Nano

This article presents a brief review of the recent research progresses achieved in the field of one-dimensional (1D) aluminum nitride (AlN) nanostructures. It mainly covers three aspects: The first one is to introduce the synthetic strategies for several classic 1D AlN nanostructures (such as nanofibers, nanobelts, nanorods, nanowires, nanotips, etc.) including template-confined reaction, arc discharge, catalyst-assisted growth, and vapor transport and related growth methods. The second is to elaborate some special physical properties, such as field emission and photoluminescence, which associate with the uniqueness of 1D AlN nanostructures. It is revealed that aligned AlN 1D nanostructures have low turn-on and threshold voltages, high emission current and small current fluctuation, and that the photoluminescence of AlN nanobelts are different from those of conventional AlN material. The third is to briefly illustrate the potential application of these 1D AlN nanostructures in composite materials. It is found that AlN nanowire is a good reinforcement for improving the mechanical and thermal properties of metal matrix composites, which can be expected to be utilized as packaging material with high strength and low thermal expansion. Finally, we summarize the major challenges in this field. Among them, a thorough understanding of the growth mechanism of 1D AlN nanostructures is the most important issue, and more precisely controlled growth is required to obtain tailored AlN nanostructures according to device applications.

We present a review on recently-developed "surface-programmed assembly" strategy for massive production of nanotube/nanowire-based devices. In this process, surface molecular patterns guide the assembly and alignment of nanotubes/nanowires onto specific locations on solid substrates without relying on external forces. The assembled structures were further utilized to fabricate functional devices such as field effect transistors and sensors. Control experiments provided us rich scientific insights including "sliding kinetics" and "lens effect" during the assembly process. Since this method does not require high-temperature processing steps or unconventional fabrication facilities, it is readily available to conventional device industry and may open up new nanodevice industry based on carbon nanotubes and nanowires.

Serving as platforms for both cellular interrogation as well as biomembrane mimicry, biotic–abiotic functionalized materials, such as block copolymeric membranes, offer the opportunity for tailored biology, where specific embedded functionalities can be rapidly engineered, on demand, without the need for genetic processing. These versatile materials enable rapid, thin film deposition of a plethora of biologically-relevant materials at the air–water interface given their amphiphilic properties, meaning that they possess alternating hydrophilic and hydrophobic components. This property confers to these materials the ability to be transferred to a wide range of substrates and materials, further enhancing their interfacial versatility. In addition, their biologically-inert, and tunable, thickness-dependent insulating properties serve as ideal bio-active substrates while maintaining the functionality of the integrated molecule (e.g., protein, effector molecule, etc.). Here, we report the application of a polyethyleneoxide–polymethylmethacrylate (PEO–PMMA) diblock and polymethyloxazoline–polydimethylsiloxane–polymethyloxazoline (PMOXA–PDMS–PMOXA) triblock copolymers as molecular anchors for tethering a broad spectrum of materials. These include carbon nanotubes for the fabrication of bioelectrodes to measure cytochrome c-mediated oxidation-reduction, as well as the anti-inflammatory molecule, dexamethasone, for the suppression of lipopolysaccharide (LPS)-induced inflammation in murine macrophages. As such, this work demonstrates the versatility, and broad applicability and impact of this platform approach towards the fabrication of multifunctional arrays of biologically-active surfaces for experimentation ranging from bio-electroactivity to studies of cellular immunity.

We show that the crystal structure of a substrate can be exploited to drive the anisotropic assembly of colloidal nanoparticles. Pentanethiol-passivated Au particles of ~ 2 nm diameter deposited from toluene onto hydrogen-passivated Si(111) surfaces form linear assemblies (rods) with a narrow width distribution. The rod orientations mirror the substrate symmetry, with a high degree of alignment along principal crystallographic axes of the Si(111) surface. There is a strong preference for anisotropic growth with rod widths substantially more tightly distributed than lengths. Entropic trapping of nanoparticles provides a plausible explanation for the formation of the anisotropic assemblies we observe.

Tunable electronic properties of nanotubes are an essential requirement for building nanotube circuits and devices. We have produced BN nanotube films with controlled electric conductivities by Au doping. The Au-doped BN nanotube films have been found to exhibit from semiconducting to metallic behavior under different Au contents. Both experimental and computing simulation studies reveal that the conductivities of the doped film are improved by the incorporation of Au atoms into nanotube walls. The doped BN nanotubes and films are expected to have potential applications in catalysts, sensors and nanoelectronics.

In microchip electrophoresis (μ-CE), sample injection is generally achieved through cross, double-T, or T-form injector structures. In these reported approaches, the separation efficiency and detection sensitivity of μ-CE is significantly influenced by the shape and size of the sample plug introduced into the separation channel or sample leakage in separation phase. Here, we present a sandwich-injection method for controlling discrete sample injection in μ-CE. This method involves four accessory arm channels in which symmetrical potentials are loaded to form a unique parallel electric field distribution at the intersection of sample and separation channels. The parallel electric field effectuate a virtual wall to confine the shape of a sample plug and depress the spreading of the sample plug at the junction of sample and separation channels, and also prevent sample leakage during separation step. The key features of this method are the ability to inject well-defined sample plugs at the original sample concentration and the ability to control the sample plug size. The virtues of the novel injection technique were demonstrated with numerical models and validated with fluorescence visualizations of electrophoretic experiments.

As a new nanomaterial, HgWO₄ nanofilms are prepared by the self-inventive technique of collodion nanoparticles-dispersal and film-formation. Their photoluminescent properties are enhanced and then controlled through nano-TiO₂ doping. These approaches not only ensure film uniformity and fluorescence (FL) enhancement, but also realize a FL increase/decrease conversion effect. The relationships between HgWO₄ nanofilms' PL intensities and TiO₂ doped amounts are in good agreement with Gaussion function, and maximum PL intensities of HgWO₄ nanofilms are located at 3.8% ratio of TiO₂ nanoparticles.

We investigate the quantum size effect in the phase coherent mesoscopic ring. A quantum dot is embedded in one arm and it is connected to one lead via tunnel barrier. Both Aharonov–Casher and Aharonov–Bohm effects are studied. A spin-dependent conductance has been deduced and it depends on the intrinsic parameters. Our results show that the strength of spin-orbit coupling depends on the size of the present device. This investigation is valuable for fabricating such spintronics devices.