Room-temperature on-chip orbital angular momentum single-photon sources

A room-temperature on-chip orbital angular momentum source that emits well-collimated single photons has been demonstrated.

Probing dark exciton navigation through a local strain landscape in a WSe2 monolayer

In WSe2 monolayers, strain has been used to control the energy of excitons, induce funneling, and realize single-photon sources. Here, we developed a technique for probing the dynamics of free excitons in nanoscale strain landscapes in such monolayers. A nanosculpted tapered optical fiber is used to simultaneously generate strain and probe the near-field optical response of WSe2 monolayers at 5 K. When the monolayer is pushed by the fiber, its lowest energy states shift by as much as 390 meV (>20% of the bandgap of a WSe2 monolayer). Polarization and lifetime measurements of these red-shifting peaks indicate they originate from dark excitons. We conclude free dark excitons are funneled to high-strain regions during their long lifetime and are the principal participants in drift and diffusion at cryogenic temperatures. This insight supports proposals on the origin of single-photon sources in WSe2 and demonstrates a route towards exciton traps for exciton condensation.

Assessment of New Composites Containing Polyamide-6 and Lead Monoxide as Shields against Ionizing Photonic Radiation based on Computational and Experimental Methods

This study aimed to introduce new composites, containing polyamide-6 (PA6) and lead monoxide (PbO), to protect against ionizing photon sources used for diagnostic and therapeutic purposes. Five composites, containing various weight percentages of PbO filler (0, 5, 10, 20, and 50%), were developed in this study. Initially, the numerical attenuation value was estimated using XMuDat program by calculating the mass attenuation coefficients at different energy levels. Next, the samples were synthesized based on the melt-mixing method in a laboratory mixing extruder, and their characteristics were determined by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Finally, experimental radiation attenuation tests were carried out. Based on the SEM results, the acceptable filler weight percentage was up to 20%; however, substantial aggregates formation was observed at the highest weight percentage. The results of XRD analysis showed a higher tendency for crystallization by decreasing the amorphous area, while increasing the filler weight percentage. Moreover, the amount of mass loss was monitored at different temperatures, revealing that the filler incorporation improved the thermal durability of the samples. According to the radiation results, a good agreement was observed between the experimental and computational data, except when aggregates formation was substantial. According to the experimental data, by increasing the lead weight percentage from 0% (crude PA6) to 50%, the half-value layer decreased from 3.13 to 0.17 cm at an energy level of 59 keV and from 7.28 to 4.97 cm at an energy level of 662 keV. Considering these promising results, the applicability of PA6/PbO composites for protection against low- and medium-energy ionizing photon sources must be investigated in future studies.

Separation of III-N partially-coalesced nanowire arrays from Si substrate

In modern optoelectronics, arrays or single nanowires (NWs) of III-N materials, in particular InGaN, separated from the original substrates are used to fabricate light-emitting diodes or single photon sources. This work describes a technology of separation super-dense arrays or arrays of partially-coalesced InGaN nanowires and single nanowires from a Si substrate by chemical etching in HF:HNO3 solution, which allows preserving the optical properties of the structure for further use.