Knowledge of the temperature dependence of the isobaric specific heat (C
) upon deep supercooling can give insights regarding the anomalous properties of water. If a maximum in C
exists at a specific ...temperature, as in the isothermal compressibility, it would further validate the liquid-liquid critical point model that can explain the anomalous increase in thermodynamic response functions. The challenge is that the relevant temperature range falls in the region where ice crystallization becomes rapid, which has previously excluded experiments. Here, we have utilized a methodology of ultrafast calorimetry by determining the temperature jump from femtosecond X-ray pulses after heating with an infrared laser pulse and with a sufficiently long time delay between the pulses to allow measurements at constant pressure. Evaporative cooling of ∼15-µm diameter droplets in vacuum enabled us to reach a temperature down to ∼228 K with a small fraction of the droplets remaining unfrozen. We observed a sharp increase in C
, from 88 J/mol/K at 244 K to about 218 J/mol/K at 229 K where a maximum is seen. The C
maximum is at a similar temperature as the maxima of the isothermal compressibility and correlation length. From the C
measurement, we estimated the excess entropy and self-diffusion coefficient of water and these properties decrease rapidly below 235 K.
Ultrafast electron pulses can be produced from sharp metallic tips illuminated by femtosecond near infrared laser pulses. Use of an array of metallic nanotips for high charge bunch generation and ...accelerator applications is also feasible but the small fraction of the emitter tip area limits the quantum efficiency. We therefore propose a submicron-pitch, high-density nanotip array device with a gate electrode, that can support surface-plasmon polaritons. From a theoretical analysis for a device with an asymmetric emitter position, a factor ~30 increased array quantum efficiency is demonstrated.
Nanoparticles of Ti3O5 have been reported to show a permanent photoinduced phase transition at room temperature. This suggests that light‐induced phase transformations of Ti3O5 nanoparticles may be ...promising for technological applications. Here, we report a photoinduced semiconductor‐to‐metal phase transition from β‐Ti3O5 to λ‐Ti3O5 nanoparticles at room temperature observed directly by time‐resolved X‐ray powder diffraction in a pump‐probe setup. The results show a partial structural change, limited by differences between pumped and probed volumes, which persists a few microseconds after excitation. The first step in the relaxation back to the ground state can be described by a single exponential decay with time constant within microsecond timescales. Analysis of the change in lattice constants enables us to estimate an average temperature increase across the phase transition, consistent with a thermally driven process.
Light switch: Nanoparticles of Ti3O5 were recently synthesized and the possibility of controlling their properties with photoinduced light‐excitations makes them suitable for memory storage devices. Understanding the mechanism of their phase transitions is crucial for their applications. Time‐resolved X‐ray diffraction is an important tool for studying the structural phase transition.
Recent years have seen dramatic developments in the technology of intense pulsed light sources in the THz frequency range. Since many dipole-active excitations in solids and molecules also lie in ...this range, there is now a tremendous potential to use these light sources to study linear and nonlinear dynamics in such systems. While several experimental investigations of THz-driven dynamics in solid-state systems have demonstrated a variety of interesting linear and nonlinear phenomena, comparatively few efforts have been made to drive analogous dynamics in molecular systems. In the present Perspective article, we discuss the similarities and differences between THz-driven dynamics in solid-state and molecular systems on both conceptual and practical levels. We also discuss the experimental parameters needed for these types of experiments and thereby provide design criteria for a further development of this new research branch. Finally, we present a few recent examples to illustrate the rich physics that may be learned from nonlinear THz excitations of phonons in solids as well as inter-molecular vibrations in liquid and gas-phase systems.
We present the main specifications of the newly constructed Swiss Free Electron Laser, SwissFEL, and explore its potential impact on ultrafast science. In light of recent achievements at current ...X-ray free electron lasers, we discuss the potential territory for new scientific breakthroughs offered by SwissFEL in Chemistry, Biology, and Materials Science, as well as nonlinear X-ray science.
Abstract
The layered transition-metal dichalcogenide WTe
2
is characterized by distinctive transport and topological properties. These properties are largely determined by electronic states close to ...the Fermi level, specifically to electron and hole pockets in the Fermi sea. In principle, these states can be manipulated by changes to the crystal structure. The precise impact of particular structural changes on the electronic properties is a strong function of the specific nature of the atomic displacements. Here, we report on time-resolved X-ray diffraction and infrared reflectivity measurements of the coherent structural dynamics in WTe
2
induced by femtosecond laser pulses excitation (central wavelength 800 nm), with emphasis on a quantitative description of both in-plane and out-of-plane vibrational modes. We estimate the magnitude of these motions, and calculate via density functional theory their effect on the electronic structure. Based on these results, we predict that phonons periodically modulate the effective mass of carriers in the electron and hole pockets up to 20%. This work opens up new opportunities for modulating the peculiar transport properties of WTe
2
on short time scales.
X-ray techniques have long been applied to chemical research, ranging from powder diffraction tools to analyse material structure to X-ray fluorescence measurements for sample composition. The ...development of high-brightness, accelerator-based X-ray sources has allowed chemists to use similar techniques but on more demanding samples and using more photon-hungry methods. X-ray Free Electron Lasers (XFELs) are the latest in the development of these large-scale user facilities, opening up new avenues of research and the possibility of more advanced applications for a range of research. The SwissFEL XFEL project at the Paul Scherrer Institute will begin user operation in the hard X-ray (2.1–12.4 keV) photon energy range in 2018 with soft X-ray (240–1930 eV) user operation to follow and here we will present the details of this project, it's operating capabilities, and some aspects of the experimental stations that will be particularly attractive for chemistry research. SwissFEL is a revolutionary new machine that will complement and extend the time-resolved chemistry efforts in the Swiss research community.
Material properties can be controlled via strain, pressure, chemical composition, or dimensionality. Nickelates are particularly susceptible due to their strong variations of the electronic and ...magnetic properties on such external stimuli. Here, we analyze the photoinduced dynamics in a single crystalline NdNiO3 film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally, we compare our results with similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced electronic ordering phase transitions.
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