Showing papers by "Zhong Chen published in 2018"

Mini-LED and Micro-LED: Promising Candidates for the Next Generation Display Technology

Abstract: Displays based on inorganic light-emitting diodes (LED) are considered as the most promising one among the display technologies for the next-generation The chip for LED display bears similar features to those currently in use for general lighting, but it size is shrunk to below 200 microns Thus, the advantages of high efficiency and long life span of conventional LED chips are inherited by miniaturized ones As the size gets smaller, the resolution enhances, but at the expense of elevating the complexity of fabrication In this review, we introduce two sorts of inorganic LED displays, namely relatively large and small varieties The mini-LEDs with chip sizes ranging from 100 to 200 μm have already been commercialized for backlight sources in consumer electronics applications The realized local diming can greatly improve the contrast ratio at relatively low energy consumptions The micro-LEDs with chip size less than 100 μm, still remain in the laboratory The full-color solution, one of the key technologies along with its three main components, red, green, and blue chips, as well color conversion, and optical lens synthesis, are introduced in detail Moreover, this review provides an account for contemporary technologies as well as a clear view of inorganic and miniaturized LED displays for the display community

Bioinspired surfaces with superamphiphobic properties : concepts, synthesis, and applications

Abstract: Among diverse wetting phenomena in surface science, superamphiphobicity is regarded as one of the most special super-antiwetting states. In this paper, a systematic summary has been generated to cover the characterization of surface wettability, the construction techniques, and selected functional applications. With respect to fabrication techniques, we will discuss the following three types of technology routes, viz., ‘pre-texturing + post-modifying’, ‘pre-modifying + post-texturing’, and in-situ one-step construction. Discussion has been made on the merits and demerits of each technology route. It is vital to rationally design or adopt appropriate construction strategies in diverse conditions. Appropriately constructed superamphiphobic multifunctional surfaces can be applied in many fields, however, most have not been scale-up and utilized for practical applications due to some specific difficulties required to be resolved in the future. These challenges and further outlook for super-antiwetting surfaces are discussed in this review.

Rational design of materials interface at nanoscale towards intelligent oil–water separation

Abstract: Oil–water separation is critical for the water treatment of oily wastewater or oil-spill accidents. The oil contamination in water not only induces severe water pollution but also threatens human beings’ health and all living species in the ecological system. To address this challenge, different nanoscale fabrication methods have been applied for endowing biomimetic porous materials, which provide a promising solution for oily-water remediation. In this review, we present the state-of-the-art developments in the rational design of materials interface with special wettability for the intelligent separation of immiscible/emulsified oil–water mixtures. A mechanistic understanding of oil–water separation is firstly described, followed by a summary of separation solutions for traditional oil–water mixtures and special oil–water emulsions enabled by self-amplified wettability due to nanostructures. Guided by the basic theory, the rational design of interfaces of various porous materials at nanoscale with special wettability towards superhydrophobicity–superoleophilicity, superhydrophilicity–superoleophobicity, and superhydrophilicity–underwater superoleophobicity is discussed in detail. Although the above nanoscale fabrication strategies are able to address most of the current challenges, intelligent superwetting materials developed to meet special oil–water separation demands and to further promote the separation efficiency are also reviewed for various special application demands. Finally, challenges and future perspectives in the development of more efficient oil–water separation materials and devices by nanoscale control are provided. It is expected that the biomimetic porous materials with nanoscale interface engineering will overcome the current challenges of oil–water emulsion separation, realizing their practical applications in the near future with continuous efforts in this field.

Progress in TiO2 nanotube coatings for biomedical applications: a review

Abstract: Titanium dioxide nanotubes (TNTs) have drawn wide attention and been extensively applied in the field of biomedicine, due to their large specific surface area, good corrosion resistance, excellent biocompatibility, and enhanced bioactivity. This review describes the preparation of TNTs and the surface modification that entrust the nanotubes with better antibacterial property and enhanced osteoblast adhesion, proliferation, and differentiation. Considering the contact between TNTs' surface and surrounding tissues after implantation, the interactions between TNTs (with properties including their diameter, length, wettability, and crystalline phase) and proteins, platelets, bacteria, and cells are illustrated. The state of the art in the applications of TNTs in dentistry, orthopedic implants, and cardiovascular stents are introduced. In particular, the application of TNTs in biosensing has attracted much attention due to its ability for the rapid diagnosis of diseases. Finally, the difficulties and challenges in the practical application of TNTs are also discussed.

Mechanically Resistant and Sustainable Cellulose-Based Composite Aerogels with Excellent Flame Retardant, Sound-Absorption, and Superantiwetting Ability for Advanced Engineering Materials

Abstract: The production of cellulose-based aerogels from the conversion of cheap and rich precursors using environmentally friendly techniques is a very attractive subject in materials chemistry. In this work, we report a facile strategy to construct flame retardant, sound-adsorption, and mechanical enhancement cellulose-based composite aerogels by the incorporation of aluminum hydroxide nanoparticles (AH NPs) into cellulose gels via an in situ sol–gel process, followed by freeze-drying to coat AH NPs on cellulose composite aerogels (AH NPs@cellulose composite aerogels). The results demonstrated that the AH NP homogeneous dispersion within cellulose aerogels and the presence of AH NPs did not have a remarkable influence on the homogeneous porous structure of cellulose aerogels when compared with cellulose aerogels prepared from the NaOH/urea/thiourea solution. The prepared composite cellulose aerogels showed excellent flame retardancy, the peak of heat release rate (PHRR) of the composite aerogels decreased signif...

A mechanically robust transparent coating for anti-icing and self-cleaning applications

Abstract: Mechanically robust, transparent coatings that display very low affinity with ice and various liquids are promising for applications in outdoor facilities and marine and aerospace structures However, such coatings are extremely challenging to prepare because some material properties required for diverse functionalities are contradictory In this study, we demonstrated a sol-gel-derived transparent coating with superior performance compared to the well-studied superhydrophobic coatings in terms of transmittance (∼978%), ice-adhesion strength, anti-frost accumulation, and self-cleaning properties We comprehensively investigated the mechanical properties of the transparent solid coating by nano-indentation, pencil scratch, cross-cut adhesion, and dolly pull-off tests according to the respective ASTM/ISO standards The coating displayed higher hardness and better scratch resistance than the state-of-the-art slippery liquid-infused porous surfaces and polymer coatings Furthermore, the coating showed good durability after sand erosion

Anisotropic Electronic Characteristics, Adsorption, and Stability of Low-Index BiVO4 Surfaces for Photoelectrochemical Applications

Abstract: Many experimental results reveal different activities among different low-index surfaces of photocatalysts. The current investigation focuses on the theoretical understanding of the electronic characteristics, surface activity, and stability of different low-index surfaces of BiVO4 toward water splitting using first-principle calculations. The results indicate that BiVO4 has four types of low-index surfaces, namely, (010)T1, (010)T2, (110)T1, and (111)T1. The different band edge potentials of the surfaces, resulting from the variation of the electrostatic potential, lead to a higher oxidation ability for (010)T1 and (010)T2 than for (110)T1 and (111)T1 surfaces. The electrons prefer to accumulate on (010)T1 and (010)T2 surfaces, whereas holes like to accumulate on (110)T1 and (111)T1 surfaces during a photocatalytic process. Moreover, investigation on the adsorbed intermediates during the water-splitting process indicates that the oxygen evolution reaction on BiVO4 surfaces is mainly dominated by the r...

Clarifying the Roles of Oxygen Vacancy in W-Doped BiVO4 for Solar Water Splitting

Abstract: Most oxide semiconductor photoanode materials for water splitting are synthesized in ambient environment. Oxygen vacancy exists in these samples making them intrinsically n-type at the as-synthesized state. Oxygen vacancy has been widely reported for enhancing the performance of a photoanode by improving the electron conductivity. Besides the effect on the bulk materials properties, oxygen vacancy also plays an important role in the interfacial charge transfer to electrolyte, on which much less attention has been paid in the past. Herein, we found that although air-annealed W-doped BiVO4 has a higher electron density, lower surface charge transfer resistance, and a slightly better light absorption than the O2-annealed sample, the latter displays a higher photocurrent density. Experimentally we found that the enhanced performance comes from a better charge separation efficiency, despite that the presence of oxygen vacancy does lead to a better charge transfer efficiency. Theoretical calculation finds that ...

Single-shot T2 mapping using overlapping-echo detachment planar imaging and a deep convolutional neural network.

Abstract: Purpose An end-to-end deep convolutional neural network (CNN) based on deep residual network (ResNet) was proposed to efficiently reconstruct reliable T2 mapping from single-shot overlapping-echo detachment (OLED) planar imaging. Methods The training dataset was obtained from simulations that were carried out on SPROM (Simulation with PRoduct Operator Matrix) software developed by our group. The relationship between the original OLED image containing two echo signals and the corresponding T2 mapping was learned by ResNet training. After the ResNet was trained, it was applied to reconstruct the T2 mapping from simulation and in vivo human brain data. Results Although the ResNet was trained entirely on simulated data, the trained network was generalized well to real human brain data. The results from simulation and in vivo human brain experiments show that the proposed method significantly outperforms the echo-detachment-based method. Reliable T2 mapping with higher accuracy is achieved within 30 ms after the network has been trained, while the echo-detachment-based OLED reconstruction method took approximately 2 min. Conclusion The proposed method will facilitate real-time dynamic and quantitative MR imaging via OLED sequence, and deep convolutional neural network has the potential to reconstruct maps from complex MRI sequences efficiently.

A Cobalt-Based Metal–Organic Framework as Cocatalyst on BiVO4 Photoanode for Enhanced Photoelectrochemical Water Oxidation

Abstract: A metal-organic framework (MOF)-modified bismuth vanadate (BiVO4 ) photoanode is fabricated by an ultrathin sheet-induced growth strategy, where ultrathin cobalt oxide sheets act as a metal source for the in situ synthesis of Co-based MOF poly[Co2 (benzimidazole)4 ] (denoted [Co2 (bim)4 ]) nanoparticles on the surface of BiVO4 . [Co2 (bim)4 ] with small particle size and high dispersion can serve as a promising cocatalyst to accept holes transferred from BiVO4 and boost surface reaction kinetics for photoelectrochemical (PEC) water oxidation. The photocurrent density of a [Co2 (bim)4 ]-modified BiVO4 photoanode can achieve 3.1 mA cm-2 under AM 1.5G illumination at 1.23 V versus the reversible hydrogen electrode (RHE), which is better than those of pristine and cobalt-based inorganic materials-modified BiVO4 photoanodes. [Co2 (bim)4 ], with porosity and abundant metal sites, exhibits a high surface charge-separation efficiency (83 % at 1.2 V versus RHE), leading to the enhanced PEC activity. This work will bring new insight into the development of MOF materials as competent cocatalysts for PEC water splitting applications.

Quantification of plasma produced OH radical density for water sterilization

Abstract: The interactions between plasma-generated excited particles and water play an integral role in sustainable degradation of pharmaceutical compounds, improving aerobic respiration of activated sludge, and efficient removal of microorganisms from water, and are fundamental to the intentional transfer of reactivity from plasmas to biological solutions for such medical applications as cancer treatment and wound healing. The physical and chemical mechanisms that govern this transfer of reactivity are complex, and include concomitant generation and consumption of species in the gas and liquid phases, and at the interface. As such, it is challenging to predict the quantities of biologically-active radicals and molecules in liquid phase from gas phase measurements alone. Rapid and accurate quantification of reactive species, such as OH radicals and H2O2 molecules within the liquid phase and their link to specific biological effects is therefore critical for medical applications of plasma-activated solutions. Using a simple, low-cost method for trapping and stabilization of OH radicals by means of salicylic acid, this work seeks to provide further insights into the physics and chemistry of generation of OH radicals within the liquid phase, and integrate these findings with decontamination outcomes for four commonly used processing gases.

Preparation of magnetically recoverable bentonite-Fe3O4-MnO2 composite particles for Cd(II) removal from aqueous solutions.

Abstract: In this study, bentonite–Fe3O4–MnO2 composite was synthesized by combining bentonite with Fe3O4 and MnO2 through co-precipitation. Vibrating-sample magnetometry, scanning electron microscopy with energy-dispersive X-ray spectrometry, transmission electron microscopy, Brunauer–Emmett–Teller measurements, and X-ray powder diffraction techniques were used to characterize the composite. The composite consists of Fe3O4 nanoparticles orderly assembled on the surface of bentonite and an outer layer of MnO2 sheets. The composite’s particles possess a saturation magnetization of 13.4–30.5 emu/g and a high specific surface area (203.89 m2/g). The adsorption behaviors of the composite in Cd(II) removal were evaluated by batch equilibrium experiments. Kinetic and isothermal data fit well the pseudo-second-order and the Freundlich models, respectively. Adsorption reached equilibrium within 30 min, and the Freundlich capacity of the composite was 35.35 mg/g. The adsorption capacity of Cd(II) increased with increasing pH and was dependent on the ionic strength. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed the combination of surface hydroxyl groups of the composite and Cd(II) in the solution. The prepared composite can be easily recycled and reused by taking advantage of its magnetic properties. The results show that the designed composite is a promising absorbent for the treatment of Cd-contaminated water.

Vandermonde Factorization of Hankel Matrix for Complex Exponential Signal Recovery—Application in Fast NMR Spectroscopy

Abstract: Many signals are modeled as a superposition of exponential functions in spectroscopy of chemistry, biology, and medical imaging. This paper studies the problem of recovering exponential signals from a random subset of samples. We exploit the Vandermonde structure of the Hankel matrix formed by the exponential signal and formulate signal recovery as Hankel matrix completion with Vandermonde factorization (HVaF). A numerical algorithm is developed to solve the proposed model and its sequence convergence is analyzed theoretically. Experiments on synthetic data demonstrate that HVaF succeeds over a wider regime than the state-of-the-art nuclear-norm-minimization-based Hankel matrix completion method, while it has a less restriction on frequency separation than the state-of-the-art atomic norm minimization and fast iterative hard thresholding methods. The effectiveness of HVaF is further validated on biological magnetic resonance spectroscopy data.

The Roles of Morphology on the Relaxation Rates of Magnetic Nanoparticles

Abstract: The shape of magnetic nanoparticles is of great importance in determining their contrast abilities for magnetic resonance imaging. Various magnetic nanoparticles have been developed to achieve high T1 or T2 relaxivities, but the mechanism on how morphology influences the water proton relaxation process is still unrevealed. Herein we synthesize manganese-doped iron oxide (MnIO) nanoparticles of the same volume with six different shapes and reveal the relationship between morphologies and T1/T2 relaxation rates. The morphology of magnetic nanoparticles largely determines the effective radius and the gradient of stray field, which in turn affects the transverse relaxation rate. The longitudinal relaxivity has positive correlation with the surface-area-to-volume ratio and the occupancy rate of effective metal ions on exposed surfaces of magnetic nanoparticles. These findings together with the summary of r2/r1 ratios could help to guide the screening for the optimal shapes of promising T1 or T2 contrast agents...

Porous gold nanocluster-decorated manganese monoxide nanocomposites for microenvironment-activatable MR/photoacoustic/CT tumor imaging

Abstract: Stimuli-responsive nanoprobes that integrate multi-modal imaging capacities are highly desirable for precise tumor visualization. Herein, novel porous gold nanocluster-decorated manganese monoxide nanocomposites (MnO@Au NCs) were synthesized via a facile approach. The porous gold nanocluster layer was germinated on the surface of the as-prepared MnO@DMSA NPs through simple reduction of chloroauric acid in the presence of hydroxylamine hydrochloride. The MnO@Au NCs could be effectively internalized by tumor cells and slowly release Mn2+ ions within the acidic tumor microenvironment, improving the visualization of the tumor morphology. Benefitting from the porous architecture, the enhanced accessibility of Mn centers to proximal water molecules greatly augmented T1-weighted MRI contrast capacity. Compared with the conventional Mn-based contrast agents, the porous Au nanoclusters on MnO@Au NCs could delay the release of Mn2+ ions and thus effectively prolong the diagnostic time window. The broad near-infrared absorption of MnO@Au NCs features a high photoacoustic imaging depth than that of conventional gold nanospheres. Moreover, the Au nanoclusters exhibited desirable X-ray computed tomography contrast and rapid clearance from the living body. The as-prepared MnO@Au NCs hold great potential for accurate tumor imaging.

A theoretical study on the surface and interfacial properties of Ni3P for the hydrogen evolution reaction

Abstract: We report a comprehensive density functional theory (DFT) study on the stability, geometric structure, electronic characteristics, and catalytic activity for the hydrogen evolution reaction (HER) on low-index Ni3P crystal surfaces, namely, the (001), (100), (110), (101) and (111) planes with different surface terminations. The results indicate that P-rich and some stoichiometric surfaces are thermodynamically stable. Eight stable surfaces were selected to investigate the electronic characteristics and catalytic activity. The (110)B facet of Ni3P is indispensable for the HER, because it not only displays improved electrocatalytic activity, but also possesses suitable potential and high stability. Increasing the active sites through doping or enlarging the surface area could be a useful strategy to improve the HER activity further. Furthermore, it was found that Ni3P requires higher energies for decomposition in the absence of O2, although it is thermodynamically unstable in aqueous solutions with most pH values and potentials. This study provides important insights into the surface properties of Ni3P for water splitting and opens up an exciting opportunity to optimize the performance of solar energy conversion devices by synthesizing preferentially exposed catalyst facets.

Effect of the size of carbon nanotubes (CNTs) on the microstructure and mechanical strength of CNTs-doped composite Sn0.3Ag0.7Cu-CNTs solder

Abstract: Carbon nanotubes (CNTs) with three different diameter ranges (10–20, 40–60, and 60–100 nm) were doped into tin-silver-copper (SAC) solder, to study the performance of the composite SAC-CNTs solder materials – as well as the effect of the size of the CNTs. It was found that all the CNTs-doped composite solder samples displayed refined microstructure, inhibited interfacial intermetallic compound (IMC) growth, and reinforced mechanical strength – while the melting point of the composite solder was close to that of the pristine solder. The reinforcement in mechanical strength was due to the doped CNTs pinned at the solder grain boundaries, which acted as second-phase particles that refined the microstructure and increased the dislocation density. The adsorbed CNTs destroyed the integrity of the interfacial IMCs, leading to reduced growth rate. Among these composite solders, CNTs with a diameter of 40–60 nm provided superior performance in refining the microstructure, lowering the IMC growth rate by 30.9% – and reinforcing the ball shear strength by 15.3% and the hardness by 16.1%. This size effect on the performance of composite solders was due to the various surface energy values for CNTs – that led to the agglomeration and adsorption of CNTs in the solder matrix and interfacial IMCs.

Scale-Up of BiVO4 Photoanode for Water Splitting in a Photoelectrochemical Cell: Issues and Challenges

Abstract: The monoclinic scheelite-type BiVO4 is recognized as one of the promising candidate materials for a photoanode because of its 9.1 % theoretical efficiency for half-cell solar-to-hydrogen conversion. Although significant research efforts have been devoted to improving the performance of the photoelectrochemical cell (PEC) of this material, they have mainly been in small anode areas with only a handful of studies on scaled-up sizes. Herein, a facile metal–organic decomposition synthesis method was used to produce scaled-up Mo-doped BiVO4 photoanodes. Multiple modifications were explored and incorporated to enhance the performance of the photoanode. A large-area (5 cm×5 cm) photoanode was successfully prepared with all modifications. The resulting photoanode gave rise to an initial photocurrent density of 2.2 mA cm−2 at 1.23 V versus reversible hydrogen electrode, under AM 1.5G illumination in a PEC, which remained at 79 % of this value after 1 h of operation. A deleterious effect of the increased anode surface area on the photocurrent density was observed, which we termed the “areal effect”. Understanding the reasons for the areal effect is indispensable for the development of large-scale PEC devices for water splitting.

An investigation on the role of W doping in BiVO4 photoanodes used for solar water splitting.

Abstract: n-Type doping has been widely employed to enhance the performance of a photoanode in a photoelectrochemical cell used for water splitting. However, little is known about how doping affects the catalytic activity during surface catalysis. Herein, we took BiVO4 as an example to investigate the effect of doping on surface catalysis from both experimental and theoretical perspectives. To enable an impartial comparison, we have prepared planar BiVO4 thin films with and without W doping. It was found that W doping had no obvious effect on the morphology, crystallinity, and light absorption of the film; however, the photocurrent was significantly enhanced upon W doping. This enhancement is contributed by two important factors: better charge separation efficiency and improved surface charge transfer efficiency. Electrochemical analysis reveals that W doping lowers the surface charge transfer resistance and forms active surface states, facilitating charge transfer. Theoretical analysis shows that W doping activates the V atoms to be reactive sites. Moreover, the adsorption energies and distance between adsorption species (OHads, Oads, and OOHads) involved in the water splitting process become more favorable for surface charge transfer. The current study provides an insight into the roles of W doping in BiVO4, especially during surface catalysis.

Low Rank Enhanced Matrix Recovery of Hybrid Time and Frequency Data in Fast Magnetic Resonance Spectroscopy

Abstract: G oal: The two dimensional magnetic resonance spectroscopy (MRS) possesses many important applications in bioengineering but suffers from long acquisition duration. Non-uniform sampling has been applied to the spatiotemporally encoded ultrafast MRS, but results in missing data in the hybrid time and frequency plane. An approach is proposed to recover this missing signal, of which enables high quality spectrum reconstruction. M ethods: The natural exponential characteristic of MRS is exploited to recover the hybrid time and frequency signal. The reconstruction issue is formulated as a low rank enhanced Hankel matrix completion problem and is solved by a fast numerical algorithm. R esults: Experiments on synthetic and real MRS data show that the proposed method provides faithful spectrum reconstruction, and outperforms the state-of-the-art compressed sensing approach on recovering low-intensity spectral peaks and robustness to different sampling patterns. C onclusion: The exponential signal property serves as an useful tool to model the time-domain MRS signals and even allows missing data recovery. The proposed method has been shown to reconstruct high quality MRS spectra from non-uniformly sampled data in the hybrid time and frequency plane. S ignificance: Low-intensity signal reconstruction is generally challenging in biological MRS and we provide a solution to this problem. The proposed method may be extended to recover signals that generally can be modeled as a sum of exponential functions in biomedical engineering applications, e.g., signal enhancement, feature extraction, and fast sampling.

Material Structure and Mechanical Properties of Silicon Nitride and Silicon Oxynitride Thin Films Deposited by Plasma Enhanced Chemical Vapor Deposition

Abstract: Silicon nitride and silicon oxynitride thin films are widely used in microelectronic fabrication and microelectromechanical systems (MEMS). Their mechanical properties are important for MEMS structures; however, these properties are rarely reported, particularly the fracture toughness of these films. In this study, silicon nitride and silicon oxynitride thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) under different silane flow rates. The silicon nitride films consisted of mixed amorphous and crystalline Si3N4 phases under the range of silane flow rates investigated in the current study, while the crystallinity increased with silane flow rate in the silicon oxynitride films. The Young’s modulus and hardness of silicon nitride films decreased with increasing silane flow rate. However, for silicon oxynitride films, Young’s modulus decreased slightly with increasing silane flow rate, and the hardness increased considerably due to the formation of a crystalline silicon nitride phase at the high flow rate. Overall, the hardness, Young modulus, and fracture toughness of the silicon nitride films were greater than the ones of silicon oxynitride films, and the main reason lies with the phase composition: the SiNx films were composed of a crystalline Si3N4 phase, while the SiOxNy films were dominated by amorphous Si–O phases. Based on the overall mechanical properties, PECVD silicon nitride films are preferred for structural applications in MEMS devices.