Enhanced bulk photovoltaic effect in two-dimensional ferroelectric CuInP2S6

The photocurrent generation in photovoltaics relies essentially on the interface of p-n junction or Schottky barrier with the photoelectric efficiency constrained by the Shockley-Queisser limit. The recent progress has shown a promising route to surpass this limit via the bulk photovoltaic effect for crystals without inversion symmetry. Here we report the bulk photovoltaic effect in two-dimensional ferroelectric CuInP2S6 with enhanced photocurrent density by two orders of magnitude higher than conventional bulk ferroelectric perovskite oxides. The bulk photovoltaic effect is inherently associated to the room-temperature polar ordering in two-dimensional CuInP2S6. We also demonstrate a crossover from two-dimensional to three-dimensional bulk photovoltaic effect with the observation of a dramatic decrease in photocurrent density when the thickness of the two-dimensional material exceeds the free path length at around 40 nm. This work spotlights the potential application of ultrathin two-dimensional ferroelectric materials for the third-generation photovoltaic cells.

Simulation of Z-Shaped Graphene Geometric Diodes Using Particle-In-Cell Monte Carlo Method in theQuasi-Ballistic Regime

Geometric diodes are planar conductors patterned asymmetrically to provide electrical asymmetry, and they have exhibited high-frequency rectification in infrared rectennas. These devices function by ballistic or quasi-ballistic transport in which the transport characteristics are sensitive to the device geometry. Common methods for predicting device performance rely on the assumption of totally ballistic transport and neglect the effects of electron momentum relaxation. We present a particle-in-cell Monte Carlo simulation method that allows the prediction of the current–voltage characteristics of geometric diodes operating quasi-ballistically, with the mean-free-path length shorter than the critical device dimensions. With this simulation method, we analyze a new diode geometry made from graphene that shows an improvement in rectification capability over previous geometries. We find that the current rectification capability of a given geometry is optimized for a specific mean-free-path length, such that arbitrarily large mean-free-path lengths are not desirable. These results present a new avenue for understanding geometric effects in the quasi-ballistic regime and show that the relationship between device dimensions and the carrier mean-free-path length can be adjusted to optimize device performance.

Monte Carlo simulation of proton- and neutron-induced radiation damage in a tantalum target irradiated by 70 MeV protons

Beams of free neutrons are an important probe to analyze the structure and dynamics of condensed matter and are produced at neutron research reactors, neutron spallation sources or compact accelerator-based neutron sources (CANS). An efficient construction of CANS with a maximized neutron yield and brilliance requires reliable knowledge of the consequences of radiation-induced material damage, the predominating bottleneck of a target’s lifetime. In the framework of the Jülich High-Brilliance neutron Source project, the impact of proton- and neutron-induced material damage of a tantalum target was investigated. The Monte Carlo codes FLUKA and SRIM were utilized to extract the number of displacements per atom resulting from atomic rearrangements. The simulations performed distinctly identify the rear of the neutron target as the most vulnerable area, with the protons as main damage contributors. The minor contribution of neutrons is a material-specific phenomenon due to their high mean free path length in tantalum. Numerical results of the simulations served to calculate average and peak damage rates $${R}_{\mathrm{d}}$$ R d (dpa/s), both in turn scaled to annual displacement doses for continuous operation in a full power year (dpa/fpy). Supplemented by the literature, a minimum target lifetime $$\tau _{\min }$$ τ min of 2.6 years (33 Ah) is concluded.

Kinetic equation having the integral scattering term with a linear form of external electrical and magnetic fields

In many cases, nobody consider any kinetic equation where the collision integral does not use clearly the values of external electric and magnetic fields. But there is some reason to use in the collision integral the above fields and to consider the ratio of the averaged deBroglie wavelength to the free-path length.

Enhanced bulk photovoltaic effect in two-dimensional ferroelectric CuInP2S6

The photocurrent generation in photovoltaics relies essentially on the interface of p-n junction or Schottey barrier with the photoelectric efficiency constrained by the Shockley-Queisser limit. The recent progresses have shown a promising route to surpass this limit via the bulk photovoltaic effect (BPVE) for crystals without inversion symmetry. Here we report the BPVE in two-dimensional (2D) ferroelectric CuInP2S6 with enhanced photocurrent density by two orders of magnitude higher than conventional bulk ferroelectric perovskite oxides. The BPVE is inherently associated to the room-temperature polar ordering in 2D CuInP2S6. We also demonstrate a crossover from 2D to 3D BPVE material with the observation of a dramatic decrease in photocurrent density when the thickness of the 2D material exceeds the free path length (\({l}_{0}\)) at around 40 nm. This work spotlights the potential application of ultrathin 2D ferroelectric materials for the third-generation photovoltaic cells.

A Continuum Model for Complex Flows of Shear Thickening Colloidal Solutions

Colloidal shear thickening fluids (STFs) have applications ranging from commercial use to those of interest to the army and law enforcement, and the oil industry. The theoretical understanding of the flow of these particulate suspensions has predominantly been focused through detailed particle simulations. While these simulations are able to accurately capture and predict the behavior of suspensions in simple flows, they are not tractable for more complex flows such as those occurring in applications. The model presented in this work, a modification of an earlier constitutive model by Stickel et al. J. Rheol. 2006, 50, 379–413, describes the evolution of a structure tensor, which is related to the particle mean free-path length. The model contains few adjustable parameters, includes nonlinear terms in the structure, and is able to predict the full range of rheological behavior including shear and extensional thickening (continuous and discontinuous). In order to demonstrate its capability for complex flow simulations, we compare the results of simulations of the model in a simple one-dimensional channel flow versus a full two-dimensional simulation. Ultimately, the model presented is a continuum model shown to predict shear and extensional thickening, as observed in experiment, with a connection to the physical microstructure, and has the capability of helping understand the behavior of STFs in complex flows.

Моделирование детектора видимого и ближнего инфракрасного электромагнитного излучения на искусственном алмазе

A method for calculation of the I – V characteristic is proposed for a detector of visible and near-IR electromagnetic radiation based on artificial diamond with allowance for vertical flow of electric current. The method can be used when the free-path length of carriers in diamond is less than the scale of variations in the concentration of carriers. The method is used to determine the following detector characteristics: the dependence of current on voltage, distribution of carrier concentration, and electric potential for a particular variant of a photodetector based on polycrystalline diamond film consisting of nanosized single crystals doped with boron.