Ambient Degradation Anisotropy and Mechanism of van der Waals Ferroelectric NbOI2.

The spontaneous centrosymmetry-breaking and robust room-temperature ferroelectricity in niobium oxide dihalides spurs a flurry of explorations into its promising second-order nonlinear optical properties, and promises potential applications in nonvolatile electro-optical and optoelectronic devices. However, the ambient stability of the niobium oxide dihalides remains questionable, which overshadows their future development. In this work, the chemical degradation of NbOI2 is comprehensively investigated using combined chemical and optical microscopies in conjunction with spectroscopies. We unveil the highly anisotropic degradation kinetics of NbOI2 driven by the hydrolysis process of the unstable dangling iodine bonds dominantly on the (010) facet and progressing along the c axis. Knowing its degradation mechanism, the NbOI2 flake can then be stabilized by the hexagonal boron nitride encapsulation, which isolates the air moisture. These findings provide direct insights into the ambient instability of NbOI2, and they deliver possible solutions to circumvent this issue, which are essential for its practical integration in photonic and electronic devices.

Unconventional polarization fatigue in van der Waals layered ferroelectric ionic conductor CuInP2S6.

Recent progress in two-dimensional ferroelectrics greatly expands the versatility and tunability in van der Waals heterostructure based electronics. However, the switching endurance issue that widely plagues conventional ferroelectrics in practical applications is hitherto unexplored for van der Waals layered ferroelectrics. Herein, we report the observation of unusual polarization fatigue behaviors in van der Waals layered CuInP2S6, which also possesses finite ionic conductivity at room temperature. The strong intertwinement of the short-range polarization switching and long-range ionic movement in conjunction with the van der Waals layered structure gives rise to unique morphological and polarization evolutions under repetitive electric cycles. With the help of concerted chemical, structural, lattice vibrational and dielectric analyses, we unravel the critical role of the synergy of ionic migration and surface oxidation on the anomalous polarization enhancement and the eventual polarization degradation. This work provides a general insight into the polarization fatigue characteristics in ionically-active van der Waals ferroelectrics and delivers potential solutions for the realization of fatigue-free capacitors.

Efficient Solar Desalination of Seawater Using a Novel Carbon Nanotube-Based Composite Aerogel.

Solar desalination of seawater is an effective approach to address the scarcity of freshwater resources. For solar steam generation, it is critical to design biodegradable, sustainable, low-cost, and high-evaporation-rate technology. This study aims to develop a novel solar desalination technology by designing and fabricating a nanocomposite material with excellent light absorption and thermal conversion properties. We designed a double-layer aerogel structure, which uses naturally abundant carboxymethyl cellulose (CMC) as the basic skeleton to achieve sustainability and biodegradability, and uses carbon nanotubes as the photothermal material for efficient light absorption to prepare a ferric tannate/carbon nanotube/carboxymethyl cellulose composite aerogel (FT-CNT-CMC aerogel). Experimental results demonstrate that the FT-CNT-CMC aerogel exhibits a high light absorption rate of 96-98% within the spectral range of 250-2400 nm, showcasing remarkable photothermal conversion performance. Under a sun intensity of 1 kW·m-2, the FT-CNT-CMC aerogel achieves a significant evaporation rate of 1.942 kg·m-2·h-1 at room temperature. Moreover, the excellent performance of the FT-CNT-CMC aerogel is validated in practical seawater desalination and organic dye wastewater purification. The FT-CNT-CMC aerogel exhibits a retention rate exceeding 99% for Na+, Mg2+, K+, and Ca2+ ions in simulated seawater, while no characteristic absorption peaks are observed in methylene blue and rhodamine B dye solutions after purification. These findings highlight the promising potential of the FT-CNT-CMC aerogel in the field of novel solar desalination, providing a viable solution to obtain freshwater.

Silicon-Based Superslippery/Superhydrophilic Striped Surface for Highly Efficient Fog Harvesting.

Fog-harvesting performance is influenced by surface wettability, patterned structure and the heat transfer coefficient. In this work, we have prepared different surfaces with a stripe array of superhydrophilic, superslippery and superslippery/superhydrophilic surfaces for fog harvesting on silicon substrates using photolithography and silver-assisted chemical etching. The surface wettability and heat transfer coefficients of the above samples have been investigated. We analyzed the contact angle, sliding angle and transport state of droplets on these surfaces. The fog-harvesting rate of all samples under different voltages of the cooling pad (V = 0, 2.0, 2.5, 3.0, 3.5 V) was measured. Results showed that the superslippery/superhydrophilic striped surface could achieve rapid droplet nucleation, directional transport and efficient collection due to its superhydrophilic striated channels and the Laplace pressure difference between different wettability regions. At a condensation voltage of 3.5 V, the fog-harvesting rate efficiencies of the uniformly striped superhydrophilic and superslippery surface were 1351 mg·cm-2·h-1 and 1265 mg·cm-2·h-1, respectively, while the fog-harvesting rate of the superslippery/superhydrophilic striped surface was 1748 mg·cm-2·h-1. Compared with the original silicon surface, the maximum fog-harvesting rate of the superslippery/superhydrophilic striped surface was improved by 86.9%. This study offers significant insights into the impact of heat transfer and silicon surface wettability on the process of fog collection.

A highly sensitive sensor for carcinoembryonic antigen based on AlGaN/GaN high-electron-mobility transistors.

Carcinoembryonic antigen (CEA) is a well-known biomarker and validated serum biomarker for lung cancer. We introduce a simple label-free method for CEA detection. Specific recognition of CEA was made possible by immobilizing CEA antibodies in the sensing region of AlGaN/GaN high-electron-mobility transistors. The biosensors have a detection limit of 1 fg ml-1in phosphate buffer solution. This approach has advantages of integration, miniaturization, low cost, and rapid detection compared to other testing methods for lung cancer and could be used in future medical diagnostics.

Switchable RAFT Polymerization Employing Photoresponsive HABI as a Mediator.

Recently, considerable interest has been devoted to developing switchable reversible addition fragmentation chain transfer (RAFT) polymerizations via photoactivation methods. Herein, a photo-deactivation strategy is introduced to regulate RAFT polymerization using photoresponsive hexaarylbiimidozole (HABI) as a mediator, which leads to switchable RAFT polymerization by repeated ON/OFF experiments. In comparison with well-known PET-RAFT polymerization, photo-deactivation RAFT (PD-RAFT) polymerization can be temporally stopped with UV light ON, where photoresponsive HABI can reversibly quench propagating radicals, resulting in switchable RAFT polymerization. The proposed mechanism of PD-RAFT polymerization in the presence of HABI involving radical quenching is based on ESR, NMR, GPC, MALDI-TOF-MS, and kinetics studies.

Self-Enhancing Photoelectrochemical Properties in van der Waals Ferroelectric CuInP2S6 by Photoassisted Acid Hydrolysis.

Transition metal thiophosphate, CuInP2S6 (CIPS), has recently emerged as a potentially promising material for photoelectrochemical (PEC) water splitting due to its intrinsic ferroelectric polarization for spontaneous photocarrier separation. However, the poor kinetics of the hydrogen evolution reaction (HER) greatly limits its practical applications. Herein, we report self-enhancing photocatalytic behavior of a CIPS photocathode due to chemically driven oxygen incorporation by photoassisted acid oxidation. The optimal oxygen-doped CIPS demonstrates a >1 order of magnitude enhancement in the photocurrent density compared to that of pristine CIPS. Through comprehensive spectroscopic and microscopic investigations combined with theoretical calculations, we disclose that oxygen doping will lower the Fermi level position and decrease the HER barrier, which further accelerates charge separation and improves the HER activity. This work may deliver a universal and facile strategy for improving the PEC performance of other van der Waals metal thiophosphates.

Normal Force-Induced Highly Efficient Mechanical Sterilization of GaN Nanopillars.

Bacterial residue is one of the main causes of diseases and economic losses. In recent years, microfabrication technology has inspired the introduction of microstructures on the surfaces of relevant materials to provide antibacterial effects. This antibacterial method has become a popular research topic due to its safety, effectiveness, and stability. However, its exact mechanism is still under debate. In this study, normal force was introduced to bacteria on GaN nanopillars to investigate the mechanical sterilization effects and a computer simulation was conducted. The results show that the normal force induces highly efficient mechanical sterilization of the nanopillars, and their surfaces impede the attachment of bacteria. This study provides insights into the antibacterial effect of nanopillars and offers a potential antibacterial tool with high efficiency.

Black Phosphorus Nanoparticles Promote Osteogenic Differentiation of EMSCs Through Upregulated TG2 Expression.

At bio-safe concentrations, black phosphorus nanoparticles activated TG2, and promote the expression of ECM, which further promoted osteogenic differentiation of EMSCs. From these results, we can conclude that black phosphorus nanoparticles are suitable as biological factors in bone tissue engineering. Black phosphorus nanoparticles (BPs) present excellent biocompatibility and good biodegradability, which have been rigorously studied and proven. However, its utilization in bone tissue engineering fields is still in its infancy. Thus, the main purpose of the present study was to investigate the effects of BPs on osteogenic differentiation of ectodermal mesenchymal stem cell (EMSC) in vitro. Biocompatible BPs with high yield were prepared with a simple and efficient ultrasonication technique. EMSCs were isolated from adult rat nasal respiratory mucosa. Then, we treated EMSCs with BPs at different concentrations in vitro and examined the effect of BPs on osteogenic differentiation of EMSCs. In addition, inhibitor of transglutaminase 2 (TG2) and western blot were used to clarify the mechanism of the promoting effect of BPs on osteogenesis. Our results indicated that BPs could significantly enhance osteogenic differentiation of EMSCs in vitro. Nevertheless, BPs had no effect on EMSCs proliferation. Mechanistically, BPs promoted osteogenesis differentiation of EMSCs through upregulating TG2 expression. These results highlight the advantage of using chemical materials for novel engineering strategies of these highly promising small molecules for bone-tissue regeneration.

Copper-assisted catalyzed etching for nanotextured black silicon with enhanced photoelectric-conversion properties.

Black silicon contains high-aspect-ratio micro/nanostructures with greatly suppressed front-surface reflection, thus possessing superior property in photoelectric devices. In this report, by a two-step copper-assisted chemical etching method, we have fabricated pyramid n+p-black silicon with optimized morphology and anti-reflectance capability, through systematically tuning the concentration of both copper ions and reducing agents, as well as the etching time. The improved optical absorption and superior charge transfer kinetics validate n+p-black silicon as a highly active photocathode in photoelectrochemical cells. The onset potential of 0.21 V vs. RHE and the saturation photocurrent density of 32.56 mA/cm2 are achieved in the optimal n+p-black silicon. In addition, the nanoporous structure with lower reflectance is also achieved in planar p-silicon via the same etching method. Moreover, the photodetectors based on planar p-black silicon show significantly enhanced photoresponsivity over a broad spectral range. This study offers a low-cost and scalable strategy to improve the photoelectric-conversion efficiency in silicon-based devices.

Effect of polarization rotation on the optical and photovoltaic properties of BiFeO3thin films.

Visible-light-active ferroelectric materials are gaining increasing attention due to the unique ferroelectric photovoltaic effect. To boost the light harvesting capability, vast research is devoted to band gap engineering by chemical substitutions, regardless of the side effect on ferroelectric polarization. Here, we focus on how polar order affects the optical and photovoltaic properties. Using BiFeO3as the model system, we induce the polarization rotation by A-site La substitution, which results in continuous reduction of optical anisotropy of the samples, as revealed by the concerted optical characterizations. This further causes the decrease of angular dependence of ferroelectric photovoltaic effect on the light polarization. The results demonstrate the inner connection of the ferroelectric polarization and optical anisotropy via the lattice degree of freedom.

Using One Photoredox Catalyst to Simultaneously Mediate Two Different Polymerizations for Photo-Triggered Multi-Component Orthogonal Polymerizations.

The development of multi-component orthogonal polymerizations (MOPs) with simple procedure and high efficiency is crucial for rational polymer synthesis. In this work, photo-triggered Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization are first investigated, employing copper(II) thioxanthone carboxylate (Cu(TX)2 ) as photoredox catalyst and sunlight as stimuli. Then, the novel MOPs using one photoredox catalyst, Cu(TX)2 to simultaneously mediate two different photopolymerizations, are successfully realized in one-pot, where photo-induced electron transfer atom transfer radical polymerization and photo-activated CuAAC polymerization can effectively proceed in a one-pot and non-interfering fashion to afford predetermined copolymers with well-defined structure.

Epitaxial growth and interfacial property of monolayer MoS2 on gallium nitride.

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) on semiconductor substrates are important for next-generation electronics and optoelectronics. In this study, we demonstrate the growth of monolayer MoS2 on a lattice-matched gallium nitride (GaN) semiconductor substrate by chemical vapor deposition (CVD). The monolayer MoS2 triangles exhibit optical properties similar to that of typical single-crystal MoS2 sheets, as verified by the Raman, photoluminescence, and morphological characterizations. The Raman and PL features and their intensity mappings suggest that the as-grown MoS2 on GaN substrate can achieve high quality and uniformity, demonstrating that GaN substrate is favorable for 2D MoS2 growth. Moreover, the interfacial property and stacking structure were investigated by first-principles density functional theory (DFT) calculations to confirm the interlayer interactions of monolayer MoS2 on GaN. Accordingly, the ability to grow high quality monolayer MoS2 on semiconductor GaN substrate would open a new route toward the synthesis of hetero and composite structures for promising electronic and optoelectronic device applications.

Fabrication of carbon quantum dots with nano-defined position and pattern in one step via sugar-electron-beam writing.

Quantum dots (QDs) are promising materials in nanophotonics, biological imaging, and even quantum computing. Precise positioning and patterning of QDs is a prerequisite for realizing their actual applications. Contrary to the traditional two discrete steps of fabricating and positioning QDs, herein, a novel sugar-electron-beam writing (SEW) method is reported for producing QDs via electron-beam lithography (EBL) that uses a carefully chosen synthetic resist, poly(2-(methacrylamido)glucopyranose) (PMAG). Carbon QDs (CQDs) could be fabricated in situ through electron beam exposure, and the nanoscale position and luminescence intensity of the produced CQDs could be precisely controlled without the assistance of any other fluorescent matter. We have demonstrated that upon combining an electron beam with a glycopolymer, in situ production of CQDs occurs at the electron beam spot center with nanoscale precision at any place and with any patterns, an advancement that we believe will stimulate innovations in future applications.

Regenerable-Catalyst-Aided, Opened to Air and Sunlight-Driven "CuAAC&ATRP" Concurrent Reaction for Sequence-Controlled Copolymer.

An ideal stimuli-responsive controlled/living radical polymerization should have the ability to manipulate the reaction through spatiotemporal "on/off" controls, achieving the polymerization under fully open conditions and allowing for precise control over macromolecular architecture with defined molecular weights and monomer sequence. In this contribution, the photo (sunlight)-induced electron transfer atom transfer radical-polymerization (PET-ATRP) can be realized to be reversibly activated and deactivated under fully open conditions utilizing one-component copper(II) thioxanthone carboxylate as multifunctional photocatalyst and oxygen scavenger. The polymerization behaviors are investigated, presenting controlled features with first-order kinetics and linear relationships between molecular weights and monomer conversions. More importantly, "CuAAC&ATRP" concurrent reaction combining PET-ATRP, photodriven deoxygenation, and photoactivated CuAAC click reaction is successfully employed to synthesize the sequence-defined multiblock functional copolymers, in which the iterative monomer additions can be easily manipulated under fully open conditions.

Controllable Hierarchical Surface Patterns of Supramolecular Hydrogels: Harnessing Buckling Instability by Confinement.

Patterned surfaces of responsive polymers find applications in diverse fields. However, it is still a great challenge to fabricate hierarchical patterns with long-range orders. Herein controllable hierarchical surface patterns that can be fabricated by combining nanoembossing techniques with the surface instability of supramolecular hydrogels are presented. Nanoembossed nanostripe arrays of polyethylene glycol (PEG)-based polyurethane-urea supramolecular hydrogels are fabricated and exposed to water, whereby the lateral expansion of nanostripes is confined and leads to the formation of folded in-plane or out-of-plane patterns depending on the aspect ratios. The direction of folds is perpendicular to the nanostripes. Both the amplitude and the wavelength of out-of-plane folds are proportional to the thickness of nanostripes. Therefore, hierarchical structures, in which one periodicity is defined by the nanoembossing processes and the other is determined by surface buckling, can be quickly fabricated in supramolecular hydrogel thin films.

Internalized compartments encapsulated nanogels for targeted drug delivery.

Drug delivery systems inspired by natural particulates hold great promise for targeted cancer therapy. An endosome formed by internalization of plasma membrane has a massive amount of membrane proteins and receptors on the surface, which is able to specifically target the homotypic cells. Herein, we describe a simple method to fabricate an internalized compartments encapsulated nanogel with endosome membrane components (EM-NG) from source cancer cells. Following intracellular uptake of methacrylated hyaluronic acid (m-HA) adsorbed SiO2/Fe3O4 nanoparticles encapsulating a crosslinker and a photoinitiator, EM-NG was readily prepared through in situ crosslinking initiated under UV irradiation after internalization. The resulting nanogels loaded with doxorubicin (DOX) displayed enhanced internalization efficiency to the source cells through a specific homotypic affinity in vitro. However, when treated with the non-source cells, the EM-NGs exhibited insignificant difference in therapeutic efficiency compared to a bare HA nanogel with DOX. This study illustrates the potential of utilizing an internalized compartments encapsulated formulation for targeted cancer therapy, and offers guidelines for developing a natural particulate-inspired drug delivery system.

Reduced graphene oxide directed self-assembly of phospholipid monolayers in liquid and gel phases.

The response of cell membranes to the local physical environment significantly determines many biological processes and the practical applications of biomaterials. A better understanding of the dynamic assembly and environmental response of lipid membranes can help understand these processes and design novel nanomaterials for biomedical applications. The present work demonstrates the directed assembly of lipid monolayers, in both liquid and gel phases, on the surface of a monolayered reduced graphene oxide (rGO). The results from atomic force microscopy indicate that the hydrophobic aromatic plane and the defect holes due to reduction of GO sheets, along with the phase state and planar surface pressure of lipids, corporately determine the morphology and lateral structure of the assembled lipid monolayers. The DOPC molecules, in liquid phase, probably spread over the rGO surface with their tails associating closely with the hydrophobic aromatic plane, and accumulate to form circles of high area surrounding the defect holes on rGO sheets. However, the DPPC molecules, in gel phase, prefer to form a layer of continuous membrane covering the whole rGO sheet including defect holes. The strong association between rGO sheets and lipid tails further influences the melting behavior of lipids. This work reveals a dramatic effect of the local structure and surface property of rGO sheets on the substrate-directed assembly and subsequent phase behavior of the supported lipid membranes.

A novel method to encapsulate a Au nanorod array in 15 nm radius multiwalled carbon nanotubes.

In this paper we demonstrate a novel complex array structure comprising well-aligned Au nanorods (10 nm in diameter) encapsulated inside 15 nm radius multiwalled carbon nanotubes (MWCNTs). A pre-aligned and open-ended nanoporous MWCNT membrane is used as the starting material. Au nanorods are precisely deposited and aligned inside the hollow channels of CNTs by inter-diffusing the HAuCl4 precursor and the reductant solution. Ultra-long Au nanowires and spherical Au nanoparticles are also observed in the CNT cavity with the same diameter in special cases. Using high-resolution TEM (HRTEM), scanning transmission electron microscopy (STEM), 3-dimensional TEM (3D-TEM) and energy dispersive X-ray spectroscopy (EDX), the precise location and composition of the encapsulated Au components with various structures are confirmed. This aligned Au@CNT endohedral material has important potential applications in nanocatalysis, waveguides, as well as in novel plasmonic devices.

Guiding the behaviors of human umbilical vein endothelial cells with patterned silk fibroin films.

Silk fibroin is an ideal blood vessel substitute due to its advantageous qualities including variable size, good suture retention, low thrombogenicity, non-toxicity, non-immunogenicity, biocompatibility, and controllable biodegradation. In this study, silk fibroin films with a variety of surface patterns (e.g. square wells, round wells plus square pillars, square pillars, and gratings) were prepared for in vitro characterization of human umbilical vein endothelial cell's (HUVEC) response. The affects of biomimetic length-scale topographic cues on the cell orientation/elongation, proliferation, and cell-substrate interactions have been investigated. The density of cells is significantly decreased in response to the grating patterns (70±3nm depth, 600±8nm pitch) and the square pillars (333±42nm gap). Most notably, we observed the contact guidance response of filopodia of cells cultured on the surface of round wells plus square pillars. Overall, our data demonstrates that the patterned silk fibroin films have an impact on the behaviors of human umbilical vein endothelial cells.