Unique modulation effects on the performance of graphene-based ammonia sensors via ultrathin bimetallic Au/Pt layers and gate voltages.

Gas sensors with superior comprehensive performance at room temperature (RT) are always desired. Here, Au, Pt and Pt/Au-decorated graphene-based field effect transistor (FET) sensors for ammonia (denoted as Au/Gr, Pt/Gr and Pt/Au/Gr, respectively) are designed and fabricated. All these devices exhibited far better RT sensing performances for ammonia compared with graphene devices. Applying positive back gate voltages can further enhance their RT performance in which the Pt/Au/Gr devices show superior RT comprehensive performance such as a response of -16.2%, a recovery time of 4.6 min, and especially a much reduced response time of 54 s for 200 ppm NH3 with a detection limit of 103 ppb at a gate voltage of +60 V, and can be potentially tailored for further performance improvement by controlling the ratios of Pt and Au. The dependences of their performance on the gate voltage except for the response time could be reasonably explained by theoretical calculations in terms of the changes of the total density of states near the Fermi level, adsorption energies, transferred charges and adsorption distances. This study provides an effective solution for performance improvement of FET-based sensors via synergistic effects of ultrathin-layer multiple-metallic decoration and gate voltage, which would promote the exploration of novel sensors.

Long-Term Highly Stable High-Voltage LiCoO2 Synthesized via a Solid Sulfur-Assisted One-Pot Approach.

Commercialized lithium cobalt oxide (LCO) only shows a relatively low capacity of ≈175 mAh g-1 despite a high theoretical capacity of ≈274 mAh g-1 . As an effective and direct strategy, increasing its charge cutoff voltage can, in principle, escalate the capacity, which is however precluded by the irreversible phase transition, oxygen loss, and severe side reactions with electrolytes normally. Herein, an in situ sulfur-assisted solid-state approach is proposed for one-pot synthesis of long-term highly stable high-voltage LCO with a novel compound structure. The coating of coherent spinel Lix Co2 O4 shells on and the gradient doping of SO4 2- polyanions into LCO are in situ realized simultaneously in terms of gas-solid interface reactions between metal oxides and generated SO2 gas from sulfur during synthesis. At 4.6 V, this LCO shows the discharge capacities of 232.4 mAh g-1 at 0.1 C (1 C = 280 mA g-1 ), 215 mAh g-1 at 1 C and 139 mAh g-1 even at 20 C and the capacity retentions of 97.4% (89.7%) after 100 (300) cycles at 1 C. This approach is facile, low-cost and up-scalable and may provide a route to improve the performance of LCO and other electrode materials greatly.

Cu/graphene interdigitated electrodes with various copper thicknesses for UV-illumination-enhanced gas sensors at room temperature.

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.

Simultaneous achievement of superior response and full recovery of titanium dioxide/graphene hybrid FET sensors for NH3 through p- to n-mode switch.

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.

The impact of advanced proteomics in the search for markers and therapeutic targets of bladder cancer.

Bladder cancer is the most common cancer of the urinary tract and can be avoided through proper surveillance and monitoring. Several genetic factors are known to contribute to the progression of bladder cancer, many of which produce molecules that serve as cancer biomarkers. Blood, urine, and tissue are commonly analyzed for the presence of biomarkers, which can be derived from either the nucleus or the mitochondria. Recent advances in proteomics have facilitated the high-throughput profiling of data generated from bladder cancer-related proteins or peptides in parallel with high sensitivity and specificity, providing a wealth of information for biomarker discovery and validation. However, the transmission of screening results from one laboratory to another remains the main disadvantage of these methods, a fact that emphasizes the need for consistent and standardized procedures as suggested by the Human Proteome Organization. This review summarizes the latest discoveries and progress of biomarker identification for the early diagnosis, projected prognosis, and therapeutic response of bladder cancer, informs the readers of the current status of proteomic-based biomarker findings, and suggests avenues for future work.

Unveiling the Roles of Trace Fe and F Co-doped into High-Ni Li-Rich Layered Oxides in Performance Improvement.

High-Ni Li-rich layered oxides (HNLOs) derived from Li-rich Mn-based layered oxides (LRMLOs) can effectively mitigate the voltage decay of LRMLOs but normally suffered from decreased capacity and cycling stability. Herein, an effective, simple, and up-scalable co-doping strategy of trace Fe and F ions via a facile expanded graphite template-sacrificed approach was proposed for improving the performance of HNLOs. The trace Fe and F co-doping can far more effectively improve both its rate capability and cycling stability in a synergistic manner compared to the introduction of individual Fe cations and F anions. The co-doping of Fe and F increased the Li-O bonds by a magnitude far larger than the summation of the increments by their individual doping, quite favorable for the performance. The trace Fe doping can escalate the capacity and enhance the rate capability significantly by increasing the components of lower valence transition metals to activate their redox reactions more effectively and improving both the electronic and ionic conduction. In contrast, trace F can improve the cycling stability remarkably by lowering the O 2p band top to suppress the lattice oxygen escape effectively which were revealed by density functional theory calculations. The co-doped cathode exhibited excellent cycling stability with a superior capacity retention of 90% after 200 cycles at 1 C, much higher than 64% for the pristine sample. This study offers an idea for synergistically improving the performance of Li-rich layered oxides by co-doping trace Fe cations and F anions simultaneously, which play a complementary role in performance improvement.

Lithium Antievaporation-Loss Engineering via Sodium/Potassium Doping Enables Superior Electrochemical Performance of High-Nickel Li-Rich Layered Oxide Cathodes.

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 Li1.2-xMxNi0.32Mn0.48O2 (M = Na, K) layered oxides via a facile expanded graphite template-sacrificed approach. Both Na- and K-doped samples exhibit excellent rate capability and cycling stability compared with the un-doped one. The Na-doped sample shows a capacity retention of 93% after 200 cycles at 1C, which is quite outstanding for HNLO. The greatly improved electrochemical performances are attributed to the increased effective Li content in the lattice via Li antievaporation-loss engineering, the expanded Li slab, the pillaring effect, the increased C2/m component, and the improved electronic conductivity. Different performances by the introduction of sodium and potassium ions may be ascribed to their different ionic radii, which give rise to their different doping behaviors and threshold doping amounts. This work provides a new idea of enhancing electrochemical performance of HNLO by doping proper alien elements to increase the lattice lithium content effectively.

Enhanced Thermoelectric Properties of Bi2 Te3 -Based Micro-Nano Fibers via Thermal Drawing and Interfacial Engineering.

High-performance thermoelectric (TE) materials with great flexibility and stability are urgently needed to efficiently convert heat energy into electrical power. Recently, intrinsically crystalline, mechanically stable, and flexible inorganic TE fibers that show TE properties comparable to their bulk counterparts have been of interest to researchers. Despite remarkable progress in moving TE fibers toward room-temperature TE conversion, the figure-of-merit value (ZT) and bending stability still need enhancement. Herein, interfacial-engineering-enhanced TE properties of micro-nano polycrystalline TE fibers fabricated by thermally drawing Bi2 Te3 -based bulks in a glass-fiber template are reported. The interfacial engineering effect comes from generating stress-induced oriented nanocrystals to increase electrical conductivity and producing strain-distorted interfaces to decrease thermal conductivity. The 4 µm-diameter fibers achieve a 40% higher ZT (≈1.4 at 300 K) than their bulk counterparts and show a reversible bending radius of 50 µm, approaching the theoretical elastic limit. This fabrication strategy works for a wide range of inorganic TE materials and benefits the development of fiber-based micro-TE devices.

Fibrils Formed by Dendron-b-oligoaniline-b-dendron Block Co-oligomer.

Novel dendritic triblock co-oligomer (14G2A3) consisting of ester dendrons and aniline oligomer was synthesized and found to self-assemble into fibrils in THF. Studies reveal that the formation of the fibrils originates from both of the amphiphilic interactions between the ester dendrons and oligoaniline, as well as the intermolecular π-π stacking among oligoanilines. The shape effect of dendrons on molecular packing was comparatively analyzed with packing parameter against its linear analogous compound. At the same time, the driving forces that dominate the final aggregating state of the block oligomer were separately investigated using the bulky-group protecting method, which allows release of the intermolecular π-π stacking of oligoaniline in a controlled manner. Results show that both the introduction of dendrons and the intermolecular π-π stacking will increase the packing parameter of the block oligomer and, consequently, cause the self-assembly morphology to evolve step by step from micelles to vesicles and finally to fibrils. The fibrils can form complexes with SWNTs to increase solubility in THF. The effective fluorescence quenching accompanied also opens a gate for the block co-oligomer to have potential applications in organic electronic devices.

p-p Heterojunction Sensors of p-Cu3Mo2O9 Micro/Nanorods Vertically Grown on p-CuO Layers for Room-Temperature Ultrasensitive and Fast Recoverable Detection of NO2.

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.

Assembly Strategy and Performance Evaluation of Flexible Thermoelectric Devices.

Although organic and composite thermoelectric (TE) materials have witnessed explosive developments in the past five years, the research of flexible TE devices is rather limited. In particular, their assembly strategies and device performance reported in the literature cannot be directly compared, due to a variety of deviances including p- and n-type component materials, shape and dimensions of p-n flexible films, and applied temperature gradient (ΔT). Here, three types of assembly strategies for flexible TE devices, that is, serial, folding, and stacking, are compared by fixing the corresponding experimental parameters. Furthermore, a convenient and general method to evaluate the flexible device performance (FDP) is put forward, that is, FDP = P max m Δ T N , where the maximum output power (P max) is divided by product mass (m), ΔT, and pair number of p-n couples (N). The FDPs for the present serial, folding, and stacking devices are 11.13, 8.87, and 0.05 nW g-1 K-1, respectively, confirming that the serial configuration is the best among the three strategies for flexible device fabrication. The preliminary evaluation method proposed herein will pave the way for a design strategy of flexible TE devices and speed up their applications in waste-heat harvesting, e-skin, wearable electronics, etc.

A Generalized Methodology of Designing 3D SERS Probes with Superior Detection Limit and Uniformity by Maximizing Multiple Coupling Effects.

Accurate design of high-performance 3D surface-enhanced Raman scattering (SERS) probes is the desired target, which is possibly implemented with a prerequisite of quantifying formidable multiple coupling effects involved. Herein, by combining theory and experiments on 3D periodic Au/SiO2 nanogrid models, a generalized methodology of accurately designing high performance 3D SERS probes is developed. Structural symmetry, dimensions, Au roughness, and polarization are successfully correlated quantitatively to intrinsic localized electromagnetic field (EMF) enhancements by calculating surface plasmon polariton (SPP), localized surface plasmon resonance (LSPR), optical standing wave effects, and their couplings theoretically, which is experimentally verified. The hexagonal SERS probes optimized by this methodology realize over two orders of magnitudes (405 times) improvement of detection limit for Rhodamine 6G model molecules (2.17 × 10-11 m) compared to the unoptimized probes with the same number density of hot spots, an enhancement factor of 3.4 × 108, a uniformity of 5.52%, and are successfully applied to the detection of 5 × 10-11 m Hg ions in water. This unambiguously results from the Au roughness-independent extra 144% contribution of LSPR effects excited by SPP interference waves as secondary sources, which is very unusual to be beyond the conventional recognition.

Pyroelectricity of water ice.

Water ice usually is thought to have zero pyroelectricity by symmetry. However, biasing it with ions breaks the symmetry because of the induced partial dipole alignment. This unmasks a large pyroelectricity. Ions were soft-landed upon 1 mum films of water ice at temperatures greater than 160 K. When cooled below 140-150 K, the dipole alignment locks in. Work function measurements of these films then show high and reversible pyroelectric activity from 30 to 150 K. For an initial approximately 10 V induced by the deposited ions at 160 K, the observed bias below 150 K varies approximately as 10 Vx(T/150 K)2. This implies that water has pyroelectric coefficients as large as that of many commercial pyroelectrics, such as lead zirconate titanate (PZT). The pyroelectricity of water ice, not previously reported, is in reasonable agreement with that predicted using harmonic analysis of a model system of SPC ice. The pyroelectricity is observed in crystalline and compact amorphous ice, deuterated or not. This implies that for water ice between 0 and 150 K (such as astrophysical ices), temperature changes can induce strong electric fields (approximately 10 MV/m) that can influence their chemistry, ion trajectories, or binding.

Carbon Nanoparticle Hybrid Aerogels: 3D Double-Interconnected Network Porous Microstructure, Thermoelectric, and Solvent-Removal Functions.

We report reduced graphene oxide (rGO)/single-walled carbon nanotube (SWCNT) hybrid aerogels with enhanced thermoelectric (TE) performance and removal of organic solvents by designing 3D double-interconnected network porous microstructures. A convenient, cost-effective, and scalable preparation procedure is proposed compared with conventional high-temperature pyrolysis and supercritical drying techniques. The obtained hybrid aerogels are systematically characterized by apparent density, scanning electron microscopy, X-ray photoemission spectroscopy, Raman spectroscopy, and porosity. An enhanced TE performance of ZT ≈ ∼8.03 × 10-3 has been achieved due to the 3D double-interconnected network porous microstructure, the energy-filtering effect, and the phonon scattering at the abundant interfaces and joints. In addition, upon a large axial compression deformation, a high degree of retention of the Seebeck coefficient and a simultaneously significant enhancement of the electrical conductivity are observed. Finally, the hybrid aerogels display high capability for the removal of diverse organic solvents and good recyclability. These findings open a new avenue for exploiting aerogels with multifunctions and widening the applications of TE materials by judicious microstructure design.

Monoclinic ZIF-8 Nanosheet-Derived 2D Carbon Nanosheets as Sulfur Immobilizer for High-Performance Lithium Sulfur Batteries.

2D hierarchically porous carbon (2D-HPC) nanosheets with unique advantages are highly desired as host materials for lithium sulfur (Li-S) batteries and other energy storage devices. Herein, we propose a self-template and organic solvent-free approach to synthesize nanosheets of monoclinic ZIF-8 at room temperature from which 2D-HPC nanosheets (ZIF-8 nanosheets carbon denoted as ZIF-8-NS-C) are derived to be an efficient sulfur immobilizer for Li-S batteries for the first time. The anisotropic nanosheets are believed to relate to the symmetry of the monoclinic structure. The 2D ZIF-8-NS-C nanosheets with embedded hierarchical pores construct an effective conductive network through "plane-to-plane" modes to endow superior electron transfer and fast electrochemical kinetics. Moreover, the nitrogen-rich feature of ZIF-8-NS-C can increase the affinity/interaction of carbon host with lithium polysulfides, favoring the cyclic performance. The sulfur/ZIF-8-NS-C (S/ZIF-8-NS-C) cathode shows a superior rate capability with high capacities of 1226 mA h g-1 at 0.2 C and 785 mA h g-1 at 2 C, and a sustainable cycling stability with a capacity attenuation of 0.12% per cycle at 0.5 C for 300 cycles. The approach proposed here pioneers the controllable design of MOF-based structures to inspire the exploration of more variable MOF-derived porous materials for energy storage applications.

Flexible n-Type High-Performance Thermoelectric Thin Films of Poly(nickel-ethylenetetrathiolate) Prepared by an Electrochemical Method.

Flexible thin films of poly(nickel-ethylenetetrathiolate) prepared by an electrochemical method display promising n-type thermoelectric properties with the highest ZT value up to 0.3 at room temperature. Coexistence of high electrical conductivity and high Seebeck coefficient in this coordination polymer is attributed to its degenerate narrow-bandgap semiconductor behavior.

Template-directed in situ polymerization preparation of nanocomposites of PEDOT:PSS-coated multi-walled carbon nanotubes with enhanced thermoelectric property.

A template-directed in situ polymerization preparation of nanocomposites of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-coated multi-walled carbon nanotubes (MWCNTs) with greatly enhanced thermoelectric property is presented. The results reveal that monomeric 3,4-ethylenedioxythiophene was successfully polymerized, enwrapping the surfaces of dispersed MWCNTs (templates) with the aid of PSS. The coated morphology was directly observed by high-resolution transmission electron microscopy. The coated layer was further characterized by energy-dispersive X-ray spectroscopy and X-ray diffraction. In addition, the interfacial interaction between PEDOT:PSS and MWCNTs was studied by Fourier transform infrared spectroscopy. Finally, the thermoelectric measurements show that the obtained PEDOT:PSS/MWCNT nanocomposites exhibited greatly enhanced electrical conductivities, Seebeck coefficients, and power factors when compared with those of neat PEDOT:PSS.

Drastically Enhanced High-Rate Performance of Carbon-Coated LiFePO4 Nanorods Using a Green Chemical Vapor Deposition (CVD) Method for Lithium Ion Battery: A Selective Carbon Coating Process.

Application of LiFePO4 (LFP) to large current power supplies is greatly hindered by its poor electrical conductivity (10(-9) S cm(-1)) and sluggish Li+ transport. Carbon coating is considered to be necessary for improving its interparticle electronic conductivity and thus electrochemical performance. Here, we proposed a novel, green, low cost and controllable CVD approach using solid glucose as carbon source which can be extended to most cathode and anode materials in need of carbon coating. Hydrothermally synthesized LFP nanorods with optimized thickness of carbon coated by this recipe are shown to have superb high-rate performance, high energy, and power densities, as well as long high-rate cycle lifetime. For 200 C (18s) charge and discharge, the discharge capacity and voltage are 89.69 mAh g(-1) and 3.030 V, respectively, and the energy and power densities are 271.80 Wh kg(-1) and 54.36 kW kg(-1), respectively. The capacity retention of 93.0%, and the energy and power density retention of 93.6% after 500 cycles at 100 C were achieved. Compared to the conventional carbon coating through direct mixing with glucose (or other organic substances) followed by annealing (DMGA), the carbon phase coated using this CVD recipe is of higher quality and better uniformity. Undoubtedly, this approach enhances significantly the electrochemical performance of high power LFP and thus broadens greatly the prospect of its applications to large current power supplies such as electric and hybrid electric vehicles.

An experimental apparatus for simultaneously measuring Seebeck coefficient and electrical resistivity from 100 K to 600 K.

In this paper, we report a fully automated experimental apparatus for measuring Seebeck coefficient and electrical resistivity of a sample simultaneously in a temperature range of 100-600 K. The Seebeck coefficient is measured using a quasi-steady temperature differential method in which two ceramic heaters are employed to alternately heat the sample. The sample holder is designed to reduce temperature disturbance on its base during a measurement cycle. To demonstrate the accuracy and reliability of the experimental setup, we have performed tests on reference materials including constantan and platinum.

Vesicles Formed by Oligostyrene-block-Oligoaniline-block-Oligostyrene Triblock Oligomer.

Novel π-conjugated coil-rod-coil triblock oligomers containing optoelectronic active oligoaniline segments were synthesized. The block oligomer can self-assemble into diverse aggregating morphologies including spherical micelles and thin-layer vesicles in THF, which is found associated with the removing of the protecting groups of oligoaniline segments. A possible mechanism was proposed to explain the self-assembly behavior changes in which chain conformation variation of the aniline segments initiated from deprotection of the nitrogen atoms is pointed to be the key factor that dominates the transition process.