Doping and ion substitution in colloidal metal halide perovskite nanocrystals.

The past decade has witnessed tremendous advances in synthesis of metal halide perovskites and their use for a rich variety of optoelectronics applications. Metal halide perovskite has the general formula ABX3, where A is a monovalent cation (which can be either organic (e.g., CH3NH3+ (MA), CH(NH2)2+ (FA)) or inorganic (e.g., Cs+)), B is a divalent metal cation (usually Pb2+), and X is a halogen anion (Cl-, Br-, I-). Particularly, the photoluminescence (PL) properties of metal halide perovskites have garnered much attention due to the recent rapid development of perovskite nanocrystals. The introduction of capping ligands enables the synthesis of colloidal perovskite nanocrystals which offer new insight into dimension-dependent physical properties compared to their bulk counterparts. It is notable that doping and ion substitution represent effective strategies for tailoring the optoelectronic properties (e.g., absorption band gap, PL emission, and quantum yield (QY)) and stabilities of perovskite nanocrystals. The doping and ion substitution processes can be performed during or after the synthesis of colloidal nanocrystals by incorporating new A', B', or X' site ions into the A, B, or X sites of ABX3 perovskites. Interestingly, both isovalent and heterovalent doping and ion substitution can be conducted on colloidal perovskite nanocrystals. In this review, the general background of perovskite nanocrystals synthesis is first introduced. The effects of A-site, B-site, and X-site ionic doping and substitution on the optoelectronic properties and stabilities of colloidal metal halide perovskite nanocrystals are then detailed. Finally, possible applications and future research directions of doped and ion-substituted colloidal perovskite nanocrystals are also discussed.

Unconventional Route to Uniform Hollow Semiconducting Nanoparticles with Tailorable Dimensions, Compositions, Surface Chemistry, and Near-Infrared Absorption.

Despite impressive recent advances in the synthesis of lead chalcogenide solid nanoparticles, there are no examples of lead chalcogenide hollow nanoparticles (HNPs) with controlled diameter and shell thickness as current synthetic approaches for HNPs have inherent limitations associated with their complexity, inability to precisely control the dimensions, and limited possibilities with regard to applicable materials. Herein, we report on an unconventional strategy for crafting uniform lead chalcogenide (PbS and PbTe) HNPs with tailorable size, surface chemistry, and near-IR absorption. Amphiphilic star-like triblock copolymers [polystyrene-block-poly(acrylic acid)-block-polystyrene and polystyrene-block-poly(acrylic acid)-block-poly(3,4-ethylenedioxythiophene)] were rationally synthesized and exploited as nanoreactors for the formation of uniform PbS and PbTe HNPs. Compared to their solid counterparts, the near-IR absorption of the HNPs is blue-shifted owing to the hollow interior. This strategy can be readily extended to other types of intriguing low-band-gap HNPs for diverse applications.

Rational coordination regulation in carbon-based single-metal-atom catalysts for electrocatalytic oxygen reduction reaction.

Single-metal-atom catalysts (SMACs) have garnered extensive attention for various electrocatalytic applications, owing to their maximum atom-utilization efficiency, tunable electronic structure, and remarkable catalytic performance. In particular, carbon-based SMACs exhibit optimal electrocatalytic activity for the oxygen reduction reaction (ORR) which is of paramount importance for several sustainable energy conversion and generation technologies, such as fuel cells and metal-air batteries. Despite continuous endeavors in developing various advanced carbon-based SMACs for electrocatalytic ORR, the rational regulation of coordination structure and thus the electronic structure of carbon-based SMACs remains challenging. In this review, we critically examine the role of coordination structure, including local coordination structure (i.e., metal atomic centers and the first coordination shell) and extended local coordination structure (i.e., the second and higher coordination shells), on the rational design of carbon-based SMACs for high-efficiency electrocatalytic ORR. Insights into the relevance between coordination structures and their intrinsic ORR activities are emphatically exemplified and discussed. Finally, we also propose the major challenges and future perspectives in the rational design of advanced carbon-based SMACs for electrocatalytic ORR. This review aims to emphasize the significance of coordination structure and deepen the insightful understanding of structure-performance relationships.

Small interfering RNA targeting N-cadherin regulates cell proliferation and migration in enzalutamide-resistant prostate cancer.

Enzalutamide is one of the options for treating patients with castration-resistant or metastatic prostate cancer. However, a substantial proportion of patients become resistant to enzalutamide after a period of treatment. Cells in these tumors typically exhibit increased proliferative and migratory capabilities, in which N-cadherin (CDH2) appear to serve an important role. In the present study, by up- and downregulating the expression of CDH2, the possible effects of CDH2 on the prostate cancer cell line LNCaP were investigated. Male sex hormone-sensitive LNCaP cells treated with 10 µM enzalutamide were named LNCaP enzalutamide-resistant (EnzaR) cells. Reverse transcription-PCR, western blotting and immunofluorescence staining were used to measure CDH2, E-cadherin, α-SMA, Snail and Slug expression. Transfection with the pCMV-CDH2 plasmid was performed for CDH2 upregulation, whilst transfection with small interfering RNA (siRNA)-CDH2 was performed for CDH2 downregulation. MTT and Cell Counting Kit-4 assays were used to evaluate the proportion of viable cancer cells. Subsequently, gap closure assay was performed to evaluate the migratory capability of both LNCaP and LNCaP EnzaR cell lines. CDH2 expression was found to be increased in LNCaP EnzaR cells compared with that in LNCaP cells. CDH2 overexpression increased cell viability and migration in both LNCaP and LNCaP EnzaR cell lines. By contrast, the opposite trend was observed after CDH2 expression was knocked down. CDH2 expression also showed a high association with that of four epithelial-mesenchymal transition markers, which was confirmed by western blotting. Based on these results, it was concluded that knocking down CDH2 expression using siRNA transfection mediated significant influence on LNCaP EnzaR cell physiology, which may be a potential therapeutic option for prostate cancer treatment.

Highly transparent superhydrophobic surfaces from the coassembly of nanoparticles (≤100 nm).

We report a simple and versatile approach to creating a highly transparent superhydrophobic surface with dual-scale roughness on the nanoscale. 3-Aminopropyltrimethoxysilane (APTS)-functionalized silica nanoparticles of two different sizes (100 and 20 nm) were sequentially dip coated onto different substrates, followed by thermal annealing. After hydrophobilization of the nanoparticle film with (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane for 30 min or longer, the surface became superhydrophobic with an advancing water contact angle of greater than 160° and a water droplet (10 µL) roll-off angle of less than 5°. The order of nanoparticles dip coated onto the silicon wafer (i.e., 100 nm first and 20 nm second or vice versa) did not seem to have a significant effect on the resulting apparent water contact angle. In contrast, when the substrate was dip coated with monoscale nanoparticles (20, 50, and 100 nm), a highly hydrophobic surface (with an advancing water contact angle of up to 143°) was obtained, and the degree of hydrophobicity was found to be dependent on the particle size and concentration of the dip-coating solution. UV-vis spectra showed nearly 100% transmission in the visible region from the glass coated with dual-scale nanoparticles, similar to the bare one. The coating strategy was versatile, and superhydrophobicity was obtained on various substrates, including Si, glass, epoxy resin, and fabrics. Thermal annealing enhanced the stability of the nanoparticle coating, and superhydrophobicity was maintained against prolonged exposure to UV light under ambient conditions.

Heavy Mediator at Quantum Dot/Graphene Heterojunction for Efficient Charge Carrier Transfer: Alternative Approach for High-Performance Optoelectronic Devices.

Two-dimensional (2D) material nanocomposites have emerged as a material system for discovering new physical phenomena and developing novel devices. However, because of the low density of states of most two-dimensional materials such as graphene, the heterostructure of nanocomposites suffers from an enhanced depletion region, which can greatly reduce the efficiency of the charge carrier transfer and deteriorate the device performance. To circumvent this difficulty, here we propose an alternative approach by inserting a second 2D mediator with a heavy effective mass having a large density of states in-between the heterojunction of 2D nanocomposites. The mediator can effectively reduce the depletion region and form a type-II band alignment, which can speed up the dissociation of electron-hole pairs and enhance charge carrier transfer. To illustrate the principle, we demonstrate a novel stretchable photodetector based on the combination of graphene/ReS2/perovskite quantum dots. Two-dimensional ReS2 acts as a mediator in-between highly absorbing perovskite quantum dots and a high-mobility graphene channel and a thiol-based linker between the ReS2 and the perovskite. It is found that the optical sensitivity can be enhanced by 22 times. This enhancement was ascribed to the improvement of the charge transfer efficiency as evidenced by optical spectroscopy measurements. The produced photosensors are capable of reaching the highest reported value of photoresponsivity (>107 A W-1) and detectivity compared to previously studied stretchable devices. Mechanical robustness with tolerable strain up to 100% and excellent stability make our device ideal for future wearable electronics.

Graphene Sandwich Stable Perovskite Quantum-Dot Light-Emissive Ultrasensitive and Ultrafast Broadband Vertical Phototransistors.

Dual-functional devices that can simultaneously detect light and emit light have a tremendous appeal for multiple applications, including displays, sensors, defense, and high-speed optical communication. Despite the tremendous efforts of scientists, the progress of integration of a phototransistor, where the built-in electric field separates the photogenerated excitons, and a light-emitting diode, where the radiative recombination can be enhanced by band offset, into a single device remains a challenge. Combining the superior properties of perovskite quantum dots (PQDs) and graphene, here we report a light-emissive, ultrasensitive, ultrafast, and broadband vertical phototransistor that can simultaneously act as an efficient photodetector and light emitter within a single device. The estimated value of the external quantum efficiency of the vertical phototransistor is ∼1.2 × 1010% with a photoresponsivity of >109 A W-1 and a response time of <50 µs, which exceed all the presently reported vertical phototransistor devices. We also demonstrate that the modulation of the Dirac point of graphene efficiently tunes both amplitude and polarity of the photocurrent. The device exhibits a green emission having a quantum efficiency of 5.6%. The moisture-insensitive and environmentally stable, light-emissive, ultrafast, and ultrasensitive broadband phototransistor creates a useful route for dual-functional optoelectronic devices.

All-Inorganic Perovskite Nanocrystals with a Stellar Set of Stabilities and Their Use in White Light-Emitting Diodes.

We report a simple, robust, and inexpensive strategy to enable all-inorganic CsPbX3 perovskite nanocrystals (NCs) with a set of markedly improved stabilities, that is, water stability, compositional stability, phase stability, and phase segregation stability via impregnating them in solid organic salt matrices (i.e., metal stearate; MSt). In addition to acting as matrices, MSt also functions as the ligand bound to the surface of CsPbX3 NCs, thereby eliminating the potential damage of NCs commonly encountered during purification as in copious past work. Quite intriguingly, the resulting CsPbX3-MSt nanocomposites display an outstanding suite of stabilities. First, they retain high emission in the presence of water because of the insolubility of MSt in water, signifying their excellent water stability. Second, anion exchange between CsPbBr3-MSt and CsPbI3-MSt nanocomposites is greatly suppressed. This can be ascribed to the efficient coating of MSt, thus effectively isolating the contact between CsPbBr3 and CsPbI3 NCs, reflecting notable compositional stability. Third, remarkably, after being impregnated by MSt, the resulting CsPbI3-MSt nanocomposites sustain the cubic phase of CsPbI3 and high emission, manifesting the strikingly improved phase stability. Finally, phase segregation of CsPbBr1.5I1.5 NCs is arrested via the MSt encapsulation (i.e., no formation of the respective CsPbBr3 and CsPbI3), thus rendering pure and stable photoluminescence (i.e., demonstration of phase segregation stability). Notably, when assembled into typical white light-emitting diode architecture, CsPbBr1.5I1.5-MSt nanocomposites exhibit appealing performance, including a high color rendering index ( Ra) and a low color temperature ( Tc). As such, the judicious encapsulation of perovskite NCs into organic salts represents a facile and robust strategy for creating high-quality solid-state luminophores for use in optoelectronic devices.

Wrinkled 2D Materials: A Versatile Platform for Low-Threshold Stretchable Random Lasers.

A stretchable, flexible, and bendable random laser system capable of lasing in a wide range of spectrum will have many potential applications in next- generation technologies, such as visible-spectrum communication, superbright solid-state lighting, biomedical studies, fluorescence, etc. However, producing an appropriate cavity for such a wide spectral range remains a challenge owing to the rigidity of the resonator for the generation of coherent loops. 2D materials with wrinkled structures exhibit superior advantages of high stretchability and a suitable matrix for photon trapping in between the hill and valley geometries compared to their flat counterparts. Here, the intriguing functionalities of wrinkled reduced graphene oxide, single-layer graphene, and few-layer hexagonal boron nitride, respectively, are utilized to design highly stretchable and wearable random laser devices with ultralow threshold. Using methyl-ammonium lead bromide perovskite nanocrystals (PNC) to illustrate the working principle, the lasing threshold is found to be ≈10 µJ cm-2 , about two times less than the lowest value ever reported. In addition to PNC, it is demonstrated that the output lasing wavelength can be tuned using different active materials such as semiconductor quantum dots. Thus, this study is very useful for the future development of high-performance wearable optoelectronic devices.

Control of morphology, photoluminescence, and stability of colloidal methylammonium lead bromide nanocrystals by oleylamine capping molecules.

Methylammonium lead bromide (CH3NH3PbBr3) thin films and nanocrystals are useful for solar cells and LED applications. In order to improve stability in ambient environment, CH3NH3PbBr3 nanocrystals have been synthesized using oleylamine as capping molecule. It was found that by increasing the oleylamine to CH3NH3PbBr3 perovskite ratio (OPR), the photoluminescence wavelengths of CH3NH3PbBr3 nanocrystals could be varied from 505nm (green) to 450nm (blue). The change in emission wavelength is associated with a morphology change from nanoplatelets of ∼10nm width at OPR<1 to nanoparticles of ∼3nm diameter at OPR>1. It is suggested that the morphology change of nanocrystals is a result of geometric packing constraint of the sizes of oleylamine and PbBr3 octahedra. The nanocrystals with OPR=0.75 maintain photoluminescence property for more than 6months in ambient condition and can sustain temperature of 150°C for 30min.

Heterozygosities and allelic frequencies of 811 dinucleotide-repeat marker loci in the Taiwanese population.

To evaluate basic informativeness of commercially available microsatellite markers in theTaiwanese population, 190 unrelated Taiwanese children were genotyped using ABI PRISM Linkage Mapping Set-HD5. The average heterozygosity in Taiwanese was slightly lower than that in Caucasians among these 811 microsatellite markers. There were 50 marker loci with heterozygosities lower than 50%. Moreover, allelic distributions at many of the loci were significantly different in two ethnic groups. The results reported here represent a valuable database for disease genes mapping in the Taiwanese population. This database can be easily accessed at the Web site of Vita Genomics, Inc. (http://www.vitagenomics.com/str.html).