S. Cottenier

A new approach to observe the radiative decay of the Th-229 nuclear isomer, and to determine its energy and radiative lifetime, is presented. Situated at a uniquely low excitation energy, this nuclear state might be a key ingredient for the development of a nuclear clock or a nuclear laser and, the search for time variations of fundamental constants like the fine structure constant. The isomer's gamma decay towards the ground state will be studied with a high-resolution vacuum ultraviolet (VUV) spectrometer after its production by the beta decay of Ac-229. The novel production method presents a number of advantages asserting its competitive nature with respect to the commonly used U-233 alpha-decay recoil source. In this paper, a feasibility analysis of this new concept, and an experimental investigation of its key ingredients, using a pure Ac-229 ion beam produced at the ISOLDE radioactive beam facility, is reported.

In the search for better thermoelectric materials, metal phosphides have not been considered to be viable candidates so far, due to their large lattice thermal conductivity. Here we study the thermoelectric properties of metal phosphide CuP2 in the monoclinic phase using first-principles calculations based on self-consistent phonon theory and electron Boltzmann transport theory. Our lattice dynamics calculations reveal that CuP2 exhibits Cu-dimer rattling modes, which strongly scatter the heat-carrying acoustic and low-lying optical phonons, resulting in an unusually low lattice thermal conductivity below 3.6 W m(-1) K-1, being about a half of the conventional thermoelectrics GeTe. We predict Seebeck coefficients, the value of which at 300 K is in good accordance with the experiment, and power factors that are superior to the conventional thermoelectrics GeTe, possibly due to flat- and dispersive-band structures with high orbital degeneracy. Finally, we assess its thermoelectric performance by evaluating the figure of merit ZT, finding that upon p-type doping ZT can reach over 1.3 at a high temperature of 700 K by optimizing the hole concentration. Our results highlight the potential of using metal phosphide CuP2 as a promising material for thermoelectric applications with practical performance and low cost.

The drive to develop maximal atom-efficient catalysts coupled to the continuous striving for more sustainable reactions has led to an ever-increasing interest in single-atom catalysis. Based on a periodic conceptual density functional theory (cDFT) approach, fundamental insights into the reactivity and adsorption of single late transition metal atoms supported on a fully hydroxylated amorphous silica surface have been acquired. In particular, this investigation revealed that the influence of van der Waals dispersion forces is especially significant for a silver (98 %) or gold (78 %) atom, whereas the oxophilicity of the Group 8-10 transition metals plays a major role in the interaction strength of these atoms on the irreducible SiO2 support. The adsorption energies for the less-electronegative row 4 elements (Fe, Co, Ni) ranged from -1.40 to -1.92 eV, whereas for the heavier row 5 and 6 metals, with the exception of Pd, these values are between -2.20 and -2.92 eV. The deviating behavior of Pd can be attributed to a fully filled d-shell and, hence, the absence of the hybridization effects. Through a systematic analysis of cDFT descriptors determined by using three different theoretical schemes, the Fermi weighted density of states approach was identified as the most suitable for describing the reactivity of the studied systems. The main advantage of this scheme is the fact that it is not influenced by fictitious Coulomb interactions between successive, charged reciprocal cells. Moreover, the contribution of the energy levels to the reactivity is simultaneously scaled based on their position relative to the Fermi level. Finally, the obtained Fermi weighted density of states reactivity trends show a good agreement with the chemical characteristics of the investigated metal atoms as well as the experimental data.