19.	Bertilson, Michael, et al. (author) Laboratory soft-x-ray microscope for cryotomography of biological specimens 2011 In: Optics Letters. - 0146-9592 .- 1539-4794. ; 36:14, s. 2728-2730 Journal article (peer-reviewed)abstract Soft-x-ray cryotomography allows quantitative and high-resolution three-dimensional imaging of intact unstained cells. To date, the method relies on synchrotron-radiation sources, which limits accessibility for researchers. Here we present a laboratory water-window microscope for cryotomography. It is based on a lambda = 2.48nm liquid-jet laser-plasma source, a normal-incidence multilayer condenser, a 30nm zone-plate objective, and a cryotilt sample holder. We demonstrate high-resolution imaging, as well as quantitative tomographic imaging, of frozen intact cells. The reconstructed tomogram of the intracellular local absorption coefficient shows details down to similar to 100nm.
20.	Bertilson, Michael, et al. (author) Numerical model for tomographic image formation in transmission x-ray microscopy 2011 In: Optics Express. - 1094-4087. ; 19:12, s. 11578-11583 Journal article (peer-reviewed)abstract We present a numerical image-formation model for investigating the influence of partial coherence, sample thickness and depth-of-focus on the accuracy of tomographic reconstructions in transmission x-ray microscopes. The model combines wave propagation through the object by finite difference techniques with Fourier methods. We include a ray-tracing model to analyse the origin of detrimental stray light in zone plate-based x-ray microscopes. These models allow optimization of x-ray microscopy systems for quantitative tomographic imaging of thick objects. Results show that both the depth-of-focus and the reconstructed local absorption coefficient are highly dependent on the degree of coherence of the optical system.
21.	Bertilsson, Michael, et al. (author) Laboratory arrangement for soft x-ray zone-plate efficiency measurements 2007 In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 78:2, s. 026103- Journal article (peer-reviewed)abstract We demonstrate a laboratory-scale arrangement for rapid and accurate measurements of the absolute and local efficiency of soft x-ray micro zone plates in the water window. This in-house instrument is based on a single-line lambda=2.88 nm liquid-jet laser-plasma source. Measurements are performed by a simultaneous comparison of first diffraction-order photon flux with the flux in a calibrated reference signal. This arrangement eliminates existing source emission fluctuations. The performance of the method is demonstrated by the result from measurements of two similar to 55 mu m diameter nickel micro zone plates, showing a groove efficiency of 12.9%+/- 1.1% and 11.7%+/- 1.0%. Furthermore, we show that spatially resolved efficiency mapping is an effective tool for a detailed characterization of local zone plate properties. Thus, this laboratory-scale instrument allows rapid feedback to the fabrication process which is important for future improvements.
22.	Björling, Alexander, et al. (author) Ptychographic characterization of a coherent nanofocused X-ray beam 2020 In: Optics Express. - : OPTICAL SOC AMER. - 1094-4087. ; 28:4, s. 5069-5076 Journal article (peer-reviewed)abstract The NanoMAX hard X-ray nanoprobe is the first beamline to take full advantage of the diffraction-limited storage ring at the MAX IV synchrotron and delivers a high coherent photon flux for applications in diffraction and imaging. Here, we characterize its coherent and focused beam using ptychographic analysis. We derive beam profiles in the energy range 6-22 keV and estimate the coherent flux based on a probe mode decomposition approach.
23.	Branny, Artur, et al. (author) X-Ray Induced Secondary Particle Counting With Thin NbTiN Nanowire Superconducting Detector 2021 In: IEEE transactions on applied superconductivity (Print). - : Institute of Electrical and Electronics Engineers (IEEE). - 1051-8223 .- 1558-2515. ; 31:4 Journal article (peer-reviewed)abstract We characterized the performance of abiased superconducting nanowire to detect X-ray photons. The device, made of a 10 nm thin NbTiN film and fabricated on a dielectric substrate (SiO2, Nb3O5) detected 1000 times larger signal than anticipated from direct X-ray absorption. We attributed this effect to X-ray induced generation of secondary particles in the substrate. The enhancement corresponds to an increase in the flux by the factor of 3.6, relative to a state-of-the-art commercial X-ray silicon drift detector. The detector exhibited 8.25 ns temporal recovery time and 82 ps timing resolution, measured using optical photons. Our results emphasize the importance of the substrate in superconducting X-ray single photon detectors.
24.	Busch, S., et al. (author) Ion acceleration with ultrafast lasers 2003 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 82:19, s. 3354-3356 Journal article (peer-reviewed)abstract Hot-electron confinement can build up fields capable of accelerating ions up to MeV energies when an ultrashort 35-fs laser pulse at similar to2x10(18) W/cm(2) interacts with a small spherical target. Singly charged ions with different masses have similar energies. A simple phenomenological model describes how ultrashort and less-energy-consumptive pulses drive ions to MeV energies. The energetic and spatial-emission characteristics of protons, deuterons and oxygen ions released from water and heavy-water droplets of similar to15 mum in size was determined for this interaction scenario.
25.	Chubarova, Elena, et al. (author) Platinum zone plates for hard X-ray applications 2011 In: Microelectronic Engineering. - : Elsevier BV. - 0167-9317 .- 1873-5568. ; 88:10, s. 3123-3126 Journal article (peer-reviewed)abstract We describe the fabrication and evaluation of platinum zone plates for 5–12 kV X-ray imaging and focusing. These nano-scale circular periodic structures are fabricated by filling an e-beam generated mold with Pt in an electroplating process. The plating recipe is described. The resulting zone plates, having outer zone widths of 100 and 50 nm, show good uniformity and high aspect ratio. Their diffraction efficiencies are 50–70% of the theoretical, as measured at the European Synchrotron Radiation Facility. Platinum shows promise to become an attractive alternative to present hard X-ray zone plate materials due to its nano-structuring properties and the potential for zone-plate operation at higher temperatures.
26.	Fernandez, Angel Rodriguez, et al. (author) NanoMAX Beamline, a nanoprobe beamline for scattering and imaging at MAX IV 2018 In: Acta Crystallographica Section A. - : INT UNION CRYSTALLOGRAPHY. - 2053-2733. ; 74, s. E317-E318 Journal article (other academic/artistic)
27.	Fruke, R., et al. (author) Imaging of a laser plasma source at 13 nm wavelength approaching submicrometer resolution 2003 In: Journal de Physique IV. - : EDP Sciences. - 1155-4339 .- 1764-7177. ; 104, s. 153-156 Journal article (peer-reviewed)abstract Radiation in the extreme ultraviolet (EUV) spectral range is of interest for lithography and microscopy. Laser produced plasmas are sources for this kind of radiation. For successful usage it is necessary to study the source properties like size, stability and emitted spectra. For the spatial characterization of such a source a beamline was built up. The source was imaged at 13, 15 and 17 nm wavelength and at different laser energies with a resolution of better than 2 mum. As target material ethanol was used which was excited by a frequency-doubled Nd:YAG laser (lambda=532 nm; 3 ns, 30 Hz). The source was mapped with a zone plate (KZP5: d=2500 mum, Deltar(n)=0,523 mum). With a magnification of 61 the images were taken with a thinned back-illuminated CCD. Additionally a periodic structure was mapped with micrometer resolution, too.
28.	Hertz, Hans, et al. (author) Laboratory cryo soft X-ray microscopy 2012 In: Journal of Structural Biology. - : Elsevier. - 1047-8477 .- 1095-8657. ; 177:2, s. 267-272 Journal article (peer-reviewed)abstract Lens-based water-window X-ray microscopy allows two- and three-dimensional (2D and 3D) imaging of intact unstained cells in their near-native state with unprecedented contrast and resolution. Cryofixation is essential to avoid radiation damage to the sample. Present cryo X-ray microscopes rely on synchrotron radiation sources, thereby limiting the accessibility for a wider community of biologists. In the present paper we demonstrate water-window cryo X-ray microscopy with a laboratory-source-based arrangement. The microscope relies on a lambda = 2.48-nm liquid-jet high-brightness laser-plasma source, normal-incidence multilayer condenser optics, 30-nm zone-plate optics, and a cryo sample chamber. We demonstrate 2D imaging of test patterns, and intact unstained yeast, protozoan parasites and mammalian cells. Overview 3D information is obtained by stereo imaging while complete 3D microscopy is provided by full tomographic reconstruction. The laboratory microscope image quality approaches that of the synchrotron microscopes, but with longer exposure times. The experimental image quality is analyzed from a numerical wave-propagation model of the imaging system and a path to reach synchrotron-like exposure times in laboratory microscopy is outlined.
29.	Hertz, Hans, et al. (author) Laboratory Water-Window X-Ray Microscopy 2009 In: 2009 IEEE LEOS ANNUAL MEETING CONFERENCE PROCEEDINGS. - 9781424436804 ; , s. 48-48 Conference paper (peer-reviewed)abstract We review recent progress in laboratory water-window microscopy including 250 W/0.8 ns/2 kHz laser-plasma liquid-jet sources, 13-nm zone width diffractive optics, diffractive optical elements for phase-contrast microscopy, <25-nm resolution microscopy using compound zone plates, tomography and applications in soil science.
30.	Hertz, Hans M., et al. (author) Laboratory X-ray micro- and nano-imaging 2009 In: Frontiers in Optics (FiO) 2009. - Washington, D.C. : Optical Society of America. - 9781557528780 Conference paper (peer-reviewed)abstract We summarize recent progress in laboratory x-ray imaging systems based on compact high-brightness liquid-jet sources, including <25 nm soft x-ray zone-plate microscopy and <10 μm (lens-free) hard x-ray phase-contrast imaging.
31.	Hertz, Hans M., et al. (author) Laboratory x-ray micro imaging : Sources, optics, systems and applications 2009 In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 186 Journal article (peer-reviewed)abstract We summarize the recent progress in laboratory-scale soft and hard x-ray micro imaging in Stockholm. Our soft x-ray work is based on liquid-jet laser-plasma sources which are combined with diffractive and multilayer optics to form laboratory x-ray microscopes. In the hard x-ray regime the imaging is based on a liquid-metal-jet electron-impact source which provides the necessary coherence to allow phase-contrast imaging with high fidelity.
32.	Holmberg, Anders, et al. (author) Towards 10-nm Soft X-Ray Zone Plate Fabrication 2011 Conference paper (peer-reviewed)abstract In this paper the latest efforts to improve our nanofabrication process for soft x‐ray zone plates is presented. The resolving power, which is proportional to the smallest outermost zone width of the zone plate, is increased by introducing cold development of the electron beam resist that is used for the patterning. With this process we have fabricated Ni zone plates with 13‐nm outermost zone and shown potential for making 11‐nm half‐pitch lines in the electron beam resist. Maintaining the diffraction efficiency of the zone plate is a great concern when the outermost zone width is decreased. To resolve this problem we have developed the so‐called Ni‐Ge zone plate in which the zone plate is build up by Ni and Ge, resulting in an increase of the diffraction efficiency. In a proof‐of‐principle experiment with 25‐nm Ni‐Ge zone plates, we have shown a doubling of the diffraction efficiency. When combined with cold development, the Ni‐Ge process has been shown to work down to 16‐nm half‐pitch. It is plausible that further refinement of the process will make it possible to go to 10‐nm outermost zone widths.
33.	Hoppe, R., et al. (author) Full characterization of a focused wavefield with sub 100 nm resolution 2013 In: Advances In X-Ray Free-Electron Lasers II. - : SPIE - International Society for Optical Engineering. - 9780819495808 ; , s. 87780G- Conference paper (peer-reviewed)abstract A hard x-ray free-electron laser (XFEL) provides an x-ray source with an extraordinary high peak-brilliance, a time structure with extremely short pulses and with a large degree of coherence, opening the door to new scientific fields. Many XFEL experiments require the x-ray beam to be focused to nanometer dimensions or, at least, benefit from such a focused beam. A detailed knowledge about the illuminating beam helps to interpret the measurements or is even inevitable to make full use of the focused beam. In this paper we report on focusing an XFEL beam to a transverse size of 125nm and how we applied ptychographic imaging to measure the complex wavefield in the focal plane in terms of phase and amplitude. Propagating the wavefield back and forth we are able to reconstruct the full caustic of the beam, revealing aberrations of the nano-focusing optic. By this method we not only obtain the averaged illumination but also the wavefield of individual XFEL pulses.
34.	Johansson, Ulf, et al. (author) NanoMAX : the hard X-ray nanoprobe beamline at the MAX IV Laboratory 2021 In: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 28, s. 1935-1947 Journal article (peer-reviewed)abstract NanoMAX is the first hard X-ray nanoprobe beamline at the MAX IV laboratory. It utilizes the unique properties of the world's first operational multi-bend achromat storage ring to provide an intense and coherent focused beam for experiments with several methods. In this paper we present the beamline optics design in detail, show the performance figures, and give an overview of the surrounding infrastructure and the operational diffraction endstation.
35.	Johansson, Ulf, et al. (author) NanoMAX: A hard x-ray nanoprobe beamline at MAX IV 2013 In: X-ray Nanoimaging: Instruments and Methods. - : SPIE. - 1996-756X .- 0277-786X. ; 8851, s. 88510-88510 Conference paper (peer-reviewed)abstract We describe the design of the NanoMAX beamline to be built among the first phase beamlines of the MAX IV facility in Lund, Sweden. NanoMAX will be a hard X-ray imaging beamline providing down to 10 nm in direct spatial resolution, enabling investigations of very small heterogeneous samples exploring methods of diffraction, scattering, absorption, phase contrast and fluorescence. The beamline will have two experimental stations using Fresnel zone plates and Kirkpatrick-Baez mirror optics for beam focusing, respectively. This paper focuses on the optical design of the beamline excluding the experimental stations but also describes general ideas about the endstations and the nano-focusing optics to be used. The NanoMAX beamline is planned to be operational late 2016.
36.	Kahnt, Maik, et al. (author) Current capabilities of the imaging endstation at the NanoMAX beamline 2023 In: AIP Conference Proceedings. - : AIP Publishing. Conference paper (peer-reviewed)abstract The new imaging endstation of the NanoMAX beamline is being designed to complement the already existing diffraction endstation: measurements with smaller beams at lower photons energies, with higher stability, in vacuum and with sample cooling at the measurement position, optimized for X-ray fluorescence mapping and ptychographic imaging in two and three spatial dimensions. This comes at the cost of reduced flexibility and fewer degrees of freedom. We hereby present the results of the in-air commissioning of the main components for the new endstation and the data quality that has already been achieved.
37.	Kaulich, B, et al. (author) TwinMic : A European Twin X-ray Microscopy Station Commissioned at ELETTRA 2006 In: Proc. 8th Int. Conf. X-ray Microscopy. ; , s. 22-25 Conference paper (peer-reviewed)
38.	Kaulich, B., et al. (author) TwinMic - Combined scanning and full-field imaging microscopy with novel contrast mechanisms 2003 In: Synchrotron Radiation News. ; 16, s. 49-52 Journal article (peer-reviewed)
39.	Korn, G., et al. (author) Ultrashort 1-kHz laser plasma hard x-ray source 2002 In: Optics Letters. - 0146-9592 .- 1539-4794. ; 27:10, s. 866-868 Journal article (peer-reviewed)abstract We achieved a continuous, stable, ultrashort pulse hard x-ray point source by focusing 1.8-W, 1-kHz, 50-fs laser pulses onto a novel, 30-mum-diameter, high-velocity, liquid-metal gallium jet. This target geometry avoids most of the debris problems of solid targets and provides nearly 4pi illumination. Photon fluxes of 5 X 10(8) photons/s are generated in a two-component spectrum consisting of a broad continuum from 4 to 14 keV and strong K-alpha and K-beta emission lines at 9.25 and 10.26 keV. This source will find wide use in time-resolved x-ray diffraction studies and other applications.
40.	Kretzschmar, Moritz, et al. (author) Multiple inert gas elimination technique by micropore membrane inlet mass spectrometry-a comparison with reference gas chromatography 2013 In: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 115:8, s. 1107-1118 Journal article (peer-reviewed)abstract The mismatching of alveolar ventilation and perfusion (V-A/Q) is the major determinant of impaired gas exchange. The gold standard for measuring V-A/Q distributions is based on measurements of the elimination and retention of infused inert gases. Conventional multiple inert gas elimination technique (MIGET) uses gas chromatography (GC) to measure the inert gas partial pressures, which requires tonometry of blood samples with a gas that can then be injected into the chromatograph. The method is laborious and requires meticulous care. A new technique based on micropore membrane inlet mass spectrometry (MMIMS) facilitates the handling of blood and gas samples and provides nearly real-time analysis. In this study we compared MIGET by GC and MMIMS in 10 piglets: 1) 3 with healthy lungs; 2) 4 with oleic acid injury; and 3) 3 with isolated left lower lobe ventilation. The different protocols ensured a large range of normal and abnormal V-A/Q distributions. Eight inert gases (SF6, krypton, ethane, cyclopropane, desflurane, enflurane, diethyl ether, and acetone) were infused; six of these gases were measured with MMIMS, and six were measured with GC. We found close agreement of retention and excretion of the gases and the constructed V-A/Q distributions between GC and MMIMS, and predicted Pa-O2 from both methods compared well with measured Pa-O2. V-A/Q by GC produced more widely dispersed modes than MMIMS, explained in part by differences in the algorithms used to calculate V-A/Q distributions. In conclusion, MMIMS enables faster measurement of V-A/Q, is less demanding than GC, and produces comparable results.
41.	Kördel, Mikael, et al. (author) Biological Laboratory X-Ray Microscopy 2019 In: X-Ray Nanoimaging. - : SPIE - International Society for Optical Engineering. - 9781510629189 Conference paper (peer-reviewed)abstract Zone-plate-based soft x-ray microscopes operating in the water window allow high-resolution and high-contrast imaging of intact cells in their near-native state. Laboratory-source-based x-ray microscopes are an important complement to the accelerator-based instruments, providing high accessibility and allowing close integration with other cell-biological techniques. Here we present recent biological applications using the Stockholm laboratory water-window x-ray microscope, which is based on a liquid-nitrogen-jet laser-plasma source. Technical improvements to the microscope in the last few years have resulted in increased x-ray flux at the sample and significantly improved stability and reliability. In addition to this, vibrations in key components have been measured, analyzed and reduced to improve the resolution to 25 nm half-period. The biological applications include monitoring the development of carbon-dense vesicles in starving human embryonic kidney cells (HEK293T), imaging the interaction between natural killer (NK) cells and HEK293T target cells, and most recently studying a newly discovered giant DNA virus and the process of viral replication inside a host amoeba. All biological imaging was done on cryo-frozen hydrated samples in 2D and in some cases 3D.
42.	Kördel, Mikael (author) Biological Laboratory X-Ray Microscopy 2020 Doctoral thesis (other academic/artistic)abstract Soft x-ray microscopy in the water window (? ≈ 2.3 − 4.3 nm) is a powerful technique for high-resolution biological imaging. The strong natural contrast between carbon-based structures and water allows visualization of hydrated and unstained samples, while providing enough transmission through up to ∼ 10 μm of organic matter. Furthermore, the full potential of this technique can be exploited by performing computed tomography, thus obtaining a complete 3D image of the object.Routine short-exposure water-window microscopy of whole cells and tissue is currently performed at synchrotron-radiation facilities around the world, but with a limited accessibility to the wider research community. For this reason, laboratory-based systems have been developed, which are now reaching maturity. The benefits compared to the synchrotron-based instruments include easier integration with complementary methods in the home laboratory, in addition to the increased access that allows for the often time-consuming optimization of experimental parameters as well as longitudinal studies.This Thesis presents recent developments of the Stockholm laboratory x-ray microscope as well as several biological applications. Work has been done on improving the mechanical and thermal stability of the microscope, resulting in a resolution of 25 nm (half period) in images of test targets. The biological applications were enabled by a significantly increased x-ray flux through the system as well as an improved operational stability. This work demonstrates 10-second exposure imaging of whole cryofixed cells, imaging of viral infections in cells, and 20 minutes total exposure cryotomography.
43.	Kördel, Mikael, et al. (author) Laboratory water-window x-ray microscopy Other publication (other academic/artistic)
44.	Kördel, Mikael, et al. (author) Laboratory water-window x-ray microscopy 2020 In: Optica. - : The Optical Society. - 2334-2536. ; 7:6, s. 658-674 Research review (peer-reviewed)abstract Soft x-ray microscopy in the water window (similar to 285-535 eV) is an emerging and unique tool for 2D and 3D imaging of unstained intact cellular samples in their near-native state with few-10-nm detail. However, present microscopes rely on the high x-ray brightness of synchrotron-radiation sources. Having access to water-window microscopy in the home laboratory would increase the impact and extend the applicability of the method. In the present paper, we review three decades of efforts to build laboratory water-window microscopes and conclude that the method is now reaching the maturity to allow biological studies. The instruments as well as their key components are quantitatively and qualitatively compared. We find that the brightness and the reliability of the laboratory source are the most critical parameters, but that the optics as well as the sample preparation also must be optimized to enable high-resolution imaging with adequate exposure times. We then describe the two sister microscopes in Stockholm and Berlin, which allow reliable high-resolution biological imaging with short exposure times of a few tens of seconds in 2D and a few tens of minutes in 3D. They both rely on a liquid-jet laser-plasma source combined with high-reflectivity normal-incidence multilayer condenser optics, high-resolution zone-plate imaging optics, CCD detection, and cryogenic sample handling. Finally, we present several examples of biological imaging demonstrating the unique properties of these instruments.
45.	Kördel, Mikael, et al. (author) Stability investigation of a cryo soft x-ray microscope by fiber interferometry 2020 In: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 91:2 Journal article (peer-reviewed)abstract We present a stability investigation of the Stockholm laboratory cryo soft x-ray microscope. The microscope operates at a wavelength of 2.48 nm and can image biological samples at liquid-nitrogen temperatures in order to mitigate radiation damage. We measured the stability of the two most critical components, sample holder and optics holder, in vacuo and at cryo temperatures at both short and long time scales with a fiber interferometer. Results revealed vibrations in the kHz range, originating mainly from a turbo pump, as well as long term drifts in connection with temperature fluctuations. With improvements in the microscope, earlier stability issues vanished and close-to diffraction-limited imaging could be achieved. Moreover, our investigation shows that fiber interferometers are a powerful tool in order to investigate position-sensitive setups at the nanometer level.
46.	Larsson, Jakob C. (author) Laboratory x-ray fluorescence tomography 2018 Doctoral thesis (other academic/artistic)abstract X-ray fluorescence (XRF) tomography is an emerging bio-imaging modality with potential for high-resolution molecular imaging in 3D. In this technique the fluorescence signal from targeted nanoparticles (NPs) is measured, providing information about the spatial distribution and concentration of the NPs inside the object. However, present laboratory XRF tomographysystems typically have limited spatial resolution (>1 mm) and suffer from long scan times and high radiation dose even at high NP concentrations, mainly due to low efficiency and poor signal-to-noise ratio (SNR). Other macroscopic biomedical imaging methods provide either structural information with high spatial resolution (e.g., CT) or functional/molecularinformation with lower resolution (e.g., PET).In this Thesis we present a laboratory XRF tomography system with high spatial resolution (sub-200 μm), low NP concentration and vastly reduced scan times and dose, opening up the possibilities for in vivo small-animal imaging research. The system consists of a high-brightness liquid-metal-jet microfocus x-ray source, x-ray focusing optics and two photon counting detectors. By using the source’s characteristic 24 keV line emission together with spectrally matched molybdenum NPs the Compton background is greatly reduced, increasing the SNR. Each measurement provides information about the spatial distribution and concentration of the NPs, as well as the absorption of the object. An iterative method is used to get aquantitative reconstruction of the XRF image. The reconstructed absorption and XRF images are finally combined into a single 3D overlay image.Using this system we have demonstrated high-resolution dual CT and XRF imaging of both phantoms and mice at radiation doses compatible with in vivo small-animal imaging.
47.	Legall, H., et al. (author) Compact X-ray microscope for the water window based on a high brightness laser plasma source 2012 In: Optics Express. - 1094-4087. ; 20:16, s. 18362-18369 Journal article (peer-reviewed)abstract We present a laser plasma based x-ray microscope for the water window employing a high-average power laser system for plasma generation. At 90 W laser power a brightness of 7.4 x 10(11) photons/(s x sr x mu m(2)) was measured for the nitrogen Ly alpha line emission at 2.478 nm. Using a multilayer condenser mirror with 0.3 % reflectivity 10(6) photons/(mu m(2) x s) were obtained in the object plane. Microscopy performed at a laser power of 60 W resolves 40 nm lines with an exposure time of 60 s. The exposure time can be further reduced to 20 s by the use of new multilayer condenser optics and operating the laser at its full power of 130 W.
48.	Legall, H., et al. (author) Spatial and spectral characterization of a laser produced plasma source for extreme ultraviolet metrology 2004 In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 75:11, s. 4981-4988 Journal article (peer-reviewed)abstract We present a laser produced plasma (LPP) source optimized for metrology and the results of its radiometric characterization. The presented (LPP) source can be used for reflectometry and spectroscopy in the soft x-ray range. For these applications, stable operation with high spectral photon yields high reliability in continuous operation and, to reach high spectral resolution, a small source size and high source point stability is necessary. For the characterization of the source, special instruments have been designed and calibrated using the soft x-ray radiometry beamline of the Physikalisch-Technische-Bundesanstalt at BESSY. These instruments are an imaging spectrometer, a double multilayer tool for in-band power measurements, a transmission slit grating spectrograph, and a pinhole camera. From the measurements a source size of 30 mumx55 mum (2sigma, horizontal by vertical) and a stability of better than 5 mum horizontally and 9 mum vertically were obtained. The source provides a flat continuous emission in the extreme ultraviolet (EUV) range around 13.4 nm and a spectral photon flux of up to 1*10(14)/(s sr 0.1 nm) at a pump laser pulse energy of 650 mJ. The shot-to-shot stability of the source is about 5% (1sigma) for laser pulse energies above 200 mJ. It is shown that an Au-LPP source provides spectrally reproducible emission with sufficient power at low debris conditions for the operation of a laboratory based EUV reflectometer and for spectroscopy.
49.	Lindblom, Magnus, et al. (author) Flexible Liquid-Filled Scintillating Fibers for X-Ray Detection 2023 In: 2023 IEEE SENSORS, SENSORS 2023 - Conference Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE). Conference paper (peer-reviewed)abstract We present the design and fabrication of flexible, liquid-filled scintillating fibers for X-ray detection made from silica fibers and silica capillaries. The scintillating fibers were characterized using ultraviolet light exposure and we also performed an experiment demonstrating X-ray detection.
50.	Lindblom, Magnus, et al. (author) High-resolution differential-interference-contrast x-ray zone plates : Design and Fabrication 2007 In: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier BV. - 0584-8547 .- 1873-3565. ; 62:6-7, s. 539-543 Journal article (peer-reviewed)abstract Differential interference contrast is a potentially powerful technique for contrast enhancement in soft X-ray microscopy. We describe the design and fabrication of single-element diffractive optical elements suitable as objectives for high-resolution differential interference contrast microscopy in the water-window spectral range. A one-dimensional pattern calculation followed by an extension to two dimensions results in a pattern resolution of 1 nm, which is well below fabrication accuracy. The same fabrication process as for normal zone plates is applicable, but special care must be taken when converting the calculated pattern to a code for e-beam lithography.

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