Because of the coupling between semiconducting and piezoelectric properties in wurtzite materials, strain-induced piezo-charges can tune the charge transport across the interface or junction, which is referred to as the piezotronic effect. For devices whose dimension is much smaller than the mean free path of carriers (such as a single atomic layer of MoS2), ballistic transport occurs. In this study, transport in the monolayer MoS2 piezotronic transistor is studied by presenting analytical solutions for two-dimensional (2D) MoS2. Furthermore, a numerical simulation for guiding future 2D piezotronic nanodevice design is presented.
A triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) were hybridized to harvest the human mechanical energy. By an effective conjunction of triboelectrification and electromagnetic induction, the hybridized nanogenerator with a radius of 2 cm and height of 1.2 cm could charge a 1,000 μF capacitor to 5.09 V after 100 cycles of vibration. This mini-sized hybrid nanogenerator could then be embedded in shoes to serve as an energy cell. Typical outdoor applications—including driving with a Global Positioning System (GPS) device, charging a Li-ion battery and a cell phone—were successfully demonstrated, suggesting its potential application in smart wearable electronics and future suits of soldiers.
In recent years, triboelectric nanogenerators have attracted much attention because of their unique potential in self-powered nanosensors and nanosystems. In this paper, we report a cylindrical spiral triboelectric nanogenerator (S-TENG), which not only can produce high electric output to power display devices, but also can be used as a self-powered displacement sensor integrated on a measurement ruler. At a sliding speed of 2.5 m/s, S-TENG can generate a short-circuit current (ISC) of 30 µA and an open-circuit voltage (VOC) of 40 V. As the power source, we fabricate a transparent and flexible hand-driven S-TENG. Furthermore, we demonstrate a self-powered S-TENG-based measuring tapeline that can accurately measure and display the pulled-out distance without the need for an extra battery. The results obtained indicate that TENG-based devices have good potential for application in self-powered measurement systems.
Molecular dynamics simulations have been used to investigate the confinement packing characteristics of small hydrophilic (N-acetyl-glycine-methylamide, Nagma) and hydrophobic (N-acetyl-leucine-methylamide, Nalma) biomolecules in large diameter single-wall carbon nanotubes (SWCNTs). We find that hydrophilic biomolecules easily fill the nanotube and self organize into a geometrical configuration which reminds the water structural organization under SWCNT confinement. The packing of hydrophilic biomolecules inside the cylinder confines all water molecules in its core, which enhances their mobility. Conversely, hydrophobic biomolecules accommodate into the nanotubes with a trend for homogeneous filling, which generate unstable small pockets of water and drive toward a state of dehydration. These results shed light on key parameters important for the encapsulation of biomolecules with direct relevance for long-term storage and prevention of degradation.
A triboelectric nanogenerator (TENG) with an organic nanocomposite electret thin film as the triboelectric layer for mechanical energy harvesting was investigated systematically. In combination with corona charging, a TENG was fabricated by using embedded-nanocapacitor-structure polytetrafluoroethylene (PTFE) impregnated with gold nanoparticles (Au-NPs). The output performances, stability, and durability of the TENGs with Au-PTFE nanocomposite films were characterized after being washed in water. It was found that the output current increases by 70% and the equivalent surface charge density (ESCD) reaches 85 μC/m2 in comparison to the virgin PTFE film. Such outstanding performance is likely due to the equivalent nanocapacitors between the Au-NPs and PTFE molecules, which serve as nano charge traps in the nanocomposite electret film under negative high-voltage corona charging. This work not only expands the practical applications of TENGs, but also opens up new possibilities for the development of high performance triboelectric materials.
Metal nanowire networks represent a promising candidate for the rapid fabrication of transparent electrodes with high transmission and low sheet-resistance values at very low deposition temperatures. A commonly encountered challenge in the formation of conductive nanowire electrodes is establishing high-quality electronic contact between nanowires to facilitate long-range current transport through the network. A new system involving nanowire ligand removal and replacement with a semiconducting sol-gel tin oxide matrix has enabled the fabrication of high-performance transparent electrodes at dramatically reduced temperatures with minimal need for post-deposition treatment.
Electronic adjustment is one of the most commonly used strategies to improve the catalytic performance of heterogeneous catalysts. We prepared hexagonal ultrathin Pd nanosheets with edges modified by gold nanoparticles (Au@Pd nanosheets) using galvanic replacement method. By virtue of the electronic interactions between the Pd nanosheets and Au nanoparticles, the Au@Pd nanosheets exhibited excellent catalytic performances in the carbonylation of iodobenzene by carbon monoxide. The novel nanocomposites could be applied as model catalysts to explore electronic effects in catalysis.
Axially coordinated metal-porphyrin-functionalized multi-walled carbon nanotube (MWCNT) nanohybrids were prepared via two different synthetic approaches (a one-pot 1,3-dipolar cycloaddition reaction and a stepwise approach that involved 1,3-dipolar cycloaddition followed by nucleophilic substitution), and characterized through spectroscopic techniques. Attachment of the tin porphyrins to the surface of the MWCNTs significantly improves their solubility and ease of processing. These axially coordinated (5,10,15,20-tetraphenylporphyrinato)tin(IV) (SnTPP)-MWCNTs exhibit significant fluorescence quenching. The third-order nonlinear optical properties of the resultant nanohybrids were studied by using the Z-scan technique at 532 nm with both nanosecond and picosecond laser pulses. The results show that the nanohybrids exhibit significant reverse saturable absorption or saturable absorption when nanosecond or picosecond pulses, respectively, are employed. Improvement in the nanosecond regime nonlinear absorption is observed on proceeding to the nanohybrids and is ascribed to a combination of the outstanding properties of MWCNTs and the chemically attached metal-porphyrins.
The strategy of combining highly conductive frameworks with abundant active sites is desirable in the preparation of alternative catalysts to commercial Pt/C for the oxygen reduction reaction (ORR). In this study, N-doped graphene (NG) and carbon nanotubes (CNT) were grown in-situ on Co-containing carbon nanofibers (CNF) to form three-dimensional (3D) interconnected networks. The NG and CNT bound the interlaced CNF together, facilitating electron transfer and providing additional active sites. The 3D interconnected fiber networks exhibited excellent ORR catalytic behavior with an onset potential of 0.924 V (vs. reversible hydrogen electrode) and a higher current density than Pt/C beyond 0.720 V. In addition, the hybrid system exhibited superior stability and methanol tolerance to Pt/C in alkaline media. This method can be extended to the design of other 3D interconnected network architectures for energy storage and conversion applications.
By means of vibrational spectroscopy and density functional theory (DFT), we investigate CO adsorption on phosphorene-based systems. We find stable CO adsorption at room temperature on both phosphorene and bulk black phosphorus. The adsorption energy and vibrational spectrum are calculated for several possible configurations of the CO overlayer. We find that the vibrational spectrum is characterized by two different C–O stretching energies. The experimental data are in good agreement with the prediction of the DFT model and reveal the unusual C–O vibrational band at 165–180 meV, activated by the lateral interactions in the CO overlayer.
Hexagonal ultrathin WO3 nano-ribbons (HUWNRs) of subnanometer thicknesses, 2–5 nm widths, and lengths of up to several micrometers were prepared by a solvothermal method. The as-prepared HUWNRs grow along the [001] direction, and the main exposed facet is the (120) crystal plane. The HUWNRs exhibit good electrochemical performance as an anode material in lithium ion batteries because of their unique structure. It is believed that these unique materials may be applied in many fields.
We report a voltage generator based on a graphene network (GN). In response to the movement of a droplet of ionic solution over a GN strip, a voltage of several hundred millivolts is observed under ambient conditions. In the voltage-generation process, the unique structure of GN plays an important role in improving the rate of electron transfer. Given their excellent mechanical properties, GNs may find applications for harvesting vibrational energy in various places such as raincoats, umbrellas, windows, and other surfaces that are exposed to rain.
Multiferroic charge-transfer crystals have drawn significant interest due to their simultaneous dipolar and spin ordering. Numerous theoretical and experimental studies have shown that the molecular stacking between donor and acceptor complexes plays an important role in tuning charge-transfer enabled multifunctionality. Herein, we show that the charge-transfer interactions can be controlled by the segregated stack, consisting of polythiophene donor- and fullerene acceptor-based all-conjugated block copolymers. Room temperature magnetic field effects, ferroelectricity, and anisotropic magnetism are observed in charge-transfer crystals, which can be further controlled by photoexcitation and charge doping. Furthermore, the charge-transfer segregated stack crystals demonstrate external stimuli controlled polarization and magnetization, which opens up their multifunctional applications for all-organic multiferroics.
We developed a high-efficiency rotating triboelectric nanogenerator (R-TENG)-enhanced multilayered antibacterial polyimide (PI) nanofiber air filters for removing ultrafine particulate matter (PM) from ambient atmosphere. Compared to single-layered PI nanofiber filters, the multilayered nanofiber filter can completely remove all of the particles with diameters larger than 0.54 μm and shows enhanced removal efficiency for smaller PM particles. After connecting with aR-TENG, the removal efficiency of the filer for ultrafine particles is further enhanced. The highest removal efficiency for ultrafine particulate matter is 94.1% at the diameter of 53.3 nm and the average removal efficiency reached 89.9%. Despite an increase in the layer number, the thickness of each individual layer of the film decreased, and hence, the total pressure drop of the filter decreased instead of increasing. Moreover, the nanofiber film exhibited high antibacterial activity because of the addition of a small amount of silver nanoparticles. This technology with zero ozone release and low pressure drop is appropriate for cleaning air, haze treatment, and bacterial control.
We demonstrate the self-formation of hexagonal nanotemplates on GaAs (111)B substrates patterned with arrays of inverted tetrahedral pyramids during metal-organic vapor phase epitaxy and its role in producing high-symmetry, site-controlled quantum dots (QDs). By combining atomic force microscopy measurements on progressively thicker GaAs epitaxial layers with kinetic Monte Carlo growth simulations, we demonstrate self-maintained symmetry elevation of the QD formation sites from three-fold to six-fold symmetry. This symmetry elevation stems from adatom fluxes directed towards the high-curvature sites of the template, resulting in the formation of a fully three-dimensional hexagonal template after the deposition of relatively thin GaAs layers. We identified the growth conditions for consistently achieving a hexagonal pyramid bottom, which are useful for producing high-symmetry QDs for efficient generation of entangled photons.
We report the investigation of the thermoelectric properties of large-scale solution-synthesized Bi2Te3 nanocomposites prepared from nanowires hotpressed into bulk pellets. A third element, Se, is introduced to tune the carrier concentration of the nanocomposites. Due to the Se doping, the thermoelectric figure of merit (ZT) of the nanocomposites is significantly enhanced due to the increased power factor and reduced thermal conductivity. We also find that thermal transport in our hot-pressed pellets is anisotropic, which results in different thermal conductivities along the in-plane and cross-plane directions. Theoretical calculations for both electronic and thermal transport are carried out to establish fundamental understanding of the material system and provide directions for further ZT optimization with adjustments to carrier concentration and mobility.
Methylammonium bismuth (III) iodide single crystals and films have been developed and investigated. We have further presented the first demonstration of using this organic–inorganic bismuth-based material to replace lead/tin-based perovskite materials in solution-processable solar cells. The organic–inorganic bismuth-based material has advantages of non-toxicity, ambient stability, and low-temperature solution-processability, which provides a promising solution to address the toxicity and stability challenges in organolead- and organotin-based perovskite solar cells. We also demonstrated that trivalent metal cation-based organic–inorganic hybrid materials can exhibit photovoltaic effect, which may inspire more research work on developing and applying organic-inorganic hybrid materials beyond divalent metal cations (Pb (II) and Sn (II)) for solar energy applications.
The wetting properties of an electrode surface are of significant importance to the performance of electrochemical devices because electron transfer occurs at the electrode/electrolyte interface. Described in this paper is a low-cost metal oxide electrocatalyst (CuO)-based high-performance sensing device using an enzyme electrode with a solid/liquid/air triphase interface in which the oxygen level is constant and sufficiently high. We apply the sensing device to detect glucose, a model test analyte, and demonstrate a linear dynamic range up to 50 mM, which is about 25 times higher than that obtained using a traditional enzyme electrode with a solid/liquid diphase interface. Moreover, we show that sensing devices based on a triphase assaying interface are insensitive to the significant oxygen level fluctuation in the analyte solution.
Integrated multilayered triboelectric nanogenerators (TENGs) are an efficient approach to solve the insufficient energy problem caused by a single-layered TENG for achieving high output power density. However, most integrated multilayered TENGs have a relatively large volume. Here, a double-induced-mode integrated triboelectric nanogenerator (DI-TENG) based on spring steel plates is presented as a cost-effective, simple, and high-performance device for ambient vibration energy harvesting. The unique stackable rhombus structure, in which spring steel plates act both as skeletons and as electrodes, can enhance the output performance and maximize space utilization. The DI-TENG with five repeated units in a volume of 12 cm × 5 cm × 0.4 cm can generate a short-circuit current of 51 μA and can transfer charges of 1.25 μC in a half period. The contrast experiment is conducted systematically and the results have proved that the DI-TENG has a great advantage over the single-induced-mode TENG (SI-TENG) with only one side of a friction layer on its electrode. Besides, the DI-TENG can easily power a commercial calculator and can be used as a door switch sensor.
Stimuli-activated targeted delivery systems for highly accurate treatment of tumors have received considerable attention in recent years. Herein, we reveal a light-activable cancer-targeting strategy that uses a complementary DNA sequence to hybridize and mask sgc8 aptamers conjugated onto photothermal agents such as gold nanorods or single-walled carbon nanotubes (SWNTs). Upon exposure to near-infrared (NIR) laser, localized photothermal heating of the surface of those nano-agents results in dehybridization of the double-stranded DNA and uncaging of the aptamer sequence to allow specific cancer-cell targeting. Utilizing doxorubicin-loaded SWNTs as a model system, targeted drug delivery to cancer cells activated by NIR light was achieved. This work demonstrates the concept of NIR-activable tumor-targeting delivery systems with controllable cancer-cell binding to potentially enable highly specific and efficient cancer therapy.
