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International audience; Spin crossover complexes are among the most studied classes of molecular switches and have attracted considerable attention for their potential technological use as active units in multifunctional devices. A fundamental step toward their practical implementation is the integration in macroscopic devices adopting hybrid vertical architectures. First, the physical properties of technological interest shown by these materials in the bulk phase have to be retained once they are deposited on a solid surface. Herein, we describe the study of a hybrid molecular inorganic junction embedding the spin crossover complex [Fe(qnal)2] (qnal = quinoline-naphthaldehyde) as an active switchable thin film sandwiched within energy-optimized metallic electrodes. In these junctions, developed and characterized with the support of state of the art techniques including synchrotron Mössbauer source (SMS) spectroscopy and focused-ion beam scanning transmission electron microscopy, we observed that the spin state conversion of the Fe(II)-based spin crossover film is associated with a transition from a space charge-limited current (SCLC) transport mechanism with shallow traps to a SCLC mechanism characterized by the presence of an exponential distribution of traps concomitant with the spin transition temperature.

Journal of synchrotron radiation 28(1), 176 - 180 (2021). doi:10.1107/S1600577520015568, Dichroism is one of the most important optical effects in both the visible and the X-ray range. Besides absorption, scattering can also contribute to dichroism. This paper demonstrates that, based on the example of polyimide, materials can show tiny dichroism even far from electronic resonances due to scattering. Although the effect is small, it can lead to a measurable polarization change and might have influence on highly sensitive polarimetric experiments., Published by Wiley-Blackwell, [S.l.]

Within this chapter, the syntheses as well as the chemical and physical properties of phthalogens are discussed. Phthalogens are compounds, which give upon thermal treatment, photo-irradiation or (electro)chemical reduction their respective (metallo)phthalocyanines (MPc's) or (metallo)naphthophthalocyanines MNc's. The applications of phthalogens from the viewpoint as precursors of MPc's and MNc's in the fields of textile-fiber coloring and surface patterning as well their original application as homogeneous catalysts are reported as well.

The electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) spectroscopies are frequently used to determine hyperfine (A) and quadrupole (Q) tensors for the paramagnetic transit...

A new polymeric silver(I) complex of imidazolidine-2-thione (Imt), {[Ag2(Imt)3](NO3)2} n (1) was prepared and its structure was determined by single-crystal X-ray diffraction analysis. The silver atoms form infinite chains with two Ag − S(Imt) − Ag strands linked to each other by sulfur atoms of μ 4-Imt ligands. Each silver(I) ion is bound to four sulfur atoms of bridging Imt ligands in a distorted tetrahedral environment. The crystal structure is stabilized by hydrogen bonding and weak argentophilic interactions. The hydrogen bonded nitrate ions connect the 1D chains to generate a 2D layer structure.

This chapter gives an overview of porphyrinoids for use in photodynamic therapy. It covers the characteristics, properties, and current treatments or porphyrin-based photosensitizers. The first section introduces the phototherapy and photodynamic therapy concepts and gives an overview of the principles of photophysical and photopharmacological aspects of potential photosensitizers. The subsequent section summarizes current treatments of clinically approved photosensitizers and those under development. A brief survey of the strategies for singlet oxygen generation enhancement and drug-delivery improvements is described in the last section.

GaAs nanowire arrays on silicon offer great perspectives in the optoelectronics and solar cell industry. To fulfill this potential, gold-free growth in predetermined positions should be achieved. Ga-assisted growth of GaAs nanowires in the form of array has been shown to be challenging and difficult to reproduce. In this work, we provide some of the key elements for obtaining a high yield of GaAs nanowires on patterned Si in a reproducible way: contact angle and pinning of the Ga droplet inside the apertures achieved by the modification of the surface properties of the nanoscale areas exposed to growth. As an example, an amorphous silicon layer between the crystalline substrate and the oxide mask results in a contact angle around 90°, leading to a high yield of vertical nanowires. Another example for tuning the contact angle is anticipated, native oxide with controlled thickness. This work opens new perspectives for the rational and reproducible growth of GaAs nanowire arrays on silicon., The authors thank the NCCR QSIT and the ERANet RUS Project InCoSiN PRI-PIMERU-2011-1422. They acknowledge European funding from ERC through grant UpCon, EU through FP7 project Nanoembrace, as well as SNF through the NCCR-QSIT and grants 121758/1 and 129775/1. S.C.B. thanks funding through the SNF Marie Heim-Vogtlin program. J.A. acknowledges the funding from the Generalitat de Catalunya 2014 SGR 1638. M.d.l.M. thanks the CSIC JaePredoc program. J.A. and M.d.l.M. thank funding from Spanish MINECO MAT2014-51480-ERC.

International audience; The spin crossover (SCO) efficiency of [57Fe(bpz)2(phen)] (where bpz = bis(pyrazol-1-yl)borohydride and phen = 9,10-phenantroline) molecules deposited on gold substrates was investigated by means of synchrotron Mössbauer spectroscopy. The spin transition was driven thermally, or light induced via the LIESST (light induced excited spin-state trapping) effect. Both sets of measurements show that, once deposited on a gold substrate, the efficiency of the SCO mechanism is modified with respect to molecules in the bulk phase. A correlation in the distribution of hyperfine parameters in the sublimated films, not evidenced so far in the bulk phase, is reported. This translates into geometrical distortions of the first coordination sphere of the iron atom that seem to correlate with the decreased spin conversion. The work reported clearly shows the potentiality of synchrotron Mössbauer spectroscopy for the characterization of nanostructured Fe-based SCO systems, thus resulting as a key tool in view of their applications in innovative nanoscale devices.

Physical review research 2(2), 023365 (2020). doi:10.1103/PhysRevResearch.2.023365, We report on the use of synthetic single-crystal diamonds for high definition x-ray polarimetry. The diamonds are precision mounted to form artificial channel-cut crystals (ACCs). Each ACC supports four consecutive reflections with a scattering angle 2ΘB of 90∘. We achieved a polarization purity of 3.0×10−10 at beamline ID18 of the European Synchrotron Radiation Facility (ESRF). When the x-ray beam's horizontal divergence was reduced through additional collimation from 17 to 8.4μrad, the polarization purity improved to 1.4×10−10. Precision x-ray polarimetry thus has reached the limit, where the purity is determined by the divergence of the beam. In particular, this result is important for polarimetry at fourth generation x-ray sources, which provide diffraction-limited x-ray beams. The sensitivity expected as a consequence of the present work will pave the way for exploring new physics such as the investigation of vacuum birefringence., Published by APS, College Park, MD

Lanthanide clusters [Ln4(μ3-OH)2(η2-accp)4((μ-O)-η2-accp)6] (Ln = Y (4), Gd (5); accp = 2-acetylcyclopentanoate) are accessible by treatment of [M(NO3)3·6H2O] (M = Y (1), Gd (2)) with 3 equiv. of Haccp (3) in presence of NaOH. The molecular structures of 4 and 5 in the solid-state are discussed. The thermal behavior of 4 and 5 was studied by TG under Ar and O2, showing multistep decomposition processes. Additionally, DSC studies were carried out under an atmosphere of O2. PXRD measurements of the TG residues confirm the formation of Ln2O3. Spin-coating experiments were carried out with 4 and 5 for Ln2O3 film deposition on silicon substrates. The layers are smooth, close and are of thicknesses of 18.87 ± 1.13 nm and 25.59 ± 4.55 nm for Ln = Y and Gd, which was evidenced by SEM and EDX studies. Field-effect transistors were successfully fabricated by deposition of carbon nanotubes on top of the Y2O3 films and formation of palladium contacts by a lift-off procedure. An on/off ratio of more than 4 orders of magnitude is achieved without considerable leakage currents. These results demonstrate the potential use of spin-coated Y2O3 as a gate dielectric in electronic devices.

The lanthanum(III) complex [Li(thf)3(μ-Cl)La{N(SiMe3)2}3] (3) was obtained by the reaction of LaCl3 with three equiv of Li[N(SiMe3)2]3 in a tetrahydrofuran solution. The molecular structure of 3 in the solid state was characterized by a tetracoordinated anionic lanthanide(III) amide in form of an adduct with LiCl(thf)3 as evidenced by single crystal X-ray structure analysis. In order to study the suitability of 3 as a precursor for the deposition of La2O3/LiLaSiO4 by thin layer deposition techniques, its thermal behavior was investigated by thermogravimetry (TG) and TG-MS-coupled studies. TG studies show a two-step decomposition process, whereby volatile decomposition products can be detected during the second decomposition step. TG measurements under an atmosphere of oxygen produced La2O3. Calcination processes of 3 under ambient atmosphere for 10 h at 1000 °C gave La2O3 and LiLaSiO4, which was confirmed by PXRD studies. Metal-organic 3 was applied as spin-coating precursor for La2O3 thin film formation giving the as-deposited layers nearly crack-free.

Nuclear resonance reflectivity from a [Dy19Gd19] × 20 superlattice has been measured utilizing the 25.652 keV nuclear level of 161Dy. The measured time spectra of nuclear resonance reflectivity make it possible to reveal the variation of the hyperfine magnetic field Bhf on dysprosium nuclei in the temperature range of 4–110 K and to determine the relaxation time of the hyperfine field, using the decay speed-up of the excited state of 161Dy nuclei.

Mössbauer reflectivity spectra and nuclear resonance reflectivity (NRR) curves have been measured using the Synchrotron Mössbauer Source (SMS) for a [57Fe/Cr]30 periodic multilayer, characterized by the antiferromagnetic interlayer coupling between adjacent 57Fe layers. Specific features of the Mössbauer reflectivity spectra measured with π-polarized radiation of the SMS near the critical angle and at the 'magnetic' maximum on the NRR curve are analyzed. The variation of the ratio of lines in the Mössbauer reflectivity spectra and the change of the intensity of the 'magnetic' maximum under an applied external field has been used to reveal the transformation of the magnetic alignment in the investigated multilayer.Mössbauer reflectivity experiments performed using the Synchrotron Mössbauer Source at the ESRF demonstrate the high efficiency of such investigations for the analysis and understanding of multilayer structures and magnetization profiles. © International Union of Crystallography, 2018. Russian Foundation for Basic Research, RFBR: 15-02-01674-a, 15-02-01502-a, 16-02-00887-a Russian Academy of Sciences, RAS Federal Agency for Scientific Organizations: 1.1.3.5, 01201463330 Funding for this research was provided by the Russian Federal Agency for Scientific Organizations on the theme ‘Spin’ No. 01201463330 and by the Project No. 1.1.3.5. of the Program No. 32 of the Presidium of Russian Academy of Sciences, and the research was supported in part by the Russian Foundation for Basic Research (Grants No. 15-02-01674-a, No. 15-02-01502-a and No. 16-02-00887-a).

The syntheses of chiral pentacoordinated fluoridosilicates and their conversion into fluorine-doped silica and mesoporous carbon are reported. Starting from 4H,4′H-2,2′-spirobi[benzo[d][1,3,2]dioxasiline] (1) and 8,8′-di-tert-butyl-4H,4′H-2,2′-spirobi[benzo[d][1,3,2]dioxasiline] (2), the corresponding fluorido complexes 3 and 4 were obtained by the addition of potassium fluoride to the spirocyclic silicon salicylic alcoholates 1 and 2 in the presence of 18-crown-6. The pentacoordinated geometry around the silicon atom of the SiO4F type in 3 and 4 was proved using single-crystal X-ray diffraction analysis. DSC measurements were used to study the thermal behavior of the compounds with regard to their usability in the twin polymerization process. Hence, polymerization of 3 and 4 and the simultaneous twin polymerization of the fluoridosilicate 3 with spirocyclic 1 gave fluorine-doped phenolic resin/silica composites as confirmed by solid state NMR spectroscopic studies (1H, 13C{1H}, 19F, and 29Si{1H}). Carbonization of the as-obtained hybrid materials and subsequent treatment with hydrofluoric acid resulted in microporous carbon with surface areas up to 1060 m2 g−1. Calcination of the hybrid materials produced fluorine-doped silica with BET surface areas up to 239 m2 g−1. Additionally, the synthesis of hybrid materials using the additive assisted twin polymerization of 1 with either tetra-n-butylammonium fluoride or KF gave either microporous carbon (1219 m2 g−1) or mesoporous silica (687 m2 g−1).

Polarization analysis of the reflected radiation has been performed in Mossbauer reflectivity measurements with a Synchrotron Mossbauer Source (SMS). Effective π→σ′ polarization selection is attained with LiF crystal ((6 2 2) 90o-reflection for 14.4 keV radiation, angular acceptance ∼ 100``) capable of high π→π′ suppression. Basic features of the reflectivity with the rotated π→σ′ polarization are revealed in the experiment with the [57Fe(10 ML)/V(20 ML)]20 multilayer. Selection of π→σ′ polarization component in Mossbauer reflectivity allows to exclude nonresonant electronic scattering, besides Mossbauer π→σ′ reflectivity spectra (R-spectra) contain only contributions from magnetized along the beam ferromagnetic phases. The antiferromagnetic iron oxides do not contribute to π→σ′ R-spectra (dichroic component is compensated). Therefore, in the Mossbauer reflectivity experiment supplemented by polarization analysis the data interpretation becomes more certain and gives information about depth position for ferromagnetic layers selectively. With this new technique we locate antiferromagnetic iron phases in the very top layer of [57Fe(10 ML)/V(20 ML)]20 multilayer and ascertain the ferromagnetic ordered iron layers in the remaining part of the structure. This new approach in Mossbauer reflectivity has interesting perspectives for investigations of hyperfine interactions for iron complexes on the surface, ultrathin layers and multilayers with complicated magnetic structures.

The synthesis, structure and thermal behavior of [Y(dbm)3(H2O)] (3) (dbm = 1,3-diphenyl-1,3-propandionate) and its use as a spin-coating precursor for Y2O3 deposition is reported. Complex 3 was prepared by the reaction of [Y(NO3)3·6H2O] (1) with 3 equiv of Hdbm (2) in presence of NaOH. The molecular structure of 3 in the solid-state was determined by single X-ray crystal diffraction. Both C1 symmetric crystallographically independent species of 3 possess a YO7 coordination setup with minor deviation from an ideal capped octahedron coordination geometry (Λ enantiomer). Complex 3 forms a 1D chain, due to intermolecular hydrogen bonds between the coordinated H2O molecule and the O atom of the dbm ligand, respectively. The thermal decomposition behavior of 3 was investigated by thermogravimetric studies in the temperature range of 40–800 °C and 40–1300 °C under an oxygen and argon atmosphere, respectively. Powder X-ray diffraction (PXRD) measurements of the residues confirmed the formation of Y2O3. Complex 3 was applied as a spin-coating precursor for yttrium oxide film formation on either Si wafers with a continuous 100 nm thick SiO2 film, or with a native oxide layer. The as-deposited Y2O3 layers are smooth, conformal, dense and transparent and are of a thickness of 27 and 30 nm, respectively.

Nanostructured epitaxial [57Fe(1.2 A)/Cr(10.5 A)]30 multilayer with ultrathin Fe layers, demonstrated Kondo-like behavior, has been investigated by means of the nuclear resonance reflectivity at low temperatures (down to 4 K) in magnetic fields up to 4 T. We detected the beginning of the magnetic phase transition at 150 K which correlates with the minimum on the electrical resistivity curve. The determined magnetic hyperfine field distribution P(Bhf) indicates an inhomogeneity of the iron environments. When we apply the very high external magnetic field up to 4 T, it aligns Bhf(i) along the direction of the external field only partially. Also it has been noticed that Bhf(i) orientations depend on the magnetic pre-history.

The bottom-up approach to replace existing devices by molecular-based systems is a subject that attracts permanently increasing interest. Molecular-based devices offer not only to miniaturize the device further, but also to benefit from advanced functionalities of deposited molecules. Furthermore, the molecules itself can be tailored to allow via their self-assembly the potential fabrication of devices with an application potential, which is still unforeseeable at this time. Herein, we review efforts to use discrete (metallo)porphyrins for the formation of (sub)monolayers by surface-confined polymerization, of monolayers formed by supramolecular recognition and of thin films formed by sublimation techniques. Selected physical properties of these systems are reported as well. The application potential of those ensembles of (metallo)porphyrins in materials science is discussed.

The high-pressure properties of a new multiferroic of the langasite family Ba3TaFe3Si2O14 were investigated in diamond-anvil cells (DAC) in the temperature range of 4.2–295 K by a new method of synchrotron Mossbauer spectroscopy. Strong enhancement of the Neel temperature T N was observed at pressures above 20 GPa associated with the structural transformation. The highest value of T N is about 130 K which is almost five times larger than the value at ambient pressure (about 27 K). It was suggested that the high value of T N appears due to redistribution of Fe ions over 3f and 2d tetrahedral sites of the langasite structure. In this case, the short Fe-O distances and favorable Fe-O-Fe bond angles create conditions for strong superexchange interactions between iron ions, and effective two-dimensional (2D) magnetic ordering appears in the (ab) plane. The separation of the sample into two magnetic phases with different T N values of about 50 and 130 K was revealed, which can be explained by the strong 2D magnetic ordering in the ab plane and 3D ordering involving inter-plane interaction.

This work reports the first example of the spectroscopic measurements of the Magneto-Optical Kerr Effect (MOKE) of films being composed of trinuclear transition metal complexes on a non-transparent substrate at room temperature. The thin films of the tailor-made trinuclear bis(oxamidato) type complex 5 ([Cu 3 (opbo n Pr 2 )(tmcd) 2 (NO 3 ) 2 ], opbo n Pr 2 = o - p henylene b is( N ’- n propyl o xamido, tmcd= trans -(1 R ,2 R )- N , N , N ′, N ′-tetramethyl-cyclohexane d iamine) and of the bis(oxamato) type complexes 11 ([Cu 2 Ni(opbaCF 3 )(pmdta) 2 (NO 3 ) 2 ], opbaCF 3 = 4-trifluoromethyl- o - p henylene b is(ox a mato), pmdta = N , N , N ,′ N ″, N ″- p enta m ethyl d iethylene t ri a mine) and 12 ([Cu 3 (opba)(bppe) 2 (NO 3 ) 2 ] (opba = o - p henylene b is(ox a mato), bppe = S-N , N - b is(2- p icolyl)−1- p henyl e thylamine) were fabricated by spin-coating and their thicknesses in the range between 0.5 µm and 2 µm was determined by spectroscopic ellipsometry. Based on the spectroscopic ellipsometry results it was also possible to determine the optical constants of the film and compare them with the absorption of the complexes in solution in order to confirm the complex integrity after the film deposition. The fabrication of high-quality films which exhibit Kerr rotation up to 0.2 mrad (11.5 mdeg) was only possible due to tailor-made synthesis, which allows circumventing intermolecular interactions of the trinuclear complexes during the film formation.

We analyze in detail the results of experimental investigations of the evolution of the thermal vibration spectra for iron atoms in iron monosilicide FeSi depending on two external parameters, viz., temperature T (in the range 46–297 K at pressure P = 0.1 MPa) and pressure P (in the range 0.1 MPa–43 GPa at temperature T = 297 K), obtained by nuclear inelastic scattering of synchrotron radiation. The decrease of the atomic volume is accompanied by a rearrangement of the phonon spectrum, which is manifested, in particular, in the splitting of the low-energy peak in the spectrum and in an increase of the energy for all phonons. The changes of the average energy of the iron atom vibrational spectrum and of the Debye energy with decreasing atomic volume are analyzed. Different versions of FeSi electron spectrum variation, which can be used to explain the observed phonon anomalies, are considered.

The densities of phonon states of thin Sn films on InSb substrates are determined during different stages of the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ to $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ phase transition using nuclear inelastic x-ray scattering. The vibrational entropy and internal energy per atom as a function of temperature are obtained by numerical integration of the phonon density of states. The free energy as a function of temperature for the nanoscale samples is compared to the free energy obtained from ab initio calculations of bulk tin in the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ and $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ phase. In thin films this phase transition is governed by the interplay between the vibrational behavior of the film (the phase transition is driven by the vibrational entropy) and the stabilizing influence of the substrate (which depends on the film thickness). This brings a deeper understanding of the role of lattice vibrations in the phase transition of nanoscale Sn.

The pressure dependence of the magnetism of the double perovskite ${\mathrm{Sr}}_{2}{\mathrm{FeOsO}}_{6}$ was investigated by temperature- and magnetic-field-dependent synchrotron $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy in the energy domain up to $\ensuremath{\sim}50$ GPa. ${\mathrm{Sr}}_{2}{\mathrm{FeOsO}}_{6}$ is known to feature antiferromagnetic ordering below ${T}_{\mathrm{N}}\ensuremath{\sim}140$ K and a change in spin structure from AF1 to AF2 near 70 K at ambient pressure. Previous Os ${L}_{2,3}$ x-ray magnetic circular dichroism (XMCD) spectra [Veiga et al., Phys. Rev. B 91, 235135 (2015)] indicated a pressure-driven change from the antiferromagnetic to the ferrimagnetic state. Raman spectra of ${\mathrm{Sr}}_{2}{\mathrm{FeOsO}}_{6}$ collected at room temperature and up to 34 GPa are in agreement with previous x-ray-diffraction studies which verified that the tetragonal ambient pressure crystal structure is retained at high pressure. The M\"ossbauer investigations show that the Fe ions remain in the +3 high-spin $({{t}_{2g}}^{3}{e}_{g}^{2})$ state over the whole pressure range. The magnetic ordering is strongly stabilized by high pressure and for $pg30$ GPa the ordering temperature is increased to above room temperature. Broad magnetic hyperfine patterns as well as coexistence of magnetic and paramagnetic signals at high pressures indicate the formation of inhomogeneous magnetic states. The shapes of applied-field M\"ossbauer spectra at low temperature are similar at 2 and 33 GPa and do not allow resolution of distinct antiferromagnetic and ferrimagnetic components. Pressure-induced spin canting in a basically antiferromagnetic spin structure or magnetic phase separation involving a pressure-induced minority ferrimagnetic phase may be the origin for the ferromagnetic XMCD signal.

Self-amplified spontaneous emission (SASE) enables X-ray free-electron lasers (XFELs) to generate hard X-ray pulses of sub-100 fs duration. However, due to the stochastic nature of SASE, the energy spectrum fluctuates from pulse to pulse. Many experiments that employ XFEL radiation require the resolution of the spectrum of each pulse. The work presented here investigates the capacity of a thin strongly bent diamond crystal to resolve the energy spectra of hard X-ray SASE pulses by studying its diffraction properties. Rocking curves of the symmetric C*(440) reflection have been measured for different bending radii. The experimental data match the theoretical modelling based on the Takagi–Taupin equations of dynamical diffraction. A uniform strain gradient has proven to be a valid model of strain deformations in the crystal.

Mössbauer reflectivity experiment with polarization selection are reported. The use of the LiF polarization analyzer allows us to get the π→σ’ peak on the reflectivity curve at the critical angle and Mössbauer π→σ’ reflectivity spectra of reasonable quality at the critical angle and also at the Bragg angles of superlattice. The impressive difference of the reflectivity spectra measured near the critical angle with and without polarizations analysis is observed for [57Fe10/V10]20 multilayer characterizing by the ferromagnetic interlayer coupling. The combined fit of the whole set of spectra measured at different angles reveals the existence of antiferromagnetic Fe oxide phases in the top three bilayers. The experiment demonstrates benefits of the Mössbauer reflectivity with polarization analysis in ultrathin surface layer investigations.

Polarization selection of the reflected radiation has been employed in M&ouml, ssbauer reflectivity measurements with a synchrotron M&ouml, ssbauer source (SMS). The polarization of resonantly scattered radiation differs from the polarization of an incident wave so the M&ouml, ssbauer reflectivity contains a scattering component with 90&deg, rotated polarization relative to the &pi, polarization of the SMS for some hyperfine transitions. We have shown that the selection of this rotated &pi, &rarr, &sigma, component from total reflectivity gives an unusual angular dependence of reflectivity characterized by a peak near the critical angle of the total external reflection. In the case of collinear antiferromagnetic interlayer ordering, the &ldquo, magnetic&rdquo, maxima on the reflectivity angular curve are formed practically only by radiation with this rotated polarization. The first experiment on M&ouml, ssbauer reflectivity with a selection of the rotated polarization discovers the predicted peak near the critical angle. The measurement of the rotated &pi, polarization component in M&ouml, ssbauer reflectivity spectra excludes the interference with non-resonant electronic scattering and simplifies the spectrum shape near the critical angle allowing for an improved data interpretation in the case of poorly resolved spectra. It is shown that the selected component of M&ouml, ssbauer reflectivity with rotated polarization is characterized by enhanced surface sensitivity, determined by the &ldquo, squared standing waves&rdquo, depth dependence. Therefore, the new approach has interesting perspectives for investigations of surfaces, ultrathin layers and multilayers having complicated magnetic structures.

Precise spectral characterization of every pulse is required in many x-ray free-electron laser (XFEL) experiments due to the fluctuating spectral content of self-amplified spontaneous emission (SASE) beams. Bent single-crystal spectrometers can provide sufficient spectral resolution to resolve the SASE spikes while also covering the full SASE bandwidth. However, strain and stresses due to the strong bending may affect the intrinsic diffraction properties of the crystal significantly and thus affect the spectral resolution of the device. This paper experimentally investigates the intrinsic diffraction properties of a strongly bent single-crystal diamond spectrometer to be implemented at the European XFEL and compares with theoretical calculations.

Recent progress in multiferroic materials and spintronic devices has renewed interest in metal oxide ferromagnetic and ferrimagnetic materials. Here, we report the preparation of thin films of nanocrystalline ferrimagnetic CoFe2O4 (CFO) using an environmentally benign aqueous solution processing route. The evolution of the structural, optical, and magnetic properties as a function of postdeposition annealing temperature is reported. For the highest annealing temperature (800 °C), the remanence, coercivity, and resistivity values are comparable with those of films fabricated by epitaxial growth methods and exceed the quality of CFO nanocrystals prepared by other wet-chemical syntheses. In addition to the ability to make high quality ferrite films, the aqueous solution processing strategy offers great flexibility for tuning film properties by incorporating or substituting additional transition metal ions.

A series of ruthenium complexes of the general type Ru(CO)2(P(n-Bu)3)2(O2CR)2 (4a, R = Me; 4b, R = Et; 4c, R = i-Pr; 4d, R = t-Bu; 4e, R = CH2OCH3; 4f, R = CF3; 4g, R = CF2CF3) was synthesized by a single-step reaction of Ru3(CO)12 with P(n-Bu)3 and the respective carboxylic acid. The molecular structures of 4b, 4c and 4e–g in the solid state are discussed. All ruthenium complexes are stable against air and moisture and possess low melting points. The physical properties including the vapor pressure can be adjusted by modification of the carboxylate ligands. The chemical vapor deposition of ruthenium precursors 4a–f was carried out in a vertical cold-wall CVD reactor at substrate temperatures between 350 and 400 °C in a nitrogen atmosphere. These experiments show that all precursors are well suited for the deposition of phosphorus-doped ruthenium layers without addition of any reactive gas or an additional phosphorus source. In the films, phosphorus contents between 11 and 16 mol% were determined by XPS analysis. The obtained layers possess thicknesses between 25 and 65 nm and are highly conformal and dense as proven by SEM and AFM studies.

We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]30 multilayer with ultrathin Fe layers and nominal thickness of the chromium spacers dCr≈2.0nm using nuclear resonance scattering of synchrotron radiation. The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has been detected at zero external field. The joint fit of the reflectivity curves and Mössbauer spectra of reflectivity measured near the critical angle and at the "magnetic" peak reveals that the magnetic structure of the multilayer is formed by two spirals, one in the odd and another one in the even iron layers, with the opposite signs of rotation. The double-spiral structure starts from the surface with the almost-Antiferromagnetic alignment of the adjacent Fe layers. The rotation of the two spirals leads to nearly ferromagnetic alignment of the two magnetic subsystems at some depth, where the sudden turn of the magnetic vectors by ∼180â (spin flop) appears, and both spirals start to rotate in opposite directions. The observation of this unusual double-spiral magnetic structure suggests that the unique properties of giant magnetoresistance devices can be further tailored using ultrathin magnetic layers. © 2018 American Physical Society.

Nature Communications 9(1), 4142 (2018). doi:10.1038/s41467-018-06457-x, A Verwey-type charge-ordering transition in magnetite at 120 K leads to the formation of linear units of three iron ions with one shared electron, called trimerons. The recently-discovered iron pentoxide (Fe$_4$O$_5$) comprising mixed-valent iron cations at octahedral chains, demonstrates another unusual charge-ordering transition at 150 K involving competing formation of iron trimerons and dimerons. Here, we experimentally show that applied pressure can tune the charge-ordering pattern in Fe$_4$O$_5$ and strongly affect the ordering temperature. We report two charge-ordered phases, the first of which may comprise both dimeron and trimeron units, whereas, the second exhibits an overall dimerization involving both the octahedral and trigonal-prismatic chains of iron in the crystal structure. We link the dramatic change in the charge-ordering pattern in the second phase to redistribution of electrons between the octahedral and prismatic iron chains, and propose that the average oxidation state of the iron cations can pre-determine a charge-ordering pattern., Published by Nature Publishing Group UK, [London]

The use of single molecule magnets (SMMs) as cornerstone elements in spintronics and quantum computing applications demands that magnetic bistability is retained when molecules are interfaced with solid conducting surfaces. Here, we employ synchrotron Mössbauer spectroscopy to investigate a monolayer of a tetrairon(III) (Fe4) SMM chemically grafted on a gold substrate. At low temperature and zero magnetic field, we observe the magnetic pattern of the Fe4 molecule, indicating slow spin fluctuations compared to the Mössbauer timescale. Significant structural deformations of the magnetic core, induced by the interaction with the substrate, as predicted by ab initio molecular dynamics, are also observed. However, the effects of the modifications occurring at the individual iron sites partially compensate each other, so that slow magnetic relaxation is retained on the surface. Interestingly, these deformations escaped detection by conventional synchrotron-based techniques, like X-ray magnetic circular dichroism, thus highlighting the power of synchrotron Mössbauer spectroscopy for the investigation of hybrid interfaces., Deposition of single molecule magnets onto surfaces is a key step for integration in devices exploiting their magnetic bistability and quantum properties. Here, Sessoli and colleagues exploit synchrotron Mössbauer spectroscopy to assess the effects of molecule-surface interactions on the magnetic properties of Fe(III) SMMs.

Kinetics of the crystallization process of Fe–Mo–Cu–B-type metallic glass is studied to fine details during heat treatment under weak external magnetic field (0.652 T). Structural arrangement as well as magnetic microstructure is followed on-fly using sophisticated method of in situ nuclear forward scattering (NFS) of synchrotron radiation. The latter provides both quantitative (relative fractions) and qualitative (hyperfine magnetic fields) temperature dependencies of all structurally different samples’ components. They belong to the amorphous residual matrix, the newly formed nanocrystalline grains, and to their surfaces, respectively. The onset of crystallization during in-field magnetic annealing starts ∼100 K earlier than that in zero field.

The impact of an external magnetic field upon changes in the crystallization kinetics of Fe 90 Zr 7 B 3 metallic glass is studied by in situ nuclear forward scattering (NFS) of synchrotron radiation. Structural and magnetic information on the whole process of nanograin formation is monitored on fly in real time by means of time domain Mossbauer effect technique. Isothermal annealing performed at 753 K under weak magnetic field ( B ext = 0.652 T) exhibits more rapid crystallization in comparison with zero-field conditions. These surprising effects of an external magnetic field upon the process of phase transformation are attributed to energetic perturbations of magnetic interactions in comparison with the thermal energy. Consequently, the formation of nucleation centers is enhanced. Such accelerated crystallization was not reported so far for metallic glasses exposed to magnetic field during annealing. The influence of magnetic field on the resulting properties is usually assessed under static conditions after annealing. The use of NFS with rapid data acquisition has allowed in situ observation of the microstructure development throughout the fast annealing processes. In this way, not only the starting and the final stages of the structure can be characterized but also the intermediate transition period states of the transformation can be followed to fine details.

The ability to rationally tune the morphology of nanostructures is a fundamental milestone in nanoscale engineering. In particular, the possibility to switch between different shapes within the same material system represents a further step in the development of complex nanoscale devices and it increases the potential of nanostructures in practical applications. We recently reported a new form of InAs nanostructures growing epitaxially on Si substrates as vertical V-shaped membranes. Here we demonstrate the possibility of modifying the shape of these nanomembranes and turning them into nanowires by modulating the surface roughness of the substrate by varying the surface treatment. We show that the growth of nanomembranes is favored on smooth surfaces. Conversely rough surfaces enhance the growth of nanowires. We also show that the V/III ratio plays a key role in determining the absolute yield, i.e. how many nanostructures form during growth. These results envisage a new degree of freedom in the engineering of bottom-up nanostructures and contribute to the achievement of nanostructure networks.

Polyamide 6/SiO2 hybrid materials were produced by a coupled polymerization reaction of three monomeric components namely 1,1′,1′′,1′′′-silanetetrayltetrakis-(azepan-2-one) (Si(ε-CL)4), 6-aminocaproic acid (ε-ACA) and ε-caprolactam (ε-CL) within one process. Si(ε-CL)4 together with ε-ACA has been found suitable as a precursor monomer for the silica and PA6 components. The accurate adjustment of the molar ratio of both components, as well as the combination of the overall process for producing the polyamide 6/SiO2 hybrid material with the hydrolytic ring opening polymerization of ε-caprolactam is of great importance to achieve homogeneous products with a low extractable content. Water in comparison with ε-ACA has been found unsuitable as an oxygen source to produce uniformly distributed silica. The procedure was carried out in a commercial laboratory autoclave at 8 bar initial pressure. The molecular structure and morphology of the hybrid materials have been investigated by solid state 29Si and 13C NMR spectroscopy, DSC and FTIR spectroscopy and electron microscopy measurements. Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

To design custom magnetic nanostructures, it is indispensable to acquire precise knowledge about the systems in the nanoscale range where the magnetism forms. In this paper we present the effect of a curved surface on the evolution of magnetism in ultrathin iron films. Nominally 70 Å thick iron films were deposited in 9 steps on 3 different types of templates: (a) a monolayer of silica spheres with 25 nm diameter, (b) a monolayer of silica spheres with 400 nm diameter and (c) for comparison a flat silicon substrate. In situ iron evaporation took place in an ultrahigh vacuum chamber using the molecular beam epitaxy technique. After the evaporation steps, time differential nuclear forward scattering spectra, grazing incidence small angle X-ray scattering images and X-ray reflectivity curves were recorded. In order to reconstruct and visualize the magnetic moment configuration in the iron cap formed on top of the silica spheres, micromagnetic simulations were performed for all iron thicknesses. We found a great influence of the template topography on the onset of magnetism and on the developed magnetic nanostructure. We observed an individual magnetic behaviour for the 400 nm spheres which was modelled by vortex formation and a collective magnetic structure for the 25 nm spheres where magnetic domains spread over several particles. Depth selective nuclear forward scattering measurements showed that the formation of magnetism begins at the top region of the 400 nm spheres in contrast to the 25 nm particles where the magnetism first appears in the region where the spheres are in contact with each other. ispartof: Nanoscale vol:7 issue:30 pages:12878-12887 ispartof: location:England status: published

Evolution of structure and local magnetic fields in (Fe(1-x)Co(x))76Mo8Cu1B15 (HITPERM) metallic glass ribbons with various amounts of Co (x = 0, 0.25, 0.5) were studied in situ using diffraction and nuclear forward scattering of synchrotron radiation. It was found that crystallization of all three glasses proceeds in two stages. In the first stage, bcc (Fe,Co) nanocrystals are formed, while in the second stage additional crystalline phases evolve. For all three glasses, the crystallization temperatures at the wheel side were found to be lower than at the air side of the ribbon. The crystallization temperatures were found to decrease with increasing Co content. The lattice parameters of the bcc nanocrystals decrease up to about 550 °C and then increase pointing to squeezing Mo atoms out of the nanograins or to interface effects between the nanocrystals and the glassy matrix. Nuclear forward scattering enabled separate evaluation of the contributions that stem from structurally different regions within the investigated samples including the newly formed nanocrystals and the residual amorphous matrix. Even minor Co content (x = 0.25) has a substantial effect not only upon the magnetic behaviour of the alloy but also upon its structure. Making use of hyperfine magnetic fields, it was possible to unveil structurally diverse positions of Fe atoms that reside in a nanocrystalline lattice with different numbers of Co nearest neighbours.

We used nuclear hyperfine spectroscopies and a 57 Fe probe layer approach to study the depth-dependent magnetic properties of ultrathin Fe films on NiO(0 0 1), a system exhibiting exchange bias. Conversion electron Mossbauer spectroscopy and nuclear resonance scattering of synchrotron radiation were employed. The samples were two Fe films with a thickness (8–10 ML) slightly above the critical thickness for the onset of ferromagnetism at room temperature, in which a 2 ML-thick probe layer, enriched in the 57 Fe Mossbauer isotope, was embedded at different depths from the Fe/NiO interface. Both techniques indicate that inside the film Fe has a metallic character, while at the interface with NiO different Fe phases are present. The main conclusion is that already a few monolayers from the interface with NiO the magnetic properties of Fe are bulk-like.

Physical review materials 1(2), 023001(2017). doi:10.1103/PhysRevMaterials.1.023001, We present a synchrotron-based x-ray scattering technique which allows disentangling magnetic propertiesof heterogeneous systems with nanopatterned surfaces. This technique combines the nanometer-range spatialresolution of surface morphology features provided by grazing incidence small angle x-ray scattering and thehigh sensitivity of nuclear resonant scattering to magnetic order. A single experiment thus allows attributingmagnetic properties to structural features of the sample; chemical and structural properties may be correlatedanalogously. We demonstrate how this technique shows the correlation between structural growth and evolutionof magnetic properties for the case of a remarkable magnetization reversal in a structurally and magneticallynanopatterned sample system., Published by APS, College Park, MD

The magnetic-field-dependent spin ordering of strained BiFeO3 films is determined using nuclear resonant scattering and Raman spectroscopy. The critical field required to destroy the cycloidal modulation of the Fe spins is found to be significantly lower than in the bulk, with appealing implications for field-controlled spintronic and magnonic devices., Work supported by ERC Consolidator grant MINT (Contract No. 615759)

The presence of carbonates in inclusions in diamonds coming from depths exceeding 670 km are obvious evidence that carbonates exist in the Earth’s lower mantle. However, their range of stability, crystal structures and the thermodynamic conditions of the decarbonation processes remain poorly constrained. Here we investigate the behaviour of pure iron carbonate at pressures over 100 GPa and temperatures over 2,500 K using single-crystal X-ray diffraction and Mössbauer spectroscopy in laser-heated diamond anvil cells. On heating to temperatures of the Earth’s geotherm at pressures to ∼50 GPa FeCO3 partially dissociates to form various iron oxides. At higher pressures FeCO3 forms two new structures—tetrairon(III) orthocarbonate Fe43+C3O12, and diiron(II) diiron(III) tetracarbonate Fe22+Fe23+C4O13, both phases containing CO4 tetrahedra. Fe4C4O13 is stable at conditions along the entire geotherm to depths of at least 2,500 km, thus demonstrating that self-oxidation-reduction reactions can preserve carbonates in the Earth’s lower mantle., Carbonates are shown to exist in the lower mantle as seen in diamond inclusions, but thermodynamic constraints are poorly understood. Here, the authors synthesise two new iron carbonate compounds and find that self-oxidation-reduction reactions can preserve carbonates in the mantle.

The synthesis, chemical and physical properties of [{AgO2CCH2OMe}n] (1) and [{AgO2CCH2OMe(PPh3)}n] (2) are reported. Consecutive reaction of AgNO3 with HO2CCH2OMe gave 1, which upon treatment with PPh3 produced 2. Coordination compound 2 forms a 1D coordination polymer in the solid state as evidenced by single crystal X-ray structure analysis. The coordination geometry at Ag+ is of the [3 + 1] type, whereby the carboxylate anions act as bridging ligands. The formation of PPh3–Ag(I) coordinative bonds results in distorted T-shaped AgPO2 units, which are stabilized further by an additional O–Ag dative bond. TG and TG–MS measurements show that 1 and 2 decompose at 190–250 °C (1) and 260–300 °C (2) via decarboxylation, involving Ag–P (2), C–C and C–O bond cleavages to give elemental silver as confirmed by PXRD studies. In order to verify if polymeric 2 is suitable as a FEBID precursor for silver deposition, its vapor pressure was determined (p170 °C = 5.318 mbar, ∆Hvap = 126.1 kJ mol−1), evincing little volatility. Also EI and ESI mass spectrometric studies were carried out. The dissociation of the silver(I) compound 2 under typical electron-driven FEBID conditions was studied by DFT (B3LYP) calculations on monomeric [AgO2CCH2OMe(PPh3)]. At an energy of the secondary electrons up to 0.8 eV elimination of PPh3 occurs, giving Ag+ and O2CCH2OMe−. Likewise, by release of PPh3 from [AgO2CCH2OMe(PPh3)] the fragment [AgO2CCH2OMe]− is formed from which Ag+ and O2CCH2OMe− is generated, further following the first fragmentation route. However, at 1.3 eV the initial step is decarboxylation giving [AgCH2OMe(PPh3)], followed by Ag–P and Ag–C bond cleavages.

Review of scientific instruments 88(8), 084501 - (2017). doi:10.1063/1.4998985, A portable double-sided pulsed laser heating system for diamond anvil cells has been developed that is able to stably produce laser pulses as short as a few microseconds with repetition frequencies up to 100 kHz. In situ temperature determination is possible by collecting and fitting the thermal radiation spectrum for a specific wavelength range (particularly, between 650 nm and 850 nm) to the Planck radiation function. Surface temperature information can also be time-resolved by using a gated detector that is synchronized with the laser pulse modulation and space-resolved with the implementation of a multi-point thermal radiation collection technique. The system can be easily coupled with equipment at synchrotron facilities, particularly for nuclear resonance spectroscopy experiments. Examples of applications include investigations of high-pressure high-temperature behavior of iron oxides, both in house and at the European Synchrotron Radiation Facility using the synchrotron Mössbauer source and nuclear inelastic scattering., Published by American Institute of Physics, [S.l.]

Physical properties of surfaces are extremely important for initiation and nucleation of crystal growth, including nanowires. In recent years, fluctuations in surface characteristics have often been related to unreproducible growth of GaAs nanowires on Si by the Ga-assisted method. We report on a systematic study of the occurrence of GaAs nanowire growth on silicon by the Ga-assisted method for different kinds of silicon oxides: native, thermal and hydrogen silsesquioxane (HSQ). We find that success in achieving nanowires and the growth conditions such as gallium rate and substrate temperature depend mainly on the physical properties of the surface: oxide stoichiometry, oxide thickness and surface roughness. These results constitute a step further towards the integration of GaAs technology on the Si platform.

We present epitaxial growth of europium (Eu) on the oxygen-induced c(6×2) reconstructed (110)Nb (niobium) surface at 150 °C and at 260 °C for various Eu coverages. The samples are characterized by reflection high-energy electron diffraction, atomic force microscopy and low-temperature in-situ nuclear resonance scattering. At a substrate temperature of 260 °C Eu forms islands with the face-centered cubic (fcc) crystal structure that is an exotic crystallographic phase for metallic europium. The deposition at 150 °C results to the already reported formation of a smooth film with hexagonal symmetry. The up to now unknown initially formed intermediate phase in this growth mode is identified as EuO-type stacking of [111]Eu layers that quickly relaxes towards that of an [0001]Eu film. The analysis of the nuclear resonance scattering data unambiguously demonstrates the formation of EuO interface at 260 °C that facilitates the stabilization of the strained fcc Eu lattice. No traces of EuO are found in the sample grown at 150 °C.

We successfully demonstrate the plasmonic coupling between metal nanoantennas and individual GaAs nanowires (NWs). In particular, by using dark-field scattering and second harmonic excitation spectroscopy in partnership with analytical and full-vector FDTD modeling, we demonstrate controlled electromagnetic coupling between individual NWs and plasmonic nanoantennas with gap sizes varied between 90 and 500 nm. The significant electric field enhancement values (up to 20×) achieved inside the NW-nanoantennas gap regions allowed us to tailor the nonlinear optical response of NWs by engineering the plasmonic near-field coupling regime. These findings represent an initial step toward the development of coupled metal???semiconductor resonant nanostructures for the realization of next generation solar cells, detectors, and nonlinear optical devices with reduced footprints and energy consumption.

The partial phonon densities of states of iron atoms in the intermetallic compound FeSi have been measured in the temperature range 46–297 K using nuclear resonant inelastic scattering of synchrotron radiation. A significant phonon softening with increasing temperature has been established. The greatest phonon softening for iron atoms is shown to occur in the region of long-wavelength acoustic phonons, for the acoustic branches near the boundary of the Brillouin zone, and for the low-lying weakly dispersive optical branches. The results obtained are analyzed in terms of the views that relate the change in the phonon density of states of iron atoms to the temperature evolution of the electronic density of state for the compound.