Tomasz Durakiewicz

A rapid method for determination of hydrogen and oxygen isotope ratios from water and hydrous minerals

Abstract A general-purpose, on-line, continuous flow method for determination of δ D and δ 18 O values of water and hydrous minerals is described. Minor modifications of commercially available equipment allow for analyses of water and solid samples, fluid inclusions and in situ hydrogen isotope determinations of hydrous minerals using a laser. The technique involves reduction of H 2 O or solid hydrous samples by reaction with glassy carbon at high temperatures. H 2 and CO are produced by reaction with the carbon at 1450°C in a helium carrier gas. Product gases are separated in a gas chromatograph and analyzed in a mass spectrometer configured to make hydrogen isotope analyses in continuous flow mode. Sample size is as small as 0.1 μl of water (or equivalent from hydrous phases) for both hydrogen and oxygen isotope ratio determinations. Waters are injected through a heated septa into the He stream; solid materials are wrapped in silver foil and dropped into the furnace using an autosampler. Using standard correction procedures, results obtained with this method are identical to those obtained conventionally with a precision for water samples of ±2‰ (1 σ ) for hydrogen and ±0.2‰ (1 σ ) for oxygen. Saline waters can be analyzed without any additional preparation. Reproducibility of δ D values from hydrous silicates is also ±2‰ The δ 18 O values of ‘dehydration’ water evolved from biotite during heating is variable and irreproducible. Total time of analysis is less than 2 min for a single hydrogen isotope analysis. Sample size can be reduced an order of magnitude by using a low He-flow rate, a narrow-bore reduction column, a capillary GC column and a more efficient open split. With the high sensitivity design, in situ measurements can be made on hydrous minerals using a CO 2 laser for sample heating. Stable isotope determinations of fluid inclusions can be made by decrepitating samples in the He-stream.

Work functions of elements expressed in terms of the Fermi energy and the density of free electrons

On the basis of Brodies definition of the work function and the length of spontaneous polarization of plasma, the following new formula for calculation of the work functions of elements has been derived: , where is the electron density parameter expressed in units of the Bohr radius, is the Fermi energy and is an empirical constant ( for the alkali metals, Ca, Sr, Ba, Ra and Tl, whereas for the remaining elements). The density parameter was calculated from the atomic mass, the bulk density of the element and the assessed number of free electrons per atom which is equal to the nominal valence of the element or, in the case of transition metals, close to this number (within ). The values obtained by using the above formula are in excellent agreement with experimental data for pure-metal polycrystalline surfaces, within 5% in most cases. A table with the work functions and with complete input data for most of the elements is presented.

Observation of topological nodal fermion semimetal phase in ZrSiS

The search for new topological phases of matter is a major new direction in condensed matter physics. Recent experimental realizations of Dirac and Weyl semimetal phases pave the way to look for other exotic phases of matter in real materials. In this paper, the authors present a systematic angle-resolved photoemission spectroscopy study of ZrSiS, a potential topological nodal semimetal candidate. Their systematic measurements establish the spinless nodal fermion semimetal phase in ZrSiS, which is supported by their first-principles calculations. This work puts forward the ZrSiS-type material family as a new platform to explore exotic states of quantum matter.

Photoemission and the electronic structure of PuCoGa5.

The electronic structure of the first Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Exceptional agreement between calculation and experiment defines a path forward for understanding the electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. The results for PuCoGa5 clearly indicate 5f electron behavior on the threshold between localized and itinerant. Comparisons to delta phase Pu metal show a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.

Effect of spin-orbit coupling on the actinide dioxides AnO2 (An=Th, Pa, U, Np, Pu, and Am): A screened hybrid density functional study

We present a systematic comparison of the lattice structures, electronic density of states, and band gaps of actinide dioxides, AnO(2) (An=Th, Pa, U, Np, Pu, and Am) predicted by the Heyd-Scuseria-Ernzerhof screened hybrid density functional (HSE) with the self-consistent inclusion of spin-orbit coupling (SOC). The computed HSE lattice constants and band gaps of AnO(2) are in consistently good agreement with the available experimental data across the series, and differ little from earlier HSE results without SOC. ThO(2) is a simple band insulator (f(0)), while PaO(2), UO(2), and NpO(2) are predicted to be Mott insulators. The remainders (PuO(2) and AmO(2)) show considerable O2p/An5f mixing and are classified as charge-transfer insulators. We also compare our results for UO(2), NpO(2), and PuO(2) with the PBE+U, self interaction correction (SIC), and dynamic mean-field theory (DMFT) many-body approximations.

Dispersion in the Mott insulator UO2: A comparison of photoemission spectroscopy and screened hybrid density functional theory

We present a comparison between the screened hybrid density functional theory of Heyd, Scuseria, and Enzerhof (HSE06) and high‐resolution photoemission (PES) measurement on a single crystal of UO2. Angle‐resolved photoemission data show a slight dispersion in the f‐orbital derived bands in good agreement with the HSE band structure. The effect of spin‐orbit coupling on the HSE band gap has also been calculated and found to be negligible.

Tuning a Schottky barrier in a photoexcited topological insulator with transient Dirac cone electron-hole asymmetry

The advent of Dirac materials has made it possible to realize two-dimensional gases of relativistic fermions with unprecedented transport properties in condensed matter. Their photoconductive control with ultrafast light pulses is opening new perspectives for the transmission of current and information. Here we show that the interplay of surface and bulk transient carrier dynamics in a photoexcited topological insulator can control an essential parameter for photoconductivity-the balance between excess electrons and holes in the Dirac cone. This can result in a strongly out of equilibrium gas of hot relativistic fermions, characterized by a surprisingly long lifetime of more than 50 ps, and a simultaneous transient shift of chemical potential by as much as 100 meV. The unique properties of this transient Dirac cone make it possible to tune with ultrafast light pulses a relativistic nanoscale Schottky barrier, in a way that is impossible with conventional optoelectronic materials.

Tunable ultrafast extreme ultraviolet source for time- and angle-resolved photoemission spectroscopy.

We present a laser-based apparatus suitable for visible pump/extreme UV (XUV) probe time-, energy-, and angle-resolved photoemission spectroscopy utilizing high-harmonic generation from a noble gas. Tunability in a wide range of energies (currently 20-36 eV) is achieved by using a time-delay compensated monochromator, which also preserves the ultrashort duration of the XUV pulses. Using an amplified laser system at 10 kHz repetition rate, approximately 10(9)-10(10) photons/s per harmonic are made available for photoelectron spectroscopy. Parallel energy and momentum detection is carried out in a hemispherical electron analyzer coupled with an imaging detector. First applications demonstrate the capabilities of the instrument to easily select the probe wavelength of choice, to obtain angle-resolved photoemission maps (GaAs and URu(2)Si(2)), and to trace ultrafast electron dynamics in an optically excited semiconductor (Ge).

Deep-water agglutinated foraminiferal changes and stable isotope profiles across the Cretaceous–Paleogene boundary in the Rotwandgraben section, Eastern Alps (Austria)

Abstract The studied interval extends from 2.5 m below to 1 m above the Cretaceous–Paleogene (K–P) boundary and encompasses the uppermost Abathomphalus mayaroensis , PO (subzones: POa — Guembelitria cretacea and POb — Globoconusa conusa ), Pα or Parvularugoglobigerina eugubina and lowermost P1 (subzone: P1a or Subbotina pseudobulloides ) planktonic foraminiferal zones. The agglutinated benthic foraminiferal assemblages of the uppermost Abathomphalus mayaroensis Zone are moderately diversified and composed of mixed epifaunal and infaunal morphogroups. In the lower part of the Guembelitria cretacea Subzone benthic foraminifers are extremely rare and represented only by a few epifaunal species; in the upper part of this subzone they are still not abundant but assemblages are again moderately diversified. In the Globoconusa conusa Subzone deep-water agglutinated foraminifers are abundant, highly diversified and represented by mixed epifaunal and infaunal morphogroups. Bulk rock stable isotope analysis shows a significant drop of both δ 13 C and δ 18 O values at the K–P boundary. It appears that a drastic decrease in abundance and diversity of deep-water agglutinated foraminifers as well as a change of the community structure from mixed epifaunal and infaunal to one dominated by epifaunal morphogroups are related to a reduction in marine primary productivity. The instantaneous environmental stress and the collapse of primary productivity, are compatible with a large bolide impact.

Thermal work function shifts for polycrystalline metal surfaces

Abstract A new approach is presented for the calculation of the thermal shifts of the work functions of polycrystalline metal surfaces by including the thermal expansion of the metal into the electron density parameter as well as Fermi energy. Calculations of d ϕ /d T as a function of temperature are performed for 74 elements, encompassing a total of 103 cases of various temperature ranges, phases and (in a few cases) orientations. It is shown that for a majority of metals d ϕ /d T is not a constant over a broad temperature range. Comparison of theoretical and experimental values indicates that the thermal lattice vibrations do not influence d ϕ /d T significantly. Our results would suggest that the use of a Kelvin probe to measure the thermal variation of ϕ may be problematic.