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In this study, we investigate the tradespace between the improvement of mid-infrared light-emitting diode efficiency through microcavity enhancement vs reduction of Auger recombination for different W-superlattice thicknesses. Several sample designs are modeled and then grown and fabricated to test the tradespace at different W-superlattice thicknesses down to the quantum well limit. In a half-cavity, with a single reflector from the top metal contact, intermediate thickness W-superlattices gave the highest efficiencies, outperforming those in the W-quantum well limit across the entire measured current range. Experimentally, we report wallplug efficiencies of 0.4% for a room temperature 3.2 μm device. W-superlattices of intermediate thickness were also found to be optimal for a full-cavity device with a bottom distributed Bragg reflector added. The resonant full cavity did strongly improve the peak spectral radiance, with a measured increase of four to five times for a 3.6 μm device, and a value that is >250 times larger than previously reported. [ABSTRACT FROM AUTHOR]

Bistability in the current–voltage characteristics of semiconductor superlattices and quantum cascade laser structures has the potential for wide-ranging applications, particularly in sensing systems. However, the interdependency of applied bias and current injection in conventional two-terminal structures has led to complications in analysis and rendered the bistability phenomenon difficult to implement in practical applications. Here, we report a new kind of electronic bistability coupled to optical switching in a resonant tunneling bipolar superlattice transistor. This bistability manifests as sharp discontinuities in the collector current with extremely small variations of the applied voltage, which arise from unstable tunneling transmission across the hetero-barrier between the two-dimensional electron gas (2DEG) at the edge of the transistor base and the collector superlattice structure. The electronic transitions between high and low quantum mechanical transmissions are demonstrated to be caused by self-consistent variations of the internal electric field at the heterointerface between the 2DEG and the superlattice. They are also present in the base current of the three-terminal device and result in sharp switching of near-infrared spontaneous light emission output from an interband radiative recombination process with a peak emission wavelength of 1.58 μ m. A comprehensive quantum mechanical theoretical model accounting for the self-consistent bistable tunneling transmission is in quantitative agreement with the experimental data. The measured peak transconductance sensitivity value of 6000 mS can be used in the highly sensitive detector and non-linear device applications. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides have emerged as promising quantum functional blocks benefitting from their unique combination of spin, valley, and layer degrees of freedom, particularly for the tremendous flexibility of moiré superlattices formed by van der Waals stacking. These degrees of freedom coupled with the enhanced Coulomb interaction in 2D structures allow excitons to serve as on-chip information carriers. However, excitons are spatially circumscribed due to their low mobility and limited lifetime. One way to overcome these limitations is through the coupling of excitons with surface plasmon polaritons (SPPs), which facilitates an interaction between remote quantum states. Here, we showcase the successful coupling of SPPs with interlayer excitons in molybdenum diselenide/tungsten diselenide heterobilayers. Our results indicate that the valley polarization can be efficiently transferred to SPPs, enabling preservation of polarization information even after propagating tens of micrometers. [ABSTRACT FROM AUTHOR]

The cooperative emission of interacting nanocrystals is an exciting topic fueled by recent reports of superfluorescence and superradiance in assemblies of perovskite nanocubes. Several studies estimated that coherent coupling is localized to a small fraction of nanocrystals (10−7–10−3) within the assembly, raising questions about the origins of localization and ways to overcome it. In this work, we examine single-excitation superradiance by calculating radiative decays and the distribution of superradiant wave function in two-dimensional CsPbBr3 nanocube superlattices. The calculations reveal that the energy disorder caused by size distribution and large interparticle separations reduces radiative coupling and leads to the excitation localization, with the energy disorder being the dominant factor. The single-excitation model clearly predicts that, in the pursuit of cooperative effects, having identical nanocubes in the superlattice is more important than achieving a perfect spatial order. The monolayers of large CsPbBr3 nanocubes (LNC = 10–20 nm) are proposed as model systems for experimental tests of superradiance under conditions of non-negligible size dispersion, while small nanocubes (LNC = 5–10 nm) are preferred for realizing the Dicke state under ideal conditions. [ABSTRACT FROM AUTHOR]

Recently, nanostructuration has been proposed to improve the performance of phase change memories. This is the case of superlattices composed of amorphous carbon and crystalline germanium telluride, which we have investigated by molecular dynamics. For this, a modified Stillinger–Weber potential is adapted to reproduce their stiffness contrast/impedance ratio. In order to study the effect of the interface interaction, two sets of parameters are used to model the interfaces with different interactions between the two materials using the properties of the softer material or the average properties between the two creating an adaptation of impedance across the layers. The effects of interface roughness and carbon diffusion at grain boundaries are studied. Using equilibrium molecular dynamics as well as the propagation of wave-packets, we show first that without impedance adaptation, the anisotropy is high, and the roughness has a marked impact on the properties. However, the introduction of impedance adaptation destroys those effects on the thermal conductivity. Finally, we show that the periodic texturing of the interface increases the transmission of in-plane transverse phonons. [ABSTRACT FROM AUTHOR]

Gauss chains are one-dimensional nonperiodic lattices in which lattice sites are located at z j = j n d , with j ∈ W , n ∈ N , and d being the underlying lattice constant. They may potentially be realized in semiconductor superlattices or tailored chain molecules. In recent work, we have characterized the electronic delocalized states for the quadratic Gauss chain n = 2 obtained using a one-dimensional transfer-matrix approach applied to the Kronig–Penney model. We here extend those results to cases of larger n , illustrating the approach for n = 3 , 4, and 5. Beginning with the structure factor, we find that the case n = 2 has a visually evident structure lacking for n > --> 2 , and this structure (or lack thereof) is reflected in the statistics of the structure factor. Turning to the electronic structure, the delocalized-state spectrum for each n is singular-continuous with delocalized states at wavevectors k for all rational multiples r s of π d with r , s ∈ N coprime in the limit of weak onsite potential parameter λ. Most states, however, become localized at a state-dependent threshold value of | λ |. The case n = 2 appears to exhibit delocalized-state spectra that most clearly reveal the hidden symmetry of these systems. Gauss chains with various n , therefore, provide a way (in principle) to realize a class of functions of number-theoretic importance. [ABSTRACT FROM AUTHOR]

The effects of in-plane strain on the dielectric constant of the Be0.25Mg0.75O rock salt superlattice are investigated through ab initio thermodynamics calculations. Based on a previous report that the long apical Be–O bond increased the dielectric constant, the in-plane compressive strain dielectric constant is expected to increase the dielectric constant. Unlike the zero-strain case, the apical Mg–O bonds also contribute to the increase in the dielectric constant under compressive strain. However, small Be ions tend to occupy narrow spaces in the MgO-based rock salt structure, which can lead to an increase in dielectric constant even under in-plane tensile strain, depending on the local position of Be ions and its interaction with O ions. At higher temperatures, several configurations under strain showed a significant increase in the dielectric constant due to the elongation of the apical Be–O bond. Considering temperature and strain comprehensively, this study suggests that the Be0.25MgO0.75O superlattice under −2% in-plane compressive strain could be a promising candidate structure for achieving a high-κ value of approximately 30. [ABSTRACT FROM AUTHOR]

The impact of unintentional incorporation of Sb in the tensile InAs layer of type-II strain-balanced InAs/InAsSb superlattices is investigated. Several coherently strained midwave and longwave superlattices are grown on (100) GaSb substrates by molecular beam epitaxy and examined using x-ray diffraction and temperature-dependent photoluminescence spectroscopy. The zero-order diffraction angle provides the average Sb mole fraction of the strain-balanced superlattice period. Analysis of the higher order diffraction angles, along with the individual layer growth times and strain, provides the InAs and InAsSb layer thicknesses. Analysis of the photoluminescence measurements provides the ground-state bandgap of the superlattice, which along with simulations of the ground-state energies of the electrons and holes using a Kronig–Penney model, specify how the Sb is distributed between the tensile and compressive layers of the period and ultimately the quantity of unintentional Sb in the InAs layer. The unintentional Sb mole fractions observed in the tensile InAs layers are 1.9% for midwave and 1.2% for longwave. When compared to superlattices with the same period and no Sb in the tensile layer, the presence of unintentional Sb blue-shifts the 77 K temperature cutoff wavelength from 6.3 to 5.3 μm for midwave and from 18.8 to 12.0 μm for longwave. [ABSTRACT FROM AUTHOR]

Aperiodic order is ubiquitous in nature and quite relevant in science and technology. There are extensive works in aperiodic structures studying fundamental characteristics in physical properties, such as fractality, self-similarity, and fragmentation. However, there are fewer reports in which aperiodicity signifies an improvement in physical quantities with practical applications. Here, we show that the aperiodicity of fractal or self-similar type optimizes the tunneling magnetoresistance and spin-valley polarization of magnetic silicene structures, raising the prospects of spin-valleytronics. We reach this conclusion by studying the spin-valley-dependent transport properties of complex (Cantor-like) magnetic silicene structures within the lines of the transfer matrix method and the Landauer–Büttiker formalism. We find that the self-similar arrangement of magnetic barriers in conjunction with structural asymmetry reduces the conductance oscillations typical of periodic magnetic silicene superlattices and more importantly makes the K ′ -spin-down conductance component dominant, resulting in nearly perfect positive and negative spin-valley polarization states accessible by simply reversing the magnetization direction. The tunneling magnetoresistance is not as prominent as in periodic magnetic silicene superlattices; however, it is better than in single magnetic junctions. Furthermore, the optimization of the spin-valley-dependent transport properties caused by the complex structure is superior than the corresponding one reported in typical aperiodic structures, such as Fibonacci and Thue–Morse magnetic silicene superlattices. [ABSTRACT FROM AUTHOR]

High-quality III–V quantum structures, advanced epitaxial technologies, and characterization methods are essential to drive the development of infrared optoelectronic materials and devices. As an important component of type II superlattices, InAs/InxGa1−xAsySb1−y would play an important role in the field of high-performance infrared detectors due to their excellent luminescence efficiency and high crystal quality. However, their interfacial characteristics and the associated minority carrier lifetime are still difficult to identify. In this paper, an atomic imaging technique was used to identify the arrangement and distribution of elements of the InAs/In0.5Ga0.5As0.5Sb0.5 superlattice. Our results confirm the epitaxy mechanism that the quaternary alloy consists of two kinds of ternary alloy in one monolayer. Moreover, by separating the cation and anion columns in the elementally resolved atomic images of the InAs/In0.5Ga0.5As0.5Sb0.5 superlattice, we demonstrate that the interfacial atomic intermixing is less than one molecular layer thickness. Therefore, benefiting from excellent interface quality, InAs/In0.5Ga0.5As0.5Sb0.5 superlattice exhibited high radiation recombination efficiency in the long-wave infrared band (∼8.5 μm), and longer minority carrier lifetime (∼810 ns at 90 K). [ABSTRACT FROM AUTHOR]

GaInN/GaN multiple quantum shell (MQS) nanowires (NWs) are of great interest as high‐efficiency micro‐light emitting diodes (micro‐LEDs), mainly due to their quantum confined Stark effect suppression and dry etching insensitivity features. Herein, morphological and device properties corresponding to NW‐LEDs with different numbers of GaInN/GaN superlattices (SLs) are evaluated. The scanning electron microscopy measurements revealed that the polar‐plane MQS are shrunken, while the semipolar‐plane underwent expansion upon the introduction of the SLs. The current density–voltage–light output analysis at low current density indicates that samples with a greater number of SL pairs exhibit higher light output. Electroluminescence spectra show that NWs lacking SLs exhibit an emission wavelength of 700 nm, which is derived from indium‐rich clusters in polar‐plane MQS, whereas those with SLs emit at a significantly shorter wavelength of 560 nm. The reduction in the polar‐plane MQS coupled with the enhancement in MQS quality resulting from the SLs is identified as the primary contributing factor. Additionally, the external quantum efficiency factor for NW‐LEDs, which remained consistent even as the emission area decreased, is assessed. These findings suggest that NW‐LEDs with SLs possess the potential to mitigate the emission degradation associated with sidewall etching and realize high‐efficiency micro‐LEDs. [ABSTRACT FROM AUTHOR]

Recent theoretical investigations have revealed unconventional transport mechanisms within high Brillouin zones of two-dimensional superlattices. Electrons can navigate along channels we call superwires, gently guided without brute force confinement. Such dynamical confinement is caused by weak superlattice deflections, markedly different from the static or energetic confinement observed in traditional wave guides or one-dimensional electron wires. The quantum properties of superwires give rise to elastic dynamical tunneling, linking disjoint regions of the corresponding classical phase space, and enabling the emergence of several parallel channels. This paper provides the underlying theory and mechanisms that facilitate dynamical tunneling assisted by chaos in periodic lattices. Moreover, we show that the mechanism of dynamical tunneling can be effectively conceptualized through the lens of a paraxial approximation. Our results further reveal that superwires predominantly exist within flat bands, emerging from eigenstates that represent linear combinations of conventional degenerate Bloch states. Finally, we quantify tunneling rates across various lattice configurations and demonstrate that tunneling can be suppressed in a controlled fashion, illustrating potential implications in future nanodevices. [ABSTRACT FROM AUTHOR]

A persistent challenge in utilizing Au nanocrystals for surface‐enhanced Raman spectroscopy (SERS) lies in achieving controllable superstructures that maximize SERS performance. Here, a novel strategy is proposed to enhance the SERS performance by precisely adjusting the tip arrangements of Au nanobipyramids (BPs) in two‐dimensional (2D) superlattices (SLs). This is achieved through ligand‐exchange of Au BPs, followed by liquid‐air interfacial assembly, resulting in large‐area, transferrable SL membranes. The key to controlling the arrangement of Au BPs in the SLs is the regulation of the amount of free ligands added during self‐assembly, which allows for the precise formation of various configurations such as tilted SLs, tip‐on‐tip SLs, and tip‐to‐tip SLs. Among these configurations, tip‐on‐tip SLs exhibit the highest enhancement factor for SERS, reaching an impressive value of 1.95×108, with uniform and consistent SERS signals across a large area. The experimental findings are further corroborated by simulations using the finite element method. This study establishes an efficient method for engineering the microstructure of 2D SLs composed of Au BPs, highlighting the importance of fine‐tuning the tip arrangements of Au BPs to regulate SERS performance. [ABSTRACT FROM AUTHOR]

A persistent challenge in utilizing Au nanocrystals for surface‐enhanced Raman spectroscopy (SERS) lies in achieving controllable superstructures that maximize SERS performance. Here, a novel strategy is proposed to enhance the SERS performance by precisely adjusting the tip arrangements of Au nanobipyramids (BPs) in two‐dimensional (2D) superlattices (SLs). This is achieved through ligand‐exchange of Au BPs, followed by liquid‐air interfacial assembly, resulting in large‐area, transferrable SL membranes. The key to controlling the arrangement of Au BPs in the SLs is the regulation of the amount of free ligands added during self‐assembly, which allows for the precise formation of various configurations such as tilted SLs, tip‐on‐tip SLs, and tip‐to‐tip SLs. Among these configurations, tip‐on‐tip SLs exhibit the highest enhancement factor for SERS, reaching an impressive value of 1.95×108, with uniform and consistent SERS signals across a large area. The experimental findings are further corroborated by simulations using the finite element method. This study establishes an efficient method for engineering the microstructure of 2D SLs composed of Au BPs, highlighting the importance of fine‐tuning the tip arrangements of Au BPs to regulate SERS performance. [ABSTRACT FROM AUTHOR]

The quantum anomalous Hall effect (QAHE) is a robust topological phenomenon that features quantized Hall resistance at zero magnetic field. We report the QAHE in a rhombohedral pentalayer graphene-monolayer tungsten disulfide (WS2) heterostructure. Distinct from other experimentally confirmed QAHE systems, this system has neither magnetic element nor moiré superlattice effect. The QAH states emerge at charge neutrality and feature Chern numbers C = ±5 at temperatures of up to about 1.5 kelvin. This large QAHE arises from the synergy of the electron correlation in intrinsic flat bands of pentalayer graphene, the gate-tuning effect, and the proximity-induced Ising spin-orbit coupling. Our experiment demonstrates the potential of crystalline two-dimensional materials for intertwined electron correlation and band topology physics and may enable a route for engineering chiral Majorana edge states. [ABSTRACT FROM AUTHOR]

Among all the cathode materials in lithium-ion batteries (LIBs), V 2 O 5 has gained a lot of attention due to its high theoretical specific capacity (∼440 mAh g−1). However, only some of the lithium-ions can be reversibly extracted after inserting into V 2 O 5 cells, making the actual reversible capacity of the crystalline V 2 O 5 cathode material much lower than its theoretical specific capacity. In this work, we prepared Li 2 O–V 2 O 5 –P 2 O 5 ternary glass by melt-quenching method. Subsequently, we grew nano-sized crystals and super-lattice structures in the glass matrix by precise heat treatment. Systematic structural, electrochemical tests and first-principles computations have shown that a reasonable amount of super-lattice structure can significantly enhance the electronic and ionic conductivity of glass matrix materials. Benefiting from this, the LVP-70-2 composite cathode exhibited excellent lithium storage performance with a stable reversible capacity of nearly ∼280 mAh g−1 at 50 mA g−1 and an outstanding cycling performance of a remaining capacity of 90 mAh g−1 at 1600 mA g−1 after 200 cycles. [ABSTRACT FROM AUTHOR]

The electronic structure of 7/9-AGNR superlattices with up to eight unit cells has been studied by means of state-of-the-art Density Functional Theory (DFT) and also by two model Hamiltonians, the first one including only local interactions (Hubbard model, Hu) while the second one is extended to allow long-range Coulomb interactions (Pariser, Parr and Pople model, PPP). Both are solved within mean field approximation. At this approximation level, our calculations show that 7/9 interfaces are better described by spin non-polarized solutions than by spin-polarized wavefunctions. Consequently, both Hu and PPP Hamiltonians lead to electronic structures characterized by a gap at the Fermi level that diminishes as the size of the system increases. DFT results show similar trends although a detailed analysis of the density of states around the Fermi level shows quantitative differences with both Hu and PPP models. Before improving model Hamiltonians, we interpret the electronic structure obtained by DFT in terms of bands of topological states: topological states localized at the system edges and extended bulk topological states that interact between them due to the long-range Coulomb terms of Hamiltonian. After careful analysis of the interaction among topological states, we find that the discrepancy between ab initio and model Hamiltonians can be resolved considering a screened long-range interaction that is implemented by adding an exponential cutoff to the interaction term of the PPP model. In this way, an adjusted cutoff distance λ = 2 allows a good recovery of DFT results. In view of this, we conclude that the correct description of the density of states around the Fermi level (Dirac point) needs the inclusion of long-range interactions well beyond the Hubbard model but not completely unscreened as is the case for the PPP model. [ABSTRACT FROM AUTHOR]

We study the transport properties of Dirac fermions in ABC trilayer graphene (ABC-TLG) superlattices. More specifically, we analyze the impact of varying the physical parameters-the number of cells, barrier/well width, and barrier heights-on electron tunneling in the ABC-TLG. In the initial stage, we solved the eigenvalue equation to determine the energy spectrum solutions for the ABC-TLG superlattices. Subsequently, we applied boundary conditions to the eigenspinors and employed the transfer matrix method to calculate transmission probabilities and conductance. For the two-band model, we identified the presence of Klein tunneling, with a notable decrease as the number of cells increased. The introduction of interlayer bias opened a gap as the number of cells increased, accompanied by an asymmetry in scattered transmission. Increasing the barrier/well width and the number of cells resulted in an amplified number of gaps and oscillations in both two-band and six-band cases. We observed a corresponding decrease in conductance as the number of cells increased, coinciding with the occurrence of a gap region. Our study demonstrates that manipulating parameters such as the number of cells, the width of the barrier/well, and the barrier heights provides a means of controlling electron tunneling and the occurrence of gaps in ABC-TLG. Specifically, the interplay between interlayer bias and the number of cells is identified as a crucial factor influencing gap formation and transmission asymmetry. [ABSTRACT FROM AUTHOR]

Zero‐dimensional lead halide perovskite nanocrystals (NCs) exhibit size‐dependent bandgap and carrier confinement compared to bulk counterparts due to the quantum confinement effect, making them essential for achieving wide‐color‐gamut displays, studying excitonic spin relaxation, and constructing superlattices. Despite their promising potential, they face a variety of technical bottlenecks, such as insufficient color reproducibility, limited large‐scale production, low stability, and toxicity. An outline of a research roadmap is provided in the review, which highlights key challenges in developing perovskite NCs for commercial applications. [ABSTRACT FROM AUTHOR]

This paper presents a detailed analysis of the thermal conductivity behaviors exhibited by a diverse array of nanostructured materials, ranging from multilayer graphene nanocomposites to semiconductor-based nanostructures such as Bi0.5Sb1.5Te3 and In0.53Ga0.47As composites. The investigation extends to superlattices, nanowires, and hybrid nanostructures, encompassing materials like hexagonal boron nitride flakes, iron oxide nanoporous films, and organic-inorganic hybrid materials. The thermal conductivity of these materials is characterized by distinct trends, with some showcasing crystal-like behavior and others demonstrating glass-like characteristics. The analysis employs empirical expressions to discern the contributions of phonons and diffusons in crystal-like materials and incorporates Peierls contributions and Arrhenius-type terms for glass-like behavior. Noteworthy observations include deviations in fitting certain materials at lower temperatures and the identification of negative diffuson contributions in specific cases. These findings contribute to a nuanced understanding of thermal transport in nanostructured materials and have implications for applications in advanced thermal management systems and thermoelectric devices. The extracted parameters provide valuable insights for researchers exploring the thermal conductivity of diverse nanostructured materials. [ABSTRACT FROM AUTHOR]

Janus monolayers of transition metal dichalcogenides (TMDCs) are promising building blocks for moiré superlattices because of their built‐in electric field and clean fabrication process. In particular, Janus TMDC monolayers can be chemically converted from conventional TMDC monolayers by atomic substitution, enabling the direct formation of lattice‐mismatched heterobilayers from TMDC bilayers. However, the moiré superlattices of Janus heterobilayers have not been studied experimentally. Herein, this work reports the fabrication and characterization of semiconductor moiré superlattices in chemically tailored Janus heterobilayers. The MoSSe/MoSe2 (or WSSe/WSe2) Janus heterobilayers are prepared by replacing the top layer Se atoms with S atoms in MoSe2 (or WSe2) bilayer using H2 plasma treatment. Scanning transmission electron microscopy reveals that an average moiré period of about 14 nm formed due to lattice mismatch resulting from the chalcogen substitutions. The cryogenic photoluminescence spectra show sharp, near‐infrared emissions, which are attributed to excitons trapped by moiré potentials based on comparison with theoretical calculations. The Janus‐based heterostructures provide a long‐period moiré system with built‐in potential even for nontwisted heterobilayers, allowing the functionalization of confined and correlated electron systems. [ABSTRACT FROM AUTHOR]

The manifestation of superconductivity in cuprate superconductors is concerted to copper-oxygen planes. To maintain charge neutrality, the copper-oxygen planes are embedded between materials, that are electronically insulating. Here, we introduce BaBiO3, LaCrO3, EuFeO3, and Ca2Fe2O5 as candidate materials. We use molecular beam epitaxy as a synthesis tool for the development of artificial superconducting superlattices in combination with infinte-layer CaCuO2. We find that (1) layer lattice matching, (2) thermodynamic compatibility and (3) absence of diffusion of any element other than Cu into CuO2 planes are key criteria to realize superconductivity. For brown-millerite Ca2Fe2O5/CaCuO2 superlattices, criteria 1–3 are met and superconductivity emerges. [ABSTRACT FROM AUTHOR]

The semiconductor minority carrier lifetime contains information about several important material properties, including Shockley–Read–Hall defect levels/concentrations and radiative/Auger recombination rates, and the complex relationships between these parameters produce a non-trivial temperature-dependence of the measured lifetime. It is tempting to fit temperature-dependent lifetime data to extract the properties of the Shockley–Read–Hall recombination centers; however, without a priori knowledge of the distribution of the Shockley–Read–Hall states across the bandgap, this fit problem is under-constrained in most circumstances. Shockley–Read–Hall lifetime data are not well-suited for the extraction of Shockley–Read–Hall defect levels but can be used effectively to extract minority carrier recombination lifetimes. The minority carrier recombination lifetime is observed at temperatures below 100 K in a Si-doped n-type InGaAs/InAsSb superlattice, and deviation from its expected temperature-dependence indicates that the capture cross section of the defect associated with Si-doping has an activation energy of 1.5 meV or a characteristic temperature of 17 K. This lower temperature regime is also preferrable for the analysis of the physics of defect introduction with displacement-damage-generating particle irradiation. [ABSTRACT FROM AUTHOR]

Ternary semiconductors such as InGaN thin films, quantum wells, and superlattices commonly exhibit alloy fluctuations that become increasingly pronounced with higher In-content. The thickness fluctuations of quantum wells and their thin cap-layers further introduce nanoscale inhomogeneities that alter the potential landscape. In this work, we present a combined theoretical and experimental study of InGaN single quantum wells with thin GaN cap-layers to unravel the influence of cap-layer thickness, compositional inhomogeneity, and thickness fluctuations on their electronic and optical properties. A pronounced spectral shift of quantum well emission for thin cap-layers between 1 and 10 nm is observed by micro-photoluminescence spectroscopy. The origin of this shift is explained by calculations of electronic band profiles and probability density overlap of carriers in the quantum well. The impact of alloy fluctuations and homogeneity for different cap-layer thicknesses is studied on both the microscale and nanoscale using UV micro-Raman scattering and tip-enhanced Raman spectroscopy (TERS). On the microscale, the alloy composition as determined by micro-Raman mapping appears very homogeneous except for the thinnest 1 nm cap-layer where small fluctuations are visible. On the nanoscale, TERS reveals local fluctuations on a 20–30 nm length scale. The influence of the cap-layer thickness on the TERS spectra is discussed regarding both the nanoscale homogeneity and the depth resolution of the near-field Raman scattering technique. Our results demonstrate the capabilities of TERS to resolve nanoscale thickness fluctuations and compositional inhomogeneities in ultra-thin semiconductor layers, even when they are buried by thin cap-layers with thicknesses below 10 nm. [ABSTRACT FROM AUTHOR]

Moiré lattices formed in twisted and lattice-mismatched van der Waals heterostructures have emerged as a platform to engineer the novel electronic and excitonic states at the nanoscale. This Perspective reviews the materials science of moiré heterostructures with a focus on the structural properties of the interface and its structural–property relationships. We first review the studies of the atomic relaxation and domain structures in moiré superlattices and how these structural studies provide critical insights into understanding the behaviors of quantum-confined electrons and excitons. We discuss the general frameworks to manipulate moiré structures and how such control can be harnessed for engineering new phases of matter and simulating various quantum phenomena. Finally, we discuss routes toward large-scale moiré heterostructures and give an outlook on their applications in quantum electronics and optoelectronics. Special emphasis will be placed on the challenges and opportunities of the reliable fabrication and dynamical manipulation of moiré heterostructures. [ABSTRACT FROM AUTHOR]

The self-assembly of colloidal nanoparticles into ordered superlattices typically uses dynamic interactions to govern particle crystallization, as these non-permanent bonds prevent the formation of kinetically trapped, disordered aggregates. However, while the use of reversible bonding is critical in the formation of highly ordered particle arrangements, dynamic interactions also inherently make the structures more prone to disassembly or disruption when subjected to different environmental stimuli. Thus, there is typically a trade-off between the ability to initially form an ordered colloidal material and the ability of that material to retain its order under different conditions. Here, we present a method for embedding colloidal nanoparticle superlattices into a polymer gel matrix. This encapsulation strategy physically prevents the nanoparticles from dissociating upon heating, drying, or the introduction of chemicals that would normally disrupt the lattice. However, the use of a gel as the embedding medium still permits further modification of the colloidal nanoparticle lattice by introducing stimuli that deform the gel network (as this deformation in turn alters the nanoparticle lattice structure in a predictable manner). Moreover, encapsulation of the lattice within a gel permits further stabilization into fully solid materials by removing the solvent from the gel or by replacing the solvent with a liquid monomer that can be photopolymerized. This embedding method therefore makes it possible to incorporate ordered colloidal arrays into a polymer matrix as either dynamic or static structures, expanding their potential for use in responsive materials. [ABSTRACT FROM AUTHOR]

The V-defect is a naturally occurring inverted hexagonal pyramid structure that has been studied in GaN and InGaN growth since the 1990s. Strategic use of V-defects in pre-quantum well superlattices or equivalent preparation layers has enabled record breaking efficiencies for green, yellow, and red InGaN light emitting diodes (LEDs) utilizing lateral injection of holes through the semi-polar sidewalls of the V-defects. In this article, we use advanced characterization techniques such as scattering contrast transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy, x-ray fluorescence maps, and atom probe tomography to study the active region compositions, V-defect formation, and V-defect structure in green and red LEDs grown on (0001) patterned sapphire and (111) Si substrates. We identify two distinct types of V-defects. The "large" V-defects are those that form in the pre-well superlattice and promote hole injection, usually nucleating on mixed (Burgers vector b = ± a ± c) character threading dislocations. In addition, "small" V-defects often form in the multi-quantum well region and are believed to be deleterious to high-efficiency LEDs by providing non-radiative pathways. The small V-defects are often associated with basal plane stacking faults or stacking fault boxes. Furthermore, we show through scattering contrast transmission electron microscopy that during V-defect filling, the threading dislocation, which runs up the center of the V-defect, will "bend" onto one of the six { 10 1 ¯ 1 } semi-polar planes. This result is essential to understanding non-radiative recombination in V-defect engineered LEDs. [ABSTRACT FROM AUTHOR]

The prospect of implementing quantum device architectures with technologically mature III–V semiconductors requires precisely controlled topologically protected edge states and bulk insulation. However, experimentally reaching this regime with III–V heterostructure epitaxy has been difficult due to charged bulk defects. Charged defects prevent bulk insulation and disturb the stability of edge states. Hence, we study carrier properties in a hybridized III–V InAs0.9Sb0.1/GaSb superlattice (SL) structure. We realize that an electron density (mobility) is limited to approximately 1012 cm−2 (104 cm2/V s). In order to understand these limits, the authors investigate the in-plane mobility of hybridized SLs as a function of current-carrying layer thickness, L, to determine scattering mechanisms that restrict carrier mobility. Although theory predicts the in-plane mobility is proportional to L6 dominated by interface roughness scattering (IRS) at low temperatures, we report that mobility follows the fourth power dependence, which is a weaker than expected from IRS theory. We attribute the discrepancy between experiment and the model to interface intermixing and wave function penetration into barrier regions. We use this understanding to develop a strategy for realizing high-performance topological materials. [ABSTRACT FROM AUTHOR]

Diamane superlattice generated by the interlayer bonding of twisted bilayer graphene (IB-TBG) has attracted much attention thanks to its excellent properties inherited from bulk diamond, as well as the versatile modulation of physical and mechanical properties, which may open up novel electronic applications. In this work, we have systematically studied the in-plane and interlayer mechanical behaviors of IB-TBG through molecular dynamics simulations and theoretical analysis by considering different structural parameters, such as the twisted angle, stack pattern, and interlayer bonding density. It is found that interlayer bonding density plays a crucial role in determining the in-plane and interlayer shear mechanical properties of IB-TBG. Both the in-plane tensile modulus and strength follow the same linear attenuation relationship with interlayer bonding density for different twisted angles and stacked patterns, while the interlayer shear modulus increases with interlayer bonding density following the same power law, and the critical shear strain of failure linearly decreases with interlayer bonding density. Furthermore, two failure modes are observed under shear deformation, i.e., the failure of interlayer bonding (mode I) and fracture of graphene sheets (mode G). Then, theoretical prediction is carried out by considering the balance of in-plane tension and interlayer shear, which can identify the two failure modes well. The results presented herein yield useful insights for designing and tuning the mechanical properties of IB-TBG. [ABSTRACT FROM AUTHOR]

While it is known that a resonant amplification of T c in two-gap superconductors can be driven by using the Fano–Feshbach resonance tuning the chemical potential near a Lifshitz transition, little is known on tuning the T c resonance by cooperative interplay of the Rashba spin–orbit coupling (RSOC) joint with phonon mediated (e-ph) pairing at selected k-space spots. Here, we present first-principles quantum calculation of superconductivity in an artificial heterostructure of metallic quantum wells with 3 nm period where quantum size effects give two-gap superconductivity with RSOC controlled by the internal electric field at the interface between the nanoscale metallic layers intercalated by insulating spacer layers. The key results of this work show that fundamental quantum mechanics effects including RSCO at the nanoscale [Mazziotti et al., Phys. Rev. B, 103, 024523 (2021)] provide key tools in applied physics for quantitative material design of unconventional high temperature superconductors at ambient pressure. We discuss the superconducting domes where T c is a function of either the Lifshitz parameter (η) measuring the distance from the topological Lifshitz transition for the appearing of a new small Fermi surface due to quantum size effects with finite spin–orbit coupling and the variable e-ph coupling g in the appearing second Fermi surface linked with the energy softening of the cut off ω 0. [ABSTRACT FROM AUTHOR]

Functional thin film superlattices with stability in extreme environments can lead to transformative performance in optical and thermal applications such as thermophotovoltaics. In this work, key issues associated with defects that prevent layer-by-layer growth in epitaxial, low-miscibility oxide superlattices are investigated. Layer protrusions, approximately 8 nm wide and 3 nm thick, arise from a strain relaxation mechanism in 8 nm bilayer superlattices of Ba(Zr0.5Hf0.5)O3/MgO and propagate through the subsequent superlattice layers forming an inverted pyramid structure that is spatially phase offset from the matrix. The density and size of these defects scales with the number of interfaces in the sample, indicating that surface roughness during growth is a significant factor in the formation of these defects. In situ high temperature transmission electron microscopy (1000 °C, in vacuo) measurement reveals that phase decomposition of Ba(Zr0.5Hf0.5)O3 and decoherence of the superlattice is nucleated by these defects. This work highlights that achieving optimum growth conditions is imperative to the synthesis of single-crystalline superlattices with sharp interfaces for optimized performance in extreme environments. [ABSTRACT FROM AUTHOR]

Pulse responses of different materials commonly used as electron sources in photoinjectors have been determined. Thin film photocathodes, such as strained GaAs/GaAsP superlattice and K2CsSb, produce fast responses. The emission intensity at time scales comparable with the acceptance of electron accelerators is found to be reasonably low, which is an advantage for operation at high beam powers. The temporal responses of these cathodes are compared with the response of bulk GaAs. [ABSTRACT FROM AUTHOR]

Wave localization by flatband mechanisms underlies prominent moiré physics and relevant applications. While typically studied in periodic superlattices, the wave-confining capability of finite-size superlattices is important both fundamentally and practically. Here, we investigate wave localization in few-cell moiré superlattices through fine tuning of band offset, which is accomplished by jointly adjusting structural parameters of constitutive lattice. Remarkably, the quality factor Q, which reflects the capability of few-cell superlattices to localize wave, can reach quite high levels with appropriate band offset. Thus, superior wave localization is feasible in few-cell superlattices, indicated by the very high Q up to 10 4 − 10 5 for single-cell superlattices and extremely high Q up to > 10 7 for double-cell superlattices. Moreover, the Q patterns are distinct for different flatband resonances and different number of cells, while narrow high-Q (∼ 10 8 ) branches appear for the triple-cell superlattices. The narrow high-Q branches are hard to be reached in practice, since it requires stringent control on structural parameters. In this respect, the double-cell superlattices are promising for exploiting unconventional effects induced by wave localization, since it can achieve extremely high-Q (> 10 7 ) resonances within a sufficiently large tuning range. These results demonstrate the profound role of band-offset tuning in achieving strong wave localization in few-cell superlattices, which is useful for on-chip applications such as lasing, optical filters, and optical harmonic generation. [ABSTRACT FROM AUTHOR]

The moiré superlattice structure has become a subject of intense interest due to its unique and intriguing properties. Key to the success of its applications is the precise manipulation of morphologies that determines the ultimate functionalities. To achieve such a goal is, however, very challenging. In this work, we present an approach for tuning moiré superlattices of suspended van der Waals structures through out-of-plane deformation. By studying the influence of out-of-plane deformation on interlayer sliding and atomic reconstruction in bilayer van der Waals structures, it is observed that interlayer sliding can overcome van der Waals potential barriers, resulting in stacking mode variations. Detailed analysis show that contraction and rotation of moiré patterns are induced, and leads to changes in the wavelength of the moiré superlattice. The approach outlined here offers opportunities for controlling and manipulating moiré superlattices. [ABSTRACT FROM AUTHOR]

The observation of the anomalous Hall effect (AHE) in 5d perovskite oxides has been challenging due to their lack or weak ferromagnetic order, which is necessary for breaking time-reversal symmetry. Here, we present compelling evidence of ferromagnetism and consequent AHE in a series of carefully designed and fabricated 5d/5d SrTaO3/SrIrO3 (STO/SIO) superlattices. The coexistence of Ta5+ and Ta4+ chemical states induces ferromagnetism in the STO layer, while the interfacial magnetic proximity effect further enhances it in the SIO layer, resulting in both ferromagnetism and AHE within the STO/SIO superlattice. Additionally, the strong spin–orbit coupling between Ta and Ir elements positively contributes to enhancing the AHE. This work offers an alternative approach for designing artificial materials with AHE and holds potential for advancing spintronics. [ABSTRACT FROM AUTHOR]

Semiconductor moiré superlattices have been shown to host a wide array of interaction-driven ground states. However, twisted homobilayers have been difficult to study in the limit of large moiré wavelengths, where interactions are most dominant. In this study, we conducted local electronic compressibility measurements of twisted bilayer WSe2 (tWSe2) at small twist angles. We demonstrated multiple topological bands that host a series of Chern insulators at zero magnetic field near a “magic angle” around 1.23°. Using a locally applied electric field, we induced a topological quantum-phase transition at one hole per moiré unit cell. Our work establishes the topological phase diagram of a generalized Kane-Mele-Hubbard model in tWSe2, demonstrating a tunable platform for strongly correlated topological phases. [ABSTRACT FROM AUTHOR]

Graphene-reinforced aluminum matrix composites have drawn remarkable attention in several fields of high-tech industries, but the understanding of their material properties remains unclear. This work reports a first-principles study of interface binding nature, mechanical strength, and electronic properties of aluminum/graphene (Al/G) composites using superlattice models as varying graphene content. Our calculations reveal the weak binding between Al and graphene layers with no new chemical bonding at the interface and the gradual decrease in binding strength as increasing graphene content. While demonstrating the enhancement of mechanical strength by interposing graphene layers, the critical value of graphene content for keeping ductility is determined to be 14.7%. Atom-projected band structures and local density of states are analyzed to get an insight into electronic conductance of superlattices. [ABSTRACT FROM AUTHOR]

The photogalvanic effect has been demonstrated to be an effective method to generate pure spin current. However, obtaining robust pure spin current remains a big challenge as most of the photo-induced pure spin current is dependent on the light polarization/phase angle, photon energies, or the spin alignment of electrodes. In this paper, we present a scheme for obtaining robust pure spin current in zigzag graphene–graphane superlattices (ZGSLs). Through systemic first-principles calculations, we demonstrate that robust generation of pure spin current can occur in ZGSLs with varying widths due to the centrosymmetry of the system's geometric structure and the antiferromagnetic magnetic features. Moreover, the generation of pure spin current does not depend on the photon energy or the polarization/phase angles for both linearly and elliptically polarized light, exhibiting very strong robustness. Our study suggests that ZGSLs could be highly promising candidates for practically realizing pure spin current in spintronics experiments, which presents an avenue for using graphene and its derivatives in advanced electronic devices. Furthermore, considering the experimental advancements in graphene and graphene-like materials, our investigation presents a universally applicable methodology for the generation of robust pure spin currents within low-dimensional graphene-like systems. [ABSTRACT FROM AUTHOR]

This work aims to study the insertion of AlCl4−$\text{AlCl}_{4}^{-}$ anion in the crystalline structure of oriented pyrolytic graphite (PG) at the point of view of the anion itself. The electronic and atomic structures of the anion at different intercalation stages are studied. In particular double‐edge (bicolor) X‐ray absorption spectroscopy at the Al and Cl K‐edges is carried out, highlighting a contraction of the anion bonding at the highest intercalation degree obtained electrochemically (stage 3), while the electronic population changes for both the edges upon cycle. [ABSTRACT FROM AUTHOR]

This research article examines the effects of atomic ordering on the structural and ferroelectric properties of (Ba, Sr) TiO3 solid solutions. Using density functional theory and molecular dynamics simulations, the study investigates how the concentration and ordering of Sr atoms influence local polarization, phase stability, and field-induced switching. The results demonstrate that atomic ordering impacts the Curie temperature, polarization, and stability of ferroelectric phases. This study contributes to our understanding of how atomic ordering affects material properties and offers insights into optimizing ferroelectric phases and functional properties in nanostructures. The document also provides additional information, references, and access to supporting data for further exploration. [Extracted from the article]

The tri-layer magnetic tunnel junction (MTJ) has surfaced as a building block for engineering next-generation integrated circuits while combining the attributes of non-volatility and meager energy consumption. Nevertheless, the perceptible switching energy (≈ 20 – 50 fJ/bit) and sub-optimal tunnelmagnetoresistance (TMR) (≈ 200 % – 300 %) have acted as major hindrances, concealing its potential to supersede the capabilities of static and dynamic random access memories. In this work, we introduce a novel device that features a minimalistic non-uniform heterostructure/superlattice instead of the oxide layer in a conventional MTJ and analyze it in the premise of the self-consistent coupling of the Non-Equilibrium-Green's Function (NEGF) and the Landau-Liftshitz-Gilbert-Slonczewski (LLGS) equation. We ascertain that the coupling of the electrodes to the proposed heterostructure renders a highly spin-selective broadband transmittance, thereby enabling a towering TMR (%) of 3.7 × 104% along with a significant reduction in the spin transfer torque (STT) switching energy (≈1.96 fJ). Furthermore, the sizable slonczewski term (Is‖) originating from the heterostructure facilitates a swift STT-switching within the scale of a few hundred picoseconds (≈400 ps). [ABSTRACT FROM AUTHOR]

This Review provides a thorough description of the experimental progress on the InN family and other relevant compounds. Although InN is of great interest, many of its properties are not well understood and are still puzzling researchers with a number of unexpected effects. These include a surprisingly small energy gap, sensitivity to applied pressure in terms of lattice stability, and poor miscibility with compounds with smaller lattice parameters, such as GaN and AlN. Special features of InN under pressure are highlighted, such as the effect of conduction band filling and the strong pressure dependence of the effective mass. Several negative and positive effects due to the presence of In have been observed. We highlight their implications for InN-based alloys and quantum structures, which are crucial materials in modern optoelectronics (light emitting diodes and laser diodes). These effects include In clustering, large piezoelectricity resulting in strong internal electric fields that reduce the optical gain in nitride heterostructures, and difficulties in growing high-In superlattices and other quantum structures. All of these effects pose challenges that need to be addressed. We show that theoretical explanations allow for the clarification of puzzling experimental observations. Discussed are (i) a reformulation of the rule describing the bandgap dependence on pressure in all III–V semiconductors; (ii) the very large bandgap curvatures in nitride alloys; and (iii) the discrepancies between theory and experiment in the optical emission from InN/GaN superlattices, leading to the conclusion that epitaxial growth of high In content InxGa1−xN (x > 0.3) quantum wells on GaN is not possible. [ABSTRACT FROM AUTHOR]

Heat transfer in layered metal-dielectric structures is considered theoretically based on an analytical solution of the Boltzmann transfer equation for the phonon distribution function. Taking into account the size effect, the problem of effective cross-plane thermal conductivity of structures containing two metal layers is analyzed in detail. If the thickness of the metal layers is less than the phonon mean free path, interlayer heat transfer is carried out predominantly by phonons, and the effective cross-plane thermal conductivity is determined by the reflection of phonons from the metal/dielectric interfaces. In the opposite case of thick metal layers, the effective cross-plane thermal conductivity is determined both by the thermal conductivity of the metal layers and by the thermal resistance of the dielectric layers. The results obtained are generalized to multilayer structures and superlattices. [ABSTRACT FROM AUTHOR]

[Display omitted] Achieving a controlled preparation of nanoparticle superstructures with spatially periodic arrangement, also called superlattices, is one of the most intriguing and open questions in soft matter science. The interest in such regular superlattices originates from the potentialities in tailoring the physicochemical properties of the individual constituent nanoparticles, eventually leading to emerging behaviors and/or functionalities that are not exhibited by the initial building blocks. Despite progress, it is currently difficult to obtain such ordered structures; the influence of parameters, such as size, softness, interaction potentials, and entropy, are neither fully understood yet and not sufficiently studied for 3D systems. In this work, we describe the synthesis and characterization of spatially ordered hierarchical structures of coated cerium oxide nanoparticles in water suspension prepared by a bottom-up approach. Covering the CeO 2 surface with amphiphilic molecules having chains of appropriate length makes it possible to form ordered structures in which the particles occupy well-defined positions. In the present case superlattice arrangement is accompanied by an improvement in photoluminescence (PL) efficiency, as an increase in PL intensity of the superlattice structure of up to 400 % compared with that of randomly dispersed nanoparticles was observed. To the best of our knowledge, this is one of the first works in the literature in which the coexistence of 3D structures in solution, such as face-centered cubic (FCC) and Frank-Kasper (FK) phases, of semiconductor nanoparticles have been related to their optical properties. [ABSTRACT FROM AUTHOR]

We present a novel method for synthesizing monodisperse, star-shaped FeCoMnOx nanocrystals with tunable concavity. Through liquid–air interfacial assembly, these colloidal nanostars can form two-dimensional superlattices, which are characterized by low packing densities. Notably, the ability to adjust the degree of concavity of nanostars allows for the tuning of the packing symmetry of the assembled superlattices. [ABSTRACT FROM AUTHOR]

In recent times, newly unveiled 2D materials exhibiting exceptional characteristics, such as MBenes and MXenes, have gained widespread application across diverse domains, encompassing electronic devices, catalysis, energy storage, sensors, and various others. Nonetheless, numerous technical bottlenecks persist in the development of high‐performance, structurally flexible, and adjustable electronic device materials. Research investigations have demonstrated that 2D van der Waals superlattices (vdW SLs) structures comprising materials exhibit exceptional electrical, mechanical, and optical properties. In this work, the advantages of both materials are combined and compose the vdW SLs structure of MBenes and MXenes, thus obtaining materials with excellent electronic properties. Furthermore, it integrates machine learning (ML) with first‐principles methods to forecast the electrical properties of MBene/MXene superlattice materials. Initially, various configurations of MBene/MXene superlattice materials are explored, revealing that distinct stacking methods exert significant influence on the electronic structure of MBene/MXene materials. Specifically, the BABA‐type stacking of CrB (layer A) and Co2CO2 MXene (layer B) is most stable configureation. Subsequently, multiple descriptors of the structure are constructed to predict the density of states  of vdW SLs through the employment of ML techniques. The best model achieves a mean absolute error (MAE) as low as 0.147 eV. [ABSTRACT FROM AUTHOR]

We investigated the ultrafast dynamics of a SrRuO3/BiFeO3 superlattice grown on a SrTiO3 substrate using a near infrared pump–probe technique at various temperatures. The superlattice exhibits a ferromagnetic order inherited from the SrRuO3 layer. The pump-induced changes in the reflectivity reveal periodic oscillations. We found that the oscillation frequency can be well explained by zone-folded acoustic phonon oscillations, whose dispersion depends on the sound velocity, density, and thickness within the supercell of each constituent layer. It is found that the observed oscillation frequency corresponds to the A1 mode, which suggests that oscillations are excited due to pump-induced expansion of the SrRuO3 layer that absorbs the pump photon. Temperature-dependent measurements reveal significant suppression of the oscillation amplitude in the ferromagnetic state. The suppressed amplitude is proportional to the square of the magnetization, M(T)2. This phenomenon can be attributed to a strong magnetostriction effect of SrRuO3 that suppresses lattice expansion upon pumping. [ABSTRACT FROM AUTHOR]

Recent studies have revealed the potential of 2D moiré superlattices as a condensed matter quantum simulator. The realization of different lattice model Hamiltonians in moiré superlattices has become the focus of researches. Here, it shows that, compared to bilayer moiré superlattices where there is only one interface, the interference between moiré patterns at different interfaces in 2D multilayer structures allows the physical realization of more complicated lattice models. The concept is demonstrated by trilayer moiré superlattices (TMSLs) of MoS2, where it finds that isolated flat moiré bands appear near the valence band edge, and they can be described by the honeycomb lattice ionic Hubbard model. More importantly, the hopping strength, the on‐site Coulomb repulsion, and the staggered potential in the TMSLs are highly tunable through the control of the twist angle, the dielectric environment, and the perpendicular electric field. It is possible to achieve various transitions between distinct quantum phases in the TMSLs, spanning from weak to strong correlation regimes. Therefore, the proposed TMSLs can serve as a good platform to study the strong correlation physics in the honeycomb lattice ionic Hubbard model. [ABSTRACT FROM AUTHOR]

Interlayer interactions are one of the crucial parameters of two‐dimensional (2D) layered materials‐based junctions. Understanding the limits of interlayer coupling and defining the "maximum building block thickness" in artificially stacked 2D layered materials are key tasks that hold significant importance, not only in fundamental physics, but also in practical applications such as electronics, photonics, and optoelectronics. Here, the interlayer coupling limits are optically investigated of a model 2D layered semiconductor, MoS2, revealing the evolution of distinct interaction mechanisms between layers via artificial stacking. As the total thickness increases, a reduction in the stacking angle influence on the properties of the homojunctions is reflected in the photoluminescence and second harmonic generation responses. The results show that the effective coupling limit for vertically stacked 2D metamaterials resides in three‐layer flakes. The findings pave the way to advanced and complex devices of 2D superlattices for photonics and optoelectronics. [ABSTRACT FROM AUTHOR]

Semiconductor nanocrystals can replace conventional bulk materials completely in displays and light‐emitting diodes. Exciton transport dominates over charge carrier transport for materials with high exciton binding energies and long ligands, such as halide perovskite nanocrystal films. Here, how beneficial superlattices – nearly perfect 3D assemblies of nanocrystals ‐ are to exciton transport is investigated. Surprisingly, the high degree of order is not as crucial as the individual nanocrystal size, which strongly influences the splitting of the excitonic manifold into bright and dark states. At very low temperatures, the energetic splitting is larger for the smallest nanocrystals, and dark levels with low oscillator strength effectively trap excitons inside individual nanocrystals, suppressing diffusion. The effect is reversed at elevated temperatures, and the larger nanocrystal size becomes detrimental to exciton transport due to enhanced exciton trapping and dissociation. The results reveal that the nanocrystal size must be strongly accounted for in design strategies of future optoelectronic applications. [ABSTRACT FROM AUTHOR]