Of late, many synthesis processes have been studied to develop irregular nano-morphologies of gold nanostructures for biomedical applications in order to increase the efficacy of nanoparticle theranostics, tune the plasmonic absorbance spectra, and increase the sensitivity of biomolecule detection through surface enhanced Raman spectroscopy. Here we report, a novel, non-seed mediated versatile single pot synthesis method capable of producing hyperbranched gold “nano-polyvilli” with more than 50–90 branching nanowires propagating from a single origin within each structure. The technique was capable of achieving precise tuning of the branch propagation where the branching could be controlled by varying the duration of incubation, temperature, and hydrogen ion concentration.
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.
Advanced permanent magnets based on rare-earth-free MnBi intermetallic alloys are considered energy-critical materials due to their applications in high temperature power electronics and green energy-related generators and motors, owing to their positive temperature coefficient of magnetic anisotropy. However, a direct method to achieve high saturation magnetization, without the significant loss of coercivity, is critical for attaining high performance MnBi magnets. Here, we demonstrate the synthesis and processing of magnetic nanocomposites, consisting of metal-redox MnBi nanoparticles and electro-spun FeCo nanowires. The composition ratio, processing dependent magnetism, and increased coercivity with increasing temperature, were studied in MnBi-FeCo nanocomposites. The magnetic performance of nanocomposites was dictated by interfacial coupling between magnetically hard MnBi and semi-hard FeCo nanowires, as well as the composition ratio and processing conditions. Solution processed MnBi-FeCo nanocomposites allow the potential for the development of high temperature and high performance rare-earth-free permanent magnets.
Electromigration in Cu has been extensively investigated as the root cause of typical breakdown failure in Cu interconnects. In this study, Cu nanowires connected to Au electrodes are fabricated and observed using in situ transmission electron microscopy to investigate the electro- and thermo-migration processes that are induced by direct current sweeps. We observe the dynamic evolution of different mass transport mechanisms. A current density on the order of 106 A/cm2 and a temperature of approximately 400 °C are sufficient to induce electro- and thermo-migration, respectively. Observations of the migration processes activated by increasing temperatures indicate that the migration direction of Cu atoms is dependent on the net force from the electric field and electron wind. This work is expected to support future design efforts to improve the robustness of Cu interconnects.
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.
Sandwich structured graphene-wrapped FeS-graphene nanoribbons (G@FeS-GNRs) were developed. In this composite, FeS nanoparticles were sandwiched between graphene and graphene nanoribbons. When used as anodes in lithium ion batteries (LIBs), the G@FeS-GNR composite demonstrated an outstanding electrochemical performance. This composite showed high reversible capacity, good rate performance, and enhanced cycling stability owing to the synergy between the electrically conductive graphene, graphene nanoribbons, and FeS. The design concept developed here opens up a new avenue for constructing anodes with improved electrochemical stability for LIBs.
The size and density of Ag nanoparticles on n-layer MoS2 exhibit thicknessdependent behavior. The size and density of these particles increased and decreased, respectively, with increasing layer number (n) of n-layer MoS2. Furthermore, the surface-enhanced Raman scattering (SERS) of Ag on this substrate was observed. The enhancement factor of this scattering varied with the thickness of MoS2. The mechanisms governing the aforementioned thickness dependences are proposed and discussed.
In-plane symmetry is an important contributor to the physical properties of two-dimensional layered materials, as well as atomically thin heterojunctions. Here, we demonstrate anisotropic/isotropic van der Waals (vdW) heterostructures of ReS2 and MoS2 monolayers, where interlayer coupling interactions and charge separation were observed by in situ Raman-photoluminescence spectroscopy, electrical, and photoelectrical measurements. We believe that these results could be helpful for understanding the fundamental physics of atomically thin vdW heterostructures and creating novel electronic and optoelectronic devices.
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.
The persistent need for a sustainable energy economy has led researchers to focus on novel energy conversion and storage technologies, inspiring the discovery of smart material designs such as hierarchical nanocomposites. These nanocomposites have proven effective in the advancement of energy-based technologies. The synergistic properties of hierarchical nanocomposites composed of two types of two-dimensional layered materials, layered double hydroxides and graphene, have resulted in improved electrochemical as well as photocatalytic performance. Synthetic strategies and their effect on the electrochemical and photocatalytic performance of these nanocomposites as high-performance supercapacitors and water oxidation catalysts are discussed in detail in this review.
In this paper, we propose a novel construction of silicon nanowire (SiNW) negative-AND (NAND) logic gates on bendable plastic substrates and describe their electrical characteristics. The NAND logic gates with SiNW channels are capable of operating with a supply voltage as low as 0.8 V, with switching and standby power consumption of approximately 1.1 and 0.068 nW, respectively. Superior electrical characteristics of each SiNW transistor, including steep subthreshold slopes, high Ion/off ratio, and symmetrical threshold voltages, are the major factors that enable nanowatt-range power operation of the logic gates. Moreover, the mechanical bendability of the logic gates indicates that they have good and stable fatigue properties.
We investigate the spin wave (SW) modes in high-aspect-ratio single-crystal ferromagnetic nanowires (FMNWs) using an all-optical time-resolved magnetooptical Kerr effect (TR-MOKE) microscope. The precessional magnetization dynamics in such FMNWs unveil the presence of uniform and quantized SW modes that can be tuned by varying the bias magnetic field (H). The frequencies of the modes are observed to decrease systematically with a decreasing magnetic field, and the number of modes in the spectrum is reduced from four to three for H < 0.7 kOe. To understand these results, we perform micromagnetic simulations that reveal the presence of edge, standing wave, and uniform SW modes in the nanowires (NWs). Our simulations clearly show how the standing wave and uniform SW modes coalesce to form a single mode with uniform precession over the entire NW for H < 0.7 kOe, reproducing the experimentally observed reduction in modes. Our study elucidates the possibility of manipulating the SW modes in magnetic nanostructures, which is useful for applications in magnonic and spintronic devices.
Multi-shelled CoFe2O4 hollow microspheres with a tunable number of layers (1–4) were successfully synthesized via a facile one-step method using cyclodextrin as a template, followed by calcination. The structural features, including the shell number and shell porosity, were controlled by adjusting the synthesis parameters to produce hollow spheres with excellent capacity and durability. This is a straightforward and general strategy for fabricating metal oxide or bimetallic metal oxide hollow microspheres with a tunable number of shells.
RuCu nanocages and core–shell Cu@Ru nanocrystals with ultrathin Ru shells were first synthesized by a one-pot modified galvanic replacement reaction. The construction of bimetallic nanocrystals with fully exposed precious atoms and a high surface area effectively realizes the concept of high atom-efficiency. Compared with the monometallic Ru/C catalyst, both the RuCu nanocages and Cu@Ru core–shell catalysts supported on commercial carbon show superior catalytic performance for the regioselective hydrogenation of quinoline toward 1,2,3,4-tetrahydroquinoline. RuCu nanocages exhibit the highest activity, achieving up to 99.6% conversion of quinoline and 100% selectivity toward 1,2,3,4-tetrahydroquinoline.
Hydrogen production from steam or autothermal alcohol reforming has been widely studied, but these methods require high temperatures and emit CO2. Here, we present a new strategy for the simultaneous room-temperature production of hydrogen and other chemicals without the emission of CO2, via the photoelectrochemical reforming of biomass-derived alcohols. The measured hydrogen quantum efficiencies reach around 80% across the entire visible solar spectrum from 450 to 850 nm, achieving an ultrahigh hydrogen production rate of 7.91 μmol/(min·cm2) under AM 1.5G illumination.
A facile method was developed to fabricate nitrogen-doped graphene microtubes (N-GMT) with ultra-thin walls of 1–4 nm and large inner voids of 1–2 μm. The successful introduction of nitrogen dopants afforded N-GMT more active sites for significantly enhanced hydrogen evolution reaction (HER) activity, achieving a current density of 10 mA·cm–2 at overpotentials of 0.464 and 0.426 V vs. RHE in 0.1 and 6 M KOH solution, respectively. This HER performance surpassed that of the best metal-free catalyst reported in basic solution, further illustrating the great potential of N-GMT as an efficient HER catalyst for real applications in water splitting and chlor-alkali processes.
We report a fuel-free, near-infrared (NIR)-driven Janus microcapsule motor. The Janus microcapsule motors were fabricated by template-assisted polyelectrolyte layer-by-layer assembly, followed by spraying of a gold layer on one side. The NIR-powered Janus motors achieved high propulsion with a maximum speed of 42 µm·s-1 in water. The propulsion mechanism of the Janus motor was attributed to the self-thermophoresis effect: The asymmetric distribution of the gold layer generated a local thermal gradient, which in turn generated thermophoretic force to propel the Janus motor. Such NIR-propelled Janus capsule motors can move efficiently in cell culture medium and have no obvious effects on the cell at the power of the NIR laser, indicating considerable promise for future biomedical applications.
The single crystalline nanostructure of organic semiconductors provides a very promising class of materials for applications in modern optoelectronic devices. However, morphology control and optoelectronic property modulation of high quality single crystalline samples remain a challenge. Here, we report the morphology-controlled growth of single crystalline nanorod arrays of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). We demonstrate that, unlike PTCDA film, PTCDA nanorods exhibits optical waveguide features, enhanced absorption, and Frenkel excitation emission in the visible region. Additionally, we measured the electrical properties of PTCDA nanorods, including the conductivity along the growth direction of the nanorod, which is roughly 0.61 S·m–1 (much higher than that of pure crystalline PTCDA films).
Silk is a widely available, edible, biocompatible, and environmentally sustainable natural material. Particulate matter (PM) pollution has drawn considerable attention because it is a serious threat to public health. Herein, we report a human-friendly silk nanofiber air filter, which exhibits superior filtration efficiency for both PM2.5 and submicron particles with obviously low pressure drop and low basis weight compared to typical commercial microfiber air filters. Additionally, other functions such as antibacterial activity could be easily integrated into the silk nanofiber air filters, enabling the fabrication of multifunctional air filters. All the above characteristics, combined with the natural abundance and biocompatibility of silk, suggest a great potential for the use of silk nanofibers as air filters, especially as comfortable and personal air purifiers.
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.
