Electronic properties of stanene, the Sn counterpart of graphene are theoretically studied using first-principles simulations. The topological to trivial insulating phase transition induced by an out-of-plane electric field or by quantum confinement effects is predicted. The results highlight the potential to use stanene nanoribbons in gate-voltage controlled dissipationless spin-based devices and are used to set the minimal nanoribbon width for such devices, which is typically approximately 5 nm.
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.
Molecular dynamics simulations showed that a basal carbon nanotube can activate and guide the fabrication of single-walled carbon nanotubes (CNTs) on its internal surface by self-assembly of edge-unpassivated graphene nanoribbons with defects. Furthermore, the distribution of defects on self-assembled CNTs is controllable. The system temperature and defect fraction are two main factors that influence the success of self-assembly. Due to possible joint flaws formed at the boundaries under a relatively high constant temperature, a technique based on increasing the temperature is adopted. Self-assembly is always successful for graphene nanoribbons with relatively small defect fractions, while it will fail in cases with relatively large ones. Similar to the self-assembly of graphene nanoribbons with defects, graphene nanoribbons with different types of dopants can also be self-assembled into carbon nanotubes. The finding provides a possible fabrication technique not only for carbon nanotubes with metallic or semi-conductive properties but also for carbon nanotubes with electromagnetic induction characteristics.
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.
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.
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.
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.
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.
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.
Since opening sizable bandgaps in bilayer graphene (BLG) was proven possible, BLG has attracted considerable attention as a promising high-mobility candidate material for many electronic and optoelectronic applications. However, the bandgaps observed in the transport experiments reported in the literature are far smaller than both the theoretical predictions and the bandgaps extracted from optical measurements. In this study, we investigate the factors preventing the formation of large bandgaps and demonstrate that a ~200-meV transport bandgap can be opened in BLG by scaling the gate dielectric and employing a ribbon channel to suppress the percolative transport. This is the largest transport bandgap that has been achieved in BLG to date.
Controlling the chemistry at the interface of nanocrystalline solids has been a challenge and an important goal to realize desired properties. Integrating two different types of materials has the potential to yield new functions resulting from cooperative effects between the two constituents. Metal–organic frameworks (MOFs) are unique in that they are constructed by linking inorganic units with organic linkers where the building units can be varied nearly at will. This flexibility has made MOFs ideal materials for the design of functional entities at interfaces and hence allowing control of properties. This review highlights the strategies employed to access synergistic functionality at the interface of nanocrystalline MOFs (nMOFs) and inorganic nanocrystals (NCs).
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.
In this work, we developed a novel triboelectricity-assisted polymer-free method for the transfer of large-area chemical vapor deposited graphene films. With the assistance of electrostatic forces from friction-generated charges, graphene sheets were successfully transferred from copper foils to flexible polymer substrates. Characterization results confirmed the presence of high quality graphene with less defects and contaminations, compared to graphene transferred by conventional poly(methyl methacrylate)-mediated processes. In addition, the graphene samples possessed outstanding electrical transport capabilities and mechanical stability, when studied as electron transfer matrixes in graphene/ZnO hybrid flexible photodetectors. Our results showed a broad application potential for this transfer method in future flexible electronics and optoelectronics.
In this study, leaf-like one-dimensional InAs nanostructures were grown by the metal–organic chemical vapor deposition method. Detailed structural characterization suggests that the nanoleaves contain relatively low-energy {122} or {133} mirror twins acting as their midribs and narrow sections connecting the nanoleaves and their underlying bases as petioles. Importantly, the mirror twins lead to identical lateral growth of the twinned structures in terms of crystallography and polarity, which is essential for the formation of lateral symmetrical nanoleaves. It has been found that the formation of nanoleaves is driven by catalyst energy minimization. This study provides a biomimic of leaf found in nature by fabricating a semiconductor nanoleaf.
Novel self-assembled architectures have received a growing amount of attention and have significant potential for application in catalysis/electrocatalysis. Herein, we take advantage of the unique coordination and self-assembly properties of arginine for the preparation of dendritic PtCu bimetallic nanoassemblies with tunable chemical composition and structure. Strong interactions between the arginine molecules are key in driving the self-assembly of primary nanocrystals. In addition, the strong coordination interactions between arginine and metal ions is responsible for the formation of Pt–Cu alloys. We also investigated the electrocatalytic activity of various dendritic PtCu bimetallic nanoassemblies towards the methanol oxidation reaction. Pt3Cu1 nanoassemblies exhibited excellent electrocatalytic activity and stability in comparison with other PtCu bimetallic nanoassemblies (Pt1Cu3, Pt1Cu1) and commercial Pt black, due to their unique dendritic structures and the synergistic effect between the Pt and Cu atoms.
In this study, a potentially universal new strategy is reported for the large-scale, low-cost fabrication of visible-light-active highly ordered heteronanostructures based on the spontaneous photoelectric-field-enhancement effect inherent in pyramidal morphology. The hierarchical vertically oriented arrayed structures comprise an active molecular co-catalyst at the apex of a visible-light-active large band gap semiconductor for low-cost solar water splitting in a neutral aqueous medium without the use of a sacrificial agent.
This paper describes a novel strategy to weaken the piezopotential screening effect by forming Schottky junctions on the ZnO surface through the introduction of Au particles onto the surface. With this approach, the piezoelectric-energyconversion performance was greatly enhanced. The output voltage and current density of the Au@ZnO nanoarray-based piezoelectric nanogenerator reached 2 V and 1 μA/cm2, respectively, 10 times higher than the output of pristine ZnO nanoarray-based piezoelectric nanogenerators. We attribute this enhancement to dramatic suppression of the screening effect due to the decreased carrier concentration, as determined by scanning Kelvin probe microscope measurements and impedance analysis. The lowered capacitance of the Au@ZnO nanoarraybased piezoelectric nanogenerator also contributes to the improved output. This work provides a novel method to enhance the performance of piezoelectric nanogenerators and possibly extends to piezotronics and piezophototronics.
We demonstrate an easy and scalable low-temperature process to convert porous ternary complex metal oxide nanoparticles from solution-synthesized core/shell metal oxide nanoparticles by thermal annealing. The final products demonstrate superior electrochemical properties with a large capacity and high stability during fast charging/discharging cycles for potential applications as advanced lithium-ion battery (LIB) electrode materials. In addition, a new breakdown mechanism was observed on these novel electrode materials.
Nanoporous (NP) Si/Cu composites are fabricated by means of alloy refining followed by facile electroless dealloying in mild conditions. NP-Si/Cu composites with a three-dimensional porous network nanoarchitecture with different Cu contents are obtained by changing the feeding ratio of alloy precursors. Owing to the rich porosity and integration of conductive Cu into a nanoporous Si backbone, the NP-Si85Cu15 composite exhibits modified conductivity and reduced volumetric expansion/fracture during repeated charging-discharging processes in lithium-ion batteries (LIBs), thus exhibiting much higher cycling reversibility than NP-Si92Cu8 and pure NP-Si. With the advantages of unique performance and easy preparation, NP-Si/Cu composite has potential for application as an advanced anode material for LIBs.
