Relativistic laser interaction with micro- and nano-scale surface structures enhances energy transfer to solid targets and yields matter in extreme conditions. We report on the comparative study of laser-target interaction mechanisms with wire-structures of different size, revealing a transition from a coherent particle heating to a stochastic plasma heating regime which occurs when migrating from micro-scale to nano-scale wires. Experiments and kinetic simulations show that large gaps between the wires favour the generation of high-energy electrons via laser acceleration into the channels while gaps smaller than the amplitude of electron quivering in the laser field lead to less energetic electrons and multi-keV plasma generation, in agreement with previously published experiments. Plasma filling of nano-sized gaps due to picosecond pedestal typical of ultrashort pulses strongly affects the interaction with this class of targets reducing the laser penetration depth to approximately one hundred nanometers. The two heating regimes appear potentially suitable for laser-driven ion/electron acceleration schemes and warm dense matter investigation respectively.

Bifacial photovoltaics (BPVs) are emerging with large momentum as promising solutions to improve energy yield and cost of PV systems. To reach its full potential, an accurate understanding of the physical characteristics of BPV technology is required. For this reason, we collected experimental data to refine a physical model of BPV. In particular, we simultaneously measured the module temperature, short circuit current (I_sc), open-circuit voltage (V_oc), power at the maximum power point (P_mpp), and the energy yield of a bifacial and a monofacial minimodule. Such minimodules, realised with the same geometry, cell technology, and module lamination, were tested under the same clear sky outdoor conditions, from morning to afternoon, for three days. The bifacial system experimentally shows higher module temperatures under operation, about 10 °C on a daily average of about 40 °C. Nevertheless, its energy yield is about 15% larger than the monofacial one. We propose a physical quantitative model that fits the experimental data of module temperature, I_sc, V_oc, P_mpp, and energy yield. The model was then applied to predict the annual energy yield of PV module strings. The effect of different PV module temperature coefficients on the energy yield is also discussed.

A systematic study of silver-catalyzed etching in (100) and (111) n-type Silicon substrates is carried out by varying the amount and the morphology of electroless deposited silver clusters. Deposition rate is very fast during the first few seconds and then it levels at a lower value of one order magnitude for both oriented wafers. For small and well separated clusters the Si nanowires formed by the etching are aligned along the (100) axes, while for large and interconnected they are oriented along the normal to the surface. For the (100) Si substrate partially covered with small silver clusters the etching proceeds both in vertical and horizontal [100] directions. For larger coverage (70%) the Ag nanoparticles sink all together along the vertical direction. For the (111) Si substrate, when the Ag nanoparticles are isolated they sink in all the equivalent [100] directions with an irregular path; when the Ag nanoparticles begin to coalesce uniform domains of Si nanowires aligned along [100] directions are formed. When the silver clusters are well interconnected (70% of coverage), the etching is vertical. Silver coverage is then another experimental parameter to induce a preferred orientation of the etched Si nanowires.