Enhanced π-π interactions between a C60 fullerene and a buckle bend on a double-walled carbon nanotube

In situ low-voltage aberration corrected transmission electron microscopy (TEM) observations of the dynamic entrapment of a C₆₀ molecule in the saddle of a bent double-walled carbon nanotube is presented. The fullerene interaction is non-covalent, suggesting that enhanced π-π interactions (van der Waals forces) are responsible. Classical molecular dynamics calculations confirm that the increased interaction area associated with a buckle is sufficient to trap a fullerene. Moreover, they show hopping behavior in agreement with our experimental observations. Our findings further our understanding of carbon nanostructure interactions, which are important in the rapidly developing field of low-voltage aberration corrected TEM and nano-carbon device fabrication.      

Tunable D peak in gated graphene

We report the gate-modulated Raman spectrum of defective graphene. We show that the intensity of the D peak can be reversibly tuned by applying a gate voltage. This effect is attributed to chemical functionalization of the graphene crystal lattice, generated by an electrochemical reaction involving the water layer trapped at the interface between silicon and graphene.     

Negative supracrystals inducing a FCC-BCC transition in gold nanocrystal superlattices

The growth of nanocrystal superlattices of 5 nm single domain Au nanocrystals at an air-toluene interface induces formation of well-defined thin films （300--400 nm） with large coherence lengths. High-resolution electron microscopy showed that polyhedral holes （negative supracrystal） were formed on the nanocrystal superlattice surface. Formation of negative supracrystals is attributed to inclusion in the superlattice of organic molecules （dodecanethiol）, which are present in concentrated zones at the air-toluene interface. The coexistence of two supracrystalline structures （bcc/fcc） is attributed to diffusion of dodecanethiol molecules resulting in a Bain deformation of the nanocrystal array.     

Superhydrophobic and antireflective nanograss-coated glass for high performance solar cells

We present a facile method for producing superhydrophobic nanograss-coated （SNGC） glass surfaces that possess both reduced reflectivity and self-cleaning properties at the air/glass interface. The refractive index of a CaF2 nanograss （NG） layer on a glass substrate, deposited by glancing angle vapor deposition, is 1.04 at 500 nm, which is the second-lowest value ever reported so far. The fluorinated NG layer gives rise to a high water contact angle （〉150°） and very efficient cleaning out of dust with water drops. Using the dual functionalities of the SNGC glass, we demonstrate superhydrophobic and antireflective organic photovoltaic cells with excellent power conversion efficiency.     

Light-controlled synthesis of uniform platinum nanodendrites with markedly enhanced electrocatalytic activity

We report a fast in situ seeding approach based on zinc（II） porphyrin （ZnP） under white light irradiation, leading to uniform spherical platinum nanodendrites with tunable sizes. The platinum nanodendrites exhibit significantly improved electrocatalytic activities toward oxygen reduction reaction （ORR） and methanol oxidation reaction （MOR） compared with commercial platinum black.     

Direct comparison of catalyst-free and catalyst-induced GaN nanowires

GaN nanowires have been grown by molecular beam epitaxy either catalyst-free or catalyst-induced by means of Ni seeds. Under identical growth conditions of temperature and V/III ratio, both types of GaN nanowires are of wurtzite structure elongated in the Ga-polar direction and are constricted by M-plane facets. However, the catalyst-induced nanowires contain many more basal-plane stacking faults and their photoluminescence is weaker. These differences can be explained as effects of the catalyst Ni seeds.      

A nanoporous oxide interlayer makes a better Pt catalyst on a metallic substrate: Nanoflowers on a nanotube bed

To improve the contact between platinum catalyst and titanium substrate, a layer of TiO2 nanotube arrays has been synthesized before depositing Pt nanoflowers by pulse electrodeposition. Dramatic improvements in electrocatalytic activity （3x） and stability （60x） for methanol oxidation were found, suggesting promising applications in direct methanol fuel cells. The 3x and 60x improvements persist for Pt/Pd catalysts used to overcome the CO poisoning problem.     

Redox-sensitive colorimetric polyaniline nanoprobes synthesized by a solvent-shift process

We have synthesized water-stable polyaniline nanoparticles coated with triarmed polyethylene glycol chains using a solvent-shift method and confirmed their colloidal size and aqueous solubility. Furthermore, we have demonstrated that the polyaniline nanoparticles can be doped with biological dopants to produce distinct color changes allowing the detection of live cancer cells.      

Studies of graphene-based nanoelectromechanical switches

Electromechanical switch devices employing suspended graphene as movable elements have been developed. Their on and off states can be controlled by modulating the electrostatic force applied to the graphene. The devices exhibit on-off ratios of up to 10⁴ and lifetimes of over 500 cycles. The prototype device demonstrates the feasibility of using multilayer graphene in electromechanical systems. Measurements of the mechanical properties of the free-standing monolayer graphene gave a value of 0.96 TPa for the Young??s modulus and a van der Waals force with silicon oxide of 0.17 nN/nm².      

Selection of single-walled carbon nanotubes according to both their diameter and chirality via nanotweezers

Diameter- and chirality-dependent interactions between aromatic molecule-based nanotweezers and single-walled carbon nanotubes (SWNTs) are revealed by density functional theory calculations. We found that the threshold diameter of selected SWNTs is determined by the end-to-end distance of the nanotweezer. Large-diameter SWNTs are preferred by a nanotweezer with an obtuse folding angle, whereas small-diameter SWNTs are favored by a nanotweezer with an acute folding angle. The adsorption can be further stabilized by the orientational alignment of the hexagonal rings of the nanotweezer and the SWNT sidewall. Therefore, by taking advantage of the supramolecular recognition ability of the aromatic molecule-based nanotweezer, SWNTs can be enriched with both controllable diameter and chirality.      

Hydroformylation of alkenes over rhodium supported on the metal-organic framework ZIF-8

A highly porous and crystalline metal-organic framework （MOF） ZIF-8 has been synthesized and used for the preparation of a supported rhodium nanoparticle catalyst （Rh@ZIF-8）. The material has been characterized by PXRD, TEM, EDX, ICP-AES and nitrogen adsorption. The catalytic properties of Rh@ZIF-8 have been investigated in the hydroformylation of alkenes, with different chain length and structure, to give the corresponding aldehydes, and showed high activity. Furthermore, after the reaction was complete, the catalyst could be easily separated from the products by simple decantation and reused five times without a significant decrease in the activity under the investigated conditions.     

Substrate-based galvanic replacement reactions carried out on heteroepitaxially formed silver templates

Galvanic replacement reactions have been widely used to transform solution dispersed silver template structures into intricate nanoshell geometries. Here, we report on the use of these same reactions to form hollow substrate-supported Au-Ag nanoshells from silver templates having a heteroepitaxial relationship with the underlying single crystal substrate. The structures obtained exhibit a nanohut geometry, show highly tunable plasmonic properties and are formed as periodic arrays using a lithography-free technique. When removed from the substrate the inverted nanohuts appear as nanobowls with a notch in the rim. The study lays the groundwork for wafer-based devices utilizing nanoshells located at site-specific locations.      

A perspective on functionalizing colloidal quantum dots with DNA

This perspective provides an overview of the techniques that have been developed for the conjugation of DNA to colloidal quantum dots (QDs), or semiconductor nanocrystals. Methods described include: ligand exchange at the QD surface, covalent conjugation of DNA to the QD surface ligands, and one-step DNA functionalization on core QDs or during core/shell QD synthesis in aqueous solution, with an emphasis on the most recent progress in our lab. We will also discuss emerging trends in DNA-functionalized QDs for potential applications.      

Flexible memristors as electronic synapses for neuro-inspired computation based on scotch tape-exfoliated mica substrates

Flexible memristor devices based on plastic substrates have attracted considerable attention due to their applications in wearable computers and integrated circuits. However, most plastic-substrate memristors cannot function or be grown in high-temperature environments. In this study, scotch-tape-exfoliated mica was used as the flexible memristor substrate in order to resolve these high-temperature issues. Our TiN/ZHO/IGZO memristor, which was constructed using a thin (10 μm) mica substrate, has superior flexibility and thermostability. After bending it 103 times, the device continues to exhibit exceptional electrical characteristics. It can also be implemented for transitions between high and low resistance states, even in temperatures of up to 300 °C. More importantly, the biological synaptic characteristics of paired-pulse facilitation/depression (PPF/PPD) and spike-timing-dependent plasticity (STDP) were observed through applying different pulse measurement modes. This work demonstrates that flexible memristor devices on mica substrates may potentially allow for the realization of high-temperature memristor applications for biologically-inspired computing systems.

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Magnetoresistance oscillations of ultrathin Pb bridges

Pb nanobridges with a thickness of less than 10 nm and a width of several hundred nm have been fabricated from single-crystalline Pb films using low-temperature molecular beam epitaxy and focus ion beam microfabrication techniques. We observed novel magnetoresistance oscillations below the superconducting transition temperature (T _C ) of the bridges. The oscillations—which were not seen in the crystalline Pb films—may originate from the inhomogeneity of superconductivity induced by the applied magnetic fields on approaching the normal state, or the degradation of film quality by thermal evolution.      

Solution-processable graphene mesh transparent electrodes for organic solar cells

Graphene mesh electrodes (GMEs) with good conductivity and transparency have been fabricated by the standard industrial photolithography and O₂ plasma etching process using graphene solutions. Organic photovoltaic (OPV) cells using GMEs as the transparent electrodes with a blend of poly-(3-hexylthiophene)/phenyl-C₆₁-butyric acid methyl ester (P3HT/PC₆₁BM) as the active layer have been fabricated and exhibit a power conversion efficiency (PCE) of 2.04%, the highest PCE for solution-processed graphene transparent electrode-based solar cells reported to date.      

Functionalization of high-moment magnetic nanodisks for cell manipulation and separation

Synthetic antiferromagnetic （SAF） nanoparticles are layer-structured particles with high single-particle magnetic moments. In order to covalently bind these nanopartides to cells, they were coated with a silica shell followed by conjugation with streptavidin. The silica coating generates both SAF@SiO2 core-shell nano- particles and silica core-free nanopartides. Using a simple magnetic separation, silica nanoparticles were removed and SAF@SiO2 nanoparticles were purified. After streptavidin conjugation, these particles were used to stain lung cancer cells, making them highly magnetically responsive. The stained cells can rotate in response to an external magnetic field and can be captured when a blood sample containing these cells flows through the sifter.     

Synthesis and characterization of WS2 inorganic nanotubes with encapsulated/intercalated CsI

WS₂ nanotubes have been filled and intercalated by molten phase caesium iodide. The presence of caesium iodide inside the WS₂ nanotubes has been determined using high-resolution transmission electron microscopy (HRTEM) coupled with electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS). Noticeably, a Moiré pattern was observed due to the interference between encapsulated CsI and WS₂ layers. The intercalation of CsI into the host concentric WS₂ lattices resulted in an increase in the interplanar spacing.      

Synthesis and purification of long copper nanowires. Application to high performance flexible transparent electrodes with and without PEDOT:PSS

We demonstrate the hydrothermal synthesis of long copper nanowires based on a simple protocol. We show that the purification of the nanowires is very important and can be achieved easily by wet treatment with glacial acetic acid. Fabrication of random networks of purified copper nanowires leads to flexible transparent electrodes with excellent optoelectronic performances （e.g., 55 Ω/sq. at 94% transparency）. The process is carried out at room temperature and no post-treatment is necessary. Hybrid materials with the conductive polymer PEDOT：PSS show similar properties （e.g., 46 Ω/sq, at 93% transparency）, with improved mechanical properties. Both electrodes were integrated in capacitive touch sensors.     

Modulating lateral strain in GaN-based epitaxial layers by patterning sapphire substrates with aligned carbon nanotube films

A novel carbon nanotube-patterned sapphire substrate (CPSS) has been utilized for the growth of GaN material and fabrication of a InGaN/GaN light emitting diode (LED) by metal-organic vapor phase epitaxy. Different lateral strain distributions and stress reductions were observed in a GaN thin film on CPSS compared with those on a conventional sapphire substrate. Nanoheteroepitaxy induced by small size nucleation islands of about 50 nm is ascribed to this significant strain modulation. The crystalline quality of the GaN thin film was also improved, as illustrated by X-ray diffraction. Performances of 1 mm × 1 mm LEDs on CPSS were also enhanced, with an operational power increase of 37.5% and higher saturation current.