Deconvoluting Energy Transport Mechanisms in Metal Halide Perovskites Using CsPbBr3 Nanowires as a Model System

Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr₃ nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr₃ nanowires, an ambipolar carrier mobility of μ = 35 cm² V⁻¹ s⁻¹ is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL.     

Feature‐Preserving Surface Completion Using Four Points

We present a user‐guided, semi‐automatic approach to completing large holes in a mesh. The reconstruction of the missing features in such holes is usually ambiguous. Thus, unsupervised methods may produce unsatisfactory results. To overcome this problem, we let the user indicate constraints by providing merely four points per important feature curve on the mesh. Our algorithm regards this input as an indication of an important broken feature curve. Our completion is formulated as a global energy minimization problem, with user‐defined spatial‐coherence constraints, allows for completion that adheres to the existing features. We demonstrate the method on example problems that are not handled satisfactorily by fully automatic methods.     

Discriminatory processor sharing queues with stationary ergodic service times and the performance of TCP in overload

In a recent paper, Bonald and Roberts (2001) [6] studied non-persistent TCP connections in transient overload conditions, under the assumption that all connections have the same round-trip times. In this paper our goal is to develop theoretical tools that will enable us to relax this assumption and obtain explicit expressions for the rate of growth of the number of connections at the system, the rate at which TCP connections leave the system, as well as the time needed for the completion of a connection. To that end, we model the system as a discriminatory processor sharing (DPS) system which we analyze under very mild assumptions on the probability distributions related to different classes of arrivals: we only assume that the arrival rates of connections exist, and that the amount of information transmitted during a connection of a given type forms a stationary ergodic sequence. We then proceed to obtain explicit expressions for the growth rate of the number of connections at the DPS system for several specific probability distributions. We check through simulations the applicability of our queueing results for modeling TCP connections sharing a bottleneck.     

Sequential batch sampling

Let {X_i} be i.i.d.{F_θ}.We consider the testing problem H₁θ<θ₀ vs H₂θ≥θ₀, where sampling is done sequentially in batches with variable batch sizes.For some parametric families {F_θ}, and under natural cost struc-ture, we characterize the Bayes procedures. This characterization of Bayes procedures lead to a similar characterization of essentially complete class of procedures.     

Bio-inspired delayed evolutionary game dynamics with?networking applications

We study in this paper some evolutionary games where competition between individuals from a large population occurs through many local interactions between randomly selected individuals. We focus on games that have the property of possessing a single interior evolutionarily stable strategy (ESS). We study in particular the effect of the time delays on the convergence of evolutionary dynamics to the ESS in an evolutionary game in which each pure strategy is associated with its own delay. In particular, we study a multiple access game as well as a Hawk and Dove game. We study the properties of the ESS in these games and also the effect of time delays on the convergence of various bio-inspired evolutionary game dynamics to the ESS.     

NROM: A novel localized trapping, 2-bit nonvolatile memory cell

This paper presents a novel flash memory cell based on localized charge trapping in a dielectric layer and on a new read operation. It is based on the storage of a nominal ~400 electrons above a n⁺/p junction. Programming is performed by channel hot electron injection and erase by tunneling enhanced hot hole injection. The new read methodology is very sensitive to the location of trapped charge above the source. This single device cell has a two physical bit storage capability. The cell shows improved erase performances, no over erase and erratic bit issues, very good retention at 250°C, and endurance up to 1M cycles. Only four masks are added to a standard CMOS process to implement a virtual ground array. In a typical 0.35 μm process, the area of a bit is 0.315 μm² and 0.188 μm² in 0.25 μm technology. All these features and the small cell size compared to any other flash cell make this device a very attractive solution for all NVM applications     

On the physical mechanism of the NROM memory erase

The purpose of this paper is to investigate the physical mechanism of NROM memory erase. Three conduction mechanisms potentially responsible of NROM erase will be analyzed (tunneling and emission of electrons through both bottom and top oxide, tunneling and injection of holes over the bottom oxide barrier) by means of standard two-dimensional simulations and ad-hoc models reproducing hole and electron transport mechanisms across the oxide not included in standard device simulators. Hot-hole injection will be identified as the actual conduction mechanism of NROM erase, and two compact models capable to describe the main characteristics of NROM erase current will be developed.     

Neural network principal components preprocessing and diffraction tomography

The use of principal component analysis in preprocessing neural network input data is explored. Four preprocessing schemes are compared in an example problem, and the theoretical basis for the results are discussed. A preconditioning method for the principal components is introduced here, combining normalisation and improved conditioning. The techniques are applied to an object location problem in diffraction tomography. The spectral analysed scattered field from an irradiated object form the input to a Multilayer Perceptron neural network, trained by backpropagation to calculate the coordinates of the object's centre in 2D.Aspects of this work were presented at the NCAF Symposium, King's College London, 9 January 1992.