Publications by authors named "Michael Krisch"

40 Publications

Transient and Efficient Vascular Permeability Window for Adjuvant Drug Delivery Triggered by Microbeam Radiation.

Cancers (Basel) 2021 04 27;13(9). Epub 2021 Apr 27.

Institute of Anatomy, University of Bern, 3012 Bern, Switzerland.

Background: Microbeam Radiation Therapy (MRT) induces a transient vascular permeability window, which offers a novel drug-delivery system for the preferential accumulation of therapeutic compounds in tumors. MRT is a preclinical cancer treatment modality that spatially fractionates synchrotron X-rays into micrometer-wide planar microbeams which can induce transient vascular permeability, especially in the immature tumor vessels, without compromising vascular perfusion. Here, we characterized this phenomenon using Chicken Chorioallantoic Membrane (CAM) and demonstrated its therapeutic potential in human glioblastoma xenografts in mice.

Methods: the developing CAM was exposed to planar-microbeams of 75 Gy peak dose with Synchrotron X-rays. Similarly, mice harboring human glioblastoma xenografts were exposed to peak microbeam doses of 150 Gy, followed by treatment with Cisplatin. Tumor progression was documented by Magnetic Resonance Imaging (MRI) and caliper measurements.

Results: CAM exposed to MRT exhibited vascular permeability, beginning 15 min post-irradiation, reaching its peak from 45 min to 2 h, and ending by 4 h. We have deemed this period the "permeability window". Morphological analysis showed partially fragmented endothelial walls as the cause of the increased transport of FITC-Dextran into the surrounding tissue and the extravasation of 100 nm microspheres (representing the upper range of nanoparticles). In the human glioblastoma xenografts, MRI measurements showed that the combined treatment dramatically reduced the tumor size by 2.75-fold and 5.25-fold, respectively, compared to MRT or Cisplatin alone.

Conclusions: MRT provides a novel mechanism for drug delivery by increasing vascular transpermeability while preserving vessel integrity. This permeability window increases the therapeutic index of currently available chemotherapeutics and could be combined with other therapeutic agents such as Nanoparticles/Antibodies/etc.
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http://dx.doi.org/10.3390/cancers13092103DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8123803PMC
April 2021

Unexpected Benefits of Multiport Synchrotron Microbeam Radiation Therapy for Brain Tumors.

Cancers (Basel) 2021 Feb 24;13(5). Epub 2021 Feb 24.

INSERM UA7, STROBE, 71 Av. des Martyrs, 38000 Grenoble, France.

Delivery of high-radiation doses to brain tumors via multiple arrays of synchrotron X-ray microbeams permits huge therapeutic advantages. Brain tumor (9LGS)-bearing and normal rats were irradiated using a conventional, homogeneous Broad Beam (BB), or Microbeam Radiation Therapy (MRT), then studied by behavioral tests, MRI, and histopathology. A valley dose of 10 Gy deposited between microbeams, delivered by a single port, improved tumor control and median survival time of tumor-bearing rats better than a BB isodose. An increased number of ports and an accumulated valley dose maintained at 10 Gy delayed tumor growth and improved survival. Histopathologically, cell death, vascular damage, and inflammatory response increased in tumors. At identical valley isodose, each additional MRT port extended survival, resulting in an exponential correlation between port numbers and animal lifespan (r = 0.9928). A 10 Gy valley dose, in MRT mode, delivered through 5 ports, achieved the same survival as a 25 Gy BB irradiation because of tumor dose hot spots created by intersecting microbeams. Conversely, normal tissue damage remained minimal in all the single converging extratumoral arrays. Multiport MRT reached exceptional ~2.5-fold biological equivalent tumor doses. The unique normal tissue sparing and therapeutic index are eminent prerequisites for clinical translation.
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http://dx.doi.org/10.3390/cancers13050936DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7956531PMC
February 2021

Complete Remission of Mouse Melanoma after Temporally Fractionated Microbeam Radiotherapy.

Cancers (Basel) 2020 Sep 17;12(9). Epub 2020 Sep 17.

Institute of Anatomy, University of Bern, 3012 Bern, Switzerland.

Background: Synchrotron Microbeam Radiotherapy (MRT) significantly improves local tumour control with minimal normal tissue toxicity. MRT delivers orthovoltage X-rays at an ultra-high "FLASH" dose rate in spatially fractionated beams, typically only few tens of micrometres wide. One of the biggest challenges in translating MRT to the clinic is its use of high peak doses, of around 300-600 Gy, which can currently only be delivered by synchrotron facilities. Therefore, in an effort to improve the translation of MRT to the clinic, this work studied whether the temporal fractionation of traditional MRT into several sessions with lower, more clinically feasible, peak doses could still maintain local tumour control.

Methods: Two groups of twelve C57Bl/6J female mice harbouring B16-F10 melanomas in their ears were treated with microbeams of 50 µm in width spaced by 200 µm from their centres. The treatment modality was either (i) a single MRT session of 401.23 Gy peak dose (7.40 Gy valley dose, i.e., dose between beams), or (ii) three MRT sessions of 133.41 Gy peak dose (2.46 Gy valley dose) delivered over 3 days in different anatomical planes, which intersected at 45 degrees. The mean dose rate was 12,750 Gy/s, with exposure times between 34.2 and 11.4 ms, respectively.

Results: Temporally fractionated MRT ablated 50% of B16-F10 mouse melanomas, preventing organ metastases and local tumour recurrence for 18 months. In the rest of the animals, the median survival increased by 2.5-fold in comparison to the single MRT session and by 4.1-fold with respect to untreated mice.

Conclusions: Temporally fractionating MRT with lower peak doses not only maintained tumour control, but also increased the efficacy of this technique. These results demonstrate that the solution to making MRT more clinically feasible is to irradiate with several fractions of intersecting arrays with lower peak doses. This provides alternatives to synchrotron sources where future microbeam radiotherapy could be delivered with less intense radiation sources.
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http://dx.doi.org/10.3390/cancers12092656DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7563854PMC
September 2020

A comparative dosimetry study of an alanine dosimeter with a PTW PinPoint chamber at ultra-high dose rates of synchrotron radiation.

Phys Med 2020 Mar 9;71:161-167. Epub 2020 Mar 9.

ESRF-The European Synchrotron, ID17 Biomedical beamline, 71 Avenue des Martyrs, 38000 Grenoble, France.

The use of synchrotron X-ray sources provides innovative approaches in radiation therapy. The unique possibility to generate quasi-parallel beams promoted the development of microbeam radiation therapy (MRT), an innovative approach able to reduce damages to normal tissues while delivering considerable doses in the lesion. Accurate dosimetry in broad-beam configuration (prior to the spatial fractionation of the incident X-ray fan) is very challenging at ultra-high dose rate synchrotron sources. The available reference dosimetry protocol based on the use of a PTW PinPoint ionization chamber was compared with alanine dosimetry at the European Synchrotron Radiation Facility (ESRF) ID17 Biomedical beamline, an orthovoltage X-ray source with an average dose rate of 11.6 kGy/s. Reference dose measurements of the alanine pellets were performed at the National Centre for Radiation Research and Technology (NCRRT) Co facility in Egypt. All alanine dosimeters were analysed by an electron paramagnetic resonance spectrometer. We determined a relative response r = 0.932 ± 0.027 (1σ) of the alanine pellets irradiated at the ESRF compared to the Co facility. Considering the appropriate corrections for the ESRF polychromatic spectrum and the different field size used, our result is in agreement with the previous work of Waldeland et al. for which the utilised alanine contained the same amount of binder, and it is consistent with the works of Anton et al. and Butler et al. for which the utilised alanine contained a higher amount of binder. We confirm that alanine is an appropriate dosimeter for ultra-high dose rate calibration of orthovoltage X-ray sources.
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http://dx.doi.org/10.1016/j.ejmp.2020.03.007DOI Listing
March 2020

Synchrotron X-Ray Boost Delivered by Microbeam Radiation Therapy After Conventional X-Ray Therapy Fractionated in Time Improves F98 Glioma Control.

Int J Radiat Oncol Biol Phys 2020 06 21;107(2):360-369. Epub 2020 Feb 21.

Inserm UA7, Rayonnement synchrotron pour la recherche médicale (STROBE), Université Grenoble Alpes, Grenoble, France.

Purpose: Synchrotron microbeam radiation therapy (MRT) is based on the spatial fractionation of the incident, highly collimated synchrotron beam into arrays of parallel microbeams depositing several hundred grays. It appears relevant to combine MRT with a conventional treatment course, preparing a treatment scheme for future patients in clinical trials. The efficiency of MRT delivered after several broad-beam (BB) fractions to palliate F98 brain tumors in rats in comparison with BB fractions alone was evaluated in this study.

Methods And Materials: Rats bearing 10 F98 cells implanted in the caudate nucleus were irradiated by 5 fractions in BB mode (3 × 6 Gy + 2 × 8 Gy BB) or by 2 boost fractions in MRT mode to a total of 5 fractions (3 × 6 Gy BB + MRT 2 × 8 Gy valley dose; peak dose 181 Gy [50/200 μm]). Tumor growth was evaluated in vivo by magnetic resonance imaging follow-up at T, T, T, T, T, and T days after radiation therapy and by histology and flow cytometry.

Results: MRT-boosted tumors displayed lower cell density and cell proliferation compared with BB-irradiated tumors. The MRT boost completely stopped tumor growth during ∼4 weeks and led to a significant increase in median survival time, whereas tumors treated with BB alone recurred within a few days after the last radiation fraction.

Conclusions: The first evidence is presented that MRT, delivered as a boost of conventionally fractionated irradiation by orthovoltage broad x-ray beams, is feasible and more efficient than conventional radiation therapy alone.
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http://dx.doi.org/10.1016/j.ijrobp.2020.02.023DOI Listing
June 2020

Technical advances in x-ray microbeam radiation therapy.

Phys Med Biol 2020 01 17;65(2):02TR01. Epub 2020 Jan 17.

Department of Radiation Oncology, School of Medicine, Technical University of Munich, Klinikum rechts der Isar, Munich, Germany. Helmholtz Centre Munich, Institute for Radiation Medicine, Munich, Germany.

In the last 25 years microbeam radiation therapy (MRT) has emerged as a promising alternative to conventional radiation therapy at large, third generation synchrotrons. In MRT, a multi-slit collimator modulates a kilovoltage x-ray beam on a micrometer scale, creating peak dose areas with unconventionally high doses of several hundred Grays separated by low dose valley regions, where the dose remains well below the tissue tolerance level. Pre-clinical evidence demonstrates that such beam geometries lead to substantially reduced damage to normal tissue at equal tumour control rates and hence drastically increase the therapeutic window. Although the mechanisms behind MRT are still to be elucidated, previous studies indicate that immune response, tumour microenvironment, and the microvasculature may play a crucial role. Beyond tumour therapy, MRT has also been suggested as a microsurgical tool in neurological disorders and as a primer for drug delivery. The physical properties of MRT demand innovative medical physics and engineering solutions for safe treatment delivery. This article reviews technical developments in MRT and discusses existing solutions for dosimetric validation, reliable treatment planning and safety. Instrumentation at synchrotron facilities, including beam production, collimators and patient positioning systems, is also discussed. Specific solutions reviewed in this article include: dosimetry techniques that can cope with high spatial resolution, low photon energies and extremely high dose rates of up to 15 000 Gy s, dose calculation algorithms-apart from pure Monte Carlo Simulations-to overcome the challenge of small voxel sizes and a wide dynamic dose-range, and the use of dose-enhancing nanoparticles to combat the limited penetrability of a kilovoltage energy spectrum. Finally, concepts for alternative compact microbeam sources are presented, such as inverse Compton scattering set-ups and carbon nanotube x-ray tubes, that may facilitate the transfer of MRT into a hospital-based clinical environment. Intensive research in recent years has resulted in practical solutions to most of the technical challenges in MRT. Treatment planning, dosimetry and patient safety systems at synchrotrons have matured to a point that first veterinary and clinical studies in MRT are within reach. Should these studies confirm the promising results of pre-clinical studies, the authors are confident that MRT will become an effective new radiotherapy option for certain patients.
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http://dx.doi.org/10.1088/1361-6560/ab5507DOI Listing
January 2020

Film dosimetry studies for patient specific quality assurance in microbeam radiation therapy.

Phys Med 2019 Sep;65:227-237

INSERM UA7 STROBE, University Grenoble-Alpes, Grenoble, France; Grenoble-Alpes University Hospital (CHU-GA), Grenoble, France.

Microbeam radiation therapy (MRT) uses synchrotron arrays of X-ray microbeams to take advantage of the spatial fractionation effect for normal tissue sparing. In this study, radiochromic film dosimetry was performed for a treatment where MRT is introduced as a dose boost in a hypofractionated stereotactic radiotherapy (SRT) scheme. The isocenter dose was measured using an ionization chamber and two dimensional dose distributions were determined using radiochromic films. To compare the measured dose distribution to the MRT treatment plan, peak and valley were displayed in separate dosemaps. The measured and computed isocenter doses were compared and a two-dimensional 2%/2 mm normalized γ-index analysis with a 90% passing rate criterion was computed. For SRT, a difference of 2.6% was observed in the dose at the isocenter from the treatment plan and film measurement, with a passing rate of 96% for the γ-index analysis. For MRT, peak and valley doses differences of 25.6% and 8.2% were observed, respectively but passing rates of 96% and 90% respectively were obtained from the normalized γ-index maps. The differences in isocenter doses measured in MRT should be further investigated. We present the methodology of patient specific quality assurance (QA) for studying MRT dose distributions and discuss ideas to improve absolute dosimetry. This patient specific QA will be used for large animal trials quality assurance where MRT will be administered as a dose boost in conventional SRT. The observed remaining discrepancies should be studied against approximations in the TPS phantom materials, beams characteristics or film read-out procedures.
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http://dx.doi.org/10.1016/j.ejmp.2019.09.071DOI Listing
September 2019

Resonant inelastic X-ray scattering of magnetic excitations under pressure.

J Synchrotron Radiat 2019 Sep 15;26(Pt 5):1725-1732. Epub 2019 Aug 15.

ESRF - The European Synchrotron, 71 Avenue des Martyrs, CS 40220, F-38043 Grenoble, France.

Resonant inelastic X-ray scattering (RIXS) is an extremely valuable tool for the study of elementary, including magnetic, excitations in matter. The latest developments of this technique have mostly been aimed at improving the energy resolution and performing polarization analysis of the scattered radiation, with a great impact on the interpretation and applicability of RIXS. Instead, this article focuses on the sample environment and presents a setup for high-pressure low-temperature RIXS measurements of low-energy excitations. The feasibility of these experiments is proved by probing the magnetic excitations of the bilayer iridate SrIrO at pressures up to 12 GPa.
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http://dx.doi.org/10.1107/S1600577519008877DOI Listing
September 2019

Synchrotron Microbeam Radiation Therapy as a New Approach for the Treatment of Radioresistant Melanoma: Potential Underlying Mechanisms.

Int J Radiat Oncol Biol Phys 2019 12 25;105(5):1126-1136. Epub 2019 Aug 25.

Institute of Anatomy, University of Bern, Bern, Switzerland. Electronic address:

Purpose: Synchrotron microbeam radiation therapy (MRT) is a method that spatially distributes the x-ray beam into several microbeams of very high dose (peak dose), regularly separated by low-dose intervals (valley dose). MRT selectively spares normal tissues, relative to conventional (uniform broad beam [BB]) radiation therapy.

Methods And Materials: To evaluate the effect of MRT on radioresistant melanoma, B16-F10 murine melanomas were implanted into mice ears. Tumors were either treated with MRT (407.6 Gy peak; 6.2 Gy valley dose) or uniform BB irradiation (6.2 Gy).

Results: MRT induced significantly longer tumor regrowth delay than did BB irradiation. A significant 24% reduction in blood vessel perfusion was observed 5 days after MRT, and the cell proliferation index was significantly lower in melanomas treated by MRT compared with BB. MRT provoked a greater induction of senescence in melanoma cells. Bio-Plex analyses revealed enhanced concentration of monocyte-attracting chemokines in the MRT group: MCP-1 at D5, MIP-1α, MIP-1β, IL12p40, and RANTES at D9. This was associated with leukocytic infiltration at D9 after MRT, attributed mainly to CD8 T cells, natural killer cells, and macrophages.

Conclusions: In light of its potential to disrupt blood vessels that promote infiltration of the tumor by immune cells and its induction of senescence, MRT could be a new therapeutic approach for radioresistant melanoma.
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http://dx.doi.org/10.1016/j.ijrobp.2019.08.027DOI Listing
December 2019

Nonadiabatic Kohn Anomaly in Heavily Boron-Doped Diamond.

Phys Rev Lett 2017 Jul 6;119(1):017001. Epub 2017 Jul 6.

Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom.

We report evidence of a nonadiabatic Kohn anomaly in boron-doped diamond, using a joint theoretical and experimental analysis of the phonon dispersion relations. We demonstrate that standard calculations of phonons using density-functional perturbation theory are unable to reproduce the dispersion relations of the high-energy phonons measured by high-resolution inelastic x-ray scattering. On the contrary, by taking into account nonadiabatic effects within a many-body field-theoretic framework, we obtain excellent agreement with our experimental data. This result indicates a breakdown of the Born-Oppenheimer approximation in the phonon dispersion relations of boron-doped diamond.
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http://dx.doi.org/10.1103/PhysRevLett.119.017001DOI Listing
July 2017

Full Elasticity Tensor from Thermal Diffuse Scattering.

Phys Rev Lett 2017 Jan 20;118(3):035502. Epub 2017 Jan 20.

European Synchrotron Radiation Facility, 71, Avenue des Martyrs, F-38000 Grenoble, France.

We present a method for the precise determination of the full elasticity tensor from a single crystal diffraction experiment using monochromatic x rays. For the two benchmark systems calcite and magnesium oxide, we show that the measurement of thermal diffuse scattering in the proximity of Bragg reflections provides accurate values of the complete set of elastic constants. This approach allows for a reliable and model-free determination of the elastic properties and can be performed together with crystal structure investigation in the same experiment.
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http://dx.doi.org/10.1103/PhysRevLett.118.035502DOI Listing
January 2017

A compact and versatile dynamic flow cryostat for photon science.

Rev Sci Instrum 2016 Nov;87(11):115103

ESRF-The European Synchrotron, CS40220, 38043 Grenoble Cedex 9, France.

We have developed a helium gas flow cryostat for use on synchrotron tender to hard X-ray beamlines. Very efficient sample cooling is achieved because the sample is placed directly in the cooling helium flow on a removable sample holder. The cryostat is compact and easy to operate; samples can be changed in less than 5 min at any temperature. The cryostat has a temperature range of 2.5-325 K with temperature stability better than 0.1 K. The very wide optical angle and the ability to operate in any orientation mean that the cryostat can easily be adapted for different X-ray techniques. It is already in use on different beamlines at the European Synchrotron Radiation Facility (ESRF), ALBA Synchrotron Light Facility (ALBA), and Diamond Light Source (DLS) for inelastic X-ray scattering, powder diffraction, and X-ray absorption spectroscopy. Results obtained at these beamlines are presented here.
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http://dx.doi.org/10.1063/1.4966270DOI Listing
November 2016

Phonon triggered rhombohedral lattice distortion in vanadium at high pressure.

Sci Rep 2016 08 19;6:31887. Epub 2016 Aug 19.

European Synchrotron Radiation Facility, 38000 Grenoble, France.

In spite of the simple body-centered-cubic crystal structure, the elements of group V, vanadium, niobium and tantalum, show strong interactions between the electronic properties and lattice dynamics. Further, these interactions can be tuned by external parameters, such as pressure and temperature. We used inelastic x-ray scattering to probe the phonon dispersion of single-crystalline vanadium as a function of pressure to 45 GPa. Our measurements show an anomalous high-pressure behavior of the transverse acoustic mode along the (100) direction and a softening of the elastic modulus C44 that triggers a rhombohedral lattice distortion occurring between 34 and 39 GPa. Our results provide the missing experimental confirmation of the theoretically predicted shear instability arising from the progressive intra-band nesting of the Fermi surface with increasing pressure, a scenario common to all transition metals of group V.
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http://dx.doi.org/10.1038/srep31887DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4990969PMC
August 2016

Formation of CaB6 in the thermal decomposition of the hydrogen storage material Ca(BH4)2.

Phys Chem Chem Phys 2016 Jul;18(29):19866-72

Materials for Energy Conversion, Empa, Ch-8600 Dübendorf, Switzerland and Crystallography, Institute for Geo- and Environmental Science, Albert-Ludwigs-University Freiburg, D-79098 Freiburg im Breisgau, Germany.

Using a combination of high resolution X-ray powder diffraction and X-ray Raman scattering spectroscopy at the B K- and Ca L2,3-edges, we analyzed the reaction products of Ca(BH4)2 after annealing at 350 °C and 400 °C under vacuum conditions. We observed the formation of nanocrystalline/amorphous CaB6 mainly and found only small contributions from amorphous B for annealing times larger than 2 h. For short annealing times of 0.5 h at 400 °C we observed neither CaB12H12 nor CaB6. The results indicate a reaction pathway in which Ca(BH4)2 decomposes to B and CaH2 and finally reacts to form CaB6. These findings confirm the potential of using Ca(BH4)2 as a hydrogen storage medium and imply the desired cycling capabilities for achieving high-density hydrogen storage materials.
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http://dx.doi.org/10.1039/c6cp02495eDOI Listing
July 2016

Resonant X-ray emission with a standing wave excitation.

Sci Rep 2016 Mar 3;6:22648. Epub 2016 Mar 3.

Department of Physics, University of Helsinki, P. O. Box 64, FI-00014, Finland.

The Borrmann effect is the anomalous transmission of x-rays in perfect crystals under diffraction conditions. It arises from the interference of the incident and diffracted waves, which creates a standing wave with nodes at strongly absorbing atoms. Dipolar absorption of x-rays is thus diminished, which makes the crystal nearly transparent for certain x-ray wave vectors. Indeed, a relative enhancement of electric quadrupole absorption via the Borrmann effect has been demonstrated recently. Here we show that the Borrmann effect has a significantly larger impact on resonant x-ray emission than is observable in x-ray absorption. Emission from a dipole forbidden intermediate state may even dominate the corresponding x-ray spectra. Our work extends the domain of x-ray standing wave methods to resonant x-ray emission spectroscopy and provides means for novel spectroscopic experiments in d- and f-electron systems.
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http://dx.doi.org/10.1038/srep22648DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4776127PMC
March 2016

In situ characterization of the decomposition behavior of Mg(BH4)2 by X-ray Raman scattering spectroscopy.

Phys Chem Chem Phys 2016 Feb 28;18(7):5397-403. Epub 2016 Jan 28.

ESRF-The European Synchrotron, Grenoble Cedex 9, France.

We present an in situ study of the thermal decomposition of Mg(BH4)2 in a hydrogen atmosphere of up to 4 bar and up to 500 °C using X-ray Raman scattering spectroscopy at the boron K-edge and the magnesium L2,3-edges. The combination of the fingerprinting analysis of both edges yields detailed quantitative information on the reaction products during decomposition, an issue of crucial importance in determining whether Mg(BH4)2 can be used as a next-generation hydrogen storage material. This work reveals the formation of reaction intermediate(s) at 300 °C, accompanied by a significant hydrogen release without the occurrence of stable boron compounds such as amorphous boron or MgB12H12. At temperatures between 300 °C and 400 °C, further hydrogen release proceeds via the formation of higher boranes and crystalline MgH2. Above 400 °C, decomposition into the constituting elements takes place. Therefore, at moderate temperatures, Mg(BH4)2 is shown to be a promising high-density hydrogen storage material with great potential for reversible energy storage applications.
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http://dx.doi.org/10.1039/c5cp06571bDOI Listing
February 2016

Probing the thermal stability and the decomposition mechanism of a magnesium-fullerene polymer via X-ray Raman spectroscopy, X-ray diffraction and molecular dynamics simulations.

Phys Chem Chem Phys 2016 Feb;18(7):5366-71

Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2, P.O. Box 64 00014 Helsinki, Finland.

We report the microscopic view of the thermal structural stability of the magnesium intercalated fullerene polymer Mg2C60. With the application of X-ray Raman spectroscopy and X-ray diffraction, we study in detail the decomposition pathways of the polymer system upon annealing at temperatures between 300 and 700 °C. We show that there are at least two energy scales involved in the decomposition reaction. Intermolecular carbon bonds, which are responsible for the formation of a 2D fullerene polymer, are broken with a relatively modest thermal energy, while the long-range order of the original polymer remains intact. With an increased thermal energy, the crystal structure in turn is found to undergo a transition to a novel intercalated cubic phase that is stable up to the highest temperature studied here. The local structure surrounding magnesium ions gets severely modified close to, possibly at, the phase transition. We used density functional theory based calculations to study the thermodynamic and kinetic aspects of the collapse of the fullerene network, and to explain the intermediate steps as well as the reaction pathways in the break-up of this peculiar C60 intermolecular bonding architecture.
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http://dx.doi.org/10.1039/c5cp07783dDOI Listing
February 2016

Lattice dynamics of α-cristobalite and the Boson peak in silica glass.

J Phys Condens Matter 2015 Aug 14;27(30):305401. Epub 2015 Jul 14.

Department of Quantum Matter Physics, University of Geneva, 24, Quai Ernest Ansermet, CH-1211 Genève, Switzerland. Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.

The lattice dynamics of the silica polymorph [Formula: see text]-cristobalite has been investigated by a combination of diffuse and inelastic x-ray scattering and ab initio lattice dynamics calculations. Phonon dispersion relations and vibrational density of states are reported and the phonon eigenvectors analyzed by a detailed comparison of scattering intensities. The experimentally validated calculation is used to identify the vibration contributing most to the first peak in the density of vibrational states. The comparison of its displacement pattern to the silica polymorphs [Formula: see text]-quartz and coesite and to vitreous silica reveals a distinct similarity and allows for decisive conclusions on the vibrations causing the so-called Boson peak in silica glass.
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http://dx.doi.org/10.1088/0953-8984/27/30/305401DOI Listing
August 2015

Toward a mineral physics reference model for the Moon's core.

Proc Natl Acad Sci U S A 2015 Mar 16;112(13):3916-9. Epub 2015 Mar 16.

Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015.

The physical properties of iron (Fe) at high pressure and high temperature are crucial for understanding the chemical composition, evolution, and dynamics of planetary interiors. Indeed, the inner structures of the telluric planets all share a similar layered nature: a central metallic core composed mostly of iron, surrounded by a silicate mantle, and a thin, chemically differentiated crust. To date, most studies of iron have focused on the hexagonal closed packed (hcp, or ε) phase, as ε-Fe is likely stable across the pressure and temperature conditions of Earth's core. However, at the more moderate pressures characteristic of the cores of smaller planetary bodies, such as the Moon, Mercury, or Mars, iron takes on a face-centered cubic (fcc, or γ) structure. Here we present compressional and shear wave sound velocity and density measurements of γ-Fe at high pressures and high temperatures, which are needed to develop accurate seismic models of planetary interiors. Our results indicate that the seismic velocities proposed for the Moon's inner core by a recent reanalysis of Apollo seismic data are well below those of γ-Fe. Our dataset thus provides strong constraints to seismic models of the lunar core and cores of small telluric planets. This allows us to propose a direct compositional and velocity model for the Moon's core.
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http://dx.doi.org/10.1073/pnas.1417490112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4386338PMC
March 2015

Improving the energy resolution of bent crystal X-ray spectrometers with position-sensitive detectors.

J Synchrotron Radiat 2014 Jul 12;21(Pt 4):762-7. Epub 2014 Jun 12.

Department of Physics, PO Box 64, FI-00014 Helsinki, Finland.

Wavelength-dispersive high-resolution X-ray spectrometers often employ elastically bent crystals for the wavelength analysis. In a preceding paper [Honkanen et al. (2014). J. Synchrotron Rad. 21, 104-110] a theory for quantifying the internal stress of a macroscopically large spherically curved analyser crystal was presented. Here the theory is applied to compensate for the corresponding decrease of the energy resolution. The technique is demonstrated with a Johann-type spectrometer using a spherically bent Si(660) analyser in near-backscattering geometry, where an improvement in the energy resolution from 1.0 eV down to 0.5 eV at 9.7 keV incident photon energy was observed.
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http://dx.doi.org/10.1107/S1600577514011163DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4861880PMC
July 2014

Diffuse scattering in Ih ice.

J Phys Condens Matter 2014 Jul;26(26):265401

Single crystals of ice Ih, extracted from the subglacial Lake Vostok accretion ice layer (3621 m depth) were investigated by means of diffuse x-ray scattering and inelastic x-ray scattering. The diffuse scattering was identified as mainly inelastic and rationalized in the frame of ab initio calculations for the ordered ice XI approximant. Together with Monte-Carlo modelling, our data allowed reconsidering previously available neutron diffuse scattering data of heavy ice as the sum of thermal diffuse scattering and static disorder contribution.
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http://dx.doi.org/10.1088/0953-8984/26/26/265401DOI Listing
July 2014

Diffuse scattering in metallic tin polymorphs.

J Phys Condens Matter 2014 Mar 3;26(11):115401. Epub 2014 Mar 3.

European Synchrotron Radiation Facility, BP 220 F-38043 Grenoble Cedex 9, France.

The lattice dynamics of the metallic tin β and γ polymorphs has been studied by a combination of diffuse scattering, inelastic x-ray scattering and density functional perturbation theory. The non-symmorphic space group of the β-tin structure results in unusual asymmetry of thermal diffuse scattering. Strong resemblance of the diffuse scattering intensity distribution in β and γ-tin were observed, reflecting the structural relationship between the two phases and revealing the qualitative similarity of the underlying electronic potential. The strong influence of the electron subsystem on inter-ionic interactions creates anomalies in the phonon dispersion relations. All observed features are described in great detail by the density functional perturbation theory for both β- and γ-tin at arbitrary momentum transfers. The combined approach delivers thus a complete picture of the lattice dynamics in harmonic description.
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http://dx.doi.org/10.1088/0953-8984/26/11/115401DOI Listing
March 2014

Dynamical crossover at the liquid-liquid transformation of a compressed molten alkali metal.

Phys Rev Lett 2013 Aug 16;111(7):077801. Epub 2013 Aug 16.

Dipartimento di Fisica, Università di Roma Sapienza, Roma, Italy.

Density-driven phase transformations are a known phenomenon in liquids. Pressure-driven transitions from an open low-density to a higher-density close-packed structure were observed for a number of systems. Here, we show a less intuitive, inverse behavior. We investigated the electronic, atomic, and dynamic structures of liquid Rb along an isothermal line at 573 K, at 1.2-27.4 GPa, by means of ab initio molecular dynamics simulations and inelastic x-ray scattering experiments. The excellent agreement of the simulations with experimental data performed up to 6.6 GPa validates the overall approach. Above 12.5 GPa, the breakdown of the nearly-free-electron model drives a transition of the pure liquid metal towards a less metallic, denser liquid, whose first coordination shell is less compact. Our study unveils the interplay between electronic, structural, and dynamic degrees of freedom along this liquid-liquid phase transition. In view of its electronic nature, we believe that this behavior is general for the first group elements, thus shedding new light into the high-pressure properties of alkali metals.
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http://dx.doi.org/10.1103/PhysRevLett.111.077801DOI Listing
August 2013

Lattice dynamics of coesite.

J Phys Condens Matter 2013 Jul 17;25(27):275401. Epub 2013 Jun 17.

European Synchrotron Radiation Facility, BP 220 F-38043 Grenoble Cedex, France.

The lattice dynamics of coesite has been studied by a combination of diffuse x-ray scattering, inelastic x-ray scattering and ab initio lattice dynamics calculations. The combined technique gives access to the full lattice dynamics in the harmonic description and thus eventually provides detailed information on the elastic properties, the stability and metastability of crystalline systems. The experimentally validated calculation was used for the investigation of the eigenvectors, mode character and their contribution to the density of vibrational states. High-symmetry sections of the reciprocal space distribution of diffuse scattering and inelastic x-ray scattering spectra as well as the density of vibrational states and the dispersion relation are reported and compared to the calculation. A critical point at the zone boundary is found to contribute strongly to the main peak of the low-energy part in the density of vibrational states. Comparison with the most abundant SiO2 polymorph--α-quartz--reveals similarities and distinct differences in the low-energy vibrational properties.
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http://dx.doi.org/10.1088/0953-8984/25/27/275401DOI Listing
July 2013

Anharmonicity due to electron-phonon coupling in magnetite.

Phys Rev Lett 2013 May 13;110(20):207204. Epub 2013 May 13.

Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, PL-31342 Kraków, Poland.

We present the results of inelastic x-ray scattering for magnetite and analyze the energies and widths of the phonon modes with different symmetries in a broad range of temperature 125 < T < 293 K. The phonon modes with X(4) and Δ(5) symmetries broaden in a nonlinear way with decreasing T when the Verwey transition is approached. It is found that the maxima of phonon widths occur away from high-symmetry points, which suggests the incommensurate character of critical fluctuations. Strong phonon anharmonicity induced by electron-phonon coupling is discovered by a combination of these experimental results with ab initio calculations which take into account local Coulomb interactions at Fe ions. It (i) explains observed anomalous phonon broadening and (ii) demonstrates that the Verwey transition is a cooperative phenomenon which involves a wide spectrum of phonons coupled to the electron charge fluctuations condensing in the low-symmetry phase.
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http://dx.doi.org/10.1103/PhysRevLett.110.207204DOI Listing
May 2013

Lattice dynamics of multiferroic BiFeO3 studied by inelastic x-ray scattering.

J Phys Condens Matter 2013 Mar 4;25(10):102201. Epub 2013 Feb 4.

European Synchrotron Radiation Facility, Grenoble, France.

We report an experimental study of the phonon dispersion in BiFeO(3) single crystals at ambient conditions by inelastic x-ray scattering (IXS). The phonon dispersions were recorded along several symmetry directions up to 35 meV. Our results compare favorably with first-principles calculations performed using density functional theory (DFT) within the local-density approximation (LDA). We resolve a discrepancy concerning the symmetry of the optical phonon branches observed by Raman spectroscopy, determine the energy of the lowest Raman and infrared silent mode, and derive a subset of the elastic moduli of BiFeO(3).
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http://dx.doi.org/10.1088/0953-8984/25/10/102201DOI Listing
March 2013

Phonons of the anomalous element cerium.

Proc Natl Acad Sci U S A 2011 Jun 19;108(23):9342-5. Epub 2011 May 19.

European Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble Cédex, France.

Many physical and chemical properties of the light rare-earths and actinides are governed by the active role of f electrons, and despite intensive efforts the details of the mechanisms of phase stability and transformation are not fully understood. A prominent example which has attracted a lot of interest, both experimentally and theoretically over the years is the isostructural γ - α transition in cerium. We have determined by inelastic X-ray scattering, the complete phonon dispersion scheme of elemental cerium across the γ → α transition, and compared it with theoretical results using ab initio lattice dynamics. Several phonon branches show strong changes in the dispersion shape, indicating large modifications in the interactions between phonons and conduction electrons. This is reflected as well by the lattice Grüneisen parameters, particularly around the X point. We derive a vibrational entropy change ΔS(γ-α)(vib) ≈ (0.33+/-0.03)k(B), illustrating the importance of the lattice contribution to the transition. Additionally, we compare first principles calculations with the experiments to shed light on the mechanism underlying the isostructural volume collapse in cerium under pressure.
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http://dx.doi.org/10.1073/pnas.1015945108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3111256PMC
June 2011

Hydration dynamics at femtosecond time scales and angstrom length scales from inelastic x-ray scattering.

Phys Rev Lett 2009 Dec 3;103(23):237402. Epub 2009 Dec 3.

Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.

We use high resolution dynamical structure factor S(q,omega) data measured with inelastic x-ray scattering to reconstruct the Green's function of water, which describes its density response to a point charge, and provides a fundamental comparative model for solvation behavior at molecular time scales and length scales. Good agreement is found with simulations, scattering and spectroscopic experiments. These results suggest that a moving point charge will modify its hydration structure, evolving from a spherical closed shell to a steady-state cylindrical hydration "sleeve".
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http://dx.doi.org/10.1103/PhysRevLett.103.237402DOI Listing
December 2009

Phonon spectroscopy at high pressure by inelastic X-ray scattering.

J Synchrotron Radiat 2009 Nov 15;16(Pt 6):707-13. Epub 2009 Sep 15.

European Synchrotron Radiation Facility, Grenoble, France.

The current status of phonon-dispersion studies at high pressure using very high energy resolution inelastic X-ray scattering is discussed. A brief description of the instrumental apparatus is given, together with an illustration of the high-pressure facilities available at the IXS beamlines ID16 and ID28 of the ESRF. Some selected examples of recent studies on crystalline and liquid samples in a diamond anvil cell are then presented.
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http://dx.doi.org/10.1107/S0909049509033743DOI Listing
November 2009

Giant Kohn anomaly and the phase transition in charge density wave ZrTe3.

Phys Rev Lett 2009 Feb 25;102(8):086402. Epub 2009 Feb 25.

European Synchrotron Radiation Facility, 6 rue Jules Horowitz, 38043 Grenoble Cedex, France.

A strong Kohn anomaly in ZrTe3 is identified in the mostly transverse acoustic phonon branch along the modulation vector q_{P} with polarization along the a;{*} direction. This soft mode freezes to zero frequency at the transition temperature T_{P}, and the temperature dependence of the frequency is strongly affected by fluctuation effects. Diffuse x-ray scattering of the incommensurate superstructure shows a power-law scaling of the intensity and the correlation length that is compatible with an order parameter of dimension n=2.
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http://dx.doi.org/10.1103/PhysRevLett.102.086402DOI Listing
February 2009
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