Effect of Oxygen Interstitial Ordering on Multiple Order Parameters in Rare Earth Ferrite.

Oxygen interstitials and vacancies play a key role in modulating the microstructure and properties of nonstoichiometric oxide systems, such as those used for superconductors and multiferroics. Key to understanding the tuning mechanisms resulting from oxygen doping is a knowledge of the precise positions of these lattice defects, and of the interaction both between these defects and with many order parameters. Here, we report how such information can, for the first time, be obtained from a sample of LuFe_{2}O_{4.22} using a range of techniques including advanced electron microscopy, atomic-resolution spectroscopy, and density functional theory calculations. The results provide quantitative atomic details of the crystal unit cell, together with a description of the ferroelastic, ferroelectric, and ferromagnetic order parameters. We elucidate also the interaction between these order parameters and the positions of the oxygen interstitials in the oxygen-enriched sample. The comprehensive analysis of oxygen interstitial ordering provides insights into understanding the coupling among different degrees of freedom in rare earth ferrites and demonstrates that oxygen content regulation is a powerful tool for tuning the microstructure and properties for this class of quantum material.

Accumulation and toxicity of intravenously-injected functionalized graphene oxide in mice.

Graphene and its functionalized derivatives have recently emerged as interesting nanomaterials with promising applications in biomedicine. In this study, the long-term in vivo biodistribution of intravenously injected nanographene oxide (NGO) functionalized with poly sodium 4-styrenesulfonate (PSS) was systematically examined and the potential toxicity over 6 months of NGO-PSS nanoparticles was investigated. Our results showed that the nanoparticles mainly accumulate in the lung, liver and spleen, where they persist for at least 6 months. These nanoparticles result in acute liver injury and chronic inflammation of the lung, liver and spleen, as evidenced by blood biochemistry results and histological examinations.

Electron field emission enhancement of vertically aligned ultrananocrystalline diamond-coated ZnO core-shell heterostructured nanorods.

Enhanced electron field emission (EFE) behavior of a core-shell heterostructure, where ZnO nanorods (ZNRs) form the core and ultrananocrystalline diamond needles (UNCDNs) form the shell, is reported. EFE properties of ZNR-UNCDN core-shell heterostructures show a high emission current density of 5.5 mA cm(-2) at an applied field of 4.25 V µm(-1) , and a low turn-on field of 2.08 V µm(-1) compared to the 1.67 mA cm(-2) emission current density (at an applied field of 28.7 V µm(-1) ) and 16.6 V µm(-1) turn-on field for bare ZNRs. Such an enhancement in the field emission originates from the unique materials combination, resulting in good electron transport from ZNRs to UNCDNs and efficient field emission of electrons from the UNCDNs. The potential application of these materials is demonstrated by the plasma illumination measurements that lowering the threshold voltage by 160 V confirms the role of ZNR-UNCDN core-shell heterostructures in the enhancement of electron emission.

Mediatorless N(2) incorporated diamond nanowire electrode for selective detection of NADH at stable low oxidation potential.

The electrocatalytic properties of a N2 incorporated diamond nanowire (N-DNW) unmodified electrode towards the oxidation of nicotinamide adenine dinucleotide (NADH) was critically evaluated. The electrochemical behavior of the N-DNW unmodified electrode was examined and compared with that of boron-doped diamond, glassy carbon electrode, and graphite electrodes. The N-DNW electrode had high selectivity and high sensitivity for the differential pulse voltammetric detection of NADH in the presence of ascorbic acid at the lower and stable oxidation potential. Moreover, it exhibited strong stability after prolonged usage. The oxidation peak potential at the N-DNW electrode remained unchanged even after exposure to the solution, followed by washing, drying, and storage in laboratory air for 20 days, with minimization of surface contamination. Therefore, the N-DNW unmodified electrode shows promise for the detection of NADH and is attractive for use in a dehydrogenase based biosensor and other analytical applications.

Fast process to decorate silver nanoparticles on carbon nanomaterials for preparing high-performance flexible transparent conductive films.

This work demonstrates a fast process to decorate silver (Ag) nanoparticles onto the functionalized few-walled carbon nanotubes (f-FWCNTs) and graphene nanosheets (f-GNs). The Ag-coated carbon nanomaterials were used as fillers, which mixed with poly(3,4-ethylenedioxythiophene)-poly(4-stryensulfonate) (PEDOT:PSS) for preparing high optoelectronic performances of flexible transparent conductive films (TCFs). The Ag nanoparticles with a particle size of approximate 5 nm were uniformly distributed on the surfaces of the f-FWCNTs (Ag@f-FWCNTs) and the f-GNs (Ag@f-GNs). The Ag ions play the role of electron acceptors during the reduction process, which increases the hole concentrations in PEDOT:PSS, f-FWCNTs, and f-GNs, therefore enhancing the electrical conductivity of the TCFs. Additionally, the Schottky barrier was decreased because of the increase of work functions of the carbon fillers caused by Ag decoration. The X-ray diffraction spectrum of Ag@f-GNs depicts the formations of the face-centered cubic Ag nanoparticles, and the peak of the (002) graphene plane slightly shifted to the lower frequency, indicating that the f-GN interlayer was intercalated with Ag ions or Ag nanoparticles. When the mixture of 2.0 wt % Ag@f-FWCNTs and 8.0 wt % Ag@f-GNs containing PEDOT:PSS dispersant was coated onto a poly(ethylene terephthalate) (PET) substrate, outstanding optoelectronic properties with a sheet resistance of 50.3 Ω/sq and a transmittance of 79.73% at a wavelength of 550 nm were achieved.

Dipole moment as the underlying mechanism for enhancing the immobilization of glucose oxidase by ferrocene-chitosan for superior specificity non-invasive glucose sensing.

Non-invasive methods for sensing glucose levels are highly desirable due to the comfortableness, simplicity, and lack of infection risk. However, the insufficient accuracy and ease of interference limit their practical medical applications. Here, we develop a non-invasive salivary glucose biosensor based on a ferrocene-chitosan (Fc-Chit) modified carbon nanotube (CNT) electrode through a simple drop-casting method. Compared with previous studies that relied mainly on trial and error for evaluation, this is the first time that dipole moment was proposed to optimize the electron-mediated Fc-Chit, demonstrating sturdy immobilization of glucose oxidase (GOx) on the electrode and improving the electron transfer process. Thus, the superior sensing sensitivity of the biosensor can achieve 119.97 µA mM-1 cm-2 in phosphate buffered saline (PBS) solution over a wide sensing range of 20-800 µM. Additionally, the biosensor exhibited high stability (retaining 95.0% after three weeks) and high specificity toward glucose in the presence of various interferents, attributed to the specific sites enabling GOx to be sturdily immobilized on the electrode. The results not only provide a facile solution for accurate and regular screening of blood glucose levels via saliva tests but also pave the way for designing enzymatic biosensors with specific enzyme immobilization through fundamental quantum calculations.

Graphene woven fabric-polydimethylsiloxane piezoresistive films for smart multi-stimuli responses.

The outstanding properties of graphene, including its electromechanical property, could be engineered for wearable electronic sensor platforms. The tubular graphene weaved into a mesh or graphene woven fabrics (GWF) has been reported as one of the most sensitive materials for deformation detection, as well as a promising temperature sensor. Herein, we present the performance of our developed flexible, stretchable, and multiple sensitive sensors fabricated from GWF embedded in polydimethylsiloxane (PDMS) film substrate. The GWF/PDMS sensor shows a pressure sensitivity of 0.0142 kPa-1 in a wide linearity range of 0-20 kPa, an outstanding Gauge factor (GF) of 582 at a strain of 6.2 %, and a very high positive sensitivity of 0.0238 °C-1 in the temperature range of 25-80 °C. A practical application as a high sensitivity air pressure sensor able to measure low pressures (in the range of Pa to kPa) was also demonstrated. This sensor platform having desirable performance characteristics is an excellent candidate for wearable devices in the healthcare sector.

Gamma-Ray Irradiation Induced Ultrahigh Room-Temperature Ferromagnetism in MoS2 Sputtered Few-Layered Thin Films.

Defect engineering is of great interest to the two-dimensional (2D) materials community. If nonmagnetic transition-metal dichalcogenides can possess room-temperature ferromagnetism (RTFM) induced by defects, then they will be ideal for application as spintronic materials and also for studying the relation between electronic and magnetic properties of quantum-confined structures. Thus, in this work, we aimed to study gamma-ray irradiation effects on MoS2, which is diamagnetic in nature. We found that gamma-ray exposure up to 9 kGy on few-layered (3.5 nm) MoS2 films induces an ultrahigh saturation magnetization of around 610 emu/cm3 at RT, whereas no significant changes were observed in the structure and magnetism of bulk MoS2 (40 nm) films even after gamma-ray irradiation. The RTFM in a few-layered gamma-ray irradiated sample is most likely due to the bound magnetic polaron created by the spin interaction of Mo 4d ions with trapped electrons present at sulfur vacancies. In addition, density functional theory (DFT) calculations suggest that the defect containing one Mo and two S vacancies is the dominant defect inducing the RTFM in MoS2. These DFT results are consistent with Raman, X-ray photoelectron spectroscopy, and ESR spectroscopy results, and they confirm the breakage of Mo and S bonds and the existence of vacancies after gamma-ray irradiation. Overall, this study suggests that the occurrence of magnetism in gamma-ray irradiated MoS2 few-layered films could be attributed to the synergistic effects of magnetic moments arising from the existence of both Mo and S vacancies as well as lattice distortion of the MoS2 structure.

Carbon nanotube rope with electrical stimulation promotes the differentiation and maturity of neural stem cells.

In recent years, the utilization of nanomaterials such as carbon nanotubes (CNTs) in the field of neuroscience has forever changed the approach to nerve-related research. The array of novel properties CNTs possess allows them to interact with neurons at the nanodimensional scale. In this study, a CNT rope substrate is developed to allow the electrical stimulation of neural stem cells (NSCs) in culture medium and the in situ observation of the response of these stem cells after stimulation. CNTs are synthesized by chemical vapor deposition and prepared into a ropelike structure with a diameter of 1 mm and length of 1.5 cm. NSCs are differentiated on the CNT rope substrate while the direction of neurite outgrowth, phenotype, and maturity of the NSCs are analyzed. Fluorescence and scanning electron microscopy demonstrate that neurite extension favors the direction of the spiral topography on the CNT rope. NSCs plated on CNT ropes are boosted towards differentiated neurons in the early culture stage when compared to conventional tissue culture plates via the analysis of neuronal gene and protein expressions by quantitative polymerase chain reaction and immunostaining, respectively. Furthermore, a set of electrical stimulation parameters (5 mV, 0.5 mA, 25 ms intermittent stimulation) promotes neuronal maturity while also increasing the speed of neurite outgrowth. These results indicate that an electroconductive CNT rope substrate along with electrical stimulation may have a synergistic effect on promoting neurite elongation and boosting effects on the differentiation of NSCs into mature neuronal cells for therapeutic application in neural regeneration.

Human Exhalation CO2 Sensor Based on the PEI-PEG/ZnO/NUNCD/Si Heterojunction Electrode.

Gas sensors based on semiconductors have outstanding sensitivity compared with the oxide-based devices; however, the high operation temperature greatly hinders its development in practical applications. Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide, and the patients with severe COPD with or without exacerbation tend to have airflow obstruction, which results in an increase of CO2 concentration and subsequent hypercapnic respiratory failure. At present, COPD detection relies on professional operation; however, the patients suffer great discomfort during the arterial blood sampling. All these facts reduce patient's willingness to test their physical health. Thus, noninvasive monitoring of CO2 levels is crucial for the early diagnosis of high-risk COPD patients. A nitrogen-incorporated ultrananocrystalline diamond (NUNCD) film exhibits excellent properties in biosensing and polyetherimide-polyethylene glycol (PEI-PEG) polymer possesses a great capability of CO2 capturing. By incorporating NUNCD into PEI-PEG film, this work focuses on ameliorating the sensitivity and selectivity of the present semiconductor CO2 sensor. From the theoretical regression analyses of the experimental results, it is found that the excellent performance of the PEI-PEG/ZnO/NUNCD/Si electrode is contributed by two main reaction layers, the adsorption layer (PEI-PEG) and the electric transfer layer (ZnO/NUNCD). The selectivity is dominated by the PEI-PEG adsorption layer and the sensitivity is directly related to the changes in the work function of the ZnO/NUNCD interface. The high aspect ratio (>10) of the flower-like ZnO structure, growth from ZnO nanoparticles, can provide a more active adsorption area, as a result, extremely enhancing the sensitivity of the CO2 sensor.

A Green Approach for High Oxidation Resistance, Flexible Transparent Conductive Films Based on Reduced Graphene Oxide and Copper Nanowires.

Copper nanowires (CuNWs)-based thin film is one of the potential alternatives to tin-doped indium oxide (ITO) in terms of transparent conductive films (TCFs). However, the severe problem of atmospheric oxidation restricts their practical applications. In this work, we develop a simple approach to fabricate highly stable TCFs through the dip-coating method using reduced graphene oxide (rGO) and CuNWs as the primary materials. Compared with previous works using toxic reduction agents, herein, the CuNWs are synthesized via a green aqueous process using glucose and lactic acid as the reductants, and rGO is prepared through the modified Hummers' method followed by a hydrogen-annealing process to form hydrogen-annealing-reduced graphene oxide (h-rGO). In the rGO/CuNWs films, the dip-coated graphene oxide layer can increase the adhesion of the CuNWs on the substrate, and the fabricated h-rGO/CuNWs can exhibit high atmospheric oxidation resistance and excellent flexibility. The sheet resistance of the h-rGO/CuNWs film only increased from 25.1 to 42.2 Ω/sq after exposure to ambient atmosphere for 30 days and remained almost unchanged after the dynamic bending test for 2500 cycles at a constant radius of 5.3 mm. The h-rGO/CuNWs TCF can be not only fabricated via a route with a superior inexpensive and safe method but also possessed competitive optoelectronic properties with high electrical stability and flexibility, demonstrating great opportunities for future optoelectronic applications.

Consequences of gamma-ray irradiation on structural and electronic properties of PEDOT:PSS polymer in air and vacuum environments.

In this work, the effects of gamma-ray irradiation (up to 3 kGy) on the structural and electronic properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), irradiated in air and vacuum environments are systematically investigated. Raman spectroscopy indicates that there is no significant change in structural conformation of PEDOT:PSS film after gamma-ray irradiation. However, the conductivity of the film decreases as a function of dose in both air and vacuum environments, which can be deduced as a result of defects created in the structure. Hall effect measurements showed higher carrier concentration when the samples are irradiated under vacuum in comparison to the air environment, whereas mobility decreases as a function of dose irrespective of the environment. Furthermore, the electron spin resonance spectra provided evidence of the evolution of polaron population after gamma-ray exposure of 3 kGy, due to the decrease in charge delocalization and molecular ordering of the molecules. This decrease in conductivity and mobility of the PEDOT:PSS films irradiated in air and vacuum environments can be mainly ascribed to the defects and radical formation after gamma-ray exposure, favoring chain scission or cross-linking of the polymers.

Correction: Consequences of gamma-ray irradiation on structural and electronic properties of PEDOT:PSS polymer in air and vacuum environments.

[This corrects the article DOI: 10.1039/D1RA03463D.].

Nitrogen-Incorporated Boron-Doped Nanocrystalline Diamond Nanowires for Microplasma Illumination.

The origin of nitrogen-incorporated boron-doped nanocrystalline diamond (NB-NCD) nanowires as a function of substrate temperature (Ts) in H2/CH4/B2H6/N2 reactant gases is systematically addressed. Because of Ts, there is a drastic modification in the dimensional structure and microstructure and hence in the several properties of the NB-NCD films. The NB-NCD films grown at low Ts (400 °C) contain faceted diamond grains. The morphology changes to nanosized diamond grains for NB-NCD films grown at 550 °C (or 700 °C). Interestingly, the NB-NCD films grown at 850 °C possess one-dimensional nanowire-like morphological grains. These nanowire-like NB-NCD films possess the co-existence of the sp3-diamond phase and the sp2-graphitic phase, where diamond nanowires are surrounded by sp2-graphitic phases at grain boundaries. The optical emission spectroscopy studies stated that the CN, BH, and C2 species in the plasma are the main factors for the origin of nanowire-like conducting diamond grains and the materialization of graphitic phases at the grain boundaries. Moreover, conductive atomic force microscopy studies reveal that the NB-NCD films grown at 850 °C show a large number of emission sites from the grains and the grain boundaries. While boron doping improved the electrical conductivity of the NCD grains, the nitrogen incorporation eased the generation of graphitic phases at the grain boundaries that afford conducting channels for the electrons, thus achieving a high electrical conductivity for the NB-NCD films grown at 850 °C. The microplasma devices using these nanowire-like NB-NCD films as cathodes display superior plasma illumination properties with a threshold field of 3300 V/µm and plasma current density of 1.04 mA/cm2 with a supplied voltage of 520 V and a lifetime stability of 520 min. The outstanding plasma illumination characteristics of these conducting nanowire-like NB-NCD films make them appropriate as cathodes and pave the way for the utilization of these materials in various microplasma device applications.

Oscillation induced worm-like locomotion of carbon nanotubes.

Harmonic oscillation of a doubly clamped single-walled carbon nanotube rope is significantly damped by the resistive force of friction at intertube contacts and the energy transmission rate has been estimated to be lower than that on a metal wire excited at similar frequency and vibrating length by one order of magnitude.

Flexible Supercapacitors Prepared Using the Peanut-Shell-Based Carbon.

In this work, we report the fabrication and performance of supercapacitors made from carbonized peanut shells, which are renewable materials with a huge annual yield and are usually discarded directly by people. With proper treatment, peanut shells could be used for many applications. Herein, we demonstrate that the peanut shells treated with carbonization and activation processes not only possess an extremely high surface area but also provide a hierarchical structure for energy storage. The performance of the electrode can be further improved by nitrogen doping and adding graphene oxide to the electrode. The electrode shows a specific capacitance of 289.4 F/g, which can be maintained at an acceptable level even at a high scanning rate. In addition, a good capacitance retention of 92.8% after 5000 test cycles demonstrates that the electrode possesses an excellent electrochemical property.

Enhancing the Efficiency of a Forward Osmosis Membrane with a Polydopamine/Graphene Oxide Layer Prepared Via the Modified Molecular Layer-by-Layer Method.

Water scarcity is one of the most critical problems that humans have to face. Working toward solving this problem, we have developed a thin-film composite (TFC) membrane using the modified molecular layer-by-layer (modified mLBL) method to fabricate polyamide (PA) active layers on different substrates. Besides, it has been found that graphene oxide (GO) contains abundant functional groups such as hydroxyl and epoxide groups, which are able to improve both the physical and chemical properties of the forward osmosis (FO) membrane. Thus, we have employed graphene oxide (GO) as the substrate and used the modified mLBL method to prepare active polydopamine/graphene oxide (PDA/GO) layers to enhance the water flux of the forward osmosis (FO) membrane. PDA/GO-coated layers could enhance the hydrophilic nature of the substrate and lower its surface roughness, which would facilitate the formation of the PA layer. Moreover, the PDA/GO coating can be applied to all substrates because of the high degree of adhesion of PDA to different substrates. In this study, the highly hydrophilic poly(vinylidene fluoride) membrane is superior in FO properties, with a water flux of 17.32 LMH and a reverse solute flux of 4.34 gMH. In addition, an excellent performance of 60.15 LMH and 14.88 gMH can be achieved when the pressure-retarded osmosis (PRO) test mode with a draw solution concentration of 2.0 M is used in the test. It shows that the membrane prepared using the novel method showed excellent FO performance, which has high potential in industrial applications such as desalination.

Influence of gamma-ray irradiation and post-annealing studies on pentacene films: the anisotropic effects on structural and electronic properties.

In this work, γ-ray irradiation effects on pentacene thin films are investigated in terms of the change in the crystallinity, and electronic structure as well as chemical states of the film. The pentacene films are γ-irradiated up to 3 kGy and then characterized using synchrotron X-ray diffraction, near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy. We found that γ-ray irradiation creates defects, resulting in a decrease of X-ray diffraction intensity both in the plane normal and in-plane directions. From angle dependent NEXAFS; the transition of C 1s to π* orbital for irradiated samples increases; suggesting that the unoccupied π* states enhance due to defects or radical formation in pentacene thin films. Additionally, the in-plane resistivity shows a decreasing trend of resistance after irradiation. This trend of increase in conductivity is also consistent with C 1s to π transition, which manifests the increase in carrier concentration. Hall effect measurements further confirmed the increase in carrier concentration as a function of dose; however, the mobility of the sample decreases as the dose rate increases due to the defects created. By post-irradiation annealing, the thin film phase diffraction intensity can be recovered. Altogether, the anisotropic studies on pentacene films disclosed that the irradiation leads to defect formation along in-plane and plane normal directions. Overall, these results suggest that pentacene is one of the robust organic electronic materials; whose structure remains mostly intact even after irradiation up to a dose of 3 kGy.

Gamma Ray Irradiation Enhances the Linkage of Cotton Fabrics Coated with ZnO Nanoparticles.

In this work, we aim to study zinc oxide (ZnO)-based functional materials over cotton fabrics and their effects after gamma ray exposure of 9 kGy. We found that the binding of the nanoparticles with cotton fabrics can be enhanced after irradiation. This could be due to the oxygen deficiency or defects created in the interface between ZnO and cotton fabrics after irradiation. Near-edge X-ray absorption fine structure and X-ray photoelectron spectroscopy (XPS) were used to detect the oxygen inadequacies generated in the interior and at the surface of the ZnO nanoparticles after gamma ray exposure. XPS results showed that the binding energy of Zn shifts by 2 eV at 1.5 kGy and by 4 eV at 9 kGy. This huge shift of about 4 eV is completely different from other works due to the reaction that takes place on the interface between ZnO nanostructures and cotton fabrics after gamma ray irradiation. Overall, this work suggests that after gamma ray irradiation, there is an enhanced level of binding between the coated functional nanoparticles and cotton fabrics, which can be advantageous for the textile industries.

Green Treatment of Phosphate from Wastewater Using a Porous Bio-Templated Graphene Oxide/MgMn-Layered Double Hydroxide Composite.

Excessive phosphorus in water is the primary culprit for eutrophication, which causes approximately $2.2 billion annual economic loss in the United States. This study demonstrates a phosphate-selective sustainable method by adopting Garcinia subelliptica leaves as a natural bio-template, where MgMn-layered double hydroxide (MgMn-LDH) and graphene oxide (GO) can be grown in situ to obtain L-GO/MgMn-LDH. After calcination, the composite shows a hierarchical porous structure and selective recognition of phosphate, which achieves significantly high and recyclable selective phosphate adsorption capacity and desorption rate of 244.08 mg-P g-1 and 85.8%, respectively. The detail variation of LDHs during calcination has been observed via in situ transmission electron microscope (TEM). Moreover, the roles in facilitating phosphate adsorption and antimicrobial ability of chemical constituents in Garcinia subelliptica leaves, biflavonoids, and triterpenoids have been investigated. These results indicate the proposed bio-templated adsorbent is practical and eco-friendly for phosphorus sustainability in commercial wastewater treatment.