We report a study of polymorphic boron nitride samples. We interpret the photoluminescence line at 6.032±0.005 eV, that can be recorded at 8K in sp2-bonded boron nitride, as being the signature of the excitonic fundamental bandgap of the Bernal (or graphitic) boron nitride polymorph (bBN). This is determined by advanced photoluminescence measurements combined with x-ray characterizations on pure hexagonal boron nitride (hBN) and on polymorphic crystal samples, later compared with the theoretical predictions of Lorenzo Sponza, et al., Physical Review B 98, 125206 (2018). The overall picture is consistent with a direct excitonic fundamental bandgap of the Bernal (or graphitic) polymorph of boron nitride. This value dXb = 6.032±0.005 eV is higher than the indirect bandgap of hBN (iXh =5.955±0.005 eV).

Planar UV-C LEDs still suffer from low efficiency, mainly due to substrate crystalline quality, p doped conductivity and extraction efficiency. One possible way to overcome partly these issues is to realize the whole UV structure on AlGaN pyramids by selective area growth in order to benefit from the advantages of such structures, i.e. the dislocation filtering and the semi polar planes. We present here a detailed study about the epitaxy of AlGaN nano-sized pyramids by metal organic vapor phase epitaxy (MOVPE) on patterned templates presenting different holes apertures and pitches as 1.5 µm and 4 µm or 100 nm and 250 nm respectively. While increasing the Al content, their height decreases while the thickness of the deposition on the mask increases whatever the design of the mask. Those changes of the pyramid shapes and deposition are directly linked to the properties of Al adatoms, i.e. low Al diffusion length. Using the conventional growth mode for the epitaxy of those pyramids did not permit the incorporation of Al from the base of the pyramids to their truncated apex. Its presence was concentrated on the edges and top of the pyramids. On the contrary, a pulsed growth mode, coupled with a strongly reduced pitch, allowed an incorporation of Al since the base of the nanopyramid, and a decrease of the deposition height on the mask. These results can be explained by the desorption of Ga species, due to the presence of H2 in the reactor chamber during the step without the metal precursors, leading to a higher Al/Ga ratio. It is even enhanced inside the holes by the reduced pitch.

The energy and its entire related infrastructure are the main drivers for a economic development andforensuringagoodlevelofemployment.Aspartofaglobalstudyaboutinternationalenergysector,weevaluate here the impact of technological changes on the state of the energy infrastructure. This studyincludes a detailed analysis of the global challenges facing the energy industry. We propose scenariosfor the development of a modernized energy infrastructure with an assessment of the entire energysystem. Our evaluation indicators are chosen in terms of the reliability of the energy infrastructure, ofits quality, of the accidents that may happen and of the consequent environmental risks. This study isparticularly adapted for forecasting the necessary measures (of technical nature, of governance kind)that have to be implemented to reduce the acceleration of the infrastructure deterioration rate. Ourresults reveal that the use of digital and information technologies has many positive impacts on thedevelopment and on the control of an efficient consumption of energy. In addition, our predictions,due to the further modernization of the energy sector, can contribute and help in the creation of preconditions that will be highly stimulating and profitable to the growth of investments in the energy infrastructure.