Metal-insulator phase transition in a VO2 thin film observed with terahertz spectroscopy

We investigate the dielectric properties of a thin VO2 film in the terahertz frequency range in the vicinity of the semiconductor-metal phase transition. Phase-sensitive broadband spectroscopy in the frequency region below the phonon bands of VO2 gives insight into the conductive properties of the film during the phase transition. We compare our experimental data with models proposed for the evolution of the phase transition. The experimental data show that the phase transition occurs via the gradual growth of metallic domains in the film, and that the dielectric properties of the film in the vicinity of the transition temperature must be described by effective-medium theory. The simultaneous measurement of both transmission and phase shift allows us to show that Maxwell-Garnett effective-medium theory, coupled with the Drude conductivity model, can account for the observed behavior, whereas the widely used Bruggeman effective-medium theory is not consistent with our findings. Our results show that even at temperatures significantly above the transition temperature the formation of a uniform metallic phase is not complete.Peter Uhd Jepsen, Bernd M. Fischer, Andreas Thoman, Hanspeter Helm, J. Y. Suh, René Lopez, and R. F. Haglund, Jr

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Dielectric Response and Collective Dynamics of Acetonitrile

Dielectric spectra in the frequency range of 0.1 ≤ ν/GHz ≤ 89 were recorded for acetonitrile, covering temperatures between − 5 and 65 °C. These data are accurately described by a single Debye equation. The obtained values for static relative permittivity, relaxation amplitude and relaxation time exhibit a smooth temperature dependence with low standard uncertainties. Thus, acetonitrile may serve as a dielectric reference for medium permittivities (ε ≈ 30 − 40). At 25 °C the dielectric spectrum was extended to 8 THz. Its analysis revealed that the short-time dynamics of acetonitrile is dominated by dipole libration and cage rattling. On the picosecond timescale these localized motions fade into rotational diffusion of the AN molecules, which is close to slip boundary conditions. Whilst static dipole–dipole correlations are present to some extent, dynamical correlations appear to be absent for diffusive dipole reorientation

Terahertz dynamics of ionic liquids from a combined dielectric relaxation, terahertz, and optical Kerr effect study: evidence for mesoscopic aggregation

To exploit the great potential of room-temperature ionic liquids (RTILs) as solvents that offer both low environmental impact and product selectivity, an understanding of the liquid structure, the microscopic dynamics, and the way in which the pertinent macroscopic properties, such as viscosity, thermal conductivity, ionic diffusion, and solvation dynamics depend on these properties, is essential. We have measured the intermolecular dynamics of the 1,3-dialkylimidazolium-based RTILs [emim][BF4], [emim][DCA], and [bmim][DCA], at 25 degrees C from below 1 GHz to 10 THz by ultrafast optical Kerr effect (OKE) spectroscopy and dielectric relaxation spectroscopy (DRS) augmented by time-domain terahertz and far-infrared FTIR spectroscopy. This concerted approach allows a more detailed analysis to be made of the relatively featureless terahertz region, where the higher frequency diffusional modes are strongly overlapped with librations and intermolecular vibrations. In the terahertz region, the signal-to-noise ratio of the OKE spectra is particularly high and the data show that there is a greater number of librational and intermolecular vibrational modes than previously detected. Of greatest interest though, is an intense low frequency (sub-alpha) relaxation that we show is in strong accordance with recent simulations that observe mesoscopic structure arising from aggregates or clusters; structure that explains the anomalous and inconveniently-high viscosities of these liquids

New Light on the Metal-Insulator Transition in VO₂: A Terahertz Perspective

We investigate the metal-insulator (MI) transition in vanadium dioxide (VO2), thin films with Terahertz Time-Domains Spectroscopy (THz-TDS). The capability of detecting both amplitude and phase of the transmission characteristics as the phase of the transmitted THz signal switches at a markedly different temperature than the transmitted amplitude. A model based on a homogeneous increase of the carrier concentration across the transition temperature accounts for this difference. The sign of the observed phase shift sets strict limits to the concentration and mobility of carriers in the metallic phase of VO2

Metal-Insulator Transition in Thin-Films and of the Dynamics of Pure Ionic Liquids An Application of THz Time-Domain Spectroscopy

zur Erlangung des akademischen Grades eines doctor rerum naturalium (Dr. rer. nat.) an der Fakultät für Mathematik und Physik der Albert-Ludwigs-Universität Freiburg im Breisgau vorgelegt vo

Molecular intercommunication between the complement and coagulation systems

The complement system as well as the coagulation system has fundamental clinical implications in the context of life-threatening tissue injury and inflammation. Associations between both cascades have been proposed, but the precise molecular mechanisms remain unknown. The current study reports multiple links for various factors of the coagulation and fibrinolysis cascades with the central complement components C3 and C5 in vitro and ex vivo. Thrombin, human coagulation factors (F) XIa, Xa, and IXa, and plasmin were all found to effectively cleave C3 and C5. Mass spectrometric analyses identified the cleavage products as C3a and C5a, displaying identical molecular weights as the native anaphylatoxins C3a and C5a. Cleavage products also exhibited robust chemoattraction of human mast cells and neutrophils, respectively. Enzymatic activity for C3 cleavage by the investigated clotting and fibrinolysis factors is defined in the following order: FXa > plasmin > thrombin > FIXa > FXIa > control. Furthermore, FXa-induced cleavage of C3 was significantly suppressed in the presence of the selective FXa inhibitors fondaparinux and enoxaparin in a concentration-dependent manner. Addition of FXa to human serum or plasma activated complement ex vivo, represented by the generation of C3a, C5a, and the terminal complement complex, and decreased complement hemolytic serum activity that defines exact serum concentration that results in complement-mediated lysis of 50% of sensitized sheep erythrocytes. Furthermore, in plasma from patients with multiple injuries (n = 12), a very early appearance and correlation of coagulation (thrombin-antithrombin complexes) and the complement activation product C5a was found. The present data suggest that coagulation/fibrinolysis proteases may act as natural C3 and C5 convertases, generating biologically active anaphylatoxins, linking both cascades via multiple direct interactions in terms of a complex serine protease system