| 1. |
- Daurer, Benedikt J., et al.
(författare)
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Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses
- 2017
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Ingår i: IUCrJ. - : INT UNION CRYSTALLOGRAPHY. - 2052-2525. ; 4, s. 251-262
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Tidskriftsartikel (refereegranskat)abstract
- This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. Aerosolized Omono River virus particles of similar to 40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to a wider than expected size distribution (from similar to 35 to similar to 300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 * 10(12) photons per mu m(2) per pulse. The full-width of the focus at half-maximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. The results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers.
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| 2. |
- Franchi, Daniele, et al.
(författare)
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Synthesis and Characterization of New Organic Dyes Containing the Indigo Core
- 2020
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Ingår i: Molecules. - : MDPI AG. - 1431-5157 .- 1420-3049. ; 25:15, s. 3377-
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Tidskriftsartikel (refereegranskat)abstract
- A new series of symmetrical organic dyes containing an indigo central core decorated with different electron donor groups have been prepared, starting from Tyrian Purple and using the Pd-catalyzed Stille-Migita coupling process. The effect of substituents on the spectroscopic properties of the dyes has been investigated theoretically and experimentally. In general, all dyes presented intense light absorption bands, both in the blue and red regions of the visible spectrum, conferring them a bright green color in solution. Using the same approach, an asymmetrically substituted D-A-pi-A green dye, bearing a triarylamine electron donor and the cyanoacrylate acceptor/anchoring group, has been synthesized for the first time and fully characterized, confirming that spectroscopic and electrochemical properties are consistent with a possible application in dye-sensitized solar cells (DSSC).
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| 3. |
- Gorkhover, Tais, et al.
(författare)
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Femtosecond X-ray Fourier holography imaging of free-flying nanoparticles
- 2018
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 12:3, s. 150-153
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast X-ray imaging on individual fragile specimens such as aerosols 1 , metastable particles 2 , superfluid quantum systems 3 and live biospecimens 4 provides high-resolution information that is inaccessible with conventional imaging techniques. Coherent X-ray diffractive imaging, however, suffers from intrinsic loss of phase, and therefore structure recovery is often complicated and not always uniquely defined 4,5 . Here, we introduce the method of in-flight holography, where we use nanoclusters as reference X-ray scatterers to encode relative phase information into diffraction patterns of a virus. The resulting hologram contains an unambiguous three-dimensional map of a virus and two nanoclusters with the highest lateral resolution so far achieved via single shot X-ray holography. Our approach unlocks the benefits of holography for ultrafast X-ray imaging of nanoscale, non-periodic systems and paves the way to direct observation of complex electron dynamics down to the attosecond timescale.
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| 4. |
- Lundholm, Ida V., et al.
(författare)
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Considerations for three-dimensional image reconstruction from experimental data in coherent diffractive imaging
- 2018
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Ingår i: IUCrJ. - : International Union of Crystallography. - 2052-2525. ; 5, s. 531-541
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Tidskriftsartikel (refereegranskat)abstract
- Diffraction before destruction using X-ray free-electron lasers (XFELs) has the potential to determine radiation-damage-free structures without the need for crystallization. This article presents the three-dimensional reconstruction of the Melbournevirus from single-particle X-ray diffraction patterns collected at the LINAC Coherent Light Source (LCLS) as well as reconstructions from simulated data exploring the consequences of different kinds of experimental sources of noise. The reconstruction from experimental data suffers from a strong artifact in the center of the particle. This could be reproduced with simulated data by adding experimental background to the diffraction patterns. In those simulations, the relative density of the artifact increases linearly with background strength. This suggests that the artifact originates from the Fourier transform of the relatively flat background, concentrating all power in a central feature of limited extent. We support these findings by significantly reducing the artifact through background removal before the phase-retrieval step. Large amounts of blurring in the diffraction patterns were also found to introduce diffuse artifacts, which could easily be mistaken as biologically relevant features. Other sources of noise such as sample heterogeneity and variation of pulse energy did not significantly degrade the quality of the reconstructions. Larger data volumes, made possible by the recent inauguration of high repetition-rate XFELs, allow for increased signal-to-background ratio and provide a way to minimize these artifacts. The anticipated development of three-dimensional Fourier-volume-assembly algorithms which are background aware is an alternative and complementary solution, which maximizes the use of data.
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| 5. |
- Passoni, Matteo, et al.
(författare)
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Energetic ions at moderate laser intensities using foam-based multi-layered targets
- 2014
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 56:4, s. 045001-
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Tidskriftsartikel (refereegranskat)abstract
- The experimental feasibility of the laser-driven ion acceleration concept with multi-layered,foam-based targets has been investigated. Targets with the required features have beenproduced and characterized, exploiting the potential of the pulsed laser deposition technique.In the intensity range 1016–1017 Wcm−2, they allow us to obtain maximum proton energies2–3 times higher compared to bare solid targets, able to reach and surpass the MeV range withboth low and ultrahigh contrast pulses. The results of two-dimensional particle-in-cellsimulations, supporting the interpretation of the experimental results, and directions to exploitthe concept also at ultrahigh intensities, are presented.
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| 6. |
- Rath, Asawari D., et al.
(författare)
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Explosion dynamics of sucrose nanospheres monitored by time of flight spectrometry and coherent diffractive imaging at the split-and-delay beam line of the FLASH soft X-ray laser
- 2014
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Ingår i: Optics Express. - 1094-4087. ; 22:23, s. 28914-28925
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Tidskriftsartikel (refereegranskat)abstract
- We use a Mach-Zehnder type autocorrelator to split and delay XUV pulses from the FLASH soft X-ray laser for triggering and subsequently probing the explosion of aerosolised sugar balls. FLASH was running at 182 eV photon energy with pulses of 70 fs duration. The delay between the pump-probe pulses was varied between zero and 5 ps, and the pulses were focused to reach peak intensities above 1016 W/cm2 with an off-axis parabola. The direct pulse triggered the explosion of single aerosolised sucrose nano-particles, while the delayed pulse probed the exploding structure. The ejected ions were measured by ion time of flight spectrometry, and the particle sizes were measured by coherent diffractive imaging. The results show that sucrose particles of 560-1000 nm diameter retain their size for about 500 fs following the first exposure. Significant sample expansion happens between 500 fs and 1 ps. We present simulations to support these observations.
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| 7. |
- Zani, Lorenzo, et al.
(författare)
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Transition metal-catalyzed cross-coupling methodologies for the engineering of small molecules with applications in organic electronics and photovoltaics
- 2019
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Ingår i: Coordination chemistry reviews. - : Elsevier. - 0010-8545 .- 1873-3840. ; 392, s. 177-236
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Forskningsöversikt (refereegranskat)abstract
- Cross-coupling reactions have played a key role in producing numerous types of it-conjugated small molecules having appealing properties for practical applications in organic electronics, especially in the field of photovoltaics. The main advantages of such synthetic methodology are the compatibility with many types of functional groups and the flexibility which allows an easy way to introduce diversity and tune the electronic and photophysical properties of the target molecules. As a result, many semiconducting and photoactive organic compounds have been synthesized using this powerful tool. In this paper we will highlight a number of selected syntheses and optimized C-C bond formation processes described in the years 2000-2018 and related to this specific field, choosing those examples which can demonstrate the enormous power of the cross-coupling processes, but also the room for improvements of these methodologies.
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