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Ni-rich layered LiNi0·6Co0·2Mn0·2O2 materials have recently drawn much attention for their high specific capacity. However, they still suffer from the cycling instability arising from Li+/Ni2+ ions mixing in crystal structure and harmful side reactions with electrolyte, especially charged at high cut-off voltage to achieve higher energy density. In this study, the Li(Ni0·6Co0·2Mn0.2)O2 (NCM622) cathode materials were prepared by sol-gel method, and Ce4+ modification was utilized to improve cycling stability and rate performance. Through XRD refinement, XPS, SEM and TEM characterization, it was found that in the case of 0.5 at% level, Ce4+ ions not only entered into the crystal lattice to replace transition metal ions, but also produced CeO2 coating on the surface of NCM622 particles. The results of electrochemical performance showed that after 100 cycles at 1 C rate, the capacity retention of NCM-0.5 sample increased by 11.03% compared to pristine sample. Besides, in the case of 5 C, the capacity of NCM-0.5 sample reached to 114.92 mAh·g−1, much higher than that of NCM-0 (91.92 mAh·g−1). The findings indicate that it is the synergistic effect of Ce4+ that endows NCM622 excellent cycling stability and rate performance at high cut-off voltage.

We report a ReSe2 passively mode-locked composite YVO4/Nd:YVO4 laser at 1.06 μm, which can stably generate pure continuous-wave mode-locking (CWML) operation at watt-level output. ReSe2, as a new type of 2-D transition metal dichalcogenides (TMDs), has the features of weak-layered dependence, broadband saturable absorption, low modulation depth and saturation intensity, which is beneficial to initiate robust CWML mechanism via nonlinear saturable absorption. By employing few-layered ReSe2 as saturable absorber, the nanosecond mode-locked pulses at fundamental repetition rate of 90.37 MHz was obtained experimentally in a composite YVO4/Nd:YVO4 laser. The maximum output power in pure CWML operation was as high as 1.1 W. The high-power CWML laser source shows potential applications in time-resolved spectroscopy, telecommunication and detection.

Trigonal tellurium (Te) is a chiral semiconductor that lacks both mirror and inversion symmetries, resulting in complex band structures with Weyl crossings and unique spin textures. Detailed time-resolved polarized reflectance spectroscopy is used to investigate its band structure and carrier dynamics. The polarized transient spectra reveal optical transitions between the uppermost spin-split H4 and H5 and the degenerate H6 valence bands (VB) and the lowest degenerate H6 conduction band (CB) as well as a higher energy transition at the L-point. Surprisingly, the degeneracy of the H6 CB (a proposed Weyl node) is lifted and the spin-split VB gap is reduced upon photoexcitation before relaxing to equilibrium as the carriers decay. Using ab initio density functional theory (DFT) calculations, we conclude that the dynamic band structure is caused by a photoinduced shear strain in the Te film that breaks the screw symmetry of the crystal. The band-edge anisotropy is also reflected in the hot carrier decay rate, which is a factor of two slower along the c-axis than perpendicular to it. The majority of photoexcited carriers near the band-edge are seen to recombine within 30 ps while higher lying transitions observed near 1.2 eV appear to have substantially longer lifetimes, potentially due to contributions of intervalley processes in the recombination rate. These new findings shed light on the strong correlation between photoinduced carriers and electronic structure in anisotropic crystals, which opens a potential pathway for designing novel Te-based devices that take advantage of the topological structures as well as strong spin-related properties., The complex band structure and carrier decay response upon photoexcitation of the chiral semiconductor tellurium remain to be unveiled. Here, the authors report unusual dynamic band modifications in Te near band-edge structure due to photoinduced symmetry breaking and strong anisotropy in carrier decay dynamics.

The outstanding ability of optical metasurfaces to tailor light's amplitude, phase, and polarization with a subwavelength resolution has attracted big interest. A multifunctional metasurface device is reported and experimentally demonstrated that integrates an arbitrary polarization profile for image concealment and a computer‐generated hybrid hologram. Herein, a high‐resolution image is hidden in the polarization profile of the light beam, while the holographic images are encoded in its phase profile for the reconstruction of two different types of holographic images. The designed polarization profile is realized based on the superposition of two different phase profiles for circular polarization states with opposite handedness. This method can further extend the design degree of freedom in optical metasurfaces, which may open an alternative avenue for anticounterfeiting, optical image encoding, and optical information security.

Piezoelectric nanogenerators have attracted intensive interest in harvesting the stray mechanical energy in the environment to power miniaturized electronics and sensors. However, their efficient integration into systems and compatibility with existing technologies for practical applications remains challenging. Here, we report for the first time the systematic, data-driven learning of the process-property-performance relation in ZnO nanowires piezoelectric nanogenerators that are synthesized and integrated through a laser-induced chemical process. An experiment-derived behavioral model was established to reveal the apparent connections between the production parameters and the output performance of the ZnO piezoelectric nanogenerator. We further demonstrated the application of such knowledge for integrating the optimized ZnO nanowires piezoelectric nanogenerator with a photosensor into a self-powered sensor system, exhibiting the potential for future system-level improvements.

We propose a reflective terahertz (THz) metalens with four focal points for polarization detection of THz beams. The metalens is composed of Z -shaped resonators with spatially variant orientations, a reflective gold layer, and a dielectric spacer between them. The polarization states of the focal points include left circular polarization, right circular polarization, an incident polarization state, and a polarization state whose major axis is rotated π / 4 in comparison with that of the incident polarization. The handedness, ellipticity, and major axis of the polarization state can be determined based on the light intensities of the focal points. The uniqueness of the designed device renders this technique very attractive for applications in compact THz polarization detection and information processing.

Flexible electronic devices involve electronic circuits fabricated onto a flexible (e.g., polymer) substrate, and they have many important applications. However, during their use, they often need to go through repeated deformations (such as bending). This may generate cracks in metallic components that often exist in a flexible electronic device and could obviously affect the device durability and reliability. Carbon nanotubes (CNTs) have a potential to enhance the metal fatigue properties. However, the previous work on the fabrication of CNT–metal composites onto a flexible substrate has been limited. This paper reports the research work on a novel laser-based approach to fabricate CNT–metal composites onto a flexible substrate, where mixtures containing CNTs and metal (silver) nanoparticles (NPs) are deposited onto the substrate through a dispensing device and then laser-sintered into CNT–metal composites. Under the studied conditions and for the tested samples, it has been found that overall the addition of CNTs has significantly enhanced the bending fatigue properties of the laser-sintered material without degrading the material electrical conductivity (which has actually been slightly increased). The laser-based approach has several potential advantages, such as the local, precise, and flexible production of CNT–metal composite patterns with small or little thermal effects to the flexible substrate and other surrounding regions, and without using a mask or vacuum. Future work is certainly still needed on this novel fabrication process.

Recent advances achieved in triboelectric nanogenerators (TENG) focus on boosting power generation and conversion efficiency. Nevertheless, obstacles concerning economical and biocompatible utilization of TENGs continue to prevail. Being an abundant natural biopolymer from marine crustacean shells, chitosan enables exciting opportunities for low-cost, biodegradable TENG applications in related fields. Here, the development of biodegradable and flexible TENGs based on chitosan is presented for the first time. The physical and chemical properties of the chitosan nanocomposites are systematically studied and engineered for optimized triboelectric power generation, transforming the otherwise wasted natural materials into functional energy devices. The feasibility of laser processing of constituent materials is further explored for the first time for engineering the TENG performance. The laser treatment of biopolymer films offers a potentially promising scheme for surface engineering in polymer-based TENGs. The chitosan-based TENGs present efficient energy conversion performance and tunable biodegradation rate. Such a new class of TENGs derived from natural biomaterials may pave the way toward the economically viable and ecologically friendly production of flexible TENGs for self-powered nanosystems in biomedical and environmental applications.

The reliable production of two-dimensional (2D) crystals is essential for the development of new technologies based on 2D materials. However, current synthesis methods suffer from a variety of drawbacks, including limitations in crystal size and stability. Here, we report the fabrication of large-area, high-quality 2D tellurium (tellurene) using a substrate-free solution process. Our approach can create crystals with process-tunable thickness, from a monolayer to tens of nanometres, and with lateral sizes of up to 100 µm. The chiral-chain van der Waals structure of tellurene gives rise to strong in-plane anisotropic properties and large thickness-dependent shifts in Raman vibrational modes, which is not observed in other 2D layered materials. We also fabricate tellurene field-effect transistors, which exhibit air-stable performance at room temperature for over two months, on/off ratios on the order of 106, and field-effect mobilities of about 700 cm^2 V^(−1) s^(−1). Furthermore, by scaling down the channel length and integrating with high-k dielectrics, transistors with a significant on-state current density of 1 A mm^(−1) are demonstrated.

Exploring efficient electrocatalysts for hydrogen production is one of the most promising pathways to face the energy crisis in the new century. Herein, we highlight metallic molybdenum nitride (MoN) nanosheets with atomic thickness as highly efficient platinum-free electrocatalysts for the hydrogen evolution reaction (HER). Theoretical calculations demonstrate that the atomically-thin MoN nanosheets show metallic behavior, which can effectively facilitate electron transport during the catalytic process. Structural analyses reveal that the surfaces of the atomically-thin MoN nanosheets are wholly comprised of apical Mo atoms, thus providing an ideal material prototype to reveal the role of Mo atoms during HER catalysis. Through detailed investigations of the HER activity, the active surface sites of the atomically-thin MoN nanosheets are identified, of which the surface Mo atoms can act as the active sites for transforming protons into hydrogen. This novel mechanism will not only broaden our vision on understanding the HER mechanism for other Mo-based electrocatalysts, but also benefit the exploration and optimization of advanced catalysts for future energy production.

We have recently reported that mouse embryonic stem cells (mESCs) are deficient in expressing type I interferons (IFNs) in response to viral infection and synthetic viral RNA analogs (Wang, R., Wang, J., Paul, A. M., Acharya, D., Bai, F., Huang, F., and Guo, Y. L. (2013) J. Biol. Chem. 288, 15926–15936). Here, we report that mESCs are able to respond to type I IFNs, express IFN-stimulated genes, and mediate the antiviral effect of type I IFNs against La Crosse virus and chikungunya virus. The major signaling components in the IFN pathway are expressed in mESCs. Therefore, the basic molecular mechanisms that mediate the effects of type I IFNs are functional in mESCs; however, these mechanisms may not yet be fully developed as mESCs express lower levels of IFN-stimulated genes and display weaker antiviral activity in response to type I IFNs when compared with fibroblasts. Further analysis demonstrated that type I IFNs do not affect the stem cell state of mESCs. We conclude that mESCs are deficient in type I IFN expression, but they can respond to and mediate the cellular effects of type I IFNs. These findings represent unique and uncharacterized properties of mESCs and are important for understanding innate immunity development and ESC physiology.

We have recently reported that mouse embryonic stem cells (mESCs) are deficient in expressing type I interferons (IFN) when exposed to viral infection and double-stranded RNA. In this study, we extended our investigation and demonstrated that single-stranded RNA and protein-encoding mRNA can induce strong IFN expression and cytotoxicity in fibroblasts and epithelial cells, but none of the effects associated with these antiviral responses were observed in mESCs. Our results provided additional data to support the conclusion that mESCs are intrinsically deficient in antiviral responses. While our findings represent a novel feature of mESCs that in itself is important for understanding innate immunity development, we exploited this property to develop a novel mRNA-mediated gene expression cell model. Direct introduction of synthetic mRNA to express desired genes has been shown as an effective alternative to DNA/viral vector-based gene expression. However, a major biological challenge is that a synthetic mRNA is detected as a viral RNA analog by the host cell, resulting in a series of adverse effects associated with antiviral responses. We demonstrate that the lack of antiviral responses in mESCs effectively avoids this problem. mESCs can tolerate repeated transfection and effectively express proteins from their synthetic mRNA with expected biological functions, as demonstrated by the expression of green fluorescent protein and the transcription factor Etv2. Therefore, mRNA-based gene expression could be developed into a novel ESC differentiation strategy that avoids safety concerns associated with viral/DNA-based vectors in regenerative medicine.

We present, by simulations, a metastructured graphene/liquid crystal hybrid tuning terahertz perfect absorber that consists of graphene disk resonator arrays above a metallic layer separated with liquid crystal substrate. The liquid crystal refractive index and the graphene Fermi level are utilized to implement double-tuning operation to push the spectra scanning limit of the terahertz absorber. Our simulations demonstrate high performance of a near-linear broad tuning region and near-unity absorbance with wide incident angle and polarization independence. The range of the resonant frequency scan is notably enlarged at a spectral ratio of as high as Δf/f=50% while ensuring absorbance beyond 90%. Such graphene/liquid crystal hybrid tuning scheme would be preferable to push the working-band limit of terahertz perfect absorbers.

Defect-rich MoS2 ultrathin nanosheets are synthesized on a gram scale for electrocatalytic hydrogen evolution. The novel defect-rich structure introduces additional active edge sites into the MoS2 ultrathin nanosheets, which significantly improves their electrocatalytic performance. Low onset overpotential and small Tafel slope, along with large cathodic current density and excellent durability, are all achieved for the novel hydrogen-evolution-reaction electrocatalyst.

Embryonic stem cells (ESCs) are considered to be a promising cell source for regenerative medicine because of their unlimited capacity for self-renewal and differentiation. However, little is known about the innate immunity in ESCs and ESC-derived cells. We investigated the responses of mouse (m)ESCs to three types of live viruses as follows: La Crosse virus, West Nile virus, and Sendai virus. Our results demonstrated mESCs were susceptible to viral infection, but they were unable to express type I interferons (IFNα and IFNβ, IFNα/β), which differ from fibroblasts (10T1/2 cells) that robustly express IFNα/β upon viral infections. The failure of mESCs to express IFNα/β was further demonstrated by treatment with polyIC, a synthetic viral dsRNA analog that strongly induced IFNα/β in 10T1/2 cells. Although polyIC transiently inhibited the transcription of pluripotency markers, the stem cell morphology was not significantly affected. However, polyIC can induce dsRNA-activated protein kinase in mESCs, and this activation resulted in a strong inhibition of cell proliferation. We conclude that the cytosolic receptor dsRNA-activated protein kinase is functional, but the mechanisms that mediate type I IFN expression are deficient in mESCs. This conclusion is further supported by the findings that the major viral RNA receptors are either expressed at very low levels (TLR3 and MDA5) or may not be active (retinoic acid-inducible gene I) in mESCs.

The innate immunity of embryonic stem cells (ESCs) has recently emerged as an important issue in ESC biology and in ESC-based regenerative medicine. We have recently reported that mouse ESCs (mESCs) do not have a functional type I interferon (IFN)-based antiviral innate immunity. They are deficient in expressing IFN in response to viral infection and have limited ability to respond to IFN. Using fibroblasts (FBs) as a cell model, the current study investigated the development of antiviral mechanisms during in vitro differentiation of mESCs. We demonstrate that mESC-differentiated FBs (mESC-FBs) share extensive similarities with naturally differentiated FBs in morphology, marker expression, and growth pattern, but their development of antiviral mechanisms lags behind. Nonetheless, the antiviral mechanisms are inducible during mESC differentiation as demonstrated by the transition of nuclear factor kappa B (NFκB), a key transcription factor for IFN expression, from its inactive state in mESCs to its active state in mESC-FBs and by increased responses of mESC-FBs to viral stimuli and IFN during their continued in vitro propagation. Together with our previously published study, the current data provide important insights into molecular basis for the deficiency of IFN expression in mESCs and the development of antiviral innate immunity during mESC differentiation.

Embryonic stem cells (ESCs) have unlimited capacity for self-renewal and can differentiate into various cell types when induced. They also have an unusual cell cycle control mechanism driven by constitutively active cyclin dependent kinases (Cdks). In mouse ESCs (mESCs). It is proposed that the rapid cell proliferation could be a necessary part of mechanisms that maintain mESC self-renewal and pluripotency, but this hypothesis is not in line with the finding in human ESCs (hESCs) that the length of the cell cycle is similar to differentiated cells. Therefore, whether rapid cell proliferation is essential for the maintenance of mESC state remains unclear. We provide insight into this uncertainty through chemical intervention of mESC cell cycle. We report here that inhibition of Cdks with olomoucine II can dramatically slow down cell proliferation of mESCs with concurrent down-regulation of cyclin A, B and E, and the activation of the Rb pathway. However, mESCs display can recover upon the removal of olomoucine II and are able to resume normal cell proliferation without losing self-renewal and pluripotency, as demonstrated by the expression of ESC markers, colony formation, embryoid body formation, and induced differentiation. We provide a mechanistic explanation for these observations by demonstrating that Oct4 and Nanog, two major transcription factors that play critical roles in the maintenance of ESC properties, are up-regulated via de novo protein synthesis when the cells are exposed to olomoucine II. Together, our data suggest that short-term inhibition of cell proliferation does not compromise the basic properties of mESCs.

We report a compact triple-band tunable perfect terahertz metamaterial absorber (TMA) at the subwavelength scale of thickness, which is composed of a planar metallic disk resonator array above a conductive ground plane separated with liquid crystal (LC) mixture. The calculations of terahertz absorption spectra demonstrate triple near-unity absorption bands in the gap plasmonic resonance coupling regime. Three resonance frequencies of the absorber exhibit continuous linear-tunability as changing the refractive index of LC. Remarkably, each peak absorbance of the triple bands maintains at a level of beyond 99% in the whole tuning operation, and the absorbance can remain more than 90% over a wide range of incident angles. Our work suggests that the LC tunable absorber scheme has the potential to overcome the basic difficulty to perform simultaneously multiband spectral tuning and near-unity absorbance with wide angle of incidence and weak polarization dependence. The proposed LC-tunable multiband perfect TMA is promising in the application of biomolecular spectra-selective terahertz imaging and sensing.

Embryonic stem cells (ESCs) represent a promising cell source for regenerative medicine. Intensive research over the past 2 decades has led to the feasibility of using ESC-differentiated cells (ESC-DCs) in regenerative medicine. However, increasing evidence indicates that ESC-DCs generated by current differentiation methods may not have equivalent cellular functions to their in vivo counterparts. Recent studies have revealed that both human and mouse ESCs as well as some types of ESC-DCs lack or have attenuated innate immune responses to a wide range of infectious agents. These findings raise important concerns for their therapeutic applications since ESC-DCs, when implanted to a wound site of a patient, where they would likely be exposed to pathogens and inflammatory cytokines. Understanding whether an attenuated immune response is beneficial or harmful to the interaction between host and grafted cells becomes an important issue for ESC-based therapy. A substantial amount of recent evidence has demonstrated that the lack of innate antiviral responses is a common feature to ESCs and other types of pluripotent cells. This has led to the hypothesis that mammals may have adapted different antiviral mechanisms at different stages of organismal development. The underdeveloped innate immunity represents a unique and uncharacterized property of ESCs that may have important implications in developmental biology, immunology, and in regenerative medicine. Stem Cells 2015;33:3165–3173

Ongoing research in triboelectric nanogenerators (TENGs) focuses on increasing power generation, but obstacles concerning economical and eco-friendly utilization of TENGs continue to prevail. Being the second most abundant biopolymer on earth, lignin offers a valuable opportunity for low-cost TENG applications in biomedical devices, benefitting from its biodegradability and biocompatibility. Here, we develop for the first time a lignin biopolymer based TENGs for harvesting mechanical energy in the environment, which shows great potential for self-powered biomedical devices among other applications and opens doors to new technologies that utilize otherwise wasted materials for economically feasible and ecologically friendly production of energy devices.

Developing single-phased white light-emitting materials with high brightness, good transferability and energy-saving economy has attracted tremendous attention during the past decades owing to their facile light manipulation and easy device fabrication. Herein, we highlight the first transferable two-dimensional (2D) white light-emitter by engineering grain boundaries in atomically-thin semiconducting nanosheets. With the merits of the abundant grain boundaries, effective surface states that can trap the photogenerated charges can be enriched, giving significant enhancement of the surface-state emission. Besides, the existence of grain boundaries can shorten the diffusion length of the charge carriers from the photogeneration zone to the recombination center, giving a higher charge concentration for radiative recombination and further enhancing the intensity of the surface-state emission. In addition, the bandgap-tunable nature of the atomically-thin nanosheets endows the tunable band-edge emission, providing the opportunity to realize white light emission synergistically. The novel white light-emitter exhibits high brightness and superior photostability, which are crucial to solid-state lighting. This work paves a new way for achieving white light emission from single-phased photoluminescent materials and will broaden the vision on developing advanced white light-emitters with high brightness and transferability.