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Pablo Molina

Publications and source records attributed to Pablo Molina.

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Chemical Vapor Deposition Growth of Boron-Carbon-Nitrogen layers from Methylamine Borane Thermolysis Products

This work investigates the growth of B-C-N layers by chemical vapor deposition using methylamine borane (MeAB) as single-source precursor. MeAB has been synthesized and characterized, paying particular attention to the analysis of its thermolysis products, which are the gaseous precursors for B-C-N growth. Samples have been grown on Cu foils and transferred onto different substrates for their morphological, structural, chemical, electronic and optical characterizations. The results of these characterizations indicate a segregation of h-BN and Graphene-like (Gr) domains. However, there is an important presence of B and N interactions with C at the Gr borders, and of C interacting at the h-BN-edges, respectively, in the obtained nano-layers. In particular, there is significant presence of C-N bonds, at Gr/h-BN borders and in the form of N doping of Gr domains. The overall B:C:N contents in the layers is close to 1:3:1.5. A careful analysis of the optical bandgap determination of the obtained B-C-N layers is presented, discussed and compared with previous seminal works with samples of similar composition.

cond-mat.mtrl-sci

Non-reciprocal second harmonic generation in ferroelectric photonic structures

Second harmonic generation is a powerful tool directly connected to the symmetry of materials. Phase transitions, lattice rotations or electromagnetic coupling in multiferroic compounds can be revealed by using second harmonic generation.[1-4] Here we show that the sense of the spontaneous electric polarization Ps in trigonal ferroelectrics can lead to a pronounced spatial dependence of the second harmonic generation. By using a two-dimensional nonlinear photonic structure we demonstrate that counter-propagating beams along the polar axis generate non-reciprocal second harmonic patterns. In optics, with some exception,[5] non-reciprocal phenomena are generally related to the breaking of time-reversal symmetry involving a magnetic field.[6,7] Here, in contrast, the non-reciprocity is inherent to the quadratic nonlinear tensor being related to the inversion symmetry breaking at the ferroelectric phase. These findings provide novel routes to generate nonreciprocal light-matter interaction processes in two-dimensional structures assembled onto polar surfaces,[8,9] including metals for plasmonics or biological compounds.

physics.optics