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.      

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.      

Clean transfer of graphene on Pt foils mediated by a carbon monoxide intercalation process

Noble metals such as Pt are a perfect substrate for the catalytic growth of monolayer graphene. However, the requirements of the subsequent transfer process are not compatible with the traditional etching method. In this work, we find that the interaction of graphene with Pt foil can be weakened through the intercalation of carbon monoxide （CO） under ambient pressure. This intercalation process occurs on both hexagonal-shape graphene islands and irregular graphene patches on changing the CO partial pressure from 0 to 0.6 MPa, as observed by scanning electron microscopy （SEM）, Raman spectroscopy and X-ray photoemission spectroscopy. We demonstrate that, on a practical timescale, the intercalation ratio is proportional to the partial pressure of CO. Furthermore, we develop a clean transfer method of CO-intercalated graphene with water as a peeling agent. We show that this method enables the transfer of tens of micrometer-scale graphene patches onto SiO2/Si, which are free from metal or oxide particle contamination. This transfer method should be a significant step towards the dean transfer of graphene, as well as the recydable use of noble metal substrates.     

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.     

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.     

Repair and stabilization in confined nanoscale systems — inorganic nanowires within single-walled carbon nanotubes

Repair is ubiquitous in biological systems, but rare in the inorganic world. We show that inorganic nanoscale systems can however possess remarkable repair and reconfiguring capabilities when subjected to extreme confinement. Confined crystallization inside single-walled carbon nanotube (SWCNT) templates is known to produce the narrowest inorganic nanowires, but little is known about the potential for repair of such nanowires once crystallized, and what can drive it. Here inorganic nanowires encapsulated within SWCNTs were seen by high-resolution transmission electron microscopy to adjust to changes in their nanotube template through atomic rearrangement at room temperature. These observations highlight nanowire repair processes, supported by theoretical modeling, that are consistent with atomic migration at fractured, ionic ends of the nanowires encouraged by long-range force fields, as well as release-blocking mechanisms where nanowire atoms bind to nanotube walls to stabilize the ruptured nanotube and allow the nanowire to reform. Such principles can inform the design of nanoscale systems with enhanced resilience.      

High-precision transfer-printing and integration of vertically oriented semiconductor arrays for flexible device fabrication

Flexible electronics utilizing single crystalline semiconductors typically require post-growth processes to assemble and incorporate the crystalline materials onto flexible substrates. Here we present a high-precision transfer-printing method for vertical arrays of single crystalline semiconductor materials with widely varying aspect ratios and densities enabling the assembly of arrays on flexible substrates in a vertical fashion. Complementary fabrication processes for integrating transferred arrays into flexible devices are also presented and characterized. Robust contacts to transferred silicon wire arrays are demonstrated and shown to be stable under flexing stress down to bending radii of 20 mm. The fabricated devices exhibit a reversible tactile response enabling silicon based, nonpiezoelectric, and flexible tactile sensors. The presented system leads the way towards high-throughput, manufacturable, and scalable fabrication of flexible devices.     

Functionalized,carbon nanotube material for the catalytic degradation of organophosphate nerve agents

Recent world events have emphasized the need to develop innovative, functional materials that will safely neutralize chemical warfare （CW） agents in situ to protect military personnel and civilians from dermal exposure. Here, we demonstrate the efficacy of a novel, proof-of-concept design for a Cu-containing catalyst, chemically bonded to a single-wall carbon nanotube （SWCNT） structural support, to effectively degrade an organophosphate simulant. SWCNTs have high tensile strength and are flexible and light-weight, which make them a desirable structural component for unique, fabric-like materials. This study aims to develop a self-decontaminating, carbon nanotube-derived material that can ultimately be incorporated into a wearable fabric or protective material to minimize dermal exposure to organophosphate nerve agents and to prevent accidental exposure during decontamination procedures. Carboxylated SWCNTs were functionalized with a polymer, which contained Cu-chelating bipyridine groups, and their catalytic activity against an organophosphate simulant was measured over time. The catalytically active, functionalized nanomaterial was characterized using X-ray fluorescence and Raman spectroscopy. Assuming zeroth-order reaction kinetics, the hydrolysis rate of the organophosphate simulant, as monitored by UV-vis absorption in the presence of the catalytically active nanomaterial, was 63 times faster than the uncatalyzed hydrolysis rate for a sample containing only carboxylated SWCNTs or a control sample containing no added nanotube materials.     

Microwave synthesis of large few-layer graphene sheets in aqueous solution of ammonia

Few-layer graphene (FLG) sheets with sizes exceeding several micrometers have been synthesized by exfoliation of expanded graphite in aqueous solution of ammonia under microwave irradiation, with an overall yield approaching 8 wt.%. Transmission electron microscopy (in bright-field and dark-field modes) together with electron diffraction patterns and atomic force microscopy confirmed that this graphene material consisted mostly of mono-, bi- or few-layer graphene (less than ten layers). The high degree of surface reduction was confirmed by X-ray photoelectron and infrared spectroscopies. In addition, the high stability of the FLG in the liquid medium facilitates the deposition of the graphene material onto several substrates via low-cost solution-phase processing techniques, opening the way to subsequent applications of the material.      

Nanocrystal-semiconductor interface: Atomic-resolution cross-sectional transmission electron microscope study of lead sulfide nanocrystal quantum dots on crystalline silicon

We report on a cross-sectional high resolution transmission electron microscope study of lead sulfide nanocrystal quantum dots （NCQDs） dispersed on electron-transparent silicon nanopillars that enables nearly atomically-resolved simultaneous imaging of the entire composite： the quantum dot, the interfacial region, and the silicon substrate. Considerable richness in the nanocrystal shape and orientation with respect to the substrate lattice is observed. The average NCQD-substrate separation is found to be significantly smaller than the length of the ligands on the NCQDs. Complementary photoluminescence measurements show that light emission from PbS NCQDs on silicon is effectively quenched which we attribute to intrinsic mechanisms of energy and charge transfer from PbS NCQDs to Si.     

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.     

Effect of carbon nanotube network morphology on thin film transistor performance

The properties of electronic devices based on carbon nanotube networks (CNTNs) depend on the carbon nanotube (CNT) deposition method used, which can yield a range of network morphologies. Here, we synthesize single-walled CNTs using an aerosol (floating catalyst) chemical vapor deposition process and deposit CNTs at room temperature onto substrates as random networks with various morphologies. We use four CNT deposition techniques: electrostatic or thermal precipitation, and filtration through a filter followed by press transfer or dissolving the filter. We study the mobility using pulsed measurements to avoid hysteresis, the on/off ratio, and the electrical noise properties of the CNTNs, and correlate them to the network morphology through careful imaging. Among the four deposition methods thermal precipitation is found to be a novel approach to prepare high-performance, partially aligned CNTNs that are dry-deposited directly after their synthesis. Our results provide new insight into the role of the network morphologies and offer paths towards tunable transport properties in CNT thin film transistors.      

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.      

Coordinated buckling of thick multi-walled carbon nanotubes under uniaxial compression

Using a generalized quasi-continuum method, we characterize the post-buckling morphologies and energetics of thick multi-walled carbon nanotubes (MWCNTs) under uniaxial compression. Our simulations identify for the first time evolving post-buckling morphologies, ranging from asymmetric periodic rippling to a helical diamond pattern. We attribute the evolving morphologies to the coordinated buckling of the constituent shells. The post-buckling morphologies result in significantly reduced effective moduli that are strongly dependent on the aspect ratio. Our simulation results provide fundamental principles to guide the future design of high-performance, MWCNT-based nanodevices.      

Silicene nanoribbons as carbon monoxide nanosensors with molecular resolution

Applications based on silicene as grown on substrates are of high interest toward actual utilization of this unique material. Here we explore, from first principles, the nature of carbon monoxide adsorption on semiconducting silicene nanoribbons and the resulting quantum conduction modulation with and without silver contacts for sensing applications. We find that quantum conduction is detectably modified by weak chemisorption of a single CO molecule on a pristine silicene nanoribbon. This modification can be attributed to the charge transfer from CO to the silicene nanoribbon and the deformation induced by the CO chemisorption. Moderate binding energies provide an optimal mix of high detectability and recoverability. With Ag contacts attached to a -1 nm silicene nanoribbon, the interface states mask the conductance modulations caused by CO adsorption, emphasizing length effects for sensor applications. The effects of atmospheric gases--nitrogen, oxygen, carbon dioxide, and water--as well as CO adsorption density and edge-dangling bond defects, on sensor functionality are also investigated. Our results reveal pristine silicene nanoribbons as a promising new sensing material with single molecule resolution.     

Nanoplasmonic colloidal suspensions for the enhancement of the luminescent emission from single-walled carbon nanotubes

Aiming to enhance the luminescence yield of carbon nanotubes, we introduce a new class of hybrid nanoplasmonic colloidal systems （π-hybrids）. Nanotubes dispersed in gold nanorod colloidal suspensions yield hybrid structures exhibiting enhanced luminescence up to a factor of 20. The novelty of the proposed enhancement mechanism relies on including metal proximity effects in addition to its localized surface plasmons. This simple, robust and flexible technique enhances the luminescence of nanotubes with chiralities whose enhancement has never reported before, for example the （8,4） tube.     

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.     

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.      

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.     

Dipole-moment-induced effect on contact electrification for triboelectric nanogenerators

Triboelectric nanogenerators （TENGs） have been demonstrated as an effective way to harvest mechanical energy to drive small electronics. The density of triboelectric charges generated on contact surfaces between two distinct materials is a critical factor for dictating the output power. We demonstrate an approach to effectively tune the triboelectric properties of materials by taking advantage of the dipole moment in polarized polyvinylidene fluoride （PVDF）, leading to substantial enhancement of the output power density of the TENG. The output voltage ranged from 72 V to 215 V under a constant contact force of 50 N. This work not only provides a new method of enhancing output power of TENGs, but also offers an insight into charge transfer in contact electrification by investigating dipole-moment-induced effects on the electrical output of TENGs.