Multispectroscopic Study of Single Xe Clusters Using XFEL Pulses

X-ray free-electron lasers (XFELs) deliver ultrashort coherent laser pulses in the X-ray spectral regime, enabling novel investigations into the structure of individual nanoscale samples. In this work, we demonstrate how single-shot small-angle X-ray scattering (SAXS) measurements combined with fluorescence and ion time-of-flight (TOF) spectroscopy can be used to obtain size- and structure-selective evaluation of the light-matter interaction processes on the nanoscale. We recorded the SAXS images of single xenon clusters using XFEL pulses provided by the SPring-8 Angstrom compact free-electron laser (SACLA). The XFEL fluences and the radii of the clusters at the reaction point were evaluated and the ion TOF spectra and fluorescence spectra were sorted accordingly. We found that the XFEL fluence and cluster size extracted from the diffraction patterns showed a clear correlation with the fluorescence and ion TOF spectra. Our results demonstrate the effectiveness of the multispectroscopic approach for exploring laser–matter interaction in the X-ray regime without the influence of the size distribution of samples and the fluence distribution of the incident XFEL pulses.

Refinement for single-nanoparticle structure determination from low-quality single-shot coherent diffraction data

Christoph Bostedt, Christophe Nicolas

With the emergence of X-ray free-electron lasers, it is possible to investigate the structure of nanoscale samples by employing coherent diffractive imaging in the X-ray spectral regime. In this work, we developed a refinement method for structure reconstruction applicable to low-quality coherent diffraction data. The method is based on the gradient search method and considers the missing region of a diffraction pattern and the small number of detected photons. We introduced an initial estimate of the structure in the method to improve the convergence. The present method is applied to an experimental diffraction pattern of an Xe cluster obtained in an X-ray scattering experiment at the SPring-8 Angstrom Compact free-electron LAser (SACLA) facility. It is found that the electron density is successfully reconstructed from the diffraction pattern with a large missing region, with a good initial estimate of the structure. The diffraction pattern calculated from the reconstructed electron density reproduced the observed diffraction pattern well, including the characteristic intensity modulation in each ring. Our refinement method enables structure reconstruction from diffraction patterns under difficulties such as missing areas and low diffraction intensity, and it is potentially applicable to the structure determination of samples that have low scattering power.

INT UNION CRYSTALLOGRAPHY2020

FM-AFM constant height imaging and force curves: high resolution study of DNA-tip interactions

Livan Bladimir Alonso Sarduy, Andrea Cerreta, Giovanni Dietler, Dusan Vobornik

Interaction of the atomic force microscopy (AFM) tip with the sample can be invasive for soft samples. Frequency Modulation (FM) AFM is gentler because it allows scanning in the non-contact regime where only attractive forces exist between the tip and the sample, and there is no sample compression. Recently, FM-AFM was used to resolve the atomic structure of single molecules of pentacene and of carbon nanotubes. We are testing similar FM-AFM-based approaches to study biological samples. We present FM-AFM experiments on dsDNA deposited on 3-aminopropyltriethoxysilane modified mica in ultra high vacuum. With flexible samples such as DNA, the substrate flatness is a sub-molecular resolution limiting factor. Non-contact topographic images of DNA show variations that have the periodicity of the right handed helix of B-form DNA - this is an unexpected result as dehydrated DNA is thought to assume the A-form structure. Frequency shift maps at constant height allow working in the non-monotonic frequency shift range, show a rich contrast that changes significantly with the tip-sample separation, and show 0.2 to 0.4 nm size details on DNA. Frequency shift versus distance curves acquired on DNA molecules and converted in force curves show that for small molecules (height

Wiley-Blackwell2012

Taking a snapshot of the triplet excited state of an OLED organometallic luminophore using X-rays

Camila Bacellar Cases Da Silveira, Martin Beck, Andrea Cannizzo, Giulia Fulvia Mancini, Samuel Menzi

OLED technology beyond small or expensive devices requires light-emitters, luminophores, based on earth-abundant elements. Understanding and experimental verification of charge transfer in luminophores are needed for this development. An organometallic multicore Cu complex comprising Cu-C and Cu-P bonds represents an underexplored type of luminophore. To investigate the charge transfer and structural rearrangements in this material, we apply complementary pump-probe X-ray techniques: absorption, emission, and scattering including pump-probe measurements at the X-ray free-electron laser SwissFEL. We find that the excitation leads to charge movement from C- and P- coordinated Cu sites and from the phosphorus atoms to phenyl rings; the Cu core slightly rearranges with 0.05 angstrom increase of the shortest Cu-Cu distance. The use of a Cu cluster bonded to the ligands through C and P atoms is an efficient way to keep structural rigidity of luminophores. Obtained data can be used to verify computational methods for the development of luminophores. OLED materials based on thermally activated delayed fluorescence have promising efficiency. Here, the authors investigate an organometallic multicore Cu complex as luminophore, by pump-probe X-ray techniques at three different facilities deriving a complete picture of the charge transfer in the triplet excited state.

NATURE PUBLISHING GROUP2020