Progress in Electronic, Energy, Biomedical and Environmental Applications of Boron Nitride and MoS Nanostructures.

In this review, we examine recent progress using boron nitride (BN) and molybdenum disulfide (MoS) nanostructures for electronic, energy, biomedical, and environmental applications. The scope of coverage includes zero-, one-, and two-dimensional nanostructures such as BN nanosheets, BN nanotubes, BN quantum dots, MoS nanosheets, and MoS quantum dots. These materials have sizable bandgaps, differentiating them from other metallic nanostructures or small-bandgap materials.

Emerging Applications of Boron Nitride Nanotubes in Energy Harvesting, Electronics, and Biomedicine.

Boron nitride nanotubes (BNNTs) are structurally and mechanically similar to carbon nanotubes (CNTs). In contrast, BNNTs exhibit unique properties for being electrically insulating and optically transparent due to the polarized boron nitride bonds. All these properties have prevented the use of BNNTs for energy harvesting and electronic devices for more than 25 years.

Two-Dimensional Gold Quantum Dots with Tunable Bandgaps.

Metallic gold nanoparticles (Au NPs) with multilayer Au atoms are useful for plasmonic, chemical, medical, and metamaterial application. In this article, we report the opening of the bandgap in substrate-supported two-dimensional (2D) gold quantum dots (Au QDs) with monolayer Au atoms. Calculations based on density functional theory suggest that 2D Au QDs are energetically favorable over 3D Au clusters when coated on hexagonal boron nitride (BN) surfaces.

Surface-charge effects on the electro-orientation of insulating boron-nitride nanotubes in aqueous suspension.

The alignment of hexagonal boron-nitride nanotubes (BNNTs) in aqueous KCl solutions under spatially uniform electric fields was examined experimentally, using direct optical visualization to probe the orientation dynamics of individual BNNTs for different electric-field frequencies. Different from most previously studied nanowires and nanotubes, BNNTs are wide-bandgap materials which are essentially insulating at room temperature. We analyze the electro-orientation of BNNTs in the general context of polarizable cylindrical particles in liquid suspensions, whose behavior can fall into different regimes, including alignment due to Maxwell-Wagner induced dipoles at high frequencies, and alignment due to fluid motion of the electrical double layer around the particles at lower frequencies.

pH responsive controlled release of anti-cancer hydrophobic drugs from sodium alginate and hydroxyapatite bi-coated iron oxide nanoparticles.

Developing a drug carrier system which could perform targeted and controlled release over a period of time is utmost concern in the pharmaceutical industry. This is more relevant when designing drug carriers for poorly water soluble drug molecules such as curcumin and 6-gingerol. Development of a drug carrier system which could overcome these limitations and perform controlled and targeted drug delivery is beneficial.

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors.

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures.

Evolution of Irradiation-Induced Vacancy Defects in Boron Nitride Nanotubes.

Irradiation-induced vacancy defects in multiwalled (MW) boron nitride nanotubes (BNNTs) are investigated via in situ high-resolution transmission electron microscope operated at 80 kV, with a homogeneous distribution of electron beam intensity. During the irradiation triangle-shaped vacancy defects are gradually generated in MW BNNTs under a mediate electron current density (30 A cm(-2)), by knocking the B atoms out. The vacancy defects grow along a well-defined direction within a wall at the early stage as a result of the curvature induced lattice strain, and then develop wall by wall.

A Simple and Universal Technique To Extract One- and Two-Dimensional Nanomaterials from Contaminated Water.

We demonstrate a universal approach to extract one- and two-dimensional nanomaterials from contaminated water, which is based on a microscopic oil-water interface trapping mechanism. Results indicate that carbon nanotubes, graphene, boron nitride nanotubes, boron nitride nanosheets, and zinc oxide nanowires can be successfully extracted from contaminated water at a successful rate of nearly 100%. The effects of surfactants, particle shape, and type of organic extraction fluids are evaluated.

Switching Behaviors of Graphene-Boron Nitride Nanotube Heterojunctions.

High electron mobility of graphene has enabled their application in high-frequency analogue devices but their gapless nature has hindered their use in digital switches. In contrast, the structural analogous, h-BN sheets and BN nanotubes (BNNTs) are wide band gap insulators. Here we show that the growth of electrically insulating BNNTs on graphene can enable the use of graphene as effective digital switches.

Room-temperature tunneling behavior of boron nitride nanotubes functionalized with gold quantum dots.

One-dimensional arrays of gold quantum dots (QDs) on insulating boron nitride nanotubes (BNNTs) can form conduction channels of tunneling field-effect transistors. We demonstrate that tunneling currents can be modulated at room temperature by tuning the lengths of QD-BNNTs and the gate potentials. Our discovery will inspire the creative use of nanostructured metals and insulators for future electronic devices.

Diameter-dependent bending modulus of individual multiwall boron nitride nanotubes.

The mechanical properties of individual multiwall boron nitride nanotubes (MWBNNTs) synthesized by a growth-vapor-trapping chemical vapor deposition method are investigated by a three-point bending technique via atomic force microscopy. Multiple locations on suspended tubes are probed in order to determine the boundary conditions of the supported tube ends. The bending moduli (EB) calculated for 20 tubes with diameters ranging from 18 to 58 nm confirm the exceptional mechanical properties of MWBNNTs, with an average EB of 760 ± 30 GPa.

Very stable electron field emission from strontium titanate coated carbon nanotube matrices with low emission thresholds.

Novel PMMA-STO-CNT matrices were created by opened-tip vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) with conformal coatings of strontium titanate (STO) and poly(methyl methacrylate) (PMMA). Emission threshold of 0.8 V/μm was demonstrated, about 5-fold lower than that of the as-grown VA-MWCNTs.

Field emission and strain engineering of electronic properties in boron nitride nanotubes.

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.

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.

Origins of thermodynamically stable superhydrophobicity of boron nitride nanotubes coatings.

Superhydrophobic surfaces are attractive as self-cleaning protective coatings in harsh environments with extreme temperatures and pH levels. Hexagonal phase boron nitride (h-BN) films are promising protective coatings due to their extraordinary chemical and thermal stability. However, their high surface energy makes them hydrophilic and thus not applicable as water repelling coatings.

In situ observation of reversible rippling in multi-walled boron nitride nanotubes.

The recent observation of high flexibility in buckled boron nitride nanotubes (BNNTs) contradicts the pre-existing belief about BN nanotube brittleness due to the partially ionic character of bonding between the B and N atoms. However, the underlying mechanisms and relationships within the nanotube remained unexplored. This study reports for the first time the buckling mechanism in multi-walled BNNTs upon severe mechanical deformation.

Stable electron field emission from PMMA-CNT matrices.

We have created PMMA-CNT matrices by embedding opened-tip vertically aligned multiwalled carbon nanotubes (VA-MWCNTs) with poly(methyl methacrylate) (PMMA). These PMMA-CNT matrices are excellent electron field emitters with an emission threshold field of 1.675 V/μm, more than 2-fold lower that that of the as-grown sample.

Recent advancements in boron nitride nanotubes.

This article provides a concise review of the recent research advancements in boron nitride nanotubes (BNNTs) with a comprehensive list of references. As the motivation of the field, we first summarize some of the attractive properties and potential applications of BNNTs. Then, latest discoveries on the properties, applications, and synthesis of BNNTs are discussed.

Induction annealing and subsequent quenching: effect on the thermoelectric properties of boron-doped nanographite ensembles.

Boron-doped nanographite ensembles (NGEs) are interesting thermoelectric nanomaterials for high temperature applications. Rapid induction annealing and quenching has been applied to boron-doped NGEs using a relatively low-cost, highly reliable, laboratory built furnace to show that substantial improvements in thermoelectric power factors can be achieved using this methodology. Details of the design and performance of this compact induction furnace as well as results of the thermoelectric measurements will be reported here.

Noncovalent functionalization of boron nitride nanotubes with poly(p-phenylene-ethynylene)s and polythiophene.

Boron nitride nanotubes (BNNTs) are functionalized and solubilized in organic solvents such as chloroform, methylene chloride, and tetrahydrofuran by using conjugated poly(p-phenylene ethynylene)s (PPEs) (polymers A and B) and polythiophene (polymer C) via a noncovalent functionalization approach through strong pi-pi stacking interactions between the conjugated polymers and BNNTs. The functionalization of BNNTs with PPEs enhanced planarization of PPEs with red shifts in both absorbance and emission of the composite materials with reference to free PPEs, whereas the functionalization of BNNTs with polythiophene disrupts the pi-conjugation, resulting in blue shifts in both the absorption and emission of the composite material.

Effective growth of boron nitride nanotubes by thermal chemical vapor deposition.

Effective growth of multiwalled boron nitride nanotubes (BNNTs) has been obtained by thermal chemical vapor deposition (CVD). This is achieved by a growth vapor trapping approach as guided by the theory of nucleation. Our results enable the growth of BNNTs in a conventional horizontal tube furnace within an hour at 1200 °C.

Growth of p-type Si nanotubes by catalytic plasma treatments.

We have demonstrated a new technique to transform bulk materials into one-dimensional nanostructures. We have shown that p-type Si nanotubes (SiNTs) can be grown by a simple dual RF plasma treatment of p-type Si substrates at 500 °C. These SiNTs have diameters of ∼50-80 nm with tubular wall thickness of ∼10-15 nm.

ZnO nanosquids: branching nanowires from nanotubes and nanorods.

One-dimensional (1D) semiconductor nanostructures are promising building blocks for future nanoelectronic and nanophotonic devices. ZnO has proven to be a multifunctional and multistructural nanomaterial with promising properties. Here we report the growth of ZnO nanosquids which can be directly grown on planar oxidized Si substrates without using catalysts and templates.