Search

Oxygen deficiencies are well recognized to have a detrimental effect on the performance of spinel LiMn2O4-δ as the cathode for non-aqueous systems, whereas the influences have not been explored for aqueous systems yet. Here, we successfully introduce oxygen deficiencies into LiMn2O4-δ by calcination of oxygen deficiency-free LiMn2O4 at 850 °C for 2 h followed by quenching in air. LiMn2O4-δ primary particles show the octahedral shape, the sizes of about 400 nm, and the larger lattice constant of 8.240 A, in contrast with the irregular shapes, the sizes of about 100 nm, and the lattice constant of 8.231 A. In the non-aqueous system, the performances for LiMn2O4-δ are inferior compared to LiMn2O4, as reported previously. However, both LiMn2O4-δ||polyimide and LiMn2O4||polyimide aqueous full cells exhibit the discharge capacity of about 105 mAh g−1 at 100 mA g−1 and the capacity retentions of 87% and 60% after 100 cycles. The plateau of H2O decomposition observed at about 1.85 V for LiMn2O4 leads to much poorer performance which is absent for LiMn2O4-δ. This study demonstrates different requirements by the cathodes in the non-aqueous and aqueous systems and offers a new idea for improving the performance and stability of the electrodes for aqueous cells.

Achievement of carbon materials with particular structures, dimensions, and sizes derived from metal organic frameworks (MOFs) with particular morphologies is very crucial for purpose-oriented appl...

Commercialized lithium cobalt oxide (LCO) only shows a relatively low capacity of ≈175 mAh g

Low-cost Mn- and Li-rich layered oxides suffer from rapid voltage decay, which can be improved by increasing the nickel content to derive high nickel Li-rich layered oxides (HNLO) but is normally accompanied by reduced capacity and inferior cycling stability. Herein, Na or K ions are successfully doped into the lattice of high nickel Li-rich Li

Discarded polystyrene foams as white wastes, at least two million tons in demand annually in China, are threatening environment and health because of their formidable degradation, which increase in...

High sensitivity, low limit of detection (LOD), and short response and recovery times at room temperature (RT) are critical for gas sensors. For NO2, different binary metal oxide-based sensors were developed to achieve superior performance at elevated temperatures instead of RT. Herein, we report on CuO@CuO and Cu3Mo2O9@CuO sensors with CuO and Cu3Mo2O9 micro/nanorods vertically aligned on the CuO layers, which were directly fabricated using a facile, low-cost, and catalyst-free chemical vapor deposition (CVD) technique. Their sensing performance tests revealed that the Cu3Mo2O9@CuO p-p heterojunction sensors exhibited a high response of 160% to 5 ppm NO2, an excellent sensitivity of 50% ppm-1, a low LOD of 2.30 ppb, a short response time of 49 s, and a rapid recovery of 241 s at RT, obviously better than those for CuO@CuO sensors. The superior performance of Cu3Mo2O9@CuO sensors could be attributed to the Schottky heterojunction formed between p-Cu3Mo2O9 micro/nanorods and p-CuO films, the catalytic effect, and the anisotropic nature of Cu3Mo2O9 micro/nanorods. This study not only provides a simple, low-cost, and batchable fabrication method of homo/heterojunction sensors with micro/nanorods vertically aligned on films but also opens an avenue for sensor design by tuning the Schottky barrier height to enhance RT performance.

The switch in the sensing mode for better identification of donor/acceptor gases with simultaneous enhancement of the sensing performance at a fixed working temperature particularly room temperature (RT) is quite challenging for gas sensors. Herein, TiO2/graphene hybrid field effect transistor (FET) sensors (TiO2/GFET) with varied hybrid areas are presented. Superior sensing and recovery performances for NH3 are achieved through sensing mode switch via gate biasing. 16.40% response and full recovery for 25 ppm NH3 are achieved for TiO2/GFET sensors with 100% titanium dioxide coverage (D100) at RT (27 °C) with 15-20% humidity upon switching sensing mode from p- to n via gate biasing. Full recovery is attributed to the Coulomb interaction between charged polar donor molecules and positively polarized surface which is enhanced by the switch from p- to n-mode. The humidity can enhance response up to -35.48% for 25 ppm NH3 with full recovery in n-mode for D100. D100 shows superior selectivity towards NH3 against both electron-acceptor NO2 and several other electron-donor analytes. The sensing behaviors for NH3 are well elucidated using energy band diagrams based on the experimental results. This study proposes a novel idea for performance improvement of FET based sensors with p- and n-type hybrid sensing materials through p (n)- to n (p)-mode switch assisted by gate biasing by incorporating suitable electron (hole) rich materials to compensate holes (electrons) in p (n)-type materials for electron donor (acceptor) gas detection.

Effective detection of NO2 and NH3 gases at room temperature (RT) is critical for environmental monitoring and protection. Here, graphene-based gas sensors (Cu/Gr device) of single layer graphene decorated by 6, 8 and 10 nm thick Cu layers with graphene instead of conventional metal as interdigital electrodes are designed and fabricated. The RT performance for both NO2 and NH3 detection can be greatly enhanced by UV light illumination which is closely related to the thickness of Cu layers in which the device with 8 nm thickness (8 nm Cu/Gr device) exhibits the best performances. Analysis of XPS reveals that Cu is partly oxidized to Cu+ and Cu2+ for 6 nm with extra Cuδ+ (1 < δ < 2) for 8 and 10 nm. The contents and distributions of copper oxides and copper in Cu layers influence the catalytic effects and the heterojunction barrier and thus the performances. The RT responses of −30.9% and −8.1% for 5 and 0.3 ppm NO2, and of +29.1% and +5.9% for 105 and 10 ppm NH3 are achieved for the 8 nm Cu/Gr device, respectively. The limits of detection (LODs) for NO2 and NH3 are 12 ppb and 17 ppb, respectively. The sensing mechanisms are discussed in terms of density functional theory (DFT) calculations and energy band diagrams. The study demonstrates an effective solution of improving the device performance by modifying the device configuration and incorporating combined oxides naturally oxidized, which provides the novel design alternatives for high performance sensors.

Nonvolatile memories have attracted a lot of interest because they retain the data when the power is interrupted. Smaller size and improved performance of nonvolatile memories are pursued both for basic research and applications. In this work, a molecular wire made of seamless junctions between semiconducting single-walled carbon nanotubes (SWNT) and partially unzipped segments of the SWNTs are reported. This novel nanostructure is demonstrated to be a nonvolatile memory, which works at room temperature under atmospheric conditions. The characteristics of the device are measured with a four-terminal configuration and a non-local voltage (Vnon-local) is used as the storage signal. An electrical hysteresis of Vnon-local is observed, wherein two states with different Vnon-local can be switched by the application of an electric field through an insulating gate device structure, exhibiting nonvolatile characteristics. Vnon-local can be modulated with external magnetic fields and the mechanism of the electrical hysteresis is attributed to the magnetic moments at the partially unzipped SWNT. The smaller size of SWNT and high working temperature may lead to the development of molecular nanomagnets as nonvolatile memory devices for practical applications. Supported by Major Nanoprojects of Ministry of Science and Technology of China (Grant Nos.2018YFA0208403, 2017YFA0207104), National Natural Science Foundation of China (21973021, 11874129), the GBA National Institute for Nanotechnology Innovation, Guangdong, China (2020B0101020003), CAS Project for Young Scientists in Basic Research (YSBR-030), Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB36000000, NBSDC-DB-18).

Optical superoscillation, a phenomenon that the local optical field can oscillate much faster than that allowed by its highest harmonic, can significantly overcome the Abbe diffraction limit. However, as the spot size is compressed below the superoscillation criteria of 0.38λ/NA, huge sidebands will inevitably appear around the central lobe with intensity hundreds of times higher than that of the central lobe. Here, we propose an approach to realize superoscillation by using destructive interference. The central lobe size can be compressed beyond the superoscillation criteria without formation of strong sidebands by destructive interference between focused fields. Such a super-resolution metalens can find its application in label-free far-field super-resolution microscopy.

Li- and Mn-rich layered oxides can deliver high reversible capacity but suffer from severe voltage decay, which seriously impedes their commercial applications. However, high-nickel Li-rich layered oxides could normally present stable discharge voltage but tend to deliver low reversible capacity. In this work, high-nickel Li-rich layered oxides are doped by Mo via a facile sol-gel route to realize both high reversible capacity and minor voltage decay simultaneously. The superior performance could be ascribed to the reduced size of primary particles, the enhanced stability of lattice oxygen and more Mn4+/3+ redox couples effectively activated during the electrochemical reactions which are realized via Mo doping. The present study offers a new strategy to achieve high-performance high-nickel Li-rich layered oxides with both the stable discharge potential and high reversible capacity by modifying their morphologies, structures and chemistries via the introduction of proper alien elements which are believed to be the potential cathode candidates for next generation lithium-ion batteries.

Chirality is an essential consideration in the field of life sciences and pharmaceutical industry because most biomolecules and pharmaceuticals are chiral, and optical rotation measurement is a simple and efficient means for identification, purity test and content detection of chiral materials. However, there are some drawbacks in existing methods, such as small measurement range, non-real-time performance, low measurement accuracy and resolution. This paper presents a novel system to implement optical rotation measurement, and pixelated polarization cameras and Stokes parameters are employed in the system. The polarization information of linearly polarized incident light can be recorded and extracted by a pixelated polarization camera and Stokes parameters respectively. Experiments demonstrate that the proposed system has the necessary advantages for optical rotation measurement, such as real time, wide range ( − 90 ° to + 90 °), high accuracy ( 1 × 1 0 − 4 °) and high resolution ( ± 6 × 1 0 − 6 °). Thus, this measurement system has great practical prospects in the hospital clinical diagnosis, chemical research, sugar production and pharmaceutical industry.

It has been well recognized that Li2CO3 is inevitably formed at the surface of nickel rich layered compounds (NRLC) upon storage in air which is usually considered to be detrimental to the performance. Actually, its formation may have been triggered during synthesis of NRLC. However, little is known of its formation during synthesis of NRLC in air and its interaction behaviors with electrolyte during electrochemical process. Herein, we successfully tailor Li2CO3 surface phase simply by controlling calcination time during synthesis of structurally well ordered LiNi0.9Mn0.1O2 particles with great similarity in structure, morphology, size and crystallinity in air using a facile sol-gel method. The thickness of Li2CO3 layer is for the first time observed to decrease with increased calcination time, accompanied by the reduced Ni2+ at surface. More oxygen vacancies caused by more Ni2+ owing to the difficulty of oxidizing Ni2+ to Ni3+ at the surface are proposed here to be responsible for the formation of more Li2CO3 for shorter calcination times. Li2CO3 surface phase is evidenced to favor not only suppressing the H2/H3 phase transition but alleviating the interaction of LiNi0.9Mn0.1O2 with electrolyte because of the coating effect, which therefore improves the cycling stability of LiNi0.9Mn0.1O2 at low rates. Therefore, this study not only provides a new insight into the surface changes of LiNi0.9Mn0.1O2 with calcination time at high temperature during synthesis in air, but opens up a new avenue to tailoring Li2CO3 surface phase as desired by controlling the oxidization extent of Ni2+ to Ni3+ to modulate oxygen vacancies at surface through employing different oxidizing atmospheres or calcination times for performance improvement or exploration of novel preparation approaches of high performance NRLC.

Superoscillation metalenses have demonstrated promising prospects in breaking the theoretical diffraction limitations on the resolution of optical devices and systems. However, most reported superoscillation metalenses have a very small field of view of several tenths of a degree, which greatly limits their applications in imaging and microscopy. Therefore, it is of critical importance to achieve absolute high resolution by increasing the numerical apertures (NAs) of optical devices and systems. Unfortunately, similar to the case in traditional optics, it is challenging to realize a large field of view at high NA, especially in the superoscillation regime. To date, no attempt has been made to achieve flat-field focusing in the superoscillation regime, to our knowledge. Here, we demonstrate a high-NA superoscillation metalens with an entrance aperture stop, which is optimized for superoscillation performance with a comparatively large field of view. The proposed flat-field superoscillation metalens has an effective NA as large as 0.89 and achieves superoscillation focusing within a field of view of 9°. Such a superoscillation metalens may offer a promising way toward superoscillation imaging and fast-scanning label-free far-field superoscillation microscopy.

Information encryption and security is a prerequisite for information technology, which can be realized by an optical metasurface owing to its arbitrary manipulation over the wavelength, polarization, phase, and amplitude of light. So far information encoding can be implemented by the metasurface in one-dimensional (1D) mode (either wavelength or polarization) only with several combinations of independent channels. Herein, we design dielectric metasurfaces by multiplexing for information encoding in a two-dimensional (2D) mode of both wavelength and polarization. Sixty-three combinations made out of six independent channels by two circular polarization states (RCP and LCP) and three visible wavelengths (633, 532, and 473 nm) are experimentally demonstrated, in sharp contrast with seven combinations by three independent channels in 1D mode. This 2D mode encoding strategy enhances the encryption security dramatically and paves a novel pathway for escalating the security level of information in multichannel ...

Light travels in a zero-index medium without accumulating a spatial phase, resulting in perfect spatial coherence. Such coherence brings several potential applications, including arbitrarily shaped waveguides, phase-mismatch-free nonlinear propagation, large-area single-mode lasers, and extended superradiance. A promising platform to achieve these applications is an integrated Dirac-cone material that features an impedance-matched zero index. Although an integrated Dirac-cone material eliminates ohmic losses via its purely dielectric structure, it still entails out-of-plane radiation loss, limiting its applications to a small scale. We design an ultra-low-loss integrated Dirac cone material by achieving destructive interference above and below the material. The material consists of a square array of low-aspect-ratio silicon pillars embedded in silicon dioxide, featuring easy fabrication using a standard planar process. This design paves the way for leveraging the perfect spatial coherence of large-area zero-index materials in linear, nonlinear, and quantum optics., Zero-index media: ultra-low loss Calculations suggest that a new design of engineered medium can simultaneously yield a refractive index of zero and low optical loss at the telecommunications wavelength of 1550 nm. The development could lead to applications in nonlinear and quantum optics benefiting from an infinite coherence length. The approach of Tian Dong and coworkers from China and the US is to embed an array of silicon pillars (about 180 nm in radius and 1100 nm high) into a matrix of silicon dioxide to create a Dirac-cone photonic-crystal slab. Importantly, if the pillar height is chosen correctly any upwards and downwards radiation out of the slab can be made to destructively interfere thus reducing propagation loss to a level of 0.15 dB/mm. The slab should be possible to fabricate using standard processes.

Novel energy devices which are capable of alleviating and/or solving the energy dilemma such as overall water splitting and fuel cells require the development of highly efficient catalysts, especially cheap high performance non-precious metal (NPM) catalysts. Here, we prepare highly efficient NPM catalysts of cobalt and nitrogen codoped carbon nanosheets (Co/N–CNSs) for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) using harmful environment-polluting waste of biomass catkins as carbon precursors via a mild mechanical exfoliation and chemical process which is facile, low-cost, environmentally friendly and up-scalable. Compared with a commercial platinum-based catalyst (commercial 20% Pt/C), the Co/N–CNS electrocatalysts show outstanding ORR activity, acceptable HER activity and long term stability with an onset potential of 0.92 V versus the reversible hydrogen electrode (vs. RHE) and a half-wave potential of 0.83 V vs. the RHE in alkaline electrolytes. The excellent performance is closely related to the presence of abundant CoNx active sites. This work offers a novel and effective approach for preparing highly efficient ORR and HER NPM electrocatalysts from waste biomass materials.

The switch in the sensing mode for better identification of donor/acceptor gases with simultaneous enhancement of the sensing performance at a fixed working temperature particularly room temperature (RT) is quite challenging for gas sensors. Herein, TiO

High sensitivity, low limit of detection (LOD), and short response and recovery times at room temperature (RT) are critical for gas sensors. For NO

A numerical modeling study based on 3D finite element method (FEM) simulation and 1D analytical solutions has been carried out to evaluate the capabilities of two ac methods for measuring in-plane thermal conductivity of thin film deposited on the back of a suspended SiNx membrane setup. Two parallel metal strips are present on the top of the dielectric membrane. One strip (S1) serves as both heater and thermometer, while another one (S2) acts as thermometer only. For a modified phase shift (MPS) method, it is crucial to extract the in-plane thermal diffusivity from the phase shift of the temperature oscillation on S2. It was found that the frequency window for carrying out the data fitting became narrower as the in-plane thermal diffusivity of the composite membrane (${\alpha_{\parallel ,C}}$) increased, primarily due to the failure of the semi-infinite width assumption in the low frequency region. To ensure the validity of the method, the upper limit of ${\alpha_{\parallel ,C}}$ should not exceed ~1.8$ \times $10-5 m2 s-1 for the specific membrane dimension under consideration (1$\times $1 mm2). On the other hand, inspired by a modified Angstrom method proposed by Zhu recently, we suggest a new data reduction methodology which takes advantage of the phase shift on both S1 and S2 as well as the amplitude on S1. Based on the simulation results, it is expected that the non-ideality associated with the three observables may be at least partially cancelled out.Therefore, the frequency window selection for carrying out the data fitting is not sensitive to the magnitude of ${\alpha_{\parallel ,C}}$. For typical specimen films whose in-plane thermal conductivity ranges from 0.84 W m-1 K-1 to 50 W m-1 K-1, the method proposed here yields a theoretical measurement uncertainty of less than 5%., Comment: 34 pages, 9 figures

In this work, octahedral LiMn2O4 (O-LMO) with exposed {111} crystal facets was prepared using MnCO3 as a precursor via solid phase reactions. O-LMO was revealed to have the superior rate performance and good cycling stability in both a three-electrode system and full aqueous batteries with Li2SO4 solution.The capacity retentions of 87% for 200 cycles at 0.1 A g-1 and 87% for 500 cycles at 1 A g-1 were achieved, in sharp contrast with 56% and 70% for the commercial LMO (C-LMO). Also, O-LMO showed the excellent performance in organic systems as well. The superior performance for both aqueous and organic systems may be related to the maintaining of octahedral structures and surface morphologies for O-LMO cycled 200 times at 0.1 A g-1 in aqueous system and the suppression of Mn dissolution and side reactions in both aqueous and organic systems, which originates from the stable {111} facets.

Metalenses are expected to play an increasingly important role in miniaturized and integrated optical imaging components/systems. However, devising broadband achromatic metalenses with high focusing efficiencies is still quite challenging. In this work, we proposed an aperture-shared partition phase cooperative manipulation approach for designing a high-efficiency broadband achromatic metalens composed of two concentric sub-metalenses. As a proof-of-concept, an achromatic polarization-independent metalens is successfully designed for the visible and near-infrared range from 450 nm to 1400 nm with the focusing efficiency over 70% for the wavelength range of 600 nm to 1400 nm. The approach reported here provides a possibility for designing a high-performance metalens, which has great potential applications in integrated optics.

In this work, we report that when a modulated force is applied to the edge of a bilayer graphene with an atomic force microscope (AFM), two kinds of folded tetralayer graphenes can be obtained: one has one rupture and the other has two ruptures. The twist angle between two bilayer graphenes is found to be in the range of 1.8°∼27.7°. Systematic Raman studies show that the position, width, and intensity of 2D and G peaks of the folded tetralayer graphene depend sensitively on these angles. Meanwhile, the intensity enhancement of G mode of twisted tetralayer graphenes has been observed at twist angles of 11.5° and 13.2°. At these two twist angles, the 2D peak of twisted tetralayer graphenes can be fitted by three Lorentzian peaks at laser energy of 2.33 and 2.41 eV. Using an AFM probe to fabricate twisted graphene has the advantages of high yield, controllable positions, and no introduction of chemical pollutants, which has many potentials in future electronics.