Investigating the Role of Vacancies on the Thermoelectric Properties of EuCuSb-Eu2ZnSb2 Alloys

AMX compounds with the ZrBeSi structure tolerate a vacancy concentration of up to 50 % on the M-site in the planar MX-layers. Here, we investigate the impact of vacancies on the thermal and electronic properties across the full EuCu_1−xZn_0.5xSb solid solution. The transition from a fully-occupied honeycomb layer (EuCuSb) to one with a quarter of the atoms missing (EuZn_0.5Sb) leads to non-linear bond expansion in the honeycomb layer, increasing atomic displacement parameters on the M and Sb-sites, and significant lattice softening. This, combined with a rapid increase in point defect scattering, causes the lattice thermal conductivity to decrease from 3 to 0.5 W mK⁻¹ at 300 K. The effect of vacancies on the electronic properties is more nuanced; we see a small increase in effective mass, large increase in band gap, and decrease in carrier concentration. Ultimately, the maximum zT increases from 0.09 to 0.7 as we go from EuCuSb to EuZn_0.5Sb.     

Near IR Bandgap Semiconducting 2D Conjugated Metal-Organic Framework with Rhombic Lattice and High Mobility

Two-dimensional conjugated metal–organic frameworks (2D c-MOFs) are emerging as a unique class of electronic materials. However, 2D c-MOFs with band gaps in the Vis-NIR and high charge carrier mobility are rare. Most of the reported conducting 2D c-MOFs are metallic (i.e. gapless), which largely limits their use in logic devices. Herein, we design a phenanthrotriphenylene-based, D_2h-symmetric π-extended ligand ( OHPTP ), and synthesize the first rhombic 2D c-MOF single crystals ( Cu₂(OHPTP) ). The continuous rotation electron diffraction (cRED) analysis unveils the orthorhombic crystal structure at the atomic level with a unique slipped AA stacking. The Cu₂(OHPTP) is a p-type semiconductor with an indirect band gap of ≈0.50 eV and exhibits high electrical conductivity of 0.10 S cm⁻¹ and high charge carrier mobility of ≈10.0 cm² V⁻¹ s⁻¹. Theoretical calculations underline the predominant role of the out-of-plane charge transport in this semiquinone-based 2D c-MOF.     

Neutron flux measurement using activated radioactive isotopes at the Baksan underground scintillation telescope

Preliminary results of a neutron background measurement at the Baksan underground scintillation telescope (BUST) are presented. The external planes of the BUST are fully covered with standard scintillation detectors shielding the internal planes and suppressing thus background events due to cosmogenic and local radioactivity. The shielded internal planes were used as target for the neutron flux registration. The experimental method is based on the delayed coincidences between signals from any of the BUST counters. It is assumed that the first signal is due to inelastic interaction of a neutron with the organic scintillator, while the second signal comes from the decay of an unstable radioactive isotope formed when the fast neutron interacts with the ¹²C nuclei. Using the Monte-Carlo method (GEANT4) we also simulated propagation of neutrons through a layer of scintillator. The experimentally found muon induced neutron flux is j =1.3_-0.3^+0.7 ×10^-10cm^-2s^-1 for neutron energies E ≥ 22MeV, which is in a qualitative agreement with similar measurements of other underground laboratories as well as with predictions of the GEANT4.     

The search for neutrino bursts from supernovae with Baksan underground scintillation telescope

The current status of the experiment on recording neutrino bursts from core collapse stars is presented. The actual observational time is 29.76 years. An upper bound of the mean frequency of core collapse supernovae in our Galaxy is f_col < 0.077 year–1 (90% CL).     

Influence of single impurity atoms on the structure, electronic, and magnetic properties of Ni5 clusters

With a gradient-corrected density functional method, we have studied computationally the influence of single impurity atoms on the structure, electronic, and magnetic properties of Ni5 clusters. The square-pyramidal isomer of bare Ni5 with six unpaired electrons was calculated 23 kJ/mol more stable than the trigonal bipyramid in its lowest-energy electronic configuration with four unpaired electrons. In a previous study on the cluster Ni4, we had obtained only one stable isomer with an O or an H impurity, but we located six minima for ONi5 and five minima for HNi5. In the most stable structures of HNi5, the H atom bridges a Ni-Ni edge at the base or the side of the square pyramid, similarly to the coordination of an H atom at the tetrahedral cluster Ni4. The most stable ONi5 isomers exhibit a trigonal bipyramidal structure of the Ni5 moiety, with the impurity coordinated at a facet, (micro3-O)Ni5, or at an apex edge, (micro-O)Ni5. We located four stable structures for a C impurity at a Ni5 cluster. As for CNi4, the most stable structure of the corresponding Ni5 complex comprises a four-coordinated C atom, (micro4-C)Ni5, and can be considered as insertion of the impurity into a Ni-Ni bond of the bare cluster. All structures with C and five with O impurity have four unpaired electrons, while the number of unpaired electrons in the clusters HNi5 varies between 3 and 7. As a rough trend, the ionization potentials and electron affinities of the clusters with impurity atoms decrease with the coordination number of the impurity. However, the position of the impurity and the shape of the metal moiety also affect the results. Coordination of an impurity atom leads to a partial oxidation of the metal atoms.     

The Carpet-3 EAS Array for Investigation of Gamma-Radiation with Energy $$\boldsymbol{E>100}$$ TeV

Physics of Atomic Nuclei - The Carpet-3 experiment for investigation of gamma radiation with energy above 100 TeV is currently being prepared at the Baksan Neutrino Observatory of the Institute for...     

The effect of double-chain surfactants on armored bubbles: a surfactant-controlled route to colloidosomes

We find that the gas phases of air bubbles covered with anionic or cationic polystyrene latex particles dissolve on exposure to cationic and catanionic surfactants. The particles on the bubble interface are released as singlets or aggregates when the surfactant has a single hydrophobic chain, while porous colloidal capsules (colloidosomes) with the same aqueous phase inside as out are obtained when the surfactant has two hydrophobic chains. The formation of colloidosomes from the particle-covered bubbles does not appear to depend significantly on the charge of the particles, which makes it unlikely that bilayers of surfactant are stabilizing the colloidosome. While the exact mechanism of formation remains an open question, our method is a simple one-step process for obtaining colloidosomes from particle-covered bubbles.     

Collectivity in neutron-deficient Pb and Po nuclei

Lifetimes of low-lying yrast states in ¹⁸⁶Pb and ¹⁹⁴Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in ¹⁸⁸Pb up to the 8⁺ state were carried out using the recoil gating method. The deformation parameters and for the prolate (^186,188Pb) and the oblate (¹⁹⁴Po) bands, respectively, have been extracted from the measured lifetimes. 27.70.+q–     

A combined density functional and x-ray diffraction study of Pt nanoparticle structure

The structure of 1.7 nm Pt nanoparticles is investigated using x-ray diffraction (XRD) measurements and density functional theory (DFT) calculations. Two types of particles are compared, those made by solution chemistry which are capped either by thiol or amine ligands, and dendrimer encapsulated particles (DENs) which do not have capping ligands. All particles were dried before analyzing their structure. Pair distribution function (PDF) data from XRD measurements show that the ligand-capped particles are more disordered than the DENs. To determine the structure of the particles and the nature of the ligand-induced disorder, we use a hybrid reverse Monte Carlo approach. A weighted average of the calculated binding energy of the particles and a goodness-of-fit parameter to the PDF data is taken as the object function, which is minimized to determine the optimal structure. A scan over different weights gives the set of pareto optimal structures, which show how well simultaneous agreement can be reached to both experiment and theory. Using an embedded atom potential to sample configuration space and DFT to refine the optimal structures, we show that the DEN structure is most consistent with a face centered cubic lattice of truncated octahedral shape. The disorder induced by the capping ligands is consistent with surface relaxation of the particle rather than disorder of the crystal structure.     

Adsorption behavior of hydrophobin and hydrophobin/surfactant mixtures at the solid-solution interface

The adsorption of surface-active protein hydrophobin, HFBII, and HFBII/surfactant mixtures at the solid-solution interface has been studied by neutron reflectivity, NR. At the hydrophilic silicon surface, HFBII adsorbs reversibly in the form of a bilayer at the interface. HFBII adsorption dominates the coadsorption of HFBII with cationic and anionic surfactants hexadecyltrimethyl ammonium bromide, CTAB, and sodium dodecyl sulfate, SDS, at concentrations below the critical micellar concentration, cmc, of conventional cosurfactants. For surfactant concentrations above the cmc, HFBII/surfactant solution complex formation dominates and there is little HFBII adsorption. Above the cmc, CTAB replaces HFBII at the interface, but for SDS, there is no affinity for the anionic silicon surface hence there is no resultant adsorption. HFBII adsorbs onto a hydrophobic surface (established by an octadecyl trimethyl silane, OTS, layer on silicon) irreversibly as a monolayer, similar to what is observed at the air-water interface but with a different orientation at the interface. Below the cmc, SDS and CTAB have little impact upon the adsorbed layer of HFBII. For concentrations above the cmc, conventional surfactants (CTAB and SDS) displace most of the HFBII at the interface. For nonionic surfactant C(12)E(6), the pattern of adsorption is slightly different, and although some coadsorption at the interface takes place, C(12)E(6) has little impact on the HFBII adsorption.