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The nonlinear optical response of a material is a sensitive probe of electronic and structural dynamics under strong light fields. The induced microscopic polarizations are usually detected via their far-field light emission, thus limiting spatial resolution. Several powerful near-field techniques circumvent this limitation by employing local nanoscale scatterers; however, their signal strength scales unfavorably as the probe volume decreases. Here, we demonstrate that time-resolved atomic force microscopy is capable of temporally and spatially resolving the microscopic, electrostatic forces arising from a nonlinear optical polarization in an insulating dielectric driven by femtosecond optical fields. The measured forces can be qualitatively explained by a second-order nonlinear interaction in the sample. The force resulting from this nonlinear interaction has frequency components below the mechanical resonance frequency of the cantilever and is thus detectable by regular atomic force microscopy methods. The capability to measure a nonlinear polarization through its electrostatic force is a powerful means to revisit nonlinear optical effects at the nanoscale, without the need for emitted photons or electrons from the surface. © 2020 National Academy of Sciences. All rights reserved., Proceedings of the National Academy of Sciences of the United States of America, 117 (33), ISSN:0027-8424, ISSN:1091-6490

The genetic material of viruses is protected by protein shells that are assembled from a large number of subunits in a process that is efficient and robust. Many of the mechanistic details underpinning efficient assembly of virus capsids are still unknown. The assembly mechanism of hepatitis B capsids has been intensively researched using a truncated core protein lacking the C-terminal domain responsible for binding genomic RNA. To resolve the assembly intermediates of hepatitis B virus (HBV), we studied the formation of nucleocapsids and empty capsids from full-length hepatitis B core proteins, using time-resolved small-angle X-ray scattering. We developed a detailed structural model of the HBV capsid assembly process using a combination of analysis with multivariate curve resolution, structural modeling, and Bayesian ensemble inference. The detailed structural analysis supports an assembly pathway that proceeds through the formation of two highly populated intermediates, a trimer of dimers and a partially closed shell consisting of around 40 dimers. These intermediates are on-path, transient and efficiently convert into fully formed capsids. In the presence of an RNA oligo that binds specifically to the C-terminal domain the assembly proceeds via a similar mechanism to that in the absence of nucleic acids. Comparisons between truncated and full-length HBV capsid proteins reveal that the unstructured C-terminal domain has a significant impact on the assembly process and is required to obtain a more complete mechanistic understanding of HBV capsid formation. These results also illustrate how combining scattering information from different time-points during time-resolved experiments can be utilized to derive a structural model of protein self-assembly pathways.

With the promise of new, more powerful neutron sources in the future, the possibilities for time-resolved neutron scattering experiments will improve and are bound to gain in interest. While there is already a large body of work on the accurate control of temperature, pressure, and magnetic fields for static experiments, this field is less well developed for time-resolved experiments on soft condensed matter and biomaterials. We present here an overview of different sample environments and technique combinations that have been developed so far and which might inspire further developments so that one can take full advantage of both the existing facilities as well as the possibilities that future high intensity neutron sources will offer.

International audience; The Bernina instrument at the SwissFEL Aramis hard X-ray free-electron laser is designed for studying ultrafast phenomena in condensed matter and material science. Ultrashort pulses from an optical laser system covering a large wavelength range can be used to generate specific non-equilibrium states, whose subsequent temporal evolution can be probed by selective X-ray scattering techniques in the range 2–12 keV. For that purpose, the X-ray beamline is equipped with optical elements which tailor the X-ray beam size and energy, as well as with pulse-to-pulse diagnostics that monitor the X-ray pulse intensity, position, as well as its spectral and temporal properties. The experiments can be performed using multiple interchangeable endstations differing in specialization, diffractometer and X-ray analyser configuration and load capacity for specialized sample environment. After testing the instrument in a series of pilot experiments in 2018, regular user operation begins in 2019.

1-Hexene is an important α-olefin for polyethylene production and is produced from ethene. Recent developments in the α-olefin industry have led to the successful commercialization of ethene trimerization catalysts. An important industrially applied ethene trimerization system uses a mixture of chromium 2-ethylhexanoate, AlEt3, AlEt2Cl, and 2,5-dimethylpyrrole (DMP). Here, we have studied the activation of this system using catalytic and spectroscopic experiments (XAS, EPR, and UV–vis) under conditions employed in industry. First, chromium 2-ethylhexanoate was prepared and characterized to be [Cr3O(RCO2)6(H2O)3]Cl. Next, the activation of chromium 2-ethylhexanoate with AlEt3, AlEt2Cl, and DMP was studied, showing immediate reduction (

Funder: ERC Grants Hetero2D, Funder: GSYNCOR, Funder: EU Graphene Flagship, Black phosphorous (BP) is a layered semiconductor with high carrier mobility, anisotropic optical response and wide bandgap tunability. In view of its application in optoelectronic devices, understanding transient photo-induced effects is crucial. Here, we investigate by time- and angle-resolved photoemission spectroscopy BP in its pristine state and in the presence of Stark splitting, chemically induced by Cs ad-sorption. We show that photo-injected carriers trigger bandgap renormalization, and a concurrent valence band flattening caused by Pauli blocking. In biased samples, photo-excitation leads to a long-lived (ns) surface photovoltage of few hundreds mV that counterbalances the Cs-induced surface band bending. This allows us to disentangle bulk from surface electronic states, and to clarify the mechanism underlying the band inversion observed in bulk samples.

Journal of synchrotron radiation 28(2), 375-382 (2021). doi:10.1107/S1600577521000151, A new concept for temporal gating of synchrotron X-ray pulses based on laser-induced thermal transient gratings is presented. First experimental tests of the concept yield a diffraction efficiency of 0.18%; however, the calculations indicate a theoretical efficiency and contrast of >30% and 10$^{���5}$, respectively. The full efficiency of the pulse picker has not been reached yet due to a long-range thermal deformation of the sample after absorption of the excitation laser. This method can be implemented in a broad spectral range (100 eV to 20 keV) and is only minimally invasive to an existing setup., Published by Wiley-Blackwell, [S.l.]

This paper presents the results of an investigation into the photooxidation of tocopherols (Tocs) dissolved in argonated and non-argonated n-hexane. During irradiation, steady-state absorption and fluorescence spectra as well as lifetimes were measured. In all experiments, the photoreactions were of the first order type. The reaction rate was higher for all Tocs in argonated solvent. A new emission band with a maximum at 298 nm as well as new absorption and fluorescence bands beyond the 300 nm connected with charge-transfer (C-T) complexes for all Tocs appeared during the irradiation of &gamma, and &delta, Toc. The above results indicate that the photooxidation process is very complex and that the observed phenomena strongly depend on the number and position of methyl groups in the chromanol ring.

Significance Internal combustion engine components experience extreme thermomechanical cycling during operation, and the continuing need to improve engine efficiency while maintaining or improving reliability drives the development of lightweight materials with improved thermal and mechanical integrity. Understanding the behavior of new materials in dynamic operation requires operando characterization tools, but conventional in situ measurements of material behavior during real engine operation are very limited, and no practical means exist to replicate such extreme dynamics for ex situ study. In this work, we demonstrate that the penetrating power of neutrons can provide noninvasive measurement of lattice strains inside components of a firing engine, enabling the operando study of complex load states and thermal gradients throughout the solid materials., Engineering neutron diffraction can nondestructively and noninvasively probe stress, strain, temperature, and phase evolutions deep within bulk materials. In this work, we demonstrate operando lattice strain measurement of internal combustion engine components by neutron diffraction. A modified commercial generator engine was mounted in the VULCAN diffractometer at the Spallation Neutron Source, and the lattice strains in both the cylinder block and head were measured under static nonfiring conditions as well as steady state and cyclic transient operation. The dynamic temporal response of the lattice strain change during transient operation was resolved in two locations by asynchronous stroboscopic neutron diffraction. We demonstrated that operando neutron measurements can allow for understanding of how materials behave throughout operational engineering devices. This study opens a pathway for the industrial and academic communities to better understand the complexities of material behavior during the operation of internal combustion engines and other real-scale devices and systems and to leverage techniques developed here for future investigations of numerous new platforms and alloys.

Time-resolved optical spectroscopy (TR-OS) has emerged as a fundamental spectroscopic tool for probing complex materials, to both investigate ground-state-related properties and trigger phase transitions among different states with peculiar electronic and lattice structures. We describe a versatile approach to perform polarization-resolved TR-OS measurements, by combining broadband detection with the capability to simultaneously probe two orthogonal polarization states. This method allows us to probe, with femtoseconds resolution, the frequency-resolved reflectivity or transmittivity variations along two mutually orthogonal directions, matching the principal axis of the crystal structure of the material under scrutiny. We report on the results obtained by acquiring the polarization-dependent transient reflectivity of two polytypes of the MoTe2 compound, with 2H and 1T’ crystal structures. We reveal marked anisotropies in the time-resolved reflectivity signal of 1T’-MoTe2, which are connected to the crystal structure of the compound. Polarization- and time- resolved spectroscopic measurements can thus provide information about the nature and dynamics of both the electronic and crystal lattice subsystems, advancing the comprehension of their inter-dependence, in particular in the case of photoinduced phase transitions; in addition, they provide a broadband measurement of transient polarization rotations.

The video-capabilities of smartphones are rapidly improving both in pixel resolution and frame-rates. Herein we use four smartphones in the &ldquo, slow-mo&rdquo, option to perform time-resolved Tomographic Particle Shadow Velocimetry of a vortex ring, using 960 fps. We use background LED-illuminated diffusers, facing each camera, for shadow particle imaging. We discuss in-depth the challenges present in synchronizing the high-speed video capture on the smartphones and steps to overcome these challenges. The resulting 3-D velocity field is compared to an instantaneous, concurrent, high-resolution snapshot with four 4k-video cameras using dual-color to encode two time-steps on a single frame. This proof-of-concept demonstration, supports realistic low-cost alternatives to conventional 3-D experimental systems.

Time-resolved luminescence measurement is a useful technique which can eliminate the background signals from scattering and short-lived autofluorescence. However, the relative instruments always require pulsed excitation sources and high-speed detectors. Moreover, the excitation and detecting shutter should be precisely synchronized by electronic phase matching circuitry, leading to expensiveness and high-complexity. To make time-resolved luminescence instruments simple and cheap, the automatic synchronization method was developed by using a mechanical chopper acted as both of the pulse generator and detection shutter. Therefore, the excitation and detection can be synchronized and locked automatically as the optical paths fixed. In this paper, we first introduced the time-resolved luminescence measurements and review the progress and current state of this field. Then, we discussed low-cost time-resolved techniques, especially chopper-based time-resolved luminescence detections. After that, we focused on auto-phase-locked method and some of its meaningful applications, such as time-gated luminescence imaging, spectrometer, and luminescence lifetime detection. Finally, we concluded with a brief outlook for auto-phase-locked time-resolved luminescence detection systems.

We have developed a compact relativistic femtosecond electron diffractometer with a radio-frequency photocathode electron gun and an electron lens system. The electron gun generated 2.5-MeV-energy electron pulses with a duration of 55 &plusmn, 5 fs containing 6.3 &times, 104 electrons per pulse. Using these pulses, we successfully detected high-contrast electron diffraction images of single crystalline, polycrystalline, and amorphous materials. An excellent spatial resolution of diffraction images was obtained as 0.027 &plusmn, 0.001 &Aring, &minus, 1. In the time-resolved electron diffraction measurement, a laser-excited ultrafast electronically driven phase transition in single-crystalline silicon was observed with a temporal resolution of 100 fs. The results demonstrate the advantages of the compact relativistic femtosecond electron diffractometer, including access to high-order Bragg reflections, single shot imaging with the relativistic femtosecond electron pulse, and the feasibility of time-resolved electron diffraction to study ultrafast structural dynamics.

We have implemented an electron-nuclear real-time propagation scheme for the calculation of transient absorption spectra. When this technique is applied to the study of ultrafast dynamics of Soret-excited zinc(II) tetraphenylporphyrin in the subpicosecond time scale, quantum beats in the transient absorption caused by impulsively excited molecular vibrations are observed. The launching mechanism of such vibrations can be regarded as a displacive excitation of the zinc-pyrrole and pyrrole C-C bonds. Fil: Bonafé, Franco Paúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Hernández, Federico Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Aradi, Bálint. Universitat Bremen; Alemania Fil: Frauenheim, Thomas. Universitat Bremen; Alemania Fil: Sanchez, Cristian Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

Kelvin probe force microscopy (KPFM) has been used for the characterization of metals, insulators, and semiconducting materials on the nanometer scale. Especially in semiconductors, the charge dynamics are of high interest. Recently, several techniques for time-resolved measurements with time resolution down to picoseconds have been developed, many times using a modulated excitation signal, e.g., light modulation or bias modulation that induces changes in the charge carrier distribution. For fast modulation frequencies, the KPFM controller measures an average surface potential, which contains information about the involved charge carrier dynamics. Here, we show that such measurements are prone to artifacts due to frequency mixing, by performing numerical dynamics simulations of the cantilever oscillation in KPFM subjected to a bias-modulated signal. For square bias pulses, the resulting time-dependent electrostatic forces are very complex and result in intricate mixing of frequencies that may, in some cases, have a component at the detection frequency, leading to falsified KPFM measurements. Additionally, we performed fast Fourier transform (FFT) analyses that match the results of the numerical dynamics simulations. Small differences are observed that can be attributed to transients and higher-order Fourier components, as a consequence of the intricate nature of the cantilever driving forces. These results are corroborated by experimental measurements on a model system. In the experimental case, additional artifacts are observed due to constructive or destructive interference of the bias modulation with the cantilever oscillation. Also, in the case of light modulation, we demonstrate artifacts due to unwanted illumination of the photodetector of the beam deflection detection system. Finally, guidelines for avoiding such artifacts are given.

We introduce a broadband single-pixel spectro-temporal fluorescence detector, combining time-correlated single photon counting (TCSPC) with Fourier transform (FT) spectroscopy. A birefringent common-path interferometer (CPI) generates two time-delayed replicas of the sample’s fluorescence. Via FT of their interference signal at the detector, we obtain a two-dimensional map of the fluorescence as a function of detection wavelength and emission time, with high temporal and spectral resolution. Our instrument is remarkably simple, as it only requires the addition of a CPI to a standard single-pixel TCSPC system, and it shows a readily adjustable spectral resolution with inherently broad bandwidth coverage.

Science, 355 (6322), ISSN:0036-8075, ISSN:1095-9203

Recently, multimodal imaging has gained an increasing interest in medical applications thanks to the inherent combination of strengths of the different techniques. For example, diffuse optics is used to probe both the composition and the microstructure of highly diffusive media down to a depth of few centimeters, but its spatial resolution is intrinsically low. On the other hand, ultrasound imaging exhibits the higher spatial resolution of morphological imaging, but without providing solid constitutional information. Thus, the combination of diffuse optical imaging and ultrasound may improve the effectiveness of medical examinations, e.g. for screening or diagnosis of tumors. However, the presence of an ultrasound coupling gel between probe and tissue can impair diffuse optical measurements like diffuse optical spectroscopy and diffuse correlation spectroscopy, since it may provide a direct path for photons between source and detector. A systematic study on the effect of different ultrasound coupling fluids was performed on tissue-mimicking phantoms, confirming that a water-clear gel can produce detrimental effects on optical measurements when recovering absorption/reduced scattering coefficients from time-domain spectroscopy acquisitions as well as particle Brownian diffusion coefficient from diffuse correlation spectroscopy ones. On the other hand, we show the suitability for optical measurements of other types of diffusive fluids, also compatible with ultrasound imaging.

We present a new full-custom instrument for time-domain diffuse optical spectroscopy developed within Horizon 2020 LUCA (Laser and Ultrasound Co-Analyzer for thyroid nodules) project. It features eight different picosecond diode lasers (in the 635 - 1050 nm range), two 1.3 × 1.3 mm2 active-area SiPMs (Silicon PhotoMultipliers) working in single-photon mode and two 10 ps resolution time-to-digital converters. A custom FPGA-based control board manages the instrument and communicates with an external computer via USB connection. The instrument proved state-of-the-art performance: an instrument response function narrower than 160 ps (fullwidth at half-maximum), a long-term measurement stability better than 1%, and an output average optical power higher than 1 mW at 40 MHz. The instrument has been validated with phantom measurements.

Time-resolved photocurrent (TRPC) spectroscopy with a variable-wavelength sub-bandgap light excitation was used to study the dynamics of the decaying photocurrent generated in the heterostructures of the AlGaN/GaN high electron mobility transistors (HEMTs) layers. In AlGaN/GaN HEMTs, reliability of the device is degraded due to the prevalence of current collapse. It is recognized that electrically active deep level defects at the surface/interfaces and the bulk in the HEMTs layers can contribute to the unwanted current collapse effect. Therefore, it is of great importance to analyze the deep level defects if the reliability of the HEMTs device is to be improved. In this research, TRPC spectroscopy was used to elucidate the origin and nature of the deep level defects by analyzing the time evolution of the photocurrent decay excited at different wavelengths of light. The two devices that show similar characteristics for wavelength-dependency on photocurrent generation were chosen, and TRPC spectroscopy was conducted on these devices. Although the two samples show similar characteristics for the wavelength-dependency on photocurrent generation, they exhibited dissimilar time-dependent photocurrent decay dynamics. This implies that TRPC spectroscopy can be used to distinguish the traps which have different origins but have the same de-trapping energy. Scopus

Time-resolved visible and infrared absorption difference spectroscopy data at both 298 and 77 K were obtained using cyanobacterial menB− mutant photosystem I particles with several non-native quinones incorporated into the A1 binding site. Data was obtained for photosystem I particles with phylloquinone (2-methyl-3-phytyl-1,4-naphthoquinone), 2-bromo-1,4-naphthoquinone, 2-chloro-1,4-naphthoquinone, 2-methyl-1,4-naphthoquinone, 2,3-dibromo-1,4-naphthoquinone, 2,3-dichloro-1,4-naphthoquinone, and 9,10-anthraquinone incorporated. Transient absorption data were obtained at 487 and 703 nm in the visible spectral range, and 1950–1100 cm−1 in the infrared region. Time constants obtained from fitting the time-resolved infrared and visible data are in good agreement. The measured time constants are crucial for the development of appropriate kinetic models that can describe electron transfer processes in photosystem I, “Modeling Electron Transfer in Photosystem I” Makita and Hastings (2016) [1]. Keywords: Photosynthesis, Photosystem I, Quinone, Bioenergetics, Time-resolved, Electron transfer

In metal nanoparticles (NPs) supracrystals, the metallic core provides some key properties, e.g. magnetization, plasmonic response or conductivity, with the ligand molecules giving rise to others like solubility, assembly or interaction with biomolecules. The formation of these supracrystals depends on a complex interplay between many forces, some stemming from the core, some from the ligands. At present, there is no known approach to characterize the local order of ligand molecules or their dynamics with atomic spatial resolution. Here, we develop a methodology based on small-angle ultrafast electron diffraction combined with angular cross-correlation analysis to characterize a two-dimensional supracrystal of dodecanethiol-coated gold NPs. We retrieve the static arrangement of the ligands, showing that at equilibrium they order in a preferential orientation on the NPs surface and throughout the two-dimensional supracrystal. Upon light excitation, positional disorder is induced in the supracrystal, while its overall homogeneity is surprisingly found to transiently increase. This suggests that transient annealing of the supracrystal takes place within few picoseconds (ps). This methodology will enable the systematic investigation of the dynamical structural properties of nano-assembled materials containing light elements, relevant for biological applications.

The formation of palladium hydride and carbide phases in palladium-based catalysts is a critical process that changes the catalytic performance and selectivity of the catalysts in important industrial reactions, such as the selective hydrogenation of alkynes or alkadienes. We present a comprehensive study of a 5 wt% carbon supported Pd nanoparticle (NP) catalyst in various environments by using in situ and operando X-ray absorption spectroscopy and diffraction, to determine the structure and evolution of palladium hydride and carbide phases, and their distribution throughout the NPs. We demonstrate how the simultaneous analysis of extended X-ray absorption fine structure (EXAFS) spectra and X-ray powder diffraction (XRPD) patterns allows discrimination between the inner “core” and outer “shell” regions of the NP during hydride phase formation at different temperatures and under different hydrogen pressures, indicating that the amount of hydrogen in the shell region of the NP is lower than that in the core. For palladium carbide, advanced analysis of X-ray absorption near-edge structure (XANES) spectra allows the detection of Pd–C bonds with carbon-containing molecules adsorbed at the surface of the NPs. In addition, H/Pd and C/Pd stoichiometries of PdHx and PdCy phases were obtained by using theoretical modelling and fitting of XANES spectra. Finally, the collection of operando time-resolved XRPD patterns (with a time resolution of 5 s) allowed the detection, during the ethylene hydrogenation reaction, of periodic oscillations in the NPs core lattice parameter, which were in phase with the MS signal of ethane (product) and in antiphase with the MS signal of H2 (reactant), highlighting an interesting direct structure–reactivity relationship. The presented studies show how a careful combination of X-ray absorption and diffraction can differentiate the structure of the core, shell and surface of the palladium NPs under working conditions and prove their relevant roles in catalysis.

Time-resolved X-ray scattering patterns from photoexcited molecules in solution are in many cases anisotropic at the ultrafast time scales accessible at X-ray Free Electron Lasers (XFELs). This anisotropy arises from the interaction of a linearly polarized UV-vis pump laser pulse with the sample, which induces anisotropic structural changes that can be captured by femtosecond X-ray pulses. In this work we describe a method for quantitative analysis of the anisotropic scattering signal arising from an ensemble of molecules and we demonstrate how its use can enhance the structural sensitivity of the time-resolved X-ray scattering experiment. We apply this method on time-resolved X-ray scattering patterns measured upon photoexcitation of a solvated di-platinum complex at an XFEL and explore the key parameters involved. We show that a combined analysis of the anisotropic and isotropic difference scattering signals in this experiment allows a more precise determination of the main photoinduced structural change in the solute, i.e. the change in Pt-Pt bond length, and yields more information on the excitation channels than the analysis of the isotropic scattering only. Finally, we discuss how the anisotropic transient response of the solvent can enable the determination of key experimental parameters such as the Instrument Response Function., Accepted for publication in Journal of Synchrotron Radiation

The term operando was coined at the beginning of this century to gather the growing efforts devoted to establish structure-activity relationships by simultaneously characterizing a catalyst performance and the relevant surface chemistry during genuine catalytic operation. This approach is now widespread and consolidated; it has become an increasingly complex but efficient junction where spectroscopy, materials science, catalysis and engineering meet. While for some characterization techniques kinetically relevant reactor cells with good resolution are recently developing, the knowledge gained with magnetic resonance and X-ray and vibrational spectroscopy studies is already huge and the scope of operando methodology with these techniques is recently expanding from studies with small amounts of powdered solids to more industrially relevant catalytic systems. Engineering catalysis implies larger physical domains, and thus all sort of gradients. Space- and time-resolved multi-technique characterization of both the solid and fluid phases involved in heterogeneous catalytic reactions (including temperature data) is key to map processes from different perspectives, which allows taking into account existing heterogeneities at different scales and facing up- and down-scaling for applications ranging from microstructured reactors to industrial-like macroreactors (operating with shaped catalytic bodies and/or in integral regime). This work reviews how operando methodology is evolving toward engineered reaction systems., This work was supported by Spanish Ministry grants CTQ2014-57578-R ‘LT-NOx’ and CTM2017-82335-R ‘RIEN2O’; and Comunidad de Madrid programme 2013/MAE2985 ‘ALCCONES.’

WOS: 000416369800026 PubMed: 29103500 A novel chitosan-based ratiometric fluorescent probe incorporating an EDTA-Eu3+ complex as the sensing unit and fluorescein dye as the internal standard was designed to detect dipicolinic acid (DPA) as an anthrax bio-marker with high sensitivity and selectivity. The fluorescence intensity of fluorescein dye attached to the chitosan backbone remains constant as an internal reference, while the Eu3+ emission increased linearly upon the consecutive addition of DPA. The selectivity studies were performed by adding different competitive aromatic ligands to the sensing environment and no signifacant fluorescence response was observed. The results demonstrated the superior selectivity of the system to DPA. Overall, this novel chitosan-based ratiometric fluorescent probe enables ratiometric and sensitive DPA detection over nanomolar concentrations (as low as 10 nM) and displays straightforward selectivity over other competitive aromatic ligands. Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [114Z088]; Konya Food and Agriculture University Strategic Products Research and Development Center (SARGEM); Nanobiz R D ltd. This research was financially supported by the Scientific and Technological Research Council of Turkey (TUBITAK), Project No: 114Z088 which is gratefully acknowledged here. The corresponding author would also like to thank Konya Food and Agriculture University Strategic Products Research and Development Center (SARGEM) and Nanobiz R & D ltd. for their support of this research.

The LinoSPAD camera system is a modular, compact and versatile time-resolved camera system, combining a linear 256 high fill factor pixel CMOS SPAD (single-photon avalanche diode) sensor with an FPGA (field-programmable gate array) and USB 3.0 transceiver board. This modularization permits the separate optimization or exchange of either the sensor front-end or the processing back-end, depending on the intended application, thus removing the traditional compromise between optimal SPAD technology on the one hand and time-stamping technology on the other hand. The FPGA firmware implements an array of 64 TDCs (time-to-digital converters) with histogram accumulators and a correction module to reduce non-linearities. Each TDC is capable of processing over 80 million photon detections per second and has an average timing resolution better than 50 ps. This article presents a complete and detailed characterization, covering all aspects of the system, from the SPAD array light sensitivity and noise to TDC linearity, from hardware/firmware/software co-design to signal processing, e.g., non-linearity correction, from power consumption to performance non-uniformity.

Time-resolved fluorescence spectroscopy (TRFS) is a new tool that can be used to investigate processes of interaction between metal ions and organic matter (OM) in soils, providing a specific analysis of the structure and dynamics of macromolecules. To the best of our knowledge, there are no studies in the literature reporting the use of this technique applied to whole/non-fractionated soil samples, making it a potential method for use in future studies. This work describes the use of TRFS to evaluate the fluorescence lifetimes of OM of whole soils from the Amazon region. Analysis was made of pellets of soils from an oxisol-spodosol system, collected in Sao Gabriel da Cachoeira (Amazonas, Brazil). The fluorescence lifetimes in the oxisol-spodosol system were attributed to two different fluorophores. One was related to complexation of an OM fraction with metals, resulting in a shorter fluorophore lifetime. A short fluorescence lifetime (2-12 ns) could be associated with simpler structures of the OM, while a long lifetime (19-66 ns) was associated with more complex OM structures. This new TRFS technique for analysis of the fluorescence lifetime in whole soil samples complies with the principles of green chemistry.

Procalcitonin (PCT) is a current, frequently-used marker for severe bacterial infection. The aim of this study was to develop a cost-effective detection kit for rapid quantitative and on-site detection of PCT. To develop the new PCT quantitative detecting kit, a double-antibody sandwich immunofluorescent assay was employed based on time-resolved immunofluorescent assay (TRFIA) combined with lateral flow immunoassay (LFIA). The performance of the new developed kit was evaluated in the aspects of linearity, precision, accuracy, and specificity. Two-hundred thirty-four serum samples were enrolled to carry out the comparison test. The new PCT quantitative detecting kit exhibited a higher sensitivity (0.08 ng/mL). The inter-assay coefficient of variation (CV) and the intra-assay CV were 5.4%–7.7% and 5.7%–13.4%, respectively. The recovery rates ranged from 93% to 105%. Furthermore, a high correlation (n = 234, r = 0.977, p < 0.0001) and consistency (Kappa = 0.875) were obtained when compared with the PCT kit from Roche Elecsys BRAHMS. Thus, the new quantitative method for detecting PCT has been successfully established. The results indicated that the newly-developed system based on TRFIA combined with LFIA was suitable for rapid and on-site detection for PCT, which might be a useful platform for other biomarkers in point-of-care tests.

International audience; Compressive sensing is a powerful tool to efficiently acquire and reconstruct an image even in diffuse optical tomography (DOT) applications. In this work, a time-resolved DOT system based on structured light illumination, compressive detection, and multiple view acquisition has been proposed and experimentally validated on a biological tissue-mimicking phantom. The experimental scheme is based on two digital micromirror devices for illumination and detection modulation, in combination with a time-resolved single element detector. We fully validated the method and demonstrated both the imaging and tomographic capabilities of the system, providing state-of-the-art reconstruction quality.

Insights into the nickel sulphide speciation of a dried oxidic Ni catalyst supported on delta-alumina were obtained by temperature-programmed sulphidation monitored by Quick-X-ray absorption with online mass spectrometry. Combination with Raman spectroscopy enabled the phase identification of sulphide phases isolated by multivariate curve regression with alternating least square analysis of the time-resolved X-ray absorption spectroscopy data.

Near-infrared spectroscopy (NIRS) is an optical technique that can measure brain tissue oxygenation and haemodynamics in real-time and at the patient bedside allowing medical doctors to access important physiological information. However, despite this, the use of NIRS in a clinical environment is hindered due to limitations, such as poor reproducibility, lack of depth sensitivity and poor brain-specificity. Time domain NIRS (or TD-NIRS) can resolve these issues and offer detailed information of the optical properties of the tissue, allowing better physiological information to be retrieved. This is achieved at the cost of increased instrument complexity, operation complexity and price. In this review, we focus on brain monitoring clinical applications of TD-NIRS. A total of 52 publications were identified, spanning the fields of neonatal imaging, stroke assessment, traumatic brain injury (TBI) assessment, brain death assessment, psychiatry, peroperative care, neuronal disorders assessment and communication with patient with locked-in syndrome. In all the publications, the advantages of the TD-NIRS measurement to (1) extract absolute values of haemoglobin concentration and tissue oxygen saturation, (2) assess the reduced scattering coefficient, and (3) separate between extra-cerebral and cerebral tissues, are highlighted; and emphasize the utility of TD-NIRS in a clinical context. In the last sections of this review, we explore the recent developments of TD-NIRS, in terms of instrumentation and methodologies that might impact and broaden its use in the hospital.

The active transport of ions across biological membranes requires their hydration shell to interact with the interior of membrane proteins. However, the influence of the external lipid phase on internal dielectric dynamics is hard to access by experiment. Using the octahelical transmembrane architecture of the copper-transporting P1B -type ATPase from Legionella pneumophila as a model structure, we have established the site-specific labeling of internal cysteines with a polarity-sensitive fluorophore. This enabled dipolar relaxation studies in a solubilized form of the protein and in its lipid-embedded state in nanodiscs. Time-dependent fluorescence shifts revealed the site-specific hydration and dipole mobility around the conserved ion-binding motif. The spatial distribution of both features is shaped significantly and independently of each other by membrane lateral pressure.

This study followed the first 20 h of flyash geopolymerization at 70 °C using time resolved Wide Angle X-ray Scattering (WAXS). The extent of dissolution of the amorphous phase of the flyash was determined to range from 29% to 54% for the different formulations trialed. The dissolution rate of the flyash significantly reduced after the first 5 h for all samples. During the formation stage of the geopolymer there were significant temporal variations in the chemistry of the dissolved solution due to the rate of flyash dissolution, with a relative standard deviation of 20%, 57% and 24% for the Si/Al, Na/Al and H/Si ratios, respectively. Utilizing the Power Law, scattering in the low angle region of the WAXS pattern combined with the geopolymer peak area yielded a measure which correlated with the compressive strength—providing a new method to measure the flyash dissolution and geopolymer formation processes independently. The evolution of several zeolite-like phases was followed, noting there are different formation mechanisms involved even within the same sample. Four samples were examined with compressive strengths ranging from 14(2)–50(9) MPa, each was synthesized with flyash from Collie Power Station (Western Australia) activated with sodium silicate solution of varying concentrations.

International audience; We introduce a new method for estimating fluid trajectories in time-resolved PIV. It relies on a Lucas-Kanade paradigm and consists in a simple and direct extension of a two-frame estimation proposed in that context. The so-called Lucas-Kanade Fluid Trajectories (LKFT) are assumed to be polynomial in time, and are found as the minimizer of a global functional, in which displacements are sought so as to match the intensities of a series of image pairs in the sequence, in the least-squares sense. All pairs involve the central image, similar to other recent time-resolved approaches (FTC and FTEE). As switching from a two-frame to a time-resolved objective simply amounts to adding terms in a functional, no significant additional algorithmic element is required, and similar to FOLKI-SPIV, the method has an important potential for GPU acceleration. Tests on synthetic data with translating and rotating motions show that in the current implementation, and using a cubic B-Spline interpolator for image deformation, LKFT has a total error comparable to that of FTEE, while improvements can still be brought to the algorithm. Besides, results on case B of the third PIV challenge confirm its ability to drastically reduce the random error in situations with low signal-to- noise ratio.

We report on the design, development, and performance assessment of a portable time-resolved system measuring absorption and scattering spectra of highly diffusive media over the 600–1350 nm range. In view of clinical use, two strategies were implemented; the first one equips the system with high responsivity in key tissue absorbing regions, whereas the second one makes the system immune to time drift. The MEDPHOT protocol was used for the performance assessment of the instrument. Finally, the system was enrolled into its first in vivo trial phase, measuring the broadband absorption and scattering spectra of human manubrium, abdomen fat tissues, and forehead for the in vivo quantification of key tissue constituents.

The processing of solution-based binary blends of the ferroelectric random copolymer poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) and the semiconducting polymer poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) applied by spin-coating and wire-bar coating is investigated. By systematic variation of blend composition, solvent, and deposition temperature it is shown that much smoother blend films can be obtained than reported thus far. At a low PFO:P(VDF-TrFE) ratio the blend film consists of disk-shaped PFO domains embedded in a P(VDF-TrFE) matrix, while an inverted structure is obtained in case the P(VDF-TrFE) is the minority component. The microstructure of the phase separated blend films is self-affine. From this observation and from the domain size distribution it is concluded that the phase separation occurs via spinodal decomposition, irrespectively of blend ratio. This is explained by the strong incompatibility of the two polymers expressed by the binary phase diagram, as constructed from thermal analysis data. Time resolved numerical simulation of the microstructure evolution during de-mixing qualitatively shows how an elevated deposition temperature has a smoothening effect as a result of the reduction of the repulsion between the blend components. The small roughness allowed the realization of bistable rectifying diodes that switch at low voltages with a yield of 100%. This indicates that memory characteristics can be tailored from the outset while processing parameters can be adjusted according to the phase behavior of the active components. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Detection of atherosclerotic plaque vulnerability has critical clinical implications for avoiding sudden death in patients with high risk of plaque rupture. We report on multimodality imaging of ex-vivo human carotid plaque samples using a system that integrates fluorescence lifetime imaging (FLIM), ultrasonic backscatter microscopy (UBM), and photoacoustic imaging (PAI). Biochemical composition is differentiated with a high temporal resolution and sensitivity at the surface of the plaque by the FLIM subsystem. 3D microanatomy of the whole plaque is reconstructed by the UBM. Functional imaging associated with optical absorption contrast is evaluated from the PAI component. Simultaneous recordings of the optical, ultrasonic, and photoacoustic data present a wealth of complementary information concerning the plaque composition, structure, and function that are related to plaque vulnerability. This approach is expected to improve our ability to study atherosclerotic plaques. The multimodal system presented here can be translated into a catheter based intraluminal system for future clinical studies.

Diffuse Optical Tomography (DOT) and Fluorescence Molecular Tomography (FMT) generally require a huge data set which poses severe limits to acquisition and computational time, especially with a multidimensional data set. The highly scattering behavior of biological tissue leads to a low bandwidth of the information spatial distribution and hence the sampling can be preferably carried out in the spatial frequency source/detector space. In this work, a time-resolved single pixel camera scheme combined with structured light illumination is presented and experimentally validated on phantoms measurements. This approach leads to a significant reduction of the data set while preserving the information content.

International audience; Near-infrared diffuse optical tomography (DOT) is a medical imaging which gives the distribution of the optical properties of biological tissues. To obtain endogenous chromophore features in the depth of a scattering medium, a multiwavelength/time-resolved (MW/TR) DOT setup was used. Reconstructions of the three-dimensional maps of chromophore concentrations of probed media were obtained by using a data processing technique which manages Mellin-Laplace Transforms of their MW/TR optical signals and those of a known reference medium. The point was to put a constraint on the medium absorption coefficient by using a material basis composed of a given set of chromophores of known absorption spectra. Experimental measurements were conducted by injecting the light of a picosecond near- infrared laser in the medium of interest and by collecting, for several wavelengths and multiple positions, the backscattered light via two fibers (with a source-detector separation of 15 mm) connected to fast-gated single-photon avalanche diodes (SPAD) and coupled to a time-correlated single-photon counting (TCSPC) system. Validations of the method were performed in simulation in the same configuration as the experiments for different combination of chromophores. Evaluation of the technique in real conditions was investigated on liquid phantoms composed of an homogenous background and a 10 mm depth inclusion formed of combination of intralipid and inks scanned at 30 positions and at three wavelengths. Both numerical and preliminary phantom experiments confirm the potential of this method to determine chromophore concentrations in the depth of biological tissues. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

We present a proof of concept prototype of a time-domain diffuse optics probe exploiting a fast Silicon PhotoMultiplier (SiPM), featuring a timing resolution better than 80 ps, a fast tail with just 90 ps decay time-constant and a wide active area of 1 mm2 . The detector is hosted into the probe and used in direct contact with the sample under investigation, thus providing high harvesting efficiency by exploiting the whole SiPM numerical aperture and also reducing complexity by avoiding the use of cumbersome fiber bundles. Our tests also demonstrate high accuracy and linearity in retrieving the optical properties and suitable contrast and depth sensitivity for detecting localized inhomogeneities. In addition to a strong improvement in both instrumentation cost and size with respect to legacy solutions, the setup performances are comparable to those of state-of-the-art time-domain instrumentation, thus opening a new way to compact, low-cost and high-performance time-resolved devices for diffuse optical imaging and spectroscopy.

International audience; We demonstrate femtosecond pump-probe transient absorption spectroscopy using a programmable dispersive filter as an ultra-fast delay line. Combined with fast synchronous detection this delay line allows for recording of 6 ps decay traces at 34 kHz. With such acquisition speed we perform single point pump-probe spectroscopy on bulk samples in 80 µs and hyperspectral pump-probe imaging over a field of view of 100 µm in less than a second. The usability of the method is illustrated on a showcase experiment to image and discriminate two pigments in a mixture.

Multivariate curve resolution -- alternating least squares (MCR-ALS) is a powerful method to infer information about short-lived chemical intermediate states created during ultrafast chemical reaction from a series of time-resolved spectra. However, the application of MCR relates to the fulfillment of a low-rank bilinear model for the decomposition of the experimental data. In ultrafast time-resolved spectroscopy, due to the presence of vibrational relaxation, continuous spectral evolution and band broadening/narrowing are observed on top of spectral variations associated to transitions between excited states. The basic assumption mentioned above may thus sometimes be questioned. In this paper, a methodology based on partially constrained MCR-ALS where classical constraints such as non-negativity are relaxed for some components is extended to hard- and soft-MCR. These models enable to describe deviations from ideal bilinearity in photoinduced processes. The application of these alternative MCR models is combined with the input of additional information available from the photophysics, both for hard-modeling constraint on the concentration profiles (kinetic rate constants for transitions) and for soft-modeling constraints (selective time domain for vibrational relaxation). Partially constrained MCR models are applied to two types of ultrafast spectroscopy data which show strong shifts and broadening of the signals, UV-visible and infrared femtosecond transient absorption spectra, respectively.

Absorption spectroscopy is known to be a powerful tool to gain spatially and temporally resolved information on excited and reactive species in a plasma discharge. Furthermore, the interaction of the discharge with short intense laser pulses can trigger the ignition and the transition into other transient states of the plasma. In this context laser-assisted ‘pump-probe’ experiments involving simultaneously generated supercontinuum radiation yield highly temporally resolved and spatially well-defined information on the transient phenomena. In this paper we demonstrate the possibility for ‘pump–probe’ experiments by initiating breakdown on a picosecond time scale (‘pump’) with a high-power beam and measuring the broadband absorption with the simultaneously provided supercontinuum (‘probe’). Since both pulses are generated from the same mode-locked master oscillator, they have a strong level of synchronization.

International audience; Silicon clathrates are unusual open-framework solids formed by tetrahedrally bonded silicon that show remarkable electronic and thermal properties. The type I structure has a primitive cubic unit cell containing cages occupied by metal atoms to give compositions such as Na(8)Si(46) and Na(2)Ba(6)Si(46). Although their structure and properties are well described, there is little understanding of the formation mechanism. Na(8)Si(46) is typically produced by metastable thermal decomposition under vacuum conditions from NaSi, itself an unusual structure containing Si(4)(4-) polyanions.,In this study, we used in situ synchrotron X-ray diffraction combined with rapid X-ray detection on samples taken through a controlled temperature ramp (25-500 degrees C at 8 degrees C/min) under vacuum conditions (10(-4) bar) to study the clathrate formation reaction. We also carried out complementary in situ high-temperature solid-state (23)Na NMR experiments using a sealed tube loaded under inert-gas-atmosphere conditions. We find no evidence for an intermediate amorphous phase during clathrate formation. Instead, we observe an unexpectedly high degree of structural coherency between the Na8Si46 clathrate and its NaSi precursor, evidenced by a smooth passage of several X-ray reflections from one structure into the other. The results indicate the possibility of an unusual, epitaxial-like, growth of the dathrate phase as Na atoms are removed from the NaSi precursor into the vacuum.

This research is focused on the 4f-5d transitions in Ce3+ centers doped into tetragonal β-SrAlF5 single crystals belonging to the I41/a space group. The presence of four non-equivalent Sr2+ sites in this compound leads to the appearance of three spectroscopically non-equivalent Ce3+ luminescence centers, which can be well distinguished using a time-resolved laser spectroscopy technique. All 4f-5d transitions have slightly varying excitation and emission energies with characteristic probabilities resulting in several decay times that can be determined experimentally. One of these centers experiences strong perturbation due to a defect nearby, probably the O2- impurity ion substituting for the F- ion and acting as a charge compensator as well. Identification of these photoluminescence centers is performed using crystal field calculations. The crystal field parameters are calculated for two identified centers using the structural data for SrAlF5; diagonalization of the crystal field Hamiltonian results in obtaining the splitting of the Ce3+ 5d states. This method allows 'regular' unperturbed Ce3+ centers with selected Sr2+ sites to be assigned. © 2011 IOP Publishing Ltd. This work was supported by RFBR (grant 07-02-00442), the Estonian Science Foundation (grant 8306) and the SR studies by the European Commission (FP7/2007-2013, grant 226716). S I Omelkov gratefully acknowledges the Archimedes Foundation (Estonia, DoRa 5 program) for a stipend supporting his PhD studies in Tartu.

International audience; Catalytic chemical vapour deposition has become a method of choice to produce carbon nanotubes (CNT), particularly for the synthesis of aligned nanotube forests. But a thorough understanding of the mechanisms for CNT nucleation, growth and alignment is still missing. In situ and time resolved experiments allowing to study these processes in real conditions are required. We have developed a specific reactor and furnace to perform such experiments using X-ray diffraction (XRD). Experiments were performed at synchrotron SOLEIL. XRD patterns were recorded as a function of time, during nucleation and growth. We present here our first results, discussing the interest of the XRD method with respect to other existing in situ methods.

A time-resolved optically stimulated exo-electron (TR-OSE) measurement system has been developed using a Photon Timer attached to a gas-flow semi-proportional pancake electron detector within a Risø TL/OSL reader. The decay rate of the exo-electron emission after the stimulation pulse depends on the probability of (1) escape of electrons into the detector gas from the conduction band by overcoming the work function of the material and (2) thermalization of electrons in the conduction band, and subsequent re-trapping/recombination. Thus, we expect the exo-electron signal to reflect the instantaneous electron concentration in the conduction band. In this study, TR-OSE and time-resolved optically stimulated luminescence (TR-OSL) were measured for the first time using quartz, K-feldspar and NaCl by stimulating the samples using pulsed blue LEDs at different temperatures between 50 and 250 °C after beta irradiation and preheating to 280 °C. The majority of TR-OSE signals from all the samples decayed much faster than TR-OSL signals irrespective of the stimulation temperatures. This suggests that the lifetime of OSL in these dosimeters arises mainly from the relaxation of an excited state of the recombination centre, rather than from residence time of an electron in the conduction band.

We report on the development of Time-resolved Ultraviolet Micro-Raman Scattering to measure transient self-heating effects in semiconductor devices. Temperature measurements are performed on AlGaN/GaN High-electron-mobility transistors (HEMTs) grown on SiC substrate. Ultraviolet excitation probes the temperature close to the AlGaN/GaN interface, in the two-dimensional electron gas (2DEG) region. This new measurement setup allows us to obtain a temporal, spectral and measured spatial resolution of 200 ns, 0.8 cm −1 and 1.7 μm respectively. The temperature accuracy is better than 5–10 K. Temperature evolution as function of time has been studied. Self-heating effects are immediately observed. A fast thermal response is demonstrated during the first microsecond after switching the device ON then, a slower thermal response is established during the second microsecond.

In this work, we discuss the reliability of soft-modelling multivariate curve resolution of transient absorption spectra of benzophenone which is chosen as a case study. The main issue concerns the recovery of short-time intermediate excited state that is probed in the UV–Visible on pico-second time scale. The corresponding spectrum and kinetic profile are provided. As such information has never been reported elsewhere, we propose to evaluate the pertinence and the robustness of the resolution through different data analysis strategies. It is shown how overfit situation can be detected analyzing the 2-way matrix of residuals. Another approach concerns the analysis of augmented data matrix. It enables to provide global solutions that are thus less affected by rotational ambiguities. The application of hard-modelling constraint on the kinetic profiles in MCR-ALS is also evaluated as a way to validate the results.