The self-assembly of heteroepitaxial GaN nanowires using either molecular beam epitaxy (MBE) or metal-organic vapor phase epitaxy (MOVPE) mostly results in wafer-scale ensembles with ultrahigh (>10 μm-2) or ultralow (<1 μm-2) densities, respectively. A simple means to tune the density of well-developed nanowire ensembles between these two extremes is generally lacking. Here, we examine the self-assembly of SiNx patches on TiN(111) substrates which are eventually acting as seeds for the growth of GaN nanowires. We first found that if prepared by reactive sputtering, the TiN surface is characterized by {100} facets for which the GaN incubation time is extremely long. Fast GaN nucleation is only obtained after deposition of a sub-monolayer of SiNx atoms prior to the GaN growth. By varying the amount of pre-deposited SiNx, the GaN nanowire density could be tuned by three orders of magnitude with excellent uniformity over the entire wafer, bridging the density regimes conventionally attainable by direct self-assembly with MBE or MOVPE. The analysis of the nanowire morphology agrees with a nucleation of the GaN nanowires on nanometric SiNx patches. The photoluminescence analysis of single freestanding GaN nanowires reveals a band edge luminescence dominated by excitonic transitions that are broad and blue shifted compared to bulk GaN, an effect that is related to the small nanowire diameter and to the presence of a thick native oxide. The approach developed here can be principally used for tuning the density of most III-V semiconductors nucleus grown on inert surfaces like 2D materials.

The mercury isotopic chain is depicted as one of the best fields to observe many phenomena related to collectivity evolution as, for instance, shape transition, shape coexistence or shape staggering. In this context, the 189Hg presents several interesting aspects and is still relatively unexplored. The nucleus has been studied at the Laboratori Nazionali di Legnaro using a fusion-evaporation reaction and the γ rays emitted have been detected by the GALILEO array, coupled with Neutron Wall and the GALILEO plunger. The presorting and the preliminary results are presented.

The shape transition in the neutron-rich Os isotopes is studied by investigating the neutron-rich 196 Os nucleus through in-beam γ -ray spectroscopy using a two-proton transfer reaction from a 198 Pt target to a 82 Se beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident γ rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of 196 Os were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even 188−198 Os isotopes. The new results suggest a smooth transition in the Os isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect γ -unstable/triaxial 0556-2813/2014/90(2)/021301 (6) 021301-1

No abstract