We report a facile solution-based approach to the in situ growth of perovskite films consisting of monolayers of CsPbBr nanoplates passivated by bulky phenylbutylammonium (PBA) cations, that is, two-dimensional layered PBA(CsPbBr)PbBr perovskites. Optimizing film formation processes leads to layered perovskites with controlled n values in the range of 12-16. The layered perovskite emitters show quantum-confined band gap energies with a narrow distribution, suggesting the formation of thickness-controlled quantum-well (TCQW) structures. The TCQW CsPbBr films exhibit smooth surface features, narrow emission line widths, low trap densities, and high room-temperature photoluminance quantum yields, resulting in high-color-purity green light-emitting diodes (LEDs) with remarkably high external quantum efficiencies (EQEs) of up to 10.4%. The solution-based approach is extended to the preparation of TCQW CsPbI films for high-color-purity red perovskite LEDs with high EQEs of up to 7.3%.

Dion–Jacobson (DJ) phase halide perovskites have attracted extensive attention in photovoltaic devices due to their significantly enhanced stability when compared with conventional 3D analogs. However, fundamental questions concerning the quantum well (QW) barrier thicknesses, which are critical to design efficient DJ phase perovskite photovoltaics, remain unknown. Herein, it is unambiguously demonstrated that QW barrier thickness, depending on bulky organic ammonium spacers with different chain lengths, such as 1.3‐propanediamine (PDA), 1.4‐butanediamine (BDA), 1.5‐pentamethylenediamine (PeDA), and 1.6‐hexamethylenediamine (HDA), allows the control of orientation and QW distribution. The DJ phase perovskites based on PDA and BDA have suitable QW barrier thicknesses, which exhibit excellent orientation and more uniform QW distribution, allowing a smooth bandgap transition that leads to longer carrier diffusion length, higher charge mobility, and lower defect density. Conversely, PeDA and HDA, with thicker QW barriers, result in lower orientation and multiple DJ perovskite phases. DJ phase perovskite photovoltaic devices based on PDA and BDA show significantly improved power conversion efficiencies (PCEs) of 14.16% and 16.38% compared with PCEs of 12.95% and 10.55% for PeDA and HDA analogs, respectively.

Luminogens with colorful ultralong organic phosphorescence (UOP) are in high demand because of various potential applications in optoelectronics. Herein, we report a concise approach to tune UOP based on the same chromophores of carbazole and phthalimide units through alkyl engineering. With flexible alkyl increase, UOP emission colors can be controllably tuned from green to orange along with lifetime variation. Furthermore, these phosphors were endowed with unexpected visible-light excitation, mechanochromism, and mechanoluminescence properties simultaneously. Additionally, colorful UOP with diverse emission lifetime was first applied to the 4D code for information encryption. These findings will open a door to explore multifunctional organic phosphorescence materials and expand their potential applications.

Since the discovery of graphene, van der Waals (vdW) two-dimensional (2D) materials have attracted considerable attention for various potential applications. Recently, a Se-terminated bismuth oxychalcogenide, Bi2O2Se, has been fabricated using the vapor deposition method. Bi2O2Se is not a vdW 2D material, but the as-grown substance shows 2D characteristics. For example, Bi2O2Se exhibits layer number-dependent absorption spectra in experiments, but until now, there has been no reasonable explanation as to why. Here, we propose a 50% Se-passivation surface model, which elucidates the production of such spectra. Our model is also consistent with recent observations using scanning tunneling microscopy. Moreover, high-resolution transmission electron microcopy observations show a broken zipper-like structure in Bi2O2Se. We ascribe Bi2O2Se as a zipper 2D material, and we summarize the characteristics of zipper 2D materials while proposing the development of others. Zipper 2D materials not only are an important subset of 2D materials but also bridge the gap between vdW 2D materials and traditional 3D materials. Because they are a big family, including insulators, semiconductors, and magnetic metals, zipper 2D materials lend themselves to a plethora of applications.

As quasi two-dimensional semiconductors, bismuth oxychalcogenides (BOXs) have been demonstrated as potential candidates for high-speed and low-power electronics because of their exceptional environmental stability and high carrier mobility. Here, thermodynamics of growth and a series of intrinsic defects in BOXs are studied using first-principles calculations. Comparing the chemical potential phase diagrams of BOXs, we find that it is easier to grow Bi2O2Se than to grow Bi2O2S or Bi2O2Te. It is most difficult to grow stable Bi2O2Te because of the existence of various binary phases. Under Se-poor conditions, the intrinsic point defects of Bi replacing Se (BiSe) and Se vacancy (VSe) can form easily and behave as donors because of low formation energy, which is the reason for the n-type character of as-grown Bi2O2Se in experiments. For Bi2O2S, the donor point defect of Bi substituting S (BiS) is also dominant, leading to an n-type carrier. This study of thermodynamics and the physics of intrinsic point defects provides a valuable understanding of BOXs.

Emerging two-dimensional (2D) layered materials have been attracting great attention as sensing materials for next-generation high-performance biological and chemical sensors. The sensor performance of 2D materials is strongly dependent on the structural defects as indispensable active sites for analyte adsorption. However, controllable defect engineering in 2D materials is still challenging. In the present work, we propose exploitation of controllably grown polycrystalline films of 2D layered materials with high-density grain boundaries (GBs) for design of ultra-sensitive ion sensors, where abundant structural defects on GBs act as favorable active sites for ion adsorption. As a proof-of-concept, our fabricated surface plasmon resonance sensors with GB-rich polycrystalline monolayer WS2 films have exhibited high selectivity and superior attomolar-level sensitivity in Hg2+ detection owing to high-density GBs. This work provides a promising avenue for design of ultra-sensitive sensors based on GB-rich 2D layered materials.

Recently, single-layer CrI 3 , a member of the chromium trihalides CrX 3 (where X = Cl, Br, or I), has been exfoliated and experimentally demonstrated as an atomically thin material suitable for twodimensional spintronics. Valley splitting due to the magnetic proximity effect has been demonstrated in a WSe 2 /CrI 3 van der Waals heterojunction. However, the understanding of the mechanisms behind the favorable performance of CrI 3 is still limited. Here, we systematically study the carrier mobility and the intrinsic point defects in CrX 3 and assess their influence on valley splitting in WSe 2 /CrI 3 by first-principles calculations. The flat-band nature induces extremely large carrier mass and ultralow carrier mobility. In addition, intrinsic point defectslocalized states in the middle of the band gapshow deep transition energy levels and act as carrier recombination centers, further lowering the carrier mobility. Moreover, vacancies in CrI 3 can enhance ferromagnetism and valley splitting in a WSe 2 /CrI 3 heterojunction, proving that chromium trihalides are excellent ferromagnetic insulators for spintronic and valleytronic applications.

As routing tables in core Internet routers grow to exceed 100 000 entries, it is becoming essential to develop methods to reduce the lookup time required to forward packets toward their destinations. In this paper, we employ a bank of novel thermally tuned fiber-Bragg-grating-based optical correlators to construct an "optical bypass" to accelerate conventional electronic Internet routers. The correlators are configured as a routing table cache that can quickly determine the destination port for a fraction of the incoming traffic by examining only a subset of the bits in an IP packet's 32-bit destination address.We also demonstrate a novel multiwavelength correlator based on fiber Bragg grating that can simultaneously recognize the header bits on multiple wavelengths for use in wavelength-division-multiplexed (WDM) systems. Using the optical bypass, routing table lookup times are reduced by an order of magnitude from microseconds to nanoseconds and are limited only by the speed of the optical switch. Index Terms-Optical communications, optical correlators, optical signal processing, wavelength-division-multiplexed (WDM) networks. I. INTRODUCTION I N present-day fiber-optic networks, data packets are converted to electrical form at each node to process their headers and make routing decisions, as shown in Fig. 1(a). As routing tables grow in size, more memory accesses are required to determine the next-hop address and appropriate output port to which to forward each packet. The associated increase in routing-table lookup times is becoming a significant source of latency in the network core. To make matters worse, the transmission capacity of optical fibers is rapidly increasing, forcing the routers to accommodate more packets, more often. Since routing tables will Manuscript