A simple fabrication scheme for molecular electronic junctions is presented with multi-walled carbon nanotubes (MWCNTs) as the top electrodes. Results indicate that our approach retains the molecular character of the chosen molecules [a self-assembled mono-layer of octadecanethiol on gold bottom electrodes] and opens the door for studying a wide variety of organothiol candidates for molecular electronics. The fabrication scheme is designed in a way that it can be modified into all-carbon devices in the future by using graphitic carbon bottom electrodes functionalized with nitrozoabenzene, for example, and MWCNTs or graphene as the top electrodes. Alternatively, the scheme is applicable for all-gold devices with gold bottom electrodes and gold nanowire top electrodes.
Category: 2012
Low-temperature synthesis of indium tin oxide nanowires as the transparent electrodes for organic light emitting devices
Low-temperature growth of indium tin oxide (ITO) nanowires (NWs) was obtained on catalyst-free amorphous glass substrates at 250 ◦C by Nd:YAG pulsed-laser deposition. These ITO NWs have branching morphology as grown in Ar ambient. As suggested by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), our ITO NWs have the tendency to grow vertically outward from the substrate surface, with the (400) plane parallel to the longitudinal axis of the nanowires. These NWs are low in electrical resistivity (1.6 × 10−4 cm) and high in visible transmittance (∼90–96%), and were tested as the electrode for organic light emitting devices (OLEDs). An enhanced current density of ∼30 mA cm−2 was detected at bias voltages of ∼19–21 V with uniform and bright emission. We found that the Hall mobility of these NWs is 2.2–2.7 times higher than that of ITO film, which can be explained by the reduction of Coulomb scattering loss. These results suggested that ITO nanowires are promising for applications in optoelectronic devices including OLED, touch screen displays, and photovoltaic solar cells.
Pulsed laser deposition of indium tin oxide nanowires in argon and helium
Nanowires of indium tin oxide (ITO) were grown on catalyst-free amorphous glass substrates at relatively low temperature of 250 °C in argon and helium ambient by the Nd:YAG pulsed laser deposition technique. All the ITO samples showed crystalline structure due to substrate heating and the (400) X-ray diffraction peak became relatively stronger as the pressure was increased. The surface morphology was also changed from compact, polycrystalline thin-film layers to a dendritic layer consisting of nanowires for some limited pressure ranges. The transition from the normal thin-film structure to nanowires was likely due to the vapor–liquid–solid mechanism but under catalyst-free condition. These nanowires tended to grow perpen-dicularly on the glass substrate, as observed with the transmission electron microscopy (TEM), which also confirmed that these nanowires were crystalline.
Field emission and strain engineering of electronic properties in boron nitride nanotubes
FE-and-Electronic-strains-Nanotech2012
The electrical properties of boron nitride (BN) nanostructures, particularly BN nanotubes (NTs), have been studied less in comparison to the counterpart carbon nanotubes. The present work investigates the field emission (FE) behavior of BNNTs under multiple cycles of FE experiments and demonstrates a strain-engineering pathway to tune the electronic properties of BNNTs. The electrical probing of individual BNNTs were conducted inside a transmission electron microscope (TEM) using an in situ electrical holder capable of applying a bias voltage of up to 110 V. Our results indicate that in the first cycle a single BNNT can exhibit the current density of ∼1 mA cm−2 at 110 V and the turn-on voltage of 325 V μm−1. However, field emission properties reduced considerably in subsequent cycles. Real-time imaging revealed the structural degradation of individual BNNTs during FE experiments. The electromechanical measurements show that the conductivity of BNNTs can be tuned by means of mechanical straining. The resistance of individual BNNTs reduced from 2000 to 769 M and the carrier concentration increased from 0.35 × 1017 to 1.1 × 1017 cm−3 by straining the samples up to 2.5%.
Functionalization, Dispersion, and Cutting of Boron Nitride Nanotubes in Water
High-quality boron nitride nanotubes (BNNTs) were functionalized for the first time with water-soluble and biocompatible PEGylated phospholipid [methoxy-poly(ethylene glycol)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N conjugates (mPEG-DSPE)]. We found that BNNTs can be suspended in water for more than 3 months without precipitation. By comparing the dispersion stability of mPEG-DSPE/BNNTs in various solvents and the related Hansen solubility parameters, we found that polarized and hydrogen bonds between water and the hydrophilic mPEG play important roles in maintaining stable dispersion of BNNTs and preventing aggregation of mPEG-DSPE/BNNTs in the solutions. This has led to the formation of composite films with well-dispersed BNNTs and the coating of self-assembled monolayer (SAM) BNNTs. Furthermore, the lengths of these functionalized BNNTs can be shorterned, for the first time, from >10 μm to ∼500 nm by ultrasonication. Experiments suggest that effective dispersion of BNNT in solution is necessary for such cutting, where effective energy transfer from the sonicator to nanotubes is achieved. Our results will form the basis for stable functionalization, dispersion, and effective cutting of BNNTs with water-soluble and biocompatible PEGylated phospholipid, which are important for biomedical and composite applications.
Origins of Thermodynamically Stable Superhydrophobicity of Boron Nitride Nanotubes Coatings
Langmuir, Publications, good images, Hydrophobic, coating