Vanadium dioxide based broadband THz metamaterial absorbers with high tunability: simulation study.

With their unprecedented flexibility in manipulating electromagnetic waves, metamaterials provide a pathway to structural materials that can fill the so-called "THz gap". It has been reported that vanadium dioxide (VO2) experiences a three orders of magnitude increase in THz electrical conductivity when it undergoes an insulator-to-metal transition. Here, we propose a VO2 based THz metamaterial absorber exhibiting broadband absorptivity that arises from the multiple resonances supported by a delicately balanced doubly periodic array of VO2 structures and numerically demonstrate that the corresponding absorption behavior is highly dependent on the VO2's THz electrical properties. Considering the phase transition induced dramatic change in VO2's material property, the proposed metamaterial absorbers have the potential for strong modulation and switching of broadband THz radiation.

A 3D self-supported coralline-like CuCo2S4@NiCo2S4 core-shell nanostructure composite for high-performance solid-state asymmetrical supercapacitors.

Rational construction of three dimensional (3D) composite structure is an important method to flexible supercapacitor electrodes and has been extensively developed. In this work, a 3D self-supported CuCo2S4@NiCo2S4 core-shell nanostructure grown on Nickel (Ni) foam, constructed by a hydrothermal method, was used as a novel supercapacitor electrode material. The unique structure possesses a large, specific surface area, rapid diffusion of electrolyte ions by numerous channels and avoids the use of additives and adhesives. The high electrical conductivity of the CuCo2S4 nanoneedle arrays can speed up electronic transmission. At a current density of 1 A g-1, the electrode material exhibits a high specific capacity of 539.2 C g-1 and cycling stability with 100% capacity retention after 5000 cycles in 3 M KOH. Furthermore, when the obtained CuCo2S4@NiCo2S4 was used as the positive electrode and an activated carbon was used as the negative electrode, a solid-state asymmetric supercapacitor was assembled. More importantly, the obtained solid-state asymmetric supercapacitor demonstrated excellent electrochemical performance. When the power density was 400 W kg-1, it delivered a high density of 23.4 W h kg-1 with a high voltage window of 1.6 V, thus demonstrating that the material has the potential for use as an efficient electrode for electrochemical capacitors. Due to its comprehensive electrochemical performance, the CuCo2S4@NiCo2S4 solid-state asymmetric supercapacitor effectively operated a red LED.

Aldehyde reduced Co3O4 to form oxygen vacancy and enhance the electrochemical performance for oxygen evolution reaction and supercapacitors.

Oxygen vacancy is a feasible approach to boost the electrochemical properties for metal oxides. In this work, a Co3O4 with abundant oxygen vacancy is synthesized via aldehyde reduction. After the procedure, the reduced Co3O4 exhibits larger electrochemical active surface areas and better electrical conductivity. These outstanding characteristics can improve its performance of catalytic and energy storage. As for catalyst of oxygen evolution reaction, the reduced Co3O4 delivers a smaller potential of 1.55 V versus the reversible hydrogen electrode to realize a current density of 10 mA cm-2 and a lower Tafel slope of 71 mV dec-1 in alkaline solution, and these values are smaller than those of pristine Co3O4. Especially the reduced Co3O4 possesses superior stability: the measurements of the polarization curves before and after 15h of stability tests basically coincide. In a supercapacitor, the positive electrode of reduced Co3O4 achieves about 1.7 times areal capacitance of pristine Co3O4 at current density of 1 mA cm-2. Significantly, the superior cycling stability is still retained. Also, an aqueous asymmetric supercapacitor is assembled to evaluate the energy storage performance of the R-Co3O4. Moreover, the oxygen vacancy formation strategy for Co3O4 may be generally extended to other metal oxides for application in energy storage and conversion.

Rational Construction of Hollow Core-Branch CoSe2 Nanoarrays for High-Performance Asymmetric Supercapacitor and Efficient Oxygen Evolution.

Metal selenides have great potential for electrochemical energy storage, but are relatively scarce investigated. Herein, a novel hollow core-branch CoSe2 nanoarray on carbon cloth is designed by a facile selenization reaction of predesigned CoO nanocones. And the electrochemical reaction mechanism of CoSe2 in supercapacitor is studied in detail for the first time. Compared with CoO, the hollow core-branch CoSe2 has both larger specific surface area and higher electrical conductivity. When tested as a supercapacitor positive electrode, the CoSe2 delivers a high specific capacitance of 759.5 F g-1 at 1 mA cm-2 , which is much larger than that of CoO nanocones (319.5 F g-1 ). In addition, the CoSe2 electrode exhibits excellent cycling stability in that a capacitance retention of 94.5% can be maintained after 5000 charge-discharge cycles at 5 mA cm-2 . An asymmetric supercapacitor using the CoSe2 as cathode and an N-doped carbon nanowall as anode is further assembled, which show a high energy density of 32.2 Wh kg-1 at a power density of 1914.7 W kg-1 , and maintains 24.9 Wh kg-1 when power density increased to 7354.8 W kg-1 . Moreover, the CoSe2 electrode also exhibits better oxygen evolution reaction activity than that of CoO.

Bifunctional bamboo-like CoSe2 arrays for high-performance asymmetric supercapacitor and electrocatalytic oxygen evolution.

Bifunctional bamboo-like CoSe2 arrays are synthesized by thermal annealing of Co(CO3)0.5OH grown on carbon cloth in Se atmosphere. The CoSe2 arrays obtained have excellent electrical conductivity, larger electrochemical active surface areas, and can directly serve as a binder-free electrode for supercapacitors and the oxygen evolution reaction (OER). When tested as a supercapacitor electrode, the CoSe2 delivers a higher specific capacitance (544.6 F g-1 at current density of 1 mA cm-2) compared with CoO (308.2 F g-1) or Co3O4 (201.4 F g-1). In addition, the CoSe2 electrode possesses excellent cycling stability. An asymmetric supercapacitor (ASC) is also assembled based on bamboo-like CoSe2 as a positive electrode and active carbon as a negative electrode in a 3.0 M KOH aqueous electrolyte. Owing to the unique stucture and good electrochemical performance of bamboo-like CoSe2, the as-assembled ACS can achieve a maximum operating voltage window of 1.7 V, a high energy density of 20.2 Wh kg-1 at a power density of 144.1 W kg-1, and an outstanding cyclic stability. As the catalyst for the OER, the CoSe2 exhibits a lower potential of 1.55 V (versus RHE) at current density of 10 mA cm-2, a smaller Tafel slope of 62.5 mV dec-1 and an also outstanding stability.

Enhanced performance of multi-dimensional CoS nanoflake/NiO nanosheet architecture with synergetic effect for asymmetric supercapacitor.

Multi-dimensional nanomaterials possess a porous structure and plenty of active sites, so they have promising prospects in supercapacitor applications. As the typical pseudocapacitance materials, interlaced CoS nanoflakes and two-dimensional NiO nanosheets were assembled into multi-dimensional CoS/NiO architectures. The fabricated CoS/NiO nanostructures on nickel foam can directly serve as the supercapacitor electrodes. Such multi-dimensional CoS/NiO architectures exhibit the enhanced electrochemical performances in the light of the cyclic voltammetry curves and galvanostatic charging-discharging (GCD) tests. A multi-dimensional CoS/NiO electrode releases a high specific capacitance of 1620 F g-1 at 1.0 A g-1, which is distinctly higher than those of pristine CoS and NiO electrodes. The CoS/NiO//nitrogen-doped carbon nanoarrays (NC) asymmetric supercapacitor (ASC) can operate stably at 1.6 V. The GCD curves of the ASC at diverse current densities within the voltage window of 0-1.6 V exhibit reasonable symmetry. The CoS/NiO//NC ASC shows great long-term cycling performance, it has 93.5% capacity retention after 3000 cycles. Electrochemical analyses and detailed material characterizations are performed to reveal the mechanism for the enhanced performance of capacitance.

Highly efficient isolation and release of circulating tumor cells based on size-dependent filtration and degradable ZnO nanorods substrate in a wedge-shaped microfluidic chip.

Circulating tumor cells (CTCs) have been regarded as the major cause of metastasis, holding significant insights for tumor diagnosis and treatment. Although many efforts have been made to develop methods for CTC isolation and release in microfluidic system, it remains significant challenges to realize highly efficient isolation and gentle release of CTCs for further cellular and bio-molecular analyses. In this study, we demonstrate a novel method for CTC isolation and release using a simple wedge-shaped microfluidic chip embedding degradable znic oxide nanorods (ZnNRs) substrate. By integrating size-dependent filtration with degradable nanostructured substrate, the capture efficiencies over 87.5% were achieved for SKBR3, PC3, HepG2 and A549 cancer cells spiked in healthy blood sample with the flow rate of 100 µL min-1. By dissolving ZnNRs substrate with an extremely low concentration of phosphoric acid (12.5 mM), up to 85.6% of the captured SKBR3 cells were released after reverse injection with flow rate of 100 µL min-1 for 15 min, which exhibited around 73.6% cell viability within 1 h after release to around 93.9% after re-cultured for 3 days. It is conceivable that our microfluidic device has great potentials in carrying on cell-based biomedical studies and guiding individualized treatment in the future.

In situ grown Ni9S8 nanorod/O-MoS2 nanosheet nanocomposite on carbon cloth as a free binder supercapacitor electrode and hydrogen evolution catalyst.

Transition metal sulfide nanostructure composites have received significant attention as energy conversion and storage devices. In this work, we report a three-dimension (3D) nanostructure with the Ni9S8 nanorods embedded in oxygen-incorporated MoS2 (O-MoS2) nanosheets for supercapacitors and hydrogen evolution catalysts. The in situ grown Ni9S8/O-MoS2 nanocomposite on carbon cloth can be used as a free binder supercapacitor electrode and hydrogen evolution catalyst. The Ni9S8/O-MoS2 nanocomposite exhibits electrochemical behaviors with a specific capacitance of 907 F g-1 (at 2 A g-1) and good cycle stability after 1200 cycles due to its unique mutual embedding 3D nanostructure. Furthermore, the Ni9S8/O-MoS2 nanocomposite also shows highly electrocatalytic features for hydrogen production with an onset overpotential of ∼150 mV and a low Tafel slope of ∼81 mV dec-1. The oxygen incorporation of MoS2 provides more active sites to participate in the catalytic process for the hydrogen evolution reaction.

In situ synthesis of 3D CoS nanoflake/Ni(OH)2 nanosheet nanocomposite structure as a candidate supercapacitor electrode.

A three-dimensional (3D) CoS/Ni(OH)2 nanocomposite structure based on CoS nanoflakes and two-dimensional (2D) Ni(OH)2 nanosheets were in situ synthesized on Ni foam by a whole hydrothermal reaction and electrodeposition process. The 3D CoS/Ni(OH)2 nanocomposite structures demonstrate the combined advantages of a sustained cycle stability of CoS and high specific capacitance from Ni(OH)2. The obtained CoS/Ni(OH)2 nanocomposite structures on Ni foam can directly serve as a binder-free electrode for a supercapacitor. For the 3D CoS/Ni(OH)2 nanocomposite electrode, the high specific capacitance is 1837 F g(-1) at a scan rate of 1 mV s(-1), which is obviously higher than both the bare CoS electrode and Ni(OH)2 electrode. The galvanostatic charge and discharge measurements illustrate that the 3D CoS/Ni(OH)2 nanocomposite electrode possesses excellent cycle stability, and it keeps a 95.8% retention of the initial capacity after 5000 cycles. Electrochemical impedance spectroscopy measurements also confirm that the 3D CoS/Ni(OH)2 nanocomposite electrode has better electrochemical characteristics. These remarkable performances can be attributed to the unique 3D nanoporous structure of CoS/Ni(OH)2 which leads to a large accessible surface area and a high stability during long-term operation. In addition, 2D Ni(OH)2 nanosheets in 3D nanocomposite structures can afford rapid mass transport and a strong synergistic effect of CoS and Ni(OH)2 as individual compositions contribute to the high performance of the nanocomposite structure electrode. These results may promote the design and implementation of nanocomposite structures in advanced supercapacitors.

Enhanced field emission from in situ synthesized 2D copper sulfide nanoflakes at low temperature by using a novel controllable solvothermal preferred edge growth route.

A facile one-pot solvothermal route using the reaction of sputtered copper film and sulfur powder in ethanol solution at a low temperature of 90 °C for 12 hours has been implemented to in situ synthesize 2D hexagonal copper sulfide (CuS) nanoflakes. Their field electron emission (FE) characteristics were investigated and were found to have a close relationship with the copper film's thickness. The lowest turn on electric field (Eon) was 2.05 V µm(-1) and the largest field enhancement factor (ß) was 7261 when the copper film's thickness was 160 nm. Furthermore, through a preferred edge growth route, patterned CuS nanoflakes were synthesized with the combined effect from a copper film seed layer and a passivation layer to further improve FE properties with an Eon of 1.65 V µm(-1) and a ß of 8351. The mechanism of the patterned CuS nanoflake preferred edge growth is reported and discussed for the first time.

Enhanced electroluminescence using Ta2O5/ZnO/HfO2 asymmetric double heterostructure in ZnO/GaN-based light emitting diodes.

ZnO/GaN-based light-emitting diodes (LEDs) with improved asymmetric double heterostructure of Ta2O5/ZnO/HfO2 have been fabricated. Electroluminescence (EL) performance has been enhanced by the HfO2 electron blocking layer and further improved by continuing inserting the Ta2O5 hole blocking layer. The origins of the emission have been identified, which indicated that the Ta2O5/ZnO/HfO2 asymmetric structure could more effectively confine carriers in the active i-ZnO layer and meanwhile suppresses of radiation from GaN. This device exhibits superior stability in long-time running. It's hoped that the asymmetric double heterostructure may be helpful for the development of the future ZnO-based LEDs.

Unusual electroluminescence from n-ZnO@i-MgO core-shell nanowire color-tunable light-emitting diode at reverse bias.

Light-emitting diodes (LEDs) based on n-ZnO@i-MgO core-shell (CS) nanowires (NWs) are herein demonstrated and characterized. MgO insulating layers were rationally introduced as shells to modify/passivate the surface defects of ZnO NWs. A high-quality ZnO/MgO interface was attained and the optically pumped near-band-edge emission of the bare ZnO NWs was greatly enhanced after cladding i-MgO shells. Electroluminescence (EL) spectra measured in the whole UV-visible range revealed that light emission can only be detected when LEDs were applied with reverse bias. Moreover, the emission color can be tuned from orange to bright white with increasing reverse bias. We explored these interesting results tentatively in terms of the energy-band diagram of the heterojunction and it was found that the interfacial i-MgO shells not only acted as an insulator to prevent a short circuit between the two electrodes, but also offered a potential energy difference so that electron tunneling was energetically possible, both of which were essential to generate the reverse-bias EL. The dipole-forbidden d-d transitions by the Laporte selection rule in the p-NiO might be the reason to why there is no light being detected from the CS NW LED under forward bias. It is hoped that this simple and facile route may provide an effective approach in designing low-cost CS NW LEDs.

Highly Efficient Isolation of Circulating Tumor Cells Using a Simple Wedge-Shaped Microfluidic Device.

OBJECTIVE: We have developed a novel simple wedge-shaped microfluidic device for highly efficient isolation of circulating tumor cells (CTCs) from cancer patient blood samples. METHODS: We used wet chemical etching and thermal bonding technologies to fabricate the wedge-shaped microdevice and performed optimization assays to obtain optimal capture parameters. Cancer cells spiked samples were used to evaluate the capture performance. Clinical assays were performed to isolate and identify CTCs from whole blood samples of patients with liver, breast, lung, and gastric cancer. RESULTS: Outlet height of 5.5 µm and flow rate of 200 µL/min were chosen as the optimal CTC-capture conditions. This method exhibited excellent isolation performance (more than 85% capture efficiency) for four cancer cell lines (HepG2, SKBR3, A549, and BGC823). In clinical assay, the platform identified CTCs 5 in 6 liver (83.3%), 8 in 10 breast (80%), 5 in 8 lung (62.5%), 5 in 9 gastric (55.6%) cancer patients, and only 1 in 25 healthy blood samples (4%). CONCLUSION: Our wedge-shaped microfluidic device had several advantages, including relatively simple fabrication, high capture efficiency, simple sample processing steps, and easy observation. SIGNIFICANCE: This method had successfully demonstrated the clinical feasibility of CTC isolation and shown a great potential of clinical usefulness in monitoring tumor prognosis and guiding individualized treatment in the future.

Metal-Organic Framework Template Derived Porous CoSe2 Nanosheet Arrays for Energy Conversion and Storage.

Porous CoSe2 on carbon cloth is prepared from a cobalt-based metal organic framework template with etching and selenization reaction, which has both a larger specific surface area and outstanding electrical conductivity. As the catalyst for oxygen evolution reaction, the porous CoSe2 achieves a lower onset potential of 1.48 V versus the reversible hydrogen electrode (RHE) and a small potential of 1.52 V (vs RHE) at an anodic current density of 10 mA cm-2. Especially, the linear sweep voltammogram curve of the porous CoSe2 is in consist with the initial curve after durability test for 24 h. When tested as an electrode for supercapacitor, it can deliver a specific capacitance of 713.9 F g-1 at current density of 1 mA cm-2 and exhibit excellent cycling stability in that a capacitance retention of 92.4% can be maintained after 5000 charge-discharge cycles at 5 mA cm-2. Our work presents a novel strategy for construction of electrochemical electrode.

Controllable synthesis of flake-like Al-doped ZnO nanostructures and its application in inverted organic solar cells.

Flake-like Al-doped ZnO (AZO) nanostructures including dense AZO nanorods were obtained via a low-temperature (100°C) hydrothermal process. By doping and varying Al concentrations, the electrical conductivity (σ) and morphology of the AZO nanostructures can be readily controlled. The effect of σ and morphology of the AZO nanostructures on the performance of the inverted organic solar cells (IOSCs) was studied. It presents that the optimized power conversion efficiency of the AZO-based IOSCs is improved by approximately 58.7% compared with that of un-doped ZnO-based IOSCs. This is attributed to that the flake-like AZO nanostructures of high σ and tunable morphology not only provide a high-conduction pathway to facilitate electron transport but also lead to a large interfacial area for exciton dissociation and charge collection by electrodes.