One-Step Preparation of Regular Micropearl Arrays for Two-Direction Controllable Anisotropic Wetting

In this paper, one simple method to control two-direction anisotropic wetting by regular micropearl arrays was demonstrated. Various micropearl arrays with large area were rapidly fabricated by a kind of improved laser interference lithography. Specially, we found that the parallel contact angle (CA) θ2 decreased from 93° to 67° as the intensity ratio of four laser beams increased from 2:1 to 30:1, while the perpendicular CA θ1 determined by the thickness of the resin remained constant. This was interpreted as the decrease of height variations Δh from 1100 to 200 nm along the parallel direction caused by the increase of the intensity ratio. According to this rule, both θ1 and θ2 could be simultaneously controlled by adjusting the height variation Δh and the resin thickness. Moreover, by combining appropriate design and low surface energy modification, a natural anisotropic rice leaf exhibiting CAs of 146° ± 2°/153° ± 3° could be mimicked by our anisotropic biosurface with the CAs 145° ± 1°/150° ± 2°. We believe that these controlled anisotropic biosurfaces will be helpful for designing smart, fluid-controllable interfaces that may be applied in novel microfluidic devices, evaporation-driven micro/nanostructures, and liquid microdroplet directional transfer

Confinement Effects in Low-Dimensional Lead Iodide Perovskite Hybrids

We use a layered solution crystal growth technique to synthesize high-quality single crystals of phenylalkylammonium lead iodide organic/inorganic hybrid compounds. Single-crystal X-ray diffraction reveals low-dimensional structures consisting of inorganic sheets separated by bilayers of the organic cations. The shortest alkyls yield two-dimensional structures consisting of inorganic sheets of corner-sharing PbI6-octahedra. However, the longer alkyls induce both corner- and face-sharing of the PbI6-octahedra, and form new compounds. Density functional theory calculations including spin–orbit coupling show quantum confinement in two dimensions for the shorter alkyls, and in one dimension for the longer alkyls, respectively. The face-sharing PbI6-octahedra create a confinement leading to effectively one-dimensional behavior. These confinement effects are responsible for the observed peak shifts in photoluminescence for the different phenylalkylammonium lead iodide hybrids. Our results show how the connectivity of the octahedra leads to confinement effects that directly tune the optical band gap

Confinement Effects in Low-Dimensional Lead Iodide Perovskite Hybrids

We use a layered solution crystal growth technique to synthesize high-quality single crystals of phenylalkylammonium lead iodide organic/inorganic hybrid compounds. Single-crystal X-ray diffraction reveals low-dimensional structures consisting of inorganic sheets separated by bilayers of the organic cations. The shortest alkyls yield two-dimensional structures consisting of inorganic sheets of corner-sharing PbI6-octahedra. However, the longer alkyls induce both corner- and face-sharing of the PbI6-octahedra, and form new compounds. Density functional theory calculations including spin–orbit coupling show quantum confinement in two dimensions for the shorter alkyls, and in one dimension for the longer alkyls, respectively. The face-sharing PbI6-octahedra create a confinement leading to effectively one-dimensional behavior. These confinement effects are responsible for the observed peak shifts in photoluminescence for the different phenylalkylammonium lead iodide hybrids. Our results show how the connectivity of the octahedra leads to confinement effects that directly tune the optical band gap

Micropatterned 2D Hybrid Perovskite Thin Films with Enhanced Photoluminescence Lifetimes

The application of luminescent materials in display screens and devices requires micropatterned structures. In this work, we have successfully printed microstructures of a two-dimensional (2D), orange-colored organic/inorganic hybrid perovskite ((C6H5CH2NH3)2PbI4) using two different soft lithography techniques. Notably, both techniques yield microstructures with very high aspect ratios in the range of 1.5–1.8. X-ray diffraction reveals a strong preferential orientation of the crystallites along the c-axis in both patterned structures, when compared to nonpatterned, drop-casted thin films. Furthermore, (time-resolved) photoluminescence (PL) measurements reveal that the optical properties of (C6H5CH2NH3)2PbI4 are conserved upon patterning. We find that the larger grain sizes of the patterned films with respect to the nonpatterned film give rise to an enhanced PL lifetime. Thus, our results demonstrate easy and cost-effective ways to manufacture patterns of 2D organic/inorganic hybrid perovskites, while even improving their optical properties. This demonstrates the potential use of color-tunable 2D hybrids in optoelectronic devices

Counterion-Mediated Ligand Exchange for PbS Colloidal Quantum Dot Superlattices

In the past years, halide capping became one of the most promising strategies to passivate the surface of colloidal quantum dots (CQDs) in thin films to be used for electronic and optoelectronic device fabrication. This is due to the convenient processing, strong n-type characteristics, and ambient stability of the devices. Here, we investigate the effect of three counterions (ammonium, methylammonium, and tetrabutylammonium) in iodide salts used for treating CQD thin films and shed light on the mechanism of the ligand exchange. We obtain two- and three-dimensional square-packed PbS CQD superlattices with epitaxial merging of nearest neighbor CQDs as a direct outcome of the ligand-exchange reaction and show that the order in the layer can be controlled by the nature of the counterion. Furthermore, we demonstrate that the acidity of the environment plays an important role in the substitution of the carboxylates by iodide ions at the surface of lead chalcogenide quantum dots. Tetrabutylammonium iodide shows lower reactivity compared to methylammonium and ammonium iodide due to the nonacidity of the cation, which eventually leads to higher order but also poorer carrier transport due to incomplete removal of the pristine ligands in the QD thin film. Finally, we show that single-step blade-coating and immersion in a ligand exchange solution such as the one containing methylammonium iodide can be used to fabricate well performing bottom-gate/bottom-contact PbS CQD field effect transistors with record subthreshold swing

Quantum Emitters with Narrow Band and High Debye–Waller Factor in Aluminum Nitride Written by Femtosecond Laser

Solid-state quantum emitters (QEs) are central components for photonic-based quantum information processing. Recently, bright QEs in III-nitride semiconductors, such as aluminum nitride (AlN), have attracted increasing interest because of the mature commercial application of the nitrides. However, the reported QEs in AlN suffer from broad phonon side bands (PSBs) and low Debye–Waller factors. Meanwhile, there is also a need for more reliable fabrication methods of AlN QEs for integrated quantum photonics. Here, we demonstrate that laser-induced QEs in AlN exhibit robust emission with a strong zero phonon line, narrow line width, and weak PSB. The creation yield of a single QE could be more than 50%. More importantly, they have a high Debye–Waller factor (>65%) at room temperature, which is the highest result among reported AlN QEs. Our results illustrate the potential of laser writing to create high-quality QEs for quantum technologies and provide further insight into laser writing defects in relevant materials

Time-Resolved Fluorescence Study of Aggregation-Induced Emission Enhancement by Restriction of Intramolecular Charge Transfer State

Cyano-substituted oligo (α-phenylenevinylene)-1,4-bis(R-cyano-4-diphenylaminostyryl)-2,5-diphenylbenzene (CNDPASDB) molecules are studied in solution and aggregate state by time-resolved fluorescence techniques. CNDPASDB exhibits a strong solvent polarity dependent characteristic of aggregation-induced emission (AIE). By time-dependent spectra, the gradual transition from local excited state to intramolecular charge transfer state with the increasing solvent polarity is clearly resolved. The transition time in high polarity solvent DMF is very fast, around 0.5 ps, resulting in a low fluorescence quantum yield. While in aggregate state, the intramolecular torsion is restricted and the local environment becomes less polar. Thus, the intramolecular charge transfer state is eliminated and efficient AIE occurs

All-Optical Reconfigurable Excitonic Charge States in Monolayer MoS₂

Excitons are quasi-particles composed of electron–hole pairs through Coulomb interaction. Due to the atomic-thin thickness, they are tightly bound in monolayer transition metal dichalcogenides (TMDs) and dominate their optical properties. The capability to manipulate the excitonic behavior can significantly influence the photon emission or carrier transport performance of TMD-based devices. However, on-demand and region-selective manipulation of the excitonic states in a reversible manner remains challenging so far. Herein, harnessing the coordinated effect of femtosecond-laser-driven atomic defect generation, interfacial electron transfer, and surface molecular desorption/adsorption, we develop an all-optical approach to manipulate the charge states of excitons in monolayer molybdenum disulfide (MoS2). Through steering the laser beam, we demonstrate reconfigurable optical encoding of the excitonic charge states (between neutral and negative states) on a single MoS2 flake. Our technique can be extended to other TMDs materials, which will guide the design of all-optical and reconfigurable TMD-based optoelectronic and nanophotonic devices

Long Exciton Diffusion Length in High Mobility Emissive Organic Semiconductor

Organic semiconductors that possess both long exciton diffusion length and high mobility emissive properties are crucial for the development of high-performance organic optoelectronic devices. However, materials with these combined characteristics are currently rare. Herein, a long exciton diffusion length was obtained in the high mobility emissive organic semiconductor trans-1,2-bis­(5-phenyldithieno­[2,3-b:3′,2′-d]­thiophen-2-yl)­ethene (BPTTE). Excellent optoelectronic properties with the maximum carrier mobility of 18.1 cm2 V–1 s–1 and high photoluminescence quantum yield (PLQY) of 21.4% were obtained for BPTTE single crystals. Notably, an impressive exciton diffusion length reaching up to 114.2 nm was also achieved, demonstrating the effective integration of optoelectrical properties in BPTTE single crystals. This work offers valuable guidance for exploring the multifunctional capabilities of high mobility organic semiconductors, a crucial aspect for enhancing the performance of organic optoelectronic devices