RESUMEN
The fascinating realm of strain engineering and wetting transitions in two-dimensional (2D) materials takes place when placed on a two-dimensional array of nanopillars or one-dimensional rectangular grated substrates. Our investigation encompasses a diverse set of atomically thin 2D materials, including transition metal dichalcogenides, hexagonal boron nitride, and graphene, with a keen focus on the impact of van der Waals adhesion energies to the substrate on the wetting/dewetting behavior on nanopatterned substrates. We find a critical aspect ratio of the nanopillar or grating heights to the period of the pattern when the wetting/dewetting transition occurs. Furthermore, energy hysteresis analysis reveals dynamic detachment and re-engagement events during height adjustments, shedding light on energy barriers of 2D monolayer transferred on patterned substrates. Our findings offer avenues for strain engineering in 2D materials, leading to promising prospects for future technological applications.
RESUMEN
This work presents a comprehensive numerical study for designing a lead-free, all-inorganic, and high-performance solar cell based on Cs2TiI6 halide perovskite with all-inorganic carrier transport layers. A rigorous ab initio density-functional theory (DFT) calculation is performed to identify the electronic and optical properties of Cs2TiI6 and, upon extraction of the existing experimental data of the material, the cell is designed and optimized to the degree of practical feasibility. Consequently, a theoretical power conversion efficiency (PCE) of 21.17% is reported with inorganic TiO2 and CuI as carrier transport layers. The calculated absorption coefficient of Cs2TiI6 reveals its enormous potential as an alternative low-bandgap material for different solar cell applications. Furthermore, the role of different point defects and the corresponding defect densities on cell performance are investigated. It is found that the possible point defects in Cs2TiI6 can form both the shallow and deep defect states, with deep defect states having a prominent effect on cell performance. For both defect states, the cell performance deteriorates significantly as the defect density increases, which signifies the importance of high-quality material processing for the success of Cs2TiI6-based perovskite solar cell technology.
RESUMEN
The electrical conductivity of a macroscopic assembly of nanomaterials is determined through a complex interplay of electronic transport within and between constituent nano-objects. Phonons play dual roles in this situation: their increased populations tend to reduce the conductivity via electron scattering, while they can boost the conductivity by assisting electrons to propagate through the potential-energy landscape. We identified a phonon-assisted coherent electron transport process between neighboring nanotubes in temperature-dependent conductivity measurements on a macroscopic film of armchair single-wall carbon nanotubes. Through atomistic modeling of electronic states and calculations of both electronic and phonon-assisted junction conductances, we conclude that phonon-assisted conductance is the dominant mechanism for observed high-temperature transport in armchair carbon nanotubes. The unambiguous manifestation of coherent intertube dynamics proves a single-chirality armchair nanotube film to be a unique macroscopic solid-state ensemble of nano-objects promising for the development of room-temperature coherent electronic devices.
RESUMEN
The weak acoustic phonon scattering in graphene monolayer leads to high mobilities even at room temperatures. We identify the dominant role of the shear phonon mode scattering on the carrier mobility in AB-stacked graphene bilayer, which is absent in monolayer graphene. Using a microscopic tight-binding model, we reproduce experimental temperature dependence of mobilities in high-quality boron nitride encapsulated bilayer samples at temperatures up to â¼200 K. At elevated temperatures, the surface polar phonon scattering from boron nitride substrate contributes significantly to the measured mobilities of 15 000 to 20000 cm^{2}/Vs at room temperature and carrier concentration nâ¼10^{12} cm^{-2}. A screened surface polar phonon potential for a dual-encapsulated bilayer and transferable tight-binding model allows us to predict mobility scaling with temperature and band gap for both electrons and holes in agreement with the experiment.